Negative electrode active material and lithium-ion battery

Abstract

The present invention provides: a negative electrode active material which has a La3Ni2Sn7 crystal structure, while having a high weight energy density; and a lithium ion battery which uses this negative electrode active material. A negative electrode active material according to one embodiment of the present disclosure is contained in a negative electrode of a lithium ion battery, and is represented by general formula M3Me2X7 (wherein M comprises at least one of La and Ca; Me comprises at least one element that is selected from the group consisting of Mn, Ni, Fe and Co; and X comprises at least one element that is selected from the group consisting of Ge, Si, Sn and Al). With respect to the XRD pattern obtained by XRD measurement wherein Cu is used for an anticathode, the half-value width of the diffraction peak of the (1 17 1) plane of the negative electrode active material is 0.4713° or more.

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode active material and a lithium ion battery. [Background Art]

[0002] Lithium ion batteries, which are charged and discharged by the movement of lithium ions (Li ions) between a positive electrode and a negative electrode, are widely used. In recent years, for the negative electrode active material contained in the negative electrode of such lithium ion batteries, Si, which has a higher capacity than graphite, has been used in addition to graphite. However, Si has a large volume change during charge and discharge, and thus has the problem that battery capacity is likely to decrease due to repeated charge and discharge cycles.

[0003] Accordingly, various alloys other than Si have been studied as negative electrode active materials for high-capacity lithium ion batteries. For example, Non Patent Document 1 describes the use of an alloy having a La3Ni2Sn7-type crystal structure as a negative electrode active material. [Prior Art Documents] [Non-Patent Documents]

[0004] [Non-Patent Document 1] Shinsuke Matsuno et al, La3Ni2Sn7Ternary Intermetallic Phase for Lithium Insertion and Deinsertion, Electrochemical and Solid-State Letters, volume 8(4), A234-A236, (2005). [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] However, the alloy having a La3Ni2Sn7-type crystal structure described in Non-Patent Document 1 has higher volumetric energy density than graphite, but lower gravimetric energy density.

[0006] The purpose of this disclosure is to provide a negative electrode active material having a La3Ni2Sn7 type crystal structure and high gravimetric energy density, and a lithium-ion battery using the same. [Means for solving the problem]

[0007] One aspect of the present disclosure is a negative electrode active material contained in the negative electrode of a lithium-ion battery, represented by the general formula M3Me2X7 (wherein M includes at least one of La and Ca, Me includes at least one element selected from the group consisting of Mn, Ni, Fe, and Co, and X includes at least one element selected from the group consisting of Ge, Si, Sn, and Al), and is characterized in that, in an XRD pattern obtained by XRD measurement using Cu as the cathode, the full width at half maximum of the diffraction peak of the (1 17 1) plane of the negative electrode active material is 0.4713° or more.

[0008] A lithium-ion battery according to one aspect of this disclosure comprises a negative electrode containing the above-mentioned negative electrode active material, a positive electrode, and a non-aqueous electrolyte. [Effects of the Invention]

[0009] The negative electrode active material relating to this disclosure can achieve a high gravimetric energy density. [Brief explanation of the drawing]

[0010] [Figure 1] This is a longitudinal cross-sectional view of a cylindrical lithium-ion battery, which is an example of an embodiment. [Figure 2] The XRD patterns of the negative electrode active materials contained in the test cells of the examples and comparative examples are shown. [Modes for carrying out the invention]

[0011] To increase the capacity of lithium-ion batteries, a negative electrode active material made by mixing graphite with silicon (Si) is used. However, since Si is expensive and its inclusion can worsen the cycle characteristics of lithium-ion batteries, various alloys other than Si are attracting attention as negative electrode active materials. For example, as a negative electrode active material for high-capacity lithium-ion batteries, Non Patent Document 1 discloses an alloy having a La3Ni2Sn7 type crystal structure. However, Non The alloy disclosed in Patent Document 1 has a higher volumetric energy density but a lower gravimetric energy density compared to graphite. As a result of diligent research, the inventors have found that the gravimetric energy density can be increased by setting the full width at half maximum of the diffraction peak of the (1 17 1) plane of the negative electrode active material to 0.4713° or higher in the XRD pattern obtained by XRD measurement using Cu as the cathode.

[0012] The following describes in detail an example of an embodiment of a lithium-ion battery using the negative electrode active material related to this disclosure. In a lithium-ion battery, charging and discharging occur by the movement of lithium ions between the positive electrode and the negative electrode. In the following, a cylindrical battery in which a wound electrode body is housed in a bottomed cylindrical outer casing is given as an example, but the outer casing is not limited to a cylindrical outer casing, and may be, for example, a rectangular outer casing, or an outer casing composed of a laminate sheet including a metal layer and a resin layer. Furthermore, the electrode body may be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked with a separator in between. Furthermore, in the following, a liquid non-aqueous electrolyte is given as an example, but the non-aqueous electrolyte is not limited to a liquid, and may be a solid.

[0013] Figure 1 is a longitudinal cross-sectional view of a cylindrical lithium-ion battery 10, which is an example of an embodiment. In the lithium-ion battery 10 shown in Figure 1, an electrode body 14 and a non-aqueous electrolyte (not shown) are housed in an outer casing 15. The electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13. As the solvent (organic solvent) for the non-aqueous electrolyte, carbonates, lactones, ethers, ketones, esters, etc., can be used, and two or more of these solvents can be mixed and used. When using a mixture of two or more solvents, it is preferable to use a mixed solvent containing a cyclic carbonate and a linear carbonate. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), etc. can be used as the linear carbonate. Non-aqueous electrolytes such as LiPF6, LiBF4, LiCF3SO3, and mixtures thereof can be used as electrolyte salts. The solubility of the electrolyte salt in the solvent can be, for example, 0.5 to 2.0 mol / L. For the sake of explanation, the side with the sealing body 16 will be referred to as "upper" and the bottom side with the outer casing 15 as "lower".

[0014] The lithium-ion battery 10 is sealed by closing the open end of the outer casing 15 with the sealing body 16. Insulating plates 17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode lead 19 extends upward through a through hole in the insulating plate 17 and is welded to the lower surface of the filter 22, which is the bottom plate of the sealing body 16. In the lithium-ion battery 10, the cap 26, which is the top plate of the sealing body 16 electrically connected to the filter 22, becomes the positive electrode terminal. On the other hand, the negative electrode lead 20 extends through a through hole in the insulating plate 18 to the bottom side of the outer casing 15 and is welded to the bottom inner surface of the outer casing 15. In the lithium-ion battery 10, the outer casing 15 becomes the negative electrode terminal. If the negative electrode lead 20 is installed at the end, the negative electrode lead 20 extends outside the insulating plate 18 to the bottom side of the outer casing 15 and is welded to the bottom inner surface of the outer casing 15.

[0015] The outer casing 15 is, for example, a metal outer casing in the shape of a bottomed cylindrical can. A gasket 27 is provided between the outer casing 15 and the sealing body 16 to ensure airtightness inside the lithium-ion battery 10. The outer casing 15 has grooves 21 that support the sealing body 16, which are formed, for example, by pressing the side surface from the outside. The grooves 21 are preferably formed in an annular shape along the circumferential direction of the outer casing 15, and their upper surface supports the sealing body 16 via the gasket 27.

[0016] The sealing body 16 has a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are stacked in order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disc shape or a ring shape, and each component except the insulating member 24 is electrically connected to one another. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheries. If the internal pressure of the battery rises due to abnormal heat generation, for example, the lower valve body 23 may rupture, causing the upper valve body 25 to bulge towards the cap 26 and separate from the lower valve body 23, thereby interrupting the electrical connection between the two. If the internal pressure rises further, the upper valve body 25 may rupture, and gas may be discharged from the opening 26a of the cap 26.

[0017] The following describes in detail the positive electrode 11, negative electrode 12, and separator 13 that constitute the electrode body 14, with particular attention paid to the negative electrode active material that constitutes the negative electrode 12.

[0018] [Positive electrode] The positive electrode 11 includes, for example, a positive electrode core and a positive electrode mixture layer provided on the surface of the positive electrode core. The positive electrode core can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum, or a film with the metal arranged on its surface. The thickness of the positive electrode core is, for example, 10 μm to 30 μm. The positive electrode mixture layer contains a positive electrode active material, a binder, and a conductive agent, and is preferably provided on both sides of the positive electrode core, excluding the portion to which the positive electrode lead 19 is connected. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a binder, and a conductive agent to the surface of the positive electrode core, drying the coating, and then compressing it to form the positive electrode mixture layer on both sides of the positive electrode core.

[0019] The positive electrode active material contains a lithium transition metal oxide as a main component. The positive electrode active material may be substantially composed only of the lithium transition metal oxide, or may be one in which inorganic compound particles such as aluminum oxide and lanthanoid-containing compounds are fixed to the particle surface of the lithium transition metal oxide. One type of the lithium transition metal oxide may be used alone, or two or more types thereof may be used in combination.

[0020] Examples of the metal element contained in the lithium transition metal oxide include nickel (Ni), cobalt (Co), manganese (Mn), aluminum (Al), boron (B), magnesium (Mg), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), strontium (Sr), zirconium (Zr), niobium (Nb), indium (In), tin (Sn), tantalum (Ta), tungsten (W) and the like. An example of a suitable lithium transition metal oxide is represented by the general formula: Li α Ni x M (1―x) αO₂ (0.1≦α≦1.2, 0.3≦x<1, M contains at least one selected from the group consisting of Co, Mn and Al), which is a composite oxide represented by the above formula.

[0021] Examples of the conductive agent contained in the positive electrode mixture layer include carbon materials such as carbon black, acetylene black, ketjen black, carbon nanotubes, carbon nanofibers, and graphite. Examples of the binder contained in the positive electrode mixture layer include fluorine resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These resins may be used in combination with a cellulose derivative such as carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like.

[0022] [Negative Electrode] The negative electrode 12 comprises, for example, a negative electrode core and a negative electrode mixture layer provided on the surface of the negative electrode core. The negative electrode core can be made of a metal foil that is stable in the potential range of the negative electrode 12, such as copper, or a film with the metal arranged on its surface. The thickness of the negative electrode core is, for example, 5 μm to 15 μm. The negative electrode mixture layer contains a negative electrode active material and a binder, and is preferably provided on both sides of the negative electrode core, excluding the portion to which the negative electrode lead 20 is connected. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and a conductive agent to the surface of the negative electrode core, drying the coating, and then compressing it to form the negative electrode mixture layer on both sides of the negative electrode core. Alternatively, the negative electrode 12 may be made by mixing a negative electrode active material and copper powder and then compressing it into pellets.

[0023] The negative electrode active material contained in the negative electrode 12 includes an alloy represented by the general formula M3Me2X7 (wherein M contains at least one of La and Ca, Me contains at least one element selected from the group consisting of Mn, Ni, Fe, and Co, and X contains at least one element selected from the group consisting of Ge, Si, Sn, and Al) (hereinafter sometimes referred to as an M3Me2X7 type alloy). An example of an M3Me2X7 type alloy is La3Ni2Sn7. The negative electrode 12 may also contain a negative electrode active material other than an M3Me2X7 type alloy. The negative electrode active material other than an M3Me2X7 type alloy is not particularly limited as long as it can reversibly intercept and release lithium ions, and for example, metals that alloy with lithium such as graphite (natural graphite, artificial graphite), silicon (Si), tin (Sn), or oxides containing metallic elements such as Si and Sn can be used.

[0024] In an XRD pattern obtained by XRD measurement using Cu as a counter cathode, the full width at half maximum of the diffraction peak of the (1 17 1) plane of the M3Me2X7-type alloy is, for example, 0.4713° or more. This makes it possible to increase the gravimetric energy density of the M3Me2X7-type alloy. The diffraction peak of the (1 17 1) plane of the M3Me2X7-type alloy is detected in the vicinity of 64°. The upper limit of the full width at half maximum of the diffraction peak of the (1 17 1) plane of the M3Me2X7-type alloy is, for example, 5°. It should be noted that the full width at half maximum of the diffraction peak of the (1 17 1) plane of a general M3Me2X7-type alloy is approximately 0.11°, and the full width at half maximum of the diffraction peak of the (1 17 1) plane of the M3Me2X7-type alloy according to the present disclosure is larger than that of the general M3Me2X7-type alloy.

[0025] XRD measurement can be performed under the following conditions using a powder X-ray diffractometer (radiation source Cu-Kα). Measurement range: 10° to 70° Scan speed: 10° / min

[0026] The volume-based median diameter (D50) of the M3Me2X7-type alloy may be, for example, 0.1 μm to 50 μm, or 1 μm to 10 μm. The D50 of the M3Me2X7-type alloy can be reduced by, for example, pulverization with a ball mill, and can be adjusted according to ball mill treatment conditions. D50 refers to the particle diameter at which the cumulative frequency in the volume-based particle size distribution reaches 50% from the smaller particle diameter side, and is also referred to as the median diameter. The particle size distribution of the M3Me2X7-type alloy can be measured using water as a dispersion medium with a laser diffraction particle size distribution analyzer (e.g., MT3000II manufactured by MicrotracBEL Corp.).

[0027] The M3Me2X7-type alloy according to the present disclosure can be produced, for example, by the following method.

[0028] <Method for producing M3Me2X7-type alloy> (1) Prepare M metal, Me metal, and X metal as raw materials, mix these raw materials in a predetermined ratio, and then arc melt them to produce an ingot of M3Me2X7 type alloy. (2) The fabricated M3Me2X7 alloy ingot is vacuum-sealed in a quartz tube and then annealed in a slow-cooling furnace. The annealing conditions are, for example, an annealing temperature of 400°C to 1000°C and a holding time of 10 to 720 hours. (3) The annealed M3Me2X7 alloy ingot is crushed, for example, in a mortar and pestle or a planetary ball mill. The ball milling conditions are, for example, a rotation speed of 100 rpm to 500 rpm and a processing time of 1 hour to 720 hours. (4) The M3Me2X7 alloy after ball milling is subjected to classification, for example, using a mesh, to remove coarse particles.

[0029] The M3Me2X7 alloy produced by the above method exhibits a full width at half maximum (FWHM) of the diffraction peak of the (1 17 1) plane in the XRD pattern obtained by XRD measurement using Cu as the cathode, which is 0.4713° or greater. It is thought that the ball milling process reduces the particle size by crushing the particles, and that the particle surface crushed and sheared by the planetary ball mill causes distortion of the crystal structure (defects, etc.), disrupting the periodicity of the atomic arrangement, resulting in a larger FWHM than before the ball milling process. It is presumed that Li ions are inserted into these defects and voids.

[0030] The binder included in the negative electrode mixture layer can be fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, etc., as in the case of the positive electrode 11. When preparing the mixture slurry using an aqueous solvent, it is preferable to use CMC or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.

[0031] The negative electrode mixture layer may contain a conductive agent. The conductive agent can homogenize the conductive paths. Examples of conductive agents included in the negative electrode mixture layer include carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNTs), graphene, graphite, and other carbon-based particles. These may be used individually or in combination of two or more types. It is preferable that the conductive agent contains CNTs. The CNTs may be single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs). Since SWCNTs can form conductive paths in the negative electrode mixture layer in a smaller amount than MWCNTs, it is preferable that the CNTs include SWCNTs.

[0032] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous membranes, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, olefin resins such as polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer containing a heat-resistant material may be formed on the surface of the separator 13. Examples of heat-resistant materials include polyamide resins such as aliphatic polyamides and aromatic polyamides (aramids), and polyimide resins such as polyamide-imides and polyimides. [Examples]

[0033] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0034] <Example 1> [Fabrication of negative electrode active material] La metal pieces, Ni wire, and Sn metal pieces were used as raw materials. The La metal pieces were made from yttrium with a purity of 3N, which were arc-melted to remove gas and then polished on the surface with a metal brush. The Ni wire was φ3 mm with a purity of 3N and manufactured by a high-purity chemical company. The Sn metal pieces were shot-shaped with a purity of 4N and manufactured by Furuuchi Chemical. These raw materials were mixed in a molar ratio of La:Ni:Sn = 3:2:7 and then arc-melted to obtain a block of alloy with a crystalline structure of La3Ni2Sn7. This block was sealed in a quartz tube under vacuum and then annealed in a muffle furnace. Annealing was carried out by raising the temperature from room temperature at 300°C / hour, reaching 680°C, holding this temperature for 48 hours, and then allowing it to cool naturally. Furthermore, the annealed alloy mass was manually crushed in a mortar for one hour, then placed in a zirconia container along with zirconia balls, and ball milling was performed using a planetary ball mill at a predetermined rotation speed for a predetermined time. The ball milling was performed in 5-minute intervals with a 5-minute pause. The powder after ball milling was classified using a 45 μm mesh to remove coarse particles. The volume-based median diameter (D50) of the prepared negative electrode active material (La3Ni2Sn7 powder) was 6.8 μm.

[0035] [Fabrication of the negative electrode] The above-mentioned negative electrode active material and Cu powder were mixed in a mass ratio of 4:6, and then compressed at a pressure of 5 MPa to produce pellets with a diameter of 7.5 mm and a height of 0.8 mm. These pellets were used as the negative electrode.

[0036] [Preparation of the opposing pole] To investigate the properties of the negative electrode active material, metallic lithium (Li) was used as the counter electrode instead of the positive electrode material. Generally, lithium-ion batteries use lithium transition metal oxides such as LiNiO2 (which typically contain transition metals such as Co, Mn, and Ni) as the positive electrode active material. However, here, in order to investigate the properties of the negative electrode active material itself, independent of the positive electrode active material, a lithium metal foil cut to φ17 mm was used as the counter electrode instead of the positive electrode active material commonly used for electrodes. This method is often used to evaluate active materials.

[0037] [Preparation of non-aqueous electrolytes] A non-aqueous electrolyte was prepared by dissolving 1.0 mol / L of LiPF6 as the electrolyte salt in a non-aqueous solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:3.

[0038] [Preparation of test cells] An electrode body was constructed by placing the negative electrode and a positive electrode made of lithium metal foil opposite each other via a separator, and the electrode body was housed in a coin-shaped outer casing. After injecting a non-aqueous electrolyte into the outer casing, the casing was sealed to obtain a coin-shaped test cell (non-aqueous electrolyte secondary battery).

[0039] <Examples 2-5> In preparing the negative electrode active material, the test cells of Examples 2 to 5 were prepared in the same manner as in Example 1, except that the ball milling time using a planetary ball mill was changed. The ball milling time was increased from Example 2 to Example 5. Specifically, in Examples 1 to 5, the ball milling time in Example 1 was the shortest, and the ball milling time in Example 5 was the longest.

[0040] <Comparative Example 1> The test cell was prepared in the same manner as in Example 1, except that a ball milling process using a planetary ball mill was not performed in the preparation of the negative electrode active material.

[0041] The battery capacity (charge capacity and discharge capacity) of each test cell in Examples 1-5 and Comparative Example 1 was evaluated using the following method. The evaluation results are shown in Table 1. Table 1 also shows the full width at half maximum of the diffraction peak of the (1 17 1) plane and the charge / discharge efficiency. Furthermore, Figure 2 shows the XRD patterns of the negative electrode active material for Examples 1, 2, 4-7 (Examples 6 and 7 will be described later) and Comparative Example 1.

[0042] [Battery capacity evaluation] In this evaluation, discharge refers to Example 1 ~5 and comparative examples 1This refers to the discharge of a battery that combines a negative electrode active material with a commonly used positive electrode, such as LiNiO2. In this context, since the coin-type battery described above uses metallic lithium (Li) as the working electrode and the counter electrode, it should technically be called charging. However, to match the charge-discharge behavior of the negative electrode in batteries that combine a positive and negative electrode in general, the terms for the charge and discharge directions are used. In other words, charging is the process of passing an electric current to lower the potential of the negative electrode, which is the working electrode, and discharging is the process of passing an electric current to raise the potential of the negative electrode, which is the working electrode.

[0043] The battery was charged with a constant current of 2.6 mA until the battery voltage reached 0.01 V, and then discharged with a constant current of 2.6 mA until the battery voltage reached 1.5 V. Two charge-discharge cycles were performed, and the charge and discharge capacities of the second cycle were measured. Note that, as mentioned above, the descriptions of charge and discharge are reversed from the usual. That is, charging is the process of passing a current to lower the potential of the working electrode until the battery voltage reaches 0 V, and discharging is the process of passing a current to raise the potential of the working electrode until the battery voltage reaches 1 V.

[0044] [Table 1]

[0045] As shown in Table 1, the test cell of the example, in which the full width at half maximum (FMAX) of the diffraction peak of the (1 17 1) plane was 0.4713° or higher, had a higher battery capacity compared to the test cell of Comparative Example 1, in which the FMAX was 0.1114°. Furthermore, the battery of the example also had a higher charge and discharge efficiency compared to the battery of Comparative Example 1.

[0046] <Example 6> [Fabrication of negative electrode active material] La metal pieces, Ni wire, and Sn metal pieces were used as raw materials. The La metal pieces were made from yttrium with a purity of 3N, which were arc-melted to remove gas and then polished on the surface with a metal brush. The Ni wire was φ3 mm with a purity of 3N and manufactured by a high-purity chemical company. The Sn metal pieces were shot-shaped with a purity of 4N and manufactured by Furuuchi Chemical. These raw materials were mixed in a molar ratio of La:Ni:Sn = 3:2:7 and then arc-melted to obtain a block of alloy with a crystalline structure of La3Ni2Sn7. This block was sealed in a quartz tube under vacuum and then annealed in a muffle furnace. Annealing was carried out by raising the temperature from room temperature at 300°C / hour, reaching 680°C, holding this temperature for 48 hours, and then allowing it to cool naturally. Furthermore, the annealed alloy mass was manually crushed in a mortar for one hour, then placed in a zirconia container along with zirconia balls, and ball milling was performed using a planetary ball mill at a predetermined rotation speed for a predetermined time. The ball milling was performed in 5-minute intervals with a 5-minute pause. The powder after ball milling was classified using a 45 μm mesh to remove coarse particles. The volume-based median diameter (D50) of the prepared negative electrode active material (La3Ni2Sn7 powder) was 6.8 μm.

[0047] [Fabrication of the negative electrode] The above-mentioned negative electrode active material, PVDF as a binder, and SWCNT as a conductive agent were mixed in a mass ratio of 97.6:0.4:2, and a negative electrode mixture slurry was prepared using N-methyl-2-pyrrolidone (NMP) as a dispersion medium. Next, the negative electrode mixture slurry was applied to a negative electrode core made of copper foil with a thickness of 10 μm, the coating was dried and compressed, and then punched out to a diameter of φ7.5 mm to obtain the negative electrode.

[0048] [Preparation of test cells] A counter electrode and a non-aqueous electrolyte were prepared in the same manner as in Example 1. A test cell was prepared using the counter electrode, non-aqueous electrolyte, and the negative electrode in the same manner as in Example 1.

[0049] <Example 7> In the preparation of the negative electrode active material, the test cell was prepared in the same manner as in Example 6, except that the rotation speed of the planetary ball mill was increased.

[0050] <Example 8> In preparing the negative electrode active material, the test cell was prepared in the same manner as in Example 6, except that the rotation speed of the planetary ball mill was increased and the ball milling time was extended.

[0051] <Comparative Example 2> The test cell was prepared in the same manner as in Example 6, except that a ball milling process using a planetary ball mill was not performed in the preparation of the negative electrode active material.

[0052] The battery capacity (charging capacity and discharging capacity) of each test cell in Examples 6-8 and Comparative Example 2 was evaluated using the following method. The evaluation results are shown in Table 2. Table 2 also shows the full width at half maximum of the diffraction peak of the (1 17 1) plane and the charge / discharge efficiency.

[0053] [Battery capacity evaluation] The battery was charged with a constant current of 0.05C until the battery voltage reached 0.01V, and then discharged with a constant current of 0.05C until the battery voltage reached 1.5V. Two charge-discharge cycles were performed, and the charge and discharge capacities of the second cycle were measured.

[0054] [Table 2]

[0055] Similar to the results in Table 1, the test cells in the examples showed higher battery capacity and charge / discharge efficiency compared to the test cells in Comparative Example 2. [Explanation of Symbols]

[0056] 10 Lithium-ion battery, 11 Positive electrode, starting end, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Outer casing, 16 Sealing body, 17,18 Insulating plate, 19 Positive electrode lead, 20 Negative electrode lead, 21 Grooved section, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Opening, 27 Gasket

Claims

1. The negative electrode active material contained in the negative electrode of a lithium-ion battery, The negative electrode active material is of general formula M ３ Me ２ X ７ (In the formula, M includes at least one of La and Ca, Me includes at least one element selected from the group consisting of Mn, Ni, Fe, and Co, and X includes at least one element selected from the group consisting of Ge, Si, Sn, and Al) A negative electrode active material wherein, in an XRD pattern obtained by XRD measurement using Cu as the cathode, the full width at half maximum of the diffraction peak of the (1 17 1) plane of the negative electrode active material is 1.0785° or more and 2.2443° or less.

2. A negative electrode comprising the negative electrode active material described in claim 1, Positive electrode and, A lithium-ion battery equipped with a non-aqueous electrolyte.

3. The lithium-ion battery according to claim 2, wherein the non-aqueous electrolyte is a solid.

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