A coated secondary battery cathode material, and a preparation method and application thereof

Abstract

The application discloses a kind of coated secondary battery positive electrode materials and preparation method and application, belong to lithium ion battery, sodium ion battery technical field.The preparation method of coated secondary battery positive electrode material of the application, comprising the following steps: (1) metal salt solution and organic phosphorus (phosphine) acid solution are mixed, and metal ion extraction load is carried out, after stratification, the upper layer solution is taken, and the organic phase solution of metal ion load is obtained;The organic phase solution of metal ion load is diluted;(2) secondary battery positive electrode material and the organic phase solution of metal ion load after dilution in step (1) are mixed, and mixed slurry is obtained;(3) the mixed slurry is solid-liquid separation, and the obtained solid is calcined to obtain coated positive electrode material.The organic phosphorus (phosphine) acid of metal ion load is used to coat secondary battery positive electrode material, significantly improve the rate and cycle performance of material, and greatly reduce the surface residual alkali of material.

Description

Technical Field

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

[0002] Ternary lithium-ion batteries are widely used in electric vehicles due to their high energy density. Meanwhile, due to the scarcity of lithium resources in China, sodium-ion batteries are increasingly emerging as a substitute. Currently, layered metal oxides are the most promising cathode material for sodium-ion batteries. However, both layered metal oxide cathode materials and ternary lithium-ion cathode materials currently suffer from poor cycle life and high residual alkali content.

[0003] Surface coating is a relatively effective method for reducing residual alkali on the surface of cathode materials and maintaining cycle performance. Common metal oxides, such as Al2O3, TiO2, and ZrO2, can effectively reduce residual alkali on the cathode material surface, and the inert coating layer can effectively prevent HF corrosion and improve the material's cycle performance. However, these substances themselves have low ionic and electronic conductivity, and large-area coating will reduce the material's rate performance. At the same time, currently, dry mixing is generally used for point coating of Al2O3, TiO2, ZrO2, etc., which results in a small coating area and limited reduction in residual alkali on the material surface. Summary of the Invention

[0004] This invention provides a coated secondary battery cathode material, its preparation method, and its application. This invention uses organophosphoric acid loaded with metal ions to coat the secondary battery cathode material, which significantly improves the rate and cycle performance of the material and greatly reduces the surface residual alkali of the material.

[0005] This invention first provides a method for preparing a coated secondary battery cathode material, comprising the following steps:

[0006] (1) Mix the metal salt solution and the organic phosphoric acid solution to perform metal ion extraction loading, let it stand and separate into layers, and take the upper layer solution to obtain the organic phase solution loaded with metal ions; dilute the organic phase solution loaded with metal ions.

[0007] (2) Mix the secondary battery positive electrode material with the diluted organic phase solution loaded with metal ions from step (1) to obtain a mixed slurry;

[0008] (3) The mixed slurry is separated into solid and liquid phases, and the resulting solid is calcined to obtain the coated secondary battery cathode material.

[0009] In the preparation method of the above-mentioned coated secondary battery cathode material, the metal salt is at least one of sulfates, chlorides or nitrates of aluminum, cobalt or zinc and chlorides of calcium, titanium or zirconium;

[0010] Specifically, the metal salt is any one of the following:

[0011] 1) Aluminum sulfate and zinc sulfate; more specifically, the molar ratio of aluminum to zinc is 3:1;

[0012] 2) Zirconium chloride and titanium chloride; more specifically, the molar ratio of zirconium to titanium is 1:1;

[0013] 3) Calcium chloride and aluminum chloride; more specifically, the molar ratio of calcium to aluminum is 1:1;

[0014] 4) Cobalt sulfate;

[0015] 5) Aluminum sulfate;

[0016] The total molar concentration of metal ions in the metal salt solution is 1 to 2 mol / L;

[0017] The pH of the metal salt solution is 1 to 6; specifically, the pH of the metal salt solution is adjusted by an acid; the acid is any one of sulfuric acid, hydrochloric acid and nitric acid;

[0018] The organic phosphoric (phosphonic) acid is at least one of bis(2-ethylhexyl) phosphate, 2-ethylhexyl 2-ethylhexyl phosphate, and bis(2,4,4-trimethylpentyl) phosphonic acid;

[0019] The solvent of the organic phosphoric (phosphonic) acid solution is sulfonated kerosene; in the organic phosphoric (phosphonic) acid solution, the volume percentage concentration of the organic phosphoric (phosphonic) acid is 20% to 40%;

[0020] The secondary battery cathode material is a lithium-ion ternary battery cathode material or a sodium-ion layered oxide cathode material.

[0021] In the preparation method of the above-mentioned coated secondary battery cathode material, the lithium-ion ternary battery cathode material is lithium nickel cobalt manganese oxide LiNi x Co y Mn 1-x-y O2, where 0.3 ≤ x < 1, 0 < y ≤ 0.3, and x + y < 1; specifically, the lithium-ion ternary battery cathode material is LiNi 0.78 Co 0.1 Mn 0.12 O2;

[0022] The sodium-ion layered oxide cathode material is any one of iron-based, manganese-based or copper-based, and its general formula is Na γ Ni x Fe yMn z M 1-x-y-z O2, where 0 ≤ x < 0.5, 0.1 < y ≤ 0.5, 0.1 < z ≤ 0.5, and x + y + z ≤ 1; M is one of Zn or Cu; 0.6 ≤ γ ≤ 1; specifically, the sodium layered oxide cathode material is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, NaNi 2 / 9Cu 1 / 9 Fe 1 / 3 Mn 1 / 3 O2;

[0023] In the preparation method of the above-mentioned coated secondary battery cathode material, in step (1), the volume ratio of the metal salt solution to the organic phosphorus (phosphine) acid solution is 6 - 9:1;

[0024] In step (1), the organic phase solution loaded with metal ions is diluted with sulfonated kerosene;

[0025] The organic phase solution loaded with metal ions is diluted by a factor of 1 - 2 in volume;

[0026] In step (2), in the mixed slurry, the solid content of the secondary battery cathode material is 500 - 800 g / L.

[0027] In the preparation method of the above-mentioned coated secondary battery cathode material, in step (1), the metal ion extraction loading is to mix and oscillate for 10 - 20 min.

[0028] In the preparation method of the above-mentioned coated secondary battery cathode material, in step (3), the calcination temperature is 500 - 700 °C; the calcination time is 6 - 10 h;

[0029] The calcination is carried out in an inert atmosphere; specifically, a nitrogen atmosphere.

[0030] In the preparation method of the above-mentioned coated secondary battery cathode material, there is a drying step before the calcination in step (3); specifically, the drying is vacuum drying, the temperature is 60 - 80 °C, and the time is 12 - 24 h.

[0031] The present invention also provides a coated secondary battery cathode material prepared by the above preparation method.

[0032] Specifically, in the coating layer of the coated secondary battery cathode material, the total mass of the coating metal element, P element and C element accounts for 0.5% - 1% of the total mass of the cathode material.

[0033] Finally, the application of the above-mentioned coated secondary battery cathode material in the preparation of a secondary battery cathode also belongs to the protection scope of the present invention.

[0034] This invention uses organophosphoric acid loaded with metal ions to coat the positive electrode material of a secondary battery. After the organophosphoric acid loaded with metal ions wets the positive electrode material, it is calcined to form a metal phosphate / C composite coating layer on the material surface, which significantly improves the rate and cycle performance of the material. At the same time, the organophosphoric acid loaded with metal ions still contains protons, which can react with the solid residual alkali on the material surface through saponification during the coating process, deeply removing the residual alkali on the surface and greatly reducing the pH of the material. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope (SEM) image of the coated lithium-ion battery cathode material prepared in Example 4. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0037] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0038] In the quantitative experiments in the following examples, three replicate experiments were set up, and the average value of the results was taken.

[0039] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0040] The sodium-ion battery cathode material NaNi in the following examples 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, NaNi 2 / 9 Cu 1 / 9 Fe 1 / 3 Mn 1 / 3 O2 was purchased from Jiangsu Xiangying New Energy Technology Co., Ltd., LiNi 0.78 Co 0.1 Mn 0.12 O2 was purchased from Rongbai Technology.

[0041] Example 1

[0042] (1) Add di(2-ethylhexyl) phosphate to sulfonated kerosene and mix at a volume ratio of 1:2 to prepare organic phase solution B;

[0043] (2) Add aluminum sulfate and zinc sulfate to deionized water and dissolve them completely to obtain a mixed salt solution with aluminum and zinc molar concentrations of 1.5 mol / L and 0.5 mol / L, respectively. Then add sulfuric acid to adjust the pH to 5 to obtain a clear aqueous solution C.

[0044] (3) Add solution B to solution C at a volume ratio of 1:6, mix thoroughly and shake for 10 min, let stand, and after the mixed solution separates into layers, take the upper layer solution to obtain organic supported phase solution D.

[0045] (4) Add solution D to sulfonated kerosene and dilute by one volume to obtain solution E;

[0046] (5) Sodium-ion battery cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was added to solution E at a solid concentration of 500 g / L, and stirred thoroughly for 20 minutes to obtain mixed slurry F;

[0047] (6) Filter the mixed slurry F, dry the resulting solid at 60°C in vacuum for 12 hours, and calcine it at 700°C in an inert atmosphere (nitrogen atmosphere) for 10 hours to obtain the coated sodium-ion battery cathode material.

[0048] According to ICP and carbon-sulfur analyzer tests, the mass contents of Al, Zn, P and C in the obtained coated sodium-ion battery cathode material are 0.20%, 0.18%, 0.25% and 0.31%, respectively.

[0049] Example 2

[0050] (1) Add 2-ethylhexyl phosphate 2-ethylhexyl ester to sulfonated kerosene and mix at a volume ratio of 1:3 to obtain organic phase solution B;

[0051] (2) Add zirconium chloride and titanium chloride to deionized water and dissolve them completely to obtain a mixed salt solution with a zirconium and titanium molar concentration of 1 mol / L. Then add sulfuric acid to adjust the pH to 1 to obtain a clear aqueous solution C.

[0052] (3) Add solution B to solution C at a volume ratio of 1:9, mix thoroughly and shake for 20 minutes, let stand, and after the mixed solution separates into layers, take the upper layer solution to obtain the upper organic supported phase solution D.

[0053] (4) Add solution D to sulfonated kerosene and dilute by 2 times by volume to obtain solution E;

[0054] (5) Sodium-ion battery cathode material NaNi 2 / 9 Cu 1 / 9 Fe 1 / 3 Mn 1 / 3 O2 was added to solution E at a solid concentration of 800 g / L, and stirred thoroughly for 40 min to obtain mixed slurry F;

[0055] (6) Filter the mixed slurry F, dry the resulting solid at 80°C in vacuum for 24 hours, and calcine it at 600°C in an inert atmosphere (nitrogen atmosphere) for 6 hours to obtain the coated sodium-ion battery cathode material.

[0056] According to ICP and carbon-sulfur analyzer tests, the mass contents of Zr, Ti, P and C in the obtained coated sodium-ion battery cathode material are 0.16%, 0.11%, 0.13% and 0.15%, respectively.

[0057] Example 3

[0058] (1) Bis(2,4,4-trimethylpentyl)phosphonic acid was added to sulfonated kerosene and mixed at a volume ratio of 1:3 to prepare organic phase solution B;

[0059] (2) Add calcium chloride and aluminum chloride to deionized water and dissolve them completely to obtain a mixed salt solution with a calcium and aluminum molar concentration of 1 mol / L. Then add hydrochloric acid to adjust the pH to 2 to obtain a clear aqueous solution C.

[0060] (3) Add solution B to solution C at a volume ratio of 1:7, mix thoroughly and shake for 20 minutes, let stand, and after the mixed solution separates into layers, take the upper layer solution to obtain the upper organic supported phase solution D.

[0061] (4) Add solution D to sulfonated kerosene and dilute by 2 times by volume to obtain solution E;

[0062] (5) Sodium-ion battery cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was added to solution E at a solid concentration of 800 g / L, and stirred thoroughly for 40 min to obtain mixed slurry F;

[0063] (6) Filter the mixed slurry F, dry the resulting solid at 60°C in vacuum for 24 hours, and calcine it at 600°C in an inert atmosphere (nitrogen atmosphere) for 6 hours to obtain the coated sodium-ion battery cathode material.

[0064] According to ICP and carbon-sulfur analyzer tests, the mass contents of Ca, Al, P and C in the obtained coated sodium-ion battery cathode material are 0.19%, 0.1%, 0.14% and 0.17%, respectively.

[0065] Example 4

[0066] (1) Add di(2-ethylhexyl) phosphate to sulfonated kerosene and mix at a volume ratio of 1:3 to obtain organic phase solution B;

[0067] (2) Cobalt sulfate was added to deionized water and dissolved completely to obtain a salt solution with a cobalt molar concentration of 2 mol / L. Then hydrochloric acid was added to adjust the pH to 5 to obtain a clear aqueous solution C.

[0068] (3) Add solution B to solution C at a volume ratio of 1:7, mix thoroughly and shake for 20 minutes, let stand, and after the mixed solution separates into layers, take the upper layer solution to obtain the upper organic supported phase solution D.

[0069] (4) Add solution D to sulfonated kerosene and dilute by 2 times by volume to obtain solution E;

[0070] (5) LiNi, a ternary cathode material for lithium-ion batteries 0.78 Co 0.1 Mn 0.12 O2 was added to solution E at a solid concentration of 800 g / L, and stirred thoroughly for 40 min to obtain mixed slurry F;

[0071] (6) Filter the mixed slurry F, dry the resulting solid under vacuum at 60°C for 24 hours, and calcine it at 600°C for 6 hours under an inert atmosphere (nitrogen atmosphere) to obtain the coated lithium-ion battery cathode material (its electron microscope image is shown in...). Figure 1 ).

[0072] According to ICP and carbon-sulfur analyzer tests, the mass contents of Co, P and C in the obtained coated lithium-ion battery cathode material are 0.28%, 0.14% and 0.16%, respectively.

[0073] Example 5

[0074] (1) Add di(2-ethylhexyl) phosphate to sulfonated kerosene and mix at a volume ratio of 1:3 to obtain organic phase solution B;

[0075] (2) Add aluminum sulfate to deionized water and dissolve it completely to obtain a salt solution with an aluminum molar concentration of 2 mol / L. Then add hydrochloric acid to adjust the pH to 5 to obtain a clear aqueous solution C.

[0076] (3) Add solution B to solution C at a volume ratio of 1:7, mix thoroughly and shake for 20 minutes, let stand, and after the mixed solution separates into layers, take the upper layer solution to obtain the upper organic supported phase solution D.

[0077] (4) Add solution D to sulfonated kerosene and dilute by 2 times by volume to obtain solution E;

[0078] (5) Sodium-ion battery cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was added to solution E at a solid concentration of 800 g / L, and stirred thoroughly for 40 min to obtain mixed slurry F;

[0079] (6) Filter the mixed slurry F, dry the resulting solid at 60°C in vacuum for 24 hours, and calcine it at 500°C in an inert atmosphere (nitrogen atmosphere) for 6 hours to obtain the coated sodium-ion battery cathode material.

[0080] According to ICP and carbon-sulfur analyzer tests, the mass contents of Al, P and C in the obtained coated sodium-ion battery cathode material are 0.19%, 0.15% and 0.17%, respectively.

[0081] Comparative Example 1

[0082] Directly using lithium-ion battery ternary material LiNi 0.78 Co 0.1 Mn 0.12 O2 was used to test the electrical properties and pH value of the materials.

[0083] Comparative Example 2

[0084] Directly using sodium-ion battery cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was used to test the electrical properties and pH value of the materials.

[0085] Comparative Example 3

[0086] Directly using sodium-ion battery cathode material NaNi 2 / 9 Cu 1 / 9 Fe 1 / 3 Mn 1 / 3 O2 was used to test the electrical properties and pH value of the materials.

[0087] Comparative Example 4

[0088] The difference from Example 5 is as follows:

[0089] Steps (2) and (3) are omitted. Solution D in step (4) is replaced with solution B in step (1), and the organic phase without metal loading is used for direct coating.

[0090] Example 6

[0091] Electrochemical performance characterization: The positive electrode materials of the examples and comparative examples were used to fabricate button cells. The positive electrode material, conductive carbon black, and polyvinylidene fluoride were ground and mixed uniformly at a mass ratio of 90:5:5. An appropriate amount of N-methylpyrrolidone was added and stirred to adjust the viscosity. The slurry was then uniformly coated onto aluminum foil and dried at 80°C for 12 hours. After the electrode sheets were rolled and pressed, they were assembled into 2016-type button cells in a glove box. The electrolyte was a 1M LiPF6 solution, in which the solvent was a mixture of EC, DEC, and DMC (volume ratio 1:1:1). The negative electrode was a lithium sheet; the separator used was a polypropylene microporous membrane.

[0092] Note: The carbon and sulfur test samples were treated with dilute acid before testing to remove the interference of sodium carbonate and sodium bicarbonate in the material on the C determination.

[0093] The test voltage range for lithium-ion battery cathode materials is 2.8–4.35V; the test voltage range for sodium-ion battery cathode materials is 1.5–4.0V. The first charge-discharge curves were tested at 0.2C, while the cycle curves were obtained by charging at 1C and discharging at 1C.

[0094] The pH value of the material was obtained by testing the pH of the filtrate in section 5.5.2 of GB / T41704-2022.

[0095] Table 1. Electrical performance data and pH values ​​of the examples and comparative samples.

[0096]

[0097] Data from Examples 4 and 1, Examples 1, 3, 5 and 2, 4, and Examples 2 and 3 show that the discharge capacity of each type of cathode material was almost unaffected after coating, but the rate performance and cycle performance of the coated material were significantly improved. Simultaneously, the pH value of the coated material also decreased significantly during the coating process, indicating that this method has a significant effect on the performance of the cathode material.

[0098] Data from Comparative Examples 1, 4 and Example 5 show that single organophosphoric acid coating treatment has a significant effect on reducing residual alkali on the material surface, while also improving the rate capability and cycle performance of the material. When loaded organophosphoric acid is used for coating, the rate capability and cycle performance of the material are further improved.

Claims

1. A method for preparing a coated secondary battery cathode material, comprising the following steps: (1) Mix the metal salt solution with the organic phosphoric acid or organic phosphonic acid solution, perform metal ion extraction loading, allow the layers to stand and separate, and take the upper layer solution to obtain the organic phase solution loaded with metal ions; dilute the organic phase solution loaded with metal ions. The metal salt is at least one of the following: sulfate, chloride or nitrate of aluminum, cobalt or zinc, and chloride of calcium, titanium or zirconium. The organophosphate or organophosphonic acid is at least one of di(2-ethylhexyl) phosphate, 2-ethylhexyl phosphate, and bis(2,4,4-trimethylpentyl)phosphonic acid; (2) Mix the secondary battery cathode material and the diluted organic phase solution loaded with metal ions from step (1) to obtain a mixed slurry; (3) The mixed slurry is separated into solid and liquid phases, and the resulting solid is calcined to obtain the coated secondary battery cathode material; In step (3), the calcination temperature is 500~700℃; the calcination time is 6~10h; The calcination is carried out in an inert atmosphere.

2. The method for preparing the coated secondary battery cathode material according to claim 1, characterized in that: The total molar concentration of metal ions in the metal salt solution is 1~2 mol / L; The pH of the metal salt solution is 1-6; The solvent for the organophosphoric acid or organophosphonic acid solution is sulfonated kerosene; the volume percentage concentration of the organophosphoric acid or organophosphonic acid in the solution is 20%~40%. The cathode material of the secondary battery is either a lithium-ion ternary battery cathode material or a sodium-ion layered oxide cathode material.

3. The method for preparing the coated secondary battery cathode material according to claim 2, characterized in that: The positive electrode material of the lithium-ion ternary battery is lithium nickel cobalt manganese oxide LiNi x Co y Mn 1-x-y O2, where 0.3 ≤ x < 1, 0 < y ≤ 0.3, and x + y < 1; The sodium ion layered oxide cathode material is any one of iron-based, manganese-based or copper-based, and its general formula is Na γ Ni x Fe y Mn z M 1-x-y-z O2, where 0 ≤ x < 0.5, 0.1 < y ≤ 0.5, 0.1 < z ≤ 0.5, and x + y + z ≤ 1; M is one of Zn or Cu; 0.6 ≤ γ ≤ 1.

4. The method for preparing the coated secondary battery cathode material according to claim 1, characterized in that: In step (1), the volume ratio of the metal salt solution to the organic phosphoric acid or organic phosphonic acid solution is 6~9:1; In step (1), the organic phase solution loaded with metal ions is diluted with sulfonated kerosene; The organic phase solution loaded with metal ions was diluted by volume by 1 to 2 times. In step (2), the solid content of the secondary battery cathode material in the mixed slurry is 500~800g / L.

5. The method for preparing the coated secondary battery cathode material according to claim 1, characterized in that: In step (1), the metal ion extraction loading is mixed and shaken for 10-20 min.

6. The method for preparing the coated secondary battery cathode material according to claim 1, characterized in that: Before calcination in step (3), there is a drying step; the drying is vacuum drying, the temperature is 60~80℃, and the time is 12~24h.

7. The coated secondary battery cathode material prepared by the preparation method according to any one of claims 1-6.

8. The coated secondary battery cathode material according to claim 7, characterized in that: In the coating layer of the coated secondary battery cathode material, the total mass of the coated metal elements, P elements and C elements accounts for 0.5% to 1% of the total mass of the cathode material.

9. The application of the coated secondary battery cathode material according to claim 7 or 8 in the preparation of secondary battery cathodes.

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