Cathode material and cathode material precursor for magnesium storage batteries, method for producing a cathode material precursor for magnesium storage batteries and method for producing a cathode material, and magnesium storage batteries

Abstract

The present invention provides a positive electrode material and a positive electrode material precursor for magnesium batteries that can reduce the operating temperature and have excellent cycle characteristics, a method for producing a positive electrode material precursor and a method for producing a positive electrode material for magnesium batteries, and a magnesium battery. [Solution] The positive electrode material for magnesium batteries consists of a compound containing Mg, has a free volume, and has a composite structure in which a part of the amorphous phase has a rock salt-type structure. 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 positive electrode material and a positive electrode material precursor for magnesium storage batteries, a method for producing a positive electrode material precursor for magnesium storage batteries, a method for producing a positive electrode material, and a magnesium storage battery. [Background technology]

[0002] Rechargeable magnesium batteries (RMBs) are attracting attention as a next-generation battery alternative to lithium-ion batteries (LIBs). By using magnesium metal as the negative electrode, magnesium batteries can achieve excellent energy density, and because magnesium is abundant in the Earth's crust, they can be manufactured relatively inexpensively.

[0003] Conventionally, oxide materials with high oxidation-reduction potentials have been expected to be used as cathode materials for magnesium batteries in order to achieve high energy density. However, oxide materials have the problem that solid-phase diffusion of Mg in the material is extremely slow compared to monovalent Li oxides and Na oxides due to the large electrostatic interactions between divalent Mg ions in the material and oxide ions and other cations (see, for example, Non-Patent Document 1).

[0004] Therefore, to solve this problem, cathode materials employing a spinel structure (see, for example, Non-Patent Document 2 or 3) or a rock salt-type 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] Furthermore, since amorphous superionic conductors exist in lithium-ion batteries, cathode materials utilizing amorphous phases were also anticipated. However, it has been reported that cathodes made of FePO4 with amorphous surfaces actually degrade electrode characteristics because the amorphous phase hinders Mg insertion (see, for example, Non-Patent Document 5). [Prior art documents]

Non-Patent Literature

[0006]

Non-Patent Literature 1

Non-Patent Literature 2

Non-Patent Literature 3

Non-Patent Literature 4

Non-Patent Literature 5

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-50055 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In the positive electrode material made of MgCr2O4 having a spinel structure described in Non-Patent Literature 2, the diffusion rate of Mg is theoretically comparable to that of lithium-ion electrode materials, but there is an energy limit, and it has the problem that it hardly functions as a positive electrode. Furthermore, in the positive electrode material having a spinel structure described in Non-Patent Literature 3, it is operated under conditions of 150°C to promote Mg diffusion, and there is a problem that further reduction in the operating temperature is necessary for practical application.

[0009] In the positive electrode material having a rock salt-type structure described in Non-Patent Document 4, Mg insertion and desorption at 90°C are achieved by promoting Mg diffusion through the synergistic effect of vacancies, Li, and Mg. However, for practical application, there was a challenge in that further reduction of the operating temperature was necessary. In addition, in the positive electrode material having a layered rock salt-type structure described in Patent Document 1, the specific surface area is 30 m². 2 Using composite oxides with a capacity of 1 / g or more allows operation even at temperatures near room temperature, but there was a problem in that the capacity rapidly decreased and the cycle characteristics deteriorated with repeated charging and discharging.

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

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

[0012] The positive electrode material for magnesium batteries according to the present invention ensures a pathway for Mg through the free volume in the amorphous phase, facilitating Mg diffusion. Therefore, it can be used as the positive electrode in magnesium batteries, and when used as such, Mg insertion and removal can be achieved even at temperatures near room temperature, reducing the operating temperature to near room temperature. Furthermore, because the free volume is maintained by the amorphous phase, the positive electrode material for magnesium batteries according to the present invention suppresses capacity degradation during repeated charging and discharging cycles, resulting in excellent cycle characteristics.

[0013] The positive electrode material for a magnesium storage battery according to the present invention preferably comprises a compound in which a metal element is bonded to a metal oxide, a metal chalcogenide, a metal halide, or a substance that becomes a polyvalent anion when ionized, and in particular, the compound preferably contains Mg and a metal oxide. In this case, the insertion and deinsertion of Mg can be further promoted at temperatures near room temperature, and better cycle characteristics can be obtained.

[0014] Also, when the compound contains a metal oxide, it is preferable that the metal oxide contains Ti and Mo. In this case, Mo can lower the reduction potential, and Ti can stabilize Mo to suppress elution, so that the insertion and desorption of Mg can be further promoted, and more excellent cycle characteristics can be obtained. The compound is Mg a Li b Ti c Mo d It may have a composition of O3 (where 0.8 ≦ a + b ≦ 1.2, a / (a + b) ≧ 0.7, 0.25 ≦ c ≦ 0.45, 0.55 ≦ d ≦ 0.75). At this time, Mg a Li b Ti 1 / 3 Mo 2 / 3 Preferably has a composition of O3. Also, the compound is Mg a Ti b Mo c It may have a composition of O (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 positive electrode material for a magnesium storage battery according to the present invention preferably consists of nanoparticles having a particle diameter smaller than 10 nm. In this case, at a temperature near room temperature, the insertion and desorption of Mg can be further promoted, and more excellent cycle characteristics can be obtained.

[0016] The precursor of the positive electrode material for a magnesium storage battery according to the first aspect of the present invention is characterized by being composed of a compound containing an alkali metal and having a composite structure having a rock salt-type structure in a part of the amorphous phase.

[0017] The method for producing a positive electrode material precursor for a magnesium battery according to the present invention is a first method for producing a positive electrode material precursor for a magnesium battery according to the present 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 an alcohol in a solvent; a solution combustion step of heating the solution mixed in the mixing step to evaporate the solvent and further combustion to obtain a compound containing the alkali metal and the metal element; and a pulverization step of pulverizing the compound obtained in the solution combustion step to obtain a positive electrode material precursor for a magnesium battery consisting of nanoparticles.

[0018] The first positive electrode material precursor for magnesium batteries according to the present invention is suitably produced by the method for producing a positive electrode material precursor for magnesium batteries according to the present invention. The method for producing a positive electrode material precursor for magnesium batteries according to the present invention involves uniformly mixing the raw materials in a mixing step and utilizing a combustion reaction in a solution combustion step to obtain fine particles having a uniform layered rock salt type structure. Furthermore, by further grinding in a grinding step until nanoparticles are obtained, the rock salt type structure can be partially retained to form an amorphous phase, and a composite structure having a rock salt type structure in part of the amorphous phase can be obtained. Thus, the method for producing a positive electrode material precursor for magnesium batteries according to the present invention can produce the first positive electrode material precursor for magnesium batteries according to the present invention.

[0019] In the method for producing a positive electrode material precursor for magnesium batteries according to the present invention, the mixing step, solution combustion step, and grinding step may each be carried out by any method, including existing methods. For example, the mixing step and the solution combustion step may be carried out using the Pechini process, and the solution combustion step may be carried out using a solution combustion method. Alternatively, the solution combustion method may be used in combination with the heat treatment of the Pechini process. Furthermore, the grinding step may be carried out using a ball mill or a hand mill.

[0020] The first positive electrode material precursor for a magnesium storage battery according to the present invention and a method for producing the same, wherein the compound is preferably composed of a metal oxide, a metal chalcogenide, a metal halide, or a substance in which a metal element is bonded to a substance that becomes a polyvalent anion when ionized, and the alkali metal, and in particular the alkali metal is Li, and the compound preferably has a composition of Li2MO3 (where M is one or more types of metal elements). Furthermore, it is preferable that M includes Ti and Mo, and the compound is Li2Ti 1 / 3 Mo 2 / 3 It is preferable that the composition contains O3. Furthermore, it is preferable that the cathode material precursor for magnesium batteries consists of nanoparticles with a particle size smaller than 10 nm.

[0021] The second positive electrode material precursor for magnesium storage batteries according to the present invention is characterized by having a composition of Li2MO3 (where M is a plurality of metal elements), having a layered rock salt type structure, and M containing Ti and Mo.

[0022] The second positive electrode material precursor for magnesium batteries according to the present invention may be manufactured by any method, for example, by an existing method such as the Peccini process. The second positive electrode material precursor for magnesium batteries according to the present invention is Li2Ti 1 / 3 Mo 2 / 3 It is preferable that the composition has O3. In this case, particularly excellent cycle characteristics can be obtained. Furthermore, it is preferable that the second positive electrode material precursor for magnesium batteries according to the present invention is used as the positive electrode of a magnesium battery and, when the magnesium battery is charged, Li in the composition is desorbed to form a composite structure having a rock salt type structure in part of the amorphous phase.

[0023] The present invention relates to a method for producing a positive electrode material for a magnesium battery, characterized in that a positive electrode material for a magnesium battery is obtained by ion-exchanging the alkali metal of the positive electrode material precursor for a magnesium battery obtained by the method for producing a positive electrode material precursor for a magnesium battery according to the present invention with Mg. Alternatively, the present invention relates to a method for producing a positive electrode material for a magnesium battery, characterized in that a positive electrode material for a magnesium battery is obtained by ion-exchanging the alkali metal of the first or second positive electrode material precursor for a magnesium battery according to the present invention with Mg.

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

[0025] In the method for producing a positive electrode material for a magnesium battery according to the present invention, the method for ion-exchanging the alkali metal of the positive electrode material precursor for a magnesium battery with Mg may be any method that enables ion exchange. Examples of ion exchange methods include immersing the positive electrode material precursor for a magnesium battery in an electrolyte containing Mg at a predetermined temperature for a predetermined time, or using the positive electrode material precursor for a magnesium battery as the positive electrode and performing one or more charging cycles. When immersing in an electrolyte, it is preferable to immerse the positive electrode material precursor for a magnesium battery in an electrolyte containing Mg at 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 a positive electrode material for magnesium storage batteries 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 near room temperature because its positive electrode contains the positive electrode material for magnesium storage batteries according to the present invention, and has excellent cycle characteristics. [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 producing a positive electrode material precursor for a magnesium storage battery and a method for producing a positive electrode material, and a magnesium storage battery. [Brief explanation of the drawing]

[0029] [Figure 1] This graph shows the time change of the cation ratio [Mg / (Mg+Li)] at electrolyte temperatures of 60°C and 90°C in an ion exchange test in which Li, a precursor of the positive electrode material for a magnesium battery, is ion-exchanged with Mg, according to the first embodiment of the present invention. [Figure 2] This is a scanning electron microscope (SEM) image of a positive electrode material precursor for a magnesium battery obtained by the method for producing a positive electrode material precursor for a magnesium battery according to the first embodiment of the present invention. [Figure 3] This is the X-ray diffraction (XRD) spectrum of a positive electrode material for a magnesium battery obtained by the method for producing a positive electrode material for a magnesium battery according to the first embodiment of the present invention. [Figure 4] This is a scanning transmission electron microscope (STEM) image of a positive electrode material for a magnesium battery obtained by the method for producing a positive electrode material for a magnesium battery according to the first embodiment of the present invention. [Figure 5]The graphs show (a) the relationship between capacity and cell voltage at 1, 2, 5, 10, 20, and 60 cycles in a constant current charge-discharge test using a full cell battery consisting of a 3-electrode cell with a magnesium battery cathode material obtained by the method for manufacturing a magnesium battery cathode material according to the first embodiment of the present invention, and (b) the relationship between the number of cycles and capacity. [Figure 6] The graphs show (a) the relationship between capacity and cell voltage at 1, 2, 5, and 10 cycles, and (b) the relationship between the number of cycles and capacity, for a constant current charge-discharge test using a full cell battery consisting of coin cells using the magnesium battery positive electrode material obtained by the method for manufacturing a magnesium battery positive electrode material according to the first embodiment of the present invention. [Figure 7] The graphs show (a) the relationship between capacity and potential at 1, 2, 5, and 15 cycles, and (b) the relationship between the number of cycles and capacity, for a constant current charge-discharge test using a full cell battery consisting of a three-electrode beaker cell using the magnesium battery positive electrode material obtained by the method for producing a magnesium battery positive electrode material according to the second embodiment of the present invention. [Figure 8] Figure 7 shows the X-ray diffraction spectra of the magnesium battery cathode material precursor obtained by the method for producing the magnesium battery cathode material precursor according to the second embodiment of the present invention, as well as the cathode material for the magnesium battery during 1 cycle, 2 cycles, 5 cycles, and 15 cycles of charge-discharge testing shown in Figure 7. [Figure 9] Figure 7 shows a transmission electron microscope (TEM) image of the positive electrode material for a magnesium battery during discharge after 15 cycles of the charge-discharge test, and the Fourier transform pattern (inset) of the area enclosed by the rectangle. [Figure 10]This diagram illustrates the charge-discharge mechanism of a positive electrode material precursor and positive electrode material for a magnesium battery according to a second embodiment of the present invention. (a) Positive electrode material precursor for a magnesium battery (as-synthesized state), (b) Positive electrode material for a magnesium battery formed by the first charge, and (c) Reversible cycle of subsequent charge and discharge. [Modes for carrying out the invention]

[0030] Embodiments of the present invention will be described below with reference to the drawings and examples.

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

[0032] The positive electrode material for the magnesium battery of the first embodiment of the present invention consists of nanoparticles with a particle size smaller than 10 nm, and Mg a Li b Ti 1 / 3 Mo 2 / 3 It consists of a compound having the composition O3 (where 0.8 ≤ a + b ≤ 1.2, a / (a + b) ≥ 0.7). Furthermore, the positive electrode material for the magnesium battery of the first embodiment of the present invention has a composite structure having free volume and a rock salt type structure in part of the amorphous phase.

[0033] The positive electrode material for magnesium batteries according to the first embodiment of the present invention has a free volume in the amorphous phase that ensures a pathway for Mg, and facilitates the diffusion of Mg. For this reason, it can be used as the positive electrode of a magnesium battery, and when used as a positive electrode, Mg insertion and deinsertion can be achieved even at temperatures near room temperature, and the operating temperature can be reduced to near room temperature. Furthermore, because the free volume of the positive electrode material for magnesium batteries according to the first embodiment of the present invention is maintained by the amorphous phase, the decrease in capacity when charging and discharging is repeated can be suppressed, and it has excellent cycle characteristics. Moreover, because the positive electrode material for magnesium batteries according to the first embodiment of the present invention consists of nanoparticles with a particle size smaller than 10 nm, Mg insertion and deinsertion can be further promoted at temperatures near room temperature, and even better cycle characteristics can be obtained.

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

[0035] Furthermore, especially when the compound contains a metal oxide, it is preferable that the metal oxide contains both Ti and Mo. In this case, the reduction potential can be lowered by Mo, and the elution can be suppressed by Ti, thereby further promoting the insertion and removal of Mg and obtaining better cycling characteristics.

[0036] The positive electrode material for a magnesium battery according to the first embodiment of the present invention can be manufactured using a magnesium battery positive electrode material precursor obtained by the method for manufacturing a magnesium battery positive electrode material precursor according to the first embodiment of the present invention. That is, the method for manufacturing a magnesium battery positive electrode material precursor according to the first embodiment of the present invention comprises a mixing step, a solution combustion step, and a grinding step.

[0037] In a specific example, the mixing and solution combustion processes utilize the Pezzini process, with solution combustion used as the heat treatment for the Pezzini process. Specifically, in the mixing process, an alkali metal, a different metal element, citric acid, and alcohol are mixed in a solvent. In the solution combustion process, the solution mixed in the mixing process is heated to evaporate the solvent, and then combusted to obtain a compound containing the alkali metal and metal element. Thus, by uniformly mixing the raw materials in the mixing process and utilizing the combustion reaction in the solution combustion process, fine particles with a uniform layered rock salt-type structure can be obtained. The composition of the resulting particulate compound varies depending on the type of alkali metal and metal element used as raw materials, but in a specific example, by using Li as the alkali metal and Ti and Mo as metal elements, Li2Ti is obtained. 1 / 3 Mo 2 / 3 It has an O3 composition.

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

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

[0040] Furthermore, the mixing and solution combustion steps may be carried out using any method capable of producing a compound containing the desired alkali metal and metal element, not limited to the Peccini process or solution combustion method, but including existing methods. Also, the grinding step may be carried out using any method capable of producing nanoparticles, not limited to methods using a ball mill or the like.

[0041] The positive electrode material for a magnesium battery according to the first embodiment of the present invention can be manufactured using the magnesium battery positive electrode material precursor thus obtained, by the method for manufacturing the magnesium battery positive electrode material according to the first embodiment of the present invention. That is, the method for manufacturing the magnesium battery positive electrode material according to the first embodiment of the present invention involves ion exchange of the alkali metal in the obtained magnesium battery positive electrode material precursor with Mg. In a specific example, ion exchange is performed by immersing the magnesium battery positive electrode material precursor in an electrolyte containing Mg at a predetermined temperature for a predetermined time. This makes it possible to obtain the magnesium battery positive electrode material according to the first embodiment of the present invention.

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

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

[0044] Using the method for producing a cathode material precursor and a cathode material for a magnesium battery according to the first embodiment of the present invention, a cathode material precursor and a cathode material for a magnesium battery were produced, and full-cell testing was performed.

[0045] To produce a precursor material for the cathode of a magnesium battery, first, the Pezzini process is used to produce lithium nitrate (LiNO3), titanium tetraisopropyl hydroxide ([(CH3)2CHO]4Ti), and ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 A mixture of (-4H2O), ammonium nitrate (NH4NO3), citric acid, and propylene glycol was placed in a container and stirred at 80°C to 120°C for 4 hours. The mixture was dried at 60°C to 70°C for 48 hours, and then heat-treated by solution combustion at 600°C for 10 hours in a 10% H2-Ar atmosphere.

[0046] The powder obtained after heat treatment was placed in a ball mill with the solvent dimethyl carbonate (DMC) and ground in an Ar atmosphere at 500 rpm for 5 minutes, repeating this 40 times. The powder after grinding in the ball mill was placed in a hand mill and further ground inside a sealed container, a glove box. In this way, Li2Ti was obtained, consisting of nanoparticles. 1 / 3 Mo 2 / 3 A precursor cathode material for magnesium batteries having an O3 composition was obtained.

[0047] Next, a conductive additive and a binder were mixed with the obtained magnesium battery positive electrode material precursor to prepare a composite electrode. This composite electrode was immersed in an electrolyte of Mg[TFSA]2 / G3 to exchange Li with Mg in the composite electrode. After immersion, the composite electrode was washed with acetonitrile and dried. This yielded a positive electrode material for a magnesium battery.

[0048] To investigate the immersion conditions during ion exchange, an ion exchange test was conducted. The test used a composite electrode prepared by mixing the obtained magnesium battery cathode material precursor with a conductive additive and a binder, along with an electrolyte of Mg[TFSA]2 / G3. The cation ratio [Mg / (Mg+Li)] in the composite electrode was determined by inductively coupled plasma atomic emission spectrometry (ICP-OES) after immersion in the electrolyte at 60°C or 90°C for 24, 72, and 168 hours. The test results are shown in Figure 1.

[0049] As shown in Figure 1, when immersed in an electrolyte solution at 90°C, the cation ratio reached 0.7 or higher after 24 hours, confirming that ion exchange was progressing sufficiently. However, when immersed in an electrolyte solution at 60°C, the cation ratio only reached about 0.6 even after 168 hours, confirming that ion exchange was not progressing well.

[0050] As shown in Figure 1, in the following, the composite electrode was used after ion exchange of Li with Mg by immersing it in an electrolyte of Mg[TFSA]2 / G3 at 90°C for 24 hours. The composition of the positive electrode material for magnesium storage batteries obtained under these conditions was analyzed by inductively coupled plasma atomic emission spectrometry (ICP-OES), and it was found that, including vacancies, Mg 0.27 Li 0.08 (Hollow) 0.32 Ti 0.11 Mo 0.22 The answer was O.

[0051] Figure 2 shows a scanning electron microscope (SEM) image of the obtained positive electrode material precursor for magnesium batteries. As shown in Figure 2, it was confirmed that the positive electrode material precursor for magnesium batteries consists of fine particles (primary particles), and that secondary particles are formed by the aggregation of these primary particles or by the formation of complexes with residual carbon.

[0052] Furthermore, Figure 3 shows the X-ray diffraction spectrum obtained from X-ray diffraction analysis of the resulting magnesium battery cathode material. Figure 4 shows a scanning transmission electron microscope (STEM) image of the obtained magnesium battery cathode material.

[0053] As shown in Figure 3, the positive electrode material for magnesium batteries exhibited peaks corresponding to the (200) and (220) planes, and a gentle peak (halo peak) was observed around 2θ=10. From these results, it was confirmed that the positive electrode material for magnesium batteries contains a mixture of rock salt-type and amorphous structures. Considering the manufacturing process, it is thought that the positive electrode material for magnesium batteries had a layered rock salt-type structure after heat treatment (before pulverization), which became amorphous upon pulverization, and that it has a composite structure in which a part of the amorphous phase has a rock salt-type structure. Furthermore, the crystallite size was determined from the (200) and (220) peaks shown in Figure 3 using Scherrer's equation to be 2.1 nm to 4.3 nm.

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

[0055] Next, a constant current charge-discharge test was performed using a full cell battery consisting of three electrodes, employing the obtained positive electrode material for magnesium storage batteries. In the test, the positive electrode 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) at a concentration of 1 M in G3 solvent was used as the reference electrode RE. In addition, 300 μL of a solution of Mg[B(HFIP)4]2 at a concentration of 0.3 M in G3 solvent was used as the electrolyte. A commercially available glass fiber filter paper (product name "Whatman® GF / F") was used as the separator.

[0056] The test involved charging and discharging 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 the number of cycles and capacity. As shown in Figures 5(a) and (b), it was confirmed that the 3-electrode cell operated at room temperature, exhibiting a discharge capacity of 100 mAh / g or more up to 10 cycles and a discharge capacity of 60 mAh / g or more up to 30 cycles.

[0057] The insertion and removal of Mg from the working electrode (positive electrode material for magnesium batteries) during charging and discharging in the test was confirmed by inductively coupled plasma atomic emission spectrometry (ICP-OES). The composition of the positive electrode material for magnesium batteries during charging and discharging in the third cycle was analyzed using ICP-OES and is shown in Table 1. As shown in Table 1, the amount of Mg increased and decreased during charging and discharging, confirming that Mg insertion and removal were occurring. Furthermore, the capacity was equivalent to 93 mAh / g, which was confirmed to be 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 performed using a full-cell battery consisting of coin cells with the obtained positive electrode material for magnesium storage batteries. In the test, the positive electrode 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). In addition, 100 μL of a solution of Mg[B(HFIP)4]2 mixed with G3 solvent at a concentration of 0.3 M was used as the electrolyte. A commercially available glass fiber filter paper (product name "Whatman® GF / F") was used as the separator.

[0060] The tests involved charging and discharging 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 6(a) shows the relationship between capacity and cell voltage after 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 even coin cells operate at room temperature and exhibit discharge capacities of 50 mAh / g or more up to 3 cycles, and 60 mAh / g or more from 4 to 10 cycles.

[0061] [Positive electrode material for magnesium storage battery according to a second embodiment of the present invention] Figures 7 to 10 show a positive electrode material and a positive electrode material precursor for a magnesium battery according to a second embodiment of the present invention, a method for producing a positive electrode material precursor for a magnesium battery, a method for producing a positive electrode material, and a magnesium battery. In the following description, redundant explanations of the same configurations and operations as those of the first embodiment of the present invention will be omitted.

[0062] The positive electrode material for the magnesium battery of the second embodiment of the present invention consists of nanoparticles with a particle size of 10 nm or more and 20 nm or less, and Mg a Ti b Mo c It consists of a compound having the composition O (where 0.10 ≤ a ≤ 0.20, 0.10 ≤ b ≤ 0.20, 0.20 ≤ c ≤ 0.35). The positive electrode material for a magnesium battery of the second embodiment of the present invention has a composite structure having free volume and a rock salt type structure in part of the amorphous phase.

[0063] In the second embodiment of the present invention, the positive electrode material for a magnesium battery has a pathway for Mg secured by the free volume in the amorphous phase, and Mg diffusion proceeds easily. Therefore, when used as the positive electrode of a magnesium battery, Mg insertion and deinsertion can be achieved even at temperatures close to room temperature, and the material can function as a positive electrode. Furthermore, since the positive electrode material for a magnesium battery in the second embodiment of the present invention consists of nanoparticles with a particle size of 10 nm to 20 nm, Mg insertion and deinsertion can be further promoted at temperatures close to room temperature, and excellent cycle characteristics can be obtained.

[0064] The positive electrode material for the magnesium battery of the second embodiment of the present invention can be manufactured using a positive electrode material precursor for the magnesium battery of the second embodiment of the present invention, which is manufactured, for example, by the Pezzini method. In a specific example, the positive electrode material precursor for the magnesium battery of the second embodiment of the present invention has a layered rock salt type structure and Li2Ti 1 / 3 Mo 2 / 3 It has the composition of O3. Li2Ti 1 / 3 Mo 2 / 3 O3 is a quasi-binary oxide of Li2MoO3 and Li2TiO3, which are Li-rich layered oxides (LLOs). The cathode material precursor for the magnesium battery in the second embodiment of the present invention is not limited to the Pezzini method; other methods, such as existing methods, may be used.

[0065] The positive electrode material for a magnesium battery according to the second embodiment of the present invention can be manufactured using the magnesium battery positive electrode material precursor obtained in this way and by the method for manufacturing the magnesium battery positive electrode material according to the second embodiment of the present invention. That is, the method for manufacturing the magnesium battery positive electrode material according to the second embodiment of the present invention involves ion exchange of the alkali metal in the obtained magnesium battery positive electrode material precursor with Mg. In a specific example, ion exchange is performed by using the magnesium battery positive electrode material precursor as the positive electrode of a magnesium battery and charging it once or more times. At this time, Li in the composition is desorbed by ion exchange, forming a composite structure having a rock salt type structure in a part of the amorphous phase. In this way, the magnesium battery positive electrode material according to the second embodiment of the present invention can be obtained.

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

[0067] The cathode material precursor and cathode material for magnesium storage batteries according to the second embodiment of the present invention can contribute to charge compensation associated with the insertion and removal of Li and Mg by the valence change of Mo between +4 and +6 during charging and discharging. Furthermore, the stabilization of Mo by Ti can suppress dissolution. As a result, the removal of Li and the insertion and removal of Mg can be further promoted, and excellent cycle characteristics can be obtained.

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

[0069] A cathode material for a magnesium battery according to a second embodiment of the present invention was manufactured and tested in a full cell. First, to manufacture the cathode material precursor for the magnesium battery, the Pechini process was used to produce lithium nitrate (LiNO3), titanium tetraisopropyl hydroxide ([(CH3)2CHO]4Ti), and ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 A mixture of (-4H2O), citric acid, and propylene glycol was placed in a container and stirred at 70°C to 100°C for 4 hours. The mixture was gradually heated to 200°C over 4 hours, dried at 200°C for 12 hours, and then the resulting solid was ground in a mortar. The resulting powder was heat-treated in air at 450°C for 10 hours, then placed in a ball mill with the solvent dimethyl carbonate (DMC), and ground at 500 rpm for 5 minutes, 40 times in an Ar atmosphere. After that, the dimethyl carbonate was dried to obtain a powder which was then mixed with a sucrose solution using N-methyl-2-pyrrolidone as the solvent. 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 material precursor for magnesium batteries was obtained, having an O3 composition and a layered rock salt structure. The crystallite size of the obtained cathode material precursor for magnesium batteries was 10.3 nm.

[0071] Next, a composite electrode was prepared by mixing a conductive additive and a binder with the obtained positive electrode material precursor for magnesium storage batteries. Using this composite electrode, a constant current charge-discharge test was performed with 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 lithium foil immersed in 1M Li(TFSA) / DEME-TFSA was used as the reference electrode RE. In addition, Mg(TFSA)2 / G3 with a molar ratio of 1 / 2.22 was used as the electrolyte.

[0072] The test involved 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. The results showed that a specific capacity of approximately 90 mAh / g was obtained during the initial 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 revealed that Li was desorbed during the initial charge, and that in subsequent cycles, reversible insertion and desorption of Li and Mg occurred in accordance with the charge-discharge cycles.

[0073] Therefore, after charging for the 10th cycle, when almost all of the Li was desorbed, each electrode was cleaned, and the electrolyte was replaced with an unused one. A charge-discharge test was then performed in a situation where only Mg contributed to insertion and desorption. As a result, the specific capacity and cycle characteristics were obtained to be almost the same as before cleaning each electrode and replacing the electrolyte, confirming that reversible insertion and desorption occurred even with only Mg. The relationship between capacity and potential at cycles 1, 2, 5, and 15 is shown in Figure 7(a), and the relationship between the number of cycles and capacity is shown in Figure 7(b). As shown in Figures 7(a) and (b), it was confirmed that the device operated at 60°C, close to room temperature, and exhibited a discharge capacity of 60 mAh / g or more up to 20 cycles.

[0074] Figure 8 shows the X-ray diffraction spectra obtained from powder X-ray diffraction analysis of the resulting positive electrode material precursor for magnesium batteries, as well as the composite electrode (positive electrode material for magnesium batteries) during 1, 2, 5, and 15 charge-discharge cycles in the charge-discharge test. As shown in Figure 8, the positive electrode material precursor for magnesium batteries has a layered rocksalt structure at the time of manufacture (As-synth.), and it was confirmed that it undergoes a phase transformation to a composite structure of amorphous phase and rocksalt structure during the first charge (1st ch.), becoming the positive electrode material for magnesium batteries. Furthermore, from the ratio of the peak area derived from the amorphous phase to the peak area derived from the rocksalt structure after the first charge, it is considered that the amorphous phase accounts for the majority. From these findings, it is considered that the positive electrode material for magnesium batteries has a composite structure in which a part of the amorphous phase has a rocksalt structure.

[0075] Figure 9 shows a transmission electron microscope (TEM) image of the positive electrode material for a magnesium battery during discharge after 15 charge-discharge cycles. The Fourier transform pattern of the area enclosed by the rectangle in Figure 9 is shown as an inset. Since no clear spots are observed in the inset, the presence of an amorphous phase is confirmed. Furthermore, the results of a compositional analysis of the area enclosed by the rectangle in Figure 9 using scanning transmission electron microscopy / energy-dispersive spectroscopy (STEM / EDS) are shown in Figure 9. The numbers in parentheses in the compositional data represent the error in the last digit of each compositional ratio. From the results shown in Figure 9, the presence of Mg in the amorphous phase is confirmed, suggesting that the amorphous phase contributes to the insertion and deinsertion of Mg.

[0076] Figure 10 shows the charge-discharge mechanism of the positive electrode material precursor and positive electrode material for magnesium batteries, which can be inferred from the above results. As shown in Figure 10, the positive electrode material precursor for magnesium batteries (As-synthesized state) during manufacturing has a layered rock salt type structure in which layers containing Li, Mo, and Ti (TM / Li layer) and layers of Li (Li layer) are layered, and because the atoms are arranged regularly, the activation barrier is large in the crystalline phase (see Figure 10(a)). When this positive electrode material precursor for magnesium batteries is used as the positive electrode of a magnesium battery, Li is desorbed during the first charge (1st charging), and a composite structure with a rock salt type structure in part of the amorphous phase is formed (see Figure 10(b)), becoming the positive electrode material for magnesium batteries. At this time, the free volume (vacancies) increases due to the desorption of Li, and the arrangement of atoms becomes random due to the amorphous phase, so a pathway with a small activation barrier is formed. This allows for the diffusion of Mg and enables the reversible insertion and removal of Mg, resulting in excellent cycle characteristics and the ability to repeatedly perform reversible charge and discharge cycles (see Figure 10(c)).

Claims

1. A positive electrode material for magnesium storage batteries, characterized by comprising a compound containing Mg, having free volume, and possessing a composite structure in which a part of the amorphous phase has a rock salt-type structure.

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

3. The positive electrode material for a magnesium storage battery according to claim 1, characterized in that the compound comprises Mg and a metal oxide.

4. The positive electrode material for a magnesium battery according to claim 3, characterized in that the metal oxide contains Ti and Mo.

5. The aforementioned compound is Mg ａ Li ｂ Ti ｃ Mo ｄ O ３ The positive electrode material for a magnesium storage battery according to claim 3, characterized by having the following composition: (wherein 0.8 ≤ a + b ≤ 1.2, a / (a + b) ≥ 0.7, 0.25 ≤ c ≤ 0.45, 0.55 ≤ d ≤ 0.75).

6. The positive electrode material for a magnesium battery according to claim 1, characterized in that it consists of nanoparticles with a particle size smaller than 10 nm.

7. The aforementioned compound is Mg ａ Ti ｂ Mo ｃ The positive electrode material for a magnesium storage battery according to claim 3, characterized by having a composition of O (where 0.10 ≤ a ≤ 0.20, 0.10 ≤ b ≤ 0.20, 0.20 ≤ c ≤ 0.35).

8. A precursor material for a magnesium battery cathode, characterized by comprising an alkali metal-containing compound and having a composite structure in which a part of the amorphous phase has a rock salt-type structure.

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

10. The alkali metal is composed of Li, The compound is Li ２ MO ３ (where M is one or more metal elements) having a composition of A characteristic feature of the cathode material precursor for a magnesium storage battery according to claim 8.

11. The positive electrode material precursor for a magnesium battery according to claim 10, characterized in that M comprises Ti and Mo.

12. The compound is Li ２ Ti １／３ Mo ２／３ O ３ A cathode material precursor for a magnesium storage battery according to claim 11, characterized by having the following composition.

13. The cathode material precursor for a magnesium battery according to claim 8, characterized in that it consists of nanoparticles with a particle size smaller than 10 nm.

14. Li ２ MO ３ A precursor material for a magnesium battery cathode, characterized by having a composition of multiple metallic elements (where M is a combination of multiple metallic elements), a layered rock salt structure, and M containing Ti and Mo.

15. Li ２ Ti １／３ Mo ２／３ O ３ A cathode material precursor for a magnesium storage battery according to claim 14, characterized by having the following composition.

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

17. A mixing step involves mixing an alkali metal, a metal element different from the alkali metal, citric acid, and alcohol in a solvent. A solution combustion step is performed to obtain a compound containing the alkali metal and the metal element by heating the solution mixed in the above mixing step to evaporate the solvent and further burning it. The process involves grinding the compound obtained in the solution combustion step to obtain a precursor of a positive electrode material for a magnesium battery consisting of nanoparticles, A method for producing a positive electrode material precursor for magnesium storage batteries, characterized by having the following properties.

18. The alkali metal is composed of Li, The positive electrode material precursor for the magnesium battery is, if the metal element is M, Li ２ MO ３ Having the composition A method for producing a positive electrode material precursor for a magnesium storage battery, as described in claim 17.

19. The method for producing a positive electrode material precursor for a magnesium battery according to claim 18, characterized in that M comprises Ti and Mo.

20. The positive electrode material precursor for the magnesium storage battery is Li ２ Ti １／３ Mo ２／３ O ３ A method for producing a positive electrode material precursor for a magnesium storage battery according to claim 19, characterized by having the following composition.

21. The method for producing a positive electrode material precursor for a magnesium battery according to claim 17, characterized in that the grinding step yields a positive electrode material precursor for a magnesium battery having a particle size smaller than 10 nm.

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

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

24. A magnesium storage battery characterized by having a positive electrode containing the positive electrode material for magnesium storage batteries described in any one of claims 1 to 7, and a negative electrode containing magnesium metal.

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