Non-aqueous electrolyte secondary battery

Abstract

A nonaqueous electrolyte secondary battery as one example of an embodiment includes a positive electrode having a positive electrode mixture layer, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The positive electrode mixture layer contains a first lithium transition metal composite oxide represented by a general formula Li x Ni 1‑y‑z Co y M z O2 (in the formula, 0.8 ≤ x ≤ 1.2, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.5, and M is at least one metal element other than Li, Ni, and Co) and a second lithium transition metal composite oxide represented by a general formula Li a Ni 2‑a‑b Me b O2 (in the formula, 0 < a ≤ 0.5, 0 ≤ b ≤ 0.5, and Me is at least one metal element other than Li and Ni). The separator has a base material and a surface layer containing inorganic particles and a binder and formed on a surface of the base material facing the positive electrode side.

Description

TECHNICAL FIELD

[0001] The present application relates to a nonaqueous electrolyte secondary battery. BACKGROUND

[0002] A nonaqueous electrolyte secondary battery has a structure in which a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte are accommodated in an exterior body. The constitution of the positive electrode, which is a main constituent element of the nonaqueous electrolyte secondary battery, greatly influences the battery characteristics including charge-discharge cycle characteristics, storage characteristics, and the like, and thus much research has been conducted on the positive electrode. For example, Patent Literatures 1 and 2 disclose a positive electrode active material for the purpose of improving the performance such as charge-discharge cycle characteristics.

[0003] The positive electrode active material disclosed in Patent Literature 1 is a composite oxide represented by the general formula Li x Ni 1-y-z-v-w Co y Al z M1 v M2 w O2, in the formula, the element M1 is at least one selected from the group consisting of Mn, Ti, Y, Nb, Mo, and W, the element M2 is at least two selected from the group consisting of Mg, Ca, Sr, Ba, and Ra, and the element M2 includes at least Mg and Ca.

[0004] In addition, the positive electrode active material disclosed in Patent Literature 2 is a composite oxide represented by [L] 3a [M] 3b [O2] 6c (L = Li; M = Ni, Mn, and Co, or Li, Ni, Mn, and Co), which contains 0.1 to 5 mol% of one or more elements selected from the group consisting of Mo, W, Nb, Ta, and Re, relative to the total molar amount of Mn, Ni, and Co.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURES

[0007] Patent Literature 1: Japanese Patent No. 4781004

[0008] Patent Literature 2: Japanese Patent No. 5359140 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] However, with the popularization of nonaqueous electrolyte secondary batteries in vehicle-mounted applications, power storage applications, and the like, there is a demand for further high performance of nonaqueous electrolyte secondary batteries, and in particular, improvement in charge-discharge cycle characteristics and storage characteristics. The existing technologies including the technologies of Patent Literatures 1 and 2 have room for improvement in the improvement of cycle characteristics and storage characteristics.

[0011] Solution to the problem

[0012] The nonaqueous electrolyte secondary battery according to the present application is characterized in that, in a nonaqueous electrolyte secondary battery provided with a positive electrode having a positive electrode mixture layer, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte, the positive electrode mixture layer contains a first lithium transition metal composite oxide represented by the general formula Li x Ni 1-y-z Co y M z O2(where 0.8≤x≤1.2, 0≤y≤0.2, 0 a Ni 2-a-b Me b O2(where 0

[0013] Effects of the invention

[0014] The nonaqueous electrolyte secondary battery according to the present application is excellent in charge-discharge cycle characteristics and storage characteristics. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Cross-sectional view of a nonaqueous electrolyte secondary battery as an example of an embodiment.

[0016] Figure 2 Enlarged view of a part of a cross section of an electrode body as an example of an embodiment. DETAILED DESCRIPTION

[0017] As described above, improvement in charge-discharge cycle characteristics and storage characteristics is an important issue in nonaqueous electrolyte secondary batteries. In particular, it is required to improve the cycle characteristics and storage characteristics while ensuring high battery capacity. The present inventors and others have conducted intensive studies on improvement in the cycle characteristics and storage characteristics, and as a result, it has been found that, by using a positive electrode mixture layer containing a first lithium transition metal composite oxide represented by the general formula Li x Ni 1-y-z Co y M z O2and a second lithium transition metal composite oxide represented by the general formula Li a Ni 2-a-b Me bThe positive electrode of the second lithium transition metal composite oxide represented by O2, and the separator having a surface layer containing inorganic particles formed on the surface of the substrate in contact with the positive electrode, the cycle characteristics and storage characteristics of the battery are specifically improved.

[0018] Although the mechanism of the combination of the first lithium transition metal composite oxide, the second lithium transition metal composite oxide and the above separator to improve the cycle characteristics is not clear, it is believed that the second lithium transition metal composite oxide protects the surface of the first lithium transition metal composite oxide and inhibits deterioration. Further, it is believed that by providing a surface layer containing inorganic particles on the surface of the substrate of the separator in contact with the positive electrode, the side reaction of the electrolyte in the positive electrode is inhibited by the interaction with the second lithium transition metal composite oxide, as a result, the cycle characteristics and storage characteristics are greatly improved.

[0019] In addition, although the first lithium transition metal composite oxide has Ni as an essential constituent component, increasing the Ni content will make it easier to balance high capacity and good cycle characteristics. The effect of adding the second lithium transition metal composite oxide is more effective when using the first lithium transition metal composite oxide with a high Ni content.

[0020] Hereinafter, an example of an embodiment of the non-aqueous electrolyte secondary battery according to the present application will be described in detail with reference to the drawings. Note that the present application includes a combination of a plurality of embodiments and modifications described below, as appropriate.

[0021] Hereinafter, a cylindrical battery in which the wound electrode body 14 is housed in a bottomed cylindrical outer can 16 is exemplified, but the outer body of the battery is not limited to the cylindrical outer can, and for example, can be a square outer can (square battery) or a coin-shaped outer can (coin-shaped battery), or can be an outer body composed of a laminated sheet including a metal layer and a resin layer (laminated battery). In addition, the electrode body can be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated with separators.

[0022] Figure 1 A diagram schematically showing a cross section of the non-aqueous electrolyte secondary battery 10 as an example of an embodiment. As shown in Figure 1 The non-aqueous electrolyte secondary battery 10 has a wound electrode body 14, a non-aqueous electrolyte, and an outer 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 outer can 16 is a bottomed cylindrical metal container that is open on one axial side, and the opening of the outer can 16 is plugged by a sealing body 17. Hereinafter, for ease of explanation, the side of the sealing body 17 of the battery is taken as the upper side, and the side of the bottom of the outer can 16 is taken as the lower side.

[0023] The positive electrode 11, the negative electrode 12, and the separator 13 that constitute the electrode body 14 are each a long strip body in a band shape, and are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. For the negative electrode 12, a size larger by one turn than the positive electrode 11 is formed in order to prevent deposition of lithium. That is, the negative electrode 12 is formed longer in the length direction and the width direction (short side direction) than the positive electrode 11. The separator 13 is formed at least in a size larger by one turn than the positive electrode 11, and for example, two pieces are arranged in a manner sandwiching 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.

[0024] The upper and lower sides of the electrode body 14 are provided with insulating plates 18 and 19, respectively. The positive electrode lead 20 and the negative electrode lead 21 are arranged in a manner extending through the insulating plates 18 and 19, respectively. Figure 1 In the example shown, the positive electrode lead 20 extends to the side of the sealing body 17 through a through hole of the insulating plate 18, and the negative electrode lead 21 extends to the side of the bottom 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 an internal terminal plate 23 of the sealing body 17 by welding or the like, and the top plate of the sealing body 17, that is, the lid 27, which is electrically connected to the internal terminal plate 23, becomes a 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 becomes a negative electrode terminal.

[0025] The outer can 16 is a metal container in a bottomed cylindrical shape that is open on one side in the axial direction, as described above. A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the airtightness of the inside of the battery and the insulation of the outer can 16 and the sealing body 17. A groove portion 22, in which a part of the side surface portion protrudes inward, is formed in the outer can 16 to support the sealing body 17. The groove portion 22 is preferably annular in shape formed along the circumferential direction of the outer can 16, and supports the sealing body 17 with its upper surface. The sealing body 17 is fixed to the upper portion of the outer can 16 by the groove portion 22 and the open end portion of the outer can 16 that is caulked to the sealing body 17.

[0026] 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 lid 27 are sequentially stacked from the side of the electrode body 14. Each member that constitutes the sealing body 17 has, for example, a circular plate shape or an annular 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 by respective central portions, and sandwich the insulating member 25 between respective peripheral portions. When the internal pressure of the battery rises due to an abnormality, the lower valve body 24 deforms in a manner to press the upper valve body 26 toward the lid 27 and breaks, and thus the current passage between the lower valve body 24 and the upper valve body 26 is cut off. When the internal pressure further rises, the upper valve body 26 breaks and gas is discharged from the opening portion of the lid 27.

[0027] Hereinafter, the operation of the battery 10 will be described with appropriate reference to the drawings. Figure 2The positive electrode 11, the negative electrode 12, the separator 13, and the nonaqueous electrolyte that constitute the nonaqueous electrolyte secondary battery 10 will be described in detail. Figure 2 A schematic view of a part of the cross section of the electrode body 14 is enlarged.

[0028] <Positive electrode>

[0029] As shown in FIG. 1, the positive electrode 11 has a positive electrode core 30 and a positive electrode mixture layer 31 formed on at least one face of the positive electrode core 30. The positive electrode core 30 can use a foil of a metal such as aluminum or an aluminum alloy that is stable in the potential range of the positive electrode 11, a thin film in which the metal is disposed on the surface layer, or the like. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder, and is preferably formed on both faces of the positive electrode core 30. A lithium transition metal complex oxide is used as the positive electrode active material. The positive electrode 11 can be manufactured by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like on the positive electrode core 30, drying the coated film, and compressing it to form the positive electrode mixture layer 31 on both faces of the positive electrode core 30. Figure 2 As the binder contained in the positive electrode mixture layer 31, a fluorine resin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVdF); a polyacrylonitrile (PAN), a polyimide, an acrylic resin, a polyolefin, or the like can be exemplified. In addition, these resins can be used in combination with a cellulose derivative such as carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. The content of the binder is, for example, 0.1 to 5% by mass or 0.5 to 3% by mass with respect to the total mass of the positive electrode mixture layer 31.

[0030] The positive electrode mixture layer 31 contains at least two kinds of lithium transition metal complex oxides. A first lithium transition metal complex oxide (hereinafter referred to as "complex oxide (A)") is a complex oxide represented by the general formula Li x Ni 1-y-z Co y M z O2(where 0.8 ≤ x ≤ 1.2, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.5, and M is at least one metal element other than Li, Ni, and Co). A second lithium transition metal complex oxide (hereinafter referred to as "complex oxide (B)") is a complex oxide represented by the general formula Li a Ni 2-a-b Me b O2(where 0 < a ≤ 0.5, 0 ≤ b ≤ 0.5, and Me is at least one metal element other than Li and Ni).

[0031]

[0032] ​In the positive electrode mixture layer 31, the charge / discharge cycle characteristics are specifically improved by the coexistence of the composite oxides (A, B). It is considered that the composite oxide (B) protects the particle surface of the composite oxide (A), effectively inhibits the deterioration of the particle surface, and as a result, the cycle characteristics are greatly improved. In particular, when the particles of the composite oxides (A, B) contact each other or contact via the carbon nanotubes (CNT), it is considered that the protective effect works more effectively. In addition, the composite oxide (B) can be mixed with the composite oxide (A) by applying a strong shear force or a compression force, and be treated to be immobilized on the surface of the composite oxide (A).

[0033] The composite oxide (B) exerts the above-described effects by being added in a small amount, but in order to maintain a high battery capacity and achieve an improvement in the cycle characteristics, there is a preferable range in the amount of the composite oxide (B) to be added. The content of the composite oxide (B) is preferably 0.05 to 10% by mass, more preferably 0.1 to 7% by mass, or 0.1 to 5% by mass, with respect to the total mass of the positive electrode mixture layer 31. Similarly, it is preferably 0.05 to 10% by mass, more preferably 0.1 to 7% by mass, or 0.1 to 5% by mass, with respect to the total mass of the positive electrode active material. If the amount of the composite oxide (B) is within this range, the cycle characteristics can be effectively improved.

[0034] In the positive electrode mixture layer 31, a composite oxide other than the composite oxides (A, B) (for example, a lithium transition metal composite oxide that does not satisfy the above-described general formula) can also be contained, within a range that does not impair the object of the present application. The composite oxides (A, B) are preferably contained in an amount of 50% by mass or more, with respect to the total mass of the positive electrode mixture layer 31. The total content of the composite oxides (A, B) is, for example, 85% by mass or more, or 90% by mass or more, or 95% by mass or more, with respect to the total mass of the positive electrode mixture layer 31. An example of a preferable content is 90 to 99% by mass, or 95 to 99% by mass.

[0035] [1st lithium transition metal composite oxide (composite oxide (A))]

[0036] The composite oxide (A) is a composite oxide represented by the above-described general formula, and contains at least one metal element M other than Li, Ni, and Co as an essential constituent element. In addition, the composite oxide (A) preferably contains Co. However, Co is particularly rare and expensive, and therefore the composite oxide (A) can substantially not contain Co. In the case where the composite oxide (A) contains Co, the Co content is 20 mol% or less, more preferably 0.1 to 10 mol%, or 0.5 to 5 mol%, with respect to the total molar amount of the metal elements other than Li. Note that the molar fraction of the metal elements in the composite oxide can be measured by inductively coupled plasma (ICP) emission spectroscopy.

[0037] The composite oxide (A) preferably has the largest content of Ni among the metal elements other than Li. The content of Ni is preferably 50 mol% or more, more preferably 70 mol% or more, and particularly preferably 80 mol% or more, relative to the total molar amount of the metal elements other than Li. An example of the preferable content of Ni is 80 to 97 mol% or 85 to 95 mol%. That is, an example of the preferable value of (1-y-z) representing the content of Ni in the above general formula is 0.80 ≤ (1-y-z) ≤ 0.97 or 0.85 ≤ (1-y-z) ≤ 0.95.

[0038] As described above, an example of the preferable composite oxide (A) is one that contains 80 mol% or more of Ni relative to the total molar amount of the metal elements other than Li. By increasing the proportion of Ni among the metal elements in the composite oxide (A), high capacity of the battery can be achieved. In addition, the composite oxide (A) rich in Ni has good compatibility with the composite oxide (B) and is also effective in improving the cycle characteristics. The composite oxide (A) can also be one that is lithium-excess type with a molar ratio of Li to transition metal exceeding 1, where x representing the content of Li in the above general formula is 0.8 ≤ x ≤ 1.2 or 0.97 ≤ x ≤ 1.2.

[0039] The composite oxide (A) contains at least one metal element M other than Li, Ni, and Co. The metal element M is, for example, at least one selected from the group consisting of Mn, W, Mg, Mo, Nb, Ti, Si, Al, Zr, B, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, and Ca, and is more preferably at least one selected from the group consisting of Mn, W, Mg, Mo, Nb, Ti, Si, Sr, Ca, and Al. Of these, at least one of Mn and Al is preferably contained. The content of the metal element M, when a plurality of elements are present, is 50 mol% or less, more preferably 0.1 to 20 mol%, or 0.5 to 10 mol%, or 1 to 5 mol%, relative to the total molar amount of the metal elements other than Li.

[0040] The composite oxide (A) has, for example, a crystal structure belonging to the space group R3-m. Furthermore, the composite oxide (A) has a layered structure including a transition metal layer, a Li layer, and an oxygen layer. In this case, the protective effect of the composite oxide (B) works more effectively, and a stable crystal structure can be maintained even if charging and discharging are repeated, and the cycle characteristics can be more effectively improved. In addition, the BET specific surface area of the composite oxide (A) is, for example, 0.2 to 2.0 m 2 / g. The BET specific surface area is measured according to the BET method (nitrogen adsorption method) described in JIS R1626.

[0041] The composite oxide (A) is, for example, a secondary particle formed by aggregation of a plurality of primary particles. An example of the median particle diameter (D50) of the composite oxide (A) on a volume basis is 3 to 20 μm or 5 to 15 μm. D50 refers to the particle diameter at which the cumulative frequency of the particle size distribution on a volume basis is 50% from the small particle diameter side, and is also referred to as the median diameter. The particle size distribution of the secondary particles of the composite oxide can be measured using a particle size distribution measuring device of the laser diffraction type (for example, MT3000II manufactured by Microtrac BEL Corporation) with water as the dispersion medium. The particle diameter of the primary particles of the composite oxide (A) is, for example, 0.05 to 1 μm. The particle diameter of the primary particles is measured as the diameter of the circumscribed circle in a cross-sectional image of the secondary particles observed using a scanning electron microscope (SEM).

[0042] In addition, a compound containing at least one metal element M2 selected from the group consisting of Sr, Ca, W, Mg, Nb, and Al (hereinafter referred to as "M2 compound") can be fixed to the surface of the particles of the composite oxide (A). The M2 compound containing the metal element M2 can be dispersed on the surface of the particles of the composite oxide (A), or can be present in a layer covering the entire surface of the particles. The thickness of the layer of the M2 compound is, for example, 0.1 to 5 nm. It is considered that the M2 compound protects the surface of the composite oxide (A), and in addition, protects the surface of the composite oxide (B), whereby the side reaction of the electrolyte at the surface of the particles of the composite oxides (A, B) is suppressed.

[0043] The M2 compound is an oxide, a hydroxide, or a carbonate. Specific examples of the M2 compound include SrO, CaO, Sr(OH)2, Ca(OH)2, SrCO3, CaCO3, and the like. The amount of the M2 compound is, for example, 0.05 to 0.5 mol% in terms of the metal element M2, with respect to the total number of moles of the metal elements other than Li constituting the composite oxide (A). The presence of the M2 compound can be confirmed by energy dispersive X-ray spectroscopy (TEM-EDX). In addition, the metal element M2 can be measured by subjecting a solution in which the composite oxide (A) is dissolved in nitric acid-hydrofluoric acid to ICP emission spectroscopic analysis.

[0044] The composite oxide (A) is produced by a first step of obtaining a composite oxide containing, for example, Ni, a metal element M, and the like; a second step of mixing the composite oxide with a Li raw material to obtain a mixture; and a third step of calcining the mixture. In the case where the M2 compound is fixed to the surface of the particles of the composite oxide (A), a raw material containing the metal element M2 (hereinafter referred to as "M2 raw material") can also be added in the second step. The composition, particle diameter, BET specific surface area, and the like of the composite oxide (A) and the M2 compound can be adjusted by controlling the mixing ratio of the raw materials, the calcination conditions in the third step, and the like.

[0045] In the first step, while stirring a solution of a metal salt containing, for example, Ni, a metal element M, and the like, an alkali solution such as sodium hydroxide is added dropwise, and a complex hydroxide containing a metal element is precipitated (co-precipitated) by adjusting the pH to the alkaline side (for example, 8.5 to 12.5). Then, by calcining the complex hydroxide, a complex oxide containing Ni, a metal element M, and the like is obtained. The calcination temperature is not particularly limited, and is, for example, 300 to 600°C.

[0046] In the second step, the complex oxide obtained in the first step, a Li raw material, and a M2 raw material as necessary are mixed to obtain a mixture. As an example of the Li raw material, Li2CO3, LiOH, Li2O2, Li2O, LiNO3, LiNO2, Li2SO4, LiOH-H2O, LiH, LiF, and the like can be given. As an example of the M2 raw material, an oxide, a hydroxide, a carbonate, a nitrate, a sulfate, and the like of M2 can be given. The mixing ratio of the complex oxide obtained in the first step to the Li raw material is adjusted, for example, so that the molar ratio of the metal element other than Li : Li becomes 1 : 0.98 to 1 : 1.22. In addition, the mixing ratio of the complex oxide to the M2 raw material is adjusted, for example, so that the molar ratio of the metal element other than Li : M2 becomes 1 : 0.0005 to 1 : 0.005.

[0047]

[0048] In the third step, the mixture obtained in the second step is calcined at a prescribed temperature and time to obtain a calcined product. The calcination of the mixture is performed by multi-stage calcination, which includes, for example, a first calcination step of calcining to a first set temperature of 450°C or higher and 680°C or lower at a first temperature increase rate under an oxygen stream in a calcination furnace, and a second calcination step of calcining to a second set temperature of higher than 680°C and 800°C or lower at a second temperature increase rate under an oxygen stream in the calcination furnace after the first calcination step. The first temperature increase rate is 1.5 to 5.5°C / min, and the second temperature increase rate is slower than the first temperature increase rate, and can be set to 0.1 to 3.5°C / min. Note that the temperature increase rate can be set to a plurality of rates in each calcination step.

[0049] The holding time of the first set temperature in the first calcination step is, for example, 0 to 5 hours, or 0 to 3 hours. Note that the holding time of the set temperature refers to the time during which the set temperature is maintained after the set temperature is reached. The holding time of the second set temperature in the second calcination step is, for example, 1 to 10 hours, or 1 to 5 hours. The calcination of the mixture is performed in an oxygen stream having an oxygen concentration of 60% or higher, and the flow rate of the oxygen stream can be set to 10 cm3 / min or more per 1 g of the mixture. 3 ​The calcination furnace is 0.2 to 4 mL / min, and 0.3 L / min or more per 1 kg of the mixture. The calcination product can be subjected to water washing, dehydration, and drying to remove impurities.

[0050] Note that M2 raw material can also be added in the 2nd process, and M2 raw material can be added in the 3rd process, during water washing of the calcination product, or during drying, for example, by heat treatment in a vacuum atmosphere at 150 to 400°C for 0.5 to 15 hours, so as to cause the M2 compound to adhere to the surface of the particles of the composite oxide (A).

[0051] [2nd lithium-transition metal composite oxide (composite oxide (B))]

[0052] As described above, the composite oxide (B) is a composite oxide represented by the general formula Li a Ni 2-a-b Me b O2 (in the formula, 0 < a ≤ 0.5, 0 ≤ b ≤ 0.5, and Me is at least one metal element other than Li and Ni). The content of the metal element Me is preferably less than the content of Li and Ni, for example, less than 10 mol% or less than 5 mol% relative to the total molar amount of the metal elements. As an example of the metal element Me, at least one selected from Cu, Sr, Ca, Nb, Si, and Al can be listed.

[0053] The composite oxide (B) does not cause release and absorption of Li due to charge and discharge, and the composition thereof does not change. In the case where this composite oxide (B) is used in combination with the composite oxide (A), the cycle characteristics of the battery are specifically improved. A plurality of composite oxides having similar compositions can be contained in the composite oxide (B). a in the above general formula is more preferably 0.1 ≤ a ≤ 0.5 or 0.2 ≤ a ≤ 0.4. If a is within this range, the cycle characteristics are more effectively improved. Note that the composition of the composite oxide (B) can be identified from an X-ray diffraction pattern, and analysis can be performed using ICP emission spectroscopy.

[0054] The composite oxide (B) is, for example, a composite oxide having at least one diffraction peak having a peak top at a diffraction angle (2θ) of 21.40° to 21.65° in synchrotron radiation X-ray diffraction (light energy 16 keV). This diffraction peak can be a broad peak in which the entire peak does not exist within the range of 2θ = 21.40° to 21.65°, as long as a peak top exists within the range. In the X-ray diffraction pattern of the composite oxide (B), for example, one peak top exists within the range of 2θ = 21.40° to 21.65°.

[0055] The X-ray diffraction pattern of the composite oxide (B) was obtained by powder X-ray diffraction method using a synchrotron radiation facility (beam line BL5S2 of Aichi Synchrotron Light Research Center) under the following conditions.

[0056] Light energy; 16 keV

[0057] Scanning range; 10 to 90°

[0058] Analytical optical system: Debye-Scherrer type

[0059] The obtained data was subjected to peak search using an identification analysis software PDXL (manufactured by Rigaku Corporation) to identify the composite oxide (B).

[0060] In the measurement using the above-described apparatus, NiO has a peak at 21.36°, and the peak shifts to the high angle side as a in the above-described general formula increases. If a in the above-described general formula is within the above-described range, a main peak exists at 21.40° to 21.65°. The composite oxide (B) can be identified by comparison with JCPDS cards including other peaks.

[0061] The composite oxide (B) is, for example, a particle having a smaller particle diameter than the composite oxide (A), and is a secondary particle in which a plurality of primary particles are aggregated. An example of the D50 of the composite oxide (B) is 1 to 15 μm, or 1 to 10 μm, or 2 to 7 μm. The D50 of the composite oxide (B) can be 1 / 2 or less, preferably 1 / 5 to 1 / 2, or 1 / 3 to 1 / 2 of the D50 of the composite oxide (A). By making the particle diameter of the composite oxide (B) smaller than the particle diameter of the composite oxide (A), a good contact state of each particle can be obtained, and the improvement effect of the cycle characteristics is enhanced. In addition, the BET specific surface area of the composite oxide (B) is, for example, 0.5 to 2.5 m 2 / g.

[0062] The composite oxide (B) exists in the positive electrode mixture layer 31, for example, in a state surrounded by a plurality of composite oxides (A). Also, the particle surfaces of the composite oxides (A, B) are in contact with each other. It is considered that in this case, the interaction of the composite oxides (A, B) is more effectively exhibited, and the improvement effect of the cycle characteristics is enhanced. Note that the composite oxide (B) is not limited to one intentionally added, but can be mixed as a by-product of the composite oxide (A), or an impurity of another positive electrode material.

[0063] The composite oxide (B) is produced by, for example, a first step of mixing a predetermined amount of a Li raw material and a Ni raw material to obtain a mixture, and a second step of calcining the mixture at 500 to 800°C for 10 to 30 hours. In the first step, the raw materials can be pulverized as needed, or a raw material containing the metal element Me can be added within a range in which the X-ray diffraction pattern of the composite oxide (B) satisfies the above conditions. In the second step, the mixture can be calcined after being formed into pellets, or can be subjected to a crushing process after calcination. The calcination of the second step is performed, for example, in the air or under an oxygen atmosphere.

[0064] As examples of the Li raw material, Li2CO3, LiOH, Li2O2, Li2O, LiNO3, LiNO2, Li2SO4, LiOH-H2O, LiH, LiF, and the like can be given. As examples of the Ni raw material, NiO, Ni(OH)2, NiCO3, NiSO4, Ni(NO3)2, and the like can be given. The mixing ratio of the Li raw material to the Ni raw material is adjusted, for example, so that the X-ray diffraction pattern of the composite oxide (B) satisfies the above conditions, and so that a in the above general formula satisfies the condition of 0 < a ≤ 0.5.

[0065] [Conductive agent]

[0066] As described above, the positive electrode mixture layer 31 contains a conductive agent. The conductive agent forms a good conductive path in the positive electrode mixture layer 31, and contributes to the low resistance of the positive electrode mixture layer 31. In the positive electrode mixture layer 31, a carbon nanotube (CNT) is contained as the conductive agent. In addition, in the positive electrode mixture layer 31, a particulate conductive agent such as carbon black, acetylene black, Ketjen black, graphite, and the like, a fibrous conductive agent such as vapor grown carbon fiber (VGCF), an electrospinning method carbon fiber, a polyacrylonitrile (PAN)-based carbon fiber, a pitch-based carbon fiber, graphene, and the like, and the like can be contained together with the CNT.

[0067] It is considered that the CNT forms a good conductive path in the positive electrode mixture layer 31, and connects the particles of the composite oxides (A, B) to each other, improves the surface protection effect by the composite oxide (B), and the cycle characteristics of the battery are specifically improved by coexisting the composite oxide (B) and the CNT. The content of the CNT is, for example, 0.01 to 5% by mass, more preferably 0.04 to 2% by mass, or 0.06 to 0.8% by mass, with respect to the total mass of the positive electrode mixture layer 31. If the content of the CNT is within this range, the cycle characteristics can be effectively improved. Only the CNT can be contained as the conductive agent in the positive electrode mixture layer 31.

[0068] The CNT can be any one of a single-layer CNT (SWCNT) and a multi-layer CNT (MWCNT). In addition, as the MWCNT, for example, a CNT of a tubular structure in which graphene sheets composed of carbon hexagons are rolled parallel to the fiber axis, a CNT of a platelet structure in which graphene sheets composed of carbon hexagons are arranged perpendicular to the fiber axis, a CNT of a herringbone structure in which graphene sheets composed of carbon hexagons are rolled with an inclination angle, or the like can be used. Two or more kinds of CNTs can be added to the positive electrode mixture layer 31.

[0069] The average diameter of the CNT is, for example, 50 nm or less, preferably 40 nm or less, more preferably 25 nm or less, or 20 nm or less. The lower limit of the average diameter of the CNT is not particularly limited, and is, for example, 1 nm or 5 nm. An example of the preferable range of the average diameter of the CNT is 1 to 20 nm, or 5 to 20 nm. If the average diameter of the CNT is within this range, the improvement effect on the cycle characteristics is enhanced compared to the case where a CNT having an average diameter outside this range is used.

[0070] The average fiber length of the CNT is, for example, 0.5 μm or more, preferably 0.7 μm or more, more preferably 0.8 μm or more, or 1 μm or more. The upper limit of the average fiber length of the CNT is not particularly limited, and is, for example, 10 μm or 5 μm. An example of the preferable range of the average fiber length of the CNT is 1 to 10 μm, or 1 to 5 μm. If the average fiber length of the CNT is within this range, the improvement effect on the cycle characteristics is enhanced compared to the case where a CNT having an average fiber length outside this range is used.

[0071] The average fiber length of the CNT is, for example, shorter than the length corresponding to the D50 of the composite oxide (B). Note that the average diameter of the CNT is measured from a surface TEM image of the positive electrode mixture layer 31, and the average fiber length is measured from a cross-sectional SEM image of the positive electrode mixture layer 31, 100 CNTs are respectively selected, the diameters and the fiber lengths are measured, and the measured values are averaged to obtain the average diameter and the average fiber length.

[0072]

[0073] As Figure 2 ​As shown, the negative electrode 12 has a negative electrode core 40 and a negative electrode mixture layer 41 formed on at least one face of the negative electrode core 40. A foil of copper, a copper alloy, or the like, which is stable in the potential range of the negative electrode, a film in which such a metal is disposed on the surface layer, or the like can be used in the negative electrode core 40. The negative electrode mixture layer 41 contains a negative electrode active material and a binder, and is preferably formed on both faces of the negative electrode core 40. In addition, a conductive agent such as CNT can be added to the negative electrode mixture layer 41. The negative electrode 12 can be manufactured by applying a negative electrode mixture slurry containing a negative electrode active material and a binder or the like on the negative electrode core 40, drying the coated film, and compressing the same to form the negative electrode mixture layer 41 on both faces of the negative electrode core 40.

[0074] In the negative electrode mixture layer 41, a carbon-based active material is contained as the negative electrode active material, and at least one of at least one of a metal element M3 selected from Si, Sn, Sb, Mg, and Ge (hereinafter referred to as "metal element M3") and an M3 compound containing the metal element M3 is contained. The content of the metal element M3 and the M3 compound is, for example, 0.5 to 30% by mass, or preferably 1 to 15% by mass, with respect to the total mass of the negative electrode active material.

[0075] The metal element M3 can be added to the negative electrode mixture layer 41, but the M3 compound is preferably added. As an example of the M3 compound, SiC, Sn02, a first silicon material (SiO) containing a silicon oxide phase and Si dispersed in the silicon oxide phase, a second silicon material (LSX) containing a lithium silicate phase and Si dispersed in the lithium silicate phase, a third silicon material (Si-C) containing a carbon phase and Si dispersed in the carbon phase, or the like can be listed. Among these, SiO, LSX, or Si-C is preferable.

[0076] As the carbon-based active material, for example, natural graphite such as flaky graphite, blocky artificial graphite, mesocarbon microbeads, or the like, or artificial graphite or the like can be used. The content of the carbon-based active material (graphite) is, for example, 70 to 99.5% by mass, or 85 to 99% by mass, with respect to the mass of the negative electrode active material. In addition, an example of the D50 of the carbon-based active material is 1 to 20 μm, or 2 to 15 μm. By using the carbon-based active material and the M3 compound in combination, good cycle characteristics can be maintained, and high capacity can be achieved.

[0077] SiO and LSX are, for example, particles having a D50 smaller than the D50 of graphite. An example of the D50 of SiO and LSX is 1 μm to 15 μm, or 3 μm to 10 μm. An electrically conductive layer composed of a material having high electrical conductivity can also be formed on the surface of the particles of SiO and LSX. An example of the preferable electrically conductive layer is a carbon coating film composed of a carbon material. The thickness of the electrically conductive layer is preferably 1 to 200 nm, or 5 to 100 nm, in consideration of ensuring electrical conductivity and diffusivity of lithium ions into the inside of the particles.

[0078] SiO has a particle structure in which fine Si particles are dispersed in a silicon oxide phase. A suitable SiO has an island structure in which fine Si particles are substantially uniformly dispersed in a matrix of amorphous silicon oxide, and is represented by the general formula SiO x (0 < x < 2). The silicon oxide phase is composed of a collection of particles finer than the Si particles. From the viewpoint of battery capacity and cycle characteristics, etc., the Si particle content is preferably 35 to 75 mass% relative to the total mass of SiO.

[0079] The average particle diameter of the Si particles dispersed in the silicon oxide phase is, for example, 500 nm or less, preferably 200 nm or less, or 50 nm or less, before charge and discharge. After charge and discharge, it is, for example, 400 nm or less, or 100 nm or less. The average particle diameter of the Si particles is obtained by observing the particle cross section of SiO using an SEM or a transmission electron microscope (TEM), as the average of the longest diameters of 100 Si particles.

[0080] LSX has a particle structure in which fine Si particles are dispersed in a lithium silicate phase. A suitable LSX has an island structure in which fine Si particles are substantially uniformly dispersed in a matrix of lithium silicate. The lithium silicate phase is composed of a collection of particles finer than the Si particles. The Si particle content is preferably 35 to 75 mass% relative to the total mass of LSX, as in the case of SiO. In addition, the average particle diameter of the Si particles is, for example, 500 nm or less, preferably 200 nm or less, or 50 nm or less, before charge and discharge.

[0081] The lithium silicate phase is preferably composed of a compound represented by the general formula Li 2z SiO (2+z) (0 < z < 2). That is, the lithium silicate phase does not contain Li4SiO4(Z = 2). Li4SiO4is an unstable compound, and shows alkalinity in reaction with water, and thus sometimes deteriorates Si to cause a decrease in charge and discharge capacity. From the viewpoints of stability, ease of production, lithium ion conductivity, etc., the lithium silicate phase is preferably composed mainly of Li2SiO3(Z = 1) or Li2Si2O5(Z = 1 / 2). In the case where the main component is Li2SiO3or Li2Si2O5, the content of the main component is preferably more than 50 mass% relative to the total mass of the lithium silicate phase, and more preferably 80 mass% or more.

[0082] Si-C comprises a carbon phase and silicon particles dispersed within the carbon phase. From the perspective of high capacity, the suitable silicon particle content of Si-C is preferably 30% by mass or more and 80% by mass or less, more preferably 35% by mass or more and 75% by mass or less, and more preferably 55% by mass or more and 70% by mass or less. The suitable average particle size of the silicon particles is generally 500 nm or less before charge / discharge, preferably 200 nm or less, and more preferably 100 nm or less. After charge / discharge, it is preferably 400 nm or less, and more preferably 100 nm or less. The average particle size of the silicon particles is determined by observing the cross-section of the Si-C particles using SEM or TEM, specifically as the average of the longest diameters of 100 silicon particles.

[0083] Similar to the case of the positive electrode 11, the binder contained in the negative electrode binder layer 41 can be made of fluoropolymers, PAN, polyimide, acrylic resins, polyolefins, etc., but styrene-butadiene rubber (SBR) is particularly preferred. Furthermore, the negative electrode binder layer 41 preferably also contains CMC or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. The combination of SBR with CMC or its salts, and PAA or its salts is suitable. The binder content relative to the mass of the negative electrode active material is, for example, 0.1 to 5% by mass.

[0084] <Separator>

[0085] like Figure 2 As shown, the separator 13 has a porous substrate 50 and a surface layer 51 formed on the surface of the substrate 50 facing the positive electrode 11. The surface layer 51 is a layer containing inorganic particles and a binder. The surface layer 51 may be formed on both sides of the substrate 50, but from the viewpoint of high capacity, it is preferable to form it only on one side of the substrate 50 facing the positive electrode 11. The separator 13 is a porous sheet sandwiched between the positive electrode 11 and the negative electrode 12 to prevent electrical contact between the two electrodes, and has ion permeability and insulation. The porosity of the separator 13 is, for example, 30% to 70%. It should be noted that the porosity of the separator 13 is determined by the porosity of the substrate 50.

[0086] The substrate 50 is a porous sheet made of resin. The thickness of the substrate 50 is, for example, 5 to 50 μm, more preferably 10 to 30 μm. The resin constituting the substrate 50 is not particularly limited; specific examples include polyolefins such as polyethylene, polypropylene, copolymers of ethylene and α-olefins, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polyetheretherketone, polyimide, fluoropolymers, and cellulose. The substrate 50 can be a single-layer structure or a laminated structure such as a three-layer structure of polyethylene / polypropylene / polyethylene.

[0087] The surface layer 51 is also porous like the base material 50, and has ion permeability and insulation. The thickness of the surface layer 51 is not particularly limited, and is preferably thinner than the thickness of the base material 50, for example, 0.5 to 10 μm, preferably 1 to 6 μm. The surface layer 51 is preferably in contact with the surface of the positive electrode mixture layer 31, and is formed on substantially the entire region of one surface of the base material 50. The surface layer 51 can be formed, for example, by applying a slurry containing inorganic particles and a binder to the entire surface of the base material 50, and then drying the coating film.

[0088] The surface layer 51 is a layer in which inorganic particles are the main component. The content of the inorganic particles is, for example, 70% by mass or more, preferably 80% by mass or more, with respect to the total mass of the surface layer 51. The content of the inorganic particles is preferably in the range of 70 to 99% by mass, or 80 to 98% by mass, or 85 to 95% by mass. The surface layer 51 has a function of suppressing damage to the separator 13 caused by electrically conductive foreign matter, deformation of the separator 13 at the time of abnormal heat generation, and the like. Further, it can be considered that the surface layer 51 in contact with the positive electrode 11 suppresses a side reaction of an electrolyte in the positive electrode 11 through interaction with the composite oxide (B), and that the cycle characteristics and storage characteristics of the battery are specifically improved by providing the surface layer 51.

[0089] As the inorganic particles contained in the surface layer 51, particles of metal oxides, metal nitrides, metal fluorides, metal carbides, aluminum hydroxide (boehmite), metal hydroxides such as magnesium hydroxide, metal carbonates such as calcium carbonate, magnesium carbonate, and barium carbonate, metal sulfates such as calcium sulfate, magnesium sulfate, and barium sulfate, and the like can be given. The inorganic particles can be used alone or in combination with two or more kinds. The D50 of the inorganic particles is, for example, 0.01 to 10 μm, preferably 0.05 to 5 μm.

[0090] Examples of the metal oxide are alumina (alumina), titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, manganese oxide, and the like. Examples of the metal nitride are titanium nitride, boron nitride, aluminum nitride, magnesium nitride, silicon nitride, and the like. Examples of the metal fluoride are aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, barium fluoride, and the like. Examples of the metal carbide are silicon carbide, boron carbide, titanium carbide, tungsten carbide, and the like. From the viewpoint of improving the cycle characteristics and storage characteristics, an example of the inorganic particles that is preferred is at least one selected from the group consisting of alumina, boehmite, and barium sulfate.

[0091] The binder contained in the surface layer 51 is not particularly limited as long as it can fix the inorganic particles to each other and to the base material 50, and has electrolyte resistance, and for example, the same binder as that used in the positive electrode mixture layer 31 and the negative electrode mixture layer 41 can be used. As specific examples, fluororesins such as PVdF and PTFE, PAN, and acrylic resins can be given. In addition, a resin having high heat resistance such as an aromatic polyamide resin can also be used. As an example of a preferred binder, at least one selected from the group consisting of an aromatic polyamide resin and an acrylic resin can be given.

[0092] [Non-aqueous electrolyte]

[0093] The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous solvent can use, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of them. The non-aqueous solvent can contain a halogen-substituted product obtained by substituting at least a part of hydrogen in these solvents with a halogen atom such as fluorine. As the halogen-substituted product, fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, fluorinated chain carboxylates such as fluorinated methyl propionate (FMP), and the like can be given. Note that the non-aqueous electrolyte is not limited to a liquid electrolyte, and can also be a solid electrolyte.

[0094] In the non-aqueous electrolyte, a sulfonimide salt can be contained as an electrolyte salt. In the non-aqueous electrolyte secondary battery 10 provided with the positive electrode 11 containing the composite oxide (A, B), it is considered that by adding a sulfonimide salt to the non-aqueous electrolyte, a good protective coating film is formed on the surface of the positive electrode active material particles, and the side reaction of the electrolyte at the particle surface can be suppressed, and the cycle characteristics are specifically improved. The concentration of the sulfonimide salt is preferably 0.05 to 2.5 mol / L, more preferably 0.1 to 2.0 mol / L, or 0.1 to 1.5 mol / L. If the content of the sulfonimide salt is within this range, the cycle characteristics can be more effectively improved.

[0095] The sulfonimide salt added to the non-aqueous electrolyte is preferably lithium sulfonimide. Lithium sulfonimide can be given, for example, lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(nonafluorobutanesulfonyl)imide, lithium bis(pentafluoroethanesulfonyl)imide (LIBETI), and the like. Among them, at least one lithium sulfonimide selected from the group consisting of LiFSI and lithium bis(trifluoromethanesulfonyl)imide is preferred. The sulfonimide salt can be used alone as one kind, or two or more kinds in combination.

[0096] The nonaqueous electrolyte can also contain other lithium salts. As examples of the other lithium salts, LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, chloroborane lithium, lithium lower aliphatic carboxylate, Li2B4O7, Li(B(C2O4)F2), and the like borate salts, and the like. Among them, from the viewpoints of ionic conductivity, electrochemical stability, and the like, it is preferable to use LiPF6.

[0097] In the nonaqueous electrolyte, it is preferable that lithium sulfonylimide coexist with a 2nd lithium salt. In this case, a combination of LiFSI and LiPF6is particularly preferable. The concentration of lithium sulfonylimide is adjusted to the above range, for example, also in the case where a 2nd lithium salt is contained. As a specific example, the concentration of lithium sulfonylimide is set to 0.1 to 1.5 mol / L, and the total concentration of lithium salts is set to 1.5 to 2.5 mol / L. The concentration of lithium sulfonylimide is, for example, 30 to 70% of the concentration of lithium salts contained in the nonaqueous electrolyte.

[0098] In addition, the nonaqueous electrolyte can contain vinylene carbonate (VC), ethylene sulfite (ES), cyclohexylbenzene (CHB), ortho-terphenyl (OTP), a propane sultone-based compound, and the like additive. Among them, from the viewpoint of high capacity and the like, it is preferable to add VC. The concentration of the additive is not particularly limited, and is, for example, 0.1 to 5 mass%.

[0099] As described above, esters and ethers can be used in the nonaqueous solvent. As examples of the esters, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, and the like; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, and the like; cyclic carboxylic acid esters such as γ-butyrolactone (GBL), γ-valerolactone (GVL), and the like; chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), and the like, and the like can be listed.

[0100] As examples of ethers, there can be mentioned cyclic ethers such as 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, and the like; chain ethers such as 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethylvinyl ether, butylvinyl ether, methylphenyl ether, ethylphenyl ether, butylphenyl ether, amylphenyl 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-dimethoxy methane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and the like.

[0101] (Modified example)

[0102] On the surface of the particles of the composite oxide (A), instead of the compound containing the metal element M2, other compounds such as a compound containing a lanthanoid element can be fixed. Alternatively, on the surface of the particles of the composite oxide (A), no fixed matter can substantially exist. Further, on the surface of the particles of the composite oxide (A), a composite oxide (B) having a small particle diameter can be fixed.

[0103] The positive electrode mixture layer can not contain CNT, and as the conductive agent, carbon black, acetylene black, ketjen black, graphite, or the like can be contained. Further, the negative electrode mixture layer can not contain the metal elements M3 and M3 compounds, and as the negative electrode active material, only a carbon-based active material such as graphite can be contained.

[0104] The non-aqueous electrolyte can not contain a sulfimide salt, and as the lithium salt, only LiPF6 can be contained.

[0105] Example

[0106] The present application is further illustrated by the following examples, but the present application is not limited to these examples.

[0107] Example 1

[0108] [Synthesis of composite oxide (Al)]

[0109] A composite hydroxide represented by [Ni 0.91 Co 0.04 Al 0.05 ](OH)2obtained by a coprecipitation method was calcined at 500°C for 8 hours to obtain a composite oxide (Ni 0.91 Co 0.04 Al 0.05O2) (Step 1). Next, lithium hydroxide (LiOH) and the above composite oxide were mixed so that the molar ratio of Li to the total amount of Ni, Co, and Al would be 1.02:1, to obtain a mixture. The mixture was calcined from room temperature to 650°C at a temperature increase rate of 2°C / min under an oxygen stream having an oxygen concentration of 95% (flow rate of 2 mL / min per 10 cm 3 5 L / min per 1 kg of the mixture) and from 650°C to 720°C at a temperature increase rate of 0.5°C / min. The calcined product was washed with water to remove impurities, to obtain a composite oxide (Al).

[0110] The composition of the composite oxide (Al) was analyzed by ICP, and the results were Li 0.91 Co 0.04 Al 0.05 O2. In addition, the crystal structure of the first lithium transition metal composite oxide was identified by X-ray diffraction method, and was found to belong to the space group R-3m. The D50 of the obtained composite oxide (Al) was 10 μm, which was measured using a Microtrac BEL MT3000II with water as the dispersion medium.

[0111] [Synthesis of Composite Oxide (Bl)]

[0112] Li2O and NiO were weighed so that the molar ratio of Li to Ni would be 0.3:1.7, pulverized, and mixed to prepare a mixture. Next, the mixture was calcined at 650°C for 20 hours under an oxygen atmosphere, and further crushed, to obtain a composite oxide (Bl). The powder X-ray diffraction measurement of the composite oxide (Bl) was performed using the above synchrotron radiation facility, and one peak having a peak top at 21.48° was confirmed in the range of 2θ = 21.40° to 21.65° of the obtained X-ray diffraction pattern. In addition, the composition of the composite oxide (Bl) was confirmed to be Li 0.3 Ni 1.7 O2by comparison with the JCPDS card including other peaks. The D50 of the obtained composite oxide (Bl) was 5 μm, which was measured using a Microtrac BEL MT3000II with water as the dispersion medium.

[0113] [Production of Positive Electrode]

[0114] A substance in which the composite oxide (A1, B1) is mixed at a mass ratio of 99.9:0.1 was used as the positive electrode active material. The positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVdF) were mixed at a solid content mass ratio of 92:5:3, and N-methylpyrrolidone (NMP) was added in an appropriate amount, followed by kneading to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to a positive electrode core composed of an aluminum foil, and the coated film was dried, calendered using a calender roll, cut into a prescribed electrode size, and a positive electrode in which positive electrode mixture layers were formed on both surfaces of the positive electrode core was obtained. Note that an exposed portion in which the surface of the positive electrode current collector was exposed was provided in a part of the positive electrode.

[0115] [Production of the negative electrode]

[0116] As the negative electrode active material, graphite and a substance in which SiO x (X = 1.0) were mixed at a mass ratio of 95:5. A negative electrode active material, a dispersion of styrene-butadiene rubber (SBR), and sodium carboxymethylcellulose (CMC-Na) were mixed at a solid content mass ratio of 98:1:1, and water was used as a dispersion medium to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both surfaces of a negative electrode core composed of a copper foil, the coated film was dried, compressed, and cut into a prescribed electrode size to produce a negative electrode in which negative electrode mixture layers were formed on both surfaces of the negative electrode core.

[0117] [Production of the nonaqueous electrolyte]

[0118] A nonaqueous electrolyte was produced by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were mixed at a volume ratio of 3:7 (25°C, 1 atm).

[0119] [Production of the test battery cell]

[0120] The above-described positive electrode provided with an aluminum positive electrode lead and the above-described negative electrode provided with a nickel negative electrode lead were wound into a spiral shape with the following separator in which a surface layer (coating layer) was formed on a surface facing the positive electrode interposed therebetween, and flatly shaped to produce a wound-type electrode body. The electrode body was housed in an exterior body composed of an aluminum laminate sheet, the above-described nonaqueous electrolyte was injected, and the opening portion of the exterior body was sealed to produce a test battery cell for evaluation.

[0121] [Separator]

[0122] Substrate: polyethylene substrate (thickness 10 μm)

[0123] Coating: A slurry was prepared by mixing alumina particles and aromatic polyamide resin at a solid component mass ratio of 90:10. The slurry was applied to one side of the substrate, and the coating film was dried to form a coating having a thickness of 5 μm.

[0124] Example 2

[0125] A test battery cell was produced in the same manner as in Example 1, except that the composite oxide (Al, Bl) was mixed at a mass ratio of 99.8:0.2 in the production of the positive electrode.

[0126] Example 3

[0127] A test battery cell was produced in the same manner as in Example 1, except that the composite oxide (Al, Bl) was mixed at a mass ratio of 99.7:0.3 in the production of the positive electrode.

[0128] Example 4

[0129] A test battery cell was produced in the same manner as in Example 2, except that the composite oxide (B2) was synthesized by mixing Li2O and NiO at a molar ratio of Li to Ni of 0.2:1.8.

[0130] Example 5

[0131] A test battery cell was produced in the same manner as in Example 2, except that the composite oxide (B3) was synthesized by mixing Li2O and NiO at a molar ratio of Li to Ni of 0.5:1.5.

[0132] Comparative Example 1

[0133] A test battery cell was produced in the same manner as in Example 1, except that the composite oxide (Bl) was not used in the production of the positive electrode.

[0134] Comparative Example 2

[0135] A test battery cell was produced in the same manner as in Comparative Example 1, except that a separator having no coating was used in the production of the positive electrode.

[0136] Comparative Example 3

[0137] A test battery cell was produced in the same manner as in Example 2, except that a separator having no coating was used in the production of the positive electrode.

[0138] Comparative Example 4

[0139] A test battery cell was produced in the same manner as in Example 2, except that the following composite oxide (BlO) was used instead of the composite oxide (Bl) in the production of the positive electrode.

[0140] [Synthesis of composite oxide (B10)]

[0141] Li2O and NiO were weighed so as to have a molar ratio of Li to Ni of 0.7:1.3, pulverized and mixed to prepare a mixture. Subsequently, the mixture was calcined at 650°C for 20 hours under an oxygen atmosphere, and then crushed to obtain the composite oxide (B10).

[0142] The evaluation of charge-discharge cycle characteristics and storage characteristics was performed on each of the test battery cells of the examples and comparative examples by the following methods. The evaluation results are shown in Table 1 together with the constitution of the positive electrode and the separator.

[0143] [evaluation of cycle characteristics (capacity retention rate)]

[0144] The test battery cell was subjected to constant current charging at 0.3C until the battery voltage was 4.3V, and constant voltage charging at 4.3V until the current value was 0.02C, in a temperature environment of 25°C. Then, it was subjected to constant current discharging at 0.05C until the battery voltage was 2.5V. This charge-discharge was performed for 30 cycles, and the capacity retention rate after 30 cycles was calculated based on the following equation. The capacity retention rate shown in Table 1 is a relative value when the capacity retention rate of the test battery cell of Comparative Example 1 is taken as a reference (100).

[0145] Capacity retention rate = (discharge capacity of the 30th cycle / discharge capacity of the 1st cycle) x 100

[0146] [evaluation of gas generation amount at the time of charge storage]

[0147] The test battery cell, of which the volume was measured by the Archimedes method, was subjected to initial charging (CCCV charging until the battery voltage was 4.2V) in a temperature environment of 25°C, and was left for 3 days in a temperature environment of 80°C in the charged state. The volume of the test battery cell after charge storage was measured by the Archimedes method, and the gas generation amount was calculated from the difference from the volume before initial charging. The gas generation amount shown in Table 1 is a relative value when the gas generation amount of the test battery cell of Comparative Example 1 is taken as a reference (100).

[0148] [Table 1]

[0149]

[0150] As is apparent from the results shown in Table 1, the test battery cells of the examples have higher capacity retention rates, excellent cycle characteristics, and less gas generation amount, and excellent storage characteristics, as compared with the test battery cells of the comparative examples. That is, in the case where the composite oxide (Al) and the composite oxide (B10) containing the composite oxide (Al) and the composite oxide (B10) are used as the positive electrode active material, the capacity retention rate is high, the cycle characteristics are excellent, and the gas generation amount is small, and the storage characteristics are excellent. a Ni 2-a-bMe b The positive electrode using the composite oxide (B1 to B3) represented by O2 (in the formula, 0 < a ≤ 0.5, 0 ≤ b ≤ 0.5, and Me is at least one metal element other than Li and Ni) and the separator having the coating on the surface in contact with the positive electrode can see the improvement of the cycle characteristics and the storage characteristics.

[0151] The use of the composite oxide (Al) alone as the positive electrode active material (Comparative Examples 1 and 2), the use of the separator having no coating (Comparative Examples 2 and 3), and the use of the composite oxide (B10) not satisfying the conditions of the above general formula instead of the composite oxide (B1 to B3) (Comparative Example 4) cannot obtain the improvement effect of the cycle characteristics and the storage characteristics as in the examples.

[0152] Explanation of Reference Numerals

[0153] 10 nonaqueous 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 wire, 21 negative electrode lead wire, 22 recessed portion, 23 internal terminal plate, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 cover body, 28 gasket, 30 positive electrode core body, 31 positive electrode mixture layer, 40 negative electrode core body, 41 negative electrode mixture layer, 50 base material, 51 surface layer

Claims

1. A nonaqueous electrolyte secondary battery comprising a positive electrode having a positive electrode mixture layer, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte, wherein the positive electrode mixture layer contains Li x Ni 1-y-z Co y M z O2, wherein 0.8≤x≤1.2, 0≤y≤0.2, 0 Li a Ni 2-a-b Me b O2, wherein 0 < a < 0.5, 0 < b < 0.5, and Me is at least one of Cu, Sr, Ca, Nb, and Al. the separator has a substrate and a surface layer, the surface layer containing inorganic particles and a binder and formed on a surface of the substrate facing the positive electrode side.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein The content of the second lithium transition metal complex oxide is 0.1 to 10 mass% relative to the total mass of the positive electrode mixture layer.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein The second lithium transition metal complex oxide is a complex oxide having at least one diffraction peak having a peak top at a diffraction angle 2Θ of 21.40 to 21.65° when the light energy of the synchrotron X-ray diffraction is 16 keV.

4. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein The surface layer contains, as the inorganic particles, at least one selected from the group consisting of aluminum oxide, aluminum hydroxide, and barium sulfate, The content of the inorganic particles is 85 to 95 mass% relative to the total mass of the surface layer.

5. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein The surface layer contains, as the binder, at least one selected from the group consisting of an aromatic polyamide resin and an acrylic resin.

6. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein The negative electrode contains, as a negative electrode active material, a carbon-based active material and a second active material, the second active material being at least one selected from the group consisting of at least one element selected from the group consisting of Si, Sn, Sb, Mg, and Ge and a compound containing the at least one element, The content of the second active material is 1 to 15 mass% relative to the total mass of the negative electrode active material.

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