阅读说明：本技术 非水电解质二次电池 (Nonaqueous electrolyte secondary battery ) 是由 木下昌洋 长田薰 于 2019-02-07 设计创作，主要内容包括：本发明的目的在于,提供一种能够抑制因电池的高温保存导致的容量降低的非水电解质二次电池。非水电解质二次电池(10)具备包含正极活性物质的正极(11)、负极(12)、和包含含氟化合物的非水电解质,所述正极活性物质具有包含Li、Ni和W的复合氧化物A、以及包含Li、Ni和任选元素W的复合氧化物B,所述复合氧化物A中的W的含量为5mol％以上,所述复合氧化物B中的W的含量为0.5mol％以下,所述复合氧化物A相对于所述复合氧化物A与所述复合氧化物B的总量的质量比率为0.002％以上且0.1％以下。(The purpose of the present invention is to provide a nonaqueous electrolyte secondary battery that can suppress a decrease in capacity due to high-temperature storage of the battery. A nonaqueous electrolyte secondary battery (10) is provided with a positive electrode (11) containing a positive electrode active material, a negative electrode (12), and a nonaqueous electrolyte containing a fluorine-containing compound, wherein the positive electrode active material comprises a composite oxide A containing Li, Ni, and W, and a composite oxide B containing Li, Ni, and optionally W, the content of W in the composite oxide A is 5 mol% or more, the content of W in the composite oxide B is 0.5 mol% or less, and the mass ratio of the composite oxide A to the total amount of the composite oxide A and the composite oxide B is 0.002% or more and 0.1% or less.)

1. A nonaqueous electrolyte secondary battery includes: a positive electrode containing a positive electrode active material, a negative electrode, and a nonaqueous electrolyte containing a fluorine-containing compound,

the positive electrode active material has: a composite oxide a containing Li, Ni, and W; and a composite oxide B containing Li, Ni and optionally W,

the content of W in the composite oxide A is 5 mol% or more,

the content of W in the composite oxide B is 0.5 mol% or less,

the mass ratio of the composite oxide A to the total amount of the composite oxide A and the composite oxide B is 0.002% or more and 0.1% or less.

2. The nonaqueous electrolyte secondary battery according to claim 1,

the content of the fluorine-containing compound in the nonaqueous electrolyte is 2 to 25 mass%.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2,

the composite oxide A is represented by the general formula Li_xNi_1-y-zW_yM_zO_2-γWherein M is at least 1 element selected from transition metal elements other than Ni and W, group 2 elements and group 13 elements, x is 0.85. ltoreq. x.ltoreq.1.05, y is 0.05. ltoreq. y.ltoreq.0.2, z is 0.01. ltoreq. z.ltoreq.0.5, and γ is-0.2. ltoreq. γ.ltoreq.0.2.

4. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3,

The composite oxide B is represented by the general formula Li_xNi_1-y-zW_yM_zO_2-γWherein M is at least 1 element selected from transition metal elements other than Ni and W, group 2 elements and group 13 elements, x is 0.85. ltoreq. x.ltoreq.1.05, y is 0.002. ltoreq. y.ltoreq.0.05, z is 0.01. ltoreq. z.ltoreq.0.5, and γ is-0.2. ltoreq. γ.ltoreq.0.2.

Technical Field

The present invention relates to a nonaqueous electrolyte secondary battery.

Background

In recent years, as a secondary battery having high output and high energy density, a nonaqueous electrolyte secondary battery has been widely used which includes a positive electrode, a negative electrode, and a nonaqueous electrolyte and which performs charge and discharge by moving lithium ions or the like between the positive electrode and the negative electrode.

As a positive electrode active material used for a positive electrode of a nonaqueous electrolyte secondary battery, a lithium nickel composite oxide, a lithium cobalt composite oxide, a lithium manganese composite oxide, and the like are known. Among these, lithium nickel composite oxides are expected as positive electrode active materials that can produce batteries with higher capacity at lower cost than lithium cobalt composite oxides and the like.

For example, patent documents 1 to 3 propose nonaqueous electrolyte secondary batteries using a tungsten-containing lithium nickel composite oxide as a positive electrode active material for the purpose of improving battery characteristics and the like.

Disclosure of Invention

Problems to be solved by the invention

However, a nonaqueous electrolyte secondary battery using a nonaqueous electrolyte containing a fluorine-containing compound may decompose the fluorine-containing compound to generate hydrogen fluoride during storage at high temperature. The generated hydrogen fluoride may cause a side reaction accompanied by elution of the transition metal in the positive electrode active material, thereby reducing the battery capacity. Such a capacity reduction due to high-temperature storage of the battery is particularly significant in the lithium nickel composite oxide.

Accordingly, an object of the present invention is to provide a nonaqueous electrolyte secondary battery using a positive electrode active material containing a lithium nickel composite oxide and a nonaqueous electrolyte containing a fluorine-containing compound, which can suppress a decrease in capacity due to high-temperature storage of the battery.

Means for solving the problems

The nonaqueous electrolyte secondary battery according to one aspect of the present invention is characterized by comprising a positive electrode containing a positive electrode active material, a negative electrode, and a nonaqueous electrolyte containing a fluorine-containing compound, wherein the positive electrode active material comprises a composite oxide a containing Li, Ni, and W, and a composite oxide B containing Li, Ni, and optionally W, the composite oxide a contains W in an amount of 5 mol% or more, the composite oxide B contains W in an amount of 0.5 mol% or less, and the mass ratio of the composite oxide a to the total amount of the composite oxide a and the composite oxide B is 0.002% or more and 0.1% or less.

Effects of the invention

According to one aspect of the present invention, in a nonaqueous electrolyte secondary battery using a positive electrode active material containing a lithium nickel composite oxide and a nonaqueous electrolyte containing a fluorine-containing compound, a decrease in capacity due to high-temperature storage of the battery can be suppressed.

Drawings

Fig. 1 is a sectional view of a nonaqueous electrolyte secondary battery as an example of the embodiment.

Detailed Description

As a result of intensive studies, the present inventors have found that a lithium nickel composite oxide containing W in a predetermined amount or more has a high ability to trap hydrogen fluoride generated by decomposition of a fluorine-containing compound in a nonaqueous electrolyte during storage of the battery at high temperatures, and have conceived a nonaqueous electrolyte secondary battery of the following embodiment.

The nonaqueous electrolyte secondary battery according to one aspect of the present invention is characterized by comprising a positive electrode containing a positive electrode active material, a negative electrode, and a nonaqueous electrolyte containing a fluorine-containing compound, wherein the positive electrode active material comprises a composite oxide a containing Li, Ni, and W, and a composite oxide B containing Li, Ni, and optionally W, the composite oxide a contains W in an amount of 5 mol% or more, the composite oxide B contains W in an amount of 0.5 mol% or less, and the mass ratio of the composite oxide a to the total amount of the composite oxide a and the composite oxide B is 0.002% or more and 0.1% or less.

According to the nonaqueous electrolyte secondary battery as one aspect of the present invention, it is estimated that hydrogen fluoride generated during high-temperature storage of the battery is efficiently captured by the composite oxide a containing 5 mol% or more of W. Here, the transition metal in the composite oxide a is eluted by the trapped hydrogen fluoride. Therefore, as the content of the composite oxide a increases, the elution amount of the transition metal also increases, and thus the capacity of the battery during high-temperature storage tends to decrease. However, as in the nonaqueous electrolyte according to one embodiment of the present invention, by setting the mass ratio of the composite oxide a to the total amount of the composite oxide a containing W in an amount of 5 mol% or more and the composite oxide B containing W in an amount of 0.5 mol% or less to 0.002% or more and 0.1% or less, hydrogen fluoride is efficiently captured from the composite oxide a having a very small ratio, the transition metal is mainly eluted from the composite oxide a, and the elution of the transition metal from the composite oxide B having a large ratio can be suppressed, and as a result, the total elution amount of the transition metal can be suppressed. As a result, it is considered that the decrease in battery capacity due to the high-temperature storage of the battery is suppressed. In addition, although the initial capacity of the battery tends to decrease as the ratio of the composite oxide a containing W of 5 mol% or more increases, the nonaqueous electrolyte secondary battery according to one aspect of the present invention has a very small ratio of the composite oxide a containing W of 5 mol% or more, and thus the initial capacity of the battery can be suppressed from decreasing.

Hereinafter, an example of the embodiment will be described in detail. The drawings referred to in the description of the embodiments are schematically illustrated, and the size ratios and the like of the components illustrated in the drawings may be different from those of the actual components.

Fig. 1 is a sectional view of a nonaqueous electrolyte secondary battery as an example of the embodiment. The nonaqueous electrolyte secondary battery 10 shown in fig. 1 includes a wound electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween, a nonaqueous electrolyte, insulating plates 18 and 19 disposed above and below the electrode body 14, respectively, and a battery case 15 accommodating these components. The battery case 15 includes a case main body 16 having a bottomed cylindrical shape, and a sealing member 17 for closing an opening of the case main body 16. Instead of the wound electrode body 14, another electrode body may be used, such as a laminated electrode body in which positive electrodes and negative electrodes are alternately laminated with separators interposed therebetween. Examples of the battery case 15 include a metal case such as a cylindrical, rectangular, coin-shaped, or button-shaped case, and a resin case (laminate battery) formed by laminating resin sheets.

The case main body 16 is, for example, a metal container having a bottomed cylindrical shape. A gasket 28 is provided between the case main body 16 and the sealing body 17 to ensure the sealing property inside the battery. The case main body 16 has, for example, a bulging portion 22 that supports the sealing member 17, and a part of the side surface portion bulges inward. The bulging portion 22 is preferably formed annularly along the circumferential direction of the case main body 16, and supports the sealing member 17 on the upper surface thereof.

Sealing body 17 has a structure in which filter member 23, lower valve 24, insulating member 25, upper valve 26, and cap 27 are stacked in this order from the electrode body 14 side. The members constituting the sealing body 17 have, for example, a disk shape or a ring shape, and the members other than the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their central portions, and an insulating member 25 is interposed between their peripheral portions. When the internal pressure rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and breaks so as to push up the upper valve body 26 toward the cap 27, thereby blocking the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further rises, the upper valve body 26 is broken, and the gas is discharged from the opening of the cap 27.

In the nonaqueous electrolyte secondary battery 10 shown in fig. 1, a positive electrode lead 20 attached to the positive electrode 11 extends toward the sealing member 17 through a through hole of the insulating plate 18, and a negative electrode lead 21 attached to the negative electrode 12 extends toward the bottom of the case body 16 through the outside of the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the filter member 23, which is the bottom plate of the sealing member 17, by welding or the like, and a cap 27, which is the top plate of the sealing member 17 electrically connected to the filter member 23, serves as a positive electrode terminal. The negative electrode lead 21 is connected to the bottom inner surface of the case main body 16 by welding or the like, and the case main body 16 serves as a negative electrode terminal.

The positive electrode 11, the negative electrode 12, the separator 13, and the nonaqueous electrolyte will be described in detail.

< Positive electrode >

The positive electrode 11 is composed of a positive electrode current collector such as a metal foil, and a positive electrode active material layer formed on the positive electrode current collector. As the positive electrode current collector, a foil of a metal such as aluminum that is stable in the potential range of the positive electrode, a film in which the metal is disposed on the surface layer, or the like can be used. The positive electrode active material layer contains, for example, a positive electrode active material, a binder, a conductive agent, and the like.

The positive electrode 11 is obtained by, for example, applying a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive agent, and the like onto a positive electrode current collector, drying the slurry to form a positive electrode active material layer on the positive electrode current collector, and rolling the positive electrode active material layer.

The positive electrode active material has a composite oxide A containing Li, Ni and W; and a composite oxide B containing Li, Ni and optionally W.

The content of W in the composite oxide a is not particularly limited if it is 5 mol% or more, and is preferably 7 mol% or more, for example, in order to more efficiently trap hydrogen fluoride. The upper limit of the W content in the composite oxide a is preferably 20 mol% or less, for example, in terms of efficiently performing charge-discharge reactions. The content of W in the complex oxide a is determined by, for example, dissolving the complex oxide a in a heated acid solution and analyzing the solution by inductively coupled plasma emission spectroscopy (ICP-AES).

The composite oxide A is preferably represented by the general formula Li in order to improve the initial capacity of the battery, for example_xNi_1-y-zW_yM_zO_2-γAnd (4) showing. Wherein M is at least 1 element selected from transition metal elements other than Ni and W, group 2 elements and group 13 elements, x is 0.85. ltoreq. x.ltoreq.1.05, y is 0.05. ltoreq. y.ltoreq.0.2, z is 0.01. ltoreq. z.ltoreq.0.5, and γ is-0.2. ltoreq. γ.ltoreq.0.2.

Examples of the transition metal element other than Ni and W contained in the composite oxide a include Co, Mn, Zr, Mo, Cr, V, Ti, and Fe, and among these, Co and Mn are preferable in terms of stabilization of the crystal structure of the positive electrode active material. The group 2 elements are Be, Mg, Ca, Sr, Ba and Ra, and among these, Mg and Ca are preferable in terms of the life of the battery. Among the group 13 elements, B, Al, Ga, In, Tl, and Nh, Al is preferable In terms of improvement of thermal stability of the positive electrode active material.

The content of W in the composite oxide B is not particularly limited if it is 0.5 mol% or less, and is preferably 0.1 mol% or more and 0.5 mol% or less, for example, in terms of suppressing a decrease in charge-discharge cycle characteristics of the battery. The content of W in the composite oxide B was determined by analysis by inductively coupled plasma emission spectrometry (ICP-AES) in the same manner as described above.

The composite oxide B is preferably represented by the general formula Li in terms of, for example, suppressing a decrease in charge-discharge cycle characteristics of a battery_xNi_1-y-zW_yM_zO_2-γAnd (4) showing. Wherein M is at least 1 element selected from transition metal elements other than Ni and W, group 2 elements and group 13 elements, x is 0.85. ltoreq. x.ltoreq.1.05, y is 0.002. ltoreq. y.ltoreq.0.05, z is 0.01. ltoreq. z.ltoreq.0.5, and γ is-0.2. ltoreq. γ.ltoreq.0.2.

Examples of the transition metal element other than Ni and W contained in the composite oxide B include Co, Mn, Zr, Mo, Cr, V, Ti, and Fe, and among these, Co and Mn are preferable in terms of stabilization of the crystal structure of the positive electrode active material. The group 2 elements are Be, Mg, Ca, Sr, Ba and Ra, and among these, Mg and Ca are preferable in terms of the life of the battery. Among the group 13 elements, B, Al, Ga, In, Tl, and Nh, Al is preferable In terms of improvement of thermal stability of the positive electrode active material.

The mass ratio of the composite oxide a to the total amount of the composite oxide a and the composite oxide B is 0.002% or more and 0.1% or less, preferably 0.02% or more and 0.08% or less, in terms of suppressing a decrease in capacity during high-temperature storage of the battery.

The content of the composite oxide A relative to the total amount of the positive electrode active material is, for example, in order to further suppress the high-temperature storage of the battery The content is preferably 0.002 mass% or more and 0.1 mass% or less, more preferably 0.02 mass% or more and 0.08 mass% or less, for the purpose of capacity reduction or the like. The content of the composite oxide B with respect to the total amount of the positive electrode active material is preferably 50 mass% or more and 99.998 mass% or less, and more preferably 70 mass% or more and 99.998 mass% or less, in terms of improving the initial capacity of the battery or the like. The positive electrode active material may contain a lithium composite oxide other than the composite oxides a and B, and may contain LiCoO, for example₂、LiMn₂O₄And Li composite oxides containing no Ni.

An example of a method for producing the composite oxide A, B will be described.

The method for producing the composite oxide A, B includes, for example: a first step (1) of mixing a Ni hydroxide with a Li compound and firing the mixture to obtain a composite oxide containing Li and Ni; and a 2 nd step of mixing a solution containing a W compound with a composite oxide containing Li and Ni so that the content of W is a predetermined amount, and heating the mixture to obtain a composite oxide containing Li, Ni and W.

The Ni hydroxide in the 1 st step may be a composite hydroxide containing other elements such as Co and Al in addition to Ni. Such a composite hydroxide is obtained by, for example, stirring an aqueous solution of a Ni salt, a Co salt, an Al salt, or the like, adding an alkaline solution such as sodium hydroxide dropwise thereto, and adjusting the pH to the alkaline side (for example, 8.5 to 11.5) to precipitate (coprecipitate) a composite hydroxide containing Ni, Co, a1, or the like. The Ni salt and the like are not particularly limited, and sulfate, chloride, nitrate and the like can be mentioned. Examples of the Li compound in the 1 st step include lithium hydroxide and lithium carbonate.

The firing temperature of the mixture in the step 1 is, for example, in the range of 500 to 900 ℃, and the firing time is, for example, in the range of 1 to 20 hours.

In the case of producing the composite oxide a, in the 2 nd step, a solution containing a W compound and a composite oxide containing Li and Ni are mixed so that W is 5 mol% or more with respect to the composite oxide. In the case of producing the composite oxide B, in the 2 nd step, a solution containing a W compound and a composite oxide containing Li and Ni are mixed so that W is 0.5 mol% or less with respect to the composite oxide.

The solution containing the W compound in the 2 nd step is preferably an alkali solution in order to easily dissolve the W compound. Examples of the W compound include tungsten oxide and tungstate.

The heating temperature of the mixture in the step 2 is, for example, in the range of 100 to 300 ℃ and the heating time is, for example, in the range of 1 to 20 hours.

Hereinafter, other materials included in the positive electrode active material layer will be described.

Examples of the conductive agent contained in the positive electrode active material layer include carbon powders such as carbon black, acetylene black, ketjen black, and graphite, and these may be used alone in 1 kind or in combination of two or more kinds.

Examples of the binder included in the positive electrode active material layer include a fluorine-based polymer, a rubber-based polymer, and the like. Examples of the fluorine-based polymer include Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and modified products thereof, and examples of the rubber-based polymer include ethylene-propylene-isoprene copolymer, ethylene-propylene-butadiene copolymer, and the like. These may be used alone in 1 kind, or two or more kinds may be used in combination.

< negative electrode >

The negative electrode 12 includes a negative electrode current collector such as a metal foil, and a negative electrode active material layer formed on the negative electrode current collector. As the negative electrode current collector, a foil of a metal such as copper that is stable in the potential range of the negative electrode, a film in which a metal is disposed on the surface layer, or the like can be used. The anode active material layer contains, for example, an anode active material, a binder, a thickener, and the like.

The negative electrode 12 is obtained by, for example, applying a negative electrode mixture slurry containing a negative electrode active material, a thickener, and a binder to a negative electrode current collector, drying the slurry to form a negative electrode active material layer on the negative electrode current collector, and rolling the negative electrode active material layer.

The negative electrode active material contained in the negative electrode active material layer is not particularly limited as long as it is a material capable of occluding and releasing lithium ions, and examples thereof include a carbon material, a metal capable of forming an alloy with lithium, an alloy containing the metal, and a compound. As the carbon material, graphite-based materials such as natural graphite, hard-to-graphitize carbon, and artificial graphite, coke-based materials, and the like can be used. The metal capable of forming an alloy with lithium is preferably silicon or tin, and silicon oxide, tin oxide, or the like to which oxygen is bonded may be used. In addition, a mixture of the carbon material and a compound of silicon or tin may be used. In addition to the above, a material such as lithium titanate having a higher charge/discharge potential than that of a carbon material or the like can be used.

As the binder included in the negative electrode active material layer, for example, a fluorine-based polymer, a rubber-based polymer, or the like can be used as in the case of the positive electrode, and a styrene-butadiene copolymer (SBR) or a modified product thereof can be used. As the binder included in the negative electrode active material layer, a fluorine-based resin, PAN, a polyimide-based resin, an acrylic resin, a polyolefin-based resin, or the like can be used as in the case of the positive electrode. When the negative electrode mixture slurry is prepared using an aqueous solvent, it is preferable to use styrene-butadiene rubber (SBR), CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, or the like, and may be a partially neutralized salt), polyvinyl alcohol (PVA), or the like.

Examples of the thickener included in the negative electrode active material layer include carboxymethyl cellulose (CMC), polyethylene oxide (PEO), and the like. These may be used alone in 1 kind, or two or more kinds may be used in combination.

< nonaqueous electrolyte >

The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent. The nonaqueous electrolyte contains a fluorine-containing compound. Here, the fluorine-containing compound contained in the nonaqueous electrolyte may be a fluorine-containing compound contained in the nonaqueous solvent, may be a fluorine-containing compound contained in the electrolyte, or may be both of them. Namely, the nonaqueous electrolyte includes: (1) a solution containing a nonaqueous solvent containing a fluorine-containing compound and an electrolyte containing no fluorine-containing compound; (2) a solution containing a nonaqueous solvent containing no fluorine-containing compound and an electrolyte containing a fluorine-containing compound, (3) a solution containing a nonaqueous solvent containing a fluorine-containing compound and an electrolyte containing a fluorine-containing compound, and the like.

Examples of the fluorine-containing compound of the nonaqueous solvent include fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2, 3-trifluoropropylene carbonate, 2, 3-difluoroethylene-2, 3-butylene carbonate, and 1, 1, 1, 4, 4, 4-hexafluoro-2, 3-butylene carbonate, and particularly, FEC is preferable from the viewpoint of suppressing the amount of hydrogen fluoride generated in a high-temperature environment.

The nonaqueous solvent may contain, in addition to the fluorine-containing compound, an organic solvent such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, or vinylene carbonate. These may be used alone or in combination of two or more.

The fluorine-containing compound as the nonaqueous solvent is preferably contained in the nonaqueous electrolyte in a range of 2 mass% to 25 mass%. When the content of the fluorine-containing compound is within the above range, the charge-discharge cycle characteristics of the battery may be inhibited from being lowered as compared with the case where the content is outside the above range.

The fluorine-containing compound as the electrolyte is preferably, for example, LiPF₆、LiBF₄、LiAsF₆、LiSbF₆、LiCF₃SO₃And the like lithium-and fluorine-containing compounds, and may also be, for example, AgF, CoF₂、CoF₃、CuF、CuF₂、FeF₂、FeF₃、MnF₂、MnF₃、SnF₂、SnF₄、TiF₃、TiF₄、ZrF₄Equal to the Li-containing fluorine-containing compound. These may be used alone or in combination of two or more.

The electrolyte may contain, for example, LiClO in addition to the fluorine-containing compound₄、LiAlCl₄、LiSCN、LiB₁₀Cl₁₀、LiCl、LiBr、LiI、Li₂B₄O₇And the like fluorine-free lithium salts. These may be used alone or in combination of two or more.

The concentration of the electrolyte is preferably 0.8 to 1.8mol per 1L of the nonaqueous solvent, for example.

< spacer >

For example, a porous sheet having ion permeability and insulation properties is used as the spacer 13. Specific examples of the porous sheet include a microporous film, a woven fabric, and a nonwoven fabric. The material of the spacer 13 is preferably an olefin resin such as polyethylene or polypropylene, or cellulose. The spacer 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. A multilayer spacer including a polyethylene layer and a polypropylene layer may be used, and a multilayer spacer in which a material such as aramid resin or ceramic is applied to the surface of the spacer may be used.