Battery

Abstract

This battery (100) has a positive electrode (23), a negative electrode (26), a separator (27), and an electrolyte solution (29), the positive electrode (23) containing lithium oxide as a positive electrode active material, the lithium oxide having an anti-fluorite crystal structure and in which a transition metal is solid-solved, and the electrolyte solution (29) containing at least one additive selected from the group consisting of organic phosphorus compounds and organic phosphorous acid compounds. The electrolyte (29) may further contain a non-aqueous solvent, and the additive may be dissolved in the non-aqueous solvent.

Description

Technical Field

[0001] The present disclosure relates to batteries. Background Art

[0002] As described in Patent Document 1, secondary batteries have long been known to utilize the redox reaction between lithium oxide (Li2O) and lithium peroxide (Li2O2). However, lithium oxide and lithium peroxide have poor electronic conductivity, resulting in high overvoltage, which has been a technical challenge.

[0003] Patent Document 2 discloses that charge overvoltage can be reduced by forming a transition metal into a solid solution in the crystal structure of lithium oxide.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 4554935

[0007] Patent Document 2: Japanese Patent No. 6179944 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] Conventionally, there is room for improvement in terms of battery cycle characteristics.

[0010] Means for solving problems

[0011] The present disclosure provides a battery,

[0012] It has a positive electrode, a negative electrode, a separator and an electrolyte.

[0013] The positive electrode contains lithium oxide as a positive electrode active material. The lithium oxide has an inverse fluorite crystal structure and contains a transition metal in a solid solution.

[0014] The electrolyte contains at least one additive selected from the group consisting of organic phosphorus compounds and organic phosphorous acid compounds.

[0015] Effects of the Invention

[0016] According to the technology of the present disclosure, the cycle characteristics of the battery can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional view showing a schematic structure of a battery according to one embodiment of the present disclosure.

[0018] Figure 2 The diagram shows the structural formulas of organophosphorus compounds and organophosphorous acid compounds.

[0019] Figure 3 Graph showing the charge end voltage of the batteries of Examples 1 to 7 and Comparative Example 1 in each cycle.

[0020] Figure 4A The X-ray diffraction pattern of the positive electrode active material in the case where the transition metal M1 is Co is shown.

[0021] Figure 4B Shown is an X-ray diffraction pattern of the positive electrode active material when the transition metal M1 is Cu.

[0022] Figure 4C Shown is an X-ray diffraction pattern of the positive electrode active material when the transition metal M1 is Fe.

[0023] Figure 5A An SEM image of the positive electrode active material of Sample 3 is shown.

[0024] Figure 5B An SEM image of the positive electrode active material of Sample 17 is shown.

[0025] Figure 6 The graph shows the charge and discharge curves of sample 1 and sample 14.

[0026] Figure 7 This is a plot of the calculated results of the integrated intensity ratio I2 / I1 and the integrated intensity ratio I3 / I1 of the positive electrode active materials of Samples 1 to 28. DETAILED DESCRIPTION

[0027] (Knowledge serving as the basis of this disclosure)

[0028] By utilizing the redox reaction between lithium oxide and lithium peroxide, a battery with a higher theoretical capacity than conventional lithium-ion batteries can be obtained. The theoretical capacity is 897 mAh per 1g of lithium oxide. On the other hand, since the lithium peroxide generated during charging is a peroxide, it is unstable and may decompose through reaction with the electrolyte. Furthermore, conventional lithium-ion batteries operate at 2.5V to 4.5V (vs. Li / Li + ) level, while the battery using lithium oxide as the positive electrode active material is charged and discharged at 1.8V~3.4V (vs.Li / Li + ) levels. This is because further increases in the charging potential generate oxygen. Specifically, the potential range used by batteries using lithium oxide as the positive electrode active material differs from that used by conventional lithium-ion batteries. Thus, lithium oxide-based positive electrode active materials have characteristics different from those used in conventional lithium-ion batteries. Therefore, detailed conditions for improving cycle characteristics, such as the composition of the electrolyte, are largely unknown.

[0029] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments.

[0030] (Implementation Method)

[0031] Figure 1 This is a cross-sectional view showing a schematic structure of a battery 100 according to one embodiment of the present disclosure. The battery 100 includes a positive electrode 23, a negative electrode 26, an electrolyte 29, a separator 27, and an outer package 28. The positive electrode 23 includes a positive electrode collector 21 and a positive electrode active material layer 22. The positive electrode active material layer 22 is disposed on the positive electrode collector 21. The negative electrode 26 includes a negative electrode collector 24 and a negative electrode active material layer 25. The negative electrode active material layer 25 is disposed on the negative electrode collector 24. The separator 27 is disposed between the positive electrode 23 and the negative electrode 26. The positive electrode 23 and the negative electrode 26 face each other with the separator 27 interposed therebetween. The positive electrode 23, the negative electrode 26, the separator 27, and the electrolyte 29 are housed in the outer package 28. The battery 100 is a typical secondary battery.

[0032] The positive electrode active material layer 22 contains lithium oxide in which a transition metal M1 is solid-dissolved (doped) as the positive electrode active material. The lithium oxide in which the transition metal M1 is solid-dissolved has an inverse fluorite crystal structure. The inverse fluorite crystal structure is a structure in which the positional relationship between cations and anions in the fluorite structure is reversed. The reason why lithium oxide in which the transition metal M1 is solid-dissolved exhibits improved electronic conductivity is not fully understood, but is believed to be as follows. When the transition metal M1 is solid-dissolved in the lithium oxide, the transition metal M1 enters the lithium site, and oxygen atoms are tetrahedrally coordinated around the transition metal M1 to form an outer orbital complex. For example, in the case of cobalt, multiple unpaired electrons are present in the 3d orbital, and these unpaired electrons impart electronic conductivity to the lithium oxide. Furthermore, assuming the valence of the transition metal M1 is +3, since lithium has a valence of +1, in order to maintain charge neutrality within the crystal, two lithium atoms must be released from the crystal in addition to the lithium atoms that have replaced the transition metal M1, forming two vacancies. These vacancies serve as lithium ion conduction paths, thereby improving the ion conductivity of lithium oxide. The lithium oxide in which the transition metal M1 is solid-dissolved may be a substitutional solid solution.

[0033] The charge and discharge reaction formulas in the battery 100 are as follows.

[0034] Reaction in cathode 23: Li2O2 + 2Li + +2e - ⇔2Li2O

[0035] Reaction in negative electrode 26: Li⇔Li + +e -

[0036] The transition metal M1 is not particularly limited as long as it can be dissolved in lithium oxide. The transition metal M1 can be, for example, an element selected from the group of elements of Groups 3 to 11 of Periods 4 and 5 of the periodic table. Specifically, the transition metal M1 can contain at least one selected from Fe, Co, and Cu. The transition metal M1 can be Fe, Co, or Cu. These elements are preferred from the perspective of suppressing the increase in the charging voltage of the battery 100 and improving the discharge capacity of the battery 100.

[0037] Lithium oxide containing a transition metal M1 solid solution in a discharged state can have the compositions shown in the following formulas (A) and (B). According to quantum science calculations, when the valence of the transition metal M1 is +3, α preferably satisfies the relationship 0.0327 ≤ α ≤ 0.1484. When the valence of the transition metal M1 is +2, α preferably satisfies the relationship 0.0490 ≤ α ≤ 0.2224.

[0038] When the valence state of transition metal M1 is +3: (Li (1-3α) M1 α )2O・・・(A)

[0039] When the valence state of transition metal M1 is +2: (Li (1-2α) M1 α )2O・・・(B)

[0040] The amount of lithium contained in the positive electrode active material is defined as m0 (mol). The amount of transition metal M1 contained in the positive electrode active material is defined as m1 (mol). The ratio (m1 / (m0 + m1)) is, for example, not less than 0.01 and not more than 0.34. By appropriately adjusting the ratio (m1 / (m0 + m1)), the increase in the charge voltage of the battery 100 can be suppressed, while the discharge capacity of the battery 100 can be increased.

[0041] The positive electrode current collector 21 is a sheet or film made of a metal material such as aluminum, an aluminum alloy, stainless steel, titanium, or a titanium alloy. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material may also be coated on the surface of the positive electrode current collector 21 as a conductive auxiliary material.

[0042] The positive electrode active material layer 22 may also contain other materials such as a conductive additive, an ion conductor, and a binder.

[0043] Conductive additives and ion conductors are used to reduce the resistance of the positive electrode 23. Examples of conductive additives include carbon materials and conductive polymer compounds. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymer compounds include polyaniline, polypyrrole, and polythiophene. At least one selected from these conductive additives may be used.

[0044] Examples of ion conductors include polymethyl methacrylate, gel electrolytes such as polymethyl methacrylate, organic solid electrolytes such as polyethylene oxide, Li7La3Zr2O 12 Inorganic solid electrolytes such as ionic conductors, etc. At least one kind selected from these ionic conductors can be used.

[0045] The binder is used to improve the binding properties of the materials constituting the negative electrode 26. Examples of the binder include polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide. At least one selected from these binders may be used.

[0046] The negative electrode current collector 24 is a sheet or film made of a metal material such as stainless steel, nickel, a nickel alloy, copper, or a copper alloy. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material may be coated on the surface of the negative electrode current collector 24 as a conductive auxiliary material.

[0047] The negative electrode active material layer 25 may contain a negative electrode active material capable of absorbing and releasing lithium. Examples of negative electrode active materials capable of absorbing and releasing lithium include lithium titanate, graphite, silicon, silicon-containing oxides, zinc alloys, lithium metal, and lithium alloys. At least one selected from these negative electrode active materials may be used. As the negative electrode active material, lithium metal is more preferably used. The theoretical capacity of the positive electrode active material disclosed herein is 897 mAh per 1 g of lithium oxide, which is more than three times greater than other positive electrode active materials used in the past. Therefore, lithium metal is suitable as a negative electrode active material.

[0048] The negative electrode active material layer 25 may contain other materials such as a conductive additive, an ion conductor, and a binder. Materials that can be used for the positive electrode active material layer 22 may be used for the negative electrode active material layer 25 .

[0049] The electrolyte 29 may be impregnated in the positive electrode 23, the negative electrode 26, and the separator 27. The electrolyte 29 may also fill the inner space of the outer package 28. The electrolyte 29 allows lithium ions to move between the positive electrode 23 and the negative electrode 26.

[0050] In this embodiment, the electrolyte 29 contains at least one additive selected from an organic phosphorus compound and an organic phosphite compound. These additives contained in the electrolyte 29 have the effect of improving the cycle characteristics of the battery 100. The reason is not yet fully understood, but it is speculated as follows. In a battery that uses the redox reaction between lithium oxide and lithium peroxide, highly reactive lithium peroxide is generated on the surface of the positive electrode by charging, and the peroxide ions oxidize and decompose the anions of the lithium salt and the molecules of the organic solvent. As a result, a high resistance layer is formed on the surface of the positive electrode, causing an increase in the charging voltage. If an organic phosphorus compound and / or an organic phosphite compound is added to the electrolyte 29 as disclosed in the present invention, the lithium peroxide generated on the surface of the positive electrode 23 dissolves into the electrolyte 29, suppressing the formation of a high resistance layer on the surface of the positive electrode 23.

[0051] The organic phosphorus compound refers to a compound having a phosphorus-carbon bond. For example, the organic phosphorus compound includes at least one compound selected from the group consisting of the compound represented by the following formula (1), the compound represented by the following formula (2), and the compound represented by the following formula (3). In the formula (1), R 1 ~R 3 Each independently represents an organic group which may have a halogen atom or a hydrogen atom. 1 ~R 3 All are hydrogen atoms. In formula (2), R 5 is an organic group which may have a halogen atom, R 4 and R 6 Each independently represents an organic group which may have a halogen atom or a hydrogen atom. 4 and R 6 In the case where both are hydrogen atoms, R 7 ~R 9 Each independently represents an organic group which may have a halogen atom. With such a structure, the effect of improving the cycle characteristics of the battery 100 is easily obtained.

[0052]

[0053] R 1 ~R 9 Each of the above groups may independently be an organic group which may have a halogen atom. With such a configuration, the effect of improving the cycle characteristics of the battery 100 is easily obtained.

[0054] Specifically, in Formula (1), Formula (2), and Formula (3), each independently represents an alkyl group having 1 to 10 carbon atoms in which at least one hydrogen atom may be substituted with a halogen atom, or a phenyl group in which at least one hydrogen atom may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms. With such a configuration, the cycle characteristics of the battery 100 can be easily improved.

[0055] In R 1 ~R 9 When an alkyl group is contained, the number of carbon atoms of the alkyl group may be 1, 2 or more and 5 or less, or 2 or 3.

[0056] In formula (1), R 1 、R 2 and R 3 The organic phosphorus compound having such a structure can sufficiently improve the cycle characteristics of the battery 100. In addition, the organic phosphorus compound having such a structure is easy to synthesize.

[0057] In formula (2), R 4 and R 6 can have the same structure, R 4 and R 6 The structure can be compared with R 5 If the organic phosphorus compound has such a structure, the effect of improving the cycle characteristics of the battery 100 can be fully obtained. In addition, the organic phosphorus compound having such a structure is easy to synthesize.

[0058] In formula (3), R 7 and R 8 can have the same structure, R 7 and R 8 The structure can be compared with R 9 If the organic phosphorus compound has such a structure, the effect of improving the cycle characteristics of the battery 100 can be fully obtained. In addition, the organic phosphorus compound having such a structure is easy to synthesize.

[0059] An organic phosphite compound is a compound in which the hydrogen atoms of phosphorous acid are replaced by organic groups. For example, an organic phosphite compound includes a compound represented by the following formula (4). In formula (4), R 10 ~R 12 Each independently represents an organic group which may have a halogen atom. With such a structure, the effect of improving the cycle characteristics of the battery 100 is easily obtained.

[0060]

[0061] Specifically, in formula (4), R 10 ~R 12 Each of the groups may independently be an alkyl group having 1 to 10 carbon atoms in which at least one hydrogen atom may be substituted with a halogen atom, or a phenyl group in which at least one hydrogen atom may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms. With such a configuration, the cycle characteristics of the battery 100 can be easily improved.

[0062] In R 10~R 12 When an alkyl group is contained, the number of carbon atoms of the alkyl group may be 1, 2 or more and 5 or less, or 2 or 3.

[0063] In formula (4), R 10 、R 11 and R 12 The organic phosphorous acid compound having such a structure can fully achieve the effect of improving the cycle characteristics of the battery 100. In addition, the organic phosphorous acid compound having such a structure is easy to synthesize.

[0064] In R 1 ~R 12 When the organic phosphorus compound and / or the organic phosphorous acid compound contains a fluorine atom, the effect of improving the cycle characteristics of the battery 100 tends to be enhanced.

[0065] The additive may include at least one selected from triethyl phosphite, triisopropyl phosphite, triphenyl phosphite, tri-o-cresyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, tris(hexafluoroisopropyl) phosphite, and tris(pentafluorophenyl)phosphine. These additives can reliably improve the cycle characteristics of the battery 100.

[0066] In order to suppress the increase in the charge termination voltage, the additive preferably contains at least one selected from triethyl phosphite, triphenyl phosphite, tri-o-cresyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, tris(hexafluoroisopropyl) phosphite, and tris(pentafluorophenyl)phosphine. More preferably, the additive contains at least one selected from triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, and tris(hexafluoroisopropyl) phosphite.

[0067] The concentration of the additive in the electrolyte 29 is not particularly limited. The concentration of the additive in the electrolyte 29 is, for example, 0.01 mol / liter to 2.00 mol / liter, preferably 0.05 mol / liter to 1.00 mol / liter. By adjusting the concentration of the additive to an appropriate range, the effect of improving the cycle characteristics of the battery 100 can be fully achieved.

[0068] In addition to the organophosphorus compound and / or the organophosphorous acid compound, the electrolyte 29 may also contain a non-aqueous solvent and a lithium salt. The organophosphorus compound and / or the organophosphorous acid compound are preferably dissolved in the non-aqueous solvent. Such a configuration can easily improve the cycle characteristics of the battery 100. The organophosphorus compound and / or the organophosphorous acid compound can be either liquid or solid at 20°C. In the case of a liquid, the organophosphorus compound and / or the organophosphorous acid compound are compatible with the non-aqueous solvent. In the case of a solid, the organophosphorus compound and / or the organophosphorous acid compound can be dissolved in the non-aqueous solvent.

[0069] As non-aqueous solvents, cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, cyclic esters, chain esters, fluorinated solvents, nitriles, etc. can be used. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. Examples of chain carbonates include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Examples of cyclic ethers include tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane. Examples of chain ethers include 1,2-dimethoxyethane and 1,2-diethoxyethane. Examples of cyclic esters include γ-butyrolactone. Examples of chain esters include methyl acetate. Examples of fluorinated solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, ethyl fluoromethyl carbonate, and dimethyl fluorocarbonate. Examples of nitriles include acetonitrile. At least one selected from these non-aqueous solvents can be used.

[0070] Examples of lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(perfluoroethylsulfonyl)imide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluorooxalatoborate. At least one selected from these lithium salts may be used.

[0071] The electrolyte 29 may also contain a gel electrolyte and / or an ionic liquid.

[0072] The gel electrolyte may be a material obtained by impregnating a polymer material with the electrolyte solution 29. Examples of the polymer material include polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, and polymers having an ethylene oxide bond.

[0073] Examples of cations constituting the ionic liquid include aliphatic chain quaternary cations, aliphatic cyclic ammonium, and nitrogen-containing heterocyclic aromatic cations. Examples of aliphatic chain quaternary cations include tetraalkylammonium, tetraalkyl As the aliphatic cyclic ammonium, pyrrolidine Morpholine Imidazolin Tetrahydropyrimidine Piperazine Piperidine As nitrogen-containing heterocyclic aromatic cations, pyridine Imidazole As anion constituting ionic liquid, PF6 - 、BF4 - 、SbF6 - 、AsF6 - 、SO3CF3 - 、N(SO2F)2 - 、N(SO2CF3)2 - 、N(SO2C2F5)2 - 、N(SO2CF3)(SO2C4F9) - 、C(SO2CF3)3 - etc. Ionic liquids may also contain lithium salts.

[0074] The separator 27 is an electrolyte layer having lithium ion conductivity. The material of the separator 27 is not particularly limited as long as it allows lithium ions to pass through. The material of the separator 27 can be at least one selected from solid electrolytes, gel electrolytes, ion exchange resin membranes, semipermeable membranes, and porous membranes. If the separator 27 is made of these materials, the safety of the battery 100 can be fully ensured. Examples of solid electrolytes include sulfide solid electrolytes such as Li2S-P2S5, Li7La3Zr2O 12 Examples include oxide solid electrolytes such as LLZ. Examples of gel electrolytes include those containing fluorine-based resins such as PVdF. Examples of ion exchange resin membranes include cation exchange membranes and anion exchange membranes. Examples of porous membranes include those made from polyolefin resins and those made from glass paper woven into nonwoven fabrics.

[0075] The outer package 28 can be made of, for example, a material obtained by laminating a metal foil such as aluminum foil with a resin film such as PET film. The outer package 28 can also be a container made of resin or metal.

[0076] The shape of the battery 100 is not limited to the laminated type, and other shapes of the battery 100 include a coin shape, a cylindrical shape, a square shape, a sheet shape, a button shape, and a flat shape.

[0077] Next, the positive electrode active material will be described in detail.

[0078] The positive electrode active material may include, in addition to lithium oxide containing a transition metal M1 in a solid solution, a transition metal oxide containing a transition metal M2. Including the transition metal oxide in the positive electrode active material suppresses increases in the charge voltage of the battery 100 and improves the discharge capacity of the battery 100.

[0079] The transition metal oxide containing the transition metal M2 has a crystal structure different from the crystal structure of lithium oxide in which the transition metal M1 is solid-dissolved. The transition metal oxide containing the transition metal M2 may include a composite oxide containing lithium and the transition metal M2. The crystal structure of the composite oxide may be different from the crystal structure of lithium oxide. The transition metal oxide containing the transition metal M2 may also not contain lithium. The transition metal oxide may include a metal oxide containing only the transition metal M2 as a metal element. The transition metal oxide containing the transition metal M2 may include at least one selected from a composite oxide containing lithium and the transition metal M2, and a metal oxide containing only the transition metal M2 as a metal element.

[0080] The transition metal M2 may be, for example, an element selected from the group of elements in Groups 3 to 11 of Periods 4 and 5 of the periodic table. The transition metal M2 may include, for example, at least one selected from Fe, Co, and Cu. The transition metal M2 may be Fe, Co, or Cu. These elements are preferred from the perspective of suppressing an increase in the charge voltage of the battery 100 and increasing the discharge capacity of the battery 100.

[0081] The transition metal M2 may be the same as or different from the transition metal M1 solid-dissolved in the crystals of lithium oxide. Typically, the transition metal M1 and the transition metal M2 are the same element or the same group of elements. The transition metal M1 and the transition metal M2 may also be the same element. When the transition metal M1 and the transition metal M2 are the same element, it is easy to control the composition of the positive electrode active material. In addition, it also has the advantages of being easy to manufacture and reducing the cost of raw materials. The transition metal oxide may be a residue of the raw material used to make the transition metal M1 solid-dissolved in lithium oxide, or it may be a by-product generated during the synthesis process of the positive electrode active material.

[0082] When the positive electrode active material includes a transition metal oxide containing a transition metal M2, the amount of lithium oxide and lithium contained in the transition metal oxide is defined as m0 (mol). The amount of transition metal M1 present in the positive electrode active material is defined as m1 (mol). The amount of transition metal M2 present in the positive electrode active material is defined as m2 (mol). The ratio (m1 + m2) / (m0 + m1 + m2) is, for example, greater than 0.01 and less than 0.34. By appropriately adjusting the ratio (m1 + m2) / (m0 + m1 + m2), the effect of suppressing the charge voltage rise and the effect of increasing the discharge capacity are enhanced.

[0083] When the transition metal M1 and the transition metal M2 are the same element, the amount m1 is the amount of the transition metal M1 present in the positive electrode active material. The above ratio is represented by (m1 / (m0+m1)).

[0084] The presence of the transition metal oxide can be confirmed by X-ray diffraction measurement. The degree of solid solution of the transition metal M1 in the lithium oxide and the appropriate amount of the transition metal oxide can be determined based on multiple diffraction peaks attributable to the lithium oxide in which the transition metal M1 is solid-dissolved and at least one diffraction peak attributable to the transition metal oxide.

[0085] In the X-ray diffraction pattern of the positive electrode active material measured using Cu-Kα radiation, the diffraction peak existing in the range of a diffraction angle 2θ of 30 to 40° is defined as the first diffraction peak. The diffraction peak existing in the range of a diffraction angle 2θ of 52° to 62° is defined as the second diffraction peak. The diffraction peak existing in the range of a diffraction angle 2θ of 40° to 50° is defined as the third diffraction peak. The first diffraction peak is a diffraction peak attributed to the (111) plane of lithium oxide. The second diffraction peak is a diffraction peak attributed to the (220) plane of lithium oxide. The third diffraction peak is a diffraction peak attributed to the crystal plane of the transition metal oxide. The integrated intensity of the first diffraction peak is defined as I1, the integrated intensity of the second diffraction peak is defined as I2, and the integrated intensity of the third diffraction peak is defined as I3. In this embodiment, the integrated intensity ratio I2 / I1 is 0.48 or greater, and the integrated intensity ratio I3 / I1 is 0.10 or greater and 1.30 or less. Meeting these conditions suppresses the increase in the charge voltage of the battery 100 and improves the discharge capacity of the battery 100. Suppressing the increase in the charge voltage also helps suppress the generation of oxygen.

[0086] The integrated intensity ratio I2 / I1 is an indicator of the degree of solid solubility of the transition metal M1 in lithium oxide. Assuming the valence of the transition metal M1 is +3, since lithium has a valence of +1, in order to maintain charge neutrality within the crystal, two lithium atoms must be released from the crystal in addition to the lithium atoms substituted with the transition metal M1. The incorporation of the transition metal M1, which has a higher valence than lithium atoms, into the crystal and the release of two lithium atoms from the crystal to maintain charge neutrality induce slight strain in the crystal structure of the lithium oxide, the parent material. The greater this strain, the higher the integrated intensity ratio I2 / I1. Quantum science calculations show a proportional relationship between the amount of transition metal M1 doped in lithium oxide and the integrated intensity ratio I2 / I1. When the solid solubility of the transition metal M1 is sufficient, the effect of suppressing the charge voltage rise and improving the discharge capacity are also enhanced. It should be noted that the theoretical integrated intensity ratio I2 / I1 for a Li2O crystal is approximately 0.33.

[0087] The integrated intensity ratio I3 / I1 is an indicator reflecting the amount of residues and / or by-products of the raw materials used to dissolve the transition metal M1 in lithium oxide. For example, when cobalt oxide or lithium cobalt oxide is used as a raw material to dissolve cobalt in lithium oxide, LiCoO2 is contained in the positive electrode active material in the form of residues and / or by-products. In this case, the reflection from the (104) plane of LiCoO2 is observed as the third diffraction peak. As the amount of residues and / or by-products decreases, the diffraction intensity of the third diffraction peak decreases, and thus the integrated intensity ratio I3 / I1 also decreases. As the amount of residues and / or by-products increases, the diffraction intensity of the third diffraction peak increases, and thus the integrated intensity ratio I3 / I1 also increases. The composition and structure of the residues and / or by-products contained in the positive electrode active material can be judged from the overall X-ray diffraction pattern including the third diffraction peak. When a transition metal oxide crystal is present, a diffraction peak appears in the range of a diffraction angle 2θ of 40° to 50° regardless of the type of transition metal.

[0088] The reasons for suppressing the effect of increasing the charge voltage and improving the discharge capacity when the transition metal M1 is appropriately solid-dissolved in lithium oxide and the residues and / or by-products do not disappear but exist appropriately are not fully understood, but the present inventors speculate as follows. During the charging process, lithium atoms are released from lithium oxide, oxygen ions are oxidized and become peroxide ions, and lithium oxide becomes lithium peroxide. Here, in the case where the positive electrode active material is composed only of a material in which the transition metal M1 is completely solid-dissolved in lithium oxide, the volume shrinkage of the positive electrode active material during the charging process becomes larger, a gap is generated between the positive electrode active material and the conductive additive, the electronic resistance of the entire electrode increases, and the charging voltage rises. In contrast, according to the present disclosure, by appropriately containing the residues and / or by-products of the transition metal M2 in the positive electrode active material, the volume shrinkage of the positive electrode active material during the charging process is suppressed by utilizing the charge compensation brought about by the valence change of the transition metal M2. As a result, the effect of suppressing the charge voltage rise and the effect of improving the discharge capacity are exerted. The fact that these effects can be obtained can be supported by the embodiments described later.

[0089] The lower limit of the integrated intensity ratio I2 / I1 may be 0.50 or 0.55. The upper limit of the integrated intensity ratio I2 / I1 is not particularly limited and may be 1.00 or 0.90. The integrated intensity ratio I2 / I1 may be 0.50 or more and 1.00 or less, 0.50 or more and 0.90 or less, 0.55 or more and 1.00 or less, or 0.55 or more and 0.90 or less.

[0090] The integrated intensity ratio I3 / I1 is preferably 0.20 or greater. The integrated intensity ratio I3 / I1 may be 1.10 or less, or 1.00 or less.

[0091] The ranges of the integrated intensity ratio I2 / I1 and the integrated intensity ratio I3 / I1 can be defined by any combination of the above values. For example, the integrated intensity ratio I2 / I1 can be 0.48 or greater, and the integrated intensity ratio I3 / I1 can be 0.20 or greater and 1.10 or less.

[0092] The integrated intensity ratio I2 / I1 may be 0.50 or more and 1.00 or less, and the integrated intensity ratio I3 / I1 may be 0.10 or more and 1.30 or less. The integrated intensity ratio I2 / I1 may be 0.50 or more and 1.00 or less, and the integrated intensity ratio I3 / I1 may be 0.20 or more and 1.10 or less. The integrated intensity ratio I2 / I1 may be 0.50 or more and 1.00 or less, and the integrated intensity ratio I3 / I1 may be 0.20 or more and 1.00 or less.

[0093] The integrated intensity ratio I2 / I1 may be 0.50 or more and 0.90 or less, and the integrated intensity ratio I3 / I1 may be 0.10 or more and 1.30 or less. The integrated intensity ratio I2 / I1 may be 0.50 or more and 0.90 or less, and the integrated intensity ratio I3 / I1 may be 0.20 or more and 1.10 or less. The integrated intensity ratio I2 / I1 may be 0.50 or more and 0.90 or less, and the integrated intensity ratio I3 / I1 may be 0.20 or more and 1.00 or less.

[0094] The integrated intensity ratio I2 / I1 can be 0.55 or more and 1.00 or less, and the integrated intensity ratio I3 / I1 can be 0.10 or more and 1.30 or less. The integrated intensity ratio I2 / I1 can be 0.55 or more and 1.00 or less, and the integrated intensity ratio I3 / I1 can be 0.20 or more and 1.10 or less. The integrated intensity ratio I2 / I1 can be 0.55 or more and 1.00 or less, and the integrated intensity ratio I3 / I1 can be 0.20 or more and 1.00 or less.

[0095] The integrated intensity ratio I2 / I1 can be 0.55 or more and 0.90 or less, and the integrated intensity ratio I3 / I1 can be 0.10 or more and 1.30 or less. The integrated intensity ratio I2 / I1 can be 0.55 or more and 0.90 or less, and the integrated intensity ratio I3 / I1 can be 0.20 or more and 1.10 or less. The integrated intensity ratio I2 / I1 can be 0.55 or more and 0.90 or less, and the integrated intensity ratio I3 / I1 can be 0.20 or more and 1.00 or less.

[0096] The integrated intensity ratio I2 / I1 of the Li2O crystal not doped with the transition metal M1 is about 0.33. If the integrated intensity ratio I2 / I1 exceeds 0.33 while maintaining the inverse fluorite crystal structure of Li2O, it can be determined that the transition metal M1 is solid-dissolved in lithium oxide.

[0097] The positive electrode active material, for example, has a secondary particle structure composed of multiple primary particles of lithium oxide and multiple primary particles of a transition metal oxide. Positive electrode active materials with such a structure can be efficiently produced using synthesis methods such as mechanochemical milling. The primary particles, for example, have a diameter on the nanometer scale. The secondary particles, for example, have a diameter on the micrometer scale.

[0098] The true density of the positive electrode active material is, for example, 2.0 g / cm 3 Above and 3.3g / cm 3 By appropriately adjusting the true density, the energy density of the battery 100 can be increased compared to conventional lithium secondary batteries. The true density can be measured by finely pulverizing the positive electrode active material and then using a pycnometer method.

[0099] The specific surface area of ​​the positive electrode active material is, for example, 1.6 m 2 / g or above and 60m 2 By appropriately adjusting the specific surface area, the energy density of the battery 100 can be increased. The specific surface area is a value obtained by the BET method.

[0100] The positive electrode active material may have a particle shape. Each particle of the positive electrode active material may have a particle size of 0.01 μm. 2 Above and 500μm 2 The following cross-sectional areas are present. By appropriately adjusting the particle size of the positive electrode active material, the cycle characteristics of the battery 100 can be improved. The cross-sectional area of ​​each particle of the positive electrode active material can be calculated using a cross-sectional SEM image of the positive electrode 23. All particles of the positive electrode active material may have a cross-sectional area within the above range, or only a portion of the particles (for example, 90% or more by number) may have a cross-sectional area within the above range.

[0101] The positive electrode active material can be produced, for example, by mechanochemical methods. First, lithium oxide powder is mixed with a raw material for the transition metal M1 to prepare a mixture. The ratio of lithium oxide to the raw material for the transition metal M1 can be determined so that the ratio (m1 / (m0+m1)) described above is within the desired range. Examples of the raw material for the transition metal M1 include oxides of the transition metal M1, composite oxides containing lithium and the transition metal M1, and single substances of the transition metal M1.

[0102] The synthesis of the positive electrode active material using a mechanochemical method can be carried out using a device such as a ball mill or a bead mill that can exert a mechanochemical effect. The atmosphere during the synthesis is not particularly limited and can be an atmospheric atmosphere, an inert atmosphere, a dry atmosphere, or an inert atmosphere that has been dried. In order to suppress the mixing of inevitable impurities such as oxygen and water, it is preferred to synthesize the positive electrode active material under a dried inert atmosphere. The inert atmosphere can, for example, use an inert gas such as nitrogen, argon, or helium.

[0103] By adjusting the number of revolutions of the device, the processing time, the processing temperature, the size of the raw material particles, the composition of the raw material of the transition metal M1, the size of the pulverizing medium and other conditions, the degree of solid dissolution of the transition metal M1 into lithium oxide can be adjusted. That is, the ratio of the integrated intensity I2 / I1 and the ratio of the integrated intensity I3 / I1 can be controlled. For example, as the number of revolutions increases and the processing time increases, the solid dissolution of the transition metal M1 into lithium oxide progresses, so the ratio I2 / I1 increases and the ratio I3 / I1 decreases. By setting the manufacturing conditions in a manner such that the ratio of the integrated intensity I2 / I1 and the ratio of the integrated intensity I3 / I1 are within the desired range, it is possible to obtain a positive electrode active material that can suppress the rise in the charging voltage and increase the discharge capacity.

[0104] (Other Implementation Methods)

[0105] (Note)

[0106] The following technology is disclosed through the description of the above embodiments.

[0107] (Technique 1)

[0108] A battery comprising a positive electrode, a negative electrode, a separator and an electrolyte.

[0109] The positive electrode contains lithium oxide as a positive electrode active material. The lithium oxide has an inverse fluorite crystal structure and contains a transition metal in a solid solution.

[0110] The electrolyte contains at least one additive selected from the group consisting of organic phosphorus compounds and organic phosphorous acid compounds.

[0111] With such a configuration, the cycle characteristics of the battery can be improved.

[0112] (Technique 2)

[0113] According to the battery of technology 1, the organic phosphorus compound includes at least one compound selected from the group consisting of the compound represented by the following formula (1), the compound represented by the following formula (2), and the compound represented by the following formula (3). Here, in the above formula (1), R 1 ~R 3 Each independently represents an organic group which may have a halogen atom or a hydrogen atom, but does not include R 1 ~R3 When all are hydrogen atoms, in the above formula (2), R 5 is an organic group which may have a halogen atom, R 4 and R 6 Each independently represents an organic group which may have a halogen atom or a hydrogen atom, but does not include R 4 and R 6 When both are hydrogen atoms, in the above formula (3), R 7 ! ~R 9 Each independently represents an organic group which may have a halogen atom. With such a structure, the effect of improving the cycle characteristics of the battery is easily obtained.

[0114]

[0115] (Technique 3)

[0116] According to the battery of technique 2, R 1 ~R 9 Each independently represents an organic group which may have a halogen atom. With such a structure, the effect of improving the cycle characteristics of the battery is easily obtained.

[0117] (Technique 4)

[0118] According to the battery of the technique 2, in the above formula (1), the above formula (2) and the above formula (3), R 1 ~R 9 Each independently represents an alkyl group having 1 to 10 carbon atoms in which at least one hydrogen atom may be substituted with a halogen atom, or a phenyl group in which at least one hydrogen atom may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms. With such a configuration, the effect of improving the cycle characteristics of the battery is easily achieved.

[0119] (Technique 5)

[0120] According to any one of the techniques 2 to 4, in the above formula (1), R 1 、R 2 and R 3 If the organophosphorus compound has such a structure, the effect of improving the cycle characteristics of the battery can be fully obtained. In addition, the organophosphorus compound having such a structure is easy to synthesize.

[0121] (Technique 6)

[0122] According to any one of the techniques 1 to 5, the organic phosphite compound includes a compound represented by the following formula (4). 10 ~R 12 Each independently represents an organic group which may have a halogen atom. With such a structure, the effect of improving the cycle characteristics of the battery is easily obtained.

[0123]

[0124] (Technique 7)

[0125] According to the battery described in Technology 6, in the above formula (4), R 10 ~R 12 Each independently represents an alkyl group having 1 to 10 carbon atoms in which at least one hydrogen atom may be substituted with a halogen atom, or a phenyl group in which at least one hydrogen atom may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms. With such a configuration, the effect of improving the cycle characteristics of the battery is easily achieved.

[0126] (Technique 8)

[0127] According to the battery of technology 6 or 7, in the above formula (4), R 10 、R 11 and R 12 If the organic phosphite compound has such a structure, the effect of improving the cycle characteristics of the battery can be fully obtained. In addition, the organic phosphite compound with such a structure is easy to synthesize.

[0128] (Technique 9)

[0129] In the battery according to claim 2 or 6, the halogen atom is a fluorine atom. When the organophosphorus compound and / or the organophosphorous acid compound contains a fluorine atom, the effect of improving the cycle characteristics of the battery tends to be enhanced.

[0130] (Technology 10)

[0131] In the battery according to technology 1, the additive includes at least one selected from triethyl phosphite, triisopropyl phosphite, triphenyl phosphite, tri-o-cresyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, tris(hexafluoroisopropyl) phosphite, and tris(pentafluorophenyl)phosphine. These additives can reliably improve the cycle characteristics of the battery.

[0132] (Technology 11)

[0133] In the battery according to any one of techniques 1 to 10, the concentration of the additive in the electrolyte is 0.01 mol / L or higher and 2.00 mol / L or lower. If the concentration of the additive is adjusted to an appropriate range, the effect of improving the cycle characteristics of the battery can be fully achieved.

[0134] (Technology 12)

[0135] The battery according to any one of techniques 1 to 11, wherein the negative electrode contains lithium metal. With such a configuration, the energy density of the battery can be increased.

[0136] (Technology 13)

[0137] According to any one of techniques 1 to 12, the positive electrode active material further comprises a transition metal oxide containing a transition metal M2, and in an X-ray diffraction pattern of the positive electrode active material measured using Cu-Kα radiation, the ratio of the integrated intensity of the second diffraction peak to the integrated intensity of the first diffraction peak is 0.48 or greater, the second diffraction peak is a diffraction peak attributable to the (220) plane of the lithium oxide and existing at a diffraction angle 2θ in the range of 52 to 62°, the first diffraction peak is a diffraction peak attributable to the (111) plane of the lithium oxide and existing at a diffraction angle 2θ in the range of 30 to 40°, the ratio of the integrated intensity of the third diffraction peak to the integrated intensity of the first diffraction peak is 0.10 or greater and 1.30 or less, the third diffraction peak is a diffraction peak attributable to the crystal plane of the transition metal oxide and existing at a diffraction angle 2θ in the range of 40° to 50°. If such a structure is adopted, the increase in charge voltage can be suppressed and the discharge capacity can be improved.

[0138] (Technology 14)

[0139] According to the battery of Technology 13, the positive electrode active material has a secondary particle structure composed of a plurality of primary particles of the lithium oxide and a plurality of primary particles of the composite oxide. A positive electrode active material having such a structure can be efficiently produced by various granulation methods.

[0140] Example

[0141] Each operation in preparing the positive electrode active material and battery production was performed in a dry atmosphere or an argon atmosphere. A dry atmosphere is an air atmosphere with a dew point of -40°C or less. Examples, comparative examples, and samples include samples obtained by performing the same operation multiple times to obtain sufficient sample quantities.

[0142] [Preparation of electrolyte]

[0143] (Comparative Example 1)

[0144] Ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1:1 to obtain a mixed solvent. LiPF6 was dissolved in the mixed solvent at a concentration of 1 mol / L to obtain an electrolyte solution of Comparative Example 1.

[0145] (Examples 1 to 7)

[0146] The electrolyte solutions of Examples 1 to 7 were obtained by adding the additives shown in Table 1 to the electrolyte solution of Comparative Example 1. For additives that are liquid at 20°C, the concentration of the additives in the electrolyte solution was adjusted to 5 vol%. For additives that are solid at 20°C, the concentration of the additives in the electrolyte solution was adjusted to 0.05 mol / L. The structural formulas of the additives shown in Table 1 are shown in FIG. Figure 2 .

[0147]

[0148] [Production of positive electrode active material]

[0149] 1.00 g of Li₂O and 0.82 g of LiCoO₂ were ground and mixed in a mortar to obtain a mixture. This mixture was placed in a planetary ball mill (Fritsch, P-7, 45 mL container) along with 45 g of zirconia balls (5 mm diameter) and milled at 420 rpm for 100 hours. This yielded a positive electrode active material.

[0150] [Battery Production]

[0151] CR2016 coin cells were fabricated using the aforementioned positive electrode active material. The positive electrode used a positive electrode mixture containing the positive electrode active material, acetylene black, and polytetrafluoroethylene in a mass ratio of 7:2:1. Lithium metal was used as the negative electrode. A polyolefin porous membrane was used as the separator. 120 μL of the electrolytes from Examples 1 to 7 and Comparative Example 1 were used as the electrolyte.

[0152] [Charge and discharge test]

[0153] The batteries of the examples and comparative examples were charged at a current value of 50 mA / g until the upper limit voltage of 3.4 V or the upper limit charge capacity of 600 mAh / g was reached. After a rest of 20 minutes, constant current discharge was performed at a current value of 50 mA / g until the voltage reached 1.8 V. After constant current discharge, constant voltage discharge was performed at 1.8 V until the current value reached 5 mA / g or 24 hours had passed. The unit "mA / g" of the current value represents the current value per 1 g of Li2O. Such a charge and discharge cycle was repeated 7 times. The discharge capacity of the 1st cycle, the discharge capacity of the 5th cycle, the discharge capacity of the 7th cycle and the capacity retention rate are shown in Table 2. The capacity retention rate is the ratio of the discharge capacity of the 7th cycle to the discharge capacity of the 1st cycle. In Table 2, the unit "mAh / g" of the capacity represents the capacity per 1 g of Li2O.

[0154]

[0155] As shown in Table 2, the battery of Comparative Example 1, which did not contain an additive, showed a significant decrease in discharge capacity starting from the fifth cycle. The battery of the Example showed higher discharge capacity even at the fifth and seventh cycles compared to the battery of Comparative Example 1. The battery of the Example showed a higher capacity retention rate than the battery of Comparative Example 1.

[0156] Figure 3 The graph shows the charge termination voltage in each cycle of the batteries of Examples 1 to 7 and Comparative Example 1. Figure 3 In the table, "Ex" represents an embodiment and "C.Ex" represents a comparative example. From the viewpoint of suppressing oxygen desorption and improving cycle characteristics, it is desirable to suppress the increase in the charge termination voltage. The charge termination voltage of the battery of Comparative Example 1 reached the upper limit voltage of 3.4V at the 6th cycle. The charge termination voltage of the battery of Example 2 reached the upper limit voltage of 3.4V at the 2nd cycle. The charge termination voltage of the batteries of Examples 1, 4 and 7 reached the upper limit voltage of 3.4V at the 7th cycle. The charge termination voltage of the batteries of Examples 3, 5 and 6 did not reach the upper limit voltage of 3.4V even at the 7th cycle. That is, in each of the examples except Example 2, especially in Examples 3, 5 and 6, the increase in the charge termination voltage was suppressed compared with Comparative Example 1.

[0157] Next, a plurality of positive electrode active materials having different production conditions and / or raw materials were prepared, and the charge voltage and discharge capacity of batteries using these positive electrode active materials were measured.

[0158] [Preparation of positive electrode active material: Co-based]

[0159] (Sample 1)

[0160] 1.00 g of Li₂O and 0.82 g of LiCoO₂ were ground and mixed in a mortar to obtain a mixture. This mixture was placed in a planetary ball mill (Fritsch, P-7, 45 mL container) along with 45 g of zirconia balls (5 mm diameter) and milled at 420 rpm for 100 hours. This yielded the positive electrode active material for Sample 1.

[0161] (Sample 2)

[0162] A positive electrode active material of Sample 2 was prepared in the same manner as Sample 1, except that the mixture was milled at 600 rpm for 36 hours.

[0163] (Sample 3)

[0164] The positive electrode active material of Sample 3 was prepared in the same manner as Sample 1 except that a planetary ball mill (manufactured by Fritsch, Model PL-7, 45 mL container) was used.

[0165] (Sample 4)

[0166] The positive electrode active material of Sample 4 was prepared on a different date and time using the same method as that for Sample 3. As described later, the main differences between Samples 3 and 4 are the volume ratio of vinylene carbonate in the battery electrolyte and the amount of the positive electrode mixture.

[0167] (Sample 5)

[0168] A positive electrode active material of Sample 5 was prepared in the same manner as Sample 1, except that 2.00 g of Li 2 O and 1.63 g of LiCoO 2 were used and the mixture was milled at 600 rpm for 100 hours.

[0169] (Sample 6)

[0170] The positive electrode active material for Sample 6 was prepared using the same method as Sample 1, except that 2.00 g of Li₂O and 1.63 g of LiCoO₂ were used, the mixture was milled at 600 rpm for 100 hours, and the resulting product was heat-treated. The heat treatment was performed in an argon atmosphere at 250°C (ambient temperature) for 6 hours. The temperature was raised over 1 hour, and the product was slowly cooled by allowing it to stand naturally after the heat treatment.

[0171] (Sample 7)

[0172] 2.00 g of Li₂O and 1.34 g of Co₃O₄ were ground and mixed in a mortar to obtain a mixture. This mixture was placed in a planetary ball mill (Fritsch, P-7, 45 mL container) along with 45 g of zirconia balls (5 mm diameter) and milled at 420 rpm for 100 hours. This yielded the positive electrode active material of Sample 7.

[0173] (Sample 8)

[0174] The positive electrode active material of Sample 8 was prepared in the same manner as Sample 1 except that 2.00 g of Li 2 O and 1.64 g of LiCoO 2 were used.

[0175] (Sample 9)

[0176] 5.00 g of Li₂O and 4.08 g of LiCoO₂ were ground and mixed in a mortar to obtain a mixture. This mixture was placed in a planetary ball mill (Fritsch, PL-7, 80 mL container) along with 98 g of zirconia balls (5 mm diameter) and milled at 420 rpm for 100 hours. This yielded the positive electrode active material of Sample 9.

[0177] (Sample 10)

[0178] A positive electrode active material of Sample 10 was prepared in the same manner as Sample 9 except that the treatment time was changed to 150 hours.

[0179] (Sample 11)

[0180] The positive electrode active material of Sample 11 was prepared in the same manner as that of Sample 3. As described below, the main differences between Sample 3 and Sample 11 are the volume ratio of vinylene carbonate in the battery electrolyte and the amount of the positive electrode mixture.

[0181] (Sample 12)

[0182] The positive electrode active material for Sample 12 was made of the same material as that for Sample 11 and was produced simultaneously. Specifically, a container for Sample 11 was placed at one position in the planetary ball mill, and a container for Sample 12 was placed at another position in the mill. As described later, the amount of positive electrode mixture used in the battery of Sample 12 differed from that used in the battery of Sample 11.

[0183] (Sample 13)

[0184] The positive electrode active material for Sample 13 was made of the same material as that for Sample 4 and was produced simultaneously. Specifically, a container for Sample 4 was placed at one position in the planetary ball mill, and a container for Sample 13 was placed at another position in the mill. As described later, the type of electrolyte and the amount of positive electrode mixture used in the battery of Sample 13 differed from those used in the battery of Sample 4.

[0185] (Sample 14)

[0186] A positive electrode active material of Sample 14 was prepared in the same manner as Sample 1 except that 2.00 g of Li 2 O and 1.64 g of LiCoO 2 were used and the treatment time was changed to 10 hours.

[0187] (Sample 15)

[0188] The positive electrode active material for Sample 15 was prepared using the same method as Sample 1, except that 2.00 g of Li₂O and 1.63 g of LiCoO₂ were used, the mixture was milled at 600 rpm for 100 hours, and the resultant was heat-treated. Heat treatment was performed in an argon atmosphere at 350°C (ambient temperature) for 6 hours. The temperature was raised over 1 hour, and after heat treatment, the material was slowly cooled by allowing it to stand naturally.

[0189] (Sample 16)

[0190] The positive electrode active material for Sample 16 was prepared using the same method as Sample 1, except that 2.00 g of Li₂O and 1.63 g of LiCoO₂ were used, the mixture was milled at 600 rpm for 100 hours, and the resulting product was heat-treated. Heat treatment was performed in an argon atmosphere at 450°C (ambient temperature) for 6 hours. The temperature was raised over 1 hour, and after heat treatment, the product was slowly cooled by allowing it to stand naturally.

[0191] [Production of positive electrode active material: Cu-based]

[0192] (Sample 17)

[0193] 2.00 g of Li₂O and 1.78 g of CuO were ground and mixed in a mortar to obtain a mixture. This mixture was placed in a planetary ball mill (Fritsch, P-7, 45 mL container) along with 45 g of zirconia balls (5 mm diameter) and milled at 600 rpm for 100 hours. This yielded the positive electrode active material of Sample 17.

[0194] (Sample 18)

[0195] A positive electrode active material of Sample 18 was prepared in the same manner as Sample 17 except that 2.00 g of Li 2 O and 0.67 g of CuO were used.

[0196] (Sample 19)

[0197] A positive electrode active material of Sample 19 was prepared in the same manner as Sample 17 except that 1.99 g of Li 2 O and 1.14 g of CuO were used.

[0198] (Sample 20)

[0199] A positive electrode active material of Sample 20 was prepared in the same manner as Sample 17 except that 2.00 g of Li 2 O and 1.43 g of CuO were used.

[0200] (Sample 21)

[0201] A positive electrode active material of Sample 21 was prepared by the same method as Sample 17 except that 1.99 g of Li 2 O and 0.66 g of CuO were used and the treatment time was changed to 48 hours.

[0202] (Sample 22)

[0203] A positive electrode active material of Sample 22 was prepared in the same manner as Sample 17 except that 2.00 g of Li 2 O and 0.47 g of CuO were used.

[0204] [Production of positive electrode active material: Fe-based]

[0205] (Sample 23)

[0206] 2.00 g of Li₂O and 1.19 g of Fe₂O₃ were ground and mixed in a mortar to obtain a mixture. This mixture was placed in a planetary ball mill (Fritsch, P-7, 45 mL container) along with 45 g of zirconia balls (5 mm diameter) and milled at 600 rpm for 100 hours. This yielded the positive electrode active material of Sample 23.

[0207] (Sample 24)

[0208] The positive electrode active material of Sample 24 was prepared in the same manner as Sample 23 except that 2.00 g of Li 2 O and 0.89 g of Fe 2 O 3 were used.

[0209] (Sample 25)

[0210] 2.00 g of Li₂O and 1.29 g of Fe₃O₄ were ground and mixed in a mortar to obtain a mixture. This mixture was placed in a planetary ball mill (Fritsch, P-7, 45 mL container) along with 45 g of zirconia balls (5 mm diameter) and milled at 420 rpm for 100 hours. This yielded the positive electrode active material of Sample 25.

[0211] (Sample 26)

[0212] 5.00 g of Li₂O and 4.01 g of FeO were ground and mixed in a mortar to obtain a mixture. This mixture was placed in a planetary ball mill (Fritsch, PL-7, 80 mL container) along with 98 g of zirconia balls (5 mm diameter) and milled at 420 rpm for 150 hours. This yielded the positive electrode active material of Sample 26.

[0213] (Sample 27)

[0214] A positive electrode active material of Sample 27 was prepared in the same manner as Sample 23 except that the mixture was milled at 420 rpm for 72 hours.

[0215] (Sample 28)

[0216] The positive electrode active material of Sample 28 was prepared in the same manner as Sample 23 except that 2.00 g of Li 2 O and 0.63 g of Fe 2 O 3 were used.

[0217] [X-ray diffraction measurement]

[0218] Powder X-ray diffraction measurement of the positive electrode active material was performed using a powder X-ray diffractometer (MiniFlex 600, manufactured by Rigaku Corporation). The measurement conditions are described below.

[0219] Cu Ka rays

[0220] Detector: HyPix400MF

[0221] Scan step: 0.02deg

[0222] Scan speed: 2 deg / min

[0223] 2θ: 10-80deg

[0224] The average spectrum of 8 measurements was used

[0225] Figure 4A The X-ray diffraction pattern of the positive electrode active material in the case where the transition metal M1 is Co is shown. Figure 4B Shown is an X-ray diffraction pattern of the positive electrode active material when the transition metal M1 is Cu. Figure 4C Shown is an X-ray diffraction pattern of the positive electrode active material when the transition metal M1 is Fe.

[0226] [Calculation of the integrated intensity ratio]

[0227] The X-ray diffraction patterns of each positive electrode active material were analyzed using analysis software (manufactured by OriginLab, OriginPro2022). That is, the integrated intensity I1 of the first diffraction peak, the integrated intensity I2 of the second diffraction peak, and the integrated intensity I3 of the third diffraction peak were calculated. When there are multiple peaks corresponding to the third diffraction peak, the Lorentz function or the Voigt function is used for peak separation. The integrated intensities of each separated peak are calculated, and their sum is regarded as the integrated intensity I3 of the third diffraction peak. For example, when Cu is used as the transition metal M1, a diffraction peak belonging to the reflection from the (013) plane of the Li2CuO2 crystal classified as the space group Immm and a diffraction peak belonging to the reflection from the (103) plane of the Li2CuO2 crystal appear in the range of diffraction angle 2θ of 40° to 50°. The sum of the integrated intensities of each peak is regarded as the integrated intensity I3 of the third diffraction peak.

[0228] The diffraction peak of Li2CuO2 (space group Immm) also appears at 49.94°, but this diffraction peak is proportional to the diffraction peak appearing in the 40°-45° range and is also weak in intensity. Therefore, as an indicator of the abundance ratio of Li2CuO2 to lithium oxide, only the integrated intensity of the diffraction peak appearing in the 40°-45° range is used in the calculation.

[0229] When Co was used as the transition metal M1, the diffraction peak attributed to the reflection from the (104) plane of LiCoO2 crystals classified in space group R-3m was considered the third diffraction peak, and the integrated intensity I3 was calculated. When Fe was used as the transition metal M1, the diffraction peaks attributed to the reflection from the (204) and (323) planes of Li5FeO4 were considered the third diffraction peak, and the integrated intensity I3 was calculated. The calculation results of the integrated intensity ratio I2 / I1 and the integrated intensity ratio I3 / I1 are shown in Table 3A.

[0230] LiCoO2 (space group R-3m) also has a diffraction peak at 49.77°, but this peak is proportional to the diffraction peak appearing in the 40°-45° range and is also weaker in intensity. Therefore, as an indicator of the abundance ratio of LiCoO2 to lithium oxide, only the integrated intensity of the diffraction peak appearing in the 40°-45° range is used in the calculation.

[0231]

[0232] [Observation using a scanning electron microscope (SEM)]

[0233] Figure 5A An SEM image of the positive electrode active material of Sample 3 is shown. Figure 5B SEM images of the positive electrode active material of Sample 17 are shown. As can be understood from these SEM images, the positive electrode active materials of Samples 3 and 17 have a secondary particle structure. The positive electrode active materials of the other samples also have a secondary particle structure.

[0234] [Determination of true density]

[0235] The true density of the positive electrode active materials of Samples 1 to 4, Sample 13, Samples 17 to 20, and Sample 22 was measured using a pycnometer method.

[0236] [Measurement of specific surface area]

[0237] The specific surface areas of the positive electrode active materials of Samples 3, 4, 11, and 12 were measured by the BET method.

[0238] [Battery Production]

[0239] CR2016 coin cells were produced using the positive electrode active materials of Samples 1 to 28. The positive electrode used a positive electrode mixture containing the positive electrode active material, acetylene black, and polytetrafluoroethylene in a mass ratio of 7:2:1. A 0.3 mm thick lithium metal foil was used as the negative electrode. A three-layer separator consisting of nonwoven fabric / polyolefin resin film / nonwoven fabric was used as the separator. Samples 13-1, 13-2, and 13-3 were identical coin cells using the positive electrode active material of Sample 13. The charge and discharge test conditions were varied.

[0240] Electrolyte A for the battery of Sample 1 was prepared as follows. Ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1:1. Vinylene carbonate was added to the mixture of ethylene carbonate and diethyl carbonate at a ratio of 1% by volume to prepare a mixed solvent. LiPF6 was dissolved in the resulting mixed solvent at a concentration of 1 mol / L to prepare Electrolyte A.

[0241] Electrolyte B was prepared in the same manner as electrolyte A except that the volume ratio of vinylene carbonate in the mixed solvent was changed to 5% by volume. Electrolyte C was prepared in the same manner as electrolyte A except that the volume ratio of vinylene carbonate in the mixed solvent was changed to 10% by volume. Electrolyte D was prepared in the same manner as electrolyte A except that vinylene carbonate was not used. The performance of the battery varied slightly depending on the amount of vinylene carbonate. However, the effect of vinylene carbonate saturated at around 1% by volume, so the difference in battery performance caused by the amount of vinylene carbonate was small.

[0242] The types of electrolytes and the amounts of positive electrode mixtures used in the batteries of Samples 1 to 28 are shown in Table 3B.

[0243]

[0244] [Charge and discharge test]

[0245] (Sample 1)

[0246] The battery of Sample 1 was charged at a current of 64.7 mA / g, with the upper voltage limit set at 3.5 V and the upper charge capacity limit set at 647 mAh / g. The charge capacity, voltage at 500 mAh / g, and voltage at 600 mAh / g are shown in Table 4. After a 20-minute rest, constant current discharge was performed at a current of 64.7 mA / g until the battery reached 1.0 V. The discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V are shown in Table 4.

[0247] The unit of capacity, "mAh / g," represents the capacity per 1g of Li2O. The unit of current value, "mA / g," represents the current value per 1g of Li2O.

[0248] (Sample 14)

[0249] The battery of Sample 14 was charged at a current of 64.7 mA / g, with the upper voltage limit set at 3.5 V and the upper charge capacity limit set at 647 mAh / g. The charge capacity, voltage at 500 mAh / g, and voltage at 600 mAh / g are shown in Table 4. After a 20-minute rest, constant current discharge was performed at a current of 64.7 mA / g until the battery reached 1.5 V. The discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V are shown in Table 4.

[0250] Figure 6 The graph shows the charge and discharge curves of sample 1 and sample 14.

[0251]

[0252] The difference between Sample 1 and Sample 14 lies in the amount of raw materials added and the grinding time. The charging voltage of the battery of Sample 14 reaches 3.5V before the charging capacity reaches 647mAh / g. Therefore, the discharge capacity of the battery of Sample 14 is small. In contrast, the charging voltage of the battery of Sample 1 is flat until it reaches the upper limit of the charging capacity of 647mAh / g. In addition, the battery of Sample 1 shows a large discharge capacity. That is, the increase in the charging voltage of the battery of Sample 1 is suppressed, and the discharge capacity is improved. It is believed that the positive electrode active material of Sample 14 contains excessive residues of raw materials. It should be noted that the amount of positive electrode mixture used in the battery of Sample 1 and the battery of Sample 14 is also different, but the effect of the difference in the amount of positive electrode mixture on the charging voltage and discharge capacity is very small compared to the difference in the physical properties of the positive electrode active material.

[0253] The batteries of Samples 1 and 14 were repeatedly charged and discharged under the above conditions. For the batteries of Samples 1 and 14, the ratio of the discharge capacity at the second cycle to the charge capacity at the second cycle was calculated as the coulombic efficiency (unit: %). The results showed that the coulombic efficiency of the battery of Sample 1 was 99.7%. The coulombic efficiency of the battery of Sample 14 was 84.1%. The battery of Sample 1 also exhibited excellent coulombic efficiency.

[0254] (Sample 2)

[0255] The battery of Sample 2 was subjected to a charge and discharge test under the same conditions as those of Sample 1. The results are shown in Table 5.

[0256] (Sample 3)

[0257] The battery of Sample 3 was charged at a current of 50.0 mA / g, with the upper voltage limit set at 3.4 V and the upper charge capacity limit set at 600 mAh / g. The charge capacity, voltage at 500 mAh / g, and voltage at 600 mAh / g are shown in Table 5. After a 20-minute rest, the battery was discharged at a constant current of 50.0 mA / g until the voltage reached 1.8 V. Thereafter, the battery was discharged at a constant voltage of 1.8 V until the current reached 5 mA / g. The discharge capacities at voltages of 2.2 V, 2.0 V, and 1.8 V are shown in Table 5.

[0258] (Sample 4)

[0259] The battery of Sample 4 was charged at a current of 50.0 mA / g, with the upper voltage limit set at 3.4 V and the upper charge capacity limit set at 600 mAh / g. The charge capacity, voltage at 500 mAh / g, and voltage at 600 mAh / g are shown in Table 5. After a 20-minute rest, constant-current discharge was performed at a current of 50.0 mA / g until the voltage reached 1.5 V. Constant-voltage discharge was then performed at 1.5 V for 66 hours. The discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V are shown in Table 5.

[0260]

[0261] Sample 2 was a sample with a higher rotation speed and a shorter treatment time than Sample 1. By increasing the rotation speed, the increase in charge voltage was suppressed and the discharge capacity was increased, similarly to Sample 1.

[0262] Samples 3 and 4 were samples in which the types of ball mills were different from those of Sample 1. Even with the changes in the types of ball mills, the increase in charge voltage was suppressed and the discharge capacity was improved, similarly to Sample 1.

[0263] The battery of Sample 2 was repeatedly charged and discharged under the above conditions. For the battery of Sample 2, the ratio of the discharge capacity at the second cycle to the charge capacity at the second cycle was calculated as the coulombic efficiency (unit: %). The coulombic efficiency of the battery of Sample 2 was 94.8%.

[0264] (Samples 5 to 7, Sample 15 and Sample 16)

[0265] The upper limit voltage is set to 3.4V, the lower limit voltage is set to 1.5V, the upper limit of the charge and discharge capacity of the first cycle is set to 300mAh / g, the upper limit of the charge and discharge capacity of the second cycle is set to 400mAh / g, and the upper limit of the charge and discharge capacity of the third cycle is set to 500mAh / g, and the batteries of samples 5 to 7, sample 15 and sample 16 are charged and discharged at a current value of 50.0mA / g. The rest time when switching from the charging process to the discharging process is 20 minutes. When 1.5V is reached before reaching the specified capacity during the discharge process, constant voltage discharge is performed at 1.5V for 1 hour. The charge capacity of the third cycle and the voltage at 500mAh / g during the charge of the third cycle are shown in Table 6. The discharge capacity at each voltage of 2.5V, 2.2V, 2.0V, 1.8V, and 1.5V during the discharge of the third cycle is shown in Table 6.

[0266] (Sample 8)

[0267] The upper limit voltage is set to 3.4V, the lower limit voltage is set to 1.8V, the upper limit of the charge and discharge capacity of the first cycle is set to 300mAh / g, the upper limit of the charge and discharge capacity of the second cycle is set to 400mAh / g, and the upper limit of the charge and discharge capacity of the third cycle is set to 500mAh / g, and the battery of sample 8 is charged and discharged with a current value of 50.0mA / g. The rest time when switching from the charging process to the discharging process is 20 minutes. During the discharge process, the voltage does not reach 1.8V before reaching the specified capacity. The charging capacity of the third cycle and the voltage at 500mAh / g during the charging of the third cycle are shown in Table 6. The discharge capacity at each voltage of 2.5V, 2.2V, 2.0V, and 1.8V during the discharge of the third cycle is shown in Table 6.

[0268] (Sample 9)

[0269] The upper limit voltage is set to 3.4V, the lower limit voltage is set to 1.8V, the upper limit of the charge and discharge capacity of the first cycle is set to 300mAh / g, the upper limit of the charge and discharge capacity of the second cycle is set to 400mAh / g, and the upper limit of the charge and discharge capacity of the third cycle is set to 500mAh / g, and the battery of sample 9 is charged and discharged with a current value of 50.0mA / g. The rest time when switching from the charging process to the discharging process is 20 minutes. When 1.8V is reached before the specified capacity is reached during the discharge process, constant voltage discharge is implemented at 1.8V and discharged until the current value reaches a current value of 5mA / g. The charge capacity of the third cycle and the voltage at 500mAh / g during the charge of the third cycle are shown in Table 6. The discharge capacity at each voltage of 2.5V, 2.2V, 2.0V, and 1.8V during the discharge of the third cycle is shown in Table 6.

[0270] (Sample 10)

[0271] The upper limit voltage was set to 3.4 V, the lower limit voltage was set to 1.8 V, the upper limit of the charge and discharge capacity of the first cycle was set to 300 mAh / g, the upper limit of the charge and discharge capacity of the second cycle was set to 400 mAh / g, and the upper limit of the charge and discharge capacity of the third cycle was set to 500 mAh / g. The battery of sample 10 was charged and discharged at a current value of 50.0 mA / g. The rest time when switching from the charge process to the discharge process was 20 minutes. During the discharge process, the voltage did not reach 1.8 V before reaching the specified capacity. The charge capacity of the third cycle and the voltage at 500 mAh / g during the charge of the third cycle are shown in Table 6. The discharge capacity at each voltage of 2.5 V, 2.2 V, 2.0 V, and 1.8 V during the discharge of the third cycle is shown in Table 6.

[0272] (Samples 11 and 12)

[0273] The upper limit voltage is set to 3.4V, the lower limit voltage is set to 1.8V, the upper limit of the charge and discharge capacity of the first cycle is set to 300mAh / g, the upper limit of the charge and discharge capacity of the second cycle is set to 500mAh / g, the upper limit of the charge and discharge capacity of the third cycle is set to 600mAh / g, and the upper limit of the charge and discharge capacity of the fourth cycle is set to 700mAh / g, and the batteries of samples 11 and 12 are charged and discharged at a current value of 50.0mA / g. The rest time when switching from the charging process to the discharging process is 20 minutes. During the discharge process, the voltage did not reach 1.8V before reaching the specified capacity. The charge capacity of the second cycle and the voltage at 500mAh / g during the charging of the second cycle are shown in Table 6. The discharge capacity at each voltage of 2.5V, 2.2V, 2.0V, and 1.8V during the discharge of the second cycle is shown in Table 6.

[0274]

[0275] The positive electrode active materials of Samples 5, 6, 15, and 16 were manufactured under identical conditions, except for the processing temperature. The battery of Sample 15 exhibited a slightly higher charge voltage and lower discharge capacity. The battery of Sample 16 exhibited lower charge and discharge capacities. In contrast, the batteries of Samples 5 and 6 exhibited lower charge voltages and higher discharge capacities.

[0276] The battery of Sample 7 contained a positive electrode active material produced using Co₃O₄ as the raw material for the transition metal M1. The battery of Sample 8 contained a positive electrode active material produced using LiCoO₂ as the raw material for the transition metal M1. Whether an oxide containing only Co or a composite oxide was used as the raw material for the transition metal M1, both suppressed the increase in charge voltage and increased the discharge capacity.

[0277] Samples 9 to 12 were samples in which the types of ball mills were different from those of Samples 5 to 8. Even with the change in the types of ball mills, the increase in charge voltage was suppressed and the discharge capacity was improved, similarly to Samples 5 to 8.

[0278] The ratio of the discharge capacity at the fourth cycle to the charge capacity at the fourth cycle was calculated as the coulombic efficiency (unit: %) for the batteries of Samples 11 and 12. The coulombic efficiency of the batteries of Samples 11 and 12 was 100.0%.

[0279] (Sample 13-1)

[0280] The battery of sample 13-1 was charged at a current of 50.0 mA / g, with the upper voltage limit set at 3.4 V and the upper charge capacity limit set at 600 mAh / g. The charge capacity, voltage at 500 mAh / g, and voltage at 600 mAh / g are shown in Table 7A. After a 20-minute rest, the battery was discharged at a constant current of 50.0 mA / g until the voltage reached 1.5 V. Thereafter, constant voltage discharge was performed at 1.5 V until the voltage reached 5 mA / g or until 24 hours had passed. The discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V are shown in Table 7A.

[0281] (Sample 13-2)

[0282] The battery of sample 13-1 was charged at a current of 64.7 mA / g, with the upper voltage limit set at 3.4 V and the upper charge capacity limit set at 647 mAh / g. The charge capacity, voltage at 500 mAh / g, and voltage at 600 mAh / g are shown in Table 7A. After a 20-minute rest, constant current discharge was performed at a current of 50.0 mA / g until the voltage reached 1.5 V. Thereafter, constant voltage discharge was performed at 1.5 V until the voltage reached 5 mA / g or until 24 hours had passed. The discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V are shown in Table 7A.

[0283]

[0284] The positive electrode active material used in the battery of Sample 13-1 and Sample 13-2 was the same. As shown in Table 7A, even when the charge-discharge test conditions were changed from those of Sample 13-1 to those of Sample 13-2, the increase in charge voltage was suppressed and the discharge capacity was improved, similar to Sample 1.

[0285] (Sample 13-3)

[0286] The upper limit voltage was set to 3.4V, the lower limit voltage was set to 1.8V, the upper limit of the charge and discharge capacity of the first cycle was set to 300mAh / g, the upper limit of the charge and discharge capacity of the second cycle was set to 400mAh / g, the upper limit of the charge and discharge capacity of the third cycle was set to 500mAh / g, the upper limit of the charge and discharge capacity of the fourth cycle was set to 600mAh / g, and the upper limit of the charge and discharge capacity of the fifth cycle was set to 700mAh / g. The battery of sample 13-3 was charged and discharged at a current value of 50.0mA / g. The rest time when switching from the charging process to the discharging process was 20 minutes. The charge capacity of the third cycle, the voltage at 500mAh / g during the charge of the third cycle, and the discharge capacity at each voltage of 2.5V, 2.2V, 2.0V, and 1.8V during the discharge of the third cycle are shown in Table 7B. Table 7C shows the charge capacity at the fifth cycle, the voltage at 700 mAh / g during charge at the fifth cycle, and the discharge capacity at voltages of 2.5 V, 2.2 V, 2.0 V, and 1.8 V during discharge at the fifth cycle.

[0287]

[0288] As shown in Table 7B and Table 7C, the battery of Sample 13-3 exhibited a low charge voltage and a large discharge capacity in both the 3rd and 5th cycles.

[0289] (Sample 21)

[0290] The battery of Sample 20 was charged at a current of 53.3 mA / g, with the upper voltage limit set at 3.4 V and the upper charge capacity limit set at 533 mAh / g. After a 20-minute rest, constant current discharge was performed at a current of 53.3 mA / g until the voltage reached 1.0 V. This cycle was repeated three times. The charge capacity of the third cycle and the voltage at 200 mAh / g during the third cycle of charge are shown in Table 8A. The discharge capacity at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V during the third cycle of discharge are shown in Table 8A.

[0291] (Samples 17 to 20 and Sample 22)

[0292] The upper limit voltage is set to 3.4V, the lower limit voltage is set to 1.5V, the upper limit of the charge and discharge capacity of the first cycle is set to 300mAh / g, the upper limit of the charge and discharge capacity of the second cycle is set to 400mAh / g, and the upper limit of the charge and discharge capacity of the third cycle is set to 500mAh / g, and the batteries of samples 17 to 20 and sample 22 are charged and discharged at a current value of 50.0mA / g. The rest time when switching from the charging process to the discharging process is 20 minutes. When 1.5V is reached before reaching the specified capacity during the discharge process, constant voltage discharge is performed at 1.5V for 1 hour. The charge capacity of the third cycle and the voltage at each capacity of the third cycle are shown in Table 8A. The discharge capacity at each voltage of 2.5V, 2.2V, 2.0V, 1.8V, and 1.5V during the discharge of the third cycle is shown in Table 8B.

[0293]

[0294]

[0295] Batteries of Samples 21 and 22 reached the upper voltage limit of 3.4 V with charge capacities of 240.8 mAh / g and 261.1 mAh / g, respectively. Furthermore, the discharge capacities of the batteries of Samples 21 and 22 were low. In contrast, the batteries of Samples 17 to 20 exhibited low charge voltages and large discharge capacities.

[0296] The reasons why the batteries of Samples 21 and 22 had high charge voltages and low discharge capacities include: a short treatment time; and a small amount of CuO.

[0297] As shown in the results of Samples 17 to 20, when the transition metal M1 is Cu, similarly to the case of Co, the effect of suppressing the increase in charge voltage and the effect of improving the discharge capacity are obtained.

[0298] (Samples 23 to 28)

[0299] Batteries for Samples 23 to 28 were charged at a current of 50.0 mA / g, with the upper voltage limit set at 3.4 V and the upper charge capacity limit set at 300 mAh / g. The charge capacity, voltage at 200 mAh / g, and voltage at 300 mAh / g are shown in Table 9. After a 20-minute rest, the batteries were discharged at a constant current of 50.0 mA / g until the voltage reached 1.5 V (1.8 V for Sample 26). Subsequently, constant voltage discharge was performed at 1.5 V (1.8 V for Sample 26) for 1 hour. The discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V are shown in Table 9.

[0300]

[0301] The charging voltages of the batteries of samples 23 to 26 were lower than those of the batteries of samples 27 and 28. The discharge capacities of the batteries of samples 27 and 28 were small. In contrast, the batteries of samples 23 to 26 showed large discharge capacities.

[0302] The reasons why the batteries of Samples 27 and 28 had high charge voltages and low discharge capacities include: low rotation speed of the device; short processing time; and small amount of Fe.

[0303] As shown in the results of Samples 23 to 26, even when the transition metal M1 is Fe, the effect of suppressing the increase in charge voltage and improving the discharge capacity is achieved, similar to the cases of Co and Cu. Furthermore, the raw material for Fe as the transition metal M1 can be any of Fe₂O₃ (Samples 23 and 24), Fe₃O₄ (Sample 25), and FeO (Sample 26).

[0304] Figure 7 This graph plots the calculated results of the integrated intensity ratio I2 / I1 and the integrated intensity ratio I3 / I1 for the positive electrode active materials of samples 1 to 28. The horizontal axis represents the integrated intensity ratio I2 / I1. The vertical axis represents the integrated intensity ratio I3 / I1. The numbers "1, 2, 3, ... 28" represent samples 1 to 28, respectively. The integrated intensity ratio I2 / I1 for the Li2O single crystal is approximately 0.33.

[0305] A small integrated intensity ratio I2 / I1 indicates a low degree of solid solubility of the transition metal M1. A large integrated intensity ratio I2 / I1 indicates a high degree of solid solubility of the transition metal M1. The integrated intensity ratio I2 / I1 of the batteries of samples 1 to 13, 17 to 20, and 23 to 26 was 0.48 or greater. It is believed that in these samples, the solid solubility of the transition metal M1 in the lithium oxide was sufficiently achieved, and the effect of improving electronic conductivity and ionic conductivity was fully achieved.

[0306] A small integrated intensity ratio, I3 / I1, indicates a low amount of residues and / or byproducts. A large integrated intensity ratio, I3 / I1, indicates a high amount of residues and / or byproducts. The integrated intensity ratios, I3 / I1, for batteries of samples 1-13, 17-20, and 23-26 were within the range of 0.10 to 1.30. This indicates that the positive electrode active materials used in these batteries contain moderate amounts of residues and / or byproducts.

[0307] Industrial applicability

[0308] The technology disclosed herein is useful for batteries such as lithium secondary batteries.

Claims

1. A battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, The positive electrode contains lithium oxide as a positive electrode active material, the lithium oxide has an inverse fluorite crystal structure and contains a transition metal in a solid solution. The electrolyte contains at least one additive selected from the group consisting of organic phosphorus compounds and organic phosphorous acid compounds.

2. The battery according to claim 1, wherein the organic phosphorus compound comprises at least one selected from the group consisting of a compound represented by the following formula (1), a compound represented by the following formula (2), and a compound represented by the following formula (3). in, In the formula (1), R 1 ~R 3 Each independently represents an organic group which may have a halogen atom or a hydrogen atom, excluding R 1 ~R 3 When all atoms are hydrogen, In the formula (2), R 5 is an organic group which may have a halogen atom, R 4 and R 6 Each independently represents an organic group which may have a halogen atom or a hydrogen atom, but excluding R 4 and R 6 When both are hydrogen atoms, In the formula (3), R 7 ~R 9 Each independently represents an organic group which may have a halogen atom.

3. The battery according to claim 2, wherein R 1 ~R 9 Each independently represents an organic group which may have a halogen atom.

4. The battery according to claim 2, wherein in the formula (1), the formula (2) and the formula (3), R 1 ~R 9 Each independently represents an alkyl group having 1 to 10 carbon atoms in which at least one hydrogen atom may be substituted by a halogen atom, or a phenyl group in which at least one hydrogen atom may be substituted by a halogen atom or an alkyl group having 1 to 10 carbon atoms.

5. The battery according to claim 2, wherein in the formula (1), R 1 、R 2 and R 3 Have the same structure.

6. The battery according to claim 1, wherein the organic phosphorous acid compound comprises a compound represented by the following formula (4): in, R 10 ~R 12 Each independently represents an organic group which may have a halogen atom.

7. The battery according to claim 6, wherein in the formula (4), R 10 ~R 12 Each independently represents an alkyl group having 1 to 10 carbon atoms in which at least one hydrogen atom may be substituted by a halogen atom, or a phenyl group in which at least one hydrogen atom may be substituted by a halogen atom or an alkyl group having 1 to 10 carbon atoms.

8. The battery according to claim 6, wherein in the formula (4), R 10 、R 11 and R 12 Have the same structure. 9 . The battery according to claim 2 , wherein the halogen atom is a fluorine atom.

10. The battery according to claim 1, wherein the additive comprises at least one selected from the group consisting of triethyl phosphite, triisopropyl phosphite, triphenyl phosphite, tri-o-cresyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, tris(hexafluoroisopropyl) phosphite, and tris(pentafluorophenyl)phosphine. 11 . The battery according to claim 1 , wherein a concentration of the additive in the electrolyte solution is 0.01 mol / liter or more and 2.00 mol / liter or less. The battery according to claim 1 , wherein the negative electrode contains lithium metal.

13. The battery according to claim 1, The positive electrode active material further comprises a transition metal oxide containing a transition metal M2, In the X-ray diffraction pattern of the positive electrode active material measured using Cu-Kα rays, The ratio of the integrated intensity of the second diffraction peak to the integrated intensity of the first diffraction peak is greater than 0.48, the second diffraction peak is a diffraction peak attributable to the (220) plane of the lithium oxide and exists in the range of the diffraction angle 2θ of 52° to 62°, and the first diffraction peak is a diffraction peak attributable to the (111) plane of the lithium oxide and exists in the range of the diffraction angle 2θ of 30° to 40°. The ratio of the integrated intensity of the third diffraction peak to the integrated intensity of the first diffraction peak is greater than 0.10 and less than 1.30, and the third diffraction peak is a diffraction peak belonging to the crystal plane of the transition metal oxide and exists in the range of the diffraction angle 2θ of 40° to 50°. 14 . The battery according to claim 13 , wherein the positive electrode active material has a secondary particle structure composed of a plurality of primary particles of the lithium oxide and a plurality of primary particles of the transition metal oxide.

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