Battery positive electrode material and its preparation method and application

Abstract

This application provides a battery cathode material, its preparation method, and application. The battery cathode material comprises a composite nanomaterial of vanadium pentasulfide and carbon, wherein the composite nanomaterial comprises a heterojunction formed by the vanadium pentasulfide and carbon. This battery cathode material has excellent electrical conductivity and ion transport capabilities, and its application in batteries can help optimize the battery's rate performance.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to battery positive electrode materials, preparation methods, and applications thereof. Background Art

[0002] With the intensification of energy crises and environmental pollution, the development of green and clean energy storage devices has become increasingly important. Lithium-ion batteries (Li-ion batteries) have widespread applications in the energy storage field. However, Li-ion batteries face challenges such as uneven lithium resource distribution, high battery costs, and safety issues, which limit their application. Compared to Li-ion batteries, zinc reserves are abundant, widely distributed, and relatively inexpensive to extract. Furthermore, aqueous Zinc-ion batteries (Zn-ion batteries) offer advantages such as high safety, low cost, high specific capacity, and environmental friendliness, making them promising candidates for large-scale energy storage devices to replace Li-ion batteries. Layered transition metal chalcogenides (TMCs) have excellent chemical stability, and their application in aqueous Zn-ion batteries has attracted considerable attention. However, layered TMCs not only have poor electrical conductivity but can also induce severe anisotropic diffusion, resulting in slow ion transport and hindering the battery's rate performance. Therefore, it is necessary to provide a new cathode material to improve the ion and electron transport efficiency and enhance the battery's electrochemical performance. Summary of the Invention

[0003] In view of this, the present application provides a battery positive electrode material, which has good electrical conductivity and ion transport capability, and its application in batteries is beneficial to improving the rate performance of the battery.

[0004] In a first aspect, the present application provides a battery positive electrode material, comprising a composite nanomaterial of pentavanadium octasulfide and carbon, wherein the composite nanomaterial comprises a heterojunction formed by pentavanadium octasulfide and carbon.

[0005] In the battery positive electrode material of the present application, pentavanadium octasulfide forms a heterojunction with carbon, which can effectively improve the conductivity of the positive electrode material and optimize the ion transmission path, so that active ions can migrate rapidly in the material, thereby obtaining good ion and electron transmission performance, thereby improving the rate performance of the secondary battery.

[0006] Optionally, the pentavanadium octasulfide has a tunnel structure and is a monoclinic crystal system.

[0007] Optionally, the space group of the pentavanadium octasulfide is C 2 / m.

[0008] Optionally, the pore size of the tunnel structure is 0.5nm to 1.5nm

[0009] Optionally, in the composite nanomaterial, the mass percentage of the carbon is 1% to 5%.

[0010] Optionally, the composite nanomaterial is a sheet-like structure, and the thickness of the composite nanomaterial is 5 nm to 20 nm.

[0011] Optionally, the lateral size of the composite nanomaterial is 0.2 μm to 20 μm.

[0012] Optionally, the size of the heterojunction is 2 nm to 20 nm.

[0013] In a second aspect, the present application provides a method for preparing a positive electrode material for a battery, comprising:

[0014] V2CT x -MXene reacts with hydrogen sulfide gas at 600°C to 1000°C to obtain a battery positive electrode material, wherein the battery positive electrode material includes a composite nanomaterial of pentavanadium octasulfide and carbon, and the composite nanomaterial includes a heterojunction formed by pentavanadium octasulfide and carbon.

[0015] Optionally, the V2CT x -MXene is obtained by etching MAX phase powder.

[0016] Optionally, the MAX phase powder includes one or more of V2AlC, V2SiC, V2PC, V2GaC, V2GeC, V2AsC, V2InC, V2SnC, and V2PbC.

[0017] Optionally, the etching comprises: mixing the MAX phase powder with an etchant, and obtaining V2CT after a hydrothermal reaction. x -MXene.

[0018] Optionally, the etchant includes one or more of hydrofluoric acid, hydrochloric acid and lithium fluoride, hydrochloric acid and sodium fluoride, hydrochloric acid and potassium fluoride, hydrochloric acid and zinc fluoride, hydrochloric acid and aluminum fluoride, and hydrochloric acid and calcium fluoride.

[0019] Optionally, the temperature of the hydrothermal reaction is 100° C. to 140° C., and the time of the hydrothermal reaction is 12 h to 48 h.

[0020] Optionally, the flow rate of the hydrogen sulfide gas is 10 mL / min to 30 mL / min.

[0021] Optionally, the V2CT x -MXene reacts with hydrogen sulfide gas at 600℃~1000℃ to obtain a battery positive electrode material, comprising: x -MXene and the first elemental sulfur are placed in the reactor respectively, the first elemental sulfur is close to the gas inlet of the reactor, the V2CT x-MXene is away from the gas inlet of the reactor; a carrier gas is introduced into the reactor, wherein the carrier gas includes hydrogen; the reactor is heated to 200°C to 250°C, kept warm for 0.5h to 1.5h, and then heated to 600°C to 1000°C.

[0022] Optionally, the V2CT x The mass ratio of MXene to the first elemental sulfur is 1:(5-20).

[0023] Optionally, the V2CT x -MXene reacts with hydrogen sulfide gas at 600°C to 1000°C to obtain a battery positive electrode material, further comprising: x -MXene and the second elemental sulfur are pre-mixed and then placed in the reactor; the V2CT x The mass ratio of -MXene to the second elemental sulfur is 1:(0.5-20).

[0024] Optionally, the carrier gas further includes an inert gas, and the volume percentage of hydrogen in the carrier gas is 8% to 12%.

[0025] Optionally, the flow rate of the carrier gas is 10 mL / min to 30 mL / min.

[0026] Optionally, the heating rate of the reactor is 3°C / min to 8°C / min.

[0027] The preparation method of the battery positive electrode material provided in the present application has a simple and controllable process and is easy to operate. The obtained battery positive electrode material has good conductivity and ion transfer rate. Applying it in a battery can enable the battery to have good rate performance.

[0028] In a third aspect, the present application provides a secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive electrode and the negative electrode, wherein the positive electrode comprises the battery positive electrode material described in the first aspect of the present application or the battery positive electrode material obtained by the preparation method of the battery positive electrode material described in the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the reaction process provided in Example 1 of the present application;

[0030] Figure 2 V2CT in Example 1 of this application x -Scanning electron microscopy image of MXene;

[0031] Figure 3 This is a scanning electron microscope image of the V5S8 and C composite nanomaterial in Example 1 of the present application;

[0032] Figure 4 This is a scanning electron microscope image of the V5S8 and C composite nanomaterial in Example 1 of the present application;

[0033] Figure 5 This is the element distribution diagram of the V5S8 and C composite nanomaterial in Example 1 of the present application;

[0034] Figure 6 This is a scanning electron microscope image of the electrode material in Comparative Example 2 of this application;

[0035] Figure 7 This is the element distribution diagram of the positive electrode material in Comparative Example 2 of this application;

[0036] Figure 8 This is a transmission electron micrograph of the V5S8 and C composite nanomaterial in Example 1 of the present application;

[0037] Figure 9 This is a characterization diagram of the heterojunction of the V5S8 and C composite nanomaterials in Example 1 of the present application, wherein: Figure 9 (a) is a representation diagram of the heterojunction structure. Figure 9 (b) is an enlarged view of the heterojunction structure;

[0038] Figure 10 This is a transmission electron microscope image of the positive electrode material in Comparative Example 2 of this application;

[0039] Figure 11 This is a high-resolution transmission electron micrograph of the positive electrode material in Comparative Example 2 of this application;

[0040] Figure 12 This is a thickness characterization diagram of the V5S8 and C composite nanomaterial in Example 1 of the present application;

[0041] Figure 13 XRD comparison diagram of the V5S8 and C composite nanomaterial of Example 1 of the present application and the positive electrode material of Comparative Example 1 and the monoclinic phase of V5S8;

[0042] Figure 14 The thermogravimetric analysis diagram of the V5S8 and C composite nanomaterial and V5S8 of Example 1 of the present application;

[0043] Figure 15 This is the crystal structure diagram of the V5S8 and C composite nanomaterial provided in Example 1 of the present application;

[0044] Figure 16 This is a cycle performance diagram of the secondary battery of Example 1 of the present application at a current of 10 A / g;

[0045] Figure 17 This is a cycle performance diagram of the secondary battery of Example 1 of the present application at a current of 0.5 A / g;

[0046] Figure 18 This is a comparison chart of the cycle performance of the secondary batteries of Example 1 and Comparative Example 2 of the present application at a current of 0.5 A / g;

[0047] Figure 19 This is a rate performance diagram of the secondary battery of Example 1 of the present application;

[0048] Figure 20 This is a comparison chart of the rate performance of the secondary batteries of Example 1 and Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0050] Currently, lithium-ion batteries are widely used in the energy storage field. However, their large-scale application in the future is limited by the shortage and uneven distribution of lithium resources, poor battery safety, and the toxicity and environmental pollution caused by organic systems. Compared with lithium-ion batteries, zinc-ion batteries use aqueous electrolytes and have advantages such as high safety, environmental friendliness, low cost, and ease of assembly. In addition, zinc-ion batteries have high energy density and abundant reserves of battery raw materials, making them highly valuable and promising in the energy storage field. However, their poor rate performance and cycle stability limit their large-scale application. Therefore, it is necessary to develop a positive electrode material for zinc-ion batteries with good rate performance.

[0051] The present application provides a battery positive electrode material, which includes pentavanadium octasulfide and a carbon composite nanomaterial (V5S8 and C composite nanomaterial), wherein carbon coexists with pentavanadium octasulfide and forms a heterojunction. The carbon in the positive electrode material can improve the conductivity of the positive electrode material. The presence of the carbon-containing heterojunction structure can, on the one hand, reduce the diffusion barrier of zinc ions in the positive electrode material, promote the transmission of zinc ions in the positive electrode material, and optimize the transmission path of ions and electrons, thereby increasing the migration rate of ions and electrons, so that the battery can obtain good rate performance; on the other hand, the heterojunction can improve the structural stability of the pentavanadium octasulfide tunnel skeleton, inhibit the lattice change of the tunnel skeleton during the insertion and deinsertion of zinc ions, enhance the robustness of the tunnel skeleton lattice, and enable the battery to have good cycle performance. In some embodiments of the present application, the size of the heterojunction is 2nm to 20nm. The size of the heterojunction can be, but is not limited to, 2nm, 4nm, 8nm, 10nm, 15nm or 20nm.

[0052] In some embodiments of the present application, pentavanadium octasulfide belongs to the monoclinic crystal system and its space group is C2 / m. The pentavanadium octasulfide of the present application has a tunnel-like structure, which is composed of vanadium vacancies arranged in the NiAs-type structure and vanadium atoms that partially occupy one-quarter of the SS octahedral positions between two adjacent VS2 monolayers. This three-dimensional tunnel-like structure can provide multiple ion migration paths, promote the rapid and reversible insertion and extraction of zinc ions, and increase the migration rate of zinc ions in the positive electrode material. In some embodiments of the present application, the pore size of the tunnel structure of the V5S8 and C composite nanomaterial is 0.5nm to 1.5nm. The pore size of the tunnel structure can be, but is not limited to, 0.5nm, 0.8nm, 1nm, 1.1nm, 1.3nm or 1.5nm. In some embodiments, the pore size of the tunnel structure is 0.8nm to 1.3nm. Tunnel structures of this size have good adaptability to zinc ions and are conducive to the migration of zinc ions in the positive electrode material.

[0053] In some embodiments of the present application, the mass percentage of carbon in the V5S8 and C composite nanomaterial is 1% to 5%. The mass percentage of carbon in the V5S8 and C composite nanomaterial can be, but is not limited to, 1%, 1.5%, 2%, 3%, 4%, or 5%. Controlling the carbon content is conducive to the formation of more heterojunctions between carbon and pentavanadium octasulfide, thereby effectively improving the ion and electron transport efficiency of the battery's positive electrode material and enhancing the battery's electrochemical performance. In some embodiments of the present application, the mass percentage of carbon in the V5S8 and C composite nanomaterial is 2% to 4%.

[0054] In some embodiments of the present application, the V5S8 and C composite nanomaterial has a sheet structure. The composite nanomaterial includes nanosheets. The nanosheet structure is beneficial for increasing the contact area between the positive electrode material and the electrolyte and improving the transmission performance of ions and electrons. In some embodiments of the present application, the thickness of the V5S8 and C composite nanomaterial is 5nm to 20nm. The thickness of the V5S8 and C composite nanomaterial can be, but is not limited to, 5nm, 8nm, 10nm, 12nm, 15nm or 20nm. When the thickness of the composite nanomaterial is smaller, it is beneficial to increase the diffusion rate of ions and improve the rate performance of the battery. In some embodiments of the present application, the lateral size of the composite nanomaterial is 0.2μm to 20μm. The lateral size of the composite nanomaterial can be, but is not limited to, 0.2μm, 0.5μm, 1μm, 3μm, 5μm, 10μm, 15μm or 20μm.

[0055] The present application combines carbon with pentavanadium octasulfide to form a composite nanomaterial and applies it as a positive electrode material in a secondary battery. The positive electrode material has good ion and electron transmission performance and structural stability, which is beneficial to improving the rate performance and cycle performance of the secondary battery.

[0056] The present application also provides a method for preparing the above-mentioned battery positive electrode material, comprising the following steps:

[0057] Step 100: Etching the MAX phase powder to obtain V2CT x -MXene;

[0058] Step 200: V2CT x -MXene reacts with hydrogen sulfide gas at 600℃~1000℃ to obtain battery positive electrode material.

[0059] In step 100 of the present application, the MAX phase powder is etched by hydrogen fluoride etching to obtain V2CT x -MXene, in which MAX phase materials are layered compounds composed of three elements, and its general chemical formula is expressed as M n+1 AX n , M represents a transition metal element (vanadium, V in this application), A represents a main group element, X represents carbon or nitrogen (carbon, C in this application), n = 1, 2, 3 ..., V2CT x -MXene is a two-dimensional vanadium carbide, and T in the molecular formula refers to the surface group of the two-dimensional material (such as O, OH, F, NH, etc.). In the embodiment of the present application, the MAX phase powder includes one or more of V2AlC, V2SiC, V2PC, V2GaC, V2GeC, V2AsC, V2InC, V2SnC, and V2PbC. The present application etches the main group elements in the MAX phase powder with hydrogen fluoride to obtain two-dimensional vanadium carbide. Two-dimensional vanadium carbide has a series of unique properties, such as high metallic conductivity, excellent dispersion quality, rich surface groups, etc. Using it as a precursor is beneficial to the preparation of high crystallinity, unique heterojunction structure of vanadium octasulfide and carbon composite nanomaterials in the subsequent process.

[0060] In some embodiments of the present application, the MAX phase powder is etched to obtain V2CT x -MXene includes: mixing MAX phase powder with etchant, and obtaining V2CT after hydrothermal reaction x -MXene, wherein the etchant includes one or more of hydrofluoric acid, hydrochloric acid and lithium fluoride, hydrochloric acid and sodium fluoride, hydrochloric acid and potassium fluoride, hydrochloric acid and zinc fluoride, hydrochloric acid and aluminum fluoride, and hydrochloric acid and calcium fluoride; the temperature of the hydrothermal reaction is 100° C. to 140° C., and the time of the hydrothermal reaction is 12 h to 48 h.

[0061] The MAX phase powder can be etched by the above method to obtain an accordion-shaped V2CT. x -MXene, the accordion-shaped V2CT x-MXene can provide a two-dimensional framework for the formation of composite nanomaterials, which is conducive to the construction of an ordered open tunnel structure in the V5S8 and C composite nanomaterials and ensures the precipitation of heterojunctions, thereby improving the ion and electron transport performance of the positive electrode material. In some embodiments of the present application, the temperature of the hydrothermal reaction during etching is 110°C to 130°C, and the hydrothermal reaction time is 20h to 40h.

[0062] In some embodiments of the present application, hydrochloric acid and lithium fluoride are used as etchants to etch the MAX phase powder to obtain an accordion-shaped V2CT x -MXene, the specific preparation method includes: adding MAX phase powder to a mixed solution of hydrochloric acid and lithium fluoride, stirring for 10 minutes to 60 minutes, transferring the solution to a polytetrafluoroethylene-lined stainless steel autoclave, reacting at 100°C to 140°C for 12 hours to 48 hours, centrifuging the reaction solution to collect the precipitate, washing the precipitate and vacuum drying it at 50°C to 70°C for 1 hour to 20 hours to obtain accordion-shaped V2CT x -MXene. In some embodiments of the present application, the MAX phase powder includes V2AlC, and the aluminum in V2AlC is easily etched, which is beneficial to improving the efficiency of the reaction. In some embodiments of the present application, in the mixed solution of hydrochloric acid and lithium fluoride, the mass ratio of lithium fluoride to hydrochloric acid is 1: (4 to 8). In some embodiments of the present application, the mass ratio of MAX phase powder, lithium fluoride and hydrochloric acid is 1: (1.5 to 3): (6 to 24). In some embodiments of the present application, the mixed solution of hydrochloric acid and lithium fluoride is obtained by dispersing 1.5g to 3g of LiF into 20mL to 40mL of hydrochloric acid with a concentration of 6mol / L to 12mol / L. In some embodiments of the present application, after the reaction solution is centrifuged to collect the precipitate, the precipitate can be washed by first washing with water until the pH of the supernatant is neutral, and then washing with ethanol, so that V2CT x -MXene has high purity.

[0063] In step 200 of the present application, hydrogen sulfide gas (H2S) has strong reducing properties. x -MXene reaction process, V2CT x -Part of the carbon in MXene falls off and reacts to form V5S8, while part of the carbon forms a heterojunction with V5S8 after cooling from high temperature, thereby obtaining a composite nanomaterial of vanadium octasulfide and carbon. In some embodiments of the present application, the flow rate of hydrogen sulfide gas is 10mL / min to 30mL / min. Controlling the flow rate of hydrogen sulfide gas is beneficial to V2CT x -MXene fully reacts to obtain a battery cathode material with good conductivity. In some embodiments of the present application, V2C xThe temperature for the reaction with hydrogen sulfide gas is 600℃~1000℃. When the reactor reaches the reaction temperature and then cools naturally, the positive electrode material of the battery is obtained. x The temperature for the reaction of MXene with hydrogen sulfide gas may be, but is not limited to, 600°C, 700°C, 750°C, 800°C, 850°C, 900°C or 1000°C. Controlling V2CT x The temperature and time of the reaction between MXene and hydrogen sulfide gas are conducive to the formation of a structurally stable composite nanomaterial of vanadium octasulfide and carbon, ensuring that the material has good electrical conductivity.

[0064] In the present application, hydrogen sulfide gas (H2S) can be directly introduced into the reactor, or hydrogen sulfide gas can be prepared in the reactor. In some embodiments of the present application, hydrogen sulfide gas is obtained by the reaction of elemental sulfur and hydrogen. Since there is no ready-made H2S gas for sale on the market and H2S gas itself is toxic, it is more reliable to obtain H2S by indirect methods from the perspective of raw materials and experimental safety. In addition, when elemental sulfur is used as the raw material, S vapor also has reducing properties at high temperatures and can react with V2CT. x -MXene reacts to generate V5S8, making the reaction more complete. In some embodiments of the present application, in order to improve the efficiency of the reaction, elemental sulfur is mixed with hydrogen and V2CT x -MXene in the same reactor. In some embodiments, the preparation method of the battery positive electrode material comprises: x -MXene and the first elemental sulfur are placed in the reactor respectively, wherein the first elemental sulfur is close to the gas inlet of the reactor, V2CT x -MXene is kept away from the air inlet of the reactor; a carrier gas including hydrogen is introduced into the reactor; the reactor is heated to 200℃~250℃, kept at this temperature for 0.5h~1.5h, and then heated to 600℃~1000℃. After the reactor reaches the set temperature, it is naturally cooled to obtain the positive electrode material of the battery. During the heating process of the reactor, elemental sulfur sublimates above 200℃ to form sulfur vapor. As the temperature continues to rise, sulfur vapor is also continuously generated and reacts with hydrogen in the carrier gas to form hydrogen sulfide gas. The hydrogen sulfide gas further reacts with V2CT x -MXene reaction to obtain a composite nanomaterial of vanadium octasulfide and carbon. In some embodiments of the present application, V2CT x -The mass ratio of MXene to the first elemental sulfur is 1:(5-20). xThe mass ratio of -MXene to the first elemental sulfur can be, but is not limited to, 1:5, 1:8, 1:10, 1:12, 1:15, or 1:20. In some embodiments of the present application, the heating rate of the reactor during the heating process is 3°C / min to 8°C / min. Controlling the heating rate of the reactor can ensure that the sulfur vapor and hydrogen react fully, thereby generating sufficient hydrogen sulfide gas and V2CT. x -MXene reaction.

[0065] In some embodiments of the present application, V2CT x -MXene and the second elemental sulfur are pre-mixed and then placed in the reactor, that is, part of the elemental sulfur in the reactor is located near the air inlet (upstream of the air flow), and part of the elemental sulfur is mixed with V2C x Mix directly. x -MXene mixed with a second elemental sulfur and placed in a reactor can further accelerate the reaction process and promote the formation of composite nanomaterials of vanadium octasulfide and carbon. In some embodiments of the present application, V2CT x -The mass ratio of MXene to the second elemental sulfur is 1:(0.5~20). x The mass ratio of -MXene to the second elemental sulfur can be, but is not limited to, 1:0.5, 1:0.8, 1:1, 1:2, 1:5, 1:10, 1:15, or 1:20. In some embodiments, the mass ratio of the first elemental sulfur to the second elemental sulfur is 1:(0.5-2). In some embodiments of the present application, V2CT x The MXene and the second elemental sulfur are mixed by grinding the mixture in an agate mortar for 5 to 20 minutes.

[0066] In some embodiments of the present application, the carrier gas includes hydrogen and an inert gas, and the volume percentage of hydrogen in the carrier gas is 8% to 12%. The volume percentage of hydrogen in the carrier gas can be, but is not limited to, 8%, 9%, 10% or 12%. Controlling the hydrogen content is conducive to fully converting sulfur powder into hydrogen sulfide, and the safety of the reaction is higher. In some embodiments of the present application, the inert gas can be one or more of nitrogen, helium, argon and hydrogen. In some embodiments of the present application, the flow rate of the carrier gas is 10mL / min to 30mL / min. In the embodiments of the present application, the reactor can be a tubular furnace.

[0067] The preparation method provided in this application is simple and easy to implement. x -MXene is used as a precursor and processed with a specific process to obtain a composite nanomaterial of vanadium octasulfide and carbon. The resulting material has high electrical conductivity and ion transfer rate. Its application in batteries is beneficial to improving the battery's rate performance.

[0068] The present application also provides a positive electrode sheet, which includes a current collector and a positive electrode material layer provided on the current collector, wherein the positive electrode material layer includes the battery positive electrode material of the present application. In the present application, the preparation of the positive electrode material layer can be to mix the battery positive electrode material, the conductive agent, the binder and the solvent to form a positive electrode slurry, and the positive electrode slurry is coated and dried to obtain the positive electrode material layer. Among them, the conductive agent, the binder and the solvent are conventional choices in the battery field. For example, the binder can be selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC) and sodium alginate. The conductive agent can be selected from one or more of carbon nanotubes, acetylene black and graphene.

[0069] The present application also provides a secondary battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive electrode and the negative electrode, wherein the positive electrode comprises the battery positive electrode plate provided in the present application.

[0070] In some embodiments of the present application, the negative electrode may include a metal zinc sheet or a zinc alloy sheet. In some embodiments of the present application, the separator may be one or more of a polyolefin microporous membrane, a polyethylene non-woven fabric-based membrane, a polypropylene-based membrane, and a glass fiber-based membrane.

[0071] In the present application, the electrolyte of the secondary battery includes an aqueous zinc salt solution. In embodiments of the present application, the zinc salt may be one or more of Zn(OTF)2 (zinc trifluoromethanesulfonate), zinc perchlorate, zinc sulfate, zinc chloride, and zinc acetate. In embodiments of the present application, the concentration of the zinc salt in the electrolyte is 0.1 mol / L to 15 mol / L. In some embodiments of the present application, the concentration of the zinc salt in the electrolyte is 1 mol / L to 4 mol / L.

[0072] The secondary battery provided by the present application has good rate performance and cycle performance due to the use of the battery positive electrode material of the present application.

[0073] The present application also provides an electronic device, which includes the secondary battery.

[0074] The technical solution of this application is further described below with reference to a number of embodiments.

[0075] Example 1

[0076] 1) Preparation of a battery positive electrode material, comprising:

[0077] V2CT xPreparation of -MXene: 1.0g of V2AlC powder was slowly added to a LiF and HCl solution (2.0g LiF was dispersed in 30mL of 12mol / L HCl) over 10 minutes. After stirring at room temperature for 30 minutes, the solution was transferred to a 50mL polytetrafluoroethylene-lined stainless steel autoclave and sealed at 120°C for 36 hours. The turbid suspension obtained after the reaction was centrifuged to collect the precipitate, washed with water and centrifuged repeatedly until the pH of the supernatant was neutral. The precipitate was further washed with ethanol and dried in vacuum at 60°C for 12 hours to obtain V2CT. x -MXene.

[0078] Preparation of vanadium octasulfide and carbon composite nanomaterials: V2CT x -MXene and sulfur powder were mixed in a weight ratio of 0.1:1 (0.2gV2CT x -MXene, and 2g of sulfur powder) were mixed and ground in an agate mortar for 10 minutes to obtain a mixed powder. Subsequently, 2g of sulfur powder was taken and placed in two separate corundum boats. The 2g of sulfur powder was placed upstream of the tube furnace, and the mixed powder was placed in the middle of the tube furnace. A carrier gas composed of H2 (8% by volume) and Ar (92% by volume) was introduced into the tube furnace. Figure 1 , Figure 1 This is a schematic diagram of the reaction process provided in Example 1 of the present application, Figure 1 In the process, sulfur powder is located on the side of the tube furnace close to the air inlet, V2CT x The mixture of -MXene and sulfur powder was located on the side away from the air inlet. The tube furnace was heated to 200°C at a heating rate of 5°C / min, kept at this temperature for 1 hour, then heated to 800°C at a heating rate of 5°C / min. After cooling to room temperature, the V5S8 and C composite nanomaterial was obtained.

[0079] 2) Preparation of secondary batteries:

[0080] Preparation of the battery positive electrode: V5S8 and C composite nanomaterials were mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 7:2:1. After being fully ground in an agate mortar, an appropriate amount of N-methylpyrrolidone was added and stirred in a dispersion and degassing mixer for 15 minutes to obtain a positive electrode slurry. The positive electrode slurry was coated on the surface of a titanium foil with a thickness of 0.01 mm using a doctor blade (100 μm) and dried under vacuum conditions to prepare a positive electrode sheet. The positive electrode sheet was cut into discs with a diameter of 12 mm as the positive electrode.

[0081] Preparation of electrolyte: Water and polyethylene glycol (400 mesh) were mixed in a mass ratio of 1:1 as a solvent to prepare a Zn(OTF)2 solution with a concentration of 3 mol / L as the electrolyte.

[0082] Preparation of the battery: A zinc foil disc with a diameter of 14 mm and a thickness of 0.1 mm is used as the negative electrode, and a glass fiber separator is used as the separator. The positive electrode, negative electrode, and separator are assembled into a battery cell, and the electrolyte is injected to obtain a secondary battery.

[0083] Comparative Example 1

[0084] A preparation method for a battery positive electrode material, comprising:

[0085] V2CT was prepared by the same method as in Example 1. x -MXene, V2CT x -MXene and sulfur powder were mixed in a weight ratio of 0.1:1 (0.2g V2CT x -MXene, 2g sulfur powder) were mixed, and the mixture was ground in an agate mortar for 10 minutes to fully mix to obtain a mixed powder. The mixed powder was placed in a corundum porcelain boat and placed on the middle side of a tube furnace. A carrier gas was introduced into the tube furnace, and the carrier gas composition was H2 (8%, volume percentage) -Ar (92%, volume percentage). The tube furnace was heated to 200°C at a heating rate of 5°C / min, kept warm for 1h, and then heated to 800°C at a heating rate of 5°C / min. After cooling to room temperature, the positive electrode material was obtained. The battery was prepared using the same method as in Example 1.

[0086] Comparative Example 2

[0087] A preparation method for a battery positive electrode material, comprising:

[0088] V2O5 and sulfur powder were mixed in a weight ratio of 0.1:1 and ground in an agate mortar for 10 minutes to thoroughly mix to obtain a mixed powder. Subsequently, 2g of sulfur powder was taken and placed in two separate corundum boats, each containing 2g of sulfur powder and the mixed powder. The 2g of sulfur powder was placed upstream of a tube furnace, and the mixed powder was placed in the middle of the tube furnace. A carrier gas consisting of H2 (8% by volume) and Ar (92% by volume) was introduced into the tube furnace. The tube furnace was heated to 200°C at a heating rate of 5°C / min, held at this temperature for 1 hour, and then heated to 800°C at a heating rate of 5°C / min. After cooling to room temperature, the positive electrode material was obtained. A battery was prepared using the same method as in Example 1.

[0089] Effect embodiment

[0090] In order to verify the structure and performance of the battery positive electrode material prepared in this application, this application also provides an effect embodiment.

[0091] 1) The morphology of the material was characterized using a field emission electron microscope (model: JSM-7800F & TEAM Octane Plus), see Figure 2, Figure 2 V2CT in Example 1 of this application x -Scanning electron microscope image of MXene, by Figure 2 It can be seen that V2CT x -MXene has an accordion-like morphology and a distinct layered structure. Figure 3 , Figure 3 This is a scanning electron microscope image of the V5S8 and C composite nanomaterial in Example 1 of the present application, Figure 3 It can be seen that the composite nanomaterial has a sheet-like structure. Figure 4 , Figure 4 This is a scanning electron microscope image of the V5S8 and C composite nanomaterial in Example 1 of the present application, Figure 4 It can be seen that the lateral size of the V5S8 and C composite nanomaterials is 3μm to 20μm. Figure 4 From the perspective of field emission scanning electron microscopy combined with EDS spectrometer, the element distribution of V5S8 and C composite nanomaterials was characterized. Figure 5 The element distribution diagram of the V5S8 and C composite nanomaterials in Example 1 of this application is as follows: Figure 5 It can be seen that the C, V and S elements are evenly distributed in the material. Figure 6 , Figure 6 This is a scanning electron microscope image of the electrode material in Comparative Example 2 of this application, Figure 6 It can be seen that the positive electrode material prepared in Comparative Example 2 is in the shape of a large round cake. The lateral size of the positive electrode material is 10 μm to 20 μm. Figure 6 From the perspective of field emission scanning electron microscopy combined with EDS spectrometer, the element distribution of the positive electrode material was characterized. Figure 7 This is the element distribution diagram of the positive electrode material in Comparative Example 2 of this application, Figure 7 It can be seen that the positive electrode material in Comparative Example 2 does not contain carbon element.

[0092] The morphology of the material was characterized using a high-resolution transmission electron microscope (model: Tecnai G2 F30). Figure 8 , Figure 8 This is a transmission electron microscope image of the V5S8 and C composite nanomaterial in Example 1 of the present application, Figure 8 It can be seen that the V5S8 and C composite nanomaterials exhibit an obvious two-dimensional layered structure. Figure 9 , Figure 9 This is a characterization diagram of the heterojunction of the V5S8 and C composite nanomaterials in Example 1 of the present application, wherein: Figure 9 (a) is a representation diagram of the heterojunction structure. Figure 9 (b) is an enlarged view of the heterojunction structure. Figure 9In (a), it can be seen that V5S8 has high crystallinity (obvious lattice fringes), and carbon presents an amorphous lattice. A heterojunction is formed between carbon (Carbon) and vanadium octasulfide (V5S8) in the composite nanomaterial. Figure 9 In (b), we can see that the lattice spacing of the V5S8 crystal plane is 0.287nm, which corresponds to the (022) crystal plane of V5S8. Figure 10 , Figure 10 This is a transmission electron microscope image of the positive electrode material in comparative example 2 of this application, Figure 10 It can be seen that the positive electrode material of Comparative Example 2 is very thick. Figure 11 , Figure 11 This is a high-resolution transmission electron microscope image of the positive electrode material in Comparative Example 2 of this application, Figure 11 It can be seen that the positive electrode material of Comparative Example 2 exhibits highly ordered stripes and is a crystalline structure, and does not contain amorphous stripes, indicating that the positive electrode material of Comparative Example 2 does not contain a heterojunction.

[0093] The thickness of nanosheets in V5S8 and C composite nanomaterials was characterized by atomic force microscopy (Model: Dimension Edge, Bruker, America). Figure 12 , Figure 12 This is a thickness characterization diagram of the V5S8 and C composite nanomaterial in Example 1 of this application. Figure 12 It can be seen that the thickness of the V5S8 and C composite nanosheets is 5nm to 20nm.

[0094] 2) X-ray diffractometer (Bruker, D8 Advance with Cu-Kα radiation) was used to characterize the phase structure of the material. Figure 13 , Figure 13 This is an XRD comparison diagram of the V5S8 and C composite nanomaterial of Example 1 of the present application and the positive electrode material of Comparative Example 1 and the monoclinic phase of V5S8. Figure 13 In the figure, the curves from top to bottom are respectively the XRD characterization curve of the positive electrode material of Comparative Example 1, the XRD characterization curve of the V5S8 and C composite nanomaterial of Example 1, and the standard curve of the monoclinic phase of V5S8 (JCPDS NO.81-1595). Figure 13 It can be seen that the V5S8 and C composite nanomaterial in Example 1 is consistent with the V5S8 characterization curve of the monoclinic phase, indicating that the V5S8 in the composite nanomaterial of the present application belongs to the monoclinic system. The positive electrode material curve of Comparative Example 1 is not consistent with the standard curve, which indicates that the sulfur powder and V2CT in Comparative Example 1 are combined. x -The product obtained by directly mixing and calcining MXene is different from the product of the present application, and it cannot obtain the V5S8 and C composite nanomaterials of the present application.

[0095] 3) The carbon content in the composite nanomaterial in Example 1 was analyzed using a thermogravimetric analyzer. Figure 14 , Figure 14 The thermogravimetric analysis diagram of V5S8 and C composite nanomaterials and V5S8 in Example 1 of this application is shown in FIG. Figure 14 The mass percentage of carbon in the composite nanomaterial can be calculated. Specifically, Figure 14 In the embodiment 1, the mass loss of the composite nanomaterial at 800°C is 14.24%, and the mass loss of pure V5S8 at 800°C is 10.21%, that is, the mass of carbon decomposed in the composite nanomaterial is 14.24%-10.21%=3.03%. Therefore, the mass percentage of carbon in the V5S8 and C composite nanomaterial in Example 1 is 3.03%.

[0096] 4) The crystal structure of the V5S8 and C composite nanomaterials in Example 1 was analyzed using VESTA software. Figure 15 , Figure 15 The crystal structure diagram of the V5S8 and C composite nanomaterial provided in Example 1 of this application is shown in FIG. Figure 15 It can be seen that the V5S8 crystal structure in the V5S8 and C composite nanomaterials shows an obvious tunnel structure.

[0097] 5) The electrochemical performance of the secondary battery of Example 1 was tested using a Blue Power test system (model: CT2001A, Wuhan Blue Power Co., Ltd.) and an electrochemical workstation (model: IVIUMnSTAT, IVIUM, the Netherlands). The specific test conditions were as follows: the battery was first activated at a current density of 0.5 A / g for 20 cycles, then charged to 1.9 V at a constant current of 10 A / g at room temperature, and then discharged to 0.3 V at a constant current of 10 A / g. The discharge and charge capacities of the battery were recorded. After 8000 cycles of charge and discharge, the discharge capacity at the 8000th cycle was recorded, and the capacity retention rate after the cycle was calculated. Please refer to Figure 16 , Figure 16 The cycle performance diagram of the secondary battery of Example 1 of the present application at a current of 10A / g is shown by Figure 16 It can be seen that the secondary battery of Example 1 has a specific capacity of 100.8 mAh / g at a current density of 10 A / g, and has a capacity of 83.3 mAh / g after 8,000 cycles, with a capacity retention rate of 83.1%.

[0098] See also Figure 17 , Figure 17 This is a cycle performance diagram of the secondary battery of Example 1 of the present application at a current of 0.5A / g, Figure 17It can be seen that the secondary battery of Example 1 has a specific capacity of 253.3 mAh / g at a current density of 0.5 A / g, and a capacity retention rate of 99% after 200 cycles. It can be seen that the battery made with the positive electrode material of Example 1 of the present application has good cycle stability and high charge-discharge specific capacity. Figure 18 , Figure 18 The graph is a comparison of the cycle performance of the secondary batteries of Example 1 and Comparative Example 2 of the present application at a current of 0.5 A / g, wherein the light curve is the battery cycle curve of Example 1, and the dark curve is the battery cycle curve of Comparative Example 2. Figure 18 It can be seen that under the same test conditions, the secondary battery of the embodiment of the present application has a higher capacity retention rate.

[0099] See also Figure 19 , Figure 19 This is a rate performance diagram of the secondary battery of Example 1 of the present application, Figure 19 It can be seen that after 50 cycles at different current densities, the specific capacity of the secondary battery of Example 1 can be restored to the initial value at the same current density, that is, it has good reversibility. This shows that the use of the battery positive electrode material of the present application can enable the battery to have high rate performance and good cycle stability. Figure 20 , Figure 20 The figure is a comparison of the rate performance of the secondary batteries of Example 1 and Comparative Example 2 of the present application, wherein the light-colored curve is the battery cycle curve of Example 1, and the dark-colored curve is the battery cycle curve of Comparative Example 2. Figure 20 It can be seen that under the same test conditions, the secondary battery of the embodiment of the present application has better rate performance.

[0100] The above is a preferred embodiment of the present application, but it should not be construed as limiting the scope of the present application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present application, and such improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A battery positive electrode material, characterized in that A composite nanomaterial comprising pentavanadium octasulfide and carbon, wherein the composite nanomaterial comprises a heterojunction formed by pentavanadium octasulfide and carbon; The pentavanadium octasulfide is a monoclinic crystal with a tunnel structure; In the composite nanomaterial, the mass percentage of the carbon is 1% to 5%.

2. The battery positive electrode material according to claim 1, wherein The pore size of the tunnel structure is 0.5 nm to 1.5 nm.

3. The battery positive electrode material according to claim 1 or 2, characterized in that The composite nano material is a sheet-like structure, the thickness of the composite nano material is 5 nm to 20 nm, and the lateral size of the composite nano material is 0.2 μm to 20 μm.

4. A method for preparing a positive electrode material for a battery, characterized in that: include: V2CT x -MXene reacts with hydrogen sulfide gas at 600°C~1000°C to obtain a battery positive electrode material, wherein the battery positive electrode material includes a composite nanomaterial of pentavanadium octasulfide and carbon, and the composite nanomaterial includes a heterojunction formed by pentavanadium octasulfide and carbon.

5. The preparation method according to claim 4, wherein The V2CT x- The battery positive electrode material is obtained by reacting MXene with hydrogen sulfide gas at 600℃~1000℃, comprising: x -MXene and the first elemental sulfur are placed in the reactor respectively, the first elemental sulfur is close to the gas inlet of the reactor, the V2CT x -MXene is away from the gas inlet of the reactor; a carrier gas is introduced into the reactor, wherein the carrier gas includes hydrogen; the reactor is heated to 200°C~250°C, kept warm for 0.5h~1.5h, and then heated to 600°C~1000°C.

6. The preparation method according to claim 5, wherein The V2CT x -The mass ratio of MXene to the first elemental sulfur is 1:(5~20).

7. The preparation method according to claim 5 or 6, characterized in that The V2CT x -MXene reacts with hydrogen sulfide gas at 600℃~1000℃ to obtain a battery positive electrode material, further comprising: x -MXene and the second elemental sulfur are pre-mixed and then placed in the reactor; the V2CT x The mass ratio of -MXene to the second elemental sulfur is 1:(0.5~20).

8. A secondary battery, characterized in that: The invention comprises a positive electrode, a negative electrode, an electrolyte and a separator located between the positive electrode and the negative electrode, wherein the positive electrode comprises the battery positive electrode material according to any one of claims 1 to 3 or the battery positive electrode material obtained by the preparation method of the battery positive electrode material according to any one of claims 4 to 7.

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