Lithium-ion battery

Abstract

The present invention provides a lithium ion battery which comprises a positive electrode having a positive electrode mixture layer that contains a positive electrode active material, and a negative electrode having a negative electrode mixture layer that contains a negative electrode active material, and which is charged and discharged by the movement of lithium ions between the positive electrode and the negative electrode. The negative electrode mixture layer contains a negative electrode active material represented by general formula La3(1-x)M3xNi2(1-y)Me2yX7 (wherein M contains at least one of Ca, Mg and Sr; Me contains at least one of Mn, Co, Cu and Fe; X contains at least one of Ge, Si, Sn and Al; 0.1 ≤ x < 0.5; and 0 < y ≤ 1).

Description

[Technical Field]

[0001] The present disclosure relates to a lithium-ion battery that includes a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a negative electrode having a negative electrode mixture layer containing a negative electrode active material, and that is charged and discharged by lithium ions moving between the positive electrode and the negative electrode. [Background technology]

[0002] Lithium-ion batteries, which are charged and discharged by the movement of lithium ions (Li ions) between the negative and positive electrodes, are widely used. Graphite-based materials are often used as the negative electrode active material in the negative electrode mixture layer of these lithium-ion batteries. Graphite-based negative electrode active materials are sometimes used together with silicon, which can cause large volume changes during charging and discharging, leading to poor capacity retention and relatively high costs.

[0003] Therefore, non-graphite-based negative electrode active materials have also been proposed. For example, Patent Document 1 describes the use of an alloy having a La3Co2Sn7 crystal structure as the negative electrode active material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4127692 Summary of the Invention

[0005] Secondary batteries that use an intermetallic compound having a La3Ni2Sn7 crystal structure as the negative electrode active material tend to have a relatively low mass energy density.

[0006] The lithium ion battery according to the present disclosure is a lithium ion battery in which charging and discharging are performed by the movement of lithium ions between a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a negative electrode having a negative electrode mixture layer containing a negative electrode active material, and the negative electrode, and the negative electrode mixture layer is a compound represented by the general formula La 3(1-x) M 3xNi 2(1-y) Me 2y X7 (wherein M includes at least one of Ca, Mg, and Sr, Me includes at least one of Mn, Co, Cu, and Fe, and X includes at least one of Ge, Si, Sn, and Al), and 0.1≦x<0.5, and 0 <y≦1である。

[0007] The lithium ion battery according to the present disclosure is a lithium ion battery in which charging and discharging are performed by the movement of lithium ions between a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a negative electrode having a negative electrode mixture layer containing a negative electrode active material, and the negative electrode, and the negative electrode mixture layer is a compound represented by the general formula La 3(1-x) M 3x Ni 2(1-y) Me 2y X7 (M contains at least one of Ca, Mg, and Sr, and Me is Mn and , X includes at least one of Ge, Si, Sn, and Al), and 0.1≦x<0.5, and 0 <y < It is characterized in that it is 1. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a longitudinal cross-sectional view of a cylindrical secondary battery 10 according to an embodiment of the present invention. [Figure 2] 1 is a graph showing the electrode potentials during charging and discharging for Examples 1 to 4 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the embodiments described herein.

[0010] "About negative electrode materials" The negative electrode material for lithium-ion batteries should preferably have high energy density and low expansion. Therefore, various research and development efforts have been conducted, and it has been proposed to use an intermetallic compound with a La3Ni2Sn7 crystal structure as the negative electrode active material. Such intermetallic compounds absorb and release Li through an intercalation reaction, which is thought to result in a low expansion rate and a long battery life.

[0011] However, the mass energy density of intermetallic compounds with a La3Ni2Sn7 crystal structure is relatively low compared to graphite-based compounds.

[0012] In the present disclosure, the La3Ni2Sn7 type crystal structure L Part of the a-sites are substituted with at least one of Ca, Mg, and Sr, and part of the Ni sites are substituted with at least one of Mn, Co, Cu, and Fe. This makes it easier for vacancies to form, increasing the number of sites available for Li absorption, which is thought to increase the charge / discharge capacity.

[0013] "Configuration of the embodiment" FIG. 1 is a longitudinal cross-sectional view of a cylindrical secondary battery 10 according to an embodiment. The secondary battery 10 shown in FIG. 1 includes an electrode assembly 14 and a nonaqueous electrolyte housed in an exterior case 15. The electrode assembly 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. Examples of nonaqueous solvents (organic solvents) for the nonaqueous electrolyte include carbonates, lactones, ethers, ketones, and esters, and two or more of these solvents can be mixed together. When two or more solvents are mixed together, a mixed solvent containing a cyclic carbonate and a chain carbonate is preferably used. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the like can be used as the chain carbonate. Examples of electrolyte salts that can be used for the non-aqueous electrolyte include LiPF, LiBF, LiCF, SO, and mixtures thereof. The amount of electrolyte salt dissolved in the non-aqueous solvent can be, for example, 0.5 to 2.0 mol / L. For ease of explanation, the following description will refer to the sealing body 16 side as "top" and the bottom side of the exterior body 15 as "bottom."

[0014] The open end of the exterior body 15 is sealed with the sealing body 16, thereby sealing the interior of the secondary battery 10. Insulating plates 17 and 18 are provided above and below the electrode body 14. The positive electrode lead 19 extends upward through a through hole in the insulating plate 17 and is welded to the underside of a filter 22, which is the bottom plate of the sealing body 16. In the secondary battery 10, a cap 26, which is the top plate of the sealing body 16 and is electrically connected to the filter 22, serves as the positive electrode terminal. On the other hand, the negative electrode lead 20 extends through a through hole in the insulating plate 18 toward the bottom of the exterior body 15 and is welded to the inner bottom surface of the exterior body 15. In the secondary battery 10, the exterior body 15 serves as the negative electrode terminal. Note that if the negative electrode lead 20 is installed at the terminal end, the negative electrode lead 20 passes outside the insulating plate 18, extends toward the bottom of the exterior body 15, and is welded to the inner bottom surface of the exterior body 15.

[0015] Exterior body 15 is, for example, a cylindrical metal exterior can with a bottom. A gasket 27 is provided between exterior body 15 and sealing body 16, ensuring the airtightness of the interior of secondary battery 10. Exterior body 15 has a grooved portion 21 that supports sealing body 16, formed, for example, by pressing the side surface from the outside. Grooved portion 21 is preferably formed in an annular shape along the circumferential direction of exterior body 15, and supports sealing body 16 on its upper surface via gasket 27.

[0016] The sealing body 16 includes 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 this order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. 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 peripheral edges. If the internal pressure of the battery increases due to abnormal heat generation, for example, the lower valve body 23 may break, causing the upper valve body 25 to bulge toward the cap 26 and separate from the lower valve body 25, thereby cutting off the electrical connection between them. If the internal pressure continues to increase, the upper valve body 25 may break, and gas may be released from the opening 26a of the cap 26.

[0017] The positive electrode 11, negative electrode 12, and separator 13 that constitute the electrode assembly 14 will be described below, with particular reference to the negative electrode active material that constitutes the negative electrode 12.

[0018] [Positive electrode] The positive electrode 11 has 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 a foil of a metal such as aluminum that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the 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 material, and is preferably provided on both sides of the positive electrode core except for the portion to which the positive electrode lead 19 is connected. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive material, etc. to the surface of the positive electrode core, drying the coating, and then compressing it to form a 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 of only a lithium transition metal oxide, or may be composed of lithium transition metal oxide particles having inorganic compound particles such as aluminum oxide or a lanthanoid-containing compound adhered to the surface of the lithium transition metal oxide particles. One type of lithium transition metal oxide may be used, or two or more types may be used in combination.

[0020] Examples of metal elements 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), and tungsten (W). An example of a suitable lithium transition metal oxide is represented by the general formula: Li α Ni x M (1―x) O2 (0.1≦α≦1.2, 0.3≦x<1, M includes at least one of Co, Mn, and Al). For example, NCA, in which part of the nickel is replaced with cobalt and aluminum is added, is used as a positive electrode material.

[0021] Examples of conductive materials 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 binders contained in the positive electrode mixture layer include fluororesins 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 cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), and the like.

[0022] [Negative electrode] The negative electrode 12 has 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 a foil of a metal, such as copper, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the 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 except for the portion to which the negative electrode lead 20 is connected. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core. A conductive material may also be added to the negative electrode mixture slurry. The conductive material can make the conductive path uniform. The negative electrode mixture layer, like the positive electrode mixture layer, may also contain a conductive material, such as acetylene black.

[0023] The negative electrode mixture layer contains a negative electrode active material represented by the general formula La 3(1-x) M 3x Ni 2(1-y) Me 2y X7(M is C a, Mg, Sr, Me includes at least one of Mn, Co, Cu, Fe, and X includes at least one of Ge, Si, Sn, and Al).

[0024] La, the negative electrode active material 3(1-x) M 3x Ni 2(1-y) Me 2y The particle size of X7 is preferably 1 to 30 μm, more preferably 2 to 20 μm, and particularly preferably 2 to 10 μm. If the particle size of the negative electrode active material is too large, the reactivity with Li decreases, and the contact area between particles decreases, resulting in increased resistance. On the other hand, if the particle size is too small, the packing density of the negative electrode active material decreases, presumably resulting in reduced capacity. The average particle size of the negative electrode active material is, for example, 3 to 15 μm or 5 to 10 μm. The particle size of the negative electrode active material is measured as the diameter of the circumscribed circle of the negative electrode active material particles in a cross-sectional image of the negative electrode mixture layer observed with a scanning electron microscope (SEM). The average particle size is calculated by averaging the particle sizes of 100 random particles.

[0025] La 3(1-x) M 3x Ni 2(1-y) Me 2y The intermetallic compound represented by X7 can be formed by arc melting, and it is preferable to anneal after arc melting.

[0026] Also, regarding the substitution rates for La and Ni, 0.1 ≦ x < 0.5 and 0 < y ≦ 1 are preferable. If the substitution rate is low, the effect is small, and if the substitution rate is large, impurities are generated, and it is presumed that the irreversible capacity increases due to the alloying reaction. Also, it is preferable to substitute La with Ca, and it is preferable to substitute Ni with Mn. Also, good results have been obtained by using Sn for X.

[0027] The negative electrode active material contains La 3(1-x) M 3x Ni 2(1-y) Me 2y including X7 as the main component (the component with the highest mass ratio), and substantially consisting of only La 3(1-x) M 3x Ni 2(1-y) Me 2y X7 may be sufficient. On the other hand, the negative electrode active material may be used in combination with other active materials such as metal compounds other than La 3(1-x) M 3x Ni 2(1-y) Me 2y X7, carbon-based active materials such as graphite, or Si-based active materials containing Si. For example, when using graphite in combination, the content of graphite may be 50 to 90% by mass based on the mass of the negative electrode active material.

[0028] For the binder contained in the negative electrode binder layer, various types can be adopted. For example, a compound containing a cyano group is adopted. As the negative electrode active material, the above La 3(1-x) M 3x Ni 2(1-y) Me 2yWhen using X7, if a commonly used binder such as polyvinylidene fluoride (PVDF) is used, the negative electrode mixture slurry tends to gel, making it difficult to apply. On the other hand, by using a binder containing a cyano group, the dispersibility of the negative electrode active material is improved and the gelation of the slurry is suppressed.

[0029] Specific examples of binders containing a cyano group include polyacrylonitrile (PAN), polymethacrylonitrile, poly-α-chloroacrylonitrile, poly-α-ethylacrylonitrile, etc. Among these, PAN or polymethacrylonitrile is preferred, and PAN is particularly preferred.

[0030] Here, binders containing cyano groups are solvent-based, and require the use of a solvent for coating. There is a demand for aqueous binders, and for example, carboxymethyl cellulose (CMC) can be used. Ammonium carboxymethyl cellulose (NH4-CMC) is particularly suitable, and it is preferable to use it in combination with SBR.

[0031] The mass ratio of the binder in the negative electrode mixture layer is preferably about 0.5 mass % to 7.0 mass %.

[0032] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous membrane, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include olefin resins such as polyethylene and 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 polyamideimides and polyimides.

[0033] <Example> The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0034] [Preparation of negative electrode] The negative electrode active material is an intermetallic compound (La) with a particle size of 2 to 20 μm and a La2Ni2Sn7 type crystal structure. 3(1-x) M 3x Ni 2(1-y) Me 2y X7) was used, with NH4-CMC and SBR (referred to as CMC / SBR) as binders and artificial graphite powder as conductive material. The negative electrode active material, binder, and conductive material were mixed in a mass ratio of 85.5:3:1.5:10, and N-methyl-2-pyrrolidone (NMP) was used as a 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 compressed, and then cut to the specified electrode size to obtain a negative electrode.

[0035] [Test cell construction] The negative electrode and a positive electrode made of lithium metal foil were arranged opposite each other with a separator interposed therebetween to form an electrode assembly, which was then housed in a coin-shaped outer can. After a predetermined non-aqueous electrolyte solution was poured into the outer can, the outer can was sealed to obtain a coin-shaped test cell (nonaqueous electrolyte secondary battery).

[0036] [Charge / discharge test] The obtained test cell was charged and discharged at a constant current under room temperature, and the positive and negative electrode potentials (V(vs. Li / Li + )) and charge / discharge capacity were investigated.

[0037] <Comparative Example 1> La2Ni2Sn7 was used as the negative electrode active material.

[0038] <Comparative Example 2> As the negative electrode active material, La 1.8 Ca 1.2 Ni2Sn7 was used.

[0039] Example 1 As the negative electrode active material, La 1.8 Ca 1.2 Ni 1.8 Mn 0.2 Sn7 was used.

[0040] <Example 2> As the negative electrode active material, La 1.8 Ca 1.2 Ni 1.8 Fe 0.2 Sn7 was used.

[0041] Example 3 As the negative electrode active material, La 1.8 Ca 1.2 Ni 1.8 Co 0.2 Sn7 was used.

[0042] Example 4 As the negative electrode active material, La 1.8 Ca 1.2 Ni 1.8 Cu 0.2 Sn7 was used.

[0043] <Comparative Example 3-6> In Comparative Example 3-6, La 3(1-x) Ca 3x The effect of Ca substitution was investigated by changing the Ca substitution rate x using Ni2Sn7. Specifically, the Ca substitution amount was 0% in Comparative Example 3, 10% in Comparative Example 4, 40% in Comparative Example 5, and 50% in Comparative Example 6.

[0044] "result" FIG. 2 shows the positive and negative electrode potentials in the charge-discharge tests of Examples 1-4 and Comparative Examples 1-2, and Table 1 shows the charge-discharge capacities thereof.

[0045] [Table 1]

[0046] It can be seen that in Examples 1-4, the charge-discharge capacity is significantly increased (more than twice as large) compared to Comparative Example 1. Furthermore, in Comparative Example 2, the charge-discharge capacity is larger than that of Comparative Example 1, but the capacity is smaller than that of Examples 1-4. It can also be seen that the material in Example 1 in which the Ni site is substituted with Mn has a particularly large capacity. Thus, it was found that the amount of Li stored is improved and the charge-discharge capacity is increased by substituting the La site and other 3d metal elements in the Ni site.

[0047] Table 2 shows the initial discharge capacity and efficiency of Comparative Examples 3 to 6. The efficiency is the value obtained by dividing the initial discharge capacity by the initial charge capacity.

[0048] [Table 2]

[0049] As described above, it can be seen that the charge-discharge capacity increases by substituting Ca for La. In particular, the charge-discharge capacity increases when the Ca substitution is 10% to 40%, but decreases when it is 50%. [Explanation of symbols]

[0050] 10 Secondary battery 11 Positive electrode 12 Negative electrode 13 Separator 14 Electrode body 15 Exterior body 16 Sealing body 17,18 Insulating plate 19 Positive lead 20 Negative lead 21 Grooved part 22 filters 23 Lower valve body 24 Insulating material 25 Upper valve 26 Cap 26a opening 27 Gasket

Claims

[Claim 1] A lithium ion battery comprising: a positive electrode having a positive electrode mixture layer containing a positive electrode active material; a negative electrode having a negative electrode mixture layer containing a negative electrode active material; and charging and discharging being performed by lithium ions moving between the positive electrode and the negative electrode, The negative electrode mixture layer is formed of a compound represented by the general formula La ３（１－ｘ） M ３ｘ Ni ２（１－ｙ） Me ２ｙ X ７ (M includes at least one of Ca, Mg, and Sr, Me is Mn, and X includes at least one of Ge, Si, Sn, and Al), and 0.1≦x<0.5 and 0<y<1. A lithium-ion battery characterized by:

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