Cathode material and cathode material precursor for magnesium storage battery, method for manufacturing cathode material precursor and cathode material for magnesium storage battery, and magnesium storage battery

Abstract

Provided are a positive electrode material and a positive electrode material precursor for a magnesium storage battery that can reduce the operating temperature and have excellent cycle characteristics, a method for manufacturing a positive electrode material precursor and a method for manufacturing a positive electrode material for a magnesium storage battery, and a magnesium storage battery. [Solution] The cathode material for magnesium storage batteries is made of a compound containing Mg, has free volume, and has a composite structure with a rock salt structure in part of the amorphous phase. The compound preferably contains Mg and a metal oxide, and the metal oxide preferably contains Ti and Mo.

Description

[Technical Field]

[0001] The present invention relates to a cathode material and a cathode material precursor for a magnesium storage battery, a method for manufacturing a cathode material precursor and a cathode material for a magnesium storage battery, and a magnesium storage battery. [Background technology]

[0002] Rechargeable magnesium batteries (RMBs) are attracting attention as a next-generation storage battery that can replace lithium-ion batteries (LIBs). Magnesium batteries can achieve excellent energy density by using magnesium metal for the anode, and can also be manufactured relatively inexpensively because magnesium is abundant in the earth's crust.

[0003] In the past, oxide materials with high redox potentials have been expected to be the cathode material for magnesium storage batteries in order to achieve high energy density. However, oxide materials have a problem in that the solid-state diffusion of Mg in the material is extremely slow compared to monovalent Li oxide or Na oxide, due to the strong electrostatic interaction between divalent Mg ions in the material and oxide ions or other cations (see, for example, Non-Patent Document 1).

[0004] To solve this problem, positive electrode materials that employ a spinel structure (see, for example, Non-Patent Document 2 or 3) or a rock salt structure (see, for example, Non-Patent Document 4 or Patent Document 1) have been proposed as crystal structures that promote the diffusion of Mg.

[0005] Since lithium-ion batteries contain amorphous superionic conductors, there were hopes for a positive electrode material that utilizes the amorphous phase. However, it has been reported that when the surface of a positive electrode made of FePO4 is made amorphous, the amorphous phase prevents Mg from being inserted, which actually deteriorates the electrode characteristics (see, for example, Non-Patent Document 5). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] RA House et al., “Mg-rich disordered rocksalt oxide cathodes for Mg-ion batteries”, J. Mater. Chem. A, 2024, <DOI: 10.1039 / D4TA02348J> [Non-patent document 2] ID Johnson et al., “Unconventional Charge Transport in MgCr2O4 and Implications for Battery Intercalation Hosts”, J. Am. Chem. Soc., 2022, 144, 31, p.14121-14131 [Non-patent document 3] S. Okamoto et al., “Intercalation and Push-Out Process with Spinel-to-Rocksalt Transition on Mg Insertion into Spinel Oxides in Magnesium Batteries”, Adv. Sci., 2015, 2, 8, 1500072 [Non-patent document 4] T. Kawaguchi et al., “Securing Cation Vacancies to Enable Reversible Mg Insertion / Extraction in Rocksalt Oxides”, J. Mater. Chem. A, 2024, 12, p.9088-9101 [Non-patent document 5] R. Zhang and C. Ling, “Unveil the Chemistry of Olivine FePO4 as Magnesium Battery Cathode”, ACS Appl. Mater. Interfaces, 2016, 8, p.18018-18026 [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-50055 Summary of the Invention [Problem to be solved by the invention]

[0008] In the cathode material made of MgCr2O4 with a spinel structure described in Non-Patent Document 2, the calculated diffusion rate of Mg is comparable to that of lithium ion electrode materials, but there is an energy limit, and it has the problem that it hardly works as a cathode. Also, in the cathode material with a spinel structure described in Non-Patent Document 3, it is operated under conditions of 150°C to promote Mg diffusion, and there is a problem that the operating temperature needs to be further reduced for practical use.

[0009] In the positive electrode material having a rock salt structure described in Non-Patent Document 4, the Mg diffusion is promoted by the concerted effect of vacancies, Li, and Mg, thereby realizing insertion and desorption of Mg at 90°C. However, for practical use, there is still a problem that the operating temperature needs to be further reduced. Also, in the positive electrode material having a layered rock salt structure described in Patent Document 1, the specific surface area is 30 m 2 By using a composite oxide with a densitometric value of 1 / g or more, the battery can operate at temperatures close to room temperature. However, repeated charge and discharge cycles cause a rapid decrease in capacity, resulting in poor cycle characteristics.

[0010] The present invention has been made in light of these problems, and aims to provide a positive electrode material and a positive electrode material precursor for a magnesium storage battery that can reduce the operating temperature and have excellent cycle characteristics, a method for manufacturing a positive electrode material precursor and a method for manufacturing a positive electrode material for a magnesium storage battery, and a magnesium storage battery. [Means for solving the problem]

[0011] In order to achieve the above object, the positive electrode material for a magnesium storage battery according to the present invention is characterized by comprising a compound containing Mg, having free volume (pores), and having a composite structure in which part of the amorphous phase has a rock salt structure.

[0012] The positive electrode material for a magnesium storage battery according to the present invention has free volume in the amorphous phase, which ensures pathways for Mg and facilitates diffusion of Mg. Therefore, it can be used in the positive electrode of a magnesium storage battery. When used as a positive electrode, it can achieve insertion and desorption of Mg even at temperatures near room temperature, allowing the operating temperature to be reduced to near room temperature. Furthermore, because the free volume is maintained by the amorphous phase, the positive electrode material for a magnesium storage battery according to the present invention can suppress capacity loss during repeated charge and discharge, resulting in excellent cycle characteristics.

[0013] In the cathode material for magnesium storage batteries according to the present invention, the compound is preferably formed by bonding Mg to a metal oxide, a metal chalcogenide, a metal halide, or a material that ionizes to form a polyvalent anion and a metal element, and particularly preferably the compound contains Mg and a metal oxide, which can further promote insertion and desorption of Mg at temperatures around room temperature, thereby achieving better cycle characteristics.

[0014] Furthermore, when the compound contains a metal oxide, the metal oxide preferably contains Ti and Mo. In this case, Mo lowers the reduction potential, and Ti stabilizes Mo and suppresses its elution, thereby further promoting the insertion and desorption of Mg, and achieving better cycle characteristics. a Li b Ti c Mo d O3 (wherein 0.8≦a+b≦1.2, a / (a+b)≧0.7, 0.25≦c≦0.45, 0.55≦d≦0.75), and in this case, Mg a Li b Ti 1 / 3 Mo 2 / 3 Preferably, the compound has a composition of MgO3. a Ti b Mo c 0 (where 0.10≦a≦0.20, 0.10≦b≦0.20, 0.20≦c≦0.35). In these cases, particularly excellent cycle characteristics can be obtained.

[0015] The cathode material for a magnesium storage battery according to the present invention is preferably made of nanoparticles having a particle size of less than 10 nm, which can further promote Mg intercalation and deintercalation at temperatures around room temperature, thereby achieving better cycle characteristics.

[0016] The positive electrode material precursor for a magnesium storage battery according to the first aspect of the present invention is characterized in that it is made of a compound containing an alkali metal and has a composite structure in which part of the amorphous phase has a rock salt structure.

[0017] The method for producing a positive electrode material precursor for a magnesium storage battery according to the present invention is a method for producing a positive electrode material precursor for a magnesium storage battery according to the first invention, and is characterized by comprising: a mixing step of mixing an alkali metal, a metal element different from the alkali metal, citric acid, and alcohol in a solvent; a solution combustion step of heating the solution mixed in the mixing step to evaporate the solvent and then burning the solution to obtain a compound containing the alkali metal and the metal element; and a grinding step of grinding the compound obtained in the solution combustion step to obtain a positive electrode material precursor for a magnesium storage battery consisting of nanoparticles.

[0018] The cathode material precursor for a magnesium storage battery according to the first aspect of the present invention is suitably produced by the method for producing a cathode material precursor for a magnesium storage battery according to the present invention. The method for producing a cathode material precursor for a magnesium storage battery according to the present invention uniformly mixes raw materials in the mixing step and utilizes a combustion reaction in the solution combustion step, thereby producing fine particles having a uniform layered rock salt structure. Furthermore, by further pulverizing to nanoparticles in the crushing step, it is possible to produce an amorphous phase while leaving some of the rock salt structure, and to obtain a composite structure in which part of the amorphous phase has the rock salt structure. In this way, the method for producing a cathode material precursor for a magnesium storage battery according to the present invention can produce the cathode material precursor for a magnesium storage battery according to the first aspect of the present invention.

[0019] In the method for producing a cathode material precursor for a magnesium storage battery according to the present invention, the mixing step, the solution combustion step, and the pulverization step may each be performed by any method, and conventional methods may be used. For example, the mixing step and the solution combustion step may be performed by the Pechini method, and the solution combustion step may be performed by the solution combustion method. Furthermore, the solution combustion method may be combined with the heat treatment of the Pechini method. Furthermore, the pulverization step may be performed by using a ball mill or a hand mill.

[0020] In the cathode material precursor for a magnesium storage battery according to the first aspect of the present invention and the manufacturing method thereof, the compound is preferably formed by combining the alkali metal with a metal oxide, a metal chalcogenide, a metal halide, or a material that becomes a polyvalent anion when ionized and a metal element, and in particular, the alkali metal is preferably Li, and the compound has a composition of Li2MO3 (where M is one or more metal elements). In addition, the M preferably contains Ti and Mo, and the compound is preferably Li2Ti 1 / 3 Mo 2 / 3 Preferably, the cathode material precursor for magnesium storage batteries is composed of nanoparticles with a particle size of less than 10 nm.

[0021] The positive electrode material precursor for a magnesium storage battery according to the second aspect of the present invention is characterized in that it has a composition of Li2MO3 (wherein M is a plurality of metal elements), has a layered rock salt structure, and M contains Ti and Mo.

[0022] The positive electrode material precursor for a magnesium storage battery according to the second aspect of the present invention may be produced by any method, for example, by an existing method such as the Pezzini method. 1 / 3 Mo 2 / 3 O3. In this case, particularly excellent cycle characteristics can be obtained. Furthermore, the positive electrode material precursor for a magnesium storage battery according to the second aspect of the present invention is preferably configured so that when used in the positive electrode of a magnesium storage battery and the magnesium storage battery is charged, Li in the composition is released and a composite structure having a rock salt structure is formed in part of the amorphous phase.

[0023] The method for producing a cathode material for a magnesium storage battery according to the present invention is characterized in that the alkali metal in the cathode material precursor for a magnesium storage battery obtained by the method for producing a cathode material precursor for a magnesium storage battery according to the present invention is ion-exchanged with Mg to obtain a cathode material for a magnesium storage battery. Alternatively, the method for producing a cathode material for a magnesium storage battery according to the present invention is characterized in that the alkali metal in the cathode material precursor for a magnesium storage battery according to the first or second present invention is ion-exchanged with Mg to obtain a cathode material for a magnesium storage battery.

[0024] The positive electrode material for a magnesium storage battery according to the present invention is suitably produced by the method for producing a positive electrode material for a magnesium storage battery according to the present invention, using a positive electrode material precursor for a magnesium storage battery obtained by the method for producing a positive electrode material precursor for a magnesium storage battery according to the present invention, or a positive electrode material precursor for a magnesium storage battery according to the first or second present invention. The method for producing a positive electrode material for a magnesium storage battery according to the present invention can reduce the operating temperature and produce a positive electrode material for a magnesium storage battery having excellent cycle characteristics.

[0025] In the method for producing a positive electrode material for a magnesium storage battery according to the present invention, the method for ion-exchanging the alkali metal of the positive electrode material precursor for a magnesium storage battery with Mg may be any method that allows ion exchange. Examples of the ion-exchange method include immersing the positive electrode material precursor for a magnesium storage battery in an electrolyte containing Mg at a predetermined temperature for a predetermined time, or using the positive electrode material precursor for a magnesium storage battery as the positive electrode of a magnesium storage battery and charging the battery one or more times. When immersing in an electrolyte, the ion exchange is preferably carried out by immersing the positive electrode material precursor for a magnesium storage battery in an electrolyte containing Mg at a temperature of 80°C or higher for 20 hours or more to ensure sufficient ion exchange.

[0026] The magnesium storage battery according to the present invention is characterized by having a positive electrode containing the positive electrode material for a magnesium storage battery according to the present invention, and a negative electrode containing magnesium metal.

[0027] The magnesium storage battery according to the present invention can operate at room temperature or a temperature close to room temperature and has excellent cycle characteristics because the positive electrode contains the positive electrode material for a magnesium storage battery according to the present invention. [Effects of the Invention]

[0028] According to the present invention, it is possible to provide a positive electrode material and a positive electrode material precursor for a magnesium storage battery that can reduce the operating temperature and have excellent cycle characteristics, a method for manufacturing a positive electrode material precursor and a method for manufacturing a positive electrode material for a magnesium storage battery, and a magnesium storage battery. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a graph showing the change over time in the cation ratio [Mg / (Mg+Li)] when the electrolyte temperature is 60°C and 90°C in an ion exchange test in which Li in a positive electrode material precursor for a magnesium storage battery is ion-exchanged with Mg in the manufacturing method of a positive electrode material for a magnesium storage battery according to the first embodiment of the present invention. [Figure 2] 1 is a scanning electron microscope (SEM) image of a positive electrode material precursor for a magnesium storage battery obtained by a manufacturing method of a positive electrode material precursor for a magnesium storage battery according to a first embodiment of the present invention. [Figure 3] 1 is an X-ray diffraction (XRD) spectrum of a positive electrode material for a magnesium storage battery obtained by a manufacturing method of a positive electrode material for a magnesium storage battery according to a first embodiment of the present invention. [Figure 4] 1 is a scanning transmission electron microscope (STEM) image of a positive electrode material for a magnesium storage battery obtained by a manufacturing method of a positive electrode material for a magnesium storage battery according to a first embodiment of the present invention. [Figure 5]FIG. 1A is a graph showing the relationship between capacity and cell voltage at 1 cycle, 2 cycles, 5 cycles, 10 cycles, 20 cycles, and 60 cycles in a constant current charge / discharge test using a full-cell battery consisting of a 3-electrode cell using, as a positive electrode, the positive electrode material for a magnesium storage battery obtained by the manufacturing method for a positive electrode material for a magnesium storage battery according to the first embodiment of the present invention; and FIG. 1B is a graph showing the relationship between the number of cycles and capacity. [Figure 6] FIG. 1A is a graph showing the relationship between capacity and cell voltage at 1 cycle, 2 cycles, 5 cycles, and 10 cycles, and FIG. 1B is a graph showing the relationship between the number of cycles and capacity, in a constant current charge-discharge test using a full-cell battery consisting of a coin cell using, for the positive electrode, the positive electrode material for a magnesium storage battery obtained by the manufacturing method for the positive electrode material for a magnesium storage battery according to the first embodiment of the present invention. [Figure 7] FIG. 10 is a graph showing (a) the relationship between capacity and potential at 1 cycle, 2 cycles, 5 cycles, and 15 cycles, and (b) the relationship between the number of cycles and capacity, in a constant current charge-discharge test using a full-cell battery consisting of a 3-electrode beaker cell using, as a positive electrode, the positive electrode material for a magnesium storage battery obtained by the manufacturing method for the positive electrode material for a magnesium storage battery according to the second embodiment of the present invention. [Figure 8] 8 shows X-ray diffraction spectra of a positive electrode material precursor for a magnesium storage battery obtained by the manufacturing method of a positive electrode material precursor for a magnesium storage battery according to the second embodiment of the present invention, and of the positive electrode material for a magnesium storage battery at 1 cycle, 2 cycles, 5 cycles, and 15 cycles of charge / discharge in the charge / discharge test shown in FIG. [Figure 9] FIG. 8 shows a transmission electron microscope (TEM) image of the cathode material for a magnesium storage battery during discharge for 15 cycles of the charge-discharge test shown in FIG. 7, and the Fourier transform pattern (inset) of the boxed area. [Figure 10]FIG. 10 is an explanatory diagram showing the charge / discharge mechanism of the positive electrode material precursor and the positive electrode material for a magnesium storage battery according to a second embodiment of the present invention, showing (a) a positive electrode material precursor for a magnesium storage battery (as-synthesized state), (b) a positive electrode material for a magnesium storage battery formed by the first charge, and (c) a reversible cycle of subsequent charge and discharge. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, embodiments of the present invention will be described with reference to the drawings and examples.

[0031] [Positive electrode material for magnesium storage battery according to the first embodiment of the present invention] 1 to 6 show a cathode material and a cathode material precursor for a magnesium storage battery according to a first embodiment of the present invention, a method for manufacturing a cathode material precursor and a cathode material for a magnesium storage battery, and a magnesium storage battery.

[0032] The positive electrode material for a magnesium storage battery according to the first embodiment of the present invention is composed of nanoparticles having a particle size of less than 10 nm, and Mg a Li b Ti 1 / 3 Mo 2 / 3 O3 (where 0.8≦a+b≦1.2, a / (a+b)≧0.7). The positive electrode material for a magnesium storage battery according to the first embodiment of the present invention has a free volume and a composite structure in which a rock salt structure is present in part of the amorphous phase.

[0033] The positive electrode material for a magnesium storage battery according to the first embodiment of the present invention has free volume in the amorphous phase, which ensures Mg pathways and facilitates Mg diffusion. Therefore, it can be used in the positive electrode of a magnesium storage battery. When used as a positive electrode, Mg insertion and desorption can be achieved even at temperatures near room temperature, allowing the operating temperature to be reduced to near room temperature. Furthermore, because the free volume is maintained by the amorphous phase, the positive electrode material for a magnesium storage battery according to the first embodiment of the present invention can suppress capacity loss during repeated charge and discharge, resulting in excellent cycle characteristics. Furthermore, because the positive electrode material for a magnesium storage battery according to the first embodiment of the present invention is made of nanoparticles with a particle diameter of less than 10 nm, Mg insertion and desorption can be further promoted at temperatures near room temperature, resulting in even better cycle characteristics.

[0034] The positive electrode material for the magnesium storage battery according to the first embodiment of the present invention is Mg a Li b Ti 1 / 3 Mo 2 / 3 The compound is not limited to a compound having the composition of O3, but may be any compound containing Mg. For example, if M is a metal element, then M a O b a metal oxide having a composition of M a (S, Se, or Te) b Metal chalcogenides having the composition M a (F, Cl, Br, or I) b or a metal halide having a composition of M, in which a metal element is bonded to a substance that becomes a polyvalent anion when ionized. a (PO4, BO3, or SO4, etc.) b The compound may be formed by combining a substance having the above composition with Mg.

[0035] In particular, when the compound contains a metal oxide, the metal oxide preferably contains Ti and Mo. In this case, Mo lowers the reduction potential, and Ti stabilizes Mo and suppresses elution, thereby further promoting insertion and desorption of Mg and achieving better cycle characteristics.

[0036] The cathode material for a magnesium storage battery according to the first embodiment of the present invention can be produced using a cathode material precursor for a magnesium storage battery obtained by the method for producing a cathode material precursor for a magnesium storage battery according to the first embodiment of the present invention. That is, the method for producing a cathode material precursor for a magnesium storage battery according to the first embodiment of the present invention includes a mixing step, a solution combustion step, and a pulverization step.

[0037] In a specific example, the mixing step and the solution combustion step use the Pezzini method, and the solution combustion method is used as the heat treatment of the Pezzini method. That is, in the mixing step, an alkali metal, a metal element other than the alkali metal, citric acid, and alcohol are mixed in a solvent. In the solution combustion step, the solution mixed in the mixing step is heated to evaporate the solvent, and then combusted to obtain a compound containing the alkali metal and the metal element. In this way, by uniformly mixing the raw materials in the mixing step and utilizing a combustion reaction in the solution combustion step, fine particles having a uniform layered rock salt structure can be obtained. The composition of the obtained particulate compound varies depending on the type of alkali metal and metal element in the raw materials. In a specific example, by using Li as the alkali metal and Ti and Mo as the metal elements, Li2Ti 1 / 3 Mo 2 / 3 It has a composition of O3.

[0038] When different alkali metals and metal elements are used as raw materials, for example, when M is a metal element, M a O b a metal oxide having a composition of M a (S, Se, or Te) b Metal chalcogenides having the composition Ma (F, Cl, Br, or I) b or a metal halide having a composition of M, in which a metal element is bonded to a substance that becomes a polyvalent anion when ionized. a (PO4, BO3, or SO4, etc.) b A compound formed by combining a substance having the above composition with the alkali metal raw material can be obtained.

[0039] In the grinding step, the compound obtained in the solution combustion step is ground to obtain a cathode material precursor for magnesium storage batteries consisting of nanoparticles with a particle size of less than 10 nm. By grinding, it is possible to make the phase amorphous while leaving some of the rock salt structure, and it is possible to obtain a cathode material precursor for magnesium storage batteries having a composite structure in which part of the amorphous phase has the rock salt structure. In a specific example, the grinding step is carried out using a ball mill or hand mill. In a specific example, the obtained cathode material precursor for magnesium storage batteries is Li2Ti 1 / 3 Mo 2 / 3 It consists of compounds with the composition O3.

[0040] The mixing step and the solution combustion step are not limited to the Pezzini method or the solution combustion method, and other methods such as existing methods may be used as long as they are capable of producing a compound containing the desired alkali metal and metal element. The pulverization step is not limited to a method using a ball mill or the like, and may be performed by any method that can obtain nanoparticles.

[0041] The positive electrode material for a magnesium storage battery according to the first embodiment of the present invention can be produced by the method for producing a positive electrode material for a magnesium storage battery according to the first embodiment of the present invention, using the thus obtained positive electrode material precursor for a magnesium storage battery. That is, the method for producing a positive electrode material for a magnesium storage battery according to the first embodiment of the present invention ion-exchanges the alkali metal in the obtained positive electrode material precursor for a magnesium storage battery with Mg. In one specific example, the ion exchange is carried out by immersing the positive electrode material precursor for a magnesium storage battery in an electrolyte containing Mg at a predetermined temperature for a predetermined time. In this way, the positive electrode material for a magnesium storage battery according to the first embodiment of the present invention can be obtained.

[0042] In the manufacturing method of the positive electrode material for a magnesium storage battery according to the first embodiment of the present invention, the method of ion exchange is not limited to the method of immersing a positive electrode material precursor for a magnesium storage battery in an electrolyte containing Mg, but may be any method that allows ion exchange, such as a method of using a positive electrode material precursor for a magnesium storage battery as the positive electrode of a magnesium storage battery and charging it one or more times.

[0043] The magnesium storage battery of the first embodiment of the present invention has a positive electrode containing the thus obtained positive electrode material for a magnesium storage battery, and a negative electrode containing magnesium metal. Because the positive electrode of the magnesium storage battery of the first embodiment of the present invention contains the positive electrode material for a magnesium storage battery of the first embodiment of the present invention, the magnesium storage battery of the first embodiment of the present invention can operate at temperatures near room temperature and has excellent cycle characteristics. [Example]

[0044] A cathode material precursor and a cathode material for a magnesium storage battery were manufactured using the manufacturing method of a cathode material precursor and a manufacturing method of a cathode material for a magnesium storage battery according to the first embodiment of the present invention, and a full cell test was carried out.

[0045] To prepare a cathode precursor for magnesium batteries, the Pezzini method is first used to synthesize lithium nitrate (LiNO), titanium tetraisopropoxide ([(CH)CHO]Ti), and ammonium molybdate tetrahydrate ((NH)MoO 24 A mixture of ammonium nitrate (NH4NO3), citric acid, and propylene glycol was placed in a container, mixed, and stirred at 80-120°C for 4 hours. The mixture was dried at 60-70°C for 48 hours, and then heated at 600°C for 10 hours in a 10% H2-Ar atmosphere, where it was subjected to a heat treatment using the solution combustion method.

[0046] The powder obtained after the heat treatment was placed in a ball mill together with the solvent dimethyl carbonate (DMC), and milled in an Ar atmosphere at 500 rpm for 5 minutes, repeated 40 times. The powder milled in the ball mill was placed in a hand mill and further milled inside a glove box, which is an airtight container. Thus, a Li2Ti nanoparticle was obtained. 1 / 3 Mo 2 / 3 A cathode material precursor for magnesium batteries with the composition of O3 was obtained.

[0047] Next, the obtained cathode material precursor for magnesium storage batteries was mixed with a conductive additive and a binder to prepare a composite electrode. The composite electrode was immersed in an electrolyte solution of Mg[TFSA]2 / G3 to ion-exchange the Li in the composite electrode with Mg. After immersion, the composite electrode was washed with acetonitrile and dried. This resulted in the production of a cathode material for magnesium storage batteries.

[0048] Here, we conducted an ion exchange test to investigate the immersion conditions during ion exchange. In the test, a composite electrode, which was a mixture of the obtained cathode material precursor for a magnesium storage battery with a conductive additive and a binder, and an electrolyte of Mg[TFSA]2 / G3 were used. The composite electrode was immersed in the electrolyte at 60°C or 90°C for 24, 72, and 168 hours, and the cation ratio [Mg / (Mg+Li)] in the composite electrode was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). The test results are shown in Figure 1.

[0049] As shown in Figure 1, when immersed in an electrolyte at 90°C, the cation ratio reached 0.7 or more after 24 hours, confirming that ion exchange had progressed sufficiently. When immersed in an electrolyte at 60°C, the cation ratio only reached about 0.6 even after 168 hours, confirming that ion exchange did not progress very well.

[0050] Based on the results shown in Figure 1, the composite electrode was immersed in an electrolyte of Mg[TFSA]2 / G3 at 90°C for 24 hours to exchange the Li in the composite electrode with Mg. The composition of the cathode material for magnesium storage batteries obtained under these conditions was analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES). The results showed that the Mg 0.27 Li 0.08 (vacancy) 0.32 Ti 0.11 Mo 0.22 It was O.

[0051] A scanning electron microscope (SEM) image of the obtained positive electrode material precursor for magnesium storage batteries is shown in Figure 2. As shown in Figure 2, it was confirmed that the positive electrode material precursor for magnesium storage batteries is composed of fine particles (primary particles), and that secondary particles are formed by the primary particles agglomerating or forming complexes with residual carbon.

[0052] The X-ray diffraction spectrum obtained by X-ray diffraction analysis of the obtained positive electrode material for a magnesium storage battery is shown in Figure 3. A scanning transmission electron microscope (STEM) image of the obtained positive electrode material for a magnesium storage battery is shown in Figure 4.

[0053] As shown in Figure 3, the positive electrode material for magnesium rechargeable batteries exhibited peaks corresponding to the (200) and (220) planes, and a gentle peak (halo peak) was observed near 2θ = 10°. These results confirmed that the positive electrode material for magnesium rechargeable batteries contains a mixture of rock salt and amorphous structures. Considering the manufacturing process, the positive electrode material for magnesium rechargeable batteries is thought to have a layered rock salt structure after heat treatment (before grinding), which became amorphous through grinding, resulting in a composite structure with rock salt structure in part of the amorphous phase. Furthermore, the crystallite size was calculated from the (200) and (220) peaks shown in Figure 3 using the Scherrer equation, yielding a value of 2.1 nm to 4.3 nm.

[0054] Furthermore, it was confirmed that the positive electrode material for magnesium storage batteries is in a state where particles with particle sizes of 10 nm to several tens of nm are dispersed, as shown in Figure 4. Since the particle size of the positive electrode material for magnesium storage batteries is estimated to be smaller than 10 nm from the HAADF-STEM image, the particles in Figure 4 are thought to be secondary particles formed by agglomeration of fine primary particles, with the positive electrode material for magnesium storage batteries being dispersed in a form embedded in the carbon by-product.

[0055] Next, a constant current charge / discharge test was conducted using the resulting cathode material for magnesium storage batteries in a full-cell battery consisting of a three-electrode cell. In the test, the cathode material for magnesium storage batteries was used as the working electrode (WE; positive electrode), metallic magnesium (Mg) was used as the counter electrode (CE; negative electrode), and lithium foil immersed in a solution of Li(TFSA) mixed at a concentration of 1 M in G3 solvent was used as the reference electrode (RE). The electrolyte used was 300 μL of Mg[B(HFIP)4]2 mixed at a concentration of 0.3 M in G3 solvent. The separator was a commercially available glass fiber filter paper (product name "Whatman® GF / F").

[0056] The test was performed at a current of 10 mA / g, a measurement voltage of 0.5 V to 3.2 V, and a measurement temperature of 25°C. Figure 5(a) shows the relationship between capacity and cell voltage at 1, 2, 5, 10, 20, and 60 cycles, and Figure 5(b) shows the relationship between cycle number and capacity. As shown in Figures 5(a) and (b), the three-electrode cell operated at room temperature, demonstrating a discharge capacity of over 100 mAh / g up to 10 cycles and a discharge capacity of over 60 mAh / g up to 30 cycles.

[0057] The insertion and desorption of Mg into and from the working electrode (the cathode material for magnesium batteries) during charge and discharge in the test was confirmed using inductively coupled plasma optical emission spectroscopy (ICP-OES). The composition of the cathode material for magnesium batteries during charge and discharge in the third cycle was analyzed using ICP-OES, and the results are shown in Table 1. As shown in Table 1, the amount of Mg increased and decreased during charge and discharge, confirming that Mg insertion and desorption were occurring. Furthermore, the capacity was equivalent to 93 mAh / g, which was 62% of the electrochemically obtained discharge capacity of 150 mAh / g (see Figure 5).

[0058] [Table 1]

[0059] Next, a constant current charge / discharge test was conducted using the resulting cathode material for magnesium storage batteries in a full-cell battery consisting of coin cells. In the test, the cathode material for magnesium storage batteries was used as the working electrode WE (positive electrode), and metallic magnesium (Mg) was used as the counter electrode CE (negative electrode). Furthermore, 100 μL of a 0.3 M Mg[B(HFIP)4]2 mixture in G3 solvent was used as the electrolyte. Furthermore, commercially available glass fiber filter paper (product name "Whatman® GF / F") was used as the separator.

[0060] The test was performed at a current of 10 mA / g, a measurement voltage of 0.5 V to 3.2 V, and a measurement temperature of 25°C, with charge and discharge being performed. Figure 6(a) shows the relationship between capacity and cell voltage for 1, 2, 5, and 10 cycles, and Figure 6(b) shows the relationship between the number of cycles and capacity. As shown in Figures 6(a) and (b), it was confirmed that the coin cell also operated at room temperature, exhibiting a discharge capacity of over 50 mAh / g up to 3 cycles and over 60 mAh / g for 4 to 10 cycles.

[0061] [Positive electrode material for magnesium storage battery according to the second embodiment of the present invention] 7 to 10 show a cathode material and a cathode material precursor for a magnesium storage battery, a method for manufacturing a cathode material precursor for a magnesium storage battery, a method for manufacturing a cathode material, and a magnesium storage battery according to the second embodiment of the present invention. Note that in the following description, redundant descriptions of the same configurations, actions, etc. as those in the first embodiment of the present invention will be omitted.

[0062] The positive electrode material for a magnesium storage battery according to the second embodiment of the present invention is made of nanoparticles having a particle diameter of 10 nm or more and 20 nm or less, and Mg a Ti b Mo c O (where 0.10≦a≦0.20, 0.10≦b≦0.20, 0.20≦c≦0.35). The positive electrode material for a magnesium storage battery according to the second embodiment of the present invention has a composite structure that has free volume and has a rock salt structure in part of the amorphous phase.

[0063] The positive electrode material for a magnesium storage battery according to the second embodiment of the present invention has free volume in the amorphous phase, ensuring pathways for Mg and facilitating Mg diffusion. Therefore, when used in the positive electrode of a magnesium storage battery, Mg insertion and desorption can be achieved even at temperatures close to room temperature, allowing the battery to function as a positive electrode. Furthermore, because the positive electrode material for a magnesium storage battery according to the second embodiment of the present invention is made of nanoparticles with particle diameters of 10 nm to 20 nm, Mg insertion and desorption can be further promoted at temperatures close to room temperature, resulting in excellent cycle characteristics.

[0064] The positive electrode material for the magnesium storage battery according to the second embodiment of the present invention can be produced using a positive electrode material precursor for the magnesium storage battery according to the second embodiment of the present invention, which is produced by, for example, the Pezzini method, etc. In a specific example, the positive electrode material precursor for the magnesium storage battery according to the second embodiment of the present invention has a layered rock salt structure and is composed of Li2Ti 1 / 3 Mo 2 / 3 It has the composition O3. Li2Ti 1 / 3 Mo 2 / 3 O3 is a pseudo-binary oxide of Li2MoO3 and Li2TiO3, which are Li-rich layered oxides (LLO). Note that the positive electrode material precursor for the magnesium storage battery according to the second embodiment of the present invention is not limited to the Pezzini method, and other methods such as existing methods may also be used.

[0065] The positive electrode material for a magnesium storage battery according to the second embodiment of the present invention can be produced by the method for producing a positive electrode material for a magnesium storage battery according to the second embodiment of the present invention using the thus obtained positive electrode material precursor for a magnesium storage battery. That is, in the method for producing a positive electrode material for a magnesium storage battery according to the second embodiment of the present invention, the alkali metal in the obtained positive electrode material precursor for a magnesium storage battery is ion-exchanged with Mg. In a specific example, the positive electrode material precursor for a magnesium storage battery is used as the positive electrode of a magnesium storage battery, and the battery is charged at least once to perform the ion exchange. During this ion exchange, Li in the composition is released, forming a composite structure having a rock salt structure in part of the amorphous phase. In this way, the positive electrode material for a magnesium storage battery according to the second embodiment of the present invention can be obtained.

[0066] In the method for producing a positive electrode material for a magnesium storage battery according to the second embodiment of the present invention, the method for ion exchange is not limited to a method in which a positive electrode material precursor for a magnesium storage battery is used as the positive electrode of the magnesium storage battery and charged at least once, but may be any method that allows ion exchange, such as a method in which a positive electrode material precursor for a magnesium storage battery is immersed in an electrolyte containing Mg.

[0067] In the positive electrode material precursor and positive electrode material for a magnesium storage battery according to the second embodiment of the present invention, Mo changes its valence between +4 and +6 during charge and discharge, thereby contributing to charge compensation associated with the insertion and desorption of Li and Mg. Furthermore, Ti stabilizes Mo, suppressing its elution. This further promotes the desorption of Li and the insertion and desorption of Mg, resulting in excellent cycle characteristics.

[0068] The magnesium storage battery of the second embodiment of the present invention has a positive electrode containing the thus obtained positive electrode material for a magnesium storage battery, and a negative electrode containing magnesium metal. Because the positive electrode of the magnesium storage battery of the second embodiment of the present invention contains the positive electrode material for a magnesium storage battery of the second embodiment of the present invention, the magnesium storage battery of the second embodiment of the present invention can operate at temperatures close to room temperature and has excellent cycle characteristics. [Example]

[0069] A cathode material for a magnesium storage battery according to the second embodiment of the present invention was manufactured and tested in a full cell. First, to manufacture a cathode material precursor for a magnesium storage battery, the Pechini method was used to mix lithium nitrate (LiNO3), titanium tetraisopropoxide ([(CH3)2CHO]4Ti), and ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 4H2O), citric acid, and propylene glycol were mixed in a container and stirred at 70-100°C for 4 hours. The mixture was gradually heated to 200°C over 4 hours and dried at 200°C for 12 hours. The resulting solid was then crushed in a mortar. The resulting powder was heat-treated in air at 450°C for 10 hours, then placed in a ball mill with dimethyl carbonate (DMC) as a solvent and crushed 40 times at 500 rpm for 5 minutes in an Ar atmosphere. The resulting powder was then mixed with a sucrose solution in N-methyl-2-pyrrolidone. The mixture was dried at 90°C for 1.5 hours and then heat-treated at 600°C for 4 hours in a 10% H2-Ar atmosphere.

[0070] Thus, Li2Ti 1 / 3 Mo 2 / 3 A cathode precursor for magnesium storage batteries was obtained, which had a layered rock salt structure and a composition of O3. The crystallite size of the obtained cathode precursor for magnesium storage batteries was 10.3 nm.

[0071] Next, a conductive additive and a binder were mixed with the resulting cathode precursor for a magnesium storage battery to prepare a composite electrode. A constant-current charge-discharge test was conducted using this composite electrode in a full-cell battery consisting of a three-electrode beaker cell. In the test, the composite electrode was used as the working electrode (WE; positive electrode), a magnesium (Mg) ribbon was used as the counter electrode (CE; negative electrode), and a lithium foil immersed in a 1M Li(TFSA) / DEME-TFSA solution was used as the reference electrode (RE). The electrolyte used was Mg(TFSA)2 / G3 with a molar ratio of 1 / 2.22.

[0072] The test consisted of 40 charge-discharge cycles at a current of 10 mA / g, a measurement potential of 1.5 V to 4.2 V, and a measurement temperature of 60°C. As a result, a specific capacity of approximately 90 mAh / g was obtained during the first discharge, and even after 40 cycles, the capacity retention rate was 78%, confirming good cycle characteristics. Analysis of the electrode composition after charge-discharge using ICP-OES confirmed that Li was desorbed during the first charge, and that reversible insertion and desorption of Li and Mg occurred in accordance with the charge-discharge cycles thereafter.

[0073] Therefore, after charging the 10th cycle, when almost all of the Li was desorbed, we washed each electrode and replaced the electrolyte with fresh one. We then conducted charge-discharge tests under conditions where only Mg contributed to intercalation and deintercalation. As a result, we obtained specific capacity and cycle characteristics that were nearly identical to those before cleaning each electrode and replacing the electrolyte, confirming that reversible intercalation and deintercalation occurred even with Mg alone. Figure 7(a) shows the relationship between capacity and potential at 1, 2, 5, and 15 cycles, and Figure 7(b) shows the relationship between cycle number and capacity. As shown in Figures 7(a) and (b), the device operated at 60°C, close to room temperature, and demonstrated a discharge capacity of over 60 mAh / g for up to 20 cycles.

[0074] Figure 8 shows the X-ray diffraction spectra obtained by powder X-ray diffraction analysis of the resulting cathode material precursor for magnesium storage batteries and the composite electrode (cathode material for magnesium storage batteries) during 1, 2, 5, and 15 charge / discharge cycles in a charge / discharge test. As shown in Figure 8, the cathode material precursor for magnesium storage batteries has a layered rocksalt structure when manufactured (as-synthesis). It was confirmed that during the first charge (first ch.), it transformed into a composite structure consisting of an amorphous phase and a rocksalt structure, becoming the cathode material for magnesium storage batteries. Furthermore, the ratio of the peak area derived from the amorphous phase to the peak area derived from the rocksalt structure after the first charge indicates that the amorphous phase accounts for the majority of the structure. Based on these findings, it is believed that the cathode material for magnesium storage batteries has a composite structure in which the rocksalt structure is part of the amorphous phase.

[0075] Figure 9 shows a transmission electron microscope (TEM) image of the cathode material for magnesium batteries after 15 discharge cycles in a charge-discharge test. The Fourier transform pattern of the boxed region in Figure 9 is shown as an inset in Figure 9. The absence of a clear spot in the inset confirmed the presence of an amorphous phase. Figure 9 also shows the results of a composition analysis of the boxed region in Figure 9 using scanning transmission electron microscopy / energy dispersive spectroscopy (STEM / EDS). The numbers in parentheses in the composition represent the error of the last digit of each composition ratio. The results in Figure 9 confirm the presence of Mg in the amorphous phase, which is thought to contribute to the insertion and desorption of Mg.

[0076] The charge-discharge mechanism of the cathode precursor and cathode material for magnesium batteries, which can be inferred from the above results, is shown in Figure 10. As shown in Figure 10, the cathode precursor for magnesium batteries (as-synthesized state) at the time of manufacture has a layered rock-salt structure consisting of a layer containing Li, Mo, and Ti (TM / Li layer) and a layer of Li (Li layer). Because the atoms are regularly arranged, the activation barrier in the crystalline phase is large (see Figure 10(a)). When this cathode precursor for magnesium batteries is used in the cathode of a magnesium battery, Li is desorbed during the first charging, forming a composite structure with a rock-salt structure in part of the amorphous phase (see Figure 10(b)), which becomes the cathode material for magnesium batteries. At this time, the desorption of Li increases the free volume (vacancies), and the amorphous phase randomizes the atomic arrangement, forming a pathway with a low activation barrier. This promotes the diffusion of Mg, enabling reversible insertion and desorption of Mg, resulting in excellent cycle characteristics, allowing for repeated reversible cycles of charge and discharge (see Figure 10(c)).

Claims

1. A positive electrode material for a magnesium storage battery, which is made of a compound containing Mg, has free volume, and has a composite structure in which part of the amorphous phase has a rock salt structure.

2. The positive electrode material for a magnesium storage battery according to claim 1, characterized in that the compound is formed by combining Mg with a metal oxide, a metal chalcogenide, a metal halide, or a substance in which a metal element is combined with a substance that becomes a polyvalent anion when ionized.

3. 2. The cathode material for magnesium storage batteries according to claim 1, wherein the compound comprises Mg and a metal oxide.

4. 4. The cathode material for magnesium storage batteries according to claim 3, wherein the metal oxide comprises Ti and Mo.

5. The compound is Mg ａ Li ｂ Ti ｃ Mo ｄ O ３ 4. The positive electrode material for a magnesium storage battery according to claim 3, characterized in that it has a composition of: (wherein 0.8≦a+b≦1.2, a / (a+b)≧0.7, 0.25≦c≦0.45, 0.55≦d≦0.75).

6. 2. The positive electrode material for magnesium storage batteries according to claim 1, characterized in that it is made of nanoparticles having a particle size of less than 10 nm.

7. The compound is Mg ａ Ti ｂ Mo ｃ 4. The positive electrode material for a magnesium storage battery according to claim 3, characterized in that it has a composition of: 0 (wherein 0.10≦a≦0.20, 0.10≦b≦0.20, 0.20≦c≦0.35).

8. A positive electrode material precursor for a magnesium storage battery, which is composed of a compound containing an alkali metal and has a composite structure in which part of the amorphous phase has a rock salt structure.

9. The positive electrode material precursor for a magnesium storage battery according to claim 8, characterized in that the compound is formed by combining the alkali metal with a metal oxide, a metal chalcogenide, a metal halide, or a substance in which a metal element is combined with a substance that becomes a polyvalent anion when ionized.

10. the alkali metal comprises Li; The compound is Li ２ MO ３ (wherein M is one or more metal elements) The positive electrode material precursor for a magnesium storage battery according to claim 8.

11. 11. The cathode material precursor for a magnesium storage battery according to claim 10, wherein M comprises Ti and Mo.

12. The compound is Li ２ Ti １／３ Mo ２／３ O ３ 12. The cathode material precursor for magnesium storage batteries according to claim 11, characterized in that it has the following composition:

13. 9. The positive electrode material precursor for magnesium storage batteries according to claim 8, characterized in that it is made of nanoparticles having a particle size of less than 10 nm.

14. Li ２ MO ３ (wherein M is a plurality of metal elements), and has a layered rock salt structure, and M contains Ti and Mo.

15. Li ２ Ti １／３ Mo ２／３ O ３ 15. The positive electrode material precursor for magnesium storage batteries according to claim 14, characterized in that it has the following composition:

16. The positive electrode material precursor for a magnesium storage battery according to claim 14, characterized in that, when used in a positive electrode of a magnesium storage battery and the magnesium storage battery is charged, Li in the composition is released to form a composite structure having a rock salt structure in part of an amorphous phase.

17. a mixing step of mixing an alkali metal, a metal element different from the alkali metal, citric acid, and alcohol in a solvent; a solution combustion step of heating the solution mixed in the mixing step to evaporate the solvent and then combusting the solution to obtain a compound containing the alkali metal and the metal element; a grinding step of grinding the compound obtained in the solution combustion step to obtain a cathode material precursor for a magnesium storage battery composed of nanoparticles; A method for producing a positive electrode material precursor for a magnesium storage battery, comprising:

18. the alkali metal comprises Li; The positive electrode material precursor for the magnesium storage battery is Li, where M is the metal element. ２ MO ３ The composition of The method for producing a positive electrode material precursor for a magnesium storage battery according to claim 17.

19. 19. The method for preparing a cathode material precursor for a magnesium storage battery according to claim 18, wherein M includes Ti and Mo.

20. The cathode material precursor for the magnesium storage battery is Li ２ Ti １／３ Mo ２／３ O ３ 20. The method for producing a positive electrode material precursor for a magnesium storage battery according to claim 19, characterized in that it has a composition of:

21. 18. The method for producing a positive electrode material precursor for a magnesium storage battery according to claim 17, wherein the pulverization step obtains the positive electrode material precursor for a magnesium storage battery having a particle size of less than 10 nm.

22. 22. A method for producing a positive electrode material for a magnesium storage battery, characterized in that the alkali metal in the positive electrode material precursor for a magnesium storage battery obtained by the method for producing a positive electrode material precursor for a magnesium storage battery according to any one of claims 17 to 21 is ion-exchanged with Mg to obtain a positive electrode material for a magnesium storage battery.

23. The method for producing a positive electrode material for a magnesium storage battery according to claim 22, characterized in that the ion exchange is carried out by immersing the positive electrode material precursor for a magnesium storage battery in an electrolyte containing Mg at 80°C or higher for 20 hours or more.

24. A magnesium storage battery comprising a positive electrode containing the positive electrode material for a magnesium storage battery according to any one of claims 1 to 7, and a negative electrode containing magnesium metal.

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