Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery comprises a negative electrode including a negative electrode mixture, a separator, a positive electrode facing the negative electrode with the separator interposed therebetween, and a non-aqueous electrolyte. The negative electrode mixture includes a negative electrode active material. The negative electrode active material includes 3% by mass or more of a silicon-containing material. The silicon-containing material includes carbon composite particles. The carbon composite particle includes a carbon phase and a silicon phase dispersed within the carbon phase. The non-aqueous electrolyte contains a 5- or 6-membered cyclic compound component including a sulfur element as a ring-constituting element.

Description

Nonaqueous electrolyte secondary battery

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

[0002] A nonaqueous electrolyte secondary battery, such as a lithium ion secondary battery, includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. A nonaqueous electrolyte solution is typically used as the nonaqueous electrolyte. The negative electrode includes a negative electrode mixture containing a negative electrode active material. The negative electrode active material is a material capable of electrochemically absorbing and desorbing lithium ions. Examples of such materials include carbonaceous materials and silicon-containing materials. Furthermore, a carbonaceous material that does not absorb or desorb lithium ions, such as carbon fiber or carbon nanotubes, may be added to the negative electrode mixture as a conductive agent.

[0003] Patent Document 1 proposes the use of a composite electrode agent in a lithium ion secondary battery, the composite electrode agent including particles containing an element capable of absorbing and desorbing lithium ions, carbon particles capable of absorbing and desorbing lithium ions, multi-walled carbon nanotubes, and carbon nanofibers.

[0004] From the viewpoint of improving negative electrodes containing an alloy-based active material, Patent Document 2 proposes a negative electrode for a non-aqueous electrolyte secondary battery, which includes a negative electrode current collector and a negative electrode active material layer that is supported on the surface of the negative electrode current collector and contains an alloy-based active material that absorbs and releases lithium ions, and which further includes a resin layer on the surface of the negative electrode active material layer that contains a resin component having lithium ion conductivity and an additive for a non-aqueous electrolyte.

[0005] JP 2014-146519 A International Publication No. 2010 / 092815

[0006] Silicon-containing materials undergo large volume changes due to the absorption and desorption of lithium ions. Carbon composite particles containing a carbon phase and a silicon phase dispersed within the carbon phase exhibit particularly large volume changes due to their large discharge capacity and high utilization of the active material. Therefore, with each charge / discharge cycle, the carbon composite particles are prone to cracking, resulting in the appearance of new surfaces. Side reactions with the electrolyte easily occur on the new surfaces, reducing the capacity during repeated charge / discharge cycles, resulting in a decrease in capacity retention and cycle performance.

[0007] One aspect of the present disclosure relates to a non-aqueous electrolyte secondary battery including: a negative electrode containing a negative electrode mixture; a separator; a positive electrode facing the negative electrode with the separator interposed therebetween; and a non-aqueous electrolyte, wherein the negative electrode mixture includes a negative electrode active material, the negative electrode active material includes 3 mass % or more of a silicon-containing material, the silicon-containing material includes carbon composite particles, the carbon composite particles include a carbon phase and a silicon phase dispersed in the carbon phase, and the non-aqueous electrolyte includes a five- or six-membered cyclic compound component including a sulfur element as a ring constituent element.

[0008] In a non-aqueous electrolyte secondary battery using a negative electrode containing carbon composite particles including a silicon phase, deterioration in cycle characteristics can be suppressed.

[0009] 1 is a partially cutaway perspective view of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure.

[0010] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0011] In non-aqueous electrolyte secondary batteries, carbonaceous materials such as graphite are generally used as negative electrode active materials. While silicon-containing materials theoretically provide higher capacity than carbonaceous materials, the large volume changes associated with the absorption and desorption of lithium ions tend to cause cracks in the active material particles, leading to the formation of new surfaces. The new surfaces are prone to side reactions with the non-aqueous electrolyte, resulting in a decrease in capacity. Therefore, even when silicon-containing materials are used, the capacity retention rate decreases during repeated charge / discharge cycles, making it difficult to ensure a sufficient lifespan. Among these, carbon composite particles containing a carbon phase and a silicon phase dispersed within the carbon phase are ideal from the perspective of achieving high capacity, as they offer a high active material utilization rate and a large discharge capacity. However, repeated charge / discharge cycles tend to cause cracks not only in the silicon phase but also in the carbon phase that constitutes the matrix due to volume changes in the silicon phase. Therefore, when carbon composite particles containing a silicon phase are used, more new surfaces are formed than when carbonaceous materials without a silicon phase are used. Consequently, the capacity retention rate decreases during repeated charge / discharge cycles, leading to poor cycle performance.

[0012] In view of the above, (1) the nonaqueous electrolyte secondary battery of the present disclosure includes a negative electrode containing a negative electrode mixture, a separator, a positive electrode facing the negative electrode via the separator, and a nonaqueous electrolyte. The negative electrode mixture includes a negative electrode active material. The negative electrode active material includes 3 mass% or more of a silicon-containing material. The silicon-containing material includes carbon composite particles. The carbon composite particles include a carbon phase and a silicon phase dispersed within the carbon phase. The nonaqueous electrolyte includes a five- or six-membered cyclic compound component containing sulfur as a ring constituent element. Hereinafter, the five- or six-membered cyclic compound component containing sulfur as a ring constituent element may simply be referred to as an S-containing cyclic compound component. Furthermore, the silicon-containing material may also be referred to as an Si-containing material, and the silicon phase may also be referred to as an Si phase.

[0013] According to the present disclosure, by using a nonaqueous electrolyte containing an S-containing cyclic compound component, when the negative electrode contains a silicon-containing material including carbon composite particles containing an Si phase, the decrease in capacity retention rate can be suppressed even with repeated charge / discharge, and the decrease in cycle characteristics can be suppressed. This is thought to be because even if cracks occur in the silicon-containing material including the carbon composite particles and new surfaces are generated during charge / discharge, the S-containing cyclic compound component forms a coating on the surface of the negative electrode active material, thereby suppressing side reactions. From this, it is thought that the coating formed on the surface, including the new surface, of the silicon-containing material including the carbon composite particles by the action of the S-containing cyclic compound component is a low-resistance coating that is unlikely to inhibit charge / discharge reactions. Furthermore, according to the present disclosure, by using a silicon-containing material including carbon composite particles in a negative electrode, a high initial discharge capacity can be ensured.

[0014] When a carbonaceous material containing no Si phase is used as the negative electrode active material, even when a non-aqueous electrolyte containing an S-containing cyclic compound component is used, the initial discharge capacity and the capacity retention rate after repeated charge and discharge are almost the same as when the non-aqueous electrolyte does not contain the S-containing cyclic compound component. In other words, it can be said that the effect of the S-containing cyclic compound component on the behavior of cycle characteristics is significantly different when a carbonaceous material containing no Si phase is used as the negative electrode active material and when carbon composite particles containing an Si phase are used.

[0015] (2) In the above (1), the silicon-containing material may further contain silicon oxide.

[0016] (3) In the above (1) or (2), the silicon-containing material may further include silicate composite particles, and the silicate composite particles may include a silicate phase and a silicon phase dispersed within the silicate phase.

[0017] (4) In any one of the above (1) to (3), the cyclic compound component may contain a sulfur element as a ring-constituting element and may also contain a cyclic compound having a carbon-carbon unsaturated bond.

[0018] (5) In any one of the above (1) to (4), the cyclic compound component may contain 1,3-propene sultone.

[0019] (6) In any one of the above (1) to (5), the concentration of the cyclic compound component in the non-aqueous electrolyte may be 2 mass % or less.

[0020] (7) In any one of the above (1) to (6), the negative electrode mixture may further contain carbon nanotubes.

[0021] (8) In any one of the above (1) to (7), the non-aqueous electrolyte may further contain fluoroethylene carbonate.

[0022] The nonaqueous electrolyte secondary battery of the present disclosure will be described in more detail below for each component, including the above (1) to (8). At least one of the above (1) to (8) may be combined with at least one of the elements described below, provided that this is not technically inconsistent.

[0023] (Negative Electrode) The negative electrode includes a negative electrode mixture. The negative electrode may include a negative electrode mixture and a negative electrode current collector that holds the negative electrode mixture. The negative electrode typically includes a layered negative electrode mixture (hereinafter referred to as a negative electrode mixture layer). The negative electrode mixture includes at least a negative electrode active material. The negative electrode mixture may further include at least one selected from the group consisting of a binder and a thickener. The negative electrode mixture may further include a conductive agent.

[0024] (Negative electrode mixture) (Negative electrode active material) The negative electrode active material contains at least a Si-containing material. The Si-containing material contains at least the above-described carbon composite particles. The negative electrode may contain a material other than the Si-containing material as the negative electrode active material.

[0025] (Si-containing material) Among the Si-containing materials, carbon composite particles contain a carbon phase and a Si phase dispersed within the carbon phase. Because the carbon phase has electronic conductivity, even if cracks occur in the carbon composite particles due to the expansion and contraction of the Si phase, the carbon composite particles are less likely to become isolated and contact points between the carbon composite particles and their surroundings are more likely to be maintained. Therefore, deterioration of cycle characteristics is more likely to be suppressed.

[0026] The carbon phase may be composed of, for example, amorphous carbon (i.e., amorphous carbon) or crystalline carbon. Amorphous carbon may be, for example, hard carbon, soft carbon, or other. Amorphous carbon generally refers to a carbonaceous material in which the average interplanar spacing d002 of the (002) plane measured by X-ray diffraction exceeds 0.340 nm. Examples of crystalline carbon include carbon having a graphite-type crystal structure, such as graphite. Crystalline carbon such as graphite refers to a carbonaceous material in which d002 is 0.340 nm or less (e.g., 0.3354 nm or more and 0.340 nm or less).

[0027] The content of the Si phase in the carbon composite particles is, for example, 30% by mass to 80% by mass, or 40% by mass to 70% by mass. Within this range, a higher initial capacity can be obtained and deterioration in cycle characteristics can be easily reduced. Furthermore, by including a relatively large amount of carbon phase, even if cracks occur in the particles due to charge and discharge, the carbon phase can easily penetrate into the formed voids, thereby easily maintaining the conductive path in the negative electrode mixture.

[0028] The content of the carbon composite particles in the negative electrode active material is, for example, 3% by mass or more, and may be 4% by mass or more, or 5% by mass or more. When the content of the carbon composite particles is within this range, the volume change associated with the absorption and desorption of lithium ions tends to cause side reactions at the newly generated surface. Therefore, the effect of using a non-aqueous electrolyte containing an S-containing cyclic compound component tends to be significant. From the viewpoint of ensuring higher cycle characteristics, the content of the carbon composite particles in the negative electrode active material is, for example, 10% by mass or less.

[0029] Carbon composite particles can be obtained, for example, by pulverizing a mixture of a carbon source and raw silicon while stirring it in a ball mill or the like to form fine particles, and then heat-treating the mixture in an inert atmosphere. Examples of carbon sources that can be used include petroleum resins such as coal pitch, petroleum pitch, and tar, as well as sugars and water-soluble resins such as carboxymethyl cellulose (CMC), polyvinylpyrrolidone, cellulose, and sucrose. When mixing the carbon source and raw silicon, the carbon source and raw silicon may be dispersed in a dispersion medium such as alcohol. The milled mixture is dried and then heated in an inert gas atmosphere, for example, at a temperature of 600°C or higher and 1000°C or lower, to carbonize the carbon source and form a carbon phase.

[0030] Examples of Si-containing materials other than carbon composite particles include elemental silicon, silicon alloys, and silicon compounds.

[0031] The Si-containing material may contain composite particles other than carbon composite particles. Examples of such composite particles include composite particles in which a Si phase (fine Si phase) is dispersed within a lithium ion conductive phase (matrix). When the Si-containing material contains such composite particles, a higher capacity can be obtained and the effect of suppressing the deterioration of cycle characteristics can be enhanced.

[0032] The lithium ion conducting phase is SiO ２It is preferable that the composite particles contain at least one selected from the group consisting of a silicate phase and a silicate phase. The lithium ion conductive phase may further contain a carbon phase. The lithium ion conductive phase may form an amorphous phase. However, this is not limited to this case, and for example, at least a portion of each of the silicate phase and the carbon phase may be a crystalline phase containing crystalline silicate or crystalline carbon as described for the carbon composite particles. Specific examples of composite particles include SiO ２ phase and SiO ２ Examples of the composite particles include composite particles containing a silicate phase and a Si phase dispersed within the silicate phase (silicate composite particles). However, the composite particles are not limited to these specific examples.

[0033] SiO ２ The phase is an amorphous phase containing 95% or more by mass of silicon dioxide. ２ Composite particles with dispersed Si phases are SiO ｘ where x is, for example, 0.5≦x<2, and may be 0.8≦x≦1.6. ｘ is, for example, obtained by heat treating silicon monoxide to produce SiO ２ The SiO phase and the fine Si phase are separated using a transmission electron microscope (TEM). ｘ When observing the particle cross section, SiO ２ The Si phase dispersed within the composite particles can be seen. Such composite particles are sometimes referred to as silicon oxides in this specification. When the negative electrode active material contains silicon oxide, it is easy to ensure a higher initial discharge capacity.

[0034] The silicate phase preferably contains at least one of an alkali metal element (a Group 1 element other than hydrogen in the long periodic table) and a Group 2 element in the long periodic table. The alkali metal element includes lithium (Li), potassium (K), sodium (Na), etc. The Group 2 element includes magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), etc. The lithium silicate phase has the formula: Li ２ｙ SiO ２＋ｙThe silicate composite particles may have a composition expressed as (0<y<2), where y may be 1 / 2 or 1. The silicate composite particles in which the Si phase is dispersed within the silicate phase can be obtained, for example, by pulverizing a mixture of silicate and raw silicon while stirring it in a ball mill or the like to form fine particles, and then heat-treating the mixture in an inert atmosphere.

[0035] The content of the Si phase dispersed in the silicate phase may be 30% by mass or more and 95% by mass or less, or 35% by mass or more and 75% by mass or less, based on the entire silicate composite particles.

[0036] The Si-containing material may contain only carbon composite particles, or may contain a combination of carbon composite particles and at least one other Si-containing material. For example, the Si-containing material may contain, in addition to the carbon composite particles, at least one selected from the group consisting of silicon oxide and silicate composite particles.

[0037] The content of silicon oxide in the negative electrode active material is, for example, 0.1% by mass or more, or may be 0.5% by mass or more, or may be 1% by mass or more. In this case, the initial discharge capacity can be further increased. The content of silicon oxide in the negative electrode active material is, for example, 5% by mass or less.

[0038] The content of the silicate composite particles in the negative electrode active material is, for example, 0.1% by mass or more, or may be 0.5% by mass or more, or may be 1% by mass or more. In this case, a higher initial discharge capacity can be ensured and a decrease in the capacity retention rate can be further suppressed. The content of the silicate composite particles in the negative electrode active material is, for example, 5% by mass or less.

[0039] The composition of the Si-containing material can be determined, for example, by obtaining a backscattered electron image of the cross section of the negative electrode mixture layer using a field emission scanning electron microscope (FE-SEM), observing the particles of the Si-containing material, and performing elemental analysis on the observed particles of the Si-containing material. For example, the battery is disassembled, the negative electrode is removed, washed with a non-aqueous solvent such as ethylene carbonate, dried, and then the cross section of the negative electrode mixture layer is processed using a cross section polisher (CP) to obtain a sample. A backscattered electron image of the cross section of the sample is taken using the FE-SEM. For elemental analysis, for example, an electron probe microanalyzer (EPMA) analysis or the like is used. Qualitative and quantitative analysis of elements may be performed using an Auger Electron Spectroscopy (AES) analyzer. The composition of the lithium ion conductive phase can also be determined by this analysis. The composition of the carbon phase can be confirmed based on d002 determined by X-ray diffraction.

[0040] The Si-containing material is usually a particulate material. The average particle size (D50) of the Si-containing material is, for example, 1 μm or more and 25 μm or less, and may be 4 μm or more and 15 μm or less. Within this range, good battery performance is likely to be obtained.

[0041] In this specification, the term "average particle size (D50)" refers to the particle size (volume average particle size) at which the volume cumulative value is 50% in the particle size distribution measured by laser diffraction scattering. For example, an "LA-750" manufactured by Horiba, Ltd. can be used as a measuring device. The average particle size of the Si-containing material may be determined from a cross-sectional sample of the negative electrode formed to obtain a backscattered electron image of the FE-SEM. The circle-equivalent diameters of the cross sections of 10 or more particles of the Si-containing material are determined, and the average value thereof is calculated as the average particle size. Here, the circle-equivalent diameter refers to the diameter of a circle having the same area as the area of ​​the particle observed in the cross section of the negative electrode.

[0042] The Si phase dispersed in the carbon phase is usually composed of multiple crystallites. The crystallite size of the Si phase is, for example, 500 nm or less, and may be 30 nm or less. The lower limit of the crystallite size of the Si phase is not particularly limited, but is, for example, 5 nm or more. The crystallite size is calculated by the Scherrer formula from the half-width of the diffraction peak assigned to the Si (111) plane in the X-ray diffraction (XRD) pattern of the Si phase.

[0043] The content of the Si phase contained in the composite particles can be measured, for example, by Si-NMR. Desirable measurement conditions for Si-NMR are shown below.

[0044] Measurement equipment: Varian solid-state nuclear magnetic resonance spectrometer (INOVA-400) Probe: Varian 7 mm CPMAS-2 MAS: 4.2 kHz MAS speed: 4 kHz Pulse: DD (45° pulse + signal acquisition time 1 H decoupled) Repetition time: 1200 sec Observation width: 100 kHz Observation center: near -100 ppm Signal acquisition time: 0.05 sec Number of accumulations: 560 Sample amount: 207.6 mg

[0045] From the viewpoint of improving electrical conductivity, at least a portion of the particle surface of the Si-containing material may be coated with a conductive layer. The conductive layer contains a conductive material such as conductive carbon. The amount of the conductive layer is, for example, 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the total of the particles of the Si-containing material and the conductive layer. The particles of the Si-containing material having a conductive layer on their surface can be obtained, for example, by mixing coal pitch or the like with the particles of the Si-containing material and heat treating the mixture in an inert atmosphere.

[0046] The content of the Si-containing material in the negative electrode active material is 3% by mass or more, preferably 4% by mass or more, and may be 5% by mass or more. When the content is within this range, a high initial capacity is obtained, but the cycle characteristics are likely to deteriorate. In the present disclosure, even in such a case, high cycle characteristics can be ensured by using a non-aqueous electrolyte containing an S-containing cyclic compound component. The ratio of the Si-containing material is, for example, 15% by mass or less, and may be 10% by mass or less. These lower and upper limits can be combined arbitrarily.

[0047] (Other Negative Electrode Active Materials) Examples of negative electrode active materials other than the Si-containing material include at least one selected from the group consisting of carbonaceous materials not containing an Si phase, Sn alone, Sn alloys, and Sn compounds (such as Sn oxides). Since the Si-containing material expands and contracts in volume with charge and discharge, a large proportion of the Si-containing material in the negative electrode active material is likely to cause poor contact between the negative electrode active material and the negative electrode current collector with charge and discharge. Carbonaceous materials expand and contract less during charge and discharge than Si-containing materials. By using a Si-containing material in combination with a carbonaceous material, the contact state between the negative electrode active material particles and between the negative electrode mixture and the negative electrode current collector can be better maintained during repeated charge and discharge. Therefore, by using a Si-containing material in combination with a carbonaceous material not containing an Si phase, it is easy to obtain excellent cycle characteristics while imparting the high capacity of the Si phase to the negative electrode.

[0048] Examples of the carbonaceous material include graphite, easily graphitizable carbon (soft carbon), and non-graphitizable carbon (hard carbon). One type of carbonaceous material may be used alone, or two or more types may be used in combination.

[0049] Among these, graphite is preferred as the carbonaceous material because of its excellent charge / discharge stability and low irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles. The graphite particles may partially contain amorphous carbon, graphitizable carbon, or non-graphitizable carbon.

[0050] Graphite is a carbonaceous material with a developed graphite crystal structure. The average interplanar spacing d002 of the (002) plane of graphite 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) is measured, for example, by the Scherrer method. When the average interplanar spacing d002 of the (002) plane of graphite and the crystallite size Lc(002) are within the above ranges, high capacity is easily obtained.

[0051] The total amount of the Si-containing material and the carbonaceous material (carbonaceous material not containing an Si phase) in the negative electrode active material is preferably 90% by mass or more, and may be 95% by mass or more or 98% by mass or more. The total amount of the Si-containing material and the carbonaceous material in the negative electrode active material is 100% by mass or less. The negative electrode active material may be composed only of the Si-containing material and the carbonaceous material.

[0052] (Binder) As the binder, for example, a resin material is used. Examples of binders include fluororesins (e.g., polytetrafluoroethylene, polyvinylidene fluoride), polyolefin resins (e.g., polyethylene, polypropylene), polyamide resins (e.g., aramid resin), polyimide resins (e.g., polyimide, polyamideimide), acrylic resins (e.g., polyacrylic acid, polymethacrylic acid, acrylic acid-methacrylic acid copolymer, ethylene-acrylic acid copolymer, or salts thereof), vinyl resins (e.g., polyvinyl acetate), and rubber-like materials (e.g., styrene-butadiene copolymer rubber (SBR)). One type of binder may be used alone, or two or more types may be used in combination.

[0053] (Thickener) Examples of thickeners include cellulose derivatives such as cellulose ether. Examples of cellulose derivatives include CMC and its modified products, methyl cellulose, etc. Modified CMC also includes salts of CMC. Examples of salts include alkali metal salts (e.g., sodium salts), ammonium salts, etc. One type of thickener may be used alone, or two or more types may be used in combination.

[0054] (Conductive Agent) Examples of the conductive agent include conductive fibers and conductive particles. Examples of the conductive fibers include carbon fibers and metal fibers. Carbon fibers also include carbon nanotubes (CNT). Examples of the conductive particles include conductive carbon (carbon black, etc.) and metal powder. One type of conductive agent may be used alone, or two or more types may be used in combination.

[0055] The volume change of the Si-containing material is large due to expansion and contraction during charging and discharging. When the negative electrode mixture contains CNTs, even if cracks occur in the particles due to expansion and contraction of the Si-containing material, the CNTs suppress the disconnection of the conductive path, making it easier to obtain higher cycle characteristics. In particular, when the content of the Si-containing material in the negative electrode active material is high (for example, when it is 4 mass% or more), the effect of CNTs is significantly observed.

[0056] CNTs are carbonaceous materials with nanometer diameters that have a cylindrical structure in which a sheet of graphene, a six-membered ring network formed by carbon atoms, is rolled up. CNTs have excellent electrical conductivity. When the number of graphene layers that make up the cylindrical structure is one, they are called single-walled carbon nanotubes (SWCNTs). When the number of layers is multiple, they are called multi-walled carbon nanotubes (MWCNTs).

[0057] The CNT preferably includes SWCNT, which makes it easier to ensure higher cycle characteristics.

[0058] The proportion of SWCNTs in the CNTs is, for example, 50% or more, or may be 75% or more, or 90% or more. The proportion of SWCNTs in the CNTs is 100% or less. The proportion of SWCNTs in the CNTs is the ratio of the number of SWCNTs to the total number of CNTs.

[0059] The presence of CNTs in the negative electrode mixture can be confirmed, for example, by an image of a cross section of the negative electrode mixture layer taken with a scanning electron microscope (SEM).

[0060] The proportion of SWCNTs in the CNTs contained in the negative electrode mixture can be determined by the following method: An image of the cross section of the negative electrode mixture layer or the CNTs is obtained using an SEM. A number of CNTs (e.g., 50 to 200) are randomly selected and observed in the SEM image, the number of SWCNTs is determined, and the proportion of the number of SWCNTs to the total number of selected CNTs is calculated.

[0061] Quantitative analysis of CNTs is performed, for example, by combining Raman spectroscopy and thermogravimetric analysis.

[0062] From the viewpoint of reducing disconnection of the conductive path during charging and discharging, the average diameter of the CNTs may be, for example, 1 nm or more and 10 nm or less, or 1 nm or more and 5 nm or less.

[0063] From the viewpoint of reducing disconnection of the conductive path during charging and discharging, the average length of the CNTs may be, for example, 1 μm or more and 100 μm or less, or 5 μm or more and 20 μm or less.

[0064] The average length and average diameter of the CNTs can be determined from an image of the cross section of the negative electrode mixture layer or the CNTs using at least one of an SEM and a TEM. More specifically, in the captured image, a plurality of CNTs (e.g., 50 to 200) are arbitrarily selected, and their lengths and diameters are measured and averaged to determine the average length and average diameter. The length of the CNTs refers to the length of the CNTs when they are stretched linearly.

[0065] The CNT content in the negative electrode mixture is, for example, 0.005% by mass to 1% by mass, or 0.01% by mass to 1% by mass, or 0.01% by mass to 0.05% by mass. When the CNT content in the negative electrode mixture is in such a range, the conductivity of the negative electrode is improved and the capacity retention rate at the beginning of the charge-discharge cycle is significantly improved.

[0066] (Negative electrode current collector) The negative electrode current collector is selected depending on the type of nonaqueous electrolyte secondary battery. Examples of the negative electrode current collector include a sheet-shaped current collector. Metal foil or the like may also be used as the current collector. Alternatively, a porous current collector may also be used as the current collector. Examples of the porous current collector include a mesh, a punched sheet, and an expanded metal.

[0067] Examples of the material for the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy.

[0068] The thickness of the negative electrode current collector is not particularly limited, and may be, for example, 1 μm or more and 50 μm or less, or 5 μm or more and 30 μm or less.

[0069] (Others) The negative electrode can be formed, for example, by applying a negative electrode slurry, in which the components of the negative electrode mixture are dispersed in a dispersion medium, to the surface of a negative electrode current collector and drying the applied film. The dried coating film may be rolled, if necessary.

[0070] The dispersion medium is not particularly limited, and examples thereof include water, alcohol (e.g., ethanol), ether (e.g., tetrahydrofuran), amide (e.g., dimethylformamide), N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof.

[0071] (Positive Electrode) The positive electrode may include a positive electrode current collector and a positive electrode mixture layer held on the surface of the positive electrode current collector. The positive electrode mixture layer can be formed by applying a positive electrode slurry, in which the positive electrode mixture is dispersed in a dispersion medium, to the surface of the positive electrode current collector and drying the applied layer. The dried coating film may be rolled as necessary. The positive electrode mixture contains a positive electrode active material as an essential component, and may contain a binder, a conductive agent, etc. as optional components. The dispersion medium can be selected, for example, from the dispersion mediums exemplified for the negative electrode.

[0072] As the positive electrode active material, for example, a composite oxide containing lithium and a transition metal is used. Examples of the transition metal include Ni, Co, and Mn. Examples of the composite oxide containing lithium and a transition metal include Li ａ CoO ２ , Li ａ NiO ２ , Li ａ MnO ２ , Li ａ Co ｂ１ Ni １－ｂ１ O ２ , Li ａ Co ｂ１ M １－ｂ１ O ｃ１ , Li ａ Ni １－ｂ１ M ｂ１ O ｃ１ , Li ａ Mn ２ O ４ , Li ａ Mn ２－ｂ１ M ｂ１ O ４Here, a = 0 to 1.2, b1 = 0 to 0.9, and c1 = 2.0 to 2.3. M is at least one element selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. The value a, which indicates the molar ratio of lithium, increases or decreases with charge and discharge.

[0073] Among them, Li ａ Ni ｂ２ M １－ｂ２ O ２ (0<a≦1.2, 0.3≦b2≦1, and M is at least one selected from the group consisting of Mn, Co, and Al) is preferred. From the viewpoint of increasing capacity, it is more preferred that 0.8≦b2≦1 or 0.85≦b2≦1 is satisfied. From the viewpoint of stability of the crystal structure, Li ａ Ni ｂ２ Co ｃ２ Al ｄ O ２ (0<a≦1.2, 0.8≦b2<1, 0<c2<0.2 (or 0<c2≦0.18), 0<d≦0.1, b2+c2+d=1) is more preferable.

[0074] The binder may be a resin material exemplified for the negative electrode. The conductive agent may be selected from the conductive agents exemplified for the negative electrode. Graphite may also be used as the conductive agent.

[0075] The shape and thickness of the positive electrode current collector can be selected from the shapes and ranges described for the negative electrode current collector. Examples of materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloys, and titanium.

[0076] (Separator) It is usually desirable to interpose a separator between the positive electrode and the negative electrode. The separator has high ion permeability and adequate mechanical strength and insulating properties. Examples of the separator include a microporous thin film, a woven fabric, and a nonwoven fabric. The separator may have a single-layer structure or a multilayer structure. A multilayer separator may be a laminate containing at least two layers selected from the group consisting of a microporous thin film, a woven fabric, and a nonwoven fabric. The separator is preferably made of polyolefin (e.g., polypropylene, polyethylene).

[0077] (Non-aqueous electrolyte) The non-aqueous electrolyte is usually used in a liquid state, but its fluidity may be limited by a gelling agent or the like. The non-aqueous electrolyte usually contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent, and further contains an additive. In the present disclosure, the non-aqueous electrolyte contains an S-containing cyclic compound component. The non-aqueous electrolyte may further contain an additive other than the S-containing cyclic compound component.

[0078] (Non-aqueous Solvent) Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include methyl formate, ethyl formate, propyl formate, methyl acetate (MA), ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The non-aqueous electrolyte may contain one type of non-aqueous solvent or a combination of two or more types.

[0079] (Lithium Salt) Examples of lithium salts include 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 , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO ２ F ２ Examples of the borate salt include lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFFOB). Examples of the imide salt include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ ), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), lithium bispentafluoroethanesulfonyl imide (LiN(C ２ F ５ SO ２ ) ２ The non-aqueous electrolyte may contain one type of lithium salt or a combination of two or more types of lithium salts.

[0080] The concentration of the lithium salt in the electrolyte is, for example, 0.5 mol / L or more and 2 mol / L or less.

[0081] (S-containing cyclic compound component) The S-containing cyclic compound component is a cyclic compound component containing an S element as a constituent element of the ring. The cyclic compound contained in the S-containing cyclic compound component may contain an oxygen element in addition to the S element constituting the ring. The S-containing cyclic compound may, for example, contain an oxygen atom as a constituent element of the ring, or may contain an oxo group (=O) bonded to the ring as a substituent, or may contain both. The oxo group may be bonded to a carbon element constituting the ring, but is preferably bonded to an S element constituting the ring.

[0082] Such an S-containing cyclic compound may be, for example, at least one selected from the group consisting of sulfate esters, sulfite esters, and sulfonate esters. Sulfate esters are those having the structure —O—S(═O) ２ Sulfite esters have the structure -O-S(=O)-O-. Sulfonate esters have the structure -S(=O) ２ The cyclic compounds have an —O— structure. The cyclic compounds also include salts of these esters. Among these, cyclic sulfites and cyclic sulfonates are preferred.

[0083] Examples of cyclic sulfates include alkylene sulfates and alkenylene sulfates. Specific examples of cyclic sulfates include ethylene sulfate, propylene sulfate, trimethylene sulfate, butylene sulfate, and vinylene sulfate. Examples of cyclic sulfites include at least one selected from the group consisting of alkylene sulfites and alkenylene sulfites. Specific examples of cyclic sulfites include ethylene sulfite, propylene sulfite, trimethylene sulfite, butylene sulfite, and vinylene sulfite. Examples of cyclic sulfonates include at least one selected from the group consisting of alkanesultones and alkene sultones. Specific examples of cyclic sulfonates include 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone.

[0084] In the S-containing cyclic compound, one or more hydrogen atoms of the compounds exemplified above may be substituted with a substituent. Examples of the substituent include an alkyl group, an alkenyl group, a hydroxyalkyl group, a hydroxy group, an alkoxy group, and a halogen atom. The number of carbon atoms in the substituent may be 1 to 4 or 1 to 3. Examples of the halogen atom include a chlorine atom and a fluorine atom.

[0085] The S-containing ring contained in the S-containing cyclic compound is usually 5- or 6-membered.

[0086] The S-containing cyclic compound component may contain one of these S-containing cyclic compounds or a combination of two or more of them. The S-containing cyclic compound component preferably contains an S-containing cyclic compound having a carbon-carbon unsaturated bond. The carbon-carbon unsaturated bond may constitute a part of the S-containing ring, or may be contained in a substituent of the S-containing ring. Examples of such a substituent include an alkenyl group (C ２－４ alkenyl groups, etc.). Specific examples of such S-containing cyclic compounds include 1,3-propene sultone, vinylene sulfite, vinylethylene sulfite, and vinylene sulfate. When the S-containing cyclic compound component contains at least 1,3-propene sultone, a coating with excellent film quality is easily formed on the surfaces of the negative electrode active material particles, including newly formed surfaces, and higher cycle characteristics are obtained. The S-containing cyclic compound component may contain 1,3-propene sultone and another S-containing cyclic compound.

[0087] In a nonaqueous electrolyte secondary battery, the concentration of the S-containing cyclic compound component in the nonaqueous electrolyte is, for example, 2% by mass or less, and may be 1% by mass or less. This concentration of the S-containing cyclic compound component is a value determined for a nonaqueous electrolyte sampled from an initial nonaqueous electrolyte secondary battery. In a nonaqueous electrolyte secondary battery, the S-containing cyclic compound component is used to form a coating, and therefore the concentration of the S-containing cyclic compound component in the nonaqueous electrolyte changes during storage or during charge-discharge cycles. Therefore, it is sufficient that the S-containing cyclic compound component remains in the nonaqueous electrolyte sampled from an initial nonaqueous electrolyte secondary battery at a concentration equal to or greater than the detection limit. The content of the S-containing cyclic compound component in the electrolyte may be 0.01% by mass or more, 0.1% by mass or more, 0.25% by mass or more, or 0.5% by mass or more. The concentration of 1,3-propene sultone may be within the above range.

[0088] The initial nonaqueous electrolyte secondary battery is, for example, a nonaqueous electrolyte secondary battery that has been assembled and subjected to break-in charging and discharging (and aging, if necessary). A commercially available nonaqueous electrolyte secondary battery may be used as the initial nonaqueous electrolyte secondary battery, and the nonaqueous electrolyte may be collected and subjected to analysis.

[0089] The concentration of the S-containing cyclic compound component in the non-aqueous electrolyte used in the production of a non-aqueous electrolyte secondary battery may be 0.1% by mass or more, 0.2% by mass or more, 0.25% by mass or more, or even 0.5% by mass or more. The content of the S-containing cyclic compound component in the electrolytic solution used in the production of a non-aqueous electrolyte secondary battery is, for example, 2% by mass or less. The concentration of 1,3-propene sultone may be in the above range.

[0090] (Others) The non-aqueous electrolyte may contain additives other than the S-containing cyclic compound component. Examples of such additives include sulfur-containing compounds other than the S-containing cyclic compound component, phosphorus-containing compounds, nitrogen-containing compounds, vinyl ethylene carbonate, FEC, and aromatic compounds (cyclohexylbenzene, fluorobenzene, etc.). Examples of sulfur-containing compounds (S-containing compounds) include at least one selected from the group consisting of chain sulfate esters (ethyl sulfate, methyl sulfate, etc.), chain sulfite esters, and chain sulfonate esters. Examples of S-containing compounds include salts of these esters (ethyl sulfate, methyl sulfate, etc.). The non-aqueous electrolyte may contain one of these additives or a combination of two or more of them.

[0091] The nonaqueous electrolyte secondary battery preferably contains FEC, which tends to provide better cycle characteristics. FEC may be contained in a small amount (e.g., 0.1% by mass or more and 2% by mass or less) as an additive, or in a relatively large amount (e.g., more than 2% by mass) as a nonaqueous solvent in the nonaqueous electrolyte.

[0092] (Other) An example of the structure of a non-aqueous electrolyte secondary battery is a structure in which an electrode group in which a positive electrode and a negative electrode are wound with a separator interposed therebetween is housed in an exterior body together with a non-aqueous electrolyte. However, the structure of a non-aqueous electrolyte secondary battery is not limited to this structure. For example, the electrode group may be a laminate type in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween. The shape of the non-aqueous electrolyte secondary battery is also not limited, and may be, for example, a cylindrical type, a prismatic type, a coin type, a button type, or a laminate type.

[0093] FIG. 1 is a schematic perspective view, partially cut away, of a prismatic nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure. The nonaqueous electrolyte secondary battery includes a bottomed prismatic battery case 4, an electrode group 1, and an electrolyte (not shown) housed within the battery case 4. The electrode group 1 includes a long, strip-shaped negative electrode, a long, strip-shaped positive electrode, and a separator interposed therebetween. The negative electrode current collector is electrically connected to a negative electrode terminal 6 provided on a sealing plate 5 via a negative electrode lead 3. The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive electrode current collector is electrically connected to the back surface of the sealing plate 5 via a positive electrode lead 2. That is, the positive electrode is electrically connected to the battery case 4, which also serves as the positive electrode terminal. The periphery of the sealing plate 5 fits into the open end of the battery case 4, and the fitting is laser-welded. The sealing plate 5 has an electrolyte injection hole, which is closed with a seal plug 8 after injection.

[0094] EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0095] Examples 1 to 3 and Comparative Examples 1 to 8 Non-aqueous electrolyte secondary batteries were fabricated and evaluated according to the following procedure. (1) Fabrication of negative electrode An appropriate amount of water was added to the negative electrode mixture and mixed to obtain a negative electrode slurry. The negative electrode mixture was a mixture of a negative electrode active material, a binder, and a conductive agent.

[0096] The components shown in Table 1 were used as the negative electrode active materials so that their content in the overall negative electrode active material was the value shown in Table 1. However, the content of each negative electrode active material was the ratio excluding the conductive layer. The negative electrode active materials shown in Table 1 are as follows: (a) Carbon composite particles: carbon composite particles containing a carbon phase and an Si phase dispersed within the carbon phase, the surface of which is coated with a conductive layer containing conductive carbon (content of Si phase in the particle excluding the conductive layer: 50 mass %, average particle size (D50) 6 μm) (b) Silicon oxide: SiO2 the surface of which is coated with a conductive layer containing conductive carbon ｘ Particles (x = 1, average particle size (D50) 5 μm) (c) Silicate composite particles: Li whose surface is coated with a conductive layer containing conductive carbon ２ｙ SiO ２＋ｙParticles (y=0.5, average particle size (D50) 10 μm) (d) Graphite particles: average particle size (D50) 25 μm

[0097] The binders used were sodium polyacrylate (PAA-Na), a sodium salt of CMC (CMC-Na), and SBR.The conductive agent used was CNT (average diameter approximately 1.6 nm, average length approximately 5 μm) containing 90% or more SWCNT.

[0098] The CNT content in the negative electrode mixture (dry solid content) was 0.05 mass %, and the PAA-Na, CMC-Na, and SBR contents in the negative electrode mixture were each 1 mass % in terms of dry solid content.

[0099] Next, the negative electrode slurry was applied to the surface of the copper foil, the coating was dried, and then the copper foil was rolled to form a negative electrode mixture layer (thickness 80 μm, density 1.6 g / cm ) on both sides of the copper foil. ３ ) was formed to obtain a negative electrode.

[0100] (2) Preparation of the positive electrode: Lithium-containing composite oxide (LiNi ０．８ Co ０．１８ Al ０．０２ O ２ To 95 parts by mass of aluminum foil, 2.5 parts by mass of acetylene black, 2.5 parts by mass of polyvinylidene fluoride, and an appropriate amount of NMP were added and mixed to obtain a positive electrode slurry. Next, the positive electrode slurry was applied to the surface of an aluminum foil, the coating was dried, and then rolled to form a positive electrode mixture layer (thickness 95 μm, density 3.6 g / cm ) on both sides of the aluminum foil. ３ ) was formed to obtain a positive electrode.

[0101] (3) Preparation of non-aqueous electrolyte: A mixed solvent of EC, DMC, and MA (EC:DMC:MA = 20:60:20 (volume ratio)) was added to LiPF ６ 1,3-propene sultone (PRES) was dissolved in the non-aqueous electrolyte solution, and FEC was mixed in the non-aqueous electrolyte solution. ６ The concentration of PRES in the non-aqueous electrolyte (concentration at the time of preparing the non-aqueous electrolyte) was set to the value (% by mass) shown in Table 1. The concentration of FEC in the non-aqueous electrolyte was set to 1% by mass.

[0102] (4) Fabrication of a Non-Aqueous Electrolyte Secondary Battery An Al positive electrode lead was attached to the positive electrode obtained above, and a Ni negative electrode lead was attached to the negative electrode obtained above. The positive electrode and negative electrode were spirally wound with a polyethylene thin film (separator) interposed therebetween in an inert gas atmosphere to fabricate a wound electrode assembly. The electrode assembly was housed in a bag-shaped exterior body formed of a laminate sheet with an Al layer, and a predetermined amount of the electrolyte solution was injected. The exterior body was then sealed to fabricate a non-aqueous electrolyte secondary battery. When the electrode assembly was housed in the exterior body, portions of the positive electrode lead and the negative electrode lead were exposed to the outside from the exterior body.

[0103] <Evaluation> The following evaluations were performed using the obtained nonaqueous electrolyte secondary battery. (1) Initial capacity In a 45°C environment, the nonaqueous electrolyte secondary battery was subjected to constant current charging at a current of 0.5 C (180 mA) until the voltage reached 4.2 V, and then to constant voltage charging at a voltage of 4.2 V until the current reached 0.05 C (18 mA). After a 10-minute break, the nonaqueous electrolyte secondary battery was subjected to constant current discharge at a current of 0.7 C (252 mA) until the voltage reached 2.5 V. The discharge capacity (Ci) at this time was determined as the initial capacity.

[0104] (2) Cycle Characteristics The cycle of charge, rest, and discharge used to determine the discharge capacity Ci was counted as one cycle, and 100 cycles were repeated to determine the discharge capacity (Cc) at the 100th cycle. The ratio (%) of the discharge capacity Cc to the initial discharge capacity Ci was determined as 100%, and this was used as an index of cycle characteristics.

[0105] The results of the Examples and Comparative Examples are shown in Table 1. In Table 1, E1 to E3 represent Examples 1 to 3, and C1 to C8 represent Comparative Examples 1 to 8. The initial capacity is expressed as a ratio (%) of the initial capacity Ci of each Example when the initial capacity Ci of Comparative Example 1 is taken as 100%.

[0106]

[0107] As shown in Table 1, when carbon composite particles in which a Si phase is dispersed within a carbon phase are used, the initial capacity is higher but the cycle performance is lower than when a carbonaceous material containing no Si phase is used as the negative electrode active material (comparison between C1 and C3 and C4). When the negative electrode active material contains silicon oxide in addition to the carbon composite particles, the degree of deterioration in the cycle performance is greater (comparison between C3 and C4).

[0108] On the other hand, when only a carbonaceous material that does not contain an Si phase is used as the negative electrode active material, even when a non-aqueous electrolyte containing an S-containing cyclic compound component is used, the initial capacity and cycle characteristics are almost the same as when a non-aqueous electrolyte that does not contain an S-containing cyclic compound component is used (compare C1 and C2).

[0109] In contrast, when carbon composite particles are used and a nonaqueous electrolyte containing an S-containing cyclic compound component is used, the deterioration of cycle characteristics is suppressed while maintaining a high initial capacity, and excellent cycle characteristics are obtained (E1 to E3). This is thought to be because the S-containing cyclic compound component acts to form a low-resistance coating on the surface of the silicon-containing material particles containing the carbon composite particles, allowing the high capacity of the negative electrode active material to be effectively utilized and preventing the charge / discharge cycle from being hindered, thereby suppressing the decrease in capacity even with repeated charge / discharge.

[0110] When silicon oxide or silicate composite particles are used as the negative electrode active material instead of carbon composite particles, a relatively high initial capacity is obtained, but the cycle characteristics are significantly reduced compared to C1 (comparison of C1 with C6 and C8). When such a negative electrode active material is used, when a non-aqueous electrolyte containing an S-containing cyclic compound component is combined, the cycle characteristics are improved to a certain extent, but are comparable to C1. These results show that when a non-aqueous electrolyte containing an S-containing cyclic compound component is combined with a negative electrode active material containing carbon composite particles, a particularly excellent effect of improving the cycle characteristics can be obtained.

[0111] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0112] The nonaqueous electrolyte secondary battery of the present disclosure is useful as a main power source for mobile communication devices, portable electronic devices, etc. However, these are merely examples, and the uses of the nonaqueous electrolyte secondary battery are not limited to these.

[0113] 1: Electrode group 2: Positive electrode lead 3: Negative electrode lead 4: Battery case 5: Sealing plate 6: Negative electrode terminal 7: Gasket 8: Sealing cap

Claims

1. A non-aqueous electrolyte secondary battery comprising a negative electrode containing a negative electrode active material, a separator, a positive electrode facing the negative electrode via the separator, and a non-aqueous electrolyte, The negative electrode active material contains a negative electrode active material, The negative electrode active material contains a silicon-containing material of 3% by mass or more, The silicon-containing material contains carbon composite particles, The carbon composite particles contain a carbon phase and a silicon phase dispersed in the carbon phase, The non-aqueous electrolyte contains a 5-membered or 6-membered cyclic compound component containing sulfur element as a constituent element of the ring, a non-aqueous electrolyte secondary battery.

2. The silicon-containing material further contains silicon oxide, the non-aqueous electrolyte secondary battery according to claim 1.

3. The silicon-containing material further contains silicate composite particles, The silicate composite particles contain a silicate phase and a silicon phase dispersed in the silicate phase, the non-aqueous electrolyte secondary battery according to claim 1 or 2.

4. The cyclic compound component contains a cyclic compound containing sulfur element as a constituent element of the ring and having a carbon-carbon unsaturated bond, the non-aqueous electrolyte secondary battery according to claim 1 or 2.

5. The cyclic compound component contains 1,3-propenesultone, the non-aqueous electrolyte secondary battery according to claim 1 or 2.

6. The concentration of the cyclic compound component in the non-aqueous electrolyte is 2% by mass or less, the non-aqueous electrolyte secondary battery according to claim 1 or 2.

7. The negative electrode active material further contains carbon nanotubes, the non-aqueous electrolyte secondary battery according to claim 1 or 2.

8. The non-aqueous electrolyte further contains fluoroethylene carbonate, the non-aqueous electrolyte secondary battery according to claim 1 or 2.