Composite sodium ion battery layered oxide positive electrode material and preparation method thereof

Abstract

The invention provides a composite sodium ion battery layered oxide positive electrode material and a preparation method thereof, the positive electrode material comprises an O3 type core layer material and a P2 type shell layer material, the chemical formula of the O3 type core layer material is NahNiiMnjFekZr1-i-j-kO2, 0.95 < = h < = 1.15, 0.25 < = i < = 0.4, 0.25 < = j < = 0.4, 0.25 < = k < = 0.4, 0.05 < = 1-i-j-k < = 0.15. The chemical formula of the P2 type shell layer material is Na < 0.7 > Ni < 0.37-p > Mg Mn < 0.63-q-r > Ti < q > Sn < r > O2, p is greater than or equal to 0.01 and less than or equal to 0.07, q is greater than or equal to 0.01 and less than or equal to 0.15, and r is greater than or equal to 0.01 and less than or equal to High charge-discharge specific capacity is provided through the O3 type core layer material, good air stability is provided through the P2 type shell layer material, and the cycle stability of the core layer material is improved by doping the zirconium element in the O3 type core layer material; by doping magnesium, titanium and tin elements in the P2 type shell material, the complex phase change of the shell material in the charge-discharge cycle process is inhibited, and the cycle stability of the shell material is improved, so that the positive electrode material has high charge-discharge specific capacity and keeps good air stability and high cycle stability at the same time.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a composite sodium-ion battery layered oxide cathode material and its preparation method. Background Technology

[0002] Sodium-ion batteries have advantages such as high specific capacity, low cost, wide operating temperature range and long cycle life, and are currently receiving increasing attention and research.

[0003] In existing technologies, layered oxide cathode materials for sodium-ion batteries have two structures: P2 type and O3 type. Among them, O3 type sodium-ion battery cathode materials have higher discharge specific capacity, but lower air stability. When the material surface is exposed to air, the structure is unstable and easily undergoes intercalation reactions with moisture and carbon dioxide in the air, leading to the precipitation of sodium ions. P2 type sodium-ion battery cathode materials have better cycle performance and air stability, and the material structure is not easily changed when placed in air for a long time, but the discharge specific capacity is lower at low voltage.

[0004] In view of this, combining P2-type sodium-ion cathode materials with O3-type sodium-ion cathode materials to develop a sodium-ion cathode material with high charge-discharge specific capacity while maintaining good air stability and high cycle stability will be of great significance to promoting the mass production and application of sodium-ion batteries. Summary of the Invention

[0005] The purpose of this application is to provide a composite layered oxide cathode material for sodium-ion batteries and its preparation method, so that the sodium-ion battery cathode material can maintain good air stability and high cycle stability while possessing high charge-discharge specific capacity. The specific technical solution is as follows:

[0006] The first aspect of this application provides a composite layered oxide cathode material for sodium-ion batteries. The cathode material includes an O3-type core layer material and a P2-type shell material coated on the surface of the O3-type core layer material. The chemical formula of the O3-type core layer material is NaHNi. i MnjFekZr 1- ij-kO2, 0.95≤h≤1.15, 0.25≤i≤0.4, 0.25≤j≤0.4, 0.25≤k≤0.4, 0.05≤1-ijk≤0.15; The chemical formula of the P2 type shell material is: Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn rO2, 0.01≤p≤0.07, 0.01≤q≤0.15, 0.01≤r≤0.07. The O3-type core material provides high charge / discharge specific capacity, while the P2-type shell material provides good air stability. Doping the O3-type core material with zirconium enhances its cycle stability, while doping the P2-type shell material with magnesium, titanium, and tin suppresses complex phase transitions during charge / discharge cycling, further improving its cycle stability. Through this core-shell structure design and the synergistic effect of the doping elements, the cathode material achieves high charge / discharge specific capacity while maintaining good air stability and high cycle stability.

[0007] In some embodiments of this application, the mass ratio of O3-type core material to P2-type shell material is 20:1 to 10:1. By controlling the mass ratio of O3-type core material and P2-type shell material within the above range, this application facilitates the full coating of P2-type shell material onto the surface of O3-type core material to form a core-shell structure, thereby obtaining a composite sodium-ion battery layered oxide cathode material with good air stability and high charge-discharge specific capacity.

[0008] In some embodiments of this application, the Dv50 of the O3 type core material is 5 μm to 8 μm, and the Dv50 of the P2 type shell material is 0.2 μm to 0.8 μm. By controlling the volume average particle size Dv50 of the O3 type core material and the P2 type shell material within the above range, this application facilitates the uniform coating of the P2 type shell material onto the surface of the O3 type core material to form a core-shell structure, thereby obtaining a composite sodium-ion battery layered oxide cathode material with good air stability and high cycle stability.

[0009] In some embodiments of this application, the sodium source of the positive electrode material is selected from at least one of sodium carbonate, sodium sulfate, or sodium nitrate; the nickel source of the positive electrode material is selected from at least one of nickel acetate, nickel nitrate, or nickel sulfate; and the manganese source of the positive electrode material is selected from at least one of manganese acetate, manganese nitrate, or manganese sulfate. Using the above materials as the sodium source of the positive electrode material facilitates the uniform diffusion of sodium ions in the core and shell structures of the positive electrode material to form a sodium ion layer; using the above materials as the nickel source of the positive electrode material helps to improve the charge-discharge specific capacity of the positive electrode material.

[0010] In some embodiments of this application, the iron source of the positive electrode material is selected from at least one of ferric chloride, ferric nitrate, or ferric sulfate, and the zirconium source of the positive electrode material is selected from at least one of zirconium nitrate, zirconium isopropoxide, or zirconium chloride. By selecting the above materials as the iron source for the O3-type core layer material, it is beneficial for the uniform doping of iron into the precursor of the O3-type core layer material, thereby facilitating the formation of a uniform and stable core layer material. By selecting the above materials as the zirconium source for the O3-type core layer material, it is beneficial for improving the conductivity of the core layer material, thereby improving the fast charge-discharge performance of the secondary battery. Simultaneously, zirconium helps reduce the side reactions between sodium ions and the electrolyte in the core layer material, slowing down the aging rate of the positive electrode material during cycling, reducing the self-discharge rate of the secondary battery, thereby improving the storage time and stability of the secondary battery and extending its service life.

[0011] In some embodiments of this application, the magnesium source of the positive electrode material is selected from at least one of magnesium carbonate, magnesium chloride, magnesium oxalate, or magnesium sulfate; the titanium source of the positive electrode material is selected from at least one of titanium oxysulfate or titanium tetrachloride; and the tin source of the positive electrode material is selected from at least one of tin tetrachloride or tin nitrate. By selecting the above materials as the magnesium source of the P2-type shell material, it is beneficial for magnesium to be uniformly doped into the P2-type shell material, suppressing harmful phase transitions in the shell material during charge and discharge, thereby improving the structural stability of the positive electrode material. By selecting the above materials as the titanium source of the P2-type shell material, it is beneficial for titanium to be uniformly doped into the P2-type shell material, thereby facilitating the formation of a uniform and stable P2-type shell material. By selecting the above materials as the tin source of the P2-type shell material, it is beneficial for tin to be uniformly doped into the P2-type shell material, thereby facilitating the formation of a uniform and stable P2-type shell material. Simultaneously, tin, as a stable element, optimizes current flow and improves stability in air when doped into the positive electrode material, thereby improving the cycle stability of the secondary battery.

[0012] A second aspect of this application provides a method for preparing a composite sodium-ion battery layered oxide cathode material, wherein the method includes:

[0013] Step 1. Preparation of O3-type core material Na h Ni i Mn j Fe k Zr 1-i-j-k O2;

[0014] Step 2. Preparation of P2-type shell material Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r O2;

[0015] Step 3. Grind, mix, and calcine the O3 core material and P2 shell material at high temperature to obtain a composite sodium-ion battery layered oxide cathode material.

[0016] This application utilizes an O3-type core material to provide a high charge-discharge specific capacity and a P2-type shell material to provide good air stability. Furthermore, doping the O3-type core material with zirconium enhances its cycle stability, while doping the P2-type shell material with magnesium, titanium, and tin suppresses complex phase transitions during charge-discharge cycles, thus improving its cycle stability. The resulting core-shell structure cathode material, obtained by grinding, mixing, and high-temperature solid-state calcination of the O3-type core material and the P2-type shell material, exhibits high charge-discharge specific capacity while maintaining good air stability and high cycle stability.

[0017] In some embodiments of this application, O3-type core material Na is prepared. h Ni i Mn j Fe k Zr 1-i-j-k O2 includes:

[0018] (1) According to the chemical formula of O3 type core material Na h Ni i Mn j Fe k Zr 1-i-j-k The stoichiometric ratios of nickel, manganese, iron, and zirconium in O2 were determined by dissolving nickel, manganese, iron, and zirconium sources in deionized water to prepare mixed metal salt solutions with a total concentration of 1.2 mol / L to 2 mol / L, where 0.25 ≤ i ≤ 0.4, 0.25 ≤ j ≤ 0.4, 0.25 ≤ k ≤ 0.4, and 0.05 ≤ 1 - ijk ≤ 0.15.

[0019] (2) Add deionized water as the base solution to the coprecipitation reaction vessel, and then purge nitrogen gas into the base solution at a flow rate of 20 mL / min to 50 mL / min. Subsequently, add the precipitant, complexing agent, and mixed metal salt solution dropwise into the coprecipitation reaction vessel to carry out the coprecipitation reaction. During the coprecipitation reaction, control the pH in the coprecipitation reaction vessel to be 11 to 12, the reaction temperature to be 50℃ to 60℃, and the stirring speed to be 500 r / min to 800 r / min.

[0020] The precipitant is a 2 mol / L sodium hydroxide solution, and the complexing agent is a 1 mol / L ammonia solution.

[0021] (3) After the mixed metal salt solution in the coprecipitation reaction vessel is finished, stop adding the precipitant and complexing agent. Then continue stirring at a stirring speed of 200 r / min to 300 r / min for aging reaction for 10 h to 20 h. Then filter and wash the obtained coprecipitation product with deionized water, and then put it into a vacuum drying oven to dry at 80 ℃ to 110 ℃ for 16 h to 24 h to obtain O3 type core layer precursor material.

[0022] (4) According to the chemical formula of O3 type core material Na h Ni i Mn j Fe k Zr 1-i-j-k The stoichiometric ratio of sodium to transition metal in O2 was used to obtain the O3-type core layer precursor material, which was then mixed uniformly with a sodium source. The mixture was then heated to 550℃ at a first heating rate of 4℃ / min and held for 6 hours in air, followed by a second heating rate of 4℃ / min to 930℃ and held for 12 hours. Finally, it was cooled to room temperature naturally to obtain the O3-type core layer material Na. h Ni i Mn j Fe k Zr 1-i-j-k O2, where 0.95≤h≤1.15, 0.25≤i≤0.4, 0.25≤j≤0.4, 0.25≤k≤0.4, and 0.05≤1-ijk≤0.15.

[0023] This application improves the cycling stability of O3-type core layer materials by doping them with zirconium. By controlling the content and ratio of each element within the aforementioned range, the cycling stability of the core layer material is significantly improved while avoiding a significant reduction in its reversible specific capacity. Controlling the total concentration of the mixed metal salt solution of nickel, manganese, iron, and zirconium, the nitrogen flow rate, the pH of the coprecipitation reaction, the coprecipitation reaction temperature, the coprecipitation reaction stirring speed, the aging reaction time, the aging reaction stirring speed, and the vacuum drying temperature and time within the aforementioned ranges facilitates the generation of uniform and stable O3-type core layer precursor materials. Furthermore, controlling the heating rate, cooling rate, and holding time helps obtain O3-type core layer materials with uniform particle size distribution and stable structure.

[0024] In some embodiments of this application, the P2-type shell material Na is prepared. 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r O2 includes:

[0025] (1) According to the P2 type shell material Na0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r The stoichiometric ratios of nickel, magnesium, manganese, titanium, and tin in O2 were determined by dissolving nickel, magnesium, manganese, titanium, and tin sources in deionized water to prepare mixed metal salt solutions with a total concentration of 0.5 mol / L to 1 mol / L, where 0.01 ≤ p ≤ 0.07, 0.01 ≤ q ≤ 0.15, and 0.01 ≤ r ≤ 0.07.

[0026] (2) Add deionized water as the base solution to the coprecipitation reaction vessel, and then purge nitrogen gas into the base solution at a flow rate of 20 mL / min to 50 mL / min. Subsequently, add the precipitant, complexing agent, and mixed metal salt solution dropwise into the coprecipitation reaction vessel to carry out the coprecipitation reaction. During the coprecipitation reaction, control the pH in the coprecipitation reaction vessel to be 11 to 12, the reaction temperature to be 50℃ to 60℃, and the stirring speed to be 500 r / min to 800 r / min.

[0027] The precipitant is a 2 mol / L sodium hydroxide solution, and the complexing agent is a 1 mol / L ammonia solution.

[0028] (3) After the mixed metal salt solution in the coprecipitation reaction vessel is finished, stop adding precipitant and complexing agent, and then continue stirring at a stirring speed of 200 r / min to 300 r / min for aging reaction for 5 h to 10 h. Then filter and wash the obtained coprecipitation product with deionized water, and then put it into a vacuum drying oven to dry at 80 ℃ to 110 ℃ for 16 h to 24 h to obtain P2 type shell precursor material;

[0029] (4) According to the P2 type shell material Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r The stoichiometric ratio of sodium to transition metal in O2 was used to determine the composition of the P2-type core precursor material and the sodium source. The mixture was then ball-milled and mixed, followed by heating to 800℃ at a rate of 4℃ / min under air atmosphere and holding for 10 hours. Afterward, it was cooled to room temperature naturally to obtain the P2-type shell material Na. 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn rO2, where 0.01≤p≤0.07, 0.01≤q≤0.15, and 0.01≤r≤0.07.

[0030] This application improves the cycle stability of the P2-type shell material by doping it with magnesium, titanium, and tin to suppress complex phase transitions during charge-discharge cycles. Controlling the content and proportion of each element within the aforementioned ranges further enhances the cycle stability of the core material. Furthermore, controlling the total concentration of the mixed metal salt solution of nickel, magnesium, manganese, titanium, and tin, the nitrogen flow rate, the pH of the coprecipitation reaction, the temperature of the coprecipitation reaction, the stirring speed of the coprecipitation reaction, the aging reaction time, the stirring speed of the aging reaction, and the vacuum drying temperature and time within the aforementioned ranges facilitates the generation of a uniform and stable O3-type core precursor material. Finally, controlling the heating rate, cooling rate, and holding time helps obtain a P2-type shell material with uniform particle size distribution, suitable size, and stable structure.

[0031] In some embodiments of this application, O3-type core material and P2-type shell material are ground, mixed, and subjected to high-temperature solid-state calcination to obtain a composite sodium-ion battery layered oxide cathode material, including:

[0032] (1) The O3 type core material is ground into particles with a Dv50 of 5μm to 8μm by air jet milling, and the P2 type shell material is ground into particles with a Dv50 of 0.2μm to 0.8μm. Then, the O3 type core material and the P2 type shell material are weighed in a weight ratio of 20:1 to 10:1 and added to a mixer and mixed evenly.

[0033] (2) The mixed O3 core material and P2 shell material are heated to 600°C in air at a heating rate of 4°C / min and kept at that temperature for 8 hours. Then, the temperature is cooled to room temperature at a natural cooling rate to obtain the composite sodium-ion battery layered oxide cathode material.

[0034] This application, by controlling the volume average particle size Dv50 and mass ratio of the O3-type core layer material and the P2-type shell material within the aforementioned range, facilitates the uniform coating of the P2-type shell material onto the surface of the O3-type core layer material to form a core-shell structure, thereby obtaining a composite sodium-ion battery layered oxide cathode material. The core-shell structure cathode material obtained by grinding, mixing, and high-temperature solid-state calcination of the O3-type core layer material and the P2-type shell material utilizes the synergistic effect of the core-shell structure design and doping elements to enable the cathode material to have a high charge-discharge specific capacity while maintaining good air stability and high cycle stability.

[0035] The beneficial effects of this application are:

[0036] This application provides a composite layered oxide cathode material for sodium-ion batteries and its preparation method. The cathode material includes an O3-type core layer material and a P2-type shell material coating the surface of the O3-type core layer material. The chemical formula of the O3-type core layer material is NahNi. i MnjFekZr 1- ij-kO2, 0.95≤h≤1.15, 0.25≤i≤0.4, 0.25≤j≤0.4, 0.25≤k≤0.4, 0.05≤1-ijk≤0.15. The chemical formula of the P2 type shell material is: Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r O2, 0.01≤p≤0.07, 0.01≤q≤0.15, 0.01≤r≤0.07. This application provides a high charge-discharge specific capacity through an O3-type core material and a P2-type shell material to provide good air stability. Furthermore, the cycling stability of the core material is improved by doping it with zirconium, and the cycling stability of the shell material is enhanced by doping it with magnesium, titanium, and tin to suppress complex phase transitions during charge-discharge cycling. This results in a cathode material that maintains both high charge-discharge specific capacity and good air stability and high cycling stability.

[0037] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0039] Figure 1 This is a scanning electron microscope image of the layered oxide cathode material of the composite sodium-ion battery in Example 1 of this application;

[0040] Figure 2 This is a scanning electron microscope image of the layered oxide cathode material of the composite sodium-ion battery in Comparative Example 1 of this application;

[0041] Figure 3 This is a particle size distribution diagram of the composite sodium-ion battery layered oxide cathode material in Example 1 of this application. Detailed Implementation

[0042] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application. Specific technical solutions are as follows:

[0043] The first aspect of this application provides a composite layered oxide cathode material for sodium-ion batteries. The cathode material includes an O3-type core layer material and a P2-type shell material coated on the surface of the O3-type core layer material. The chemical formula of the O3-type core layer material is NaHNi. i MnjFekZr 1- ij-kO2, 0.95≤h≤1.15, 0.25≤i≤0.4, 0.25≤j≤0.4, 0.25≤k≤0.4, 0.05≤1-ijk≤0.15; The chemical formula of the P2 type shell material is: Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r O2, 0.01≤p≤0.07, 0.01≤q≤0.15, 0.01≤r≤0.07. The O3-type core material provides high charge / discharge specific capacity, while the P2-type shell material provides good air stability. Doping the O3-type core material with zirconium enhances its cycle stability, while doping the P2-type shell material with magnesium, titanium, and tin suppresses complex phase transitions during charge / discharge cycling, further improving its cycle stability. Through this core-shell structure design and the synergistic effect of the doping elements, the cathode material achieves high charge / discharge specific capacity while maintaining good air stability and high cycle stability.

[0044] In some embodiments of this application, the mass ratio of O3-type core material to P2-type shell material is 20:1 to 10:1. By controlling the mass ratio of O3-type core material and P2-type shell material within the above range, this application facilitates the full coating of P2-type shell material onto the surface of O3-type core material to form a core-shell structure, thereby obtaining a composite sodium-ion battery layered oxide cathode material with good air stability and high charge-discharge specific capacity.

[0045] In some embodiments of this application, the Dv50 of the O3 type core layer material is 5 μm to 8 μm, and the Dv50 of the P2 type shell material is 0.2 μm to 0.8 μm. By controlling the volume average particle size Dv50 of the O3 type core layer material and the P2 type shell material within the above range, this application facilitates the uniform coating of the P2 type shell material onto the surface of the O3 type core layer material to form a core-shell structure, thereby obtaining a composite sodium-ion battery layered oxide cathode material with good air stability and high cycle stability. Here, Dv50 represents the particle size that, from the smallest particle size side, reaches 50% of the total volumetric particle size distribution.

[0046] In some embodiments of this application, the sodium source of the positive electrode material is selected from at least one of sodium carbonate, sodium sulfate, or sodium nitrate; the nickel source of the positive electrode material is selected from at least one of nickel acetate, nickel nitrate, or nickel sulfate; and the manganese source of the positive electrode material is selected from at least one of manganese acetate, manganese nitrate, or manganese sulfate. Using the above materials as the sodium source of the positive electrode material facilitates the uniform diffusion of sodium ions in the core and shell structures of the positive electrode material to form a sodium ion layer; using the above materials as the nickel source of the positive electrode material helps to improve the charge-discharge specific capacity of the positive electrode material.

[0047] In some embodiments of this application, the iron source of the positive electrode material is selected from at least one of ferric chloride, ferric nitrate, or ferric sulfate, and the zirconium source of the positive electrode material is selected from at least one of zirconium nitrate, zirconium isopropoxide, or zirconium chloride. By selecting the above materials as the iron source for the O3-type core layer material, it is beneficial for the uniform doping of iron into the precursor of the O3-type core layer material, thereby facilitating the formation of a uniform and stable core layer material. By selecting the above materials as the zirconium source for the O3-type core layer material, it is beneficial for improving the conductivity of the core layer material, thereby improving the fast charge-discharge performance of the secondary battery. Simultaneously, zirconium helps reduce the side reactions between sodium ions and the electrolyte in the core layer material, slowing down the aging rate of the positive electrode material during cycling, reducing the self-discharge rate of the secondary battery, thereby improving the storage time and stability of the secondary battery and extending its service life.

[0048] In some embodiments of this application, the magnesium source of the positive electrode material is selected from at least one of magnesium carbonate, magnesium chloride, magnesium oxalate, or magnesium sulfate; the titanium source of the positive electrode material is selected from at least one of titanium oxysulfate or titanium tetrachloride; and the tin source of the positive electrode material is selected from at least one of tin tetrachloride or tin nitrate. By selecting the above materials as the magnesium source of the P2-type shell material, it is beneficial for magnesium to be uniformly doped into the P2-type shell material, suppressing harmful phase transitions in the shell material during charge and discharge, thereby improving the structural stability of the positive electrode material. By selecting the above materials as the titanium source of the P2-type shell material, it is beneficial for titanium to be uniformly doped into the P2-type shell material, thereby facilitating the formation of a uniform and stable P2-type shell material. By selecting the above materials as the tin source of the P2-type shell material, it is beneficial for tin to be uniformly doped into the P2-type shell material, thereby facilitating the formation of a uniform and stable P2-type shell material. Simultaneously, tin, as a stable element, optimizes current flow and improves stability in air when doped into the positive electrode material, thereby improving the cycle stability of the secondary battery.

[0049] The second aspect of this application provides a method for preparing a composite sodium-ion battery layered oxide cathode material, wherein the method includes: Step 1. Preparing an O3-type core layer material Na h Ni i Mn j Fe k Zr 1-i-j-k O2; Step 2. Preparation of P2-type shell material Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r O2; Step 3. Grind, mix, and calcine the O3 type core material and the P2 type shell material at high temperature to obtain a composite sodium-ion battery layered oxide cathode material.

[0050] This application utilizes an O3-type core material to provide a high charge-discharge specific capacity and a P2-type shell material to provide good air stability. Furthermore, doping the O3-type core material with zirconium enhances its cycle stability, while doping the P2-type shell material with magnesium, titanium, and tin suppresses complex phase transitions during charge-discharge cycles, thus improving its cycle stability. The resulting core-shell structure cathode material, obtained by grinding, mixing, and high-temperature solid-state calcination of the O3-type core material and the P2-type shell material, exhibits high charge-discharge specific capacity while maintaining good air stability and high cycle stability.

[0051] In some embodiments of this application, O3-type core material Na is prepared. h Ni i Mn jFe k Zr 1-i-j-k O2 includes: (1) according to the chemical formula of O3 type core material Na h Ni i Mn j Fe k Zr 1-i-j-k The stoichiometric ratios of nickel, manganese, iron and zirconium in O2 were determined by weighing nickel, manganese, iron and zirconium sources and dissolving them in deionized water to prepare a mixed metal salt solution with a total concentration of nickel, manganese, iron and zirconium of 1.2 mol / L to 2 mol / L, wherein 0.25≤i≤0.4, 0.25≤j≤0.4, 0.25≤k≤0.4, 0.05≤1-ijk≤0.15; (2) Deionized water was added to the coprecipitation reaction vessel as the base liquid, and then nitrogen gas was introduced into the base liquid at a flow rate of 20 mL / min to 50 mL / min. Subsequently, the precipitant, complexing agent and mixed metal salt solution were added dropwise to the coprecipitation reaction vessel to carry out the coprecipitation reaction. During the coprecipitation reaction, the coprecipitation was controlled. The pH in the precipitation reaction vessel is 11 to 12, the reaction temperature is 50℃ to 60℃, and the stirring speed is 500r / min to 800r / min. The precipitant is a 2mol / L sodium hydroxide solution and the complexing agent is a 1mol / L ammonia solution. (3) After the mixed metal salt solution in the coprecipitation reaction vessel is finished, stop adding the precipitant and complexing agent. Then continue stirring at a stirring speed of 200r / min to 300r / min for aging reaction for 10h to 20h. Then filter and wash the obtained coprecipitate with deionized water. Then put it in a vacuum drying oven and dry it at 80℃ to 110℃ for 16h to 24h to obtain O3 type core layer precursor material. (4) According to the chemical formula of O3 type core layer material Na h Ni i Mn j Fe k Zr 1-i-j-k The stoichiometric ratio of sodium to transition metal in O2 was used to obtain the O3-type core layer precursor material, which was then mixed uniformly with a sodium source. The mixture was then heated to 550℃ at a first heating rate of 4℃ / min and held for 6 hours in air, followed by a second heating rate of 4℃ / min to 930℃ and held for 12 hours. Finally, it was cooled to room temperature naturally to obtain the O3-type core layer material Na. h Ni i Mn j Fe k Zr 1-i-j-kO2, wherein 0.95≤h≤1.15, 0.25≤i≤0.4, 0.25≤j≤0.4, 0.25≤k≤0.4, 0.05≤1-ijk≤0.15. This application improves the cycling stability of the O3-type core layer material by doping it with zirconium. By controlling the content and proportion of each element within the above ranges, the cycling stability of the core layer material is significantly improved while avoiding a significant decrease in its reversible specific capacity. Controlling the total concentration of the mixed metal salt solution of nickel, manganese, iron, and zirconium, the nitrogen flow rate, the pH of the coprecipitation reaction, the coprecipitation reaction temperature, the stirring speed of the coprecipitation reaction, the aging reaction time, the stirring speed of the aging reaction, and the vacuum drying temperature and time within the above ranges is beneficial for generating a uniform and stable O3-type core layer precursor material. Controlling the heating rate, cooling rate, and holding time is beneficial for obtaining an O3-type core layer material with uniform particle size distribution and stable structure.

[0052] In some embodiments of this application, the P2-type shell material Na is prepared. 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r O2 includes: (1) according to the P2 type shell material Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn rThe stoichiometric ratios of nickel, magnesium, manganese, titanium and tin in O2 were determined by weighing nickel, magnesium, manganese, titanium and tin sources respectively and dissolving them in deionized water to prepare a mixed metal salt solution with a total concentration of nickel, magnesium, manganese, titanium and tin of 0.5 mol / L to 1 mol / L, wherein 0.01≤p≤0.07, 0.01≤q≤0.15, 0.01≤r≤0.07; (2) Deionized water was added to the coprecipitation reaction vessel as the base liquid, and then nitrogen gas was introduced into the base liquid at a flow rate of 20 mL / min to 50 mL / min. Subsequently, the precipitant, complexing agent and mixed metal salt solution were added dropwise to the coprecipitation reaction vessel to carry out the coprecipitation reaction. During the coprecipitation reaction, the coprecipitation was controlled. The pH in the precipitation reaction vessel is 11 to 12, the reaction temperature is 50℃ to 60℃, and the stirring speed is 500r / min to 800r / min. The precipitant is a 2mol / L sodium hydroxide solution and the complexing agent is a 1mol / L ammonia solution. (3) After the mixed metal salt solution in the coprecipitation reaction vessel is finished, stop adding the precipitant and complexing agent. Then continue stirring at a stirring speed of 200r / min to 300r / min for aging reaction for 5h to 10h. Then filter and wash the obtained coprecipitate with deionized water and then put it in a vacuum drying oven at 80℃ to 110℃ for 16h to 24h to obtain P2 type shell precursor material. (4) According to the P2 type shell material Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r The stoichiometric ratio of sodium to transition metal in O2 was used to determine the composition of the P2-type core precursor material and the sodium source. The mixture was then ball-milled and mixed, followed by heating to 800℃ at a rate of 4℃ / min under air atmosphere and holding for 10 hours. Afterward, it was cooled to room temperature naturally to obtain the P2-type shell material Na. 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn rO2, wherein 0.01≤p≤0.07, 0.01≤q≤0.15, 0.01≤r≤0.07. This application suppresses complex phase transitions in the shell material during charge-discharge cycles by doping it with magnesium, titanium, and tin, thereby improving the cycle stability of the shell material. By controlling the content and proportion of each element within the above range, the cycle stability of the core material is improved. By controlling the total concentration of the mixed metal salt solution of nickel, magnesium, manganese, titanium, and tin, the nitrogen flow rate, the pH of the coprecipitation reaction, the temperature of the coprecipitation reaction, the stirring speed of the coprecipitation reaction, the aging reaction time, the stirring speed of the aging reaction, and the vacuum drying temperature and time within the above range, it is beneficial to generate a uniform and stable O3 type core precursor material. By controlling the heating rate, cooling rate, and holding time, it is beneficial to obtain a P2 type shell material with uniform particle size distribution, suitable size, and stable structure.

[0053] In some embodiments of this application, the composite sodium-ion battery layered oxide cathode material is obtained by grinding, mixing, and high-temperature solid-state calcination of O3-type core material and P2-type shell material. The process includes: (1) grinding O3-type core material into particles with Dv50 of 5μm to 8μm and P2-type shell material into particles with Dv50 of 0.2μm to 0.8μm by air jet milling, and then weighing O3-type core material and P2-type shell material in a weight ratio of 20:1 to 10:1 and adding them into a mixer for uniform mixing; (2) heating the mixed O3-type core material and P2-type shell material to 600℃ in air at a heating rate of 4℃ / min and holding it at that temperature for 8h; and then cooling it to room temperature at a natural cooling rate to obtain the composite sodium-ion battery layered oxide cathode material. This application, by controlling the volume average particle size Dv50 and mass ratio of the O3-type core layer material and the P2-type shell material within the aforementioned range, facilitates the uniform coating of the P2-type shell material onto the surface of the O3-type core layer material to form a core-shell structure, thereby obtaining a composite sodium-ion battery layered oxide cathode material. The core-shell structure cathode material obtained by grinding, mixing, and high-temperature solid-state calcination of the O3-type core layer material and the P2-type shell material utilizes the synergistic effect of the core-shell structure design and doping elements to enable the cathode material to have a high charge-discharge specific capacity while maintaining good air stability and high cycle stability.

[0054] The secondary battery of this application also includes a separator. This application does not impose any particular restrictions on the separator, and those skilled in the art can choose one according to actual needs, as long as it can achieve the purpose of this application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), cellulose, polyimide (PI), or polyamide; the type of separator may include, but is not limited to, at least one of dry membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0055] The secondary battery of this application also includes an electrolyte. This application does not impose any particular limitations on the electrolyte; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. For example, at least one of ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), vinylene carbonate (VC), or fluoroethylene carbonate (FEC) can be mixed in a certain mass ratio to obtain a non-aqueous organic solvent, and then a sodium salt can be added to dissolve and mix evenly. This application does not impose any particular limitations on the above-mentioned "mass ratio," as long as the purpose of this application is achieved. This application does not limit the type of sodium salt, as long as the purpose of this application is achieved. For example, the sodium salt may include at least one of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetraphenylborate [NaB(C6H5)4], sodium trifluoromethanesulfonate (NaCF3SO3), sodium fluorosilicate (NaSiF6), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium dioxolaneborate (NaBOB), or sodium difluorooxolaneborate (NaDFOB). This application does not impose any particular limitation on the concentration of the sodium salt in the electrolyte, as long as it achieves the purpose of this application. For example, the concentration of the sodium salt may be from 1.0 mol / L to 2.0 mol / L.

[0056] The positive electrode sheet of this application may include a positive electrode material layer and a positive electrode current collector. The positive electrode material layer of this application may also include a conductive agent and a binder. The conductive agent includes at least one of conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, or graphene. The binder includes at least one of polyvinylidene fluoride, sodium polyacrylate, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, or polypropylene. This application does not impose any particular limitation on the mass ratio of positive electrode material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the mass ratio of positive electrode material, conductive agent, and binder in the positive electrode material layer is (70-95):(5-10):(5-10).

[0057] This application does not impose any particular limitation on the positive electrode current collector, as long as it achieves the purpose of this application. For example, the positive electrode current collector may comprise aluminum foil, aluminum alloy foil, or a composite current collector. This application also does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector may be from 5 μm to 20 μm. In this application, the positive electrode active material layer may be disposed on one surface or on two surfaces in the thickness direction of the positive electrode current collector. It should be noted that the term "surface" here can refer to the entire area of ​​the positive electrode current collector or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0058] This application does not impose any particular limitation on the preparation method of the positive electrode sheet. Any preparation method known in the art can be selected, as long as it can achieve the purpose of this application. For example, the preparation method of the positive electrode sheet includes, but is not limited to, the following steps: dispersing the active material, conductive agent and binder in N-methylpyrrolidone (NMP) solvent and mixing to form a uniform positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector; and obtaining the positive electrode sheet after drying, cold pressing, cutting, slitting and re-drying.

[0059] Example

[0060] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0061] Test methods and equipment:

[0062] Scanning electron microscopy test of layered oxide cathode material for composite sodium-ion batteries:

[0063] The composite sodium-ion battery layered oxide cathode materials in each embodiment and comparative example were tested using scanning electron microscopy (SEM). The instrument's focused electron beam excited the sample surface, generating secondary electrons, backscattered electrons, and characteristic X-rays, which were then collected and analyzed for the material's surface microstructure and micro-area composition. SEM testing conditions: working distance 10 mm to 30 mm, objective aperture 50 μm to 500 μm, accelerating voltage 10 kV to 20 kV, and the testing instrument was a Hitachi S3400.

[0064] Particle size testing of O3-type core material and P2-type shell material:

[0065] The particle size test method refers to GB / T 19077-2016. The Dv50 of the O3-type nuclear layer material and the P2-type shell layer material is tested using a laser particle size analyzer. During the test, when the laser beam passes through the dispersed particle sample, the particle size measurement is completed by measuring the intensity of the scattered light. The refractive index of the particles used in the test is 2.61. Each sample is tested three times, and the final particle size is the average of the three tests to obtain Dv50. Laser particle size analyzer model: Forbus FBS-1570ZXP, test range 0.1μm to 500μm.

[0066] Test of the initial charge-discharge specific capacity and cycle performance of the secondary battery at 0.1C, 2-4V:

[0067] Assemble the composite sodium-ion battery layered oxide cathode materials in each example and each comparative example into sodium-ion button cells, and then use the Blue Power series battery test system (LAND CT3002A) for charge-discharge testing: At room temperature, charge at a constant current of 0.1C (1C = 150 mAh / g) until the voltage reaches 4V, then charge at a constant voltage of 4V until the current is lower than 0.05C to make it in a fully charged state at 4V. Subsequently, discharge at a constant current of 0.1C until the voltage reaches 2V and stop. The obtained capacity is recorded as the initial discharge specific capacity.

[0068] After that, repeat the above steps for 1000 charge and discharge cycles, and record the discharge specific capacity of the 1000th cycle. Cycle capacity retention rate = (discharge specific capacity of the 1000th cycle / discharge specific capacity of the first cycle) × 100%.

[0069] Test of the air stability of the composite sodium-ion battery layered oxide cathode material:

[0070] After storing the composite sodium-ion battery layered oxide cathode materials in each example and each comparative example in the air at a temperature of 25°C and a relative humidity of 50% for 72 hours, dry them in a vacuum drying oven at 80°C for 24h, and then prepare and test sodium-ion button cells with the same process. The obtained initial discharge capacity is recorded as the initial discharge specific capacity after being placed in the air for 72h.

[0071] Example 1

[0072] <Preparation of O3-type nuclear layer material>

[0073] (1) According to the chemical formula of the O3-type nuclear layer material Na 1.08 Ni 0.33 Mn 0.32 Fe 0.25 Zr 0.1The stoichiometric ratios of nickel, manganese, iron, and zirconium elements in O2. Weigh 0.33 mol of nickel nitrate [Ni(NO3)2], 0.32 mol of manganese nitrate [Mn(NO3)2], 0.25 mol of iron nitrate [(Fe(NO3)3], and 0.1 mol of zirconium nitrate [(Zr(NO3)4] and dissolve them in deionized water to prepare a mixed metal salt solution with a total concentration of nickel, manganese, iron, and zirconium of 1.6 mol / L;

[0074] (2) Add deionized water to the coprecipitation reaction vessel as the bottom liquid, then introduce nitrogen into the bottom liquid with a nitrogen flow rate of 35 mL / min. Subsequently, add the precipitating agent, complexing agent, and the mixed metal salt solution dropwise into the coprecipitation reaction vessel for coprecipitation reaction. During the coprecipitation reaction, control the pH in the coprecipitation reaction vessel to be 11.5, the reaction temperature to be 55 °C, and the stirring speed to be 650 r / min. Among them, the precipitating agent is a 2 mol / L sodium hydroxide solution, and the complexing agent is a 1 mol / L ammonia water solution;

[0075] (3) After the injection of the mixed metal salt solution in the coprecipitation reaction vessel is completed, stop adding the precipitating agent and complexing agent, and then continue to stir at a stirring speed of 240 r / min for an aging reaction for 15 h. Then, filter and wash the obtained coprecipitation product with deionized water, and then place it in a vacuum drying oven to dry at 100 °C for 20 h to obtain an O3-type core layer precursor material;

[0076] (4) According to the stoichiometric ratio of sodium element in the O3-type core layer material chemical formula Na 1.08 Ni 0.33 Mn 0.32 Fe 0.25 Zr 0.1 O2 and the O3-type core layer precursor material, weigh 0.57 mol of sodium carbonate (Na2CO3) and 1 mol of the above-prepared O3-type core layer precursor material and put them into a ball mill jar for ball milling. Among them, the ball mill rotation speed is 400 rpm, and the ball milling time is 10 h; then, in an air atmosphere, heat it at a first-stage heating rate of 4 °C / min to 550 °C and hold for 6 h, and then heat it at a second-stage heating rate of 4 °C / min to 930 °C and hold for 12 h; subsequently, cool it to room temperature at a natural cooling rate, and then obtain the O3-type core layer material Na 1.08 Ni 0.33 Mn 0.32 Fe 0.25 Zr 0.1 O2. Among them, when weighing the sodium source, an additional 5 mol% excess is added based on the original molar amount of sodium element to supplement the sodium element loss during the high-temperature sintering process.

[0077] <Preparation of P2-type shell layer material>

[0078] (1) According to the chemical formula of P2 type shell material Na 0.7 Ni 0.33 Mg 0.04 Mn 0.51 Ti 0.08 Sn 0.04 The stoichiometric ratios of sodium, nickel, magnesium, manganese, titanium, and tin in O2 were determined by weighing out 0.33 mol of nickel nitrate [Ni(NO3)2], 0.04 mol of magnesium chloride (MgCl2), 0.51 mol of manganese nitrate [Mn(NO3)2], 0.08 mol of titanium tetrachloride (TiCl4), and 0.04 mol of tin tetrachloride (SnCl4) and dissolving them in deionized water to prepare a mixed metal salt solution with a total concentration of 0.75 mol / L for nickel, magnesium, manganese, titanium, and tin.

[0079] (2) Add deionized water as a base liquid to the coprecipitation reaction vessel, and then introduce nitrogen gas into the base liquid at a flow rate of 35 mL / min. Subsequently, add the precipitant, complexing agent and the mixed metal salt solution dropwise into the coprecipitation reaction vessel to carry out the coprecipitation reaction. During the coprecipitation reaction, control the pH in the coprecipitation reaction vessel to be 11.5, the reaction temperature to be 55℃, and the stirring speed to be 650 r / min. The precipitant is a 2 mol / L sodium hydroxide solution and the complexing agent is a 1 mol / L ammonia solution.

[0080] (3) After the mixed metal salt solution in the coprecipitation reaction vessel is finished, stop adding precipitant and complexing agent, and then continue stirring at a stirring speed of 240 r / min for 7.5 h of aging reaction. Then filter and wash the obtained coprecipitation product with deionized water, and then put it into a vacuum drying oven to dry at 100 °C for 20 h to obtain P2 type shell precursor material.

[0081] (4) According to the P2 type shell material Na 0.7 Ni 0.33 Mg 0.04 Mn 0.51 Ti 0.08 Sn 0.04 The stoichiometric ratio of sodium to transition metal in O2 was determined by weighing 0.37 mol of sodium carbonate (Na2CO3) and 1 mol of the prepared P2-type core precursor material and placing them in a ball mill jar for ball milling at 400 rpm for 20 h. The mixture was then heated to 800 °C at a rate of 4 °C / min under air atmosphere and held for 10 h. Afterward, it was cooled to room temperature naturally to obtain the P2-type shell material Na2CO3. 0.7 Ni 0.33 Mg 0.04Mn 0.51 Ti 0.08 Sn 0.04 O2, wherein when weighing the sodium source, an additional 5 mol% is added on top of the original molar amount of sodium element to compensate for the sodium element loss during the high-temperature sintering process.

[0082] <Preparation of Composite Sodium-Ion Battery Layered Oxide Cathode Materials>

[0083] (1) The O3 core material was ground into particles with a Dv50 of 6.5 μm by air jet milling, and the P2 shell material was ground into particles with a Dv50 of 0.5 μm. Then, the O3 core material and the P2 shell material were weighed at a weight ratio of 15:1 and added to a mixer and mixed evenly.

[0084] (2) The mixed O3 core material and P2 shell material are heated to 600°C in air at a heating rate of 4°C / min and kept at that temperature for 8 hours. Then, the temperature is cooled to room temperature at a natural cooling rate to obtain the composite sodium-ion battery layered oxide cathode material.

[0085] <Preparation of the positive electrode>

[0086] The composite sodium-ion battery layered oxide cathode material prepared above, and the composite sodium-ion battery layered oxide cathode material that has been stored in air at 25°C and 50% relative humidity for 72 hours and then dried in a vacuum drying oven at 80°C for 24 hours, were mixed with polyvinylidene fluoride (PVDF) and conductive carbon black (SP) at a mass ratio of 80:10:10, and N-methylpyrrolidone (NMP) was added as a solvent. After stirring evenly, the mixture was coated on one surface of the cathode current collector aluminum foil, and then placed in an 80°C forced-air drying oven for 2 hours, and then placed in an 80°C vacuum drying oven for 24 hours. Finally, it was punched using a button cell slicing machine equipped with a 10mm diameter punching die to obtain the cathode electrode sheet.

[0087] <Preparation of Electrolyte>

[0088] In a glove box protected by inert argon gas and with water and oxygen content <0.1ppm, 1mol / L sodium hexafluorophosphate (NaPF6) was dissolved in an organic solvent with a volume ratio of 1:1 of ethylene carbonate (EC): diethyl carbonate (DEC) and mixed thoroughly to obtain an electrolyte.

[0089] <Preparation of the diaphragm>

[0090] A porous polypropylene film with a thickness of 12μm was used.

[0091] <Preparation of Sodium-ion Batteries>

[0092] In a glove box under the protection of inert argon gas with the water and oxygen content < 0.1 ppm, a CR2032 button sodium-ion battery for testing was assembled in the order of negative electrode shell, sodium metal sheet, electrolyte, separator, electrolyte, positive electrode sheet, gasket, spring sheet, and positive electrode shell, and finally encapsulated by a button battery encapsulation machine.

[0093] Examples 2 to 6

[0094] Except that in the preparation of the <O3-type core layer material>, the stoichiometric ratios of sodium, nickel, manganese, iron, and zirconium elements were adjusted as shown in Table 1, the rest was the same as in Example 1.

[0095] Examples 7 to 10

[0096] Except that in the preparation of the <P2-type shell layer material>, the stoichiometric ratios of sodium, nickel, magnesium, manganese, titanium, and tin elements were adjusted as shown in Table 1, the rest was the same as in Example 1.

[0097] Examples 11 to 12

[0098] Except that in the preparation of the <composite sodium-ion battery layered oxide cathode material>, the mass ratio of the O3-type core layer material to the P2-type shell layer material was adjusted as shown in Table 1, the rest was the same as in Example 1.

[0099] Examples 13 to 14

[0100] Except that in the preparation of the <O3-type core layer material>, the total concentration of nickel, manganese, iron, and zirconium elements in the core layer precursor material was adjusted as shown in Table 2, in the preparation of the <P2-type shell layer material>, the total concentration of nickel, magnesium, manganese, titanium, and tin elements in the shell layer precursor material was adjusted as shown in Table 2, and in the preparation of the <composite sodium-ion battery layered oxide cathode material>, the grinding time of the O3-type core layer material and the P2-type shell layer material was adjusted to adjust the Dv50 of the O3-type core layer material and the P2-type shell layer material as shown in Table 1, the rest was the same as in Example 1.

[0101] Examples 15 to 16

[0102] Except that in the preparation of the <O3-type core layer material> and the <P2-type shell layer material>, the raw material types of each element were regulated as shown in Table 1, the rest was the same as in Example 1.

[0103] Example 17

[0104] Except in the <Preparation of O3-Type Core Layer Material>, as shown in Table 2, the control step (2) is "adding deionized water to the coprecipitation reaction vessel as the bottom liquid, then introducing nitrogen into the bottom liquid with a nitrogen flow rate of 20 mL / min. Subsequently, the precipitating agent, complexing agent, and mixed metal salt solution are respectively dropped into the coprecipitation reaction vessel for coprecipitation reaction. During the coprecipitation reaction, the pH in the coprecipitation reaction vessel is controlled at 11, the reaction temperature is 50 °C, and the stirring speed is 500 r / min. Among them, the precipitating agent is a 2 mol / L sodium hydroxide solution, and the complexing agent is a 1 mol / L ammonia water solution"; the control step (3) is "after the injection of the mixed metal salt solution in the coprecipitation reaction vessel is completed, stop dropping the precipitating agent and complexing agent, then continue to stir at a stirring speed of 200 r / min for an aging reaction for 10 h. Then, the obtained coprecipitation product is filtered and washed with deionized water, and then placed in a vacuum drying oven and dried at 80 °C for 16 h".

[0105] In the <Preparation of P2-Type Shell Layer Material>, as shown in Table 2, except that the control step (2) is "adding deionized water to the coprecipitation reaction vessel as the bottom liquid, then introducing nitrogen into the bottom liquid with a nitrogen flow rate of 35 mL / min. Subsequently, the precipitating agent, complexing agent, and the mixed metal salt solution are respectively dropped into the coprecipitation reaction vessel for coprecipitation reaction. During the coprecipitation reaction, the pH in the coprecipitation reaction vessel is controlled at 11.5, the reaction temperature is 55 °C, and the stirring speed is 650 r / min. Among them, the precipitating agent is a 2 mol / L sodium hydroxide solution, and the complexing agent is a 1 mol / L ammonia water solution"; the control step (3) is "after the injection of the mixed metal salt solution in the coprecipitation reaction vessel is completed, stop dropping the precipitating agent and complexing agent, then continue to stir at a stirring speed of 240 r / min for an aging reaction for 5 h. Then, the obtained coprecipitation product is filtered and washed with deionized water, and then placed in a vacuum drying oven and dried at 80 °C for 16 h", the rest are the same as in Example 1.

[0106] Example 18

[0107] Except in the preparation of the <O3-type core layer material>, as shown in Table 2, the control step (2) is "adding deionized water to the coprecipitation reaction vessel as the bottom liquid, then introducing nitrogen gas into the bottom liquid with a nitrogen gas flow rate of 50 mL / min, and subsequently dripping the precipitating agent, complexing agent, and mixed metal salt solution into the coprecipitation reaction vessel respectively for coprecipitation reaction. During the coprecipitation reaction, control the pH in the coprecipitation reaction vessel to be 12, the reaction temperature to be 60 °C, and the stirring speed to be 800 r / min. Among them, the precipitating agent is a 2 mol / L sodium hydroxide solution, and the complexing agent is a 1 mol / L ammonia water solution"; the control step (3) is "after the injection of the mixed metal salt solution in the coprecipitation reaction vessel ends, stop dripping the precipitating agent and complexing agent, and then continue to stir at a stirring speed of 300 r / min for aging reaction for 20 h, and then filter and wash the obtained coprecipitation product with deionized water, and then place it in a vacuum drying oven and dry at 120 °C for 24 h".

[0108] In the preparation of the <P2-type shell layer material>, as shown in Table 2, the control step (2) is "adding deionized water to the coprecipitation reaction vessel as the bottom liquid, then introducing nitrogen gas into the bottom liquid with a nitrogen gas flow rate of 35 mL / min, and subsequently dripping the precipitating agent, complexing agent, and mixed metal salt solution into the coprecipitation reaction vessel respectively for coprecipitation reaction. During the coprecipitation reaction, control the pH in the coprecipitation reaction vessel to be 11.5, the reaction temperature to be 55 °C, and the stirring speed to be 650 r / min. Among them, the precipitating agent is a 2 mol / L sodium hydroxide solution, and the complexing agent is a 1 mol / L ammonia water solution"; the control step (3) is "after the injection of the mixed metal salt solution in the coprecipitation reaction vessel ends, stop dripping the precipitating agent and complexing agent, and then continue to stir at a stirring speed of 240 r / min for aging reaction for 10 h, and then filter and wash the obtained coprecipitation product with deionized water, and then place it in a vacuum drying oven and dry at 120 °C for 24 h". Except for this, the rest are the same as in Example 1.

[0109] Comparative Examples 1 to 3

[0110] Except in the preparation of the <O3-type core layer material>, adjust the stoichiometric ratios of sodium, nickel, manganese, iron, and zirconium elements as shown in Table 1, and in the preparation of the <P2-type shell layer material>, adjust the stoichiometric ratios of sodium, nickel, magnesium, manganese, titanium, and tin elements as shown in Table 1. Except for this, the rest are the same as in Example 1.

[0111] Table 1

[0112]

[0113]

[0114] Table 2

[0115]

[0116]

[0117] Table 3

[0118]

[0119] Referring to Tables 1 to 3, and comparing Examples 1 to 18 with Comparative Examples 1 to 3, this application demonstrates that the O3-type core material provides a high charge-discharge specific capacity, while the P2-type shell material provides good air stability. Furthermore, doping the O3-type core material with zirconium enhances the cycle stability of the core material, and doping the P2-type shell material with magnesium, titanium, and tin suppresses complex phase transitions during charge-discharge cycling, thereby improving the cycle stability of the shell material. Through the synergistic effect of the core-shell structure design and the doping elements, the cathode material achieves both high charge-discharge specific capacity and good air stability and high cycle stability.

[0120] Specifically, as can be seen from Examples 1 to 10 and Comparative Examples 1 to 3 in Tables 1 and 3, this application controls the content and ratio of each element in the O3 core material by adjusting the cathode material, which includes an O3-type core layer material and a P2-type shell material coating the surface of the O3-type core layer material, to satisfy the following condition: Na h Ni i Mn j Fe k Zr 1-i-j-k O2, 0.95≤h≤1.15, 0.25≤i≤0.4, 0.25≤j≤0.4, 0.25≤k≤0.4, 0.05≤1-ijk≤0.15; the content and proportion of each element in the P2 type shell material are adjusted to satisfy: Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r O2, 0.01≤p≤0.07, 0.01≤q≤0.15, 0.01≤r≤0.07, is beneficial for improving the discharge specific capacity of the cathode material while maintaining good air stability and high cycle stability. Figure 1 This is a scanning electron microscope image of the layered oxide cathode material of the composite sodium-ion battery in Example 1. Figure 1 As can be seen, the overall structure of the cathode material is relatively clear, the surface morphology is regular and dense, and the size distribution is relatively uniform. Figure 2 The image shows a scanning electron microscope (SEM) image of the layered oxide cathode material of the composite sodium-ion battery in Comparative Example 1.Figure 2 As can be seen, the particles of the cathode material are relatively adherent, lack a clear edge structure, and have a relatively uneven particle size distribution. This indicates that by controlling the stoichiometric ratio of the elements in the cathode material within the range of this application, it is beneficial to obtain a composite sodium-ion battery layered oxide cathode material with a clear structure, regular morphology, and relatively uniform size distribution.

[0121] As can be seen from Examples 1, 11 to 12 in Tables 1 and 3, by adjusting the mass ratio of O3-type core material and P2-type shell material within the scope of this application, it is beneficial to make the P2-type shell material fully cover the surface of the O3-type core material and form a core-shell structure, thereby obtaining a composite sodium-ion battery layered oxide cathode material with good air stability and high charge-discharge specific capacity.

[0122] As can be seen from Examples 1, 13 to 14 in Tables 1 and 3, this application, by controlling the Dv50 of the O3 type core layer material to be 5 μm to 8 μm and the Dv50 of the P2 type shell material to be 0.2 μm to 0.8 μm, facilitates the uniform coating of the P2 type shell material onto the surface of the O3 type core layer material to form a core-shell structure, thereby obtaining a composite sodium-ion battery layered oxide cathode material with good air stability and high cycle stability. Specifically, Figure 3 The particle size distribution chart of the cathode material in Embodiment 1 of this application is shown below. Figure 3 As can be seen, the volume average particle size Dv50 of the cathode material is 7 μm, and the particle size distribution width is relatively narrow. This indicates that by controlling the concentration of the mixed metal salt solution of O3-type core layer precursor material and P2-type shell layer precursor material within the scope of this application, the particle size of the cathode precursor material obtained is relatively uniform. This, in turn, results in a uniform particle size distribution of the final composite sodium-ion battery layered oxide cathode material.

[0123] As can be seen from Examples 1, 15 to 16 in Tables 1 and 3, this application, by controlling the types of raw materials of each element in the cathode material within the scope of this application, is beneficial to obtaining a cathode material with high charge-discharge specific capacity while maintaining good air stability and high cycle stability.

[0124] The nitrogen flow rate, pH, reaction temperature, and stirring speed during the coprecipitation reaction, as well as the aging time, stirring speed, and vacuum drying temperature and time during the aging process, typically affect the electrochemical performance of the cathode material. As can be seen from Examples 1, 17, and 18 in Tables 1 to 3, by adjusting the above process parameters within the scope of this application, it is beneficial to obtain O3-type core-layer precursor materials and P2-type shell-layer precursor materials with better morphology, thereby obtaining cathode materials with high charge-discharge specific capacity while maintaining good air stability and high cycle stability.

[0125] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0126] The above are merely preferred embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A composite layered oxide cathode material for sodium-ion batteries, wherein, The positive electrode material comprises an O3-type core layer material and a P2-type shell material coating the surface of the O3-type core layer material. The chemical formula of the O3-type core layer material is: Na h Ni i Mn j Fe k Zr 1-i-j-k O2, 0.95≤h≤1.15, 0.25≤i≤0.4, 0.25≤j≤0.4, 0.25≤k≤0.4, 0.05≤1-ijk≤0.15, 0.05≤1-ijk≤0.15; the chemical formula of the P2 type shell material is: Na 0.7 Ni 0.37- p Mg p Mn 0.63-q-r Ti q Sn r O2, 0.01≤p≤0.07, 0.01≤q≤0.15, 0.01≤r≤0.

07.

2. The composite sodium-ion battery layered oxide cathode material according to claim 1, wherein, The mass ratio of the O3 type core material to the P2 type shell material is 20:1 to 10:

1.

3. The composite sodium-ion battery layered oxide cathode material according to claim 1, wherein, The Dv50 of the O3 type core material is 5 μm to 8 μm, and the Dv50 of the P2 type shell material is 0.2 μm to 0.8 μm.

4. The composite sodium-ion battery layered oxide cathode material according to claim 1, wherein, The sodium source of the positive electrode material is selected from at least one of sodium carbonate, sodium sulfate, or sodium nitrate; the nickel source of the positive electrode material is selected from at least one of nickel acetate, nickel nitrate, or nickel sulfate; and the manganese source of the positive electrode material is selected from at least one of manganese acetate, manganese nitrate, or manganese sulfate.

5. The composite sodium-ion battery layered oxide cathode material according to claim 1, wherein, The iron source of the positive electrode material is selected from at least one of ferric chloride, ferric nitrate, or ferric sulfate, and the zirconium source of the positive electrode material is selected from at least one of zirconium nitrate, zirconium isopropoxide, or zirconium chloride.

6. The composite sodium-ion battery layered oxide cathode material according to claim 1, wherein, The magnesium source of the positive electrode material is selected from at least one of magnesium chloride, magnesium carbonate, or magnesium sulfate; the titanium source of the positive electrode material is selected from at least one of titanium oxysulfate or titanium tetrachloride; and the tin source of the positive electrode material is selected from at least one of tin tetrachloride or tin nitrate.

7. A method for preparing a composite sodium-ion battery layered oxide cathode material according to any one of claims 1 to 6, wherein, The method includes: Step 1. Preparation of O3-type core material Na h Ni i Mn j Fe k Zr 1-i-j-k O2; Step 2. Preparation of P2-type shell material Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r O2; Step 3. Grind, mix, and calcine the O3 core material and the P2 shell material at high temperature to obtain a composite sodium-ion battery layered oxide cathode material.

8. The method for preparing the composite sodium-ion battery layered oxide cathode material according to claim 7, wherein, The preparation of O3-type core material Na h Ni i Mn j Fe k Zr 1-i-j-k O2 includes: (1) According to the chemical formula of O3 type core material Na h Ni i Mn j Fe k Zr 1-i-j-k The stoichiometric ratios of nickel, manganese, iron, and zirconium in O2 were determined by dissolving nickel, manganese, iron, and zirconium sources in deionized water to prepare mixed metal salt solutions with a total concentration of 1.2 mol / L to 2 mol / L, where 0.25 ≤ i ≤ 0.4, 0.25 ≤ j ≤ 0.4, 0.25 ≤ k ≤ 0.4, and 0.05 ≤ 1 - ijk ≤ 0.

15. (2) Deionized water is added to the coprecipitation reaction vessel as the base solution. Nitrogen gas is then introduced into the base solution at a flow rate of 20 mL / min to 50 mL / min. Subsequently, the precipitant, complexing agent, and the mixed metal salt solution are added dropwise to the coprecipitation reaction vessel to carry out the coprecipitation reaction. During the coprecipitation reaction, the pH in the coprecipitation reaction vessel is controlled at 11 to 12, the reaction temperature is controlled at 50°C to 60°C, and the stirring speed is controlled at 500 r / min to 800 r / min. Wherein, the precipitant is a 2 mol / L sodium hydroxide solution, and the complexing agent is a 1 mol / L ammonia solution; (3) After the mixed metal salt solution in the coprecipitation reaction vessel is finished, stop adding the precipitant and complexing agent. Then continue stirring at a stirring speed of 200 r / min to 300 r / min for aging reaction for 10 h to 20 h. Then filter and wash the obtained coprecipitation product with deionized water, and then put it into a vacuum drying oven to dry at 80 ℃ to 110 ℃ for 16 h to 24 h to obtain O3 type core layer precursor material. (4) According to the chemical formula of O3 type core material Na h Ni i Mn j Fe k Zr 1-i-j-k The stoichiometric ratio of sodium to transition metal in O2 was used to determine the composition of the O3-type core layer precursor material and the sodium source. These were then ball-milled and mixed. The mixture was then heated to 550°C at a first heating rate of 4°C / min under air and held for 6 hours. Next, it was heated to 930°C at a second heating rate of 4°C / min and held for 12 hours. Finally, it was cooled to room temperature naturally to obtain the O3-type core layer material, Na. h Ni i Mn j Fe k Zr 1-i-j-k O2, where 0.95≤h≤1.15, 0.25≤i≤0.4, 0.25≤j≤0.4, 0.25≤k≤0.4, and 0.05≤1-ijk≤0.

15.

9. The method for preparing the composite sodium-ion battery layered oxide cathode material according to claim 7, wherein, The preparation of P2-type shell material Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r O2 includes: (1) According to the P2 type shell material Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r The stoichiometric ratios of nickel, magnesium, manganese, titanium, and tin in O2 were determined by dissolving nickel, magnesium, manganese, titanium, and tin sources in deionized water to prepare mixed metal salt solutions with a total concentration of 0.5 mol / L to 1 mol / L, where 0.01 ≤ p ≤ 0.07, 0.01 ≤ q ≤ 0.15, and 0.01 ≤ r ≤ 0.

07. (2) Deionized water is added to the coprecipitation reaction vessel as the base solution. Nitrogen gas is then introduced into the base solution at a flow rate of 20 mL / min to 50 mL / min. Subsequently, the precipitant, complexing agent, and the mixed metal salt solution are added dropwise to the coprecipitation reaction vessel to carry out the coprecipitation reaction. During the coprecipitation reaction, the pH in the coprecipitation reaction vessel is controlled at 11 to 12, the reaction temperature is controlled at 50°C to 60°C, and the stirring speed is controlled at 500 r / min to 800 r / min. Wherein, the precipitant is a 2 mol / L sodium hydroxide solution, and the complexing agent is a 1 mol / L ammonia solution; (3) After the mixed metal salt solution in the coprecipitation reaction vessel is finished, stop adding precipitant and complexing agent, and then continue stirring at a stirring speed of 200 r / min to 300 r / min for aging reaction for 5 h to 10 h. Then filter and wash the obtained coprecipitation product with deionized water, and then put it into a vacuum drying oven to dry at 80 ℃ to 110 ℃ for 16 h to 24 h to obtain P2 type shell precursor material; (4) According to the P2 type shell material Na 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r The stoichiometric ratio of sodium to transition metal in O2 was used to determine the composition of the P2-type core precursor material and the sodium source. The mixture was then ball-milled and mixed, followed by heating to 800°C at a rate of 4°C / min under air atmosphere and holding for 10 hours. Afterward, it was cooled to room temperature naturally to obtain the P2-type shell material Na. 0.7 Ni 0.37-p Mg p Mn 0.63-q-r Ti q Sn r O2, where 0.01≤p≤0.07, 0.01≤q≤0.15, and 0.01≤r≤0.

07.

10. The method for preparing the composite sodium-ion battery layered oxide cathode material according to claim 7, wherein, The O3-type core material and the P2-type shell material are ground, mixed, and subjected to high-temperature solid-state calcination to obtain a composite sodium-ion battery layered oxide cathode material comprising: (1) The O3 type core material is ground into particles with a Dv50 of 5μm to 8μm by air jet milling, and the P2 type shell material is ground into particles with a Dv50 of 0.2μm to 0.8μm. Then, the O3 type core material and the P2 type shell material are weighed in a weight ratio of 20:1 to 10:1 and added to a mixer and mixed evenly. (2) The mixed O3 core material and P2 shell material are heated to 600°C in air at a heating rate of 4°C / min and kept at that temperature for 8 hours. Then, the temperature is cooled to room temperature at a natural cooling rate to obtain the composite sodium-ion battery layered oxide cathode material.

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