Non-aqueous electrolyte and non-aqueous secondary battery

Abstract

This application relates to non-aqueous electrolytes and non-aqueous secondary batteries. A non-aqueous electrolyte is provided, comprising: a non-aqueous solvent including acetonitrile and vinylene carbonate; and the following general formula (1): R1-A-R2 (1) {wherein, A represents a divalent group having the structure shown in any of the following formulas (1-2) to (1-5), R1 and R2 are each independently an aryl group, or an alkyl group having 1 to 4 carbon atoms optionally substituted with a halogen atom, or an alkyl group, or a vinylene group optionally substituted with a halogen atom, or an aryl group optionally substituted with a halogen atom, or R1 and R2 are bonded to each other to form a cyclic structure optionally having unsaturated bonds with A.} The total content of the aforementioned vinylene carbonate and the aforementioned compound of general formula (1) is 0.1% by volume or more and less than 10% by volume relative to the total amount of the aforementioned non-aqueous solvent, and the content of the aforementioned vinylene carbonate is less than the content of the aforementioned compound of general formula (1).

Description

[0001] This application is a divisional application of Chinese patent application filed on September 11, 2020, with application number 202080060897.0 and invention title "Non-aqueous electrolyte and non-aqueous secondary battery". Technical Field

[0002] This invention relates to non-aqueous electrolytes and non-aqueous secondary batteries. Background Technology

[0003] Non-aqueous secondary batteries, such as lithium-ion batteries, are lightweight, high-energy, and long-life, and are widely used as power sources for various portable electronic devices. In recent years, non-aqueous secondary batteries have expanded their applications in industrial applications, such as power tools, and in vehicles such as electric cars and electric bicycles. Furthermore, they have also attracted attention in the field of power storage, such as residential energy storage systems.

[0004] Lithium-ion batteries use non-aqueous electrolytes. For example, a combination of high-dielectric solvents such as cyclic carbonates and low-viscosity solvents such as low-chain carbonates is commonly used. Furthermore, to form an SEI (Solid Electrolyte Interface) on the negative electrode surface and utilize it to suppress the reductive decomposition of the non-aqueous solvent, it is ideal to add electrode protection additives such as vinylene carbonate. Additionally, it is known that LiPF6, typically present in non-aqueous electrolytes, reacts with trace amounts of water in the non-aqueous electrolyte to produce HF, effectively forming LiF, a component of the negative electrode SEI.

[0005] In recent years, with the expansion of the large-scale energy storage industry centered on electric vehicles, there is an urgent need for further increases in energy density and fast charging capabilities in non-aqueous secondary batteries. Recently, there has been active development towards achieving high energy density by using lithium-containing metal oxides with a high nickel ratio in the positive electrode active material and by creating thick-film electrodes. However, the significant challenge of fast charging remains.

[0006] For example, Patent Document 1 discloses a non-aqueous secondary battery that operates with a thick-film electrode using a highly ion-conductive electrolyte. It also reports a method for enhancing the SEI (Sediment Intake) by combining various electrode protection additives. Similarly, Patent Document 2 reports the use of specific organic lithium salts to enhance the SEI and suppress the decomposition of highly ion-conductive electrolytes. Patent Document 3 describes a method of containing acetonitrile, inorganic lithium salts, and cyclic anhydrides such as succinic anhydride in a non-aqueous electrolyte to delay gas generation from the non-aqueous secondary battery, thereby enhancing the negative electrode SEI and obtaining excellent battery characteristics. Patent Document 4 describes the use of a non-aqueous electrolyte containing ethylene sulfite and vinylene carbonate to obtain a non-aqueous secondary battery with excellent storage and cycling characteristics. Patent Document 5 describes the use of a combination of ethylene sulfite derivatives and vinylene carbonate derivatives to suppress the decomposition or compositional changes of the non-aqueous electrolyte, thereby improving the discharge capacity at low temperatures and the storage capacity at high temperatures. Patent document 6 describes a technique for adding a trialkoxyvinylsilane to a non-aqueous electrolyte to provide a non-aqueous secondary battery with excellent internal resistance reduction and battery expansion suppression.

[0007] Furthermore, the high energy density and rapid charging of non-aqueous secondary batteries increase the risk of battery fire, thus requiring further safety measures.

[0008] For example, Patent Document 7 reports a silane crosslinking separator containing a silane-modified polyolefin. The silane crosslinking reaction of the silane-modified polyolefin occurs through contact between the separator and a non-aqueous electrolyte, creating a silane crosslinking section within the separator, thereby achieving both low-temperature shut-off and high-temperature burst resistance. The aforementioned silane crosslinking reaction uses hydrogen fluoride (HF) produced by the hydrolysis of LiPF6 in the non-aqueous electrolyte as a catalyst. Patent Document 8 reports a silane crosslinking separator that, by using a silane crosslinking separator containing trace amounts of metal, captures excess HF that catalyzes the bond-breaking reaction at the silane crosslinking site, thereby improving the long-term cycling characteristics of the energy storage device.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: International Publication No. 2013 / 062056

[0012] Patent Document 2: International Publication No. 2012 / 057311

[0013] Patent Document 3: International Publication No. 2018 / 169028

[0014] Patent Document 4: Japanese Patent Application Publication No. 2002-25611

[0015] Patent Document 5: Japanese Patent Application Publication No. 2016-85836

[0016] Patent Document 6: Japanese Patent Application Publication No. 2013-175410

[0017] Patent Document 7: International Publication No. 2020 / 075866

[0018] Patent Document 8: Japanese Patent Application Publication No. 2020-61312

[0019] Non-patent literature

[0020] Non-patent literature 1: Chem. Eur. J., 15, 186 (2009)

[0021] Non-patent literature 2: Acc. Chem. Res., 14, 246 (1981)

[0022] Non-patent literature 3: The Chemistry of Organic Silicon Compounds Vol.2, Wiley (1998), Chap.4 Summary of the Invention

[0023] The problem the invention aims to solve

[0024] In the past, when non-aqueous secondary batteries were fast-charged at a speed higher than that used by electronic devices (referred to as "fast charging"), the lithium ions in the non-aqueous electrolyte diffused slowly. As a result, the supply of lithium ions on the negative electrode side was not timely, causing the battery voltage to reach its upper limit and preventing it from being fully charged to the specified battery capacity.

[0025] By using a non-aqueous electrolyte with high ionic conductivity as described in Patent Documents 1-3, lithium-ion diffusion between electrodes was solved. However, due to the low lithium-ion conductivity of the coating on the negative electrode side, lithium metal was observed to deposit on the surface of the negative electrode active material (referred to as "electrodeposition"), and good fast charging performance was not obtained.

[0026] Patent Document 4 does not disclose acetonitrile, and even with the addition of ethylene sulfite and vinylene carbonate to conventional non-aqueous electrolytes using carbonate solvents as described in the patent document, sufficient capacity was not obtained during fast charging. Similarly, Patent Document 5 does not disclose acetonitrile. The detailed mechanism has not been elucidated, but it is known that the addition of ethylene sulfite and vinylene carbonate to a non-aqueous electrolyte containing acetonitrile reduces high-temperature durability.

[0027] Patent document 6 investigated the use of trialkoxyvinylsilane in a mixed non-aqueous solvent of ethylene carbonate and methyl ethyl carbonate, but did not investigate the use of other solvents or additives.

[0028] However, there is still room for improvement in non-aqueous electrolytes, which are a component of non-aqueous secondary batteries, from the perspective of addressing capacity reduction during fast charging.

[0029] Non-aqueous electrolytes containing acetonitrile with LiPF6 as the main lithium salt exhibit low high-temperature durability. This is because the PF5 formed by the reaction of LiPF6 with trace amounts of water in the non-aqueous electrolyte promotes the proton extraction reaction at the α-position of acetonitrile via Lewis acid catalysis, leading to the generation of excess HF. Excess HF corrodes electrode and current collector materials, causes solvent decomposition, and negatively impacts battery performance.

[0030] It can be argued that when the silane crosslinking separator described in Patent Document 7 is used in combination with a non-aqueous electrolyte containing acetonitrile, excessive HF catalyzes the bond breaking reaction at the silane crosslinking sites, thereby reducing long-term cycling performance. Furthermore, Patent Document 8 attempts to capture HF using trace metals, but when trace metals are used in combination with a non-aqueous electrolyte containing acetonitrile, the long-term HF capture function is insufficient.

[0031] In addition, non-aqueous secondary batteries with separators possessing excellent mechanical strength often exhibit superior safety, but also have high resistance. At high-rate output, the movement speed of lithium ions within the separator rate-controlled the output performance; therefore, the higher the resistance of the separator, the lower the output performance.

[0032] The present invention was made in view of the above circumstances, and the object of the present invention is primarily to provide an acetonitrile-containing non-aqueous electrolyte capable of suppressing or preventing capacity reduction during rapid charging of a non-aqueous secondary battery and preventing voltage plateaus, as well as a non-aqueous secondary battery having the same.

[0033] The present invention also aims to provide an acetonitrile-containing non-aqueous electrolyte that uses LiFSO3 as both a HF generator and a buffer, adjusting its content to an appropriate range to suppress the generation of excess HF at high temperatures. Furthermore, a non-aqueous secondary battery is provided in which a separator containing an island structure formed by calcium aggregates is used as the separator, thereby capturing HF generated within the battery through reaction with calcium and suppressing the generation of excess HF. Moreover, a non-aqueous secondary battery is provided in which a separator with excellent mechanical strength is combined with a highly ion-conductive acetonitrile-containing non-aqueous electrolyte, thereby improving the lithium-ion migration speed within the separator at high-rate output, thus balancing safety and output performance.

[0034] The present invention also aims to provide a non-aqueous secondary battery that uses lithium iron phosphate with an olivine-type structure as the positive electrode active material to suppress metal dissolution under high temperature conditions and controls the contents of acetonitrile, ethylene carbonate, vinylene carbonate, and oxygen / sulfur compounds within a specified range, thereby suppressing the increase in the resistance of the negative electrode and improving high-temperature cycling performance.

[0035] Solution for solving the problem

[0036] In order to solve the above-mentioned problems, the inventors conducted repeated and in-depth research and found that the above problems could be solved by using a non-aqueous electrolyte or a non-aqueous secondary battery having the following configuration, thus completing the present invention. An example of the embodiments of the present invention is as follows. [1]

[0038] A non-aqueous electrolyte comprising:

[0039] Non-aqueous solvents containing acetonitrile and vinylene carbonate, and

[0040] The compounds represented by the following general formula (1),

[0041] R1-A-R2 ·····(1)

[0042] {In the formula, A represents a divalent group having the structure shown in any of the following formulas (1-2) to (1-5),}

[0043]

[0044] R1 and R2 each independently represent an alkyl group having 1 to 4 carbon atoms, optionally substituted with an aryl or halogen atom; or a vinylene group, optionally substituted with a halogen atom; or an aryl group, optionally substituted with an alkyl or halogen atom; or R1 and R2 bonded together to form a cyclic structure with optional unsaturated bonds with A.

[0045] The total content of the aforementioned vinylene carbonate and the compound represented by the aforementioned general formula (1) is 0.1% by volume or more and less than 10% by volume relative to the total amount of the aforementioned non-aqueous solvent, and,

[0046] The content of the aforementioned vinylene carbonate is less than the content of the compound shown in the aforementioned general formula (1). [2]

[0048] According to the non-aqueous electrolyte described in item 1, the content of the aforementioned vinylene carbonate is 0.1 to 3.5% by volume relative to the total amount of the aforementioned non-aqueous solvent.

[0049] The volume ratio of the compound represented by the aforementioned general formula (1) to the aforementioned vinylene carbonate is: 1.5 × vinylene carbonate content ≤ content of the compound represented by general formula (1) ≤ 2.4 × vinylene carbonate content. [3]

[0051] According to the non-aqueous electrolyte of claim 1 or 2, wherein the compound represented by the aforementioned general formula (1) contains ethylene sulfite. [4]

[0053] The non-aqueous electrolyte according to any one of claims 1 to 3 further comprises a lithium salt, said lithium salt comprising LiFSO3 in a total amount of less than 200 ppm by mass relative to the aforementioned non-aqueous electrolyte. [5]

[0055] According to the non-aqueous electrolyte described in item 4, the aforementioned lithium salt comprises a lithium-containing imide salt. [6]

[0057] According to the non-aqueous electrolyte described in item 5, the aforementioned lithium salt comprises the aforementioned lithium-containing imide salt and LiPF6 at a molar concentration of LiPF6 < lithium-containing imide salt. [7]

[0059] The non-aqueous electrolyte according to item 5 or 6 contains lithium bis(fluorosulfonyl)imide as the aforementioned lithium-containing imide salt. [8]

[0061] According to any one of items 4 to 7, the content of the aforementioned lithium salt is 0.1 to 40 parts by mass relative to 100 parts by mass of the aforementioned non-aqueous electrolyte. [9]

[0063] According to any one of items 1 to 8, the content of the aforementioned acetonitrile is 5% by volume or more and 97% by volume or less relative to the total amount of the aforementioned non-aqueous solvent.

[10]

[0065] The non-aqueous electrolyte according to any one of items 1 to 9, wherein the aforementioned non-aqueous solvent further comprises a compound represented by the following general formula (3),

[0066]

[0067] {In the formula, R7~R 10 Each of the following is independently an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a phenyl group, optionally having substituents, and optionally containing an unsaturated bond in the carbon bond.

[11]

[0069] The non-aqueous electrolyte according to any one of items 1 to 10 has a recovery charging capacity retention rate of 90% or more in a non-aqueous secondary battery having the aforementioned non-aqueous electrolyte.

[12]

[0071] A non-aqueous electrolyte comprising:

[0072] Non-aqueous solvents containing acetonitrile of 5% to 97% by volume and

[0073] Lithium salts containing less than 200 ppm by mass of LiFSO3 relative to the total amount of non-aqueous electrolyte.

[13]

[0075] According to the non-aqueous electrolyte of claim 12, wherein the aforementioned lithium salt comprises a lithium-containing imide salt.

[14]

[0077] According to the non-aqueous electrolyte of claim 12 or 13, the aforementioned lithium salt comprises the aforementioned lithium-containing imide salt and LiPF6 at a molar concentration of LiPF6 < lithium-containing imide salt.

[15]

[0079] A non-aqueous secondary battery comprising the non-aqueous electrolyte as described in any one of claims 1 to 14.

[16]

[0081] According to item 15, the non-aqueous secondary battery has a recovery charging capacity retention rate of over 90%.

[17]

[0083] The non-aqueous secondary battery according to claim 15 or 16 further comprises a separator having the following regions:

[0084] During TOF-SIMS measurements with a surface area of ​​100 μm, more than one calcium-containing island structure was detected, and the size of the aforementioned island structure was 9 μm. 2 Above and 245μm 2 The following areas.

[18]

[0086] According to the non-aqueous secondary battery described in item 17, when there are two or more of the aforementioned calcium-containing island structures in the aforementioned separator, the minimum and maximum distances between the weighting centers of each of the aforementioned island structures are both 6 μm or more and 135 μm or less.

[19]

[0088] According to the non-aqueous secondary battery of claim 17 or 18, the aforementioned separator comprises a substrate as a first layer and a second layer laminated on at least one surface of the aforementioned substrate.

[0089] The thickness ratio of the aforementioned substrate to the aforementioned second layer is 0.5 or more and 10 or less.

[0090] The aforementioned second layer comprises at least one selected from the group consisting of ceramics, aromatic polyamide resins, and polyvinylidene fluoride (PVDF).

[20]

[0092] The non-aqueous secondary battery according to any one of claims 17 to 19, wherein the aforementioned separator comprises a silane-modified polyolefin. [twenty one]

[0094] According to the non-aqueous secondary battery of claim 20, when the aforementioned separator comes into contact with the aforementioned non-aqueous electrolyte, the silane crosslinking reaction of the aforementioned silane-modified polyolefin begins. [twenty two]

[0096] The non-aqueous secondary battery according to claim 15 or 16 further comprises a separator, the separator comprising a substrate as a first layer and a second layer laminated on at least one side of the substrate, the second layer comprising an aromatic polyamide resin. [twenty three]

[0098] The non-aqueous secondary battery according to claim 15 or 16 further comprises a separator, which is formed by applying an inorganic pigment to a substrate containing nonwoven fabric. [twenty four]

[0100] The non-aqueous secondary battery according to item 15 or 16 further comprises a separator, wherein the separator is formed by applying inorganic pigments to a substrate containing nonwoven fabric, and as a layer structure, a layer mainly composed of inorganic pigments, a layer composed of inorganic pigments and substrate fibers, and a layer mainly composed of substrate fibers are sequentially overlapped.

[25]

[0102] The non-aqueous secondary battery according to any one of claims 15 to 24, wherein the aforementioned non-aqueous electrolyte further comprises ethylene carbonate, and,

[0103] The positive electrode active material, which is the positive electrode contained in the aforementioned non-aqueous secondary battery, includes the formula Li w The compound with an olivine-type structure is shown in FePO4 {where w is 0.05~1.1}.

[0104] The effects of the invention

[0105] First, according to the present invention, in a non-aqueous secondary battery having a non-aqueous electrolyte, resistive components that propagate from the positive electrode side to the negative electrode side are blocked. As a result, a good negative electrode coating that maintains lithium-ion conductivity is maintained, thus suppressing or preventing capacity reduction during fast charging and preventing voltage plateaus.

[0106] Secondly, according to the present invention, the amount of HF generated can be controlled by adjusting the content of LiFSO3. This suppresses battery degradation at high temperatures, effectively forms LiF as a component of the negative electrode SEI at room temperature, and promotes silane crosslinking when silane-modified polyolefins are used as separators.

[0107] Furthermore, according to the present invention, calcium is unevenly distributed within the separator in an aggregated island structure, thereby enabling HF capture. Calcium is gradually consumed in stages from the surface of the island structure, thus maintaining the effect over a long period. This allows for long-term suppression of battery degradation and, when silane-modified polyolefins are used in the separator, the silane cross-linked structure can be maintained for an extended period.

[0108] Furthermore, according to the present invention, the rate-controlled movement speed of lithium ions within the separator can be increased when acetonitrile is used in a non-aqueous electrolyte and output at a high rate. This results in a non-aqueous secondary battery with improved output performance and no compromise in safety.

[0109] Finally, according to the present invention, a non-aqueous secondary battery is provided as follows: by using lithium iron phosphate with an olivine-type structure as the positive electrode active material, metal dissolution under high temperature conditions is suppressed, and by controlling the contents of acetonitrile, ethylene carbonate, and ethylene carbonate and oxygen / sulfur-containing compounds within a specified range, the increase in resistance of the negative electrode is suppressed, thereby improving high-temperature cycle performance. Attached Figure Description

[0110] Figure 1 A top view illustrating an example of a non-aqueous secondary battery according to one embodiment is shown.

[0111] Figure 2 for Figure 1 A cross-sectional view of a non-aqueous secondary battery along the AA line.

[0112] Figure 3 This is a schematic diagram illustrating the voltage plateau observed in the charging curve of a non-aqueous secondary battery.

[0113] Figure 4 An image showing the TOF-SIMS analysis results of a battery separator according to one embodiment.

[0114] Figure 5 This is an example of filtering a three-dimensional image in image processing using the TOF-SIMS spectrum.

[0115] Figure 6 This is an example of filtering a two-dimensional image in image processing of the TOF-SIMS spectrum.

[0116] Figure 7 An example of the state of the TOF-SIMS spectrum after image processing (1)~(2).

[0117] Figure 8 An example of the state of the TOF-SIMS spectrum after image processing (1) to (8). Detailed Implementation

[0118] The following is a detailed description of the method for carrying out the present invention (hereinafter referred to as "this embodiment"). The present invention is not limited to the following embodiment, and various modifications can be made without departing from its gist. In this specification, numerical ranges indicated by "~" include the values ​​stated before and after them. In this embodiment, "non-aqueous electrolyte" refers to an electrolyte in which water accounts for 1% or less by mass relative to the total amount of the non-aqueous electrolyte. The non-aqueous electrolyte of this embodiment is preferably as water-free as possible, but may contain trace amounts of water if it does not impede solving the problem of the present invention. This water content, in terms of the amount relative to the total amount of the non-aqueous electrolyte, is 300 ppm by mass or less, preferably 200 ppm by mass or less. For the non-aqueous electrolyte, as long as it has the structure required to solve the problem of the present invention, other constituent elements can be appropriately selected and used from known non-aqueous electrolytes available in lithium-ion batteries.

[0119] The non-aqueous electrolyte of the first embodiment

[0120] The non-aqueous electrolyte of this embodiment (hereinafter also referred to as "electrolyte") contains a non-aqueous solvent, an inorganic lithium salt, and an oxygen / sulfur compound represented by the following general formula (1).

[0121] R1-A-R2 ·····(1)

[0122] {In the formula, A represents a divalent group having the structure shown in any of the following formulas (1-2) to (1-5),}

[0123]

[0124] R1 and R2 each independently represent an alkyl group having 1 to 4 carbon atoms optionally substituted with an aryl or halogen atom, or a vinylene optionally substituted with a halogen atom, or an aryl group optionally substituted with an alkyl or halogen atom, or R1 and R2 are bonded together to form a cyclic structure optionally having unsaturated bonds with A.

[0125] As is desired, the non-aqueous electrolyte may further contain components other than the oxygen / sulfur compounds shown in general formula (1).

[0126] The non-aqueous electrolyte of this embodiment preferably has a freezing point of less than -40°C. A freezing point of less than -40°C can be controlled by the types, mixing ratios, and mixing conditions of the various components of the non-aqueous electrolyte. In low-temperature environments of non-aqueous secondary batteries (e.g., discharge tests at -40°C), this helps improve discharge characteristics and maintain discharge capacity. The components of the non-aqueous electrolyte are described below.

[0127] <Oxygen / sulfur compounds represented by general formula (1)>

[0128] In this embodiment, when the oxygen / sulfur compound represented by the above general formula (1) is included in the non-aqueous electrolyte in an appropriate amount, the following tendency is found: during the rapid charging of the non-aqueous secondary battery containing the non-aqueous electrolyte, capacity reduction is suppressed or prevented.

[0129] The oxygen-containing / sulfur compound represented by the above general formula (1) has a divalent group having the structure shown in any of the above formulas (1-2) to (1-5), such as sulfinyl group, sulfate group, sulfite group, sulfonyl group, sulfate ion, etc., as group A. Among them, from the viewpoint of SEI durability and lithium ion conductivity, it is preferable to have a divalent group having the structure shown in the above formulas (1-3) and / or (1-4), and more preferably to have a divalent group having the structure shown in the above formula (1-3).

[0130] The alkyl groups with 1 to 4 carbon atoms, represented by R1 and R2 and optionally substituted with aryl or halogen atoms, are preferably alkyl groups with 1 to 4 carbon atoms and optionally substituted with phenyl or halogen atoms. Specifically, examples of alkyl groups include methyl, ethyl, propyl, isopropyl, and butyl. Examples of aryl groups that serve as substituents include phenyl, naphthyl, and anthracene, with phenyl being preferred. Examples of halogen atoms that serve as substituents for alkyl groups include fluorine, chlorine, and bromine atoms. These substituents can be substituted in multiple ways on the alkyl group, or both the aryl group and the halogen atom can be substituted.

[0131] The aryl groups represented by R1 and R2, which are optionally substituted with alkyl or halogen atoms, are preferably phenyl, naphthyl, or anthracene, more preferably phenyl, and even more preferably phenyl, which is optionally substituted with alkyl or halogen atoms. Examples of aryl groups include phenyl, naphthyl, and anthracene, with phenyl being preferred. Furthermore, the alkyl group that forms the aryl group is preferably an alkyl group having 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, and butyl. The halogen atom that forms the aryl group is preferably a fluorine atom, a chlorine atom, or a bromine atom. These substituents can be substituted in multiple ways on the aryl group, or both the alkyl group and the halogen atom can be substituted.

[0132] For R1 and R2, fluorine, chlorine, and bromine atoms are preferred as substituents for the vinylidene group. These substituents can be substituted in multiple ways on the vinylidene group, or both the vinylidene group and the halogen atom can be substituted.

[0133] The cyclic structure formed by R1 and R2 bonded together with A is preferably a 4-membered ring or more, with a 5-membered ring structure being more preferred. Additionally, a double bond may be present. R1 and R2, which are bonded together, are preferably divalent hydrocarbon groups, and their carbon number is preferably 1 to 6. Specifically, examples include -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2CH2CH2CH2-, -CH2CH2CH2CH2CH2-, -CH=CH-, -CH=CHCH2-, -CH=CHCH2-, and -CH2CH=CHCH2-. Furthermore, one or more hydrogen atoms in these groups may be substituted by one or more of alkyl (e.g., methyl and ethyl), halogen (e.g., fluorine, chlorine, and bromine), and aryl (e.g., phenyl). R1 ​​and R2 may be the same or different from each other.

[0134] Specific examples of the oxygen- / sulfur-containing compounds represented by general formula (1) may be at least one selected from the group consisting of dimethyl sulfite, diethyl sulfite, dimethyl sulfoxide, sulfolane, 3-cyclobutene sulfone, ethylene sulfite, propylene sulfite, 1,3-propenesulfonyl and 1,3-propanesulfonyl, diphenyl sulfone, phenyl vinyl sulfone, divinyl sulfone, methyl vinyl sulfone, ethyl vinyl sulfone, and 1,3,2-dioxothiacyclohexane 2-oxide. From the viewpoint of suppressing or preventing capacity reduction during rapid charging of non-aqueous secondary batteries, dimethyl sulfite, diethyl sulfite, dimethyl sulfite, ethylene sulfite, propylene sulfite, and 1,3,2-dioxothiacyclohexane 2-oxide are preferred, ethylene sulfite and / or 1,3,2-dioxothiacyclohexane 2-oxide are more preferred, and ethylene sulfite is particularly preferred.

[0135] The negative electrode protective coating derived from vinylene carbonate (VC) has high resistance, and therefore, in excess, it tends to cause battery expansion due to performance degradation during rapid charging, low-temperature environments, and gas generation during decomposition. Ethylene sulfite, compared to other oxygen / sulfur compounds, has a lower lowest unoccupied molecular orbital (LUMO) energy level, and can be reduced and decomposed at a lower potential than VC, thus promoting the formation of the negative electrode protective coating. This allows for a reduction in the amount of VC added, addressing the problems caused by VC-derived negative electrode protective coatings. Furthermore, the negative electrode protective coating formed by the interaction of ethylene sulfite and VC exhibits low resistance over a wide temperature range and high durability against acetonitrile, thus promising further synergistic effects. It should be noted that the inventors have experimentally clarified that the negative electrode protective coating derived solely from ethylene sulfite cannot suppress the reduction and decomposition of acetonitrile. Based on this experimental fact, it is reasonable to assume that the pre-activated ethylene sulfite reacts with VC to form a composite, robust negative electrode protective coating, rather than ethylene sulfite and VC forming negative electrode protective coatings independently. It can be assumed that all oxygen- or sulfur-containing compounds represented by general formula (1) exhibit interaction with VC through the same mechanism.

[0136] The oxygen- or sulfur-containing compounds represented by general formula (1) can be used alone or in combination of two or more. When two or more oxygen- or sulfur-containing compounds are combined, the structures of the divalent groups A in each compound can be the same or different.

[0137] The non-aqueous solvent in this embodiment contains acetonitrile and vinylene carbonate (VC), and may also contain, as needed, heterocyclic and / or halogenated cyclic compounds, chain compounds, silicon-containing compounds, etc. as additional components.

[0138] In the non-aqueous electrolyte of this embodiment, vinylene carbonate (VC) and the oxygen / sulfur compound represented by general formula (1) satisfy the following relationships (I) and (II).

[0139] (I) The total content of VC and oxygen / sulfur compounds represented by general formula (1) is more than 0.1% by volume and less than 10% by volume relative to the total amount of non-aqueous solvents.

[0140] (II) The volume ratio is VC content < the content of oxygen / sulfur compounds shown in general formula (1).

[0141] By satisfying the relationship (I) above, it is possible to suppress the generation of decomposition gases caused by excessive VC and oxygen / sulfur compounds as shown in general formula (1) and the increase in internal resistance caused by decomposition deposits, which is a condition that can be conceived to some extent by those skilled in the art. However, by satisfying the relationship (II) above, it is entirely unknown whether the actual effect of combining oxygen / sulfur compounds as shown in general formula (1) with VC can be achieved, exhibiting fast charging performance and thus low-temperature performance at a level that cannot be achieved when the negative electrode protective coating derived from VC is dominant. If the volume ratio of VC exceeds the volume ratio of oxygen / sulfur compounds as shown in general formula (1), the properties of the negative electrode protective coating derived from VC become dominant, and it is difficult to benefit even when using non-aqueous solvents such as acetonitrile that contribute to high ionic conductivity. The effect of (II) above is not conceivable based on the common sense that the effects of VC and oxygen / sulfur compounds as shown in general formula (1) are considered equally until now, and it is impossible to realize that setting (II) above as a discontinuous threshold is possible unless in a very harsh environment with electrodeposition, such as repeated fast charging.

[0142] The non-aqueous electrolyte of this embodiment achieves a balance between the VC content (as shown in general formula (1)) that does not cause an increase in negative electrode resistance, a decrease in battery performance at fast charging and low temperatures (especially -40°C), and a level of gas generation, the content of oxygen / sulfur compounds (as shown in general formula (1)) that does not reduce battery capacity, and the VC content and the content of oxygen / sulfur compounds (as shown in general formula (1)) that stabilize the battery by forming an SEI. From this point of view, it is preferable that the VC and the oxygen / sulfur compounds (as shown in general formula (1) further satisfy at least one of the following relationships (III) and (IV).

[0143] (III) The volume ratio is 1.5×VC content ≤ the content of oxygen / sulfur compounds shown in general formula (1) ≤ 2.4×VC content.

[0144] (IV) The VC content relative to the total amount of non-aqueous solvents is 0.1 to 3.5 vol%, 0.2 to 3 vol%, or 0.3 to 2.5 vol%.

[0145] By satisfying the relationship described in (III) above, the problems specific to acetonitrile can be solved in particular. In order to suppress the reductive decomposition of acetonitrile, it is also necessary to prevent the negative electrode protective coating derived from the oxygen-containing / sulfur compound shown in general formula (1) from existing alone. For example, considering the molar number of ethylene sulfite to VC, the molar number of ethylene sulfite with a volume ratio of 1.5 × VC content is 1.25 times that of VC. That is, it is necessarily more molar than VC. In addition, the molar number of ethylene sulfite with a volume ratio of 2.4 × VC content is twice that of VC. That is, it corresponds to the case of the two-terminal reaction between ethylene sulfite and VC. By ensuring that the volume ratio of VC to the oxygen-containing / sulfur compound shown in general formula (1) is within the range described in (III) above, it is possible to suppress the increased possibility of separate coatings of VC and the oxygen-containing / sulfur compound shown in general formula (1), which are the causes of the degradation reaction of acetonitrile.

[0146] By satisfying the relationship described above (IV), the minimum necessary amount of the negative electrode protective coating is guaranteed. Given that the reductive decomposition of acetonitrile cannot be suppressed solely by the negative electrode protective coating derived from ethylene sulfite, it can be assumed that the main component of the negative electrode protective coating is always VC. The negative electrode protective coating is strengthened by the interaction of the oxygen / sulfur compound shown in general formula (1) with VC, but by ensuring that the VC content is within the range described above (IV), the negative electrode can be reliably protected before the reductive decomposition of acetonitrile begins.

[0147] Regarding the non-aqueous secondary battery containing the non-aqueous electrolyte of the first embodiment, from the viewpoint of suppressing or preventing capacity reduction and avoiding voltage plateaus during fast charging, it is preferable that the non-aqueous electrolyte, in addition to containing a non-aqueous solvent and an oxygen / sulfur compound as shown in general formula (1), also contains a lithium salt comprising LiFSO3 in a total amount of 200 ppm by mass relative to the non-aqueous electrolyte. As will be described later, a voltage plateau indicates electrodeposition. An appropriate amount of LiFSO3 suppresses the generation of HF, and therefore also suppresses excess LiF as a reaction product of HF. Thus, the increase in internal resistance can be suppressed.

[0148] Non-aqueous electrolyte of the second embodiment

[0149] The non-aqueous electrolyte in this embodiment contains:

[0150] Non-aqueous solvents containing acetonitrile; and

[0151] Lithium salts containing less than 200 ppm by mass of LiFSO3 relative to the total amount of non-aqueous electrolyte.

[0152] In the non-aqueous electrolyte of this embodiment, from the viewpoint of suppressing the decrease in ionic conductivity at low temperatures (e.g., -10°C), the lithium salt preferably contains a lithium-containing imide salt.

[0153] The non-aqueous electrolyte of this embodiment contains lithium hexafluorophosphate (LiPF6) and lithium-containing imide salt. From the viewpoint of inhibiting the association between lithium salt and acetonitrile at low temperatures (e.g., -10°C) and the low-temperature cycling characteristics of the battery, it is preferable that the content of LiPF6 < the content of lithium-containing imide salt.

[0154] In the non-aqueous electrolyte of this embodiment, from the viewpoint of suppressing the decrease in ionic conductivity at low temperatures (e.g., -10°C), the lithium imide salt preferably contains lithium bis(fluorosulfonyl)imide (abbreviated as LiFSI).

[0155] The non-aqueous electrolyte of this embodiment may further contain other additives besides those mentioned above.

[0156] The non-aqueous electrolyte of the third embodiment

[0157] The non-aqueous electrolyte of this embodiment contains: a non-aqueous solvent comprising acetonitrile, ethylene carbonate and vinylene carbonate; and an oxygen / sulfur compound represented by the above general formula (1).

[0158] The non-aqueous electrolyte of this embodiment may further contain other additives besides those mentioned above.

[0159] From the viewpoint of suppressing the increase in internal resistance and gas volume during repeated charge-discharge cycles at high temperatures, the non-aqueous solvent of this embodiment preferably contains the oxygen / sulfur compound, ethylene carbonate, and vinylene carbonate shown in the above general formula (1).

[0160] The constituent elements of the first, second, and third embodiments can be combined or interchanged. Common or preferred configurations in the first, second, and third embodiments will be described below.

[0161] <Non-aqueous solvents>

[0162] The "non-aqueous solvent" mentioned in this embodiment refers to the elements remaining after excluding lithium salts and various additives from the non-aqueous electrolyte. In this embodiment, acetonitrile is included as the non-aqueous solvent. The presence of acetonitrile in the non-aqueous solvent improves the ionic conductivity of the non-aqueous electrolyte, thereby enhancing the diffusion of lithium ions within the battery. Therefore, especially with a positive electrode where the positive electrode active material layer is thickened to increase the filling amount of the positive electrode active material, lithium ions can diffuse well to the region near the current collector, which is difficult for lithium ions to reach, even during high-load discharge. Thus, sufficient capacity can be derived even under high-load discharge, resulting in a non-aqueous secondary battery with excellent load characteristics.

[0163] Furthermore, the inclusion of acetonitrile in the non-aqueous solvent improves the fast-charging characteristics of non-aqueous secondary batteries. In constant-current (CC)-constant-voltage (CV) charging of non-aqueous secondary batteries, the charging capacity per unit time during CC charging is greater. Using acetonitrile as the non-aqueous solvent expands the CC-chargeable area (extending the CC charging time) and also increases the charging current, thus significantly shortening the time from the start of charging to full charge for non-aqueous secondary batteries.

[0164] Furthermore, acetonitrile has superior thermal conductivity compared to conventional carbonate solvents, thus enabling the heat rise during nail penetration tests to be evenly diffused throughout the battery and relieving thermal shrinkage of the separator. Therefore, by incorporating acetonitrile into a non-aqueous solvent, a non-aqueous secondary battery with excellent safety can be obtained.

[0165] It should be noted that acetonitrile is prone to electrochemical reduction and decomposition. Therefore, when using acetonitrile, it is preferable to take the following measures: use acetonitrile and other solvents (e.g., non-protic solvents other than acetonitrile) as non-aqueous solvents, and / or add electrode protection additives for forming a protective coating on the electrode.

[0166] The acetonitrile content is preferably 5% by volume or more and 97% by volume or less relative to the total amount of non-aqueous solvent. More preferably, the acetonitrile content is 8% by volume or more or 10% by volume or more, and even more preferably 15% by volume or more. More preferably, this value is 85% by volume or less, and even more preferably 66% by volume or less. When the acetonitrile content is 5% by volume or more relative to the non-aqueous solvent, the ionic conductivity increases, exhibiting high output characteristics, which in turn promotes the dissolution of lithium salts. The additives described later suppress the increase in battery internal resistance; therefore, when the acetonitrile content in the non-aqueous solvent is within the above-mentioned range, there is a tendency to improve high-temperature cycling characteristics and other battery characteristics.

[0167] Examples of solvents included in the non-aqueous solvent of this embodiment include alcohols such as methanol and ethanol, and aprotic solvents. Among these, aprotic solvents are preferred as non-aqueous solvents. However, the non-aqueous solvent may also contain solvents other than aprotic solvents, without hindering the resolution of the problems of this invention.

[0168] Examples of nonprotic solvents other than acetonitrile include cyclic carbonates, fluoroethylene carbonates, lactones, organic compounds containing sulfur atoms, chain fluorinated carbonates, cyclic ethers, mononitriles other than acetonitrile, alkoxy-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, chain ethers, fluorinated ethers, ketones, and compounds obtained by substituting some or all of the H atoms of the aforementioned nonprotic solvents with halogen atoms.

[0169] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, vinylene carbonate, 4,5-dimethylvinylene carbonate, and ethylene ethylene carbonate.

[0170] Examples of fluoroethylene carbonates include 4-fluoro-1,3-dioxolane-2-one, 4,4-difluoro-1,3-dioxolane-2-one, cis-4,5-difluoro-1,3-dioxolane-2-one, trans-4,5-difluoro-1,3-dioxolane-2-one, 4,4,5-trifluoro-1,3-dioxolane-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolane-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolane-2-one.

[0171] Examples of lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone.

[0172] Examples of organic compounds containing sulfur atoms include ethylene sulfite, propylene sulfite, butyl sulfite, pentene sulfite, sulfolane sulfonate, sulfolane sulfonate, 3-cyclobutene sulfonate, 3-methyl sulfolane sulfonate, 1,3-propane sulpholactone, 1,4-butane sulpholactone, 1-propene 1,3-sulpholactone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite.

[0173] Examples of chain carbonates include methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, and ethyl propyl carbonate.

[0174] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane and 1,3-dioxane;

[0175] Examples of mononitriles other than acetonitrile include propionitrile, butyronitrile, valerate, benzonitrile, and acrylonitrile.

[0176] Examples of alkoxy-substituted nitriles include methoxyacetonitrile and 3-methoxypropionitrile;

[0177] Examples of dinitrile include malononitrile, succinate, methylsuccinate, glutaronitrile, 2-methylglutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanhexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanoctane, 2,7-dicyanoctane, 1,9-dicyanonane, 2,8-dicyanonane, 1,10-dicyandecane, 1,6-dicyandecane, and 2,4-dimethylglutaronitrile, and ethylene glycol bis(propionitrile) ether;

[0178] Examples of cyclic nitrile include benzonitrile;

[0179] Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl neovalerate, methyl 2-methylbutyrate, methyl hexanoate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl neovalerate, ethyl 2-methylbutyrate, ethyl hexanoate, propyl acetate, propyl propionate, propyl isobutyrate, propyl isovalerate, propyl isovalerate, propyl valerate, propyl neovalerate, propyl 2-methylbutyrate, propyl hexanoate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, and so on. Isopropyl valerate, isopropyl neovalerate, isopropyl 2-methylbutyrate, isopropyl hexanoate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl neovalerate, butyl 2-methylbutyrate, butyl hexanoate, isobutyl acetate, isobutyl propionate, isobutyl isobutyrate, isobutyl butyrate, isobutyl isovalerate, isobutyl valerate, isobutyl neovalerate, isobutyl 2-methylbutyrate, isobutyl hexanoate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, tert-butyl isovalerate, tert-butyl valerate, tert-butyl neovalerate, tert-butyl 2-methylbutyrate, and tert-butyl hexanoate;

[0180] Examples of chain ethers include dimethoxyethane, diethyl ether, 1,3-dioxolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0181] As fluorinated ethers, examples of general formulas include Rf aa -OR bb (where Rf) aa It is an alkyl group containing a fluorine atom, and R bb The compound shown is an organic group (which may be selected from those containing fluorine atoms).

[0182] Examples of ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone; and,

[0183] As a compound obtained by replacing some or all of the H atoms of the aforementioned aprotic solvent with halogen atoms, compounds in which the halogen atom is fluorine can be listed as an example.

[0184] Here, examples of fluorinated chain carbonates include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethylmethyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. These fluorinated chain carbonates can be represented by the following general formula:

[0185] R cc -OC(O)OR dd

[0186] {where R is the formula} cc and R dd The free radicals CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf are selected. ee (where Rf) ee It consists of at least one of the groups represented by an alkyl group having 1 to 3 carbon atoms obtained by replacing a hydrogen atom with at least one fluorine atom, and R cc and / or R dd It contains at least one fluorine atom.

[0187] In addition, examples of fluorinated short-chain fatty acid esters include fluorinated short-chain fatty acid esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Fluorinated short-chain fatty acid esters can be represented by the following general formula:

[0188] R ff -C(O)OR gg

[0189] {where R is the formula} ff The free radicals are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3CF2H, CFH2, CF2H, and CF2Rf. hh CFHRf hh and CH2Rf ii At least one of the groups, R gg The free radicals CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf are selected. ii At least one of the groups, Rf hh Rf is an alkyl group having 1 to 3 carbon atoms obtained by optionally replacing a hydrogen atom with at least one fluorine atom. ii An alkyl group having 1 to 3 carbon atoms obtained by replacing a hydrogen atom with at least one fluorine atom, and R ff and / or R gg Contains at least one fluorine atom, in R ffIn the case of CF2H, R gg It's not CH3.

[0190] In this embodiment, the aprotic solvent other than acetonitrile can be used alone, or two or more can be used in combination.

[0191] For the non-aqueous solvent in this embodiment, from the viewpoint of improving the stability of the non-aqueous electrolyte, it is preferable to use one or more of cyclic carbonates and linear carbonates in combination with acetonitrile. From this viewpoint, it is more preferable for the non-aqueous solvent in this embodiment to be used in combination with acetonitrile using cyclic carbonates, and even more preferable to use a combination of both cyclic carbonates and linear carbonates in combination with acetonitrile.

[0192] When cyclic carbonates are used in combination with acetonitrile, the cyclic carbonates particularly preferably comprise ethylene carbonate, vinylene carbonate, and / or fluoroethylene carbonate.

[0193] From the perspectives of non-aqueous electrolyte ionic conductivity, low-temperature solidification resistance, and gas generation suppression, non-aqueous solvents preferably contain additional components such as silicon-containing compounds.

[0194] As a non-aqueous solvent, the silicon-containing compound is preferably a compound represented by the following general formula (3):

[0195]

[0196] {In the formula, R7~R 10 Each of the following is independently an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a phenyl group, optionally having substituents, and optionally containing an unsaturated bond in the carbon bond.

[0197] The content of the compound shown in general formula (3) is preferably 0.01 to 1 part by mass relative to 100 parts by mass of the non-aqueous electrolyte.

[0198] For the groups R7~R in general formula (3) 10 As an alkyl group having 1 to 4 carbon atoms, methyl, ethyl, n-propyl, or isopropyl, as well as n-butyl, sec-butyl, isobutyl, or tert-butyl, etc., can be selected. As an alkoxy group having 1 to 4 carbon atoms, methoxy, ethoxy, etc., can be selected. Additionally, groups R7 to R... 10 It can be a group derived from an alkyl or alkoxy group having a substituent on a carbon group of 1 to 4 carbons or from an unsaturated bond configured in a carbon bond.

[0199] Specific examples of compounds represented by general formula (3) are selected from allyltrimethylsilane, allyltriethylsilane, triethoxymethylsilane, triethoxyvinylsilane and R7~R 10 At least one of the groups consisting of compounds in which at least one is phenyl.

[0200] Lithium salts

[0201] The lithium salt in this embodiment contains LiFSO3. HFSO3, which is generated by the cation exchange between LiFSO3 and protons, produces HF through the following equilibrium reaction (1). Therefore, it is speculated that the LiFSO3 in this invention reacts with trace amounts of water in the non-aqueous electrolyte to produce HF.

[0202]

[0203] In addition, when the non-aqueous electrolyte containing acetonitrile contains LiPF6 in the form of lithium salt, it is speculated that LiFSO3 captures excess HF through the following equilibrium reaction (2).

[0204]

[0205] Under conditions of excess HF, equilibrium reaction (1) is unlikely to proceed to the right, so the reaction of HFSO3 generated by equilibrium reaction (2) to generate HF again is unlikely to occur.

[0206] The HF generated by the above equilibrium reaction effectively forms LiF, which is a component of the negative electrode SEI, and acts as a catalyst to promote the silane crosslinking reaction when silane-modified polyolefins are used in the separator.

[0207] In this invention, the content of LiFSO3 relative to the total amount of the non-aqueous electrolyte is more than 0 ppm by mass, preferably 0.1 ppm by mass or more, more preferably 1 ppm by mass or more, and even more preferably 10 ppm by mass or more. Furthermore, the content of LiFSO3 relative to the total amount of the non-aqueous electrolyte is preferably 200 ppm by mass or less, more preferably 150 ppm by mass or less, and even more preferably 100 ppm by mass or less. By adjusting the content of LiFSO3 to the above range, the amount of HF generated can be adjusted to an appropriate range, the generation of excess HF at high temperatures can be suppressed, and LiF, as a component of the negative electrode SEI, can be effectively formed, and the silane crosslinking reaction of the silane-modified polyolefin can be promoted. However, if the content of LiFSO3 is too high, it is presumed that it will undergo reductive decomposition at the negative electrode and accumulate on the negative electrode surface, or that excessive LiF will be generated and accumulate on the negative electrode surface due to the increased HF content, thereby increasing the internal resistance. Therefore, from the viewpoint of suppressing the degradation of battery performance such as output performance, it is also preferable to adjust the content of LiFSO3 to the above range.

[0208] As LiFSO3, it can be used either commercially available or synthesized based on known literature. For example, LiFSO3 can be synthesized using the method described in Japanese Patent Application Publication No. 2019-196306.

[0209] When using LiFSI as the lithium salt, it often contains a certain amount of LiFSO3 as a raw material impurity. As a method to adjust the LiFSO3 content in this invention, for example, after dissolving LiFSI in a non-aqueous solvent, a molecular sieve is added to the mixed solution and left for a certain period of time to reduce the LiFSO3 content. Then, the LiFSO3 content in the mixed solution is checked; it only needs to be within the concentration range of this invention. If there is too much, the contact time with the molecular sieve is extended; if there is too little, the contact time with the molecular sieve is shortened. Commercially available or synthetic molecular sieves can be used. Furthermore, after adding the molecular sieve, the mixed solution can be appropriately heated or stirred.

[0210] In this embodiment, the lithium salt preferably comprises a lithium imide salt, more preferably a LiN(SO2C) salt. m F 2m+1 )2 {where m is an integer from 0 to 8.} shows the lithium imide salt.

[0211] The lithium salt in this embodiment may further include lithium-containing imide salts, and one or more selected from fluorine-containing inorganic lithium salts, organic lithium salts, and other lithium salts.

[0212] From the viewpoint of maintaining the ionic conductivity of the non-aqueous electrolyte and the charge / discharge efficiency of the non-aqueous secondary battery, the lithium salt content is preferably 0.1 to 40 parts by mass relative to 100 parts by mass of the non-aqueous electrolyte, more preferably 0.2 to 38 parts by mass, 0.5 to 36 parts by mass, or 1 to 35 parts by mass.

[0213] (Contains lithium imide salt)

[0214] The lithium-containing imide salt preferably contains at least one of LiN(SO2F)2 and LiN(SO2CF3)2. This is because it can effectively suppress the decrease in ionic conductivity in low-temperature regions such as -10°C or -30°C, thus obtaining excellent low-temperature characteristics.

[0215] The saturation concentration of the lithium-containing imide salt relative to acetonitrile is higher than that of LiPF6. This suppresses the association and precipitation of lithium salt and acetonitrile at low temperatures; therefore, the lithium salt preferably contains the lithium-containing imide salt at a molar concentration where LiPF6 < the molar concentration of the lithium-containing imide salt. Furthermore, from the viewpoint of ensuring the ion supply to the non-aqueous electrolyte in this embodiment, the content of the lithium-containing imide salt is preferably 0.5 mol or more and 3.0 mol or less per 1 L of non-aqueous solvent.

[0216] By adjusting the content of lithium imide salt, the increase in resistance during high-temperature heating can be suppressed more effectively.

[0217] (Fluorine-containing inorganic lithium salts)

[0218] The lithium salt in this embodiment may include fluorine-containing inorganic lithium salts. Here, "fluorine-containing inorganic lithium salt" refers to a lithium salt whose anion does not contain carbon atoms, contains fluorine atoms, and is soluble in acetonitrile. Fluorine-containing inorganic lithium salts can form a passivation coating on the surface of the positive electrode current collector, inhibiting the corrosion of the positive electrode current collector.

[0219] Examples of fluorine-containing inorganic lithium salts include LiPF6, LiBF4, LiAsF6, Li2SiF6, LiSbF6, and Li2B. 12 F b H 12-b {In the formula, b is an integer from 0 to 3.} The lithium salts shown can be selected from one or more of them.

[0220] Ideally, the fluorinated inorganic lithium salt should be a compound of LiF and a Lewis acid. When using a fluorinated inorganic lithium salt with phosphorus atoms, it readily releases free fluorine atoms, making it more preferable. A representative fluorinated inorganic lithium salt is LiPF6, which releases PF6 anions upon dissolution. As a fluorinated inorganic lithium salt, a fluorinated inorganic lithium salt with boron atoms readily captures excess free acid components, making it preferred. From this perspective, LiBF4 is preferred.

[0221] When acetonitrile-containing non-aqueous electrolytes include LiPF6 as the main lithium salt, high-temperature durability is low. This is because PF5, formed by the reaction of LiPF6 with trace amounts of water in the non-aqueous electrolyte, acts as a Lewis acid catalyst, promoting the proton extraction reaction at the α-position of acetonitrile and promoting the generation of excess HF. At this point, the amount of HF generated exceeds the HF buffering capacity of LiFSO3, making it difficult to achieve sufficient high-temperature durability. Therefore, the lithium salt preferably contains LiPF6 at a molar concentration less than that of the lithium imide salt. When the LiPF6 content is within the above range, the generation of excess HF exceeding the HF buffering capacity of LiFSO3 can be suppressed.

[0222] The content of fluorinated inorganic lithium salt in the non-aqueous electrolyte of this embodiment is preferably 0.01 mol or more, more preferably 0.1 mol or more, and even more preferably 0.25 mol or more per 1 L of non-aqueous solvent. When the content of fluorinated inorganic lithium salt is within the above range, there is a tendency for increased ionic conductivity and high output characteristics. In addition, the amount per 1 L of non-aqueous solvent is preferably 2.8 mol or less, more preferably 1.5 mol or less, and even more preferably 1.0 mol or less. When the content of fluorinated inorganic lithium salt is within the above range, there is a tendency for increased ionic conductivity, high output characteristics, and suppression of the decrease in ionic conductivity at low temperatures associated with increased viscosity. Furthermore, there is a tendency to maintain the excellent performance of the non-aqueous electrolyte while improving high-temperature cycling characteristics and other battery characteristics.

[0223] The content of fluorinated inorganic lithium salt in the non-aqueous electrolyte of this embodiment, calculated per 1L of non-aqueous solvent, can be, for example, 0.05 mol or more and 1.0 mol or less.

[0224] (Organic lithium salts)

[0225] The lithium salt in this embodiment may include organic lithium salts. "Organic lithium salt" refers to a lithium salt other than a lithium imide salt that contains a carbon atom in its anion and is soluble in acetonitrile.

[0226] Organolithium salts with oxalate groups can be cited as examples. Specific examples of organolithium salts with oxalate groups include the organolithium salts represented by LiB(C2O4)2, LiBF2(C2O4), LiPF4(C2O4), and LiPF2(C2O4)2, among which at least one lithium salt selected from the lithium salts represented by LiB(C2O4)2 and LiBF2(C2O4) is preferred. Furthermore, it is more preferable to use one or more of these lithium salts together with a fluorine-containing inorganic lithium salt. This organolithium salt with oxalate groups can be added to a non-aqueous electrolyte, and it can also be contained in the negative electrode (negative electrode active material layer).

[0227] Regarding the amount of organolithium salt added to the non-aqueous electrolyte in this embodiment, from the viewpoint of better ensuring its effectiveness, it is preferably 0.005 mol or more, more preferably 0.01 mol or more, further preferably 0.02 mol or more, and particularly preferably 0.05 mol or more per 1L of non-aqueous solvent. However, there is a concern that excessive amounts of the aforementioned organolithium salt with oxalate groups in the non-aqueous electrolyte may lead to precipitation. Therefore, the amount of the aforementioned organolithium salt with oxalate groups added to the non-aqueous electrolyte is preferably less than 1.0 mol, more preferably less than 0.5 mol, and further preferably less than 0.2 mol per 1L of non-aqueous solvent.

[0228] It is known that organolithium salts with oxalate groups are poorly soluble in low-polarity organic solvents, particularly in chain carbonates. In this embodiment, the content of the organolithium salt in the non-aqueous electrolyte, measured per liter of non-aqueous solvent, can be, for example, 0.01 mol or more and 0.5 mol or less.

[0229] It should be noted that organolithium salts containing oxalate groups sometimes contain trace amounts of lithium oxalate. Therefore, when mixed as a non-aqueous electrolyte, they may react with trace amounts of moisture contained in other raw materials to form a new white precipitate of lithium oxalate. Therefore, the lithium oxalate content in the non-aqueous electrolyte of this embodiment is preferably suppressed to below 500 ppm.

[0230] (Other lithium salts)

[0231] In addition to the lithium salts described above, the lithium salts in this embodiment may also include other lithium salts. Specific examples of other lithium salts include:

[0232] LiClO4, LiAlO4, LiAlCl4, LiB 10 Cl 10 Inorganic lithium salts such as chloroborane (Li) whose anions do not contain fluorine atoms;

[0233] LiCF3SO3, LiCF3CO2, Li2C2F4(SO3)2, LiC(CF3SO2)3, LiC n F （2n+1） SO3 {where n≥2}, lower aliphatic carboxylic acids Li, tetraphenylboronic acid Li, LiB(C3O4H2)2 and other organic lithium salts;

[0234] LiPF5 (CF3) Equation LiPF n (C) p F 2p+1 ) 6-n [In the formula, n is an integer from 1 to 5, and p is an integer from 1 to 8] represents an organic lithium salt;

[0235] LiBF3 (CF3) Equation LiBF q (C) s F 2s+1 ) 4-q [In the formula, q is an integer from 1 to 3, and s is an integer from 1 to 8] represents an organolithium salt;

[0236] Lithium salts formed by bonding with polyvalent anions;

[0237] The following formula (XXa):

[0238] LiC(SO2R) jj (SO2R) kk (SO2R) ll (XXa)

[0239] {where R is the formula} jj R kk and R ll Choose any of the same or different perfluoroalkyl groups, representing 1 to 8 carbon atoms.

[0240] The following formula (XXb):

[0241] LiN (SO2OR) mm (SO2OR) nn (XXb)

[0242] {where R is the formula} mm and R nnChoose any of the same or different perfluoroalkyl groups, representing those with 1 to 8 carbon atoms.

[0243] The following formula (XXc):

[0244] LiN(SO2R) oo (SO2OR) pp (XXc)

[0245] {where R is the formula} oo and R pp Choose any perfluoroalkyl group, whether the same or different, representing 1 to 8 carbon atoms.} Each of the organolithium salts, etc., can be used together with one or more of the fluorine-containing inorganic lithium salts.

[0246] The amount of other lithium salts added to the non-aqueous electrolyte can be appropriately set in the range of more than 0.01 mol and less than 0.5 mol, for example, based on the amount in 1L of non-aqueous solvent.

[0247] <Additives for Electrode Protection>

[0248] The non-aqueous electrolyte of this embodiment may contain an additive for protecting the electrode (electrode protection additive). The electrode protection additive may substantially overlap with the substance that acts as a solvent for dissolving lithium salts (i.e., the aforementioned non-aqueous solvent). The electrode protection additive is preferably a substance that helps improve the performance of the non-aqueous electrolyte and the non-aqueous secondary battery, and also includes substances that do not directly participate in the electrochemical reaction.

[0249] Specific examples of additives for electrode protection include:

[0250] Fluorinated ethylene carbonates, represented by 4-fluoro-1,3-dioxolane-2-one, 4,4-difluoro-1,3-dioxolane-2-one, trans-4,5-difluoro-1,3-dioxolane-2-one, cis-4,5-difluoro-1,3-dioxolane-2-one, 4,4,5-trifluoro-1,3-dioxolane-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolane-2-one and 4,4,5-trifluoro-5-methyl-1,3-dioxolane-2-one;

[0251] Cyclic carbonates containing unsaturated bonds, such as vinylene carbonate, 4,5-dimethyl vinylene carbonate, and ethylene ethylene carbonate.

[0252] Lactones represented by γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone and ε-caprolactone;

[0253] Cyclic ethers, represented by 1,4-dioxane;

[0254] Cyclic sulfur compounds, represented by ethylene sulfite, propylene sulfite, butyl sulfite, pentenyl sulfite, sulfolane, 3-cyclobutene sulfone, 3-methylcyclobutene sulfone, 1,3-propane sulpholactone, 1,4-butane sulpholactone, 1-propene 1,3-sulpholactone, and tetramethylene sulfoxide,

[0255] They can be used individually or in combination of two or more.

[0256] The content of the electrode protection additive in the non-aqueous electrolyte is preferably 0.1 to 30% by volume, more preferably 0.3 to 15% by volume, further preferably 0.4 to 8% by volume, and particularly preferably 0.5 to 4% by volume, relative to the total amount of non-aqueous solvent.

[0257] In this embodiment, the higher the content of the electrode protection additive, the better it suppresses the degradation of the non-aqueous electrolyte. However, the lower the content of the electrode protection additive, the better the high output characteristics of the non-aqueous secondary battery under low-temperature conditions. Therefore, by adjusting the content of the electrode protection additive to the above-mentioned range, there is a tendency to maintain the basic functions of a non-aqueous secondary battery and to give full play to the excellent performance of the non-aqueous electrolyte based on its high ionic conductivity. Furthermore, by preparing the non-aqueous electrolyte with this composition, the cycle performance, high output performance under low-temperature conditions, and other battery characteristics of the non-aqueous secondary battery can be improved.

[0258] Acetonitrile readily undergoes electrochemical reduction and decomposition. Therefore, for non-aqueous solvents containing acetonitrile, as electrode protection additives for forming SEI on the negative electrode, it is preferable to include one or more cyclic aprotic polar solvents, and more preferably, one or more cyclic carbonates containing unsaturated bonds.

[0259] As a cyclic carbonate containing unsaturated bonds, vinylene carbonate is preferred. The content of vinylene carbonate in the non-aqueous electrolyte relative to the total amount of the non-aqueous solvent is preferably 0.1 vol% or more and 3.5 vol% or less, more preferably 0.2 vol% or more and 3 vol% or less, and even more preferably 0.3 vol% or more and 2.5 vol% or less. This allows for more effective improvement in low-temperature durability, providing a secondary battery with excellent low-temperature performance.

[0260] Vinylene carbonate, used as an electrode protection additive, suppresses the reductive decomposition reaction of acetonitrile on the negative electrode surface. On the other hand, excessive coating formation leads to a decrease in low-temperature performance. Therefore, by adjusting the amount of vinylene carbonate added to the above range, the interfacial (coating) resistance can be reduced to a lower level, thus suppressing cycling degradation at low temperatures.

[0261] <Acid anhydride>

[0262] The non-aqueous secondary battery of this embodiment is stabilized by the decomposition of a portion of the non-aqueous electrolyte during the initial charge, forming an SEI on the negative electrode surface. To more effectively enhance this SEI, an anhydride can be added. When acetonitrile is used as the non-aqueous solvent, there is a tendency for the SEI strength to decrease with increasing temperature; however, the addition of an anhydride promotes SEI enhancement. Therefore, by using this anhydride, the increase in internal resistance over time caused by thermal processes can be effectively suppressed.

[0263] Specific examples of acid anhydrides include chain anhydrides such as acetic anhydride, propionic anhydride, and benzoic anhydride; cyclic anhydrides such as malonic anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, or naphthalene-1,4,5,8-tetracarboxylic acid dianhydride; and mixed anhydrides with structures formed by the dehydration condensation of two different carboxylic acids, or different types of acids such as carboxylic acids and sulfonic acids. They can be used alone or in combination of two or more.

[0264] For the non-aqueous secondary battery of this embodiment, it is preferable to enhance the SEI before the reduction and decomposition of the non-aqueous solvent. Therefore, it is preferable to include at least one cyclic anhydride that functions earlier during the initial charge. This cyclic anhydride may consist of only one type or multiple types. Alternatively, it may include cyclic anhydrides other than these. Furthermore, the cyclic anhydride preferably includes at least one of succinic anhydride, maleic anhydride, and phthalic anhydride.

[0265] If the electrolyte is a non-aqueous solution containing at least one of succinic anhydride, maleic anhydride, and phthalic anhydride, a robust SEI can be formed at the negative electrode, more effectively suppressing the increase in resistance during high-temperature heating. The inclusion of succinic anhydride is particularly preferred. This suppresses side reactions and more effectively forms a robust SEI at the negative electrode.

[0266] In the case where the non-aqueous electrolyte of this embodiment contains an anhydride, its content is preferably in the range of 0.01 parts by mass or more and 10 parts by mass or less, more preferably 0.05 parts by mass or more and 1 part by mass or less, and even more preferably 0.1 parts by mass or more and 0.5 parts by mass or less, based on the amount of 100 parts by mass of the non-aqueous electrolyte.

[0267] The acid anhydride preferably contains a non-aqueous electrolyte. On the other hand, as long as the acid anhydride functions in a non-aqueous secondary battery, at least one battery component selected from the group consisting of a positive electrode, a negative electrode, and a separator can contain acid anhydride. As a method for containing acid anhydride in a battery component, it can be included in the battery component during manufacturing, or it can be impregnated into the battery component through post-processing such as coating, impregnation, or spray drying.

[0268] <Any Additives>

[0269] In this embodiment, in order to improve the charge-discharge cycle characteristics of the non-aqueous secondary battery, enhance its high-temperature storage performance, and improve its safety (e.g., prevent overcharging), any additives (acid anhydrides and additives other than electrode protection additives) may be appropriately contained in the non-aqueous electrolyte.

[0270] Examples of suitable additives include sulfonates, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphates (such as ethyl diethylphosphonoethyl ester (EDPA); (C2H5O)2(P=O)-CH2(C=O)OC2H5, tri(trifluoroethyl phosphate) (TFEP); (CF3CH2O)3P=O, triphenyl phosphate (TPP); (C6H5O)3P=O, triallyl phosphate; (CH2=CHCH2O)3P=O, etc.), and nitrogen-containing cyclic compounds without steric hindrance around non-shared electron pairs (such as pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.). Phosphate esters, in particular, are effective as additives because they inhibit side reactions during storage.

[0271] In this embodiment, when the non-aqueous electrolyte contains any other additives, the content of such additives, in terms of the total amount of the non-aqueous electrolyte, is preferably in the range of 0.01% by mass or more and 10% by mass or less, more preferably 0.02% by mass or more and 5% by mass or less, and even more preferably 0.05% to 3% by mass. By adjusting the content of such other additives to the above range, there is a tendency to impart better battery characteristics without impairing the basic functions of a non-aqueous secondary battery.

[0272] <Ionic conductivity of non-aqueous electrolytes>

[0273] In non-aqueous secondary batteries, when the separator of the preferred embodiment described later is combined with a non-aqueous electrolyte with low ionic conductivity, the migration speed of lithium ions is rate-controlled by the ionic conductivity of the non-aqueous electrolyte, sometimes resulting in unsatisfactory input / output characteristics. Therefore, in this embodiment, the ionic conductivity of the non-aqueous electrolyte is preferably 10 mS / cm or more, more preferably 15 mS / cm, and even more preferably 20 mS / cm.

[0274] <Method for manufacturing non-aqueous electrolytes>

[0275] The non-aqueous electrolyte of this embodiment can be manufactured by mixing a non-aqueous solvent, a lithium salt, and any required additives (electrode protection additives, acid anhydrides, and any other additives, etc.) together by any means.

[0276] Battery separators

[0277] In another aspect of the present invention, a separator for a battery (hereinafter also simply referred to as "separator") is provided. The separator requires both insulation and ion permeability, and is therefore typically formed from insulating materials such as paper, nonwoven fabric made of polyolefin, or microporous membrane made of resin, which are insulating materials with porous structures. Particularly when using a separator in a non-aqueous electrolyte secondary battery, which has a positive and negative electrode capable of absorbing / releasing lithium, and a non-aqueous electrolyte in which the electrolyte is dissolved in a non-aqueous solvent, a polyolefin microporous membrane with a dense and uniform porous structure that can be used to construct the separator is excellent as the separator substrate. Therefore, the separator of this embodiment may comprise a polyolefin microporous membrane.

[0278] From the perspective of balancing battery safety and output performance, the separator preferably comprises the following two layers:

[0279] (First layer) Substrate; and

[0280] (Second layer) A layer that is laminated on at least one side of a substrate.

[0281] From the same point of view, the thickness ratio of the substrate (first layer) to the second layer is preferably 0.5 or more and 10 or less.

[0282] In this embodiment, the weight-average molecular weight of the separator is preferably 100,000 or more and 10,200,000 or less, more preferably 150,000 or more and 8,000,000 or less.

[0283] (First floor)

[0284] From the viewpoint of resisting oxidation-reduction degradation of the separator and constructing a dense and uniform porous structure, the substrate for the first layer is preferably a microporous membrane made of polyolefin.

[0285] (Microporous membranes made of polyolefins)

[0286] Polyolefin microporous membranes can be monolayer membranes consisting of a single polyolefin microporous layer, multilayer membranes consisting of multiple polyolefin microporous layers, or multilayer membranes consisting of a polyolefin resin layer and a layer containing other resins as the main component.

[0287] In the case of a two-layer membrane formed by two polyolefin-containing microporous layers, the polyolefin composition of the two layers can be different. In the case of a multilayer membrane formed by three or more polyolefin-containing microporous layers, the polyolefin composition of the outermost and innermost layers can be different, for example, it can be a three-layer membrane.

[0288] The thickness of the polyolefin microporous membrane is preferably 1.0 μm or more, more preferably 2.0 μm or more, even more preferably 3.0 μm or more, 4.0 μm or more, or 5.5 μm or more. A membrane thickness of 1.0 μm or more tends to further improve membrane strength. Furthermore, the thickness of the microporous membrane is preferably 100 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. A membrane thickness of 100 μm or less tends to further improve ion permeability.

[0289] (Second layer)

[0290] The second layer is a layer laminated on at least one side of the substrate. The second layer can be disposed on one or both sides of the substrate, and is preferably disposed such that at least a portion of the substrate is exposed.

[0291] From the viewpoint of heat resistance of the separator and safety of the battery, the second layer preferably contains heat-resistant resin and inorganic filler, and may also contain thermoplastic polymer resin, any additives, etc. as desired.

[0292] (Heat-resistant resin)

[0293] In this embodiment, as the heat-resistant resin, a resin with a melting point exceeding 150°C, a resin with a melting point exceeding 250°C, or, for resins that have no substantial melting point, a resin with a thermal decomposition temperature exceeding 250°C is preferred. Examples of such heat-resistant resins include fully aromatic polyamides, polyimides, polyamide-imides, polysulfones, polyethersulfones, polyketones, polyethers, polyetherketones, polyetherimides, cellulose; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose. From the viewpoint of durability, fully aromatic polyamides (also known as aromatic polyamide resins) are preferred, and para-aromatic polyamides and / or meta-aromatic polyamides are more preferred. Furthermore, from the viewpoint of porous layer formation and redox resistance, meta-aromatic polyamides are preferred.

[0294] When using aromatic polyamides as heat-resistant resins, the preferred concentration ratio of terminal groups in the aromatic polyamide is [COOX{where X represents hydrogen, alkali metal, or alkaline earth metal}] / [NH2]≥1. For example, terminal carboxyl groups such as COONa have the effect of removing SEI that is undesirable to be generated on the negative electrode side of the battery. Therefore, when using aromatic polyamides with more terminal carboxyl groups than terminal amine groups, there is a tendency to obtain non-aqueous electrolyte secondary batteries with long-term stable discharge capacity.

[0295] (Thermoplastic resin)

[0296] The second layer may contain thermoplastic resin (excluding the heat-resistant resin described above). The second layer may contain at least 60% by mass, more preferably at least 90% by mass, further preferably at least 95% by mass, and particularly preferably at least 98% by mass relative to its total amount of thermoplastic resin.

[0297] Examples of thermoplastic resins include:

[0298] Polyolefin resins such as polyethylene, polypropylene, and α-polyolefin;

[0299] Fluorinated polymers such as polyvinylidene fluoride and polytetrafluoroethylene, or copolymers containing them;

[0300] Diene polymers containing conjugated dienes such as butadiene and isoprene as monomer units, or copolymers containing them, or their hydrides;

[0301] Acrylic polymers containing (meth)acrylate, (meth)acrylic acid, etc. as monomer units and without polyalkylene glycol units; acrylic polymers containing (meth)acrylate, (meth)acrylic acid, etc. as monomer units and with one or two polyalkylene glycol units; or copolymers thereof or their hydrogenated derivatives.

[0302] Rubber products such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate;

[0303] Polyalkylene glycols such as polyethylene glycol and polypropylene glycol do not have polymerizable functional groups;

[0304] Resins such as polyphenylene ether, polyphenylene sulfide, and polyester;

[0305] A copolymer of olefinic unsaturated monomers having alkylene glycol units repeating in a number of 3 or more as copolymer units; and

[0306] Their combination.

[0307] From the viewpoint of improving the safety of batteries with separators, thermoplastic polymers preferably contain polymeric units of (meth)acrylate or (meth)acrylic acid.

[0308] From the viewpoint of improving the safety of batteries with separators in puncture tests, the glass transition temperature (Tg) of the thermoplastic resin is preferably in the range of -40°C to 105°C, and more preferably in the range of -38°C to 100°C.

[0309] From the viewpoints of wettability to the substrate, adhesion between the substrate (first layer) and the second layer, and adhesion to the electrode, the second layer preferably contains a polymer with a glass transition temperature below 20°C. From the viewpoints of anti-adhesion and ion permeability, it is preferable to contain a polymer with a glass transition temperature of 20°C or higher.

[0310] The thermoplastic resins described above can be manufactured using the corresponding monomers or comonomers through known polymerization methods. Suitable polymerization methods include, for example, solution polymerization, emulsion polymerization, and bulk polymerization.

[0311] In this embodiment, since a second layer can be easily formed by coating, it is preferable to form a particulate thermoplastic resin by emulsion polymerization, and use the resulting thermoplastic resin emulsion in the form of an aqueous latex.

[0312] (Inorganic packing)

[0313] There are no particular limitations on the inorganic filler used in the second layer, but inorganic fillers with a melting point above 200°C, high electrical insulation, and electrochemical stability within the operating range of lithium-ion secondary batteries are preferred.

[0314] Inorganic fillers can take various shapes, such as granular, plate-like, scaly, needle-like, columnar, spherical, polyhedral, and blocky. A variety of inorganic fillers with these shapes can be combined for use.

[0315] The average particle size (D50) of the inorganic filler is preferably 0.2 μm or more and 2.0 μm or less, more preferably more than 0.2 μm and 1.2 μm or less. From the viewpoint of suppressing thermal shrinkage at high temperatures (e.g., 150°C or more, 200°C or more, or 200°C or more) or improving the barbell impact failure test performance at high temperatures even when the second layer is relatively thin (e.g., the second layer thickness is 5 μm or less, or 4 μm or less), it is preferable to adjust the D50 of the inorganic filler to the above range. As a method for adjusting the particle size and distribution of the inorganic filler, for example, methods such as using a suitable pulverizing device such as a ball mill, bead mill, or spray mill to pulverize the inorganic filler to reduce the particle size can be listed.

[0316] In the second layer, it is preferable that, in addition to the heat-resistant resin, it also contains inorganic fillers, and more preferably, it contains 25% to 95% by mass of inorganic fillers based on the mass of the second layer. More than 25% by mass of inorganic fillers is preferred for dimensional stability and heat resistance at high temperatures, while less than 95% by mass of inorganic fillers is preferred for strength, processability, or moldability.

[0317] Furthermore, from the viewpoint of improving battery safety at high temperatures, the second layer preferably contains 30% to 90% by mass of inorganic filler with an average particle size in the range of 0.2 μm to 0.9 μm, based on the mass of the second layer, and more preferably contains 32% to 85% by mass.

[0318] As inorganic fillers, there are no particular limitations. Examples include oxide ceramics such as alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics made from silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide (AlO(OH)), potassium titanate, talc, kaolinite, dickite, perlite, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. These can be used individually or in combination.

[0319] Among them, from the perspective of improving electrochemical stability and heat resistance of the separator, aluminum oxide compounds such as alumina and aluminum hydroxide are preferred; as well as aluminum silicate compounds such as kaolinite, dickite, perlite, halloysite, and pyrophyllite that do not have ion exchange capacity.

[0320] It should be noted that alumina exists in many crystalline forms, including α-alumina, β-alumina, γ-alumina, and θ-alumina, all of which are suitable for use. Among them, α-alumina is thermally and chemically stable, and is therefore preferred.

[0321] Aluminum oxide compounds, particularly aluminum hydroxide (AlO(OH)), are preferred. From the viewpoint of preventing internal short circuits caused by lithium dendrite formation, boehmite is more preferred as aluminum hydroxide. Using boehmite-based particles as the inorganic filler constituting the second layer maintains high permeability and enables a very lightweight porous layer. Furthermore, the thinner porous layer suppresses thermal shrinkage of the microporous membrane at high temperatures, exhibiting excellent heat resistance. Synthetic boehmite that can reduce ionic impurities that adversely affect the characteristics of electrochemical devices is further preferred.

[0322] As an aluminum silicate compound without ion exchange capacity, kaolin, which is mainly composed of kaolin minerals, is more preferred due to its low cost and easy availability. Among kaolin, wet kaolin and calcined kaolin obtained by calcination are known. In this embodiment, calcined kaolin is particularly preferred. Calcined kaolin is particularly preferred from the viewpoint of electrochemical stability because its water of crystallization is released during calcination, thereby removing impurities.

[0323] From the viewpoint of high-temperature safety of the battery, the thickness of the second layer is preferably less than 7 μm and more preferably less than 6 μm on each single side of the substrate (first layer). From the viewpoint of improving heat resistance and insulation, the thickness of the second layer can be greater than 0.01 μm, greater than 0.1 μm, or greater than 0.5 μm.

[0324] From the viewpoint of battery cycle performance and safety, the second layer preferably includes at least one of the components described above, selected from the group consisting of ceramics, aromatic polyamide resins and polyvinylidene fluoride (PVDF).

[0325] When the second layer is configured only on a portion of the substrate, the configuration pattern of the second layer can be, for example, dotted, striped, grid-like, banded, honeycomb-like, irregular, and combinations thereof.

[0326] (Polyolefins)

[0327] The polyolefin used in this embodiment is not particularly limited, and examples include homopolymers of ethylene or propylene, or copolymers formed from at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene. From the viewpoint that it can be heat-set at higher temperatures (sometimes abbreviated as "HS") without clogging the pores, high-density polyethylene (homopolymer) and low-density polyethylene are more preferred, and high-density polyethylene (homopolymer) is even more preferred. It should be noted that one type of polyolefin may be used alone, or two or more types may be used in combination.

[0328] Ultra-high molecular weight polyethylene (UHMWPE) is preferably used in combination with silane-modified polyolefins. Generally, UHMWPE refers to polyethylene with a weight-average molecular weight of 1,000,000 or higher.

[0329] <Silane crosslinking reaction>

[0330] The separator for the battery preferably comprises a silane-modified polyolefin. More preferably, the silane-modified polyolefin is contained in a substrate (i.e., a microporous membrane made of polyolefin).

[0331] Battery separators containing silane-modified polyolefins preferably initiate a silane crosslinking reaction of the silane-modified polyolefin upon contact with a non-aqueous electrolyte. Examples of silane-modified polyolefins include silane-grafted modified polyethylene and silane-grafted modified polypropylene. It is believed that the functional groups contained in the polyolefin constituting the separator undergo crosslinking in the amorphous portion and are not introduced into the crystalline portion of the polyolefin. Therefore, the separator of this embodiment forms a crosslinked structure using the chemical substances in the non-aqueous electrolyte upon contact with it, thereby suppressing the increase of internal stress or deformation of the manufactured battery, and improving safety in tests such as nail penetration.

[0332] When silane-modified polyolefin is included in a substrate (microporous membrane made of polyolefin), the substrate may include (A) silane-grafted modified polyethylene, (B) silane-grafted modified polypropylene, (C) polyethylene (polyethylene different from the aforementioned silane-grafted modified polyethylene: hereinafter also simply referred to as "polyethylene"), etc. Furthermore, the membrane rupture temperature determined by thermomechanical analysis (TMA) is 170~210°C. Furthermore, based on a total of 100% by mass of silane-grafted modified polyethylene, silane-grafted modified polypropylene, polyethylene, and one or more components (D) as optional blends, the content ratio of silane-grafted modified polyethylene is 2~50% by mass, the content ratio of silane-grafted modified polypropylene is 1~40% by mass, the content ratio of polyethylene is 5~95% by mass, and the content ratio of optional components is 0~10% by mass. Thus, a high-quality separator (e.g., with fewer resin aggregates in the separator) can be achieved, and furthermore, by including such a separator, high battery safety can be ensured.

[0333] It should be noted that, as an arbitrary component, components different from any of (A) to (C) may be listed. For example, at least one of the polymers or additives described below that are different from any of (A) to (C) may be listed. The arbitrary component is not limited to one. The separator may contain multiple polymers different from any of (A) to (C), may contain multiple additives, or may contain both the polymer and the additive. When the separator contains multiple arbitrary components, the total content of these multiple arbitrary components may be less than 10% by mass.

[0334] Regarding this, in microporous membranes, high-temperature rupture resistance can be exhibited by constructing silane crosslinked structures (gel structures) using silane-grafted modified polyethylene and silane-grafted modified polypropylene. This is presumably because the polypropylene dispersed in the mixed resin is suitably linked to each other, the polyethylene to each other, and / or the polypropylene and polyethylene through the silane crosslinked structure. That is, it can be considered that the polypropylene is crosslinked to each other, and that the polypropylene and polyethylene are crosslinked in a compatible manner, thereby forming a contact layer between them. At this point, the polypropylene becomes the core, and the contact layer surrounding the core becomes the shell, thus forming a core-shell structure dispersed in the polyethylene. Furthermore, it can be considered that the polyethylene also undergoes crosslinking to each other, thereby changing the overall morphology of the microporous membrane, thus maintaining the membrane shape even when the melting point of polyethylene (e.g., around 130°C to 140°C) is near or above the melting point of polypropylene (e.g., around 170°C). In addition, the morphology of the microporous membrane as a whole changes, thereby increasing the tensile elongation. As a result, it is expected that the possibility of the separator breaking when the battery is deformed by external force can be reduced.

[0335] From the viewpoint of ensuring high-temperature rupture resistance and improving tensile elongation, based on the above total of 100% by mass, the content of silane-grafted modified polyethylene is preferably 3% by mass or more, more preferably 4% by mass or more, more preferably 49.5% by mass or less, and more preferably 49% by mass or less.

[0336] Furthermore, based on the same viewpoint as above, and taking the total of 100% by mass as a benchmark, the content of silane-grafted modified polypropylene is preferably 1.5% by mass or more, more preferably 2% by mass or more, preferably 39.5% by mass or less, and more preferably 39% by mass or less.

[0337] Furthermore, based on the same viewpoint as above, with a total of 100% by mass as a benchmark, the content of polyethylene (polyethylene different from the silane-grafted modified polyethylene mentioned above) is preferably 10% by mass or more, more preferably 12% by mass or more, preferably 94.5% by mass or less, and more preferably 94% by mass or less.

[0338] (A) Silane-grafted modified polyethylene and (B) Silane-grafted modified polypropylene)

[0339] Silane-grafted modified polyethylene is composed of a polyethylene main chain with alkoxysilane groups grafted onto the main chain. Similarly, silane-grafted modified polypropylene is composed of a polypropylene main chain with alkoxysilane groups grafted onto the main chain.

[0340] In the case of either silane-grafted modified polyethylene or silane-grafted modified polypropylene, it is presumed that the alkoxysilyl group is converted to a silanol group via a water-based hydrolysis reaction, undergoing a cross-linking reaction to form a siloxane bond (refer to the formula below; the ratio of T0 structure to T1, T2, or T3 structure is arbitrary). There are no particular limitations on the alkoxylated compounds substituted with alkoxysilyl groups; examples include methoxylated compounds, ethoxylated compounds, butoxylated compounds, etc. For example, in the formula below, multiple methyl groups (-Me) can each independently be converted to ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, etc.

[0341]

[0342] In the case of either silane-grafted modified polyethylene or silane-grafted modified polypropylene, the main chain and the graft are connected by covalent bonds. There are no particular limitations on the structure forming the covalent bonds; examples include alkyl groups, ethers, glycols, and esters. In the case of either silane-grafted modified polyethylene or silane-grafted modified polypropylene, before the crosslinking reaction, the grafting rate, relative to the ethylene unit and expressed in vinylsilanol units, is preferably 2.0 mol% or less, more preferably 1.7 mol% or less.

[0343] The polyethylene constituting silane-grafted modified polyethylene can be composed of a single type of ethylene or two or more types of ethylene. Two or more types of silane-grafted modified polyethylene composed of different types of ethylene can be used in combination.

[0344] The polypropylene constituting silane-grafted modified polypropylene can be composed of a single type of propylene or two or more types of propylene. Two or more silane-grafted modified polypropylenes composed of different propylenes can be used in combination.

[0345] The polypropylene constituting silane-grafted modified polypropylene is preferably a homopolymer of propylene.

[0346] The preferred density of the silane-modified polyolefin is 0.90~0.96 g / cm³. 3 Furthermore, the melt flow rate (MFR) is 0.2~5 g / min.

[0347] The preferred viscosity-average molecular weight (Mv) of either silane-modified polyethylene or silane-modified polypropylene is 20,000–150,000 and the density is 0.90–0.96 g / cm³. 3 Furthermore, the melt flow rate (MFR) of silane-modified polyethylene at 190°C is 0.2~5 g / min, while that of silane-modified polypropylene at 230°C.

[0348] Regarding the condensation reaction of silane-modified polyolefins, the reaction is promoted by acting as a catalyst under acidic, alkaline, or low-nucleophilic conditions. The siloxane bonds formed by the condensation exhibit high thermodynamic stability. The bond energy of CC is 86 kcal·mol-1. -1 The bond energy of C-Si is 74 kcal·mol⁻¹. -1 The bond energy of Si-O is 128 kcal·mol⁻¹. -1 This implies the thermodynamic stability of siloxane bonds (Non-Patent Literature 1, 2). Therefore, by having a certain concentration of HF and / or H2SO4 in the reaction system, the cross-linking reaction of siloxane-modified polyolefins in the polymer structure of the separator can be carried out in high yield, thereby constructing a highly heat-resistant structure in the separator.

[0349] Furthermore, Si-containing compounds are highly reactive with F anions; therefore, the cross-linking sites formed by siloxane bonds may be decomposed due to the high concentration of F anions. The Si-F bond energy is very high, at 160 kcal / cl·mol⁻¹. -1The Si-F bond possesses high thermodynamic stability, therefore it is assumed that the F anion is continuously consumed until its concentration in the system reaches a constant level during the equilibrium reaction (Non-Patent Literature 1, 2). It is speculated that the decomposition reaction at the crosslinking point caused by the F anion is a cleavage reaction of the C-Si or Si-Osi bonds of the siloxane bond. Previous reports have indicated that in experiments estimating the bond dissociation energy of Si-X using the compound Me3Si-X, the bond dissociation energy D of Si-X was D=394±8 kJ / mol when X=Me, D=513±11 kJ / mol when X=Ome, and D=638±5 kJ / mol when X=F (Non-Patent Literature 3). Furthermore, under acidic conditions, considering the stability of the products after the cleavage of the C-Si or Si-OSi bonds of the siloxane bond, it is speculated that the Si-OSi bond is easily cleaved into Si-F and HO-Si. Therefore, it is believed that when the concentration of F anions in the reaction system reaches a certain level, the siloxane bonds with cross-linking points may be decomposed, potentially reducing the heat resistance of the separator.

[0350] This invention discovers that by utilizing HFSO3 to generate a certain amount of HF and H2SO4 within the system through an equilibrium reaction, the cross-linking reaction of siloxane bonds can be promoted, thus controlling the cross-linking reaction within the battery of a separator with high heat resistance. Furthermore, the decomposition reaction of HFSO3 is an equilibrium reaction, therefore it can continuously initiate the cross-linking reaction of siloxane bonds over a long period, significantly increasing the probability of the cross-linking reaction. The amorphous structure of polyethylene is a highly entangled structure; even if only a portion of the cross-linked structure is formed, its entropic elasticity increases significantly. Therefore, the molecular mobility of the amorphous portion is reduced, making it difficult to form siloxane bonds for all silanol units. This invention investigates the addition under various conditions, fundamentally solving this problem.

[0351] <Calcium-containing island structure>

[0352] In this embodiment, the separator is preferably one in which at least one calcium-containing island structure with a size of 9 μm is detected during TOF-SIMS measurement over a 100 μm square area. 2 Above and 245μm 2 The following is a preferred size for the calcium-containing island structure: 10 μm. 2 The above, and more preferably 11μm 2 That's all. Furthermore, the size of the calcium-containing island structure is more preferably 230 μm. 2 The following, and more preferably 214μm 2 the following.

[0353] Furthermore, in this embodiment, the separator is preferably such that, when TOF-SIMS measurement is performed on a 100 μm square area and two or more calcium-containing island structures are detected, either the minimum or maximum distance between the weighted center positions of the island structures is 6 μm or more and 135 μm or less. More preferably, the distance between the weighted center positions is 8 μm or more, and even more preferably 10 μm or more. Additionally, more preferably, the distance between the weighted center positions is 130 μm or less, and even more preferably 125 μm or less.

[0354] When manufacturing batteries using non-aqueous electrolytes containing LiFSO3, excessive HF may exist within the battery due to unevenness caused by water introduced into various components. In this embodiment, by incorporating calcium-containing island structures in the separator, the HF in the system can be consumed in the form of CaF2, thereby controlling the HF concentration.

[0355] Calcium is distributed unevenly within the separator, forming aggregated island structures. Calcium reacts with HF to form CaF2, suggesting it may act as an HF trap. Furthermore, calcium is gradually consumed in stages from the surface of the island structures; therefore, it is hypothesized that its uneven distribution within the separator can maintain its effectiveness rather than be completely consumed in a short time. This, in turn, can suppress battery degradation over a long period.

[0356] Furthermore, if an excess of HF is present in the silane crosslinking separator after crosslinking, it may catalyze the bond-breaking reaction, which is the reverse of the crosslinking reaction. Therefore, it is speculated that by continuously capturing HF using unevenly distributed calcium, the bond-breaking reaction can be suppressed, thereby improving the long-term stability of the crosslinking structure of the silane crosslinking separator.

[0357] Furthermore, when the electrolyte contains LiPF6, the generation of excessive F anions due to uneven water content is also considered. Therefore, it was found through experiments that by setting a calcium-containing island structure in the separator, the stability of the siloxane bond can be ensured, and the cross-linking structure of the separator can be maintained for a long time.

[0358] (Non-woven fabric separator)

[0359] The separator in this embodiment may include nonwoven fabric. Examples of nonwoven fabric separators in this embodiment include separators formed by sequentially layering layers of nonwoven fabric and inorganic pigments, and layers primarily composed of inorganic pigments, on a substrate primarily composed of nonwoven fabric.

[0360] When nonwoven fabric separators contain inorganic pigments, they can be formed by imparting inorganic pigments to a substrate containing nonwoven fabric. Alternatively, sometimes nonwoven fabric separators do not have a layer that mixes nonwoven fabric and inorganic pigments; instead, they are formed by two layers with inorganic pigments as the main component on a substrate with nonwoven fabric as the main component.

[0361] The separator containing nonwoven fabric in this embodiment can be manufactured as follows: A liquid containing inorganic pigment (hereinafter referred to as "coating liquid") is applied to the surface of a nonwoven fabric substrate, and then dried while at least a portion of the coating liquid has penetrated into the interior of the nonwoven fabric substrate. It should be noted that the portion formed by drying the coating liquid is called a "coating layer".

[0362] The nonwoven fabric substrate used in the separator of this embodiment is not particularly limited. Methods for forming nonwoven sheets from fibers include spunbonding, meltblowing, electrospinning, and wet spinning. For obtaining a thin and dense nonwoven fabric, the wet spinning method is preferred. Methods for bonding fibers include chemical bonding and hot-melt bonding. For obtaining a nonwoven fabric with a smooth surface, the hot-melt bonding method is preferred.

[0363] Examples of fibers used to form the nonwoven fabric in this embodiment include polyolefins such as polypropylene and polyethylene, polyesters such as polyethylene terephthalate, polyethylene isophthalate, and polyethylene naphthalate, acrylic fibers such as polyacrylonitrile, various synthetic fibers such as 6,6 nylon and 6 nylon, various cellulose pulps such as wood pulp, hemp pulp, and cotton pulp, rayon, and cellulose-based regenerated fibers such as lyocell. Among these, nonwoven fabrics primarily composed of polyester or polypropylene are preferred for reasons such as heat resistance and low moisture absorption. The preferred fiber diameter of the fibers forming the nonwoven fabric also depends on the properties of the coating liquid used, but is preferably in the range of 2 to 8 μm.

[0364] The coating layer in this embodiment comprises an inorganic pigment and a binder resin. As the inorganic pigment, alumina such as α-alumina, β-alumina, and γ-alumina, alumina hydrates such as boehmite, magnesium oxide, and calcium oxide can be used. Among these, α-alumina or alumina hydrates are preferred from the perspective of high stability for the electrolyte used in lithium-ion batteries. As the binder resin, various synthetic resins such as styrene-butadiene resin, acrylate resin, methacrylate resin, and fluoropolymers such as polyvinylidene fluoride can be used. The amount of binder resin relative to the inorganic pigment is preferably 0.1 to 30% by mass.

[0365] In addition to the aforementioned inorganic pigments and binders, the coating liquid can also be formulated with various dispersants such as polyacrylic acid and sodium carboxymethyl cellulose, various thickeners such as hydroxyethyl cellulose, sodium carboxymethyl cellulose, and polyethylene oxide, as well as various wetting agents, preservatives, defoamers, and other additives as needed.

[0366] In this embodiment, the battery characteristics deteriorate in the absence of a substrate, particularly the cycle performance. Without a substrate, it is assumed that the layer containing inorganic pigments is directly exposed to the potential between the electrodes, resulting in the formation of decomposition products due to electrochemical reactions.

[0367] Furthermore, in the nonwoven fabric separator of this embodiment, the thickness of the substrate is preferably 2 μm or more, and less than three times the thickness of the mixed layer of nonwoven fabric and inorganic pigment. When the thickness of the substrate is 2 μm or more, the battery characteristics (especially the cycle characteristics) become better. This is believed to be because, while the interface between the electrode and the separator is complex, when the thickness of the substrate layer is 2 μm or more, it is less likely that a portion of the layer mixed with inorganic pigment will come into contact with the electrode, and decomposition products from electrochemical reactions are less likely to be generated.

[0368] Furthermore, when the thickness of the substrate is less than three times the thickness of the layer mixed with inorganic pigments, the battery characteristics (especially cycle characteristics) become good. This is presumably because the compressive modulus of the layer mixed with inorganic pigments is higher than that of the substrate, and therefore, by setting the thickness within this range, electrode expansion during charging can be suppressed.

[0369] Furthermore, in the nonwoven separator of this embodiment, the proportion of inorganic pigments in the layer containing inorganic pigments preferably decreases continuously or in stages from the pigment-dominant layer side toward the substrate side. Batteries using separators with this structure exhibit particularly good cycle characteristics. More preferably, the proportion of inorganic pigments in the portion of the layer containing inorganic pigments extending to a depth of 1 / 4 from the pigment-dominant layer side is at least 1.5 times the proportion of inorganic pigments in the portion extending to a depth of 3 / 4. This results in a separator with particularly good cycle characteristics for the battery.

[0370] It should be noted that the term "depth" in this embodiment will be explained. First, the "depth" in the layer with inorganic pigments as the main component, the layer mixed with nonwoven fabric and inorganic pigments, and the substrate will be explained. In each layer, the "depth" expressed as "length" refers to the distance L1 in the opposite direction when the surface of each layer or the boundary surface with the adjacent layer is set to "depth 0 (zero)". In each layer, the "depth" expressed as "ratio" refers to the ratio (L1 / L2) of the distance L1 to the total thickness L2 of each layer.

[0371] Next, the concept of "depth" in the separator or nonwoven substrate will be explained. In the separator or nonwoven substrate, "depth" expressed as "length" refers to the distance L3 in the opposite direction when one surface of the separator or nonwoven substrate is set to "depth 0 (zero)". In the separator or substrate, "depth" expressed as "ratio" refers to the ratio (L3 / L4) of the distance L3 relative to the total thickness L4 of the separator or substrate.

[0372] In this embodiment, "a layer mainly composed of inorganic pigments" refers to an area where the proportion of inorganic pigments exceeds 1 / 4 when the cross-section of the separator is observed under an electron microscope. The "substrate" has an inorganic pigment content of less than 1 / 4 when the cross-section of the separator is observed under an electron microscope. Furthermore, "a layer mixed with nonwoven fabric and inorganic pigments" refers to an area where the inorganic pigment content is between 1 / 4 and 1 / 4 when the cross-section of the separator is observed under an electron microscope.

[0373] In this embodiment, the "inorganic pigment content ratio" refers to the volume ratio of inorganic pigment to nonwoven fabric. When scanning a section of the separator at a certain depth using a scanning electron microscope (SEM) in a linear fashion, it can be calculated as "length of the portion identified as inorganic pigment" / "length of the portion identified as nonwoven fabric". If either the inorganic pigment or the nonwoven fabric contains a unique element not present in the other, or contains elements in both but at significantly different proportions, the material can be identified using energy-dispersive X-ray spectroscopy (EDS).

[0374] To obtain a separator formed by sequentially stacking a substrate with nonwoven fabric as the main component, a layer mixed with nonwoven fabric and inorganic pigments, and a layer with inorganic pigments as the main component, the penetration depth of the coating liquid is adjusted. In this embodiment, the penetration depth of the coating liquid is preferably set to be more than 1 / 4 of the thickness of the nonwoven fabric substrate and less than (thickness of the nonwoven fabric substrate - 2) μm.

[0375] One method for adjusting the penetration depth of the coating liquid is as follows. A first method involves adjusting the substrate fibers constituting the nonwoven fabric substrate. In this method, to achieve a shallower penetration depth, the blending ratio of fine fibers is increased. To achieve a deeper penetration depth, the blending ratio of fine fibers is decreased. Furthermore, the penetration depth can be adjusted by changing the amount of surfactants such as oils, dispersants, and / or defoamers adhering to the surface of the substrate fibers. For example, to achieve a shallower penetration depth, the amount of oils and dispersants adhering to the substrate fibers is reduced. In this embodiment, the amount of oils, etc., adhering to the substrate fibers is preferably in the range of 0.01 to 1% by mass.

[0376] As a second method, there is a method of adjusting the viscosity of the coating liquid (high shear viscosity, low shear viscosity). In this method, to achieve a shallow penetration depth, the viscosity of the coating liquid can be increased. To achieve a deeper penetration depth, the viscosity of the coating liquid can be decreased. Methods for adjusting the viscosity of the coating liquid include adjusting the concentration of solid components, adding a thickener, adjusting the amount of thickener added, and adjusting the temperature of the coating liquid. In this embodiment, the type B viscosity of the coating liquid is preferably in the range of 10 to 10000 mPa·s, more preferably in the range of 200 to 2000 mPa·s. By adjusting the type B viscosity to this range, the separator of this embodiment can be easily obtained.

[0377] As a third method, there is a method for adjusting the surface tension of the coating liquid. In this method, to achieve a shallow penetration depth, the surface tension of the coating liquid is increased. To achieve a deeper penetration depth, the surface tension of the coating liquid is decreased. Methods for adjusting the surface tension of the coating liquid include adding a wetting agent, adjusting the amount of wetting agent added, and adjusting the temperature of the coating liquid. In this embodiment, the surface tension of the coating liquid when it is aqueous is preferably 30~70 mN / m, and particularly preferably 45~65 mN / m. By using a surface tension within this range for the aqueous coating liquid, the separator of this embodiment can be easily obtained.

[0378] As a fourth method, there is a method for selecting a coating method. In this method, to achieve a shallow penetration depth of the coating liquid, a coating method in which the dynamic pressure in the direction in which the coating liquid is injected into the nonwoven fabric substrate is difficult to exert is used. To achieve a deep penetration depth of the coating liquid, a coating method in which the dynamic pressure in the direction in which the coating liquid is injected into the nonwoven fabric substrate is easy to exert is used. Examples of coating methods in which the dynamic pressure in the direction in which the coating liquid is injected into the nonwoven fabric substrate is difficult to exert include mold coating and curtain coating. Examples of coating methods in which the dynamic pressure in the direction in which the coating liquid is injected into the nonwoven fabric substrate is easy to exert include dip coating, blade coating, and rod coating. As an example of a coating method between the two, gravure coating is an example. In this embodiment, from the perspective of being able to easily adjust the penetration depth, gravure coating with a matching reverse direction is preferred. In particular, it is even more preferred to use a small-diameter gravure plate with a diameter of 150 mm or less.

[0379] By appropriately combining these methods, the penetration depth of the coating liquid can be adjusted, and it can also be set to be more than 1 / 4 of the thickness of the nonwoven substrate and less than (the thickness of the nonwoven substrate - 2) μm.

[0380] [Manufacturing method for battery separators]

[0381] (Manufacturing method of polyolefin microporous membrane)

[0382] As a method for manufacturing a separator for batteries, the following description focuses on the case where the polyolefin microporous membrane is a single-layer membrane (flat membrane), but does not exclude other forms besides flat membranes. The method for manufacturing the microporous membrane in this embodiment includes the following steps:

[0383] (1) Sheet forming process;

[0384] (2) Stretching process;

[0385] (3) Porous body forming process; and

[0386] (4) Heat treatment process.

[0387] The method for manufacturing the microporous membrane in this embodiment may include, as needed, a resin modification process or a mixing process before the sheet forming process (1), and / or a winding / cutting process after the heat treatment process (3).

[0388] In the mixing process, a mixing machine is used to mix polyolefins with other resins as needed, as well as plasticizers or inorganic materials. The polyolefin composition used in the mixing process may contain known additives such as dehydration condensation catalysts, plasticizers, metallic soaps such as calcium stearate or zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments, depending on the requirements. In this embodiment, the ratio of these resins is preferably adjusted according to the viscosity-average molecular weight of the polyethylene and silane-modified polyolefin used.

[0389] The polyolefin supplied in the mixing process or sheet forming process (1) is not limited to olefin homopolymers, but can be a polyolefin copolymerized from monomers having functional groups, or a functional group modified polyolefin.

[0390] If a polyolefin raw material lacks functional groups that can participate in the formation of a cross-linked structure, or if the molar fraction of such functional groups does not meet the specified ratio, the polyolefin raw material can be supplied to a resin modification process to introduce functional groups into the resin backbone or increase the molar fraction of functional groups, thereby obtaining a functional group-modified polyolefin. The resin modification process can be carried out using known methods.

[0391] There are no particular limitations on the plasticizer used; examples include organic compounds that can form a homogeneous solution with polyolefins at temperatures below their boiling points. More specifically, examples include decahydronaphthalene, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decanol, nonanol, diphenyl ether, n-decane, n-dodecane, and paraffin oil. Among these, paraffin oil and dioctyl phthalate are preferred. A single plasticizer can be used, or two or more can be used in combination. The proportion of the plasticizer is not particularly limited; however, from the viewpoint of the porosity of the resulting microporous membrane, it is preferable that the polyolefin and the silane-grafted modified polyolefin account for at least 20% by mass relative to the total mass, and from the viewpoint of the viscosity during melt mixing, it is preferably 90% by mass or less.

[0392] The sheet forming process (1) involves extruding the obtained compound, or a mixture of polyolefin and plasticizer, cooling and solidifying it, and shaping it into a sheet to obtain a sheet. There are no particular limitations on the sheet forming method; for example, a method of solidifying a melted and extruded compound by compression cooling can be listed. As for cooling methods, methods such as direct contact with cooling media like cold air or cooling water, or contact with rollers or presses cooled by refrigerant, can be listed. From the perspective of excellent film thickness control, methods involving contact with rollers or presses cooled by refrigerant are preferred.

[0393] The stretching process (2) involves extracting plasticizers or inorganic materials from the obtained sheet as needed, and then stretching the sheet at least along a uniaxial direction. Examples of sheet stretching methods include MD uniaxial stretching using a roller stretching machine, TD uniaxial stretching using a tenter frame, successive biaxial stretching using a combination of a roller stretching machine and a tenter frame or a tenter frame and a tenter frame, and simultaneous biaxial stretching using a simultaneous biaxial tenter frame or blow molding. From the viewpoint of obtaining a more uniform film, simultaneous biaxial stretching is preferred. From the viewpoint of film thickness uniformity, elongation, porosity, and average pore size balance, the total aspect ratio is preferably 8 times or more, more preferably 15 times or more, and even more preferably 20 times or more or 30 times or more. With a total aspect ratio of 8 times or more, there is a tendency to easily obtain a stretched material with high strength and good thickness distribution. Furthermore, from the viewpoint of preventing breakage, this aspect ratio can be 250 times or less.

[0394] The porous body forming process (3) is a process of extracting plasticizer from the stretched material after the stretching process to make the stretched material porous. There is no particular limitation on the extraction method of the plasticizer, and for example, the method of immersing the stretched material in the extraction solvent or rinsing the stretched material with the extraction solvent can be listed. There is no particular limitation on the extraction solvent, and for example, a substance that is a poor solvent for polyolefins and a good solvent for plasticizers or inorganic materials, and whose boiling point is lower than the melting point of polyolefins is preferred. There is no particular limitation on such extraction solvent, and for example, hydrocarbons such as n-hexane or cyclohexane; halogenated hydrocarbons such as dichloromethane or 1,1,1-trichloroethane and fluorocarbons; alcohols such as ethanol or isopropanol; ketones such as acetone or 2-butanone; and alkaline water can be listed. One extraction solvent can be used alone, or two or more solvents can be used in combination.

[0395] The heat treatment step (4) is a step after the stretching step whereby the plasticizer is extracted from the sheet as needed and further heat-treated to obtain a microporous membrane. There are no particular limitations on the heat treatment method; for example, heat setting methods such as stretching and relaxation operations using a tenter frame or roller stretching machine can be listed. The relaxation operation refers to a shrinkage operation performed along the mechanical direction (MD) and / or width direction (TD) of the membrane at a specified temperature and relaxation rate. The relaxation rate is the value obtained by dividing the MD dimension of the membrane after the relaxation operation by the MD dimension of the membrane before the operation; or by dividing the TD dimension of the membrane after the relaxation operation by the TD dimension of the membrane before the operation; or, in the case where both MD and TD have been relaxed, by multiplying the relaxation rate of MD by the relaxation rate of TD.

[0396] The winding / cutting process involves cutting the obtained microporous membrane as needed and winding it onto a specified core.

[0397] In the post-processing step, when the obtained polyolefin microporous membrane is pre-treated, the subsequent coating solution is easily applied, and the adhesion between the polyolefin microporous membrane as the first layer and the second layer is improved, which is therefore preferred. Examples of surface treatment methods include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

[0398] (Configuration method for the second layer)

[0399] The second layer can be configured on the substrate, for example, by coating a coating liquid containing a heat-resistant resin and / or a thermoplastic resin onto the substrate. Alternatively, the heat-resistant resin and / or thermoplastic resin can be synthesized by emulsion polymerization, and the resulting emulsion can be used directly as the coating liquid. The coating liquid preferably contains undesirable solvents such as water, a mixture of water and a water-soluble organic medium (e.g., methanol or ethanol).

[0400] For methods of coating a microporous membrane (substrate) made of polyolefin with a coating liquid containing a heat-resistant resin and / or a thermoplastic resin, there are no particular limitations as long as the method can achieve the desired coating pattern, coating thickness, and coating area. For example, known methods for coating with a coating liquid containing inorganic particles can be used.

[0401] There are no particular limitations on methods for removing solvent from the coating film after coating, as long as they do not adversely affect the substrate (first layer) and the second layer. For example, methods that fix the substrate while drying it at a temperature below its melting point can be listed; methods that perform vacuum drying at low temperature; methods that impregnate the heat-resistant resin and / or thermoplastic resin with a solvent that is unfavorable to the heat-resistant resin and / or thermoplastic resin, causing the heat-resistant resin and / or thermoplastic resin to solidify into granules, while simultaneously extracting the solvent, etc.

[0402] <Method for manufacturing calcium-containing island structures>

[0403] In the manufacturing process of separators, calcium stearate of a certain concentration is mixed into the raw materials when they are fed into an extruder, thereby forming calcium island structures within the separator. However, when using raw materials with significantly different molecular weights, differences in solubility and viscosity exist between the raw materials. Furthermore, the molecular weight of the resin raw material ranges from tens of thousands to millions of g / mol, while that of calcium stearate is 284 g / mol, making it thermodynamically difficult to uniformly disperse calcium stearate within the resin raw material. Moreover, in the case of melt mixing containing silane-modified polyolefins, units with heterofunctional groups are present, making dispersion even more difficult. In such complex mixed resins, shear stirring at high speeds using an extruder improves the uniformity of calcium stearate dispersion; however, the finely adjacent and dispersed island structures lead to an excessive consumption of F anions from the non-aqueous electrolyte. Additionally, the shear stirring at high speeds using an extruder degrades the molecular weight of the polyolefin, significantly impairing the mechanical strength and porosity of the separator.

[0404] In this invention, it was discovered that raw materials with Mv=2 million to 9 million (raw material A) and Mv=500,000 to 2 million (raw material B) are used as polyolefin raw materials, and raw materials with Mv=20,000 to 150,000 (raw material C) are used as silane-modified polyolefin raw materials, for a total of three types. Furthermore, by adjusting the ratio according to the molecular weight, the construction of calcium-containing island structures with defined size and dispersion can be controlled.

[0405] It should be noted that, in the above raw material composition, preferably, the proportion of raw material C in the whole is 5% to 60% by mass, and the ratio of raw material A to raw material B is 8:2 to 0.5:9.5.

[0406] The separator obtained by the method including the various processes described above can be used in a non-aqueous secondary battery having the non-aqueous electrolyte described above and positive and negative electrodes capable of absorbing / releasing lithium, and can be preferably used in a lithium-ion secondary battery.

[0407] Non-aqueous secondary batteries

[0408] The non-aqueous electrolyte of this embodiment can be used to construct a non-aqueous secondary battery.

[0409] The non-aqueous secondary battery of this embodiment is constructed by housing the positive electrode, negative electrode, separator, and non-aqueous electrolyte in a suitable battery casing.

[0410] The preferred non-aqueous secondary battery of this embodiment is one that has been tested to achieve 15 mA / cm² using the method described in detail in the Example section. 2 The recovery charging capacity retention rate after constant current charging is 90% or more, more preferably 92% or more, 94% or more, or 96% or more. It should be noted that there is no upper limit to the recovery charging capacity retention rate, for example, it is preferably 100% or less, less than 100%, 99% or less, or less than 99%.

[0411] Furthermore, it is preferable that the current density of the non-aqueous secondary battery in this embodiment is 15 mA / cm². 2 During the fast charging test, within the voltage range of 3.9~4.2V, no voltage plateau was observed in the charging curve. In this manual, "voltage plateau" refers to... Figure 3 The slope of the charging curve during CC (Constant Current) charging becomes relatively flat in the region shown. Furthermore, the current density is 15 mA / cm². 2 The charging curve during the fast charging test can be, for example, as shown below. Figure 3 The charge-voltage curve is shown. In this embodiment, the phenomenon that "the slope of the charging curve becomes relatively flat" refers to the region where, when a specific region of the charging curve is approximated as y=ax+b, the value of a is less than 1 / 3 of the maximum value of a. According to this embodiment, "no visible voltage plateau" has been found to be one of the indicators for determining that electrodeposition (lithium (Li) metal deposition at the negative electrode surface) has not occurred.

[0412] Specifically, as a non-aqueous secondary battery in this embodiment, it can be... Figure 1 and 2 The diagram shows a non-aqueous secondary battery 100. Here, Figure 1 To illustrate the top view of a non-aqueous secondary battery, Figure 2 for Figure 1 AA-line cross-section diagram.

[0413] Figure 1, Figure 2 The non-aqueous secondary battery 100 shown is a pouch-type battery. The non-aqueous secondary battery 100 contains a stacked electrode assembly and a non-aqueous electrolyte (not shown) within the space 120 of the battery casing 110. The stacked electrode assembly is formed by stacking a positive electrode 150 and a negative electrode 160 separated by a separator 170. The battery casing 110 is, for example, made of aluminum laminate film. At the outer periphery of the space formed by two aluminum laminate films, the upper and lower films are heat-fused to seal the space. The stacked assembly, formed by sequentially stacking the positive electrode 150, the separator 170, and the negative electrode 160, is impregnated with a non-aqueous electrolyte. However, this… Figure 2 In order to avoid complicating the drawings, the layers constituting the battery casing 110 and the layers of the positive electrode 150 and negative electrode 160 are not shown separately.

[0414] The aluminum laminate forming the battery casing 110 is preferably made by coating both sides of aluminum foil with a polyolefin-based resin.

[0415] The positive electrode 150 is connected to the positive electrode lead 130 within the non-aqueous secondary battery 100. Although not shown, the negative electrode 160 is also connected to the negative electrode lead 140 within the non-aqueous secondary battery 100. Furthermore, regarding the positive electrode lead 130 and the negative electrode lead 140, each has one end extended to the outside of the battery casing 110 in a manner that allows connection to external devices, etc., and these ionomer portions are heat-fused together with one side of the battery casing 110.

[0416] Figure 1 and 2 The non-aqueous secondary battery 100 shown in the diagram has a stacked electrode body with one positive electrode 150 and one negative electrode 160. However, the number of stacked positive electrode 150 and negative electrode 160 can be appropriately increased according to the capacity design. When there are multiple stacked electrode bodies with multiple positive electrode 150 and negative electrode 160, the tabs of the same electrode can be joined to each other by welding or the like, and then joined to a lead body by welding or the like, and then removed to the outside of the battery. The tabs of the same electrode can be in the form of an exposed portion of a current collector, or in the form of a metal sheet welded to the exposed portion of the current collector, etc.

[0417] The positive electrode 150 consists of a positive current collector and a positive active material layer. The negative electrode 160 consists of a negative current collector and a negative active material layer.

[0418] The positive electrode active material layer contains positive electrode active material, and the negative electrode active material layer contains negative electrode active material.

[0419] The positive electrode 150 and the negative electrode 160 are arranged opposite each other with the positive electrode active material layer and the negative electrode active material layer separated by a separator 170.

[0420] The following sections will describe the various elements constituting the non-aqueous secondary battery of this embodiment.

[0421] <positive electrode>

[0422] In the non-aqueous secondary battery of this embodiment, the positive electrode has a layer of positive electrode active material on one or both sides of the positive electrode current collector.

[0423] [Positive current collector]

[0424] The positive current collector is made of metal foil such as aluminum foil, nickel foil, or stainless steel foil. The positive current collector may have a carbon coating on its surface or be processed into a mesh shape. The thickness of the positive current collector is preferably 5-40 μm, more preferably 7-35 μm, and even more preferably 9-30 μm.

[0425] [Positive electrode active material layer]

[0426] The positive electrode active material layer contains positive electrode active material, and may further contain conductive additives and / or binders as needed.

[0427] (Positive electrode active material)

[0428] The positive electrode active material layer preferably comprises a material capable of absorbing and releasing lithium ions. Using such a material tends to result in high voltage and high energy density, and is therefore preferred.

[0429] As a positive electrode active material, examples include positive electrode active materials containing at least one transition metal element selected from the group consisting of Ni, Mn and Co, and preferably at least one lithium-containing metal oxide represented by the following general formula (a):

[0430] Li p Ni q Co r Mn s M t O u ·····(a)

[0431] {In the formula, M is at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba, and is within the range of 0 < p < 1.3, 0 < q < 1.2, 0 < r < 1.2, 0 ≤ s < 0.5, 0 ≤ t < 0.3, 0.7 ≤ q + r + s + t ≤ 1.2, and 1.8 < u < 2.2, and p is a value that depends on the charge / discharge state of the battery.}

[0432] In addition, examples of positive electrode active materials include:

[0433] Lithium cobalt oxides, represented by LiCoO2;

[0434] Lithium manganese oxides, represented by LiMnO2, LiMn2O4 and Li2Mn2O4;

[0435] Lithium nickel oxides, represented by LiNiO2;

[0436] With LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.75 Co 0.15 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.85 Co 0.075 Mn 0.075 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.81 Co 0.1 Al 0.09 O2, LiNi 0.85 Co 0.1 Al 0.05 Li, represented by O2 z MO2 (where M contains at least one transition metal element selected from the group consisting of Ni, Mn and Co, and represents two or more metal elements selected from the group consisting of Ni, Mn, Co, Al and Mg, and z represents a number greater than 0.9 and less than 1.2) represents a lithium-containing composite metal oxide.

[0437] With MnO2, FeO2, FeS2, V2O5, V6O 13 Metal oxides or metal chalcogenides with tunnel and layered structures, represented by TiO2, TiS2, MoS2 and NbSe2;

[0438] sulfur;

[0439] Conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0440] In particular, when the Ni content ratio q of the Li metal oxide shown in general formula (a) is 0.5 < q < 1.2, it is preferred to simultaneously reduce the amount of Co, a rare metal, and increase the energy density.

[0441] Here, there is a tendency for degradation to occur at lower voltages as the Ni content increases. The lithium metal oxide-containing positive electrode active material shown in general formula (a) contains an active site that causes oxidative degradation of the non-aqueous electrolyte, and this active site sometimes consumes compounds added on the positive electrode side to protect the negative electrode. In particular, acid anhydrides are particularly susceptible to this effect. Especially when acetonitrile is used as a non-aqueous solvent, the consumption of acid anhydrides on the positive electrode side becomes a problem.

[0442] From the viewpoint of long lifespan, lithium phosphorus metal oxides containing iron (Fe) atoms and having an olivine crystal structure are preferred, and lithium phosphorus metal oxides with an olivine structure as shown in the following formula (Xba) are even more preferred:

[0443] Li w M II PO4 (Xba)

[0444] {where M} II This indicates the presence of one or more transition metal elements containing Fe. The value of w depends on the charge / discharge state of the battery and represents a number from 0.05 to 1.10.

[0445] From the viewpoint of the lithium-phosphorus metal oxide shown in the above formula (Xba), a phosphoric acid metal oxide containing Li and Fe is more preferred, and the most preferred is one containing Fe. As a specific example of a lithium-phosphorus metal oxide containing Fe and having an olivine-type structure, the formula Li can be cited. w The compound shown is FePO4 {where w is 0.05~1.1}.

[0446] As the positive electrode active material in this embodiment, a lithium-containing metal oxide as described above can be used alone, or other positive electrode active materials can be used in combination with the lithium-containing metal oxide.

[0447] Furthermore, these additive decomposition products carried to and accumulated on the positive electrode side not only contribute to the increased internal resistance of non-aqueous secondary batteries but also accelerate the degradation of lithium salts. Consequently, the protection of the negative electrode surface becomes insufficient. In order to deactivate the active sites that essentially oxidize and degrade the non-aqueous electrolyte, it is preferable to have components that function as control or neutralizers for Jan-Taylor deformation. Therefore, the positive electrode active material preferably contains at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

[0448] For the same reasons as above, the surface of the positive electrode active material is preferably covered with a compound containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. Furthermore, the surface of the positive electrode active material is more preferably covered with an oxide containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. Moreover, when the surface of the positive electrode active material is covered with at least one oxide selected from the group consisting of ZrO2, TiO2, Al2O3, NbO3, and LiNbO2, it does not hinder the permeation of lithium ions, and is therefore further preferred.

[0449] It should be noted that the positive electrode active material can be a lithium-containing compound other than the lithium-containing metal oxide shown in formula (a). Examples of such lithium-containing compounds include, for instance, composite oxides containing lithium and transition metal elements, metal chalcogenides containing lithium, metal phosphate compounds containing lithium and transition metal elements, and metal silicate compounds containing lithium and transition metal elements. From the viewpoint of obtaining higher voltage, metal phosphate compounds containing lithium and at least one transition metal element selected from the group consisting of Co, Ni, Mn, Fe, Cu, Zn, Cr, V, and Ti are particularly preferred as lithium-containing compounds.

[0450] More specifically, examples of lithium-containing compounds include those represented by formula (XX-1):

[0451] Li v M I D2 (XX-1)

[0452] {In the formula, D represents the chalcogenide element, M...} I This indicates a battery containing at least one transition metal element, where the value of v depends on the battery's state of charge / discharge and is expressed as a number from 0.05 to 1.10.

[0453] The following compounds are represented by formula (XX-2):

[0454] Li w M II PO4 (XX-2)

[0455] {In the formula, D represents the chalcogenide element, M...} II This indicates a mixture of at least one transition metal element, where the value of w depends on the battery's state of charge / discharge and is expressed as a number from 0.05 to 1.10.

[0456] The following compounds are represented by formula (XX-3):

[0457] Li t M III uSiO4 (XX-3)

[0458] {In the formula, D represents the chalcogenide element, M...} III This indicates a mixture of one or more transition metal elements, where t depends on the battery's state of charge / discharge and represents a number from 0.05 to 1.10, and u represents a number from 0 to 2.

[0459] The lithium-containing compound shown in formula (XX-1) above has a layered structure, while the compounds shown in formulas (XX-2) and (XX-3) above have an olivine structure. These lithium-containing compounds may also be modified for purposes such as structural stabilization by replacing a portion of the transition metal element with Al, Mg, or other transition metal elements, including these metal elements at grain boundaries, replacing a portion of the oxygen atom with fluorine atoms, or covering at least a portion of the surface of the positive electrode active material with other positive electrode active materials.

[0460] The positive electrode active material can be used alone or in combination of two or more. From the perspective of reversibly and stably absorbing and releasing lithium ions and achieving high energy density, the positive electrode active material layer preferably contains at least one transition metal element selected from Ni, Mn and Co.

[0461] When lithium-containing compounds and other positive electrode active materials are used in combination as positive electrode active materials, the ratio of the two is preferably 80% by mass or more, more preferably 85% by mass or more, relative to the ratio of lithium-containing compounds used in all positive electrode active materials.

[0462] (Conductive additive)

[0463] Examples of conductive additives include carbon black, represented by graphite, acetylene black, and Ketjen black, as well as carbon fiber. The content of the conductive additive, in terms of 100 parts by mass relative to the positive electrode active material, is preferably 10 parts by mass or less, more preferably 1 to 5 parts by mass.

[0464] (Adhesive)

[0465] Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The binder content, in terms of 100 parts by mass of the positive electrode active material, is preferably 6 parts by mass or less, more preferably 0.5 to 4 parts by mass.

[0466] [Formation of the positive electrode active material layer]

[0467] The positive electrode active material layer is formed by coating a slurry containing a positive electrode agent onto the positive electrode current collector, drying (removing the solvent), and pressing as needed. The slurry containing the positive electrode agent is formed by dispersing a positive electrode agent obtained by mixing the positive electrode active material with, as needed, conductive additives and binders in a solvent. Known solvents can be used as such solvents. Examples include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0468] <negative electrode>

[0469] In this embodiment of the non-aqueous secondary battery, the negative electrode has a layer of negative electrode active material on one or both sides of the negative electrode current collector.

[0470] [Negative current collector]

[0471] The negative current collector can be made of metal foil such as copper foil, nickel foil, or stainless steel foil. Additionally, the negative current collector can have a carbon coating applied to its surface or be processed into a mesh shape. The thickness of the negative current collector is preferably 5-40 μm, more preferably 6-35 μm, and even more preferably 7-30 μm.

[0472] [Negative electrode active material layer]

[0473] The negative electrode active material layer contains negative electrode active material, and may further contain conductive additives and / or binders as needed.

[0474] (Negative electrode active material)

[0475] Examples of negative electrode active materials include carbon materials such as amorphous carbon (hard carbon), graphite (artificial graphite, natural graphite), pyrolytic carbon, coke, glassy carbon, calcined organic polymers, mesophase carbon microspheres, carbon fibers, activated carbon, carbon colloids, and carbon black; as well as lithium metal, metal oxides, metal nitrides, lithium alloys, tin alloys, Si materials, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, and organic polymers. One type of negative electrode active material can be used alone, or two or more can be used in combination. Examples of Si materials include silicon, Si alloys, and Si oxides.

[0476] From the perspective of improving battery voltage, the negative electrode active material layer preferably contains substances that can operate at voltages below 0.4V (vs. Li / Li). + Materials that absorb lithium ions at a potential of ) are used as negative electrode active materials.

[0477] The non-aqueous electrolyte of this embodiment has the following advantages: even when Si material is used as the negative electrode active material, various degradation phenomena accompanying negative electrode volume changes during repeated charge-discharge cycles can be suppressed. Therefore, in the non-aqueous secondary battery of this embodiment, using Si material, such as silicon alloy, as the negative electrode active material is a preferred approach in terms of possessing high capacity derived from Si material and excellent charge-discharge cycle characteristics.

[0478] In this embodiment, the negative electrode active material may include Si material, especially SiO. x (In the formula, 0.5 ≤ x ≤ 1.5). The Si material can be any of the following forms: crystalline, low-crystalline, and amorphous. In addition, when using Si material as the negative electrode active material, the conductivity between the active material particles is improved when the surface of the active material is covered with a conductive material, which is therefore preferred.

[0479] The operating potential of silicon is approximately 0.5V (vsLi / Li). + At this point, it is slightly higher than the working potential of graphite by about 0.05V (vsLi / Li). + Therefore, using Si materials reduces the risk of lithium deposition. Acetonitrile, used in the non-aqueous solvent of this embodiment, may undergo a reduction reaction with lithium metal, causing gas generation. Therefore, a negative electrode active material that is less prone to lithium deposition is preferred when used in combination with a non-aqueous electrolyte containing acetonitrile.

[0480] On the other hand, negative electrode active materials with excessively high operating potentials will lead to a decrease in the energy density of the battery. Therefore, from the viewpoint of improving energy density, negative electrode active materials are preferably at a voltage below 0.4V (vs. Li / Li). + It operates at a potential of ).

[0481] The content of Si material relative to the total amount of the negative electrode active material layer is preferably in the range of 0.1% by mass or more and 100% by mass or less, more preferably in the range of 1% by mass or more and 80% by mass or less, and even more preferably in the range of 3% by mass or more and 60% by mass or less. By adjusting the content of Si material to the above range, a balance between high capacity and charge-discharge cycle performance of the non-aqueous secondary battery can be ensured.

[0482] (Conductive additive)

[0483] Examples of conductive additives include carbon black, represented by graphite, acetylene black, and Ketjen black, as well as carbon fiber. The content of the conductive additive relative to 100 parts by mass of the negative electrode active material is preferably 20 parts by mass or less, more preferably 0.1 to 10 parts by mass.

[0484] (Adhesive)

[0485] Examples of binders include carboxymethyl cellulose, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, and fluororubber. Diene-based rubbers, such as styrene-butadiene rubber, can also be used. The binder content is preferably 10 parts by mass or less, more preferably 0.5 to 6 parts by mass, relative to 100 parts by mass of the negative electrode active material.

[0486] [Formation of the negative electrode active material layer]

[0487] The negative electrode active material layer is formed by coating a slurry containing a negative electrode agent onto the negative electrode current collector, drying (removing the solvent), and pressing as needed. The slurry containing the negative electrode agent is formed by dispersing a negative electrode agent obtained by mixing a negative electrode active material with conductive additives and / or binders as needed in a solvent. Examples of such solvents include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0488] <Battery casing>

[0489] The battery casing of the non-aqueous secondary battery in this embodiment can be constructed using known methods. For example, a battery canister or a laminated film casing can be used as the battery casing.

[0490] As a battery canister, a metal canister made of materials such as steel, stainless steel, aluminum, or cladding material can be used.

[0491] The laminated film housing can be made by overlapping two sheets with the hot-melt resin side facing inwards, or by bending it so that the hot-melt resin side faces inwards, and then heat-sealing the ends to seal it, thus using it as a housing in this sealed state. When using the laminated film housing, a positive lead (or a positive terminal and a lead tab connected to the positive terminal) can be connected to the positive current collector, and a negative lead (or a negative terminal and a lead tab connected to the negative terminal) can be connected to the negative current collector. At this time, the laminated film housing is sealed with the ends of the positive and negative leads (or the lead tabs connected to the positive and negative terminals respectively) extended to the outside of the housing.

[0492] As the outer shell of the laminated film, for example, a laminated film formed of three layers consisting of hot-melt resin / metal film / resin can be used.

[0493] The aluminum laminate forming the battery casing 110 is preferably made of double-sided aluminum foil coated with a polyolefin-based resin.

[0494] <Shape of non-aqueous secondary batteries>

[0495] The non-aqueous secondary battery of this embodiment can be shaped as square, cylindrical, oval, button, coin, flat, laminated, etc.

[0496] The non-aqueous secondary battery of this embodiment is particularly preferred for square, cylindrical, and laminated types.

[0497] <Manufacturing Method of Non-Aqueous Secondary Batteries>

[0498] The non-aqueous secondary battery of this embodiment can be manufactured using the aforementioned non-aqueous electrolyte, positive electrode, negative electrode, separator, and battery casing by known methods.

[0499] First, a laminate consisting of a positive electrode, a negative electrode, and a separator is formed. This can be achieved, for example, in the following configuration:

[0500] The positive and negative electrodes are wound together in a stacked state with long strips of separators sandwiched between them to form a stacked structure.

[0501] The positive and negative electrodes are cut into multiple sheets with a certain area and shape to obtain positive electrode sheets and negative electrode sheets, forming a laminated structure with the positive and negative electrode sheets sandwiched between separator sheets.

[0502] The long strip of separator is folded in a Z-shape to form a stacked structure in which positive and negative electrode plates are alternately inserted between the separators.

[0503] Next, the above-mentioned laminate is placed inside the battery casing, and the non-aqueous electrolyte of this embodiment is injected into the battery casing. The laminate is then immersed in the non-aqueous electrolyte and sealed, thereby enabling the manufacture of the non-aqueous secondary battery of this embodiment.

[0504] As another method, the non-aqueous electrolyte of this embodiment is impregnated into a substrate formed of a polymer material, a gel-state electrolyte membrane is pre-made, and a laminated structure is formed using sheet-shaped positive electrode, negative electrode, the obtained electrolyte membrane and separator, and then housed in a battery casing, thereby enabling the manufacture of a non-aqueous secondary battery.

[0505] It should be noted that regarding electrode configuration, if the outer periphery of the negative electrode active material layer overlaps with the outer periphery of the positive electrode active material layer, or if there are excessively narrow sections in the non-opposing portions of the negative electrode active material layer, electrode misalignment may occur during battery assembly. This raises concerns about reduced charge-discharge cycle characteristics in non-aqueous secondary batteries. To prevent this, it is preferable to pre-fix the electrode positions using tapes such as polyimide tape, polyphenylene sulfide tape, or PP tape, or adhesives.

[0506] When using a non-aqueous electrolyte containing acetonitrile, due to its high ionic conductivity, lithium ions released from the positive electrode during the initial charge of a non-aqueous secondary battery may diffuse throughout the negative electrode. In non-aqueous secondary batteries, the area of ​​the negative electrode active material layer is typically larger than that of the positive electrode active material layer. However, when lithium ions diffuse to a location within the negative electrode active material layer that is not opposite to the positive electrode active material layer and are trapped, these lithium ions cannot be released during the initial discharge and instead remain at the negative electrode. Therefore, the contribution of these unreleased lithium ions becomes irreversible capacity. For this reason, the initial charge-discharge efficiency is sometimes lower in non-aqueous secondary batteries using non-aqueous electrolytes containing acetonitrile.

[0507] On the other hand, when the area of ​​the positive electrode active material layer is larger than that of the negative electrode active material layer, or when both are the same, current concentration is more likely to occur at the edge of the negative electrode active material layer during charging, making it easier for lithium dendrites to form.

[0508] Regarding the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion of the positive electrode active material layer opposite to the negative electrode active material layer, based on the above reasons, it is preferably greater than 1.0 and less than 1.1, more preferably greater than 1.002 and less than 1.09, further preferably greater than 1.005 and less than 1.08, and particularly preferably greater than 1.01 and less than 1.08. In non-aqueous secondary batteries using a non-aqueous electrolyte containing acetonitrile, reducing the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion of the positive electrode active material layer opposite to the negative electrode active material layer can improve the initial charge-discharge efficiency.

[0509] Reducing the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion of the positive electrode active material layer opposite to the negative electrode active material layer means limiting the proportion of the area of ​​the portion of the negative electrode active material layer that is not opposite to the positive electrode active material layer. This minimizes the amount of lithium ions released from the positive electrode during the initial charge that are absorbed by the portion of the negative electrode active material layer that is not opposite to the positive electrode active material layer (i.e., the amount of lithium ions that are not released from the negative electrode during the initial discharge and become irreversible capacity). Therefore, by designing the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion of the positive electrode active material layer opposite to the negative electrode active material layer within the aforementioned range, it is possible to improve the battery's load characteristics due to the use of acetonitrile, increase the battery's initial charge-discharge efficiency, and further suppress lithium dendrite formation.

[0510] The non-aqueous secondary battery of this embodiment can function as a battery through the initial charge, but during the initial charge, a portion of the non-aqueous electrolyte decomposes, thereby stabilizing it. The initial charge is preferably performed at 0.001~0.3C, more preferably at 0.002~0.25C, and even more preferably at 0.003~0.2C. Performing a constant voltage charge during the initial charge also yields preferred results. The designed capacity is achieved using a constant current of 1C for 1 hour of discharge. By setting a longer voltage range for the lithium salt to participate in the electrochemical reaction, a stable and robust SEI is formed on the electrode surface, suppressing the increase in internal resistance. Furthermore, the reaction products are not only firmly fixed to the negative electrode 160, but also impart good effects to components other than the negative electrode 160, such as the positive electrode 150 and the separator 170. Therefore, considering the electrochemical reaction of the lithium salt dissolved in the non-aqueous electrolyte during the initial charge is very effective.

[0511] The non-aqueous secondary battery 100 in this embodiment can also be used as a battery pack formed by connecting multiple non-aqueous secondary batteries 100 in series or parallel. From the viewpoint of managing the charge and discharge state of the battery pack, the operating voltage range of each battery is preferably 2 to 5V, more preferably 2.5 to 5V, and particularly preferably 2.75V to 5V.

[0512] The above describes the forms used to implement the present invention. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from its spirit.

[0513] Example

[0514] The present invention will be further described in detail below with reference to embodiments, but the present invention is not limited to these embodiments.

[0515] Implementation Method 1

[0516] (1) Preparation of non-aqueous electrolyte

[0517] Various non-aqueous solvents, various acid anhydrides and various additives are mixed in a non-active atmosphere to a specified concentration, and then various lithium salts are added in a specified concentration to prepare a non-aqueous electrolyte (S1) to (S44).

[0518] The abbreviations for non-aqueous solvents, lithium salts, and additives in Tables 1-1 to 1-6 have the following meanings. Additionally, the mass parts of additives in Tables 1-1 to 1-6 represent mass parts relative to 100 parts by mass of the non-aqueous electrolyte excluding additives.

[0519] (Lithium salts)

[0520] LiPF6: Lithium hexafluorophosphate

[0521] LiFSI: Lithium bis(fluorosulfonyl)imide

[0522] LiBOB: Lithium dioxalatoborate

[0523] LiFSO3: Lithium fluorosulfonate

[0524] (Non-aqueous solvent)

[0525] AcN: Acetonitrile

[0526] EMC: Ethyl methyl carbonate

[0527] EC: Ethylene carbonate

[0528] VC: Vinylene carbonate

[0529] FEC: Ethylene fluorocarbonate

[0530] DFA: 2,2-Difluoroethyl acetate

[0531] DEC: Diethyl carbonate

[0532] GBL: γ-Butyrolactone

[0533] MBL: α-methyl-γ-butyrolactone

[0534] (Additives: Other)

[0535] SAH: Succinic anhydride

[0536] TEVS: Triethoxyvinylsilane

[0537] [Table 1-1]

[0538]

[0539] [Table 1-2]

[0540]

[0541] [Table 1-3]

[0542]

[0543] [Table 1-4]

[0544]

[0545] [Table 1-5]

[0546]

[0547] [Table 1-6]

[0548]

[0549] (2) Fabrication of non-aqueous secondary batteries

[0550] (2-1) Production of the positive electrode

[0551] (2-1-1) Fabrication of the positive electrode (P1)

[0552] A composite oxide of lithium, nickel, manganese, and cobalt (LiNi) will be used as the positive electrode active material in (A). 0.5 Mn 0.3 Co 0.2 O2), acetylene black powder as (B) conductive additive, and polyvinylidene fluoride (PVDF) as (C) binder are mixed in a mass ratio of 93.9:3.3:2.8 to obtain a positive electrode mixture.

[0553] N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture at 68% by mass of solids, and the mixture was further mixed to obtain a slurry containing the positive electrode mixture. On one side of an aluminum foil with a thickness of 15 μm and a width of 280 mm, which serves as the positive electrode current collector, the slurry containing the positive electrode mixture was coated using a three-roll transfer coating machine while adjusting the unit area weight of the coating to form a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was removed by drying in a hot air drying oven. The resulting electrode roll was trimmed on both sides and subjected to reduced pressure drying at 130°C for 8 hours. Then, it was calendered using a roller press to achieve a density of 2.7 g / cm³ for the positive electrode active material layer. 3 This yields a positive electrode (P1) containing a positive active material layer and a positive current collector. The weight per unit area, excluding the positive current collector, is 9.3 mg / cm². 2 .

[0554] (2-1-2) Preparation of the positive electrode (P2)

[0555] A composite oxide of lithium, nickel, manganese, and cobalt (LiNi) will be used as the positive electrode active material in (A). 0.8 Mn 0.1 Co 0.1 O2), acetylene black powder as (B) conductive additive, and polyvinylidene fluoride (PVDF) as (C) binder are mixed in a mass ratio of 94:3:3 to obtain a positive electrode mixture.

[0556] N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture at a concentration of 68% by mass of solids, and the mixture was further mixed to obtain a slurry containing the positive electrode mixture. On one side of an aluminum foil with a thickness of 15 μm and a width of 280 mm, which serves as the positive electrode current collector, the slurry containing the positive electrode mixture was coated using a three-roll transfer coating machine while adjusting the unit area weight of the coating to form a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was removed by drying in a hot air drying oven. The resulting electrode roll was trimmed on both sides and subjected to reduced pressure drying at 130°C for 8 hours. Then, it was calendered using a roller press to achieve a density of 2.9 g / cm³ for the positive electrode active material layer. 3 This yields a positive electrode (P2) comprising a positive active material layer and a positive current collector. The weight per unit area, excluding the positive current collector, is 16.6 mg / cm². 2 .

[0557] (2-2) Fabrication of the negative electrode

[0558] (2-2-1) Fabrication of the negative electrode (N1)

[0559] Graphite powder as (a) the negative electrode active material, and carboxymethyl cellulose (density 1.60 g / cm³) as (C) the binder 3 Solution (solid content concentration 1.83% by mass) and diene rubber (glass transition temperature: -5℃, number average particle size at dryness: 120nm, density 1.00g / cm³) 3 Dispersion medium: water and solid component concentration 40% by mass) were mixed at a solid component mass ratio of 97.4:1.1:1.5 to obtain the negative electrode mixture.

[0560] Water was added as a solvent to the obtained negative electrode mixture at a concentration of 45% by mass of solids, and the mixture was further mixed to prepare a slurry containing the negative electrode mixture. On one side of a copper foil with a thickness of 8 μm and a width of 280 mm, which would serve as the negative electrode current collector, a three-roll transfer coating machine was used to coat the foil, adjusting the unit area weight of the slurry containing the negative electrode mixture, to form a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was removed by drying in a hot air drying oven. The resulting electrode roll was trimmed on both sides and subjected to reduced pressure drying at 80°C for 12 hours. Then, it was calendered using a roller press to achieve a density of 1.4 g / cm³ for the negative electrode active material layer. 3 This yields a negative electrode (N1) containing a negative electrode active material layer and a negative electrode current collector. The weight per unit area, excluding the negative electrode current collector, is 5.9 mg / cm³. 2 .

[0561] (2-2-2) Fabrication of the negative electrode (N2)

[0562] A negative electrode mixture is obtained by mixing graphite powder (a) as the negative electrode active material, acetylene black powder (B) as the conductive additive, and polyvinylidene fluoride (PVDF) (C) as the binder in a mass ratio of 90.0:3.0:7.0.

[0563] Water was added as a solvent to the obtained negative electrode mixture at a concentration of 45% by mass of solids, and the mixture was further mixed to prepare a slurry containing the negative electrode mixture. On one side of a copper foil with a thickness of 8 μm and a width of 280 mm, which would serve as the negative electrode current collector, a three-roll transfer coating machine was used to coat the foil, adjusting the unit area weight of the slurry containing the negative electrode mixture, to form a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was removed by drying in a hot air drying oven. The resulting electrode roll was trimmed on both sides and subjected to reduced pressure drying at 80°C for 12 hours. Then, it was calendered using a roller press to achieve a density of 1.4 g / cm³ for the negative electrode active material layer. 3 This yields a negative electrode (N2) comprising a negative electrode active material layer and a negative electrode current collector. The weight per unit area, excluding the negative electrode current collector, is 11.9 mg / cm². 2 .

[0564] (2-3) Battery assembly

[0565] (2-3-1) Assembly of coin-type non-aqueous secondary battery

[0566] A polypropylene gasket is placed inside the CR2032 battery casing (SUS304 / Al cladding). A positive electrode (P1), obtained as described above and cut into a disc shape with a diameter of 15.958 mm, is placed in its center with the positive active material layer facing upwards. Above this, a glass fiber filter paper (Advantech Co., Ltd., GA-100), cut into a disc shape with a diameter of 16.156 mm, is placed. After injecting 150 μL of non-aqueous electrolyte (S1~S27), a negative electrode (N1), obtained as described above and cut into a disc shape with a diameter of 16.156 mm, is placed with the negative active material layer facing downwards. Then, spacers and springs are placed inside the battery casing, and the battery cover is closed and sealed tightly with a sealing machine. Any overflowing non-aqueous electrolyte is wiped away with a waste cloth. The non-aqueous electrolyte was kept at 25°C for 12 hours to allow it to be fully mixed into the laminate, thus obtaining a coin-shaped non-aqueous secondary battery (P1 / N1).

[0567] By following the same steps, a coin-shaped non-aqueous secondary battery (P2 / N2) is obtained, which uses P2 as the positive electrode, N2 as the negative electrode, and S11 and S28~S32 as the non-aqueous electrolyte.

[0568] (2-3-2) Assembly of small non-aqueous secondary batteries

[0569] A positive electrode obtained by punching a disk shape with a diameter of 15.958 mm, as described above, and a negative electrode obtained by punching a disk shape with a diameter of 16.156 mm, as described above, are overlapped on both sides of the separators (B1~B3) to obtain a laminate. This laminate is inserted into a disk-shaped battery casing made of SUS. Next, 200 μL of non-aqueous electrolyte (S38~S44) is injected into the battery casing. After immersing the laminate in the non-aqueous electrolyte, the battery casing is sealed and kept at 25°C for 12 hours to allow the non-aqueous electrolyte to be fully mixed into the laminate, resulting in a small non-aqueous secondary battery (P1 / N1).

[0570] Through the same steps, we obtained a positive electrode using P2, a negative electrode using N2, and a separator made of polyethylene microporous membrane (thickness 21μm, air permeability 285 seconds / 100cm). 3 A coin-type non-aqueous secondary battery (P2 / N2) with a porosity of 41% and using S29 and S33~S37 non-aqueous electrolytes.

[0571] (2-4) Fabrication of the separator

[0572] (2-4-1) Fabrication of the separator (B1)

[0573] [Preparation of silane-grafted modified polyolefins]

[0574] The raw material polyolefin used in silane graft-modified polyolefins has a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. It can be a copolymer of propylene or butene into α-olefins. While the raw material polyethylene is melt-blended using an extruder, an organic peroxide (di-tert-butyl peroxide) is added to generate free radicals within the α-olefin polymer chain. Then, a trimethoxyalkoxy compound is injected into the melt-blended compound to replace the vinylsilane, resulting in an addition reaction. Through the addition reaction, alkoxysilyl groups are introduced into the α-olefin polymer to form a silane graft structure. Additionally, to simultaneously adjust the free radical concentration in the system, an appropriate amount of antioxidant (pentaerythritol tetratetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added to inhibit the chain reaction (gelling) within the α-olefin. The obtained silane-grafted polyolefin molten resin was cooled in water, granulated, and then dried at 80°C for 2 days to remove moisture and unreacted trimethoxyalkoxylated vinylsilane. It should be noted that the residual concentration of unreacted trimethoxyalkoxylated vinylsilane in the granules was below 3000 ppm.

[0575] <Making of the base material as the first layer>

[0576] 30% by mass of polyethylene homopolymer with a viscosity average molecular weight of 3,000,000 (ultra-high molecular weight polyethylene (A)), 50% by mass of polyethylene homopolymer with a viscosity average molecular weight of 700,000 (polyethylene (B)), and 20% by mass of silane-grafted polyethylene (silane-modified polyethylene (C)) with an MFR of 0.4 g / min obtained by modifying vinyl silane with trimethoxyalkoxylates using polyolefin with a viscosity average molecular weight of 125,000 as raw material (the resin composition of (A):(B):(C) is 3:5:2). Then, 1000 ppm by mass of pentaerythritol tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant is added relative to the total resin. The mixture is dry-mixed using a drum mixer to obtain a mixture. It should be noted that 3000 ppm of calcium stearate is added relative to ultra-high molecular weight polyethylene (A). The resulting mixture is fed into a twin-screw extruder under a nitrogen atmosphere using a feeder. In addition, liquid paraffin (dynamic viscosity at 37.78°C 7.59 × 10⁻⁶) was injected into the extruder barrel using a plunger pump. -5 m 2 / s).

[0577] The mixture is melt-blended with liquid paraffin in an extruder, with the feeder and pump adjusted so that the liquid paraffin content in the extruded polyolefin composition is 70% by mass (i.e., the polymer concentration is 30% by mass). The melt-blending conditions are set at a temperature of 230°C, a screw speed of 240 rpm, and an ejection rate of 18 kg / h.

[0578] Next, the molten compound is extruded through a T-die onto a cooling roller with a surface temperature controlled at 25°C and then cast to obtain a gel sheet (sheet-shaped molded body) with an unprocessed film thickness of 1370 μm.

[0579] Next, the sheet-shaped preform is fed into a biaxial tenter frame for biaxial stretching to obtain a stretched material. The stretching conditions are set as follows: MD ratio 7.0, TD ratio 6.4 (i.e., 7 × 6.4), and biaxial stretching temperature 122°C. Then, the stretched gel sheet is immersed in a dichloromethane bath to extract and remove liquid paraffin. The dichloromethane is then dried to remove the solid material, resulting in a porous body. Next, the porous body is fed into a TD tenter frame for heat setting (HS) at a temperature of 133°C and a stretch ratio of 1.9. Then, a relaxation operation is performed to a TD ratio of 1.75 to obtain a microporous membrane. Finally, the ends of the obtained microporous membrane are trimmed, and it is wound into a master roll with a width of 1100 mm and a length of 5000 m.

[0580] During the above evaluation, the microporous membrane unwound from the master roll is cut as needed and used as the evaluation substrate (first layer). For the obtained evaluation substrate, the membrane thickness, air permeability, porosity, etc. are measured, as shown in Table 4.

[0581] <The Construction of the Second Layer>

[0582] [Synthesis methods of resin adhesives]

[0583] Acrylic latex used as a resin binder is manufactured by the following method.

[0584] In a reaction vessel equipped with a stirrer, reflux cooler, dropping tank, and thermometer, 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) and 0.5 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) as emulsifiers were added. Next, the temperature inside the reaction vessel was raised to 80°C, and while maintaining this temperature, 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added to obtain an initial mixture. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the emulsion was added dropwise from the dropping tank to the reaction vessel over a period of 150 minutes.

[0585] It should be noted that the above emulsion was prepared by mixing 70 parts by weight of butyl acrylate; 29 parts by weight of methyl methacrylate; 1 part by weight of methacrylic acid; 3 parts by weight of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) and 3 parts by weight of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) as emulsifiers; 7.5 parts by weight of 2% aqueous solution of ammonium persulfate; and 52 parts by weight of deionized water using a homogenizer for 5 minutes.

[0586] After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature. The resulting emulsion was adjusted to pH 8.0 with a 25% ammonium hydroxide aqueous solution, and a small amount of water was added to obtain an acrylic latex with a solid content of 40%. The obtained acrylic latex had a number average particle size of 145 nm and a glass transition temperature of -30°C.

[0587] A dispersion was prepared by uniformly dispersing 95 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (solid content conversion) of an aqueous solution of ammonium polycarboxylate (SAN NOPCO SN Dispersant 5468, 40% solid content concentration) as an ionic dispersant in 100 parts by mass of water. The resulting dispersion was then subjected to a bead mill (chamber volume 200 cc, zirconia bead diameter 0.1 mm, filling rate 80%) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm, thus preparing a slurry containing inorganic particles. 2.0 parts by mass (solid content conversion) of the acrylic latex prepared above as a resin binder was added to the particle size-adjusted dispersion.

[0588] Next, the microporous membrane is continuously fed out from the above-mentioned microporous membrane master roll, and a slurry containing inorganic particles is coated on one side of the microporous membrane using a gravure reverse coating machine. Then, it is dried in a 60°C dryer to remove water, and wound up to obtain the master roll of the separator.

[0589] During evaluation, the separators unwound from the master roll will be cut as needed and used as evaluation separators. It should be noted that for the inorganic particle types in the second layer of Table 4, these inorganic particles will be referred to as "ceramics".

[0590] (2-4-2) Fabrication of the separator (B2)

[0591] Using the physical properties recorded in Table 4 as a target, the separator (B2) is manufactured in the same way as described in (2-4-1) above.

[0592] (2-4-3) Fabrication of the separator (B3)

[0593] <Making of the base material as the first layer>

[0594] A mixture was prepared by adding 100% by mass of pentaerythritol tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate as an antioxidant to 100% by mass of polyethylene homopolymer with a viscosity-average molecular weight of 500,000, and dry mixing using a drum mixer. Note that 3000 ppm of calcium stearate was added relative to the polyethylene homopolymer. The resulting mixture was fed into a twin-screw extruder under a nitrogen atmosphere. Separately, liquid paraffin (kinetic viscosity at 37.78°C 7.59 × 10⁻⁶) was injected into the extruder barrel using a plunger pump. -5 m 2 / s).

[0595] The mixture is melt-blended with liquid paraffin in an extruder, with the feeder and pump adjusted so that the liquid paraffin content in the extruded polyolefin composition is 70% by mass (i.e., the polymer concentration is 30% by mass). The melt-blending conditions are set at a temperature of 230°C, a screw speed of 240 rpm, and an ejection rate of 18 kg / h.

[0596] Next, the molten compound is extruded through a T-die onto a cooling roller with a surface temperature controlled at 25°C and then cast to obtain a gel sheet (sheet-shaped molded body) with an unprocessed film thickness of 1370 μm.

[0597] Next, the sheet-shaped preform is fed into a biaxial tenter frame for biaxial stretching to obtain a stretched material. The stretching conditions are set as follows: MD ratio 7.0, TD ratio 6.4 (i.e., 7 × 6.3), and biaxial stretching temperature 128°C. Then, the stretched gel sheet is immersed in a dichloromethane bath to extract and remove liquid paraffin. The dichloromethane is then dried to remove the solid material, resulting in a porous body. Next, the porous body is fed into a TD tenter frame for heat setting (HS) at a temperature of 133°C and a stretch ratio of 1.95. Then, a relaxation operation is performed to a TD ratio of 1.75 to obtain a microporous membrane. Finally, the ends of the obtained microporous membrane are trimmed, and it is wound into a master roll with a width of 1100 mm and a length of 5000 m.

[0598] During the above evaluation, the microporous membrane unwound from the master roll is cut as needed and used as the evaluation substrate (first layer). For the obtained evaluation substrate, the membrane thickness, air permeability, porosity, etc. are measured, as shown in Table 4.

[0599] <The Construction of the Second Layer>

[0600] Using the physical properties recorded in Table 4 as the target, a second layer is made using the same method as described in (2-4-1) above.

[0601] (3) Evaluation of non-aqueous secondary batteries

[0602] For the coin-type non-aqueous secondary batteries (P1 / N1) obtained as described above (Examples 1-10 and Comparative Examples 1-17), firstly, initial charge treatment and initial charge-discharge capacity measurement were performed according to the steps described in (3-1). Next, each coin-type non-aqueous secondary battery was evaluated according to the steps described in (3-2). It should be noted that the charge-discharge was performed using a charge-discharge apparatus ACD-M01A (trade name) manufactured by ASKAELECTRONIC CO., LTD. and a programmable temperature bath IN804 (trade name) manufactured by Yamato Scientific Co., Ltd.

[0603] In this manual, 1C refers to the current value at which a fully charged battery is expected to discharge at a constant current for 1 hour.

[0604] Specifically, for coin-type non-aqueous secondary batteries (P1 / N1), coin-type non-aqueous secondary batteries (P2 / N2), small non-aqueous secondary batteries (P1 / N1), and small non-aqueous secondary batteries (P2 / N2), 1C refers to the current value expected to discharge from a fully charged state of 4.2V to 3.0V with a constant current and end the discharge in 1 hour.

[0605] Assemble according to the steps in (2-3-1) above. The coin-shaped non-aqueous secondary battery (P1 / N1) and the small non-aqueous secondary battery (P1 / N1) are 3mAh-class batteries, and their fully charged battery voltage is determined to be 4.2V, equivalent to a 1C current value of 3mA. Similarly, the coin-shaped non-aqueous secondary battery (P2 / N2) and the small non-aqueous secondary battery (P2 / N2) are 6mAh-class batteries, and their fully charged battery voltage is determined to be 4.2V, equivalent to a 1C current value of 6mA. In the following text, unless otherwise specified, for convenience, descriptions of current and voltage values ​​will be omitted.

[0606] (3-1) Initial charge and discharge treatment of non-aqueous secondary batteries

[0607] The ambient temperature of the coin-type non-aqueous secondary battery (P1 / N1) was set to 25°C, and it was charged with a constant current equivalent to 0.1C until fully charged. Then, it was charged with a constant voltage for 1.5 hours. Next, the battery was discharged to the specified voltage with a constant current equivalent to 0.3C. The initial efficiency was calculated by dividing the discharge capacity by the charge capacity. For batteries with an initial efficiency of less than 80%, the specified battery capacity was not met, making it difficult to obtain accurate evaluation results, and therefore subsequent evaluation tests could not be conducted. The discharge capacity at this point was taken as the initial capacity. The same steps were used to perform the initial charge-discharge treatment on coin-type non-aqueous secondary batteries (P2 / N2), small non-aqueous secondary batteries (P1 / N1), and small non-aqueous secondary batteries (P2 / N2).

[0608] (3-2) Fast charging test of non-aqueous secondary batteries

[0609] The following steps are used to calculate the recovery charging capacity retention rate. First, after the initial charge-discharge process, charge to 4.2V with a constant current of 0.2C. Let this charging current capacity be defined as the charging capacity A. After discharging with a constant current of 0.5C, use 15mA / cm² as the maximum charging current density. 2The capacitor is charged to 4.2V with a constant current. Then, it is discharged with a constant current of 0.5C, and then charged again to 4.2V with a constant current of 0.2C. The charging current capacity at this point is set as the charging capacity C. The charging capacity C at 100% is set as the recovery charging capacity maintenance rate.

[0610] Restored charging capacity maintenance rate = (Charging capacity C / Charging capacity A) × 100%

[0611] It should be noted that after calculating the aforementioned charging capacity A, and using 15 mA / cm² as the maximum charging current density... 2 Before constant current charging, the charging capacity C can be kept constant, and the device can be repeatedly charged and discharged at various current values. Additionally, a maximum charging current density of 15 mA / cm² can be used. 2 After constant current charging and before being charged again with a constant current of 0.2C to 4.2V, the charging capacity C can be repeatedly charged and discharged at various current values ​​within a range that remains unchanged. The range where the charging capacity C remains unchanged means that the error between the charging capacity C value and the value when the charging and discharging were not repeatedly charged and discharged at various current values ​​is within 3%.

[0612] (3-2-1) Fast charging test of coin-type non-aqueous secondary battery (P1 / N1) and small non-aqueous secondary battery (P1 / N1)

[0613] For various non-aqueous secondary batteries (P1 / N1) that have undergone initial charge-discharge treatment using the method described in (3-1) above, the ambient temperature is set to 25°C, and they are charged to 4.2V with a constant current of 0.6mA (equivalent to 0.2C). This charging current capacity is defined as the charging capacity A. Then, they are discharged with a current of 1.5mA (equivalent to 0.5C) until they reach 2.7V, and then discharged at a constant voltage of 2.7V until the current decreases to 0.3mA (equivalent to 0.1C). This same charge-discharge cycle is then performed 5 times.

[0614] Next, charge to 4.2V with a constant current of 15mA (equivalent to 5C). Then, discharge to 2.7V with a current of 1.5mA (equivalent to 0.5C), and then discharge at a constant voltage of 2.7V until the current decays to 0.3mA (equivalent to 0.1C). Then, perform 5 cycles of the same charge and discharge process.

[0615] Next, at 30mA (15mA / cm) equivalent to 10C. 2Charge the capacitor to 4.2V with a constant current. Set this charging current capacity as the charging capacity B. Then, discharge it with a current of 1.5mA (equivalent to 0.5C) until it reaches 2.7V. Then, discharge it with a constant voltage of 2.7V until the current decreases to 0.3mA (equivalent to 0.1C). Then, perform 5 cycles of the same charge and discharge process.

[0616] Next, various non-aqueous secondary batteries were charged to 4.2V with a constant current of 0.6mA (equivalent to 0.2C). This charging current capacity was designated as the charging capacity C. Then, the batteries were discharged with a current of 1.5mA (equivalent to 0.5C) until they reached 2.7V. After that, they were discharged at a constant voltage of 2.7V until the current decreased to 0.3mA (equivalent to 0.1C). This same charge-discharge cycle was then performed 5 times, for a total of 20 charge-discharge cycles.

[0617] (3-2-2) Calculation of fast-charging capacity retention rate of coin-type non-aqueous secondary battery (P1 / N1) and small non-aqueous secondary battery (P1 / N1)

[0618] For various non-aqueous secondary batteries (P1 / N1) that underwent fast charging tests using the method described in (3-2-1) above, the fast charging capacity retention rate is calculated based on the following formula. At this time, refer to... Figure 3 A charging curve was constructed, and the presence or absence of a voltage plateau was observed within the voltage range of 3.9~4.2V. The results are shown in Tables 2-1 and 2-2.

[0619] Fast charging capacity retention rate = (Charging capacity B / Charging capacity A) × 100%

[0620] (3-2-3) Calculation of the recovery charge capacity retention rate of coin-type non-aqueous secondary batteries (P1 / N1) and small non-aqueous secondary batteries (P1 / N1)

[0621] For various non-aqueous secondary batteries (P1 / N1) that underwent fast charging tests using the method described in (3-2-1) above, the recovery charge capacity retention rate was calculated based on the following formula. The results are shown in Tables 2-1 and 2-2.

[0622] Restored charging capacity maintenance rate = (Charging capacity C / Charging capacity A) × 100%

[0623] [Examples 1-10 and Comparative Examples 1-17]

[0624] Here, the test results of the coin-type non-aqueous secondary battery (P1 / N1) are explained.

[0625] Fast charging capacity retention rate is an indicator that the higher the value, the more charge can be made in a short time. The fast charging capacity retention rate is preferably 40% or higher, more preferably 45% or higher, and even more preferably 50% or higher.

[0626] The recovery charge capacity retention rate is an indicator of irreversible capacity in fast charging tests. A higher value indicates less irreversible lithium loss during fast charging, resulting in more usable battery capacity after fast charging. Preferably, the recovery charge capacity retention rate is 90% or higher, more preferably 95% or higher, and even more preferably 97% or higher. On the other hand, a recovery charge capacity retention rate exceeding 100% indicates ongoing side reactions within the battery, and is preferably below 100%. Even with a high fast charging capacity retention rate, a low recovery charge capacity retention rate leads to faster capacity loss. Therefore, to meet practical battery performance requirements, both fast charging capacity retention rate and recovery charge capacity retention rate must be satisfied.

[0627] The voltage plateau observed in the 3.9–4.2 V range of the charging curve suggests lithium metal electrodeposition on the negative electrode surface. When lithium metal is electrodeposited on the negative electrode surface, reduction and decomposition of the non-aqueous electrolyte occurs on the lithium metal surface, leading to battery degradation. Therefore, it is preferable if no voltage plateau is observed.

[0628] [Table 2-1]

[0629]

[0630] In Examples 1-10, results meeting the acceptable level were obtained in all tests. On the other hand, Comparative Examples 1-2 and 4-17 all produced voltage plateaus. In Comparative Examples 1 and 6, which used non-aqueous electrolytes formed from conventional carbonate solvents, the ionic conductivity was low compared to acetonitrile-containing non-aqueous electrolytes, resulting in a fast-charging capacity retention rate far inferior to that of the Examples. In Comparative Example 2, even when using an acetonitrile-containing non-aqueous electrolyte with high ionic conductivity, the movement of lithium ions was hindered because the oxygen / sulfur compound shown in general formula (1) was not used to construct the SEI on the negative electrode surface, and the fast-charging capacity retention rate was also significantly lower than that of the Examples. In Comparative Example 3, after continuous charging far exceeding the specified battery capacity during the initial charge, the subsequent discharge capacity was only 0.4 mAh compared to the usual battery capacity of 3 mAh. From this result, it can be concluded that when only ethylene sulfite is added without adding vinylene carbonate, an acetonitrile-containing non-aqueous electrolyte will not form a good negative electrode SEI during the initial charge, and the acetonitrile reduction and decomposition reaction will continue. For Comparative Example 3, the initial efficiency was less than 80%, therefore a fast-charging test after the initial charge-discharge treatment could not be performed. In Comparative Examples 4 and 10, the amount of vinylene carbonate added was greater than the amount of ethylene sulfite added, and the total amount of vinylene carbonate and ethylene sulfite added exceeded 10% by volume. This not only stemmed from the dominant properties of the negative electrode SEI due to vinylene carbonate, but also from the excessive additive causing an unnecessary increase in internal resistance, thus hindering lithium-ion movement and significantly reducing the fast-charging capacity retention rate compared to the examples. In Comparative Example 7, although the total amount of vinylene carbonate and ethylene sulfite added was less than 10% by volume, the amount of vinylene carbonate added was greater than the amount of ethylene sulfite added, and the dominant properties of the negative electrode SEI due to vinylene carbonate resulted in a significantly reduced recovery charging capacity retention rate compared to the examples. In Comparative Example 5, although the amount of vinylene carbonate added was less than that of ethylene sulfite added, the total amount of vinylene carbonate and ethylene sulfite added exceeded 10% by volume. Due to the excessive additives, the internal resistance increased beyond what was necessary, resulting in a lower recovery capacity retention rate compared to the examples. In Comparative Examples 8, 9, and 11-17, the non-aqueous electrolytes did not contain the oxygen / sulfur compounds represented by general formula (1), making it impossible to form a good negative electrode SEI. Therefore, the recovery charge capacity retention rate was less than 90% or more than 100%. It was considered that irreversible degradation occurred during fast charging.

[0631] Based on the above results, in this embodiment, by adjusting the amount of vinylene carbonate and the oxygen / sulfur compound represented by general formula (1) to an appropriate ratio, excellent fast charging performance can be achieved, and the generation of voltage plateaus can be prevented. Furthermore, irreversible degradation and electrodeposition during fast charging can be suppressed, thus exhibiting excellent recovery charging capacity retention.

[0632] [Examples 11-16 and Comparative Examples 18-20]

[0633] Here, the test results for small non-aqueous secondary batteries (P1 / N1) are explained.

[0634] [Table 2-2]

[0635]

[0636] In Examples 11-16, regardless of the type of separator, all tests yielded results meeting the acceptable level. On the other hand, in Comparative Examples 18-20, which used non-aqueous electrolytes formed from conventional carbonate solvents, a voltage plateau occurred due to insufficient ionic conductivity. Furthermore, in Comparative Examples 18-20, the capacity recovery retention rate was significantly lower than in the Examples.

[0637] (3-2-4) Fast charging test of coin-type non-aqueous secondary battery (P2 / N2) and small non-aqueous secondary battery (P2 / N2)

[0638] For various non-aqueous secondary batteries (P2 / N2) that have undergone initial charge-discharge treatment using the method described in (3-1) above, the ambient temperature is set to 25°C, and the battery is charged to 4.2V with a constant current of 1.2mA (equivalent to 0.2C). This charging current capacity is defined as the charging capacity A. Then, the battery is discharged at a current of 3mA (equivalent to 0.5C) until it reaches 2.7V, and then discharged at a constant voltage of 2.7V until the current decreases to 0.6mA (equivalent to 0.1C). This same charge-discharge cycle is then performed 5 times.

[0639] Next, charge to 4.2V with a constant current of 18mA (equivalent to 3C). Then, discharge to 2.7V with a current of 3mA (equivalent to 0.5C), and then discharge at a constant voltage of 2.7V until the current decreases to 0.6mA (equivalent to 0.1C). Then, perform 5 cycles of the same charge and discharge process.

[0640] Next, at 30mA (15mA / cm) equivalent to 5C. 2 Charge the capacitor to 4.2V with a constant current. Set this charging current capacity as the charging capacity B. Then, discharge it at a current of 3mA (equivalent to 0.5C) until it reaches 2.7V. Then, discharge it at a constant voltage of 2.7V until the current decreases to 0.6mA (equivalent to 0.1C). Then, perform 5 cycles of the same charge and discharge process.

[0641] Next, various non-aqueous secondary batteries were charged to 4.2V with a constant current of 1.2mA (equivalent to 0.2C). This charging current capacity was designated as the charging capacity C. Then, the batteries were discharged at a current of 3.0mA (equivalent to 0.5C) until they reached 2.7V. After that, they were discharged at a constant voltage of 2.7V until the current decreased to 0.6mA (equivalent to 0.1C). This same charge-discharge cycle was then performed 5 times, for a total of 20 charge-discharge cycles.

[0642] (3-2-5) Calculation of fast-charging capacity retention rate of coin-shaped non-aqueous secondary batteries (P2 / N2) and small non-aqueous secondary batteries (P2 / N2).

[0643] For various non-aqueous secondary batteries (p2 / N2) that underwent fast charging tests using the method described in (3-2-4) above, the fast charging capacity retention rate was calculated based on the formula described in (3-2-2) above. At this time, refer to... Figure 3 A charging curve was constructed, and the presence or absence of a voltage plateau was observed within the voltage range of 3.9~4.2V. The results are shown in Tables 3-1 and 3-2.

[0644] (3-2-6) Calculation of the recovery charge capacity retention rate of coin-type non-aqueous secondary batteries (P2 / N2) and small non-aqueous secondary batteries (P2 / N2).

[0645] For various non-aqueous secondary batteries (P2 / N2) that underwent fast charging tests using the method described in (3-2-5) above, the recovery charge capacity retention rate was calculated based on the formula described in (3-2-3) above. The results are shown in Tables 3-1 and 3-2.

[0646] [Examples 17-21 and Comparative Example 21]

[0647] Here, the test results for coin-type non-aqueous secondary batteries (P2 / N2) are explained. For coin-type non-aqueous secondary batteries (P2 / N2), the fast charging capacity retention rate is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more.

[0648] The recovery charge capacity retention rate is preferably 95% or higher, more preferably 97% or higher, and even more preferably 98% or higher. Even when the fast charge capacity retention rate is high, the capacity of a battery with a low recovery charge capacity retention rate decreases rapidly. Therefore, in order to meet practical battery performance requirements, both fast charge capacity retention rate and recovery charge capacity retention rate need to be satisfied.

[0649] The voltage plateau observed in the 3.9–4.2 V range of the charging curve suggests lithium metal electrodeposition on the negative electrode surface. When lithium metal is electrodeposited on the negative electrode surface, reduction and decomposition of the non-aqueous electrolyte occurs on the lithium metal surface, leading to battery degradation. Therefore, it is preferable to avoid observing a voltage plateau.

[0650] [Table 3-1]

[0651]

[0652] In Examples 17-21, results meeting the acceptable level were obtained in all tests. On the other hand, in Comparative Example 21, which was a non-aqueous electrolyte formed from a conventional carbonate solvent, the fast-charge capacity retention rate and recovery-charge capacity retention rate were lower than those in Examples 17-21, and a voltage plateau was also observed.

[0653] [Examples 22-25 and Comparative Examples 22-23]

[0654] Here, the test results for small non-aqueous secondary batteries (P2 / N2) are explained. For small non-aqueous secondary batteries (P2 / N2), the fast charging capacity retention rate is preferably 20% or more, more preferably 21% or more, and even more preferably 23% or more.

[0655] The recovery charge capacity retention rate is preferably 95% or higher, more preferably 96% or higher, and even more preferably 97% or higher. Even when the fast charge capacity retention rate is high, the capacity of a battery with a low recovery charge capacity retention rate decreases rapidly. Therefore, in order to meet practical battery performance requirements, both fast charge capacity retention rate and recovery charge capacity retention rate need to be satisfied.

[0656] The voltage plateau observed in the 3.9–4.2 V range of the charging curve suggests lithium metal electrodeposition on the negative electrode surface. When lithium metal is electrodeposited on the negative electrode surface, reduction and decomposition of the non-aqueous electrolyte occurs on the lithium metal surface, leading to battery degradation. Therefore, it is preferable to avoid observing a voltage plateau.

[0657] [Table 3-2]

[0658]

[0659] In Examples 22-25, results meeting the acceptable level were obtained in all tests. On the other hand, in Comparative Examples 22-23, where the non-aqueous electrolyte did not contain oxygen / sulfur compounds, a voltage plateau was observed.

[0660] Typically, ethylene carbonate enhances the SEI (Sediment Injection) of the negative electrode formed by the reductive decomposition of ethylene carbonate. However, especially in the case of non-aqueous electrolytes containing acetonitrile, the decomposition potentials of acetonitrile and ethylene carbonate are sometimes similar, leading to an increase in internal resistance. Therefore, there is a concern that this phenomenon may also reduce fast-charging performance. Thus, the amount of ethylene carbonate needs to be adjusted to an appropriate range. In the examples 23-25, where the amount of ethylene carbonate is low, the fast-charging capacity retention rate is higher compared to Example 22.

[0661] (3-3) Cyclic test of small non-aqueous secondary battery (P2 / N2) at 50℃

[0662] For the small non-aqueous secondary battery (P2 / N2) that underwent its first charge-discharge treatment using the method described in (3-1) above, the ambient temperature was set to 50°C. First, the battery was charged with a constant current of 9mA (equivalent to 1.5C) until it reached 4.2V. Then, it was charged with a constant voltage of 4.2V until the current decreased to 0.3mA (equivalent to 0.05C). Next, the battery was discharged to 3.0V with a constant current of 9mA. One charge and one discharge cycle was considered one cycle, and 100 charge-discharge cycles were performed. The discharge capacity of the 100th cycle, with the discharge capacity of the first cycle set to 100%, was used as the capacity retention rate in the 50°C cycle test.

[0663] [Examples 26-29 and Comparative Examples 24-25]

[0664] Here, the experimental results shown in Table 3-3 are explained.

[0665] The capacity retention rate in the 50°C cycle test represents the ratio of the discharge capacity in the 100th cycle to the discharge capacity in the 1st cycle. The higher the value, the less the battery capacity deteriorates during repeated charge-discharge cycles at high temperatures. The capacity retention rate is preferably 85% or higher, more preferably 86% or higher, and even more preferably 88% or higher.

[0666] [Table 3-3]

[0667]

[0668] As shown in Table 3-3, in Examples 26-29, the capacity retention rate decreased less when cycling at 50°C, and the cycling performance was improved at high temperatures.

[0669] [Table 4]

[0670]

[0671] Third Implementation Method

[0672] (1) Preparation of non-aqueous electrolyte

[0673] As shown in Tables 1-6 above, various non-aqueous solvents are mixed in a non-active atmosphere to a specified concentration, and various lithium salts are added in a specified concentration to prepare a non-aqueous electrolyte (S45) to (S47).

[0674] (2) Fabrication of coin-type non-aqueous secondary battery (P3 / N3)

[0675] (2-1) Fabrication of the positive electrode (P3)

[0676] Lithium iron phosphate (LiFePO4) with an olivine-type structure, which serves as (A) the positive electrode active material, carbon black powder, which serves as (B) the conductive additive, and polyvinylidene fluoride (PVDF), which serves as the binder, are mixed in a mass ratio of 89:3:8 to obtain a positive electrode mixture.

[0677] N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture at a concentration of 68% by mass of solids, and the mixture was further mixed to obtain a slurry containing the positive electrode mixture. On one side of an aluminum foil with a thickness of 15 μm and a width of 280 mm, which serves as the positive electrode current collector, the slurry containing the positive electrode mixture was coated using a three-roll transfer coating machine while adjusting the unit area weight of the coating to form a coating pattern with a width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was removed by drying in a hot air drying oven. The resulting electrode roll was trimmed on both sides and subjected to reduced pressure drying at 130°C for 8 hours. Then, it was calendered using a roller press to achieve a density of 1.8 g / cm³ for the positive electrode active material layer. 3 This yields a positive electrode (P3) comprising a positive active material layer and a positive current collector. The weight per unit area, excluding the positive current collector, is 11.0 mg / cm². 2 .

[0678] (2-2) Fabrication of the negative electrode (N3)

[0679] A negative electrode mixture is obtained by mixing graphite powder (as the negative electrode active material), carbon black powder (as the conductive additive), and polyvinylidene fluoride (PVDF) (as the binder) in a solid component mass ratio of 90.0 for the negative electrode active material, 3.0 for the conductive additive, and 7.0 for the binder.

[0680] Water was added as a solvent to the obtained negative electrode mixture at a concentration of 45% by mass of solids, and the mixture was further mixed to prepare a slurry containing the negative electrode mixture. On one side of a copper foil with a thickness of 8 μm and a width of 280 mm, which would serve as the negative electrode current collector, the slurry containing the negative electrode mixture was coated using a three-roll transfer coating machine while adjusting the unit area weight of the slurry. This resulted in a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was removed by drying in a hot air drying oven. The resulting electrode roll was trimmed on both sides and subjected to reduced pressure drying at 80°C for 12 hours. Then, it was calendered using a roller press to achieve a density of 1.3 g / cm³ for the negative electrode active material layer. 3 This yields a negative electrode (N3) containing a negative electrode active material layer and a negative electrode current collector. The weight per unit area, excluding the negative electrode current collector, is 5.4 mg / cm³. 2 .

[0681] (2-3) Assembly of coin-type non-aqueous secondary battery (P3 / N3)

[0682] A polypropylene gasket is placed inside the CR2032 battery casing (SUS304 / Al cladding). A positive electrode (P3), obtained as described above and cut into a disc shape with a diameter of 15.958 mm, is placed in its center with the positive active material layer facing upwards. Above this, a glass fiber filter paper (Advantech Co., Ltd., GA-100), cut into a disc shape with a diameter of 16.156 mm, is placed. After injecting 150 μL of non-aqueous electrolyte (S45~S47), a negative electrode (N3), obtained as described above and cut into a disc shape with a diameter of 16.156 mm, is placed with the negative active material layer facing downwards. Then, spacers and springs are placed inside the battery casing, and the battery cover is closed and sealed tightly with a sealing machine. Any overflowing non-aqueous electrolyte is wiped away with a waste cloth. The non-aqueous electrolyte was kept at 25°C for 12 hours to allow it to be fully mixed into the laminate, thus obtaining a coin-shaped non-aqueous secondary battery (P3 / N3).

[0683] (3) Evaluation of coin-type non-aqueous secondary batteries (P3 / N3)

[0684] For the coin-shaped non-aqueous secondary batteries (P3 / N3) obtained as described above (Examples 30-32), firstly, the initial charge treatment and initial charge-discharge capacity were measured according to the steps in (3-1) below. Next, each coin-shaped non-aqueous secondary battery (P3 / N3) was evaluated according to the steps in (3-2). It should be noted that the charge-discharge was performed using a charge-discharge apparatus ACD-M01A (trade name) manufactured by ASKA ELECTRONIC CO., LTD. and a programmable temperature bath IN804 (trade name) manufactured by Yamato Scientific Co., LTD.

[0685] In this manual, 1C refers to the current value at which a fully charged battery is expected to discharge at a constant current for 1 hour.

[0686] Specifically, in coin-type non-aqueous secondary batteries (P3 / N3), 1C refers to the current value expected to discharge from a fully charged state of 4.2V to 2.5V with a constant current and end the discharge in 1 hour.

[0687] Assemble according to the steps in (2-3) above. The coin-shaped non-aqueous secondary battery (P3 / N3) is a 3mAh battery, and its fully charged battery voltage is determined to be 4.2V, equivalent to a 1C current value of 3mA. In the following text, unless otherwise specified, the descriptions of current and voltage values ​​will be omitted for convenience.

[0688] (3-1) Initial charge and discharge treatment of non-aqueous secondary batteries

[0689] The ambient temperature of the coin-type non-aqueous secondary battery (P3 / N3) was set to 25°C. It was charged at a constant current equivalent to 0.1C until fully charged, then charged at a constant voltage for 1.5 hours. Next, the battery was discharged at a constant current equivalent to 0.3C to the specified voltage. The initial efficiency was calculated by dividing the discharge capacity by the charging current capacity. This discharge capacity was then used as the initial capacity. For batteries with an initial efficiency of less than 80%, the specified battery capacity was not met, making it difficult to obtain accurate evaluation results, and therefore subsequent evaluation tests could not be conducted.

[0690] (3-2) Fast charging test of non-aqueous secondary batteries (P3 / N3)

[0691] For the coin-type non-aqueous secondary battery (P3 / N3) that underwent its initial charge-discharge treatment using the method described in (3-1) above, the ambient temperature was set to 25°C, and it was charged to 4.2V with a constant current of 0.6mA (equivalent to 0.2C). This charging current capacity was defined as the charging capacity A. Then, it was discharged with a current of 1.5mA (equivalent to 0.5C) until it reached 2.0V, and then discharged at a constant voltage of 2.0V until the current decreased to 0.3mA (equivalent to 0.1C). This same charge-discharge cycle was then performed 5 times.

[0692] Next, charge to 4.2V with a constant current of 15mA (equivalent to 5C). Then, discharge to 2.0V with a current of 1.5mA (equivalent to 0.5C), and then discharge at a constant voltage of 2.0V until the current decays to 0.3mA (equivalent to 0.1C). Then, perform 5 cycles of the same charge and discharge process.

[0693] Next, at 30mA (15mA / cm) equivalent to 10C. 2 Charge the capacitor to 4.2V with a constant current. Set this charging current capacity as the charging capacity B. Then, discharge it with a current of 1.5mA (equivalent to 0.5C) until it reaches 2.0V. Then, discharge it with a constant voltage of 2.0V until the current decreases to 0.3mA (equivalent to 0.1C). Then, perform 5 cycles of the same charge and discharge process.

[0694] Next, the coin-type non-aqueous secondary battery was charged to 4.2V with a constant current of 0.6mA (equivalent to 0.2C). This charging current capacity was designated as the charging capacity C. Then, it was discharged with a current of 1.5mA (equivalent to 0.5C) until it reached 2.0V, after which it was discharged at a constant voltage of 2.0V until the current decreased to 0.3mA (equivalent to 0.1C). This same charge-discharge cycle was then performed 5 times, for a total of 20 charge-discharge cycles.

[0695] For non-aqueous secondary batteries that underwent fast charging tests using the methods described above, the fast charging capacity retention rate was calculated based on the following formula. At this time, refer to... Figure 3 A charging curve was constructed, and the presence or absence of a voltage plateau was observed within the voltage range of 3.0~4.2V. The results are shown in Table 5-1.

[0696] Fast charging capacity retention rate = (Charging capacity B / Charging capacity A) × 100%

[0697] For non-aqueous secondary batteries that underwent fast charging tests using the methods described above, the recovery charge capacity retention rate was calculated based on the following formula. The results are shown in Table 5-1.

[0698] Restored charging capacity maintenance rate = (Charging capacity C / Charging capacity A) × 100%

[0699] [Examples 30-32]

[0700] Here, the test results of the coin-type non-aqueous secondary battery (P3 / N3) are explained.

[0701] Fast charging capacity retention rate is an indicator that the higher the value, the more charge can be made in a short time. The fast charging capacity retention rate is preferably 40% or higher, more preferably 43% or higher, and even more preferably 45% or higher.

[0702] The recovery charge capacity retention rate is an indicator of irreversible capacity in fast charging tests. A higher value indicates less irreversible lithium loss during the fast charging test, resulting in greater battery capacity usable after fast charging. Preferably, the recovery charge capacity retention rate is 90% or higher, more preferably 95% or higher, and even more preferably 97% or higher.

[0703] The voltage plateau observed in the 3.0–4.2 V range of the charging curve suggests lithium metal electrodeposition on the negative electrode surface. When lithium metal is electrodeposited on the negative electrode surface, reduction and decomposition of the non-aqueous electrolyte occurs on the lithium metal surface, leading to battery degradation. Therefore, it is preferable to avoid observing a voltage plateau.

[0704] [Table 5-1]

[0705]

[0706] In Examples 30-32, results meeting the acceptable level were obtained in all tests.

[0707] (3-3) Cyclic test at 50°C for coin-type non-aqueous secondary batteries (P3 / N3)

[0708] For the coin-type non-aqueous secondary battery (P3 / N3) that underwent its first charge-discharge treatment using the method described in (3-1) above, the ambient temperature was set to 50°C. First, it was charged with a constant current of 4.5mA (equivalent to 1.5C) until it reached 4.2V. Then, it was charged with a constant voltage of 4.2V until the current decayed to 0.15mA (equivalent to 0.05C). Next, it was discharged with a constant current of 4.5mA to 2.5V. One charge and one discharge cycle was considered one cycle, and 100 charge-discharge cycles were performed. The discharge capacity of the 100th cycle, with the discharge capacity of the first cycle set to 100%, was used as the capacity retention rate in the 50°C cycle test.

[0709] For the coin-shaped non-aqueous secondary battery (P3 / N3) that underwent a 50°C cycle test using the above method, the DCIR was calculated based on the following formula. The results are shown in Table 5-2.

[0710] DCIR = (Voltage 10 seconds after the start of self-discharge - Voltage before the start of discharge) / Current [Ω]

[0711] The DCIR increase rate during the 50℃ cyclic test was calculated based on the following formula. The results are shown in Table 5-2.

[0712] DCIR increase rate = DCIR in the 100th cycle / DCIR in the 1st cycle × 100 [%]

[0713] [Examples 33-35]

[0714] Here, the experimental results shown in Table 5-2 are explained.

[0715] The capacity retention rate in the 50°C cycle test represents the ratio of the discharge capacity in the 100th cycle to the discharge capacity in the 1st cycle. A higher value indicates less capacity degradation during repeated charge-discharge cycles at high temperatures. The capacity retention rate is preferably 88% or higher, more preferably 89% or higher, and even more preferably 90% or higher. DCIR (Direct Current Internal Resistance) increases slowly as the battery deteriorates, leading to a decrease in battery capacity. Excessive enhancement of the SEI (Self-Isolation) of the negative electrode increases DCIR, resulting in a large voltage drop at the beginning of discharge, making it impossible to achieve the desired battery capacity. Therefore, the DCIR in the 1st cycle is preferably 41Ω or less, more preferably 40.5Ω or less, and even more preferably 40Ω or less. The DCIR increase rate is preferably 120% or less, more preferably 115% or less, and even more preferably 111% or less.

[0716] [Table 5-2]

[0717]

[0718] It was confirmed that in Examples 33-34, the capacity reduction during high-temperature cycling tests was minimal, the increase rate of DCIR was suppressed, and the cycling performance was improved. On the other hand, in Example 35, which used a non-aqueous electrolyte without ethylene carbonate, compared with Examples 33-34, the increase of DCIR during 50°C cycling tests was greater, and the capacity retention rate during 50°C cycling tests was lower.

[0719] Based on the above results, it is confirmed that in this embodiment, by combining the inclusion formula Li wThe compound with an olivine-type structure, represented by FePO4 {where w is 0.05~1.1}, serves as the positive electrode active material. Together with an electrolyte containing acetonitrile and ethylene carbonate, with the ethylene carbonate and ethylene sulfite adjusted to an appropriate ratio, a high-temperature resistant negative electrode SEI is formed on the negative electrode surface. This negative electrode exhibits excellent high-temperature cycling performance and has low initial resistance.

[0720] Implementation Method 2

[0721] (1) Preparation of non-aqueous electrolyte

[0722] Various non-aqueous solvents were mixed at predetermined concentrations under an inactive atmosphere, and then various lithium salts were added at predetermined concentrations to prepare non-aqueous electrolytes (S101) to (S112). The compositions of these non-aqueous electrolytes are shown in Table 6.

[0723] <Explanation of abbreviations in Table 6>

[0724] (Non-aqueous solvent)

[0725] AN: Acetonitrile

[0726] EMC: Ethyl methyl carbonate

[0727] EC: Ethylene carbonate

[0728] ES: Ethyl sulfite

[0729] VC: Vinylene carbonate

[0730] (Lithium salts)

[0731] LiPF6: Lithium hexafluorophosphate

[0732] LiFSI: Lithium bis(fluorosulfonyl)imide (LiN(SO2F)2)

[0733] LiFSO3: Lithium fluorosulfonate

[0734] [Table 6]

[0735]

[0736] (2) Preservation test of non-aqueous electrolyte

[0737] (2-1) Storage test of non-aqueous electrolyte at 25°C or 85°C for 1 hour

[0738] For the non-aqueous electrolytes (S101)~(S106) and (S38)~(S40) obtained as described above, a storage test was conducted at 25°C or 85°C for 1 hour.

[0739] The non-aqueous electrolyte was collected into a SUS container inside an argon chamber, sealed, and stored in a constant temperature bath at 25°C or 85°C for 1 hour. Then, the stored non-aqueous electrolyte was neutralized and titrated with a 0.01M sodium hydroxide-methanol solution, and the acid content was determined in HF form. The results were evaluated according to the following criteria.

[0740] Evaluation Criteria:

[0741] A: When the value is 0.01 ppm or higher but less than 20 ppm by mass

[0742] B: When the value is 20 ppm or higher but less than 60 ppm by mass

[0743] C: When the value is 60 ppm or higher but less than 100 ppm by mass

[0744] D: When it is above 100 ppm by mass

[0745] E: When less than 0.01 ppm by mass

[0746] Excessive HF corrodes electrode and current collector materials, causes solvent decomposition, and adversely affects battery performance. Therefore, the HF generation after storage at 25°C or 85°C for 1 hour is preferably less than 100 ppm by mass, more preferably less than 60 ppm by mass, and even more preferably less than 20 ppm by mass. Furthermore, the small amount of HF generated at room temperature acts as a catalyst to promote the formation of the SEI in the negative electrode or the silane crosslinking reaction of silane-modified polyolefins. Therefore, the HF generation after storage at 25°C for 1 hour is preferably 0.01 ppm by mass or more. The experimental results are shown in Table 7-1.

[0747] [Table 7-1]

[0748]

[0749] Regarding the HF generation after storage at 85°C for 1 hour, a comparison between Examples 101-107 and Comparative Examples 101-102 shows that by adjusting the LiFSO3 content to an appropriate range, the HF generation under high-temperature conditions can be adjusted to 0.01 ppm by mass or more and less than 100 ppm by mass. Specifically, a comparison of Examples 101-107 shows that by including LiPF6 in a range where LiPF6 < lithium imide salt content, the HF generation under high-temperature conditions can be suppressed to 0.01 ppm by mass or more and less than 60 ppm by mass; and by not containing LiPF6, the HF generation under high-temperature conditions can be suppressed to 0.01 ppm by mass or more and less than 20 ppm by mass.

[0750] Furthermore, when comparing Examples 101-107 with Comparative Example 102 regarding the HF generation after storage at 25°C for 1 hour, it was found that by adjusting the LiFSO3 content to an appropriate range, the HF generation at room temperature could be adjusted to 0.01 ppm by mass or more. Specifically, a comparison of Examples 101-103, 105-107 with Example 104 showed that by containing no LiPF6, or containing LiPF6 within a range where LiPF6 < the lithium imide salt content, the HF generation at room temperature could be suppressed to 0.01 ppm by mass or more and less than 20 ppm by mass.

[0751] (2-2) Storage test of non-aqueous electrolyte at 85℃ for 24 hours

[0752] For the non-aqueous electrolytes (S101) to (S105) obtained as described above, a storage test at 85°C for 24 hours was conducted.

[0753] Inside an argon chamber, a non-aqueous electrolyte was collected into an inner tube (3 mm in diameter) of an NMR tube, capped, and sealed with a sealing film. The inner tube was then stored at 85°C for 24 hours. Afterward, the inner tube was removed from the argon chamber and inserted into an outer tube containing a DMSO-d6 solution containing C6H2F4, for NMR analysis using a double-tube method. The NMR apparatus used was an ECS400 manufactured by JEOL RESONANCE Co., Ltd. The measurement conditions were: 45° pulse, 256 pulses, and a measurement temperature of 25°C. The amount of hydrogen fluoride (HF) produced was quantified based on the NMR results.

[0754] Excessive HF corrodes electrode and current collector materials, and causes solvent decomposition, which adversely affects battery performance. Therefore, the amount of HF generated after storage at 85°C for 24 hours is preferably below 1000 ppm by mass, more preferably below 500 ppm by mass, and even more preferably below 100 ppm by mass. The test results are shown in Table 7-2.

[0755] [Table 7-2]

[0756]

[0757] Regarding the HF generation after storage at 85°C for 24 hours, a comparison between Examples 108-111 and Comparative Example 103 shows that by adjusting the LiFSO3 content to an appropriate range, the HF generation under high-temperature conditions can be reduced to below 1000 ppm by mass. Specifically, a comparison of Examples 108-111 shows that by including LiPF6 in a range where LiPF6 < lithium imide salt content, the HF generation under high-temperature conditions can be suppressed to below 500 ppm by mass; and by omitting LiPF6, the HF generation under high-temperature conditions can be suppressed to below 100 ppm by mass.

[0758] (3) Fabrication of coin-type non-aqueous secondary batteries

[0759] (3-1) Production of the positive electrode

[0760] Lithium iron phosphate (LiFePO4) with an olivine-type structure, used as the positive electrode active material, carbon black powder, used as a conductive additive, and polyvinylidene fluoride (PVDF), used as a binder, are mixed in a mass ratio of 84:10:6 to obtain a positive electrode mixture.

[0761] N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture at a concentration of 68% by mass of solids, and the mixture was further mixed to obtain a slurry containing the positive electrode mixture. On one side of an aluminum foil with a thickness of 15 μm and a width of 280 mm, which serves as the positive electrode current collector, the slurry containing the positive electrode mixture was coated using a three-roll transfer coating machine while adjusting the unit area weight of the coating to form a coating pattern with a width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was removed by drying in a hot air drying oven. The resulting electrode roll was trimmed on both sides and subjected to reduced pressure drying at 130°C for 8 hours. Then, it was calendered using a roller press to achieve a density of 1.9 g / cm³ for the positive electrode active material layer. 3 This yields a positive electrode containing a positive active material layer and a positive current collector. The weight per unit area, excluding the positive current collector, is 17.5 mg / cm². 2 .

[0762] (3-2) Fabrication of the negative electrode

[0763] A negative electrode mixture is obtained by mixing graphite powder (as the negative electrode active material), carbon black powder (as the conductive additive), and carboxymethyl cellulose and styrene-butadiene rubber (as the binder) in a solid component mass ratio of 95.7:0.5:3.8.

[0764] Water was added as a solvent to the obtained negative electrode mixture at a concentration of 45% by mass of solids, and the mixture was further mixed to prepare a slurry containing the negative electrode mixture. On one side of a copper foil with a thickness of 8 μm and a width of 280 mm, which would serve as the negative electrode current collector, a three-roll transfer coating machine was used to coat the foil, adjusting the unit area weight of the slurry containing the negative electrode mixture, to form a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was removed by drying in a hot air drying oven. The resulting electrode roll was trimmed on both sides and subjected to reduced pressure drying at 80°C for 12 hours. Then, it was calendered using a roller press to achieve a density of 1.5 g / cm³ for the negative electrode active material layer. 3 This yields a negative electrode comprising a negative electrode active material layer and a negative electrode current collector. The weight per unit area, excluding the negative electrode current collector, is 7.5 mg / cm². 2 .

[0765] (3-3) Assembly of coin-type non-aqueous secondary batteries

[0766] A polypropylene gasket is placed in the CR2032 battery casing (SUS304 / Al cladding). A positive electrode, obtained by punching a disc shape with a diameter of 15.958 mm as described above, is placed in its center with the positive active material layer facing upwards. A filter paper, obtained by punching a disc shape with a diameter of 16.156 mm, made of glass fiber filter paper (Advantech Co., Ltd., GA-100), is placed above it. After injecting 150 μL of non-aqueous electrolyte, a negative electrode, obtained by punching a disc shape with a diameter of 16.156 mm as described above, is placed with the negative active material layer facing downwards. Then, spacers and springs are placed, the battery cover is closed, and the battery is sealed tightly with a sealing machine. Excess non-aqueous electrolyte is wiped away with a waste cloth. The battery is kept at 25°C for 12 hours to allow the non-aqueous electrolyte to fully mix into the laminate, resulting in a coin-shaped non-aqueous secondary battery.

[0767] (4) Evaluation of coin-type non-aqueous secondary batteries

[0768] For the coin-shaped non-aqueous secondary batteries obtained as described above, firstly, the initial charge treatment and initial charge-discharge capacity were measured according to the steps described in (4-1). Next, each coin-shaped non-aqueous secondary battery was evaluated according to the steps described in (4-2). It should be noted that the charge-discharge was performed using a charge-discharge apparatus ACD-M01A (trade name) manufactured by ASKA ELECTRONIC CO., LTD. and a programmable temperature bath IN804 (trade name) manufactured by Yamato Scientific Co., LTD.

[0769] Here, 1C refers to the current value at which a fully charged battery is expected to discharge at a constant current for one hour.

[0770] (4-1) Initial charge and discharge treatment of coin-type non-aqueous secondary batteries

[0771] The ambient temperature of the coin-type non-aqueous secondary battery was set to 25°C. It was charged with a constant current of 0.46mA (equivalent to 0.1C) until it reached 3.8V. Then, it was charged with a constant voltage of 3.8V until the current decayed to 0.05C. Finally, it was discharged with a constant current of 1.38mA (equivalent to 0.3C) to 2.5V.

[0772] (4-2) 25℃ Cyclic Test

[0773] For the coin-type non-aqueous secondary battery that underwent its initial charge-discharge treatment using the method described in (4-1) above, the ambient temperature was set to 25°C. After reaching 3.8V with a constant current of 6.9mA (equivalent to 1.5C), it was charged at a constant voltage of 3.8V until the current decayed to 0.05C. Then, it was discharged to 2.5V with a current of 6.9mA (equivalent to 1.5C). One charge-discharge cycle was performed, and 100 charge-discharge cycles were completed. It should be noted that in the 1st, 50th, and 100th cycles, the battery was charged with a constant current of 4.6mA (equivalent to 1C) to reach 3.8V, then charged at a constant voltage of 3.8V until the current decayed to 0.05C, and then discharged to 2.5V with a constant current of 1.38mA (equivalent to 0.3C).

[0774] The discharge capacity of the 99th cycle during the cycle test, with the discharge capacity of the first cycle during the initial charge-discharge treatment set at 100%, is taken as the 25°C cycle capacity retention rate and evaluated according to the following criteria.

[0775] Evaluation Criteria:

[0776] A: When the capacity maintenance rate is above 80%

[0777] B: When the capacity maintenance rate is above 70% but below 80%

[0778] C: When the capacity maintenance rate is less than 70%

[0779] The 25°C cycle capacity retention rate serves as an indicator of output performance and battery degradation during long-term use at room temperature. It is believed that a higher value indicates less capacity reduction during long-term use at room temperature, thus maintaining high output performance over a longer period. Therefore, a 25°C cycle capacity retention rate of 70% or higher is preferred, and more preferably 80% or higher. The evaluation results are shown in Table 8.

[0780] (4-3) Measurement of AC impedance

[0781] For the coin-shaped non-aqueous secondary battery that underwent a 25°C cycling test using the method described in (4-2) above, after reaching 3.8V with a constant current of 4.6mA (equivalent to 1C), it was charged with a constant voltage of 3.8V until the current decayed to 0.05C, and then AC impedance was measured. The measurements were performed using a Solartron Frequency Response Analyzer 1400 (trade name) and a Solartron Potentio-Galvanostat 1470E (trade name). An AC signal was applied while varying the frequency from 1000kHz to 0.01Hz, and the impedance was measured from the voltage / current response signal to determine the AC impedance value. The AC impedance value was read as the real component (Z') of the impedance at a frequency of 1kHz. Furthermore, the amplitude of the applied AC voltage was set to ±5mV, and the ambient temperature of the battery during AC impedance measurement was set to 25°C.

[0782] The AC impedance value at 1 kHz is equivalent to the sum of the interfacial impedance component and the bulk resistance component of the negative electrode. The battery components and electrolyte composition used in this experiment were identical, excluding the amount of LiFSO3 added; therefore, the bulk resistance component did not differ. Thus, it is considered that the smaller this value, the more it suppresses the increase in the interfacial impedance component of the negative electrode during the 25°C cycling test. The evaluation results are shown in Table 8.

[0783] [Table 8]

[0784]

[0785] In Comparative Example 104, where the LiFSO3 content was more than 200 ppm by mass, the capacity retention rate at 25°C was less than 70%, while in Examples 112-113, the capacity retention rate at 25°C was more than 80%. In Comparative Example 104, with its high LiFSO3 content, the AC impedance after cycling at 25°C was higher than in Examples 112-113. It is speculated that this is due to the reduction and decomposition of LiFSO3 at the negative electrode, leading to its accumulation on the negative electrode surface, or the increased HF content causing excessive LiF to be generated and accumulated on the negative electrode surface, thus increasing the internal resistance and reducing the capacity retention rate at 25°C. Based on these results, it is preferable to control the LiFSO3 content in the non-aqueous electrolyte within a specified range.

[0786] (5) Long-term cycling performance / safety performance evaluation after long-term cycling

[0787] (5-1) Fabrication / Evaluation of Separators

[0788] (5-1-1) Fabrication of the separator (A01)

[0789] [Preparation of silane-grafted modified polyolefins]

[0790] The raw material polyolefin used in silane graft-modified polyolefins has a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. It can be a copolymer of propylene or butene into α-olefins. While the raw material polyethylene is melt-blended using an extruder, an organic peroxide (di-tert-butyl peroxide) is added to generate free radicals within the α-olefin polymer chain. Then, a trimethoxyalkoxy compound is injected into the melt-blended compound to replace the vinylsilane, resulting in an addition reaction. Through the addition reaction, alkoxysilyl groups are introduced into the α-olefin polymer to form a silane graft structure. Additionally, to simultaneously adjust the free radical concentration in the system, an appropriate amount of antioxidant (pentaerythritol tetratetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added to inhibit the chain reaction (gelling) within the α-olefin. The obtained silane-grafted polyolefin molten resin was cooled in water, granulated, and then dried at 80°C for 2 days to remove moisture and unreacted trimethoxyalkoxylated vinylsilane. It should be noted that the residual concentration of unreacted trimethoxyalkoxylated vinylsilane in the granules was below 3000 ppm.

[0791] <Making of the base material as the first layer>

[0792] A mixture was prepared by adding 30% by mass of polyethylene homopolymer (ultra-high molecular weight polyethylene (A)) with a viscosity average molecular weight of 3,000,000 and 50% by mass of polyethylene homopolymer (polyethylene (B)) with a viscosity average molecular weight of 700,000, and 20% by mass of silane-grafted polyethylene (silane-modified polyethylene (C)) with an MFR of 0.4 g / min, obtained by modifying vinyl silane with trimethoxyalkoxy compounds using a polyolefin with a viscosity average molecular weight of 125,000 as a raw material (the resin composition of (A):(B):(C) is 3:5:2). Then, 1000 ppm by mass of pentaerythritol tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant was added relative to the total amount, and the mixture was dry-mixed using a drum mixer to obtain a mixture. It should be noted that 3000 ppm of calcium stearate was added relative to ultra-high molecular weight polyethylene (A). The resulting mixture was fed into a twin-screw extruder under a nitrogen atmosphere using a feeder. In addition, liquid paraffin (dynamic viscosity at 37.78°C 7.59 × 10⁻⁶) was injected into the extruder barrel using a plunger pump. -5 m 2 / s).

[0793] The mixture is melt-blended with liquid paraffin in an extruder, with the feeder and pump adjusted so that the liquid paraffin content in the extruded polyolefin composition is 70% by mass (i.e., the polymer concentration is 30% by mass). The melt-blending conditions are set at a temperature of 230°C, a screw speed of 240 rpm, and an ejection rate of 18 kg / h.

[0794] Next, the molten compound is extruded through a T-die onto a cooling roller with a surface temperature controlled at 25°C and then cast to obtain a gel sheet (sheet-shaped molded body) with an unprocessed film thickness of 1370 μm.

[0795] Next, the sheet-shaped material is fed into a biaxial tenter frame for biaxial stretching to obtain a stretched product. The stretching conditions are set as follows: MD ratio 7.0, TD ratio 6.4 (i.e., 7 × 6.3), and biaxial stretching temperature 122°C. Then, the stretched gel sheet is immersed in a dichloromethane bath to extract and remove liquid paraffin. The dichloromethane is then dried to remove the solid material, resulting in a porous body. Next, the porous body is fed into a TD tenter frame for heat setting (HS) at a temperature of 133°C and a stretch ratio of 1.9. Then, a relaxation operation is performed to a TD ratio of 1.75 to obtain a microporous membrane. Finally, the ends of the obtained microporous membrane are trimmed, and it is wound into a master roll with a width of 1100 mm and a length of 5000 m.

[0796] During the above evaluation, the microporous membrane unwound from the master roll is cut as needed and used as the evaluation substrate (first layer). For the obtained evaluation substrate, the membrane thickness, air permeability, porosity, etc. are measured, as shown in Table 9-1.

[0797] <The Construction of the Second Layer>

[0798] [Synthesis methods of resin adhesives]

[0799] Acrylic latex used as a resin binder is manufactured by the following method.

[0800] In a reaction vessel equipped with a stirrer, reflux cooler, dropping tank, and thermometer, 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) and 0.5 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) as emulsifiers were added. Next, the temperature inside the reaction vessel was raised to 80°C, and while maintaining this temperature, 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added to obtain an initial mixture. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the emulsion was added dropwise from the dropping tank to the reaction vessel over a period of 150 minutes.

[0801] It should be noted that the above emulsion was prepared by mixing 70 parts by weight of butyl acrylate; 29 parts by weight of methyl methacrylate; 1 part by weight of methacrylic acid; 3 parts by weight of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) and 3 parts by weight of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) as emulsifiers; 7.5 parts by weight of 2% aqueous solution of ammonium persulfate; and 52 parts by weight of deionized water using a homogenizer for 5 minutes.

[0802] After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature. The resulting emulsion was adjusted to pH 8.0 with a 25% ammonium hydroxide aqueous solution, and a small amount of water was added to obtain an acrylic latex with a solid content of 40%. The obtained acrylic latex had a number average particle size of 145 nm and a glass transition temperature of -30°C.

[0803] A dispersion was prepared by uniformly dispersing 95 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (solid content conversion) of an aqueous solution of ammonium polycarboxylate (SAN NOPCO SN Dispersant 5468, 40% solid content concentration) as an ionic dispersant in 100 parts by mass of water. The resulting dispersion was then subjected to a bead mill (chamber volume 200 cc, zirconia bead diameter 0.1 mm, filling rate 80%) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm, thus preparing a slurry containing inorganic particles. 2.0 parts by mass (solid content conversion) of the acrylic latex prepared above as a resin binder was added to the particle size-adjusted dispersion.

[0804] Next, the microporous membrane is continuously fed out from the above-mentioned microporous membrane master roll, and a slurry containing inorganic particles is coated on one side of the microporous membrane using a gravure reverse coating machine. Then, it is dried in a 60°C dryer to remove water, and wound up to obtain the master roll of the separator.

[0805] During evaluation, the separators unwound from the master roll will be cut as needed and used as evaluation separators. It should be noted that for the inorganic particle types in the second layer of Tables 9-1 to 9-3, these inorganic particles will be referred to as "ceramics".

[0806] (5-1-2) Fabrication of separators (A02) to (A15)

[0807] Aiming at the physical properties listed in Tables 9-1 to 9-3, at least one of the following conditions is changed: the type or viscosity-average molecular weight of the homopolymer polyethylene, melt mixing conditions, setting stretching conditions, heat setting conditions, and relaxation operation conditions. Furthermore, the composition of the second layer is changed as shown in Tables 9-1 to 9-3. Apart from these changes, the separator is manufactured using the same method as described in (5-1-1) above. It should be noted that the abbreviations for the inorganic particles in Tables 9-1 to 9-3 are detailed below.

[0808] "PVDF" (PVDF-HFP / Inorganic)

[0809] Prepare alumina (Al2O3) particles and polyvinylidene fluoride-hexafluoropropylene as a fluorine-based resin. Mix the two together, and then mix the mixture with cyanoethyl polyvinyl alcohol and acetone in a mass ratio of 19.8 / 0.2 / 80 to make it uniformly dispersed, thereby preparing a coating liquid. Coat the single side of the polyolefin microporous membrane using a gravure coating machine to form a second layer with the thicknesses shown in Tables 9-1 to 9-3.

[0810] "Para-aramid / inorganic substances"

[0811] 150 parts by mass of p-phenylenediamine were added to 5000 parts by mass of an N-methyl-2-pyrrolidone (NMP) / calcium chloride solution (calcium chloride concentration = 7.1% by mass) and dissolved / stirred under a N2 atmosphere. Then, 273.94 parts by mass of terephthaloyl chloride were added and stirred for 1 hour to obtain a polyterephthalamide polymer solution. 1000 parts by mass of the polymer solution, 3000 parts by mass of NMP, and 143.4 parts by mass of alumina (Al2O3) particles were stirred and mixed, and dispersed using a homogenizer to obtain a coating slurry. Using a drum-mounted rod coater, the coating slurry was coated onto one side of a polyolefin microporous membrane with a gap of 20 μm to 30 μm. It was dried at approximately 70°C to form a second layer, resulting in a composite separator.

[0812] "Meso-aramid / inorganic substances"

[0813] Meta-aromatic polyamide and boehmite with an average particle size of 0.6 μm were adjusted and mixed at a mass ratio of 1:1. This mixture was then combined with a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (mass ratio = 1:1) at a meta-aromatic polyamide concentration of 3% by mass to obtain a coating slurry. Using a Mayer rod coater, the coating slurry was coated onto one side of a polyolefin microporous membrane with a gap of 20 μm to 30 μm to obtain a coated separator. The coated separator was then immersed in a coagulation solution at a mass ratio of water:DMAc:TPG = 2:1:1 and a temperature of 35°C, followed by water washing / drying to form a second layer, resulting in a composite separator.

[0814] (5-1-3) Evaluation of separators

[0815] (i) Detection method for silane-modified polyolefins contained in separators

[0816] When the silane-modified polyolefin contained in the separator is cross-linked, it is insoluble or has insufficient solubility in organic solvents, making it sometimes difficult to directly determine the content of silane-modified polyolefin from the separator. In such cases, as sample pretreatment, methyl orthoformate, which does not cause side reactions, is used to decompose the siloxane bonds into methoxysilanols, followed by solution NMR analysis. This allows for the detection of silane-modified polyolefin contained in the separator or its GPC determination. The pretreatment experiment can be performed according to Japanese Patent Nos. 3529854 and 3529858.

[0817] Specifically, the detection method for silane-modified polyolefins contained in the separator can utilize the silane-modified polyolefins used as raw materials in the manufacture of the separator. 1 H or 13 Identification by C-NMR. The following explains... 1 H and 13 An example of a C-NMR determination method.

[0818] ( 1 (H-NMR measurement)

[0819] The sample was dissolved in o-dichlorobenzene-d4 at 140℃ to obtain a proton resonance frequency of 600MHz. 1 H-NMR spectrum. 1 The determination conditions for H-NMR are as follows.

[0820] Device: Bruker AVANCE NEO 600

[0821] Sample tube diameter: 5mmφ

[0822] Solvent: o-dichlorobenzene-d4

[0823] Measurement temperature: 130℃

[0824] Pulse angle: 30°

[0825] Pulse wait time: 1 second

[0826] Total number of times: 1000 or more

[0827] Sample concentration: 1 wt / vol%

[0828] ( 13 (NMR determination of C)

[0829] The sample was dissolved in o-dichlorobenzene-d4 at 140 °C to obtain 13 C-NMR spectrum. 13 The C-NMR measurement conditions are as follows.

[0830] Device: Bruker AVANCE NEO 600

[0831] Sample tube diameter: 5mmφ

[0832] Solvent: o-dichlorobenzene-d4

[0833] Measurement temperature: 130℃

[0834] Pulse angle: 30°

[0835] Pulse wait time: 5 seconds

[0836] Total number of times: 10,000 or more

[0837] Sample concentration: 10 wt / vol%

[0838] pass 1 H and / or 13 C-NMR determination can confirm the amount of silane unit modification and alkyl modification in silane-modified polyolefins, and can also identify the presence of (-CH2-Si) in silane-modified polyolefins within the separator. 1 H, 0.69ppm, t; 13 C, 6.11 ppm, s).

[0839] (ii) Weight-average molecular weight and number-average molecular weight

[0840] Using a Waters ALC / GPC 150C (trademark), a calibration curve was prepared by measuring standard polystyrene under the following conditions. Additionally, the following polymers were measured under the same conditions, and their weight-average molecular weights were calculated based on the calibration curves using the following method.

[0841] Pillars: 2 x Tosoh GMH6-HT (trademark) + 2 x GMH6-HTL (trademark)

[0842] Mobile phase: o-dichlorobenzene

[0843] Detector: Differential refractometer

[0844] Flow rate: 1.0 ml / min

[0845] Column temperature: 140℃

[0846] Sample concentration: 0.1 wt%

[0847] (Weight-average molecular weight and number-average molecular weight of polyethylene and polypropylene)

[0848] Each molecular weight component in the obtained calibration curve is multiplied by 0.43 (Q factor of polyethylene / Q factor of polystyrene = 17.7 / 41.3) or 0.64 (Q factor of polypropylene / Q factor of polystyrene = 26.4 / 41.3) to obtain the molecular weight distribution curve converted from polyethylene or polypropylene, from which the weight-average molecular weight and number-average molecular weight can be calculated. It should be noted that, due to chromatographic limitations, accurate determination of molecular weight distribution is difficult in regions with molecular weights above 1 million.

[0849] (Weight-average molecular weight of the resin composition)

[0850] The Q factor value of the polyolefin with the largest mass fraction is used, and the weight-average molecular weight is calculated in the same manner as in the case of polyethylene.

[0851] (iii) Viscosity-average molecular weight (Mv)

[0852] Based on ASTM-D4020, determine the limiting viscosity [η] of decahydronaphthalene solvent at 135°C. Calculate the Mv of polyethylene and silane-modified polyethylene using the following formula.

[0853] [η] = 6.77 × 10 -4 Mv 0.67

[0854] (iv) Melt flow rate (MFR) (g / min)

[0855] The MFR value can be determined by using the Toyo Seiki Melt Indexer F-F01 to measure the weight of the resin extruded from polyethylene and silane-modified polyethylene at 190°C and a load of 2.16 kg for 10 minutes. MFR for polypropylene can be determined at 230°C.

[0856] (v) Thickness TA (μm)

[0857] Using a miniature thickness gauge KBM (trademark) from Toyo Seiki, the thicknesses of the first and second layers were measured at room temperature of 23±2℃ and relative humidity of 60%. Specifically, the thicknesses of five points were measured at approximately equal intervals along the total width of the object in the TD direction, and their average values ​​were obtained.

[0858] (vi) Porosity (%)

[0859] Cut a 10cm × 10cm square sample from the microporous membrane (substrate) and calculate its volume (cm³). 3 ) and mass (g), based on them and density (g / cm³) 3 The porosity can be calculated using the following formula.

[0860] It should be noted that the density of the mixture is calculated based on the density of each raw material and the mixing ratio.

[0861] Porosity (%) = (Volume - Mass / Density of the mixture) / Volume × 100

[0862] (vii) Breathability (seconds / 100cm) 3 )

[0863] According to JIS P-8117 (2009), the air permeability of the sample was determined using a G-B2 (trademark) air permeability meter manufactured by Toyo Seiki Co., Ltd.

[0864] (5-2) TOF-SIMS analysis / image processing of separators

[0865] (5-2-1) TOF-SIMS Analysis of Separator

[0866] For the separators obtained as described above, TOF-SIMS analysis was performed. A nano-TOF spectrometer manufactured by ULVAC-PHI, INC. was used as the TOF-SIMS mass spectrometer. The analytical conditions are as described below.

[0867] <Image Measurement Conditions>

[0868] Primary ion: Bismuth (Bi)

[0869] Accelerating voltage: 30kV

[0870] Ion current: approximately 0.5 nA (as DC)

[0871] Analysis area: 100μm × 100μm

[0872] Analysis time: 90 minutes

[0873] Detected ions: positive ions (m / z=40)

[0874] Neutralization: Electron gun + Ar monomer ions

[0875] Vacuum level: Approximately 5.0 × 10⁻⁶ -5 Pa

[0876] <Depth Measurement Conditions>

[0877] Analysis Conditions

[0878] Primary ion: Bismuth (Bi)

[0879] Accelerating voltage: 30kV

[0880] Ion current: Approximately 1.2 nA (as DC)

[0881] Analysis area: 100μm × 100μm

[0882] Analysis time: 5 frames / cycle

[0883] Detected ions: positive ions (m / z=40)

[0884] Neutralization: Electron gun + Ar monomer ions

[0885] Vacuum level: Approximately 5.0 × 10⁻⁶ -5 Pa

[0886] Splashing Conditions

[0887] Sputtered Ions: GCIB (AR) 2500 + )

[0888] Accelerating voltage: 20kV

[0889] Ion current: approximately 5 nA

[0890] Sputtering area: 400μm × 400μm

[0891] Splashing time: 30 seconds / cycle

[0892] Neutralization: Electron gun + Ar monomer ions

[0893] Under the above conditions, the spectroscopic detection of calcium ions (equivalent to positive ions with m / z=40) was performed. As an example, the TOF-SIMS analysis results of separator A01 are shown below. Figure 4 .

[0894] (5-2-2) Image Processing

[0895] For the image data of the TOF-SIMS spectrum obtained as described above, image processing is performed according to the following steps.

[0896] (1) Fabricate a filter that matches the beam shape (diameter 2μm, pixel resolution 0.39μm). Show the 3D image of the filter in... Figure 5 , two 3D image shown Figure 6 .

[0897] <Methods for Calculating Filter Values>

[0898] The fspecial function in the Image Processing Toolbox of MATLAB, a numerical computation software developed by Mathworks, is used to calculate the result.

[0899] fspecia("gaussian", [13 13], 1.69865)

[0900] (2) Apply the created filter to two-dimensional data.

[0901] (3) Calculate the mean and standard deviation of the two-dimensional data after applying the filter.

[0902] (4) Use the mean + standard deviation × 3 as the threshold for binarization.

[0903] (In the case of a normal distribution, 99.74% of the values ​​converge within the range of mean + standard deviation × 3, therefore the intention is to extract the numerically unique components.)

[0904] (5) Perform a 7-pixel dilation and contraction and connect the nearby extraction areas.

[0905] (6) Remove areas with small size (less than 50 pixels).

[0906] (7) Calculate the parameters for the remaining regions.

[0907] Extract area (pixels) and centroid position (x0, y0).

[0908] The maximum value in the region, the average value of the region, and the weighted center position (xm, ym).

[0909] (8) Calculate the distance between the centers of gravity of each weight.

[0910] The weighted centroid option of the regionprops function in the Image Processing Toolbox of MATLAB, a numerical computation software manufactured by Mathworks, is used to calculate it.

[0911] regionprops(cc,I,'WeightedCentroid')

[0912] Here, cc is a variable representing the extracted region, and I is a variable storing the two-dimensional data after the filter has been applied.

[0913] As an example, the results of image processing (1) to (2) of the TOF-SIMS analysis results of separator A01 are shown below. Figure 7 The results of image processing (1) to (8) are shown below. Figure 8 .

[0914] The island structures of calcium ions were identified through the above processing, and their number, size, and distance between weighted center positions were calculated. The results are shown in Tables 9-1 to 9-3.

[0915] (5-3) Fabrication of laminated non-aqueous secondary batteries

[0916] (5-3-1) Production of the positive electrode

[0917] The positive electrode active material is a nickel, manganese, and cobalt composite oxide (LiNiMnCoO2) (NMC) (Ni:Mn:Co = 1:1:1 (elemental ratio), density 4.70 g / cm³). 3 90.4% by mass of graphite powder (KS6) as a conductive additive (density 2.26 g / cm³). 3 1.6% by mass of number-average particle size (6.5 μm) and acetylene black powder (AB) (density 1.95 g / cm³). 3 The number-average particle size (48 nm) was 3.8% by mass, and PVDF (density 1.75 g / cm³) was used as a resin binder. 3 4.2% by mass were mixed and dispersed in NMP to prepare a slurry. This slurry was coated onto a 20μm thick aluminum foil to serve as the positive electrode current collector using a die coater. After drying at 130°C for 3 minutes, it was compressed using a roller press to form the positive electrode. At this point, the coating amount of positive electrode active material on each single side was 109 g / m². 2 .

[0918] (5-3-2) Fabrication of the negative electrode

[0919] Graphite powder A (density 2.23 g / cm³) will be used as the negative electrode active material. 3 Number-average particle size 12.7 μm) 87.6% by mass, graphite powder B (density 2.27 g / cm³) 3A slurry was prepared by dispersing 9.7% by mass of carboxymethyl cellulose ammonium salt (6.5 μm number average particle size), 1.4% by mass of carboxymethyl cellulose ammonium salt (converted to solids content, 1.83% by mass aqueous solution), and 1.7% by mass of diene rubber latex (converted to solids content, 40% by mass aqueous solution) in purified water. This slurry was then coated onto a 12 μm thick copper foil to form the negative electrode current collector using a die coater. After drying at 120°C for 3 minutes, the foil was compressed using a roller press to form the negative electrode. At this point, the amount of negative electrode active material coated on each side was 52 g / m². 2 .

[0920] (5-3-3) Assembly of laminated non-aqueous secondary batteries

[0921] As described above, the positive and negative electrodes are sandwiched together with a separator (the separator of the embodiment or the separator of the comparative example) with the coating surfaces of each electrode facing each other to form a laminated electrode body. This laminated electrode body is then housed in a 100mm × 60mm aluminum laminate shell and vacuum-dried at 80°C for 5 hours to remove moisture. Next, the aforementioned non-aqueous electrolyte (S110) or (S111) is injected into the shell, and the shell is sealed to produce a laminated (pouch-type) non-aqueous secondary battery. This laminated non-aqueous secondary battery has a designed capacity of 3Ah and a rated voltage of 4.2V.

[0922] (5-4) Evaluation of long-term cycle performance of laminated non-aqueous secondary batteries

[0923] For the laminated non-aqueous secondary batteries obtained as described above, firstly, an initial charge treatment is performed according to the steps below (5-4-1). Next, the cycle characteristics of each laminated non-aqueous secondary battery are evaluated according to the steps below (5-4-2). It should be noted that charging and discharging are performed using the ASKA ELECTRONIC CO., LTD. charge / discharge apparatus ACD-M01A (trade name) and the Yamato Scientific CO., LTD. programmable temperature bath IN804 (trade name).

[0924] Here, 1C refers to the current value at which a fully charged battery is expected to discharge at a constant current for 1 hour. In the evaluations (5-4-1) to (5-4-2) below, 1C specifically refers to the current value at which a fully charged battery is expected to discharge at a constant current from 4.2V to 3.0V for 1 hour.

[0925] (5-4-1) Initial charge-discharge treatment of laminated non-aqueous secondary batteries

[0926] The battery was charged at an ambient temperature of 25°C with a constant current of 0.075A (equivalent to 0.025C) until it reached 3.1V. Then, it was charged at a constant voltage of 3.1V for 1.5 hours. After a 3-hour rest period, the battery was charged again with a constant current of 0.15A (equivalent to 0.05C) until it reached 4.2V. This was then charged at a constant voltage of 4.2V for 1.5 hours. Finally, the battery was discharged to 3.0V with a constant current of 0.45A (equivalent to 0.15C).

[0927] (5-4-2) Cyclic test of laminated non-aqueous secondary battery

[0928] For batteries that have undergone initial charge-discharge treatment using the method described in (5-4-1) above, a cycle test is performed. It should be noted that the cycle test begins 3 hours after the ambient temperature of the battery is set to 25°C. First, the battery is charged at a constant current of 3A (equivalent to 1C) until it reaches 4.2V, then charged at a constant voltage of 4.2V for a total of 3 hours. Then, the battery is discharged to 3.0V at a constant current of 3A. Each charge and discharge cycle is considered one cycle, and 1000 charge-discharge cycles are performed. The discharge capacity of the 1000th cycle, with the discharge capacity of the first cycle set to 100%, is taken as the capacity retention rate after 1000 cycles. Batteries with high capacity retention rates are evaluated as having good cycle characteristics. The evaluation results are shown in Tables 9-1 to 9-3. It should be noted that the capacity retention rate after 1000 cycles is preferably 60% or higher.

[0929] (5-5) Prick test of laminated non-aqueous secondary battery after 1000 cycles

[0930] The laminated non-aqueous secondary battery, having undergone cycle characteristic testing as described in step (5-4-2), was placed on an iron plate in a temperature-controlled explosion-proof chamber. At the center of the laminated secondary battery, the temperature inside the explosion-proof chamber was set to 40°C. A 3.0 mm diameter iron nail was driven through the battery at a speed of 2 mm / s, and the process was maintained with the nail in place. The temperature of a thermocouple placed inside the nail, designed to allow measurement of the internal temperature of the laminated battery after penetration, was measured to assess the possibility of fire.

[0931] Using the same method, 100 newly fabricated laminated secondary battery samples were evaluated repeatedly, and the number of samples that did not ignite (not ignited) was calculated as a percentage using the following formula. The evaluation results are shown in Tables 9-1 to 9-3.

[0932] Evaluation result (%) = (100 × number of samples that did not reach the point of ignition / total number of samples)

[0933] The preferred pass rate for nail penetration evaluation is above 50%.

[0934] [Table 9-1]

[0935]

[0936] [Table 9-2]

[0937]

[0938] [Table 9-3]

[0939]

[0940] The separator does not contain 9μm 2 Above and 245μm 2 In Examples 125-128 and 136-139, which have calcium island structures of the following sizes, the capacity retention rate after 1000 cycles is less than 60%, while in Examples 114-123 and 129-134, the capacity retention rate after 1000 cycles is over 60%. This indicates that incorporating calcium island structures of a specific size into the separator improves long-term cycling performance. This is presumably because calcium traps HF generated within the battery over a long period, thus suppressing solvent decomposition caused by HF. Furthermore, the reduction of HF in the non-aqueous electrolyte alters the equilibrium reaction of LiFSO3, shifting it towards a reduction in LiF, which is one of the causes of increased internal resistance. As a result, this is believed to contribute to improved cycling performance.

[0941] The separator described in Examples 125 or 136 is a separator manufactured by the method described in Patent Document 8, and does not contain 9μm. 2 Above and 245μm 2 The following are examples of calcium island structures of a specific size. The separators described in the embodiments containing calcium island structures of a specific size exhibited higher values ​​for long-term cycling characteristics after 1000 cycles and subsequent spike safety compared to Examples 125 or 136, suggesting that calcium island structures of a specific size are important for improving the long-term cycling characteristics of the battery.

[0942] Furthermore, based on a comparison of Examples 125-126, 136-137 with Examples 114-115, 129, the separator contains 9μm 2 Above and 245μm 2 The following sizes of calcium island structures showed a significant increase in the nail penetration safety test pass rate. This is presumably because calcium traps HF generated within the battery for extended periods, thereby inhibiting the breaking reaction of siloxane bonds in the separator and maintaining the cross-linked structure over a long period.

[0943] Furthermore, based on the comparison between Examples 122-123 and Examples 114-121, it is suggested that the thickness ratio of the separator substrate (first layer) to the aforementioned second layer is preferably 0.5 or more and 10 or less.

[0944] (6) Crosslinking experiment of silane-modified separators impregnated with non-aqueous electrolyte

[0945] (6-1) Electrolyte immersion test of silane-modified separator (A01)

[0946] A sample measuring TD100mm × MD100mm was collected from the silane-modified separator (A01) before the formation of the cross-linked structure and used as the sample piece. Under an inactive atmosphere, the sample piece was placed in a stainless steel basin immersed in 100mL of each of the various non-aqueous electrolytes shown in Table 10 for 6 hours. Then, the sample piece was removed from the basin, washed sequentially with ethanol and acetone, and then vacuum dried for 1 hour.

[0947] (6-2) Determination of heat shrinkage rate at 150℃

[0948] A sample sheet measuring TD100mm × MD100mm was collected from the silane-modified separator (A01) before the formation of the crosslinking structure as the pre-crosslinking sample and placed in an oven at 150℃ for 1 hour. During this time, the sample sheet was held between two sheets of paper without direct contact with warm air. After the sample sheet was removed from the oven and cooled, the area of ​​the sample sheet was measured, and the thermal shrinkage rate (T1) at 150℃ before the formation of the crosslinking structure was calculated using the following formula.

[0949] Heat shrinkage rate at 150℃ (%) = (10000 (mm) 2 - Area of ​​the heated sample piece (mm²) 2 ))×100 / 10000

[0950] Furthermore, the sample sheet that underwent a non-aqueous electrolyte immersion test using the method described in (6-1) above was used as a cross-linked sample, and the same operation as above was performed to calculate the thermal shrinkage rate (T2) at 150°C after the cross-linked structure was formed. The thermal shrinkage rate (T2) was then divided by the thermal shrinkage rate (T1) to obtain the ratio (T2 / T1). The results were evaluated according to the following criteria.

[0951] Evaluation Criteria:

[0952] 〇 (No crosslinking): The value of T2 / T1 is less than 0.15 times.

[0953] × (with cross-linking): The value of T2 / T1 is greater than 0.15 times.

[0954] The formation of cross-linked structures leads to a tendency for a reduction in thermal shrinkage compared to the state before cross-linking. A T2 / T1 ratio below 0.15 indicates the formation of a cross-linked structure, while a T2 / T1 ratio above 0.15 indicates the absence of a cross-linked structure. The evaluation results are shown in Table 10.

[0955] [Table 10]

[0956]

[0957] In Comparative Example 105, which did not contain LiFSO3, no cross-linked structure was formed in the separator, while in Examples 140-142, which contained an amount of LiFSO3 within a specified range, a cross-linked structure was formed in the separator. Based on the above, it can be seen that by adjusting the LiFSO3 content in the non-aqueous electrolyte to an appropriate range, a cross-linked structure of silane-modified polyolefin can be formed.

[0958] (7) Output / Safety Performance Evaluation

[0959] (7-1) Fabrication of a small non-aqueous secondary battery

[0960] (7-1-1) Making the positive electrode

[0961] A composite oxide of lithium, nickel, manganese, and cobalt (LiNi) will be used as the positive electrode active material. 0.5 Mn 0.3 Co 0.2 O2), acetylene black powder as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of 93.9:3.3:2.8 to obtain a positive electrode mixture.

[0962] N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture at 68% by mass of solids, and the mixture was further mixed to obtain a slurry containing the positive electrode mixture. On one side of an aluminum foil with a thickness of 15 μm and a width of 280 mm, which serves as the positive electrode current collector, the slurry containing the positive electrode mixture was coated using a three-roll transfer coating machine while adjusting the unit area weight of the coating to form a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was removed by drying in a hot air drying oven. The resulting electrode roll was trimmed on both sides and subjected to reduced pressure drying at 130°C for 8 hours. Then, it was calendered using a roller press to achieve a density of 2.7 g / cm³ for the positive electrode active material layer. 3 This yields a positive electrode containing a positive active material layer and a positive current collector. The weight per unit area, excluding the positive current collector, is 9.3 mg / cm². 2 .

[0963] (7-1-2) Fabrication of the negative electrode

[0964] Graphite powder, used as the negative electrode active material, and carboxymethyl cellulose (density 1.60 g / cm³), used as a binder, were also included. 3 Solution (solid content concentration 1.83% by mass) and diene rubber (glass transition temperature: -5℃, number average particle size at dryness: 120nm, density 1.00g / cm³) 3 Dispersion medium: water and solid component concentration 40% by mass) were mixed at a solid component mass ratio of 97.4:1.1:1.5 to obtain the negative electrode mixture.

[0965] Water was added as a solvent to the obtained negative electrode mixture at a concentration of 45% by mass of solids, and the mixture was further mixed to prepare a slurry containing the negative electrode mixture. On one side of a copper foil with a thickness of 8 μm and a width of 280 mm, which would serve as the negative electrode current collector, a three-roll transfer coating machine was used to coat the foil, adjusting the unit area weight of the slurry containing the negative electrode mixture, to form a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was removed by drying in a hot air drying oven. The resulting electrode roll was trimmed on both sides and subjected to reduced pressure drying at 80°C for 12 hours. Then, it was calendered using a roller press to achieve a density of 1.4 g / cm³ for the negative electrode active material layer. 3 This yields a negative electrode comprising a negative electrode active material layer and a negative electrode current collector. The weight per unit area, excluding the negative electrode current collector, is 5.9 mg / cm². 2 .

[0966] (7-1-3) Assembly of small non-aqueous secondary batteries

[0967] A positive electrode obtained by punching a disk shape with a diameter of 15.958 mm, as described above, and a negative electrode obtained by punching a disk shape with a diameter of 16.156 mm, as described above, are overlapped on both sides of a separator to obtain a laminate. This laminate is then inserted into a disk-shaped battery casing made by SUS. Next, 0.2 mL of non-aqueous electrolyte is injected into the battery casing. After immersing the laminate in the non-aqueous electrolyte, the battery casing is sealed and kept at 25°C for 12 hours to allow the non-aqueous electrolyte to fully mix into the laminate, resulting in a small non-aqueous secondary battery.

[0968] (7-2) Evaluation of the output performance of small non-aqueous secondary batteries

[0969] For the small non-aqueous secondary batteries obtained as described above, firstly, the initial charge treatment and initial charge-discharge capacity were measured according to the steps in (7-2-1). Next, each small non-aqueous secondary battery was evaluated according to the steps in (7-2-2). It should be noted that the charge-discharge was performed using a charge-discharge apparatus ACD-M01A (trade name) manufactured by ASKA ELECTRONIC CO., LTD. and a programmable temperature bath IN804 (trade name) manufactured by Yamato Scientific Co., LTD.

[0970] Here, 1C refers to the current value at which a fully charged battery is expected to discharge at a constant current for one hour.

[0971] (7-2-1) Initial charge and discharge treatment of small non-aqueous secondary batteries

[0972] The ambient temperature of the small non-aqueous secondary battery was set to 25°C. It was charged with a constant current of 0.075mA (equivalent to 0.025C) until it reached 3.1V, then charged at a constant voltage of 3.1V for 1.5 hours. After a 3-hour rest period, the battery was charged with a constant current of 0.15mA (equivalent to 0.05C) until it reached 4.2V, then charged at a constant voltage of 4.2V for 1.5 hours. Finally, the battery was discharged to 3.0V with a constant current of 0.45mA (equivalent to 0.15C).

[0973] (7-2-2) Output Test

[0974] For a small non-aqueous secondary battery that has undergone its first charge-discharge treatment using the method described in (7-2-1) above, the ambient temperature is set to 25°C, and it is charged to 4.2V with a constant current of 0.3mA (equivalent to 0.1C). After reaching 4.2V, it is charged at a constant voltage of 4.2V until the current decreases to 0.005mA. Then, it is discharged to 3.0V with a current of 0.9mA (equivalent to 0.3C).

[0975] Next, it is charged to 4.2V with a constant current of 3mA (equivalent to 1C). After reaching 4.2V, it is charged with a constant voltage of 4.2V until the current value decays to 0.005mA. Then, it is discharged to 3.0V with a current of 3mA (equivalent to 1C).

[0976] Next, it is charged to 4.2V with a constant current of 3mA (equivalent to 1C). After reaching 4.2V, it is charged with a constant voltage of 4.2V until the current value decays to 0.005mA. Then, it is discharged to 3.0V with a current value of 6mA (equivalent to 2C).

[0977] Next, it is charged to 4.2V with a constant current of 3mA (equivalent to 1C). After reaching 4.2V, it is charged with a constant voltage of 4.2V until the current value decays to 0.005mA. Then, it is discharged to 3.0V with a current value of 9mA (equivalent to 3C).

[0978] Next, it is charged to 4.2V with a constant current of 3mA (equivalent to 1C). After reaching 4.2V, it is charged with a constant voltage of 4.2V until the current decays to 0.005mA. Then, it is discharged to 3.0V with a current of 15mA (equivalent to 5C). The 5C discharge capacity when the discharge capacity of the first cycle during the initial charge-discharge process is set to 100% is calculated as the 5C capacity retention rate.

[0979] Next, it is charged to 4.2V with a constant current of 3mA (equivalent to 1C). After reaching 4.2V, it is charged with a constant voltage of 4.2V until the current decays to 0.005mA. Then, it is discharged to 3.0V with a current of 30mA (equivalent to 10C). The 10C discharge capacity is calculated as the 10C capacity retention rate when the discharge capacity of the first cycle during the initial charge-discharge process is set to 100%.

[0980] The 10C capacity retention rate is used as an indicator of output performance at room temperature, preferably 55% or more, and more preferably 65% ​​or more. The evaluation results are shown in Table 11.

[0981] Next, the battery is charged to 4.2V with a constant current of 3mA (equivalent to 1C). After reaching 4.2V, it is charged with a constant voltage of 4.2V until the current decreases to 0.005mA. Then, it is discharged to 3.0V with a current of 60mA (equivalent to 20C). The 20C discharge capacity when the discharge capacity of the first cycle during the initial charge-discharge process is set as 100% is calculated as the 20C capacity retention rate. The 20C capacity retention rate is used as an indicator of the output performance at room temperature, preferably 10% or more, and more preferably 30% or more.

[0982] The evaluation results are shown in Table 11.

[0983] (7-3) Fabrication of laminated non-aqueous secondary batteries

[0984] (7-3-1) Production of the positive electrode

[0985] The positive electrode is produced using the method described in (5-3-1) above.

[0986] (7-3-2) Fabrication of the negative electrode

[0987] The negative electrode is made using the method described in (5-3-2) above.

[0988] (7-3-3) Assembly of laminated non-aqueous secondary batteries

[0989] The laminated non-aqueous secondary battery is assembled using the method described in (5-3-3) above, with separators (B1) to (B3) as separators and (S38) to (S42) and (S103) as non-aqueous electrolytes.

[0990] (7-4) Evaluation of spikes in laminated non-aqueous secondary batteries

[0991] For the laminated non-aqueous secondary battery obtained as described above, the initial charging process was performed according to the steps in (7-4-1) below. It should be noted that the charging and discharging were performed using the ASKA ELECTRONIC CO., LTD. charging and discharging apparatus ACD-M01A (trade name) and the Yamato Scientific CO., LTD. programmable thermostat IN804 (trade name).

[0992] Here, 1C refers to the current value at which a fully charged battery is expected to discharge at a constant current for 1 hour. In the evaluation below (7-4-1), 1C specifically refers to the current value at which a fully charged battery is expected to discharge at a constant current from 4.2V to 3.0V for 1 hour.

[0993] (7-4-1) Initial charge-discharge treatment of laminated non-aqueous secondary batteries

[0994] The battery was charged at an ambient temperature of 25°C with a constant current of 0.075A (equivalent to 0.025C) until it reached 3.1V. Then, it was charged at a constant voltage of 3.1V for 1.5 hours. After a 3-hour rest period, the battery was charged again with a constant current of 0.15A (equivalent to 0.05C) until it reached 4.2V. This was then charged at a constant voltage of 4.2V for 1.5 hours. Finally, the battery was discharged to 3.0V with a constant current of 0.45A (equivalent to 0.15C).

[0995] (7-4-2) Nail penetration test of laminated non-aqueous secondary battery

[0996] The laminated non-aqueous secondary battery, having undergone the initial charge-discharge treatment described in step (7-4-1), was placed on an iron plate in a temperature-controlled explosion-proof chamber. At the center of the laminated secondary battery, the temperature inside the explosion-proof chamber was set to 40°C. A 3.0 mm diameter iron nail was driven through the battery at a speed of 2 mm / s, and the process was maintained with the nail in place. The temperature of a thermocouple placed inside the nail, designed to allow measurement of the internal temperature of the laminated battery after penetration, was measured to assess the presence or absence of fire. Ten newly manufactured laminated secondary battery samples were evaluated using the same method, and the number of samples that did not ignite (not ignited) was calculated as a percentage using the following formula. The evaluation results are shown in Table 11.

[0997] Evaluation result (%) = (100 × number of samples that did not reach the point of ignition / total number of samples)

[0998] The preferred pass rate for nail penetration evaluation is above 50%.

[0999] [Table 11]

[1000]

[1001] Regarding the 10C capacity retention rate, according to Comparative Examples 106-107, when the combination of a non-aqueous electrolyte without acetonitrile and LiFSO3 with silane crosslinked separators (B1)-(B2) resulted in a 10C capacity retention rate of less than 55%. On the other hand, according to Examples 143-151, when the non-aqueous electrolyte contained acetonitrile and LiFSO3, the 10C capacity retention rate was greater than 65% regardless of the type of separator. It is believed that the buffering effect of LiFSO3 shifts the flow towards a reduction in LiF, which is one of the causes of increased internal resistance, thus contributing to further improvements in output performance.

[1002] Regarding the 20C capacity retention rate, according to Comparative Examples 106-107, when the combination of a non-aqueous electrolyte without acetonitrile and LiFSO3 with silane crosslinking separators (B1)-(B2) resulted in a 20C capacity retention rate of less than 10%. On the other hand, according to Examples 143-151, when the non-aqueous electrolyte contained acetonitrile and LiFSO3, regardless of the type of separator, the 20C capacity retention rate was greater than 30%.

[1003] Regarding the nail penetration safety test pass rate, when using separator (B3) as a low-resistance separator, the nail penetration safety test pass rate was less than 50% regardless of the type of non-aqueous electrolyte. On the other hand, when using silane crosslinked separators (B1) to (B2), the nail penetration safety test pass rate was more than 50% regardless of the type of non-aqueous electrolyte.

[1004] Based on the above results, it can be seen that the output performance is improved when the non-aqueous electrolyte contains acetonitrile and LiFSO3. Furthermore, by combining the non-aqueous electrolyte containing acetonitrile and LiFSO3 with the silane crosslinking separator, both output performance and safety performance can be balanced.

[1005] (8) Fabrication / Safety Evaluation of Aromatic Polyamide Separators

[1006] (8-1) Fabrication of the separator

[1007] (8-1-1) Fabrication of the separator (A16)

[1008] <Making of the base material as the first layer>

[1009] A mixture was prepared by adding 100% by mass of pentaerythritol tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate as an antioxidant to 100% by mass of polyethylene homopolymer with a viscosity-average molecular weight of 700,000, and then dry-mixing using a drum mixer. The resulting mixture was then fed into a twin-screw extruder under a nitrogen atmosphere. Separately, liquid paraffin (kinetic viscosity at 37.78°C 7.59 × 10⁻⁶) was injected into the extruder barrel using a plunger pump. -5 m 2 / s).

[1010] The mixture is melt-blended with liquid paraffin in an extruder, with the feeder and pump adjusted so that the liquid paraffin content in the extruded polyolefin composition is 70% by mass (i.e., the polymer concentration is 30% by mass). The melt-blending conditions are set at a temperature of 230°C, a screw speed of 240 rpm, and an ejection rate of 18 kg / h.

[1011] Next, the molten compound is extruded through a T-die onto a cooling roller with a surface temperature controlled at 25°C and then cast to obtain a gel sheet (sheet-shaped molded body) with an unprocessed film thickness of 1370 μm.

[1012] Next, the sheet-shaped preform is fed into a biaxial tenter frame for biaxial stretching to obtain a stretched material. The stretching conditions are set as follows: MD ratio 7.0, TD ratio 6.4 (i.e., 7 × 6.3), and biaxial stretching temperature 128°C. Then, the stretched gel sheet is immersed in a dichloromethane bath to extract and remove liquid paraffin. The dichloromethane is then dried to remove the solid material, resulting in a porous body. Next, the porous body is fed into a TD tenter frame for heat setting (HS) at a temperature of 133°C and a stretch ratio of 1.95. Then, a relaxation operation is performed to a TD ratio of 1.75 to obtain a microporous membrane. Finally, the ends of the obtained microporous membrane are trimmed, and it is wound into a master roll with a width of 1100 mm and a length of 5000 m.

[1013] During the above evaluation, the microporous membrane unwound from the master roll is cut as needed and used as the evaluation substrate (first layer). For the obtained evaluation substrate, the membrane thickness, air permeability, porosity, etc. are measured, as shown in Table 12.

[1014] <The Construction of the Second Layer>

[1015] Create the second layer using the same method as described in (5-1-1) above.

[1016] (8-1-2) Fabrication of separators (A17) to (A18)

[1017] Using the physical property values ​​listed in Table 12 as the target, the separators (A17) to (A18) are manufactured using the same method as described in (8-1-1) above. It should be noted that the separator (A18) does not contain a second layer; only the substrate (first layer) is used as the separator.

[1018] (8-2) Fabrication of laminated non-aqueous secondary batteries

[1019] (8-2-1) Production of the positive electrode

[1020] The positive electrode is produced using the method described in (5-3-1) above.

[1021] (8-2-2) Fabrication of the negative electrode

[1022] The negative electrode is made using the method described in (5-3-2) above.

[1023] (8-2-3) Assembly of laminated non-aqueous secondary batteries

[1024] The laminated non-aqueous secondary battery is assembled using the method described in (5-3-3) above, with separators (A16) to (A18) used as separators and (S110) used as the non-aqueous electrolyte.

[1025] (8-3) Nail penetration test of laminated non-aqueous secondary battery

[1026] For the laminated non-aqueous secondary battery obtained as described above, the initial charging process was performed according to the steps in (8-3-1) below. It should be noted that the charging and discharging were performed using the ASKA ELECTRONIC CO., LTD. charging and discharging apparatus ACD-M01A (trade name) and the Yamato Scientific co., ltd. programmable thermostat IN804 (trade name).

[1027] Here, 1C refers to the current value at which a fully charged battery is expected to discharge at a constant current for 1 hour. In the evaluation below (8-3-1), 1C specifically refers to the current value at which a fully charged battery is expected to discharge at a constant current from 4.2V to 3.0V for 1 hour.

[1028] (8-3-1) Initial charge-discharge treatment of laminated non-aqueous secondary batteries

[1029] The battery was charged at an ambient temperature of 25°C with a constant current of 0.075A (equivalent to 0.025C) until it reached 3.1V. Then, it was charged at a constant voltage of 3.1V for 1.5 hours. After a 3-hour rest period, the battery was charged again with a constant current of 0.15A (equivalent to 0.05C) until it reached 4.2V. This was then charged at a constant voltage of 4.2V for 1.5 hours. Finally, the battery was discharged to 3.0V with a constant current of 0.45A (equivalent to 0.15C).

[1030] (8-3-2) Nail penetration test of laminated non-aqueous secondary battery

[1031] The laminated non-aqueous secondary battery, having undergone the initial charge-discharge treatment described in step (8-3-1), was placed on an iron plate in a temperature-controlled explosion-proof chamber. At the center of the laminated secondary battery, the temperature inside the explosion-proof chamber was set to 40°C. A 3.0 mm diameter iron nail was driven through the battery at a speed of 2 mm / s, and the process was maintained with the nail in place. The temperature of a thermocouple placed inside the nail, designed to allow measurement of the internal temperature of the laminated battery after penetration, was measured to assess the presence or absence of fire. This method was repeated with 100 newly manufactured laminated secondary battery samples, and the number of samples that did not ignite (not ignited) was calculated as a percentage using the following formula. The evaluation results are shown in Table 12.

[1032] Evaluation result (%) = (100 × number of samples that did not reach the point of ignition / total number of samples)

[1033] The preferred pass rate for the nail puncture evaluation is above 50%. The evaluation results are shown in Table 12.

[1034] [Table 12]

[1035]

[1036] A comparison of Examples 152-153 and Example 154 shows that including aramid in the second layer significantly increases the pass rate of the nail puncture safety test and improves safety. This is presumably because including aramid resin with excellent heat resistance in the second layer can suppress deformation of the separator caused by the temperature rise associated with internal short circuits during nail puncture.

[1037] (9) Fabrication / evaluation of non-woven fabric separators

[1038] (9-1) Fabrication of non-woven fabric separators

[1039] (9-1-1) Fabrication of non-woven fabric separator (A19)

[1040] <Preparation of Nonwoven Fabric Substrate 1>

[1041] A homogeneous papermaking slurry with a concentration of 1% by mass was prepared by dispersing 40 parts by mass of oriented crystalline polyethylene terephthalate (PET) short fibers with a fineness of 0.06 dtex (average fiber diameter 2.3 μm) and fiber length of 3 mm, 20 parts by mass of oriented crystalline PET short fibers with a fineness of 0.1 dtex (average fiber diameter 3.1 μm) and fiber length of 3 mm, and 40 parts by mass of a single-component binder PET short fibers (softening point 120℃, melting point 230℃) with a fineness of 0.2 dtex (average fiber diameter 4.1 μm) and fiber length of 3 mm in water using a pulper. This papermaking slurry was then subjected to a process with an air permeability of 270 cm⁻¹. 3 / cm 2 A tilting paper machine with a [plain weave, grosgrain weave] forming wire is used to wet-brush the paper. The binder is then bonded with PET short fibers using a 135°C drum dryer to achieve nonwoven fabric strength, resulting in a unit area weight of 12 g / m². 2 The nonwoven fabric is then subjected to hot calendering treatment using a 1-roll gap hot calender comprising a dielectric heating jacketed roller (metal heating roller) and an elastic roller, under conditions of hot roller temperature of 200°C, linear pressure of 100kN / m, and processing speed of 30m / min, to produce a nonwoven fabric substrate 1 with a thickness of 18μm.

[1042] <Preparation of Coating Liquid 1>

[1043] With a volume average particle size of 2.2 μm and a specific surface area of ​​3 m², 2 100 parts of boehmite (at a mass concentration of 1 g) are mixed with 120 parts of a 0.3% sodium carboxymethyl cellulose aqueous solution (at a mass concentration of 1 g) having a viscosity of 200 mPa·s at 25°C, and stirred thoroughly. Then, 300 parts of a 0.5% sodium carboxymethyl cellulose aqueous solution (at a mass concentration of 1 g) having a viscosity of 7000 mPa·s at 25°C, and 10 parts of a carboxyl-modified styrene-butadiene resin (SBR) emulsion (50% solids concentration) with a glass transition temperature of 5°C and a volume average particle size of 0.2 μm are mixed and stirred to prepare coating solution 1. It should be noted that the type B viscosity of coating solution 1 is 1020 mPa·s.

[1044] <Fabrication of Non-woven Fabric Dividers (A19)>

[1045] On the nonwoven fabric substrate 1, the coating liquid 1 is applied using a gravure coating machine with a reverse-contrast coating method to achieve an oven-dry coating amount of 16 g / m². 2 The separator (A19) was coated and dried in a manner that produces a thickness of 34 μm.

[1046] (9-1-2) Fabrication of non-woven fabric separators (A20) ~ (A21)

[1047] On the peel surface of the process paper, coating liquid 1 is applied using a gravure coating machine in a reverse matching manner at an oven-dry coating amount of 16 g / m². 2 The coating process involves gently attaching the nonwoven fabric substrate 1 to the coated surface before drying, followed by drying. Then, the process paper is peeled off to create a separator (A20) with a thickness of 34 μm.

[1048] In addition, the nonwoven fabric substrate 1 prepared in (7-1-1) is used as a separator (A21).

[1049] (9-1-3) Evaluation of separators

[1050] (i) thickness

[1051] Cross sections of each separator were observed using a SEM apparatus equipped with EDS (Field Emission Scanning Electron Microscope (JEOL, JSM-06700F)). Furthermore, the area where aluminum (Al) was detected was defined as "boehmite as an inorganic pigment." The area where Al was not detected and a solid structure existed was defined as "polyethylene terephthalate fiber as a substrate fiber." The depth at which the inorganic pigment content was 4 / 1 was defined as "the boundary between the layer primarily composed of inorganic pigment and the layer mixed with nonwoven fabric and inorganic pigment." The depth at which the inorganic pigment content was 1 / 4 was defined as "the boundary between the layer mixed with nonwoven fabric and inorganic pigment and the layer primarily composed of substrate fiber."

[1052] The thicknesses (thicknesses I, II, and III) of the "layer mainly composed of inorganic pigments," the "layer mixed with nonwoven fabric and inorganic pigments," and the "layer mainly composed of substrate fibers" were determined from these "boundary lines." In the case where "the mixed layer reaches the opposite side of the pigment-based main layer," the thickness III of the "substrate fiber main layer" was considered "0 (zero)." The evaluation results are shown in Table 13.

[1053] (9-2) Fabrication of laminated non-aqueous secondary batteries (9-2-1) Fabrication of the positive electrode

[1054] The positive electrode is produced using the method described in (5-3-1) above.

[1055] (9-2-2) Fabrication of the negative electrode

[1056] The negative electrode is made using the method described in (5-3-2) above.

[1057] (9-2-3) Fabrication of laminated non-aqueous secondary batteries

[1058] The laminated non-aqueous secondary battery is assembled using the method described in (5-3-3) above, with non-woven fabric separators (A19) to (A21) as separators and (S110) as the non-aqueous electrolyte.

[1059] (9-3) Nail penetration test of laminated non-aqueous secondary battery

[1060] For the laminated non-aqueous secondary battery obtained as described above, the initial charging process was performed according to the steps in (9-3-1) below. It should be noted that the charging and discharging were performed using the ASKA ELECTRONIC CO., LTD. charging and discharging apparatus ACD-M01A (trade name) and the Yamato Scientific co., ltd. programmable thermostat IN804 (trade name).

[1061] Here, 1C refers to the current value at which a fully charged battery is expected to discharge at a constant current for 1 hour. In the evaluation below (9-3-1), 1C specifically refers to the current value at which a fully charged battery is expected to discharge at a constant current from 4.2V to 3.0V for 1 hour.

[1062] (9-3-1) Initial charge-discharge treatment of laminated non-aqueous secondary batteries

[1063] The battery was charged at an ambient temperature of 25°C with a constant current of 0.075A (equivalent to 0.025C) until it reached 3.1V. Then, it was charged at a constant voltage of 3.1V for 1.5 hours. After a 3-hour rest period, the battery was charged again with a constant current of 0.15A (equivalent to 0.05C) until it reached 4.2V. This was then charged at a constant voltage of 4.2V for 1.5 hours. Finally, the battery was discharged to 3.0V with a constant current of 0.45A (equivalent to 0.15C).

[1064] (9-3-2) Nail penetration test of laminated non-aqueous secondary battery

[1065] The laminated non-aque...

Claims

1. A non-aqueous electrolyte, comprising: Non-aqueous solvents containing acetonitrile and vinylene carbonate, and, Ethyl sulfite, The combined content of the vinylene carbonate and the ethylene sulfite is 0.1% by volume or more but less than 10% by volume relative to the total amount of the non-aqueous solvent, and The content of vinylene carbonate is less than the content of ethylene sulfite. The content of the vinylene carbonate relative to the total amount of the non-aqueous solvent is 0.1-3.5% by volume, and The content of acetonitrile is more than 5% by volume and less than 97% by volume relative to the total amount of the non-aqueous solvent.

2. The non-aqueous electrolyte according to claim 1, wherein, The volume ratio of ethylene sulfite to vinylene carbonate is: 1.5 × vinylene carbonate content ≤ ethylene sulfite content ≤ 2.4 × vinylene carbonate content.

3. The non-aqueous electrolyte according to claim 1 or 2, further comprising a lithium salt, wherein the lithium salt comprises LiFSO3 in a total amount of less than 200 ppm by mass relative to the non-aqueous electrolyte.

4. The non-aqueous electrolyte according to claim 3, wherein, The lithium salt includes a lithium imide salt.

5. The non-aqueous electrolyte according to claim 4, wherein, The lithium salt comprises the lithium-containing imide salt and LiPF6 at a molar concentration of LiPF6 < lithium-containing imide salt.

6. The non-aqueous electrolyte according to claim 4 or 5, comprising lithium bis(fluorosulfonyl)imide as the lithium-containing imide salt.

7. The non-aqueous electrolyte according to any one of claims 3 to 6, wherein, The content of the lithium salt is 0.1 to 40 parts by mass relative to 100 parts by mass of the non-aqueous electrolyte.

8. The non-aqueous electrolyte according to any one of claims 1 to 7, wherein, The non-aqueous solvent also includes a compound represented by the following general formula (3). In equation (3), R7~R 10 Each of the following is independently an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a phenyl group, optionally having substituents, and optionally containing an unsaturated bond in the carbon bond.

9. The non-aqueous electrolyte according to any one of claims 1 to 8, wherein in a non-aqueous secondary battery containing the non-aqueous electrolyte, the recovery charging capacity retention rate is 90% or more.

10. A non-aqueous secondary battery comprising the non-aqueous electrolyte according to any one of claims 1 to 9.

11. The non-aqueous secondary battery according to claim 10 has a recovery charging capacity retention rate of over 90%.

12. The non-aqueous secondary battery according to claim 10 or 11, further comprising a separator having the following regions: During TOF-SIMS measurements with a surface area of ​​100 μm, more than one calcium-containing island structure was detected, and the size of the island structure was 9 μm. 2 Above and 245μm 2 The following areas.

13. The non-aqueous secondary battery according to claim 12, wherein, When there are two or more calcium-containing island structures in the separator, the minimum and maximum distances between the weighted center positions of each island structure are both greater than 6 μm and less than 135 μm.

14. The non-aqueous secondary battery according to claim 12 or 13, wherein, The separator comprises a substrate as a first layer and a second layer laminated on at least one surface of the substrate. The thickness ratio of the substrate to the second layer is 0.5 or more and 10 or less. The second layer comprises at least one selected from the group consisting of ceramics, aromatic polyamide resins, and polyvinylidene fluoride (PVDF).

15. The non-aqueous secondary battery according to any one of claims 12 to 14, wherein, The separator comprises a silane-modified polyolefin.

16. The non-aqueous secondary battery according to claim 15, wherein, When the separator comes into contact with the non-aqueous electrolyte, the silane crosslinking reaction of the silane-modified polyolefin begins.

17. The non-aqueous secondary battery according to claim 10 or 11, further comprising a separator, the separator comprising a substrate as a first layer and a second layer laminated on at least one surface of the substrate, the second layer comprising an aromatic polyamide resin.

18. The non-aqueous secondary battery according to claim 10 or 11, further comprising a separator, said separator being formed by applying an inorganic pigment to a substrate comprising a nonwoven fabric.

19. The non-aqueous secondary battery according to claim 10 or 11, further comprising a separator, said separator being formed by applying inorganic pigments to a substrate containing nonwoven fabric, wherein as a layer structure, a layer mainly composed of inorganic pigments, a layer composed of inorganic pigments and substrate fibers, and a layer mainly composed of substrate fibers are sequentially overlapped.

20. The non-aqueous secondary battery according to any one of claims 10 to 19, wherein, The non-aqueous electrolyte also contains ethylene carbonate, and, The positive electrode active material, which is the positive electrode contained in the non-aqueous secondary battery, includes the formula Li w The compound shown in the FePO4 formula has an olivine-type structure, where w ranges from 0.05 to 1.

1.

21. The non-aqueous electrolyte according to claim 2, wherein, The content of the vinylene carbonate is 0.3 to 2.5 volumes relative to the total amount of the non-aqueous solvent.

22. The non-aqueous electrolyte according to claim 1, wherein, The non-aqueous solvent also contains cyclic carbonates and chain carbonates.

23. The non-aqueous electrolyte according to claim 3, wherein, The lithium salt contains LiFSO3 in a total amount of 0.1 ppm by mass or more relative to the non-aqueous electrolyte.

24. The non-aqueous electrolyte according to claim 4, wherein, The content of the lithium imide salt is more than 0.5 mol and less than 3.0 mol per 1L of non-aqueous solvent.

25. The non-aqueous secondary battery according to claim 14, wherein, The substrate is a microporous membrane made of polyolefin.

26. The non-aqueous electrolyte according to claim 1, wherein, The content of acetonitrile relative to the total amount of the non-aqueous solvent is more than 10% by volume and less than 85% by volume.

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