Positive electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes a positive electrode core material, and a positive electrode mixture layer formed on the surface of the positive electrode core material. The positive electrode includes a C10 or lower sugar alcohol, the sugar alcohol content being less than 5 mass% relative to the mass of a positive electrode active substance contained within the positive electrode mixture layer. The sugar alcohol is, for example, included within the positive electrode mixture layer. If the positive electrode mixture layer has a multilayer structure including a first layer and a second layer, the sugar alcohol content is preferably higher in the second layer than in the first layer.

Description

Technical Field

[0001] The present disclosure relates to a positive electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery using the positive electrode.

Background Art

[0002] In recent years, non-aqueous electrolyte secondary batteries such as lithium ion batteries have been widely used in applications requiring high capacity, such as in-vehicle applications and power storage applications. In addition, non-aqueous electrolyte secondary batteries are required to have a function of suppressing heat generation when an abnormality occurs. Since an electrode assembly, which is a main component of a non-aqueous electrolyte secondary battery, greatly affects these performances, many studies have been conducted on positive electrodes. For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery in which a porous layer containing filler particles of a metal hydroxide is formed between at least one of a positive electrode and a negative electrode constituting the electrode assembly and a separator. Patent Document 1 describes the effect that it was confirmed that the battery is excellent in safety in an internal foreign matter short circuit test.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

[0004] In non-aqueous electrolyte secondary batteries, improving the heat generation suppression function when an abnormality occurs is an important issue. In particular, in high-capacity batteries, a rapid temperature rise is likely to occur when an abnormality occurs, so a more advanced heat generation suppression function is required. In addition, it is necessary to improve the heat generation suppression function without causing a decrease in battery capacity, but it is not easy to achieve both high capacity and an excellent heat generation suppression function. Conventional techniques including the invention disclosed in Patent Document 1 still have room for improvement in achieving both high capacity and an excellent heat generation suppression function.

[0005] The positive electrode for a non-aqueous electrolyte secondary battery according to this disclosure is a positive electrode for a non-aqueous electrolyte secondary battery comprising a positive electrode core material and a positive electrode mixture layer formed on the surface of the positive electrode core material, wherein the positive electrode contains a sugar alcohol having 10 or fewer carbon atoms, and the sugar alcohol content is less than 5% by mass relative to the mass of the positive electrode active material contained in the positive electrode mixture layer.

[0006] The non-aqueous electrolyte secondary battery according to this disclosure is characterized by comprising the positive electrode, the negative electrode, and the non-aqueous electrolyte.

[0007] The positive electrode for a non-aqueous electrolyte secondary battery according to this disclosure can provide a non-aqueous electrolyte secondary battery with high capacity and excellent heat generation suppression function in the event of an abnormality. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. [Figure 2] This is a cross-sectional view of the positive electrode, which is another example of an embodiment. [Figure 3] This is a cross-sectional view of the positive electrode, which is another example of an embodiment. [Modes for carrying out the invention]

[0009] As described above, achieving both high capacity and excellent heat suppression in non-aqueous electrolyte secondary batteries is a crucial challenge. To solve this problem, the inventors diligently investigated and succeeded in realizing a non-aqueous electrolyte secondary battery that ensures high capacity while also exhibiting excellent heat suppression in the event of an abnormality by using a positive electrode containing a sugar alcohol with 10 or fewer carbon atoms in an amount of less than 5% by mass relative to the mass of the positive electrode active material.

[0010] The sugar alcohols contained in the positive electrode are thought to undergo an endothermic hydration reaction when a battery malfunction occurs. This hydration reaction is a reaction between water and sugar alcohol, and is triggered by the water generated when the electrolyte decomposes during a battery malfunction. Therefore, under normal use of the battery, if the sugar alcohol content is less than 5% by mass relative to the mass of the positive electrode active material, it will not affect the battery performance. Sugar alcohols with 10 or fewer carbon atoms have a large latent heat, so adding them to the positive electrode can highly suppress heat generation during malfunctions. Although the metal hydroxide fillers disclosed in Patent Document 1 also have a large latent heat, it is difficult to rapidly suppress heat generation like with sugar alcohols with 10 or fewer carbon atoms.

[0011] Hereinafter, with reference to the drawings, an example of an embodiment of a positive electrode for a non-aqueous electrolyte secondary battery according to this disclosure, and an example of an embodiment of a non-aqueous electrolyte secondary battery using said positive electrode will be described in detail. Note that configurations obtained by selectively combining the multiple embodiments and modifications described below are included in this disclosure.

[0012] In the following, a cylindrical battery in which a wound electrode body 14 is housed in a bottomed cylindrical outer casing 16 is given as an example. However, the battery casing is not limited to a cylindrical outer casing, and may be, for example, a rectangular outer casing (rectangular battery) or an outer casing made of a laminate sheet including a metal layer and a resin layer (laminated battery). Furthermore, the electrode body may be a laminated electrode body in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators in between.

[0013] Figure 1 is a schematic diagram showing a cross-section of a non-aqueous electrolyte secondary battery 10, which is an example of an embodiment. As shown in Figure 1, the non-aqueous electrolyte secondary battery 10 comprises a wound electrode body 14, a non-aqueous electrolyte (not shown), and an outer casing 16 that houses the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape via the separator 13. The outer casing 16 is a bottomed cylindrical metal container with one side open in the axial direction, and the opening of the outer casing 16 is sealed by a sealing body 17. In the following, for convenience of explanation, the side of the battery with the sealing body 17 will be referred to as the top, and the bottom side of the outer casing 16 as the bottom.

[0014] Non-aqueous electrolytes comprise a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Non-aqueous solvents may also contain halogen-substituted solvents, in which at least some of the hydrogen atoms of these solvents are replaced with halogen atoms such as fluorine. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and mixtures thereof. Examples of electrolyte salts include lithium salts such as LiPF6. Non-aqueous electrolytes are not limited to liquid electrolytes and may also be solid electrolytes.

[0015] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 are all elongated strip-shaped bodies that are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed to be slightly larger in dimensions than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal direction and the width direction (short direction) than the positive electrode 11. The separator 13 is formed to be at least slightly larger in dimensions than the positive electrode 11, and two separators are arranged so as to sandwich the positive electrode 11. The electrode body 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

[0016] Insulating plates 18 and 19 are positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 extends outside the insulating plate 19 towards the bottom of the outer can 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 becomes the negative electrode terminal.

[0017] As described above, the outer casing 16 is a bottomed cylindrical metal container with one side open in the axial direction. A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure airtightness inside the battery and insulation between the outer casing 16 and the sealing body 17. The outer casing 16 has a grooved portion 22 formed on its side, which protrudes inward to support the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The sealing body 17 is fixed to the upper part of the outer casing 16 by the grooved portion 22 and the open end of the outer casing 16 which is crimped to the sealing body 17.

[0018] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, with the insulating member 25 interposed between their respective peripheries. When a malfunction occurs in the battery and the internal pressure rises, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0019] The following will provide a detailed explanation of the positive electrode 11, the negative electrode 12, and the separator 13, with particular emphasis on the positive electrode 11.

[0020] [Positive electrode] The positive electrode 11 includes a positive electrode core material 30 and a positive electrode mixture layer 31 formed on the surface of the positive electrode core material 30. The positive electrode core material 30 can be a foil of a metal that is stable in the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. An example of the positive electrode core material 30 is an aluminum or aluminum alloy foil with a thickness of 10 to 20 μm. The positive electrode mixture layer 31 includes a positive electrode active material, a conductive agent, and a binder, and is preferably formed on both sides of the positive electrode core material 30. An example of the thickness of the positive electrode mixture layer 31 is 50 to 150 μm on one side of the positive electrode core material 30.

[0021] The positive electrode 11 can be produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like onto a positive electrode core material 30, drying the applied coating film, and then compressing the coating to form positive electrode mixture layers 31 on both surfaces of the positive electrode core material 30. As will be described in detail later, the positive electrode 11 contains a sugar alcohol having 10 or less carbon atoms, and the content of the sugar alcohol is less than 5% by mass relative to the mass of the positive electrode active material.

[0022] The positive electrode mixture layer 31 contains a particulate lithium metal composite oxide as the positive electrode active material. The lithium metal composite oxide is a composite oxide containing, in addition to Li, metal elements such as Co, Mn, Ni, and Al. The metal element constituting the lithium metal composite oxide is at least one selected from the group consisting of, for example, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from the group consisting of Co, Ni, and Mn. Examples of suitable composite oxides include lithium metal composite oxides containing Ni, Co, and Mn, and lithium metal composite oxides containing Ni, Co, and Al.

[0023] The volume-based median diameter (D50) of the positive electrode active material is, for example, 1 to 25 μm, and preferably 3 to 20 μm. D50 refers to the particle diameter at which the cumulative frequency from the smaller particle diameter side in a volume-based particle size distribution reaches 50%, and is also called the median diameter. The particle size distribution of the positive electrode active material can be measured using a laser diffraction particle size distribution analyzer (for example, MT3000II manufactured by MicrotracBEL Corp.) with water as a dispersion medium. The content of the positive electrode active material is, for example, 90 to 99.5% by mass relative to the mass of the positive electrode mixture layer 31. Note that the average particle diameter of the positive electrode active material, which is obtained from an SEM image of a cross-section of the positive electrode by the same method as that for the average particle diameter of the sugar alcohol described later, is substantially the same value as D50 measured using a laser diffraction particle size distribution analyzer.

[0024] Examples of conductive agents included in the positive electrode mixture layer 31 include carbon black such as acetylene black and Ketjenblack, graphite, carbon nanotubes (CNTs), carbon nanofibers, and graphene. The preferred content of the conductive agent varies depending on the type of conductive agent, but for example, it is 0.1 to 10% by mass, and more preferably 0.2 to 5% by mass, relative to the mass of the positive electrode mixture layer 31.

[0025] Examples of binders included in the positive electrode mixture layer 31 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. These resins may also be used in combination with carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc. The binder content is, for example, 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, relative to the mass of the positive electrode mixture layer 31.

[0026] As described above, the positive electrode 11 contains a sugar alcohol with 10 or fewer carbon atoms. Sugar alcohols are linear or cyclic polyhydric alcohols in which the carbonyl groups of sugars are reduced, and they have a large latent heat and function as a heat absorber. When a battery malfunction occurs, it is important to be able to suppress heat generation at, for example, 150-250°C. By adding a sugar alcohol with 10 or fewer carbon atoms to the positive electrode 11, effective heat absorption can be achieved at this temperature. However, if the number of carbon atoms in the sugar alcohol exceeds 10, the heat generation suppression effect when a battery malfunction occurs decreases significantly.

[0027] The sugar alcohol content is less than 5% by mass relative to the mass of the positive electrode active material contained in the positive electrode mixture layer 31. If the amount of sugar alcohol added is 5% or more of the mass of the positive electrode active material, the heat generation suppression function in the event of an abnormality improves, but the battery capacity decreases rapidly. Although sugar alcohol exhibits a heat generation suppression effect even with the addition of a small amount, the sugar alcohol content relative to the mass of the positive electrode active material is preferably 0.5% by mass or more, and more preferably 1% by mass or more. In this case, the heat generation suppression effect in the event of a battery abnormality becomes more pronounced.

[0028] Sugar alcohols, for example, together with the positive electrode active material, Combination layer It is contained in 31. The sugar alcohol is a particle whose average particle size is smaller than the average particle size of the positive electrode active material, and is dispersed in the positive electrode mixture layer 31. By adding sugar alcohol to the above positive electrode mixture slurry, the sugar alcohol can be contained in the positive electrode mixture layer 31. Sugar alcohol is contained in the positive electrode Combination layer The sugar alcohol may be dispersed throughout the entire layer rather than being concentrated in a portion of layer 31. Preferably, the sugar alcohol is contained in each positive electrode mixture layer 31 formed on both sides of the positive electrode core material 30. In each positive electrode mixture layer 31, the sugar alcohol is contained at substantially the same concentration.

[0029] The number of carbon atoms in the sugar alcohol is preferably 8 or less, and more preferably 6 or less. Furthermore, the number of carbon atoms in the sugar alcohol is preferably 4 or more. When sugar alcohols with 4 to 6 carbon atoms are added to the positive electrode 11, they function effectively at 150 to 250°C, and the heat generation suppression effect during battery malfunctions becomes more pronounced. Specific examples of suitable sugar alcohols include erythritol, sreitol, pentaerythritol, xylitol, arabitol, mannitol, sorbitol, galactitol, and inositol.

[0030] The sugar alcohol is preferably a chain-like molecule with 4 to 6 carbon atoms, and more specifically, it is preferably at least one selected from the group consisting of erythritol, slayitol, pentaerythritol, xylitol, mannitol, and sorbitol. Among these, slayitol and mannitol are particularly preferred.

[0031] The average particle size of sugar alcohols is, for example, 0.05 to 5 μm, preferably 0.1 to 2 μm. When the average particle size of sugar alcohols is within this range, a more effective endothermic effect occurs at 150 to 250°C compared to when the average particle size is outside this range, and the heat generation suppression effect in the event of a battery malfunction becomes more pronounced. The average particle size of sugar alcohols can be adjusted, for example, by a high-shear mixer. The average particle size of sugar alcohols is also measured by observing the cross-section of the positive electrode using a scanning electron microscope (SEM). Specifically, the diameter of the circumscribed circle of the sugar alcohol particles extracted from the SEM image of the cross-section of the positive electrode is defined as the particle size, and the average particle size of the sugar alcohols is determined by averaging the particle sizes of 100 randomly selected particles.

[0032] Figure 2 is a cross-sectional view of a positive electrode including a multilayer positive electrode mixture layer 31. In the positive electrode illustrated in Figure 2, the positive electrode mixture layer 31 includes a first layer 31a formed on the positive electrode core material 30 side and a second layer 31b formed on the positive electrode core material 30 via the first layer 31a. In this case, it is preferable that the sugar alcohol content is higher in the second layer 31b than in the first layer 31a. In other words, the positive electrode mixture layer 31 includes a first layer 31a with a low sugar alcohol content and a second layer 31b with a higher sugar alcohol content than the first layer 31a. In this case, it becomes easier to achieve both high capacity and excellent heat suppression function.

[0033] The sugar alcohol content in the second layer 31b is, for example, 1.3 times or more than the sugar alcohol content in the first layer 31a. In this case, the effect of improving heat generation suppression becomes more pronounced. The sugar alcohol may be contained substantially only in the second layer 31b. The positive electrode mixture layer 31 has a two-layer structure with different sugar alcohol contents, but it may also have three or more layers. The positive electrode mixture layer 31 may have a concentration gradient such that the sugar alcohol content increases as it moves away from the positive electrode core material 30.

[0034] The types and concentrations of the positive electrode active material, conductive agent, and binder may be the same or different in the first layer 31a and the second layer 31b. In this embodiment, the same type of positive electrode active material, conductive agent, and binder are used in the first layer 31a and the second layer 31b, respectively. Furthermore, the concentrations of the conductive agent and binder relative to the mass of the positive electrode active material are substantially the same in each layer. That is, the first layer 31a and the second layer 31b are layers that differ only in the concentration of sugar alcohol relative to the mass of the positive electrode active material. The type of sugar alcohol may be the same or different in the first layer 31a and the second layer 31b.

[0035] The positive electrode illustrated in Figure 2 can be prepared using two types of positive electrode slurry with different sugar alcohol content relative to the mass of the positive electrode active material. After applying a first positive electrode slurry with a low sugar alcohol content onto the positive electrode core material 30, a second positive electrode slurry with a high sugar alcohol content is applied on the coating to form a two-layer positive electrode slurry 31 including a first layer 31a and a second layer 31b.

[0036] Figure 3 is a cross-sectional view of a positive electrode including a surface layer 32 containing a sugar alcohol. The positive electrode illustrated in Figure 3 includes a surface layer 32 formed on a positive electrode mixture layer 31. The surface layer 32 is a layer with a higher sugar alcohol content than the positive electrode mixture layer 31. The surface layer 32 is composed of, for example, a sugar alcohol and a binder, and can be formed by applying a slurry containing the sugar alcohol and binder to the surface of the positive electrode mixture layer 31. In the example shown in Figure 3, the sugar alcohol may not be substantially included in the positive electrode mixture layer 31, but substantially only in the surface layer 32.

[0037] The thickness of the surface layer 32 is preferably 50% or less of the thickness of the positive electrode mixture layer 31. Since it is difficult to accurately compare the thickness ratio of the positive electrode mixture layer 31 and the surface layer 32, when comparing each layer by mass ratio, the mass of the surface layer 32 is, for example, 0.1 to 5%, and more preferably 0.14 to 1%, of the mass of the positive electrode mixture layer 31. If the mass ratio of the positive electrode mixture layer 31 and the surface layer 32 is within this range, it becomes easy to achieve both high capacity and excellent heat generation suppression function.

[0038] Negative Electrode The negative electrode 12 includes a negative electrode core material 40 and a negative electrode mixture layer 41 formed on a surface of the negative electrode core material 40. For the negative electrode core material 40 , a foil of a metal that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film having such a metal disposed on the surface layer can be used. An example of the negative electrode core material 40 is a copper or copper alloy foil having a thickness of 5 to 15 µm. The negative electrode mixture layer 41 contains a negative electrode active material, a binder, and optionally a conductive agent, and is preferably formed on both surfaces of the negative electrode core material 40. The thickness of the negative electrode mixture layer 41 is, for example, 30 to 150 µm on one side of the negative electrode core material 40. The negative electrode 12 can be produced by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and the like onto the negative electrode core material 40, drying the coating film, and then compressing it to form the negative electrode mixture layer 41 on both surfaces of the negative electrode core material 40.

[0039] The negative electrode mixture layer 41 contains, as a negative electrode active material, a carbon-based active material that can reversibly occlude and release lithium ions. A suitable carbon-based active material is graphite, such as natural graphite including flaky graphite, massive graphite, and earthy graphite, and artificial graphite including massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). Further, from the viewpoint of improving energy density and the like, a Si-containing Si-based active material may also be used as the negative electrode active material.

[0040] Examples of the Si-based active material include silicon alloys, silicon compounds, and composite materials containing Si. Among these, composite materials containing Si are preferable. A suitable composite material is composite particles including an ion conductive layer and Si particles dispersed in the ion conductive layer. A conductive layer may be formed on a surface of the Si-containing composite particles. An example of such composite particles has a sea-island structure in which fine Si particles are substantially uniformly dispersed in an amorphous silicon oxide phase, and as a whole is represented by the general formula SiO x (0 < x ≤ 2), which is the composite particle. Further, the ion conductive layer may have the general formula Li 2z SiO (2+z) (0 < z < 2), which is a silicate phase, or may be an amorphous carbon phase.

[0041] The binder included in the negative electrode mixture layer 41 can be, for example, PAN, polyimide, acrylic resin, polyolefin, styrene-butadiene rubber (SBR), etc. The negative electrode mixture layer 41 may also contain CMC or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. Conductive agents such as carbon black and CNTs may also be added to the negative electrode mixture layer 41.

[0042] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator 13.

[0043] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphoric acid compounds. The filler layer can be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13. [Examples]

[0044] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0045] <Example 1> [Fabrication of the positive electrode] As the positive electrode active material, LiNi 0.91 Co 0.06 Al 0.03A composite oxide represented by O2 with an average particle size of 5.9 μm was used. The positive electrode active material, acetylene black, polyvinylidene fluoride, and xylitol were mixed in a solid content mass ratio of 100:1:1:1, and a positive electrode mixture slurry was prepared using N-methyl-2-pyrrolidone (NMP) as the dispersion medium. Next, this positive electrode mixture slurry was applied to both sides of a positive electrode core made of aluminum foil, the coating was dried, and the material was compressed using a roller. After that, the positive electrode core was cut to a predetermined electrode size to obtain a positive electrode with positive electrode mixture layers formed on both sides of the positive electrode core. The average particle size of xylitol in the positive electrode mixture layer was 1.8 μm (the average particle size of xylitol used in other examples and comparative examples was the same).

[0046] [Fabrication of the negative electrode] The negative electrode active material consists of 95 parts by mass of graphite and 5 parts by mass of SiO2. X A mixture of a Si-containing material represented by (X=1) was used. The negative electrode active material, the sodium salt of CMC, and the dispersion of SBR were mixed in a solid content mass ratio of 100:1:1, and water was used as the dispersion medium to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to a negative electrode core made of copper foil, the coating was dried and rolled, and then the negative electrode core was cut to a predetermined electrode size to obtain a negative electrode in which negative electrode mixture layers were formed on both sides of the negative electrode core.

[0047] [Preparation of non-aqueous electrolyte solution] A non-aqueous electrolyte was prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7 (at 25°C) to a concentration of 1 M.

[0048] [Preparation of test cells] A wound electrode body was fabricated by winding the positive and negative electrodes, to which leads were attached, via a separator. The electrode body was inserted into an aluminum laminate film enclosure and vacuum-dried at 105°C for 2 hours. Subsequently, a non-aqueous electrolyte was injected into the enclosure, and the opening of the enclosure was sealed to obtain a test cell (non-aqueous electrolyte secondary battery).

[0049] <Example 2> In preparing the positive electrode, the test cell was prepared in the same manner as in Example 1, except that the amount of xylitol added was changed to 3% by mass relative to the mass of the positive electrode active material.

[0050] <Example 3> In preparing the cathode, the test cell was prepared in the same manner as in Example 1, except that mannitol with an average particle size of 1.5 μm (the average particle size of the mannitol used in the other examples and comparative examples was the same) was used instead of xylitol.

[0051] <Example 4> The test cell was prepared in the same manner as in Example 2, except that mannitol was used instead of xylitol in the preparation of the positive electrode.

[0052] <Example 5> In preparing the cathode, the test cell was prepared in the same manner as in Example 1, except that slayitol with an average particle size of 1.5 μm (the average particle size of the slayitol used in the other examples and comparative examples was the same) was used instead of xylitol.

[0053] <Example 6> The test cell was prepared in the same manner as in Example 2, except that slateol was used instead of xylitol in the preparation of the positive electrode.

[0054] <Comparative Example 1> The test cell was prepared in the same manner as in Example 1, except that a sugar alcohol (xylitol) was not added during the preparation of the cathode.

[0055] <Comparative Example 2> In preparing the cathode, the test cell was prepared in the same manner as in Example 1, except that magnesium hydroxide with an average particle size of 2.9 μm (the average particle size of magnesium hydroxide in Comparative Example 3 was the same) was used instead of xylitol.

[0056] <Comparative Example 3> The test cell was prepared in the same manner as in Example 2, except that magnesium hydroxide was used instead of xylitol in the preparation of the positive electrode.

[0057] <Comparative Example 4> In preparing the positive electrode, the test cell was prepared in the same manner as in Example 1, except that the amount of xylitol added was changed to 5% by mass relative to the mass of the positive electrode active material.

[0058] <Comparative Example 5> In preparing the positive electrode, the test cell was prepared in the same manner as in Example 3, except that the amount of mannitol added was changed to 5% by mass relative to the mass of the positive electrode active material.

[0059] <Comparative Example 6> In preparing the positive electrode, the test cell was prepared in the same manner as in Example 5, except that the amount of slateol added was changed to 5% by mass relative to the mass of the positive electrode active material.

[0060] The performance of each test cell in the examples and comparative examples was evaluated using the method described below. The evaluation results are shown in Table 1.

[0061] [Measuring cell capacity] The test cells under evaluation were charged at 0.2C with a constant current until the cell voltage reached 4.2V under a temperature environment of 25°C, and then discharged at 0.5C with a constant current until the cell voltage reached 2.5V. The discharge capacity during this charge and discharge process was determined as the cell capacity.

[0062] [Measurement of heat generation] A positive electrode plate was cut to 2 x 2 cm and a negative electrode plate to 2.1 x 2.1 cm, and these were placed opposite each other to create an evaluation cell. A nail-piercing test was then performed using the following procedure.

[0063] Under 25°C conditions, the evaluation cell was charged at 0.2C until the cell voltage reached 4.2V, and then charged at a constant voltage until the current value was equivalent to 0.05C. Afterward, under 25°C conditions, the tip of a round nail (2.7mm in diameter) was placed in contact with the center of the charged cell. The nail was driven in at a speed of 1mm / second. The nail stopped immediately after detecting a drop in cell voltage due to an internal short circuit. Measurements of the short-circuit current (I) and cell voltage (V) were continued for an arbitrary period of time after the cell was short-circuited by the nail. The amount of heat generated over this arbitrary period was calculated by integrating the product of the current (I) and voltage (V) (power) over time.

[0064] [Table 1]

[0065] As shown in Table 1, all of the test cells in the examples exhibited superior heat suppression capabilities, generating less heat during abnormal occurrences compared to the test cells of Comparative Examples 1-3, in which sugar alcohol was not added to the positive electrode. Furthermore, the test cells in the examples had a higher capacity compared to the test cells of Comparative Examples 4-6, in which the sugar alcohol addition rate to the positive electrode active material was 5% by mass or more. The capacity of the test cells in Comparative Examples 4-6 was significantly reduced.

[0066] As is clear from these results, a high-capacity non-aqueous electrolyte secondary battery with excellent heat suppression capabilities can only be realized when a positive electrode is used in which a sugar alcohol with 10 or fewer carbon atoms is added in an amount of less than 5% by mass relative to the positive electrode active material. [Explanation of Symbols]

[0067] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer casing, 17 Sealing body, 18,19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating material, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode core material, 31 Positive electrode mixture layer, 31a First layer, 31b Second layer, 32 Surface layer, 40 Negative electrode core material, 41 Negative electrode mixture layer

Claims

1. A positive electrode for a non-aqueous electrolyte secondary battery, comprising a positive electrode core material and a positive electrode mixture layer formed on the surface of the positive electrode core material, The positive electrode contains a sugar alcohol with 10 or fewer carbon atoms. A positive electrode for a non-aqueous electrolyte secondary battery, wherein the sugar alcohol content is less than 5% by mass relative to the mass of the positive electrode active material contained in the positive electrode mixture layer.

2. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the sugar alcohol is at least one selected from the group consisting of erythritol, sreitol, pentaerythritol, xylitol, mannitol, and sorbitol.

3. The positive electrode mixture layer includes a first layer formed on the positive electrode core material side and a second layer formed on the positive electrode core material via the first layer. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the sugar alcohol content is higher in the second layer than in the first layer.

4. The positive electrode includes a surface layer formed on the positive electrode mixture layer, The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the sugar alcohol content is higher in the surface layer than in the positive electrode mixture layer.

5. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the average particle size of the sugar alcohol is smaller than the average particle size of the positive electrode active material, and is 0.1 to 2 μm.

6. A positive electrode according to any one of claims 1 to 5, The negative electrode and, Non-aqueous electrolytes, A secondary battery equipped with these features.

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