Ternary positive electrode material, preparation method and application thereof

Abstract

This application provides a ternary cathode material, its preparation method, and its application. The structural formula of the ternary cathode material is Li(Ni) x Co y Mn z O2@Li5FeO4, where 0.6≤x<1, 0<y≤0.4, 0

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, for example, a ternary cathode material and a preparation method thereof and application thereof. BACKGROUND

[0002] Lithium ion batteries are widely used in many fields such as 3C electronic products, electric vehicles and chemical energy storage due to their high energy density, long cycle life and other advantages, and are the research hotspot in the field of new energy. As one of the key materials of lithium ion batteries, the cathode material plays a decisive role in the performance of the battery.

[0003] Lithium nickel cobalt manganese oxide ternary cathode material has the advantages of high specific capacity, good cycle stability and low price, and has good application prospect in the field of power batteries. The ternary cathode material is divided into different types according to the ratio of nickel, cobalt and manganese. With the increase of nickel content, the specific capacity of the material gradually increases, but the cycle stability becomes weaker. The high nickel content in the material leads to serious residual alkali and nickel lithium ion mixing on the surface of the particles, which affects the structural stability.

[0004] Increasing the surface stability of high-nickel materials is the key to improving their cycle performance. For example, forming a coating layer on the surface of the ternary precursor, preparing a multi-layer core-shell structure, etc., can improve the cycle performance of the material.

[0005] While pursuing cycle stability, there is also a higher requirement for high rate and low internal resistance. CN115084500A discloses a preparation method of a polymorphic ternary material, and the internal structure of the particles is hollow, which increases the specific surface area of the material. However, for ternary materials, although the hollow structure can reduce the internal resistance, the nickel content of the inner pore wall is high, and the contact with the electrolyte will reduce the structural stability. CN111029542A discloses a lithium ion battery ternary cathode material coated with Prussian blue type material and a preparation method thereof. The lithium ion battery ternary cathode material is coated with Prussian blue type material, the internal core layer is a ternary cathode material, and the shell layer is a Prussian blue type material. However, the preparation process is complex, and the cycle performance of the prepared cathode material needs to be improved.

[0006] Therefore, how to prepare a ternary cathode material with stable cycle performance is an important research direction in the field. SUMMARY

[0007] The following is a summary of the subject matter described in detail in this document. This summary is not intended to limit the scope of protection of the claims.

[0008] The purpose of the present application is to provide a ternary cathode material and a preparation method thereof and application thereof.

[0009] To achieve this purpose, the technical scheme adopted by the present application is as follows:

[0010] One of the purposes of the embodiments of the present application is to provide a ternary positive electrode material, the structural formula of the ternary positive electrode material is Li(Ni x Co y Mn z )O2@Li5FeO4, wherein 0.6<=x<1, 0<y<=0.4, 0<x+y<1. The inside of the ternary positive electrode material is a hollow structure, and the nickel content of the ternary positive electrode material increases first and then decreases from inside to outside.

[0011] The value of x can be 0.6, 0.7, 0.8 or 0.9, and the value of y can be 0.1, 0.2, 0.3 or 0.4, but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0012] As an optional technical solution of the embodiments of the present application, a lithium supplement coating layer is deposited on the inner wall of the hollow structure of the positive electrode material.

[0013] In one embodiment, the lithium supplement coating layer is lithium ferrate.

[0014] The lithium supplement coating layer in the embodiments of the present application can play a role in supplementing lithium and protecting the inner layer material, preventing Ni 4+ from reacting with the electrolyte, and enhancing the cycle stability and the first charge-discharge efficiency of the material.

[0015] The second purpose of the embodiments of the present application is to provide a preparation method of a ternary positive electrode material, the preparation method comprising the following steps:

[0016] Lithium phosphate, sodium ferrocyanide, divalent iron salt and complexing agent are co-precipitated to obtain NaFe[Fe(CN)6]@Li3PO4, lithium chloride is added to obtain a template LiFe[Fe(CN)6]@Li3PO4, and the ternary positive electrode material is prepared using the template.

[0017] In the embodiments of the present application, the lithium phosphate and lithium-rich prussian blue material complex LiFe[Fe(CN)6]@Li3PO4 are used as a template, a ternary material precursor is synthesized by co-precipitation, mixed with a lithium source and calcined, C and N in the template are converted into gas and removed, and a ternary material with a hollow structure in the inside is constructed, which can increase the specific surface area and increase the degree of electrolyte infiltration.

[0018] In the embodiments of the present application, the content of nickel in the ternary material prepared from the core to the surface layer first increases and then decreases, thereby reducing the content of unstable Ni 4+ in the hollow inner layer and the surface layer which contacts the electrolyte, reducing the degree of electrolyte corrosion of the material, and reducing the amount of residual alkali on the surface, thereby improving the cycle performance.

[0019] As an optional technical solution in the embodiments of this application, the complexing agent includes sodium citrate.

[0020] In one embodiment, the coprecipitation method includes: dispersing lithium phosphate in deionized water to obtain a suspension, dissolving sodium ferrocyanide in deionized water to obtain a sodium ferrocyanide solution, dissolving ferrous salt and sodium citrate in deionized water to obtain an iron salt-sodium citrate solution, and simultaneously adding the sodium ferrocyanide solution and the iron salt-sodium citrate solution to the suspension to coprecipitate NaFe[Fe(CN)6]@Li3PO4.

[0021] In one embodiment, the molar ratio of Prussian blue to lithium phosphate in NaFe[Fe(CN)6]@Li3PO4 in step (1) is 1:5 to 1:3, wherein the molar ratio can be 1:5, 1:4 or 1:3, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0022] In one embodiment, the molar ratio of lithium chloride to NaFe[Fe(CN)6]@Li3PO4 is 1.2:1 to 2:1, wherein the molar ratio can be 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0023] In the embodiments of this application, lithium chloride is in excess. The excess lithium chloride undergoes a displacement reaction with NaFe[Fe(CN)6]@Li3PO4 to obtain LiFe[Fe(CN)6]@Li3PO4.

[0024] As an optional technical solution in the embodiments of this application, the method for preparing ternary cathode materials using the template agent includes the following steps:

[0025] (1) Add the template agent LiFe[Fe(CN)6]@Li3PO4 to a mixture of nickel salt, cobalt salt and manganese salt to obtain solution A. Add the template agent LiFe[Fe(CN)6]@Li3PO4 to a mixture of nickel salt, cobalt salt and manganese salt to obtain solution B. Mix the precipitant and complexing agent to obtain solution C.

[0026] (2) Mix solutions A, B and C from step (1) to obtain an intermediate liquid. Adjust the pH, age and separate the solid and liquid in sequence to obtain a ternary cathode material precursor.

[0027] (3) The ternary cathode material precursor and lithium salt described in step (2) are mixed and calcined to obtain the ternary cathode material.

[0028] As an optional technical solution in the embodiments of this application, the molar ratio of nickel salt, cobalt salt and manganese salt in solution A in step (1) is 1:(0.8~1.2):(0.8~1.2), wherein the molar ratio can be 1:0.8:0.8, 1:0.8:0.9, 1:0.8:1, 1:0.8:1.1, 1:0.8:1.2, 1:0.9:0.8, 1:0.9:0.9, or 1:0.9:1. The values ​​are 1:0.9:1.1, 1:0.9:1.2, 1:1.0:0.8, 1:1.0:0.9, 1:1.0:1, 1:1.0:1.1, 1:1.0:1.2, 1:1.2:0.8, 1:1.2:0.9, 1:1.2:1, 1:1.2:1.1, or 1:1.2:1.2, but are not limited to the listed values; other unlisted values ​​within this range also apply.

[0029] In one embodiment, the total concentration of nickel salt, cobalt salt and manganese salt in solution A is 1 to 3 mol / L. The concentration can be 1 mol / L, 2 mol / L or 3 mol / L, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] In one embodiment, the nickel salt in solution A includes nickel sulfate and / or nickel nitrate.

[0031] In one embodiment, the cobalt salt in solution A includes cobalt sulfate and / or cobalt nitrate.

[0032] In one embodiment, the manganese salt in solution A includes manganese sulfate and / or manganese nitrate.

[0033] In one embodiment, the mass ratio of the total amount of nickel salt, cobalt salt, and manganese salt in solution A to the template agent is 1:45 to 100. The mass ratio can be 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, or 1:100, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] As an optional technical solution in the embodiments of this application, the molar ratio of nickel salt, cobalt salt and manganese salt in solution B in step (1) is 8:(0.8~1.2):(0.8~1.2), wherein the molar ratio can be 8:0.8:0.8, 8:0.8:0.9, 8:0.8:1, 8:0.8:1.1, 8:0.8:1.2, 8:0.9:0.8, 8:0.9:0.9, or 8:0.9:1. The values ​​are 8:0.9:1.1, 8:0.9:1.2, 8:1.0:0.8, 8:1.0:0.9, 8:1.0:1, 8:1.0:1.1, 8:1.0:1.2, 8:1.2:0.8, 8:1.2:0.9, 8:1.2:1, 8:1.2:1.1, or 8:1.2:1.2, but are not limited to the listed values; other unlisted values ​​within this range also apply.

[0035] In one embodiment, the total concentration of nickel salt, cobalt salt and manganese salt in solution B is 1 to 3 mol / L. The concentration can be 1 mol / L, 2 mol / L or 3 mol / L, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] In one embodiment, the nickel salt in solution B includes nickel sulfate and / or nickel nitrate.

[0037] In one embodiment, the cobalt salt in solution B includes cobalt sulfate and / or cobalt nitrate.

[0038] In one embodiment, the manganese salt in solution B includes manganese sulfate and / or manganese nitrate.

[0039] In one embodiment, the total mass ratio of nickel salt, cobalt salt, and manganese salt in solution B to the template agent is 1:45 to 100. The mass ratio can be 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, or 1:100, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] As an optional technical solution in the embodiments of this application, the precipitant in step (1) includes sodium hydroxide.

[0041] In one embodiment, the concentration of sodium hydroxide is 2 to 8 mol / L, wherein the concentration can be 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L or 8 mol / L, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0042] In one embodiment, the complexing agent in step (1) includes ammonia.

[0043] In one embodiment, the concentration of the ammonia water is 5 to 20 g / L, wherein the concentration may be 5 g / L, 8 g / L, 10 g / L, 12 g / L, 14 g / L, 16 g / L, 18 g / L or 20 g / L, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0044] As an optional technical solution in the embodiments of this application, the mixing method in step (2) includes: adding solution A and solution C dropwise into the reaction vessel at a speed u1, while adding solution B dropwise into solution A at a speed u2, and then adding solution A into solution B at a speed u1, while maintaining the stirring speed in the reaction vessel at 200-600 rpm. The speed can be 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, or 600 rpm, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] In one embodiment, the temperature of the reactor is 45–65°C, wherein the temperature may be 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, or 65°C, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0046] In one embodiment, u1 is 7 to 15 mL / h, where u1 can be 7 mL / h, 8 mL / h, 9 mL / h, 10 mL / h, 11 mL / h, 12 mL / h, 13 mL / h, 14 mL / h or 15 mL / h, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, and u2 = 3u1.

[0047] In one embodiment, a protective gas is introduced into the reactor during the mixing process.

[0048] As an optional technical solution in the embodiments of this application, step (2) of adjusting pH includes: adjusting the pH of the reactor to 10.0 to 12.0, wherein the pH can be 10.0, 10.2, 10.4, 10.6, 10.8, 11.0, 11.2, 11.4, 11.6, 11.8 or 12.0, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0049] In one embodiment, the aging time in step (2) is 8 to 15 hours, wherein the time can be 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] In one embodiment, the solid-liquid separation in step (2) is followed by washing and drying.

[0051] In one embodiment, the number of washes is ≥3 times, wherein the number of washes can be 3, 4, 5, 6, 7, 8, 9, or 10 times, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0052] In one embodiment, the drying temperature is 80–120°C, wherein the temperature may be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, or 120°C, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0053] In one embodiment, the drying time is 10 to 12 hours, where the time can be 10 hours, 11 hours, or 12 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] As an optional technical solution in the embodiments of this application, the molar ratio of the ternary cathode material precursor and the lithium salt in step (3) is 1:1.01 to 1.1. The molar ratio can be 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09 or 1:1.1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] In one embodiment, the lithium salt in step (3) comprises lithium hydroxide and / or lithium carbonate.

[0056] In one embodiment, the calcination in step (3) includes a first calcination and a second calcination.

[0057] In one embodiment, the atmosphere for the first calcination in step (3) is an inert atmosphere.

[0058] In one embodiment, the temperature of the first calcination is 600-700°C, wherein the temperature may be 600°C, 620°C, 640°C, 660°C, 680°C or 700°C, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0059] In one embodiment, the first calcination time is 2 to 4 hours, wherein the time can be 2 hours, 3 hours or 4 hours, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0060] In one embodiment, the atmosphere for the second calcination is an oxygen atmosphere.

[0061] In one embodiment, the second calcination temperature is 700–950°C, wherein the temperature may be 700°C, 750°C, 800°C, 850°C, 900°C, or 950°C, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0062] In one embodiment, the second calcination time is 10 to 16 hours, wherein the time can be 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, or 16 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0063] In the embodiments of this application, the hollow ternary material precursor, after being calcined with the lithium source in two stages under inert and oxygen atmospheres, converts the C and N in the template agent into gases and removes them, thus constructing a hollow ternary material, which can increase the specific surface area and increase the wetting degree of the electrolyte.

[0064] In this embodiment, the first calcination is carried out under an inert atmosphere. First, calcination under an inert atmosphere carbonizes Prussian blue, and some iron reacts with Li3PO4 to form lithium iron phosphate (LiFePO4), which improves the electrochemical performance of the ternary cathode material. Then, calcination is carried out under an oxygen atmosphere, where nickel, cobalt, and manganese oxidize and react with lithium salts to form lithium nickel cobalt manganese oxide. Simultaneously, iron further oxidizes and reacts with lithium to produce lithium ferrite (Li5FeO4), which deposits on the inner wall of the pores, forming a lithium-replenishing coating layer. This layer provides lithium replenishment and protection for the inner material, preventing Ni from... 4+ It reacts with the electrolyte to enhance the material's cycle stability and initial charge / discharge efficiency.

[0065] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0066] Compared with related technologies, the beneficial effects of this application are as follows:

[0067] The hollow gradient ternary cathode material prepared in this application exhibits a gradual increase and subsequent decrease in nickel content from the core to the surface. This reduces the unstable Ni content in the hollow inner and surface layers that comes into contact with the electrolyte. 4+The content of [unclear] reduces the degree of electrolyte corrosion on the material, while also reducing the amount of residual alkali on the surface, improving cycle performance. The initial discharge capacity at 0.1C can reach more than 195mAh / g, and the capacity retention rate after 100 cycles can reach more than 90%. Detailed Implementation

[0068] The technical solution of this application will be further described below through specific implementation methods.

[0069] Example 1

[0070] This embodiment provides a method for preparing a ternary cathode material, the method comprising:

[0071] (1) Preparation of template agent: 0.15 mol lithium phosphate was dispersed in 1 L of deionized water to obtain suspension A. 0.1 mol / L sodium ferrocyanide aqueous solution B was prepared. A mixture of 0.1 mol / L ferrous sulfate and 0.1 mol / L sodium citrate solution C was prepared. 25 mL of solution B and 25 mL of solution C were simultaneously injected into 50 mL of suspension A. After co-precipitation reaction, a Prussian blue coated lithium phosphate (NaFe[Fe(CN)6]@Li3PO4) suspension was obtained. Then, excess lithium chloride was added to carry out a displacement reaction to obtain the template agent LiFe[Fe(CN)6]@Li3PO4.

[0072] (2) Prepare salt solutions A (Ni:Co:Mn=1:1:1) and B (Ni:Co:Mn=8:1:1) with a concentration of 2 mol / L by preparing nickel sulfate, cobalt sulfate, and manganese sulfate. Add the template agent LiFe[Fe(CN)6]@Li3PO4 to solutions A and B respectively and mix well. The mass ratio of template agent to (nickel salt + cobalt salt + manganese salt) is 1:80. Prepare solution C with sodium hydroxide as precipitant and ammonia water as complexing agent, wherein the concentration of sodium hydroxide solution is 4 mol / L and the concentration of ammonia is 8 g / L.

[0073] (3) Solution A and solution C were slowly added dropwise to the reactor at a rate of 10 mL / h. At the same time, solution B was slowly added dropwise to solution A at a rate of 30 mL / h. Then, solution A was added to solution B at a rate of 10 mL / h. The stirring speed in the reactor was kept at 400 rpm. The temperature in the reactor was controlled at 55℃ and the pH was 10. The mixture was aged for 10 h. During the reaction, a protective gas was introduced into the reaction system. The aged mixture was separated into solid and liquid components, washed three times with deionized water, and dried at 100℃ for 10 h to obtain the ternary cathode material precursor.

[0074] (4) Weigh the ternary cathode material precursor and lithium hydroxide in step (3) by molar ratio 1:1.05, mix them by ball milling, calcine them at 650°C for 3 hours under nitrogen atmosphere, and then calcine them at 850°C for 12 hours under oxygen atmosphere to obtain the ternary cathode material.

[0075] Example 2

[0076] This embodiment provides a method for preparing a ternary cathode material, the method comprising:

[0077] (1) The preparation of the template agent is the same as in Example 1;

[0078] (2) Prepare salt solutions A (Ni:Co:Mn=1:1:1) and B (Ni:Co:Mn=8:1:1) with a concentration of 1 mol / L by preparing nickel sulfate, cobalt sulfate, and manganese sulfate. Add the template agent LiFe[Fe(CN)6]@Li3PO4 to solutions A and B respectively and mix well. The mass ratio of template agent to (nickel salt + cobalt salt + manganese salt) is 1:100. Prepare solution C with sodium hydroxide as precipitant and ammonia water as complexing agent, wherein the concentration of sodium hydroxide solution is 2 mol / L and the concentration of ammonia is 5 g / L.

[0079] (3) Solution A and solution C were slowly added dropwise to the reactor at a rate of 10 mL / h. At the same time, solution B was slowly added dropwise to solution A at a rate of 30 mL / h. Then, solution A was added to solution B at a rate of 10 mL / h. The stirring speed in the reactor was kept at 300 rpm. The temperature in the reactor was controlled at 45℃ and the pH was 10. The mixture was aged for 10 h. During the reaction, a protective gas was introduced into the reaction system. The aged mixture was separated into solid and liquid components, washed three times with deionized water, and dried at 80℃ for 12 h to obtain the ternary cathode material precursor.

[0080] (4) Weigh the ternary cathode material precursor and lithium hydroxide in step (3) at a molar ratio of 1:1.01, mix them by ball milling, calcine them at 600°C for 4 hours in a nitrogen atmosphere, and then calcine them at 700°C for 16 hours in an oxygen atmosphere to obtain the ternary cathode material.

[0081] Example 3

[0082] This embodiment provides a method for preparing a ternary cathode material, the method comprising:

[0083] (1) The preparation of the template agent is the same as in Example 1;

[0084] (2) Prepare salt solutions A (Ni:Co:Mn=1:1:1) and B (Ni:Co:Mn=8:1:1) with a concentration of 3 mol / L by preparing nickel sulfate, cobalt sulfate, and manganese sulfate. Add the template agent LiFe[Fe(CN)6]@Li3PO4 to solutions A and B respectively and mix well. The mass ratio of template agent to (nickel salt + cobalt salt + manganese salt) is 1:45. Prepare solution C with sodium hydroxide as precipitant and ammonia as complexing agent, wherein the concentration of sodium hydroxide solution is 8 mol / L and the concentration of ammonia is 20 g / L.

[0085] (3) Solution A and solution C were slowly added dropwise to the reactor at a rate of 15 mL / h. At the same time, solution B was slowly added dropwise to solution A at a rate of 45 mL / h. Then, solution A was added to solution B at a rate of 15 mL / h. The stirring speed in the reactor was kept at 600 rpm. The temperature in the reactor was controlled at 65℃ and the pH was 12. The mixture was aged for 8 h. During the reaction, a protective gas was introduced into the reaction system. The aged mixture was separated into solid and liquid components, washed three times with deionized water, and dried at 120℃ for 10 h to obtain the ternary cathode material precursor.

[0086] (4) Weigh the precursor and lithium hydroxide at a molar ratio of 1:1.1, mix them by ball milling, and calcine them in an oxygen atmosphere. First, calcine them at 700°C for 2 hours in a nitrogen atmosphere, and then calcine them at 950°C for 10 hours in an oxygen atmosphere to obtain the ternary cathode material.

[0087] Comparative Example 1

[0088] This comparative example provides a method for preparing a hollow ternary cathode material, the method comprising:

[0089] (1) The preparation of the template agent is the same as in Example 1;

[0090] (2) Prepare a 2 mol / L salt solution A (Ni:Co:Mn=8:1:1) with nickel sulfate, cobalt sulfate and manganese sulfate. Add the template agent LiFe[Fe(CN)6]@Li3PO4 to the salt solution and mix well. The mass ratio of the template agent to (nickel salt + cobalt salt + manganese salt) is 1:80. Prepare solution B with sodium hydroxide as precipitant and ammonia as complexing agent. The concentration of sodium hydroxide solution is 4 mol / L and the concentration of ammonia is 8 g / L.

[0091] (3) Solution A and solution B were slowly added dropwise to the reactor at a rate of 30 mL / h. The stirring speed in the reactor was kept at 400 rpm. The temperature in the reactor was controlled at 55℃ and the pH was 10. The mixture was aged for 10 h. During the reaction, a protective gas was introduced into the reaction system. The aged mixture was separated into solid and liquid, washed three times with deionized water, and dried at 100℃ for 10 h to obtain the ternary cathode material precursor.

[0092] (4) Weigh the ternary cathode material precursor and lithium hydroxide in step (3) by molar ratio 1:1.05, mix them by ball milling, calcine them at 650°C for 3 hours under nitrogen atmosphere, and then calcine them at 850°C for 12 hours under oxygen atmosphere to obtain the ternary cathode material.

[0093] Comparative Example 2

[0094] This comparative example provides a method for preparing a ternary cathode material, the method comprising:

[0095] (1) Prepare salt solutions A (Ni:Co:Mn=1:1:1) and B (Ni:Co:Mn=8:1:1) with a concentration of 2mol / L by preparing nickel sulfate, cobalt sulfate and manganese sulfate. Add NaHCO3 to solutions A and B respectively and mix well. The mass ratio of template agent to (nickel salt + cobalt salt + manganese salt) is 1:80.

[0096] (2) Solution C is prepared using sodium hydroxide as a precipitant and ammonia as a complexing agent, wherein the concentration of sodium hydroxide solution is 4 mol / L and the concentration of ammonia is 8 g / L;

[0097] (3) Add solutions A and C slowly to the reaction vessel at a rate of 10 mL / h, while adding solutions B slowly to solutions A at a rate of 30 mL / h. Then add solutions A to solutions B at a rate of 10 mL / h. Keep the stirring speed in the reaction vessel at 400 rpm, control the temperature in the reaction vessel at 55℃, the pH at 10, and age for 10 h. During the reaction, introduce protective gas into the reaction system.

[0098] (4) Separate the solid and liquid of the aged mixture, wash it three times with deionized water, and dry it at 100℃ for 10h to obtain the ternary cathode material precursor.

[0099] (5) Weigh the precursor and lithium hydroxide at a molar ratio of 1:1.05, mix them by ball milling, and calcine them at 850°C for 12 hours under an oxygen atmosphere to obtain the ternary cathode material.

[0100] The ternary cathode materials prepared in Examples 1-3 and Comparative Examples 1-2 were assembled into batteries, and their electrochemical performance was tested by charge-discharge and cycle tests. The test methods are shown in Table 1.

[0101] The battery preparation method includes: making the obtained material into a positive electrode sheet; dissolving ternary material, binder PVDF and conductive agent SP in NMP at a mass ratio of 8:1:1, stirring to form a slurry, coating the slurry on aluminum foil, drying, and assembling into a coin cell.

[0102] Table 1

[0103] Initial discharge capacity 0.1 C (mAh / g) Capacity retention rate (%) after 100 cycles Example 1 195.3 90.5 Example 2 194.7 91.1 Example 3 196.0 90.7 Comparative Example 1 195.1 88.3 Comparative Example 2 184.6 81.2

[0104] As shown in the table above, the specific capacity and cycle performance of Examples 1-3 and Comparative Example 1 are significantly better than those of Comparative Example 2. This is because Examples 1-3 and Comparative Example 1 used LiFe[Fe(CN)6]@Li3PO4 as a template agent, which formed an iron-containing coating layer during the two calcination processes. This coating layer can supplement lithium and protect the inner layer material, preventing Ni from entering the lithium matrix. 4+The reaction with the electrolyte enhances the cycle stability and initial charge-discharge efficiency of the material. The cycle performance of Examples 1-3 is further improved compared to Comparative Example 1 because the nickel content in the ternary cathode material of Examples 1-3 first increases and then decreases from the core to the surface, thus reducing the unstable Ni content in the hollow inner layer and surface layer that comes into contact with the electrolyte. 4+ The content of [specific substance] reduces the degree of electrolyte corrosion on materials, while also reducing the amount of residual alkali on the surface and improving cycle performance.

[0105] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A ternary cathode material, the structural formula of the ternary cathode material being Li(Ni x Co y Mn z )O2@Li5FeO4, where 0.6 ≤ x < 1, 0 < y ≤ 0.4, 0 < x + y < 1, the interior of the ternary cathode material being a hollow structure, and the nickel content of the ternary cathode material increasing first and then decreasing from the inside to the outside; A lithium-filling coating layer is deposited on the inner wall of the hollow structure of the cathode material; The lithium-replenishing coating is lithium ferrite.

2. A method for preparing the ternary cathode material as described in claim 1, the method comprising: Lithium phosphate, sodium ferrocyanide, ferrous salt and complexing agent were co-precipitated to obtain NaFe[Fe(CN)6]@Li3PO4. Lithium chloride was added to obtain the template agent LiFe[Fe(CN)6]@Li3PO4. The ternary cathode material was prepared using the template agent.

3. The preparation method according to claim 2, wherein, The complexing agent includes sodium citrate.

4. The preparation method according to claim 2, wherein, The coprecipitation method includes: dispersing lithium phosphate in deionized water to obtain a suspension, dissolving sodium ferrocyanide in deionized water to obtain a sodium ferrocyanide solution, dissolving ferrous salt and sodium citrate in deionized water to obtain an iron salt-sodium citrate solution, and simultaneously adding the sodium ferrocyanide solution and the iron salt-sodium citrate solution to the suspension to coprecipitate NaFe[Fe(CN)6]@Li3PO4.

5. The preparation method according to claim 2, wherein, The molar ratio of Prussian blue to lithium phosphate in the NaFe[Fe(CN)6]@Li3PO4 is 1:5 to 1:

3.

6. The preparation method according to claim 2, wherein, The molar ratio of lithium chloride to NaFe[Fe(CN)6]@Li3PO4 is 1.2:1 to 2:

1.

7. The preparation method according to claim 2, wherein, The method for preparing ternary cathode materials using the template agent includes the following steps: (1) Add the template agent LiFe[Fe(CN)6]@Li3PO4 to a mixture of nickel salt, cobalt salt and manganese salt to obtain solution A. Add the template agent LiFe[Fe(CN)6]@Li3PO4 to a mixture of nickel salt, cobalt salt and manganese salt to obtain solution B. Mix the precipitant and complexing agent to obtain solution C. (2) Mix solutions A, B and C from step (1) to obtain an intermediate liquid. Adjust the pH, age and separate the solid and liquid in sequence to obtain the ternary cathode material precursor. (3) The ternary cathode material precursor and lithium salt described in step (2) are mixed and calcined to obtain the ternary cathode material.

8. The preparation method according to claim 7, wherein, In step (1), the molar ratio of nickel salt, cobalt salt and manganese salt in solution A is 1:(0.8~1.2):(0.8~1.2).

9. The preparation method according to claim 7, wherein, The total concentration of nickel salt, cobalt salt and manganese salt in solution A is 1~3 mol / L.

10. The preparation method according to claim 7, wherein, The nickel salt in solution A includes nickel sulfate and / or nickel nitrate.

11. The preparation method according to claim 7, wherein, The cobalt salt in solution A includes cobalt sulfate and / or cobalt nitrate.

12. The preparation method according to claim 7, wherein, The manganese salt in solution A includes manganese sulfate and / or manganese nitrate.

13. The preparation method according to claim 7, wherein, The total mass ratio of nickel salt, cobalt salt, and manganese salt in solution A to the template agent is 1:45~100.

14. The preparation method according to claim 7, wherein, In step (1), the molar ratio of nickel salt, cobalt salt and manganese salt in solution B is 8:(0.8~1.2):(0.8~1.2).

15. The preparation method according to claim 7, wherein, The total concentration of nickel salt, cobalt salt, and manganese salt in solution B is 1~3 mol / L.

16. The preparation method according to claim 7, wherein, The nickel salt in solution B includes nickel sulfate and / or nickel nitrate.

17. The preparation method according to claim 7, wherein, The cobalt salt in solution B includes cobalt sulfate and / or cobalt nitrate.

18. The preparation method according to claim 7, wherein, The manganese salt in solution B includes manganese sulfate and / or manganese nitrate.

19. The preparation method according to claim 7, wherein, The total mass ratio of nickel salt, cobalt salt, and manganese salt in solution B to the template agent is 1:45~100.

20. The preparation method according to claim 7, wherein, The precipitant in step (1) includes sodium hydroxide.

21. The preparation method according to claim 20, wherein, The concentration of sodium hydroxide is 2~8 mol / L.

22. The preparation method according to claim 7, wherein, The complexing agent in step (1) includes ammonia.

23. The preparation method according to claim 22, wherein, The concentration of the ammonia water is 5~20 g / L.

24. The preparation method according to claim 7, wherein, The mixing method described in step (2) includes: adding solution A and solution C dropwise into the reaction vessel at a rate u1, adding solution B dropwise into the reaction vessel at a rate u2, while maintaining the stirring speed in the reaction vessel at 200~600 rpm.

25. The preparation method according to claim 24, wherein, The temperature of the reactor is 45~65℃.

26. The preparation method according to claim 24, wherein, The u1 is 7~15mL / h, and u2=3u1.

27. The preparation method according to claim 24, wherein, During the mixing process, a protective gas is introduced into the reactor.

28. The preparation method according to claim 7, wherein, Step (2) involves adjusting the pH of the reactor to 10.0~12.

0.

29. The preparation method according to claim 7, wherein, The aging time in step (2) is 8 to 15 hours.

30. The preparation method according to claim 7, wherein, After solid-liquid separation in step (2), the mixture is washed and dried.

31. The preparation method according to claim 30, wherein, The washing process is repeated ≥3 times.

32. The preparation method according to claim 30, wherein, The drying temperature is 80~120℃.

33. The preparation method according to claim 30, wherein, The drying time is 10-12 hours.

34. The preparation method according to claim 7, wherein, In step (3), the molar ratio of the ternary cathode material precursor to the lithium salt is 1:1.01~1.

1.

35. The preparation method according to claim 7, wherein, The lithium salt in step (3) includes lithium hydroxide and / or lithium carbonate.

36. The preparation method according to claim 7, wherein, The calcination in step (3) includes a first calcination and a second calcination.

37. The preparation method according to claim 36, wherein, The atmosphere for the first calcination is an inert atmosphere.

38. The preparation method according to claim 36, wherein, The first calcination temperature is 600~700℃.

39. The preparation method according to claim 36, wherein, The first calcination time is 2-4 hours.

40. The preparation method according to claim 36, wherein, The atmosphere for the second calcination is an oxygen atmosphere.

41. The preparation method according to claim 36, wherein, The second calcination temperature is 700~950℃.

42. The preparation method according to claim 36, wherein, The second calcination time is 10~16h.