Non-aqueous electrolyte secondary battery and method for manufacturing the same

Abstract

The present application provides a non-aqueous electrolyte secondary battery capable of improving low-temperature output characteristics. The problem can be solved by a secondary battery provided with a non-aqueous electrolyte containing fluorosulfate ions, difluorophosphate ions, and dioxyborate ions, and satisfying [FSO3 ‑ ] > [PO2F2 ‑ ] > [BOB ‑ ] in the non-aqueous electrolyte.

Description

Technical Field

[0001] This invention relates to non-aqueous electrolytes and energy devices using them. Background Technology

[0002] In a wide range of applications, from consumer power supplies for mobile phones and laptops to automotive power supplies and large-scale stationary power supplies, energy devices using non-aqueous electrolytes, such as secondary batteries, double-layer capacitors, and lithium-ion capacitors, have been put into practical use. However, in recent years, the demand for high-performance energy devices has been continuously increasing, especially for non-aqueous electrolyte secondary batteries, which require high-level performance in various battery characteristics, such as capacity, input / output, charge / discharge rate characteristics, and safety.

[0003] Especially when using lithium-ion batteries as the power source for electric vehicles, the vehicles require a large amount of energy during startup and acceleration, and must efficiently regenerate the significant energy generated during deceleration. Therefore, lithium-ion batteries are required to have high output and input characteristics. Furthermore, since electric vehicles are used outdoors, and to enable rapid startup and acceleration even in cold weather, lithium-ion batteries are particularly required to have high input-output characteristics (low internal impedance) at temperatures as low as -20°C.

[0004] To date, numerous techniques have been explored for improving the initial characteristics of non-aqueous electrolyte secondary batteries, addressing various battery components, including the active materials of the positive and negative electrodes and the non-aqueous electrolyte. A known technique involves adding lithium fluorosulfonate (FSO3Li) to the non-aqueous electrolyte to improve the low-temperature performance of non-aqueous electrolyte secondary batteries (e.g., Patent Document 1).

[0005] In addition, Patent Document 2 discloses a technology for providing a non-aqueous electrolyte secondary battery with excellent input and output characteristics by using a non-aqueous electrolyte containing lithium difluorophosphate (LiPO2F2) and lithium dioxalate borate (LiBOB), and further containing a salt having an intramolecular FS bond.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-50153

[0009] Patent Document 2: Japanese Patent Application Publication No. 2016-184462 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] As mentioned above, with the increasing demand for high-performance non-aqueous electrolyte secondary batteries in recent years, there is a need for further improvement in the performance of non-aqueous electrolyte secondary batteries, especially the improvement of input-output characteristics at low temperatures.

[0012] On the other hand, especially during the initial charging stage after battery assembly, a film called the Solid Electrolyte Interphase (SEI) forms on the negative electrode. This SEI is closely related to battery performance, such as capacity, output characteristics, and durability. Generally, it is known that a dense and uniform SEI can be formed by reducing the initial charging current or stopping charging midway and allowing it to stand, thereby improving battery performance.

[0013] However, the inventors conducted in-depth research and found that for non-aqueous electrolyte secondary batteries using the electrolyte described in Patent Documents 1-2, the output characteristics in low-temperature environments become insufficient in the initial charge / discharge / aging / inspection process (hereinafter also referred to as "battery break-in operation") after the battery assembly process, if the aging temperature is not high enough.

[0014] It should be noted that the above-mentioned "charge / discharge / aging treatment / inspection process (battery break-in operation)" should be considered to include some or more of the charge / discharge process, aging treatment process, and shipment inspection process after the battery assembly process, which are common and usually implemented in the manufacturing process of lithium-ion batteries (e.g., refer to "On-board technology of lithium secondary batteries, causes of degradation / failure and countermeasures", Technical Information Association, 1st edition, August 5, 2011).

[0015] The present invention was made in view of the above circumstances, and its object is to provide a non-aqueous electrolyte secondary battery that can improve low-temperature output characteristics.

[0016] Methods for solving problems

[0017] The inventors, through research, speculate the following reason for this phenomenon: In batteries using non-aqueous electrolytes containing lithium dioxaborate and lithium difluorophosphate, if the aging treatment temperature in the aging process after battery assembly is too low, the reduction reaction of the electrolyte on the negative electrode surface becomes uneven, resulting in a deviation in the amount of film formed on the negative electrode surface. This leads to areas with abundant film and areas with sparse film on the negative electrode surface simultaneously. Under such conditions, when performing the aforementioned input / output test, the resistance of the areas with abundant film is high, thus reducing battery output. On the other hand, by sufficiently increasing the aging treatment temperature, the reduction reaction of the electrolyte on the negative electrode surface occurs uniformly, forming a uniform film on the negative electrode surface, thus increasing battery output.

[0018] In addition, Patent Documents 1 and 2 disclose technologies for providing non-aqueous electrolyte secondary batteries with excellent input and output characteristics by using lithium fluorosulfonate, lithium difluorophosphate and lithium dioxalateborate in combination. However, these technologies cannot prevent the above-mentioned non-uniformity of the negative electrode film, and there is still room for further improvement in characteristics.

[0019] Therefore, the inventors conducted in-depth research to solve the above-mentioned problems and found that the output characteristics of non-aqueous electrolyte secondary batteries in low-temperature environments can be improved by using the following non-aqueous electrolyte, which contains fluorosulfonic acid ions, difluorophosphate ions and dioxalate borate ions, and the content of fluorosulfonic acid ions, difluorophosphate ions and dioxalate borate ions in the non-aqueous electrolyte is within a specific range, thus completing the present invention.

[0020] That is, the present invention provides the specific methods shown below [1] to [7].

[0021] [1] A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte containing fluorosulfonic acid ions, difluorophosphate ions, and dioxaborate ions, wherein...

[0022] The above-mentioned non-aqueous electrolyte refers to the concentration of fluorosulfonic acid ions [FSO3] in the non-aqueous electrolyte. - The concentration of difluorophosphate ions [PO2F2] - The concentrations of oxalate and borate ions [BOB] - A non-aqueous electrolyte that satisfies the following formula (1).

[0023] [FSO3 - ]>[PO2F2 - ]>[BOB - (1)

[0024] [2] According to the non-aqueous electrolyte secondary battery described in [1], the non-aqueous electrolyte is a non-aqueous electrolyte that satisfies the following formulas (2) and (3).

[0025] ([FSO3 - ]+[PO2F2 - ]) / ([PO2F2 - ]+[BOB - ])>1.8 (2)

[0026] [FSO3 - <1.3% by mass (3)

[0027] [3] According to the non-aqueous electrolyte secondary battery described in [1] or [2], the voltage change of the non-aqueous electrolyte secondary battery when stored in a high-temperature environment of 4.1V and above 60°C for 24 hours is above 33mV.

[0028] [4] The non-aqueous electrolyte secondary battery according to any one of [1] to [3], wherein the non-aqueous electrolyte contains aluminum ions of more than 1 ppm by mass and less than 100 ppm by mass.

[0029] [5] The non-aqueous electrolyte secondary battery according to any one of [1] to [4] includes a negative electrode and a positive electrode capable of absorbing / releasing lithium ions.

[0030] [6] According to the non-aqueous electrolyte secondary battery of [5], the positive electrode has a current collector and a positive electrode active material layer disposed on the current collector, wherein the positive electrode active material layer contains at least one selected from lithium / cobalt composite oxide, lithium / cobalt / nickel composite oxide, lithium / manganese composite oxide, lithium / cobalt / manganese composite oxide, lithium / nickel composite oxide, lithium / nickel / manganese composite oxide, and lithium / cobalt / nickel / manganese composite oxide.

[0031] [7] A method for manufacturing a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte containing fluorosulfonic acid ions, difluorophosphate ions and dioxaborate ions, the manufacturing method comprising:

[0032] In the battery assembly process of assembling a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte, the concentration of fluorosulfonic acid ions [FSO3] in the aforementioned non-aqueous electrolyte is... - The concentration of difluorophosphate ions [PO2F2] - The concentrations of oxalate and borate ions [BOB] - Satisfy the following equation (1); and

[0033] An aging process for aging the aforementioned non-aqueous electrolyte secondary batteries in a temperature range of 50°C to 80°C.

[0034] [FSO3 - ]>[PO2F2 - ]>[BOB - (1)

[0035] The effects of the invention

[0036] By using the specific non-aqueous electrolyte of this invention, a non-aqueous electrolyte secondary battery that can improve low-temperature output characteristics can be obtained, and the non-aqueous electrolyte secondary battery can be manufactured. Detailed Implementation

[0037] The following describes embodiments of the present invention. These embodiments are merely examples (representative examples) of the present invention, and the present invention is not limited to these embodiments. Furthermore, the present invention can be implemented with arbitrary modifications without departing from its essential points.

[0038] <1. Non-aqueous electrolyte>

[0039] In one embodiment of the present invention, the non-aqueous electrolyte used in the non-aqueous secondary battery contains fluorosulfonic acid ions (FSO3). - ), difluorophosphate ions (PO2F2) - ) and dioxalate borate ions (BOB) - Their content is within a specific range.

[0040] Furthermore, the non-aqueous electrolyte preferably contains aluminum ions at a concentration of 1 ppm to 100 ppm by mass. It can be presumed that by containing specific amounts of aluminum ions, fluorosulfonic acid ions, difluorophosphate ions, and dioxalate-borate ions in the non-aqueous electrolyte, FSO3… - (fluorosulfonic acid ions) or PO2F2 - One or more of (difluorophosphate ions) or dioxaborate ions can coordinate or interact with aluminum ions, thereby improving the reduction resistance of aluminum ions, inhibiting the negative electrode reduction reaction, and thus improving the charging and storage characteristics in high-temperature environments.

[0041] The following is a detailed explanation of non-aqueous electrolytes.

[0042] <1-1. Components contained in non-aqueous electrolytes>

[0043] <1-1-1. Fluorosulfonic acid ions (FSO3) - >

[0044] The non-aqueous electrolyte in this embodiment contains FSO3. - As counterions to fluorosulfonic acid ions, both monovalent and divalent cations can be used. Preferred monovalent cations are lithium ions, sodium ions, and potassium ions, with lithium ions being particularly preferred. Preferred divalent cations are magnesium ions and calcium ions, with magnesium ions being particularly preferred. These cations can be used alone or in combination of two or more. In a particularly preferred embodiment, FSO3... - It is contained in the non-aqueous electrolyte in the form of lithium fluorosulfonate (FSO3Li).

[0045] FSO3 - The content only needs to meet the requirement of <1-2.FSO3 as explained later. - PO2F2 - and BOB - The relationship in the relation > is not specifically limited. When using a monovalent cation, FSO3 -The content of FSO3 in the non-aqueous electrolyte is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.10% by mass or more. On the other hand, as an upper limit, there is no particular limitation, but it is preferably 10.0% by mass or less, more preferably 7.0% by mass or less, even more preferably 5.0% by mass or less, particularly more preferably 4.0% by mass or less, and especially preferably 3.0% by mass or less. When a divalent cation is used, FSO3 - The content of in the non-aqueous electrolyte is preferably 0.002% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.20% by mass or more. On the other hand, as an upper limit, there is no particular limitation, but it is preferably 20.0% by mass or less, more preferably 14.0% by mass or less, even more preferably 10.0% by mass or less, particularly more preferably 8.0% by mass or less, and especially preferably 6.0% by mass or less. When using a monovalent cation and a divalent cation in combination as counterions to the fluorosulfonic acid ion, the above-mentioned FSO3 is achieved. - Preparation can be carried out using a concentration range method. In this specification, FSO3 in the non-aqueous electrolyte... - The content (mass%) of [FSO3] is related to the concentration of fluorosulfonic acid ions in the non-aqueous electrolyte. - The meanings are the same.

[0046] In FSO3 - When the content of FSO3 in the non-aqueous electrolyte is below 10.0% by mass, the negative electrode reduction reaction does not increase with the increase of the internal resistance of the non-aqueous electrolyte secondary battery, which is preferable from this point of view. When it is above 0.001% by mass, the generation of FSO3... - From the perspective of the effectiveness of this application, it is preferred. Therefore, within the above-mentioned range, the charging and retention characteristics in high-temperature environments can be improved by suppressing negative electrode reduction reactions in high-temperature environments.

[0047] FSO3 - It can be synthesized using known methods or obtained from commercially available products. It is used for determining FSO3 in the aforementioned non-aqueous electrolyte and non-aqueous electrolyte secondary battery. - There are no particular restrictions on the methods used to determine the content; any publicly known method can be used. Specific examples include: ion chromatography, etc. 19 Nuclear magnetic resonance spectroscopy (hereinafter sometimes referred to as "NMR"), etc.

[0048] <1-1-2. Difluorophosphate ions (PO₂F₂) - >

[0049] The non-aqueous electrolyte in this embodiment contains PO2F2. -As counterions to difluorophosphate ions, both monovalent and divalent cations can be used. Preferred monovalent cations are lithium ions, sodium ions, and potassium ions, with lithium ions being particularly preferred. Preferred divalent cations are magnesium ions and calcium ions, with magnesium ions being particularly preferred. These cations can be used alone or in combination of two or more. In a particularly preferred embodiment, PO₂F₂... - It is contained in a non-aqueous electrolyte in the form of lithium difluorophosphate (LiPO2F2).

[0050] PO2F2 - The content only needs to meet the requirement of <1-2.FSO3 as explained later. - PO2F2 - and BOB - The relationship in the relation > is not specifically limited. Specifically, when PO2F2 is used as a monovalent cation, - The lower limit of the content of PO2F2, based on the total amount of non-aqueous electrolyte, is preferably 0.001% by mass or more, more preferably 0.010% by mass or more, and even more preferably 0.10% by mass or more. Furthermore, the upper limit, based on the total amount of non-aqueous electrolyte, is preferably 1.3% by mass or less, more preferably 1.2% by mass or less, and even more preferably 1.1% by mass or less. When a divalent cation is used, PO2F2... - The lower limit of the content of PO2F2, based on the total amount of non-aqueous electrolyte, is preferably 0.002% by mass or more, more preferably 0.020% by mass or more, and even more preferably 0.20% by mass or more. Furthermore, the upper limit, based on the total amount of non-aqueous electrolyte, is preferably 2.6% by mass or less, more preferably 2.4% by mass or less, and even more preferably 2.2% by mass or less. When using both monovalent and divalent cations as counterions to difluorophosphate ions, the aforementioned PO2F2 content is achieved. - Preparation can be carried out using a concentration range method. In this specification, PO2F2 in the non-aqueous electrolyte... - The content (mass%) of [PO2F2] is related to the concentration of difluorophosphate ions in the non-aqueous electrolyte. - The meanings are the same.

[0051] PO2F2 - When the concentration is within the preferred range described above, it is more likely to exhibit the effect of improving the initial output in low-temperature environments.

[0052] Here, the electrolyte contains PO2F2. -In this case, the preparation of the electrolyte can be carried out by known methods and is not particularly limited. Examples include: adding LiPO2F2, synthesized separately by known methods, to the electrolyte; or pre-containing water in the battery components such as the active material and electrodes, and generating PO2F2 in the system when assembling the battery using an electrolyte containing LiPF6. - The method. In this embodiment, any method can be used.

[0053] As a measure of PO2F2 in the above-mentioned non-aqueous electrolyte and non-aqueous electrolyte secondary battery. - There are no particular restrictions on the methods used to determine the content; any publicly known method can be used. Specific examples include: ion chromatography, etc. 19 F NMR, etc.

[0054] <1-1-3. Dioxaloylborate ion (BOB) - >

[0055] The non-aqueous electrolyte in this embodiment contains boron oxalate ions (BOB). - As counterions to diasoxaloborate ions, both monovalent and divalent cations can be used. Preferred monovalent cations are lithium ions, sodium ions, and potassium ions, with lithium ions being particularly preferred. Preferred divalent cations are magnesium ions and calcium ions, with magnesium ions being particularly preferred. These cations can be used alone or in combination of two or more. In a particularly preferred embodiment, diasoxaloborate ions are contained in the non-aqueous electrolyte in the form of lithium diasoxaloborate (LiBOB).

[0056] BOB - The content only needs to meet the requirement of <1-2.FSO3 as explained later. - PO2F2 - and BOB - The relationship in the relation > is not specifically limited. Specifically, when BOB is used as a monovalent cation, - The lower limit of the content of [the substance] is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.10% by mass or more, based on the total amount of non-aqueous electrolyte. Furthermore, the upper limit is preferably 2% by mass or less, more preferably 1% by mass or less, and even more preferably 0.8% by mass or less, based on the total amount of non-aqueous electrolyte. When a divalent cation is used, BOB [the substance]... -The lower limit of the content of [the substance] is preferably 0.002% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.20% by mass or more, based on the total amount of non-aqueous electrolyte. Furthermore, the upper limit is preferably 4% by mass or less, more preferably 2% by mass or less, and even more preferably 1.6% by mass or less, based on the total amount of non-aqueous electrolyte. When using both monovalent and divalent cations as counterions to bis(oxalato)borate ions, the above-mentioned BOB [content] is achieved. - Preparation can be carried out using a concentration range method. In this specification, BOB in non-aqueous electrolytes... - The content (mass%) of oxalate and borate ions in the non-aqueous electrolyte is related to the concentration of oxalate and borate ions ([BOB)). - The meanings are the same.

[0057] BOB - When the concentration is within the above-mentioned preferred range, it is easier to exhibit improved battery durability, such as high-temperature storage characteristics and cycle characteristics.

[0058] BOB - It can be synthesized using known methods or obtained from commercially available products. Here, the electrolyte contains BOB. - The preparation of the electrolyte in this case can be carried out by known methods and is not particularly limited. For example, adding LiBOB synthesized separately by a known method to the electrolyte can be used. In this embodiment, any method can be used. The method for determining BOB in the above-mentioned non-aqueous electrolyte and non-aqueous electrolyte secondary battery is described below. - There are no particular restrictions on the methods used to determine the content; any publicly known method can be used. Specific examples include: ion chromatography, etc. 11 B NMR, etc. The following is about BOB. - The analytical method based on ion chromatography is described below. The non-aqueous electrolyte was collected into a volumetric flask, and the volume was adjusted to 50 mL with ultrapure water. The oxalic acid content was determined using an ion chromatograph (IC: Thermo Fishcer Scientific, ICS-2000), and converted to BOB (Bio-Oxygen Absorption Rate). - The amount of BOB in non-aqueous electrolytes can be determined. - Content. The NMR-based analytical method is described below. The non-aqueous electrolyte is diluted in deuterated DMSO, and LiBF4 is added as a standard. The content is then determined. 19 F NMR and 11 BNMR. The integral ratio of LiPF6 to BOB- can be determined by analyzing the LiBF4 peak. Based on the LiPF6 concentration obtained using ion chromatography, the BOB- concentration can be calculated. - concentration.

[0059] <1-2.FSO3 - PO2F2 - and BOB - Relationship >

[0060] FSO3 in non-aqueous electrolytes - Concentration of [FSO3] - ]), PO2F2 - The concentration of [PO2F2] - ]) and BOB - concentration ([BOB) - It is preferable to satisfy the following relationship (1).

[0061] [FSO3 - ]>[PO2F2 - ]>[BOB - (1)

[0062] Furthermore, it is even more desirable to satisfy the relationship of the following equations (2) and (3).

[0063] ([FSO3 - ]+[PO2F2 - ]) / ([PO2F2 - ]+[BOB - ])>1.8 (2)

[0064] [FSO3 - <1.3% by mass (3)

[0065] When the relationship in equation (1) above is satisfied, FSO3 - It can prevent PO2F2 - and BOB - The localized high molecular weight coating forms a thin and uniform negative electrode coating, thus more easily exhibiting the effect of improving the initial output in low-temperature environments. Furthermore, when the relationships in equations (2) and (3) above are satisfied, the output from BOB... - The increase in film resistance can come from FSO3. - and PO2F2 - The film suppresses the electrolyte, thus making it easier to exhibit the effect of improving the initial output in low-temperature environments. As has been practically verified in the embodiments described later, in the non-aqueous electrolytes used in the non-aqueous secondary batteries of the present invention, they are particularly preferably contained in the form of lithium fluorosulfonate (FSO3Li), lithium difluorophosphate (LiPO2F2), and lithium dioxalate borate (LiBOB).

[0066] <1-3. Electrolytes>

[0067] Similar to conventional non-aqueous electrolytes, the non-aqueous electrolyte of this embodiment typically contains an electrolyte as a component. There are no particular limitations on the electrolyte that can be used in the non-aqueous electrolyte of this embodiment; known electrolytes can be used. Specific examples of electrolytes will be described in detail below.

[0068] <1-3-1. Lithium Salts>

[0069] Lithium salts are typically used as the electrolyte in the non-aqueous electrolyte of this embodiment. There are no particular limitations on the lithium salt used, as long as it is known to be usable in this application; one or more lithium salts can be used, as listed below. However, it should be noted that the lithium salts mentioned in this section do not include FSO3Li, LiPO2F2, and LiBOB as described above.

[0070] Examples can be listed as follows:

[0071] Inorganic lithium salts such as LiBF4, LiClO4, LiAlF4, LiSbF6, LiTaF6, and LiWF7;

[0072] Lithium fluorophosphates such as LiPF6;

[0073] Lithium tungstate salts such as LiWOF5;

[0074] Lithium carboxylate salts such as CF3CO2Li;

[0075] Lithium sulfonate salts such as CH3SO3Li;

[0076] Lithium imide salts such as LiN(FSO2)2 and LiN(CF3SO2)2;

[0077] Methyl lithium salts such as LiC(FSO2)3;

[0078] Lithium oxalate salts such as lithium difluorooxalate borate;

[0079] In addition, fluorine-containing organic lithium salts such as LiPF4(CF3)2; etc.

[0080] From the perspective of further improving the charge / discharge rate characteristics and impedance characteristics, the lithium salt is preferably selected from inorganic lithium salts, lithium fluorophosphates, lithium sulfonates, lithium imides, and lithium oxalates.

[0081] There are no particular limitations on the total concentration of these electrolytes in the non-aqueous electrolyte, but relative to the total amount of the non-aqueous electrolyte, it is typically 8% by mass or more, preferably 8.5% by mass or more, and more preferably 9% by mass or more. Furthermore, its upper limit is typically 18% by mass or less, preferably 17% by mass or less, and more preferably 16% by mass or less. When the total electrolyte concentration is within the above range, the conductivity becomes suitable for battery operation, thus tending to obtain sufficient output characteristics.

[0082] <1-4. Non-aqueous solvents>

[0083] Similar to conventional non-aqueous electrolytes, the non-aqueous electrolyte of this embodiment typically contains a non-aqueous solvent for dissolving the aforementioned electrolyte as its main component. There are no particular limitations on the non-aqueous solvent used herein, and known organic solvents can be used. Examples of organic solvents include saturated cyclic carbonates, chain carbonates, carboxylic acid esters, ether compounds, or sulfone compounds. While not particularly limited to these organic solvents, saturated cyclic carbonates, chain carbonates, or carboxylic acid esters are preferred, and more preferably saturated cyclic carbonates or chain carbonates. These organic solvents can be used alone or in combination of two or more. As a combination of two or more non-aqueous solvents, a combination of two or more selected from saturated cyclic carbonates, chain carbonates, and carboxylic acid esters is preferred, and a combination of saturated cyclic carbonates or chain carbonates is more preferably.

[0084] <1-4-1. Saturated Cyclic Carbonates>

[0085] Saturated cyclic carbonates are typically alkylene carbonates having 2 to 4 carbon atoms. From the viewpoint of improving battery characteristics by increasing lithium-ion dissociation, saturated cyclic carbonates having 2 to 3 carbon atoms are preferred. Alternatively, saturated cyclic carbonates can also be cyclic carbonates containing fluorine atoms, such as ethylene monofluorocarbonate.

[0086] Examples of saturated cyclic carbonates include ethylene carbonate, propylene carbonate, and butyl carbonate. Ethyl carbonate and propylene carbonate are preferred, and ethylene carbonate, which is less prone to oxidation / reduction, is more preferred. A single saturated cyclic carbonate can be used alone, or two or more can be used in any combination and ratio.

[0087] The content of saturated cyclic carbonate is not particularly limited and is arbitrary within a range that does not significantly impair the effects of the present invention. However, relative to the total amount of solvent in the non-aqueous electrolyte, the lower limit of the content when using only one type is generally 3% by volume or more, preferably 5% by volume or more. By setting it within this range, a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, which is suitable for achieving good high-current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte secondary battery. In addition, the upper limit is generally 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. By setting it within this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, thereby tending to improve stability during high-temperature storage.

[0088] It should be noted that the volume % in this invention refers to the volume ratio [%] at 25°C and 1 atmosphere.

[0089] <1-4-2. Chain carbonates>

[0090] As a chain carbonate, chain carbonates with 3 to 7 carbon atoms are generally used. In order to adjust the viscosity of the electrolyte to an appropriate range, chain carbonates with 3 to 5 carbon atoms are preferred.

[0091] Specifically, examples of chain carbonates include: dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, methyl ethyl carbonate, methyl n-propyl carbonate, n-butyl methyl carbonate, isobutyl methyl carbonate, tert-butyl methyl carbonate, ethyl n-propyl carbonate, n-butyl ethyl carbonate, isobutyl ethyl carbonate, tert-butyl ethyl carbonate, etc.

[0092] The preferred materials are dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, methyl ethyl carbonate, and methyl n-propyl carbonate, with dimethyl carbonate, diethyl carbonate, and dimethyl ethyl carbonate being particularly preferred.

[0093] Alternatively, fluorine-containing chain carbonates (hereinafter referred to as "fluorinated chain carbonates") are preferred. There are no particular restrictions on the number of fluorine atoms in a fluorinated chain carbonate, as long as it is 1 or more, but it is usually 6 or less, preferably 4 or less. When a fluorinated chain carbonate has multiple fluorine atoms, these fluorine atoms can be bonded to the same carbon atom or to different carbon atoms. Examples of fluorinated chain carbonates include dimethyl fluorocarbonate derivatives, methyl ethyl fluorocarbonate derivatives, and diethyl fluorocarbonate derivatives.

[0094] Examples of fluorodimethyl carbonate derivatives include: methyl fluoromethyl carbonate, methyl difluoromethyl carbonate, methyl trifluoromethyl carbonate, bis(fluoromethyl) carbonate, bis(difluoromethyl) carbonate, and bis(trifluoromethyl) carbonate.

[0095] Examples of fluoromethyl ethyl carbonate derivatives include: methyl 2-fluoroethyl carbonate, ethyl fluoromethyl carbonate, methyl 2,2-difluoroethyl carbonate, 2-fluoroethyl fluoromethyl carbonate, ethyl difluoromethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, 2,2-difluoroethyl fluoromethyl carbonate, 2-fluoroethyl difluoromethyl carbonate, and ethyl trifluoromethyl carbonate.

[0096] Examples of fluorodiethyl carbonate derivatives include: ethyl-(2-fluoroethyl) carbonate, ethyl-(2,2-difluoroethyl) carbonate, bis(2-fluoroethyl) carbonate, ethyl-(2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl-2'-fluoroethyl carbonate, bis(2,2-difluoroethyl) carbonate, 2,2,2-trifluoroethyl-2'-fluoroethyl carbonate, 2,2,2-trifluoroethyl-2',2'-difluoroethyl carbonate, and bis(2,2,2-trifluoroethyl) carbonate.

[0097] Chain carbonates can be used alone or in any combination and ratio of two or more.

[0098] The content of the chain carbonate is not particularly limited, but relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 15% by volume or more, preferably 20% by volume or more, and more preferably 25% by volume or more. Furthermore, it is typically 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. By keeping the content of the chain carbonate within the above range, it is easy to achieve an appropriate viscosity for the non-aqueous electrolyte, suppress the decrease in ionic conductivity, and thus achieve a good range of output characteristics for the non-aqueous electrolyte secondary battery. When using two or more chain carbonates in combination, it is sufficient to ensure that the total amount of the chain carbonate meets the above range.

[0099] Furthermore, by combining ethylene carbonate in specific amounts relative to specific chain carbonates, battery performance can be significantly improved.

[0100] For example, when dimethyl carbonate and ethyl methyl carbonate are selected as specific chain carbonates, the content of ethylene carbonate is not particularly limited and is arbitrary within a range that does not significantly impair the effects of the present invention. However, relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 15% by volume or more, preferably 20% by volume or more, and typically 45% by volume or less, preferably 40% by volume or less. Relative to the total amount of solvent in the non-aqueous electrolyte, the content of dimethyl carbonate is typically 20% by volume or more, preferably 30% by volume or more, and typically 50% by volume or less, preferably 45% by volume or less. The content of ethyl methyl carbonate is typically 20% by volume or more, preferably 30% by volume or more, and typically 50% by volume or less, preferably 45% by volume or less. By keeping the content within the above ranges, there is a tendency for excellent high-temperature stability and suppression of gas generation.

[0101] <1-4-3. Ether Compounds>

[0102] As ether compounds, chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms are preferred.

[0103] Ether compounds can be used alone, or in any combination and ratio of two or more.

[0104] The content of ether compounds is not particularly limited and is arbitrary within a range that does not significantly impair the effects of the present invention. In a non-aqueous solvent, it is typically 1% by volume or more, preferably 2% by volume or more, and more preferably 3% by volume or more. Furthermore, it is typically 30% by volume or less, preferably 25% by volume or less, and more preferably 20% by volume or less. When using two or more ether compounds in combination, the total amount of ether compounds should satisfy the above-mentioned range. When the content of ether compounds is within the above-mentioned preferred range, it is easy to ensure the improved ionic conductivity resulting from the increased lithium-ion dissociation degree and decreased viscosity of the chain ethers. In addition, when the negative electrode active material is a carbonaceous material, the co-intercalation phenomenon of the chain ethers and lithium ions can be suppressed, thus enabling the input / output characteristics and charge / discharge rate characteristics to reach an appropriate range.

[0105] <1-4-4. Sulfone compounds>

[0106] As a sulfone compound, there are no particular restrictions on whether it is cyclic or chain-like. However, in the case of a cyclic sulfone, compounds with 3 to 6 carbon atoms are generally preferred, and more preferably 3 to 5 carbon atoms are preferred. In the case of a chain-like sulfone, compounds with 2 to 6 carbon atoms are generally preferred, and more preferably 2 to 5 carbon atoms are preferred. In addition, there are no particular restrictions on the number of sulfonyl groups in one molecule of a sulfone compound, and it is usually 1 or 2.

[0107] Examples of cyclic sulfones include: trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones as monosulfone compounds; and trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones as disulfone compounds. From the viewpoint of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, and hexamethylene disulfones are more preferred, and tetramethylene sulfones (sulfolane) are particularly preferred.

[0108] As sulfolane compounds, sulfolane and / or sulfolane derivatives are preferred (hereinafter, sulfolane will also be referred to as "sulfolane compounds"). As sulfolane derivatives, compounds obtained by replacing one or more hydrogen atoms bonded to the carbon atoms constituting the sulfolane ring with fluorine atoms or alkyl groups are preferred.

[0109] Sulfone compounds can be used alone, or in any combination and ratio of two or more.

[0110] The content of sulfone compounds is not particularly limited and can be arbitrary within a range that does not significantly impair the effects of the present invention. However, relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 0.3% by volume or more, preferably 0.5% by volume or more, more preferably 1% by volume or more, and typically 40% by volume or less, preferably 35% by volume or less, more preferably 30% by volume or less. When using two or more sulfone compounds in combination, the total amount of sulfone compounds should satisfy the above range. When the content of sulfone compounds is within the above range, an electrolyte with excellent high-temperature storage stability is tended to be obtained.

[0111] <1-4-5. Carboxylic Acid Esters>

[0112] As a carboxylic acid ester, a chain-like carboxylic acid ester is preferred, and a saturated chain-like carboxylic acid ester is more preferred. In addition, the total number of carbon atoms in a carboxylic acid ester is usually 3 to 7. From the viewpoint of improving battery characteristics by enhancing output characteristics, a carboxylic acid ester with a total number of carbon atoms of 3 to 5 is preferred.

[0113] Examples of carboxylic acid esters include saturated chain carboxylic acid esters such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl pivalate, and ethyl pivalate, as well as unsaturated chain carboxylic acid esters such as methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate. Among these, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl pivalate, and ethyl pivalate are preferred. From the viewpoint of improving output characteristics, methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate are more preferred. A single carboxylic acid ester can be used alone, or two or more can be used in any combination and ratio.

[0114] The content of carboxylic acid esters is not particularly limited and can be arbitrary within a range that does not significantly impair the effects of the present invention. However, its lower limit, relative to the total amount of solvent in the non-aqueous electrolyte, is typically 3% by volume or more, preferably 5% by volume or more. By setting it within this range, a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, which is suitable for achieving good high-current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte secondary battery. Furthermore, the upper limit is typically 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. By setting it within this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, thereby tending to improve stability during high-temperature storage.

[0115] It should be noted that the volume % in this invention refers to the volume at 25°C and 1 atmosphere.

[0116] <1-5. Other fluorosulfonates>

[0117] There are no particular limitations on the counterions of fluorosulfonate ions contained in other fluorosulfonates; examples include rubidium, cesium, barium, and NR. 13 R 14 R 15 R 16 (where R is in the formula) 13 ~R 16 Each organic group (independently representing 1 to 12 hydrogen or carbon atoms) represents ammonium, etc., except in the case of <1-1-1. Fluorosulfonic acid ions (FSO3). - Cations other than those listed in the specification. It should be noted that in this specification, FSO3... - It contains fluorosulfonic acid ions that constitute other fluorosulfonates.

[0118] Other examples of fluorosulfonates include rubidium fluorosulfonate and cesium fluorosulfonate.

[0119] Other fluorosulfonates can be used alone, or in combination of two or more in any ratio. Furthermore, compared to the overall non-aqueous electrolyte of this embodiment, FSO... 3- The total content of cations contained in the non-aqueous electrolyte and other fluorosulfonates is typically 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and typically 15% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, further preferably 3% by mass or less, particularly more preferably 2% by mass or less, and especially preferably 1% by mass or less. When using two or more other fluorosulfonates in combination, as long as FSO is made... 3- The total amount of cations contained in the fluorosulfonate and other fluorosulfonates must meet the above range.

[0120] Within this range, the expansion of non-aqueous electrolyte secondary batteries during charging and discharging can be appropriately suppressed.

[0121] <1-6. Additives>

[0122] In the non-aqueous electrolyte of this embodiment, the following additives may also be included within the range that can achieve the effects of the present invention.

[0123] Unsaturated cyclic carbonates such as vinylene carbonate, vinyl ethylene carbonate, or ethynyl ethylene carbonate;

[0124] Carbonate compounds such as methoxyethyl-methyl carbonate;

[0125] Spirocyclic compounds such as methyl-2-propynyl oxalate;

[0126] Sulfur-containing compounds such as ethylene glycol sulfite;

[0127] Isocyanate compounds such as 1,3-bis(isocyanate methyl)cyclohexane and diisocyanates containing cyclohexene alkyl groups;

[0128] Nitrogen-containing compounds such as 1-methyl-2-pyrrolidone;

[0129] Hydrocarbon compounds such as cycloheptane;

[0130] Fluorinated aromatic compounds such as fluorobenzene;

[0131] Silane compounds such as trimethylsilyl borate;

[0132] Ester compounds such as 2-(methanesulfonyloxy)propionic acid 2-propynyl ester;

[0133] Lithium salts such as lithium ethyl methoxycarbonyl phosphonate;

[0134] Isocyanates such as triallyl isocyanurate; etc.

[0135] These additives can be used alone or in combination of two or more. By adding these additives, the capacity retention and cycle performance after high-temperature storage can be improved.

[0136] There are no particular restrictions on the content of other additives, and they can be arbitrary as long as they do not significantly impair the effects of the present invention. Relative to the total amount of the non-aqueous electrolyte, the content of other additives is typically 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and typically 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less. Within this range, there is a tendency for the effects of other additives to be sufficiently manifested, and for improved high-temperature storage stability to be improved. When using two or more other additives in combination, it is sufficient that the total amount of other additives meets the above-mentioned range.

[0137] In this specification, the composition of the non-aqueous electrolyte refers to the composition of the battery containing the non-aqueous electrolyte at the time of shipment. It is not necessarily required to analyze the composition of the non-aqueous electrolyte at the time of shipment. It is sufficient to manufacture the battery by measuring the content of the constituent components during the manufacturing of the non-aqueous electrolyte or during the injection of the non-aqueous electrolyte into the battery, ensuring that the composition at the time of shipment meets the desired range.

[0138] That is, the non-aqueous electrolyte can be prepared by mixing the components in a predetermined ratio to achieve the desired composition. Furthermore, after preparing the non-aqueous electrolyte, the electrolyte itself can be analyzed to confirm its composition. Alternatively, the non-aqueous electrolyte can be recovered from the completed non-aqueous electrolyte secondary battery for analysis. As a method for recovering the non-aqueous electrolyte, methods include partially or completely opening the battery container or providing a hole in the battery container to collect the electrolyte. The electrolyte can be recovered by centrifuging the opened battery container, or by adding an extraction solvent (e.g., preferably acetonitrile dehydrated to a water content of 10 ppm or less) to the opened battery container or by contacting the extraction solvent with the battery element. The non-aqueous electrolyte recovered in this way can be analyzed. Additionally, the recovered non-aqueous electrolyte can be diluted to meet analytical conditions before analysis.

[0139] As for analytical methods for non-aqueous electrolytes, the optimal method varies depending on the type of composition of the non-aqueous electrolyte. Examples include inductively coupled plasma atomic emission spectrometry (ICP), nuclear magnetic resonance (NMR), gas chromatography, ion chromatography, and liquid chromatography. The NMR-based analytical method will be described below. In an inert gas atmosphere, the non-aqueous electrolyte is dissolved in a dehydrated solvent (dehydrated to below 10 ppm) and added to an NMR tube for NMR measurement. Alternatively, a double-layered tube can be used, with the non-aqueous electrolyte added to one layer and the dehydrated solvent added to the other for NMR measurement. Examples of dehydrated solvents include deuterated acetonitrile and deuterated dimethyl sulfoxide. To determine the concentration of the components of the non-aqueous electrolyte, a given amount of standard substance can be dissolved in the dehydrated solvent, and the concentration of each component can be calculated based on the ratio of the spectra. Alternatively, the concentration of one or more components constituting the non-aqueous electrolyte can be determined beforehand using other analytical methods such as gas chromatography, and the concentration can be calculated based on the ratio of the chromatograms of the known-concentration component to those of the other components. The nuclear magnetic resonance (NMR) analyzer used is preferably one with a proton resonance frequency of 400 MHz or higher. Examples of nuclei that can be determined include... 1 H, 31 P, 19 F, 11 B, etc.

[0140] These analytical methods can be used individually or in combination of two or more.

[0141] <2. Non-aqueous electrolyte secondary batteries>

[0142] One embodiment of the non-aqueous electrolyte secondary battery of the present invention includes a positive electrode and a negative electrode capable of absorbing and releasing metal ions, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte secondary battery includes the non-aqueous electrolyte of one embodiment of the present invention described above. More specifically, it includes: a positive electrode having a current collector and a positive electrode active material layer disposed on the current collector; a negative electrode having a current collector and a negative electrode active material layer disposed on the current collector and capable of absorbing and releasing metal ions; and a non-aqueous electrolyte.

[0143] <2-1. Battery Composition>

[0144] The non-aqueous electrolyte secondary battery of this embodiment, except for the aforementioned non-aqueous electrolyte, is the same as that of conventionally known non-aqueous electrolyte secondary batteries. It typically has the following configuration: a positive electrode and a negative electrode are stacked with a porous membrane (separator) impregnated with the aforementioned non-aqueous electrolyte, and these are housed in a casing (outer body). Therefore, the shape of the non-aqueous electrolyte secondary battery of this embodiment is not particularly limited, and it can be any shape such as cylindrical, square, laminated, coin-shaped, or large.

[0145] <2-2. Non-aqueous electrolyte>

[0146] The non-aqueous electrolyte described in one embodiment of the present invention is used as the non-aqueous electrolyte. It should be noted that, without departing from the spirit of the present invention, other non-aqueous electrolytes may also be used in conjunction with the described non-aqueous electrolyte.

[0147] <2-3. Positive Electrode>

[0148] In one embodiment of the present invention, the positive electrode has a current collector and a layer of positive electrode active material disposed on the current collector.

[0149] The following is a detailed description of the positive electrode of the non-aqueous electrolyte secondary battery that can be used in this embodiment.

[0150] <2-3-1. Positive Electrode Active Material>

[0151] The following section explains the positive electrode active materials that can be used in the positive electrode.

[0152] (1) Composition

[0153] As a positive electrode active material, any material capable of electrochemically adsorbing / releasing metal ions is acceptable, without particular limitations. For example, a material capable of electrochemically adsorbing / releasing lithium ions is preferred, and it is more preferable to contain at least one selected from lithium / cobalt composite oxides, lithium / cobalt / nickel composite oxides, lithium / manganese composite oxides, lithium / cobalt / manganese composite oxides, lithium / nickel composite oxides, lithium / nickel / manganese composite oxides, and lithium / cobalt / nickel / manganese composite oxides. This is because the redox potentials of the transition metals contained in these composite oxides are suitable for use as positive electrode materials in secondary batteries, making them suitable for high-capacity applications.

[0154] The transition metal component of the aforementioned composite oxide (also known as a lithium transition metal oxide) may include Ni, Co, and / or Mn. Other metals include V, Ti, Cr, Fe, Cu, Al, Mg, Zr, Er, etc., with Ti, Fe, Al, Mg, Zr, etc. being preferred. Specific examples of lithium transition metal oxides include LiCoO2 and LiNi. 0.85 Co 0.10 Al 0.05 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.05 Ni 0.33 Mn 0.33 Co 0.33 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, Li 1.05 Ni 0.50 Mn 0.29 Co 0.21 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiMn2O4, LiMn 1.8 Al 0.2 O4, LiMn 1.5 Ni 0.5 O4, etc.

[0155] Alternatively, two or more of the above-mentioned positive electrode active materials may be used in combination. Similarly, at least one of the above-mentioned positive electrode active materials may be used in combination with other positive electrode active materials. Examples of other positive electrode active materials include transition metal oxides, transition metal phosphate compounds, transition metal silicate compounds, and transition metal borate compounds, which are not listed above.

[0156] Furthermore, the transition metals used in lithium transition metal phosphate compounds are preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples include: iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7; cobalt phosphates such as LiCoPO4; manganese phosphates such as LiMnPO4; and materials in which a portion of the transition metal atoms that constitute the main body of these lithium transition metal phosphate compounds are replaced by other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, and W.

[0157] Lithium iron phosphate compounds are preferred. This is because iron is not only abundant and inexpensive, but also has low harmfulness. Specifically, in the above examples, LiFePO4 is a more preferred example.

[0158] (2) Surface coating

[0159] Materials with a different composition (hereinafter appropriately referred to as "surface-attached material") attached to the surface of the aforementioned positive electrode active material can also be used. Examples of surface-attached materials include: oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0160] These surface-adhesive substances can be attached to the surface of the positive electrode active material by methods such as: dissolving or suspending the surface-adhesive substance in a solvent to impregnate it into the positive electrode active material and then drying it; dissolving or suspending the surface-adhesive substance precursor in a solvent to impregnate it into the positive electrode active material and then reacting it by heating; or adding the surface-adhesive substance to the positive electrode active material precursor and simultaneously calcining it. It should be noted that, in the case of carbon attachment, a method can also be used to mechanically attach the carbonaceous material subsequently in the form of, for example, activated carbon.

[0161] The mass of the surface-attached material adhering to the surface of the positive electrode active material is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more. In addition, it is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less.

[0162] By utilizing surface-attached substances, oxidation reactions of non-aqueous electrolytes on the surface of the positive electrode active material can be suppressed, thereby improving battery life. Furthermore, when the amount of attached material is within the aforementioned range, its effect is fully realized without hindering the entry and exit of lithium ions or easily leading to increased resistance.

[0163] (3) Shape

[0164] The shape of the positive electrode active material particles can take the forms previously used, such as block, polyhedral, spherical, ellipsoidal, plate, needle-like, columnar, etc. Alternatively, secondary particles can be formed by the aggregation of primary particles, and the shape of these secondary particles can be spherical or ellipsoidal.

[0165] (4) Method for manufacturing positive electrode active material

[0166] There are no particular limitations on the method of manufacturing the positive electrode active material without departing from the essential points of this invention. Several methods can be listed, and the conventional method used for manufacturing inorganic compounds can be adopted.

[0167] In particular, various methods can be considered to prepare spherical or ellipsoidal active substances. For example, the following method can be listed: dissolve or pulverize and disperse transition metal raw materials such as transition metal nitrates and sulfates, and other raw materials of other elements used as needed, in a solvent such as water, adjust the pH while stirring, prepare and recover spherical precursors, dry the precursors as needed, add Li sources such as LiOH, Li2CO3, and LiNO3, and calcine at high temperature to obtain active substances.

[0168] Another example of a method is as follows: Transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, and oxides, and other raw materials of other elements used as needed, are dissolved or pulverized and dispersed in a solvent such as water. The precursors are dried and shaped into spherical or ellipsoidal shapes using a spray dryer or similar device. Li sources such as LiOH, Li2CO3, and LiNO3 are then added to the precursors, and the mixture is calcined at a high temperature to obtain the active material.

[0169] In addition, as another example of a method, the following method can be listed: Transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, oxides, etc., and Li sources such as LiOH, Li2CO3, LiNO3, etc., as well as other raw materials of elements used as needed, are dissolved or pulverized and dispersed in a solvent such as water, and dried and shaped into spherical or ellipsoidal precursors using a spray dryer or the like, and the precursors are calcined at high temperature to obtain active substances.

[0170] <2-3-2. Positive Electrode Structure and Fabrication Method>

[0171] The following describes the structure and manufacturing method of the positive electrode that can be used in this embodiment.

[0172] (Method for making the positive electrode)

[0173] The positive electrode can be fabricated by forming a layer of positive electrode active material containing positive electrode active material particles and a binder on a current collector. The positive electrode using the positive electrode active material can be manufactured using any known method. For example, the positive electrode active material, binder, and conductive materials and thickeners used as needed can be dry-mixed and formed into a sheet, which is then pressed onto the positive electrode current collector. Alternatively, these materials can be dissolved or dispersed in a liquid medium to form a slurry, which is then coated onto the positive electrode current collector and dried, thereby forming a layer of positive electrode active material on the current collector, thus obtaining the positive electrode.

[0174] The content of the positive electrode active material in the positive electrode active material layer is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. Furthermore, it is preferably 99.9% by mass or less, and even more preferably 99% by mass or less. When the content of the positive electrode active material is within the above range, the capacitance can be sufficiently ensured. Furthermore, the strength of the positive electrode is also sufficiently ensured. It should be noted that the positive electrode active material powder in this invention can be used alone, or two or more with different compositions or different powder properties can be combined in any combination and proportion. When using two or more active materials in combination, it is preferable to use the aforementioned composite oxide containing lithium and manganese as the powder component. This is because cobalt or nickel are scarce and expensive metals. In large batteries requiring high capacity, such as those for automotive applications, the increased amount of active material used would be costly. Therefore, it is preferable to use manganese, a cheaper transition metal, as the main component.

[0175] <2-4. Negative Electrode>

[0176] The following describes negative electrode active materials that can be used as negative electrodes. There are no special restrictions on any material that can electrochemically adsorb / release metal ions as a negative electrode active material. Specific examples include carbonaceous materials and other materials with carbon as a constituent element, and alloy materials. These materials can be used alone, or in combination of two or more.

[0177] <2-4-1. Negative Electrode Active Material>

[0178] As mentioned above, carbonaceous materials and alloy materials can be listed as negative electrode active materials.

[0179] Examples of carbonaceous materials mentioned above include: (1) natural graphite, (2) artificial graphite, (3) amorphous carbon, (4) carbon-coated graphite, (5) graphite-coated graphite, and (6) resin-coated graphite.

[0180] Examples of natural graphite (1) include scaly graphite, flake graphite, soil graphite, and / or graphite particles obtained by using these graphites as raw materials and subjecting them to treatments such as spheroidization and densification. Among these natural graphites, from the viewpoint of particle filling properties and charge / discharge rate characteristics, spherical or ellipsoidal graphite that has undergone spheroidization treatment is particularly preferred.

[0181] As a device for the above-mentioned spheroidization process, for example, a device that repeatedly applies mechanical actions such as compression, friction, and shearing forces, which are mainly impact forces and also include particle interactions, to the particles can be used.

[0182] Specifically, a preferred device is one that has a rotor with multiple blades inside the casing, and applies mechanical actions such as impact compression, friction, and shearing force to the (1) natural graphite raw material introduced into the casing through the high-speed rotation of the rotor, thereby performing spheroidization treatment. In addition, a device having a mechanism that repeatedly applies mechanical actions by circulating the raw material is preferred.

[0183] For example, when using the above-described apparatus for spheroidization, it is preferable to set the circumferential speed of the rotating rotor to 30–100 m / s, more preferably 40–100 m / s, and even more preferably 50–100 m / s. Furthermore, while spheroidization can be achieved simply by passing the material through the apparatus, it is preferable to circulate or retain the material within the apparatus for at least 30 seconds, and more preferably to circulate or retain the material within the apparatus for at least one minute.

[0184] As for (2) artificial graphite, examples include: materials made by graphitizing organic compounds such as coal tar pitch, coal-based heavy crude oil, atmospheric residue oil, petroleum-based heavy crude oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polystyrene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene ether, furfuryl alcohol resin, phenolic resin, and imide resin at temperatures typically above 2500°C and typically below 3200°C, and then crushing and / or classifying them as needed.

[0185] At this point, silicon-containing compounds, boron-containing compounds, etc., can also be used as graphitization catalysts. Additionally, artificial graphite obtained by graphitizing mesophase carbon microspheres separated during the heat treatment of asphalt can be cited as an example. Furthermore, artificial graphite composed of granulated particles formed from primary particles can also be cited. For example, graphite particles are formed by aggregating or combining multiple flattened particles obtained by mixing and graphitizing mesophase carbon microspheres, graphitizable carbonaceous material powders such as coke, graphitizable binders such as tar and asphalt, and graphitization catalysts, and then pulverizing them as needed, so that their orientation faces are not parallel.

[0186] As for (3) amorphous carbon, examples include: amorphous carbon particles produced by heat treatment more than once at a temperature range (400-2200℃) where graphitization will not occur, using easily graphitized carbon precursors such as tar and pitch as raw materials; and amorphous carbon particles produced by heat treatment using difficult-to-graphitize carbon precursors such as resin as raw materials.

[0187] As for (4) carbon-coated graphite, the following materials can be listed. Natural graphite and / or artificial graphite are mixed with carbon precursors such as tar, pitch, resin, etc., and subjected to heat treatment once or more in the range of 400 to 2300°C. The obtained natural graphite and / or artificial graphite are used as core graphite, and amorphous carbon is used to coat them to obtain a carbon-graphite composite. This carbon-graphite composite can be listed as carbon-coated graphite (4).

[0188] Furthermore, the aforementioned composite can be in the form of amorphous carbon covering the entire or part of the surface of the core graphite, or it can be in the form of multiple primary particles composited using carbon derived from the aforementioned carbon precursor as a binder. Additionally, the aforementioned carbon-graphite composite can also be obtained by reacting hydrocarbon gases such as benzene, toluene, methane, propane, and aromatic volatile components with natural and / or artificial graphite at high temperatures to deposit carbon (CVD) on the graphite surface.

[0189] As for graphite-coated graphite (5), the following materials can be obtained: Natural graphite and / or artificial graphite, along with carbon precursors of easily graphitizable organic compounds such as tar, pitch, and resin, are mixed and heat-treated once or more in the range of approximately 2400–3200°C. The obtained natural graphite and / or artificial graphite are used as the core graphite, and the entire or part of the surface of the core graphite is coated with graphitizers to obtain graphite-coated graphite (5).

[0190] (6) Resin-coated graphite can be obtained, for example, by mixing natural graphite and / or artificial graphite with resin, drying at a temperature below 400°C, using the resulting natural graphite and / or artificial graphite as core graphite, and coating the core graphite with resin, etc.

[0191] In addition, the carbonaceous materials described above (1) to (6) can be used alone or in any combination and ratio of two or more.

[0192] Organic compounds such as tar, asphalt, and resin used in the carbonaceous materials described in (2) to (5) above can be selected from coal-based heavy crude oil, direct-flow heavy crude oil, decomposed petroleum heavy crude oil, aromatic hydrocarbons, N-ring compounds, S-ring compounds, polystyrene, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins that are capable of carbonization. Additionally, to adjust the viscosity during mixing, the raw material organic compounds can be dissolved in low-molecular-weight organic solvents for use.

[0193] Furthermore, natural graphite and / or artificial graphite used as raw materials for nuclear graphite are preferably natural graphite that has undergone spheroidization treatment.

[0194] Furthermore, regarding the aforementioned alloy materials that can be used as negative electrode active materials, as long as they can adsorb / release lithium, they can be elemental lithium, elemental metals and alloys used to form lithium alloys, or any compound among their oxides, carbides, nitrides, silicides, sulfides, or phosphides, without particular limitation. Regarding the elemental metals and alloys used to form lithium alloys, materials containing metals / semi-metals of Group 13 and Group 14 (i.e., other than carbon) are preferred; elemental metals of aluminum, silicon, and tin, and alloys or compounds containing these atoms are more preferred; and materials having silicon or tin as a constituent element, such as elemental metals of silicon and tin, and alloys or compounds containing these atoms, are even more preferred.

[0195] These materials can be used alone, or in any combination and ratio of two or more.

[0196] <Metal particles capable of forming alloys with Li>

[0197] When using elemental metals and alloys that form lithium alloys, or their oxides, carbides, nitrides, silicides, sulfides, or phosphides as negative electrode active materials, the metals capable of forming alloys with Li are in particle form. Methods for confirming that the metal particles are capable of forming alloys with Li include: identification of the metal particle phase using X-ray diffraction, observation of particle structure and elemental analysis using electron microscopy, and elemental analysis using fluorescent X-rays.

[0198] As the metal particles capable of forming alloys with Li, any conventionally known metal particles can be used. However, from the viewpoint of capacity and cycle life of non-aqueous electrolyte secondary batteries, the metal particles are preferably selected from, for example, metals or compounds thereof selected from Fe, Co, Sb, Bi, Pb, Ni, Ag, Si, Sn, Al, Zr, Cr, P, S, V, Mn, As, Nb, Mo, Cu, Zn, Ge, In, Ti, and W. Alternatively, alloys formed of two or more metals can be used, and the metal particles can also be alloy particles formed of two or more metallic elements. Among these metal particles, metals or metal compounds selected from Si, Sn, As, Sb, Al, Zn, and W are preferred.

[0199] Examples of such metal compounds include metal oxides, metal nitrides, and metal carbides. Alternatively, alloys formed from two or more metals may also be used.

[0200] Among metal particles capable of forming alloys with Li, Si or Si metal compounds are preferred. Si metal compounds are preferably Si metal oxides. Si or Si metal compounds are preferred from the viewpoint of increasing battery capacity. In this specification, Si or Si metal compounds are collectively referred to as Si compounds. Specifically, SiO2 can be listed as a Si compound. x SiN x SiC x SiZ x O y (Z = C, N), etc. The preferred Si compound is a Si metal oxide, which, if expressed by a general formula, is SiO. x The general formula SiO x It can be obtained from Si dioxide (SiO2) and metallic Si (Si), and its x value is usually 0 ≤ x < 2. SiO x The theoretical capacity is greater than that of graphite, and amorphous Si or nanoscale Si crystals make it easier for alkali metal ions such as lithium ions to enter and exit, thus enabling high capacity.

[0201] Specifically, Si metal oxides can be represented as SiO. xThe compound has x ≤ 0 < x < 2, more preferably 0.2 or more and 1.8 or less, further preferably 0.4 or more and 1.6 or less, and particularly preferably 0.6 or more and 1.4 or less. Within this range, the battery has high capacity and can reduce the irreversible capacity reduction caused by the combination of Li and oxygen.

[0202] <Oxygen content of metal particles capable of forming alloys with Li>

[0203] There are no particular limitations on the oxygen content of the metal particles capable of forming alloys with Li, but it is typically 0.01% by mass to 8% by mass, preferably 0.05% by mass to 5% by mass. Regarding the oxygen distribution within the particles, it can exist near the surface, inside the particles, or uniformly within the particles, but it is particularly preferred to exist near the surface. When the oxygen content of the metal particles capable of forming alloys with Li is within the above range, the volume expansion that occurs during the charging and discharging of non-aqueous electrolyte secondary batteries can be suppressed due to the strong bond between the metal particles and O (oxygen atoms), resulting in excellent cycle characteristics, and is therefore preferred.

[0204] <Anode active material containing metal particles and graphite particles capable of forming alloys with Li>

[0205] The negative electrode active material can be a substance containing metal particles capable of forming alloys with Li and graphite particles. This negative electrode active material can be a mixture of metal particles capable of forming alloys with Li and graphite particles in an independent particle state, or it can be a composite material in which metal particles capable of forming alloys with Li exist on the surface and / or inside the graphite particles.

[0206] Regarding the aforementioned composite material of metal particles and graphite particles capable of forming alloys with Li (also referred to as composite particles), there are no particular limitations as long as the particles contain both metal particles capable of forming alloys with Li and graphite particles. However, particles in which the metal particles capable of forming alloys with Li and graphite particles are integrated through physical and / or chemical bonding are preferred. A more preferred form is a state in which the metal particles capable of forming alloys with Li and graphite particles are dispersed within the particles to the extent that each solid component is present at least on the surface and inside the composite particle, and a form in which graphite particles are present to enable them to form an integrated composite through physical and / or chemical bonding. A more specific preferred form is a composite material composed at least of metal particles capable of forming alloys with Li and graphite particles, and this composite material (negative electrode active material) is characterized in that metal particles capable of forming alloys with Li are present in the gaps within the graphite particles, preferably natural graphite particles having a folded structure including curved surfaces. In addition, the gap can be a void, or it can contain amorphous carbon, graphitic materials, resin, or other substances that can buffer the expansion and contraction of metal particles that can form alloys with Li.

[0207] <Proportion of metal particles capable of forming alloys with Li>

[0208] The proportion of metal particles capable of forming alloys with Li, relative to the total amount of metal particles and graphite particles capable of forming alloys with Li, is typically 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 2.0% by mass or more. Furthermore, it is typically 99% by mass or less, preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, even more preferably 25% by mass or less, even more preferably 20% by mass or less, particularly preferably 15% by mass or less, and most preferably 10% by mass or less. Within this range, it is preferable from the perspective of controlling side reactions on the Si surface and obtaining sufficient capacity in a non-aqueous electrolyte secondary battery.

[0209] Coverage ratio

[0210] In this embodiment, the negative electrode active material may also be coated with a carbonaceous material or a graphitic material. From the viewpoint of lithium-ion acceptability, coating with an amorphous carbonaceous material is preferred. This coating rate is typically 0.5% to 30%, preferably 1% to 25%, and more preferably 2% to 20%. From the viewpoint of reversible capacity during battery assembly, the upper limit of the coating rate is preferably set within the above range. From the viewpoint that the carbonaceous material forming the nucleus can be uniformly coated with amorphous carbon to achieve robust granulation, and from the viewpoint of particle size obtained when pulverized after firing, the lower limit of the coating rate is preferably set within the above range.

[0211] It should be noted that the final coating rate (content rate) of the negative electrode active material derived from the carbide of the organic compound can be calculated using the following formula based on the amount of negative electrode active material, the amount of organic compound, and the residual carbon rate determined by the micro-method based on JIS K 2270.

[0212] Formula: Coating rate (%) of carbides derived from organic compounds = (mass of organic compounds × residual carbon rate × 100) / {mass of negative electrode active material + (mass of organic compounds × residual carbon rate)}

[0213] <Internal gap ratio>

[0214] The internal gap ratio of the negative electrode active material is typically 1% or more, preferably 3% or more, more preferably 5% or more, and even more preferably 7% or more. It is also typically less than 50%, preferably 40% or less, more preferably 30% or less, and even more preferably 20% or less. If this internal gap ratio is too small, there is a tendency for the liquid volume within the particles of the negative electrode active material in a non-aqueous electrolyte secondary battery to decrease. On the other hand, if the internal gap ratio is too large, there is a tendency for the interparticle gaps to decrease during electrode fabrication. From the viewpoint of charge-discharge characteristics, the lower limit of the internal gap ratio is preferably set to the above range, and from the viewpoint of diffusion of the non-aqueous electrolyte, the upper limit is preferably set to the above range. Furthermore, as mentioned above, the gap can be a void, or it can contain amorphous carbon, graphitic materials, resin, or other substances that can buffer the expansion and contraction of metal particles capable of forming alloys with Li, or the gap can be filled with these substances.

[0215] <2-4-2. Composition and Manufacturing Method of the Negative Electrode>

[0216] The negative electrode can be manufactured using any known method without significantly impairing the effectiveness of the invention. For example, it can be formed by adding a binder, solvent, desired thickener, conductive material, filler, etc., to the negative electrode active material to prepare a slurry, coating the slurry onto the current collector, drying it, and then pressing it.

[0217] Furthermore, alloy-type anode materials can be manufactured using any known method. Specifically, methods for manufacturing the anode include, for example, adding binders and conductive materials to the aforementioned anode active material and then directly rolling the resulting material to form a sheet electrode; or compression molding to form a sheet electrode. However, a common method is to form a thin film layer (anode active material layer) containing the aforementioned anode active material on a current collector (hereinafter sometimes referred to as "anode current collector") using methods such as coating, vapor deposition, sputtering, or plating. In this case, binders, tackifiers, conductive materials, and solvents are added to the aforementioned anode active material to form a slurry, which is then coated onto the anode current collector and dried. The slurry is then pressed to achieve high density, thereby forming the anode active material layer on the anode current collector.

[0218] Materials that can be used as negative electrode current collectors include steel, copper, copper alloys, nickel, nickel alloys, and stainless steel. Among these materials, copper foil is preferred due to its ease of processing into thin films and its cost.

[0219] The thickness of the negative electrode current collector is typically 1 μm or more, preferably 5 μm or more, and typically 100 μm or less, preferably 50 μm or less. When the thickness of the negative electrode current collector is too thick, it can sometimes lead to an excessive reduction in the overall capacity of the non-aqueous electrolyte secondary battery. Conversely, when it is too thin, it can sometimes make operation difficult.

[0220] It should be noted that, in order to improve the adhesion effect with the negative electrode active material layer formed on the surface, it is preferable to roughen the surface of these negative electrode current collectors beforehand. Examples of surface roughening methods include: sandblasting, calendering using rough-surfaced rollers, mechanical polishing using abrasive paper with adhering abrasive particles, grinding stones, diamond wheels, wire brushes with steel wires, etc., electrolytic polishing, and chemical polishing.

[0221] In addition, to reduce the mass of the negative electrode current collector and increase the energy density per unit mass of the battery, open-type negative electrode current collectors such as expanded alloys and perforated metals can be used. For this type of negative electrode current collector, its mass can be arbitrarily changed by altering its aperture ratio. Furthermore, when negative electrode active material layers are formed on both sides of this type of negative electrode current collector, the anchoring effect of the through-hole makes peeling of the negative electrode active material layer less likely. However, if the aperture ratio is too high, the contact area between the negative electrode active material layer and the negative electrode current collector will be smaller, which may actually reduce the adhesion strength.

[0222] The slurry used to form the negative electrode active material layer is usually made by adding binders, thickeners, etc., to the negative electrode material. It should be noted that the term "negative electrode material" in this specification refers to materials including both the negative electrode active material and conductive materials.

[0223] The content of negative electrode active material in the negative electrode material is typically 70% by mass or more, particularly preferably 75% by mass or more, and typically 97% by mass or less, particularly preferably 95% by mass or less. If the content of negative electrode active material is too low, the secondary battery using the resulting negative electrode tends to have insufficient capacity; if it is too high, the content of conductive material becomes relatively insufficient, thus making it difficult to ensure the conductivity when manufacturing the negative electrode. It should be noted that when using two or more negative electrode active materials in combination, it is sufficient as long as the total amount of negative electrode active material meets the above-mentioned range.

[0224] Examples of conductive materials used for the negative electrode include metallic materials such as copper and nickel, and carbon materials such as graphite and carbon black. These conductive materials can be used individually or in any combination and ratio of two or more. In particular, carbon materials are preferred as they also function as active materials. The content of conductive material in the negative electrode material is typically 3% by mass or more, preferably 5% by mass or more, and typically 30% by mass or less, preferably 25% by mass or less. If the content of conductive material is too low, there is a tendency for insufficient conductivity; if the content of conductive material is too high, it will lead to a relative deficiency in the content of the negative electrode active material, thus tending to reduce battery capacity and strength. It should be noted that when using two or more conductive materials in combination, it is sufficient to ensure that the total amount of conductive material meets the above-mentioned range.

[0225] As a binder for the negative electrode, any binder can be used as long as it is a material safe for the solvents and electrolytes used in the manufacture of the electrode. Examples include: polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, etc. These binders can be used alone or in any combination and ratio of two or more. The binder content is typically 0.5 parts by mass or more, preferably 1 part by mass or more, relative to 100 parts by mass of the negative electrode material; it is also typically 10 parts by mass or less, preferably 8 parts by mass or less. If the binder content is too low, the resulting negative electrode tends to have insufficient strength; if it is too high, the battery capacity and conductivity tend to be insufficient due to the relatively insufficient content of the negative electrode active material. It should be noted that when using two or more binders in combination, the total amount of binder should meet the above-mentioned range.

[0226] Examples of thickeners used for the negative electrode include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. These thickeners can be used alone or in any combination and ratio of two or more. Thickeners are used as needed, but when using thickeners, the content of the thickener in the negative electrode active material layer is generally preferably in the range of 0.5% by mass or more and 5% by mass or less.

[0227] The slurry used to form the negative electrode active material layer can be prepared as follows: A conductive material, binder, and thickener, as needed, are mixed into the aforementioned negative electrode active material, and an aqueous solvent or an organic solvent is used as the dispersion medium to prepare the slurry. Water is typically used as the aqueous solvent, but organic solvents such as alcohols like ethanol and cyclic amides like N-methylpyrrolidone can also be used in combination in a range of 30% by mass or less relative to water. Examples of organic solvents include cyclic amides such as N-methylpyrrolidone, linear amides such as N,N-dimethylformamide and N,N-dimethylacetamide, aromatic hydrocarbons such as anisole, toluene, and xylene, and alcohols such as butanol and cyclohexanol. Preferably, cyclic amides such as N-methylpyrrolidone, linear amides such as N,N-dimethylformamide and N,N-dimethylacetamide are preferred. It should be noted that any one of these solvents can be used alone, or two or more can be combined in any combination and proportion.

[0228] The obtained slurry is coated onto the aforementioned negative electrode current collector and dried. Then, a negative electrode active material layer is formed by pressing, thereby obtaining the negative electrode. There are no particular limitations on the coating method; any known method can be used. There are also no particular limitations on the drying method; known methods such as natural drying, heat drying, and reduced pressure drying can be used.

[0229] <Electrode density>

[0230] There are no particular restrictions on the electrode structure when the negative electrode active material is polarized, but the density of the negative electrode active material present on the current collector is preferably 1 g·cm³. -3 The above, and more preferably 1.2 g·cm -3 The above, and especially preferred, is 1.3 g·cm³. -3 In addition, the preferred value is 2.2 g·cm³. -3 The following, and more preferably, is 2.1 g·cm⁻¹ -3 The following, and more preferably 2.0 g·cm -3 The following, and particularly preferred, is 1.9 g·cm³. -3The following applies: When the density of the negative electrode active material on the current collector exceeds the above range, it may cause damage to the negative electrode active material particles, leading to an increase in the initial irreversible capacity of the non-aqueous electrolyte secondary battery, or a deterioration in high-current-density charge-discharge characteristics due to a decrease in the permeability of the non-aqueous electrolyte near the current collector / negative electrode active material interface. Conversely, when the density is below the above range, it may lead to a decrease in the conductivity between the negative electrode active materials, an increase in battery resistance, and a decrease in capacity per unit volume.

[0231] <Conductive Materials>

[0232] As a conductive material, any known conductive material can be used. Specific examples include metallic materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; and carbonaceous materials such as amorphous carbon such as needle coke. It should be noted that these conductive materials can be used individually, or in any combination and ratio of two or more.

[0233] The content of conductive material in the positive electrode active material layer is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more. Furthermore, it is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 15% by mass or less. When the content is within the above range, conductivity can be sufficiently ensured. Furthermore, it is also easy to prevent a decrease in battery capacity.

[0234] <Adhesive>

[0235] There are no special restrictions on the binder used in manufacturing the positive electrode active material layer, as long as it is a material that is stable relative to the non-aqueous electrolyte and the solvent used in manufacturing the electrode.

[0236] When using a coating method, there are no special limitations on materials that can be dissolved or dispersed in the liquid medium used in manufacturing the electrode. Specific examples include: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as SBR (styrene-butadiene rubber), NBR (nitrile rubber), fluororubber, isoprene rubber, butadiene rubber, and ethylene propylene rubber; styrene-butadiene-styrene block copolymers or their hydrogenated products, and EPDM (ethylene-propylene rubber). Thermoplastic elastomers such as styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers, or their hydrogenated products; soft resin-like polymers such as syndiotactic 1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with ionic conductivity of alkali metal ions (especially lithium ions). It should be noted that any one of the above substances may be used alone, or two or more may be combined in any combination and proportion.

[0237] The binder content in the positive electrode active material layer is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more. It is also preferably 80% by mass or less, more preferably 60% by mass or less, even more preferably 40% by mass or less, and particularly preferably 10% by mass or less. When the binder ratio is within the above range, the positive electrode active material can be sufficiently maintained, ensuring the mechanical strength of the positive electrode, thus resulting in good battery performance such as cycle characteristics. Furthermore, it also prevents a decrease in battery capacity and conductivity.

[0238] <Liquid Medium>

[0239] The liquid medium used in the preparation of the slurry for forming the positive electrode active material layer can be any solvent that can dissolve or disperse the positive electrode active material, conductive material, binder, and thickener used as needed. There are no special restrictions on its type, and any solvent among aqueous solvents and organic solvents can be used.

[0240] Examples of aqueous media include water and mixtures of alcohol and water. Examples of organic media include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and polar aprotic solvents such as hexamethylphosphoramide and dimethyl sulfoxide. It should be noted that these solvents can be used alone or in any combination and proportion.

[0241] <Tackifier>

[0242] When using an aqueous medium as the liquid medium for forming the slurry, it is preferable to use a tackifier and a latex such as styrene-butadiene rubber (SBR) for slurry preparation. Tackifiers are typically used to adjust the viscosity of the slurry.

[0243] There are no limitations on the type of thickener used, provided it does not significantly affect the effectiveness of the invention. Specific examples include: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts. These thickeners can be used alone or in any combination and ratio of two or more.

[0244] When using a thickener, the proportion of the thickener relative to the positive electrode active material is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.6% by mass or more. It is also preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less. Within these ranges, the coatability becomes good, and consequently, the proportion of active material in the positive electrode active material layer becomes sufficient, thus easily avoiding problems such as reduced battery capacity and increased resistance between positive electrode active materials.

[0245] <Compaction>

[0246] To increase the filling density of the positive electrode active material, it is preferable to use a manual press or roller press to compact the positive electrode active material layer obtained by coating and drying the slurry on the current collector. The preferred density of the positive electrode active material layer is 1 g·cm³. -3 The above, and more preferably 1.5 g·cm -3 The above, especially preferred, is 2g·cm -3 In addition, the preferred concentration is 4g·cm³. -3 The following, and more preferably, is 3.5 g·cm³. -3 The following, especially preferred, is 3g·cm -3the following.

[0247] When the density of the positive electrode active material layer is within the above range, the permeability of the non-aqueous electrolyte near the current collector / active material interface will not decrease, and the charge-discharge characteristics at high current densities will be particularly good. Furthermore, the conductivity between active materials is less likely to decrease, and the battery resistance is less likely to increase.

[0248] <Current Collector>

[0249] There are no special restrictions on the material used for the positive current collector; any known material can be used. Specific examples include: metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbonaceous materials such as carbon cloth and carbon paper. Among these, metallic materials are preferred, with aluminum being particularly preferred.

[0250] Regarding the shape of the current collector, for metallic materials, examples include metal foil, metal cylinder, metal coil, metal plate, metal film, expanded alloy, perforated metal, and foamed metal; for carbonaceous materials, examples include carbon plate, carbon film, and carbon cylinder. Among these, metal film is preferred. It should be noted that the film can also be appropriately formed into a mesh.

[0251] The current collector can have any thickness, but is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. It is also preferably 1 mm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. When the thickness of the current collector is within the above range, it can sufficiently provide the strength required for the current collector. Furthermore, operability is also improved.

[0252] There is no particular limitation on the ratio of the thickness of the current collector to the thickness of the positive electrode active material layer. The ratio of (thickness of the active material layer on one side before the non-aqueous electrolyte is injected) to (thickness of the current collector) is preferably 150 or less, more preferably 20 or less, particularly preferably 10 or less, and preferably 0.1 or more, more preferably 0.4 or more, particularly preferably 1 or more.

[0253] When the thickness ratio of the current collector to the positive electrode active material layer is within the above-mentioned range, the current collector is less likely to generate heat due to Joule heating during high current density charging and discharging. Furthermore, the volume ratio of the current collector to the positive electrode active material is less likely to increase, which can prevent a decrease in battery capacity.

[0254] <Electrode Area>

[0255] From the viewpoint of high output and improved stability at high temperatures, it is preferable that the area of ​​the positive electrode active material layer is larger than the outer surface area of ​​the battery casing. Specifically, the sum of the positive electrode areas is preferably 20 times or more, and more preferably 40 times or more, relative to the surface area of ​​the non-aqueous electrolyte secondary battery casing. The outer surface area of ​​the casing refers to: for a square shape with a base, the total area calculated from the longitudinal, transverse, and thickness dimensions of the casing portion containing the power generation element, excluding the terminal protrusions; for a cylindrical shape with a base, the geometric surface area calculated by approximating the casing portion containing the power generation element as a cylinder, excluding the terminal protrusions. The sum of the positive electrode areas is the geometric surface area of ​​the positive electrode composite material layer opposite to the direction of the composite material layer containing the negative electrode active material; for a structure in which positive electrode composite material layers are formed on both sides with a current collector foil in between, it refers to the sum of the areas calculated from each side separately.

[0256] <Discharge Capacity>

[0257] When using the aforementioned non-aqueous electrolyte, the improved low-temperature discharge characteristics are more pronounced when the capacity (capacity at which the battery is discharged from a fully charged state to a discharged state) of the battery element housed in the non-aqueous electrolyte secondary battery is 1 ampere-hour (Ah) or more. Therefore, the positive electrode plate is designed such that the discharge capacity is at least 3 Ah (ampere-hours) at full charge, more preferably 4 Ah or more, and preferably 100 Ah or less, more preferably 70 Ah or less, and particularly preferably 50 Ah or less.

[0258] Within the aforementioned range, the voltage drop caused by electrode reaction resistance during high current output will not become excessive, preventing power efficiency degradation. Furthermore, the temperature distribution will not become excessive due to internal battery heating during pulse charging and discharging, avoiding durability degradation from repeated charging and discharging, and preventing a decrease in heat dissipation efficiency due to rapid heating during abnormalities such as overcharging or internal short circuits.

[0259] <Thickness of the positive electrode plate>

[0260] The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity, high output and high speed characteristics, the thickness of the positive electrode active material layer after subtracting the thickness of the current collector is preferably 10 μm or more, more preferably 20 μm or more, and preferably 200 μm or less, more preferably 100 μm or less, relative to one side of the current collector.

[0261] <2-5. Partition>

[0262] To prevent short circuits, a separator is typically sandwiched between the positive and negative electrodes. In this case, the non-aqueous electrolyte of this embodiment is usually impregnated within the separator.

[0263] There are no special restrictions on the material or shape of the separator, and any known separator can be used as long as it does not significantly impair the effect of the present invention. Among them, resins, glass fibers, inorganic materials, etc., formed from materials that are stable to the non-aqueous electrolyte of this embodiment can be used, and porous sheet or non-woven fabric-like materials with excellent liquid retention properties are preferred.

[0264] Materials used as resin or fiberglass separators include, for example, polyethylene, polyolefins such as polypropylene, polytetrafluoroethylene, polyethersulfone, and glass filter sheets. Glass filter sheets and polyolefins are preferred, and polyolefins are even more preferred. These materials can be used individually or in any combination and ratio of two or more.

[0265] The thickness of the separator described above is arbitrary, but it is typically 1 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and typically 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. If the separator is too thin compared to the above range, it may lead to a decrease in insulation and mechanical strength. Conversely, if it is too thick compared to the above range, it may not only lead to a decrease in battery performance such as rate characteristics, but also to a decrease in the overall energy density of the non-aqueous electrolyte secondary battery.

[0266] Furthermore, when using porous materials such as porous sheets or nonwoven fabrics as separators, the porosity of the separator is arbitrary, but it is typically 20% or more, preferably 35% or more, more preferably 45% or more, and typically 90% or less, preferably 85% or less, more preferably 75% or less. If the porosity is too small compared to the above ranges, there is a tendency for the membrane resistance to increase, leading to a deterioration in rate characteristics. Conversely, if the porosity is too large compared to the above ranges, there is a tendency for the mechanical strength of the separator to decrease and its insulation to deteriorate.

[0267] Furthermore, the average pore size of the separator is arbitrary, but it is typically 0.5 μm or less, preferably 0.2 μm or less, and usually 0.05 μm or more. When the average pore size exceeds this range, short circuits are more likely to occur. Conversely, when it is below this range, it may lead to increased film resistance and decreased rate characteristics.

[0268] On the other hand, as inorganic materials, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate can be used. Materials in particle or fiber shape can be used.

[0269] As its form, it can be made of thin film materials such as non-woven fabric, woven fabric, or microporous membrane. Among the thin film shapes, films with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm are preferred. In addition to the above-mentioned independent thin film shapes, the following separators can also be used: separators formed by using a resin-based binder to form a composite porous layer containing the aforementioned inorganic particles on the surface of the positive and / or negative electrodes. For example, a porous layer can be formed on both sides of the positive electrode using a fluororesin binder, in which 90% of the particles are alumina particles with a particle size of less than 1 μm.

[0270] <2-6. Battery Design>

[0271] [Electrode Set]

[0272] The electrode assembly can be any structure, either a stacked structure formed by separating the positive and negative electrode plates with the separator, or a structure obtained by winding the positive and negative electrode plates into a spiral shape with the separator. The proportion of the electrode assembly volume in the battery's internal volume (hereinafter referred to as the electrode assembly occupancy rate) is typically 40% or more, preferably 50% or more, and typically 90% or less, preferably 80% or less. From the viewpoint of battery capacity, it is preferable that the lower limit of the electrode assembly occupancy rate is within the aforementioned range. Furthermore, from the viewpoint of battery performance under repeated charge / discharge cycles, high-temperature storage, and other characteristics, and from the viewpoint of preventing the operation of the gas release valve to avoid releasing internal pressure to the outside, it is preferable that the upper limit of the electrode assembly occupancy rate is within the aforementioned range to ensure sufficient clearance space. If the clearance space is too small, the internal pressure may increase due to the battery being at high temperatures, causing component expansion or an increase in the vapor pressure of the electrolyte liquid components. This leads to a decrease in battery performance under repeated charge / discharge cycles, high-temperature storage, and other characteristics. Furthermore, it may sometimes be necessary for the gas release valve to operate to release internal pressure to the outside.

[0273] [Cell current collector structure]

[0274] There are no particular limitations on the current collector structure, but in order to more effectively realize the improvement in discharge characteristics caused by the aforementioned non-aqueous electrolyte, it is preferable to manufacture a structure that reduces the resistance of the wiring and bonding portions. When the internal resistance is reduced in this way, the effects of using the aforementioned non-aqueous electrolyte can be particularly well utilized.

[0275] When the electrode assembly has the aforementioned stacked structure, it is preferable to use a structure formed by bundling the metal core portions of each electrode layer together and welding them to terminals. Since the internal resistance increases as the area of ​​a single electrode increases, it is also preferable to use a method of providing multiple terminals within the electrode to reduce resistance. When the electrode assembly has the aforementioned wound structure, the internal resistance can be reduced by providing multiple lead structures on the positive and negative electrodes respectively and bundling them to terminals.

[0276] [Protective Components]

[0277] Examples of protective components include PTCs (Positive Temperature Coefficients) that increase resistance when abnormally heated or when excessive current flows, temperature fuses, thermistors, and valves (current cut-off valves) that cut off the current flowing through the circuit by causing a rapid increase in the internal pressure and temperature of the battery when abnormally heated. Preferably, these protective components are those that do not operate under conditions of normal high-current use. From a high-output perspective, it is even more preferable to design them in a way that prevents abnormal heating and thermal runaway even without protective components.

[0278] [Exterior body]

[0279] The non-aqueous electrolyte secondary battery of this embodiment is typically constructed by housing the aforementioned non-aqueous electrolyte, negative electrode, positive electrode, separator, etc., within an outer casing (outer housing). There are no limitations on this outer casing; any known outer casing may be used as long as it does not significantly impair the effects of the present invention.

[0280] There are no special restrictions on the material of the outer casing, as long as it is a stable substance relative to the non-aqueous electrolyte used. Specifically, the following are preferred materials: nickel-plated steel sheet, stainless steel, aluminum or aluminum alloy, magnesium alloy, nickel, titanium and other metals, or laminated films of resin and aluminum foil.

[0281] Among the metal casings used above, examples include casings with the following structures: a sealed encapsulation structure formed by fusing metals together using laser welding, resistance welding, or ultrasonic welding; or a riveted structure formed by using the aforementioned metals with a resin gasket in between. Among the laminated casings used above, examples include sealed encapsulation structures formed by thermally fusing resin layers together. To improve sealing, a resin different from the resin used in the laminate can be sandwiched between the resin layers. In particular, when a sealed structure is formed by thermally fusing resin layers via current collectors, due to the bonding between the metal and resin, it is preferable to use a resin with polar groups or a modified resin with introduced polar groups as the resin sandwiched between the resin layers.

[0282] In addition, the shape of the outer casing is arbitrary, and can be any shape such as cylindrical, square, laminated, coin-shaped, large, etc.

[0283] <2-7. Battery break-in operation>

[0284] [Initial charge]

[0285] The non-aqueous electrolyte secondary battery prepared as described above is subjected to its first charge. As charging conditions, the upper limit voltage is preferably 3.5 to 4.4V. At voltages below 3.5V, there is a tendency to not sufficiently obtain the effect of improving discharge capacity; furthermore, at voltages above 4.4V, lithium deposition at the negative electrode may occur, leading to a decrease in capacity. The charging current is preferably in the range of 2C or less. At currents above 2C (1C represents the current value required for 1 hour of charging or discharging, the same below), there is a tendency to not sufficiently obtain the effect of improving the discharge current. Furthermore, if the time from the end of assembly of the non-aqueous electrolyte secondary battery to the start of the first charge becomes longer, it will lead to a decrease in productivity; therefore, it is preferable to perform the first charge within 5 days.

[0286] Here, in the embodiments of the present invention, the initial charge is performed in a temperature environment above room temperature, specifically in a temperature range of 25°C to 60°C. By performing the initial charge in a temperature range of 25°C to 60°C, the discharge capacity can be further improved. At temperatures below 25°C, there is a tendency that the effect of improving discharge capacity cannot be sufficiently obtained; furthermore, at temperatures above 60°C, the negative electrode may sometimes dissolve in the film, leading to a decrease in initial characteristics. Therefore, by performing the initial charge in a temperature range of 25°C to 60°C, the initial characteristics of the non-aqueous electrolyte secondary battery become excellent.

[0287] Storage in high-temperature environments (aging process)

[0288] As described above, non-aqueous electrolyte secondary batteries that have undergone initial charging are stored in a high-temperature environment (hereinafter sometimes referred to as "aging treatment (process)"). As storage conditions in a high-temperature environment, the battery voltage is preferably 3.5V or higher, more preferably 3.55V or higher, and particularly preferably 3.6V or higher. On the other hand, the upper limit is preferably 4.4V or lower, more preferably 4.3V or lower, and particularly preferably 4.2V or lower. At voltages below 3.5V, no reduction reaction occurs on the negative electrode surface, so the effect of improving initial characteristics may not be sufficiently obtained. Furthermore, since battery voltage is related to the state of charge (SOC), SOC can also be used instead of battery voltage as a storage condition in a high-temperature environment. SOC can be determined based on the battery voltage using the charge-discharge curve of a non-aqueous electrolyte secondary battery; for example, SOC is preferably 17% or higher, more preferably 22% or higher, and particularly preferably 30% or higher. On the other hand, the upper limit is preferably 98% or lower, more preferably 96% or lower, and particularly preferably 95% or lower. When the concentration is below 17%, no reduction reaction occurs on the negative electrode surface, so the effect of improving initial characteristics is sometimes insufficient. When the concentration is above 98%, an excessive film forms on the negative electrode surface, which sometimes leads to increased resistance and decreased battery output. The storage time in a high-temperature environment is preferably 12 hours or more, more preferably 14 hours or more, and particularly preferably 16 hours or more. On the other hand, the upper limit is preferably 200 hours or less, more preferably 150 hours or less, and particularly preferably 100 hours or less. When the storage time is less than 12 hours, a reduction reaction does not occur sufficiently on the negative electrode surface, so the effect of improving initial characteristics is sometimes insufficient. When the storage time is longer than 200 hours, an excessive film forms on the negative electrode surface, which tends to lead to increased resistance and decreased battery output. The storage temperature in a high-temperature environment is preferably 50°C or more, more preferably 55°C or more, and particularly preferably 60°C or more, as a lower limit. On the other hand, the upper limit is preferably 80°C or less, more preferably 75°C or less, and particularly preferably 70°C or less. Below 50°C, the reduction reaction of the electrolyte on the negative electrode surface becomes uneven, resulting in variations in the amount of film formed on the negative electrode surface, leading to areas with both abundant and sparse film. Under such conditions, during the aforementioned input / output tests, the areas with abundant film exhibit higher resistance, sometimes causing a decrease in battery output. Above 80°C, there is a tendency for the negative electrode film formed during the initial charge to dissolve, resulting in a decrease in initial characteristics. Therefore, by storing the battery within the above-mentioned temperature range, the reduction reaction of the electrolyte on the negative electrode surface occurs uniformly, forming a uniform film on the negative electrode surface, thus resulting in excellent initial characteristics of the non-aqueous electrolyte secondary battery.

[0289] The voltage change of the battery when stored in a high-temperature environment, particularly the voltage change after 24 hours of storage in a high-temperature environment above 50°C, preferably above 60°C and below 80°C, is preferably 33mV or more, more preferably 35mV or more, and especially preferably 40mV or more. On the other hand, the upper limit is preferably 100mV or less, more preferably 75mV or less, and especially preferably 50mV or less. When the voltage is less than 33mV, the reduction reaction will not occur sufficiently on the surface of the negative electrode, so sometimes the effect of improving the initial characteristics cannot be fully obtained. When the voltage is greater than 100mV, an excessive film will form on the surface of the negative electrode, which may sometimes lead to increased resistance and reduced battery output.

[0290] To enhance the coating on the negative electrode surface, non-aqueous electrolyte secondary batteries that have completed their break-in operation can also be stored in high-temperature environments multiple times.

[0291] Example

[0292] The present invention will now be described in more detail with reference to embodiments and examples, but the present invention is not limited to these embodiments without departing from its essential points.

[0293] <Examples 1-1 to 1-4, Comparative Examples 1-1 to 1-8>

[0294] [Making the negative electrode]

[0295] A slurry was prepared by mixing 98 parts by weight of natural graphite with 1 part by weight of an aqueous dispersion of sodium carboxymethyl cellulose (1% by weight) as a thickener and binder, and 1 part by weight of an aqueous dispersion of styrene-butadiene rubber (50% by weight). The slurry was then coated onto one side of a 10 μm thick copper foil, dried, and pressed to obtain a negative electrode.

[0296] [The production of the positive electrode]

[0297] The positive electrode, Li(Ni), will be used as the positive electrode active material. 1 / 3 Mn 1 / 3 Co 1 / 3 A slurry was prepared by mixing 85 parts by weight of O2, 10 parts by weight of acetylene black as a conductive material, and 5 parts by weight of polyvinylidene fluoride (PVdF) as a binder in N-methylpyrrolidone solvent using a disperser. The slurry was uniformly coated on one side of an aluminum foil with a thickness of 15 μm and dried before being pressed to obtain a positive electrode.

[0298] [Preparation of non-aqueous electrolytes]

[0299] In a dry argon atmosphere, dry LiPF6 was dissolved in a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (volume ratio 30:35:35) at a concentration of 1.1 mol / L to prepare basic electrolyte 1. FSO3Li, LiPO2F2, and LiBOB were added to the basic electrolyte 1 prepared above to prepare the non-aqueous electrolytes listed in Table 1 below. The concentrations of fluorosulfonic acid ions are indicated in parentheses in the table [FSO3Li]. - The concentration of difluorophosphate ions [PO2F2] - The concentrations of oxalate and borate ions [BOB] - ].

[0300] Manufacturing of non-aqueous electrolyte secondary batteries

[0301] A battery element was fabricated by sequentially stacking the above-mentioned positive electrode, negative electrode, and polyethylene separator in the order of negative electrode, separator, and positive electrode. With the positive and negative electrode terminals protruding, the battery element was inserted into a bag made of a laminated film, and then the prepared non-aqueous electrolyte was injected into the bag. The bag was then vacuum-sealed to fabricate a laminated non-aqueous electrolyte secondary battery. The laminated film was obtained by coating both sides of aluminum (40 μm thick) with a resin layer.

[0302] [Battery break-in period]

[0303] To improve the adhesion between electrodes, the non-aqueous electrolyte secondary battery was clamped between glass plates and charged in a constant-current-constant-voltage (CC-CV) bath at 25°C to 4.2V at a current equivalent to 1 / 6C, then discharged at 1 / 6C to 2.5V. It was then CC-CV charged at 1 / 6C to 4.1V. Aging treatment was then performed at 60°C for 24 hours, or at 45°C for 24 hours. The battery was then discharged at 1 / 6C to 2.5V to stabilize it. Furthermore, a break-in period was conducted by CC-CV charging at 1 / 6C to 4.2V, followed by discharging at 1 / 6C to 2.5V.

[0304] In this embodiment, in order to investigate in detail the impact of the storage temperature during the aging process on the initial output characteristics of the battery after the break-in operation, the initial output characteristics of batteries that underwent break-in operation at two different storage temperatures were compared and evaluated. In addition, after the aging process, the composition of the non-aqueous electrolyte used in the solution preparation was confirmed to satisfy formula (1) based on the results of ion chromatography.

[0305] [Evaluation of initial output characteristics]

[0306] After the battery break-in period evaluation, the battery was charged to 3.72V at a constant current of 1 / 6C at 25°C. It was then discharged at -20°C at 0.5C, 1.0C, 1.5C, 2.0C, and 2.5C, and its voltage was measured after 5 seconds. The resistance value (Ω) was calculated based on the slope of the current-voltage line. Table 1 shows the relative values ​​(%) of the resistance values ​​(reference resistance value) when aging treatment was performed at 60°C for 24 hours in Example 1-1, with 100.0 as the reference resistance value. It should be noted that, in this example, from a practical point of view, a resistance value below the reference resistance value when aging treatment was performed at 60°C for 24 hours is considered acceptable.

[0307] [Table 1]

[0308]

[0309] As shown in Table 1, the embodiments satisfying the relationship [FSO3-]>[PO2F2-]>[BOB-] exhibit excellent initial output characteristics. Furthermore, it is observed that at a storage temperature of 45°C, the change in battery voltage before and after storage is less than 33mV, while at a storage temperature of 60°C, the change in battery voltage before and after storage is greater than 33mV. Additionally, compared to the cases satisfying the relationship [FSO3-]>[PO2F2-]>[BOB-] and a storage temperature of 60°C (the storage temperature for Examples 1-1 to 1-4 is 60°C), the initial output characteristics are reduced in the cases satisfying the relationship [FSO3-]>[PO2F2-]>[BOB-] and a storage temperature of 45°C (the storage temperature for Examples 1-1 to 1-4 is 45°C).

[0310] Furthermore, it can be seen that, compared to the case where the relationship [FSO3-]>[PO2F2-]>[BOB-] is satisfied and the storage temperature is 60°C (the storage temperature in Examples 1-1 to 1-4 is 60°C), the situation where [FSO3-]>[PO2F2-] does not satisfy the condition... - ]>[BOB - In the case of the relationship between […] (Comparative Examples 1-1 to 1-8), the initial output characteristics decreased regardless of the storage temperature. Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-8 show that by using FSO3… - PO2F2 - and BOB - The content of the non-aqueous electrolyte is within a specific range, and the voltage change when stored in a high-temperature environment is above 33mV, which can improve the output characteristics of the non-aqueous electrolyte secondary battery in a low-temperature environment.

[0311] <Examples 2-1 to 2-4, Comparative Examples 2-1 to 2-7>

[0312] [Making the negative electrode]

[0313] The negative electrode was fabricated using the same method as in Example 1-1, except that a slurry containing the negative electrode active material was coated on both sides of the copper foil.

[0314] [The production of the positive electrode]

[0315] Li(Ni)2, used as the positive electrode active material, was dispersed using a disperser. 0.5 Mn 0.3 Co 0.2 A slurry was prepared by mixing 90 parts by weight of O2, 7 parts by weight of acetylene black as a conductive material, and 3 parts by weight of polyvinylidene fluoride (PVdF) as a binder in N-methylpyrrolidone solvent. This slurry was then uniformly coated onto one side of a 15 μm thick aluminum foil, dried, and pressed to form a positive electrode.

[0316] [Preparation of non-aqueous electrolytes]

[0317] The non-aqueous electrolytes described in Table 2 below were prepared using the same method as in Examples 1-1, etc. The concentrations of fluorosulfonic acid ions [FSO3] are shown in parentheses in the table. - The concentration of difluorophosphate ions [PO2F2] - The concentrations of oxalate and borate ions [BOB] - ].

[0318] Manufacturing of non-aqueous electrolyte secondary batteries

[0319] A non-aqueous electrolyte secondary battery was fabricated using the same method as in Examples 1-1, etc.

[0320] [Battery break-in period]

[0321] The battery break-in operation was performed using the same method as in Examples 1-1. After the aging process, the composition of the non-aqueous electrolyte used in the preparation of the liquid was also confirmed to satisfy formula (1) based on the results of ion chromatography.

[0322] [Evaluation of initial output characteristics]

[0323] After the battery break-in period evaluation, the battery was charged to 3.72V at a constant current of 1 / 6C at 25°C. It was then discharged at -20°C at 0.5C, 1.0C, 1.5C, 2.0C, and 2.5C, and its voltage was measured after 5 seconds. The resistance value (Ω) was calculated based on the slope of the current-voltage line. Table 2 shows the relative values ​​(%) of the resistance values ​​(reference resistance value) when aging treatment was performed at 60°C for 24 hours in Example 2-1, with 100.0 as the reference resistance value. It should be noted that, in this example, from a practical point of view, a resistance value below the reference resistance value when aging treatment was performed at 60°C for 24 hours is considered acceptable.

[0324] [Table 2]

[0325]

[0326] As shown in Table 2, the embodiments satisfying the relationship [FSO3-]>[PO2F2-]>[BOB-] exhibit excellent initial output characteristics. Furthermore, it is observed that at a storage temperature of 45°C, the change in battery voltage before and after storage is less than 33mV, while at a storage temperature of 60°C, the change in battery voltage before and after storage is greater than 33mV. Additionally, compared to the cases satisfying the relationship [FSO3-]>[PO2F2-]>[BOB-] and a storage temperature of 60°C (the storage temperature in Examples 2-1 to 2-4 is 60°C), the initial output characteristics are reduced in the cases satisfying the relationship [FSO3-]>[PO2F2-]>[BOB-] and a storage temperature of 45°C (the storage temperature in Examples 2-1 to 2-4 is 45°C).

[0327] Furthermore, it was found that, compared to the case where the relationship [FSO3-]>[PO2F2-]>[BOB-] is satisfied and the storage temperature is 60°C (the storage temperature in Examples 2-1 to 2-4 is 60°C), the initial output characteristics decrease regardless of the storage temperature when the relationship [FSO3-]>[PO2F2-]>[BOB-] is not satisfied (Comparative Examples 2-1 to 2-7). Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-7 show that by using a non-aqueous electrolyte with FSO3-, PO2F2-, and BOB- contents within a specific range, and with a voltage change of 33mV or more when stored in a high-temperature environment, the output characteristics of the non-aqueous electrolyte secondary battery in a low-temperature environment can be improved.

[0328] <Examples 3-1 to 3-4, Comparative Examples 3-1 to 3-4>

[0329] [Making the negative electrode]

[0330] The negative electrode was fabricated using the same method as in Example 1-1.

[0331] [The production of the positive electrode]

[0332] The positive electrode was prepared using the same method as in Example 1-1.

[0333] [Preparation of non-aqueous electrolytes]

[0334] In a dry argon atmosphere, aluminum fluorosulfonate (Al(FSO3)3) was diluted with EC, EMC, and DMC to achieve the aluminum ion concentrations shown in Table 3, and the solvent composition was such that the volume ratio of ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC) was 30:35:35. Sufficiently dried LiPF6 was dissolved at 1.1 mol / L (based on the concentration in the non-aqueous electrolyte) to prepare basic electrolyte 2. FSO3Li, LiPO2F2, and LiBOB were added to the above-prepared basic electrolyte 2 to prepare the non-aqueous electrolytes described in Table 3 below. The concentrations of fluorosulfonate ions [FSO3] are shown in parentheses in the table. - The concentration of difluorophosphate ions [PO2F2] - The concentrations of oxalate and borate ions [BOB] - ].

[0335] It should be noted that in Table 3, the aluminum element at 0 ppm (excluding aluminum element) refers to the result after adding FSO3 to the above basic electrolyte 1. - PO2F2 - BOB - The non-aqueous electrolytes listed in Table 3 below were prepared. Additionally, in Table 3, FSO3... - PO2F2 - BOB - The content indicates the amount added. The aluminum element (aluminum ion) content is a value obtained based on the results of inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis described later. It should be noted that the "content (mass%)" and "content (mass ppm)" in the table are the contents when basic electrolyte 1 is set to 100% by mass.

[0336] <Determination of Aluminum Content in Non-Aqueous Electrolytes>

[0337] A 100 μL (approximately 130 mg) fraction of the non-aqueous electrolyte was taken. The fraction was weighed into a PTFE beaker, and an appropriate amount of concentrated nitric acid was added. After wet decomposition on a hot plate, the volume was adjusted to 50 mL. The aluminum content was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES, Thermo Fischer Scientific, iCAP 7600duo) via a Li and acid concentration matching calibration curve method.

[0338] Manufacturing of non-aqueous electrolyte secondary batteries

[0339] A battery element was fabricated by sequentially stacking the above-mentioned positive electrode, negative electrode, and polyethylene separator in the order of negative electrode, separator, and positive electrode. This battery element was then inserted into a bag made of a laminated film, with the terminals of the positive and negative electrodes protruding. The prepared non-aqueous electrolyte was then injected into the bag, followed by vacuum sealing to fabricate a laminated non-aqueous electrolyte secondary battery. The laminated film was obtained by coating both sides of aluminum (40 μm thick) with a resin layer.

[0340] [Battery break-in period]

[0341] The battery break-in operation was performed using the same method as in Examples 1-1. After the aging process, the composition of the non-aqueous electrolyte used in the preparation of the liquid was also confirmed by ion chromatography to satisfy formula (1).

[0342] [Evaluation of initial output characteristics]

[0343] After the battery break-in period evaluation, the battery was charged to 3.72V at a constant current of 1 / 6C at 25°C. It was then discharged at -20°C at 0.5C, 1.0C, 1.5C, 2.0C, and 2.5C, and its voltage was measured after 5 seconds. The resistance value (Ω) was determined based on the slope of the current-voltage line. Table 3 shows the relative values ​​(%) when the resistance value of Example 3-1 containing 19 ppm of aluminum (the reference resistance value) is set to 100.0. It should be noted that, in this example, from a practical point of view, a resistance value below the reference resistance value during aging treatment at 60°C for 24 hours is considered acceptable.

[0344] [Table 3]

[0345]

[0346] As shown in Table 3, compared with the case that satisfies the relationship [FSO3-]>[PO2F2-]>[BOB-] and contains 19 ppm of aluminum (19 ppm by mass of aluminum in Examples 3-1 to 3-4), the initial output characteristics are reduced when the relationship [FSO3-]>[PO2F2-]>[BOB-] is satisfied and aluminum ions are not present (0 ppm by mass of aluminum in Examples 3-1 to 3-4).

[0347] Furthermore, it was found that, compared to the case where the relationship [FSO3-]>[PO2F2-]>[BOB-] was satisfied and the aluminum content was 19 ppm (19 ppm by mass of aluminum in Examples 3-1 to 3-4), the initial output characteristics decreased regardless of the aluminum content in the case where the relationship [FSO3-]>[PO2F2-]>[BOB-] was not satisfied (Comparative Examples 3-1 to 3-4). Examples 3-1 to 3-4 and Comparative Examples 3-1 to 3-4 demonstrate that by using a non-aqueous electrolyte with FSO3-, PO2F2-, and BOB- contents within a specific range, and with the electrolyte containing a given amount of aluminum ions, the output characteristics of the non-aqueous electrolyte secondary battery in a low-temperature environment can be further improved.

[0348] Industrial applicability

[0349] The non-aqueous electrolyte according to embodiments of the present invention enables the manufacture of non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary batteries that improve low-temperature output characteristics, and is therefore useful. Thus, the non-aqueous electrolyte of the present invention and energy devices such as non-aqueous electrolyte secondary batteries using it can be used for a wide variety of known applications. Specific examples include: laptops, pen-based computers, mobile computers, e-book players, mobile phones, portable fax machines, portable copiers, portable printers, surround sound headphones, cameras, LCD TVs, handheld vacuum cleaners, portable CD players, mini disk drives, wireless transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, engines, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, watches, power tools, flashlights, cameras, household backup power supplies, office backup power supplies, load balancing power supplies, natural energy storage power supplies, lithium-ion capacitors, etc.

Claims

1. A non-aqueous electrolyte secondary battery, comprising a non-aqueous electrolyte containing fluorosulfonic acid ions, difluorophosphate ions, and dioxaborate ions, wherein, The non-aqueous electrolyte is defined as the concentration of fluorosulfonic acid ions in the non-aqueous electrolyte, expressed as a percentage by mass [FSO3]. - The concentration of difluorophosphate ions (in mass%) [PO₂F₂] - The concentration of borate ions (by mass%) and dioxalate ions [BOB] - Non-aqueous electrolytes that satisfy the following formula (1) [FSO3 - ]>[PO2F2 - ]>[BOB - ](1), The non-aqueous electrolyte secondary battery was subjected to an aging process in a temperature environment ranging from 50°C to 80°C.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The non-aqueous electrolyte is a non-aqueous electrolyte that satisfies the following equations (2) and (3). ([FSO3 - ]+[PO2F2 - ]) / ([PO2F2 - ]+[BOB - ])>1.8(2) [FSO3 - <1.3% of mass (3).

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The voltage change of the non-aqueous electrolyte secondary battery was greater than 33mV when it was stored in a high-temperature environment above 60°C for 24 hours at a voltage of 4.1V.

4. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The non-aqueous electrolyte contains aluminum ions at a concentration of more than 1 ppm by mass and less than 100 ppm by mass.

5. The non-aqueous electrolyte secondary battery according to claim 1 or 2, comprising a negative electrode and a positive electrode capable of absorbing / releasing lithium ions.

6. The non-aqueous electrolyte secondary battery according to claim 5, wherein, The positive electrode has a current collector and a positive electrode active material layer disposed on the current collector, wherein the positive electrode active material layer contains at least one selected from lithium / cobalt composite oxide, lithium / cobalt / nickel composite oxide, lithium / manganese composite oxide, lithium / cobalt / manganese composite oxide, lithium / nickel composite oxide, lithium / nickel / manganese composite oxide, and lithium / cobalt / nickel / manganese composite oxide.

7. A method for manufacturing a non-aqueous electrolyte secondary battery, wherein the non-aqueous electrolyte secondary battery comprises a non-aqueous electrolyte containing fluorosulfonic acid ions, difluorophosphate ions, and dioxaborate ions. The manufacturing method includes: In the battery assembly process of assembling a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte, the concentration of fluorosulfonic acid ions in the non-aqueous electrolyte, expressed as a percentage by mass [FSO3], is... - The concentration of difluorophosphate ions (in mass%) [PO₂F₂] - The concentration of borate ions (by mass%) and dioxalate ions [BOB] - Satisfy the following equation (1); and The aging process involves aging the non-aqueous electrolyte secondary battery in a temperature range of 50°C to 80°C. [FSO3 - ]>[PO2F2 - ]>[BOB - ](1)。

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