Positive electrode active material for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

Abstract

The present invention provides a positive electrode active material which improves the discharge capacity of a battery. This positive electrode active material contains a first lithium metal composite oxide which is represented by general formula xLiyM1O2-(1-x)LizM1O2 (wherein 0 < x ≤ 1, 1.5 ≤ y ≤ 2.5, 0.9 ≤ z ≤ 1.5, and M1 represents one or more elements that are selected from the group consisting of transition metals, Al, Si, Sn, Ge, Sb, Bi, Mg, Ca and Sr); the first lithium metal composite oxide has a layered structure, while comprising Li element that is coordinated to the position of the oxygen tetrahedron; and the particle diameters of the primary particles are from 0.5 μm to 15 μm.

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. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, which are charged and discharged by transferring Li ions between a positive electrode and a negative electrode, have been widely used for some time, and in recent years, there has been a demand for further improvements in battery characteristics. Patent Document 1 discloses a secondary battery that contains Li2NiO2 in the positive electrode, thereby supplying a sufficient amount of Li ions to the negative electrode during charging, thereby improving overdischarge characteristics and suppressing a decrease in battery capacity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2005-521220 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Li2NiO2 has poor reversibility in the absorption and release of Li ions, and the inclusion of Li2NiO2 in the positive electrode may actually reduce the discharge capacity of the battery. The technology in Patent Document 1 does not take into consideration the irreversibility of Li2NiO2, and there is still room for improvement.

[0005] Therefore, an object of the present disclosure is to provide a positive electrode active material that improves the discharge capacity of a battery. [Means for solving the problem]

[0006] The positive electrode active material for a nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure is a material represented by the general formula xLi y MO2-(1-x)Li zA first lithium metal composite oxide represented by M1O2 (where 0 < x ≤ 1, 1.5 ≤ y ≤ 2.5, 0.9 ≤ z ≤ 1.5, and M1 is one or more elements selected from the group consisting of transition metals and Al, Si, Sn, Ge, Sb, Bi, Mg, Ca, and Sr) is included. The first lithium metal composite oxide has a layered structure and has a Li element coordinated at the tetrahedral position of oxygen, and the particle size of the primary particles is 0.5 to 15 μm.

[0007] A non-aqueous electrolyte secondary battery which is one aspect of the present disclosure includes a positive electrode containing the above positive electrode active material for a non-aqueous electrolyte secondary battery, a negative electrode, and a non-aqueous electrolyte. The negative electrode contains a negative electrode active material, and the negative electrode active material is Si, SiC, SiO α (0 < α < 2), Li β SiO γ (1 < β ≤ 4, 1 < γ ≤ 4), and contains 3% or more of one or a mixture of two or more selected from the group consisting of Sn, SnO2, Sb, and Ge. [Advantages of the Invention]

[0008] According to the positive electrode active material for a non-aqueous electrolyte secondary battery which is one aspect of the present disclosure, the discharge capacity of the battery can be improved. [Brief Description of the Drawings]

[0009] [Figure 1] It is a cross-sectional view of a non-aqueous electrolyte secondary battery which is an example of an embodiment. [Modes for Carrying Out the Invention]

[0010] Non-aqueous electrolyte secondary batteries are charged and discharged by transferring Li ions between the positive and negative electrodes. During charging and discharging, some of the Li ions that migrate from the positive electrode to the negative electrode remain absorbed in the negative electrode active material and are not released from the negative electrode during discharge, resulting in a decrease in the battery's capacity retention. This phenomenon is observed even when using carbon-based materials such as graphite, but is particularly pronounced when using non-reversible materials such as silicon-based materials. To prevent this decrease in capacity retention, a method has been investigated in which the positive electrode contains Li2NiO2 as a Li filler, thereby supplying a sufficient amount of Li ions to the negative electrode during charging. However, Li2NiO2 has poor reversibility in the absorption and release of Li ions, and the inclusion of Li2NiO2 in the positive electrode can actually reduce the battery's discharge capacity.

[0011] The inventors conducted extensive research to solve the above-mentioned problems and found that using a first lithium metal composite oxide having a primary particle size of 0.5 to 15 μm and a predetermined composition and structure as a positive electrode active material specifically improves the discharge capacity of a battery. During charging, when Li, which is coordinated at the tetrahedral oxygen sites, is supplied to the negative electrode, the volume of the lithium metal composite oxide changes significantly. However, by making the primary particle size relatively large, such as 0.5 to 15 μm, cracking of the secondary particles can be suppressed, presumably improving the discharge capacity compared to when the positive electrode contains LiNiO. Furthermore, by further including a second lithium metal composite oxide having a secondary particle size larger than that of the first lithium metal composite oxide in the positive electrode active material, the packing density of the positive electrode mixture layer can be improved, thereby improving the capacity density of the positive electrode.

[0012] An example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail below. Hereinafter, a cylindrical battery in which a wound electrode body is housed in a cylindrical exterior body will be exemplified. However, the electrode body is not limited to the wound type, and may be a laminated type in which multiple positive electrodes and multiple negative electrodes are alternately stacked one by one with separators interposed therebetween. Furthermore, the exterior body is not limited to a cylindrical shape, and may be, for example, a prismatic or coin-shaped body, or may be a battery case made of a laminate sheet including a metal layer and a resin layer.

[0013] Fig. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment. As illustrated in Fig. 1, the nonaqueous electrolyte secondary battery 10 includes an electrode assembly 14, a nonaqueous electrolyte (not shown), and a battery case 15 that accommodates the electrode assembly 14 and the nonaqueous electrolyte. 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. The battery case 15 includes a cylindrical outer can 16 with a bottom, and a sealing member 17 that closes the opening of the outer can 16.

[0014] The electrode assembly 14 is composed of a long positive electrode 11, a long negative electrode 12, two long separators 13, a positive electrode tab 20 joined to the positive electrode 11, and a negative electrode tab 21 joined to the negative electrode 12. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the longitudinal direction and width direction (short direction). The two separators 13 are formed to be at least slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11, for example.

[0015] The nonaqueous electrolyte secondary battery 10 includes insulating plates 18 and 19 disposed above and below the electrode assembly 14. In the example shown in Fig. 1 , a positive electrode tab 20 attached to the positive electrode 11 passes through a through-hole in the insulating plate 18 and extends toward the sealing body 17, and a negative electrode tab 21 attached to the negative electrode 12 passes outside the insulating plate 19 and extends toward the bottom of the outer can 16. The positive electrode tab 20 is connected to the underside of a bottom plate 23 of the sealing body 17 by welding or the like, and a cap 27 of the sealing body 17 electrically connected to the bottom plate 23 serves as the positive electrode terminal. The negative electrode tab 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0016] The outer can 16 is, for example, a cylindrical metal container with a bottom. A gasket 28 is provided between the outer can 16 and the sealing body 17, sealing the internal space of the battery case 15. The outer can 16 has a grooved portion 22 that supports the sealing body 17, formed, for example, by pressing the side surface from the outside. The grooved 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.

[0017] The sealing body 17 has a structure in which, in order from the electrode body 14 side, a bottom plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0018] The positive electrode 11, negative electrode 12, separator 13, and nonaqueous electrolyte that constitute the nonaqueous electrolyte secondary battery 10 will be described in detail below, particularly the positive electrode active material contained in the positive electrode mixture layer 31 that constitutes the positive electrode 11.

[0019] [Positive electrode] The positive electrode 11 has a positive electrode current collector 30 and a positive electrode mixture layer 31 formed on both sides of the positive electrode current collector 30. The positive electrode current collector 30 can be a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on its surface. The positive electrode mixture layer 31 may contain a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like to the surface of the positive electrode current collector 30, drying the coating, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode current collector 30.

[0020] Examples of the conductive agent contained in the positive electrode active material layer 31 include carbon-based materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode active material layer 31 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. These resins may be used in combination with carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), or the like.

[0021] The positive electrode active material contained in the positive electrode active material layer 31 is a general formula xLi y M1O2-(1-x)Li z M1O2 (0 < x ≤ 1, 1.5 ≤ y ≤ 2.5, 0.9 ≤ z ≤ 1.5, M1 is one or more elements selected from the group consisting of transition metals and Al, Si, Sn, Ge, Sb, Bi, Mg, Ca, and Sr) and contains a first lithium metal composite oxide represented by.

[0022] The general formula xLi representing the first lithium metal composite oxide y M1O2-(1-x)Li z In M1O2, M is preferably one or more elements selected from the group consisting of Ni, Co, Mn, Fe, and Al.

[0023] The first lithium metal composite oxide has a layered structure and has a Li element coordinated at the tetrahedral position of oxygen in one primary particle. The layered structure of the first lithium metal composite oxide includes, for example, a transition metal layer, a Li layer, and an oxygen layer. The Li layer is a layer in which Li reversibly enters and exits.

[0024] The first lithium metal composite oxide is mainly composed of the space group R3-m and may have a region of the space group P3-m1 as a stacking defect. By introducing a region of the space group P3-m1 as a stacking defect while mainly having the space group R3-m, the discharge capacity can be improved. The general formula xLi representing the first lithium metal composite oxide y M1O2-(1-x)Li zIn M1O2, x and (1 - x) respectively indicate the ratios of the regions of space group P3 - m1 and space group R3 - m. x satisfies 0 < x ≤ 1, and preferably 0.01 ≤ x < 0.4. If x is less than 0.4, the average discharge voltage of the battery can be increased.

[0025] The general formula xLi representing the first lithium metal composite oxide y M1O2-(1 - x)Li z The value of x in M1O2 can be calculated by the following formula from the integrated intensity S1 of 17.1° or more and less than 18.1° and the integrated intensity S2 of 18.1° or more and less than 19.1°, which are measured by XRD measurement of CuKα. x = S1 / (S1 + S2)

[0026] The XRD measurement may be performed under the following conditions using, for example, a powder X-ray diffractometer (manufactured by Rigaku Corporation, trade name "RINT-TTR", radiation source Cu-Kα). Measurement range: 15 - 120° Scan speed: 4° / min Analysis range: 30 - 120° Background: B-spline Profile function: Split pseudo-Voigt function ICSD No.: 98 - 009 - 4814

[0027] In the state of being discharged to 1.5V, the first lithium metal composite oxide has a composition represented by the general formula xLi y M1O2-(1 - x)Li z M1O2 (0 < x ≤ 1, 1.5 ≤ y ≤ 2.5, 0.9 ≤ z ≤ 1.5, M1 is the above M1) may have a composition. The composition of the first lithium metal composite oxide changes with the charge and discharge of the battery, but recovers to the above composition by discharging to 1.5V.

[0028] The first lithium metal composite oxide is, for example, a secondary particle formed by agglomeration of a plurality of primary particles. The particle size of the primary particles constituting the secondary particle is 0.5 to 15 μm. By making the primary particle size relatively large, 0.5 to 15 μm, cracking of the secondary particles can be suppressed. The primary particle size is measured as the diameter of the circumscribed circle in a particle image observed with a scanning electron microscope (SEM).

[0029] The particle size D1 of the secondary particles of the first lithium metal composite oxide is the volume-based median size (D50), and is, for example, 0.1 to 30 μm. D50 refers to the particle size at which the cumulative frequency of the smallest particle size in the volume-based particle size distribution is 50%, and is also called the median size. The particle size distribution of the first lithium metal composite oxide can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II, manufactured by Microtrack Bell Corporation) with water as the dispersion medium.

[0030] The positive electrode active material is of the general formula Li w The positive electrode active material may further contain a second lithium metal composite oxide represented by M2O2 (0.9≦w≦1.5, M2 is one or more elements selected from the group consisting of Ni, Co, Mn, Fe, and Al). Note that the positive electrode active material may contain a lithium metal composite oxide other than the first lithium metal composite oxide and the second lithium metal composite oxide, or other compounds, as long as the object of the present disclosure is not impaired.

[0031] The second lithium metal composite oxide is, for example, a secondary particle formed by agglomeration of a plurality of primary particles. The particle size of the primary particles constituting the secondary particle is, for example, 0.05 to 1 μm. The particle size D2 of the secondary particles is a volume-based median diameter (D50) of, for example, 1 to 30 μm. The primary particle size and secondary particle size of the second lithium metal composite oxide can be measured in the same manner as for the first lithium metal composite oxide.

[0032] The ratio (D1 / D2) of the secondary particle diameter D1 of the first lithium metal composite oxide to the secondary particle diameter D2 of the second lithium metal composite oxide preferably satisfies 0.15 < D1 / D2 < 1.0. Thereby, the packing density of the positive electrode active material layer is improved, and the capacity density of the positive electrode can be improved.

[0033] In the positive electrode active material, the ratio of the mass of the first lithium metal composite oxide to the total mass of the first lithium metal composite oxide and the second lithium metal composite oxide is preferably 10 to 90%, more preferably 15 to 50%, and particularly preferably 20 to 40%. Within this range, the capacity density of the positive electrode can be further improved.

[0034] The first lithium metal composite oxide can be prepared, for example, by immersing a lithium metal composite oxide (X) having a space group R3-m and Li metal in a benzophenone 2Me-THF solution in which benzophenone is dissolved in 2-methyltetrahydrofuran (2-MeTHF), stirring at room temperature for 1 to 24 hours, and then filtering. By the above process, a space group P3-m1 is introduced as a stacking defect into the lithium metal composite oxide (X) having a space group R3-m. The ratio of introducing the space group P3-m1 can be adjusted, for example, by temperature, the concentration of benzophenone in 2-MeTHF, stirring time, etc.

[0035] The lithium metal composite oxide (X) having a space group R3-m can be synthesized, for example, by adding a Li source to a metal composite compound containing no Li, mixing them, and firing at 200°C to 1050°C. Examples of the metal composite compound include oxides, hydroxides, carbonate compounds, etc. containing Ni, Mn, etc. Examples of the Li source include LiOH, etc. For example, by increasing the Ni content in the metal composite compound, the Ni content in the lithium metal composite oxide (Y) increases. The metal composite compound can be prepared, for example, by heat-treating a hydroxide prepared by a coprecipitation method.

[0036] The second lithium metal composite oxide can be prepared in the same manner as the lithium metal composite oxide (X) having the space group R3-m. For example, D2 can be made larger than D1 by lengthening the precipitation time when preparing the coprecipitate used as the Ni and Mn source for the second lithium metal composite oxide, or by setting the calcination temperature when preparing the second lithium metal composite oxide higher than the calcination temperature when preparing the first lithium metal composite oxide.

[0037] [Negative electrode] The negative electrode 12 includes a negative electrode current collector 40 and a negative electrode mixture layer 41 formed on both sides of the negative electrode current collector 40. The negative electrode current collector 40 may be a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film having such a metal disposed on its surface. The negative electrode mixture layer 41 may contain a negative electrode active material and a binder. The thickness of the negative electrode mixture layer 41 is, for example, 10 μm to 150 μm on one side of the negative electrode current collector 40. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and the like to the surface of the negative electrode current collector 40, drying the coating, and then rolling the coating to form the negative electrode mixture layer 41 on both sides of the negative electrode current collector 40. Note that lithium metal may be precipitated on the negative electrode 12 in a charged state.

[0038] The negative electrode active material contained in the negative electrode mixture layer 41 is not particularly limited as long as it can reversibly absorb and release lithium ions, and generally, a carbon-based material such as graphite is used. The graphite may be any of natural graphite such as flake graphite, lump graphite, and amorphous graphite, or artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. Furthermore, metals that alloy with Li, such as Si and Sn, metal compounds containing Si and Sn, and lithium-titanium composite oxides may also be used as the negative electrode active material. Furthermore, these may be coated with carbon. Examples of the negative electrode active material include Si, SiC, SiO α (0<α<2), Li β SiO γ (1<β≦4, 1<γ≦4), it is preferable that the alloy contains 3% or more of a mixture of one or more elements selected from the group consisting of Sn, SnO2, Sb, and Ge.

[0039] The binder contained in the negative electrode mixture layer 41 may be a fluorine-containing resin such as PTFE or PVdF, PAN, polyimide, acrylic resin, or polyolefin, as in the case of the positive electrode 11, but is preferably styrene-butadiene rubber (SBR). The negative electrode mixture layer 41 may also contain CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like.

[0040] [Separator] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a laminated structure. Furthermore, the surface of the separator 13 may be provided with a highly heat-resistant resin layer such as an aramid resin, or a filler layer containing an inorganic compound filler.

[0041] [Non-aqueous electrolyte] The non-aqueous electrolyte includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent that can be used include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms in these solvents are substituted with halogen atoms such as fluorine. Examples of the halogen-substituted compound include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0042] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0043] Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methyl phenyl ether. and chain ethers such as ethyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0044] The electrolyte salt is preferably a lithium salt. Examples of lithium salts include LiBF, LiClO, LiPF, LiAsF, LiSbF, LiAlCl, LiSCN, LiCF, SO, LiCF, CO, Li(P(C), O)F, and LiPF.6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, borate salts such as Li2B4O7, Li(B(C2O4)F2), LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 SO2){l, m are integers of 0 or more}, and imide salts such as these may be mentioned. The lithium salt may be used alone or in combination of two or more. Among these, from the viewpoints of ionic conductivity, electrochemical stability, etc., it is preferable to use LiPF6. The concentration of the lithium salt is, for example, 0.8 mol to 1.8 mol per liter of the non-aqueous solvent. Further, vinylene carbonate or a propane sultone-based additive may be added.

Examples

[0045] Hereinafter, the present disclosure will be further described by way of examples and comparative examples, but the present disclosure is not limited to the following examples.

[0046] <Example 1> [Production of positive electrode active material] The nickel-manganese composite hydroxide having a composition of Ni 0.8 Mn 0.2 (OH)2 obtained by coprecipitation was heat-treated at 500 °C to obtain a nickel-manganese composite oxide having a composition of Ni 0.8 Mn 0.2 O2. Next, the nickel-manganese composite oxide and LiOH were mixed so that the molar ratio of the total amount of Ni and Mn to Li became 1.02:1. After firing this mixture at 800 °C for 40 hours and then pulverizing, a lithium metal composite oxide (X) having R3-m was obtained. The lithium metal composite oxide (X) had a primary particle diameter of 2 μm and a secondary particle diameter of 3.8 μm.

[0047] The lithium metal composite oxide (X) and Li metal were immersed in a 1 mol / L benzophenone 2Me-THF solution, stirred at room temperature for 12 hours, and then filtered to prepare a first lithium metal composite oxide, which was used as a positive electrode active material. As a result of XRD measurement, the x of the positive electrode active material (first lithium metal composite oxide) was found to be 0.33.

[0048] [Preparation of positive electrode] The positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) were mixed in a solids mass ratio of 96.3:2.5:1.2, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added. The mixture was then kneaded to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to both sides of a positive electrode core made of aluminum foil, and the coating was dried. The coating was then rolled using a roller and cut to a predetermined electrode size, resulting in a positive electrode having a positive electrode mixture layer formed on both sides of the positive electrode core.

[0049] [Preparation of non-aqueous electrolyte] A non-aqueous solvent was prepared by mixing fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:6. LiPF6 was dissolved in the non-aqueous solvent at a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[0050] [Test cell construction] An electrode assembly was fabricated by attaching lead wires to the positive electrode and the counter electrode made of Li metal, and arranging the positive electrode and the counter electrode facing each other with a polyolefin separator in between. This electrode assembly and the non-aqueous electrolyte were enclosed in an exterior body made of an aluminum laminate film to fabricate a test cell.

[0051] [Discharge capacity measurement] In a temperature environment of 25°C, the battery was charged at a constant current of 0.2 C until the cell voltage reached 4.5 V, and then charged at a constant voltage of 0.02 C at 4.5 V. Subsequently, the battery was discharged at a constant current of 0.2 C until the cell voltage reached 2.5 V. The discharge capacity in this charge-discharge cycle was measured.

[0052] <Comparative Example 1> In the preparation of the positive electrode active material, the firing conditions were changed to 800°C for 10 hours, and the primary particle size of the lithium metal composite oxide (X) was set to 0.3 μm and the secondary particle size to 4.8 μm. Except for this, a test cell was prepared and evaluated in the same manner as in Example 1. As a result of XRD measurement, x of the positive electrode active material was found to be 0.33.

[0053] The discharge capacities of Example 1 and Comparative Example 1 are shown in Table 1. Table 1 also shows the secondary particle diameter and primary particle diameter of the positive electrode active material.

[0054] [Table 1]

[0055] As shown in Table 1, the test cell of Example 1 has an improved discharge capacity compared to the test cell of Comparative Example 1.

[0056] <Example 2> In the preparation of the positive electrode active material, the first lithium metal composite oxide of Example 1 and a separately prepared composition of LiNi 0.8 Mn 0.2 A test cell was prepared in the same manner as in Example 1, except that a positive electrode active material was prepared by mixing P3-m1 and a second lithium metal composite oxide having a secondary particle diameter of 17.0 μm in a mass ratio of 30:70. Using this test cell, the charge capacity density and discharge capacity density described below were measured in addition to the discharge capacity described above. The proportion (x) of P3-m1 in the entire mixed positive electrode was 0.1.

[0057] [Calculation of charge capacity density and discharge capacity density] In the above charge-discharge cycle, the charge capacity was measured together with the discharge capacity. The mass of the positive electrode active material contained in the positive electrode mixture layer was divided by the volume of the positive electrode mixture layer to calculate the density of the positive electrode active material in the positive electrode mixture layer. Based on these values, the charge capacity density and the discharge capacity density were calculated and evaluated using the following formula: Charge capacity density (mAh / cm 3) = charging capacity (mAh / g) × density of the positive electrode active material in the positive electrode mixture layer (g / cm 3 ) Discharge capacity density (mAh / cm 3 ) = discharge capacity (mAh / g) × density of the positive electrode active material in the positive electrode mixture layer (g / cm 3 )

[0058] <Comparative Example 2> A test cell was prepared and evaluated in the same manner as in Example 2, except that in preparing the positive electrode active material, the first lithium metal composite oxide of Comparative Example 1 and the second lithium metal composite oxide were mixed in a mass ratio of 30:70 to prepare the positive electrode active material.

[0059] <Reference example 1> In the preparation of the positive electrode active material, a test cell was prepared in the same manner as in Example 2, except that the second lithium metal composite oxide was used as the positive electrode active material, and an evaluation was carried out.

[0060] <Reference example 2> In preparing the positive electrode active material, the size of the first lithium metal composite oxide was changed to a primary particle diameter of 2 μm and a secondary particle diameter of 4.4 μm, and the first lithium metal composite oxide was used as the positive electrode active material. Except for this, a test cell was prepared and evaluated in the same manner as in Example 2. As a result of XRD measurement, x of the positive electrode active material was found to be 0.2.

[0061] The charge capacity densities and discharge capacity densities of Example 2, Comparative Example 1, and Reference Examples 1 and 2 are shown in Table 1. Table 1 also shows the secondary particle diameter, primary particle diameter, and proportion (x) of P3-m1 in the entire mixed positive electrode of the first lithium metal composite oxide, the secondary particle diameter of the second lithium metal composite oxide, the mixing ratio of the first lithium metal composite oxide to the second lithium metal composite oxide, and the density of the positive electrode active material in the positive electrode mixture layer.

[0062] [Table 2]

[0063] As shown in Table 2, the test cell of Example 2 has improved charge capacity density and discharge capacity density compared to the test cell of Comparative Example 2. The test cell of Example 2 also had higher charge capacity density and discharge capacity density compared to the test cells of Reference Examples 1 and 2, which consist of only one type of lithium metal composite oxide. [Explanation of symbols]

[0064] 10 non-aqueous electrolyte secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 battery case, 16 outer can, 17 sealing body, 18, 19 insulating plate, 20 positive electrode tab, 21 negative electrode tab, 22 grooved portion, 23 bottom plate, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 cap, 28 gasket, 30 positive electrode current collector, 31 positive electrode mixture layer, 40 negative electrode current collector, 41 negative electrode mixture layer

Claims

1. A non-aqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material for a non-aqueous electrolyte secondary battery, a negative electrode, and a non-aqueous electrolyte, General formula xLi ｙ M1O ２ -(1-x)Li ｚ M1O ２ (0.01≦x<0.4, 1.5≦y≦2.5, 0.9≦z≦1.5, M1 is a transition metal and one or more elements selected from the group consisting of Al, Si, Sn, Ge, Sb, Bi, Mg, Ca, and Sr), and the first lithium metal composite oxide exhibits a composition in which the first lithium metal composite oxide and the second lithium metal composite oxide coexist as a multiphase structure within the same crystal, the first lithium metal composite oxide has a layered structure, has Li elements coordinated to tetrahedral oxygen positions, and has a primary particle size of 0.5 to 15 μm; A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the first lithium metal composite oxide recovers to a composition represented by the general formula xLi y M1O 2 -(1-x)Li z M1O 2 (0<x≦1, 1.5≦y≦2.5, 0.9≦z≦1.5, and M1 is the M1) when discharged to 1.5 V.

2. 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the first lithium metal composite oxide is mainly composed of space group R3-m and has P3-m1 regions as stacking faults.

3. 3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein M1 is at least one element selected from the group consisting of Ni, Co, Mn, Fe, and Al.

4. General formula Li ｗ M2O ２ 4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, further comprising a second lithium metal composite oxide represented by the formula: (0.9≦w≦1.5, M2 is one or more elements selected from the group consisting of Ni, Co, Mn, Fe, and Al).

5. 5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, wherein a ratio (D1 / D2) of a secondary particle diameter D1 of the first lithium metal composite oxide to a secondary particle diameter D2 of the second lithium metal composite oxide satisfies 0.15<D1 / D2<1.

0.

6. A secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, a negative electrode, and a non-aqueous electrolyte, the negative electrode includes a negative electrode active material, The negative electrode active material is Si, SiC, SiO α (0<α<2), Li β SiO γ (1<β≦4, 1<γ≦4), Sn, SnO ２ 1. A non-aqueous electrolyte secondary battery comprising 3% or more of a mixture of one or more elements selected from the group consisting of Sb, Sb, and Ge.

7. 7. The nonaqueous electrolyte secondary battery according to claim 6, wherein lithium metal is deposited on the negative electrode in a charged state.

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