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

Abstract

The invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery. A positive electrode active material for use in a non-aqueous electrolyte secondary battery, the positive electrode active material comprising: a lithium transition metal composite oxide containing at least 80 mol% or more of Ni and Al with respect to the total number of moles of metal elements other than Li; a surface modification layer containing at least Ca is provided on the surface of the primary particles of the lithium transition metal composite oxide.

Description

[0001] This application is a divisional application of the invention patent application with application number 202080077788.X, application date September 17, 2020, and invention name “Positive electrode active material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery”. Technical Field

[0002] The present disclosure relates to a positive electrode active material for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery. Background Art

[0003] In recent years, lithium transition metal composite oxides with high Ni content have attracted much attention as positive electrode active materials with high energy density. For example, Patent Document 1 discloses a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises a general formula Li x Ni y Co z M m O 2 (wherein, M is an element selected from Ba, Sr, and B, 0.9≤x≤1.1, 0.5≤y≤0.95, 0.05≤z≤0.5, 0.0005≤m≤0.02) and the BET specific surface area value is 0.8m 2 / g or less.

[0004] In addition, Patent Document 2 discloses a positive electrode active material for a non-aqueous electrolyte secondary battery having α-NaFeO 2 The structure contains one or two selected from the group consisting of Mn, Ni and Co as transition metal elements, and an alkaline earth metal and W are present on the surface of particles of the lithium transition metal composite oxide.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2003-100295

[0008] Patent Document 2: Japanese Patent Application Publication No. 2018-129221 Summary of the invention

[0009] When a lithium transition metal composite oxide with a high Ni content is used as the positive electrode active material of a non-aqueous electrolyte secondary battery, the amount of Li captured during charging is large, so there is a problem that the layered crystal structure is destroyed and the capacity is reduced due to repeated charge and discharge. It should be noted that the technology disclosed in Patent Documents 1 and 2 still has room for improvement in charge and discharge cycle characteristics.

[0010] A positive electrode active material for a non-aqueous electrolyte secondary battery as one embodiment of the present invention comprises: a lithium transition metal composite oxide containing at least 80 mol % of Ni and Al relative to the total molar number of metal elements other than Li; and a surface modification layer containing at least Ca formed on the surface of primary particles of the lithium transition metal composite oxide.

[0011] A nonaqueous electrolyte secondary battery as one embodiment of the present disclosure includes: a positive electrode including the positive electrode active material for a nonaqueous electrolyte secondary battery; a negative electrode; and a nonaqueous electrolyte.

[0012] A non-aqueous electrolyte secondary battery positive electrode active material as one aspect of the present disclosure includes a lithium transition metal composite oxide with a high Ni content, which can be beneficial to improving the charge and discharge cycle characteristics of the battery. According to the non-aqueous electrolyte secondary battery positive electrode active material as one aspect of the present disclosure, a high-capacity non-aqueous electrolyte secondary battery can be provided that suppresses the reduction of battery capacity accompanying charge and discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a cross-sectional view of a nonaqueous electrolyte secondary battery as an example of an embodiment. DETAILED DESCRIPTION

[0014] In the layered structure of the lithium transition metal composite oxide contained in the positive electrode active material, the transition metal layer, Li layer, oxygen layer, etc., and the Li ions present in the Li layer reversibly enter and exit, so that the charge and discharge reaction of the battery is carried out. In the case of using a lithium transition metal composite oxide with a high Ni content, a large amount of Li ions are taken from the Li layer when the battery is charged, so the layered structure sometimes becomes unstable. The surface of the lithium transition metal composite oxide whose layered structure becomes unstable will form a metamorphic layer due to the reaction with the electrolyte. The structural change of the lithium transition metal composite oxide will be further carried out with the metamorphic layer as the starting point, so the battery capacity gradually decreases with charging and discharging.

[0015] Therefore, the inventors of the present invention have conducted in-depth research to solve the above-mentioned problems, and found that the positive electrode active material having a surface modification layer containing Ca on the surface of the lithium transition metal composite oxide containing a predetermined amount of Al suppresses the reaction with the electrolyte on the surface by utilizing the synergistic effect of Al and Ca, and the layered structure is stabilized at the same time, so the battery capacity can be suppressed from decreasing with charge and discharge. It is speculated that since Al does not produce an oxidation number change during charge and discharge, the structure of the transition metal layer is stabilized by being included in the transition metal layer. In addition, it is speculated that Ca utilizes electronic interaction to suppress the erosion of the surface modification layer caused by the electrolyte.

[0016] Hereinafter, an example of an embodiment of the non-aqueous electrolyte secondary battery disclosed in the present invention is described in detail. Hereinafter, a cylindrical battery in which a wound electrode body is housed in a cylindrical battery case is exemplified, but the electrode body is not limited to a wound type, and may also be a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked one by one through a separator. In addition, the battery case is not limited to a cylindrical shape, and may be, for example, a square, a coin shape, etc., or may be a battery case composed of a laminate sheet comprising a metal layer and a resin layer.

[0017] Figure 1 FIG. 2 is a cross-sectional view of a nonaqueous electrolyte secondary battery 10 as an example of an embodiment. Figure 1 As shown in the example, the nonaqueous electrolyte secondary battery 10 includes: an electrode body 14, a nonaqueous electrolyte (not shown), and a battery case 15 that accommodates the electrode body 14 and the nonaqueous electrolyte. The electrode body 14 has a winding structure in which the positive electrode 11 and the negative electrode 12 are wound with a separator 13 interposed therebetween. The battery case 15 is composed of an outer shell can 16 in a cylindrical shape with a bottom, and a sealing body 17 that seals the opening of the outer shell can 16.

[0018] The electrode body 14 is composed of a long positive electrode 11, a long negative electrode 12, two long separators 13, a positive electrode tab 20 joined to the positive electrode 11, and a negative electrode tab 21 joined to the negative electrode 12. In order to prevent lithium precipitation, the negative electrode 12 is formed to be one size larger than the positive electrode 11. That is, the negative electrode 12 is formed in a manner longer than the positive electrode 11 in the length direction and the width direction (short direction). The two separators 13 are formed in a size at least one size larger than the positive electrode 11, and are arranged, for example, to sandwich the positive electrode 11.

[0019] The nonaqueous electrolyte secondary battery 10 includes insulating plates 18 and 19 disposed above and below the electrode body 14 , respectively. Figure 1 In the example shown, the positive electrode tab 20 attached to the positive electrode 11 extends to the sealing body 17 side through the through hole of the insulating plate 18, and the negative electrode tab 21 attached to the negative electrode 12 extends to the bottom side of the outer can 16 through the outer side of the insulating plate 19. The positive electrode tab 20 is connected to the lower surface of the bottom plate 23 of the sealing body 17 by welding or the like, and the cover 27 of the sealing body 17 electrically connected to the bottom plate 23 becomes the positive terminal. The negative electrode tab 21 is connected to the bottom inner surface of the outer can 16 by welding or the like, and the outer can 16 becomes the negative terminal.

[0020] The outer shell can 16 is, for example, a metal container in a cylindrical shape with a bottom. A gasket 28 is provided between the outer shell can 16 and the sealing body 17 to seal the internal space of the battery case 15. The outer shell can 16 has, for example, a grooved portion 22 formed by applying pressure to the side surface from the outside to support the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer shell can 16, and the sealing body 17 is supported by its upper surface.

[0021] The sealing body 17 has a structure in which a bottom plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26 and a cover 27 are stacked in order from the electrode body 14 side. The components constituting the sealing body 17 have, for example, a disc shape or a ring shape, and the 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 to each other at their respective central portions, and an insulating member 25 is sandwiched between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heat release, the lower valve body 24 is deformed and broken in a manner that pushes the upper valve body 26 toward the cover 27 side, and the current path between the lower valve body 24 and the upper valve body 26 is blocked. When the internal pressure rises further, the upper valve body 26 breaks, and gas is discharged from the opening of the cover 27.

[0022] The positive electrode 11 , the negative electrode 12 , the separator 13 , and the nonaqueous electrolyte constituting the nonaqueous electrolyte secondary battery 10 , particularly the positive electrode active material contained in the positive electrode composite material layer 31 constituting the positive electrode 11 , will be described in detail below.

[0023] [positive electrode]

[0024] The positive electrode 11 has: a positive electrode collector 30, and a positive electrode composite material layer 31 formed on both sides of the positive electrode collector 30. The positive electrode collector 30 can use a foil of a metal such as aluminum or aluminum alloy that is stable within the potential range of the positive electrode 11, a thin film of the metal configured on the surface, etc. The positive electrode composite material layer 31 contains: a positive electrode active material, a conductive material, and a binding material. The thickness of the positive electrode composite material layer 31 is, for example, 10 μm to 150 μm on one side of the positive electrode collector 30. The positive electrode 11 can be manufactured by coating a positive electrode slurry containing a positive electrode active material, a conductive material, and a binding material on the surface of the positive electrode collector 30, drying the coating film, and then compressing it to form a positive electrode composite material layer 31 on both sides of the positive electrode collector 30.

[0025] As the conductive material contained in the positive electrode composite material layer 31, carbon materials such as carbon black, acetylene black, Ketjen black, and graphite can be exemplified. As the binding material contained in the positive electrode composite material layer 31, fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, etc. can be exemplified. These resins can be used in combination with carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), etc.

[0026] The positive electrode active material includes: a lithium transition metal composite oxide; and a surface modification layer containing at least Ca formed on the surface of the primary particles of the lithium transition metal composite oxide. The lithium transition metal composite oxide contains at least 80 mol% of Ni and Al relative to the total molar amount of metal elements other than Li. By making the content of Ni in the lithium transition metal composite oxide 80 mol% or more relative to the total molar amount of metal elements other than Li, a battery with a high capacity can be obtained.

[0027] The content of Ni in the lithium transition metal composite oxide is preferably 90 mol% or more relative to the total molar amount of metal elements other than Li. Thereby, a battery with a higher capacity can be obtained. On the other hand, when the content of Ni exceeds 96 mol% relative to the total molar amount of metal elements other than Li, the contents of Al and Ca are too small to ensure the stability of the layered structure and surface structure of the lithium transition metal composite oxide.

[0028] The lithium transition metal composite oxide has a layered structure. Examples of the layered structure of the lithium transition metal composite oxide include a layered structure belonging to the space group R-3m, a layered structure belonging to the space group C2 / m, etc. Among these, from the viewpoints of high capacity and stability of the crystal structure, etc., a layered structure belonging to the space group R-3m is preferred.

[0029] The lithium transition metal composite oxide can be a composite oxide represented by the general formula Li a Ni x Al y Co z M w O 2-b (where 0.95 < a < 1.05, 0.8 ≤ x ≤ 0.96, 0 < y ≤ 0.10, 0 ≤ z ≤ 0.15, 0 ≤ w ≤ 0.1, 0 ≤ b < 0.05, x + y + z + w = 1, and M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn). It should be noted that in the positive electrode active material, within the range not detrimental to the purpose of the present disclosure, a lithium transition metal composite oxide other than that represented by the above general formula, or other compounds, may be included. The molar fractions of the metal elements contained in the whole particles of the lithium transition metal composite oxide can be measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES), an electron probe microanalyzer (EPMA), an energy dispersive X-ray spectrometer (EDX), etc.

[0030] The a representing the proportion of Li in the lithium transition metal composite oxide preferably satisfies 0.95 ≤ a < 1.05, more preferably 0.97 ≤ a ≤ 1.03. When a is less than 0.95, the battery capacity may sometimes decrease compared to the case where a satisfies the above range. When a is 1.05 or more, since more Li compound is added compared to the case where a satisfies the above range, it is sometimes uneconomical from the viewpoint of production cost.

[0031] The y representing the content of Al in the lithium transition metal composite oxide relative to the total molar number of metal elements other than Li preferably satisfies 0 < y ≤ 0.10, more preferably 0.03 ≤ y ≤ 0.07. Considering that the oxidation number of Al does not change during charge and discharge, the structure of the transition metal layer is stabilized by being included in the transition metal layer. On the other hand, when y > 0.10, Al impurities are generated and the battery capacity decreases. Al can be, for example, uniformly dispersed in the layered structure of the lithium transition metal composite oxide, or can be present in a part of the layered structure.

[0032] Co and M (M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn) are optional components. The z and w representing the contents of Co and M in the lithium transition metal composite oxide relative to the total molar number of metal elements other than Li preferably satisfy 0 ≤ z ≤ 0.15 and 0 ≤ w ≤ 0.1, respectively. Since Co is very expensive, it is preferable to suppress the Co content rate from the viewpoint of manufacturing cost.

[0033] The lithium transition metal composite oxide is, for example, secondary particles aggregated from a plurality of primary particles. The particle size of the primary particles constituting the secondary particles is, for example, 0.05 μm to 1 μm. The particle size of the primary particles is measured as the diameter of the circumscribed circle in the particle image observed by a scanning electron microscope (SEM). A surface modification layer exists on the surface of the primary particles. In other words, the surface modification layer exists on the surface of the secondary particles of the lithium transition metal composite oxide, or exists at the interface where the primary particles are in contact with each other.

[0034] The lithium transition metal composite oxide is particles having a volume-based median particle size (D50) of, for example, 3 μm to 30 μm, preferably 5 μm to 25 μm, and particularly preferably 7 μm to 15 μm. D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution becomes 50% starting from a smaller particle size, and is also called the median diameter. The particle size distribution of the lithium transition metal composite oxide can be measured using a laser diffraction type particle size distribution measuring device (for example, MT3000II manufactured by MicrotracBEL Corp.) with water as the dispersion medium.

[0035] The lithium transition metal composite oxide has a surface layer present on the inner side from the surface and a main body present on the inner side of the surface layer. The thickness of the surface layer is, for example, 1 nm to 5 nm.

[0036] The thickness of the surface modification layer is, for example, 0.1 nm to 5 nm. Within this range, the reaction of the surface of the lithium transition metal composite oxide with the electrolyte can be suppressed, and thus the decrease in battery capacity accompanying charge and discharge can be suppressed.

[0037] The surface modification layer contains at least Ca. The surface modification layer may contain Ca or a compound containing Ca. Examples of the compound containing Ca include CaO, Ca(OH) 2 , and CaCO 3 .

[0038] The content of Ca in the surface modification layer relative to the total molar number of metal elements other than Li when performing composition analysis using energy dispersive X-ray spectroscopy (TEM-EDX) can be set to 1.5 mol% to 20 mol%. If within this range, the charge and discharge cycle characteristics of the battery can be further improved through the synergistic effect with Al. Here, the composition of the surface modification layer in the positive electrode active material and the composition of the main body and the surface layer of the lithium transition metal composite oxide can be analyzed as follows: TEM-EDX can be used to analyze each part in the cross section of the primary particle of the positive electrode active material to determine the content of Ni, Co, Al, M and Ca. It should be noted that since the surface modification layer is thinner than the spot diameter of the irradiated electron beam, the composition of the surface layer is affected by the composition of the adjacent surface modification layer. Even if a trace amount of Ca is detected in the measurement result of the surface layer, it is considered that there is actually no Ca in the surface layer.

[0039] Furthermore, it is preferred that the lithium transition metal composite oxide does not have a peak derived from CaO in the X-ray diffraction spectrum obtained by X-ray diffraction measurement. When CaO is contained to a degree detected by X-ray diffraction measurement, a decrease in charge and discharge capacity may occur. Here, the X-ray diffraction spectrum is obtained, for example, using a powder X-ray diffraction apparatus (Rigaku Co., Ltd., trade name "RINT-TTR", radiation source Cu-Kα) according to a powder X-ray diffraction method based on the following conditions.

[0040] Measuring range: 15-120°

[0041] Scanning speed: 4° / min

[0042] Resolution range: 30-120°

[0043] Background: B-Splines

[0044] Curve function: Segmented fitting Voigt function

[0045] Binding condition: Li(3a)+Ni(3a)=1

[0046] Ni(3a)+Ni(3b)=y (y is the Ni content ratio of each)

[0047] ICSD No.:98-009-4814

[0048] The surface modification layer may further contain Al. In other words, the surface modification layer may further contain at least one selected from Al or a compound containing Al, and a compound containing Ca and Al. Examples of the compound containing Al include Al 2 O 3 In addition, as a compound containing Ca and Al, CaAl 2 O 4 and Ca 3 Al 2 O 6 The surface modification layer may further contain Li.

[0049] The molar ratio of Al to Ni in the surface modification layer when analyzing the composition by energy dispersive X-ray spectroscopy (TEM-EDX) can be greater than the molar ratio of Al to Ni in the main body. Thus, the charge and discharge cycle characteristics of the battery can be further improved through the synergistic effect with Ca.

[0050] In addition, the molar ratio of Al to Ni in the surface modification layer when analyzing the composition by energy dispersive X-ray spectroscopy (TEM-EDX) is preferably more than 2 times the molar ratio of Al to Ni in the main body. If it is within this range, the charge and discharge cycle characteristics of the battery can be significantly improved.

[0051] Next, an example of a method for producing a positive electrode active material including a lithium transition metal composite oxide and a surface modification layer will be described.

[0052] The method for producing a positive electrode active material, for example, comprises the following steps: a first step of obtaining a composite oxide containing Ni, Al and an arbitrary metal element; a second step of mixing the composite oxide obtained in the first step with a lithium compound to obtain a mixture; and a third step of calcining the mixture. The composition and thickness parameters of the surface layer and the surface modification layer in the finally obtained positive electrode active material are adjusted by, for example, controlling the mixing ratio of the raw materials in the second step, the calcination temperature and time in the third step, etc.

[0053] In the first step, for example, a solution of a metal salt containing Ni, Al and any metal element (Co, Mn, Fe, etc.) is stirred while an alkaline solution such as sodium hydroxide is added dropwise, and the pH is adjusted to the alkaline side (e.g., 8.5 to 12.5), so that a composite hydroxide containing Ni, Al and any metal element is precipitated (coprecipitated), and the composite hydroxide is roasted to obtain a composite oxide containing Ni, Al and any metal element. The roasting temperature is not particularly limited, for example, in the range of 300° C. to 600° C.

[0054] In the second step, the composite oxide obtained in the first step is mixed with a lithium compound and a calcium compound to obtain a mixture. Examples of the lithium compound include Li 2 CO 3 、LiOH、Li 2 O 2 , Li 2 O、LiNO 3 、LiNO 2 , Li 2 SO 4 、LiOH·H 2 O, LiH, LiF, etc. Examples of calcium compounds include Ca(OH) 2 , CaO, CaCO 3 、CaSO 4 、Ca(NO 3 ) 2 Etc. From the perspective of facilitating the adjustment of the above parameters within the above-defined range, the mixing ratio of the composite oxide obtained in the first step and the lithium compound is preferably set to, for example, a ratio in the range of 1:0.98 to 1:1.1, in which the molar ratio of the metal element other than Li: Li is 1. In addition, from the perspective of facilitating the adjustment of the above parameters within the above-defined range, the mixing ratio of the composite oxide obtained in the first step and the calcium compound is preferably set to, for example, a ratio in the range of 1:0.0005 to 1:0.02, in which the molar ratio of the metal element other than Li: Ca is 1. In the second step, when the composite oxide obtained in the first step is mixed with the lithium compound and the calcium compound, other metal raw materials may be added as needed. Other metal raw materials include oxides of metal elements other than the metal elements constituting the composite oxide obtained in the first step, etc.

[0055] In the third step, the mixture obtained in the second step is roasted at a specified temperature and time to obtain the positive electrode active material of the present embodiment. The roasting of the mixture in the third step, for example, has a multi-stage roasting process, which includes: a first roasting process, roasting in a roasting furnace, under an oxygen flow, at a first heating rate until a first set temperature of 450°C to 680°C; and, a second roasting process, roasting the roasted product obtained by the first roasting process in a roasting furnace, under an oxygen flow, at a second heating rate until a second set temperature of more than 680°C and less than 800°C. Here, the first heating rate is in the range of 1.5°C / min to 5.5°C / min, and the second heating rate is slower than the first heating rate, and is in the range of 0.1°C / min to 3.5°C / min. Through this multi-stage roasting, in the positive electrode active material of the present embodiment finally obtained, the composition and thickness parameters of the surface layer and the surface modification layer can be adjusted to the above-mentioned limited range. It should be noted that the first heating rate and the second heating rate can be set in multiples as long as they are within the above-defined ranges. From the perspective of adjusting the above-mentioned parameters of the lithium transition metal composite oxide to within the above-defined ranges, the holding time of the first set temperature in the first roasting process is preferably less than 5 hours, and more preferably less than 3 hours. The holding time of the first set temperature refers to the time for maintaining the first set temperature after reaching the first set temperature. From the perspective of adjusting the above-mentioned parameters of the lithium transition metal composite oxide to within the above-defined ranges, the holding time of the second set temperature in the second roasting process is preferably 1 hour to 10 hours, and more preferably 1 hour to 5 hours. The holding time of the second set temperature refers to the time for maintaining the second set temperature after reaching the second set temperature. When the mixture is roasted, from the perspective of adjusting the above-mentioned parameters to within the above-defined ranges, for example, in an oxygen flow with an oxygen concentration of more than 60%, the flow rate of the oxygen flow is adjusted to 10% per 10 cm 3 In the calcining furnace, the flow rate was set to 0.2 mL / min to 4 mL / min and to 0.3 L / min or more per 1 kg of the mixture.

[0056] The molar fraction of the metal element contained in the positive electrode active material obtained above was measured by inductively coupled plasma (ICP) emission spectroscopy and can be expressed by the general formula Li a Ni x Al y Co z M w Ca α O 2-b(wherein, 0.95 < a < 1.05, 0.8 ≤ x ≤ 0.96, 0 < y ≤ 0.10, 0 ≤ z ≤ 0.15, 0 ≤ w ≤ 0.1, 0.0005 ≤ α ≤ 0.02, 0 ≤ b < 0.05, x + y + z + w = 1, and M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn). It should be noted that Ca is contained in the surface modification layer present on the surface of the lithium transition metal composite oxide, and Ca is not solid-soluble in the lithium transition metal composite oxide. In addition, a part of Al may also be contained in the surface modification layer.

[0057] [Negative electrode]

[0058] The negative electrode 12 has: a negative electrode current collector 40 and negative electrode composite material layers 41 formed on both surfaces of the negative electrode current collector 40. For the negative electrode current collector 40, foils of metals such as copper and copper alloys that are stable within the potential range of the negative electrode 12, thin films of such metals disposed on the surface layer, etc. can be used. The negative electrode composite material layer 41 contains a negative electrode active material and a binder. The thickness of the negative electrode composite material layer 41 is, for example, 10 μm to 150 μm on one side of the negative electrode current collector 40. The negative electrode 12 can be fabricated by coating a negative electrode composite material slurry containing a negative electrode active material, a binder, etc. on the surface of the negative electrode current collector 40, drying the coating film, and then rolling it to form the negative electrode composite material layers 41 on both surfaces of the negative electrode current collector 40.

[0059] As the negative electrode active material contained in the negative electrode composite material layer 41, there is no particular limitation as long as it can reversibly absorb and release lithium ions. Generally, carbon materials such as graphite are used. The graphite can be natural graphite such as flake graphite, massive graphite, and earthy graphite, artificial massive graphite, graphitized mesophase carbon microbeads, etc., and all are acceptable. In addition, as the negative electrode active material, metals alloyed with Li such as Si and Sn, metal compounds containing Si, Sn, etc., lithium titanium composite oxides, etc. can be used. In addition, those provided with a carbon coating film thereon can also be used. For example, a Si-containing compound represented by SiO x (0.5 ≤ x ≤ 1.6) or a Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by Li 2y SiO (2+y) (0 < y < 2) can be used in combination with graphite.

[0060] The binder contained in the negative electrode composite material layer 41 can be the same as that of the positive electrode 11. Fluorine-containing resins such as PTFE and PVdF, PAN, polyimide, acrylic resins, polyolefins, etc. can be used, and styrene-butadiene rubber (SBR) is preferably used. In addition, the negative electrode composite material layer 41 can contain CMC or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc.

[0061] [Separator]

[0062] For example, a porous sheet having ion permeability and insulation can be used as the separator 13. Specific examples of the porous sheet include microporous films, woven fabrics, nonwoven fabrics, etc. As the material of the separator 13, polyolefins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator 13 can be a single-layer structure or a laminated structure. In addition, a resin layer with high heat resistance such as aramid resin or a filler layer containing a filler of an inorganic compound can be provided on the surface of the separator 13.

[0063] [Non-aqueous electrolyte]

[0064] The non-aqueous electrolyte, for example, comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. For example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more thereof can be used in the non-aqueous solvent. The non-aqueous solvent can contain a halogen substituted body formed by replacing at least a portion of the hydrogen of these solvents with a halogen atom such as fluorine. As the halogen substituted body, fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, fluorinated chain carboxylates such as methyl fluoropropionate (FMP), etc. can be cited.

[0065] Examples of the above-mentioned esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate, chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate, cyclic carboxylates such as γ-butyrolactone (GBL) and γ-valerolactone (GVL), and chain carboxylates such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0066] Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, ethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, Ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and other chain ethers, etc.

[0067] The electrolyte salt is preferably a lithium salt. As examples of the lithium salt, LiBF 4 , LiClO 4 , LiPF 6 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , LiSCN, LiCF 3 SO 3 , LiCF 3 CO 2 , Li(P(C 2 O 4 )F 4 ), LiPF 6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, Li 2 B 4 O 7 , Li(B(C 2 O 4 )F 2 ), etc. borate salts, LiN(SO 2 CF 3 ) 2 , LiN(C 1 F 2l+1 SO 2 )(C m F 2m+1 SO 2 ){l, m are integers of 0 or more} etc. imide salts, etc. These lithium salts can be used alone or in combination of multiple kinds. Among them, from the viewpoints of ionic conductivity, electrochemical stability, etc., LiPF 6 is preferably used. The concentration of the lithium salt is, for example, 0.8 mol to 1.8 mol per 1 L of the non-aqueous solvent. In addition, vinylene carbonate, propanesultone-based additives can be further added.

[0068] <Examples>

[0069] Hereinafter, the present disclosure will be further described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0070] [Production of Positive Electrode Active Material]

[0071] <Example 1>

[0072] With respect to the general formula Ni 0.90 Co0.05 Al 0.05 O 2 The metal composite oxide was mixed with calcium hydroxide (Ca(OH) 2 ) were mixed, and lithium hydroxide monohydrate (LiOH·H 2 O) was mixed. The mixture was calcined from room temperature to 650°C at a heating rate of 2°C / min under an oxygen flow with an oxygen concentration of 95% (a flow rate of 10 L / min per 1 kg of the mixture), and then calcined from 650°C to 720°C at a heating rate of 1°C / min. The calcined product was washed with water to remove impurities, thereby obtaining the positive electrode active material of Example 1. The composition of the positive electrode active material of Example 1 was analyzed by ICP-AES, and the result was Li 0.99 Ni 0.899 Co 0.05 Al 0.05 Ca 0.001 O 2 .

[0073] <Example 2>

[0074] Compared with the general formula Ni 0.90 Co 0.05 Al 0.05 O 2 The metal composite oxide was mixed with calcium hydroxide (Ca(OH) 2 ) were mixed, and the positive electrode active material of Example 2 was obtained in the same manner as in Example 1. The composition of the positive electrode active material of Example 2 obtained was Li 0.99 Ni 0.899 Co 0.05 Al 0.05 Ca 0.0015 O 2 .

[0075] <Comparative Example>

[0076] Not mixed with calcium hydroxide (Ca(OH) 2 ), calcined from room temperature to 650°C at a heating rate of 3.0°C / min, and then calcined from 650°C to 720°C at a heating rate of 1°C / min. A positive electrode active material was obtained in the same manner as in Example 1. The composition of the obtained positive electrode active material is Li 0.99 Ni 0.90 Co 0.05 Al 0.05 O 2This was used as the positive electrode active material of the comparative example. It should be noted that 0.01 mol % of Ca was detected in the comparative example. This amount of Ca was very small compared to the amount of Ca contained in Examples 1 and 2, and therefore it was considered that it had no effect on the experimental results.

[0077] TEM-EDX measurement was performed on the positive electrode active materials of Examples 1, 2 and Comparative Examples, and composition analysis was performed on the main body, surface layer and surface modification layer of the lithium transition metal composite oxide. The main body is measured at an internal position of the lithium transition metal composite oxide that is more than 15 nm away from the inner side of the surface. For Examples 1 and 2, measurements were performed at two points different from the first observation point and the second observation point. The results are shown in Table 1. The molar % of Ni, Co and Al in Table 1 is the total of Ni, Co and Al recorded as 100. It should be noted that X-ray diffraction measurements were performed on Examples 1, 2 and Comparative Examples, but in any case, there was no peak derived from CaO in the X-ray diffraction spectrum.

[0078] [Table 1]

[0079]

[0080] A small amount of Ca was detected in the surface layer of the second measuring point of Example 1 and the first measuring point and the second measuring point of Example 2, but as mentioned above, it is believed that there is actually no Ca in the surface layer. The electron energy loss spectroscopy (TEM-EELS) implemented separately also confirmed that Ca exists only in the surface modification layer. In other words, in Examples 1 and 2, Ca is only present in the surface modification layer. On the other hand, in the comparative example without adding Ca, Ca is not detected in any part. In addition, in Examples 1 and 2, Al is contained in large quantities in the order of surface modification layer, surface layer, and main body. On the other hand, in the comparative example, the Al content of all parts is roughly the same.

[0081] Next, using the positive electrode active materials of Examples 1 and 2 and Comparative Example, test battery cells were prepared as follows.

[0082] [Production of positive electrode]

[0083] The positive electrode active material of Examples 1, 2 and Comparative Examples is mixed in a ratio of 95 parts by mass, acetylene black as a conductive material is mixed in a ratio of 3 parts by mass, and polyvinylidene fluoride as a binder is mixed in a ratio of 2 parts by mass, and mixed with N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. Next, the slurry is applied to a positive electrode collector formed of an aluminum foil having a thickness of 15 μm, and after the coating is dried, the coating is rolled using a calendering roller and cut into a specified electrode size to obtain a positive electrode having a positive electrode composite material layer formed on both sides of the positive electrode core. It should be noted that a portion of the positive electrode is provided with an exposed portion exposed on the surface of the positive electrode core. The positive electrode is also made in the same manner in other embodiments and comparative examples.

[0084] [Production of negative electrode]

[0085] Natural graphite is used as the negative electrode active material. The negative electrode active material is mixed with sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) at a solid content mass ratio of 100:1:1 in an aqueous solution to prepare a negative electrode composite material slurry. The negative electrode composite material slurry is applied to both sides of a negative electrode core formed by copper foil, and after the coating film is dried, the coating film is rolled with a calendering roller and cut into a specified electrode size to obtain a negative electrode having a negative electrode composite material layer formed on both sides of the negative electrode core. It should be noted that an exposed portion where the surface of the negative electrode core is exposed is provided on a part of the negative electrode.

[0086] [Preparation of non-aqueous electrolyte]

[0087] Ethylene carbonate (EC), ethyl methyl carbonate (MEC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. Lithium hexafluorophosphate (LiPF 6 ) was dissolved in the mixed solvent at a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte.

[0088] [Production of test battery cells]

[0089] An aluminum lead was installed on the exposed portion of the positive electrode containing the positive electrode active material of Examples 1, 2 and Comparative Example, and a nickel lead was installed on the exposed portion of the negative electrode. The positive electrode and the negative electrode were spirally wound with a polyolefin separator interposed therebetween, and then press-formed in the radial direction to produce a flat wound electrode body. The electrode body was housed in an outer shell, and after the non-aqueous electrolyte was injected, the opening of the outer shell was sealed to obtain a test battery cell.

[0090] [Evaluation of capacity maintenance rate]

[0091] The following cycle test was performed on the battery fabricated by incorporating the positive electrode containing the positive electrode active material of Examples 1 and 2 and Comparative Example. The discharge capacity at the 1st cycle and the discharge capacity at the 30th cycle of the cycle test were determined, and the capacity retention rate was calculated according to the following formula.

[0092] Capacity retention rate (%) = (discharge capacity at the 30th cycle ÷ discharge capacity at the 1st cycle) × 100

[0093] <Cyclic test>

[0094] The test battery cell was charged at a constant current of 0.2 It until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 1 / 100 It. Thereafter, the battery was discharged at a constant current of 0.2 It until the battery voltage reached 2.5 V. This charge and discharge cycle was repeated 30 times.

[0095] The capacity retention rates of Examples 1 and 2 and the comparative example are shown in Table 2. The capacity retention rates of the test cells of Examples 1 and 2 shown in Table 2 are expressed relatively, with the capacity retention rate of the test cell of Comparative Example 1 being 100%.

[0096] [Table 2]

[0097]

[0098] As shown in Table 2, Examples 1 and 2 using the positive electrode active material containing Ca in the surface modification layer have higher capacity retention rates than the comparative example using the positive electrode active material not containing Ca in the surface modification layer.

[0099] Description of Reference Numerals

[0100] 10Non-aqueous electrolyte secondary battery

[0101] 11 Positive electrode

[0102] 12 Negative electrode

[0103] 13 Dividers

[0104] 14 Electrode body

[0105] 15Battery housing

[0106] 16 shell tank

[0107] 17 Sealing body

[0108] 18, 19 insulation board

[0109] 20 positive electrode tabs

[0110] 21 Negative electrode tab

[0111] 22 groove part

[0112] 23 bottom plate

[0113] 24 Lower valve body

[0114] 25 Insulation components

[0115] 26 Upper valve body

[0116] 27 Cover

[0117] 28 gasket

[0118] 30 Positive electrode collector

[0119] 31 positive electrode composite material layer

[0120] 40 negative electrode collector

[0121] 41 negative electrode composite material layer

Claims

1. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, include: The first step is to obtain a lithium transition metal composite oxide containing at least 80 mol % of Ni and Al relative to the total molar number of metal elements other than Li; In a second step, the composite oxide obtained in the first step is mixed with a lithium compound and a calcium compound to obtain a mixture; and The third step is to calcine the mixture; The third step comprises: A first calcination step of calcining at a first temperature increase rate under an oxygen flow to a first set temperature of 450° C. to 680° C.; and a second calcination step of calcining at a second temperature increase rate under an oxygen flow until a second set temperature exceeds 680° C. and is not more than 800° C., wherein the second temperature increase rate is slower than the first temperature increase rate; As a result, a surface modification layer containing at least Ca is formed on the surface of the primary particles of the lithium-transition metal composite oxide.

2. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, In the second step, the calcium compound is Ca(OH) 2 , CaO, CaCO 3 、CaSO 4 、Ca(NO 3 ) 2 At least one of .

3. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, In the second step, the mixing ratio of the composite oxide obtained in the first step and the calcium compound is such that the molar ratio of the metal element other than Li:Ca is in the range of 1:0.0005 to 1:0.

02.

4. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, In the third step, after the calcination, water washing is performed.

5. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, In the third step, the first temperature increase rate is in a range of 1.5° C. / min to 5.5° C. / min.

6. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, In the third step, the second temperature increase rate is in a range of 0.1° C. / min to 3.5° C. / min.

7. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, In the third step, after reaching the first set temperature, the first set temperature is maintained for 5 hours or less.

8. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, In the third step, after reaching the second set temperature, the second set temperature is maintained for 1 hour to 10 hours.

9. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, The Ca is not solid-soluble in the lithium-transition metal composite oxide.

10. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, The surface modification layer further contains Al.

11. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, The lithium transition metal composite oxide is represented by the general formula Li a Ni x Al y Co z M w O 2-b wherein 0.95 < a < 1.05, 0.8 ≤ x ≤ 0.96, 0 < y ≤ 0.10, 0 ≤ z ≤ 0.15, 0 ≤ w ≤ 0.1, 0 ≤ b < 0.05, x + y + z + w = 1, and M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn.

12. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, The lithium transition metal composite oxide has a surface layer present on the inner side from the surface and a main body present on the inner side of the surface layer. The molar ratio of Al to Ni in the surface modification layer when the composition is analyzed by energy dispersive X-ray spectroscopy (TEM-EDX) is greater than the molar ratio of Al to Ni in the main body.

13. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, The molar ratio of Al to Ni in the surface modification layer when the composition is analyzed by energy dispersive X-ray spectroscopy (TEM-EDX) is at least twice the molar ratio of Al to Ni in the main body.

14. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, The content of Ca in the surface modification layer when the composition is analyzed by energy dispersive X-ray spectroscopy (TEM-EDX) is 1.5 mol % to 20 mol % based on the total molar number of metal elements excluding Li.

15. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, The content of Ni in the lithium transition metal composite oxide is 90 mol % or more relative to the total number of moles of metal elements excluding Li.

16. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, in, The lithium transition metal composite oxide including the surface modification layer has no peak derived from CaO in an X-ray diffraction spectrum obtained by X-ray diffraction measurement.

17. A method for producing a non-aqueous electrolyte secondary battery, comprising: producing a battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte produced using the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 16.

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