A sodium-ion battery cathode material, its preparation method and application

Abstract

The application discloses a sodium ion battery positive electrode material and a preparation method and application thereof, and the positive electrode material comprises a layered oxide and a solid electrolyte layer coated on the surface of the layered oxide. n Ni x M y O2, and the content of the Ni element gradually decreases and the content of the M element gradually increases from the core to the surface of the layered oxide. The precursor salt with gradient distribution of metal elements is prepared by one-step precipitation method, and then is mixed and calcined with a sodium source and an inorganic acid root ion source in steps or one step to obtain the sodium ion battery positive electrode material with the solid electrolyte in situ coated on the surface of the layered oxide. The positive electrode material has high content of active metal components in the core, stable overall structure, and the surface solid electrolyte layer can reduce the interface side reaction of the electrolyte and the layered oxide, and improve ion diffusion, so that the sodium ion battery constructed by the positive electrode material has high capacity, long cycle life and excellent rate performance.

Description

Technical Field

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

[0002] With the increasing popularity of electric vehicles, the demand for lithium-ion batteries is also growing. However, the Earth's lithium resources are very limited and unevenly distributed. Even considering the recycling of power lithium-ion batteries, the available lithium resources cannot supply the ever-increasing number of electric vehicles. Therefore, it is necessary to find alternatives to lithium-ion batteries to meet the demand for large-scale energy storage, and sodium-ion batteries have attracted widespread attention. The biggest advantage of sodium-ion batteries is their low cost and abundant reserves. Sodium has an abundance of 2.64% in the Earth's crust, ranking sixth among all elements, while lithium has an abundance of only 0.006%. Sodium-ion batteries mainly consist of positive electrode materials, electrolytes, separators, and negative electrode materials, with the battery performance primarily determined by the positive and negative electrode materials.

[0003] In recent years, significant progress has been made in the research of anode materials and electrolytes. In contrast, the development of cathode materials has been relatively slow, and the specific capacity of cathode materials is far lower than that of anode materials. Therefore, improving and enhancing the performance of cathode materials is crucial for the development of sodium-ion batteries. The main cathode materials for sodium-ion batteries include: transition metal layered oxides, such as tunnel-type layered oxides with low sodium content, P2-type layered oxides with a sodium content of approximately 0.55-0.75%, and O3-type layered oxides with a sodium content of over 0.8%; polyanionic materials, such as phosphates, fluorophosphates, pyrophosphates, and sulfates; Prussian blue compounds, such as cyanides formed by the coordination of transition metals with Na; and sodium-containing organic polymers. Among these, P2 and O3-type transition metal layered oxides have the highest theoretical capacity, while O3-type materials, with their higher initial Na content than P2-type materials, typically also exhibit higher capacity.

[0004] Similar to ternary lithium-ion batteries, Ni 2+ / Ni 3+ / Ni 4+Redox pairs exhibit the greatest potential in sodium-ion battery systems. Therefore, theoretically, nickel-based layered oxide sodium-ion cathode materials possess high voltage and high capacity characteristics. However, nickel-based layered oxides are prone to many adverse reactions and structural instability phenomena at high voltages, such as multiphase transformations in the 2-4V voltage range, particle breakage caused by cell changes during charge and discharge, interfacial side reactions between the electrode and electrolyte, and dissolution of transition metals, leading to severe irreversible capacity decay during charge and discharge. Core-shell structures, with an electrochemically active high-nickel material as the core and an inactive metal ion material that maintains structural stability, can meet the requirements of high capacity and long cycle life. However, these core-shell structured layered oxide cathode materials are prone to grain boundaries or even interstitial spaces at the core-shell interface, resulting in high impedance and low ionic conductivity. Furthermore, the uniformity of the primary ions formed in the precursor is poor, which is detrimental to the overall performance of the cathode material. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a sodium-ion battery cathode material, its preparation method, and its applications. A precursor salt is prepared via a one-step precipitation method, where the Ni content gradually decreases from the core to the surface, while the M content gradually increases. This precursor salt is then mixed with a sodium source and an inorganic anion source in steps or in one step and calcined to obtain a sodium-ion battery cathode material with a solid electrolyte in situ coated on the surface of a layered oxide. This cathode material exhibits a high content of active metal components in the core, a stable overall structure, and the solid electrolyte layer on the surface reduces interfacial side reactions between the electrolyte and the layered oxide, promoting sodium ion diffusion. Consequently, the sodium-ion battery constructed from this material possesses high capacity, long cycle life, and excellent rate performance.

[0006] Specifically, the following technical solutions are provided:

[0007] The first aspect of the present invention provides a sodium-ion battery cathode material comprising a layered oxide and a solid electrolyte layer coated on the surface of the layered oxide;

[0008] The chemical formula of the layered oxide is Na. n Ni x M y O2, wherein the Ni content of the layered oxide gradually decreases and the M content gradually increases from the core to the surface;

[0009] The solid electrolyte layer comprises one or more of sodium phosphate, sodium silicate, and sodium pyrophosphate, and the solid electrolyte layer contains at least one of the elements M.

[0010] Wherein, M is selected from one or more of Ti, Co, Mn, Zn, Fe, Al and Cu;

[0011] 0.8≤n≤1.1, 0.4≤x≤0.75, x+y=1.

[0012] Furthermore, the molar ratio of the layered oxide to the solid electrolyte in the solid electrolyte layer is preferably 1:(0.01-0.1);

[0013] Furthermore, the layered oxide Na n Ni x M y O2 is also doped with element A, which is selected from one or more of Mo, W, Sb, Nb, Sn, Ca, Sr, Li, Y, V, Cr, La, Ti, Co, Mn, Mg, Zn, Fe, Al and Cu, and element A and element M are selected from different elements; the doping amount of element A in the layered oxide is not higher than 0.1.

[0014] A second aspect of this invention provides a method for preparing the sodium-ion battery cathode material described in the first aspect, comprising the following steps:

[0015] S1: Provide mixed solution A and mixed solution B, which are obtained by dissolving Ni source and M source in water; wherein...

[0016] The concentration of the Ni source in the mixed solution A is greater than the concentration of the Ni source in the mixed solution B;

[0017] The concentration of source M in mixed solution A is less than the concentration of source M in mixed solution B;

[0018] The metal element M in the M source is selected from one or more of Ti, Co, Mn, Mg, Zn, Fe, Al and Cu;

[0019] S2: The mixed solution B in S1 is continuously pumped into a container containing mixed solution A to form a precursor solution. At the same time, the precursor solution is continuously pumped into a continuously stirred reaction vessel, and a precipitant and a complexing agent are added to react and obtain the precursor salt.

[0020] S3: The precursor salt prepared in S2 is mixed evenly with a sodium source, and a layered oxide is obtained by a first calcination treatment. The layered oxide is then heated and stirred with an inorganic acid anion source in the presence of a dispersant. The solid is separated and collected for a second calcination treatment to obtain the sodium-ion battery cathode material; or,

[0021] The precursor salt prepared by S2 is heated and stirred with sodium source and inorganic acid anion source in the presence of dispersant. The solid is separated and collected for pre-calcination treatment, and then sintered to obtain the sodium-ion battery cathode material.

[0022] Further, in S1, the ratio of the total molar concentration of metal elements in the mixed solution A to the total molar concentration of metal elements in the mixed solution B is preferably 1:(0.65-1.05), more preferably, the total molar concentration of metal elements in the mixed solution A is 1-10 mol / L.

[0023] Further, in S1, the molar ratio of Ni to M in the mixed solution A is preferably 1:(0.02-1), and the molar ratio of Ni to M in the mixed solution B is preferably 1:(1.3-5).

[0024] Further, in S1, the Ni source is selected from one or more of nickel carbonate, nickel sulfate, nickel acetate, nickel chloride, nickel nitrate, and nickel phosphate; the M source is selected from one or more of carbonate, sulfate, acetate, chloride, nitrate, and phosphate.

[0025] Further, in S1, the mixed solution A and the mixed solution B also contain an A source; preferably, the A element in the A source is selected from one or more of Mo, W, Sb, Nb, Sn, Ca, Sr, Li, Y, V, Cr, La, Ti, Co, Mn, Mg, Zn, Fe, Al and Cu.

[0026] Further, in S1, the molar ratio of Ni to A in the mixed solution A is preferably 1:(0-0.4), and the molar ratio of Ni to A in the mixed solution B is preferably 1:(0-0.65); more preferably, the concentration of A in the mixed solution A is greater than or equal to the concentration of A in the mixed solution B.

[0027] Further, in S2, the precipitant is selected from one or more of NaOH, NaHCO3, and Na2CO3.

[0028] Furthermore, in S2, the complexing agent is preferably NH3·H2O.

[0029] Furthermore, in S2, the rate of continuous stirring is preferably 500-1000 rpm.

[0030] Furthermore, in S2, the pH of the reaction is preferably 9-12, the reaction temperature is preferably 50-90℃, and the reaction time is preferably 12-24h.

[0031] Furthermore, in S2, the reaction is carried out under a protective atmosphere, which includes, but is not limited to, nitrogen and / or argon.

[0032] Further, in S3, the ratio of the total molar amount of metal elements in the precursor salt to the molar amount of sodium elements in the sodium source is preferably 1:(1-1.1); more preferably, the sodium source is selected from one or more of sodium carbonate, sodium acetate, sodium oxalate, and sodium nitrate.

[0033] Further, in S3, the molar ratio of the layered oxide to the inorganic anion ions in the inorganic anion source is preferably 1:(0.01-0.1); more preferably, the inorganic anion source is selected from one or more of phosphoric acid source, silicate source, and pyrophosphate source; the phosphoric acid source is selected from one or more of phosphoric acid, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, aluminum phosphate, zirconium phosphate, zirconium hydrogen phosphate, magnesium phosphate, yttrium phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and magnesium ammonium phosphate; the silicate source is selected from one or more of silicic acid, sodium silicate, sodium metasilicate, sodium orthosilicate, and potassium silicate; and the pyrophosphate source is selected from one or more of pyrophosphate, sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate, and potassium pyrophosphate.

[0034] Further, in S3, the dispersant is selected from one or more of ethanol, propanol, and N-methylpyrrolidone.

[0035] Furthermore, in S3, the temperature of the first calcination treatment is preferably 700-1000℃, and the time of the first calcination treatment is preferably 10-20h; the first calcination treatment is carried out in the presence of oxygen.

[0036] Furthermore, in S3, the heating and stirring temperature is preferably 50-90℃, the heating and stirring time is preferably 3-6h, and the heating and stirring rate is preferably 200-800rpm.

[0037] Furthermore, in S3, the temperature of the second calcination treatment is preferably 400-700℃, and the time of the second calcination treatment is preferably 5-10h.

[0038] Further, in S3, the temperature of the pre-firing treatment is preferably 400-700℃, and the time of the pre-firing treatment is preferably 3-6h; the temperature of the sintering treatment is preferably 700-1000℃, and the time of the sintering treatment is preferably 10-20h.

[0039] A third aspect of the present invention provides a positive electrode sheet comprising the sodium-ion battery positive electrode material described in the first aspect or the sodium-ion battery positive electrode material prepared by the preparation method described in the second aspect.

[0040] A fourth aspect of the present invention provides a sodium-ion battery, comprising the positive electrode sheet described in the third aspect.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] 1. This invention provides a sodium-ion battery cathode material comprising a layered oxide with a gradient distribution of metal elements and a solid electrolyte layer coated on the surface of the layered oxide. Specifically, from the inside to the outside of the layered oxide, the Ni content gradually decreases, while the content of the relatively inactive metal M gradually increases. This allows the cathode material to achieve high capacity while reducing surface strain, which helps suppress surface cracks and electrolyte penetration, and reduces interfacial side reactions and metal ion dissolution. Simultaneously, the NASICON-type solid electrolyte coating on the surface of the layered oxide can suppress interfacial side reactions with the electrolyte and reduce metal ion dissolution. As a fast ion conductor, it can also promote Na+ ion exchange. + Diffusion is beneficial for improving capacity and rate performance.

[0043] 2. This invention also provides a method for preparing the above-mentioned sodium-ion battery cathode material. First, a precursor salt is prepared by a one-step precipitation method, in which the Ni content gradually decreases from the core to the surface, while the M content gradually increases. Then, this precursor salt is mixed with a sodium source and an inorganic anion source in steps or in one step and calcined to obtain a sodium-ion battery cathode material in situ coated with a solid electrolyte on the surface of a layered oxide. The precursor salt powder prepared by the above one-step precipitation method exhibits good structural uniformity of its primary particles, with no obvious interfaces from the inside to the outside, making it less prone to phase separation between layers with different metal element distributions, and demonstrating good structural stability. However, during the experiment, it was found that the high content of M element on the surface of the precursor salt could not completely react with the sodium source to form layered oxides that could enter the cathode material cell. Instead, it formed nanoparticles of M oxides on the particle surface, hindering sodium ion diffusion and reducing ionic conductivity and capacity. Based on this, the present invention introduces an inorganic acid anion source, which can react with residual sodium and M oxides on the surface of the layered oxide to form a NASICON-type solid electrolyte. This effectively reduces impedance and gas generation, and increases capacity. Furthermore, it eliminates the need to synthesize or purchase NASICON-type solid electrolyte materials to coat the layered oxide to improve ionic conductivity, thereby effectively reducing preparation costs. The above preparation method is simple to operate, has good process controllability, and the prepared sodium-ion battery cathode material has excellent performance, making it suitable for mass production.

[0044] 3. Sodium-ion batteries constructed using the above-mentioned sodium-ion battery cathode materials have high capacity, long cycle life, and excellent rate performance. Attached Figure Description

[0045] Figure 1 SEM image of the pre-coated layered oxide prepared in Example 1;

[0046] Figure 2 Here is a SEM image of the coated cathode material prepared in Example 1;

[0047] Figure 3The image shows the XRD overlay of the layered oxide and cathode material prepared in Example 1.

[0048] Figure 4 SEM image of the pre-coated layered oxide prepared in Example 6;

[0049] Figure 5 SEM image of the coated cathode material prepared in Example 6;

[0050] Figure 6 The image shows the XRD overlay of the layered oxide and cathode material prepared in Example 6. Detailed Implementation

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. "Comprising" or "containing" as used herein means that it may include or contain other components in addition to the stated components. "Comprising" or "containing" as used herein may also be replaced with the closed form "is" or "consisting of".

[0052] As described in the background section, nickel-based layered oxide sodium-ion battery cathode materials are prone to many adverse reactions and structural instability under high voltages. These include multiphase transformations within the 2-4V voltage range, cell changes causing particle breakage during charge and discharge, interfacial side reactions between the electrode and electrolyte, and transition metal dissolution, leading to severe irreversible capacity decay during charge and discharge. A core-shell structure, with an electrochemically active high-nickel material as the core and a structurally stable inactive metal ion material as the shell, aims to meet the demands for high capacity and long cycle life. However, this type of core-shell layered oxide cathode material is prone to grain boundaries and even interstitial spaces at the core-shell interface, resulting in high impedance and low ionic conductivity. Furthermore, the uniformity of the primary ions formed in the precursor is poor, which is detrimental to the overall performance of the cathode material.

[0053] To address the aforementioned problems, this invention provides a sodium-ion battery cathode material comprising a layered oxide and a solid electrolyte layer coated on the surface of the layered oxide; wherein,

[0054] The chemical formula of the layered oxide is Na. n Ni x M y O2, wherein the Ni content of the layered oxide gradually decreases and the M content gradually increases from the core to the surface;

[0055] The solid electrolyte layer comprises one or more of sodium phosphate, sodium silicate, and sodium pyrophosphate, and the solid electrolyte layer contains at least one of the elements M.

[0056] Wherein, M is selected from one or more of Ti, Co, Mn, Zn, Fe, Al and Cu;

[0057] 0.8≤n≤1.1, 0.4≤x≤0.75, x+y=1.

[0058] In this invention, the M element contained in the solid electrolyte layer originates from the M oxide residue of the layered oxide. Preferably, the solid electrolyte is obtained by reacting an inorganic acid anion source with residual sodium and M oxide on the surface of the layered oxide.

[0059] In this invention, the molar ratio of layered oxide to solid electrolyte in the above-mentioned sodium-ion battery cathode material is preferably 1:(0.01-0.1), for example 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, etc., including but not limited to the molar ratios listed above.

[0060] In this invention, layered oxide Na n Ni x M y O2 is also doped with element A, wherein element A can be selected from one or more of Mo, W, Sb, Nb, Sn, Ca, Sr, Li, Y, V, Cr, La, Ti, Co, Mn, Mg, Zn, Fe, Al and Cu, and element A and element M are selected from different elements; preferably, the doping amount of element A in the layered oxide is not higher than 0.1.

[0061] The present invention also provides a method for preparing the above-mentioned sodium-ion battery cathode material, comprising the following steps:

[0062] S1: Provide mixed solution A and mixed solution B, which are obtained by dissolving Ni source and M source in water; wherein...

[0063] The concentration of the Ni source in the mixed solution A is greater than the concentration of the Ni source in the mixed solution B;

[0064] The concentration of source M in mixed solution A is less than the concentration of source M in mixed solution B;

[0065] The metal element M in the M source is selected from one or more of Ti, Co, Mn, Mg, Zn, Fe, Al and Cu;

[0066] S2: The mixed solution B in S1 is continuously pumped into a container containing mixed solution A to form a precursor solution. At the same time, the precursor solution is continuously pumped into a continuously stirred reaction vessel, and a precipitant and a complexing agent are added to react and obtain the precursor salt.

[0067] S3: The precursor salt prepared in S2 is mixed evenly with a sodium source, and a layered oxide is obtained by a first calcination treatment. The layered oxide is then heated and stirred with an inorganic acid anion source in the presence of a dispersant. The solid is separated and collected for a second calcination treatment to obtain the sodium-ion battery cathode material; or,

[0068] The precursor salt prepared by S2 is heated and stirred with sodium source and inorganic acid anion source in the presence of dispersant. The solid is separated and collected for pre-calcination treatment, and then sintered to obtain the sodium-ion battery cathode material.

[0069] Unlike existing nickel-based layered oxide materials with core-shell structures, such as those prepared by first creating a core precursor precipitate and then dispersing it in a shell precursor metal solution to form a nickel-negative core and a nickel-poor shell, these core-shell layered oxide cathode materials are prone to grain boundaries or even interstitial spaces at the core-shell interface. This results in higher impedance and lower ionic conductivity, and the poor uniformity of the primary ions in the precursor is detrimental to the overall performance of the cathode material. This invention uses a one-step precipitation method to prepare precursor salt powder with gradually decreasing Ni content and gradually increasing M content from the core to the surface. The primary particles exhibit good structural uniformity, with no obvious interfaces from the inside to the outside, reducing the likelihood of phase separation between layers with different metal element distributions. This results in good structural stability, which is beneficial for reducing impedance and improving ionic conductivity. More importantly, the inventors discovered during experiments that the layered oxides prepared using the above method contain residual sodium and impurity oxides (such as M oxides) on their surface. This is because the high content of M elements on the precursor salt surface cannot completely react with the sodium source to form layered oxides that enter the cathode material cell. Instead, they form nanoparticles of M oxides on the particle surface. The presence of these impurity oxides hinders sodium ion diffusion and reduces ionic conductivity and capacity. This invention introduces an inorganic acid radical ion source, which can react with the residual sodium and M oxides on the surface of the layered oxides to form a NASICON-type solid electrolyte. This effectively reduces impedance and gas generation, increases capacity, and eliminates the need to synthesize or purchase NASICON-type solid electrolyte materials to coat the layered oxides and improve ionic conductivity, thereby effectively reducing preparation costs.

[0070] In this invention, in S1, the ratio of the total molar concentration of metal elements in mixed solution A to the total molar concentration of metal elements in mixed solution B is preferably 1:(0.65-1.05), for example, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.05, etc.; more preferably, the total molar concentration of metal elements in mixed solution A is 1-10 mol / L, for example, 2 mol / L, 4 mol / L, 6 mol / L, 8 mol / L, etc., including but not limited to the molar concentrations listed above.

[0071] In this invention, in S1, the molar ratio of Ni to M in mixed solution A is preferably 1:(0.02-1), for example 1:0.1, 1:0.2, 1:0.25, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, etc., and the molar ratio of Ni to M in mixed solution B is preferably 1:(1.3-5), for example 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, etc.; preferably, the Ni source can be selected from one or more of nickel carbonate, nickel sulfate, nickel acetate, nickel chloride, nickel nitrate, and nickel phosphate; the M source can be selected from one or more of carbonate, sulfate, acetate, chloride, nitrate, and phosphate.

[0072] In this invention, in S1, mixed solution A and mixed solution B further contain an A source; preferably, the A element in the A source is selected from one or more of Mo, W, Sb, Nb, Sn, Ca, Sr, Li, Y, V, Cr, La, Ti, Co, Mn, Mg, Zn, Fe, Al, and Cu; more preferably, the molar ratio of Ni element to A element in mixed solution A is 1:(0-0.4), and the molar ratio of Ni element to A element in mixed solution B is 1:(0-0.65); in some preferred embodiments, the concentration of A element in mixed solution A is greater than or equal to the concentration of A element in mixed solution B.

[0073] In this invention, in S2, the precipitant can be selected from one or more of NaOH, NaHCO3, and Na2CO3, and the complexing agent is preferably NH3·H2O.

[0074] In this invention, in step S2, the precursor solution is continuously pumped into a continuously stirred reaction vessel to make the solution in the reaction vessel more uniform, thereby obtaining a precursor salt with a uniform structure; preferably, the continuous stirring rate is 500-1000 rpm.

[0075] In this invention, in step S2, the pH of the reaction system is controlled within the range of 9-12, the reaction temperature is preferably 50-90℃, and the reaction time is preferably 12-24h. The nickel content of the precursor solution continuously pumped into the reaction vessel gradually decreases, while the M content gradually increases. By controlling the pH, temperature, and stirring speed of the reaction system, initial precipitation is carried out to form crystals with high nickel content. Then, during the outward growth process, the nickel content gradually decreases and the M content gradually increases, thereby forming a precursor salt with a gradually decreasing nickel content and a gradually increasing M content from the inside out. Preferably, the reaction is carried out under a protective atmosphere, which includes, but is not limited to, nitrogen and / or argon.

[0076] In this invention, in S3, the ratio of the total molar amount of metal elements in the precursor salt to the molar amount of sodium elements in the sodium source is preferably 1:(1-1.1), for example 1.05; wherein the sodium source can be selected from one or more of sodium carbonate, sodium acetate, sodium oxalate, and sodium nitrate.

[0077] In this invention, in step S3, the molar ratio of the layered oxide to the inorganic anion ions in the inorganic anion source is preferably 1:(0.01-0.1), for example, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, etc., including but not limited to the molar ratios listed above; more preferably, the inorganic anion source can be selected from a phosphate source or a silica source. The phosphoric acid source is selected from one or more of phosphoric acid, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, aluminum phosphate, zirconium phosphate, zirconium hydrogen phosphate, magnesium phosphate, yttrium phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and magnesium ammonium phosphate; the silicate source is selected from one or more of silicic acid, sodium silicate, sodium metasilicate, sodium orthosilicate, and potassium silicate; and the pyrophosphate source is selected from one or more of pyrophosphate, sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate, and potassium pyrophosphate.

[0078] In this invention, in step S3, the dispersant is selected from one or more of ethanol, propanol, and N-methylpyrrolidone. The dispersant allows the layered oxide to be mixed more evenly with the inorganic acid anion source, thereby forming a uniform solid electrolyte coating layer on the surface of the layered oxide.

[0079] In this invention, in step S3, the preferred temperature for the first calcination treatment is 700-1000℃, such as 700℃, 800℃, 900℃, 1000℃, etc., and the preferred time for the first calcination treatment is 10-20h, such as 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, etc., including but not limited to the times listed above. The first calcination treatment is carried out in the presence of oxygen. The precursor salt and sodium source are calcined in the presence of oxygen to form a layered oxide with an elemental gradient distribution structure. Then, it is heated and stirred with an inorganic acid anion source, causing the inorganic acid anion source to react with the residual sodium and M oxide on the surface of the layered oxide. Finally, a second calcination treatment is performed to form a layered oxide on the surface of the layered oxide. To form a solid electrolyte coating layer, preferably, the heating and stirring temperature is 50-90℃, such as 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, etc., and the heating and stirring time is preferably 3-6h, such as 4h or 5h, etc., and the heating and stirring rate is preferably 200-800rpm, such as 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, etc., and the second calcination temperature is preferably 400-700℃, such as 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, etc., and the second calcination time is 5-10h, such as 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0080] In this invention, in step S3, the precursor salt can be directly mixed with a sodium source and an inorganic acid anion source, and then pre-calcined and sintered to prepare a sodium-ion battery cathode material. The pre-calcination temperature is preferably 400-700℃, such as 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, etc., and the pre-calcination time is preferably 3-6h, such as 3h, 4h, 5h, 6h, etc. The sintering temperature is preferably 700-1000℃, such as 700℃, 800℃, 900℃, 1000℃, etc., and the sintering time is preferably 10-20h, such as 10h, 12h, 14h, 16h, 18h, 20h, etc., including but not limited to the temperatures or times listed above.

[0081] The present invention also provides a positive electrode sheet comprising the sodium-ion battery positive electrode material prepared by the above-described preparation method.

[0082] In addition, the present invention also provides a sodium-ion battery, including the above-mentioned positive electrode sheet, which exhibits high capacity, long cycle life and excellent rate performance.

[0083] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0084] Example 1

[0085] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0086] (1) Preparation of mixed solution A: Weigh out the corresponding nickel sulfate, manganese sulfate and titanium chloride in molar ratio of Ni:Mn:Ti=8:1:1 and dissolve them in deionized water to prepare mixed solution A with a molar concentration of 4mol / L.

[0087] Preparation of mixed solution B: Weigh out the corresponding nickel sulfate, manganese sulfate and titanium chloride in a molar ratio of Ni:Mn:Ti = 2:3:5 and dissolve them in deionized water to prepare mixed solution B with a molar concentration of 4.2 mol / L;

[0088] (2) The mixed solution B prepared in step (1) is continuously pumped into a container containing mixed solution A to form a precursor solution. At the same time, the precursor solution is continuously pumped into a 5L continuously stirred reactor, and 4mol / L NaOH and 2mol / L NH3·H2O are pumped into the reactor. During the reaction, the pH value is controlled at about 11. The reaction is carried out at a temperature of 90℃ and a stirring speed of 1000rpm for 24h. Then, after aging, filtration, washing and drying, the precursor powder Ni is obtained. 0.5 Mn 0.2 Ti 0.3 (OH)2.

[0089] (3) Weigh and mix the precursor powder prepared in step (2) with sodium carbonate at a molar ratio of (Ni+Mn+Ti):Na = 1:1.05. Sinter the mixture at 900℃ for 12 h in an air atmosphere in a muffle furnace. After cooling, pulverize to obtain layered oxide powder NaNi. 0.5 Mn 0.2 Ti 0.3 O2.

[0090] (4) The layered oxide powder NaNi prepared in step (3) 0.5 Mn 0.2 Ti 0.3 O2 and ammonium dihydrogen phosphate are reacted in a molar ratio of NaNi 0.5 Mn 0.2 Ti 0.3 O2:PO4 3-Weigh out the components in a 1:0.03 ratio and mix them thoroughly in ethanol. Heat and stir in an oil bath at 90°C until the reaction is complete. Filter, wash, and dry the mixture. Sinter it in a muffle furnace at 500°C for 6 hours under air atmosphere. After cooling, sieve to obtain the cathode material 0.01(NaTi2(PO4)3)@NaNi. 0.5 Mn 0.2 Ti 0.3 O2.

[0091] The layered oxide powder NaNi prepared in this embodiment 0.5 Mn 0.2 Ti 0.3 O2 and positive electrode material 0.03 (Na) 3- 4x Ti x PO4)@NaNi 0.5 Mn 0.2 Ti 0.3 The SEM images of O2 are as follows: Figure 1 , 2 As shown, by Figure 1 , 2 It can be seen that the layered oxide particles prepared in this embodiment have a large number of small particles adhering to their surface, while the cathode material particles prepared by ammonium dihydrogen phosphate post-treatment have a clean surface. Figure 2 As shown in the figure, it is speculated that the small particles on the surface of the layered oxide react with ammonium dihydrogen phosphate to form a solid electrolyte that coats the surface of the layered oxide.

[0092] The layered oxide NaNi prepared in this embodiment 0.5 Mn 0.2 Ti 0.3 O2 and cathode material 0.01(NaTi2(PO4)3)@NaNi 0.5 Mn 0.2 Ti 0.3 The XRD pattern of O2 is as follows: Figure 3 As shown, it is consistent with the R-3m structure, both being O3-type cathode materials, with layered oxides NaNi 0.5 Mn 0.2 Ti 0.3 O2 exhibits observable diffraction peaks at 25° and 47° belonging to the TiO2 phase, while the XRD pattern of the cathode material prepared by ammonium dihydrogen phosphate post-treatment does not show this impurity phase. This further indicates that by introducing ammonium dihydrogen phosphate, it can fully react with TiO2 to form a thin coating layer on the particle surface.

[0093] Example 2

[0094] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0095] (1) Preparation of mixed solution A: Weigh out the corresponding nickel sulfate, cobalt sulfate and manganese sulfate in molar ratio of Ni:Co:Mn=8:1:1 and dissolve them in deionized water to prepare mixed solution A with a molar concentration of 4mol / L.

[0096] Preparation of mixed solution B: Weigh out the corresponding nickel sulfate, cobalt sulfate and manganese sulfate in a molar ratio of Ni:Co:Mn = 2:3:5, and dissolve them in deionized water to prepare mixed solution B with a molar concentration of 4.2 mol / L;

[0097] (2) The mixed solution B prepared in step (1) is continuously pumped into a container containing mixed solution A to form a precursor solution. At the same time, the precursor solution is continuously pumped into a 5L continuously stirred reactor, and 4mol / L NaOH and 2mol / L NH3·H2O are pumped into the reactor. During the reaction, the pH value is controlled at about 11. The reaction is carried out at a temperature of 90℃ and a stirring speed of 1000rpm for 24h. Then, after aging, filtration, washing and drying, the precursor powder Ni is obtained. 0.5 Co 0.2 Mn 0.3 (OH)2.

[0098] (3) The precursor powder prepared in step (2) is mixed with sodium carbonate, sodium silicate, and ammonium dihydrogen phosphate in a molar ratio of (Ni+Co+Mn):Na:SiO4. 4- :PO4 3- Weigh out the components in a ratio of 1:1.05:0.02:0.01 and mix them thoroughly in ethanol. Heat and stir in an oil bath at 90°C until the reaction is complete. After complete reaction, filter, wash, and dry. Pre-sinter in a muffle furnace at 500°C for 6 hours under air atmosphere, then raise the temperature to 900°C and sinter for 12 hours. After cooling, sieve to obtain the positive electrode material 0.02(Na2MnSiO4)·0.01(Na 0.33 Mn 0.67 PO4)@NaNi 0.5 Co 0.2 Mn 0.3 O2.

[0099] Example 3

[0100] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0101] (1) Preparation of mixed solution A: Weigh out the corresponding nickel sulfate, zinc sulfate and manganese sulfate in molar ratio of Ni:Zn:Mn=8:1:1 and dissolve them in deionized water to prepare mixed solution A with a molar concentration of 4mol / L.

[0102] Preparation of mixed solution B: Weigh out the corresponding nickel sulfate, zinc sulfate and manganese sulfate in a molar ratio of Ni:Zn:Mn = 2:3:5 and dissolve them in deionized water to prepare mixed solution B with a molar concentration of 4.2 mol / L;

[0103] (2) The mixed solution B prepared in step (1) is continuously pumped into a container containing mixed solution A to form a precursor solution. At the same time, the precursor solution is continuously pumped into a 5L continuously stirred reactor, and 4mol / L NaOH and 2mol / L NH3·H2O are pumped into the reactor. During the reaction, the pH value is controlled at about 11. The reaction is carried out at a temperature of 90℃ and a stirring speed of 1000rpm for 24h. Then, after aging, filtration, washing and drying, the precursor powder Ni is obtained. 0.5 Zn 0.2 Mn 0.3 (OH)2.

[0104] (3) The precursor powder prepared in step (2) is mixed with sodium carbonate, sodium silicate, and ammonium dihydrogen phosphate in a molar ratio of (Ni+Zn+Mn):Na:SiO4. 4- :PO4 3- Weigh out the components in a ratio of 1:1.05:0.02:0.01 and mix them thoroughly in ethanol. Heat and stir in an oil bath at 90°C until the reaction is complete. After complete reaction, filter, wash, and dry. Pre-sinter in a muffle furnace at 500°C for 6 hours under air atmosphere, then raise the temperature to 900°C and sinter for 12 hours. After cooling, sieve to obtain the positive electrode material 0.02(Na2MnSiO4)·0.01(Na 0.33 Mn 0.67 PO4)@NaNi 0.5 Zn 0.2 Mn 0.3 O2.

[0105] Example 4

[0106] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0107] (1) Preparation of mixed solution A: Weigh out the corresponding nickel sulfate, copper sulfate and manganese sulfate in molar ratio of Ni:Cu:Mn=8:1:1 respectively, and dissolve them in deionized water to prepare mixed solution A with a molar concentration of 4mol / L;

[0108] Preparation of mixed solution B: Weigh out the corresponding nickel sulfate, copper sulfate and manganese sulfate in a molar ratio of Ni:Cu:Mn = 2:3:5 and dissolve them in deionized water to prepare mixed solution B with a molar concentration of 4.2 mol / L;

[0109] (2) The mixed solution B prepared in step (1) is continuously pumped into a container containing mixed solution A to form a precursor solution. At the same time, the precursor solution is continuously pumped into a 5L continuously stirred reactor, and 4mol / L NaOH and 2mol / L NH3·H2O are pumped into the reactor. During the reaction, the pH value is controlled at about 11. The reaction is carried out at a temperature of 90℃ and a stirring speed of 1000rpm for 24h. Then, after aging, filtration, washing and drying, the precursor powder Ni is obtained. 0.5 Cu 0.2 Mn 0.3 (OH)2.

[0110] (3) The precursor powder prepared in step (2) is mixed with sodium carbonate, sodium silicate, and ammonium dihydrogen phosphate in a molar ratio of (Ni+Cu+Mn):Na:SiO4. 4- :PO4 3- Weigh out the components in a ratio of 1:1.05:0.02:0.01 and mix them thoroughly in ethanol. Heat and stir in an oil bath at 90°C until the reaction is complete. After complete reaction, filter, wash, and dry. Pre-sinter in a muffle furnace at 500°C for 6 hours under air atmosphere, then raise the temperature to 900°C and sinter for 12 hours. After cooling, sieve to obtain the positive electrode material 0.02(Na2MnSiO4)·0.01(Na 0.33 Mn 0.67 PO4)@NaNi 0.5 Cu 0.2 Mn 0.3 O2.

[0111] Example 5

[0112] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0113] (1) Preparation of mixed solution A: Weigh out the corresponding nickel sulfate, ferric sulfate and manganese sulfate in molar ratio of Ni:Fe:Mn=4:1:1 and dissolve them in deionized water to prepare mixed solution A with a molar concentration of 4mol / L.

[0114] Preparation of mixed solution B: Weigh out the corresponding nickel sulfate and manganese sulfate in a molar ratio of Ni:Mn = 1:3 and dissolve them in deionized water to prepare mixed solution B with a molar concentration of 4.2 mol / L;

[0115] (2) The mixed solution B prepared in step (1) is continuously pumped into a container containing mixed solution A to form a precursor solution. At the same time, the precursor solution is continuously pumped into a 5L continuously stirred reactor, and 4mol / L NaOH and 2mol / L NH3·H2O are pumped into the reactor. During the reaction, the pH value is controlled at about 11. The reaction is carried out at a temperature of 90℃ and a stirring speed of 1000rpm for 24h. Then, after aging, filtration, washing and drying, the precursor powder Ni is obtained. 0.5 Fe 0.1 Mn 0.4 (OH)2.

[0116] (3) Weigh and mix the precursor powder prepared in step (2) with sodium carbonate at a molar ratio of (Ni+Fe+Mn):Na = 1:1.05. Sinter the mixture at 900℃ for 12 h in an air atmosphere in a muffle furnace. After cooling, pulverize to obtain layered oxide powder NaNi. 0.5 Fe 0.1 Mn 0.4 O2.

[0117] (4) The layered oxide powder NaNi prepared in step (3) 0.5 Fe 0.1 Mn 0.4 O2 and aluminum phosphate in the molar ratio NaNi 0.5 Fe 0.1 Mn 0.4 O2:PO4 3- Weigh out the mixture at a ratio of 1:0.03 and mix thoroughly in ethanol. Heat and stir in an oil bath at 90°C until the reaction is complete. Filter, wash, and dry the mixture. Sinter in a muffle furnace at 500°C for 6 hours under air atmosphere. After cooling, sieve to obtain the cathode material 0.01(Na2AlMn(PO4)3)@NaNi. 0.5 Fe 0.1 Mn 0.4 O2.

[0118] Example 6

[0119] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0120] (1) Preparation of mixed solution A: Weigh out the corresponding nickel sulfate and manganese sulfate in a molar ratio of Ni:Mn = 4:1 and dissolve them in deionized water to prepare mixed solution A with a molar concentration of 4 mol / L.

[0121] Preparation of mixed solution B: Weigh out the corresponding nickel sulfate and manganese sulfate in a molar ratio of Ni:Mn = 1:4 and dissolve them in deionized water to prepare mixed solution B with a molar concentration of 4.2 mol / L;

[0122] (2) The mixed solution B prepared in step (1) is continuously pumped into a container containing mixed solution A to form a precursor solution. At the same time, the precursor solution is continuously pumped into a 5L continuously stirred reactor, and 4mol / L NaOH and 2mol / L NH3·H2O are pumped into the reactor. During the reaction, the pH value is controlled at about 11. The reaction is carried out at a temperature of 90℃ and a stirring speed of 1000rpm for 24h. Then, after aging, filtration, washing and drying, the precursor powder Ni is obtained. 0.5 Mn 0.5 (OH)2.

[0123] (3) Weigh and mix the precursor powder prepared in step (2) with sodium carbonate at a molar ratio of (Ni+Mn):Na = 1:1.05. Sinter the mixture at 900℃ for 12 h in an air atmosphere in a muffle furnace. After cooling, pulverize to obtain layered oxide powder NaNi. 0.5 Mn 0.5 O2.

[0124] (4) The layered oxide powder NaNi prepared in step (3) 0.5 Mn 0.5 O2 and disodium dihydrogen pyrophosphate in a molar ratio of NaNi 0.5 Mn 0.5 O2:P2O7 4- Weigh and mix the components in a ratio of 1:0.03 until homogeneous. Sinter the mixture at 500°C for 6 hours in an air atmosphere in a muffle furnace. After cooling, sieve to obtain the cathode material 0.01(Na4Mn(P2O7)2)@NaNi. 0.5 Mn 0.5 O2.

[0125] Positive electrode material NaNi 0.5 Mn 0.5 O2 and 0.01(Na4Mn(P2O7)2)@NaNi 0.5 Mn 0.5 The SEM images of O2 are as follows: Figure 4 , 5 As shown, Figure 4 Small particles are attached to the surface of the granules. Figure 5 The particle surface is relatively clean. The cathode material is NaNi. 0.5 Mn 0.5 O2 and 0.01(Na4Mn(P2O7)2)@NaNi 0.5 Mn 0.5 The XRD pattern of O2 is as follows: Figure 6 As shown, it is consistent with the R-3m structure and is an O3 type cathode material. However, the former has impurity peaks at 35° and 42°, corresponding to the MnO phase, while the latter has no impurity phase. This indicates that MnO reacts fully with disodium dihydrogen pyrophosphate to form a thin coating layer on the particle surface.

[0126] Comparative Example 1

[0127] This comparative example relates to the preparation of a sodium-ion battery cathode material, differing from Example 1 only in that the metal elements are uniformly distributed in the layered oxide, without a gradient structure; the specific operation is as follows:

[0128] (1) Preparation of precursor solution: Weigh out the corresponding nickel sulfate, manganese sulfate and titanium chloride in molar ratio of Ni:Mn:Ti=5:2:3 and dissolve them in deionized water to prepare a precursor solution with a molar concentration of 4mol / L.

[0129] (2) The precursor solution prepared in step (1) was pumped into a 5L continuously stirred reactor, and 4mol / L NaOH and 2mol / L NH3·H2O were pumped into the reactor. During the reaction, the pH value was controlled at around 11, and the reaction was carried out at a temperature of 90℃ and a stirring speed of 1000rpm for 24h. Then, after aging, filtration, washing and drying, precursor powder N was obtained. i0.5 Mn 0.2 Ti 0.3 (OH)2.

[0130] Steps (3) and (4) are the same as in Example 1, and the positive electrode material 0.03(Na3PO4)@NaNi is prepared. 0.5 Mn 0.2 Ti 0.3 O2.

[0131] Comparative Example 2

[0132] This comparative example relates to the preparation of a sodium-ion battery cathode material. The only difference from Example 1 is that the layered oxide is first surface-treated with oxalic acid before adding the inorganic acid ion source. The specific operation is as follows:

[0133] Steps (1)-(3) are the same as in Example 1;

[0134] (4) The layered oxide powder NaNi prepared in step (3) 0.5 Mn 0.2 Ti 0.3 O2 was added to a 0.1 mol / L oxalic acid ethanol solution, heated and stirred in an oil bath at 60°C, and after the reaction was complete, filtered and washed to remove M2 oxide and residual sodium from the surface of the layered oxide powder. The molar ratio was NaNi. 0.5 Mn 0.2 Ti 0.3Weigh out sodium phosphate (O2:PO4 = 1:0.03), add the layered oxide powder and sodium phosphate to ethanol, heat and stir in an oil bath at 90°C until the reaction is complete, filter, wash, and dry, sinter in a muffle furnace at 500°C for 6 hours under air atmosphere, cool and sieve to obtain the finished cathode material 0.03(Na3PO4)@NaNi. 0.5 Mn 0.2 Ti 0.3 O2.

[0135] Comparative Example 3

[0136] This comparative example relates to the preparation of a sodium-ion battery cathode material. The only difference from Example 1 is that in step (4), a solid electrolyte layer is coated on the surface of the layered oxide by adding ammonium dihydrogen phosphate and titanium chloride. The specific operation is as follows:

[0137] Steps (1)-(3) are the same as in Example 1;

[0138] (4) The layered oxide powder NaNi prepared in step (3) 0.5 Mn 0.2 Ti 0.3 O2 reacts with ammonium dihydrogen phosphate and titanium chloride in a molar ratio of NaNi 0.5 Mn 0.2 Ti 0.3 O2:PO4 3- Weigh out Ti = 1:0.03:0.02 and mix thoroughly in ethanol. Heat and stir in an oil bath at 90°C until the reaction is complete. Filter, wash, and dry. Sinter in a muffle furnace at 500°C for 6 hours under air atmosphere. After cooling, sieve to obtain the cathode material 0.01(NaTi2(PO4)3)@NaNi. 0.5 Mn 0.2 Ti 0.3 O2.

[0139] Comparative Example 4

[0140] This comparative example relates to the preparation of a sodium-ion battery cathode material, differing from Example 6 only in that the metal elements are uniformly distributed in the layered oxide, without a gradient structure; the specific operation is as follows:

[0141] (1) Preparation of precursor solution: Weigh out the corresponding nickel sulfate and manganese sulfate in a molar ratio of Ni:Mn = 1:1 and dissolve them in deionized water to prepare a precursor solution with a molar concentration of 4 mol / L.

[0142] (2) The precursor solution prepared in step (1) was pumped into a 5L continuously stirred reactor, and 4mol / L NaOH and 2mol / L NH3·H2O were pumped into the reactor. During the reaction, the pH value was controlled at about 11, and the reaction was carried out at a temperature of 90℃ and a stirring speed of 1000rpm for 24h. Then, after aging, filtration, washing and drying, the precursor powder Ni was obtained. 0.5 Mn 0.5 (OH)2.

[0143] Step (3) is the same as in Example 4, and the positive electrode material 0.01(Na4P2O7)@NaNi is prepared. 0.5 Mn 0.5 O2.

[0144] Comparative Example 5

[0145] This comparative example relates to the preparation of a sodium-ion battery cathode material. The only difference from Example 6 is that the layered oxide is first surface-treated with oxalic acid before adding the inorganic acid ion source. The specific operation is as follows:

[0146] Steps (1)-(3) are the same as in Example 4;

[0147] (4) The layered oxide powder NaNi prepared in step (3) 0.5 Mn 0.5 O2 was added to an ethanol solution of 0.1 mol / L oxalic acid, heated and stirred in an oil bath at 60°C, and after the reaction was complete, filtered and washed. Then, in step (4), the above-treated layered oxide powder NaNi was processed. 0.5 Co 0.2 Mn 0.3 O2 and disodium dihydrogen pyrophosphate in a molar ratio of NaNi 0.5 Mn 0.5 O2:P2O7 4- Weigh out the mixture at a ratio of 1:0.03 and mix thoroughly in ethanol. Heat and stir in an oil bath at 90°C until the reaction is complete. Filter, wash, and dry the mixture. Sinter in a muffle furnace at 500°C for 6 hours under air atmosphere. After cooling, sieve to obtain the positive electrode material 0.01 (Na4P2O7@NaNi). 0.5 Mn 0.5 O2.

[0148] Application and performance testing

[0149] The sodium-ion battery cathode materials prepared in the above embodiments and comparative examples were used to construct sodium-ion coin cells. The specific operations are as follows:

[0150] Positive electrode sheet: The positive electrode material, conductive carbon black and PVDF binder are ground evenly in a mass ratio of 8:1:1, and then an appropriate amount of NMP is added to make a slurry. The slurry is evenly coated on the pretreated aluminum foil, dried and rolled, and then cut into 14mm circular positive electrode sheets.

[0151] Negative electrode sheet: Sodium metal sheet with a diameter of 14mm and a thickness of 0.2mm;

[0152] Separator: Whatman GF / F glass fiber with a diameter of 16mm;

[0153] Electrolyte: The electrolyte is 1 mol / L NaPF6, the solvent is DC and DEC (volume ratio 1:1), and 5% FEC additive;

[0154] The above-mentioned positive electrode, separator, negative electrode, and electrolyte were assembled in a glove box filled with high-purity argon to obtain a CR2032 coin cell.

[0155] The electrochemical performance of the CR2032 coin cells constructed with different sodium-ion battery cathode materials was tested using the Blue Battery Testing System:

[0156] Charge specific capacity and discharge specific capacity test: Charge to 4.0V with a constant current density of 13mA / g and record the charge specific capacity. Then discharge to 2.0V with a constant current density of 13mA / g and record the discharge specific capacity. Calculate the coulombic efficiency = (discharge specific capacity / charge specific capacity) × 100%.

[0157] Cyclic performance test: After activation by charging and discharging for 2 cycles at a current density of 13mA / g, charge to 4.0V at a constant current density of 130mA / g, and then discharge to 2.0V at a constant current density of 130mA / g. Record the initial discharge specific capacity. Cycle 50 times and record the discharge specific capacity on the 50th cycle. Calculate the capacity retention rate after 50 cycles = (discharge specific capacity on the 50th cycle / initial discharge specific capacity) × 100%.

[0158] The test results are shown in Table 1 below:

[0159] Table 1

[0160]

[0161] As can be seen from Examples 1 and Comparative Examples 1 and 2, and Examples 6 and Comparative Examples 4 and 5, the gradient setting of different element contents in layered oxides with different nickel-containing systems (Example 1 vs. Comparative Example 1, Example 6 vs. Comparative Example 4) is beneficial to improving the capacity, coulombic efficiency, and cycle stability of sodium-ion batteries. Furthermore, the coating layer formed by introducing an inorganic acid radical ion source to react with residual sodium and impurity oxides on the surface of the layered oxide (Example 1 vs. Comparative Example 2, Example 6 vs. Comparative Example 5) can effectively improve the coulombic efficiency, rate performance, and cycle stability of the battery. Therefore, it can be seen that using an inorganic acid radical ion source to treat the coating layer containing residual sodium and impurity oxides is more beneficial to promoting sodium ion diffusion and improving battery capacity and structural stability than directly constructing pure NASICON electrolyte on the surface of the layered oxide.

[0162] In addition, unlike Example 1, Comparative Example 3 constructs a solid electrolyte coating layer on the surface of layered oxides by directly introducing inorganic acid radical ion sources and metal salts. The sodium-ion battery constructed with the cathode material prepared by this method has inferior capacity, coulombic efficiency, rate performance and capacity retention compared to the sodium-ion battery constructed with the cathode material prepared in Example 1. It is speculated that this is because the residual impurity oxides on the surface of the layered oxides are not consumed by parallel charging, but instead increase the impedance of the cathode material and reduce the capacity of the battery.

[0163] The embodiments described above are merely preferred examples to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, The method comprises the following steps: S1: providing a mixed solution A and a mixed solution B, the mixed solution A and the mixed solution B being obtained by dissolving a Ni source and an M source in water; wherein, the concentration of the Ni source in the mixed solution A is greater than the concentration of the Ni source in the mixed solution B; the concentration of the M source in the mixed solution A is less than the concentration of the M source in the mixed solution B; S2: continuously pumping the mixed solution B in S1 into a container containing the mixed solution A to form a precursor solution, continuously pumping the precursor solution into a continuously stirred reaction container, and adding a precipitating agent and a complexing agent to react to obtain a precursor salt; S3: uniformly mixing the precursor salt prepared in S2 with a sodium source, and performing first calcination to obtain a layered oxide, and then performing heating and stirring in the presence of a dispersant with an inorganic acid ion source, separating and collecting the solid to perform second calcination to obtain the sodium ion battery positive electrode material; or, performing heating and stirring in the presence of a dispersant with the precursor salt prepared in S2, an inorganic acid ion source and a sodium source, separating and collecting the solid to perform pre-sintering, and then performing sintering to obtain the sodium ion battery positive electrode material; the inorganic acid ion source is selected from one or more of a phosphoric acid source, a silicic acid source and a pyrophosphoric acid source; the sodium ion battery positive electrode material comprises a layered oxide and a solid electrolyte layer coated on the surface of the layered oxide; The chemical general formula of the layered oxide is Na n Ni x M y O2, the content of the Ni element gradually decreases and the content of the M element gradually increases from the core to the surface of the layered oxide. the solid electrolyte layer comprises one or more of a sodium-containing phosphate, a sodium-containing silicate and a sodium-containing pyrophosphate, and at least contains one element of the M element in the solid electrolyte layer; wherein M is selected from one or more of Ti, Co, Mn, Zn, Fe, Al and Cu; 0.8≤n≤1.1, 0.4≤x≤0.75, x+y=1.

2. The production method according to claim 1, characterized by, In S1: the ratio of the total molar concentration of metal elements in the mixed solution A to the total molar concentration of metal elements in the mixed solution B is 1:(0.65-1.05); and the total molar concentration of metal elements in the mixed solution A is 1-10 mol / L; the molar ratio of Ni elements to M elements in the mixed solution A is 1:(0.02-1), and the molar ratio of Ni elements to M elements in the mixed solution B is 1:(1.3-5); the Ni source is selected from one or more of nickel sulfate, nickel acetate, nickel chloride and nickel nitrate; and the M source is selected from one or more of a sulfate, an acetate, a chloride and a nitrate.

3. The production method according to claim 1 or 2, characterized by, In S1: the mixed solution A and the mixed solution B further comprise an A source; the A element in the A source is selected from one or more of Mo, W, Sb, Nb, Sn, Ca, Sr, Li, Y, V, Cr, La, Ti, Co, Mn, Mg, Zn, Fe, Al and Cu, and the A element and the M element are selected from different elements; the molar ratio of Ni elements to A elements in the mixed solution A is 1:(0-0.4), and the molar ratio of Ni elements to A elements in the mixed solution B is 1:(0-0.65); the concentration of the A element in the mixed solution A is greater than or equal to the concentration of the A element in the mixed solution B.

4. The method of claim 1, wherein, In S2, at least one of the following features is included: (1) the precipitant is selected from one or more of NaOH, NaHCO3, Na2CO3; (2) the complexing agent is NH3·H2O; (3) the rate of continuous stirring is 500-1000 rpm; (4) the pH of the reaction is 9-12, the temperature of the reaction is 50-90 ℃, and the time of the reaction is 12-24 h; the reaction is carried out under a protective atmosphere.

5. The preparation method according to claim 1, characterized in that, In S3, at least one of the following features is included: (1) the ratio of the total molar amount of metal elements in the precursor salt to the molar amount of sodium elements in the sodium source is 1:(1-1.1); the sodium source is selected from one or more of sodium carbonate, sodium acetate, sodium oxalate, and sodium nitrate; (2) the molar ratio of the layered oxide to the inorganic acid radical ion source is 1:(0.01-0.1); the phosphoric acid source is selected from one or more of phosphoric acid, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, zirconium hydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and ammonium magnesium phosphate, the silicic acid source is selected from one or more of sodium silicate, sodium metasilicate, sodium orthosilicate, and potassium silicate, and the pyrophosphoric acid source is selected from one or more of sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate, and potassium pyrophosphate; (3) the dispersant is selected from one or more of ethanol, propanol, and N-methyl pyrrolidone; (4) the temperature of the first calcination treatment is 700-1000 ℃, and the time of the first calcination treatment is 10-20 h; the first calcination treatment is carried out in the presence of oxygen; (5) the temperature of the heating stirring is 50-90 ℃, the time of the heating stirring is 3-6 h, and the rate of the heating stirring is 200-800 rpm; (6) the temperature of the second calcination treatment is 400-700 ℃, and the time of the second calcination treatment is 5-10 h.

6. The method of claim 1, wherein, In S3, the temperature of the pre-burning treatment is 400-700 ℃, and the time of the pre-burning treatment is 3-6 h; the temperature of the sintering treatment is 700-1000 ℃, and the time of the sintering treatment is 10-20 h.

7. The sodium-ion battery cathode material prepared by the method of any one of claims 1-6, characterized in that, The layered oxide and a solid-state electrolyte layer coated on the surface of the layered oxide are included; The chemical general formula of the layered oxide is Na n Ni x M y O2, the content of Ni element gradually decreases and the content of M element gradually increases from the core to the surface of the layered oxide. The solid-state electrolyte layer includes one or more of a sodium-containing phosphate, a sodium-containing silicate, and a sodium-containing pyrophosphate, and at least one element of M elements is included in the solid-state electrolyte layer; wherein M is selected from one or more of Ti, Co, Mn, Zn, Fe, Al, and Cu; 0.8≤n≤1.1, 0.4≤x≤0.75, and x+y=1.

8. The sodium-ion battery cathode material of claim 7, wherein, The molar ratio of the layered oxide to the solid-state electrolyte in the solid-state electrolyte layer is 1:(0.01-0.1); said layered oxide Na n Ni x M y O2is further doped with an A element selected from one or more of Mo, W, Sb, Nb, Sn, Ca, Sr, Li, Y, V, Cr, La, Ti, Co, Mn, Mg, Zn, Fe, Al and Cu, and the A element is selected from a different element than the M element; the amount of A element doped in the layered oxide is not higher than 0.

1.

9. A positive electrode sheet characterized by comprising: The sodium-ion battery cathode material of claim 7 or 8 is included.

10. A sodium-ion battery, characterized in that, The positive electrode sheet of claim 9 is included.

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