Positive electrode active material for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery

Abstract

The positive electrode active material of one example of the embodiments contains: a first lithium transition metal composite oxide represented by the general formula Li a Ni b M1 1‑b O2(1.5 ≤ a ≤ 2.5, 0.95 ≤ b ≤ 1.00, and M1 is at least one metal element other than Li and Ni); and a second lithium transition metal composite oxide represented by the general formula Li c Ni 2‑c‑d M2 d O2(0

Description

Technical Field

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

[0002] A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, and has a structure in which they are housed in an outer package. Regarding the structure of the positive electrode, which is a main component of the non-aqueous electrolyte secondary battery, since it has a great influence on battery characteristics, many studies have been conducted on the positive electrode. For example, Patent Document 1 discloses a lithium secondary battery, which aims to improve the capacity retention rate in the initial stage of a cycle test, contains 1 to 10% by weight of Li2NiO2 as a positive electrode active material, and contains a mixture selected from Si, SiC, SiO x (0 < x < 2), Sn, SnO2, Sb, and Ge, and a carbon-based material.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent No. 6058151 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] As described in Patent Document 1, when Li2NiO2 is contained in the positive electrode, Li ions that compensate for the irreversibility of the negative electrode are supplied to the negative electrode, and a decrease in the capacity retention rate in the initial stage of the cycle test is suppressed. On the other hand, as a result of research by the present inventors, it was found that if Li2NiO2 is added to the positive electrode, the resistance increases during charge and discharge. Li2NiO2 releases Li during initial charging and changes to LiNiO2. It is considered that since LiNiO2 is highly active and easily causes side reactions with the electrolyte, the battery resistance increases. The technique of Patent Document 1 does not consider the increase in resistance during charge and discharge cycles, and there is still room for improvement.

[0008] An object of the present invention is to provide a positive electrode active material that can suppress an increase in resistance during charge and discharge cycles of a non-aqueous electrolyte secondary battery.

[0009] Solutions to the Problems

[0010] The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is characterized by containing: a general formula Li a Ni b M1 1- bA first lithium transition metal composite oxide represented by O2 (where 1.5 ≤ a ≤ 2.5, 0.95 ≤ b ≤ 1.00, and M1 is at least one metal element other than Li and Ni); and a general formula Li c Ni 2-c-d M2 d O2 (where 0 < c ≤ 0.5, 0 ≤ d ≤ 0.5, and M2 is at least one metal element other than Li and Ni), a second lithium transition metal composite oxide.

[0011] The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte containing the above positive electrode active material.

[0012] Effects of the Invention

[0013] In the non-aqueous electrolyte secondary battery using the positive electrode active material of the present invention, an increase in resistance during charge-discharge cycling can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an embodiment.

[0015] Figure 2 A view showing an enlarged part of the cross-section of an electrode body as an example of an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] In a non-aqueous electrolyte secondary battery, during initial charging and the initial stage of a cycle test, the following phenomenon was found: A part of the Li ions moving from the positive electrode to the negative electrode remained absorbed by the negative electrode active material, did not release from the negative electrode during discharge, and the capacity retention rate of the battery decreased. This phenomenon can be observed even when using a conventional carbon-based material such as graphite as the negative electrode active material, but it is particularly significant when using a material such as a Si compound. Therefore, in order to suppress the decrease in the capacity retention rate, a method of adding Li2NiO2 to the positive electrode and supplying Li ions to the positive electrode to compensate for the irreversibility of the negative electrode has been proposed. Li2NiO2 acts as a filling agent for supplying Li ions during initial charging. On the other hand, it is known that since Li2NiO2 releases Li during initial charging and changes to highly active LiNiO2, due to the side reaction between LiNiO2 and the electrolyte, deterioration and decomposition of LiNiO2 occur, and deposition of decomposition products on the negative electrode, etc., resulting in an increase in resistance.

[0017] The inventors of the present invention conducted in-depth research to solve the above problems and found that by using the above general formula Li a Ni b M1 1-b O2 and the above general formula Li c Ni 2-c-d M2 in combination, the first lithium transition metal composite oxide shown, and the above general formula Li c Ni 2-c-d M2d The second lithium transition metal composite oxide, represented by O2, specifically suppresses the rise in battery resistance. The mechanism by which these two composite oxides are used in combination to suppress the rise in resistance is not yet clear, but it is believed that the second composite oxide protects the particle surface of the first composite oxide and suppresses the side reactions between the first composite oxide and the electrolyte after Li release.

[0018] Hereinafter, with reference to the accompanying drawings, a detailed description will be provided of an example embodiment of the positive electrode active material of the present invention and a non-aqueous electrolyte secondary battery using the positive electrode active material. It should be noted that the various embodiments and modifications described below are selectively combined and also included in the present invention.

[0019] The following example illustrates a cylindrical battery in which a wound electrode body 14 is housed in a bottomed cylindrical outer casing 16. However, the outer casing of the battery is not limited to a cylindrical outer casing. For example, it can be a square outer casing (square battery), a coin-shaped outer casing (coin-shaped battery), or an outer casing composed of a laminate containing a metal layer and a resin layer (laminated battery). In addition, the electrode body can also be a laminated electrode body in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators.

[0020] Figure 1 A cross-sectional view illustrating one example of an embodiment of a non-aqueous electrolyte secondary battery 10. (See diagram below.) Figure 1 As shown, the non-aqueous electrolyte secondary battery 10 includes a wound electrode body 14, a non-aqueous electrolyte, an outer container 16 for housing the electrode body 14, and an outer container 16 for housing 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 into a spiral shape with the separator 13 in between. The outer container 16 is a bottomed cylindrical metal container with an opening on one axial side, and the opening of the outer container 16 is blocked by a sealing body 17. For ease of explanation, the side with the sealing body 17 of the battery is shown as the top, and the bottom side of the outer container 16 is shown as the bottom.

[0021] The positive electrode 11, negative electrode 12, and spacer 13 constituting the electrode body 14 are all strip-shaped elongated bodies, which are alternately stacked radially in the electrode body 14 by being wound into a vortex shape. To prevent lithium deposition, the negative electrode 12 is formed to be one size larger than the positive electrode 11. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the long side direction and the width direction (short side direction). The spacer 13 is formed to be at least one size larger than the positive electrode 11, and two sheets are arranged to clamp 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.

[0022] Insulating plates 18 and 19 are respectively disposed above and below the electrode body 14. Figure 1In the example shown, the positive lead 20 extends through the through hole in the insulating plate 18 to the sealing body 17 side, and the negative lead 21 extends through the outer side of the insulating plate 19 to the bottom side of the outer can 16. The positive lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the top plate, i.e., the cover 27, of the sealing body 17, which is electrically connected to the internal terminal plate 23, becomes the positive terminal. The negative lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 becomes the negative terminal.

[0023] As described above, the outer can 16 is a bottomed cylindrical metal container with an opening on one axial side. A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the airtightness of the battery interior and the insulation between the outer can 16 and the sealing body 17. A groove 22 is formed on the outer can 16, with a portion of its side protruding inward to support the sealing body 17. The groove 22 is preferably formed in a ring shape along the circumference of the outer can 16, and its upper surface supports the sealing body 17. The sealing body 17 is fixed to the upper part of the outer can 16 by the groove 22 and the open end of the outer can 16 riveted to the sealing body 17.

[0024] 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 cover 27 are stacked sequentially from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a circular or annular shape, and all components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected through their respective central portions, and the insulating member 25 is sandwiched between their respective peripheral portions. When the battery malfunctions and the internal pressure rises, the lower valve body 24 deforms and ruptures by pressing the upper valve body 26 towards the cover 27, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure rises further, the upper valve body 26 ruptures, and gas is released from the opening of the cover 27.

[0025] The following is for reference only. Figure 2 The positive electrode 11, negative electrode 12, separator 13, and non-aqueous electrolyte constituting the non-aqueous electrolyte secondary battery 10 are described in detail, especially the positive electrode 11. Figure 2 This is a schematic diagram showing an enlarged portion of the cross-section of the electrode body 14.

[0026] Positive electrode

[0027] like Figure 2As shown, the positive electrode 11 has a positive electrode core 30 and a positive electrode mixture layer 31 formed on at least one surface of the positive electrode core 30. The positive electrode core 30 can use foils of metals such as aluminum and aluminum alloys that are stable within the potential range of the positive electrode 11, thin films formed by disposing such metals on the surface layer, and the like. The positive electrode mixture layer 31 contains a positive electrode active material, a binder, and a conductive agent, and it is preferably formed on both surfaces of the positive electrode core 30. The positive electrode active material uses a lithium transition metal composite oxide. The positive electrode 11 can be manufactured as follows: A positive electrode mixture slurry containing a positive electrode active material, a binder, and a conductive agent is coated on the positive electrode core 30, the coating film is dried and then compressed, and the positive electrode mixture layer 31 is formed on both surfaces of the positive electrode core 30, thereby manufacturing it.

[0028] Examples of the binder contained in the positive electrode mixture layer 31 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resins, polyolefins, and the like. In addition, these resins can be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, and polyethylene oxide (PEO). The content of the binder is, for example, 0.1 to 5% by mass, or 0.5 to 3% by mass, relative to the total mass of the positive electrode mixture layer 31.

[0029] Examples of the conductive agent contained in the positive electrode mixture layer 31 include particulate conductive agents such as carbon black, acetylene black, Ketjen black, and graphite, fibrous conductive agents such as vapor-grown carbon fibers (VGCF), electrospun carbon fibers, polyacrylonitrile (PAN)-based carbon fibers, pitch-based carbon fibers, graphene, and carbon nanotubes (CNT). The content of the conductive agent is, for example, 0.01 to 5% by mass, or 0.05 to 3% by mass, relative 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 composite oxides. The first lithium transition metal composite oxide (hereinafter referred to as "composite oxide (A)") is a composite oxide represented by the general formula Li a Ni b M1 1-b O2 (where 1.5 ≤ a ≤ 2.5, 0.95 ≤ b ≤ 1.00, and M1 is at least one metal element other than Li and Ni). The second lithium transition metal composite oxide (hereinafter referred to as "composite oxide (B)") is a composite oxide represented by the general formula Li c Ni<![CDATA[ 2-c-d ]]M2 d O2 (where 0 < c ≤ 0.5, 0 ≤ d ≤ 0.5, and M2 is at least one metal element other than Li and Ni).

[0031] In the positive electrode mixture layer 31, the specific increase in resistance during initial charge and discharge is suppressed by the coexistence of the composite oxide (A, B). It is considered that the composite oxide (B) protects the particle surface of the composite oxide (A), effectively suppressing the deterioration of the particle surface, and suppressing the side reaction between the composite oxide (A) and the electrolyte. As a result, the increase in resistance is effectively suppressed. It should be noted that a strong shearing force and a compressive force can be applied to the composite oxide (B) and mixed with the composite oxide (A) for immobilization treatment on the surface of the composite oxide (A).

[0032] The above effects are achieved by adding a small amount of the composite oxide (B). However, from the perspective of maintaining a high capacity and effectively suppressing the increase in resistance, there is a preferred range for the addition amount of the composite oxide (B). With respect to the mass of the composite oxide (A, B), the content of the composite oxide (B) is preferably 0.1 to 20% by mass, more preferably 0.5 to 20% by mass, or 1 to 15% by mass, or 2 to 15% by mass. If the amount of the composite oxide (B) is within this range, the increase in resistance can be effectively suppressed.

[0033] The positive electrode mixture layer 31 preferably further contains a third lithium transition metal composite oxide (hereinafter referred to as "composite oxide (C)"). The composite oxide (C) is a composite oxide represented by the general formula Li x Ni 1-y-z Co y M3 z O2 (where 0.8 ≤ x ≤ 1.2, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.5, and M3 is at least one metal element other than Li, Ni, and Co). When the composite oxide (A, B) and the composite oxide (C) are used in combination, a non-aqueous electrolyte secondary battery 10 with a higher capacity and highly suppressed increase in resistance can be achieved.

[0034] For example, from the perspective of ensuring the battery capacity, it is preferable to add more composite oxide (C) than the composite oxide (A, B) to the positive electrode mixture layer 31. With respect to the mass of the composite oxide (A, B, C), the content of the composite oxide (A, B) is preferably 0.1 to 15% by mass, more preferably 0.5 to 15% by mass, or 1 to 15% by mass, or 1 to 10% by mass. If the amount of the composite oxide (A, B) is within this range, Li ions that fill the irreversibility of the negative electrode 12 during initial charging are sufficiently supplied from the positive electrode 11, suppressing the decrease in the capacity retention rate at the initial stage of the cycle test, and effectively suppressing the increase in resistance.

[0035] It should be noted that, without prejudice to the purpose of this invention, the positive electrode additive layer 31 may contain composite oxides other than composite oxides (A, B, C) (e.g., lithium transition metal composite oxides that do not satisfy the above general formulas). The composite oxides (A, B, C) preferably comprise 50% by mass or more relative to the total mass of the positive electrode additive layer 31. The total content of the composite oxides (A, B, C) relative to the total mass of the positive electrode additive layer 31 is, for example, 85% by mass or more, or 90% by mass or more, or 95% by mass or more. A suitable content is, for example, 90-99% by mass, or 95-99% by mass.

[0036] [First Lithium Transition Metal Composite Oxide (Composite Oxide (A))]

[0037] As described above, the composite oxide (A) is of the general formula Li a Ni b M1 1-b The composite oxide represented by O2 (where 1.5≤a≤2.5, 0.95≤b≤1.00, and M1 is at least one metallic element other than Li and Ni) has a content of metallic element M1 that is less than the content of Li and Ni, and is less than 5 mol% relative to the total molar amount of metallic elements other than Li, or it can be substantially 0 mol%. Examples of metallic element M1 include at least one selected from Cu, Sr, Ca, Nb, Si, and Al. It should be noted that the composition of the composite oxide (A) can be determined using ICP-based spectral analysis.

[0038] During initial charging, the composite oxide (A) supplies Li ions to the negative electrode 12 to compensate for the irreversibility of the negative electrode active material, thus suppressing the decrease in capacity retention during the initial stage of cycling tests. Furthermore, the composite oxide (A) may release Li during initial charging and transform into highly active LiNiO2. It is believed that side reactions between this LiNiO2 and the electrolyte lead to the degradation of the composite oxide (A), the deposition of decomposition reactants on the negative electrode 12, and an increase in battery resistance. However, the composite oxide (B) effectively suppresses this increase in resistance.

[0039] The composite oxide (A) has, for example, a crystal structure belonging to space group Immm, at least before the initial charge-discharge. Furthermore, after the initial charge-discharge, the composite oxide (A) has the general formula Li. a Ni b M1 1-bThe composition is shown in O2 (0.5≤a≤1.5). It should be noted that even after the initial charge and discharge, the composite oxide (A) releases and stores Li ions to some extent during charge and discharge, but to ensure battery capacity, it is preferable to add a composite oxide (C). The composite oxide (A) can contain various composite oxides with similar compositions, or it can contain compounds that do not satisfy the above general formula, such as Li2O and NiO.

[0040] Composite oxides (A) are, for example, secondary particles formed by the aggregation of multiple primary particles. The median particle size (D50) of composite oxides (A) on a volumetric basis is, for example, 1–15 μm, or 1–10 μm. D50 refers to the particle size at which the frequency accumulates to 50% from the smallest particle size in the volumetric particle size distribution; it is also called the median diameter. The particle size distribution of secondary particles of composite oxides can be determined using a laser diffraction-based particle size distribution measuring device (e.g., MicrotracBEL MT3000II) with water as the dispersion medium.

[0041] The particle size of the primary particles of the composite oxide (A) is, for example, 0.05 μm to 1 μm. The particle size of the primary particles is determined as the diameter of the circumcircle in a cross-sectional image of the secondary particles observed by scanning electron microscopy (SEM). Furthermore, the BET specific surface area of ​​the composite oxide (A) is, for example, 0.5 to 2.5 m². 2 / g. BET specific surface area was determined according to the BET method (nitrogen adsorption method) as described in JIS R1626.

[0042] In the positive electrode additive layer 31, the composite oxide (B) exists, for example, surrounded by multiple composite oxides (A). Furthermore, the particle surfaces of the composite oxides (A, B) are in contact with each other. It is believed that in this case, the interaction between the composite oxides (A, B) is more effectively manifested, improving the suppression effect of resistance rise. It should be noted that the composite oxide (B) is not limited to intentionally added substances; it can be incorporated as a byproduct of other composite oxides or as an impurity in other positive electrode materials.

[0043] The composite oxide (A) is manufactured, for example, via the following steps: Step 1, in which a specified amount of Li raw material and Ni raw material are mixed to obtain a mixture; Step 2, in which the mixture is calcined at 500°C to 800°C for 10 to 30 hours. In Step 1, the raw material may be pulverized as needed, or a raw material containing the metal element M1 may be added within the range satisfying the above general formula. Furthermore, in Step 2, the mixture may be shaped into granules before calcination, or it may be crushed after calcination. The calcination in Step 2 is, for example, carried out in an inert gas atmosphere such as nitrogen.

[0044] As an example of the Li raw material, Li2CO3, LiOH, Li2O2, Li2O, LiNO3, LiNO2, Li2SO4, LiOH·H2O, LiH, LiF, etc. can be cited. As an example of the Ni raw material, NiO, Ni(OH)2, NiCO3, NiSO4, Ni(NO3)2, etc. can be cited. As the M1 raw material, for example, oxides, hydroxides, carbonates, nitrates, sulfates, etc. of M1 can be cited. The mixing ratio of each raw material can be adjusted so that the composition of the composite oxide (A) satisfies the above general formula. For example, Li2O and NiO are mixed so that the molar ratio of Li to Ni is 2 to 2.1, thereby obtaining Li2NiO2.

[0045] As described above, the composite oxide (A) may contain Li2O and NiO. For example, when Li2O and NiO are used as raw materials, they may be contained as unreacted components in the composite oxide (A). In addition, when the composite oxide (A) and N-methylpyrrolidone (NMP) are mixed at a mass ratio of 0.1:20, stirred and stored at room temperature for 24 hours, the amount of Li extracted in NMP is preferably 100 μmol / g or less. By this method, the amount of Li present in a state that can be easily extracted by NMP in the composite oxide (A) can be measured. When the amount of Li extracted in NMP exceeds 100 μmol / g, the properties of the positive electrode mixture slurry may deteriorate.

[0046] [Second lithium transition metal composite oxide (composite oxide (B))]

[0047] As described above, the composite oxide (B) is Li c Ni 2-c-d M2 d O2 (where 0 < c ≤ 0.5, 0 ≤ d ≤ 0.5, and M2 is at least one metal element other than Li and Ni) of the composite oxide. The content of the metal element M2 is preferably less than the contents of Li and Ni. For example, it is 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 M2, at least one selected from Cu, Sr, Ca, Nb, Si, and Al can be cited.

[0048] For the composite oxide (B), no Li release or storage occurs during charging and discharging, and its composition remains unchanged. When such a composite oxide (B) is used in combination with the composite oxide (A), it specifically suppresses the rise in battery resistance. The composite oxide (B) can contain multiple composite oxides with similar compositions. In the above general formula, c is more preferably 0.1 ≤ c ≤ 0.5, or 0.2 ≤ c ≤ 0.4. If c is within this range, the rise in resistance is suppressed more effectively. It should be noted that the composition of the composite oxide (B) can be identified by X-ray diffraction patterns or analyzed using ICP emission spectrophotometry.

[0049] The composite oxide (B) is, for example, a composite oxide having at least one diffraction peak with a apex at a diffraction angle (2θ) of 21.40° to 21.65° in synchrotron X-ray diffraction (light energy 16 keV). This diffraction peak may have a apex within the range of 2θ = 21.40° to 21.65°, or it may be a broad peak where none of the peaks exist within this range. In the X-ray diffraction pattern of the composite oxide (B), for example, a apex exists within the range of 2θ = 21.40° to 21.65°.

[0050] The X-ray diffraction pattern of the composite oxide (B) was obtained by powder X-ray diffraction under the following conditions using a synchrotron radiation facility (optical path BL5S2 of the Aichi Synchrotron Radiation Center).

[0051] Light energy: 16keV

[0052] Scanning range: 10–90°

[0053] Analyzing optical system: Debye-Scherrer type

[0054] The obtained data were analyzed using the PDXL (Rigaku Corporation) identification software to locate peaks and identify the composite oxide (B). In measurements using the aforementioned apparatus, NiO exhibited a peak at 21.36°, shifting towards higher angles as the value of 'c' in the above formula increased. If 'c' in the above formula falls within the specified range, a main peak exists between 21.40° and 21.65°. The composite oxide (B) could be identified by comparison with a JCPDS card that included other peaks.

[0055] The composite oxide (B) is, for example, a secondary particle formed by the aggregation of multiple primary particles, with a particle size smaller than that of the composite oxide (A). An example of the D50 of the composite oxide (B) is 1–15 μm, or 1–10 μm, or 2–7 μm. By making the particle size of the composite oxide (B) smaller than that of the composite oxide (A), good contact between the particles can be obtained, improving the suppression effect of resistance rise. Furthermore, the BET specific surface area of ​​the composite oxide (B) is, for example, 0.5–2.5 m². 2 / g.

[0056] For the composite oxide (B), in the positive electrode mixture layer 31, it exists, for example, in a state surrounded by a plurality of composite oxides (A). Moreover, the particle surfaces of the composite oxides (A, B) are in contact with each other. In this case, it is considered that the interaction of the composite oxides (A, B) is more effectively exhibited, and the effect of suppressing the increase in resistance is improved. It should be noted that the composite oxide (B) is not limited to a deliberately added substance, and may be mixed as a by-product of other composite oxides or an impurity of other positive electrode materials.

[0057] The composite oxide (B) is manufactured, for example, through the following processes: a first process of mixing a specified amount of a Li raw material and a Ni raw material to obtain a mixture; a second process of firing the mixture at 500 to 800°C for 10 to 30 hours. In the first process, the raw materials can be pulverized as needed, and a raw material containing a metal element M2 can also be added within the range where the X-ray diffraction pattern of the composite oxide (B) satisfies the above conditions. In addition, in the second process, the mixture can be formed into pellets and then fired, or it can be subjected to a crushing process after firing. The firing in the second process is carried out, for example, in the atmosphere or an oxygen atmosphere.

[0058] As an example of the Li raw material, Li2CO3, LiOH, Li2O2, Li2O, LiNO3, LiNO2, Li2SO4, LiOH·H2O, LiH, LiF, etc. can be cited. As an example of the Ni raw material, NiO, Ni(OH)2, NiCO3, NiSO4, Ni(NO3)2, etc. can be cited. The mixing ratio of the Li raw material and the Ni raw material is adjusted, for example, in such a way that the X-ray diffraction pattern of the composite oxide (B) satisfies the above conditions and the c in the above general formula satisfies the condition of 0 < c ≤ 0.5.

[0059] [The third lithium transition metal composite oxide (composite oxide (C))]

[0060] The composite oxide (C) is the above general formula Li x Ni 1-y-z Co y M3 zA composite oxide represented by O2 (where 0.8 ≤ x ≤ 1.2, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.5, and M3 is at least one metal element other than Li, Ni, and Co) contains at least one metal element M3 other than Li, Ni, and Co as an essential constituent element. In addition, the composite oxide (C) preferably contains Co. However, Co is particularly scarce and expensive, so the composite oxide (C) may substantially not contain Co. When the composite oxide (C) contains Co, the Co content is 20 mol% or less, more preferably 0.1 to 10 mol%, or 0.5 to 5 mol%, relative to the total molar amount of metal elements other than Li. It should be noted that the molar ratio of metal elements in the composite oxide can be determined by inductively coupled plasma (ICP) optical emission spectrometry.

[0061] For the composite oxide (C), among the metal elements other than Li, the content of Ni is preferably the highest. The Ni content 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 metal elements other than Li. A suitable example of the Ni content is 80 to 97 mol%, or 85 to 95 mol%. That is, a suitable example of (1 - y - z) representing the Ni content in the above general formula is 0.80 ≤ (1 - y - z) ≤ 0.97, or 0.85 ≤ (1 - y - z) ≤ 0.95.

[0062] As described above, a suitable example of the composite oxide (C) is a composite oxide containing 80 mol% or more of Ni relative to the total molar amount of metal elements other than Li. By increasing the proportion of Ni in the metal elements of the composite oxide (C), high capacity of the battery can be achieved. In addition, the Ni-rich composite oxide (C) has good compatibility with the composite oxide (B), and is also effective from the perspective of improving the cycle characteristics. X representing the Li content in the above general formula is 0.8 ≤ x ≤ 1.2, or 0.97 ≤ x ≤ 1.2, and the composite oxide (C) can be a lithium-excess type composite oxide with a molar ratio of Li to transition metals exceeding 1.

[0063] The composite oxide (C) contains at least one metallic element M3 other than Li, Ni, and Co. The metallic element M3 is, for example, selected from at least one of Mn, W, Mg, Mo, Nb, Ti, Si, Al, Zr, B, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, and Ca, more preferably selected from at least one of Mn, W, Mg, Mo, Nb, Ti, Si, Sr, Ca, and Al. Preferably, it contains at least one of Mn and Al. The content of metallic element M3, when there are multiple elements, is the total amount, and is less than 50 mol% relative to the total molar amount of metallic elements other than Li, more preferably 0.1–20 mol%, or 0.5–10 mol%, or 1–5 mol%.

[0064] The composite oxide (C) has, for example, a crystal structure belonging to space group R3-m. Furthermore, the composite oxide (C) has a layered structure comprising a transition metal layer, a Li layer, and an oxygen layer. In this case, the composite oxide (A,B) functions more effectively, maintaining a stable crystal structure even with repeated charge-discharge cycles. The composite oxide (C) is, for example, a secondary particle formed by the aggregation of multiple primary particles. An example of the D50 of the composite oxide (C) is 3–20 μm, or 5–15 μm. The particle size of the primary particles of the composite oxide (C) is, for example, 0.05 μm–1 μm. Furthermore, the BET specific surface area of ​​the composite oxide (C) is, for example, 0.2–2.0 m². 2 / g.

[0065] Furthermore, a compound containing at least one of Sr, Ca, W, Mg, Nb, and Al (hereinafter referred to as "metal element M4") may be immobilized on the particle surface of the composite oxide (C). The M4 compound containing metal element M4 may exist as dots on the particle surface of the composite oxide (C) or as a layer covering the entire particle surface. The thickness of the M4 compound layer is, for example, 0.1–5 nm. It is believed that the M4 compound protects the surface of the composite oxide (C) and also the surface of the composite oxides (A, B), thereby suppressing electrolyte side reactions on the particle surface of the composite oxides (A, B, C).

[0066] M4 compounds are oxides, hydroxides, or carbonates. Specific examples of M4 compounds include SrO, CaO, Sr(OH)₂, Ca(OH)₂, SrCO₃, and CaCO₃. The amount of M4 compound relative to the total molar amount of the metal elements other than Li constituting the complex oxide (C) is, for example, 0.05–0.5 mol% when converted to the metal element M4. The presence of M4 compounds can be confirmed by energy-dispersive X-ray spectroscopy (TEM-EDX). Furthermore, for the metal element M4, a solution of the complex oxide (C) dissolved in fluorinated nitric acid can be determined using ICP-N spectroscopy.

[0067] The composite oxide (C) is manufactured, for example, through the following steps: a first step to obtain a composite oxide containing the metal element M3, etc.; a second step to mix the composite oxide with a Li raw material to obtain a mixture; and a third step to calcine the mixture. When fixing the M4 compound onto the surface of the composite oxide (C) particles, a raw material containing the metal element M4 (hereinafter referred to as "M4 raw material") may be added in the second step. The composition, particle size, BET specific surface area, etc., of the composite oxide (C) and the M4 compound can be adjusted by controlling the mixing ratio of the raw materials and the calcination conditions in the third step.

[0068] In the first step, for example, while stirring a solution of a metal salt containing metal elements such as Ni and M3, an alkaline solution such as sodium hydroxide is added dropwise to adjust the pH towards the alkaline side (e.g., 8.5–12.5), thereby causing the composite hydroxide containing the metal elements to precipitate (co-precipitate). Then, by calcining this composite hydroxide, a composite oxide containing Ni, M3, etc., is obtained. There are no particular limitations on the calcination temperature; for example, it is 300–600°C.

[0069] In the second step, the composite oxide obtained in the first step, the Li raw material, and the required M4 raw material are mixed to obtain a mixture. Examples of Li raw materials include Li₂CO₃, LiOH, Li₂O₂, Li₂O, LiNO₃, LiNO₂, Li₂SO₄, LiOH·H₂O, LiH, and LiF. Examples of M4 raw materials include oxides, hydroxides, carbonates, nitrates, and sulfates of M4. The mixing ratio of the composite oxide obtained in the first step to the Li raw material is adjusted, for example, by a molar ratio of metal elements other than Li to Li of 1:0.98 to 1:1.22. Furthermore, the mixing ratio of the composite oxide to the M4 raw material is adjusted, for example, by a molar ratio of metal elements other than Li to M4 of 1:0.0005 to 1:0.005.

[0070] In the third step, the mixture obtained in the second step is fired at a specified temperature and time to obtain a fired product. The firing of the mixture may be carried out, for example, through multi-stage firing, which includes: a first firing step, firing in a firing furnace under an oxygen flow at a first heating rate to a first set temperature of 450°C or higher and 680°C or lower; and a second firing step, after the first firing step, firing in a firing furnace under an oxygen flow at a second heating rate to a second set temperature of 680°C or higher and 800°C or lower. The first heating rate is 1.5–5.5°C / min, and the second heating rate is slower than the first heating rate, and can be 0.1–3.5°C / min. It should be noted that multiple heating rates can be set in each firing step.

[0071] The holding time of the first set temperature in the first firing process is, for example, 0 to 5 hours, or 0 to 3 hours. It should be noted that the holding time of the set temperature refers to the time spent maintaining the set temperature after it has been reached. The holding time of the second set temperature in the second firing process is, for example, 1 to 10 hours, or 1 to 5 hours. The firing of the mixture is carried out in an oxygen flow with an oxygen concentration of 60% or higher, and the firing furnace is per 10 cm... 3 The oxygen flow rate can be 0.2–4 mL / min, and the flow rate of oxygen per 1 kg of the mixture can be 0.3 L / min or higher. For the calcined product, impurities can be removed by washing with water, dehydration, and drying.

[0072] It should be noted that M4 material may not be added in the second step, but may be added in the third step, during washing of the calcined product, or during drying. For example, heat treatment at 150-400°C for 0.5-15 hours in a vacuum atmosphere may be performed to fix the M4 compound on the particle surface of the composite oxide (C).

[0073] <Negative electrode>

[0074] like Figure 2 As shown, the negative electrode 12 has a negative electrode core 40 and a negative electrode binder layer 41 formed on at least one surface of the negative electrode core 40. The negative electrode core 40 can be a foil of a metal that is stable within the potential range of the negative electrode, such as copper or a copper alloy, or a thin film with the metal disposed on the surface. The negative electrode binder layer 41 contains a negative electrode active material and a binder, and it is preferred to form it on both surfaces of the negative electrode core 40. In addition, a conductive agent can be added to the negative electrode binder layer 41. The negative electrode 12 can be manufactured by coating a negative electrode binder slurry containing a negative electrode active material and a binder onto the negative electrode core 40, drying the coating film, and then compressing it to form the negative electrode binder layer 41 on both surfaces of the negative electrode core 40.

[0075] In the negative electrode mixture layer 41, a carbon-based active material is included as the negative electrode active material, and at least one metal selected from Si, Sn, Sb, Mg, and Ge (hereinafter referred to as "metal element M5") and at least one of M5 compounds containing the metal element M5 are included. With respect to the total mass of the negative electrode active material, the content of the metal element M5 and the M5 compound is, for example, 0.5 to 30% by mass, preferably 1 to 15% by mass.

[0076] The metal element M5 can be added to the negative electrode mixture layer 41, but it is preferred to add the M5 compound. As an example of the M5 compound, SiC, SnO2, 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, etc. can be cited. Among them, SiO, LSX, or Si-C is preferred.

[0077] The carbon-based active material can be, for example, natural graphite such as flake graphite, massive artificial graphite, graphitized mesophase carbon microspheres, etc. artificial graphite. With respect to the mass of the negative electrode active material, the content of the carbon-based active material (graphite) is, for example, 70 to 99.5% by mass, or 85 to 99% by mass. 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 in combination with the M5 compound, high capacity can be achieved while maintaining good cycle characteristics.

[0078] SiO and LSX are, for example, particles with a D50 smaller than that of graphite. An example of the D50 of SiO and LSX is 1 μm to 15 μm, or 3 μm to 10 μm. A conductive layer composed of a material with high conductivity can be formed on the surface of the SiO and LSX particles. An example of a suitable conductive layer is a carbon coating composed of a carbon material. Considering the ensuring of conductivity and the diffusibility of Li ions into the particle interior, the thickness of the conductive layer is preferably 1 to 200 nm, or 5 to 100 nm.

[0079] SiO has a particle structure in which fine Si particles are dispersed in a silicon oxide phase. 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 an aggregate of particles finer than the Si particles. From the viewpoint of balancing battery capacity and cycle characteristics, the content ratio of the Si particles with respect to the total mass of SiO is preferably 35 to 75% by mass.

[0080] The average particle diameter of Si particles dispersed in the silica phase is, for example, 500 nm or less before charge-discharge, preferably 200 nm or less, or 50 nm or less. After charge-discharge, it is, for example, 400 nm or less, or 100 nm or less. For the average particle diameter of Si particles, the particle cross-section of SiO is observed using SEM or a transmission electron microscope (TEM), and the average value of the longest diameters of 100 Si particles is obtained (the same applies to LSX and Si-C).

[0081] LSX has a particle structure in which fine Si particles are dispersed in the lithium silicate phase. Suitable LSX has a sea-island structure in which fine Si particles are dispersed substantially uniformly in the matrix of lithium silicate. The lithium silicate phase is composed of an aggregate of particles finer than Si particles. Similarly to the case of SiO, the content of Si particles is preferably 35 to 75% by mass relative to the total mass of LSX. In addition, the average particle diameter of Si particles is, for example, 500 nm or less before charge-discharge, preferably 200 nm or less, or 50 nm or less.

[0082] The lithium silicate phase preferably consists of a compound represented by the general formula Li 2z SiO (2+z) (0 < z < 2). That is, Li4SiO4 (Z = 2) is not contained in the lithium silicate phase. Li4SiO4 is an unstable compound, reacts with water to show alkalinity, and sometimes causes Si to deteriorate, resulting in a decrease in charge-discharge capacity. From the viewpoints of stability, ease of production, and lithium ion conductivity, the lithium silicate phase preferably has Li2SiO3 (Z = 1) or Li2Si2O5 (Z = 1 / 2) as the main component. When Li2SiO3 or Li2Si2O5 is the main component, the content of this main component is preferably more than 50% by mass, more preferably 80% by mass or more, relative to the total mass of the lithium silicate phase.

[0083] Si-C has a carbon phase and silicon particles dispersed in the carbon phase. From the viewpoint of achieving high capacity, etc., the content of silicon particles in suitable Si-C is preferably 30% by mass or more and 80% by mass or less, preferably 35% by mass or more and 75% by mass or less, more preferably 55% by mass or more and 70% by mass or less. The average particle diameter of suitable silicon particles is generally 500 nm or less before charge-discharge, preferably 200 nm or less, more preferably 100 nm or less. After charge-discharge, it is preferably 400 nm or less, more preferably 100 nm or less.

[0084] The binder included in the negative electrode binder layer 41 can be the same as that in the case of the positive electrode 11, using fluoropolymers, PAN, polyimide, acrylic resins, polyolefins, etc., but styrene-butadiene rubber (SBR) is particularly preferred. Furthermore, the negative electrode binder layer 41 preferably contains CMC or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. It is suitable to use SBR in combination with CMC or its salts, and PAA or its salts. The binder content is, for example, 0.1 to 5% by mass relative to the mass of the negative electrode active material.

[0085] <Separator>

[0086] 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 can 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 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.

[0087] 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, but 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.

[0088] The surface layer 51, like the substrate 50, is porous, exhibiting ion permeability and insulation. The thickness of the surface layer 51 is not particularly limited, but it is preferably thinner than the substrate 50, for example, 0.5–10 μm, more preferably 1–6 μm. It is preferable that the surface layer 51 is in contact with the surface of the positive electrode binder layer 31 and is formed over approximately the entire area of ​​one side of the substrate 50. The surface layer 51 can be formed, for example, by coating the entire surface of the substrate 50 with a slurry containing inorganic particles and a binder, followed by drying.

[0089] The surface layer 51 is a layer with inorganic particles as the main component. The content of inorganic particles relative to the total mass of the surface layer 51 is, for example, 70% by mass or more, preferably 80% by mass or more. Suitable ranges for the content of inorganic particles are 70-99% by mass, 80-98% by mass, or 85-95% by mass. The surface layer 51 has the function of suppressing damage to the separator 13 caused by conductive foreign matter and deformation of the separator 13 during abnormal heating. Furthermore, it is believed that the surface layer 51, which is in contact with the positive electrode 11, suppresses side reactions of the electrolyte on the positive electrode 11 caused by interaction with the composite oxide (B). By providing the surface layer 51, the cycle characteristics and storage characteristics of the battery are specifically improved.

[0090] Examples of inorganic particles included in the surface layer 51 include metal oxides, metal nitrides, metal fluorides, metal carbides, aluminum hydroxide (boehmite), magnesium hydroxide and other metal hydroxides, calcium carbonate, magnesium carbonate, barium carbonate and other metal carbonates, calcium sulfate, magnesium sulfate, barium sulfate and other metal sulfates. One type of inorganic particle can be used alone, or two or more types can be used in combination. The D50 of the inorganic particles is, for example, 0.01–10 μm, preferably 0.05–5 μm.

[0091] Examples of metal oxides include aluminum oxide (bauxite), titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, and manganese oxide. Examples of metal nitrides include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, and silicon nitride. Examples of metal fluorides include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, and barium fluoride. Examples of metal carbides include silicon carbide, boron carbide, titanium carbide, and tungsten carbide. From the viewpoint of improving recycling and preservation characteristics, a suitable inorganic particle is selected from at least one of bauxite, boehmite, and barium sulfate.

[0092] The binder included in the surface layer 51 is not particularly limited as long as it is a material capable of fixing inorganic particles to each other and to the substrate 50, and possessing electrolyte resistance. For example, the same material used in the positive electrode binder layer 31 and the negative electrode binder layer 41 can be used. Specific examples include fluoropolymers such as PVdF and PTFE, PAN, and acrylic resins. Furthermore, resins with high heat resistance, such as aromatic amide resins, can also be used. As a suitable binder, at least one selected from aromatic amide resins and acrylic resins can be used.

[0093] Non-aqueous electrolytes

[0094] The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these can be used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine. Examples of the halogen-substituted product include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP). It should be noted that the non-aqueous electrolyte is not limited to a liquid electrolyte and may also be a solid electrolyte.

[0095] In the non-aqueous electrolyte, a sulfonylimide salt is contained as the electrolyte salt. In the non-aqueous electrolyte secondary battery 10 having a positive electrode 11 containing a composite oxide (A, B) or a composite oxide (A, B, C), by adding a sulfonylimide salt to the non-aqueous electrolyte, it is considered that a good protective film is formed on the surface of the particles of the positive electrode active material, suppressing side reactions of the electrolyte on the particle surface, and specifically improving the cycle characteristics. The concentration of the sulfonylimide 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. When the content of the sulfonylimide salt is within this range, the cycle characteristics can be improved more effectively.

[0096] The sulfonylimide salt added to the non-aqueous electrolyte is preferably lithium sulfonylimide. Examples of lithium sulfonylimide include lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide, lithium bis(nonafluorobutanesulfonyl)imide, lithium bis(pentafluoroethanesulfonyl)imide (LIBETI), etc. Among them, at least one lithium sulfonylimide selected from LiFSI and lithium bis(trifluoromethylsulfonyl)imide is preferred. The sulfonylimide salt can be used alone or in combination of two or more.

[0097] In the non-aqueous electrolyte, other lithium salts can further be contained. Examples of other lithium salts include 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, lithium chloroborane, lithium lower aliphatic carboxylic acid, borate salts such as Li2B4O7, Li(B(C2O4)F2), etc. Among them, from the viewpoints of ionic conductivity, electrochemical stability, etc., LiPF6 is preferably used.

[0098] In the non-aqueous electrolyte, lithium sulfonamide and a second lithium salt are preferably coexisting. In this case, a combination of LiFSI and LiPF6 is particularly preferred. When a second lithium salt is present, the concentration of lithium sulfonamide is also adjusted to, for example, the range described above. As a specific example, the concentration of lithium sulfonamide is set to 0.1 to 1.5 mol / L, and the total concentration of the lithium salt is set to 1.5 to 2.5 mol / L. The concentration of lithium sulfonamide is, for example, 30 to 70% of the concentration of lithium salts contained in the non-aqueous electrolyte.

[0099] In addition, non-aqueous electrolytes may contain additives such as vinylene carbonate (VC), ethylene sulfite (ES), cyclohexylbenzene (CHB), o-terphenyl (OTP), and propanesulfonic acid lactone compounds. Among these, VC is preferred for increasing capacity. The concentration of the additives is not particularly limited, but is typically 0.1% to 5% by mass.

[0100] As mentioned above, non-aqueous solvents can include esters and ethers. Examples of esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butyl 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).

[0101] Examples of ethers include 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-eucalyptol, crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, and ethyl ethyl ether. Alkenyl ethers, butyl vinyl ethers, methyl phenyl ethers, ethyl phenyl ethers, butyl phenyl ethers, pentyl phenyl ethers, methoxytoluene, benzyl ethyl ethers, diphenyl ethers, dibenzyl ethers, 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, tetraethylene glycol dimethyl ether, and other chain ethers.

[0102] Example

[0103] The present invention will be further described below through embodiments, but the present invention is not limited to these embodiments.

[0104] (Experimental Example 1)

[0105] <Example 1>

[0106] [Synthesis of composite oxide (Al)]

[0107] Li₂O and NiO were weighed at a Li:Ni molar ratio of 2.05:1, pulverized, and mixed to prepare a mixture. This mixture was then calcined at 650°C for 20 hours under a nitrogen atmosphere, and further pulverized to obtain a composite oxide (A₁). The composite oxide (A₁) contained Li₂NiO₂, Li₂O, and NiO, and its crystal structure was identified as belonging to space group Immm by X-ray diffraction. When the composite oxide (A₁) was mixed with NMP at a mass ratio of 0.1:20, stirred, and stored at room temperature for 24 hours, the amount of Li extracted by NMP was 87 μmol / g. The D₅₀ of the composite oxide (A₁) was determined to be 10 μm using a MicrotracBEL MT3000II with water as the dispersion medium (the same method applies below).

[0108] [Synthesis of composite oxide (B1)]

[0109] Li₂O and NiO were weighed at a Li:Ni molar ratio of 0.3:1.7, pulverized, and mixed to prepare a mixture. This mixture was then calcined at 650°C for 20 hours under an oxygen atmosphere, and further pulverized to obtain a composite oxide (B₁). X-ray diffraction analysis of the composite oxide (B₁) using the aforementioned synchrotron radiation facility revealed a single peak at 21.48° within the range of 2θ = 21.40° to 21.65° of the obtained X-ray diffraction pattern. Furthermore, comparison with a JCPDS card containing other peaks confirmed that the composite oxide (B₁) consisted of Li. 0.3 Ni 1.7 O2. The D50 of the composite oxide (B1) is 5 μm.

[0110] [The production of the positive electrode]

[0111] A composite oxide (Al, B1) mixed in a mass ratio of 95:5 is used as the positive electrode active material. The positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVdF) are mixed in a solid component mass ratio of 92:5:3, and an appropriate amount of NMP is added. The mixture is then kneaded to prepare a positive electrode slurry. This positive electrode slurry is coated onto a positive electrode core made of aluminum foil. After the coating dries, it is rolled using rolling mills and cut into specified electrode sizes, resulting in a positive electrode with positive electrode slurry layers formed on both sides of the positive electrode core. It should be noted that a portion of the positive electrode has an exposed portion that protrudes from the surface of the positive electrode core.

[0112] [Preparation of non-aqueous electrolytes]

[0113] A non-aqueous electrolyte was prepared by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent consisting of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 (25°C, 1 atmosphere).

[0114] [Fabrication of the Experimental Battery Cell]

[0115] As the negative electrode, a Li foil cut to a specified size is used. An aluminum lead is installed on the exposed portion of the fabricated positive electrode, and a nickel lead is installed at a specified position on the negative electrode. The positive and negative electrodes are positioned opposite each other using a polyolefin separator to form an electrode body. This electrode body is then housed within an outer casing, and after injecting the prepared non-aqueous electrolyte, the opening of the outer casing is sealed to obtain the experimental battery cell.

[0116] <Example 2>

[0117] In the fabrication of the positive electrode, the composite oxides (Al, B1) were mixed at a mass ratio of 98:2. Otherwise, the test cell was fabricated in the same manner as in Example 1.

[0118] <Example 3>

[0119] In the fabrication of the positive electrode, the composite oxides (A1, B1) were mixed at a mass ratio of 90:10. Otherwise, the test cell was fabricated in the same manner as in Example 1.

[0120] <Example 4>

[0121] In the fabrication of the positive electrode, the composite oxides (Al, B1) were mixed at a mass ratio of 85:15. Otherwise, the test cell was fabricated in the same manner as in Example 1.

[0122] <Example 5>

[0123] Li₂O and NiO were mixed in a molar ratio of Li to Ni of 0.2:1.8 to synthesize a composite oxide (B₂). Otherwise, experimental battery cells were fabricated in the same manner as in Example 1.

[0124] <Example 6>

[0125] Li₂O and NiO were mixed in a molar ratio of Li to Ni of 0.5:1.5 to synthesize a composite oxide (B₃). Otherwise, experimental battery cells were fabricated in the same manner as in Example 1.

[0126] <Comparative Example 1>

[0127] In the fabrication of the positive electrode, composite oxide (B1) is not used. Otherwise, the test cell is fabricated in the same manner as in Example 1.

[0128] <Comparative Example 2>

[0129] In the fabrication of the positive electrode, the following composite oxide (B10) is used instead of the composite oxide (B1), and otherwise the test cell is fabricated in the same manner as in Example 1.

[0130] [Synthesis of composite oxide (B10)]

[0131] Li₂O and NiO were weighed in a Li:Ni molar ratio of 0.7:1.3, pulverized and mixed to prepare a mixture. The mixture was then calcined at 650°C for 20 hours under an oxygen atmosphere and further crushed to obtain a composite oxide (B₁₀).

[0132] <Comparative Example 3>

[0133] In the fabrication of the positive electrode, nickel oxide (B11) was used instead of composite oxide (B1), and otherwise the test cell was fabricated in the same manner as in Example 1.

[0134] For each test battery cell in the Examples and Comparative Examples, the resistance rise rate was evaluated using the following method. The evaluation results are shown in Table 1 along with the configuration of the positive electrode. The resistance values ​​shown in Table 1 are relative to the resistance rise rate (100) of the test battery cell in Comparative Example 1.

[0135] [Evaluation of resistance rise rate]

[0136] Using the HIOKI BT3562 battery tester (measuring source frequency: 1kHz), the resistance after one cycle and the resistance after 15 cycles of the following cyclic test were determined, and the rate of increase in resistance was calculated using the following formula.

[0137] Resistance rise rate = (Resistance after 15 cycles - Resistance after 1 cycle) / (Resistance after 1 cycle)

[0138] <Cyclic Test>

[0139] At 25°C, the test battery cell was charged at a constant current of 0.3C to a battery voltage of 4.3V, and then charged at a constant voltage of 4.3V to a current of 0.02C. Afterward, it was discharged at a constant current of 0.05C to a battery voltage of 2.5V. This charge-discharge cycle was repeated 15 times.

[0140] [Table 1]

[0141]

[0142] As can be seen from the results shown in Table 1, the resistance rise of the test battery cells in the embodiments was suppressed to a lower level compared to the test battery cells in the comparative examples after 15 cycles. In other words, the resistance rise of the battery was specifically suppressed when using a positive electrode containing composite oxide (A1) and composite oxide (B1 to B3).

[0143] In the cases where composite oxide (A1) is used alone (Comparative Example 1), in the cases where composite oxide (B10) is used instead of composite oxide (B1-B3) and does not satisfy the above general formula (Comparative Example 2), and in the cases where nickel oxide (B11) is used (Comparative Example 3), the resistance rise suppression effect as in the examples cannot be obtained. Furthermore, it is evident that using oxides such as B10 and B11 in combination actually increases the resistance compared to using composite oxide (A1) alone.

[0144] (Experimental Example 2)

[0145] <Example 7>

[0146] [Synthesis of composite oxides (C1)]

[0147] [Ni] obtained by coprecipitation method 0.91 Co 0.04 Al 0.05 The composite hydroxide shown in [(OH)2] was calcined at 500°C for 8 hours to obtain the composite oxide (Ni). 0.91 Co 0.04 Al 0.05 O2 (Step 1). Next, lithium hydroxide (LiOH) and the above-mentioned composite oxide are mixed in a molar ratio of Li to Ni, Co, and Al of 1.02:1 to obtain a mixture. This mixture is then subjected to an oxygen flow of 95% oxygen concentration (per 10 cm). 3 The mixture was calcined at a flow rate of 2 mL / min and 5 L / min per kg of the mixture, from room temperature to 650°C at a heating rate of 2°C / min, and then calcined at 720°C from 650°C to 0.5°C / min. The calcined product was washed with water to remove impurities, yielding a composite oxide (C1).

[0148] ICP analysis showed that the composite oxide (C1) had a composition of LiNi. 0.91 Co 0.04 Al 0.05 O2. Furthermore, the crystal structure of the composite oxide (C1) was identified as belonging to space group R-3m by X-ray diffraction. The D50 of the composite oxide (C1) was determined to be 10 μm using a MicrotracBEL MT3000II with water as the dispersion medium.

[0149] In the fabrication of the positive electrode, the composite oxides (Al, B1, C1) were mixed in a mass ratio of 4.75:0.25:95. Otherwise, the test cell was fabricated in the same manner as in Example 1.

[0150] <Comparative Example 4>

[0151] In the fabrication of the positive electrode, the composite oxides (Al, Cl) were mixed at a mass ratio of 5:95. Otherwise, the test cell was fabricated in the same manner as in Example 1.

[0152] For each test cell of Example 7 and Comparative Example 4, cycling tests and resistance rise rate evaluations were performed using the same method as in Experimental Example 1. The evaluation results are shown in Table 2 along with the configuration of the positive electrode. The resistance values ​​shown in Table 1 are relative to the resistance rise rate (100) of the test cell of Comparative Example 4.

[0153] [Table 2]

[0154]

[0155] As can be seen from the results shown in Table 2, the resistance rise of the test battery cell in the embodiment was suppressed to a lower level compared to the test battery cell in the comparative example after 15 cycles. That is, even when mixed with composite oxide (C1), the resistance rise of the battery was specifically suppressed when using a positive electrode containing composite oxide (A1) and composite oxide (B1).

[0156] Example 7 is prepared by mixing the positive electrode active material used in Example 1 with the composite oxide (C1) at a weight ratio of 5:95. The increase in resistance is suppressed. Therefore, it is presumed that the same effect can be exhibited even when the positive electrode active material and the composite oxide (C1) used in Examples 2 to 6 are mixed.

[0157] Explanation of reference numerals in the attached figures

[0158] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive lead, 21 Negative lead, 22 Groove section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating component, 26 Upper valve body, 27 Cover, 28 Gasket, 30 Positive electrode core, 31 Positive electrode flux layer, 40 Negative electrode core, 41 Negative electrode flux layer

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: General formula Li a Ni b M1 1-b The first lithium transition metal composite oxide shown in O2, wherein 1.5≤a≤2.5, 0.95≤b≤1.00, and M1 is at least one metal element other than Li and Ni; and General formula Li c Ni 2-c-d M2 d The second lithium transition metal composite oxide represented by O2, where 0 < c ≤ 0.5, 0 ≤ d ≤ 0.5, and M2 is at least one metal element other than Li and Ni.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, The content of the second lithium transition metal composite oxide is 0.1 to 20% by mass relative to the mass of the first and second lithium transition metal composite oxides.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The first lithium transition metal composite oxide has a crystal structure belonging to space group 1mm.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The first lithium transition metal composite oxide comprises Li2O and NiO.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The second lithium transition metal composite oxide has at least one diffraction peak with a apex at a diffraction angle of 2θ 21.40°~21.65° during synchrotron X-ray diffraction, wherein the light energy during synchrotron X-ray diffraction is 16keV.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, further comprising a tertiary lithium transition metal composite oxide represented by the general formula Li x Ni 1-y-z Co y M3 z O2, wherein 0.8 ≤ x ≤ 1.2, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.5, and M3 is at least one metal element other than Li, Ni, and Co.

7. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein, The content of the first and second lithium transition metal composite oxides is 0.1 to 15% by mass relative to the mass of the first to third lithium transition metal composite oxides.

8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein, The third lithium transition metal composite oxide has a crystal structure belonging to space group R3-m.

9. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein, The surface of the third lithium transition metal composite oxide particles is coated with a compound containing at least one metal element selected from Sr, Ca, W, Mg, Nb and Al.

10. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 9, wherein, The amount of the compound containing at least one metal element selected from Sr, Ca, W, Mg, Nb and Al, excluding Li, relative to the metal elements of the third lithium transition metal composite oxide, is 0.05 to 0.5 mol in terms of the metal element.

11. A non-aqueous electrolyte secondary battery comprising: a positive electrode, a negative electrode, and a non-aqueous electrolyte, all comprising the positive electrode active material for a non-aqueous electrolyte secondary battery as described in any one of claims 1 to 10.

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