Non-aqueous secondary batteries

Abstract

A nonaqueous secondary battery comprising: a positive electrode that includes a lithium-and-transition-metal composite oxide including at least nickel as a transition metal; a negative electrode that includes a silicon-containing material; a separator that is interposed between the positive electrode and the negative electrode; and an electrolyte, wherein the electrolyte includes a sultone compound and a nitrile compound, and 1≤A / B≤10 is satisfied where the sultone compound concentration in the electrolyte is A mass% and the nitrile compound concentration in the electrolyte is B mass%.

Description

[Technical Field]

[0001] This disclosure relates to a non-aqueous secondary battery. [Background technology]

[0002] Patent Document 1 proposes an electrolyte for lithium secondary batteries comprising a lithium salt, a non-aqueous organic solvent, an additive containing fluoroethylene carbonate, vinyl-containing carbonate, substituted or unsubstituted C2-C10 cyclic sulfate esters, and a dinitrile compound, wherein the vinyl-containing carbonate includes vinylene carbonate, vinylethylene carbonate, or a combination thereof, and the cyclic sulfate ester includes 1,3-propanesultone, 1,3-propanediol cyclic sulfate ester, or a combination thereof.

[0003] Patent Document 2 proposes a non-aqueous electrolyte comprising a lithium salt and a non-aqueous solvent for dissolving it, characterized in that the non-aqueous electrolyte contains a predetermined carbonate compound and further contains one or more compounds having a cyano group and / or cyclic sulfonic acid ester compounds. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent No. 5414658 (Japanese Unexamined Patent Publication No. 2011-192632) [Patent Document 2] Japanese Patent No. 5664056 (Japanese Unexamined Patent Publication No. 2012-64473) [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In non-aqueous secondary batteries, such as lithium-ion batteries, research is underway to use lithium transition metal composite oxides containing nickel (Ni) as the positive electrode in order to increase its capacity. While cobalt (Co) was conventionally used as the transition metal, in recent years, efforts have been made to increase the proportion of Ni in the transition metal and reduce the proportion of expensive Co, thereby increasing the capacity and lowering the cost of the positive electrode.

[0006] Meanwhile, in order to increase the capacity of the negative electrode, studies are underway to use silicon (Si)-containing materials as the negative electrode. The higher the silicon phase content in the Si-containing material, the more advantageous it is for increasing capacity.

[0007] However, in lithium transition metal composite oxides, increasing the proportion of Ni and decreasing the proportion of Co in the transition metal promotes side reactions involving the reduction of Ni and oxidative decomposition of the electrolyte, which tends to increase gas generation and positive electrode resistance (DCIR).

[0008] In contrast, adding a nitrile compound to the electrolyte tends to suppress side reactions at the positive electrode. However, if the negative electrode contains a Si-containing material, the side reaction between the nitrile compound and the silicon phase is promoted, which tends to increase the negative electrode resistance (DCIR). [Means for solving the problem]

[0009] One aspect of this disclosure relates to a non-aqueous secondary battery comprising a positive electrode containing a lithium transition metal composite oxide containing at least nickel as a transition metal, a negative electrode containing a silicon-containing material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte contains a sultone compound and a nitrile compound, and in the electrolyte, when the concentration of the sultone compound is A by mass and the concentration of the nitrile compound is B by mass, 1 ≤ A / B ≤ 10. [Effects of the Invention]

[0010] According to the present disclosure, even when the positive electrode contains a lithium transition metal composite oxide containing Ni and the negative electrode contains a Si-containing material, an increase in DCIR can be suppressed. The novel features of the present invention are described in the appended claims, but the present invention relates to both the constitution and the content, and will be better understood from the following detailed description in conjunction with the drawings, along with other objects and features of the present invention.

Brief Description of the Drawings

[0011] [Figure 1] It is a perspective view of a non-aqueous secondary battery according to an embodiment of the present disclosure with a part cut away.

Mode for Carrying Out the Invention

[0012] The non-aqueous secondary battery according to the present disclosure includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution. The positive electrode contains a composite oxide N as a positive electrode active material. Here, among lithium transition metal composite oxides, a lithium transition metal composite oxide containing at least nickel as a transition metal is referred to as composite oxide N. On the other hand, the negative electrode contains a silicon-containing material as a negative electrode active material.

[0013] [Electrolytic Solution] The electrolytic solution contains a sultone compound (i.e., a cyclic sulfonic acid ester) and a nitrile compound. If the electrolytic solution does not contain a nitrile compound, side reactions at the positive electrode are significant, and the increase in DCIR and gas generation also become significant. When a nitrile compound is included in the electrolytic solution, side reactions at the positive electrode are suppressed. However, since side reactions at the negative electrode become significant, ultimately DCIR increases. In contrast, when the electrolytic solution further contains a sultone compound, the sultone compound is also decomposed together when the nitrile compound is decomposed. As a result, a high-quality composite film in which decomposition products of the nitrile compound and the sultone compound are complexed is formed on the surface of the Si-containing material. When such a composite film is formed, further decomposition reactions of the nitrile compound and the sultone compound are suppressed.

[0014] However, when the concentration of the sultone compound in the electrolyte is A by mass% and the concentration of the nitrile compound in the electrolyte is B by mass%, it is important that the ratio of A to B (A / B) satisfies 1 ≤ A / B ≤ 10. If the A / B ratio is less than 1, the components derived from the sultone compound will be insufficient in the composite coating, making it difficult to form a high-quality composite coating and increasing DCIR. To form a high-quality composite coating, the content of the nitrile compound in the electrolyte must be greater than or equal to the content of the sultone compound. However, if the A / B ratio exceeds 10, the components derived from the sultone compound will be excessive in the composite coating, making it difficult to form a high-quality composite coating. A composite coating formed with an appropriately controlled A / B ratio has a moderate thickness and a well-balanced composition. In particular, it is desirable that the A / B ratio satisfies 2 ≤ A / B ≤ 5. Such a composite coating contains a moderate amount of components derived from the sultone compound and has excellent Li ion conductivity, so it is less likely to cause an increase in DCIR. The suppression of DCIR increase is particularly noticeable when the State of Charge (SOC) is low.

[0015] In the electrolyte contained in the battery at the beginning of the charge-discharge cycle, or in the electrolyte before it is injected into the battery, the A value, which indicates the concentration (mass%) of the sultone compound, and the B value, which indicates the concentration (mass%) of the nitrile compound, should satisfy, for example, 0.01 ≤ A ≤ 1.5 and 0.01 ≤ B ≤ 1. If A or B is less than 0.01, it may be difficult to obtain a significant effect. On the other hand, if A or B exceeds the upper limit of the above range, the side reactions due to the decomposition of the sultone compound or nitrile compound will proceed excessively, resulting in significant gas generation and difficulty in forming a composite film.

[0016] The value of A can be 0.1 ≤ A ≤ 1.5, 0.2 ≤ A ≤ 1.5, 0.5 ≤ A ≤ 1.5, or 0.5 ≤ A ≤ 1.0.

[0017] The value of B can be 0.01 ≤ B ≤ 0.8, 0.05 ≤ B ≤ 0.7, 0.1 ≤ B ≤ 0.7, or 0.1 ≤ B ≤ 0.5.

[0018] In non-aqueous secondary batteries, the concentrations of sultone and nitrile compounds in the electrolyte may change during storage or charging / discharging. Therefore, it is sufficient that sultone and nitrile compounds remain in the electrolyte sampled from a non-aqueous secondary battery at concentrations above the detection limit. The content of sultone compounds in the electrolyte sampled from a non-aqueous secondary battery may be, for example, 0.0001% by mass or more. The content of nitrile compounds in the electrolyte sampled from a non-aqueous secondary battery may also be, for example, 0.0001% by mass or more. In this case as well, the A / B ratio may satisfy 1 ≤ A / B ≤ 10 (and furthermore, 2 ≤ A / B ≤ 5) as it reflects the initial A and B values.

[0019] The content of sultone compounds and nitrile compounds in non-aqueous electrolytes can be determined, for example, by gas chromatography under the following conditions. Equipment used: Manufactured by Shimadzu Corporation, GC-2010 Plus Column: J&W HP-1 (film thickness 1 μm, inner diameter 0.32 mm, length 60 m) Column temperature: Increase the temperature from 50°C to 90°C at a rate of 5°C / min, maintain at 90°C for 15 minutes, then increase the temperature from 90°C to 250°C at a rate of 10°C / min, maintain at 250°C for 15 minutes. Split ratio: 1 / 50 Linear speed: 30.0cm / sec Inlet temperature: 270℃ Injection volume: 1μL Detector: FID 290℃ (sens.10 1 )

[0020] (Sultone compounds) Sultone compounds are cyclic sulfonic acid esters. Sultone compounds may also be compounds containing a carbon-carbon unsaturated bond (C=C) (hereinafter referred to as unsaturated sultone compounds). The presence of an unsaturated bond further improves the durability of the composite coating. The unsaturated bond may be located within the ring.

[0021] Examples of sultone compounds include those represented by the following general formula (1).

[0022] [ka]

[0023] R in general formula (1) 1 ~R 6 Each of these is independently either a hydrogen atom or a substituent. Substituents include halogen atoms, hydrocarbon groups, hydroxyl groups, amino groups, ester groups, etc.

[0024] Hydrocarbon groups include alkyl groups and alkenyl groups. Alkyl and alkenyl groups may be linear or branched. Alkyl groups include methyl, ethyl, n-propyl, and isopropyl groups. Alkenyl groups include vinyl, 1-propenyl, and 2-propenyl groups. At least one hydrogen atom of a hydrocarbon group may be substituted with a halogen atom.

[0025] From the viewpoint of ensuring good viscosity of the non-aqueous electrolyte and improving the solubility of the solute, the hydrocarbon group is preferably an alkyl group having 1 to 5 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms.

[0026] In general formula (1), n ​​is R 5 and R 6 This indicates the number of repeating methylene groups having R. n is an integer from 1 to 3. If n is 2 or 3, each methylene group has R 5 and R 6 They may be the same as each other, or they may be different.

[0027] Examples of compounds represented by general formula (1) include 1,3-propanesultone (PS), 1,4-butanesultone, 1,5-pentanesultone, 2-fluoro-1,3-propanesultone, 2-fluoro-1,4-butanesultone, and 2-fluoro-1,5-pentanesultone. PS is preferred among these due to its particularly strong interaction with the silicate phase.

[0028] In addition, examples of the sultone compound include compounds (unsaturated sultone compounds) represented by the following general formula (2).

[0029] [Chemical formula]

[0030] R in the general formula (2) 1 , R 4 , R 5 and R 6 , and n are the same as R 1 , R 4 , R 5 and R 6 in the general formula (1), and n.

[0031] Specific examples of the compound represented by the general formula (2) include 1,3-propene sultone (PRES), 1,4-butene sultone, 1,5-pentene sultone, 2-fluoro-1,3-propene sultone, 2-fluoro-1,4-butene sultone, 2-fluoro-1,5-pentene sultone, and the like. From the viewpoint of particularly large interaction with the silicate phase, PRES is particularly preferred. PRES may account for 50% by mass or more, further 70% by mass or more, or 90% by mass or more of the sultone compound in the electrolyte.

[0032] (Nitrile compound) The nitrile compound may be a mononitrile compound having one nitrile group, a dinitrile compound having two nitrile groups, or a nitrile compound having three or more nitrile groups. The number of nitrile groups in the nitrile compound may be 5 or less, or 4 or less. The nitrile compound may be at least one selected from the group consisting of mononitrile compounds and dinitrile compounds having no hydrogen at the α-position of the nitrile group. However, nitrile compounds having three or more nitrile groups tend to increase the viscosity of the electrolyte. Therefore, dinitriles having two nitrile groups are desirable.

[0033] The properties of the composite coating differ depending on the number of nitrile groups in the nitrile compound. Dinitrile compounds form composite coatings with lower resistance than mononitrile compounds and with higher homogeneity than trinitrile compounds. Furthermore, dinitrile compounds have a high ability to form composite coatings even in small amounts and exhibit superior stability within batteries. Mononitrile compounds, which do not have hydrogen at the α-position of the nitrile group, exhibit similar properties.

[0034] The following are specific examples of nitrile compounds, but nitrile compounds are not limited to those listed below. Furthermore, nitrile compounds may be used individually or in any combination of two or more types.

[0035] Specific examples of nitrile compounds include pivalonitrile, malononitrile, succinonitrile, glutalonitrile, adiponitrile, pimelonitrile, suberonitrile, azeranitrile, sebaconitrile, undecanedinitrile, dodecanedinitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, tert-butylmalononitrile, methylsuccinonitrile, 2,2-dimethylsuccinonitrile, and 2,3-dimethylsuccinonitrile. Nonitrile, 2,3,3-trimethylsuccinonitrile, 2,2,3,3-tetramethylsuccinonitrile, 2,3-diethyl-2,3-dimethylsuccinonitrile, 2,2-diethyl-3,3-dimethylsuccinonitrile, bicyclohexyl-1,1-dicarbonitrile, bicyclohexyl-2,2-dicarbonitrile, bicyclohexyl-3,3-dicarbonitrile, 2,5-dimethyl-2,5-hexanedicarbonitrile, 2,3-diisobutyl -2,3-dimethylsuccinonitrile, 2,2-diisobutyl-3,3-dimethylsuccinonitrile, 2-methylglutaronitrile, 2,3-dimethylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,3,3-tetramethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 2,2,3,4-tetramethylglutaronitrile, 2,3,3,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 2,6- Examples include dicyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, 3,3'-(ethylenedioxy)dipropionitrile, 3,3'-(ethylenedithio)dipropionitrile, 3,9-bis(2-cyanoethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane, butanenitrile, phthalonitrile, etc.

[0036] Among them, NC-C m H 2mCompounds represented by -CN (where m is an integer from 1 to 10), compounds having one phenyl group, and mononitrile compounds that do not have hydrogen at the α-position of the nitrile group are readily available. Examples of such compounds include succinonitrile (NC-C2H4-CN), glutalonitrile (NC-C3H6-CN), adiponitrile (NC-C4H8-CN), and pimeronitrile (NC-C5H 10 -CN), Suberonitrile (NC-C6H 12 Examples include nitrile (NC-C6H5-CN), phthalonitrile (NC-C6H5-CN), and pivalonitrile. These may be used individually or in combination of two or more. These compounds may constitute 50% by mass or more, and even 70% by mass or more, or 90% by mass or more, of the nitrile compounds in the electrolyte.

[0037] (Non-aqueous solvent) The electrolyte contains a non-aqueous solvent and an electrolyte salt, in addition to the sultone compound and nitrile compound. Examples of non-aqueous solvents include cyclic carbonate esters, linear carbonate esters, cyclic carboxylic acid esters, and linear carboxylic acid esters. Examples of cyclic carbonate esters include propylene carbonate (PC) and ethylene carbonate (EC). Examples of linear carbonate esters include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of linear carboxylic acid esters include methyl formate, ethyl formate, propyl formate, methyl acetate (MA), ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The electrolyte may contain one non-aqueous solvent or a combination of two or more non-aqueous solvents.

[0038] (Electrolyte salts) Lithium salts are preferred as the electrolyte salt. Examples of lithium salts include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, and LiB 10 Cl 10Examples include lithium lower aliphatic carboxylates, LiCl, LiBr, LiI, borates, and imide salts. Examples of borates include lithium difluorooxalate borate and lithium bisoxalate borate. Examples of imide salts include lithium bisfluorosulfonylimide (LiN(FSO2)2) and lithium bistrifluoromethanesulfonate (LiN(CF3SO2)2). The electrolyte may contain one electrolyte salt or a combination of two or more. The concentration of the electrolyte salt in the electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less.

[0039] The electrolyte may contain other additives. Examples of other additives include at least one selected from the group consisting of vinylene carbonate, fluoroethylene carbonate (FEC), and vinylethylene carbonate. In particular, when the electrolyte contains FEC, a better quality composite film is formed on the surface of the Si-containing material. In the electrolyte, the concentration of FEC may be, for example, 5% by mass or more and 20% by mass or less.

[0040] [Negative electrode] The negative electrode contains a negative electrode active material. The negative electrode typically comprises a negative electrode current collector and a layered negative electrode mixture (hereinafter referred to as the negative electrode mixture layer) held by the negative electrode current collector. The negative electrode mixture layer can be formed by coating the surface of the negative electrode current collector with a negative electrode slurry, which is obtained by dispersing the components of the negative electrode mixture in a dispersion medium, and drying it. The dried coating may be rolled if necessary.

[0041] The negative electrode mixture may contain a negative electrode active material as an essential component, and may also contain binders, thickeners, conductive agents, etc., as optional components.

[0042] (Negative electrode active material) The negative electrode active material includes at least a Si-containing material. The negative electrode active material may further include another material capable of electrochemically intercalating and releasing lithium ions. An example of such a material is a carbonaceous material. The negative electrode may include metallic lithium, lithium alloys, etc. The Si-containing material may contain minute lithium alloy particles when lithium ions are intercalated.

[0043] Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). A single carbonaceous material may be used, or two or more may be used in combination. Among these, graphite is preferred as the carbonaceous material due to its excellent charge-discharge stability and low irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0044] To achieve a good balance between excellent cycle characteristics and high capacity, it is desirable to use both Si-containing materials and carbonaceous materials. The proportion of Si-containing material in the total of Si-containing material and carbonaceous material is, for example, 0.5% by mass or more, but may also be 1% by mass or more, or 2% by mass or more. If improvement of cycle characteristics is given greater importance, the proportion of Si-containing material in the total of Si-containing material and carbonaceous material is, for example, 30% by mass or less, but may also be 20% by mass or less, 15% by mass or less, or 10% by mass or less.

[0045] Examples of Si-containing materials include elemental Si, silicon alloys, silicon compounds, and composite materials containing a lithium-ion conductive phase and a silicon phase dispersed in the lithium-ion conductive phase. As the lithium-ion conductive phase, at least one selected from the group consisting of a silicon oxide phase, a silicate phase, and a carbon phase may be used. Such composite materials are suitable for providing a high capacity to the negative electrode while suppressing direct contact between the silicon phase and the electrolyte. As the Si-containing material, at least one selected from the group consisting of the following first composite material, second composite material, and third composite material may be used.

[0046] <First composite material> The first composite material includes a silicon oxide phase (lithium ion conductive phase) and a silicon phase dispersed in the silicon oxide phase. The first composite material is excellent in terms of high stability and small volume change among Si-containing materials. The high stability is considered to be due to the small size of the silicon phase dispersed in the silicon oxide phase, which makes deep charging difficult to proceed. The silicon oxide phase has a relatively large number of sites that irreversibly trap lithium ions, and thus has a tendency to have a large irreversible capacity among Si-containing materials. The first composite material may have a larger irreversible capacity than the second composite material. The trapping of lithium ions by the silicon oxide phase is considered to enhance the structural stability of the first composite material and also contribute to the suppression of volume change.

[0047] The first composite material can be obtained, for example, by heating silicon oxide in a non-oxidizing atmosphere having an inert gas such as argon and performing a disproportionation reaction. In the disproportionation reaction, Si microcrystals can be uniformly formed in the silicon oxide phase. The size of the Si particles generated by the disproportionation reaction is small. For example, the average particle size can be less than 100 nm, and can also be in the range of 5 nm to 50 nm. The main component (e.g., 95 to 100% by mass) of the silicon oxide phase is silicon dioxide. That is, the first composite material may include a SiO2 phase and a silicon phase dispersed in the SiO2 phase. In this case, the first composite material can be represented by the general formula SiO x The range of the x value may be 0 < x < 2, but may preferably be 0.9 ≤ x ≤ 1.1, or x = 1.

[0048] The average particle size of the first composite material may be 1 to 20 μm, preferably 5 to 12 μm. Within the above particle size range, it is easy to relieve the stress caused by the volume change of the Si-containing material during charge and discharge, and it is easy to obtain good cycle characteristics.

[0049] <The second composite material> The second composite material comprises a silicate phase (lithium-ion conductive phase) and a silicon phase dispersed within the silicate phase. The silicate phase may contain, for example, at least one element selected from the group consisting of Group 1 and Group 2 elements of the long-period periodic table. Examples of Group 1 and Group 2 elements of the long-period periodic table include lithium (Li), potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Other elements that may be included include aluminum (Al), boron (B), lanthanum (La), phosphorus (P), zirconium (Zr), and titanium (Ti). Among these, a silicate phase containing lithium (hereinafter also referred to as the lithium silicate phase) is preferred because it has a small irreversible capacity and high initial charge-discharge efficiency. In other words, the second composite material may include a lithium silicate phase and a silicon phase dispersed within the lithium silicate phase. The second composite material including a lithium silicate phase and a silicon phase dispersed within the lithium silicate phase will hereinafter also be referred to as LSX.

[0050] The lithium silicate phase may be any oxide phase containing lithium (Li), silicon (Si), and oxygen (O), and may also contain other elements. The atomic ratio of O to Si in the lithium silicate phase, O / Si, is, for example, greater than 2 and less than 4. This is advantageous in terms of stability and lithium ion conductivity. Preferably, O / Si is greater than 2 and less than 3. The atomic ratio of Li to Si in the lithium silicate phase, Li / Si, is, for example, greater than 0 and less than 4. Examples of elements other than Li, Si, and O that may be included in the lithium silicate phase include iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), and aluminum (Al).

[0051] The lithium silicate phase is given by the formula: Li 2z SiO 2+zIt may have a composition represented by (0 < z < 2). From the viewpoints of stability, ease of production, lithium ion conductivity, etc., z preferably satisfies the relationship of 0 < z < 1, and more preferably z = 1 / 2.

[0052] <The third composite material> The third composite material includes a carbon phase (lithium ion conductive phase) and a silicon phase dispersed in the carbon phase (hereinafter, the third composite material is also referred to as a Si-C material). The carbon phase can be composed of, for example, amorphous carbon. The amorphous carbon may be, for example, hard carbon, soft carbon, or the like. The amorphous carbon can be obtained, for example, by sintering a carbon source in an inert atmosphere and pulverizing the obtained sintered body. The Si-C material can be obtained, for example, by mixing a carbon source and Si particles, stirring the mixture while pulverizing it with a stirrer such as a ball mill, and then firing the mixture in an inert atmosphere. As the carbon source, for example, saccharides such as carboxymethyl cellulose (CMC), polyvinylpyrrolidone, cellulose, sucrose, and water-soluble resins may be used. When mixing the carbon source and Si particles, for example, the carbon source and Si particles may be dispersed in a dispersion medium such as alcohol.

[0053] The second and third composite materials are excellent in that they have a small irreversible capacity. This is because the silicate phase and the carbon phase have few sites that irreversibly trap lithium ions. By using the second and / or third composite materials, excellent charge-discharge efficiency can be obtained. The effect is particularly remarkable at the initial stage of charge-discharge.

[0054] The silicon phase content in the second and third composite materials can be independently set to, for example, 40% by weight or more, 45% by weight or more, 50% by weight or more, or 65% by weight or more. Alternatively, the silicon phase content can be set to, for example, 80% by weight or less, 75% by weight or less, 70% by weight or less, or 65% by weight or less. Within the range in which the upper and lower limits can be arbitrarily selected from the above, it becomes easier to achieve both high battery capacity and improved cycle characteristics. Unlike the first composite material, whose manufacturing method is limited, the silicon phase content of the second and third composite materials can be arbitrarily changed, making it easier to design high-capacity negative electrodes.

[0055] The Si particle content in each Si-containing material (each composite material) can be measured by Si-NMR. The following describes the desirable measurement conditions for Si-NMR.

[0056] Measurement device: Varian Solid State Nuclear Magnetic Resonance Spectrometer (INOVA-400) Probe: Varian 7mm CPMAS-2 MAS: 4.2kHz MAS speed: 4kHz Pulse: DD (45° pulse + 1H signal acquisition time decoupler) Repeat time: 1200 sec Observation width: 100kHz Observation center: around -100 ppm Signal acquisition time: 0.05 sec Total count: 560 Sample quantity: 207.6 mg

[0057] The silicon phase dispersed within the silicate phase and / or carbon phase is typically composed of multiple crystallites. The crystallite size of the silicon phase is preferably, for example, 30 nm or less. In this case, the volume change due to the expansion and contraction of Si particles during charging and discharging can be minimized, further improving the cycle characteristics. The lower limit of the crystallite size is not particularly limited, but is, for example, 5 nm or more. The crystallite size is calculated using Scherrer's formula from the full width at half maximum of the diffraction peaks attributed to the Si(111) plane in the X-ray diffraction (XRD) pattern of the silicon phase.

[0058] The average particle sizes of the second and third composite materials may be independently 1 to 20 μm or 5 to 12 μm. Within this particle size range, stress due to volume changes in the Si-containing material during charging and discharging is easily relieved, making it easier to obtain good cycle characteristics. The average particle size of each Si-containing material (each composite material) refers to the particle size at which the integrated volume value in the particle size distribution measured by laser diffraction scattering method becomes 50% (volume-average particle size). For the measuring device, for example, the "LA-750" manufactured by HORIBA, Ltd. can be used.

[0059] The composition of the composite material can be analyzed, for example, by the following method. First, the battery is disassembled, the negative electrode is removed, washed with a non-aqueous solvent such as ethylene carbonate, and dried. Then, the negative electrode composite layer is cross-sectioned using a cross-section polisher (CP) to obtain a sample. A backscattered electron image of the sample cross-section is obtained using a field emission scanning electron microscope (FE-SEM) to observe the cross-section of the composite material. Qualitative and quantitative elemental analysis of the observed second composite material can then be performed using an Auger electron spectroscopy (AES) analyzer (acceleration voltage 10kV, beam current 10nA).

[0060] For example, a resin material can be used as the binder for the negative electrode. Examples of binders include fluororesins, polyolefin resins, polyamide resins, polyimide resins, acrylic resins, vinyl resins, and rubber-like materials (e.g., styrene-butadiene copolymer (SBR)). The binder may be used alone or in combination of two or more types.

[0061] Examples of thickening agents include cellulose derivatives such as cellulose ether. Examples of cellulose derivatives include carboxymethylcellulose (CMC) and its modified forms, and methylcellulose. A single thickening agent may be used alone, or two or more may be used in combination.

[0062] Examples of conductive materials include carbon nanotubes (CNTs), carbon fibers other than CNTs, and conductive particles (e.g., carbon black, graphite).

[0063] The dispersion medium used in the negative electrode slurry is not particularly limited, but examples include water, alcohol, N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof.

[0064] For example, a metal foil may be used as the negative electrode current collector. The negative electrode current collector may be porous. Examples of materials for the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy. The thickness of the negative electrode current collector is not particularly limited, but for example, it may be 1 to 50 μm, or 5 to 30 μm.

[0065] [Positive electrode] The positive electrode contains a positive electrode active material. The positive electrode typically comprises a positive electrode current collector and a layered positive electrode mixture (hereinafter referred to as the "positive electrode mixture layer") held by the positive electrode current collector. The positive electrode mixture layer can be formed by coating a positive electrode slurry, which is obtained by dispersing the components of the positive electrode mixture in a dispersion medium, onto the surface of the positive electrode current collector and drying it. The dried coating may be rolled if necessary. The positive electrode mixture contains a positive electrode active material as an essential component and may contain binders, thickeners, etc., as optional components.

[0066] (Cathode active material) The positive electrode active material can be any material that can be used as a positive electrode active material for non-aqueous secondary batteries (especially lithium-ion secondary batteries), but from the viewpoint of increasing capacity, it contains at least a lithium transition metal composite oxide (composite oxide N) containing nickel as a transition metal. The proportion of composite oxide N in the positive electrode active material is, for example, 70% by mass or more, may be 90% by mass or more, or 95% by mass or more.

[0067] The composite oxide N may be, for example, a lithium transition metal composite oxide having a layered rock salt structure and containing Ni and at least one element selected from the group consisting of Co, Mn, and Al. Hereinafter, a lithium transition metal composite oxide having a layered rock salt structure and containing Ni and at least one element selected from the group consisting of Co, Mn, and Al, in which the proportion of Ni among the metal elements other than Li is 80 atomic% or more, will also be referred to as "composite oxide HN". The proportion of composite oxide HN in the composite oxide N used as a positive electrode active material is, for example, 90 mass% or more, may be 95 mass% or more, or may be 100%.

[0068] The higher the proportion of Ni, the more lithium ions can be extracted from the composite oxide HN during charging, thereby increasing capacity. However, the Ni in composite oxide HN with increased capacity tends to have a higher valence state. Also, as the proportion of Ni increases, the proportion of other elements decreases relatively. In this case, the crystal structure tends to become unstable, and side reactions are more likely to occur with repeated charging and discharging. On the particle surface of composite oxide HN with a high Ni content, Ni is more likely to change into a crystal structure that makes reversible intercalation and release of lithium ions difficult.

[0069] In the non-aqueous secondary battery described herein, even though a composite oxide HN with a high Ni content is used as the positive electrode and a Si-containing material is used as the negative electrode, the increase in DCIR can be suppressed by using an electrolyte containing a sultone compound and a nitrile compound.

[0070] When the silicon phase content in the silicon-containing material of the negative electrode is C mass%, and the nickel content relative to all metals other than lithium in the composite oxide N is D mol%, the positive and negative electrodes may be designed to satisfy 1 ≤ D / C ≤ 1.9, and even 1.5 ≤ D / C ≤ 1.9. In this case, if the electrolyte does not contain nitrile compounds, side reactions involving the reduction of Ni and oxidative decomposition of the electrolyte become significant, and there is a strong tendency for gas generation and positive electrode resistance (DCIR) to increase. Also, if the electrolyte does not contain slutone compounds, even if nitrile compounds are included in the electrolyte, side reactions at the negative electrode become significant, and there is a strong tendency for gas generation and negative electrode resistance (DCIR) to increase. In contrast, when the A / B ratio is controlled within the above range, DCIR can be reduced even when 1 ≤ D / C ≤ 1.9 is satisfied, and the increase in DCIR is particularly suppressed when the charge state is low (low SOC).

[0071] When the silicon phase content in the silicon-containing material is C mass%, and the cobalt content relative to all metals other than lithium in the composite oxide N is Emol%, the positive and negative electrodes may be designed to satisfy 0 ≤ E / C ≤ 0.1. In this case, the crystal structure of the composite oxide N tends to become unstable, so the effect of controlling the A / B ratio within the above range is significant, and the effect of reducing DCIR becomes more apparent.

[0072] Co, Mn, and Al contribute to stabilizing the crystal structure of composite oxide HN with a high Ni content. However, from the standpoint of reducing manufacturing costs, a lower Co content is preferable. Composite oxide HN with a low Co content (or no Co at all) may also contain Mn and Al.

[0073] The proportion of Co among metal elements other than Li is preferably 10 atomic percent or less, more preferably 5 atomic percent or less, and it is not necessary to include Co at all. From the viewpoint of stabilizing the crystal structure of the composite oxide HN, it is desirable to include 1 atomic percent or more, or 1.5 atomic percent or more, of Co.

[0074] The proportion of Mn in the metal elements other than Li may be 10 atomic percent or less, or 5 atomic percent or less. The proportion of Mn in the metal elements other than Li may be 1 atomic percent or more, or 3 atomic percent or more, or 5 atomic percent or more. When limiting the range, these upper and lower limits can be combined arbitrarily.

[0075] The proportion of Al among metal elements other than Li may be 10 atomic percent or less, or 5 atomic percent or less. The proportion of Al among metal elements other than Li may be 1 atomic percent or more, 3 atomic percent or more, or 5 atomic percent or more. When limiting the range, these upper and lower limits can be combined arbitrarily.

[0076] A composite oxide HN is, for example, one with the formula: Li α Ni (1-x1-x2-y-z) Co x1 Mn x2 Al y M z O 2+β It is represented as follows: Element M is an element other than Li, Ni, Co, Mn, Al, and oxygen.

[0077] In the above formula, α, which represents the atomic ratio of lithium, is, for example, 0.95 ≤ α ≤ 1.05. α increases or decreases with charging and discharging. In (2 + β), which represents the atomic ratio of oxygen, β satisfies -0.05 ≤ β ≤ 0.05.

[0078] The atomic ratio of Ni, represented by 1-x1-x2-yz (=v), is, for example, 0.8 or greater, and may also be 0.85 or greater, or 0.90 or greater, or 0.95 or greater. Similarly, the atomic ratio of Ni, represented by v, may be 0.98 or less, or 0.95 or less. When limiting the range, these upper and lower limits can be combined in any way.

[0079] x1, which represents the atomic ratio of Co, is, for example, less than or equal to 0.1 (0 ≤ x1 ≤ 0.1), and may also be less than or equal to 0.08, less than or equal to 0.05, or less than or equal to 0.01. When x1 is 0, it includes the case where Co is below the detection limit.

[0080] The x² value, which represents the atomic ratio of Mn, is, for example, less than or equal to 0.1 (0 ≤ x² ≤ 0.1), and may also be less than or equal to 0.08, less than or equal to 0.05, or less than or equal to 0.03. x² may also be greater than or equal to 0.01, or greater than or equal to 0.03. Mn contributes to the stabilization of the crystal structure of the composite oxide HN, and the inclusion of inexpensive Mn in the composite oxide HN is advantageous for cost reduction. When limiting the range, these upper and lower limits can be combined arbitrarily.

[0081] The atomic ratio of Al, represented by y, is, for example, 0.1 or less (0 ≤ y ≤ 0.1), and may also be 0.08 or less, 0.05 or less, or 0.03 or less. y may also be 0.01 or greater, or 0.03 or greater. Al contributes to the stabilization of the crystal structure of the composite oxide HN. When limiting the range, these upper and lower limits can be combined arbitrarily.

[0082] The value of z that represents the atomic ratio of element M is, for example, 0 ≤ z ≤ 0.10, and 0 <z≦0.05でもよく、0.001≦z≦0.01でもよい。

[0083] Element M may be at least one selected from the group consisting of Ti, Zr, Nb, Mo, W, Fe, Zn, B, Si, Mg, Ca, Sr, Sc, and Y. In particular, when at least one selected from the group consisting of Nb, Sr, and Ca is included in the composite oxide HN, it is thought that the surface structure of the composite oxide HN is stabilized, resistance is reduced, and metal elution is further suppressed. Element M is more effective when it is concentrated near the particle surface of the composite oxide HN.

[0084] The elemental content of the composite oxide N can be measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), electron probe microanalyzer (EPMA), or energy dispersive X-ray spectroscopy (EDX), etc.

[0085] The composite oxide N is, for example, a secondary particle formed by the aggregation of multiple primary particles. The particle size of the primary particles is, for example, between 0.05 μm and 1 μm. The average particle size of the secondary particles of the composite oxide N is, for example, between 3 μm and 30 μm, and may also be between 5 μm and 25 μm.

[0086] In this specification, the average particle size of secondary particles refers to the particle size at which the integrated volume value in the particle size distribution measured by laser diffraction scattering (volume-average particle size) becomes 50%. Such a particle size is sometimes referred to as D50. For the measuring device, for example, the "LA-750" manufactured by HORIBA, Ltd. can be used.

[0087] For example, a resin material can be used as the binder for the positive electrode. Examples of binders include fluororesins, polyolefin resins, polyamide resins, polyimide resins, acrylic resins, and vinyl resins. The binder may be used alone or in combination of two or more types.

[0088] Examples of conductive materials include carbon nanotubes (CNTs), carbon fibers other than CNTs, and conductive particles (e.g., carbon black, graphite).

[0089] The dispersion medium used in the positive electrode slurry is not particularly limited, but examples include water, alcohol, N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof.

[0090] For example, a metal foil may be used as the positive electrode current collector. The positive electrode current collector may be porous. Examples of porous current collectors include nets, perforated sheets, and expanded metal. Examples of materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloys, and titanium. The thickness of the positive electrode current collector is not particularly limited, but for example, it may be 1 to 50 μm, or 5 to 30 μm.

[0091] [Separator] It is desirable to interpose a separator between the positive and negative electrodes. The separator should have high ion permeability and appropriate mechanical strength and insulating properties. As the separator, a microporous thin film, woven fabric, nonwoven fabric, etc., can be used. As the material of the separator, polyolefins such as polypropylene and polyethylene are preferred.

[0092] One example of a non-aqueous secondary battery structure is one in which an electrode group, consisting of a positive electrode and a negative electrode wound around a separator, is housed together with an electrolyte in an outer casing. However, the structure is not limited to this, and other forms of electrode groups may be used. For example, a stacked electrode group in which the positive electrode and negative electrode are stacked with a separator in between may also be used. The shape of the battery is also not limited; for example, it may be cylindrical, prismatic, coin-type, button-type, laminate-type, etc.

[0093] Below, the structure of a rectangular non-aqueous secondary battery, as an example of a non-aqueous secondary battery according to the present invention, will be described with reference to Figure 1.

[0094] The battery comprises a bottomed rectangular battery case 4, an electrode group 1 housed within the battery case 4, and an electrolyte (not shown). The electrode group 1 has a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator interposed between them. The negative electrode current collector of the negative electrode is electrically connected to a negative electrode terminal 6 provided on a sealing plate 5 via a negative electrode lead 3. The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive electrode current collector of the positive electrode is electrically connected to the back surface of the sealing plate 5 via a positive electrode lead 2. That is, the positive electrode is electrically connected to the battery case 4, which also serves as the positive electrode terminal. The periphery of the sealing plate 5 fits into the open end of the battery case 4, and the fitting portion is laser-welded. The sealing plate 5 has an injection hole for a non-aqueous electrolyte, which is sealed by a seal 8 after injection.

[0095] The present disclosure will be described in detail below based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0096] Examples 1-7 and Comparative Examples 1-3 A non-aqueous secondary battery was fabricated and evaluated using the following procedure. (1) Preparation of the positive electrode LiNi, a composite oxide HN, is used as the positive electrode active material. 0.91 Co 0.04 Al 0.05 O2 was used (D=91, E=4). A positive electrode slurry was obtained by mixing 100 parts by mass of composite oxide HN (average particle size 12 μm), 1 part by mass of carbon nanotubes, 1 part by mass of polyvinylidene fluoride, and an appropriate amount of NMP. Next, the positive electrode slurry was applied to both sides of an aluminum foil, the coating was dried, and then the foil was rolled to form a positive electrode mixture layer on both sides of the aluminum foil, thereby obtaining the positive electrode.

[0097] (2) Fabrication of the negative electrode A negative electrode active material was obtained by mixing a silicon-containing material (average particle size 5 μm) and graphite (average particle size 20 μm) in a mass ratio of 5:95. The silicon-containing material used was a composite material (LSX) comprising a lithium silicate phase (Li2Si2O5) and a silicon phase dispersed within the lithium silicate phase. The silicon content in the LSX was 55% by mass (C=55, D / C=1.65, E / C=0.07). A negative electrode slurry was prepared by mixing 98 parts by mass of the negative electrode active material, 1 part by mass of sodium salt of CMC (CMC-Na), 1 part by mass of SBR, and an appropriate amount of water. Next, the negative electrode slurry was applied to both sides of a copper foil, which was to be used as the negative electrode current collector. After drying the coating, the foil was rolled to form a negative electrode mixture layer on both sides of the copper foil, thereby obtaining the negative electrode.

[0098] (3) Preparation of electrolyte An electrolyte was prepared by dissolving LiPF6 in a mixed solvent of FEC, EC, EMC, and DMC (FEC:EC:EMC:DMC = 10:5:5:80 (volume ratio)), and then dissolving the sultone compound and nitrile compound shown below in the concentrations shown in Table 1. The concentration of LiPF6 in the electrolyte was 1.3 mol / L. The concentrations of the sultone compound and nitrile compound in the electrolyte are the initial concentrations in the electrolyte immediately after preparation.

[0099] The sultone compounds and nitrile compounds shown in Table 1 are listed below. <Sultone compound (Compound A)> PRES:1,3-Propensulton

[0100] <Nitrile compound (Compound B)> t-BCN: Pivalonitrile (tert-C4H9-CN) ScCN: Sucinonitrile (NC-C2H4-CN) AdCN: Adiponitrile (NC-C4H8-CN)

[0101] (4) Making a battery One end of an aluminum positive electrode lead was attached to the positive electrode. One end of a nickel negative electrode lead was attached to the negative electrode. The positive and negative electrodes were wound together via a polyethylene separator to create an electrode assembly. After vacuum drying the electrode assembly at 105°C for 2 hours, it was housed in a bottomed cylindrical battery case that also served as the negative electrode terminal. An iron battery case was used. Next, electrolyte was injected into the battery case, and the opening of the battery case was closed using a metal sealing body that also served as the positive electrode terminal. At this time, a resin gasket was interposed between the sealing body and the opening end of the battery case. The other end of the positive electrode lead was connected to the sealing body, and the other end of the negative electrode lead was connected to the inner bottom surface of the battery case. In this way, an 18650 type cylindrical lithium-ion secondary battery was manufactured. In Table 1, A1 to A7 are the batteries of Examples 1 to 7, and B1 to B3 are the batteries of Comparative Examples 1 to 3.

[0102] (5) Evaluation <Initial DCIR> In a temperature environment of 25°C, the battery was charged at a constant current of 0.2It until the voltage reached 4.2V, and then charged at a constant voltage of 4.2V until the current reached 0.02It. After that, it was rested for 20 minutes. In this way, a battery with SOC 100% was obtained. The obtained battery with SOC 100% was discharged at a constant current of 0.3It until the state of charge (SOC) reached 10%. For the battery with SOC 10%, the voltage values when discharging for 10 seconds at each current value of 0A, 0.1A, 0.5A, and 1.0A were measured. The initial DCIR was calculated from the absolute value of the slope when approximating the relationship between the discharge current value and the voltage value after 10 seconds to a straight line by the least squares method.

[0103] <Charge and discharge cycle> After measuring the initial DCIR, 100 cycles of charge and discharge of the battery were performed under the following conditions. 〈Charge〉 Under an environment of 25°C, it was charged at a constant current of 0.2It until the voltage reached 4.2V, and then charged at a constant voltage of 4.2V until the current reached 0.02It. The battery after constant voltage charging was rested for 20 minutes.

[0104] 〈Discharge〉 After resting, under an environment of 25°C, it was discharged at a constant current of 0.3It until the voltage reached 2.5V.

[0105] <DCIR increase rate> For the battery after 100 cycles, DCIR(100) was obtained in the same procedure as the initial DCIR, and the DCIR increase rate was obtained from the following formula. DCIR increase rate (%) = 100×(DCIR(100) - initial DCIR) / initial DCIR

[0106] 《Comparative Example 4》 A battery B4 was fabricated in the same manner as in Example 1, except that no silicon-containing material was used (C = 0) as the negative electrode active material, and only graphite (average particle size 20μm) was used.

[0107] 《Comparative Example 5》 Battery B5 was fabricated in the same manner as Comparative Example 1, except that only graphite (average particle size 20 μm) was used as the negative electrode active material, without using a silicon-containing material (C=0).

[0108] [Table 1]

[0109] Table 1 shows that even when nitrile compounds are used to suppress the rise in DCIR and gas generation originating from the positive electrode, the DCIR increase rate is extremely high in battery B1, which does not use slutone compounds. Furthermore, even when slutone compounds are used, batteries B2 and B3, where the A / B ratio does not satisfy 1 ≤ A / B ≤ 10, show almost no effect in suppressing the DCIR increase rate. On the other hand, batteries A1 to A7, which satisfy 1 ≤ A / B ≤ 10 or 2 ≤ A / B ≤ 5, show a significant suppression of the DCIR increase rate. Note that the DCIR increase rate of battery B1, which does not use slutone compounds, is 30%, so batteries A1 to A7 show an improvement of more than 10% in the DCIR increase rate. On the other hand, when graphite alone is used as the negative electrode active material, the difference in the DCIR increase rate between battery B4, which uses slutone compounds, and battery B5, which does not use slutone compounds, was only slight. From this, it can be understood that the increase in negative electrode resistance (DCIR) when using nitrile compounds is a problem specific to when the negative electrode contains Si-containing material. [Industrial applicability]

[0110] The non-aqueous secondary battery described herein is suitable for use as a main power source for mobile communication devices, portable electronic devices, and in-vehicle power sources, but its applications are not limited to these. Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. [Explanation of symbols]

[0111] 1: Electrode group, 2: Positive lead, 3: Negative lead, 4: Battery case, 5: Sealing plate, 6: Negative terminal, 7: Gasket, 8: Sealing plug

Claims

1. A positive electrode comprising a lithium transition metal composite oxide containing at least nickel as a transition metal, A negative electrode containing a silicon-containing material, A separator interposed between the positive electrode and the negative electrode, Equipped with an electrolyte, The electrolyte comprises a sultone compound and a nitrile compound. In the electrolyte, when the concentration of the sultone compound is A by mass and the concentration of the nitrile compound is B by mass, 1 ≤ A / B ≤ 10 Satisfying the conditions, The silicon-containing material comprises a lithium-ion conductive phase and a silicon phase dispersed in the lithium-ion conductive phase. When the content of the silicon phase in the silicon-containing material is C by mass%, and the content of nickel relative to all metals other than lithium in the lithium transition metal composite oxide is D mol%, 1.5 ≤ D / C ≤ 1.9 A non-aqueous secondary battery that satisfies the following conditions.

2. 2 ≤ A / B ≤ 5 A non-aqueous secondary battery according to claim 1, satisfying the requirements.

3. 0.01 ≤ A ≤ 1.5 0.01 ≤ B ≤ 1 A non-aqueous secondary battery according to claim 1 or 2, satisfying the requirements.

4. The non-aqueous secondary battery according to any one of claims 1 to 3, wherein the sultone compound has an unsaturated bond.

5. The non-aqueous secondary battery according to any one of claims 1 to 4, wherein the nitrile compound is at least one selected from the group consisting of mononitrile compounds and dinitrile compounds, and the mononitrile compound does not have hydrogen at the α position of the nitrile group.

6. The electrolyte further comprises fluoroethylene carbonate, The non-aqueous secondary battery according to any one of claims 1 to 5, wherein the concentration of the fluoroethylene carbonate in the electrolyte is 5% by mass or more and 20% by mass or less.

7. The lithium transition metal composite oxide further comprises at least one selected from the group consisting of Co, Mn, and Al. When the cobalt content relative to all metals other than lithium in the lithium transition metal composite oxide is defined as Emol%, 0 ≤ E / C ≤ 0.1 A non-aqueous secondary battery according to any one of claims 1 to 6, satisfying the requirements of the claim.

8. A positive electrode comprising a lithium transition metal composite oxide containing at least nickel as a transition metal, A negative electrode containing a silicon-containing material, A separator interposed between the positive electrode and the negative electrode, Equipped with an electrolyte, The electrolyte comprises a sultone compound and a nitrile compound. The sultone compound has an unsaturated bond, In the electrolyte, when the concentration of the sultone compound is A by mass and the concentration of the nitrile compound is B by mass, 2 ≤ A / B ≤ 5 0.1 ≤ A ≤ 1.5 0.05 ≤ B ≤ 0.7 A non-aqueous secondary battery that satisfies the following conditions.

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