Metal complex particle, electrode, battery, and method for manufacturing metal complex particle

Abstract

To provide metal complex particles or the like which can improve charge / discharge cycle characteristics when the charge / discharge rate of a battery is high.SOLUTION: The metal complex particle contains potassium ion, hexacyanoferrate ion, nickel ion and manganese ion, and the ratio of the nickel element to the total molar amount of the nickel element and the manganese element is 0.01 mol% to 10 mol%, and an application thereof is provided.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to metal complex particles, electrodes, batteries, and methods for producing metal complex particles. [Background technology]

[0002] Currently, non-aqueous electrolyte secondary batteries are widely used as high energy density secondary batteries, which use a non-aqueous electrolyte and perform charging and discharging by moving, for example, lithium ions between a positive electrode and a negative electrode.

[0003] Potassium-ion batteries are expected to be the next-generation battery that will replace lithium-ion batteries.

[0004] For example, Patent Document 1 describes a compound having the composition formula K 1-x (Mn y Cu 1-y ) 1+0.5x A Prussian blue analogue, represented as [Fe(CN)6]·nH2O, has been described. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-246303 Summary of the Invention [Problem to be solved by the invention]

[0006] When the charge / discharge rate of a battery is high, improvement in charge / discharge cycle characteristics is required. In view of the above circumstances, an object of one embodiment of the present disclosure is to provide metal complex particles that can improve the charge-discharge cycle characteristics when the charge-discharge rate of a battery is high. Another problem to be solved by another embodiment of the present disclosure is to provide an electrode and a battery including the metal complex particles. Another problem to be solved by another embodiment of the present disclosure is to provide a method for producing the metal complex particles. [Means for solving the problem]

[0007] The means for solving the above problems include the following means. <1> containing potassium ions, ferricyanide ions, nickel ions, and manganese ions; Metal complex particles, in which the ratio of elemental nickel to the total molar amount of elemental nickel and elemental manganese is 0.01 mol % to 10 mol %. <2> Nickel element is unevenly distributed on the surface. <1> The metal complex particles according to claim 1. <3> <1> or <2> An electrode comprising the metal complex particles according to claim 1. <4> <3> A battery comprising the electrode according to claim 1. <5> The method includes a step of mixing manganese hexacyanoferrate, potassium hexacyanoferrate, and nickel chloride to produce metal complex particles containing potassium ions, hexacyanoferrate ions, nickel ions, and manganese ions, A method for producing metal complex particles, wherein the molar ratio of the amount of nickel chloride used to the amount of manganese hexacyanoferrate used is 0.01 to 0.5. [Effects of the Invention]

[0008] According to one embodiment of the present disclosure, metal complex particles are provided that can improve the charge-discharge cycle characteristics when the charge-discharge rate of a battery is high (82.5 mA / g or higher). According to another embodiment of the present disclosure, there are provided an electrode and a battery including the metal complex particles. According to another embodiment of the present disclosure, there is provided a method for producing the above metal complex particles. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 1 is a schematic diagram showing an example of a cell configuration of a battery according to the present disclosure. [Figure 2] FIG. 2 is a graph showing the relationship between the discharge capacity and the number of cycles in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples. In the present specification, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0011] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

[0012] [Metal complex particles] The metal complex particles according to the present disclosure contain potassium ions, ferricyanide ions, nickel ions, and manganese ions, with the proportion of elemental nickel relative to the total molar amount of elemental nickel and manganese being 0.01 mol % to 10 mol %.

[0013] Potassium manganese(II) hexacyanoferrate(II) is known to be inexpensively synthesized. Potassium manganese(II) hexacyanoferrate(II) exhibits high energy density when used as the positive electrode of potassium-ion batteries. However, it has been found that when the battery is charged and discharged at a high rate, repeated charging and discharging does not maintain the discharge capacity.

[0014] In contrast, the metal complex particles according to the present disclosure contain nickel ions, and the ratio of nickel element to the total molar amount of nickel element and manganese element is 0.01 mol % to 10 mol %, so that even if the charge / discharge rate of the battery is fast, the discharge capacity can be maintained even after repeated charge / discharge.

[0015] The metal complex particles according to the present disclosure contain potassium ions, ferricyanide ions, nickel ions, and manganese ions. The electrolyte may contain ions other than potassium ions, ferricyanide ions, nickel ions, and manganese ions.

[0016] Examples of other ions include sodium ions, cobalt ions, iron ions, and copper ions.

[0017] The composition of the metal complex particles can be confirmed by elemental analysis.

[0018] The proportion of nickel element in the metal complex particles according to the present disclosure is preferably 0.004 atomic % to 0.4 atomic %, and more preferably 0.008 atomic % to 0.2 atomic %, relative to all atoms in the metal complex particles.

[0019] In the metal complex particles according to the present disclosure, the proportion of elemental nickel relative to the total molar amount of elemental nickel and elemental manganese is 0.01 mol % to 10 mol %, preferably 0.05 mol % to 5 mol %, and more preferably 0.1 mol % to 3 mol %.

[0020] By setting the proportion of nickel element to 0.01 mol % to 10 mol %, the discharge capacity can be maintained even after repeated charging and discharging when the charge and discharge rate of the battery is high (82.5 mA / g or higher). Furthermore, by keeping the proportion of nickel element at 10 mol % or less, the discharge capacity can be increased.

[0021] In the metal complex particles according to the present disclosure, the nickel element is preferably unevenly distributed on the surface. The uneven distribution of nickel element on the surface can be confirmed using FIB-STEM / EDS. When the metal complex particles according to the present disclosure are used in a battery, the nickel element is unevenly distributed on the surface, and therefore, even if the charge / discharge rate of the battery is high, a high discharge capacity can be maintained even after repeated charge / discharge.

[0022] On the surface of the metal complex particle, the ratio of elemental nickel to the total molar amount of elemental nickel and elemental manganese is preferably 1 mol% to 20 mol%, more preferably 2 mol% to 15 mol%, and even more preferably 5 mol% to 10 mol%.

[0023] The ratio of elemental nickel to the total molar amount of elemental nickel and elemental manganese on the surface of a metal complex particle is measured by the following method: EDS spectra of Ni and Mn on the particle surface are measured, and the intensity ratio is calculated.

[0024] The proportion of potassium element in the metal complex particles according to the present disclosure is preferably 7.0 atomic % to 11.8 atomic % and more preferably 10.3 atomic % to 11.8 atomic % based on the total atoms in the metal complex particles.

[0025] The particle size of the metal complex particles is not particularly limited, but from the viewpoint of battery performance, it is preferably 1 μm to 5 μm. Particle size is measured using a scanning electron microscope (SEM).

[0026] [Metal Complex Particle Manufacturing Method] The method for producing metal complex particles according to the present disclosure includes a step of mixing manganese hexacyanoferrate, potassium hexacyanoferrate, and nickel chloride to produce metal complex particles containing potassium ions, hexacyanoferrate ions, nickel ions, and manganese ions. The molar ratio of the amount of nickel chloride to the amount of manganese hexacyanoferrate used is 0.01 to 0.5.

[0027] The salt constituting manganese hexacyanoferrate may be a sodium salt, a potassium salt, or both a sodium salt and a potassium salt.

[0028] Manganese potassium hexacyanoferrate can be obtained, for example, by reacting sodium hexacyanoferrate (II) with manganese chloride, followed by the addition of potassium chloride.

[0029] The method for mixing manganese hexacyanoferrate, potassium hexacyanoferrate, and nickel chloride is not particularly limited, and may be, for example, a method in which nickel chloride is added to an aqueous solution containing manganese hexacyanoferrate, potassium hexacyanoferrate, and water.

[0030] By adjusting the molar ratio of the amount of nickel chloride used to the amount of manganese hexacyanoferrate used to 0.01 to 0.5, it is possible to appropriately incorporate nickel ions into the metal complex particles, and thus when the metal complex particles are used in a battery, the battery exhibits excellent charge-discharge cycle characteristics even when the charge-discharge rate is high.

[0031] When the charge / discharge rate of the battery is high, the molar ratio of the amount of nickel chloride used to the amount of manganese hexacyanoferrate used is preferably 0.05 to 0.2, from the viewpoint of obtaining a high discharge capacity even after repeated charge / discharge.

[0032] [electrode] The electrode according to the present disclosure preferably contains the above-described metal complex particles. The metal complex particles are preferably contained in the positive electrode as a positive electrode active material.

[0033] By using an electrode containing the metal complex particles in a battery, the charge-discharge cycle characteristics can be improved when the charge-discharge rate of the battery is high.

[0034] (positive electrode) From the viewpoint of durability and formability, the positive electrode preferably contains a positive electrode active material, a conductive additive, and a binder.

[0035] The shape and size of the positive electrode are not particularly limited, and can be made to a desired shape and size according to the shape and size of the battery to be used.

[0036] From the viewpoint of the output power and charge / discharge capacity of the battery, the positive electrode preferably contains 10 mass % or more of the positive electrode active material relative to the total mass of the positive electrode, more preferably 20 mass % or more, even more preferably 50 mass % or more, and particularly preferably 70 mass % or more.

[0037] -Conductive additive- The positive electrode used in the present disclosure preferably contains a conductive additive in order to improve the rate characteristics (output) of the positive electrode. Preferred examples of the conductive aid include carbon such as carbon blacks, graphites, carbon nanotubes (CNTs), and vapor grown carbon fibers (VGCFs). Examples of carbon blacks include acetylene black, oil furnace black, ketjen black, etc. Among them, from the viewpoint of conductivity, at least one conductive aid selected from the group consisting of acetylene black and ketjen black is preferred, and acetylene black or ketjen black is more preferred.

[0038] The conductive additives may be used alone or in combination of two or more.

[0039] The mixing ratio of the positive electrode active material and the conductive additive is not particularly limited, but the content of the conductive additive in the positive electrode is preferably 1% by mass to 80% by mass, more preferably 2% by mass to 60% by mass, even more preferably 5% by mass to 50% by mass, and particularly preferably 5% by mass to 25% by mass, relative to the total mass of the positive electrode active material contained in the positive electrode. Within the above range, a positive electrode with higher output and excellent durability can be obtained.

[0040] The conductive additive and the positive electrode active material can be mixed together in an inert gas atmosphere to coat the positive electrode active material with the conductive additive. Examples of the inert gas include nitrogen gas and argon gas, and argon gas is preferred. Furthermore, when mixing the conductive additive and the positive electrode active material, a pulverization / dispersion treatment may be performed using a dry ball mill or a bead mill to which a small amount of a dispersing medium such as water has been added. The pulverization / dispersion treatment can improve the adhesion and dispersibility between the conductive additive and the positive electrode active material, thereby increasing the electrode density.

[0041] -Binder- From the viewpoint of formability, the positive electrode preferably contains a binder. The binder is not particularly limited, and known binders can be used, including polymer compounds, such as fluororesins, polyolefin resins, rubber polymers, polyamide resins, polyimide resins (such as polyamideimides), glutamic acid, and cellulose ethers.

[0042] Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-TFE fluororubber), polyethylene, aromatic polyamide, cellulose, styrene-butadiene rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer, hydrogenated products thereof, styrene-ethylene rubber, Examples of suitable polymers include styrene-butadiene-styrene copolymers, styrene-isoprene-styrene block copolymers, hydrogenated products thereof, syndiotactic 1,2-polybutadiene, ethylene-vinyl acetate copolymers, propylene-α-olefin (having 2 to 12 carbon atoms) copolymers, glutamic acid, starch, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethylhydroxyethyl cellulose, nitrocellulose, polyacrylic acid, sodium polyacrylate, and polyacrylonitrile.

[0043] The binder may be used alone or in combination of two or more kinds.

[0044] The mixing ratio of the positive electrode active material and the binder is not particularly limited, but the content of the binder in the positive electrode is preferably 0.5% by mass to 30% by mass, more preferably 1% by mass to 20% by mass, and even more preferably 2% by mass to 15% by mass, relative to the total mass of the positive electrode active material contained in the positive electrode. When the content is within the above range, excellent moldability and durability are achieved.

[0045] The method for manufacturing a positive electrode containing a positive electrode active material, a conductive additive, and a binder is not particularly limited. For example, the positive electrode active material, the conductive additive, and the binder may be mixed and pressure-molded, or a method may be used in which a slurry described below is prepared to form a positive electrode.

[0046] -Current collector- The positive electrode preferably includes a current collector. Examples of the current collector include foil, mesh, expanded grid (expanded metal), punched metal, etc., made of a conductive material such as nickel, aluminum, stainless steel (SUS), etc. The mesh opening, wire diameter, mesh number, etc. are not particularly limited, and conventionally known current collectors can be used. The shape of the current collector is not particularly limited and may be selected according to the desired shape of the positive electrode, for example, a foil shape, a plate shape, or the like. Among these, the current collector is preferably an aluminum current collector.

[0047] The method for forming a positive electrode on a current collector is not particularly limited, but an example is a method in which a positive electrode active material, a conductive additive, a binder, and an organic solvent or water are mixed to prepare a positive electrode active material slurry, and the slurry is then applied to the current collector. Examples of organic solvents include amines such as N,N-dimethylaminopropylamine and diethyltriamine, ethers such as ethylene oxide and tetrahydrofuran, ketones such as methyl ethyl ketone, esters such as methyl acetate, and aprotic polar solvents such as dimethylacetamide and N-methyl-2-pyrrolidone. The prepared slurry is applied to a current collector, dried, and then fixed by pressing, etc., to produce a positive electrode. Examples of methods for applying the slurry to a current collector include slit die coating, screen coating, curtain coating, knife coating, gravure coating, and electrostatic spraying.

[0048] [battery] The battery according to the present disclosure preferably includes an electrode containing the metal complex particles. The battery according to the present disclosure preferably includes, for example, a positive electrode, a negative electrode, an electrolyte, and a separator. The battery according to the present disclosure may also include various known materials used in batteries, such as a battery case, spacers, gaskets, and springs. As described above, the metal complex particles are preferably contained in the positive electrode as a positive electrode active material.

[0049] The method for manufacturing the battery is not particularly limited, and known methods can be applied. The shape of the battery is not particularly limited, and known battery shapes such as cylindrical, square, and coin shapes can be used.

[0050] Batteries according to the present disclosure are particularly useful as potassium ion batteries.

[0051] (Negative electrode) The negative electrode preferably contains a negative electrode active material. The negative electrode active material is not particularly limited, and examples thereof include metallic lithium; metal materials containing silicon, tin, etc.; and carbon materials such as graphite, activated carbon, cokes, hard carbon, carbon black, pyrolytic carbons, carbon fiber, and fired organic polymer compounds.

[0052] The negative electrode may also contain known additives used in the manufacture of battery negative electrodes. Examples of the additives include a conductive additive, a binder, and a current collector. Examples of the conductive additive, binder, and current collector include the same conductive additive, binder, and current collector as those that may be contained in the positive electrode.

[0053] The shape and size of the negative electrode are not particularly limited, and can be made to a desired shape and size in accordance with the shape and size of the battery to be used.

[0054] (electrolyte) The electrolytic solution preferably contains an electrolyte and a solvent.

[0055] -Electrolytes- When the battery is a potassium ion battery, the electrolyte is not particularly limited as long as it contains a potassium salt compound as the main electrolyte.

[0056] In the case of an aqueous electrolyte, examples of the potassium salt compound include KClO, KPF, KNO, KOH, KCl, KSO, and KS. The electrolyte may contain only one type of potassium salt compound, or two or more types of potassium salt compounds.

[0057] In the case of a non-aqueous electrolyte, it is preferable to dissolve the electrolyte (e.g., KPF6, KBF4, CF3SO3K, KAsF6, KB(C6H5)4, CH3SO3K, KN(SO2CF3)2, KN(SO2C2F5)2, KC(SO2CF3)3, KN(SO3CF3)2, etc.) in a solvent described below. Of these, the potassium salt compound is preferably KPF6. The concentration of the electrolyte in the electrolytic solution is not particularly limited, but is preferably 0.1 mol / L to 2 mol / L, and more preferably 0.5 mol / L to 1.5 mol / L.

[0058] -solvent- Examples of solvents include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, isopropyl methyl carbonate, vinylene carbonate, fluoroethylene carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane. Carbonate compounds (carbonate compounds); Ether compounds such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran; Ester compounds such as methyl formate, methyl acetate, and γ-butyrolactone; Nitrile compounds such as acetonitrile and butyronitrile; Amide compounds such as N,N-dimethylformamide and N,N-dimethylacetamide; Carbamate compounds such as 3-methyl-2-oxazolidone; Examples include sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propane sultone; and compounds in which hydrogen atoms in the above compounds are substituted with fluorine atoms.

[0059] Among these, from the viewpoints of the life span and coulombic efficiency of the battery or capacitor, the electrolyte preferably contains at least one solvent selected from the group consisting of carbonate ester compounds and ether compounds, and more preferably contains at least one solvent selected from the group consisting of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethylene carbonate, and propylene carbonate.

[0060] The electrolyte solution may contain only one type of solvent, or two or more types of solvents.

[0061] The electrolytic solution may contain other additives in addition to the electrolyte and the solvent. Other additives include, for example, fluoroethylene carbonate (FEC), vinylene carbonate (VC), and ethylene sulfite (ES). The electrolyte may also contain an overcharge inhibitor, a dehydrating agent, a deoxidizing agent, and the like.

[0062] (separator) The separator serves to physically separate the positive and negative electrodes to prevent internal short circuits. The separator is made of a porous material, the pores of which are impregnated with an electrolyte, and has ion permeability (particularly, permeability to at least potassium ions) to ensure the battery reaction.

[0063] As the separator, for example, a resin porous membrane or a nonwoven fabric can be used. The separator may be formed of only a porous membrane layer or a nonwoven fabric layer, or may be formed as a laminate of multiple layers with different compositions and forms. Examples of the laminate include a laminate having multiple resin porous layers with different compositions, and a laminate having a porous membrane layer and a nonwoven fabric layer.

[0064] The material of the separator can be selected taking into consideration the operating temperature of the battery, the composition of the electrolyte, and the like. Examples of resins contained in the fibers forming the porous membrane and nonwoven fabric include polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyphenylene sulfide resins such as polyphenylene sulfide and polyphenylene sulfide ketone; polyamide resins such as aromatic polyamide resins (e.g., aramid resins); and polyimide resins. These resins may be used alone or in combination of two or more. The fibers forming the nonwoven fabric may also be inorganic fibers such as glass fibers.

[0065] The separator is preferably a separator containing at least one material selected from the group consisting of glass, polyolefin resin, polyamide resin, and polyphenylene sulfide resin, and among these, a glass filter is more preferred as the separator. The shape and size of the separator are not particularly limited and may be selected appropriately according to the desired shape of the battery.

[0066] An example of a battery according to the present disclosure is the battery shown in FIG. FIG. 1 is a schematic diagram illustrating an example of a battery 10 according to the present disclosure. The battery 10 shown in FIG. 1 is a coin-type battery, and is formed by stacking, in order from the negative electrode side, a negative electrode side battery case 12, a gasket 14, a negative electrode 16, a separator 18, a positive electrode 20, a spacer 22, a leaf spring 24, and a positive electrode side battery case 26, and then fitting the battery case 12 and the battery case 26 together. The separator 18 is impregnated with an electrolyte (not shown). [Example]

[0067] The present invention will be explained in more detail below with reference to examples, but the present disclosure is not limited to the following examples.

[0068] Metal complex particles A and metal complex particles B were synthesized.

[0069] <Synthesis of Metal Complex Particle A (KMnHCF)> Solution A was obtained by dissolving sodium hexacyanoferrate (II) decahydrate (4 mmol) in 100 mL of a 0.04 mol / L aqueous solution of trisodium citrate. Solution B was obtained by dissolving manganese(II) chloride (4 mmol) in 100 mL of a 0.04 mol / L aqueous solution of trisodium citrate. Solution B was added dropwise to Solution A at a rate of 0.5 mL / min under a nitrogen atmosphere. The mixture was then stirred for 15 hours. 100 mL of a 3 mol / L aqueous potassium chloride solution was then added, and the mixture was stirred for 6 hours. The resulting precipitate was collected by suction filtration. After washing with ion-exchanged water and ethanol, it was dried at 150°C for 15 hours to obtain metal complex particles A. Using an inductively coupled plasma atomic emission spectrometry (ICP-AES) device, the composition of metal complex particle A was determined to be Na 0.05 K 1.54 Mn[Fe(CN)6] 0.87 It was confirmed that this is the case.

[0070] <Synthesis of Metal Complex Particles B (KMnHCF-KNiHCF)> The metal complex particles A (4 mmoL) and potassium hexacyanoferrate (II) decahydrate (0.4 mmoL) were added to 100 mL of ion-exchanged water and stirred to obtain a solution C. Nickel (II) chloride hexahydrate (0.4 mmol) was dissolved in 100 mL of ion-exchanged water to obtain a solution D. Solution D was added dropwise to Solution C at a rate of 0.5 mL / min under a nitrogen atmosphere. The mixture was then stirred for 15 hours. The resulting precipitate was collected by suction filtration. After washing with ion-exchanged water and ethanol, it was dried at 150°C for 15 hours to obtain metal complex particles B. Using an inductively coupled plasma atomic emission spectrometry (ICP-AES) device, the composition of metal complex particle B was determined to be Na 0.24 K 1.07 Ni 0.003 Mn 0.997 [Fe(CN)6] 0.83 It was confirmed that this is the case. Furthermore, EDS (energy dispersive X-ray spectroscopy) using STEM (scanning transmission electron microscope) revealed that the ratio of nickel element to the total molar amount of nickel element and manganese element on the surface of metal complex particle B was 5.6 mol %.

[0071] [Constant current charge / discharge test] Example 1 The metal complex particles B, Ketjen black (product name "EC600JD", manufactured by Lion Specialty Chemicals), and PVDF (product name "#9100", manufactured by Kureha Corporation) were mixed in a mass ratio of 70:20:10 to form a working electrode. Activated carbon (product name "YP50F", manufactured by Kuraray Co., Ltd.), Ketjen black, and PTFE were mixed in a mass ratio of 80:10:10 to form a counter electrode. As a reference electrode, Ag / Ag + Electrodes were used. As the electrolyte, a 1 mol / L KPF6 solution (EC:PC=1:1 (volume ratio)) was used. A glass filter (product name "GB-100R" manufactured by Advantec Co., Ltd.) was used as the separator.

[0072] A constant current charge / discharge test was carried out using a three-electrode cell (product name "SB9", manufactured by EC Frontier Co., Ltd.). The potential range was -1.33 to 0.47 V (vs. Ag + The current density was 15.5 mA / g for cycles 1 to 5, 49, and 50, and for every 50 cycles thereafter (e.g., cycle 100, cycle 150), and for the cycles before that (e.g., cycle 99, cycle 149). For cycles other than those mentioned above, the current density was 82.5 mA / g. 15.5 mA / g is a condition of a relatively slow charge / discharge rate, and 82.5 mA / g is a condition of a relatively fast charge / discharge rate.

[0073] <Comparative Example 1> A constant current charge-discharge test was carried out in the same manner as in Example 1, except that the metal complex particles B were changed to the metal complex particles A.

[0074] FIG. 2 is a graph showing the relationship between the discharge capacity and the number of cycles in Example 1 and Comparative Example 1.

[0075] In Example 1, metal complex particles were used that contained potassium ions, hexacyanoferrate ions, nickel ions, and manganese ions, and the ratio of nickel element to the total molar amount of nickel element and manganese element was 0.01 mol % to 10 mol %. Therefore, no decrease in discharge capacity was observed up to the 150th cycle, and it was found that the charge-discharge cycle characteristics were excellent.

[0076] On the other hand, it was found that the discharge capacity decreased as the charge / discharge rate increased in Comparative Example 1. Specifically, the discharge capacity at the 148th cycle was 74.4% of the discharge capacity at the 6th cycle. [Explanation of symbols]

[0077] 10: secondary battery, 12: battery case (negative electrode side), 14: gasket, 16: negative electrode, 18: separator, 20: positive electrode, 22: spacer, 24: leaf spring, 26: battery case (positive electrode side)

Claims

1. containing potassium ions, ferricyanide ions, nickel ions, and manganese ions; Metal complex particles, wherein the ratio of elemental nickel to the total molar amount of elemental nickel and elemental manganese is 0.01 mol % to 10 mol %.

2. The metal complex particle according to claim 1 , wherein the nickel element is unevenly distributed on the surface.

3. An electrode comprising the metal complex particles according to claim 1 or 2.

4. A battery comprising the electrode according to claim 3.

5. The method includes a step of mixing manganese hexacyanoferrate, potassium hexacyanoferrate, and nickel chloride to produce metal complex particles containing potassium ions, hexacyanoferrate ions, nickel ions, and manganese ions, The method for producing metal complex particles, wherein the molar ratio of the amount of nickel chloride used to the amount of manganese hexacyanoferrate used is 0.01 to 0.5.

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