A double-layer coated ternary positive electrode material, a preparation method and application thereof

Abstract

This invention belongs to the field of battery electrode technology, specifically relating to a double-layer coated ternary cathode material, its preparation method, and its application. The preparation method of the double-layer coated ternary cathode material provided by this invention includes the following steps: 1) mixing the ternary cathode material with a phosphorus source and then heat-treating it in an oxygen atmosphere to obtain a single-layer coated ternary cathode material; 2) mixing the single-layer coated ternary cathode material obtained in step 1) with 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and then sintering to obtain the double-layer coated ternary cathode material. The preparation method of this invention can effectively improve the capacity retention rate and cycle stability of existing ternary cathode materials.

Description

Technical Field

[0001] This invention belongs to the field of battery electrode technology, specifically relating to a double-layer coated ternary cathode material, its preparation method, and its application. Background Technology

[0002] Currently, driven by the economies of scale in the new energy vehicle market, the power battery market is developing rapidly, and the requirements for power batteries are becoming increasingly stringent. Lithium-ion batteries, in particular, possess advantages such as high energy density and environmental friendliness, making them suitable for applications in portable electronic devices and hybrid electric vehicles. The specific capacity and structural stability of the cathode material directly affect the overall performance of lithium-ion batteries. Currently, high-nickel ternary cathode materials, such as nickel-cobalt-aluminum (NCA) ternary cathode materials, exhibit superior theoretical specific capacity and energy density compared to other cathode materials. However, existing NCA ternary cathode materials suffer from problems during charge-discharge processes, including surface structure reconstruction, Li-Ni mixing, interfacial side reactions, and bulk structure changes, resulting in poor cycle stability. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor cycle stability of existing ternary cathode materials, thereby providing a double-layer coated ternary cathode material, its preparation method and application.

[0004] This invention provides a method for preparing a double-layer coated ternary cathode material, comprising the following steps:

[0005] 1) The ternary cathode material is mixed with a phosphorus source and then heat-treated in an oxygen atmosphere to obtain a single-layer coated ternary cathode material;

[0006] 2) The monolayer-coated ternary cathode material obtained in step 1) is mixed with 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and then sintered to obtain the bilayer-coated ternary cathode material.

[0007] Preferably, the phosphorus source in step 1) is selected from at least one of Li3PO4, Co3(PO4)2, Mn3(PO4)2, and Mg3(PO4)2;

[0008] The molar ratio of the ternary cathode material to the phosphorus source is 1:(0.001-0.0035).

[0009] Preferably, the heat treatment temperature in step 1) is 600-800℃ and the heat treatment time is 10-15h;

[0010] In step 2), the mass of the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt accounts for 25%-50% of the total mass of the monolayer coated ternary cathode material and the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0011] The sintering temperature in step 2) is 300-600℃, and the sintering time is 4-6h;

[0012] The combustion atmosphere is nitrogen.

[0013] Preferably, the chemical formula of the ternary cathode material in step 1) is LiNi. x Co y Al z O2, and 0.8≤x≤0.9, 0.075≤y≤0.1, 0.02≤z≤0.045, x+y+z=1.

[0014] Preferably, the preparation method of the ternary cathode material in step 1) includes the following steps:

[0015] S1: Mix nickel source, cobalt source and water to form a mixed solution, then add precipitant and ammonia solution to carry out co-precipitation reaction, and separate solid and liquid to obtain ternary cathode material precursor;

[0016] S2: The ternary cathode material precursor obtained in step S1 is mixed with a lithium source and an aluminum source, and then preheated and calcined to obtain the ternary cathode material.

[0017] Preferably, the molar ratio of nickel in the nickel source, cobalt in the cobalt source, lithium in the lithium source, and aluminum in the aluminum source is (0.9-0.99):(0.01-0.1):(1.01-1.06):(0.02-0.04);

[0018] The nickel source is selected from at least one of nickel acetate, nickel nitrate, and nickel sulfate;

[0019] The cobalt source is selected from at least one of cobalt acetate, cobalt nitrate, and cobalt sulfate.

[0020] Preferably, the total molar concentration of nickel and cobalt sources in the mixed solution in step S1 is 3-12 mol / L;

[0021] The precipitant is selected from an aqueous sodium hydroxide solution;

[0022] The molar concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 3-12 mol / L;

[0023] The molar concentration of ammonia in the ammonia solution is 3-14 mol / L;

[0024] The coprecipitation reaction temperature is 60-75℃, and the coprecipitation reaction speed is 500-800 rpm;

[0025] Optionally, the pH of the reaction solution can be controlled to be 11.5-13.5 and the ammonia value of the reaction solution can be 5-15 g / L by using a precipitant and an ammonia solution.

[0026] Optionally, after the solid-liquid separation step, the method may further include washing, drying, and demagnetizing the separated solid.

[0027] Preferably, the lithium source in step S2 is selected from at least one of lithium carbonate and lithium hydroxide;

[0028] The aluminum source is selected from at least one of alumina and aluminum hydroxide;

[0029] The preheating temperature is 300-600℃, the preheating time is 4-6 hours, and the preheating atmosphere is oxygen;

[0030] The calcination temperature is 700-800℃, the calcination time is 10-15h, and the calcination atmosphere is oxygen.

[0031] This invention provides a double-layer coated ternary cathode material, which is prepared by the above-described method for preparing double-layer coated ternary cathode materials.

[0032] The present invention also provides an application of the above-described double-layer coated ternary cathode material in lithium-ion batteries.

[0033] The technical solution of this invention has the following advantages:

[0034] 1. The double-layer coated ternary cathode material provided by this invention includes the following steps: 1) mixing the ternary cathode material with a phosphorus source and then heat-treating it in an oxygen atmosphere to obtain a single-layer coated ternary cathode material; 2) mixing the single-layer coated ternary cathode material obtained in step 1) with 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and then sintering to obtain the double-layer coated ternary cathode material. The phosphorus source coating of this invention not only mitigates the side reactions between the material and the electrolyte, improves the poor cycling and low safety issues of nickel-rich layered oxide cathode materials, and enhances ion transport performance, but also, compared with metal compound coating without a phosphorus source, synergistically forms stronger metal-oxygen bonds with metal ions, further improving the stability of the material. After sintering, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt can be carbonized into pure carbon without producing intermediate products, thus achieving pure carbon coating. 1-Butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt possesses a carbon chain structure, low vapor pressure, is non-volatile, and exhibits high chemical stability. This allows it to provide a stable carbon source for coating even under high pressure conditions. The combined effect of heat treatment of the phosphorus source coating layer and sintering of the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt coating layer creates an even more stable structure, contributing to improved material stability. Furthermore, the electrical conductivity of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt can reach 10⁻⁶. -2 The increased conductivity, on the order of S / cm, allows for a reduction in the amount of inactive conductive carbon used in subsequent electrode fabrication while maintaining the same effect. It also reduces electrode porosity and electrolyte usage, increases the proportion of organic electrode active materials, and further improves the energy density and capacity retention of the ternary cathode material. This invention effectively improves the capacity retention and cycle stability of the ternary cathode material by first coating the outer layer of the ternary cathode material with a phosphorus source followed by heat treatment and then coating it with 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and calcining.

[0035] 2. The double-layer coated ternary cathode material provided by this invention employs a simple combination of solid-state and carbothermal reduction methods, resulting in a simple preparation process that does not generate large amounts of wastewater and is environmentally friendly. Compared to cobalt-free ternary cathode materials, the double-layer coated ternary cathode material of this invention exhibits higher rate performance. Detailed Implementation

[0036] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0037] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0038] Example 1

[0039] This embodiment provides a method for preparing a double-layer coated ternary cathode material, including the following steps:

[0040] 1) A mixed solution of 0.90 mol nickel sulfate, 0.1 mol cobalt sulfate, and deionized water was placed in a reaction vessel. The total molar concentration of nickel and cobalt sources in the mixed solution was 3 mol / L. Then, 4 mol / L NaOH solution and 8 mol / L ammonia solution were added to control the pH of the reaction solution to 11.8, and the ammonia value of the reaction solution was 9 g / L. A co-precipitation reaction was carried out at 65℃ with continuous stirring at 550 rpm. Solid-liquid separation was performed, and the collected solid was washed, dried, and demagnetized to obtain the ternary cathode material precursor. The ternary cathode material precursor was mixed with 1.025 mol LiOH and 0.011 mol Al2O3, preheated at 500℃ for 4 h in a pure oxygen atmosphere, and then calcined at 710℃ for 10 h to obtain the ternary cathode material LiNi. 0.88 Co 0.098 Al 0.022 O2; 1 mol of the prepared ternary cathode material was mixed with 0.0025 mol of Li3PO4 material and then heat-treated in a pure oxygen atmosphere at a temperature of 650℃ for 10 h to obtain a single-layer coated ternary cathode material.

[0041] 2) The monolayer-coated ternary cathode material obtained in step 1) is mixed with 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, wherein the mass of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt accounts for 35% of the total mass of the monolayer-coated ternary cathode material and the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. The mixture is kept at 600°C for 6 hours under a pure nitrogen atmosphere to obtain the double-layer-coated ternary cathode material.

[0042] Example 2

[0043] This embodiment provides a method for preparing a double-layer coated ternary cathode material, including the following steps:

[0044] 1) A mixed solution of 0.90 mol nickel sulfate, 0.1 mol cobalt sulfate, and deionized water was placed in a reaction vessel. The total molar concentration of nickel and cobalt sources in the mixed solution was 12 mol / L. Then, 12 mol / L NaOH solution and 3 mol / L ammonia solution were added to control the pH of the reaction solution to 13.5, and the ammonia value of the reaction solution was 15 g / L. A co-precipitation reaction was carried out at 60℃ with continuous stirring at 500 rpm. Solid-liquid separation was performed, and the collected solid was washed, dried, and demagnetized to obtain the ternary cathode material precursor. The ternary cathode material precursor was mixed with 1.025 mol LiOH and 0.011 mol Al2O3, preheated at 600℃ for 4 h in a pure oxygen atmosphere, and then calcined at 800℃ for 10 h to obtain the ternary cathode material LiNi. 0.88 Co 0.098 Al 0.022 O2; 1 mol of the prepared ternary cathode material was mixed with 0.001 mol of Li3PO4 material and then heat-treated in a pure oxygen atmosphere at a temperature of 600℃ for 15 h to obtain a single-layer coated ternary cathode material.

[0045] 2) The monolayer-coated ternary cathode material obtained in step 1) is mixed with 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, wherein the mass of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt accounts for 45% of the total mass of the monolayer-coated ternary cathode material and the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. The mixture is kept at 300°C for 6 hours under a pure nitrogen atmosphere to obtain the double-layer-coated ternary cathode material.

[0046] Example 3

[0047] This embodiment provides a method for preparing a double-layer coated ternary cathode material, including the following steps:

[0048] 1) A mixed solution of 0.9 mol nickel nitrate, 0.1 mol cobalt nitrate, and deionized water was placed in a reaction vessel. The total molar concentration of nickel and cobalt sources in the mixed solution was 7 mol / L. Then, 4 mol / L NaOH solution and 8 mol / L ammonia solution were added to control the pH of the reaction solution to 11.5, and the ammonia value of the reaction solution was 5 g / L. A co-precipitation reaction was carried out at 65℃ with continuous stirring at 550 rpm. Solid-liquid separation was performed, and the collected solid was washed, dried, and demagnetized to obtain a ternary cathode material precursor. The ternary cathode material precursor was mixed with 1.025 mol LiOH and 0.011 mol Al2O3, preheated at 300℃ for 6 h in a pure oxygen atmosphere, and then calcined at 700℃ for 15 h to obtain the ternary cathode material LiNi. 0.88 Co 0.098 Al 0.022O2; 1 mol of the prepared ternary cathode material was mixed with 0.0035 mol of Li3PO4 material and then heat-treated in a pure oxygen atmosphere at a temperature of 600℃ for 15 h to obtain a single-layer coated ternary cathode material.

[0049] 2) The monolayer-coated ternary cathode material obtained in step 1) is mixed with 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, wherein the mass of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt accounts for 25% of the total mass of the monolayer-coated ternary cathode material and the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. The mixture is kept at 600°C for 4 hours under a pure nitrogen atmosphere to obtain the double-layer-coated ternary cathode material.

[0050] Example 4

[0051] This embodiment provides a method for preparing a double-layer coated ternary cathode material, including the following steps:

[0052] 1) A mixed solution of 0.90 mol nickel sulfate, 0.1 mol cobalt sulfate, and deionized water was placed in a reaction vessel. The total molar concentration of nickel and cobalt sources in the mixed solution was 3 mol / L. Then, 4 mol / L NaOH solution and 8 mol / L ammonia solution were added to control the pH of the reaction solution to 11.8, and the ammonia value of the reaction solution was 9 g / L. A co-precipitation reaction was carried out at 75℃ with continuous stirring at 800 rpm. Solid-liquid separation was performed, and the collected solid was washed, dried, and demagnetized to obtain a ternary cathode material precursor. The ternary cathode material precursor was mixed with 1.025 mol LiOH and 0.011 mol Al2O3, preheated at 500℃ for 4 h in a pure oxygen atmosphere, and then calcined at 710℃ for 10 h to obtain the ternary cathode material LiNi. 0.88 Co 0.098 Al 0.022 O2; 1 mol of the prepared ternary cathode material was mixed with 0.0025 mol of Li3PO4 material and then heat-treated in a pure oxygen atmosphere at a temperature of 700℃ for 13 h to obtain a single-layer coated ternary cathode material.

[0053] 2) The monolayer-coated ternary cathode material obtained in step 1) is mixed with 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, wherein the mass of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt accounts for 50% of the total mass of the monolayer-coated ternary cathode material and the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. The mixture is kept at 500°C for 5 hours under a pure nitrogen atmosphere to obtain the double-layer-coated ternary cathode material.

[0054] Comparative Example 1

[0055] This comparative example provides a method for preparing a ternary cathode material, including the following steps:

[0056] 1) A mixed solution of 0.90 mol nickel sulfate, 0.1 mol cobalt sulfate, and deionized water was placed in a reaction vessel. The total molar concentration of nickel and cobalt sources in the mixed solution was 3 mol / L. Then, 4 mol / L NaOH solution and 8 mol / L ammonia solution were added to control the pH of the reaction solution to 11.8, and the ammonia value of the reaction solution was 9 g / L. A co-precipitation reaction was carried out at 65℃ with continuous stirring at 550 rpm. Solid-liquid separation was performed, and the collected solid was washed, dried, and demagnetized to obtain the ternary cathode material precursor. The ternary cathode material precursor was mixed with 1.025 mol LiOH and 0.011 mol Al2O3, preheated at 500℃ for 4 h in a pure oxygen atmosphere, and then calcined at 710℃ for 10 h to obtain the ternary cathode material LiNi. 0.88 Co 0.098 Al 0.022 O2; 1 mol of the prepared ternary cathode material was mixed with 0.0025 mol of Li3PO4 material and then heat-treated in a pure oxygen atmosphere at a temperature of 650℃ for 10 h to obtain a single-layer coated ternary cathode material.

[0057] 2) The monolayer coated ternary cathode material obtained in step 1) is mixed with 1-allyl-3-methylimidazolium p-toluenesulfonate, wherein the mass of 1-allyl-3-methylimidazolium p-toluenesulfonate accounts for 35% of the total mass of the monolayer coated ternary cathode material and 1-allyl-3-methylimidazolium p-toluenesulfonate. The mixture is kept at 600°C for 6 hours under a pure nitrogen atmosphere to obtain the coated ternary cathode material.

[0058] Comparative Example 2

[0059] This comparative example provides a method for preparing a ternary cathode material, including the following steps:

[0060] 1) A mixed solution of 0.90 mol nickel sulfate, 0.1 mol cobalt sulfate, and deionized water was placed in a reaction vessel. The total molar concentration of nickel and cobalt sources in the mixed solution was 3 mol / L. Then, 4 mol / L NaOH solution and 8 mol / L ammonia solution were added to control the pH of the reaction solution to 11.8, and the ammonia value of the reaction solution was 9 g / L. A co-precipitation reaction was carried out at 65℃ with continuous stirring at 550 rpm. Solid-liquid separation was performed, and the collected solid was washed, dried, and demagnetized to obtain the ternary cathode material precursor. The ternary cathode material precursor was mixed with 1.025 mol LiOH and 0.011 mol Al2O3, preheated at 500℃ for 4 h in a pure oxygen atmosphere, and then calcined at 710℃ for 10 h to obtain the ternary cathode material LiNi. 0.88 Co 0.098 Al 0.022 O2; 1 mol of the prepared ternary cathode material was mixed with 0.0025 mol of aluminum nitrate and then heat-treated in a pure oxygen atmosphere at a temperature of 650℃ for 10 h to obtain a single-layer coated ternary cathode material.

[0061] 2) Mix the monolayer coated ternary cathode material obtained in step 1) with glucose, wherein the mass of glucose accounts for 35% of the total mass of the monolayer coated ternary cathode material and glucose. Keep the mixture at 600°C for 6 hours under a pure nitrogen atmosphere to obtain the coated ternary cathode material.

[0062] Comparative Example 3

[0063] This comparative example provides a method for preparing a ternary cathode material, including the following steps:

[0064] A mixed solution of 0.90 mol nickel sulfate, 0.1 mol cobalt sulfate, and deionized water was placed in a reaction vessel. The total molar concentration of nickel and cobalt sources in the mixed solution was 3 mol / L. Then, 4 mol / L NaOH solution and 8 mol / L ammonia solution were added to control the pH of the reaction solution to 11.8, and the ammonia value of the reaction solution was 9 g / L. A co-precipitation reaction was carried out at 65℃ with continuous stirring at 550 rpm. Solid-liquid separation was performed, and the collected solid was washed, dried, and demagnetized to obtain a ternary cathode material precursor. The ternary cathode material precursor was mixed with 1.025 mol LiOH and 0.011 mol Al2O3, preheated at 500℃ for 4 h in a pure oxygen atmosphere, and then calcined at 710℃ for 10 h to obtain the ternary cathode material LiNi. 0.88 Co 0.098 Al 0.022O2; 1 mol of the prepared ternary cathode material was mixed with 0.0025 mol of Li3PO4 material and then heat-treated in a pure oxygen atmosphere at a temperature of 650℃ for 10 h to obtain the coated ternary cathode material.

[0065] Comparative Example 4

[0066] This comparative example provides a method for preparing a ternary cathode material, including the following steps:

[0067] 1) A mixed solution of 0.90 mol nickel sulfate, 0.1 mol cobalt sulfate, and deionized water was placed in a reaction vessel. The total molar concentration of nickel and cobalt sources in the mixed solution was 3 mol / L. Then, 4 mol / L NaOH solution and 8 mol / L ammonia solution were added to control the pH of the reaction solution to 11.8, and the ammonia value of the reaction solution was 9 g / L. A co-precipitation reaction was carried out at 65℃ with continuous stirring at 550 rpm. Solid-liquid separation was performed, and the collected solid was washed, dried, and demagnetized to obtain the ternary cathode material precursor. The ternary cathode material precursor was mixed with 1.025 mol LiOH and 0.011 mol Al2O3, preheated at 500℃ for 4 h in a pure oxygen atmosphere, and then calcined at 710℃ for 10 h to obtain the ternary cathode material LiNi. 0.88 Co 0.098 Al 0.022 O2;

[0068] 2) Mix 1 mol of the ternary cathode material obtained in step 1) with 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, wherein the mass of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt accounts for 35% of the total mass of the ternary cathode material and the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. Keep at 600°C for 6 hours under a pure nitrogen atmosphere to obtain the coated ternary cathode material.

[0069] Comparative Example 5

[0070] This comparative example provides a method for preparing a ternary cathode material, including the following steps:

[0071] 1) A mixed solution of 0.90 mol nickel sulfate, 0.1 mol cobalt sulfate, and deionized water was placed in a reaction vessel. The total molar concentration of nickel and cobalt sources in the mixed solution was 3 mol / L. Then, 4 mol / L NaOH solution and 8 mol / L ammonia solution were added to control the pH of the reaction solution to 11.8, and the ammonia value of the reaction solution was 9 g / L. A co-precipitation reaction was carried out at 65℃ with continuous stirring at 550 rpm. Solid-liquid separation was performed, and the collected solid was washed, dried, and demagnetized to obtain the ternary cathode material precursor. The ternary cathode material precursor was mixed with 1.025 mol LiOH and 0.011 mol Al2O3, preheated at 500℃ for 4 h in a pure oxygen atmosphere, and then calcined at 710℃ for 10 h to obtain the ternary cathode material LiNi. 0.88 Co 0.098 Al 0.022 O2; 1 mol of the prepared ternary cathode material was mixed with 0.0025 mol of alumina material and then heat-treated in a pure oxygen atmosphere at a temperature of 650℃ for 10 h to obtain the coated ternary cathode material.

[0072] Comparative Example 6

[0073] This comparative example provides a method for preparing a double-layer coated ternary cathode material, including the following steps:

[0074] 1) A mixed solution of 0.90 mol nickel sulfate, 0.1 mol cobalt sulfate, and deionized water was placed in a reaction vessel. The total molar concentration of nickel and cobalt sources in the mixed solution was 3 mol / L. Then, 4 mol / L NaOH solution and 8 mol / L ammonia solution were added to control the pH of the reaction solution to 11.8, and the ammonia value of the reaction solution was 9 g / L. A co-precipitation reaction was carried out at 65℃ with continuous stirring at 550 rpm. Solid-liquid separation was performed, and the collected solid was washed, dried, and demagnetized to obtain the ternary cathode material precursor. The ternary cathode material precursor was mixed with 1.025 mol LiOH and 0.011 mol Al2O3, preheated at 500℃ for 4 h in a pure oxygen atmosphere, and then calcined at 710℃ for 10 h to obtain the ternary cathode material LiNi. 0.88 Co 0.098 Al 0.022 O2; 1 mol of the prepared ternary cathode material was mixed with 0.0025 mol of nickel oxide material and then heat-treated in a pure oxygen atmosphere at a temperature of 650℃ for 10 h to obtain a single-layer coated ternary cathode material.

[0075] 2) The monolayer-coated ternary cathode material obtained in step 1) is mixed with 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, wherein the mass of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt accounts for 35% of the total mass of the monolayer-coated ternary cathode material and the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. The mixture is kept at 600°C for 6 hours under a pure nitrogen atmosphere to obtain the double-layer-coated ternary cathode material.

[0076] Test case

[0077] The ternary cathode materials from Examples 1-4 and Comparative Examples 1-6 were used as cathode materials for lithium-ion batteries to prepare coin cells. The preparation method is as follows: The cathode material (ternary cathode material prepared in Examples 1-4 or Comparative Examples 1-6), the binder being polyvinylidene fluoride (PVDF), the conductive agent being conductive carbon black (SP), and the solvent being N-methylpyrrolidone (NMP) were mixed in a ratio of 95g:1g:4g:220mL, stirred to form a slurry, coated on copper foil, and dried and rolled to obtain a cathode sheet; lithium hexafluorophosphate (LiPF6) was used as the electrolyte, and a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 was used as the solvent to prepare an electrolyte solution with a concentration of 1mol / L; a lithium metal sheet was used as the counter electrode, and a polypropylene (PP) membrane was used as the separator. The coin cells were assembled in an argon-filled glove box.

[0078] Electrochemical performance tests were conducted on coin cells containing ternary cathode materials from Examples 1-4 and Comparative Examples 1-6. The tests were performed using a Wuhan Landian CT2001A battery tester with a charge / discharge voltage range of 2.5-4.25V. The capacity retention rate was tested after 50 cycles at charge / discharge rates of 0.2C, 0.5C, and 2C. The test results are shown in Table 1.

[0079] Table 1

[0080]

[0081] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a double-layer coated ternary cathode material, characterized in that, Includes the following steps: 1) The ternary cathode material is mixed with a phosphorus source and then heat-treated in an oxygen atmosphere to obtain a single-layer coated ternary cathode material; The general chemical formula of the ternary cathode material is LiNi. x Co y Al z O2, and 0.8≤x≤0.9, 0.075≤y≤0.1, 0.02≤z≤0.045, x+y+z=1; 2) The monolayer-coated ternary cathode material obtained in step 1) is mixed with 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and then sintered to obtain the bilayer-coated ternary cathode material.

2. The method for preparing the double-layer coated ternary cathode material according to claim 1, characterized in that, The phosphorus source mentioned in step 1) is selected from at least one of Li3PO4, Co3(PO4)2, Mn3(PO4)2, and Mg3(PO4)2; The molar ratio of the ternary cathode material to the phosphorus source is 1:(0.001-0.0035).

3. The method for preparing the double-layer coated ternary cathode material according to claim 1 or 2, characterized in that, The heat treatment temperature in step 1) is 600-800℃, and the heat treatment time is 10-15h; In step 2), the mass of the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt accounts for 25%-50% of the total mass of the monolayer coated ternary cathode material and the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. The sintering temperature in step 2) is 300-600℃, and the sintering time is 4-6h; The sintering atmosphere is nitrogen.

4. The method for preparing the double-layer coated ternary cathode material according to any one of claims 1-3, characterized in that, The preparation method of the ternary cathode material described in step 1) includes the following steps: S1: Mix nickel source, cobalt source and water to form a mixed solution, then add precipitant and ammonia solution to carry out co-precipitation reaction, and separate solid and liquid to obtain ternary cathode material precursor; S2: The ternary cathode material precursor obtained in step S1 is mixed with a lithium source and an aluminum source, and then preheated and calcined to obtain the ternary cathode material.

5. The method for preparing the double-layer coated ternary cathode material according to claim 4, characterized in that, The molar ratio of nickel in the nickel source, cobalt in the cobalt source, lithium in the lithium source, and aluminum in the aluminum source is (0.9-0.99):(0.01-0.1):(1.01-1.06):(0.02-0.04). The nickel source is selected from at least one of nickel acetate, nickel nitrate, and nickel sulfate; The cobalt source is selected from at least one of cobalt acetate, cobalt nitrate, and cobalt sulfate.

6. The method for preparing the double-layer coated ternary cathode material according to claim 4 or 5, characterized in that, The total molar concentration of nickel and cobalt sources in the mixed solution described in step S1 is 3-12 mol / L; The precipitant is selected from an aqueous sodium hydroxide solution; The molar concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 3-12 mol / L; The molar concentration of ammonia in the ammonia solution is 3-14 mol / L; The coprecipitation reaction temperature is 60-75℃, and the coprecipitation reaction speed is 500-800 rpm.

7. The method for preparing the double-layer coated ternary cathode material according to claim 6, characterized in that, The pH of the reaction solution was controlled to be 11.5-13.5 using a precipitant and an ammonia solution, and the ammonia value of the reaction solution was 5-15 g / L.

8. The method for preparing the double-layer coated ternary cathode material according to claim 6, characterized in that, Following the solid-liquid separation step, the method further includes washing, drying, and demagnetizing the separated solid.

9. The method for preparing the double-layer coated ternary cathode material according to any one of claims 4-8, characterized in that, The lithium source mentioned in step S2 is selected from at least one of lithium carbonate and lithium hydroxide; The aluminum source is selected from at least one of alumina and aluminum hydroxide; The preheating temperature is 300-600℃, the preheating time is 4-6 hours, and the preheating atmosphere is oxygen; The calcination temperature is 700-800℃, the calcination time is 10-15h, and the calcination atmosphere is oxygen.

10. A double-layer coated ternary cathode material, characterized in that, It is prepared by the preparation method of the double-layer coated ternary cathode material according to any one of claims 1-9.

11. The application of the double-layer coated ternary cathode material according to claim 10 in lithium-ion batteries.

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