A cathode material for an anion-variable-valence layered sulfide magnesium battery and a preparation method thereof

Abstract

The present invention relates to the technical field of battery materials, and particularly relates to a cathode material for a magnesium battery of an anion-variable-valence layered sulfide and a preparation method thereof. The cathode material comprises Mg n V 1‑x Cr x S2, where 0 ≤ n ≤ 0.5 and 0 < x < 1. The specific preparation method is as follows: Take substances containing Mg source, V source, Cr source, and S source, and mix them evenly according to the atomic molar ratio of Mg:V:Cr:S being n:(1 - x):x:2; Place the mixed raw materials in step one in a closed reaction vessel under the protection of an inert gas; Heat the reaction vessel to 600 - 1400 °C, hold for 2 - 72 h, and after cooling, obtain Mg n V 1‑x Cr x S2. Applying Mg n V 1‑x Cr x S2 to the cathode of a magnesium battery can achieve the technical effects of increasing the working voltage of the battery and improving the energy density of the cathode material.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and particularly relates to a cathode material for an anion-variable-valence layered sulfide magnesium battery and a preparation method thereof. Background Art

[0002] Since the commercialization of lithium-ion battery technology in the 1990s of the last century, it has quickly dominated the energy storage field. Lithium-ion batteries have advantages such as high energy density, long life, and low self-discharge rate, which have greatly promoted the development of technologies such as portable electronic devices, electric vehicles, and drones. However, lithium resources are limited and unevenly distributed. In contrast, magnesium is one of the most abundant chemical elements in the earth's crust. Therefore, the development of magnesium batteries will effectively alleviate the shortage of lithium resources and is of great significance to the development of China's energy storage industry. In addition, magnesium metal can achieve deposition and dissolution with a Coulomb efficiency close to 100% and no dendrite generation. The magnesium metal negative electrode also has advantages such as high volume energy density (3833 mAh cm -3 ) and low redox potential (-2.37 V vs. SHE).

[0003] At present, the development of magnesium batteries is mainly limited by the lack of suitable cathode materials. The ionic radius of magnesium ions is similar to that of lithium ions. Since it carries two units of positive charge and has a large charge density, when diffusing in the cathode material, it generally has a strong electrostatic interaction with the lattice of the cathode material, resulting in slow kinetics, which greatly restricts the development of magnesium battery cathode materials. At present, the research on magnesium battery cathode materials mainly focuses on two categories: transition metal oxides and sulfides. The electrostatic interaction between the sulfide lattice and magnesium ions is weaker than that of oxides, and it has faster reaction kinetics. However, most of the reported sulfide cathode materials are based on the variable valence of simple transition metal elements, and sulfur anions do not participate in the redox reaction. Limited by one electron transfer corresponding to each transition metal element, the capacity is low, and it is difficult to obtain a potential high energy density. Summary of the Invention

[0004] Aiming at the defects of the prior art, the present invention provides a cathode material for an anion-variable-valence layered sulfide magnesium battery and a preparation method thereof, and solves the technical problems of low capacity and low energy density of magnesium batteries existing in the prior art.

[0005] According to the first aspect of the present invention, a cathode material for an anion-variable-valence sulfide magnesium battery is provided, and the cathode material includes Mg n V 1-x Cr x S2, where 0 ≤ n ≤ 0.5 and 0 < x < 1.

[0006] According to another aspect of the present invention, a preparation method for the cathode material of the anion-variable-valence sulfide magnesium battery is provided, which specifically includes the following steps:

[0007] Step 1: Take materials containing Mg source, V source, Cr source, and S source, and mix them evenly according to the atomic molar ratio of Mg: V: Cr: S of n: (1-x): x: 2, wherein 0≤n≤0.5, 0<x<1;

[0008] Step 2: placing the mixed raw materials from step 1 into a sealed reaction vessel under the protection of inert gas;

[0009] Step 3: Heat the reaction vessel to 600~1400℃, maintain for 2~72h, and then cool down to obtain Mg n V 1-x Cr x S2.

[0010] In some embodiments, the Mg source is selected from magnesium and / or magnesium-containing compounds; the V source is selected from vanadium and / or vanadium-containing compounds; the Cr source is selected from chromium and / or chromium-containing compounds; and the S source is selected from sulfur and / or sulfur-containing compounds.

[0011] Preferably, in step three, the heating and cooling rates are both 0.5-20°C / min.

[0012] According to another aspect of the present invention, a magnesium battery is provided, the magnesium battery comprising a positive electrode, a negative electrode and an electrolyte; the positive electrode comprises the positive electrode material Mg n V 1-x Cr x S2; the negative electrode is magnesium.

[0013] Preferably, the positive electrode further includes a conductive additive and a binder.

[0014] Preferably, the Mg n V 1-x Cr x The mass percentage of S2 in the positive electrode is 40%-98%; the mass percentage of the conductive additive in the positive electrode is 1%-40%; and the mass percentage of the binder in the positive electrode is 1%-20%.

[0015] Preferably, the conductive additive is selected from one or more of acetylene black, conductive carbon black, Ketjen black, carbon nanotubes or graphene;

[0016] Preferably, the binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, hydroxymethyl cellulose, sodium alginate, polyacrylic acid or styrene-butadiene rubber.

[0017] Preferably, the electrolyte includes a solute and a solvent. The solute is selected from one or more of magnesium bis(trifluoromethylsulfonyl)imide, magnesium chloride, magnesium trifluoromethanesulfonate, phenylmagnesium chloride, magnesium borohydride, and aluminum chloride; the solvent is selected from one or more of ethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, 1,2-diethoxyethane, dimethyl ether, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether.

[0018] The concentration of the solute in the solvent is 0.01 - 4 mol / L.

[0019] Generally speaking, compared with the prior art, the above technical solutions conceived by the present invention mainly have the following technical advantages.

[0020] 1. The present invention uses the cathode material Mg n V 1-x Cr x S2 of an anion-variable valent layered sulfide for a magnesium battery. The 3d orbit of the transition metal Cr overlaps with the 3p orbit of the non-metal S. During the charge and discharge process of the battery, in the anion-variable valent layered sulfide cathode material Mg n V 1-x Cr x S2, not only do the valence states of the conventional transition metal V cations (+2 and +4) change, but the valence states of the S anions (-1 and -2) also change. Through the change in the valence state of the S anions, high capacity can be achieved. At the same time, the 3d orbits of the transition metals V and Cr have relatively low energy levels, which can increase the working voltage of the battery. The combination of the above high capacity and high working voltage can achieve the technical effect of further improving the energy density of the cathode material.

[0021] 2. The cathode material Mg n V 1-x Cr x S2 of the anion-variable valent layered sulfide magnesium battery of the present invention has a crystal structure of layered sulfide, belonging to the hexagonal crystal system, P m1 space group. In the layered sulfide, the 3d orbit of the transition metal and the 3p orbit of sulfur are highly hybridized, generating highly delocalized electrons on the metal and sulfur, which is beneficial to accommodating the charge of magnesium ions and improving the kinetic performance of the reaction; the layered structure also provides more magnesium ion insertion sites and better diffusion channels, thereby improving the capacity and kinetic performance; at the same time, the transition metal elements V, Cr, etc. that form the layered sulfide have relatively low 3d orbit energy levels and can output a higher working voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 For the layered sulfide Mg n V 1-x Cr xSchematic diagram of the spatial structure of S2.

[0023] Figure 2 For the layered sulfide Mg provided in Examples 1-4 of the present invention 0.5 V 0.5 Cr 0.5 S2, Mg 0.5 V 0.9 Cr 0.1 S2, Mg 0.5 V 0.75 Cr 0.25 S2, Mg 0.5 V 0.25 Cr 0.75 X-ray diffraction pattern of S2 in the charged state.

[0024] Figure 3 For the layered sulfide Mg provided in Example 1 of the present invention 0.5 V 0.5 Cr 0.5 Scanning electron microscope image of S2 in the charged state.

[0025] Figure 4 For the layered sulfide Mg provided in Example 1 of the present invention 0.5 V 0.5 Cr 0.5 Scanning electron microscope element distribution map of S2 in the charged state; in the figure, a is the element distribution map of V, Cr and S; b is the element distribution map of V; c is the element distribution map of S; d is the element distribution map of Cr.

[0026] Figure 5 For the layered sulfide Mg provided in Example 1 of the present invention 0.5 V 0.5 Cr 0.5 Galvanostatic charge-discharge curve of a magnesium battery with S2 as the positive electrode material at a current density of 50 mA g -1 Current density condition.

[0027] Figure 6 For the layered sulfide Mg provided in Example 1 of the present invention 0.5 V 0.5 Cr 0.5 Cycling performance graph of a magnesium battery with S2 as the positive electrode material.

[0028] Figure 7 For the layered sulfide Mg provided in Example 1 of the present invention 0.5 V 0.5 Cr 0.5 Rate performance graph of a magnesium battery with S2 as the positive electrode material.

[0029] Figure 8 For the layered sulfide Mg provided in Example 1 of the present invention 0.5V 0.5 Cr 0.5 Electron energy loss spectra of V atoms in the L3 electron shell collected at different voltages in a magnesium battery.

[0030] Figure 9 The layered sulfide Mg provided in Example 1 of the present invention 0.5 V 0.5 Cr 0.5 Electron energy loss spectra of Cr atoms in the L3 electron shell collected at different voltages in a magnesium battery.

[0031] Figure 10 The layered sulfide Mg provided in Example 1 of the present invention 0.5 V 0.5 Cr 0.5 X-ray photoelectron spectra of V collected at different voltages in a magnesium battery.

[0032] Figure 11 The layered sulfide Mg provided in Example 1 of the present invention 0.5 V 0.5 Cr 0.5 X-ray photoelectron spectra of Cr collected at different voltages in a magnesium battery.

[0033] Figure 12 The layered sulfide Mg provided in Example 1 of the present invention 0.5 V 0.5 Cr 0.5 X-ray photoelectron spectra of S collected at different voltages in a magnesium battery.

[0034] Figure 13 The layered sulfide Mg provided in Example 1 of the present invention 0.5 V 0.5 Cr 0.5 Galvanostatic intermittent titration technique (GITT) test curves of S2 / Mg coin cells.

[0035] Figure 14 The layered sulfide Mg provided in Example 1 of the present invention 0.5 V 0.5 Cr 0.5 Magnesium ion diffusion coefficients in S2 / Mg coin cells.

[0036] Figure 15 The layered sulfide Mg provided in Example 2 of the present invention 0.5 V 0.9 Cr 0.1 Scanning electron microscope images of S2 in the charged state.

[0037] Figure 16 The layered sulfide Mg provided in Example 2 of the present invention 0.5V 0.9 Cr 0.1 The constant current charge-discharge curves of the magnesium battery with S2 as the cathode material under a current density of 50 mA g -1 are shown as follows.

[0038] Figure 17 The scanning electron microscope image of the layered sulfide Mg 0.5 V 0.75 Cr 0.25 S2 in the charged state provided in Example 3 of the present invention.

[0039] Figure 18 The scanning electron microscope image of the layered sulfide Mg 0.5 V 0.75 Cr 0.25 The constant current charge-discharge curves of the magnesium battery with S2 as the cathode material under a current density of 50 mA g -1 are shown as follows.

[0040] Figure 19 The scanning electron microscope image of the layered sulfide Mg 0.5 V 0.25 Cr 0.75 S2 in the charged state provided in Example 4 of the present invention.

[0041] Figure 20 The scanning electron microscope image of the layered sulfide Mg 0.5 V 0.25 Cr 0.75 The constant current charge-discharge curves of the magnesium battery with S2 as the cathode material under a current density of 50 mA g -1 are shown as follows. Detailed Description of the Invention

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0043] According to the first aspect of the present invention, a cathode material for an anion-variable-valence sulfide magnesium battery is provided, and the cathode material includes Mg n V 1-x Cr x S2, where 0 ≤ n ≤ 0.5 and 0 < x < 1.

[0044] According to another aspect of the present invention, a preparation method for the cathode material of the anion-variable-valence sulfide magnesium battery is provided, which specifically includes the following steps:

[0045] Step 1: Take materials containing Mg source, V source, Cr source, and S source, and mix them evenly according to the atomic molar ratio of Mg: V: Cr: S of n: (1-x): x: 2, wherein 0≤n≤0.5, 0<x<1;

[0046] Step 2: placing the mixed raw materials from step 1 into a sealed reaction vessel under the protection of inert gas;

[0047] Step 3: Heat the reaction vessel to 600~1400℃, maintain for 2~72h, and then cool down to obtain Mg n V 1-x Cr x S2.

[0048] In some embodiments, the Mg source is selected from magnesium and / or magnesium-containing compounds; the V source is selected from vanadium and / or vanadium-containing compounds; the Cr source is selected from chromium and / or chromium-containing compounds; and the S source is selected from sulfur and / or sulfur-containing compounds.

[0049] In some embodiments, the mixing in step 1 is specifically: manual grinding in a mortar; or mechanical stirring or ball milling at 50-1000 rpm for 10-1200 minutes.

[0050] In some embodiments, the inert gas in step 2 is a mixture of one or more of argon, nitrogen, helium, neon, krypton, and xenon;

[0051] In some embodiments, the reaction vessel in step 2 is a jointed stainless steel tube, a sealed quartz tube, a reaction kettle or an alloy reactor.

[0052] In some embodiments, in step three, the heating and cooling rates are both 0.5-20°C / min.

[0053] According to another aspect of the present invention, a magnesium battery is provided, comprising a positive electrode, a negative electrode and an electrolyte; the positive electrode comprises the positive electrode material Mg n V 1-x Cr x S2; the negative electrode is magnesium.

[0054] In some embodiments, the positive electrode further includes a conductive additive and a binder.

[0055] In some embodiments, the Mg n V 1-x Cr x The mass percentage of S2 in the positive electrode is 40%-98%; the mass percentage of the conductive additive in the positive electrode is 1%-40%; and the mass percentage of the binder in the positive electrode is 1%-20%.

[0056] In some embodiments, the conductive additive is selected from one or more of acetylene black, conductive carbon black, Ketjen black, carbon nanotubes, or graphene;

[0057] In some embodiments, the binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, hydroxymethyl cellulose, sodium alginate, polyacrylic acid, or styrene-butadiene rubber.

[0058] In some embodiments, the electrolyte includes a solute and a solvent, and the concentration of the solute in the solvent is 0.01 - 4 mol / L.

[0059] In some embodiments, the solute includes one or more of magnesium bis(trifluoromethylsulfonyl)imide, magnesium chloride, magnesium trifluoromethanesulfonate, phenylmagnesium chloride, magnesium borohydride, or aluminum chloride; the solvent includes one or more of ethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, 1,2-diethoxyethane, dimethyl ether, diethylene glycol dimethyl ether, or triethylene glycol dimethyl ether.

[0060] Example 1

[0061] This example provides the preparation and performance testing of a layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 cathode material.

[0062] Synthesis of layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2: Weigh 0.5 mmol of MgS powder, 0.5 mmol of V powder, 0.5 mmol of Cr powder, and 1.5 mmol of S powder, and manually grind them in a mortar for 30 minutes; put the obtained mixed powder into an infrared tablet pressing mold, apply a pressure of 10 MPa to obtain a cylindrical thin sheet, and seal it in a quartz tube filled with argon; place the sealed quartz tube in a tube furnace and heat it at a heating rate of 0.6 °C / min. When the temperature rises to 750 °C, keep it at a constant temperature for 48 hours, then slowly cool it to 250 °C at a rate of 0.5 °C / min, and finally cool it naturally to room temperature to obtain the anion-variable-valence layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2.

[0063] Weigh Mg 0.5 V 0.5 Cr 0.5S2, conductive carbon black (Super P) and polytetrafluoroethylene (PVDF) were dispersed in N-methylpyrrolidone (NMP) to form a slurry. The slurry was coated onto aluminum foil using a doctor blade and dried in an oven to obtain the positive electrode sheet.

[0064] In a glove box filled with argon, the positive electrode sheet, magnesium foil, and a 0.5 M Mg(TFSI)2 2-methoxyethylamine (MOEA) / ethylene glycol dimethyl ether (DME) electrolyte were assembled into a button-type magnesium battery. The magnesium battery was subjected to a constant current charge-discharge test with a voltage range of 0.4 - 2 V and a current density of 50 mA g -1 。

[0065] Figure 3 For the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2, a scanning electron microscope image in the charged state. Figure 4 For the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2, a scanning electron microscope elemental distribution map in the charged state. Figure 5 For the layered sulfide Mg 0.5 V 0.5 Cr 0.5 For the magnesium battery with S2 as the positive electrode material at a current density of 50 mA g -1 The constant current charge-discharge curve under the current density condition. Figure 6 For the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 as the positive electrode material, the cycling performance graph of the magnesium battery with a voltage range of 0.4 - 2 V and a current density of 50 mA g -1 。 Figure 7 For the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 as the positive electrode material, the rate performance graph of the magnesium battery. Figure 8 For the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2, the electron energy loss spectrum of the V atomic L3 electron shell electrons collected at different voltages in the magnesium battery. Figure 9 [[ID=..]]For the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2, the electron energy loss spectrum of the Cr atomic L3 electron shell electrons collected at different voltages in the magnesium battery.Figure 10 The layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 X-ray photoelectron spectra of V collected at different voltages in a magnesium battery. Figure 11 The layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 X-ray photoelectron spectra of Cr collected at different voltages in a magnesium battery. Figure 12 The layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 X-ray photoelectron spectra of S collected at different voltages in a magnesium battery. Figure 13 The layered sulfide Mg 0.5 V 0.5 Cr 0.5 Galvanostatic intermittent titration technique (GITT) test curves of Mg||layered sulfide Mg Figure 14 The layered sulfide Mg 0.5 V 0.5 Cr 0.5 Diffusion coefficients of magnesium ions in Mg||layered sulfide Mg coin cells.

[0066] From Figure 3 it can be seen that the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 is a lamellar structure with particle sizes in the micron range, showing good crystallinity. From Figure 4 it can be seen that the elements in the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 are evenly distributed. From Figure 5 - 6 it can be seen that the discharge capacity of a magnesium battery using the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 as the positive electrode is 154.8 mAh g -1 , and the capacity remains at 96 mAh g in the first 50 cycles -1 , with a Coulombic efficiency close to 100%, indicating that the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 has excellent cycle stability; there are significant voltage plateaus during charge and discharge, demonstrating that the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 undergoes an intercalation reaction in the magnesium battery. FromFigure 7 It can be seen that even at 300 mA g -1 At a current density of 0.5 V 0.5 Cr 0.5 The S2 positive electrode can still release 89 mAh g -1 The capacity shows that it has good rate performance. Figure 8 - 9 It can be seen that the valence state of V undergoes reversible changes during the charge and discharge process, while the valence state of Cr does not change significantly. Figure 10 - 12 It can be seen that the layered sulfide Mg 0.5 V 0.5 Cr 0.5 During the charge and discharge process of S2, both the cation V and the anion S changed valence, that is, the anion valence changed, while no obvious valence change was observed for the Cr element.

[0067] The kinetic properties are discussed further below. 0.5 V 0.5 Cr 0.5 The reaction kinetics of the S2 sample were measured using the constant current intermittent titration technique (GITT) to measure the magnesium ion diffusion coefficient of the sample. In the third cycle, after a discharge cycle or charge cycle at 50 mA / g every 30 minutes, the battery was allowed to relax for 15 minutes under open circuit to reach quasi-equilibrium. The constant current intermittent titration (GITT) method was used to measure the magnesium ion diffusion coefficient of the layered sulfide. 0.5 V 0.5 Cr 0.5 The curve of S2 / Mg button battery is as follows Figure 13 shown. Figure 14 The layered sulfide Mg obtained from the constant current intermittent titration (GITT) method is shown. 0.5 V 0.5 Cr 0.5 The diffusion coefficient of magnesium ions in the S2 / Mg button battery during charge and discharge is higher than that of the layered sulfide Mg 0.5 V 0.5 Cr 0.5 S2 has better dynamic performance.

[0068] Example 2

[0069] This embodiment provides a layered sulfide Mg 0.5 V 0.9 Cr 0.1 Preparation and performance testing of S2 positive electrode materials.

[0070] Layered sulfide Mg 0.5 V 0.9 Cr 0.1Synthesis of MgVCrS₂: Weigh 0.5 mmol of MgS powder, 0.9 mmol of V powder, 0.1 mmol of Cr powder, and 1.5 mmol of S powder, and manually grind them in a mortar for 30 minutes; put the obtained mixed powder into an infrared tablet press mold, apply a pressure of 10 MPa to obtain a cylindrical thin sheet, and seal it into a quartz tube filled with argon; place the sealed quartz tube in a tube furnace and heat it at a heating rate of 0.6 °C / min. When the temperature rises to 750 °C, keep it at a constant temperature for 48 hours, then slowly cool it to 250 °C at a rate of 0.5 °C / min, and finally cool it naturally to room temperature to obtain the layered sulfide Mg 0.5 V 0.9 Cr 0.1 S₂.

[0071] Weigh the layered sulfide Mg 0.5 V 0.9 Cr 0.1 S₂, Super P, and PVDF in a mass ratio of 7:2:1, disperse them into NMP to make a slurry, use a spatula to coat the slurry onto an aluminum foil, and dry it in an oven to obtain a positive electrode plate.

[0072] In a glove box filled with argon, assemble the positive electrode plate, magnesium foil, and 0.5 M Mg(TFSI)₂ MOEA / DME electrolyte into a button-type magnesium battery. Perform a constant current charge-discharge test on the battery, where the voltage range is 0.4 - 2 V and the current density is 50 mA g -1 .

[0073] Figure 15 This is the scanning electron microscope image of the layered sulfide Mg 0.5 V 0.9 Cr 0.1 S₂ in the charged state. Figure 16 This is the constant current charge-discharge curve of the magnesium battery with the layered sulfide Mg 0.5 V 0.9 Cr 0.1 S₂ as the positive electrode material. It can be seen through Figure 15 that the layered sulfide Mg 0.5 V 0.9 Cr 0.1 S₂ has a lamellar structure, and the particle size is in the micron level, showing good crystallinity. It can be seen through Figure 16 that the layered sulfide Mg 0.5 V 0.9 Cr 0.1 S₂ has a discharge capacity of 96 mAh g -1 , and a charge capacity of 95 mAh g -1 .

[0074] Example 3

[0075] This example provides a preparation and performance test of a layered sulfide Mg 0.5 V 0.75 Cr 0.25 S2 cathode material.

[0076] Synthesis of layered sulfide Mg 0.5 V 0.75 Cr 0.25 S2: Weigh 0.5 mmol of MgS powder, 0.75 mmol of V powder, 0.25 mmol of Cr powder, and 1.5 mmol of S powder, and manually grind them in a mortar for 30 minutes; put the obtained mixed powder into an infrared tablet press mold, apply a pressure of 10 MPa to obtain a cylindrical thin sheet, and seal it in a quartz tube filled with argon; place the sealed quartz tube in a tube furnace and heat it at a heating rate of 0.6 °C / min. When the temperature rises to 750 °C, keep it at a constant temperature for 48 hours, then slowly cool it to 250 °C at a rate of 0.5 °C / min, and finally cool it naturally to room temperature; obtain layered sulfide Mg 0.5 V 0.75 Cr 0.25 S2.

[0077] Weigh layered sulfide Mg 0.5 V 0.75 Cr< / / 0.25 S2, Super P, and PVDF in a mass ratio of 7:2:1, disperse them into NMP to make a slurry, use a scraper to coat the slurry on an aluminum foil, and dry it in an oven to obtain a positive electrode sheet.

[0078] In a glove box filled with argon, assemble the positive electrode sheet, magnesium foil, and 0.5 M Mg(TFSI)2 MOEA / DME electrolyte into a button-type magnesium battery. Perform a constant current charge-discharge test on the battery, where the voltage range is 0.4 - 2V and the current density is 50 mA g -1 .

[0079] Figure 17 This is the scanning electron microscope image of the layered sulfide Mg 0.5 V 0.75 Cr 0.25 S2 in the charged state. Figure 18 This is the constant current charge-discharge curve of a magnesium battery using the layered sulfide Mg 0.5 V 0.75 Cr 0.25 S2 as the cathode material. It can be seen through Figure 17 that the layered sulfide Mg 0.5 V0.75 Cr 0.25 S2 has a lamellar structure with particle sizes in the micron range, showing good crystallinity. By Figure 18 it can be seen that the layered sulfide Mg 0.5 V 0.75 Cr 0.25 S2 has a discharge capacity of 127 mAh g -1 , and a charge capacity of 134 mAh g -1 .

[0080] Example 4

[0081] This example provides a preparation and performance test of a layered sulfide Mg 0.5 V 0.25 Cr 0.75 S2 cathode material.

[0082] The synthesis of the layered sulfide Mg 0.5 V 0.25 Cr 0.75 S2: Weigh 0.5 mmol of MgS powder, 0.25 mmol of V powder, 0.75 mmol of Cr powder, and 1.5 mmol of S powder, and manually grind them in a mortar for 30 minutes; put the obtained mixed powder into an infrared tablet press mold, apply a pressure of 10 MPa to obtain a cylindrical thin sheet, and seal it in a quartz tube filled with argon; place the sealed quartz tube in a tube furnace and heat it at a heating rate of 0.6 °C / min. When the temperature rises to 750 °C, keep it at a constant temperature for 48 hours, then slowly cool it to 250 °C at a rate of 0.5 °C / min, and finally cool it naturally to room temperature to obtain the layered sulfide Mg 0.5 V 0.25 Cr 0.75 S2.

[0083] Weigh the layered sulfide Mg 0.5 V 0.25 Cr 0.75 S2, Super P, and PVDF at a mass ratio of 7:2:1, disperse them into NMP to make a slurry, use a scraper to coat the slurry onto an aluminum foil, and dry it in an oven to obtain a positive electrode sheet.

[0084] In a glove box filled with argon, assemble the positive electrode sheet, magnesium foil, and 0.5 M Mg(TFSI)2 MOEA / DME electrolyte into a button-type magnesium battery. Perform a constant current charge-discharge test on the battery, where the voltage range is 0.4 - 2V and the current density is 50 mA g -1 .

[0085] Figure 19 For the layered sulfide Mg provided in Example 4 of the present invention0.5 V 0.75 Cr 0.25 Scanning electron microscope image of S2 in the charged state. Figure 20 The layered sulfide Mg provided in Example 4 of the present invention 0.5 V 0.75 Cr 0.25 Charge-discharge curves of the magnesium battery with S2 as the cathode material. By Figure 19 It can be seen that the layered sulfide Mg 0.5 V 0.25 Cr 0.75 S2 is a lamellar structure with particle sizes in the micron range, showing good crystallinity. By Figure 20 It can be seen that the layered sulfide Mg 0.5 V 0.25 Cr 0.75 The discharge capacity of S2 is 118 mAh g -1 , and the charge capacity is 137 mAh g -1 .

[0086] Figure 2 The layered sulfide Mg provided in Examples 1-4 of the present invention 0.5 V 0.5 Cr 0.5 S2, Mg 0.5 V 0.9 Cr 0.1 S2, Mg 0.5 V 0.75 Cr 0.25 S2, Mg 0.5 V 0.25 Cr 0.75 X-ray diffraction patterns of S2 in the charged state. From Figure 2 It can be seen that the compounds provided in Examples 1-4 of the present invention all have the same crystal structure as the standard layered sulfide VS2, and as the Cr substitution ratio increases, the diffraction peak of X-ray at 15° shifts to the right, indicating that the layer spacing gradually increases.

[0087] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A cathode material for an anion-variable-valence type magnesium sulfide battery, characterized in that, The positive electrode material includes Mg n V 1-x Cr x S2, where 0 ≤ n ≤ 0.5 and 0 < x < 1; the Mg n V 1-x Cr x S2 has a crystal structure of layered sulfide, belonging to the hexagonal crystal system, P m1 space group, where the 3d orbit of the transition metal Cr overlaps with the 3p orbit of the non-metal S; the preparation method of the positive electrode material specifically includes the following steps: Step 1: Take materials containing Mg source, V source, Cr source, and S source, and mix them evenly according to the atomic molar ratio of Mg: V: Cr: S of n: (1-x): x: 2, wherein 0≤n≤0.5, 0<x<1; Step 2: placing the mixed raw materials from step 1 into a sealed reaction vessel under the protection of inert gas; Step 3: Heat the reaction vessel to 600~1400 °C, hold for 2~72 h, and obtain Mg after cooling n V 1-x Cr x S2 2. The preparation method of the cathode material of the anion-variable-valence type magnesium sulfide battery according to claim 1, characterized in that The specific steps include: Step 1: Take materials containing Mg source, V source, Cr source, and S source, and mix them evenly according to the atomic molar ratio of Mg: V: Cr: S of n: (1-x): x: 2, wherein 0≤n≤0.5, 0<x<1; Step 2: placing the mixed raw materials from step 1 into a sealed reaction vessel under the protection of inert gas; Step 3: Heat the reaction vessel to 600 - 1400 °C, hold for 2 - 72 h, and after cooling, obtain Mg n V 1-x Cr x S2 3. The preparation method of the cathode material for the anion variable-valence type magnesium sulfide battery according to claim 2, characterized in that, The Mg source is selected from magnesium and / or magnesium-containing compounds; the V source is selected from vanadium and / or vanadium-containing compounds; the Cr source is selected from chromium and / or chromium-containing compounds; and the S source is selected from sulfur and / or sulfur-containing compounds.

4. The preparation method of the cathode material of the anion-variable-valence type magnesium sulfide battery according to claim 2, wherein In step 3, the heating and cooling rates are both 0.5-20°C / min.

5. A magnesium battery, characterized in that, The magnesium battery comprises a positive electrode, a negative electrode and an electrolyte; the positive electrode comprises the positive electrode material according to claim 1; and the negative electrode is magnesium.

6. The magnesium battery according to claim 5, characterized in that, The positive electrode also includes a conductive additive and a binder.

7. A magnesium battery according to claim 6, characterized in that, The Mg n V 1-x Cr x The mass percentage of S2 in the positive electrode is 40% - 98%; the mass percentage of the conductive additive in the positive electrode is 1% - 40%; the mass percentage of the binder in the positive electrode is 1% - 20%.

8. A magnesium battery according to claim 7, wherein The conductive additive is selected from one or more of acetylene black, conductive carbon black, Ketjen black, carbon nanotubes, and graphene; The binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, hydroxymethyl cellulose, sodium alginate, polyacrylic acid, and styrene-butadiene rubber.

9. A magnesium battery according to claim 5, characterized in that, The electrolyte includes a solute and a solvent; the solute is selected from one or more of magnesium bis(trifluoromethylsulfonyl)imide, magnesium chloride, magnesium trifluoromethylsulfonate, phenylmagnesium chloride, magnesium borohydride, and aluminum chloride; the solvent is selected from one or more of ethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, 1,2-diethoxyethane, dimethyl ether, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether.

10. A magnesium battery according to claim 9, wherein, The concentration of the solute in the solvent is 0.01-4 mol / L.

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