Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure comprises: an electrode group including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte. The negative electrode includes a negative electrode mixture layer containing a negative electrode active material, the negative electrode active material includes a silicon-containing material, the mass content of the silicon-containing material in the negative electrode mixture layer is 3.5 mass% or more, and the non-aqueous electrolyte includes a chain acid anhydride containing fluorine.

Description

Non-aqueous electrolyte secondary battery

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

[0002] A non-aqueous electrolyte secondary battery comprises an electrode group and a non-aqueous electrolyte. The electrode group includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. Various studies have been conducted on non-aqueous electrolyte secondary batteries to improve the capacity retention rate.

[0003] Patent Document 1 discloses a lithium battery including at least one electrochemical cell containing a lithium ion conductive electrolyte containing at least one sulfone solvent, at least one additive selected from anhydride compounds, and at least one lithium salt, wherein the electrolyte has the formula LiNi as an active material ０．４ Mn １．６ O ４ or LiNi ０．５ Mn １．５ O ４ lithiated oxide, and a negative electrode containing Li ４ Ti ５ O １２ as an active material. Patent Document 1 also discloses that the lithium battery configured as described above exhibits excellent cycle performance. That is, Patent Document 1 discloses that in a non-aqueous electrolyte, when a sulfone solvent is used as the non-aqueous solvent and an anhydride compound is added as an additive to the sulfone solvent, the capacity retention rate of the lithium battery can be improved.

[0004] Patent Document 2 discloses a non-aqueous electrolyte battery comprising at least a positive electrode mainly composed of a positive electrode active material, a negative electrode mainly composed of a negative electrode active material, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains fluoride of an acid anhydride. Patent Document 2 also discloses that in a non-aqueous electrolyte battery configured as described above, during the initial charge, the fluoride of the acid anhydride decomposes on the surface of the negative electrode, such as a graphite negative electrode, and a lithium-ion permeable protective film is formed on the surface of the negative electrode, so that charging and discharging can be performed sufficiently from the second cycle onward. In other words, Patent Document 2 discloses that by using fluoride of an acid anhydride as a non-aqueous solvent in the non-aqueous electrolyte, the capacity retention rate of the non-aqueous electrolyte battery can be improved.

[0005] Japanese Patent Publication No. 2017-505521, Japanese Patent Publication No. 2003-86244

[0006] In non-aqueous electrolyte secondary batteries such as lithium-ion batteries, silicon-containing materials are sometimes used as negative electrode active materials to increase capacity. Although silicon-containing materials have a high lithium-ion absorption capacity, they expand significantly during charging due to lithium-ion absorption and contract significantly during discharging due to lithium-ion release. In other words, when the negative electrode contains a silicon-containing material as the negative electrode active material, significant expansion and contraction occur in the negative electrode during charging and discharging. This significant expansion and contraction in the negative electrode can cause a decrease in the capacity retention rate of the non-aqueous electrolyte secondary battery. This decrease in the capacity retention rate of the non-aqueous electrolyte secondary battery becomes more pronounced as the content of silicon-containing material in the negative electrode increases.

[0007] However, various prior art documents, including Patent Documents 1 and 2, have not adequately examined how to suppress the decrease in volume retention rate caused by the expansion and contraction of silicon-containing materials.

[0008] Therefore, the objective of this disclosure is to provide a non-aqueous electrolyte secondary battery that can suppress the decrease in capacity retention rate.

[0009] One aspect of the present invention relates to a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery comprises an electrode group including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The negative electrode comprises a negative electrode mixture layer containing a negative electrode active material. The negative electrode active material contains a silicon-containing material, and the mass content of silicon element in the negative electrode mixture layer is 3.5% by mass or more. The non-aqueous electrolyte contains a fluorine-containing chain acid anhydride.

[0010] According to this disclosure, it is possible to provide a non-aqueous electrolyte secondary battery that can suppress the decrease in capacity retention rate.

[0011] This is a schematic cross-sectional view showing a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure.

[0012] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values, materials, etc. may be applied as long as the effects of this disclosure are obtained. Notwithstanding, known components may be applied to components of parts that are characteristic of this disclosure. In this specification, when "the range of numerical values ​​A to numerical values ​​B" is used, that range includes numerical values ​​A and B.

[0013] In the following explanation, when examples are given for the lower and upper limits of numerical values ​​related to specific physical properties or conditions, any combination of either of the given lower limits and any of the given upper limits is permitted, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, unless otherwise specified, one type may be selected and used alone, or two or more types may be used in combination.

[0014] This disclosure includes any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims. In other words, any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims is possible, as long as it does not result in a technical inconsistency.

[0015] [Non-aqueous electrolyte secondary battery] A non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure comprises an electrode group including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0016] In the non-aqueous electrolyte secondary battery according to the embodiments of this disclosure, the negative electrode comprises a negative electrode mixture layer containing a negative electrode active material, and the negative electrode active material contains a silicon-containing material. In the non-aqueous electrolyte secondary battery according to the embodiments of this disclosure, the mass content of silicon element in the negative electrode mixture layer is 3.5% by mass or more. In the non-aqueous electrolyte secondary battery according to the embodiments of this disclosure, the non-aqueous electrolyte contains a fluorine-containing chain acid anhydride.

[0017] In the non-aqueous electrolyte secondary battery according to the embodiments of this disclosure, it is important that (i) the mass content of silicon element in the negative electrode mixture layer is 3.5% by mass or more, and (ii) the non-aqueous electrolyte contains a fluorine-containing linear acid anhydride. The reasons for this are explained below.

[0018] In non-aqueous electrolyte secondary batteries, suppressing the decrease in capacity retention rate is required to extend the battery's lifespan. The decrease in capacity retention rate in non-aqueous electrolyte secondary batteries occurs, for example, when the non-aqueous solvent contained in the non-aqueous electrolyte comes into contact with the surface of the negative electrode active material over time and undergoes reductive decomposition. Therefore, to suppress the time-dependent contact between the non-aqueous solvent and the surface of the negative electrode active material, the surface of the negative electrode active material is usually covered with an SEI (Solid Electrolyte Interphase) film during the initial charge and discharge. The SEI film is usually formed when organic components contained in the non-aqueous electrolyte (for example, a part of the non-aqueous solvent) undergo reductive decomposition on the surface of the negative electrode active material. In other words, the SEI film is usually formed as an organic film.

[0019] Furthermore, in conventional non-aqueous electrolyte secondary batteries, silicon-containing materials are sometimes used as negative electrode active materials to increase capacity. Although silicon-containing materials have a high lithium ion absorption capacity, they expand significantly during charging due to lithium ion absorption and contract significantly during discharging due to lithium ion release. The negative electrode active material is usually contained in the negative electrode mixture layer, and in such cases, significant expansion and contraction occur in the negative electrode mixture layer during charging and discharging. The higher the silicon-containing material content in the negative electrode mixture layer, the greater the degree of expansion and contraction of the negative electrode mixture layer during charging and discharging.

[0020] Incidentally, the SEI coating formed as an organic film often lacks structural density and does not necessarily possess sufficient strength. Therefore, as described above, if large expansion and contraction occur in the negative electrode mixture layer during charging and discharging of a non-aqueous electrolyte secondary battery, cracks may occur in the SEI coating formed as an organic film. In this case, there is a concern that the non-aqueous solvent contained in the non-aqueous electrolyte will come into contact with the surface of the negative electrode active material over time, and that the reductive decomposition of the non-aqueous solvent will progress over time. Furthermore, there is a concern that the capacity retention rate of the non-aqueous electrolyte secondary battery will decrease due to the reductive decomposition of the non-aqueous solvent over time.

[0021] Here, in the non-aqueous electrolyte secondary battery of the present disclosure, as described above, (ii) the non-aqueous electrolyte contains a fluorine-containing linear acid anhydride. In this case, the fluorine-containing linear acid anhydride is coordinated to the lithium ion, and the lithium ion reduction reaction (Li ＋ +e － →Li) can be advanced. As a result, Li ２ It is thought that an inorganic compound such as O or LiF can be generated, and the surface of the negative electrode active material can be covered with this inorganic compound. That is, an inorganic coating (for example, Li ２It is thought that the surface of the negative electrode active material can be covered with an SEI coating formed as (O or LiF). Furthermore, it is thought that such an inorganic coating has a higher structural density and sufficient strength than an organic coating formed by the reductive decomposition of organic components.Therefore, in a non-aqueous electrolyte secondary battery, as described above, (i) the mass content of silicon element in the negative electrode mixture layer is 3.5% by mass or more, in other words, even if the content of silicon-containing material in the negative electrode mixture layer is high and the degree of expansion and contraction of the negative electrode mixture layer during charging and discharging is large, it is thought that cracking of the SEI coating formed as an inorganic coating can be suppressed.As a result, it is thought that the non-aqueous solvent contained in the non-aqueous electrolyte will come into contact with the surface of the negative electrode active material over time, and the reductive decomposition of the non-aqueous solvent will proceed over time, thereby suppressing the progress of reductive decomposition of the non-aqueous solvent over time.

[0022] The following describes an example of a non-aqueous electrolyte secondary battery of this disclosure in which the negative electrode comprises a negative electrode mixture layer.

[0023] <Non-aqueous electrolytes> Non-aqueous electrolytes consist of a non-aqueous solvent, a salt, and a fluorine-containing linear acid anhydride. The fluorine-containing linear acid anhydride is classified as an additive. That is, non-aqueous electrolytes contain a fluorine-containing linear acid anhydride as an additive. Non-aqueous electrolytes may be an electrolyte solution, or they may be in a state where fluidity is restricted by a gelling agent or the like. Lithium salts are usually used as the salt. The salt and additives are basically dissolved in the non-aqueous solvent. On the other hand, to the extent that the effects of the invention are not significantly impaired, some of the salt or additives may precipitate without dissolving in the non-aqueous solvent.

[0024] Furthermore, the non-aqueous electrolyte recovered from a non-aqueous electrolyte secondary battery may contain little to no additives (e.g., fluorine-containing linear acid anhydrides). In this case, the non-aqueous electrolyte secondary battery may contain reduction products of the additives. Even in such cases, the non-aqueous electrolyte collected from the non-aqueous electrolyte secondary battery will still contain additives in a detectable amount (amount above the detection limit). Therefore, it can be confirmed that the non-aqueous electrolyte contains additives.

[0025] (Non-aqueous solvent) The non-aqueous solvent may contain carbonate esters. The carbonate ester may be the main component of the non-aqueous solvent. For example, the carbonate ester may account for 60% or more by volume of the non-aqueous solvent, or 70% or more by volume of the non-aqueous solvent, or 80% or more by volume, or 90% by volume. The carbonate ester may account for 100% by volume of the non-aqueous solvent. In other words, the entire non-aqueous solvent may be carbonate ester. When the carbonate ester is the main component of the non-aqueous solvent, transition metals are more easily eluted from the positive electrode and more easily precipitated at the negative electrode.

[0026] On the other hand, in the case of a non-aqueous electrolyte where the carbonate ester contains ethylene carbonate, the mass content of the lithium salt relative to the total mass of the non-aqueous electrolyte is C Ｌｉ The mass content of ethylene carbonate is set to C ＥＣ In that case, C Ｌｉ and C ＥＣ C Ｌｉ / C ＥＣ It is preferable that the condition >1 is satisfied. That is, in a non-aqueous electrolyte, C Ｌｉ C ＥＣ It is preferable that it contains more than [a certain amount]. By satisfying this relationship, the frequency of contact between fluorine-containing linear acid anhydrides and lithium ions in a non-aqueous electrolyte can be increased. This makes it easier to further coordinate fluorine-containing linear acid anhydrides to lithium ions in a non-aqueous electrolyte. As a result, an inorganic film (e.g., Li) ２ The SEI coating, formed as O or LiF, makes it easier to further adequately cover the surface of the negative electrode active material.

[0027] The non-aqueous electrolyte preferably contains two or more non-aqueous solvents. The carbonate ester may contain both cyclic carbonate esters and linear carbonate esters.

[0028] Examples of cyclic carbonate esters include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC).

[0029] Examples of linear carbonate esters include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0030] The volume content of ethylene carbonate in the total volume of the non-aqueous solvent is preferably 20% by volume or less. The volume content of ethylene carbonate in the total volume of the non-aqueous solvent may be 15% by volume or less. Furthermore, the volume content of ethylene carbonate in the total volume of the non-aqueous solvent is preferably 5% by volume or more. The volume content of ethylene carbonate in the non-aqueous solvent may be 8% by volume. By having the volume content of ethylene carbonate in the total volume of the non-aqueous solvent within the above range, C Ｌｉ / C ＥＣ >1 becomes easier to satisfy. This makes it easier to further coordinate fluorine-containing linear acid anhydrides to lithium ions in non-aqueous electrolytes. As a result, inorganic coating (e.g., Li ２ The SEI coating, formed as (containing O or LiF), makes it easier to further adequately cover the surface of the negative electrode active material. In addition, by keeping the volume content of ethylene carbonate in relation to the total volume of the non-aqueous solvent within the above range, the balance of physical properties of the non-aqueous electrolyte is more easily maintained.

[0031] The non-aqueous solvent may contain fluoroethylene carbonate (FEC) as a cyclic carbonate. The carbonate group (-O-C=O-O- group) of fluoroethylene carbonate makes it difficult for metal ions to coordinate due to the electron-withdrawing effect of the fluorine atom. Therefore, by using fluoroethylene carbonate, the elution of transition metals can be further suppressed. From the viewpoint of maintaining the balance of physical properties of the non-aqueous electrolyte, it is preferable that the non-aqueous solvent contains both ethylene carbonate and fluoroethylene carbonate.

[0032] The non-aqueous solvent may contain small amounts of other solvents in addition to the carbonate ester. Examples of other solvents include cyclic carboxylic acid esters, linear carboxylic acid esters, cyclic ethers, and linear ethers.

[0033] 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. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of linear ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methylphenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0034] (Salt) Lithium salts are usually used as salts. 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 Examples include lithium lower aliphatic carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO4). ２ F ２Examples of borates include lithium difluorobis(oxalato)phosphate (LiDFBOP) and lithium tetrafluoro(oxalato)phosphate. Examples of borates include lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LIDFOB). Examples of imide salts include lithium bisfluorosulfonylimide (LiN(FSO)). ２ ) ２ ), bistrifluoromethanesulfonate lithium (LiN(CF ３ SO ２ ) ２ ), trifluoromethanesulfonic acid nonafluorobutanesulfonic acid lithium (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), and bispentafluoroethanesulfonate lithium (LiN(C) ２ F ５ SO ２ ) ２ Examples include the following. The non-aqueous electrolyte may contain one lithium salt alone, or it may contain a combination of two or more lithium salts.

[0035] The concentration of the lithium salt may be, for example, 1.3 mol / L or more and 2.5 mol / L or more and 1.5 mol / L or more and 2.5 mol / L or less, from the viewpoint of facilitating the coordination of fluorine-containing linear acid anhydrides to lithium ions in a non-aqueous electrolyte.

[0036] (Additives) As described above, the non-aqueous electrolyte contains a fluorine-containing linear acid anhydride as an additive. The fluorine-containing linear acid anhydride preferably has the structure represented by the following chemical formula (1). Having the structure represented by the following chemical formula (1) makes it easier to further coordinate the fluorine-containing linear acid anhydride with lithium ions.

[0037]

[0038] However, in the above chemical formula (1), R １ and R２ Each of these is independently a functional group having an alkyl group, alkenyl group, or alkynyl group with 1 to 6 carbon atoms, or a benzene ring with 6 to 8 carbon atoms. １ and R ２ At least one hydrogen element is substituted with a fluorine element. Note that functional groups with more than 8 carbon atoms have significant steric hindrance. Therefore, this is undesirable as it makes it difficult to coordinate lithium ions to fluorine-containing linear acid anhydrides. In other words, an inorganic coating as an SEI coating (for example, Li ２ This is undesirable because it results in inferior ability to form (including O or LiF).

[0039] The fluorine-containing linear acid anhydride is preferably at least one selected from the group consisting of difluoroacetic anhydride, trifluoroacetic anhydride, heptafluorobutyric anhydride, pentafluoropropionic anhydride, and 4-trifluoromethylbenzoic anhydride. This makes it easier to further coordinate the fluorine-containing linear acid anhydride to the lithium ion.

[0040] Difluoroacetic anhydride has the molecular formula: (CF ２ HCO) ２ As shown by O, acetic anhydride (molecular formula: (CH ３ CO) ２ Trifluoroacetic anhydride is a chain-like acid anhydride in which four of the six hydrogen elements contained in (O) are replaced by fluorine elements, and its molecular formula is (CF ３ CO) ２ As indicated by O, acetic anhydride is a chain-like acid anhydride in which all six hydrogen atoms are replaced by fluorine atoms.

[0041] Heptafluorobutyric acid anhydride has the molecular formula: (CF ３ CF ２ CF ２ CO) ２ As shown by O, butyric anhydride (molecular formula: (CH) ３ CH ２ CH ２ CO) ２ It is a chain-like acid anhydride in which all 14 hydrogen elements in (O) are substituted.

[0042] Pentafluoropropionic anhydride has the molecular formula: (CF ３ CF ２ CO) ２ As indicated by O, propionic anhydride (molecular formula: (CH) ３ CH ２ CO) ２ O) is a chain-like acid anhydride in which all 10 hydrogen elements are replaced by fluorine elements.

[0043] 4-Trifluoromethylbenzoic anhydride is a chain-like acid anhydride in which six of the 14 hydrogen atoms in di(p-toluic acid) anhydride (or bis(4-methylbenzoic acid) anhydride) (in other words, all of the hydrogen atoms in the methyl group) are replaced by fluorine atoms, as shown in the chemical formula (2) below.

[0044]

[0045] From the viewpoint of balancing the liquid properties, the content of fluorine-containing linear acid anhydride relative to the total mass of the non-aqueous electrolyte is preferably 2% by mass or less. The content of fluorine-containing linear acid anhydride relative to the total mass of the non-aqueous electrolyte may be 0.01% by mass or more and 2% by mass or less, 0.1% by mass or more and 2% by mass or less, 0.5% by mass or more and 2% by mass or less, or 0.5% by mass or more and 1.5% by mass or less.

[0046] The content of each component in a non-aqueous electrolyte can be determined, for example, using gas chromatography under the following conditions: Conditions and measuring instrument: Shimadzu GC-2010 Plus; Column: J&W HP-1 (diameter 1 μm x length 60 m); Linear velocity: 30.0 cm / sec; Inlet temperature: 270°C; Detector: FID 290°C (sense 10°C) １ )

[0047] <Positive Electrode> The positive electrode comprises, for example, a positive electrode current collector and a positive electrode mixture layer provided on the surface of the positive electrode current collector. The positive electrode current collector is made of a sheet-like conductive material. The positive electrode mixture layer is supported on one or both surfaces of the positive electrode current collector. The positive electrode mixture layer is usually a layer or film composed of a positive electrode mixture. The thickness of the positive electrode mixture layer is, for example, 10 μm to 150 μm per side of the positive electrode current collector. The positive electrode mixture contains a positive electrode active material as an essential component.

[0048] The positive electrode mixture layer may contain a conductive agent as an optional component. Examples of conductive agents include carbon-based materials such as carbon black (CB), carbon nanotubes (CNT), graphene, and graphite. Examples of carbon black include acetylene black (AB) and Ketjenblack (KB). The conductive agent may be used alone or in combination of two or more types.

[0049] The positive electrode mixture layer may contain a binder as an optional component. Examples of binders include fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. Examples of fluororesins include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF). The binder may be used alone or in combination of two or more types.

[0050] As the positive electrode current collector, for example, a non-porous conductive substrate or a porous conductive substrate can be used. Examples of non-porous conductive substrates include metal foil. Examples of porous conductive substrates include meshes, nets, and perforated sheets. Examples of materials that make up the positive electrode current collector include aluminum, titanium, aluminum alloys, and titanium alloys.

[0051] As the positive electrode active material, for example, a lithium-containing composite oxide can be used. The lithium-containing composite oxide may have a layered rock salt structure. The layered rock salt structure may belong to, for example, space group R-3m, space group C2 / m, or other space groups. It is preferable that the layered rock salt structure belongs to space group R-3m in order to achieve high capacity and to have high stability of the crystal structure. The layered rock salt structure of the lithium-containing composite oxide may include a transition metal layer, a Li layer, and an oxygen layer.

[0052] In order to achieve high capacity, the lithium-containing composite oxide may have a Ni content of 50 atomic percent or more among the metal elements other than Li, or it may have a Ni content of 80 atomic percent or more, or it may have a Ni content of 90 atomic percent or more.

[0053] In order to stabilize the crystal structure and improve the heat resistance of the battery, in lithium-containing composite oxides, the proportion of Al among metal elements other than Li (Al content) may be greater than 0 atomic percent and 18.5 atomic percent or less, or 4 atomic percent or more and 10 atomic percent or less.

[0054] The content of each metal element in lithium-containing composite oxides can be measured, for example, by inductively coupled plasma (ICP) emission spectroscopy.

[0055] Lithium-containing composite oxides include, for example, those with the general formula: Li ａ Ni ｘ Co ｙ Al ｚ M1 ｗ O ２－ｂ It may also be a composite oxide represented by the above general formula. However, in the above general formula, 0.8 ≤ a ≤ 1.2, 0.5 ≤ x ≤ 0.95, 0 ≤ y ≤ 0.16, 0 ≤ z ≤ 0.185, 0 ≤ w ≤ 0.5, 0 ≤ b < 0.05, and x + y + z + w = ​​1. Also, in the above general formula, M1 is at least one element selected from the group consisting of Mn, Fe, Ti, Si, Nb, Zr, Mo, Sr, W, B, Ca, and Zn. In the above general formula, M1 is preferably Mn. Note that lithium-containing composite oxides are sometimes called lithium-containing transition metal oxides.

[0056] <Negative Electrode> The negative electrode comprises a negative electrode mixture layer containing a negative electrode active material. The negative electrode may also include a negative electrode current collector. In this case, the negative electrode mixture layer may be provided on the surface of the negative electrode current collector. The negative electrode current collector is made of a sheet-like conductive material. The negative electrode mixture layer may be supported on one or both surfaces of the negative electrode current collector. The negative electrode mixture layer is usually a layer or film composed of a negative electrode mixture. The thickness of the negative electrode mixture layer is, for example, 10 μm to 150 μm per side of the negative electrode current collector. As described above, the negative electrode mixture layer contains a negative electrode active material as an essential component. The negative electrode mixture layer may also contain binders, conductive agents, and thickeners as optional components.

[0057] The negative electrode active material includes materials that electrochemically intercept and release lithium ions, lithium metals, and lithium alloys. Examples of materials that electrochemically intercept and release lithium ions include carbon materials and alloy materials.

[0058] Examples of carbon materials include graphite, easily graphitizable carbon (soft carbon), and poorly graphitizable carbon (hard carbon). Graphite is preferred as the carbon material because it provides excellent stability during charging and discharging and has low irreversible capacity.

[0059] Graphite is a carbonaceous material in which a graphite-type crystal structure is well-developed. The interplanar spacing d002 of the (002) planes of graphite, as measured by X-ray diffraction, may be, for example, 0.340 nm or less, or 0.3354 nm or more and 0.340 nm or less. The crystallite size Lc(002) of graphite may be, for example, 5 nm or more, or 5 nm or more and 200 nm or less. The crystallite size Lc(002) can be measured, for example, by the Scherrer method. When the interplanar spacing d002 of the (002) planes of graphite and the crystallite size Lc(002) are within the above ranges, high capacity is easily obtained.

[0060] Alloy materials are materials that contain at least one metal capable of forming an alloy with lithium. Examples of alloy materials include silicon, tin, silicon alloys, tin alloys, silicon oxide, tin oxide, and silicon-containing materials. As described above, the non-aqueous electrolyte secondary battery according to the embodiment of this disclosure contains a silicon-containing material as the negative electrode active material, and the mass content of silicon elements in the negative electrode mixture layer is 3.5% by mass or more. Furthermore, it is desirable that the upper limit of the mass content of silicon elements in the negative electrode mixture layer is 30% by mass or less. This makes it easier to achieve both high capacity and improved cycle characteristics in a non-aqueous electrolyte secondary battery. Moreover, even if the negative electrode mixture layer contains a relatively large amount of silicon-containing material as described above, and the degree of expansion and contraction of the negative electrode mixture layer during charging and discharging is particularly large, the non-aqueous electrolyte secondary battery according to the embodiment of this disclosure has an inorganic coating (for example, Li ２ Since the surface of the negative electrode active material is covered with an SEI coating formed as (containing O or LiF), cracking of the SEI coating on the surface of the negative electrode active material can be suppressed. Therefore, the decrease in the capacity retention rate of the non-aqueous electrolyte secondary battery caused by the reductive decomposition of the non-aqueous solvent over time can be suppressed.

[0061] The mass content of silicon in the negative electrode mixture layer can be determined, for example, by analyzing samples taken from 10 arbitrary locations in the negative electrode mixture layer using ICP, and then taking the arithmetic mean of the 10 analytical values. ICP analysis can be performed using the "iCAP7400" manufactured by Thermo Fisher.

[0062] A silicon-containing material includes, for example, a lithium ion conducting phase and a silicon phase dispersed in the lithium ion conducting phase. Examples of the lithium ion conducting phase include a silicon oxide phase, a silicate phase, and a carbon phase. The content of the silicon phase in the lithium ion conducting phase may be, for example, 30% by mass or more and 95% by mass or less, or 35% by mass or more and 75% by mass or less. A silicon-containing material may be used alone or in combination of two or more types.

[0063] The main component of the silicon oxide phase (for example, 95 to 100% by mass) may be silicon dioxide. When a silicon-containing material comprises a silicon oxide phase as a lithium ion conductive phase, such a silicon-containing material may be represented by SiO ｘ , where x satisfies, for example, the relationship 0.5 ≤ x < 2. x may satisfy the relationship 0.8 ≤ x ≤ 1.6. The silicon oxide phase may be an amorphous phase. SiO ｘ can be obtained, for example, by a disproportionation reaction of silicon monoxide.

[0064] A silicate phase is preferred in terms of low irreversible capacity. From the viewpoint of high initial charge-discharge efficiency, it is preferable to use a lithium-containing silicate phase (hereinafter also referred to as a lithium silicate phase) as the silicate phase.

[0065] The lithium silicate phase only needs to be an oxide phase containing lithium (Li), silicon (Si), and oxygen (O). The lithium silicate phase may contain elements other than lithium, silicon, and oxygen. In the lithium silicate phase, the atomic ratio of O to Si (O / Si) is, for example, more than 2 and less than 4. O / Si is preferably more than 2 and less than 3. In the lithium silicate phase, the atomic ratio of Li to Si (Li / Si) is, for example, more than 0 and less than 4. The lithium silicate phase has the formula: Li ２ｚ SiO ２＋ｚ and may have a composition represented by . In the above formula, 0 < z < 2. z preferably satisfies the relationship 0 < z < 1, and more preferably z = 1 / 2. Examples of elements other than lithium, silicon, and oxygen include iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), and aluminum (Al).

[0066] The carbon phase may be composed of, for example, amorphous carbon with low crystallinity (i.e., amorphous carbon). The amorphous carbon may be, for example, hard carbon, soft carbon, or other carbon. Further, the carbon phase may contain amorphous carbon.

[0067] Silicon-containing materials containing a carbon phase can be obtained, for example, by grinding a mixture of a carbon source and raw silicon while stirring in a ball mill or the like to produce fine particles, and then heat-treating the finely particles in an inert atmosphere. As carbon sources, for example, sugars such as carboxymethylcellulose (CMC) and water-soluble resins such as polyvinylpyrrolidone can be used.

[0068] A silicon-containing material and a carbon material may be used in combination as the negative electrode active material. The silicon-containing material expands and contracts in volume during charging and discharging. Therefore, if the proportion of silicon-containing material in the negative electrode active material is high, poor contact between the negative electrode active material and the negative electrode current collector is more likely to occur during charging and discharging. On the other hand, by using a combination of silicon-containing material and a carbon material, the negative electrode can be made higher capacity, and excellent cycle characteristics can be achieved.

[0069] The proportion of silicon-containing material in the total of silicon-containing material and carbon material is preferably 5 to 100% by mass, and more preferably 7 to 50% by mass. This makes it easier to achieve both high capacity and improved cycle characteristics in a non-aqueous electrolyte secondary battery.

[0070] As the negative electrode current collector, for example, a non-porous conductive substrate or a porous conductive substrate can be used. Examples of non-porous conductive substrates include metal foil. Examples of porous conductive substrates include meshes, nets, and perforated sheets. Examples of materials that make up the negative electrode current collector include copper, nickel, copper alloys, nickel alloys, and stainless steel.

[0071] The composition of silicon-containing materials can be determined, for example, by obtaining a backscattered electron image of the cross-section of the negative electrode mixture layer using an electrolytic emission scanning electron microscope (FE-SEM), observing the silicon-containing material particles in this backscattered electron image, and performing elemental analysis on the observed silicon-containing material particles. Elemental analysis can be performed using methods such as electron probe microanalyzer (EPMA).

[0072] The negative electrode mixture layer may contain a binder. Examples of binders include fluororesins, polyolefin resins, polyamide resins, polyimide resins, acrylic resins, vinyl resins, and rubber-like materials. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride; examples of polyolefin resins include polyethylene and polypropylene; examples of polyamide resins include aramid resins; examples of polyimide resins include polyimide and polyamideimide. Examples of acrylic resins include polyacrylic resins, polymethacrylic resins, acrylic acid-methacrylic acid copolymers, ethylene-acrylic acid copolymers, and salts thereof; examples of vinyl resins include polyvinyl acetate; and examples of rubber-like materials include styrene-butadiene copolymer rubber (SBR). The binder may be used alone or in combination of two or more types.

[0073] The negative electrode mixture layer may contain a thickening agent. Examples of thickening agents include cellulose derivatives such as cellulose ether. Examples of cellulose derivatives include carboxymethylcellulose (CMC) and its modified forms, as well as methylcellulose. Modified forms of CMC also include salts of CMC. Examples of salts include alkali metal salts such as sodium salts, and ammonium salts. The thickening agent may be used alone or in combination of two or more types.

[0074] The negative electrode mixture layer may contain a conductive agent. Examples of conductive agents include conductive fibers and conductive particles. Examples of conductive fibers include carbon nanotubes (CNTs). Examples of conductive particles include conductive carbon particles and metal powders. Examples of conductive carbon particles include carbon black, and examples of carbon black include acetylene black (AB) and Ketjen black (KB). The conductive agent may be used alone or in combination of two or more types.

[0075] <Separator> The separator has high ion permeability and appropriate mechanical strength and insulating properties. As the separator, for example, a microporous thin film, a woven fabric, or a nonwoven fabric can be used. The separator may be a laminate of a microporous thin film and a woven fabric, a laminate of a microporous thin film and a nonwoven fabric, or a laminate of a woven fabric and a nonwoven fabric. It is preferable to use polyolefins (for example, polypropylene and polyethylene) as the material for forming the separator.

[0076] One example of the structure of a non-aqueous electrolyte secondary battery is a structure in which a group of electrodes (hereinafter also referred to as a wound electrode group) formed by winding strip-shaped positive electrodes and strip-shaped negative electrodes in the longitudinal direction via a strip-shaped separator, and a non-aqueous electrolyte are housed in an outer casing such as an electrode can. On the other hand, a non-aqueous electrolyte secondary battery may also have a stacked electrode group instead of a wound electrode group. A stacked electrode group is a group of electrodes in which strip-shaped positive electrodes and strip-shaped negative electrodes are stacked via a strip-shaped separator and are not wound in the longitudinal direction.

[0077] Battery casings typically have a bottomed cylindrical shape. A bottomed cylindrical battery casing has a circular bottom plate and cylindrical side walls rising from the outer edge of the circular bottom plate. In a battery casing, the surface facing the bottom plate (the surface facing in the height direction) is open. Battery casings are made of at least a metal containing iron. Examples of materials for forming battery casings include iron (Fe), Fe alloys, and stainless steel. Preferably, a nickel plating layer is formed on the inner surface of the battery casing (more specifically, the inner surface of the bottom plate and the inner surface of the side walls). The thickness of the nickel plating layer may be, for example, 0.1 μm or more and less than 2 μm, or 0.1 μm or more and 1 μm or less. The shape of a battery casing is not limited to a bottomed cylindrical shape. The shape of a battery casing may be, for example, a bottomed rectangular tubular shape.

[0078] Furthermore, the outer casing is not limited to a battery case. Also, the form of the non-aqueous electrolyte secondary battery is not particularly limited. Examples of non-aqueous electrolyte secondary batteries include cylindrical, prismatic, coin-type, button-type, and laminated types.

[0079] The structure of a non-aqueous electrolyte secondary battery will be described below with reference to Figure 1. Figure 1 is a longitudinal cross-sectional view of a cylindrical secondary battery according to one embodiment of the present disclosure. However, the present disclosure is not limited to the following configuration.

[0080] The non-aqueous electrolyte secondary battery 10 comprises an electrode group 18, a non-aqueous electrolyte (not shown), and a bottomed cylindrical battery case 22 that houses these components. The electrode group 18 is formed by winding a positive electrode 15 and a negative electrode 16 via a separator 17. The battery case 22 is made of iron or stainless steel, as described above. A nickel plating layer may be formed on the inner surface of the battery case 22.

[0081] At the opening of the battery case 22, the sealing body 11 is crimped and fixed via a gasket 21. This seals the inside of the battery. The sealing body 11 comprises a valve body 12, a metal plate 13, and an annular insulating member 14 interposed between the valve body 12 and the metal plate 13. The valve body 12 and the metal plate 13 are connected to each other at their respective centers. The positive electrode lead 15a, which is led out from the positive electrode 15, is connected to the metal plate 13. Therefore, the valve body 12 functions as an external terminal for the positive electrode.

[0082] The negative electrode lead 16a, which is led out from the negative electrode 16, is connected to the inner surface of the bottom plate of the battery can 22. An annular groove 22a is formed near the open end of the battery can 22. A first insulating plate 23 is placed between one end face of the electrode group 18 and the annular groove 22a. A second insulating plate 24 is placed between the other end face of the electrode group 18 and the bottom plate of the battery can.

[0083] (Note) The following technologies are disclosed in accordance with the above description. (Technology 1) A non-aqueous electrolyte secondary battery comprising: an electrode group including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the negative electrode comprises a negative electrode mixture layer containing a negative electrode active material, the negative electrode active material contains a silicon-containing material, the mass content of silicon element in the negative electrode mixture layer is 3.5% by mass or more, and the non-aqueous electrolyte contains a fluorine-containing linear acid anhydride. (Technology 2) The non-aqueous electrolyte secondary battery according to Technology 1, wherein the content of the fluorine-containing linear acid anhydride relative to the total mass of the non-aqueous electrolyte is 2% by mass or less. (Technology 3) The fluorine-containing linear acid anhydride has the following chemical formula (1): It has a structure represented by the above chemical formula (1), and in the above chemical formula, R １ and R ２ Each of these is independently a functional group having an alkyl group, alkenyl group, or alkynyl group with 1 to 6 carbon atoms, or a benzene ring with 6 to 8 carbon atoms, and the R １ and R ２The non-aqueous electrolyte secondary battery according to Technique 1 or 2, wherein at least one hydrogen element of is substituted with a fluorine element. (Technique 4) The fluorine-containing acid anhydride is at least one selected from the group consisting of difluoroacetic anhydride, trifluoroacetic anhydride, heptafluorobutyric anhydride, pentafluoropropionic anhydride, and 4-trifluoromethylbenzoic anhydride, The non-aqueous electrolyte secondary battery according to Technique 3. (Technique 5) The non-aqueous electrolyte includes a non-aqueous solvent and a lithium salt, The non-aqueous solvent includes ethylene carbonate, where C is the mass content of the lithium salt based on the total mass of the non-aqueous electrolyte Ｌｉ and C is the mass content of the ethylene carbonate ＥＣ , the C Ｌｉ and the C ＥＣ satisfy C Ｌｉ / C ＥＣ >1, The non-aqueous electrolyte secondary battery according to any one of Techniques 1 to 4. (Technique 6) The concentration of the lithium salt in the non-aqueous electrolyte is 1.3 mol / L or more and 2.5 mol / L or less, The non-aqueous electrolyte secondary battery according to Technique 5. (Technique 7) The volume content of ethylene carbonate relative to the total volume of the non-aqueous solvent is 5% by volume or more and 20% by volume or less, The non-aqueous electrolyte secondary battery according to Technique 5 or 6. (Technique 8) The silicon-containing material includes an ion conductive phase and a silicon phase dispersed inside the ion conductive phase, The non-aqueous electrolyte secondary battery according to any one of Techniques 1 to 7. (Technique 9) The ion conductive phase includes an amorphous carbon phase, The non-aqueous electrolyte secondary battery according to Technique 8. (Technique 10) The mass content of the silicon phase in the silicon-containing material is 30% by mass or more and 60% by mass or less, The non-aqueous electrolyte secondary battery according to Technique 8 or 9.

[0084] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0085] (Example 1) (1) Preparation of the positive electrode First, a suitable amount of N-methyl-2-pyrrolidone (NMP) was added to the positive electrode mixture and mixed to obtain a positive electrode mixture slurry. The positive electrode mixture is a lithium-containing transition metal oxide (composition formula is LiNi ０．９０ Co ０．０５ Mn ０．０５ O ２ The mixture contained 95 parts by mass of ) , 2.5 parts by mass of acetylene black, and 2.5 parts by mass of polyvinylidene fluoride. The lithium-containing transition metal oxide represented by the above composition formula is also called NMC. Next, the cathode mixture slurry was applied to both sides of the aluminum foil to form a coating film, the coating films formed on both sides were dried, and the dried coating films were rolled. As a result, a cathode mixture layer (thickness 95 μm, density 3.6 g / cm³) was formed on both sides of the aluminum foil. ３ A positive electrode was obtained in which a ) was formed.

[0086] (2) Preparation of the negative electrode First, a negative electrode slurry was obtained by adding an appropriate amount of water to the negative electrode mixture and mixing. The negative electrode mixture was a mixture of a negative electrode active material, a binder, and a conductive agent. The negative electrode active material was a mixture of a silicon-containing material and graphite (average particle size (D50) of 25 μm). The silicon-containing material was a composite material containing a carbon phase (ionic conductive phase) and a silicon phase dispersed in the carbon phase. The mass content of the silicon phase in the silicon-containing material was in the range of 30% by mass or more and 60% by mass or less. In the silicon-containing material, the carbon phase contained an amorphous carbon phase. In the negative electrode active material, the mass ratio of the silicon-containing material to graphite was adjusted so that the mass content of silicon element in the negative electrode mixture layer was 3.5% by mass. Sodium polyacrylate (PAA-Na), sodium salt of CMC (CMC-Na), and SBR were used as binders. The mass content of PAA-Na, CMC-Na, and SBR in the negative electrode mixture was set to 1% by mass each. Next, the negative electrode mixture slurry was applied to both sides of the copper foil to form a coating film, and then the coating films formed on both sides were dried, and the dried coating films were rolled. As a result, a negative electrode mixture layer (thickness 80 μm, density 1.6 g / cm³) was formed on both sides of the copper foil. ３ A negative electrode was obtained in which a ) was formed.

[0087] (3) Preparation of non-aqueous electrolyte A non-aqueous solvent containing ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and vinylene carbonate (VC) is mixed with a lithium salt LiPF ６ A non-aqueous electrolyte was prepared by dissolving the additive difluoroacetic anhydride. In the non-aqueous electrolyte according to Example 1, the volume content of ethylene carbonate (EC) relative to the total volume of the non-aqueous solvent was 14% by volume. In addition, in the non-aqueous electrolyte according to Example 1, LiPF ６ The concentration was 1.3 mol / L. Furthermore, the content of difluoroacetic anhydride relative to the total mass of the nonaqueous electrolyte was 0.5% by mass. In addition, in the nonaqueous electrolyte secondary battery according to Example 1, LiPF was used relative to the total mass of the nonaqueous electrolyte. ６ The mass content of C Ｌｉ The mass content of ethylene carbonate (EC) is set to C ＥＣ In that case, C Ｌｉ / C ＥＣ The value was 1.1.

[0088] (4) Fabrication of a non-aqueous electrolyte secondary battery One end of an Al positive electrode lead was attached to the positive electrode obtained as described above. Also, one end of a Ni negative electrode lead was attached to the negative electrode obtained as described above. In an inert gas atmosphere, the positive electrode and negative electrode were wound in a spiral shape with a polyethylene thin film (separator) in between to fabricate a wound electrode group. After placing the first insulating plate on the lower end surface of the wound electrode group, the electrode group with the first insulating plate was placed in a battery case. Then, the other end of the negative electrode lead was resistance welded to the bottom of the battery case. An iron can with nickel plating on the inner surface was used as the battery case. After placing the second insulating plate on the upper end surface of the electrode group, an annular groove was formed near the open end of the battery case. Next, after connecting the other end of the positive electrode lead to the metal plate of the safety mechanism provided in the sealing body, the non-aqueous electrolyte prepared as described above was injected into the battery case. Next, a sealing body was supported in the annular groove formed in the battery case via a gasket, and then the open end of the battery case was crimped to the periphery of the sealing body. This completed the fabrication of the non-aqueous electrolyte secondary battery according to Example 1.

[0089] (Example 2) A non-aqueous electrolyte secondary battery according to Example 2 was prepared in the same manner as in Example 1, except that heptafluorobutyric acid anhydride was used instead of difluoroacetic acid anhydride as an additive to the non-aqueous electrolyte.

[0090] (Example 3) A non-aqueous electrolyte secondary battery according to Example 3 was prepared in the same manner as in Example 1, except that pentafluoropropionic anhydride was used instead of difluoroacetic anhydride as an additive to the non-aqueous electrolyte.

[0091] (Example 4) In the negative electrode active material, the mass ratio of silicon-containing material to graphite was adjusted so that the mass content of silicon element in the negative electrode mixture layer was 5.0% by mass, and in the non-aqueous electrolyte, the volume content of ethylene carbonate (EC) relative to the total volume of aqueous solvent was set to 10% by volume, and LiPF ６ The concentration of C is set to 1.8 mol / L. Ｌｉ / C ＥＣ A non-aqueous electrolyte secondary battery according to Example 4 was prepared in the same manner as in Example 1, except that the ratio was set to 2.0.

[0092] (Comparative Example 1) In a non-aqueous electrolyte, without using an additive, C Ｌｉ / C ＥＣ A non-aqueous electrolyte secondary battery according to Comparative Example 1 was prepared in the same manner as in Example 1, except that the ratio was set to 0.8.

[0093] (Comparative Example 2) A non-aqueous electrolyte secondary battery according to Comparative Example 2 was prepared in the same manner as in Example 1, except that propionic anhydride was used as an additive to the non-aqueous electrolyte.

[0094] (Comparative Example 3) A non-aqueous electrolyte secondary battery according to Comparative Example 3 was prepared in the same manner as in Example 1, except that valeric acid anhydride was used as an additive to the non-aqueous electrolyte.

[0095] (Comparative Example 4) A non-aqueous electrolyte secondary battery according to Comparative Example 4 was prepared in the same manner as in Example 1, except that 2-fluorosuccinic anhydride was used as an additive to the non-aqueous electrolyte.

[0096] (Comparative Example 5) In a non-aqueous electrolyte, no additives were used, and the volume content of ethylene carbonate (EC) relative to the total volume of the aqueous solvent was 25% by volume, and C Ｌｉ / CＥＣ A non-aqueous electrolyte secondary battery according to Comparative Example 5 was prepared in the same manner as in Example 4, except that the ratio was set to 0.8.

[0097] (Comparative Example 6) A non-aqueous electrolyte secondary battery according to Comparative Example 6 was prepared in the same manner as in Example 4, except that no additives were used in the non-aqueous electrolyte.

[0098] (Comparative Example 7) In the negative electrode active material, the mass ratio of silicon-containing material to graphite was adjusted so that the mass content of silicon element in the negative electrode mixture layer was 1.0% by mass, and in the non-aqueous electrolyte, no additives were used, and the volume content of ethylene carbonate (EC) relative to the total volume of the aqueous solvent was set to 20% by volume, and LiPF ６ The concentration of C is set to 1.0 mol / L. Ｌｉ / C ＥＣ A non-aqueous electrolyte secondary battery according to Example 4 was prepared in the same manner as in Example 1, except that the value was set to 0.8.

[0099] (Comparative Example 8) A non-aqueous electrolyte secondary battery according to Comparative Example 8 was prepared in the same manner as in Comparative Example 7, except that propionic anhydride was used as an additive in the non-aqueous electrolyte. In the non-aqueous electrolyte according to Comparative Example 8, the content of propionic anhydride relative to the total mass of the non-aqueous electrolyte was 0.5% by mass.

[0100] (Comparative Example 9) A non-aqueous electrolyte secondary battery according to Comparative Example 9 was prepared in the same manner as in Comparative Example 8, except that 2-fluorosuccinic anhydride was used as an additive in the non-aqueous electrolyte.

[0101] For each example (Examples 1-4 and Comparative Examples 1-9), the mass content of silicon, the concentration of lithium salt, the volume content of ethylene carbonate (EC), and C Ｌｉ / C ＥＣ The types of additives are shown in Table 1 below.

[0102]

[0103] [Evaluation] <Initial Capacity> Charge and discharge tests were conducted using the non-aqueous electrolyte secondary batteries of each example (Examples 1-4 and Comparative Examples 1-9) as follows. Constant current charging was performed with a current of 0.5C until the voltage reached 4.2V, and then constant voltage charging was performed with a voltage of 4.2V until the current reached 0.05C. Next, constant current discharge was performed with a current of 0.2C until the voltage reached 2.5V. The rest period between charging and discharging was 60 minutes. The charging and discharging were performed in an environment of 25°C. The discharge capacity during the first discharge performed in this manner was determined as the initial capacity. The results are shown in Table 2 below. Table 2 below shows the ratio of the initial capacity of the non-aqueous electrolyte secondary batteries of each example (vs Comparative Example 7) when the initial capacity of the non-aqueous electrolyte secondary battery of Comparative Example 7 is set to 100.

[0104] <Capacity Retention Rate> For each example of the non-aqueous electrolyte secondary battery, the above charge-discharge cycle was repeated 300 times, with one cycle being the charge-discharge cycle. The discharge capacity C1 at the 300th cycle was then determined. The ratio of the discharge capacity C1 to the initial capacity (C0) X1 = C1 / C0 was then calculated, and this calculated value was defined as the capacity retention rate. The results are shown in Table 2 below. In Table 2 below, for the non-aqueous electrolyte secondary batteries of Examples 1 to 3, the ratio of the capacity retention rate X1 when the capacity retention rate X1 of Comparative Example 1 is set to 100 is shown (vs Comparative Example 1). For Examples 4 and 6, the ratio of the capacity retention rate X1 when the capacity retention rate X1 of Comparative Example 5 is set to 100 is shown (vs Comparative Example 5). For Comparative Examples 8 and 9, the ratio of the capacity retention rate X1 when the capacity retention rate X1 of Comparative Example 7 is set to 100 is shown (vs Comparative Example 7).

[0105]

[0106] Table 2 shows that the non-aqueous electrolyte secondary batteries according to Examples 1 to 3 exhibit a suppressed decrease in capacity retention rate compared to the non-aqueous electrolyte secondary battery according to Comparative Example 1, and the non-aqueous electrolyte secondary battery according to Example 4 exhibits a suppressed decrease in capacity retention rate compared to the non-aqueous electrolyte secondary battery according to Comparative Example 5.

[0107] 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.

[0108] The non-aqueous electrolyte secondary battery described herein can be used in applications where it is required to suppress a decrease in cycle life.

[0109] 10: Non-aqueous electrolyte secondary battery, 11: Sealing body, 12: Valve body, 13: Metal plate, 14: Insulating member, 15: Positive electrode, 15a: Positive electrode lead, 16: Negative electrode, 16a: Negative electrode lead, 17: Separator, 18: Electrode group, 21: Gasket, 22: Battery can, 22a: Groove, 23: First insulating plate, 24: Second insulating plate

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode group including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the negative electrode comprises a negative electrode mixture layer containing a negative electrode active material, the negative electrode active material contains a silicon-containing material, the mass content of silicon element in the negative electrode mixture layer is 3.5% by mass or more, and the non-aqueous electrolyte contains a fluorine-containing chain acid anhydride.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the fluorine-containing linear acid anhydride relative to the total mass of the non-aqueous electrolyte is 2% by mass or less.

3. The fluorine-containing linear acid anhydride has the following chemical formula (1): It has a structure represented by the above chemical formula (1), and in the above chemical formula, R １ and R ２ Each of these is independently a functional group having an alkyl group, alkenyl group, or alkynyl group with 1 to 6 carbon atoms, or a benzene ring with 6 to 8 carbon atoms, and the R １ and R ２ A non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein at least one hydrogen element is substituted with a fluorine element.

4. The non-aqueous electrolyte secondary battery according to claim 3, wherein the fluorine-containing acid anhydride is at least one selected from the group consisting of difluoroacetic anhydride, trifluoroacetic anhydride, heptafluorobutyric anhydride, pentafluoropropionic anhydride, and 4-trifluoromethylbenzoic anhydride.

5. The non-aqueous electrolyte comprises a non-aqueous solvent and a lithium salt, the non-aqueous solvent comprises ethylene carbonate, and wherein C represents the mass content of the lithium salt relative to the total mass of the non-aqueous electrolyte Ｌｉ and when C represents the mass content of the ethylene carbonate ＥＣ , said C Ｌｉ and said C ＥＣ satisfy C Ｌｉ / C ＥＣ >1, the non-aqueous electrolyte secondary battery according to claim 1.

6. The non-aqueous electrolyte secondary battery according to claim 5, wherein the concentration of the lithium salt in the non-aqueous electrolyte is 1.3 mol / L or more and 2.5 mol / L or less.

7. The non-aqueous electrolyte secondary battery according to claim 5 or 6, wherein the volume content of ethylene carbonate relative to the total volume of the non-aqueous solvent is 5% by volume or more and 20% by volume or less.

8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the silicon-containing material comprises an ionic conductive phase and a silicon phase dispersed within the ionic conductive phase.

9. The non-aqueous electrolyte secondary battery according to claim 8, wherein the ion conducting phase includes an amorphous carbon phase.

10. The non-aqueous electrolyte secondary battery according to claim 8 or 9, wherein the mass content of the silicon phase in the silicon-containing material is 30% by mass or more and 60% by mass or less.

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