Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery and Non-Aqueous Electrolyte Secondary Battery

Abstract

This positive electrode active material for a non-aqueous electrolyte secondary battery contains a lithium transition metal composite oxide represented by the composition formula LixMnyNizAlaMbO2-cFc (in the formula, M represents at least two elements selected from Ti, Co, Si, Sr, Nb, W, Mo, P, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K, and Bi; 1.0 < x ≤ 1.2; 0.4 ≤ y ≤ 0.8; 0 ≤ z ≤ 0.4; 0 < a < 0.01; 0 < b < 0.03; 0 < c < 0.1; and x+y+z+a+b ≤ 2).

Description

Technical Field

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

Background Art

[0002] In non-aqueous electrolyte secondary batteries such as lithium-ion batteries, the positive electrode active material greatly affects battery performance such as input / output characteristics, capacity, and cycle characteristics. Generally, lithium transition metal composite oxides containing metal elements such as Ni, Co, Mn, and Al are used as the positive electrode active material. Since the properties of lithium transition metal composite oxides vary greatly depending on their composition, many studies have been conducted on the types and amounts of additive elements.

[0003] For example, Patent Document 1 discloses a positive electrode active material for a non-aqueous electrolyte secondary battery represented by the composition formula Li x Ni 1-y Co y-z M z O 2-a X b (where M is at least Al), having a lattice constant of the a-axis measured by X-ray diffraction of 2.81 to 2.91 Å, a lattice constant of the c-axis of 13.7 to 14.4 Å, and a ratio of the diffraction peak intensity of the (104) plane to the peak intensity of the (003) plane of 0.3 to 0.8.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] Lithium-excess composite oxides with a molar ratio of Li to transition metal exceeding 1 have also been proposed. Lithium-excess composite oxides are expected as next-generation cathode active materials with high capacity, but there are problems such as easy elution of transition metals. It is known that adding F to lithium-excess composite oxides suppresses the elution of transition metals and improves durability. However, in this case, there is a problem that the resistance increases and the capacity decreases.

[0006] The cathode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure has a composition formula Li x Mn y Ni z Al a M b O 2-c F c (In the formula, M is two or more elements selected from Ti, Co, Si, Sr, Nb, W, Mo, P, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K, Bi; 1.0 < x ≤ 1.2, 0.4 ≤ y ≤ 0.8, 0 ≤ z ≤ 0.4, 0 < a < 0.01, 0 < b < 0.03, 0 < c < 0.1, x + y + z + a + b ≤ 2), and includes a lithium transition metal composite oxide represented thereby.

[0007] The non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a cathode containing the above cathode active material, an anode, a separator interposed between the cathode and the anode, and a non-aqueous electrolyte.

[0008] According to the present disclosure, a cathode active material with high capacity can be provided. According to the cathode active material according to the present disclosure, both high capacity and high durability can be achieved.

Brief Description of the Drawings

[0009]

Figure 1

Embodiments for Carrying Out the Invention

[0010] As described above, when F is added to a lithium-excess type composite oxide, elution of transition metals is suppressed and durability is improved, but on the other hand, resistance increases and capacity decreases. Note that in a lithium transition metal composite oxide, when many Li are desorbed, the crystal structure is likely to become unstable, but by adding Al, the structure is stabilized. Therefore, by adding Al, charging up to a high voltage becomes possible, contributing to an increase in capacity. However, simply adding Al cannot achieve as high a capacity as expected.

[0011] As a result of intensive studies to solve the above problems, the present inventors have found that by adding Al and two or more specific elements to a lithium-excess type F-containing composite oxide containing at least Mn as a transition metal, the capacity can be increased. When two or more of Al and specific elements are added, for example, the capacity is specifically improved as compared with the case where one of Al and specific elements is added.

[0012] Hereinafter, with reference to the drawings, an example of an embodiment of a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the positive electrode active material according to the present disclosure will be described in detail. It is initially assumed that a plurality of embodiments and modification examples described below can be selectively combined.

[0013] Hereinafter, a cylindrical battery in which a wound electrode body 14 is housed in a bottomed cylindrical outer can 16 will be exemplified, but the outer body is not limited to a cylindrical outer can, and may be, for example, a rectangular outer can (rectangular battery) or a coin-shaped outer can (coin-shaped battery), or an outer body (laminated battery) composed of a laminated sheet including a metal layer and a resin layer. Further, the electrode body may be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated with a separator interposed therebetween.

[0014] FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery 10 which is an example of an embodiment. As shown in FIG. 1, the non-aqueous electrolyte secondary battery 10 includes a wound electrode body 14, a non-aqueous electrolyte, and an exterior can 16 that houses the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 has 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 with the separator 13 interposed therebetween. The exterior can 16 is a bottomed cylindrical metal container with one side in the axial direction open, and the opening of the exterior can 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the side of the battery where the sealing body 17 is located is regarded as the upper side, and the bottom side of the exterior can 16 is regarded as the lower side.

[0015] The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. For the non-aqueous solvent, for example, esters, ethers, nitriles, amides, and a mixed solvent of two or more of these are used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine. For the electrolyte salt, for example, lithium salts such as LiPF 6 are used. Note that the non-aqueous electrolyte is not limited to a liquid electrolyte and may be a solid electrolyte.

[0016] The positive electrode 11, the negative electrode 12, and the separator 13 that constitute the electrode body 14 are all strip-shaped long bodies, and are alternately laminated in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed with dimensions slightly larger than those of the positive electrode 11 in order to prevent precipitation of lithium. That is, the negative electrode 12 is formed longer than the positive electrode 11 in the longitudinal direction and the width direction (short side direction). The two separators 13 are formed with dimensions at least slightly larger than those of the positive electrode 11 and are arranged, for example, 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.

[0017] Insulating plates 18 and 19 are respectively arranged above and below the electrode body 14. In the example shown in FIG. 1, the positive electrode lead 20 extends toward the sealing body 17 through the through-hole of the insulating plate 18, and the negative electrode lead 21 extends toward the bottom side of the outer can 16 through the outside of the insulating plate 19. 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 electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0018] A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the sealing property inside the battery. A groove portion 22 for supporting the sealing body 17, in which a part of the side surface portion projects inward, is formed in the outer can 16. The groove portion 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and supports the sealing body 17 on its upper surface. The sealing body 17 is fixed to the upper part of the outer can 16 by the groove portion 22 and the open end portion of the outer can 16 caulked to the sealing body 17.

[0019] 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 laminated in order from the electrode body 14 side. Each member constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each member except the insulating member 25 is electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and the insulating member 25 is interposed between the peripheral edges of each. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 is deformed and broken so as to push up the upper valve body 26 toward the cap 27 side, thereby cutting off 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 breaks, and gas is discharged from the opening of the cap 27.

[0020] Hereinafter, the positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 will be described in detail, particularly the positive electrode active material constituting the positive electrode 11.

[0021] [Positive Electrode] The positive electrode 11 has a positive electrode core body and a positive electrode composite layer provided on the surface of the positive electrode core body. For the positive electrode core body, a foil of a metal stable within the potential range of the positive electrode 11 such as aluminum or an aluminum alloy, a film having the metal disposed on the surface layer, etc. can be used. The positive electrode composite layer contains a positive electrode active material, a conductive material, and a binder, and is preferably provided on both sides of the positive electrode core body. The positive electrode 11 can be manufactured, for example, by applying a positive electrode composite slurry containing a positive electrode active material, a conductive material, a binder, etc. onto the positive electrode core body, drying the coating film, and then compressing it to form the positive electrode composite layer on both sides of the positive electrode core body.

[0022] Examples of the conductive material contained in the positive electrode composite layer include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode composite layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, etc. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0023] The positive electrode active material has the compositional formula Li x Mn y Ni z Al a M b O 2-c F c (wherein M is two or more elements selected from Ti, Co, Si, Sr, Nb, W, Mo, P, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K, Bi; 1.0 < x ≤ 1.2, 0.4 ≤ y ≤ 0.8, 0 ≤ z ≤ 0.4, 0 < a < 0.01, 0 < b < 0.03, 0 < c < 0.1, x + y + z + a + b ≤ 2), and contains a lithium transition metal composite oxide represented thereby. The composite oxide is a Li-excess system material in which the molar ratio of Li to the transition metal exceeds 1, a predetermined amount of fluoride ions is introduced, and a part of O is substituted by F.

[0024] The positive electrode active material is mainly composed of a composite oxide represented by the above compositional formula. Here, the main component means the component with the highest mass ratio among the constituent components of the composite oxide. In the positive electrode 11, as the positive electrode active material, a composite oxide other than the composite oxide represented by the above compositional formula (for example, a composite oxide that is not a Li-excess type or a composite compound that does not contain fluoride ions) may be used in combination, but the content of the above composite oxide is preferably 50% by mass or more, and may be substantially 100% by mass. The composition of the composite oxide can be measured using an ICP emission spectroscopic analyzer (iCAP6300 manufactured by Thermo Fisher Scientific).

[0025] The lithium transition metal composite oxide represented by the above compositional formula may contain Ni in addition to Li, Mn, and Al. Further, it contains, as essential components, two or more elements selected from Ti, Co, Si, Sr, Nb, W, Mo, P, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K, and Bi. Among them, Ti, Co, Nb, Ge, Mg, Si, and Sr are preferable.

[0026] In the above compositional formula, it is particularly preferable that M is two or more selected from Ti, Co, and Nb. That is, M is any one of (1) Co and Ti, (2) Co and Nb, (3) Ti and Nb, and (4) Co, Ti, and Nb. Also, the molar ratio (b) of M is preferably 0 < b < 0.02, more preferably 0.001 ≤ b ≤ 0.015, and particularly preferably 0.0002 ≤ b ≤ 0.010. When the element M is selected from the combinations of (1) to (4) above, the effect of improving the capacity appears more significantly.

[0027] In the above composition formula, the molar ratio of Li (x) is 1.0 <x≦1.2であって、好ましくは1.1≦x≦1.2である。Mnのモル比(y)は、0.4≦y≦0.8であって、好ましくは0.45≦y≦0.6である。Alのモル比(a)は、0<a<0.01であって、好ましくは0.001≦a≦0.007であり、より好ましくは0.002≦a≦0.005である。Li、Mn、Alのモル比が当該範囲内であれば、容量の改善効果がより顕著に現れる。Niは任意成分であるが、例えば、0.05≦z≦0.3の量で含有されることが好ましい。

[0028] In the lithium transition metal composite oxide represented by the above composition formula, the total molar amount (x+y+z+a+b) of Li, Mn, Ni, Al, and M is 2 or less, and preferably 2. In other words, it is preferable that the composite oxide is a Li-excess composite oxide, and not a cation-excess composite oxide. In addition, the molar ratio (c) of F is 0 <c≦0.1であって、好ましくは0.05≦x≦0.085である。所定量のFを添加することにより、遷移金属の溶出が抑制され、耐久性が向上する。

[0029] A specific example of a suitable lithium transition metal composite oxide is a lithium-excess type F-containing composite oxide that contains Mn, Ni, Al, and Co, and at least one of Ti and Nb. The composite oxide does not substantially contain elements other than Mn, Ni, Al, Co, Ti, Nb, Li, O, and F. The molar ratio of each of Co, Ti, and Nb is preferably 0.01 or less, more preferably 0.001 to 0.007, and particularly preferably 0.002 to 0.005, and is, for example, equal to or less than the molar ratio of Al.

[0030] The lithium transition metal composite oxide of this embodiment can be synthesized, for example, by mixing carbonates containing Mn and Ni, compounds containing Al, Co, Ti, Nb, etc. (for example, aluminum hydroxide, cobalt sulfate, titanium oxide, niobium oxide, etc.), and lithium fluoride (LiF), and calcining the mixture. An example of the calcination conditions is 700 to 900°C for 10 to 30 hours.

[0031] Negative electrode The negative electrode 12 has a negative electrode core body and a negative electrode composite layer provided on the surface of the negative electrode core body. For the negative electrode core body, a foil of a metal stable within the potential range of the negative electrode 12 such as copper, or a film having the metal disposed on the surface layer can be used. The negative electrode composite layer preferably contains a negative electrode active material and a binder, and is provided on both sides of the negative electrode core body. The negative electrode 12 can be manufactured, for example, by applying a negative electrode composite slurry containing a negative electrode active material, a conductive material, a binder, etc. on the surface of the negative electrode core body, drying the coating film, and then compressing to form the negative electrode composite layer on both sides of the negative electrode core body.

[0032] The negative electrode composite layer contains, as the negative electrode active material, for example, a carbon-based active material that reversibly occludes and releases lithium ions. Suitable carbon-based active materials are graphite such as flaky graphite, massive graphite, earthy graphite, etc., artificial graphite such as massive artificial graphite (MAG), graphitized mesophase carbon microbeads (MCMB), etc. Further, as the negative electrode active material, a Si-based active material composed of at least one of Si and Si-containing compounds may be used, or a carbon-based active material and a Si-based active material may be used in combination.

[0033] As the conductive material contained in the negative electrode composite layer, similar to the case of the positive electrode 11, carbon materials such as carbon black, acetylene black, ketjen black, graphite, etc. can be used. As the binder contained in the negative electrode composite layer, similar to the case of the positive electrode 11, fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc. can also be used, but it is preferable to use styrene-butadiene rubber (SBR). Further, the negative electrode composite layer preferably further contains CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. Among them, it is preferable to use SBR in combination with CMC or its salt, and PAA or its salt.

[0034] Separator For the separator 13, a porous sheet having ion permeability and insulation properties is used. Specific examples of the porous sheet include microporous thin films, woven fabrics, non-woven fabrics, etc. As the material of the separator 13, polyolefins such as polyethylene, polypropylene, and copolymers of ethylene and α-olefins, cellulose, etc. are suitable. The separator 13 may have either a single-layer structure or a laminated structure. On the surface of the separator 13, a heat-resistant layer containing inorganic particles, a heat-resistant layer composed of a highly heat-resistant resin such as aramid resin, polyimide, polyamideimide, etc. may be formed.

[0035] <Example> Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0036] <Example 1> [Synthesis of Lithium Transition Metal Composite Oxide] A carbonate containing Mn and Ni in a molar ratio of 2:1, aluminum hydroxide, cobalt sulfate, titanium oxide, and lithium fluoride were mixed, and the mixture was calcined at 800 °C for 20 hours under an oxygen stream to obtain a lithium transition metal composite oxide represented by the composition formula Li 1.167 Mn 0.55 Ni 0.275 Al 0.002 Co 0.002 Ti 0.002 O 1.92 F 0.08 O.

[0037] [Fabrication of Positive Electrode] The above lithium transition metal composite oxide was used as the positive electrode active material. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed at a solid content mass ratio of 7:2:1, and a positive electrode composite material slurry was prepared using N-methyl-2-pyrrolidone (NMP) as the dispersion medium. Next, the positive electrode composite material slurry was coated on a positive electrode core made of aluminum foil, the coating film was dried and compressed, and then cut into a predetermined electrode size to obtain a positive electrode.

[0038] [Preparation of Non-Aqueous Electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a predetermined volume ratio. To this mixed solvent, LiPF 6 was added to obtain a non-aqueous electrolyte solution.

[0039] [Fabrication of Test Cell] An electrode body was constructed by oppositely arranging a positive electrode and a negative electrode made of a lithium metal foil with a separator interposed therebetween, and the electrode body was housed in a coin-shaped exterior can. After injecting the non-aqueous electrolyte solution into the exterior can, the exterior can was sealed to obtain a coin-shaped test cell (non-aqueous electrolyte secondary battery).

[0040] The initial capacity of the test cell was evaluated by the following method, and the evaluation results are shown in Tables 1 to 3 together with the composition of the positive electrode active material.

[0041] [Evaluation of Initial Capacity] The test cell was charged with a constant current of 0.05C up to a battery voltage of 5.2V at room temperature, then rested for 20 minutes, and then discharged with a constant current of 0.05C down to a battery voltage of 2.5V, and the discharge capacity was measured.

[0042] [Examples 2 to 7, Comparative Examples 1 to 3] In the synthesis of the lithium transition metal composite oxide, except that the types of raw materials and the mixing ratio of the raw materials were changed so that the compositions shown in Tables 1 to 3 were obtained (the contents of Ni and Mn were the same as in Example 1), test cells were fabricated and the initial capacity was evaluated in the same manner as in Example 1.

[0043] [Table 1]

[0044] [Table 2]

[0045] [Table 3]

[0046] As shown in Table 1, the test cells of the examples using, as the positive electrode active material, a lithium-excess type F-containing composite oxide containing Mn, Ni, and Al and added with two or more elements selected from Co and elements selected from Ti, Nb, Ge, Mg, and Si had a higher capacity than the test cell of Comparative Example 1 that did not contain Co, Ti, etc. In particular, in the test cells of Examples 1, 2, and 6 using composite oxides containing Co and Ti, Co and Nb, and Co, Ti, and Nb, the initial capacity was greatly improved.

[0047] As shown in Table 2, it is difficult to increase the capacity by adding only Ti to a lithium-excess type F-containing composite oxide containing Mn, Ni, and Al. However, by adding Co, Nb, Si, etc. in addition to Ti, the capacity of the test cell is specifically improved.

[0048] Similarly, as shown in Table 3, it is difficult to increase the capacity by adding only Nb to a lithium-excess type F-containing composite oxide containing Mn, Ni, and Al. However, by adding Co, Ti, etc. in addition to Nb, the capacity of the test cell is specifically improved.

[0049] As described above, by adding two or more specific elements selected from Co, Ti, Nb, etc. together with Al to a lithium-excess type F-containing composite oxide containing at least Mn as a transition metal, the capacity can be greatly improved.

Explanation of Reference Numerals

[0050] 10 Non-aqueous electrolyte secondary battery 11 Positive electrode 12 Negative electrode 13 Separator 14 Electrode body 16 Outer can 17 Sealing body 18, 19 Insulating plate 20 Positive electrode lead 21 Negative electrode lead 22 Grooved portion 23 Internal terminal plate 24 Lower valve body 25 Insulating member 26 Upper valve body 27 Cap 28 Gasket

Claims

1. Compositional formula Li ｘ Mn ｙ Ni ｚ Al ａ M ｂ O ２－ｃ F ｃ (In the formula, M is two or more elements selected from Ti, Co, Nb, Ge, Mg, and Si; 1.0 < x ≤ 1.2, 0.4 ≤ y ≤ 0.8, 0 ≤ z ≤ 0.4, 0 < a < 0.01, 0 < b < 0.03, 0 < c < 0.1, x + y + z + a + b ≤ 2), and the positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide represented by the formula

2. Constituent Li ｘ Mn ｙ Ni ｚ Al ａ M ｂ O ２－ｃ F ｃ In this case, M is two or more selected from Ti, Co, and Nb, and the molar ratio (b) of M is 0 < b < 0.

02. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1.

3. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material according to claim 1 or 2, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

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