Sodium battery positive electrode material with heterostructure as well as preparation method and application of sodium battery positive electrode material

Abstract

The invention relates to the technical field of batteries, and discloses a sodium battery positive electrode material with a heterostructure and a preparation method and application thereof.The preparation method comprises the steps that 1, a nickel source, a manganese source and a first solvent are subjected to first mixing, and a solution A is obtained; carrying out second mixing on a niobium source and a second solvent to obtain a solution B; (2) under a protective atmosphere, carrying out a co-precipitation reaction on the solution A, the solution B, a precipitator solution and a complexing agent solution to obtain a first precursor material; (3) performing third mixing on the first precursor material, a lithium source and a sodium source, and performing first heat treatment to obtain a second precursor material; and (4) carrying out second heat treatment on the second precursor material to obtain the sodium battery positive electrode material with the heterostructure. According to the preparation method provided by the invention, a coprecipitation reaction is combined with a two-time heat treatment process, and the cathode material with a heterostructure, which is uniform in distribution and stable in structure, is prepared, so that the electrochemical performance of a battery is improved.

Description

Technical Field

[0001] This invention relates to the field of batteries, specifically to a sodium-ion cathode material with a heterostructure, its preparation method, and its application. Background Technology

[0002] Lithium-doped sodium-ion layered oxide cathode materials are considered promising candidates for power batteries due to their high energy density, cost advantages, and reliable safety. However, the practical application of these materials still faces several key challenges: irreversible anionic redox reactions easily occur under high voltages, the intrinsic diffusion coefficient of sodium ions is low, electrochemical reactions are preferentially initiated from the surface, the materials are prone to irreversible phase transitions during cycling, and interfacial stability is poor. These issues limit further breakthroughs in their electrochemical performance. Therefore, improving the overall performance by controlling and optimizing the crystal structure of cathode materials has become a current research focus.

[0003] Among numerous structural control strategies, constructing heterostructures has attracted widespread attention due to its ability to effectively suppress irreversible phase transitions during cycling, enhance interfacial stability, improve ion / electron transport dynamics, and alleviate micro-stress within materials, thereby significantly improving rate performance and structural durability. However, existing methods for preparing heterostructures suffer from the following drawbacks: First, at the process level, the rapid quenching process used in conventional preparation processes can cause structural stress and processing difficulties in the material. Because this process requires the high-temperature sintered block cathode material to be quickly immersed in a low-temperature solution, the inner and outer layers of the material generate huge thermal stress due to rapid and uneven shrinkage. This stress not only easily leads to the generation of microcracks in the material and reduces the structural integrity, but also makes it difficult to accurately control the overall uniformity of the prepared "disordered rock salt / layered heterostructure", thus restricting its performance improvement effect.

[0004] Secondly, at the structural selection level, the existing technology for constructing rock-salt phase heterostructures inherently suffers from kinetic bottlenecks. The high ion migration barrier in the rock-salt phase leads to a relatively low sodium ion diffusion rate. Therefore, even if such a heterostructure is successfully constructed, it is not the optimal choice in terms of rate performance and kinetic characteristics.

[0005] Third, in terms of overall benefits, the rapid quenching process used in the preparation of cathode materials by existing technologies is a post-processing technology with stringent requirements for equipment and process control. It not only increases the complexity of operation and safety hazards, but the performance gains it brings are also limited by the aforementioned stress and structural type issues, resulting in a low overall "cost-effectiveness". Summary of the Invention

[0006] In view of this, the present invention provides a sodium-doped cathode material with a heterostructure, its preparation method and application, to solve the problems that existing preparation processes cannot guarantee the structural integrity and uniformity of lithium sodium-doped cathode materials, cannot prepare cathode materials with excellent rate performance and kinetic performance, and have complex preparation processes, high cost and high energy consumption.

[0007] In a first aspect, the present invention provides a method for preparing a sodium-ion cathode material with a heterostructure, the method comprising the following steps: (1) The nickel source, manganese source and the first solvent are mixed to obtain solution A; The niobium source and the second solvent are mixed a second time to obtain solution B; (2) Under a protective atmosphere, the solution A and the solution B undergo a co-precipitation reaction with the precipitant solution and the complexing agent solution to obtain the first precursor material; (3) The first precursor material is mixed with lithium source and sodium source in a third mixture, and then the product obtained after the third mixture is subjected to a first heat treatment to obtain the second precursor material; (4) The second precursor material is subjected to a second heat treatment to obtain the sodium electrode material with heterostructure.

[0008] In an optional implementation, the molar ratio of nickel in the nickel source and manganese in the manganese source in step (1) is a:b, wherein 0.1≤a≤0.3, 0.58≤b≤0.79, and a+b<1.

[0009] Optionally, the nickel source includes at least one of nickel nitrate, nickel carbonate, nickel sulfate, and nickel acetate.

[0010] Optionally, the manganese source includes at least one of manganese nitrate, manganese carbonate, manganese sulfate, and manganese acetate.

[0011] In one optional embodiment, the total molar concentration of the metal elements in solution A in step (1) is 1.0-2.5 mol / L.

[0012] In one optional embodiment, the molar concentration of niobium in solution B in step (1) is 0.05-0.15 mol / L.

[0013] Optionally, the niobium source includes at least one of niobium oxalate, niobium pentoxide, niobium ethanol, and niobium pentachloride.

[0014] In an optional embodiment, the ratio of the total molar amount of metal elements in solution A to the molar amount of niobium elements in solution B in step (2) is (a+b):c, where 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, and a+b+c<1.

[0015] In one alternative embodiment, the concentration of the precipitant solution in step (2) is 4-6 mol / L, calculated as hydroxide ions.

[0016] In one optional embodiment, the concentration of the complexing agent solution in step (2) is 2-4 mol / L.

[0017] In an optional embodiment, the specific process of the coprecipitation reaction in step (2) includes: under the protective atmosphere, adding solution A and solution B into the reaction vessel, and then adding the precipitant solution and the complexing agent solution in parallel into the reaction vessel to carry out the coprecipitation reaction.

[0018] In one alternative embodiment, the protective atmosphere includes a nitrogen atmosphere and an inert atmosphere.

[0019] In one alternative embodiment, the coprecipitation reaction in step (2) is accompanied by stirring at a speed of 400-800 rpm.

[0020] In one alternative embodiment, the temperature of the coprecipitation reaction in step (2) is 50-60°C.

[0021] In an alternative embodiment, the product obtained after the coprecipitation reaction in step (2) is further separated, washed and dried.

[0022] Optionally, the separation method includes at least one of vacuum filtration and centrifugation.

[0023] Optionally, the washing continues until the washing solution is neutral.

[0024] Furthermore, in an alternative embodiment, the drying includes vacuum drying.

[0025] In one optional embodiment, the co-current flow rate of the precipitant solution is 0.5-1.5 L / h.

[0026] Optionally, the precipitant in the precipitant solution includes at least one of sodium hydroxide and potassium hydroxide.

[0027] In one optional embodiment, the co-current flow rate of the complexing agent solution is 0.2-0.6 L / h.

[0028] Optionally, the complexing agent solution includes ammonia.

[0029] In one alternative embodiment, the amount of precipitant solution added is increased until the pH of the coprecipitation reaction system reaches 10.5-11.5.

[0030] In one optional embodiment, the amount of complexing agent solution added is such that the concentration of the complexing agent in the system of the coprecipitation reaction is 0.1-0.3 g / L.

[0031] In one optional embodiment, after the precipitant solution and the complexing agent solution are added in parallel, a co-precipitation reaction is continued for 1-3 hours.

[0032] In one alternative implementation, the rotational speed of the third mixing in step (3) is 200-400 rpm.

[0033] In one alternative implementation, the third mixing time in step (3) is 6-8 hours.

[0034] In an alternative embodiment, the product obtained after the third mixing in step (3) is further dried.

[0035] In one alternative implementation, the heating rate of the first heat treatment in step (3) is 1-5 °C / min.

[0036] In one optional embodiment, the holding temperature of the first heat treatment in step (3) is 400-500℃.

[0037] In one optional implementation, the heat treatment holding time in step (3) is 4-6 hours.

[0038] In an alternative implementation, the atmosphere for the first heat treatment in step (3) includes an oxygen-containing atmosphere.

[0039] In this invention, the heating rate, holding temperature, holding time and treatment atmosphere of the first heat treatment are controlled in order to decompose carbonates or hydroxides and to initiate the initial solid-phase reaction.

[0040] In one alternative implementation, after the first heat treatment in step (3), the obtained product is further subjected to a first cooling, a first grinding, and tableting in sequence.

[0041] Optionally, the first cooling method includes furnace cooling.

[0042] Optionally, the pressure of the tablet is 180-220 MPa.

[0043] The present invention further compresses the product after the first heat treatment into tablets and then performs a second heat treatment to reduce fly ash and enhance the contact between particles, which is beneficial to a full reaction.

[0044] In one optional embodiment, the heating rate of the second heat treatment in step (4) is 2-5 °C / min.

[0045] In one optional embodiment, the holding temperature of the second heat treatment in step (4) is 700-900℃.

[0046] In one optional implementation, the heat treatment time in step (4) is 8-15 hours.

[0047] In an alternative embodiment, the atmosphere for the second heat treatment in step (4) includes an oxygen-containing atmosphere.

[0048] In one alternative embodiment, after the second heat treatment in step (4), the obtained product is further subjected to a second cooling, a second grinding, and a sieve.

[0049] Further, in an optional embodiment, the specific process of the second cooling after the second heat treatment in step (4) includes: controlling the cooling rate to 1-3℃ / min to cool down to 180-200℃, and then cooling it to room temperature with the furnace.

[0050] It should be noted that "room temperature" in this invention refers to 20-30℃.

[0051] The second heat treatment process provided by this invention controls the heating rate, treatment temperature, time, and atmosphere to allow the oxide in the second precursor material to react with the doped niobium element, generating a second phase in situ. This second phase then spontaneously forms a heterostructure with the main phase, completing the crystallization and interface construction of the heterostructure cathode material. By controlling the cooling rate, the aim is to regulate the crystallization integrity of the material, release thermal stress, and stabilize the heterostructure interface, thereby ultimately obtaining a cathode material with a stable structure and excellent cycle performance.

[0052] Optionally, the sieve used for sieving has a mesh size of 300-500.

[0053] In an optional embodiment, in step (3), the ratio of the total molar amount of metal elements in the first precursor material to the molar amount of lithium elements in the lithium source is (a+b+c):d, where 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, 0.1≤d≤0.2, and a+b+c+d=1.

[0054] In an optional embodiment, the sodium element in the sodium source added in step (3) is 101-103% of the molar amount of sodium element required to prepare the sodium-electric cathode material with heterostructure, and the molar ratio of lithium element in the lithium source to sodium element in the sodium source is d:(1.01-1.03)x, where 0.1≤d≤0.2, x is the molar amount of sodium element required to prepare the sodium-electric cathode material with heterostructure, and 0<x≤1.

[0055] It should be noted that, in order to compensate for the loss of sodium through volatilization during the high-temperature sintering process, this invention employs a specific excess of sodium source content.

[0056] Optionally, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate, and lithium acetate.

[0057] Optionally, the sodium source includes at least one of sodium carbonate, sodium sulfate, sodium nitrate, and sodium acetate.

[0058] In one optional embodiment, the obtained sodium-ion cathode material with a heterostructure comprises a main phase and a second phase.

[0059] Furthermore, in an optional implementation, the main phase is Na. x-3c Ni a Mn b Li d O 2-4c The second phase is Na3NbO4, and the molar ratio of the main phase to the second phase is 1:c, wherein 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, 0.1≤d≤0.2, a+b+c+d=1, and 0<x<1.

[0060] Furthermore, in an optional embodiment, the resulting sodium-ion cathode material with a heterostructure has the chemical formula Na. x-3c Ni a Mn b Li d O 2-4c -cNa3NbO4, where 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, 0.1≤d≤0.2, a+b+c+d=1, 0<x<1.

[0061] In a second aspect, the present invention provides a sodium-electric cathode material with a heterostructure, which is prepared by the preparation method described in the first aspect.

[0062] In one alternative embodiment, the sodium-ion cathode material with a heterostructure comprises a main phase and a second phase.

[0063] Furthermore, in an optional implementation, the main phase is Na. x-3c Ni a Mn b Li d O 2-4c The second phase is Na3NbO4, and the molar ratio of the main phase to the second phase is 1:c, wherein 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, 0.01≤d≤0.02, a+b+c+d=1, and 0<x<1.

[0064] Furthermore, in an optional embodiment, the chemical formula of the sodium-ion cathode material with a heterostructure is Na. x-3c Ni a Mn b Li d O 2-4c -cNa3NbO4, where 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, 0.01≤d≤0.02, a+b+c+d=1, 0<x<1.

[0065] Thirdly, the present invention provides a sodium-ion battery, the sodium-ion battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode material, the positive electrode material comprising the sodium-ion battery positive electrode material with a heterostructure as described in the second aspect.

[0066] The technical solution of this invention has the following advantages: 1. The present invention provides a method for preparing a sodium-ion battery cathode material with a heterostructure, the method comprising the following steps: (1) mixing a nickel source, a manganese source and a first solvent to obtain solution A; mixing a niobium source and a second solvent to obtain solution B; (2) co-precipitating solutions A and B with a precipitant solution and a complexing agent solution under a protective atmosphere to obtain a first precursor material; (3) mixing the first precursor material with a lithium source and a sodium source in a third mixture, and then subjecting the product obtained after the third mixture to a first heat treatment to obtain a second precursor material; (4) subjecting the second precursor material to a second heat treatment to obtain the sodium-ion battery cathode material with a heterostructure. The preparation method provided by this invention introduces the high-valence metal element niobium through a co-precipitation reaction, achieving a uniform atomic-level distribution of niobium in the material. The charge imbalance induced by the high-valence niobium drives spontaneous segregation of the element. During subsequent first and second heat treatments, a uniformly distributed and structurally stable heterostructure is spontaneously formed in situ within the bulk phase of the sodium-doped lithium cathode material. This effectively avoids the stress damage to the structure caused by severe external thermal shock in existing processes, achieving the generation of a uniform and controllable heterostructure. This provides structural assurance for achieving sodium-doped cathode materials with superior electrochemical performance. Furthermore, the preparation method of this invention constructs a heterostructure with high ionic conductivity and good uniformity. The resulting sodium-doped lithium cathode material with a specific heterostructure has a wider ion migration channel, effectively compensating for the insufficient kinetic performance of existing rock-salt phase heterostructure sodium-doped lithium cathode materials, effectively reducing the interfacial resistance of the electrode material, and improving the rate performance of the sodium-doped lithium cathode material. Furthermore, the uniformly distributed heterostructure obtained by the preparation method of this invention can improve the crystal structure while effectively isolating the electrode from the electrolyte and improving the conductivity and ion transport performance between the electrode material and the electrolyte. The preparation process also forms oxygen vacancies on the surface of the sodium-doped lithium cathode material, which, together with the heterostructure, enhances the cycle performance of the sodium cathode material. In addition, the co-precipitation reaction process provided by this invention, combined with two heat treatment processes, mitigates the dangerous and complex rapid quenching introduced by disorder. The preparation process is simple, low-cost, and suitable for large-scale production.

[0067] 2. This invention provides a sodium-ion cathode material with a heterostructure. By utilizing the heterostructure to improve the crystal structure of the cathode material, it can solve the problems of low sodium ion diffusion coefficient, poor interface stability, and irreversible phase transition in lithium-doped sodium-ion cathode materials during cycling. The provided sodium-ion cathode material has good uniformity of niobium and lithium doping and uniform distribution of the heterostructure, exhibiting excellent rate performance and kinetic performance, thereby effectively optimizing the electrochemical performance of lithium-doped sodium-ion cathode materials. Attached Figure Description

[0068] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0069] Figure 1 The X-ray diffraction (XRD) patterns of the products prepared by the preparation methods provided in Example 1 and Comparative Example 1 of this invention are shown.

[0070] Figure 2 yes Figure 1 In the X-ray diffraction (XRD) pattern, 2θ = 13-20 ° The corresponding enlarged image. Detailed Implementation

[0071] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0072] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0073] Example 1 This embodiment provides a method for preparing a sodium-ion cathode material with a heterostructure, including the following steps: (1) Nickel nitrate and manganese nitrate are mixed with deionized water according to the molar ratio of nickel to manganese of 0.2:0.64 to prepare a solution A with a total concentration of 1 mol / L of metal elements (nickel and manganese).

[0074] Niobium oxalate was stirred with deionized water at 60°C until completely dissolved, to prepare a solution B with a niobium concentration of 0.1 mol / L.

[0075] (2) Add solutions A and B obtained in step (1) to a constant-temperature reactor filled with nitrogen protective gas, with the ratio of the total molar amount of manganese and nickel to the molar amount of niobium being 0.84:0.03. Maintain the temperature of the reaction system at 55°C. Stir the solution in the constant-temperature reactor at a speed of 600 rpm. Add a 5 mol / L sodium hydroxide solution and a 3 mol / L ammonia solution in parallel flow to the constant-temperature reactor containing solutions A and B. The parallel flow rate of the sodium hydroxide solution is 1 L / h, and the parallel flow rate of the ammonia solution is 0.4 L / h, until... The pH of the reaction system in the constant-temperature reactor was 11, and the concentration of ammonia in the reaction system was 0.2 g / L. The co-flow addition of sodium hydroxide solution and ammonia was stopped. Then, the materials in the constant-temperature reactor were stirred at the same speed for 2 hours under the same temperature and protective atmosphere to carry out the co-precipitation reaction. Then, the product obtained from the co-precipitation reaction was filtered to obtain a solid product. The solid product was then washed repeatedly with deionized water and anhydrous ethanol until the washing liquid was neutral. The washed product was placed in a vacuum drying oven and vacuum dried at 100°C for 12 hours to obtain the first precursor material.

[0076] (3) The first precursor material obtained in step (2) is placed in a planetary ball mill with sodium carbonate (Na2CO3), lithium hydroxide (LiOH·H2O) and anhydrous ethanol. The mixture is ball-milled at 300 rpm for 7 h, and then dried at 80 °C. The dried product is then heated to 450 °C at a rate of 3 °C / min and held for 5 h in air for the first heat treatment. The product obtained from the first heat treatment is then cooled to 25 °C in the furnace and taken out for the first grinding. The product after the first grinding is pressed into a disc under a pressure of 200 MPa to obtain the second precursor material.

[0077] The ratio of the total molar amount of metal elements in the first precursor material to the molar amount of lithium in lithium hydroxide is 0.87:0.13, and the molar ratio of sodium in sodium carbonate (Na2CO3) to lithium in lithium hydroxide is (0.8×1.02):0.13.

[0078] (4) The second precursor material obtained in step (3) is placed in a tube furnace for a second heat treatment. The specific process is as follows: under an oxygen atmosphere, the temperature is raised to 900°C at a rate of 5°C / min and held for 15 hours; then the temperature is lowered to 200°C at a rate of 2°C / min, and then cooled to 25°C with the furnace to remove the product. The product obtained after the second heat treatment is ground and then sieved through a 400-mesh sieve to obtain a sodium electrode material with a heterostructure.

[0079] In this embodiment, the sodium-ion cathode material with a heterostructure obtained by the above preparation method includes a main phase and a second phase, wherein the main phase is Na.0.71 Ni 0.2 Mn 0.64 Li 0.13 O 1.88 The second phase is Na3NbO4, with the chemical formula Na. 0.71 Ni 0.2 Mn 0.64 Li 0.13 O 1.88 -0.03Na3NbO4.

[0080] Example 2 This embodiment provides a method for preparing a sodium-ion cathode material with a heterostructure, including the following steps: (1) Nickel carbonate and manganese carbonate are mixed with deionized water according to the molar ratio of nickel to manganese of 0.1:0.79 to prepare a solution A with a total concentration of metal elements (nickel and manganese) of 2.5 mol / L.

[0081] Niobium oxalate was stirred with deionized water at 60°C until completely dissolved, to prepare a solution B with a niobium concentration of 0.05 mol / L.

[0082] (2) Add solutions A and B obtained in step (1) to a constant-temperature reactor filled with nitrogen protective gas, with the ratio of the total molar amount of manganese and nickel to the molar amount of niobium being 0.89:0.01. Maintain the temperature of the reaction system at 50°C. Stir the solution in the constant-temperature reactor at a speed of 400 rpm. Add a 4 mol / L potassium hydroxide solution and a 2 mol / L ammonia solution in parallel flow to the constant-temperature reactor containing solutions A and B. The parallel flow rate of the sodium hydroxide solution is 0.5 L / h, and the parallel flow rate of the ammonia solution is 0.2 L / h, until... The pH of the reaction system in the constant-temperature reactor was 10.5, and the concentration of ammonia in the reaction system was 0.1 g / L. The co-flow addition of sodium hydroxide solution and ammonia was stopped. Then, the materials in the constant-temperature reactor were stirred at the same speed for 3 hours under the same temperature and protective atmosphere to carry out the co-precipitation reaction. Then, the product obtained from the co-precipitation reaction was filtered to obtain a solid product. The solid product was then washed repeatedly with deionized water and anhydrous ethanol until the washing liquid was neutral. The washed product was placed in a vacuum drying oven and vacuum dried at 80°C for 10 hours to obtain the first precursor material.

[0083] (3) The first precursor material obtained in step (2) is placed in a planetary ball mill with sodium carbonate (Na2CO3), lithium hydroxide (LiOH·H2O) and anhydrous ethanol. The mixture is ball-milled at 200 rpm for 8 hours and then dried at 80°C. The dried product is then heated to 400°C at a rate of 1°C / min and held for 6 hours in an air atmosphere for the first heat treatment. The product obtained from the first heat treatment is then cooled to 25°C in the furnace and removed. The product is then ground for the first time. The ground product is then pressed into discs under a pressure of 180 MPa to obtain the second precursor material.

[0084] The ratio of the total molar amount of metal elements in the first precursor material to the molar amount of lithium elements in lithium hydroxide is 0.9:0.1, and the molar ratio of sodium elements in sodium carbonate (Na2CO3) to lithium elements in lithium hydroxide is (0.6×1.01):0.1.

[0085] (4) The second precursor material obtained in step (3) is placed in a tube furnace for a second heat treatment. The specific process is as follows: under an oxygen atmosphere, the temperature is raised to 700°C at a rate of 2°C / min and held for 10 hours; then the temperature is lowered to 180°C at a rate of 1°C / min, and then cooled to 25°C with the furnace to remove the product. The product obtained after the second heat treatment is ground and then sieved through a 300-mesh sieve to obtain a sodium electrode material with a heterostructure.

[0086] In this embodiment, the sodium-ion cathode material with a heterostructure obtained by the above preparation method includes a main phase and a second phase, wherein the main phase is Na. 0.57 Ni 0.1 Mn 0.79 Li 0.1 O 1.96 The second phase is Na3NbO4, with the chemical formula Na. 0.57 Ni 0.1 Mn 0.79 Li 0.1 O 1.96 -0.01Na3NbO4.

[0087] Example 3 This embodiment provides a method for preparing a sodium-ion cathode material with a heterostructure, including the following steps: (1) Nickel carbonate and manganese carbonate are mixed with deionized water according to the molar ratio of nickel to manganese of 0.3:0.58 to prepare a solution A with a total concentration of 2 mol / L of metal elements (nickel and manganese).

[0088] Niobium oxalate was stirred with deionized water at 60°C until completely dissolved, to prepare a solution B with a niobium concentration of 0.15 mol / L.

[0089] (2) Add solutions A and B obtained in step (1) to a constant-temperature reactor filled with nitrogen protective gas, with the ratio of the total molar amount of manganese and nickel to the molar amount of niobium being 0.88:0.02. Maintain the temperature of the reaction system at 60°C. Stir the solution in the constant-temperature reactor at a speed of 800 rpm. Add a 6 mol / L sodium hydroxide solution and a 4 mol / L ammonia solution in parallel flow to the constant-temperature reactor containing solutions A and B. The parallel flow rate of the sodium hydroxide solution is 1.5 L / h, and the parallel flow rate of the ammonia solution is 0.6 L / h. The pH of the reaction system in the constant-temperature reactor was adjusted to 11.5, and the concentration of ammonia in the reaction system was 0.3 g / L. The co-flow addition of sodium hydroxide solution and ammonia was stopped. Then, the materials in the constant-temperature reactor were stirred at the same speed for 1 hour under the same temperature and protective atmosphere to carry out the co-precipitation reaction. The product obtained from the co-precipitation reaction was then filtered to obtain a solid product. The solid product was then washed repeatedly with deionized water and anhydrous ethanol until the washing liquid was neutral. The washed product was then placed in a vacuum drying oven and vacuum dried at 90°C for 8 hours to obtain the first precursor material.

[0090] (3) The first precursor material obtained in step (2) is placed in a planetary ball mill with sodium carbonate (Na2CO3), lithium hydroxide (LiOH·H2O) and anhydrous ethanol. The mixture is ball-milled at 400 rpm for 6 h, and then dried at 80 °C. The dried product is then heated to 500 °C at a rate of 5 °C / min and held for 4 h in air for the first heat treatment. The product obtained from the first heat treatment is then cooled to 25 °C in the furnace and taken out for the first grinding. The product after the first grinding is pressed into a disc under a pressure of 190 MPa to obtain the second precursor material.

[0091] The ratio of the total molar amount of metal elements in the first precursor material to the molar amount of lithium elements in lithium hydroxide is 0.9:0.1, and the molar ratio of sodium elements in sodium carbonate (Na2CO3) to lithium elements in lithium hydroxide is (0.95×1.01):0.1.

[0092] (4) The second precursor material obtained in step (3) is placed in a tube furnace for a second heat treatment. The specific process is as follows: under an oxygen atmosphere, the temperature is raised to 800°C at a rate of 3°C / min and held for 8 hours; then the temperature is lowered to 190°C at a rate of 3°C / min, and then cooled to 25°C with the furnace to remove the product. The product obtained after the second heat treatment is ground and then sieved through a 500-mesh sieve to obtain a sodium electrode material with a heterostructure.

[0093] In this embodiment, the sodium-ion cathode material with a heterostructure obtained by the above preparation method includes a main phase and a second phase, wherein the main phase is Na. 0.89 Ni 0.3 Mn 0.58 Li 0.1 O 1.92 The second phase is Na3NbO4, with the chemical formula Na. 0.89 Ni 0.3 Mn 0.58 Li 0.1 O 1.92 -0.02Na3NbO4.

[0094] Example 4 The only difference between this embodiment and Example 1 is that: in step (1), the molar ratio of nickel to manganese in the mixed nickel nitrate and manganese nitrate is 0.2:0.665; in step (2), the ratio of the total molar amount of manganese and nickel to the molar amount of niobium in solutions A and B is 0.865:0.005. The resulting sodium-ion cathode material with a heterostructure includes a main phase and a second phase, with the main phase being Na. 0.785 Ni 0.2 Mn 0.665 Li 0.13 O 1.98 The second phase is Na3NbO4, with the chemical formula Na. 0.785 Ni 0.2 Mn 0.665 Li 0.13 O 1.98 -0.005Na3NbO4. All other contents are the same as in Example 1.

[0095] Example 5 The only difference between this embodiment and Example 1 is that: in step (1), the molar ratio of nickel to manganese in the mixed nickel nitrate and manganese nitrate is 0.2:0.63; in step (2), the ratio of the total molar amount of manganese and nickel to the molar amount of niobium in solutions A and B is 0.83:0.04. The resulting sodium-ion cathode material with a heterostructure includes a main phase and a second phase, with the main phase being Na. 0.68 Ni 0.2 Mn 0.63 Li 0.13 O 1.84 The second phase is Na3NbO4, with the chemical formula Na. 0.68 Ni 0.2 Mn 0.63 Li 0.13 O 1.84 -0.04Na3NbO4. All other contents are the same as in Example 1.

[0096] Example 6 The only difference between this embodiment and Example 1 is that the total concentration of metal elements in solution A in step (1) is 3.5 mol / L. All other contents are the same as in Example 1.

[0097] Example 7 The only difference between this embodiment and Example 1 is that the molar ratio of sodium in the sodium carbonate (Na2CO3) added in step (3) to lithium in lithium hydroxide is (0.8×1):0.13, meaning that the amount of sodium carbonate added is appropriate rather than excessive. All other contents are the same as in Example 1.

[0098] Example 8 The only difference between this embodiment and Embodiment 1 is that the temperature of the second heat treatment in step (4) is 650°C. All other contents are the same as in Embodiment 1.

[0099] Example 9 The only difference between this embodiment and Embodiment 1 is that the temperature of the second heat treatment in step (4) is 950°C. All other contents are the same as in Embodiment 1.

[0100] Example 10 The only difference between this embodiment and Embodiment 1 is that, in step (4), the temperature after the second heat treatment is reduced from 900°C to 25°C by furnace cooling. All other contents are the same as in Embodiment 1.

[0101] Comparative Example 1 The only difference between this comparative example and Example 1 is that steps (1) to (2) of preparing the first precursor material are omitted, and in step (3), nickel-manganese hydroxide is used as the first precursor material and placed in a planetary ball mill with sodium carbonate (Na2CO3), lithium hydroxide (LiOH·H2O), and anhydrous ethanol. The molar ratio of nickel to manganese in the first precursor material is 0.2:0.67. All other contents are the same as in Example 1.

[0102] Comparative Example 2 The only difference between this comparative example and Example 1 is that the first heat treatment process in step (3) is omitted, and the product dried in step (3) is directly placed in the tube furnace in step (4) for the second heat treatment. All other contents are the same as in Example 1.

[0103] Comparative Example 3 The only difference between this comparative example and Example 1 is that the second heat treatment process in step (4) is omitted. All other contents are the same as in Example 1.

[0104] The positive electrode materials provided in the above embodiments and comparative examples were used to prepare coin cells. The specific preparation method was as follows: the sodium-ion positive electrode materials prepared in the above embodiments and comparative examples, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black were mixed in a mass ratio of 90:5:5. N-methylpyrrolidone (NMP) solvent was added for homogenization to obtain a positive electrode slurry. The positive electrode slurry was coated onto the surface of the current collector (aluminum foil) to form a positive electrode sheet. A sodium metal sheet was used as the negative electrode sheet. The separator was a Whatman GF / D glass fiber separator. The electrolyte consisted of 1 mol / L NaClO4 dissolved in a 1:1 volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed solvent, with 5 wt% fluoroethylene carbonate (FEC) added. The sodium-ion coin cells were assembled in an argon glove box (where water < 0.01 ppm and oxygen < 0.01 ppm). Finally, the electrical performance of the cells was tested.

[0105] The electrical performance test conditions are as follows: (1) Capacity retention rate after 50 cycles at 1C: First, the sodium-ion coin cell was activated by charge and discharge. Specifically, the battery was charged at a constant current of 0.1C to 4.3V in a constant temperature environment of 25℃, and then charged at a constant voltage until the current dropped to 0.05C. Then it was left to stand for 10 minutes. Subsequently, it was discharged at a constant current of 0.1C to 3.0V to complete one charge and discharge cycle. This process was repeated twice to activate the battery cycle. Then, the sodium-ion coin cell was tested for stability by cycle testing: At a charge and discharge rate of 1C, continuous constant current charge and discharge cycle tests were performed in the voltage range of 3.0V-4.3V for a total of 50 cycles. The discharge capacity of the 1st and 50th cycles was recorded, and the capacity retention rate (discharge capacity of the 50th cycle / discharge capacity of the 1st cycle × 100%) was calculated to evaluate the long-term service life of the battery.

[0106] (2) Discharge specific capacity at 5C: In the voltage range of 3.0V-4.3V, at a charge-discharge rate of 5C, a continuous charge-discharge test was conducted, and the discharge specific capacity of the first cycle was recorded.

[0107] (3) Interface resistance: The test was conducted under constant temperature conditions using an electrochemical workstation (model: VMP2). Before the test, the sodium-ion coin cell assembled with the cathode materials provided in the above examples and comparative examples was placed in a constant temperature environment of 25±0.5℃ and left to stand for at least 2 hours until the open circuit voltage change rate was less than 1mV / min and reached a stable state. Then, the parameters were set in the workstation software as follows: a sinusoidal AC voltage disturbance signal with an amplitude of 5mV was superimposed on the stable open circuit voltage as the DC bias basis; the frequency scanning range was set to 100kHz to 5mHz, the scanning method was logarithmic frequency sweep from high frequency to low frequency, and the sampling density was at least 6 points per ten octaves. After the test was completed, the interface impedance value was recorded.

[0108] The test results are shown in Table 1: Table 1

[0109] As can be seen from Table 1, the preparation method provided by this invention introduces the high-valence metal element niobium through a co-precipitation reaction, achieving a uniform atomic-level distribution of niobium in the material. The charge imbalance induced by the high-valence niobium metal element drives spontaneous segregation of the element. During the subsequent first and second heat treatments, a uniformly distributed and structurally stable heterostructure is spontaneously formed in situ within the bulk phase of the lithium sodium-doped cathode material, thereby effectively reducing the interfacial resistance of the electrode material and improving the rate performance and cycle stability of the lithium sodium-doped cathode material.

[0110] Compared with Example 1, Comparative Example 1 omits niobium doping, thus failing to form a heterostructured lithium-doped sodium battery cathode material, and consequently failing to improve the cycle stability and rate performance of sodium-ion batteries.

[0111] Figure 1 and Figure 2 These are the X-ray diffraction (XRD) patterns of the products prepared by the methods provided in Example 1 and Comparative Example 1, respectively. Figure 1 and Figure 2 As can be seen, compared with Comparative Example 1, the X-ray diffraction (XRD) pattern of the final product prepared by the preparation method provided in Example 1 shows a weaker diffraction peak at 16.34°, which clearly points to the main characteristic peak of Na3NbO4. This also shows that the preparation method provided in Example 1 successfully prepared a heterostructure containing a main phase and a second phase.

[0112] Compared with Example 1, Comparative Example 2 omits the first heat treatment process, which leads to the violent decomposition of residues causing particle bursting, hard agglomeration, and loss of morphology. Furthermore, it also leads to disordered crystallization, severe cation mixing, numerous crystal defects, and loss of lithium salt, resulting in inaccurate stoichiometry of the obtained sodium-ion battery.

[0113] Compared with Example 1, Comparative Example 3 omitted the second heat treatment process, thus failing to form a lithium-doped sodium-ion cathode material with a heterostructure. Compared with the lithium-doped sodium-ion cathode material with a heterostructure prepared in Example 1, the conventional lithium-doped and niobium-doped sodium-ion cathode materials formed therefrom have poor cycle stability and rate performance, and higher interface resistance.

[0114] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a sodium-ion cathode material with a heterostructure, characterized in that, The preparation method includes the following steps: (1) The nickel source, manganese source and the first solvent are mixed to obtain solution A; The niobium source and the second solvent are mixed a second time to obtain solution B; (2) Under a protective atmosphere, the solution A and the solution B undergo a co-precipitation reaction with the precipitant solution and the complexing agent solution to obtain the first precursor material; (3) The first precursor material is mixed with lithium source and sodium source in a third mixture, and then the product obtained after the third mixture is subjected to a first heat treatment to obtain the second precursor material; (4) The second precursor material is subjected to a second heat treatment to obtain the sodium electrode material with heterostructure.

2. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of nickel in the nickel source to manganese in the manganese source is a:b, where 0.1≤a≤0.3, 0.58≤b≤0.79, and a+b<1; And / or, the total molar concentration of the metal elements in solution A in step (1) is 1.0-2.5 mol / L; And / or, the molar concentration of niobium in solution B in step (1) is 0.05-0.15 mol / L.

3. The preparation method according to claim 1 or 2, characterized in that, In step (2), the ratio of the total molar amount of metal elements in solution A to the molar amount of niobium elements in solution B is (a+b):c, where 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, and a+b+c<1; And / or, the concentration of the precipitant solution in step (2) is 4-6 mol / L, calculated as hydroxide ions; And / or, the concentration of the complexing agent solution in step (2) is 2-4 mol / L; And / or, the specific process of the coprecipitation reaction in step (2) includes: under the protective atmosphere, adding solution A and solution B into the reaction vessel, and then adding the precipitant solution and the complexing agent solution in parallel into the reaction vessel to carry out the coprecipitation reaction; And / or, the protective atmosphere includes a nitrogen atmosphere and an inert atmosphere; And / or, the coprecipitation reaction described in step (2) is accompanied by stirring, the stirring speed being 400-800 rpm; And / or, the temperature of the coprecipitation reaction in step (2) is 50-60℃; And / or, after the coprecipitation reaction described in step (2), the obtained product is further separated, washed and dried; Preferably, the drying includes vacuum drying.

4. The preparation method according to claim 3, characterized in that, The co-current flow rate of the precipitant solution is 0.5-1.5 L / h; And / or, the co-current flow rate of the complexing agent solution is 0.2-0.6 L / h; And / or, the amount of the precipitant solution added is until the pH of the system in the coprecipitation reaction reaches 10.5-11.5; And / or, the amount of complexing agent solution added is until the concentration of the complexing agent in the system of the coprecipitation reaction is 0.1-0.3 g / L; And / or, after the precipitant solution and the complexing agent solution are added in parallel, a co-precipitation reaction is continued for 1-3 hours.

5. The preparation method according to any one of claims 1-4, characterized in that, The rotational speed of the third mixing step (3) is 200-400 rpm; And / or, the third mixing time in step (3) is 6-8 hours; And / or, the product obtained after the third mixing in step (3) is further dried; And / or, in step (3), the heating rate of the first heat treatment is 1-5℃ / min; And / or, in step (3), the holding temperature of the first heat treatment is 400-500℃; And / or, in step (3), the heat treatment holding time for the first heat treatment is 4-6 hours; And / or, in step (3), the atmosphere of the first heat treatment includes an oxygen-containing atmosphere.

6. The preparation method according to any one of claims 1-5, characterized in that, Step (3) After the first heat treatment, the obtained product is subjected to a first cooling, a first grinding and tableting in sequence; And / or, in step (4), the heating rate of the second heat treatment is 2-5℃ / min; And / or, in step (4), the holding temperature of the second heat treatment is 700-900℃; And / or, in step (4), the heat treatment holding time for the second heat treatment is 8-15 hours; And / or, in step (4), the atmosphere of the second heat treatment includes an oxygen-containing atmosphere; And / or, after the second heat treatment in step (4), the obtained product is subjected to a second cooling, a second grinding and sieving in sequence; Preferably, the specific process of the second cooling after the second heat treatment in step (4) includes: controlling the cooling rate to 1-3℃ / min to cool down to 180-200℃, and then cooling it to room temperature with the furnace.

7. The preparation method according to any one of claims 1-6, characterized in that, Step (3) The ratio of the total molar amount of metal elements in the first precursor material to the molar amount of lithium elements in the lithium source is (a+b+c):d, where 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, 0.1≤d≤0.2, and a+b+c+d=1; And / or, the sodium element in the sodium source added in step (3) is 101-103% of the molar amount of sodium element required to prepare the sodium-electric cathode material with heterostructure, and the molar ratio of lithium element in the lithium source to sodium element in the sodium source is d:(1.01-1.03)x, where 0.1≤d≤0.2, x is the molar amount of sodium element required to prepare the sodium-electric cathode material with heterostructure, and 0<x≤1; And / or, the obtained sodium-ion cathode material with heterostructure includes a main phase and a second phase; Preferably, the main phase is Na. x-3c Ni a Mn b Li d O 2-4c The second phase is Na3NbO4, and the molar ratio of the main phase to the second phase is 1:c, wherein 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, 0.1≤d≤0.2, a+b+c+d=1, and 0<x<1; Preferably, the chemical formula of the obtained sodium-ion cathode material with heterostructure is Na. x-3c Ni a Mn b Li d O 2-4c -cNa3NbO4, where 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, 0.1≤d≤0.2, a+b+c+d=1, 0<x<1.

8. A sodium-ion cathode material with a heterostructure, characterized in that, The sodium-ion cathode material with heterostructure is prepared by the preparation method according to any one of claims 1-7.

9. The sodium-ion cathode material with a heterostructure according to claim 8, characterized in that, The sodium-ion cathode material with a heterostructure includes a main phase and a second phase; Preferably, the main phase is Na. x-3c Ni a Mn b Li d O 2-4c The second phase is Na3NbO4, and the molar ratio of the main phase to the second phase is 1:c, wherein 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, 0.01≤d≤0.02, a+b+c+d=1, and 0<x<1; And / or, the chemical formula of the sodium-ion cathode material with heterostructure is Na x-3c Ni a Mn b Li d O 2-4c -cNa3NbO4, where 0.1≤a≤0.3, 0.58≤b≤0.79, 0.01≤c≤0.03, 0.01≤d≤0.02, a+b+c+d=1, 0<x<1.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material, and the positive electrode material includes the sodium-ion positive electrode material with a heterostructure as described in claim 8 or 9.

Images