Non-aqueous electrolyte secondary battery

Abstract

The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode contains a negative electrode active material capable of electrochemically storing and releasing lithium. The negative electrode active material contains a composite material, the composite material contains a silicate phase and silicon particles dispersed in the silicate phase, and the silicate phase contains at least one of an alkali metal and an alkaline earth metal. The content of the silicon particles in the composite material is greater than 40% by mass and 80% by mass or less. The non-aqueous electrolyte contains a sultone compound, and the content of the sultone compound in the non-aqueous electrolyte is 2% by mass or less.

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte secondary battery. Background Art

[0002] In recent years, non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, have high voltage and high energy density, and thus are highly expected as power sources for small household use, power storage devices, and electric vehicles. When high energy density of a battery is required, as a negative electrode active material having a high theoretical capacity density, utilization of a material containing silicon (Silicon) that alloyizes with lithium is highly expected.

[0003] Patent Document 1 proposes a non-aqueous electrolyte secondary battery using a composite material of a lithium silicate phase represented by Li 2u SiO 2+u (0 < u < 2) and silicon particles dispersed in the lithium silicate phase.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: WO 2016 / 035290 Summary of the Invention

[0007] However, with further high performance of electronic devices and the like, for non-aqueous electrolyte secondary batteries highly expected as their power sources, further high capacity is required. When the composite material described in Patent Document 1 is used as the negative electrode active material, as a method for further increasing the capacity, it is possible to consider increasing the amount of silicon particles contained in the composite material.

[0008] However, when the amount of silicon particles contained in the composite material is increased, the degree of expansion and contraction of the composite material during charge and discharge becomes larger, and particle cracks of the composite material become likely to occur. With the expansion and contraction of the composite material and particle cracks, the coating film formed on the surface of the composite material is damaged, the active surface of the composite material is exposed, and the non-aqueous solvent comes into contact with the surface and is liable to decompose. Decomposition of the non-aqueous solvent causes deterioration of the non-aqueous electrolyte, and the cycle characteristics sometimes decrease. In addition, the amount of gas generated with the decomposition of the non-aqueous solvent sometimes increases.

[0009] In view of the above, on the one hand, the present invention relates to a non-aqueous electrolyte secondary battery, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode contains a negative electrode active material capable of electrochemically storing and releasing lithium. The negative electrode active material contains a composite material, which contains a silicate phase and silicon particles dispersed in the silicate phase. The silicate phase contains at least one of an alkali metal and an alkaline earth metal. The content of the silicon particles in the composite material is greater than 40% by mass and 80% by mass or less. The non-aqueous electrolyte contains a sultone compound, and the content of the sultone compound in the non-aqueous electrolyte is 2% by mass or less.

[0010] Through the present invention, the non-aqueous electrolyte secondary battery can achieve both high capacity and suppression of gas generation during battery storage and improvement of cycle characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic perspective view of a part of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention being cut. DETAILED DESCRIPTION OF THE INVENTION

[0012] The non-aqueous electrolyte secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode contains a negative electrode active material capable of electrochemically storing and releasing lithium. The negative electrode active material contains a composite material, which contains a silicate phase and silicon particles dispersed in the silicate phase. The silicate phase contains at least one of an alkali metal and an alkaline earth metal. The content of the silicon particles in the composite material is greater than 40% by mass and 80% by mass or less. The non-aqueous electrolyte contains a sultone compound, and the content of the sultone compound in the non-aqueous electrolyte is 2% by mass or less.

[0013] In a battery with a high-capacity composite material having a silicon particle content greater than 40% by mass, by using a non-aqueous electrolyte containing a specific amount of a sultone compound, high capacity, suppression of gas generation during battery storage, and improvement of cycle characteristics can be achieved simultaneously.

[0014] The sultone compound forms a high-quality film (SEI: Solid Electrolyte Interface) on the surface of the composite material. The film derived from the sultone compound has excellent durability (strength) and also excellent followability (flexibility) with respect to the expansion and contraction of the composite material. Therefore, the destruction of the film due to the expansion and contraction of the composite material and particle cracks during charge and discharge is suppressed.

[0015] In a non-aqueous electrolyte secondary battery using a high-capacity composite material as the negative electrode active material, when the non-aqueous electrolyte contains a sultone compound, the durability and followability of the film are specifically improved. The main reasons for this are considered to be the following (a) to (c).

[0016] (a) The silicate phase is alkaline, so the decomposition reaction of the sultone compound on the surface of the composite material is promoted, and a dense and uniform coating film is easily formed. (b) The silicate phase is alkaline, so a strong interaction is likely to occur between the coating film derived from the sultone compound and the composite material (silicate phase). (c) The reduction potential of the sultone compound is relatively high, so a coating film derived from the sultone compound is easily formed preferentially on the surface of the composite material.

[0017] As described above, by suppressing the damage of the coating film, the exposure of the active surface of the composite material is suppressed. Thereby, by the contact of the non-aqueous solvent with the active surface of the composite material, the decomposition of the non-aqueous solvent is suppressed, and the reduction of the cycle characteristics and the gas generation accompanying the decomposition of the non-aqueous solvent are suppressed.

[0018] From the viewpoint of forming a high-quality coating film, the non-aqueous electrolyte may contain a sultone compound and vinylene carbonate (VC), fluoroethylene carbonate (FEC) (hereinafter referred to as VC, etc.).

[0019] Generally, a part of VC, etc. is used for the initial coating film formation, and the remaining VC, etc. is used for repairing the coating film damaged by the repetition of charge and discharge. However, when using a high-capacity composite material, the coating film is easily damaged due to the expansion and contraction of the composite material, the amount of VC, etc. used for repairing the coating film increases, the gas generation amount increases, and sometimes the cycle characteristics deteriorate.

[0020] In contrast, in the present invention, the non-aqueous electrolyte contains a sultone compound. The reduction potential of the sultone compound is higher than that of VC, etc., so a coating film derived from the sultone compound is formed preferentially. The coating film derived from VC, etc. is mainly formed on the coating film derived from the sultone compound and can act as a part of the coating film. The coating film derived from the sultone compound is difficult to be damaged, so the repair of the coating film based on the remaining VC, etc. is suppressed, the gas generation accompanying the repair of the coating film is suppressed, and the reduction of the cycle characteristics is suppressed.

[0021] The sultone compound is a cyclic sulfonic acid ester. The sultone compound may be a compound having a carbon-carbon unsaturated bond in the ring (hereinafter referred to as an unsaturated sultone compound). Due to the presence of the unsaturated bond, the durability of the coating film, etc. is further improved.

[0022] As the sultone compound, for example, a compound represented by the following general formula (1) can be cited.

[0023]

[0024] R in the general formula (1) 1 ~R 6 are each independently a hydrogen atom or a substituent. The substituent includes a halogen atom, a hydrocarbon group, a hydroxyl group, an amino group, an ester group, etc.

[0025] The hydrocarbyl group includes an alkyl group, an alkenyl group, etc. The alkyl group and the alkenyl group may be linear or branched. The alkyl group includes a methyl group, an ethyl group, a n-propyl group, an isopropyl group, etc. The alkenyl group includes a vinyl group, a 1-propenyl group, a 2-propenyl group, etc. At least one of the hydrogen atoms of the hydrocarbyl group is optionally substituted by a halogen atom.

[0026] From the viewpoints of ensuring good viscosity of the non-aqueous electrolyte and improving solubility, the hydrocarbyl group is preferably an alkyl group having 1 to 5 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms.

[0027] In the general formula (1), n represents the number of repetitions of the methylene group having R 5 and R 6 . n is an integer of 1 to 3. When n is 2 or 3, R 5 and R 6 each methylene group has may be the same as or different from each other.

[0028] Specific examples of the compound represented by the general formula (1) include 1,3-propane sultone (PS), 1,4-butane sultone, 1,5-pentane sultone, 2-fluoro-1,3-propane sultone, 2-fluoro-1,4-butane sultone, 2-fluoro-1,5-pentane sultone, etc. From the viewpoint of having a particularly large interaction with the silicate phase, PS is preferred among them.

[0029] In addition, examples of the sultone compound include compounds (unsaturated sultone compounds) represented by the following general formula (2).

[0030]

[0031] R 1 , R 4 , R 5 and R 6 in the general formula (2), and n are the same as R 1 , R 4 , R 5 and R 6 in the general formula (1), and n.

[0032] Specific examples of the compound represented by the general formula (2) include 1,3-propenyl sultone (PRS), 1,4-butene sultone, 1,5-pentene sultone, 2-fluoro-1,3-propenyl sultone, 2-fluoro-1,4-butene sultone, 2-fluoro-1,5-pentene sultone, etc. From the viewpoint of having a particularly large interaction with the silicate phase, PRS is preferred among them.

[0033] The content of the sultone compound in the non-aqueous electrolyte (mass ratio relative to the total mass of the non-aqueous electrolyte) is 2% by mass or less. When the content of the sultone compound in the non-aqueous electrolyte is greater than 2% by mass, an excessive film is formed, the reaction resistance increases, and sometimes the cycle characteristics deteriorate. The content of the sultone compound in the non-aqueous electrolyte can be determined, for example, by gas chromatography-mass spectrometry (GCMS).

[0034] Before the first charge of the battery (or before injecting the liquid into the battery), the content of the sultone compound in the non-aqueous electrolyte may be 0.1% by mass or more and 2% by mass or less, and may be 0.2% by mass or more and 1% by mass or less. When the content of the sultone compound in the non-aqueous electrolyte is 0.1% by mass or more, a film derived from the sultone compound is easily formed sufficiently.

[0035] During the charge and discharge of the battery, at least a part of the sultone compound is reductively decomposed and used for film formation. Therefore, in the battery after charge and discharge (for example, the initial battery that has been charged and discharged several times), the content of the sultone compound in the non-aqueous electrolyte can be less than 2% by mass. When the content of the sultone compound in the preparation of the non-aqueous electrolyte is 1% by mass or less, for example, the content of the sultone compound in the non-aqueous electrolyte of the battery after the first charge is 50 ppm or less. The content of the sultone compound contained in the non-aqueous electrolyte taken out of the battery can be a trace amount close to the detection limit. If the presence of the sultone compound can be confirmed, its corresponding effects can be confirmed.

[0036] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. From the viewpoints of wide potential window and high conductivity, the lithium salt preferably contains at least one of LiN(SO 2 F) 2 (hereinafter referred to as LFSI.) and LiPF 6 . LFSI is easily formed into a high-quality film on the surface of the composite material. The resistance of the film derived from LFSI is small, and by using LFSI and the sultone compound together, a mixed film with a smaller resistance than the film formed by the sultone compound alone can be formed. In addition, LiPF 6 can moderately form a passivation film on the positive electrode current collector and the like, so the corrosion of the positive electrode current collector and the like is suppressed, and the battery reliability is improved.

[0037] The concentration of LFSI in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 1.0 mol / L or less. The concentration of LiPF 6 in the non-aqueous electrolyte is preferably 0.5 mol / L or more and 1.5 mol / L or less. The total concentration of LFSI and LiPF 6 in the non-aqueous electrolyte is preferably 1 mol / L or more and 2 mol / L or less. By using LFSI and LiPF at the concentrations within the above ranges together6 When this is the case, the effects based on the above-mentioned LFSI and LiPF can be obtained with good balance, and the initial charge-discharge efficiency of the battery is further improved. 6 The negative electrode active material contains at least a high-capacity composite material. By controlling the amount of silicon particles dispersed in the silicate phase, further high-capacity can be achieved. Since the silicon particles are dispersed in the silicate phase, the expansion and contraction of the composite material during charge and discharge are suppressed. Therefore, the composite material is beneficial for improving the high-capacity and cycle characteristics of the battery.

[0038] The silicate phase contains at least one of an alkali metal (Group 1 element of the long-period periodic table) and an alkaline earth metal (Group 2 element of the long-period periodic table). The alkali metals include lithium (Li), potassium (K), sodium (Na), etc. The alkaline earth metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), etc. Among them, from the viewpoint of small irreversible capacity and high initial charge-discharge efficiency, a silicate phase containing lithium (hereinafter also referred to as a lithium silicate phase) is preferred. That is, a composite material containing a lithium silicate phase and silicon particles dispersed in the lithium silicate phase (hereinafter also referred to as LSX or negative electrode material LSX) is preferred.

[0039] In order to improve the high-capacity and cycle characteristics, the content of silicon particles in the composite material must be greater than 40% by mass and 80% by mass or less. When the content of silicon particles in the composite material is 40% by mass or less, the capacity of the composite material becomes small, and it is difficult to obtain the target initial capacity. When the content of silicon particles in the composite material is greater than 80% by mass, the degree of expansion and contraction of the composite material during charge and discharge becomes too large, the coating film is damaged, and sometimes the cycle characteristics deteriorate and the gas generation amount increases.

[0040] From the viewpoint of high-capacity, the content of silicon particles in the composite material is preferably 50% by mass or more, more preferably 55% by mass or more. At this time, the diffusivity of lithium ions is good, and excellent load characteristics can be easily obtained. On the other hand, from the viewpoint of improving the cycle characteristics, the content of silicon particles in the composite material is preferably 75% by mass or less, more preferably 70% by mass or less. At this time, the surface of the silicon particles exposed without being covered by the silicate phase is reduced, and the reaction between the non-aqueous electrolyte and the silicon particles is easily suppressed.

[0041] The content of silicon particles can be measured by Si-NMR. Hereinafter, the ideal measurement conditions of Si-NMR are shown.

[0042] Measuring device: manufactured by Varian, solid nuclear magnetic resonance spectrometer (INOVA-400)

[0043] Probe: Varian 7mMCPMAS-2

[0044] Probe: Varian 7mMCPMAS-2

[0045] MAS: 4.2 kHz

[0046] MAS speed: 4 kHz

[0047] Pulse: DD (45° pulse + signal read time 1H decoupling)

[0048] Repetition time: 1200 seconds

[0049] Observation width: 100 kHz

[0050] Observation center: around -100 ppm

[0051] Signal read time: 0.05 seconds

[0052] Number of accumulations: 560

[0053] Sample amount: 207.6 mg

[0054] The negative electrode active material preferably further contains a carbon material that electrochemically stores and releases lithium ions. Since the composite material expands and contracts during charge and discharge, when the ratio thereof in the negative electrode active material increases, poor contact may sometimes occur between the particles of the negative electrode active material or between the negative electrode active material and the negative electrode current collector during charge and discharge. On the other hand, by using the composite material and the carbon material in combination, it is easy to impart the high capacity of the silicon particles to the negative electrode and obtain excellent cycle characteristics.

[0055] From the viewpoint of increasing the capacity, the proportion of the composite material in the total of the composite material and the carbon material is preferably greater than 0.5% by mass, more preferably 1% by mass or more, and still more preferably 2% by mass or more. From the viewpoint of improving the cycle characteristics, the proportion of the composite material in the total of the composite material and the carbon material is preferably less than 30% by mass, more preferably 20% by mass or less, and still more preferably 15% by mass or less.

[0056] Examples of the carbon material include graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), etc. Among them, graphite with excellent charge-discharge stability and less irreversible capacity is preferred. Graphite refers to a material having a graphite-type crystal structure, and includes, for example, natural graphite, artificial graphite, graphitized mesophase carbon particles, etc. The carbon material may be used alone or in combination of two or more.

[0057] Within the range that does not impair the effects of the present invention, the negative electrode may further contain a small amount of SiO x (0 < x < 2) and other negative electrode active materials. SiO x containing SiO 2 phase and silicon particles dispersed in the SiO 2 phase. SiO xThe surface can also form a coating film derived from a sultone compound. However, in the case of SiO x In the case of SiO 2 The phase is neutral, so it is difficult to obtain a dense and uniform coating film with excellent durability and the like in the case of a composite material.

[0058] [Negative electrode material LSX]

[0059] Hereinafter, the negative electrode material LSX will be described in further detail.

[0060] The crystallite size of the silicon particles dispersed in the lithium silicate phase is, for example, 10 nm or more. The silicon particles have a particulate phase of silicon (Si) elemental substance. When the crystallite size of the silicon particles is set to 10 nm or more, the surface area of the silicon particles can be suppressed to be small, so that deterioration of the silicon particles accompanied by the generation of irreversible capacity is difficult to occur. The crystallite size of the silicon particles can be calculated by the Scherrer formula based on the half-value width of the diffraction peak attributed to the Si(111) plane in the X-ray diffraction (XRD) pattern of the silicon particles.

[0061] The structural stability of the negative electrode material LSX is also excellent. Since the silicon particles are dispersed in the lithium silicate phase, the expansion and contraction of the negative electrode material LSX during charge and discharge are suppressed. From the viewpoint of suppressing the cracking of the silicon particles themselves, the average particle size of the silicon particles is preferably 500 nm or less, more preferably 200 nm or less, and further preferably 50 nm or less before the first charge. After the first charge, the average particle size of the silicon particles is preferably 400 nm or less, more preferably 100 nm or less. By refining the silicon particles, the volume change during charge and discharge becomes smaller, and the structural stability of the negative electrode material LSX is further improved.

[0062] The average particle size of the silicon particles is measured by observing a cross-sectional SEM (scanning electron microscope) photograph of the negative electrode material LSX. Specifically, the average particle size of the silicon particles is obtained by averaging the maximum diameters of any 100 silicon particles. The silicon particles are formed by the aggregation of multiple crystallites.

[0063] The lithium silicate phase is an oxide phase containing lithium (Li), silicon (Si), and oxygen (O). The atomic ratio of O to Si in the lithium silicate phase: O / Si is, for example, greater than 2 and less than 4. When O / Si is greater than 2 and less than 4 (z in the formula described later is 0 < z < 2), it is advantageous in terms of stability and lithium ion conductivity. O / Si is preferably greater than 2 and less than 3 (z in the formula described later is 0 < z < 1). The atomic ratio of Li to Si in the lithium silicate phase: Li / Si is, for example, greater than 0 and less than 4. In the lithium silicate phase, in addition to Li, Si, and O, trace amounts of other elements such as iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), and aluminum (Al) may also be included.

[0064] The lithium silicate phase may have a formula: Li 2z SiO 2+z with 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.

[0065] The lithium silicate phase has fewer sites that can react with lithium compared to the SiO x in 2 the SiO x phase. Therefore, compared with SiO x , LSX is less likely to have an irreversible capacity during charge and discharge. When silicon particles are dispersed in the lithium silicate phase, excellent charge and discharge efficiency can be obtained at the initial stage of charge and discharge. In addition, the content of silicon particles can be arbitrarily changed, so a high-capacity negative electrode can be designed.

[0066] The composition of the lithium silicate phase Li 2z SiO 2+z can be analyzed, for example, by the following method.

[0067] First, measure the mass of the sample of the negative electrode material LSX. Then, calculate the contents of carbon, lithium, and oxygen contained in the sample as follows. Next, subtract the carbon content from the mass of the sample, calculate the contents of lithium and oxygen in the residue, and find the ratio of 2z to (2 + z) based on the molar ratio of lithium (Li) and oxygen (O).

[0068] The carbon content is measured using a carbon / sulfur analyzer (e.g., EMIA-520 type manufactured by Horiba, Ltd.). Weigh the sample on a magnetic plate, add a combustion aid, insert it into a combustion furnace heated to 1350 °C (carrier gas: oxygen), and detect the amount of carbon dioxide gas generated during combustion by infrared absorption. The standard curve is made, for example, using carbon steel (carbon content 0.49%) manufactured by Bureau of Analysed Sampe. Ltd., and the carbon content of the sample is calculated (high-frequency induction heating furnace combustion - infrared absorption method).

[0069] The oxygen content is measured using an oxygen / nitrogen / hydrogen analyzer (e.g., EGMA-830 type manufactured by Horiba, Ltd.). Put the sample into a Ni capsule, and together with Sn pellets and Ni pellets as a flux, put them into a carbon crucible heated with an electric power of 5.75 kW, and detect the released carbon monoxide gas. The standard curve is made using the standard sample Y 2 O 3 and the oxygen content of the sample is calculated (inert gas fusion - non-dispersive infrared absorption method).

[0070] Regarding the lithium content, the sample is completely dissolved with hot fluonitric acid (a mixed acid of heated hydrofluoric acid and nitric acid). After filtering and removing the carbon from the dissolved residue, the resulting filtrate is analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES) and the lithium content is determined. A standard curve is prepared using a commercially available standard solution of lithium, and the lithium content of the sample is calculated.

[0071] The silicon content is the amount obtained by subtracting the carbon content, oxygen content, and lithium content from the mass of the sample of the negative electrode material LSX. This silicon content includes the contributions of both silicon present in the form of silicon particles and silicon present in the form of lithium silicate. The content of silicon particles is determined by Si-NMR measurement, and the content of silicon present in the form of lithium silicate in the negative electrode material LSX is determined.

[0072] The negative electrode material LSX is preferably formed into particulate material having an average particle diameter of 1 to 25 μm, and more preferably 4 to 15 μm (hereinafter also referred to as LSX particles). In the above particle diameter range, it is easy to relieve the stress caused by the volume change of the negative electrode material LSX accompanying charge and discharge, and it is easy to obtain good cycle characteristics. The surface area of the LSX particles also becomes appropriate, and the capacity reduction caused by the side reaction with the non-aqueous electrolyte is also suppressed.

[0073] The average particle diameter of the LSX particles refers to the particle diameter (volume average particle diameter) at which the volume cumulative value becomes 50% in the particle size distribution measured by laser diffraction scattering method. As the measuring device, for example, "LA-750" manufactured by Horiba, Ltd. can be used.

[0074] The LSX particles preferably have a conductive material covering at least a part of their surface. Since the lithium silicate phase lacks electron conductivity, the conductivity of the LSX particles also tends to decrease. By covering the surface with a conductive material, the conductivity can be dramatically improved. The conductive layer is preferably as thin as not substantially affecting the average particle diameter of the LSX particles.

[0075] Next, the non-aqueous electrolyte secondary battery according to the embodiment of the present invention will be described in detail. The non-aqueous electrolyte secondary battery includes, for example, the following negative electrode, positive electrode, and non-aqueous electrolyte.

[0076] [Negative electrode]

[0077] The negative electrode includes, for example, a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector and containing a negative electrode active material. The negative electrode mixture layer can be formed by coating a negative electrode paste in which a negative electrode mixture is dispersed in a dispersion medium on the surface of the negative electrode current collector and drying it. If necessary, the dried coating film can be rolled. The negative electrode mixture layer can be formed on one surface of the negative electrode current collector or on both surfaces.

[0078] For the negative electrode mixture, as an essential component, it may contain the above composite material (such as LSX) as the negative electrode active material. As optional components, it may contain a binder, a conductive agent, a thickener, etc. The silicon particles in the composite material can absorb and store a large amount of lithium ions, thus contributing to the high capacity of the negative electrode. In the negative electrode mixture, as the negative electrode active material, it may also contain a carbon material that can electrochemically absorb and release lithium ions.

[0079] The proportion of the composite material in the total of the composite material and the carbon material in the negative electrode mixture is preferably, for example, 0.5% by mass or more, more preferably 1% by mass or more, and still more preferably 2% by mass or more. From the viewpoint of improving the cycle characteristics, the proportion of the composite material in the total of the composite material and the carbon material in the negative electrode mixture is preferably, for example, 30% by mass or less, more preferably 20% by mass or less, and still more preferably 15% by mass or less.

[0080] As the negative electrode current collector, a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh body, a net-like body, a punched sheet, etc.) can be used. As the material of the negative electrode current collector, stainless steel, nickel, nickel alloy, copper, copper alloy, etc. can be exemplified. The thickness of the negative electrode current collector is not particularly limited. From the viewpoint of the balance between the strength and light weight of the negative electrode, it is preferably 1 to 50 μm, and more preferably 5 to 20 μm.

[0081] As the binder, resin materials can be exemplified, such as fluororesins such as polytetrafluoroethylene and polyvinylidene fluoride (PVDF); polyolefin resins such as polyethylene and polypropylene; polyamide resins such as aramid resins; polyimide resins such as polyimide and polyamideimide; acrylic resins such as polyacrylic acid, methyl polyacrylate, and ethylene-acrylic acid copolymer; vinyl resins such as polyacrylonitrile and polyvinyl acetate; polyvinylpyrrolidone; polyethersulfone; rubber-like materials such as styrene-butadiene copolymer rubber (SBR), etc. The binder can be used alone or in combination of two or more.

[0082] As the conductive agent, carbon materials such as acetylene black and carbon nanotubes; conductive fiber materials such as carbon fiber and metal fiber; carbon fluoride; metal powder materials such as aluminum; conductive whisker materials such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; organic conductive materials such as benzene derivatives, etc. can be exemplified. The conductive agent can be used alone or in combination of two or more.

[0083] As the thickener, carboxymethyl cellulose (CMC) and its modified products (including salts such as Na salt), cellulose derivatives such as methyl cellulose (such as cellulose ether); saponified products of polymers having vinyl acetate units such as polyvinyl alcohol; polyethers (such as polyalkylene oxides such as polyethylene oxide), etc. can be cited. The thickener can be used alone or in combination of two or more.

[0084] There is no particular limitation on the dispersion medium, and examples thereof include water, alcohols such as ethanol, ethers such as tetrahydrofuran, amides such as dimethylformamide, N-methyl-2-pyrrolidone (NMP), or a mixed solvent thereof.

[0085] [Positive electrode]

[0086] The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. The positive electrode mixture layer can be formed as follows: a positive electrode paste obtained by dispersing a positive electrode mixture in a dispersion medium is coated on the surface of the positive electrode current collector and dried to form the layer. Rolling of the dried coating film can be performed as needed. The positive electrode mixture layer can be formed on one surface of the positive electrode current collector or on both surfaces.

[0087] In the positive electrode mixture, as essential components, a positive electrode active material can be included, and as optional components, a binder, a conductive agent, a thickening agent, etc. can be included.

[0088] As the positive electrode active material, a lithium-containing composite oxide can be used. Examples include Li a CoO 2 、Li a NiO 2 、Li a MnO 2 、Li a CO b Ni 1-b O 2 、Li a CO b M 1-b O c 、Li a Ni 1-b M b O c 、Li a Mn 2 O 4 、Li a Mn 2-b M b O 4 、LiMePO 4 、Li 2 MePO 4F. Here, M is at least one selected from the group consisting of Na, Mg, Ca, Zn, Ga, Ge, Sn, Sc, Ti, V, Cr, Y, Zr, W, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, Bi, and B. Me contains at least a transition element (for example, contains at least one selected from the group consisting of Mn, Fe, Co, and Ni). 0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.9, 2.0 ≤ c ≤ 2.3. It should be noted that the value of a showing the molar ratio of lithium is the value in the discharged state, corresponding to the value after just making the active material, and it will increase or decrease through charge and discharge.

[0089] Among them, Li is preferred a Ni b M 1-b O 2 (M is at least one selected from the group consisting of Mn, Co, and Al, 0 < a ≤ 1.2, 0.3 ≤ b ≤ 1). The lithium nickel composite oxide shown. From the viewpoint of high capacity, it is more preferably satisfied that 0.85 ≤ b ≤ 1. From the viewpoint of the stability of the crystal structure, as M, it is further preferably Li containing Co and Al a Ni b CO c AL d O 2 (0 < a ≤ 1.2, 0.85 ≤ b < 1, 0 < c < 0.15, 0 < d ≤ 0.1, b + c + d = 1).

[0090] As the binder and the conductive agent, those exemplified in the negative electrode can be used. As the conductive agent, graphite such as natural graphite and artificial graphite can be used.

[0091] The shape and thickness of the positive electrode current collector can be selected respectively according to the shape and range of the negative electrode current collector. As the material of the positive electrode current collector, for example, stainless steel, aluminum, aluminum alloy, titanium, etc. can be exemplified.

[0092] [Non-aqueous electrolyte]

[0093] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

[0094] The concentration of the lithium salt in the non-aqueous electrolyte is preferably, for example, 0.5 mol / L or more and 2 mol / L or less. By controlling the lithium salt concentration within the above range, a non-aqueous electrolyte with excellent ion conductivity and moderate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0095] As the non-aqueous solvent (main solvent), for example, cyclic carbonates (excluding unsaturated cyclic carbonates and cyclic carbonates having a fluorine atom, which are used in the additives described later), chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, etc. can be used. As the cyclic carbonate, propylene carbonate (PC), ethylene carbonate (EC), etc. can be mentioned. As the chain carbonate, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. can be mentioned. As the cyclic carboxylic acid ester, γ-butyrolactone (GBL), γ-valerolactone (GVL), etc. can be mentioned. As the chain carboxylic acid ester, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, etc. can be mentioned. The non-aqueous solvent can be used alone or in combination of two or more.

[0096] As the lithium salt, for example, LiClO 4 , LiBF 4 , LiPF 6 , LiAlCl 4 , LiSbF 6 , LiSCN, LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiB 10 Cl 10 , lithium salts of lower aliphatic carboxylic acids, LiCl, LiBr, LiI, borate salts, imide salts, etc. As the borate salts, lithium bis(1,2-benzenediolato(2-)-O,O’)borate, lithium bis(2,3-naphthalenediolato(2-)-O,O’)borate, lithium bis(2,2’-biphenyldiolato(2-)-O,O’)borate, lithium bis(5-fluoro-2-hydroxy-1-benzenesulfonato-O,O’)borate, etc. can be mentioned. As the imide salts, LFSI, lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 )) 2 ), lithium nonafluorobutanesulfonyltrifluoromethanesulfonimide (LiN(CF 3 SO 2 )(C 4 F 9 SO 2 )), lithium bis(pentafluoroethanesulfonyl)imide (LiN(C 2 F 5 SO 2 )) 2 ), etc. Among these, at least one of LiPF 6 and LFSI is preferred. The lithium salt can be used alone or in combination of two or more.

[0097] The non-aqueous electrolyte may also contain other additives. The other additives include cyclic carbonates having at least one carbon-carbon unsaturated bond (hereinafter also referred to as unsaturated cyclic carbonates), cyclic carbonates having fluorine atoms, and the like. The unsaturated cyclic carbonates and the cyclic carbonates having fluorine atoms contribute to the formation of a high-quality coating film on the surface of LSX. However, since the reduction potential of the sultone compound is high, a coating film can be formed more preferentially than the additives. The addition amount of the other additives (mass ratio relative to the whole non-aqueous electrolyte) is, for example, 1% by mass or more and 10% by mass or less.

[0098] Examples of the unsaturated cyclic carbonate include vinylene carbonate (VC), ethylene vinylene carbonate, diethylene vinylene carbonate, and the like. Examples of the cyclic carbonate having a fluorine atom include fluoroethylene carbonate (FEC), and the like. The other additives may be used alone or in combination of two or more.

[0099] [Separator]

[0100] It is generally desirable to insert a separator between the positive electrode and the negative electrode. The separator has a high ion permeability and has appropriate mechanical strength and insulation properties. As the separator, a microporous film, a woven fabric, a non-woven fabric, or the like can be used. As the material of the separator, polyolefins such as polypropylene and polyethylene are preferred.

[0101] As an example of the structure of the non-aqueous electrolyte secondary battery, a structure in which an electrode group formed by winding a positive electrode and a negative electrode with a separator and a non-aqueous electrolyte are housed in an outer package can be cited. Alternatively, other types of electrode groups such as a laminated electrode group formed by laminating a positive electrode and a negative electrode with a separator can be applied instead of the wound electrode group. The non-aqueous electrolyte secondary battery can be, for example, in the form of a cylindrical type, a square type, a coin type, a button type, a laminated type, or the like.

[0102] Figure 1 It is a schematic perspective view showing a cut-away part of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

[0103] The battery includes a bottomed square battery case 4, and an electrode group 1 and a non-aqueous electrolyte (not shown) housed in the battery case 4. The electrode group 1 has a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator inserted therebetween to prevent direct contact. The electrode group 1 is formed by winding the negative electrode, the positive electrode, and the separator around a flat-shaped core and then removing the core.

[0104] One end of the negative electrode lead 3 is mounted on the negative electrode current collector of the negative electrode by welding or the like. The other end of the negative electrode lead 3 is electrically connected to the negative terminal 6 provided on the sealing plate 5 by means of a resin insulating plate (not shown). The negative terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. One end of the positive electrode lead 2 is mounted on the positive electrode current collector of the positive electrode by welding or the like. The other end of the positive electrode lead 2 is connected to the back surface of the sealing plate 5 by means of an insulating plate. That is, the positive electrode lead 2 is electrically connected to the battery case 4 which also serves as the positive terminal. The insulating plate isolates the electrode group 1 from the sealing plate 5 and isolates the negative electrode lead 3 from the battery case 4. The periphery of the sealing plate 5 is fitted into the opening end of the battery case 4, and the fitting portion is laser welded. Thus, the opening of the battery case 4 is sealed by the sealing plate 5. The injection hole for the non-aqueous electrolyte provided in the sealing plate 5 is plugged by a plug 8.

[0105] Hereinafter, the present invention will be specifically described based on examples and comparative examples, and the present invention is not limited to the following examples.

[0106] <Example 1>

[0107] [Preparation of negative electrode material LSX]

[0108] Silica and lithium carbonate were mixed so that the atomic ratio: Si / Li became 1.05, and the mixture was fired in air at 950 °C for 10 hours, whereby the formula: Li 2 Si 2 O 5 (z = 0.5) shown lithium silicate was obtained. The obtained lithium silicate was pulverized so that the average particle size became 10 μm.

[0109] Lithium silicate (Li 2 Si 2 O 5 ) having an average particle size of 10 μm and raw material silicon (3N, average particle size 10 μm) were mixed at a mass ratio of 40:60. The mixture was filled in a pot (made of SUS, volume: 500 mL) of a planetary ball mill (manufactured by Fritsch, P-5), 24 SUS balls (diameter 20 mm) were placed in the pot, the lid was closed, and the mixture was pulverized at 200 rpm for 50 hours in an inert atmosphere.

[0110] Next, in an inert atmosphere, the powdery mixture was taken out, and in an inert atmosphere, in a state where pressure was applied by a hot press, it was fired at 800 °C for 4 hours to obtain a sintered body (negative electrode material LSX) of the mixture.

[0111] After that, the negative electrode material LSX was pulverized, and after passing through a 40-μm sieve, the obtained LSX particles were mixed with coal tar pitch (manufactured by JFE Chemical Corporation, MCP250), and the mixture was fired at 800 °C in an inert atmosphere to form a conductive layer by covering the surface of the LSX particles with conductive carbon. The coverage amount of the conductive layer was set to 5% by mass based on the total mass of the LSX particles and the conductive layer. After that, using a sieve, LSX particles having a conductive layer with an average particle size of 5 μm were obtained.

[0112] By XRD analysis of the LSX particles, the crystallite size of the silicon particles calculated by the Scherrer formula based on the diffraction peak attributed to the Si(111) plane was 15 nm.

[0113] By analyzing the composition of the lithium silicate phase by the above methods (high-frequency induction furnace combustion-infrared absorption method, inert gas fusion-nondispersive infrared absorption method, inductively coupled plasma atomic emission spectrometry (ICP-AES)), the Si / Li ratio was 1.0, and the Li 2 Si 2 O 5 content was 40% by mass (the content of silicon particles was 60% by mass).

[0114] [Fabrication of negative electrode]

[0115] The LSX particles having a conductive layer and graphite were mixed at a mass ratio of 5:95 and used as the negative electrode active material. The negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed at a mass ratio of 97.5:1:1.5, water was added, and then stirred using a mixer (manufactured by PRIMIX Corporation, T.K.HIVIS MIX) to prepare a negative electrode slurry.

[0116] Next, the negative electrode slurry was coated on the surface of the copper foil such that the mass of the negative electrode binder per 1 m 2 became 190 g, and after drying the coating film, rolling was performed to fabricate a negative electrode having a negative electrode binder layer with a density of 1.5 g / cm 3 formed on both sides of the copper foil.

[0117] [Fabrication of positive electrode]

[0118] Lithium nickel composite oxide (LiNi 0.8 CO 0.18 Al 0.02 O 2) Acetylene black and polyvinylidene fluoride. After adding N-methyl-2-pyrrolidone (NMP), it was stirred using a mixer (manufactured by PRIMIX Corporation, T.K.HIVIS MIX) to prepare a positive electrode paste. Then, the positive electrode paste was coated on the surface of the aluminum foil, and after the coating film was dried, it was rolled to produce a positive electrode having a positive electrode mixture layer with a density of 3.6 g / cm 3 formed on both sides of the aluminum foil.

[0119] [Preparation of Non-aqueous Electrolyte]

[0120] A non-aqueous electrolyte in which a lithium salt is dissolved in a non-aqueous solvent was prepared. The non-aqueous solvent used was a solution obtained by adding a sultone compound, fluoroethylene carbonate (FEC), and vinylene carbonate (VC) to a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The volume ratio of EC, DMC, and EMC was set to 10:80:10. The content of the sultone compound in the non-aqueous electrolyte (mass ratio relative to the whole non-aqueous electrolyte) was set to 1% by mass. The sultone compound used was 1,3-propylene sultone (PRS). The content of FEC in the non-aqueous electrolyte (mass ratio relative to the whole non-aqueous electrolyte) was set to 2% by mass. The content of VC in the non-aqueous electrolyte (mass ratio relative to the whole non-aqueous electrolyte) was set to 2% by mass. The lithium salt used was LiPF 6 . The concentration of LiPF 6 in the non-aqueous electrolyte was set to 1.2 mol / L.

[0121] [Fabrication of Non-aqueous Electrolyte Secondary Battery]

[0122] Tabs were respectively attached to each electrode, and in such a manner that the tabs were located at the outermost peripheral part, the positive electrode and the negative electrode were wound in a spiral shape with a separator to fabricate an electrode assembly. The electrode assembly was inserted into an outer package made of an aluminum laminated film, vacuum dried at 105 °C for 2 hours, then the non-aqueous electrolyte was injected, and the opening of the outer package was sealed to obtain Battery A1.

[0123] [Example 2]

[0124] In the preparation of the negative electrode material LSX, lithium silicate (Li 2 Si 2 O 5 ) with an average particle size of 10 μm and raw material silicon (3N, average particle size 10 μm) were mixed at a mass ratio of 45:55. Regarding the obtained LSX particles having a conductive layer, the content of Li 2 Si 2 O 5 measured by Si-NMR was 45% by mass (the content of silicon particles was 55% by mass).

[0125] In addition to the above, battery A2 was fabricated by the same method as in Example 1.

[0126] <Example 3>

[0127] In the preparation of the negative electrode material LSX, lithium silicate (Li 2 Si 2 O 5 ) with an average particle size of 10 μm and raw material silicon (3N, average particle size of 10 μm) were mixed at a mass ratio of 20:80. Regarding the obtained LSX particles with a conductive layer, the content of Li 2 Si 2 O 5 determined by Si-NMR was 20% by mass (the content of silicon particles was 80% by mass).

[0128] In addition to the above, battery A3 was fabricated by the same method as in Example 1.

[0129] <Example 4>

[0130] In the preparation of the negative electrode, LSX particles with a conductive layer and graphite were mixed at a mass ratio of 10:90 and used as the negative electrode active material. In addition to this, battery A4 was fabricated by the same method as in Example 1.

[0131] <Example 5>

[0132] In the preparation of the negative electrode, LSX particles with a conductive layer and graphite were mixed at a mass ratio of 15:85 and used as the negative electrode active material. In addition to this, battery A5 was fabricated by the same method as in Example 1.

[0133] <Example 6>

[0134] In the preparation of the non-aqueous electrolyte, except that the content of PRS in the non-aqueous electrolyte was set to 0.5% by mass, battery A6 was fabricated by the same method as in Example 1.

[0135] <Example 7>

[0136] In the preparation of the non-aqueous electrolyte, the lithium salts used were LiPF 6 and LFSI. The concentration of LiPF 6 in the non-aqueous electrolyte was set to 1.0 mol / L. The concentration of LFSI in the non-aqueous electrolyte was set to 0.2 mol / L.

[0137] In addition to the above, battery A7 was fabricated by the same method as in Example 1.

[0138] <Example 8>

[0139] In the preparation of the non-aqueous electrolyte, the lithium salts used were LiPF 6and LFSI. The concentration of LiPF in the non-aqueous electrolyte 6 was set to 0.6 mol / L. The concentration of LFSI in the non-aqueous electrolyte was set to 0.6 mol / L.

[0140] Except as described above, Battery A8 was fabricated in the same manner as in Example 1.

[0141] <Example 9>

[0142] In the preparation of the negative electrode material LSX, lithium silicate (Li 2 Si 2 O 5 ) with an average particle size of 10 μm and raw material silicon (3N, average particle size of 10 μm) were mixed at a mass ratio of 45:55. Regarding the obtained LSX particles having a conductive layer, the content of Li 2 Si 2 O 5 measured by Si-NMR was 45% by mass (the content of silicon particles was 55% by mass).

[0143] In the preparation of the non-aqueous electrolyte, 1,3-propane sultone (PS) at 1% by mass was included as the sultone compound in the non-aqueous electrolyte instead of PRS.

[0144] Except as described above, Battery A9 was fabricated in the same manner as in Example 1.

[0145] <Example 10>

[0146] In the preparation of the non-aqueous electrolyte, except that the content of PRS in the non-aqueous electrolyte was set to 2% by mass, Battery A10 was fabricated in the same manner as in Example 1.

[0147] <Example 11>

[0148] In the preparation of the non-aqueous electrolyte, except that the content of PRS in the non-aqueous electrolyte was set to 0.1% by mass, Battery A11 was fabricated in the same manner as in Example 1.

[0149] <Comparative Example 1>

[0150] In the preparation of the negative electrode material LSX, lithium silicate (Li 2 Si 2 O 5 ) with an average particle size of 10 μm and raw material silicon (3N, average particle size of 10 μm) were mixed at a mass ratio of 60:40. Regarding the obtained LSX particles having a conductive layer, the content of Li 2 Si 2 O 5 measured by Si-NMR was 60% by mass (the content of silicon particles was 40% by mass).

[0151] Except as described above, Battery B1 was fabricated in the same manner as in Example 1.

[0152] <Comparative Example 2>

[0153] In the preparation of the negative electrode material LSX, lithium silicate (Li 2 Si 2 O 5 ) with an average particle size of 10 μm and raw material silicon (3N, average particle size of 10 μm) were mixed at a mass ratio of 10:90. Regarding the obtained LSX particles with a conductive layer, the content of Li 2 Si 2 O 5 determined by Si-NMR was 10% by mass (the content of silicon particles was 90% by mass).

[0154] Except as described above, Battery B2 was fabricated in the same manner as in Example 1.

[0155] <Comparative Example 3>

[0156] In the preparation of the non-aqueous electrolyte, except that the non-aqueous electrolyte did not contain PRS, Battery B3 was fabricated in the same manner as in Example 1.

[0157] <Comparative Example 4>

[0158] In the preparation of the negative electrode material LSX, lithium silicate (Li 2 Si 2 O 5 ) with an average particle size of 10 μm and raw material silicon (3N, average particle size of 10 μm) were mixed at a mass ratio of 45:55. Regarding the obtained LSX particles with a conductive layer, the content of Li 2 Si 2 O 5 determined by Si-NMR was 45% by mass (the content of silicon particles was 55% by mass).

[0159] In the preparation of the non-aqueous electrolyte, the non-aqueous electrolyte was not made to contain PRS.

[0160] Except as described above, Battery B4 was fabricated in the same manner as in Example 1.

[0161] <Comparative Example 5>

[0162] In the preparation of the negative electrode material LSX, lithium silicate (Li 2 Si 2 O 5 ) with an average particle size of 10 μm and raw material silicon (3N, average particle size of 10 μm) were mixed at a mass ratio of 20:80. Regarding the obtained LSX particles with a conductive layer, the content of Li 2Si 2 O 5 The content of is 20% by mass (the content of silicon particles is 80% by mass).

[0163] In the preparation of the non-aqueous electrolyte, the non-aqueous electrolyte is not made to contain PRS.

[0164] Except as described above, battery B5 was fabricated in the same manner as in Example 1.

[0165] <Comparative Example 6>

[0166] In the preparation of the non-aqueous electrolyte, except that the content of PRS in the non-aqueous electrolyte was set to 2.1% by mass, battery A11 was fabricated in the same manner as in Example 1.

[0167] Except as described above, battery B6 was fabricated in the same manner as in Example 1.

[0168] <Comparative Example 7>

[0169] In the fabrication of the negative electrode, SiO particles (average particle size 10 μm, x = 1) were used instead of LSX particles having a conductive layer. The SiO particles and graphite were mixed at a mass ratio of 5:95 and used as the negative electrode active material.

[0170] Except as described above, battery B7 was fabricated in the same manner as in Example 1.

[0171] Regarding each of the above fabricated batteries, evaluation was performed according to the following method.

[0172] [Evaluation 1: Initial capacity]

[0173] Regarding each of the fabricated batteries, in an environment at 25°C, constant current charging was performed at a current of 0.3It until the voltage reached 4.2V, and then constant voltage charging was performed at 4.2V until the current reached 0.015It. Thereafter, constant current discharging was performed at a current of 0.3It until the voltage reached 2.75V. The pause period between charging and discharging was set to 10 minutes. Charging and discharging were performed in an environment at 25°C. The discharge capacity at this time was used as the initial capacity and calculated. The evaluation results are shown in Table 1.

[0174] It should be noted that (1 / X)It represents the current, (1 / X)It (A) = rated capacity (Ah) / X (h), and X represents the time required to charge or discharge the electricity of the rated capacity part. For example, 0.5It means X = 2, and the current value is rated capacity (Ah) / 2 (h).

[0175] [Evaluation 2: Cycle capacity retention rate]

[0176] Constant current charging is carried out at a current of 0.3It until the voltage reaches 4.2V. After that, constant voltage charging is carried out at a constant voltage of 4.2V until the current becomes 0.015It. Then, constant current discharging is carried out at a current of 0.3It until the voltage reaches 2.75V. The pause period between charging and discharging is set to 10 minutes. The charge and discharge are carried out in an environment of 25°C.

[0177] The charge and discharge are repeated under the above charge and discharge conditions. The ratio (percentage) of the discharge capacity of the 50th cycle to the discharge capacity of the 1st cycle is obtained as the cycle capacity retention rate.

[0178] The evaluation results are shown in Table 1.

[0179] [Evaluation 3: Gas generation amount during battery storage]

[0180] After repeating the charge and discharge 5 cycles under the same conditions as in the above Evaluation 1, and then charging under the same conditions as in the above Evaluation 1. The battery in the charged state is stored in an environment of 80°C for 3 days, and the amount of gas generated inside the battery during storage is obtained. The evaluation results are shown in Table 1.

[0181] [Table 1]

[0182]

[0183] In batteries A1 to A11, a film derived from PRS is moderately formed on the surface of the LSX particles, so the cycle capacity retention rate is high and the gas generation amount during battery storage is small.

[0184] In addition, regarding battery A1, after repeating the charge and discharge 1 cycle under the same conditions as in the above Evaluation 1, and then charging under the same conditions as in the above Evaluation 1. Battery A1 in the charged state is disassembled, and the components of the non-aqueous electrolyte are analyzed by gas chromatography-mass spectrometry. As a result, the residual PRS amount in the non-aqueous electrolyte of battery A1 is 50 ppm.

[0185] In battery B1, a non-aqueous electrolyte with a PRS content of 1% by mass is used, but the content of silicon particles in the LSX particles is as low as 40% by mass, so the initial capacity is reduced.

[0186] In battery B2, a non-aqueous electrolyte with a PRS content of 1% by mass is used, but the content of silicon particles in the LSX particles is as high as 90% by mass. Therefore, the expansion and contraction of the LSX particles during charge and discharge are very large, and the film cannot follow the expansion and contraction of the LSX particles and is damaged, resulting in a decrease in the cycle capacity retention rate and an increase in the gas generation amount.

[0187] In batteries B3 to B5, the content of silicon particles in the LSX particles is 55% by mass or more and 80% by mass or less. However, since a non-aqueous electrolyte not containing PRS is used, the coating film is damaged, the cycle capacity retention rate decreases, and the gas generation amount increases.

[0188] In battery B6, the content of silicon particles in the LSX particles is 60% by mass. However, since a non-aqueous electrolyte with a PRS content of more than 2% by mass is used, an excessive coating film derived from PRS is formed on the surface of the LSX particles, the reaction resistance increases, and the cycle capacity retention rate decreases.

[0189] In battery B7, a non-aqueous electrolyte with a PRS content of 1% by mass is used, but SiO particles are used instead of LSX particles with a silicon content of more than 40%, so the initial capacity decreases. The SiO in the SiO particles 2 phase is neutral, so the coating film derived from PRS cannot be formed tightly and uniformly on the surface of the SiO particles, and the durability of the coating film is insufficient, etc., the cycle capacity retention rate decreases, and the gas generation amount increases. In addition, the irreversible capacity of the SiO particles is also larger than that of the LSX particles, so the cycle capacity retention rate decreases.

[0190] Industrial Applicability

[0191] The non-aqueous electrolyte secondary battery of the present invention is useful as a main power source for mobile object communication devices, portable electronic devices, etc.

[0192] Explanation of Reference Numerals

[0193] 1 Electrode group

[0194] 2 Positive electrode lead

[0195] 3 Negative electrode lead

[0196] 4 Battery case

[0197] 5 Sealing plate

[0198] 6 Negative terminal

[0199] 7 Gasket

[0200] 8 Plug

Claims

1. A non-aqueous electrolyte secondary battery comprising: a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode contains a negative electrode active material capable of electrochemically storing and releasing lithium, the negative electrode active material contains a composite material, the composite material containing a silicate phase and silicon particles dispersed in the silicate phase, the silicate phase contains at least one of an alkali metal and an alkaline earth metal, the content of the silicon particles in the composite material is 50% by mass or more and 70% by mass or less, the non-aqueous electrolyte contains a sultone compound, the content of the sultone compound in the non-aqueous electrolyte is 2% by mass or less, the non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent, The lithium salt includes LiN(SO 2 F) 2 and LiPF 6 , The concentration of LiN(SO 2 F) 2 in the non-aqueous electrolyte is 0.1 mol / L or more and 1.0 mol / L or less.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, the content of the sultone compound in the non-aqueous electrolyte is 0.1% by mass or more and 2% by mass or less.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, the silicate phase is an oxide phase containing lithium, silicon, and oxygen, the atomic ratio of oxygen to silicon in the silicate phase: O / Si is greater than 2 and less than 4.

4. The non-aqueous electrolyte secondary battery according to claim 3, wherein, The composition of the silicate phase is represented by the formula: Li 2z SiO 2+z as shown z in the formula satisfies the relationship 0 < z < 2.

5. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, the content of the silicon particles in the composite material is 55% by mass or more and 70% by mass or less.

6. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, the sultone compound contains 1,3-propenyl sultone.

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