Battery

Abstract

According to the present invention, a positive electrode 23 has an antifluorite crystal structure and contains lithium oxide in which a transition metal is solid-solved, and an electrolyte solution 29 contains an additive. The additive includes at least one substance that is selected from the group consisting of a phosphoric acid ester, a sulfonic acid ester, a cyclic carbonic acid ester, a benzene derivative, and a radical scavenger. The concentration of the additive in the electrolyte solution is, for example, 0.01 mol / liter to 2.0 mol / liter inclusive.

Description

battery

[0001] The present disclosure relates to batteries.

[0002] It has long been known that the redox reaction between lithium oxide (LiO) and lithium peroxide (LiO) can be applied to secondary batteries, as described in Patent Document 1. However, one of the technical challenges has been the poor electronic conductivity of lithium oxide and lithium peroxide, and the large overvoltage.

[0003] Patent Document 2 discloses that charging overvoltage can be reduced by dissolving a transition metal in the crystal structure of lithium oxide.

[0004] Patent No. 4554935 Patent No. 6179944

[0005] The prior art has room for improvement in terms of battery cycle characteristics.

[0006] The present disclosure provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode has an inverse fluorite crystal structure and contains lithium oxide having a transition metal dissolved therein as a positive electrode active material, and the electrolyte contains an additive, wherein the additive contains at least one selected from the group consisting of a phosphate ester represented by the following formula (1), a sulfonate ester represented by the following formula (2), a cyclic carbonate ester represented by the following formula (3), a benzene derivative, and a radical scavenger, wherein in the formula (1), R 1 , R 2 and R 3 are each independently an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an alkynyl group, a phenyl group, a phenyl group in which at least one hydrogen atom may be substituted by an alkyl group having 1 to 5 carbon atoms, or a silyl group, in which at least one hydrogen atom contained in these groups may be substituted by a halogen atom; R 1 and R 2 may be bonded to form a cyclic structure, and in the formula (2), R 4 and R 5are each independently an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an alkynyl group, a phenyl group, a phenyl group in which at least one hydrogen atom may be substituted by an alkyl group having 1 to 5 carbon atoms, or a silyl group, in which at least one hydrogen atom contained in these groups may be substituted by a halogen atom; R 4 and R 5 may be bonded to form a cyclic structure, and in the formula (3), R 6 and R 7 are each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or a vinyl group, and R 6 and R 7 at least one of the above contains a vinyl group, and the benzene derivative is a compound having a structure in which at least one substituent is bonded to a benzene ring, and the substituent is an alkyl group having 1 to 10 carbon atoms, an aryl group, or a carbonate group.

[0007] According to the technology of the present disclosure, the cycle characteristics of a battery can be improved.

[0008] FIG. 1 is a cross-sectional view showing a schematic configuration of a battery according to an embodiment of the present disclosure. FIG. 2A is a diagram showing the structural formulas of various phosphate esters represented by formula (1). FIG. 2B is a diagram showing the structural formulas of various phosphate esters represented by formula (1). FIG. 3 is a diagram showing the structural formulas of various sulfonate esters represented by formula (2). FIG. 4 is a diagram showing the structural formulas of various benzene derivatives. FIG. 5A shows an X-ray diffraction pattern of a positive electrode active material in which the transition metal M1 is Co. FIG. 5B shows an X-ray diffraction pattern of a positive electrode active material in which the transition metal M1 is Cu. FIG. 5C shows an X-ray diffraction pattern of a positive electrode active material in which the transition metal M1 is Fe. FIG. 6A shows an SEM image of the positive electrode active material of Sample 3. FIG. 6B shows an SEM image of the positive electrode active material of Sample 17. FIG. 7 is a graph showing charge-discharge curves of Sample 1 and Sample 14. FIG. 8 is a graph plotting the calculation 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.

[0009] (Findings that form the basis of this disclosure) 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 1 g of lithium oxide. On the other hand, the lithium peroxide generated during charging is unstable because it is a peroxide, and there is a concern that it may decompose due to a reaction with the electrolyte. Furthermore, conventional lithium-ion batteries have a low voltage of 2.5 V to 4.5 V (vs. Li / Li + ), whereas batteries using lithium oxide as the positive electrode active material are charged and discharged at a voltage of 1.8V to 3.4V (vs. Li / Li + ) is charged and discharged. This is because oxygen gas is generated when the charging potential is increased beyond this range. In other words, the potential range used in batteries using lithium oxide as the positive electrode active material is different from that used in conventional lithium-ion batteries. As such, lithium oxide-based positive electrode active materials have different characteristics from the positive electrode active materials used in conventional lithium-ion batteries. Therefore, the detailed conditions for improving cycle characteristics, such as the composition of the electrolyte, have not been clarified.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0011] (Embodiment) FIG. 1 is a cross-sectional view showing a schematic configuration of a battery 100 according to an 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 exterior casing 28. The positive electrode 23 includes a positive electrode current collector 21 and a positive electrode active material layer 22. The positive electrode active material layer 22 is disposed on the positive electrode current collector 21. The negative electrode 26 includes a negative electrode current collector 24 and a negative electrode active material layer 25. The negative electrode active material layer 25 is disposed on the negative electrode current collector 24. A 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 exterior casing 28. The battery 100 is typically a secondary battery.

[0012] The positive electrode active material layer 22 contains lithium oxide doped with a transition metal M1 as a positive electrode active material. The lithium oxide doped with the transition metal M1 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 the electronic conductivity of the lithium oxide doped with the transition metal M1 is improved is not entirely clear, but it can be considered as follows. When the transition metal M1 is dissolved in the lithium oxide, the transition metal M1 occupies the lithium site, and oxygen atoms are tetrahedral coordinated around the transition metal M1 to form an outer orbital complex. For example, in the case of cobalt, multiple unpaired electrons exist in the 3d orbital, and these unpaired electrons impart electronic conductivity to the lithium oxide. Furthermore, assuming that the valence of the transition metal M1 is +3, the valence of lithium is +1. Therefore, in order to maintain charge neutrality within the crystal, two lithium atoms are released from the crystal in addition to the lithium atoms substituted for the transition metal M1, forming two vacancies. These vacancies serve as conduction paths for lithium ions, improving the ionic conductivity of the lithium oxide. The lithium oxide in which the transition metal M1 is dissolved can be a substitutional solid solution.

[0013] The charge / discharge reaction in the battery 100 is as follows: Reaction at the positive electrode 23: Li2O2 + 2Li + +2e - ⇔2LiO Reaction at the negative electrode 26: Li ⇔ Li + +e -

[0014] The transition metal M1 is not particularly limited as long as it can be solid-soluble in lithium oxide. The transition metal M1 may be, for example, an element selected from the group of elements of Groups 3 to 11 of the fourth and fifth periods of the periodic table. Specifically, the transition metal M1 may include at least one element selected from the group consisting of Fe, Co, Cu, Ni, and Mn. The transition metal M1 may be Fe, Co, or Cu. These elements are desirable from the viewpoints of suppressing an increase in the charging voltage of the battery 100 and improving the discharge capacity of the battery 100.

[0015] The lithium oxide in which the transition metal M1 is dissolved may have a composition represented by the following formulas (A) and (B) in a discharged state. According to quantum scientific 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.

[0016] When the valence of the transition metal M1 is +3: (Li (1-3α) M1 α ) 2O... (A) When the valence of the transition metal M1 is +2: (Li (1-2α) M1 α ) 2O... (B)

[0017] 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, 0.01 or more and 0.34 or less. By appropriately adjusting the ratio (m1 / (m0+m1)), it is possible to suppress an increase in the charging voltage of the battery 100 and improve the discharge capacity of the battery 100.

[0018] 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 be applied to the surface of the positive electrode current collector 21 as a conductive auxiliary material.

[0019] The positive electrode active material layer 22 may contain other materials such as a conductive additive, an ion conductor, and a binder.

[0020] The conductive additive and the ion conductor are used to reduce the resistance of the positive electrode 23. Examples of the conductive additive include a carbon material and a conductive polymer compound. Examples of the carbon material include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of the conductive polymer compound include polyaniline, polypyrrole, and polythiophene. At least one selected from these conductive additives can be used.

[0021] Examples of ionic conductors include gel electrolytes such as polymethyl methacrylate and polymethyl methacrylate, organic solid electrolytes such as polyethylene oxide, and Li7La3Zr2O 12 At least one selected from these ion conductors can be used.

[0022] The binder is used to improve the binding properties of the materials constituting the negative electrode 26. Examples of binders 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 can be used.

[0023] 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 applied to the surface of the negative electrode current collector 24 as a conductive auxiliary material.

[0024] The negative electrode active material layer 25 may contain a negative electrode active material capable of absorbing and desorbing lithium. Examples of negative electrode active materials capable of absorbing and desorbing 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 can be used. It is more preferable to use lithium metal as the negative electrode active material. The theoretical capacity of the positive electrode active material according to the present disclosure is 897 mAh per gram of lithium oxide, which is more than three times larger than other positive electrode active materials conventionally used. Therefore, lithium metal is suitable as the negative electrode active material.

[0025] The negative electrode active material layer 25 may contain other materials such as a conductive additive, an ion conductor, a binder, etc. Materials that can be used for the positive electrode active material layer 22 as the conductive additive, the ion conductor, and the binder can also be used for the negative electrode active material layer 25.

[0026] The electrolyte solution 29 may be impregnated into the positive electrode 23, the negative electrode 26, and the separator 27. The electrolyte solution 29 may fill the internal space of the exterior casing 28. The electrolyte solution 29 functions to allow lithium ions to move between the positive electrode 23 and the negative electrode 26.

[0027] In this embodiment, the electrolytic solution 29 contains an additive, which includes at least one selected from the group consisting of a phosphate ester represented by the following formula (1), a sulfonate ester represented by the following formula (2), a cyclic carbonate ester represented by the following formula (3), a benzene derivative, and a radical scavenger.

[0028]

[0029] In formula (1), R 1 , R 2 and R 3 are each independently an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an alkynyl group, a phenyl group, a phenyl group in which at least one hydrogen atom may be substituted with an alkyl group having 1 to 5 carbon atoms, or a silyl group. At least one hydrogen atom contained in these groups may be substituted with a halogen atom. 1 and R 2may be bonded to form a cyclic structure.

[0030] In formula (2), R 4 and R 5 are each independently an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an alkynyl group, a phenyl group, a phenyl group in which at least one hydrogen atom may be substituted with an alkyl group having 1 to 5 carbon atoms, or a silyl group. At least one hydrogen atom contained in these groups may be substituted with a halogen atom. 4 and R 5 may be bonded to form a cyclic structure.

[0031] In formula (3), R 6 and R 7 are each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or a vinyl group. 6 and R 7 At least one of the groups contains a vinyl group.

[0032] A benzene derivative is a compound having a structure in which at least one substituent is bonded to a benzene ring. The substituent is an alkyl group having 1 to 10 carbon atoms, an aryl group, or a carbonate group.

[0033] The various additives contained in the electrolyte solution 29 have the effect of improving the cycle characteristics of the battery 100. Although the reason for this is not entirely clear, it is presumed that in the case of phosphate esters, sulfonate esters, cyclic carbonate esters, and benzene derivatives, these additives or their decomposition products form a coating on the surface of the active material, preventing contact between the active material and the electrolyte solution 29 and suppressing decomposition of the electrolyte solution 29 and oxygen desorption from the positive electrode active material. In the case of phosphate esters, sulfonate esters, and cyclic carbonate esters, it is presumed that the coating is formed by decomposition of these ester moieties. In particular, in the case of cyclic esters, it is presumed that ring opening occurs easily, leading to the formation of a coating. Therefore, it is presumed that the structure of moieties other than the ester moiety has little effect.

[0034] The radical scavenger is presumed to capture oxygen radicals that may be generated in the side reaction process of the oxidation-reduction reaction in the positive electrode 23. Therefore, it is considered that a compound that can capture oxygen radicals can be used as an additive for the battery 100 of this embodiment.

[0035] In formula (1), R 1 , R 2 and R 3 At least one selected from the following may be a silyl group represented by the following formula (4): 8 , R 9 and R 10 are each independently an organic group or a hydrogen atom. A phosphate ester having such a structure can sufficiently improve the cycle characteristics of the battery 100. The organic group may be an alkyl group having 1 to 5 carbon atoms, and at least one hydrogen atom contained in the alkyl group may be substituted with a halogen atom.

[0036]

[0037] In formula (1) and / or formula (2), the silyl group may be a trialkylsilyl group.

[0038] In formula (1), R 1 , R 2 and R 3 may have the same structure. A phosphate ester having such a structure can sufficiently improve the cycle characteristics of the battery 100. In addition, a phosphate ester having such a structure is easy to synthesize.

[0039] 2A and 2B are diagrams showing the structural formulas of various phosphate esters represented by formula (1). The phosphate esters include (a) trimethyl phosphate, (b) triethyl phosphate, (c) tributyl phosphate, (d) tripentyl phosphate, (e) tris(2-ethylhexyl) phosphate, (f) triphenyl phosphate, (g) tricresyl phosphate, (h) 2-ethylhexyldiphenyl phosphate, (i) tris(2-butoxyethyl) phosphate, (j) tris(1,1,1,3,3,3-hexafluoro-2-propyl) phosphate, (k) trifluoroethylethylene phosphate, (l) 2-methoxy-1,3,2- Examples include dioxaphospholane 2-oxide, (m) tripropargyl phosphate, (n) tris(trimethylsilyl) phosphate, (o) tris(triethylsilyl) phosphate, (p) triallyl phosphate, (q) tris(tert-butyldimethylsilyl) phosphate, (r) tris(1H,1H,5H-octafluoropentyl) phosphate, (s) tris(2,2,2-trifluoroethyl) phosphate, (t) tris(2-chloroethyl) phosphate, and (u) tris(1,3-dichloro-2-propyl) phosphate. At least one selected from these phosphate esters can be used.

[0040] The phosphate ester may contain tris(trimethylsilyl)phosphate (TMSP), which is effective in improving the cycle characteristics of the battery 100.

[0041] 3 is a diagram showing the structural formulas of various sulfonate esters represented by formula (2). Examples of sulfonate esters include (a) 1,3-propane sultone, (b) 1-propene 1,3-sultone, (c) 1,4-butane sultone, and (d) 1,8-naphthosultone. At least one selected from these sulfonate esters can be used.

[0042] The sulfonate ester may include a cyclic sulfonate ester, which can sufficiently improve the cycle characteristics of the battery 100.

[0043] Examples of the cyclic carbonate represented by formula (3) include vinyl ethylene carbonate, vinylene carbonate, etc. At least one selected from these cyclic carbonates can be used.

[0044] The cyclic carbonate may contain vinyl ethylene carbonate, which is effective in improving the cycle characteristics of the battery 100.

[0045] 4 shows the structural formulas of various benzene derivatives. Examples of benzene derivatives include (a) o-xylene, (b) m-xylene, (c) p-xylene, (d) diphenylpropane, (e) phenyl-tert-butyl carbonate, and (f) cyclohexylbenzene. At least one selected from these benzene derivatives can be used.

[0046] The benzene derivative may include an alkylbenzene. Specifically, the benzene derivative may include cyclohexylbenzene. In this case, the effect of improving the cycle characteristics of the battery 100 can be sufficiently obtained.

[0047] The radical scavenger may contain 2,2,6,6-tetramethylpiperidine 1-oxyl, which is effective in improving the cycle characteristics of the battery 100.

[0048] The volume ratio of the additive in the electrolyte solution is, for example, 0.01% by volume or more and 20% by volume or less. Adjusting the volume ratio of the additive within an appropriate range can sufficiently improve the cycle characteristics of the battery 100. The volume ratio of the additive in the electrolyte solution is preferably 0.1% by volume or more and 15% by volume or less, and more preferably 1.0% by volume or more and 15% by volume or less.

[0049] The concentration of the additive in the electrolytic solution 29 may be 0.01 mol / L or more and 2.0 mol / L or less, and preferably 0.02 mol / L or more and 0.50 mol / L or less. By adjusting the concentration of the additive within an appropriate range, the effect of improving the cycle characteristics of the battery 100 can be sufficiently obtained.

[0050] The concentration of the radical scavenger in the electrolytic solution 29 may be 0.01 mol / L or more and 0.4 mol / L or less. When the concentration of the radical scavenger is adjusted to an appropriate range, the effect of improving the cycle characteristics of the battery 100 can be sufficiently obtained.

[0051] The electrolyte solution 29 may contain, in addition to the additives described above, a non-aqueous solvent and a lithium salt. The additive is preferably dissolved in the non-aqueous solvent. This configuration is likely to improve the cycle characteristics of the battery 100.

[0052] Examples of non-aqueous solvents that can be used include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, cyclic esters, chain esters, fluorine-containing solvents, and nitriles. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, chloroethylene carbonate, difluoroethylene carbonate, and styrene 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 fluorine-containing solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethyl carbonate. The nitrile may be acetonitrile, etc. At least one selected from these non-aqueous solvents may be used.

[0053] Examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. At least one selected from these lithium salts can be used.

[0054] The electrolytic solution 29 may include a gel electrolyte and / or an ionic liquid.

[0055] The gel electrolyte can be a material obtained by impregnating a polymer material with the electrolytic solution 29. Examples of the polymer material include polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, and polymers having ethylene oxide bonds.

[0056] Examples of cations constituting ionic liquids include aliphatic chain quaternary cations, aliphatic cyclic ammonium, and nitrogen-containing heterocyclic aromatic cations. Examples of aliphatic chain quaternary cations include tetraalkylammonium and tetraalkylphosphonium. Examples of aliphatic cyclic ammonium include pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperaziniums, and piperidiniums. Examples of nitrogen-containing heterocyclic aromatic cations include pyridiniums and imidazoliums. Examples of anions constituting ionic liquids include PF6 - , BF4 - , SbF6 - , AsF6 - , SO3CF3 - , N(SO2F)2 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) - , C(SO2CF3)3 - The ionic liquid may contain a lithium salt.

[0057] The separator 27 is an electrolyte layer having lithium ion conductivity. There are no particular limitations on the material of the separator 27 as long as it allows the passage of lithium ions. The material of the separator 27 can be at least one selected from the group consisting of 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 sufficiently ensured. Examples of solid electrolytes include sulfide solid electrolytes such as Li2S-P2S5, Li7La3Zr2O 12 Examples of the electrolyte include oxide solid electrolytes such as LLZ. Examples of the gel electrolyte include gel electrolytes containing fluororesins such as PVdF. Examples of the ion exchange resin membrane include cation exchange membranes and anion exchange membranes. Examples of the porous membrane include porous membranes made of polyolefin resins and porous membranes made of glass paper obtained by weaving glass fibers into nonwoven fabric.

[0058] The exterior 28 is made of a material obtained by laminating a metal foil such as an aluminum foil with a resin film such as a PET film, for example. The exterior 28 may also be a resin or metal container.

[0059] The shape of the battery 100 is not limited to the laminated type. Other shapes of the battery 100 include a coin type, a cylindrical type, a square type, a sheet type, a button type, and a flat type.

[0060] Next, the positive electrode active material will be described in more detail.

[0061] The positive electrode active material may contain a transition metal oxide containing a transition metal M2 in addition to lithium oxide having a transition metal M1 dissolved therein. The presence of a transition metal oxide in the positive electrode active material suppresses an increase in the charging voltage of the battery 100 and improves the discharge capacity of the battery 100.

[0062] The transition metal oxide containing the transition metal M2 has a crystal structure different from that of lithium oxide in which the transition metal M1 is dissolved. The transition metal oxide containing the transition metal M2 may include a double oxide containing lithium and the transition metal M2. The crystal structure of the double oxide may be different from that of lithium oxide. The transition metal oxide containing the transition metal M2 may not contain lithium. The transition metal oxide may include a metal oxide containing only the transition metal M2 as the metal element. The transition metal oxide containing the transition metal M2 may include at least one selected from the group consisting of a double oxide containing lithium and the transition metal M2 and a metal oxide containing only the transition metal M2 as the metal element.

[0063] The transition metal M2 may be, for example, an element selected from the group of elements of Groups 3 to 11 of the fourth and fifth periods of the periodic table. The transition metal M2 includes, for example, at least one element selected from the group consisting of Fe, Co, Cu, Ni, and Mn. The transition metal M2 may be Fe, Co, Cu, Ni, or Mn. These elements are desirable from the viewpoint of suppressing an increase in the charging voltage of the battery 100 and from the viewpoint of improving the discharge capacity of the battery 100.

[0064] The transition metal M2 may be the same as or different from the transition metal M1 solid-solubilized in the lithium oxide crystal. Typically, the transition metal M1 and the transition metal M2 are the same element or group of elements. The transition metal M1 and the transition metal M2 may 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, there are advantages such as ease of production and reduced raw material costs. The transition metal oxide may be a residue of the raw material used to dissolve the transition metal M1 in the lithium oxide, or a by-product generated during the synthesis of the positive electrode active material.

[0065] When the positive electrode active material includes a transition metal oxide containing a transition metal M2, the amount of lithium contained in the lithium oxide and 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, 0.01 or more and 0.34 or less. By appropriately adjusting the ratio (m1 + m2) / (m0 + m1 + m2), the effect of suppressing an increase in charge voltage and the effect of improving discharge capacity are enhanced.

[0066] When the transition metals M1 and M2 are the same element, the amount of substance m1 is the amount of substance of the transition metal M1 present in the positive electrode active material. The above ratio is expressed as (m1 / (m0+m1)).

[0067] The presence of the transition metal oxide can be confirmed by X-ray diffraction measurement. The degree of dissolution of the transition metal M1 in the lithium oxide and a suitable amount of the transition metal oxide can be identified based on multiple diffraction peaks attributed to the lithium oxide in which the transition metal M1 is dissolved and at least one diffraction peak attributed to the transition metal oxide.

[0068] In the X-ray diffraction pattern of the positive electrode active material measured using Cu-Kα radiation, a diffraction peak present in the range of a diffraction angle 2θ of 30° to 40° is defined as a first diffraction peak. A diffraction peak present in the range of a diffraction angle 2θ of 52° to 62° is defined as a second diffraction peak. A diffraction peak present in the range of a diffraction angle 2θ of 40° to 50° is defined as a third diffraction peak. The first diffraction peak is a diffraction peak attributable to the (111) plane of lithium oxide. The second diffraction peak is a diffraction peak attributable to the (220) plane of lithium oxide. The third diffraction peak is a diffraction peak attributable to a 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 as I2, and the integrated intensity of the third diffraction peak as I3. In this embodiment, the ratio of integrated intensities I / I is 0.48 or more, and the ratio of integrated intensities I / I is 0.10 or more and 1.30 or less. By satisfying these conditions, an increase in the charging voltage of the battery 100 can be suppressed and the discharge capacity of the battery 100 can be improved. Suppressing an increase in the charging voltage also leads to suppression of oxygen gas generation.

[0069] The integrated intensity ratio I2 / I1 is an index reflecting the degree of solid solubility of the transition metal M1 in the lithium oxide crystal. Assuming that the valence of the transition metal M1 is +3, the valence of lithium is +1. Therefore, two lithium atoms are released from the crystal in addition to the lithium atoms substituted for the transition metal M1 to maintain charge neutrality within the crystal. The incorporation of the transition metal M1, which has a valence higher than that of the lithium atoms, into the crystal and the release of two lithium atoms from the crystal to maintain charge neutrality cause minute distortions in the crystalline structure of the lithium oxide matrix. The greater the distortion, the greater the integrated intensity ratio I2 / I1. According to quantum science calculations, there is a proportional relationship between the amount of transition metal M1 doped into the lithium oxide and the integrated intensity ratio I2 / I1. Sufficient solid solubility of the transition metal M1 also enhances the effects of suppressing increases in charging voltage and improving discharge capacity. The theoretical integrated intensity ratio I2 / I1 of Li2O crystal is approximately 0.33.

[0070] 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 as a residue and / or by-product. In this case, 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 therefore 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 therefore 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 determined from the entire X-ray diffraction pattern including the third diffraction peak. When a transition metal oxide crystal is present, a diffraction peak appears in the diffraction angle 2θ range of 40° to 50°, regardless of the type of transition metal.

[0071] The reason why the effect of suppressing an increase in charge voltage and improving discharge capacity is enhanced when the transition metal M1 is appropriately dissolved in lithium oxide and the residues and / or by-products are appropriately present without disappearing is not entirely clear, but the inventors speculate as follows. During the charging process, lithium atoms are removed from the lithium oxide, oxygen ions are oxidized to peroxide ions, and the lithium oxide is converted to lithium peroxide. Here, if the positive electrode active material is composed only of lithium oxide in which the transition metal M1 is completely dissolved, the volumetric shrinkage of the positive electrode active material during the charging process is significant, creating voids between the positive electrode active material and the conductive additive, increasing the electronic resistance of the entire electrode and causing an increase in charge voltage. In contrast, according to the present disclosure, the appropriate presence of residues and / or by-products containing the transition metal M2 in the positive electrode active material suppresses the volumetric shrinkage of the positive electrode active material during the charging process by utilizing charge compensation due to the change in valence of the transition metal M2. As a result, the effect of suppressing an increase in charge voltage and the effect of improving discharge capacity are exhibited. The achievement of these effects is supported by the examples described below.

[0072] The lower limit of the integrated intensity ratio I / I may be 0.50 or 0.55. The upper limit of the integrated intensity ratio I / I is not particularly limited and may be 1.00 or 0.90. The integrated intensity ratio I / I 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.

[0073] The ratio of integrated intensities I3 / I1 is preferably 0.20 or more. The ratio of integrated intensities I3 / I1 may be 1.10 or less, or may be 1.00 or less.

[0074] The ranges of the integrated intensity ratios I / I and I / I may be defined by any combination of the above values. For example, the integrated intensity ratio I / I may be 0.48 or more, and the integrated intensity ratio I / I may be 0.20 or more and 1.10 or less.

[0075] 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.

[0076] 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.

[0077] The integrated intensity ratio I2 / I1 may be 0.55 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 0.55 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 0.55 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.

[0078] The integrated intensity ratio I2 / I1 may be 0.55 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 0.55 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 0.55 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.

[0079] The integrated intensity ratio I / I of a LiO crystal not doped with a transition metal M1 is approximately 0.33. When the integrated intensity ratio I / I exceeds 0.33 while maintaining the inverse fluorite crystal structure of LiO, it can be determined that the transition metal M1 is dissolved in lithium oxide.

[0080] The positive electrode active material has a structure of secondary particles composed of, for example, multiple primary particles of lithium oxide and multiple primary particles of a transition metal oxide. A positive electrode active material having such a structure can be efficiently produced by a synthesis method such as mechanochemical milling. The primary particles have diameters on the order of nanometers, for example. The secondary particles have diameters on the order of micrometers, for example.

[0081] The true density of the positive electrode active material is, for example, 2.0 g / cm 3 3.3g / cm or more 3 By appropriately adjusting the true density, the energy density of the battery 100 can be improved compared to conventional lithium secondary batteries. The true density can be measured by a pycnometer method after finely pulverizing the positive electrode active material.

[0082] The specific surface area of ​​the positive electrode active material is, for example, 1.6 m 2 / g or more 60m2 / g or less. By appropriately adjusting the specific surface area, it is possible to improve the energy density of the battery 100. The specific surface area is a value determined by the BET method.

[0083] The positive electrode active material may have a particulate shape. Each particle of the positive electrode active material has a size of 0.01 μm or less. 2 500 μm or more 2 The positive electrode active material particles may have a cross-sectional area within the range specified above. 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 range specified above, or only a portion of the particles (e.g., 90% or more by number) may have a cross-sectional area within the range specified above.

[0084] The positive electrode active material can be produced, for example, by a mechanochemical method. First, a mixture is prepared by mixing lithium oxide powder with a raw material for the transition metal M1. The ratio of the lithium oxide to the raw material for the transition metal M1 can be determined so that the ratio (m1 / (m0+m1)) described above falls within a desired range. Examples of raw materials for the transition metal M1 include an oxide of the transition metal M1, a composite oxide containing lithium and the transition metal M1, and a simple substance of the transition metal M1.

[0085] The synthesis of the positive electrode active material by the mechanochemical method is carried out using a device capable of exerting a mechanochemical effect, such as a ball mill or a bead mill. The atmosphere during the synthesis is not particularly limited and may be an air atmosphere, an inert atmosphere, a dry atmosphere, or a dry inert atmosphere. In order to suppress the incorporation of inevitable impurities such as oxygen and water, it is desirable to synthesize the positive electrode active material in a dry inert atmosphere. For the inert atmosphere, for example, an inert gas such as nitrogen, argon, or helium is used.

[0086] The degree of solid solubility of the transition metal M1 in lithium oxide can be adjusted by adjusting conditions such as the rotation speed of the apparatus, treatment time, treatment temperature, raw material particle size, raw material composition of the transition metal M1, and size of the grinding media. That is, the integrated intensity ratios I2 / I1 and I3 / I1 can be controlled. For example, as the rotation speed and treatment time increase, the solid solubility of the transition metal M1 in lithium oxide progresses, and the ratios I2 / I1 increase and I3 / I1 decrease. By setting the production conditions so that the integrated intensity ratios I2 / I1 and I3 / I1 fall within the desired ranges, a positive electrode active material can be obtained that can suppress an increase in charge voltage and improve discharge capacity.

[0087] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0088] (Technology 1) A battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode has an inverse fluorite crystal structure and contains lithium oxide having a transition metal dissolved therein as a positive electrode active material, and the electrolyte contains an additive, and the additive contains at least one selected from the group consisting of a phosphate ester represented by the following formula (1), a sulfonate ester represented by the following formula (2), a cyclic carbonate ester represented by the following formula (3), a benzene derivative, and a radical scavenger, wherein in the formula (1), R 1 , R 2 and R 3 are each independently an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an alkynyl group, a phenyl group, a phenyl group in which at least one hydrogen atom may be substituted by an alkyl group having 1 to 5 carbon atoms, or a silyl group, in which at least one hydrogen atom contained in these groups may be substituted by a halogen atom; R 1 and R 2 may be bonded to form a cyclic structure, and in the formula (2), R 4 and R 5are each independently an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an alkynyl group, a phenyl group, a phenyl group in which at least one hydrogen atom may be substituted by an alkyl group having 1 to 5 carbon atoms, or a silyl group, in which at least one hydrogen atom contained in these groups may be substituted by a halogen atom; R 4 and R 5 may be bonded to form a cyclic structure, and in the formula (3), R 6 and R 7 are each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or a vinyl group, and R 6 and R 7 at least one of the above-mentioned compounds contains a vinyl group, and the benzene derivative is a compound having a structure in which at least one substituent is bonded to a benzene ring, and the substituent is an alkyl group having 1 to 10 carbon atoms, an aryl group, or a carbonate group.

[0089] With this configuration, the cycle characteristics of the battery can be improved.

[0090] (Technology 2) The battery according to Technology 1, wherein the volume ratio of the additive in the electrolyte solution is 0.01% by volume or more and 20% by volume or less. By adjusting the volume ratio of the additive within an appropriate range, the effect of improving the cycle characteristics of the battery can be sufficiently obtained.

[0091] (Technology 3) The battery according to Technology 1 or 2, wherein the concentration of the additive in the electrolyte solution is 0.01 mol / L or more and 2.0 mol / L or less. By adjusting the concentration of the additive within an appropriate range, the effect of improving the cycle characteristics of the battery can be sufficiently obtained.

[0092] (Technology 4) In the formula (1), R 1 , R 2 and R 3 At least one selected from the group consisting of: is a silyl group represented by the following formula (4), and in the formula (4), R 8 , R 9 and R 10and are each independently an organic group or a hydrogen atom. A phosphate ester having such a structure can sufficiently improve the cycle characteristics of the battery.

[0093] (Technology 5) In the formula (1), R 1 , R 2 and R 3 The battery according to any one of Techniques 1 to 4, wherein the phosphate ester has the same structure as the battery. The phosphate ester having such a structure can sufficiently improve the cycle characteristics of the battery.

[0094] (Technology 6) The battery according to any one of Technologies 1 to 5, wherein the phosphate ester includes at least one selected from the group consisting of trimethyl phosphate, triethyl phosphate, tributyl phosphate, tripentyl phosphate, tris(2-ethylhexyl) phosphate, triphenyl phosphate, tricresyl phosphate, 2-ethylhexyldiphenyl phosphate, tris(2-butoxyethyl) phosphate, tris(1,1,1,3,3,3-hexafluoro-2-propyl) phosphate, trifluoroethylethylene phosphate, 2-methoxy-1,3,2-dioxaphospholane 2-oxide, tripropargyl phosphate, tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, triallyl phosphate, tris(tert-butyldimethylsilyl), tris(1H,1H,5H-octafluoropentyl) phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(2-chloroethyl) phosphate, and tris(1,3-dichloro-2-propyl) phosphate. In this case, the effect of improving the cycle characteristics of the battery can be sufficiently obtained.

[0095] (Technology 7) The battery according to any one of Technologies 1 to 6, wherein the sulfonate ester includes a cyclic sulfonate ester. In this case, the effect of improving the cycle characteristics of the battery can be sufficiently obtained.

[0096] (Technology 8) The battery according to any one of Technologies 1 to 6, wherein the sulfonate ester includes at least one selected from the group consisting of 1,3-propane sultone, 1-propene 1,3-sultone, 1,4-butane sultone, and 1,8-naphthosultone. In this case, the effect of improving the cycle characteristics of the battery can be sufficiently obtained.

[0097] (Technology 9) The battery according to any one of Techniques 1 to 8, wherein the cyclic carbonate includes at least one selected from the group consisting of vinyl ethylene carbonate and vinylene carbonate. In this case, the effect of improving the cycle characteristics of the battery can be sufficiently obtained.

[0098] (Technology 10) The battery according to any one of Technologies 1 to 9, wherein the benzene derivative includes at least one selected from the group consisting of o-xylene, m-xylene, p-xylene, diphenylpropane, phenyl-tert-butyl carbonate, and cyclohexylbenzene. In this case, the effect of improving the cycle characteristics of the battery can be sufficiently obtained.

[0099] (Technology 11) The battery according to any one of Technologies 1 to 10, wherein the radical scavenger contains 2,2,6,6-tetramethylpiperidine 1-oxyl. In this case, the effect of improving the cycle characteristics of the battery can be sufficiently obtained.

[0100] (Technology 12) The battery according to any one of Techniques 1 to 11, wherein the concentration of the radical scavenger in the electrolyte solution is 0.01 mol / L or more and 0.4 mol / L or less. By adjusting the concentration of the radical scavenger within an appropriate range, the effect of improving the cycle characteristics of the battery can be sufficiently obtained.

[0101] (Technology 13) The positive electrode active material has a particulate shape, and the particles of the positive electrode active material have a particle size of 0.01 μm or less. 2 500 μm or more 2 13. The battery according to any one of techniques 1 to 12, having the following cross-sectional area: By appropriately adjusting the particle size of the positive electrode active material, the cycle characteristics of the battery can be improved.

[0102] (Technology 14) The battery according to any one of Technologies 1 to 13, wherein the negative electrode contains lithium metal. With this configuration, the energy density of the battery can be increased.

[0103] (Technology 15) The battery according to any one of technologies 1 to 13, wherein 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 a second diffraction peak attributable to a (220) plane of the lithium oxide present in a diffraction angle 2θ range of 52° to 62° to the integrated intensity of a first diffraction peak attributable to a (111) plane of the lithium oxide present in the diffraction angle 2θ range of 30° to 40° is 0.48 or more, and the ratio of the integrated intensity of a third diffraction peak attributable to a crystal plane of the transition metal oxide present in the diffraction angle 2θ range of 40° to 50° to the integrated intensity of the first diffraction peak is 0.10 to 1.30. This configuration can suppress an increase in charge voltage and improve discharge capacity.

[0104] (Technology 16) The battery according to Technology 15, 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. A positive electrode active material having such a structure can be efficiently produced by various granulation methods.

[0105] Hereinafter, each operation in the preparation of the positive electrode active material and each operation in the preparation of the battery were 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. Some of the examples, comparative examples, and samples included those in which the same operation was performed multiple times in order to obtain a sufficient amount of sample.

[0106] [Preparation of Electrolyte Solution] (Reference Examples 1 and 2) Ethylene carbonate and diethyl carbonate were mixed in 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 the electrolyte solution of Reference Example 1. The compositions of the electrolyte solutions of Reference Examples 1 and 2 were the same.

[0107] (Examples 1 to 8) The additives shown in Table 1 were added to the electrolyte solution of Reference Example 1 to obtain the electrolyte solutions of Examples 1 to 8. The concentrations of the additives in each electrolyte solution were as shown in Table 1.

[0108] The only difference between Example 1 and Example 2 is the charging conditions. That is, the battery of Example 1 using the electrolyte of Example 1 was subjected to constant current charging at a current value of 50 mA / g until a voltage of 3.4 V was reached. The battery of Example 2 using the electrolyte of Example 2 was subjected to constant current charging at a current value of 50 mA / g until a voltage of 3.18 V was reached, and then constant voltage charging at a constant voltage of 3.18 V until a charge capacity of 600 mAh / g was reached. In Table 1, "CC" stands for constant current charging. "CCCV" stands for constant current / constant voltage charging. The only difference between Reference Example 1 and Reference Example 2 is the charging conditions.

[0109]

[0110] [Preparation of Positive Electrode Active Material] In an Ar glove box, 1.00 g of Li2O and 0.82 g of LiCoO2 were crushed and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (Fritsch, P-7 type, 45 mL container) together with 45 g of zirconia balls (diameter 5 mm), and the mixture was milled at 420 rpm for 100 hours. This produced a positive electrode active material.

[0111] [Battery Fabrication] A coin battery conforming to the CR2016 standard was fabricated using the above-described positive electrode active material. A positive electrode composite containing the positive electrode active material, acetylene black, and polytetrafluoroethylene in a mass ratio of 7:2:1 was used. Lithium metal was used for the negative electrode. A polyolefin porous membrane was used for the separator. 120 μL of the electrolyte solutions of Examples 1 to 8, Reference Example 1, and Reference Example 2 was used as the electrolyte solution.

[0112] [Charge-Discharge Test: Upper Limit Voltage 3.4 V Condition] The batteries of Examples 1, 5 to 7, and Reference Example 1 were charged at a current of 50 mA / g until the voltage reached 3.4 V. After a 20-minute rest, they were discharged at a constant current of 0.40 mA until the voltage reached 1.8 V. After the constant current discharge, they were discharged at a constant voltage of 1.8 V until the current reached 5 mA / g. The current value unit "mA / g" represents the current value per 1 g of LiO. This charge-discharge cycle was repeated five or ten times. Table 2A shows the charge and discharge capacities at the first, fifth, and tenth cycles. The capacity retention rate at the tenth cycle is the ratio of the discharge capacity at the tenth cycle to the discharge capacity at the first cycle. In Tables 2A and 2B, the capacity unit "mAh / g" represents the capacity per 1 g of LiO.

[0113]

[0114] As shown in Table 2A, the discharge capacities at the 5th cycle of the batteries of Examples 1, 5, 6, and 7 were higher than that of the battery of Reference Example 1. The discharge capacity retention rate at the 10th cycle of the battery of Example 1 was higher than that of the battery of Reference Example 1. These results indicate that the cycle characteristics of the battery were improved by the various additives.

[0115] [Charge / Discharge Test: Upper Limit Voltage 3.18 V Condition] The batteries of Examples 2 to 4, Example 8, and Reference Example 2 were subjected to constant current charging at a current value of 50 mA / g until the voltage reached 3.18 V, and then constant voltage charging at a constant voltage of 3.18 V until the charge capacity reached 600 mAh / g. After a 20-minute rest, the batteries were discharged at a constant current of 0.40 mA until the voltage reached 1.8 V. After the constant current discharge, the batteries were discharged at a constant voltage of 1.8 V until the current reached 5 mA / g. This charge / discharge cycle was repeated 5 or 10 times. The charge capacities and discharge capacities at the first, fifth, and tenth cycles are shown in Table 2B.

[0116]

[0117] As shown in Table 2B, the discharge capacities at the fifth cycle of the batteries of Examples 2, 3, 4, and 8 were higher than that of the battery of Reference Example 2. The discharge capacity retention rates at the tenth cycle of the batteries of Examples 2 to 4 were higher than that of the battery of Reference Example 2. These results indicate that the cycle characteristics of the batteries were improved by the various additives.

[0118] Next, a plurality of positive electrode active materials were produced using different production conditions and / or raw materials, and the charge voltages and discharge capacities of batteries using these positive electrode active materials were examined.

[0119] [Preparation of Positive Electrode Active Material: Co-Based] (Sample 1) 1.00 g of Li2O and 0.82 g of LiCoO2 were crushed and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (Fritsch, P-7 type, 45 mL container) together with 45 g of zirconia balls (diameter 5 mm), and the mixture was milled at 420 rpm for 100 hours. This yielded the positive electrode active material of Sample 1.

[0120] (Sample 2) 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.

[0121] (Sample 3) A 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, PL-7 type, 45 mL container) was used.

[0122] (Sample 4) The positive electrode active material of Sample 4 was prepared on a different date and time by the same method as the positive electrode active material of Sample 3. As will be described later, the main differences between Sample 3 and Sample 4 are the volume ratio of vinylene carbonate in the battery electrolyte and the amount of the positive electrode mixture.

[0123] (Sample 5) A positive electrode active material of Sample 5 was prepared in the same manner as Sample 1, except that 2.00 g of Li2O and 1.63 g of LiCoO2 were used and the mixture was milled at 600 rpm for 100 hours.

[0124] (Sample 6) The positive electrode active material of Sample 6 was prepared in the same manner as Sample 1, except that 2.00 g of Li2O and 1.63 g of LiCoO2 were used, and the mixture was milled at 600 rpm for 100 hours, followed by heat treatment. The heat treatment was carried out in an argon atmosphere at 250°C (ambient temperature) for 6 hours. The temperature was raised over 1 hour, and the material was allowed to cool naturally after the heat treatment.

[0125] (Sample 7) 2.00 g of Li2O and 1.34 g of Co3O4 were crushed and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (Fritsch, P-7 type, 45 mL container) together with 45 g of zirconia balls (diameter 5 mm), and the mixture was milled at 420 rpm for 100 hours. This yielded the positive electrode active material of Sample 7.

[0126] (Sample 8) A positive electrode active material of Sample 8 was prepared in the same manner as Sample 1, except that 2.00 g of Li2O and 1.64 g of LiCoO2 were used.

[0127] (Sample 9) 5.00 g of LiO and 4.08 g of LiCoO were crushed and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (Fritsch, PL-7, 80 mL container) together with 98 g of zirconia balls (diameter 5 mm), and the mixture was milled at 420 rpm for 100 hours. This yielded the positive electrode active material of Sample 9.

[0128] (Sample 10) 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.

[0129] (Sample 11) The positive electrode active material of Sample 11 was prepared in the same manner as the positive electrode active material of Sample 3. As will be described later, 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.

[0130] (Sample 12) The positive electrode active material of Sample 12 was made of the same material as the positive electrode active material of Sample 11 and was produced at the same time. Specifically, the container for Sample 11 was set at one position of a planetary ball mill, and the container for Sample 12 was set at another position of the planetary ball mill. However, as described below, the amount of positive electrode composite used in the battery of Sample 12 was different from the amount of positive electrode composite used in the battery of Sample 11.

[0131] (Sample 13) The positive electrode active material of Sample 13 was made of the same material as the positive electrode active material of Sample 4 and was prepared at the same time. Specifically, the container for Sample 4 was set at one position of a planetary ball mill, and the container for Sample 13 was set at another position of the planetary ball mill. However, as will be described later, the type of electrolyte and the amount of positive electrode composite used in the battery of Sample 13 were different from the type of electrolyte and the amount of positive electrode composite used in the battery of Sample 4.

[0132] (Sample 14) A positive electrode active material of Sample 14 was prepared in the same manner as Sample 1, except that 2.00 g of Li2O and 1.64 g of LiCoO2 were used and the treatment time was changed to 10 hours.

[0133] (Sample 15) The positive electrode active material of Sample 15 was prepared in the same manner 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 then heat-treated. The heat treatment was carried out in an argon atmosphere at 350°C (ambient temperature) for 6 hours. The temperature was raised over a period of 1 hour, and the product was then allowed to cool naturally after the heat treatment.

[0134] (Sample 16) The positive electrode active material of Sample 16 was prepared in the same manner as Sample 1, except that 2.00 g of LiO and 1.63 g of LiCoO were used, the mixture was milled at 600 rpm for 100 hours, and the resulting product was then heat-treated. The heat treatment was carried out in an argon atmosphere at 450°C (ambient temperature) for 6 hours. The temperature was raised over a 1-hour period, and the product was then allowed to cool naturally after the heat treatment.

[0135] [Preparation of Positive Electrode Active Material: Cu-Based] (Sample 17) 2.00 g of LiO and 1.78 g of CuO were ground and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (Fritsch, P-7 type, 45 mL container) together with 45 g of zirconia balls (diameter 5 mm), and the mixture was milled at 600 rpm for 100 hours. This yielded the positive electrode active material of Sample 17.

[0136] (Sample 18) A positive electrode active material of Sample 18 was prepared in the same manner as Sample 17, except that 2.00 g of Li2O and 0.67 g of CuO were used.

[0137] (Sample 19) A positive electrode active material of Sample 19 was prepared in the same manner as Sample 17, except that 1.99 g of Li2O and 1.14 g of CuO were used.

[0138] (Sample 20) A positive electrode active material of Sample 20 was prepared in the same manner as Sample 17, except that 2.00 g of Li2O and 1.43 g of CuO were used.

[0139] (Sample 21) A positive electrode active material of Sample 21 was prepared in the same manner as Sample 17, except that 1.99 g of Li2O and 0.66 g of CuO were used and the treatment time was changed to 48 hours.

[0140] (Sample 22) A positive electrode active material of Sample 22 was prepared in the same manner as Sample 17, except that 2.00 g of Li2O and 0.47 g of CuO were used.

[0141] [Preparation of Positive Electrode Active Material: Fe-Based] (Sample 23) 2.00 g of Li2O and 1.19 g of Fe2O3 were crushed and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (Fritsch, P-7 type, 45 mL container) together with 45 g of zirconia balls (diameter 5 mm), and the mixture was milled at 600 rpm for 100 hours. This yielded the positive electrode active material of Sample 23.

[0142] (Sample 24) A positive electrode active material of Sample 24 was prepared in the same manner as Sample 23, except that 2.00 g of Li2O and 0.89 g of Fe2O3 were used.

[0143] (Sample 25) 2.00 g of Li2O and 1.29 g of Fe3O4 were crushed and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (Fritsch, P-7 type, 45 mL container) together with 45 g of zirconia balls (diameter 5 mm), and the mixture was milled at 420 rpm for 100 hours. This yielded the positive electrode active material of Sample 25.

[0144] (Sample 26) 5.00 g of LiO and 4.01 g of FeO were crushed and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (Fritsch, PL-7, 80 mL container) together with 98 g of zirconia balls (diameter 5 mm), and the mixture was milled at 420 rpm for 150 hours. This yielded the positive electrode active material of Sample 26.

[0145] (Sample 27) 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.

[0146] (Sample 28) A positive electrode active material of Sample 28 was prepared in the same manner as Sample 23, except that 2.00 g of Li2O and 0.63 g of Fe2O3 were used.

[0147] [X-ray Diffraction Measurement] Powder X-ray diffraction measurement of the positive electrode active material was carried out. For the X-ray diffraction measurement, a powder X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation) was used. The measurement conditions are as follows.

[0148] Cu Ka line Detector: HyPix400MF Scan step: 0.02deg Scan speed: 2 deg / min 2θ: 10-80deg Average spectrum of 8 measurements

[0149] Fig. 5A shows the X-ray diffraction pattern of the positive electrode active material when the transition metal M1 is Co, Fig. 5B shows the X-ray diffraction pattern of the positive electrode active material when the transition metal M1 is Cu, and Fig. 5C shows the X-ray diffraction pattern of the positive electrode active material when the transition metal M1 is Fe.

[0150] [Calculation of Integrated Intensity Ratio] The X-ray diffraction pattern of each positive electrode active material was analyzed using analytical software (OriginPro2022, manufactured by OriginLab). Specifically, 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 multiple peaks corresponding to the third diffraction peak were present, peak separation was performed using a Lorentz function or a Voigt function. The integrated intensities of each separated peak were calculated, and their sum was considered to be the integrated intensity I3 of the third diffraction peak. For example, when Cu is used as the transition metal M1, a diffraction peak attributed to reflection from the (013) plane of Li2CuO2 crystal classified in the space group Immm and a diffraction peak attributed to reflection from the (103) plane of Li2CuO2 crystal appear in the diffraction angle 2θ range of 40° to 50°. The sum of the integrated intensities of each peak was considered to be the integrated intensity I3 of the third diffraction peak.

[0151] Although a diffraction peak of LiCuO (space group Immm) also appears at 49.94°, this diffraction peak is proportional to the diffraction peak appearing in the range of 40° to 45° and is weaker in intensity. Therefore, only the integrated intensity of the diffraction peak appearing in the range of 40° to 45° was used in the calculation as an index showing the abundance ratio of LiCuO to lithium oxide.

[0152] When Co was used as the transition metal M1, the diffraction peak attributable to reflection from the (104) plane of the LiCoO2 crystal, which is classified into the space group R-3m, was regarded as the third diffraction peak, and the integrated intensity I3 was calculated. When Fe was used as the transition metal M1, the diffraction peaks attributable to reflection from the (204) and (323) planes of Li5FeO4 were regarded as 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.

[0153] Although a diffraction peak of LiCoO2 (space group R-3m) also appears at 49.77°, this diffraction peak is proportional to the diffraction peak appearing in the range of 40° to 45° and is weaker in intensity. Therefore, only the integrated intensity of the diffraction peak appearing in the range of 40° to 45° was used in the calculation as an index showing the abundance ratio of LiCoO2 to lithium oxide.

[0154]

[0155] [Observation by Scanning Electron Microscope (SEM)] Fig. 6A shows an SEM image of the positive electrode active material of Sample 3. Fig. 6B shows an SEM image of the positive electrode active material of Sample 17. As can be seen from these SEM images, the positive electrode active materials of Samples 3 and 17 had a secondary particle structure. The positive electrode active materials of the other samples also had a similar secondary particle structure.

[0156] [Measurement of True Density] The true densities of the positive electrode active materials of Samples 1 to 4, Sample 13, Samples 17 to 20, and Sample 22 were measured by a pycnometer method.

[0157] [Measurement of Specific Surface Area] The specific surface areas of the positive electrode active materials of Samples 3, 4, 11, and 12 were measured by the BET method.

[0158] [Battery Fabrication] Coin batteries conforming to the CR2016 standard were fabricated using the positive electrode active materials of Samples 1 to 28. A positive electrode composite containing the positive electrode active material, acetylene black, and polytetrafluoroethylene in a mass ratio of 7:2:1 was used for the positive electrode. A lithium metal foil with a thickness of 0.3 mm was used for the negative electrode. A three-layer separator consisting of nonwoven fabric / polyolefin resin film / nonwoven fabric was used for the separator. The batteries of Samples 13-1, 13-2, and 13-3 were identical coin batteries using the positive electrode active material of Sample 13, but were subjected to different charge-discharge test conditions.

[0159] The electrolyte solution A used in the battery of Sample 1 was prepared as follows: Ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 1:1. Vinylene carbonate was added to the mixture of ethylene carbonate and diethyl carbonate at a ratio of 1 volume percent to obtain a mixed solvent. LiPF6 was dissolved in the resulting mixed solvent at a concentration of 1 mol / L to prepare electrolyte solution A.

[0160] Electrolyte solution B was prepared in the same manner as electrolyte solution A, except that the volume ratio of vinylene carbonate in the mixed solvent was changed to 5% by volume. Electrolyte solution C was prepared in the same manner as electrolyte solution A, except that the volume ratio of vinylene carbonate in the mixed solvent was changed to 10% by volume. Electrolyte solution D was prepared in the same manner as electrolyte solution A, except that vinylene carbonate was not used. Battery performance varies slightly depending on the amount of vinylene carbonate. However, the effect of vinylene carbonate saturates at about 1% by volume, so the difference in battery performance due to the amount of vinylene carbonate is small.

[0161] The type of electrolyte and the amount of positive electrode mixture used in the batteries of Samples 1 to 28 are shown in Table 3B.

[0162]

[0163] [Charge / Discharge Test] (Sample 1) The upper voltage limit was set to 3.5 V, the upper charge capacity limit was set to 647 mAh / g, and the battery of Sample 1 was charged at a current value of 64.7 mA / 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 value of 64.7 mA / g down to 1.0 V. Table 4 shows the discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V.

[0164] The unit of capacity "mAh / g" represents the capacity per 1 g of Li 2 O. The unit of current value "mA / g" represents the current value per 1 g of Li 2 O.

[0165] (Sample 14) The upper voltage limit was set to 3.5 V, the upper charge capacity limit was set to 647 mAh / g, and the battery of Sample 14 was charged at a current value of 64.7 mA / 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 value of 64.7 mA / g down to 1.5 V. Table 4 shows the discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V.

[0166] FIG. 7 is a graph showing charge / discharge curves of Sample 1 and Sample 14.

[0167]

[0168] The differences between Sample 1 and Sample 14 are the amount of raw materials charged and the milling time. The charge voltage of the battery of Sample 14 reached 3.5 V before the charge capacity reached 647 mAh / g. Therefore, the discharge capacity of the battery of Sample 14 was low. In contrast, the charge voltage of the battery of Sample 1 remained flat until it reached the upper limit of the charge capacity of 647 mAh / g. The battery of Sample 1 also exhibited a large discharge capacity. In other words, the increase in charge voltage of the battery of Sample 1 was suppressed and the discharge capacity was improved. It is believed that the positive electrode active material of Sample 14 contained excessive raw material residues. Note that the amount of positive electrode composite used in the batteries of Sample 1 and Sample 14 also differed, but the effect of the difference in the amount of positive electrode composite on the charge voltage and discharge capacity was very small compared to the difference in the physical properties of the positive electrode active material.

[0169] The batteries of Sample 1 and Sample 14 were repeatedly charged and discharged under the above conditions. For the batteries of Sample 1 and Sample 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: %). As a result, 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 had excellent coulombic efficiency.

[0170] (Sample 2) A charge / discharge test was carried out on the battery of Sample 2 under the same conditions as Sample 1. The results are shown in Table 5.

[0171] (Sample 3) The upper voltage limit was set to 3.4 V, the upper charge capacity limit was set to 600 mAh / g, and the battery of Sample 3 was charged at a current value of 50.0 mA / 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 value of 50.0 mA / g to 1.8 V. Then, discharge was performed at a constant voltage of 1.8 V until the current value 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.

[0172] (Sample 4) The battery of Sample 4 was charged at a current of 50.0 mA / g with an upper voltage limit of 3.4 V and an upper charge capacity limit of 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 to 1.5 V. Subsequently, constant-voltage discharge at 1.5 V was performed for 66 hours. Table 5 shows the discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V.

[0173]

[0174] Sample 2 is a sample in which the rotation speed is higher and the treatment time is shorter than those of Sample 1. By increasing the rotation speed, the increase in charge voltage was suppressed, and the discharge capacity was improved, similar to Sample 1.

[0175] Samples 3 and 4 are samples in which the type of ball mill used was different from that of Sample 1. Even when the type of ball mill was changed, similar to Sample 1, the increase in charge voltage was suppressed and the discharge capacity was improved.

[0176] The battery of Sample 2 was repeatedly charged and discharged under the above conditions. 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: %) for the battery of Sample 2. As a result, the coulombic efficiency of the battery of Sample 2 was 94.8%.

[0177] (Samples 5 to 7, Sample 15, and Sample 16) The upper voltage limit was 3.4 V, the lower voltage limit was 1.5 V, the upper limit of the charge / discharge capacity for the first cycle was 300 mAh / g, the upper limit of the charge / discharge capacity for the second cycle was 400 mAh / g, and the upper limit of the charge / discharge capacity for the third cycle was 500 mAh / g. The batteries for Samples 5 to 7, Sample 15, and Sample 16 were charged and discharged at a current value of 50.0 mA / g. The rest time when transitioning from the charge process to the discharge process was 20 minutes. If the voltage reached 1.5 V before reaching the predetermined capacity during the discharge process, a constant voltage discharge at 1.5 V was performed for 1 hour. The charge capacity at the third cycle and the voltage at 500 mAh / g during the third cycle charge are shown in Table 6. The discharge capacity at the third cycle discharge at voltages of 2.5 V, 2.2 V, 2.0 V, 1.8 V, and 1.5 V are shown in Table 6.

[0178] (Sample 8) The upper voltage limit was set to 3.4 V, the lower voltage limit to 1.8 V, the upper limit of the charge / discharge capacity for the first cycle to 300 mAh / g, the upper limit of the charge / discharge capacity for the second cycle to 400 mAh / g, and the upper limit of the charge / discharge capacity for the third cycle to 500 mAh / g. The battery of Sample 8 was charged and discharged at a current value of 50.0 mA / g. The rest time when transitioning 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 predetermined capacity. The charge capacity at the third cycle and the voltage at 500 mAh / g during the third cycle charge are shown in Table 6. The discharge capacities at voltages of 2.5 V, 2.2 V, 2.0 V, and 1.8 V during the third cycle discharge are shown in Table 6.

[0179] (Sample 9) The upper voltage limit was 3.4 V, the lower voltage limit was 1.8 V, the upper charge / discharge capacity limit for the first cycle was 300 mAh / g, the upper charge / discharge capacity limit for the second cycle was 400 mAh / g, and the upper charge / discharge capacity limit for the third cycle was 500 mAh / g. The battery of Sample 9 was charged and discharged at a current value of 50.0 mA / g. The rest time when transitioning from the charge process to the discharge process was 20 minutes. If the voltage reached 1.8 V before reaching the predetermined capacity during the discharge process, a constant voltage discharge was performed at 1.8 V and the discharge was continued until a current value of 5 mA / g was reached. The charge capacity at the third cycle and the voltage at 500 mAh / g during the third cycle charge are shown in Table 6. The discharge capacities at voltages of 2.5 V, 2.2 V, 2.0 V, and 1.8 V during the third cycle discharge are shown in Table 6.

[0180] (Sample 10) The upper voltage limit was set to 3.4 V, the lower voltage limit to 1.8 V, the upper limit of the charge / discharge capacity for the first cycle to 300 mAh / g, the upper limit of the charge / discharge capacity for the second cycle to 400 mAh / g, and the upper limit of the charge / discharge capacity for the third cycle 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 transitioning from the charge process to the discharge process was 20 minutes. The voltage did not reach 1.8 V before reaching the predetermined capacity during the discharge process. The charge capacity at the third cycle and the voltage at 500 mAh / g during the third cycle charge are shown in Table 6. The discharge capacities at voltages of 2.5 V, 2.2 V, 2.0 V, and 1.8 V during the third cycle discharge are shown in Table 6.

[0181] (Samples 11 and 12) The upper voltage limit was set to 3.4 V, the lower voltage limit to 1.8 V, the upper limit of the charge / discharge capacity for the first cycle to 300 mAh / g, the upper limit of the charge / discharge capacity for the second cycle to 500 mAh / g, the upper limit of the charge / discharge capacity for the third cycle to 600 mAh / g, and the upper limit of the charge / discharge capacity for the fourth cycle to 700 mAh / g. The batteries of Samples 11 and 12 were charged and discharged at a current value of 50.0 mA / g. The rest time when transitioning 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 predetermined capacity. The charge capacity for the second cycle and the voltage at 500 mAh / g during the second charge cycle are shown in Table 6. The discharge capacity during the second discharge cycle at voltages of 2.5 V, 2.2 V, 2.0 V, and 1.8 V are shown in Table 6.

[0182]

[0183] The positive electrode active materials of Samples 5, 6, 15, and 16 were prepared under the same conditions except for the treatment temperature. The battery of Sample 15 had a slightly high charge voltage and a low discharge capacity. The battery of Sample 16 also had low charge and discharge capacities. In contrast, the batteries of Samples 5 and 6 exhibited low charge voltages and large discharge capacities.

[0184] The battery of Sample 7 includes a positive electrode active material produced using Co3O4 as a raw material for the transition metal M1. The battery of Sample 8 includes a positive electrode active material produced using LiCoO2 as a raw material for the transition metal M1. Whether an oxide containing only Co or a composite oxide was used as a raw material for the transition metal M1, the effects of suppressing an increase in charging voltage and improving discharge capacity were obtained.

[0185] Samples 9 to 12 are samples in which the type of ball mill is different from that of Samples 5 to 8. Even when the type of ball mill was changed, the increase in charge voltage was suppressed and the discharge capacity was improved, similar to Samples 5 to 8.

[0186] The coulombic efficiency (unit: %) was calculated as the ratio of the discharge capacity at the fourth cycle to the charge capacity at the fourth cycle for the batteries of Samples 11 and 12. As a result, the coulombic efficiency of the batteries of Samples 11 and 12 was both 100.0%.

[0187] (Sample 13-1) The upper voltage limit was set to 3.4 V, the upper charge capacity limit was set to 600 mAh / g, and the battery of Sample 13-1 was charged at a current value of 50.0 mA / 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 value of 50.0 mA / g to 1.5 V. Thereafter, constant voltage discharge was performed at 1.5 V until the discharge reached 5 mA / g or until 24 hours had elapsed. The discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V are shown in Table 7A.

[0188] (Sample 13-2) The upper voltage limit was set to 3.4 V, the upper charge capacity limit was set to 647 mAh / g, and the battery of Sample 13-1 was charged at a current value of 64.7 mA / 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 value of 50.0 mA / g to 1.5 V. Thereafter, constant voltage discharge was performed at 1.5 V until the discharge reached 5 mA / g or until 24 hours had elapsed. The discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V are shown in Table 7A.

[0189]

[0190] The positive electrode active material used in the battery of Sample 13-1 and the battery of 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, as in Sample 1.

[0191] (Sample 13-3) The upper limit voltage was 3.4 V, the lower limit voltage was 1.8 V, the upper limit of the charge / discharge capacity at the first cycle was 300 mAh / g, the upper limit of the charge / discharge capacity at the second cycle was 400 mAh / g, the upper limit of the charge / discharge capacity at the third cycle was 500 mAh / g, the upper limit of the charge / discharge capacity at the fourth cycle was 600 mAh / g, and the upper limit of the charge / discharge capacity at the fifth cycle was 700 mAh / g. The battery of Sample 13-3 was charged and discharged at a current value of 50.0 mA / g. The rest time when transitioning from the charge process to the discharge process was 20 minutes. The charge capacity at the third cycle, the voltage at 500 mAh / g during the third cycle charge, and the discharge capacity at voltages of 2.5 V, 2.2 V, 2.0 V, and 1.8 V during the third cycle discharge are shown in Table 7B. The charge capacity at the fifth cycle, the voltage at 700 mAh / g during the fifth cycle of charge, and the discharge capacity at voltages of 2.5 V, 2.2 V, 2.0 V, and 1.8 V during the fifth cycle of discharge are shown in Table 7C.

[0192]

[0193]

[0194] As shown in Tables 7B and 7C, the battery of Sample 13-3 exhibited a low charge voltage and a large discharge capacity in both the third and fifth cycles.

[0195] (Sample 21) The upper voltage limit was set to 3.4 V, the upper charge capacity limit was set to 533 mAh / g, and the battery of Sample 20 was charged at a current value of 53.3 mA / g. After a 20-minute rest, constant-current discharge was performed at a current value of 53.3 mA / g down to 1.0 V. This cycle was repeated three times. The charge capacity at the third cycle and the voltage at 200 mAh / g during the third cycle charge are shown in Table 8A. The discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V during the third cycle discharge are shown in Table 8B.

[0196] (Samples 17 to 20 and Sample 22) The upper voltage limit was 3.4 V, the lower voltage limit was 1.5 V, the upper limit of the charge / discharge capacity for the first cycle was 300 mAh / g, the upper limit of the charge / discharge capacity for the second cycle was 400 mAh / g, and the upper limit of the charge / discharge capacity for the third cycle was 500 mAh / g. The batteries of Samples 17 to 20 and Sample 22 were charged and discharged at a current value of 50.0 mA / g. The rest time when transitioning from the charge process to the discharge process was 20 minutes. If the voltage reached 1.5 V before reaching the predetermined capacity during the discharge process, a constant voltage discharge at 1.5 V was performed for 1 hour. The charge capacity at the third cycle and the voltage at each capacity at the third cycle are shown in Table 8A. The discharge capacity at the third cycle discharge at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V is shown in Table 8B.

[0197]

[0198]

[0199] The batteries of Samples 21 and 22 reached an upper voltage limit of 3.4 V with charge capacities of 240.8 mAh / g and 261.1 mAh / g, respectively. The discharge capacities of the batteries of Samples 21 and 22 were also low. In contrast, the batteries of Samples 17 to 20 showed low charge voltages and large discharge capacities.

[0200] The reasons for the high charge voltage and low discharge capacity of the batteries of Samples 21 and 22 include the short treatment time and the small amount of CuO.

[0201] As shown by the results of Samples 17 to 20, when the transition metal M1 was Cu, the effect of suppressing the rise in charge voltage and the effect of improving discharge capacity were obtained, similar to the case of Co.

[0202] (Samples 23 to 28) The upper voltage limit was set to 3.4 V, the upper charge capacity limit was set to 300 mAh / g, and the batteries of Samples 23 to 28 were charged at a current value of 50.0 mA / 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, constant-current discharge was performed at a current value of 50.0 mA / g to 1.5 V (1.8 V for Sample 26). Subsequently, constant-voltage discharge at 1.5 V (1.8 V for Sample 26) was performed for 1 hour. Table 9 shows the discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V.

[0203]

[0204] The charging voltages of the batteries of Samples 23 to 26 were lower than the charging voltages 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.

[0205] The reasons for the high charging voltage and low discharge capacity of the batteries of Samples 27 and 28 include the low rotation speed of the device, the short treatment time, and the small amount of Fe.

[0206] As shown by the results of Samples 23 to 26, when the transition metal M1 was Fe, the effect of suppressing the rise in charge voltage and the effect of improving discharge capacity were obtained, similar to the cases of Co and Cu. Furthermore, as the source of Fe as the transition metal M1, any of Fe2O3 (Samples 23 and 24), Fe3O4 (Sample 25), and FeO (Sample 26) could be used.

[0207] 8 is a graph plotting the calculation results of the integrated intensity ratios I / I and I / I of the positive electrode active materials of Samples 1 to 28. The horizontal axis represents the integrated intensity ratio I / I. The vertical axis represents the integrated intensity ratio I / I. The numbers "1, 2, 3...28" represent Samples 1 to 28, respectively. The integrated intensity ratio I / I for the LiO single crystal is approximately 0.33.

[0208] 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 ratios I2 / I1 of the batteries of Samples 1 to 13, 17 to 20, and 23 to 26 were 0.48 or more. It is believed that in these samples, the solid solution of the transition metal M1 in lithium oxide progressed sufficiently, and the effect of improving electronic conductivity and ionic conductivity was sufficiently obtained.

[0209] A small integrated intensity ratio I3 / I1 indicates a small amount of residues and / or by-products. A large integrated intensity ratio I3 / I1 indicates a large amount of residues and / or by-products. The integrated intensity ratios I3 / I1 of the batteries of Samples 1 to 13, 17 to 20, and 23 to 26 were in the range of 0.10 to 1.30. In other words, the positive electrode active materials used in these batteries contained a moderate amount of residues and / or by-products.

[0210] The technology of the present disclosure 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, wherein the positive electrode has an inverse fluorite crystal structure and contains lithium oxide having a transition metal dissolved therein as a positive electrode active material, and the electrolyte contains an additive, wherein the additive contains at least one selected from the group consisting of a phosphate ester represented by the following formula (1), a sulfonate ester represented by the following formula (2), a cyclic carbonate ester represented by the following formula (3), a benzene derivative, and a radical scavenger, wherein in the formula (1), R 1 , R 2 and R 3 are each independently an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an alkynyl group, a phenyl group, a phenyl group in which at least one hydrogen atom may be substituted by an alkyl group having 1 to 5 carbon atoms, or a silyl group, in which at least one hydrogen atom contained in these groups may be substituted by a halogen atom; R 1 and R 2 may be bonded to form a cyclic structure, and in the formula (2), R 4 and R 5 are each independently an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an alkynyl group, a phenyl group, a phenyl group in which at least one hydrogen atom may be substituted by an alkyl group having 1 to 5 carbon atoms, or a silyl group, in which at least one hydrogen atom contained in these groups may be substituted by a halogen atom; R 4 and R 5 may be bonded to form a cyclic structure, and in the formula (3), R 6 and R 7 are each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or a vinyl group, and R 6 and R 7 at least one of the above-mentioned compounds contains a vinyl group, and the benzene derivative is a compound having a structure in which at least one substituent is bonded to a benzene ring, and the substituent is an alkyl group having 1 to 10 carbon atoms, an aryl group, or a carbonate group.

2. The battery according to claim 1, wherein the volume ratio of the additive in the electrolyte is 0.01% by volume or more and 20% by volume or less.

3. The battery according to claim 1, wherein the concentration of the additive in the electrolyte is 0.01 mol / liter or more and 2.0 mol / liter or less.

4. In the formula (1), R 1 , R 2 and R 3 At least one selected from the following is a silyl group represented by the following formula (4), 8 , R 9 and R 10 The battery of claim 1 , wherein each of the groups is independently an organic group or a hydrogen atom.

5. In the formula (1), R 1 , R 2 and R 3 The battery of claim 1 , wherein the first and second electrodes have the same structure.

6. The battery of claim 1, wherein the phosphate ester comprises at least one selected from the group consisting of trimethyl phosphate, triethyl phosphate, tributyl phosphate, tripentyl phosphate, tris(2-ethylhexyl) phosphate, triphenyl phosphate, tricresyl phosphate, 2-ethylhexyldiphenyl phosphate, tris(2-butoxyethyl) phosphate, tris(1,1,1,3,3,3-hexafluoro-2-propyl) phosphate, trifluoroethylethylene phosphate, 2-methoxy-1,3,2-dioxaphospholane 2-oxide, tripropargyl phosphate, tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, triallyl phosphate, tris(tert-butyldimethylsilyl), tris(1H,1H,5H-octafluoropentyl) phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(2-chloroethyl) phosphate, and tris(1,3-dichloro-2-propyl) phosphate.

7. The battery according to claim 1, wherein the sulfonate ester comprises a cyclic sulfonate ester.

8. The battery according to claim 1, wherein the sulfonic acid ester comprises at least one selected from the group consisting of 1,3-propane sultone, 1-propene 1,3-sultone, 1,4-butane sultone, and 1,8-naphthosultone.

9. The battery according to claim 1, wherein the cyclic carbonate includes at least one selected from the group consisting of vinyl ethylene carbonate and vinylene carbonate.

10. The battery according to claim 1, wherein the benzene derivative includes at least one selected from the group consisting of o-xylene, m-xylene, p-xylene, diphenylpropane, phenyl-tert-butyl carbonate, and cyclohexylbenzene.

11. The battery of claim 1, wherein the radical scavenger comprises 2,2,6,6-tetramethylpiperidine 1-oxyl.

12. The battery according to claim 1, wherein the concentration of the radical scavenger in the electrolyte is 0.01 mol / liter or more and 0.4 mol / liter or less.

13. The positive electrode active material has a particulate shape, and the particles of the positive electrode active material have a size of 0.01 μm or less. 2 500 μm or more 2 10. The battery of claim 1 having a cross-sectional area of:

14. The battery of claim 1, wherein the negative electrode comprises lithium metal.

15. The battery according to claim 1, wherein 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 a second diffraction peak assigned to a (220) plane of the lithium oxide present in a diffraction angle 2θ range of 52° to 62° to the integrated intensity of a first diffraction peak assigned to a (111) plane of the lithium oxide present in the diffraction angle 2θ range of 30° to 40° is 0.48 or more, and the ratio of the integrated intensity of a third diffraction peak assigned to a crystal plane of the transition metal oxide present in the diffraction angle 2θ range of 40° to 50° to the integrated intensity of the first diffraction peak is 0.10 or more and 1.30 or less.

16. The battery according to claim 15, 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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