Positive electrode active material and secondary battery

Abstract

Provided are: a positive electrode active material having a high initial charge capacity; and a secondary battery. The positive electrode active material contains a lithium nickel oxide represented by a compositional formula of LidNi1-a-b-cCoaAlbMcO2, where M represents at least one element selected from Na, Cu, W, Fe, and Zn, and 0≤a≤0.2, 0≤b≤0.2, 0≤c≤0.1, and 0.90≤d≤1.1 are satisfied. When N represents the number of unpaired electrons of nickel ions per 1 g of the lithium nickel oxide, μeff represents an effective magnetic moment derived from nickel ions, H represents an applied magnetic field of 0.1T, and kB represents the Boltzmann constant, Nμeff 2H / 3kB equals 6.46×10-3-6.87×10-3 (J·K) / (g·T).

Description

Positive electrode active material and secondary battery

[0001] The present invention relates to a positive electrode active material and a secondary battery.

[0002] Patent Document 1 discloses a battery using lithium nickel oxide.

[0003] Japanese Patent Application Laid-Open No. 2018-20950

[0004] However, in the lithium nickel oxide described in Patent Document 1, when nickel atoms are arranged at the lithium sites, the amount of lithium ions that contribute to charge and discharge decreases, which may result in a decrease in the initial charge capacity.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide a positive electrode active material and a secondary battery having a high initial charge capacity.

[0006] The positive electrode active material according to one embodiment of the present invention has a composition formula of Li ｄ Ni １－ａ－ｂ－ｃ Co ａ Al ｂ M ｃ O ２ wherein M is at least one element selected from Na, Cu, W, Fe, and Zn, and the ranges of 0≦a≦0.2, 0≦b≦0.2, 0≦c≦0.1, and 0.90≦d≦1.1 are satisfied, and N is the number of unpaired electrons of nickel ions per gram of the lithium nickel oxide, μ eff is the effective magnetic moment due to nickel ions, H is the applied magnetic field of 0.1 T, k Ｂ is the Boltzmann constant, Nμ eff ２ H / 3k Ｂ is 6.46 x 10 －３ (J・K) / (g・T) or more 6.87×10 －３ It is less than (J·K) / (g·T).

[0007] A secondary battery according to one aspect of the present invention is a secondary battery including a positive electrode containing a positive electrode active material, a negative electrode, and an electrolyte, wherein the positive electrode active material has a composition formula of Li ｄ Ni １－ａ－ｂ－ｃ Co ａ Al ｂ M ｃO ２ wherein M is at least one element selected from Na, Cu, W, Fe, and Zn, and 0≦a≦0.2, 0≦b≦0.2, 0≦c≦0.1, and 0.90≦d≦1.1 are satisfied, and when the secondary battery is in a fully charged state, N is the number of unpaired electrons of nickel ions per 1 g of the lithium nickel oxide, μ eff is the effective magnetic moment due to nickel ions, H is the applied magnetic field of 0.1 T, k Ｂ is the Boltzmann constant, Nμ eff ２ H / 3k Ｂ is 6.46 x 10 －３ (J・K) / (g・T) or more 6.87×10 －３ It is less than (J·K) / (g·T).

[0008] According to the present invention, it is possible to provide a positive electrode active material and a secondary battery having a high initial charge capacity.

[0009] Fig. 1 is a cross-sectional view showing an example of a secondary battery according to a first embodiment. Fig. 2 is an enlarged cross-sectional view showing a part of a cross section of the electrode body according to Fig. 1. Fig. 3 is a cutaway view showing another example of the secondary battery according to the first embodiment. Fig. 4 is a schematic view of a cross section taken along line IV-IV in Fig. 3.

[0010] Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to this embodiment.

[0011] (Secondary battery) Fig. 1 is a cross-sectional view showing an example of a secondary battery according to the first embodiment. The secondary battery 1 shown in Fig. 1 is a laminated lithium-ion secondary battery. As shown in Fig. 1, the secondary battery 1 includes a battery element 20, an exterior member 30, and an adhesive 32.

[0012] The battery element 20 is provided inside an exterior member 30. As shown in FIG. 1 , the battery element 20 includes an electrode body 200, a positive electrode lead 21, and a negative electrode lead 22. The positive electrode lead 21 is a terminal drawn from a positive electrode 210 (described later) to the outside of the exterior member 30. That is, the positive electrode lead 21 is a terminal that serves as a positive electrode of the secondary battery 1. In FIG. 1 , the positive electrode lead 21 is provided on an end surface of the electrode body 200. The negative electrode lead 22 is a terminal drawn from the inside of a negative electrode 220 (described later) to the outside of the exterior member 30. That is, the negative electrode lead 22 is a terminal that serves as a negative electrode of the secondary battery 1. In FIG. 1 , the negative electrode lead 22 is provided on an end surface of the electrode body 200. Details of the electrode body 200 will be described later.

[0013] The exterior member 30 is a case in which the battery element 20 is housed. The exterior member 30 includes two exterior sheets 30a and 30b. The exterior sheets 30a and 30b each include an insulating layer, a metal layer, and an outermost layer. In the example of FIG. 1 , the exterior sheet 30a has a recess 31. As a result, the battery element 20 is housed in the exterior member 30 by housing the battery element 20 in the recess 31 and bonding the peripheral edges of the exterior sheets 30a and 30b.

[0014] The exterior sheets 30a, 30b are constructed by laminating an insulating layer, a metal layer, and an outermost layer in this order from the inside, i.e., the side where the battery element 20 is provided, and then bonding them together by lamination or other processing. The insulating layers of the exterior sheets 30a, 30b are made of resins such as polyethylene, polypropylene, modified polyethylene, modified polypropylene, and polyolefin resins containing ethylene or propylene as monomers. This allows the exterior sheets 30a, 30b to reduce the moisture permeability of the secondary battery 1 and improve its airtightness. The metal layers of the exterior sheets 30a, 30b are metal plate or foil materials such as aluminum, stainless steel, nickel, and iron. The outermost layer may be made of any material, but is preferably made of the same resin as the insulating layer or a material with high resistance to tearing and punctures, such as nylon.

[0015] The adhesive 32 is a member for making the exterior member 30 airtight. The adhesive 32 is provided between the exterior member 30 and the positive electrode lead 21 and the negative electrode lead 22. The material of the adhesive 32 preferably has adhesion to the positive electrode lead 21 and the negative electrode lead 22. For example, when the positive electrode lead 21 and the negative electrode lead 22 are made of a metal material, the adhesive 32 is made of a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene. This allows the adhesive 32 to seal the gap between the exterior member 30 and the positive electrode lead 21 and the negative electrode lead 22, thereby making the interior of the exterior member 30 airtight.

[0016] Fig. 2 is an enlarged cross-sectional view showing a portion of the cross section of the electrode assembly in Fig. 1. More specifically, Fig. 2 is a cross-sectional view showing a portion of one layer of a positive electrode 210 and one layer of a negative electrode 220 of the electrode assembly 200. As shown in Fig. 2, the electrode assembly 200 includes a positive electrode 210, a negative electrode 220, and a separator 230. In the secondary battery 1, the electrode assembly 200 has a structure in which the positive electrode 210 and the negative electrode 220 are stacked in the thickness direction with the separator 230 interposed therebetween. The positive electrode 210 and the negative electrode 220 included in the electrode assembly 200 are layered members for the charge / discharge reaction of the secondary battery 1 according to the first embodiment.

[0017] The positive electrode 210 includes a positive electrode current collector 211 and a positive electrode active material layer 212. In the positive electrode 210, the positive electrode current collector 211 is laminated between the positive electrode active material layers 212.

[0018] The positive electrode current collector 211 is a conductive layer, and may be made of, for example, aluminum foil, stainless steel foil, etc. In the example of Fig. 1 , the positive electrode current collector 211 has a rectangular shape in plan view in the thickness direction, with protrusions on the positive electrode lead 21 side. The protrusions of the positive electrode current collector 211 are connected to the positive electrode lead 21.

[0019] The positive electrode active material layer 212 is a layer containing a positive electrode active material. The positive electrode active material layer 212 includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive additive. The positive electrode active material layer 212 is not limited to the materials listed above, and may further include, for example, a dispersant.

[0020] The positive electrode active material has the composition formula Liｄ Ni １－ａ－ｂ－ｃ Co ａ Al ｂ M ｃ O ２ The lithium nickel oxide includes a lithium nickel oxide having the formula: where element M is at least one element selected from Na, Cu, W, Fe, and Zn. The formulas 0≦a≦0.2, 0≦b≦0.2, 0≦c≦0.1, and 0.90≦d≦1.1 are satisfied. That is, the lithium nickel oxide may not contain Co, Al, and element M. The values ​​of element M and a, b, and c can be identified or measured by ICP (Inductively Coupled Plasma) emission spectroscopy.

[0021] Here, N is the number of unpaired electrons per gram of lithium nickel oxide, μ eff is the effective magnetic moment, H is the applied magnetic field of 0.1 T, k Ｂ is the Boltzmann constant, Nμ eff ２ H / 3k Ｂ is 6.46 x 10 －３ (J・K) / (g・T) or more 6.87×10 －３ (J·K) / (g·T) or less. This allows the initial charge capacity to be improved. On the other hand, Nμ eff ２ H / 3k Ｂ is 6.46 x 10 －３ When the ratio is less than (J·K) / (g·T), the divalent nickel ions (Ni ２＋ ) is large, and the amount of nickel placed at the lithium site is large, so the amount of lithium ions contributing to charge and discharge is reduced, and the initial charge capacity may decrease. eff ２ H / 3k Ｂ is 6.87 x 10 －３ If it is greater than (J·K) / (g·T), the resistance of the positive electrode active material increases, which may result in a decrease in the initial charge capacity.

[0022] Nμ eff ２ H / 3k Ｂcan be measured by the effective magnetic moment method using a SQUID (Superconducting Quantum Interference Device). More specifically, a positive electrode active material is removed from a fully charged battery, a 0.1 T magnetic field is applied to the positive electrode active material as a measurement sample, and the magnetic moment m per 1 g of the measurement sample is measured using a SQUID. In this disclosure, when the operating voltage range is known from the battery package, the battery pack package, and the documents associated with their specifications and instructions, the fully charged state refers to the state in which the upper limit voltage of the operating voltage range is reached. Furthermore, when the upper limit of the operating voltage range is not clearly stated, the battery and battery pack are connected to a charging device, etc., and the voltage profile during charging is measured. The voltage at the end of charging under the control of the charging circuit, etc., is defined as the full charge voltage, and the fully charged state refers to the state in which the full charge voltage is reached.

[0023] Nμ eff ２ H / 3k Ｂ is calculated from the magnetic moment m measured above. eff ２ H / 3k Ｂ In the calculation, the valence that nickel ions can take is divalent (Ni ２＋ ) and trivalent (Ni ３＋ ) only, and Ni ２＋ and Ni ３＋ is assumed to have a low spin electron configuration. In this electron configuration, Ni ２＋ and Ni ３＋ All have unpaired electrons. eff ２ H / 3k Ｂ is calculated by the following formula (1) based on the Curie-Weiss law: In formula (1), N is the number of unpaired electrons of nickel ions per 1 g of the measurement sample, and Ni ２＋ and Ni ３＋ is the sum of the number of unpaired electrons possessed by μ ｅｆｆ is the magnitude of the effective magnetic moment originating from nickel ions, H is the magnitude of the magnetic field applied during measurement and is a constant of 0.1 T, and k Ｂ is the Boltzmann constant, T is the measurement temperature, θ is the Weiss temperature, and m ０is the magnetic moment due to the diamagnetic effect of the closed-shell electrons of the nickel ion.

[0024]

[0025] The magnitude of the effective magnetic moment μ due to nickel ions ｅｆｆ is expressed by the following formula (2): where S is the spin quantum number, and Ni ２＋ In this case, S=1 and Ni ３＋ In this case, S = 1 / 2. Also, μ Ｂ is the Bohr magneton, and g ０ is the g-factor of a free electron. From this, the calculated Nμ eff ２ H / 3k Ｂ By calculating the spin quantum number S from the value of Ni ２＋ and Ni ３＋ The molar ratio can be calculated.

[0026]

[0027] The positive electrode binder contained in the positive electrode active material layer 212 may be any material, and may include, for example, one or more of synthetic rubber and polymer compounds. Examples of synthetic rubber include styrene-butadiene rubber, fluorine-based rubber, and ethylene propylene diene. Examples of polymer compounds include polyvinylidene fluoride (PVdF) and polyimide.

[0028] The positive electrode conductive additive contained in the positive electrode active material layer 212 may be any material, and may include, for example, carbon. Examples of carbon include graphite, carbon black, acetylene black, and ketjen black. However, the positive electrode conductive additive contained in the positive electrode active material layer 212 is not limited to these materials as long as it is a conductive material, and may also be a metal material, a conductive polymer, or the like.

[0029] The negative electrode 220 includes a negative electrode current collector 221 and a negative electrode active material layer 222. In the negative electrode 220, the negative electrode current collector 221 is laminated between the negative electrode active material layers 222.

[0030] The negative electrode current collector 221 is a conductor, and for example, copper foil or the like can be used. In the example of Fig. 1 , the shape of the negative electrode current collector 221 is a rectangular sheet having protrusions on the negative electrode lead 22 side when viewed in a plan view in the thickness direction. The protrusions of the negative electrode current collector 221 are connected to the negative electrode lead 22.

[0031] The negative electrode active material layer 222 is a layer containing a negative electrode active material. The negative electrode active material layer 222 is not limited to being made of only a negative electrode active material, and may also contain, for example, a conductive additive and a binder.

[0032] The negative electrode active material refers to a reducing agent that can absorb and desorb charge carriers of the secondary battery 1 through charge and discharge reactions, such as a carbon material, a metal, a semimetal, a silicon alloy or compound, or a tin (Sn) alloy or compound.

[0033] The negative electrode active material containing silicon includes, for example, elemental silicon, silicon alloys, and silicon compounds. Examples of silicon alloys that can be used as the negative electrode active material include those containing at least one element selected from the group consisting of tin (Sn), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and chromium (Cr) as the second constituent element other than silicon. Examples of silicon compounds that can be used as the first negative electrode active material include silicon oxide (SiO ｘ Examples of the negative electrode active material include those containing oxygen (O) or carbon (C), such as silicon carbide (SiC), and may contain the second constituent element described above in addition to silicon. The negative electrode active material may also be doped with Li. ｘ In this case, it is preferable that Li is pre-doped by doping with Li in the process of producing the negative electrode 220. ｘThe negative electrode active material may be a composite of Si and other materials such as carbon, or a composite of a Si alloy and other materials such as carbon. In this case, the irreversible capacity can be reduced. In addition, it is preferable that the particle surfaces of the negative electrode active material are partially or entirely coated with carbon. This can improve the electronic conductivity of the particle surfaces of the negative electrode active material.

[0034] Examples of carbon materials that can be used as the negative electrode active material include MCMB (MesoCarbon MicroBeads), artificial graphite, natural graphite, non-graphitizable carbon, and graphitizable carbon. More specifically, examples of materials that can be used as the negative electrode active material include pyrolytic carbons, cokes, glassy carbon fiber, fired organic polymer compounds, activated carbon, and carbon blacks. Examples of cokes include pitch coke, needle coke, and petroleum coke. Here, fired organic polymer compounds are produced by firing a polymer compound such as a phenolic resin or a furan resin at an appropriate temperature and carbonizing it.

[0035] The negative electrode active material is not limited to those listed above, and may contain other negative electrode active materials, such as metals, semimetal alloys or compounds, and tin (Sn) alloys or compounds, which can absorb and release lithium. Examples of metals and semimetals that can be used as negative electrode active materials include tin (Sn), lead (Pb), aluminum (Al), indium (In), zinc (Zn), antimony (Sb), bismuth (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y), and hafnium (Hf). Among these, germanium, tin, and lead are preferred. Tin is more preferred because it has a high ability to absorb and release lithium and can achieve a high energy density.

[0036] Examples of tin alloys that can be used as the negative electrode active material include those containing at least one of nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as a second constituent element other than tin. Examples of tin compounds that can be used as the negative electrode active material include those containing oxygen or carbon, and may contain the above-mentioned second constituent element in addition to tin.

[0037] The separator 230 is a film that insulates the positive electrode 210 from the negative electrode 220. The separator 230 is provided between the main surface of the positive electrode 210 and the main surface of the negative electrode 220 so that the positive electrode 210 and the negative electrode 220 do not come into direct contact with each other. In the example of Fig. 1 , the shape of the separator 230 is a rectangular sheet when viewed in plan in the thickness direction.

[0038] The separator 230 is preferably made of a material that is electrically stable, chemically stable with respect to the positive electrode active material, the negative electrode active material, and the electrolyte, and is insulating. The separator 230 can be made of, for example, a polymer nonwoven fabric, a porous film, or a layer of glass or ceramic fibers. The separator 230 is more preferably made of a porous polyolefin film. This improves battery safety by preventing short circuits and providing a shutdown effect.

[0039] The electrolyte solution is impregnated into the separator 230. In the example of Fig. 1, the electrolyte solution fills the space inside the exterior member 30. The electrolyte solution is a non-aqueous electrolyte solution containing an electrolyte salt and a solvent that dissolves the electrolyte salt.

[0040] The electrolyte salt is, for example, lithium perchlorate (LiClO ４ ), lithium hexafluorophosphate (LiPF ６ ), lithium tetrafluoroborate (LiBF ４ ), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO ２ CF ３ ) ２ ), lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO ２ C ２ F５ ) ２ ), lithium hexafluoroarsenate (LiAsF ６ ) and other lithium salts.

[0041] Examples of the solvent include lactone-based solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone; carbonate-based solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; ether-based solvents such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; nitrile-based solvents such as acetonitrile; sulfolane-based solvents; phosphoric acids; phosphate ester solvents; and pyrrolidones.

[0042] The electrolytic solution may further contain an additive such as a fluorinated carboxylic acid ester, a sulfonic acid ester, a sulfonic acid anhydride, or a carboxylic acid anhydride.

[0043] The battery according to the first embodiment has been described above, but the secondary battery according to the first embodiment is not limited to that shown in Fig. 1. Other examples will be described below using the drawings, but the same components as those in Figs. 1 and 2 will be designated by reference numerals and will not be described again.

[0044] Fig. 3 is a cutaway view showing a different example of the secondary battery according to the first embodiment. Fig. 4 is a schematic view of a cross section taken along line IV-IV in Fig. 3. The secondary battery 1A shown in Figs. 3 and 4 differs from the example shown in Fig. 1 in that an electrode body 200A is wound around a positive electrode lead 21A and a negative electrode lead 22A.

[0045] The battery element 20A is provided inside the exterior member 30. As shown in FIG. 4 , the battery element 20A includes an electrode body 200A, a positive electrode lead 21A, a negative electrode lead 22A, and a protective material 23. The positive electrode lead 21A is a terminal drawn from inside the battery element 20A to the outside of the exterior member 30, and the positive electrode lead 21A is provided near the center of the battery element 20A. The negative electrode lead 22A is a terminal drawn from inside the battery element 20A to the outside of the exterior member 30, and the negative electrode lead 22A is provided near the center of the battery element 20A. The protective material 23 is a member that protects the outside of the battery element 20A. The protective material 23 is provided so as to be wrapped around the electrode body 200A. The protective material 23 is, for example, an insulating tape.

[0046] 4 , the electrode assembly 200A is a laminate for the charge / discharge reaction of the secondary battery 1A according to the first embodiment. The electrode assembly 200A includes a positive electrode 210A including a positive electrode current collector 211A and a positive electrode active material layer 212A, a negative electrode 220A including a negative electrode current collector 221A and a negative electrode active material layer 222A, and a separator 230A. The electrode assembly 200A has a structure in which the positive electrode lead 21A and the negative electrode lead 22A are wound around the center, and is laminated in the following order from the outside, i.e., from the protective material 23 side: the negative electrode current collector 221A, the negative electrode active material layer 222A, the separator 230A, the positive electrode active material layer 212A, the positive electrode current collector 211A, the positive electrode active material layer 212A, the separator 230A, and the negative electrode active material layer 222A. In the electrode body 200A, no layers other than the negative electrode current collector 221A, separator 230A, and positive electrode current collector 211A are provided near the positive electrode lead 21A and the negative electrode lead 22A. With this structure, the positive electrode current collector 211A is connected to the positive electrode lead 21A, and the negative electrode current collector 221A is connected to the negative electrode lead 22A.

[0047] As described above, the positive electrode active material according to the first embodiment has the composition formula Li ｄ Ni １－ａ－ｂ－ｃ Co ａ Al ｂ M ｃ O ２The lithium nickel oxide includes a lithium nickel oxide represented by the formula (I) where M is at least one element selected from Na, Cu, W, Fe, and Zn, and satisfies the following conditions: 0≦a≦0.2, 0≦b≦0.2, 0≦c≦0.1, and 0.90≦d≦1.1. N is the number of unpaired electrons of nickel ions per gram of lithium nickel oxide, μ eff is the effective magnetic moment due to nickel ions, H is the applied magnetic field of 0.1 T, k Ｂ is the Boltzmann constant, Nμ eff ２ H / 3k Ｂ is 6.46 x 10 －３ (J・K) / (g・T) or more 6.87×10 －３ (J·K) / (g·T) or less. This allows the initial charge capacity to be improved.

[0048] The secondary battery 1 according to the first embodiment is a battery including a positive electrode 210 containing a positive electrode active material, a negative electrode 220, and an electrolyte. ｄ Ni １－ａ－ｂ－ｃ Co ａ Al ｂ M ｃ O ２ where M is at least one element selected from Na, Cu, W, Fe, and Zn, and satisfies 0≦a≦0.2, 0≦b≦0.2, 0≦c≦0.1, and 0.90≦d≦1.1. When the secondary battery 1 is in a fully charged state, N is the number of unpaired electrons of nickel ions per 1 g of the lithium nickel oxide, μ eff is the effective magnetic moment due to nickel ions, H is the applied magnetic field of 0.1 T, k Ｂ is the Boltzmann constant, Nμ eff ２ H / 3k Ｂ is 6.46 x 10 －３ (J・K) / (g・T) or more 6.87×10 －３ (J·K) / (g·T) or less. This allows the initial charge capacity to be improved.

[0049] (Method for manufacturing a positive electrode mixture) An example of a method for manufacturing a positive electrode active material according to the first embodiment will be described below. Note that the method for manufacturing a positive electrode mixture according to this embodiment is merely an example and is not limited to the following. First, an aqueous sulfate solution of Ni, Al, and Co is prepared, and then the sulfate solution is added to an alkaline aqueous solution and stirred to precipitate a coprecipitate. Here, the alkaline aqueous solution can be an aqueous solution of an ammonia solution, a hydroxide of element M, or the like. The sulfate aqueous solution does not need to contain Al or Co. Thereafter, the coprecipitate is washed and dried, and lithium hydroxide is mixed therewith to prepare a precursor. The precursor is then calcined to obtain lithium nickel oxide as the positive electrode active material.

[0050] Here, it is preferable that the precursor of lithium nickel oxide is fired at a temperature rising rate of 100° C. / min or more. ｅｆｆ ２ H / 3k Ｂ 6.46 x 10 －３ (J・K) / (g・T) or more 6.92×10 －３ (J·K) / (g·T) or less, and the initial charge capacity can be improved.

[0051] Examples will be described below. Table 1 shows examples and comparative examples. Note that the present invention is not limited to these examples.

[0052]

[0053] Example 1 A positive electrode according to Example 1 was produced by the following method.

[0054] The positive electrode active material according to Example 1 was prepared by the following method.

[0055] First, nickel (II) sulfate heptahydrate was dissolved in distilled water to obtain an aqueous sulfate solution with a molar concentration of Ni ions of 1.5 mol / L.

[0056] Then, an alkaline aqueous solution containing ammonium at a concentration of 10 mol / L and sodium hydroxide at a concentration of 5 mol / L was charged into a 2 L reaction vessel, the reaction vessel was heated to 50°C with a heater, and the sulfate aqueous solution was added while stirring with a paddle-type stirring blade. The sulfate aqueous solution was added at a rate of 5.0 g / min over 24 hours. The sulfate aqueous solution was added so as to maintain the pH at 11.0. This resulted in the precipitation of a coprecipitate.

[0057] The obtained coprecipitate was washed by repeatedly filtering under pressure and dispersing in distilled water to remove impurities. The washing was completed when the electrical conductivity of the filtrate became less than 20 mS / m. The washed coprecipitate was dried by heating at 100°C for 10 hours and then sieved through a 90 μm mesh sieve. This resulted in the D ５０ The diameter was 10 μm.

[0058] The obtained coprecipitate and lithium hydroxide (purity 99.99%, D ５０ The precursor was heated at a rate of 100°C / min in an atmosphere containing 97% by volume of oxygen, fired at 660°C for 20 hours, and cooled to 30°C at a rate of 5°C / min to obtain a fired product. The fired product was sieved through a 90 μm mesh to obtain the cathode active material according to Example 1. As a result, the D of the cathode active material according to Example 1 was obtained. ５０ The diameter was 10 μm.

[0059] Thereafter, 95% by mass of the positive electrode active material according to Example 1, 3% by mass of carbon black as a positive electrode conductive assistant, and 2% by mass of polyvinylidene fluoride as a positive electrode binder were mixed and dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry positive electrode mixture.

[0060] Then, this slurry-like positive electrode mixture was uniformly applied to a strip-shaped aluminum foil (positive electrode current collector) having a thickness of 15 μm to form a coating film. Next, this coating film was dried with hot air and then compression-molded using a roll press to form a positive electrode sheet having a positive electrode active material layer. The prepared positive electrode sheet was punched to a diameter of 16.5 mm and vacuum-dried at 120 ° C. for 10 hours using a vacuum dryer to obtain a positive electrode according to Example 1.

[0061] The negative electrode according to Example 1 was fabricated by laminating a negative electrode active material layer on a negative electrode current collector layer. The negative electrode active material layer according to Example 1 was fabricated by punching a 0.24 mm thick lithium (Li) foil into a disk with a diameter of 17 mm. The negative electrode current collector layer according to Example 1 was a 200 μm thick stainless steel (SUS) plate.

[0062] The separator according to Example 1 was prepared by punching a polyolefin sheet having a thickness of 15 μm into a disk having a diameter of 17.5 mm.

[0063] The electrolyte solution according to Example 1 was prepared by dissolving lithium hexafluorophosphate (LiPF ) as a solute in a solvent containing 30% by mass of ethylene carbonate (EC) and 70% by mass of ethyl methyl carbonate (EMC). ６ ) was dissolved to a concentration of 1 mol / L.

[0064] The battery according to Example 1 was fabricated by the following method. First, the fabricated negative electrode was placed in a stainless steel cup-shaped anode cup. The negative electrode current collector was placed so that it was in contact with the anode cup. The fabricated separator was then laminated on the negative electrode active material layer. Then, 150 μL of the fabricated electrolyte was impregnated into the separator, so that it also penetrated into the gap between the negative electrode and the anode cup. The fabricated positive electrode was then laminated on the separator so that the positive electrode active material layer was in contact with the separator. An aluminum plate was then laminated on the positive electrode current collector layer of the positive electrode, and a stainless steel cup-shaped cathode cup was laminated on the aluminum plate. A gasket made of an insulating material was then provided between the periphery of the anode cup and the periphery of the cathode cup. The anode cup and the cathode cup were then sealed using a crimping machine to form an exterior housing, thereby fabricating the battery according to Example 1.

[0065] <Analysis of Positive Electrode Active Material> The positive electrode active material was analyzed by the effective magnetic moment method. ｅｆｆ ２ H / 3k Ｂ The measurement by the effective magnetic moment method was carried out by applying a magnetic field H of 0.1 T with a SQUID. As shown in Table 1, the measurement by the effective magnetic moment method resulted in Nμｅｆｆ ２ H / 3k Ｂ is 6.92 x 10 －３ (J K) / (g T). And Nμ ｅｆｆ ２ H / 3k Ｂ Based on the value of Ni of the positive electrode active material ３＋ and Ni ２＋ The molar ratio of Ni in the positive electrode active material is ３＋ and Ni ２＋ The calculation was carried out assuming that the positive electrode active material was composed of only Ni. ３＋ and Ni ２＋ The molar ratio was calculated to be 0.98555:0.01445.

[0066] <<Initial Charge / Discharge Test>> An initial charge / discharge test was performed on the prepared battery. The initial charge / discharge test was performed in a thermostatic chamber at 25°C. In the initial charge / discharge test, the prepared battery was charged at a constant current / constant voltage of 0.1 C to an upper limit voltage of 4.25 V / a lower limit current of 0.005 C, then rested for 10 minutes, and discharged at a current of 0.1 C to a lower limit voltage of 2.0 V, and the initial charge capacity was measured. The initial charge / discharge capacity was calculated per 1 g of the positive electrode active material.

[0067] (Example 2) In Example 2, as shown in Table 1, a battery was fabricated and measured in the same manner as in Example 1, except that the firing temperature of the precursor was set to 680°C. As a result of measurement by the effective magnetic moment method, Nμ ｅｆｆ ２ H / 3k Ｂ is 6.87 x 10 －３ (J·K) / (g·T). ３＋ and Ni ２＋ The molar ratio of the two compounds was calculated to be 0.98544:0.01456.

[0068] (Example 3) In Example 3, as shown in Table 1, a battery was fabricated and measured in the same manner as in Example 1, except that the firing temperature of the precursor was set to 700°C. As a result of measurement by the effective magnetic moment method, Nμ ｅｆｆ ２ H / 3k Ｂ is 6.47 x 10 －３ (J·K) / (g·T).３＋ and Ni ２＋ The molar ratio of the two compounds was calculated to be 0.98452:0.01548.

[0069] (Example 4) In Example 4, as shown in Table 1, a battery was fabricated and measured in the same manner as in Example 1, except that the precursor was fired at 720°C. As a result of measurement by the effective magnetic moment method, Nμ ｅｆｆ ２ H / 3k Ｂ is 6.46 x 10 －３ (J·K) / (g·T). ３＋ and Ni ２＋ The molar ratio of the two compounds was calculated to be 0.98454:0.01546.

[0070] (Comparative Example 1) In Comparative Example 1, a battery was fabricated and measured in the same manner as in Example 1, except that the precursor temperature was increased at 5°C / min and the firing temperature was set to 700°C, as shown in Table 1. As a result of measurement by the effective magnetic moment method, Nμ ｅｆｆ ２ H / 3k Ｂ is 6.93 x 10 －３ (J·K) / (g·T). ３＋ and Ni ２＋ The molar ratio of the two compounds was calculated to be 0.98557:0.01443.

[0071] (Comparative Example 2) In Comparative Example 2, a battery was fabricated and measured in the same manner as in Example 1, except that the precursor temperature was increased at 5°C / min and the firing temperature was set to 720°C, as shown in Table 1. As a result of measurement by the effective magnetic moment method, Nμ ｅｆｆ ２ H / 3k Ｂ is 6.40 x 10 －３ (J·K) / (g·T). ３＋ and Ni ２＋ The molar ratio of the two compounds was calculated to be 0.98438:0.01563.

[0072] As shown in Table 1, in Examples 1 to 4, Nμ ｅｆｆ ２ H / 3k Ｂ 6.46 x 10 －３(J・K) / (g・T) or more 6.92×10 －３ By making it (J K) / (g T) or less, Nμ ｅｆｆ ２ H / 3k Ｂ is 6.92 x 10 －３ Nμ of Comparative Example 1 and the positive electrode active material greater than (J·K) / (g·T) ｅｆｆ ２ H / 3k Ｂ is 6.46 x 10 －３ The initial charge-discharge capacity was improved compared to Comparative Example 2, in which the ratio was less than (J·K) / (g·T).

[0073] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and equivalents thereof are also included in the present invention.

[0074] REFERENCE SIGNS LIST 1, 1A Secondary battery 20, 20A Battery element 21, 21A Positive electrode lead 22, 22A Negative electrode lead 23 Protective material 30 Exterior member 30a, 30b Exterior sheet 31 Recess 32 Adhesive material 200, 200A Electrode body 210, 210A Positive electrode 211, 211A Positive electrode current collector 212, 212A Positive electrode active material layer 220, 220A Negative electrode 221, 221A Negative electrode current collector 222, 222A Negative electrode active material layer 230, 230A Separator

Claims

1. The formula is Li ｄ Ni １－ａ－ｂ－ｃ Co ａ A ｂ M ｃ O ２ M is at least one element selected from Na, Cu, W, Fe, and Zn, and 0≦a≦0.2, 0≦b≦0.2, 0≦c≦0.1, and 0.90≦d≦1.1 are satisfied, N is the number of unpaired electrons of nickel ions per gram of the lithium nickel oxide, μ eff is the effective magnetic moment due to nickel ions, H is the applied magnetic field of 0.1 T, k Ｂ If is the Boltzmann constant, Nμ eff ２ H / 3k Ｂ is 6.46 x 10 －３ (J・K) / (g・T) or more 6.87×10 －３ (J·K) / (g·T) or less.

2. A secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode, and an electrolyte, wherein the positive electrode active material has a composition formula of Li ｄ Ni １－ａ－ｂ－ｃ Co ａ A ｂ M ｃ O ２ M is at least one element selected from Na, Cu, W, Fe, and Zn, and satisfies 0≦a≦0.2, 0≦b≦0.2, 0≦c≦0.1, and 0.90≦d≦1.1, and N is the number of unpaired electrons of nickel ions per gram of the lithium nickel oxide when the secondary battery is in a fully charged state, μ eff is the effective magnetic moment due to nickel ions, H is the applied magnetic field of 0.1 T, k Ｂ If is the Boltzmann constant, Nμ eff ２ H / 3k Ｂ is 6.46 x 10 －３ (J・K) / (g・T) or more 6.87×10 －３ A secondary battery having a capacitance of (J·K) / (g·T) or less.

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