Composite ternary positive electrode material, preparation method therefor and use thereof

Abstract

A composite ternary positive electrode material, a preparation method therefor and a use thereof. The preparation method comprises the following steps: (1) mixing a mixed salt solution of a calcium salt and a tin salt with an alkali solution to obtain a mixed solution; (2) mixing a ternary precursor with the mixed solution, performing solid-liquid separation to obtain a solid material, slurrying the solid material, and then adding hydrofluoric acid to undergo a reaction to obtain a composite ternary precursor; and (3) mixing the composite ternary precursor with a lithium source and performing sintering treatment to obtain the composite ternary positive electrode material. Alkali washing using the alkali solution containing tin and calcium can not only remove sulfur impurities but can also dope the precursor with calcium and tin; furthermore, after modification using hydrofluoric acid to generate fluoride, an oxide can be isolated from an electrolyte solution, reducing side reactions in the charging and discharging process, so that the cycling performance of the material is significantly enhanced.

Description

A composite ternary positive electrode material and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a composite ternary positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, considered a new generation of green, high-energy batteries due to their high energy consumption, long lifespan, and low pollution, have been widely used in a wide range of applications, including mobile phones, digital cameras, computers, and electric vehicles. As a crucial component of lithium-ion batteries, the positive electrode material determines their ultimate performance. Currently, the most researched positive electrode materials include lithium cobalt oxide, lithium manganese oxide, and layered nickel cobalt manganese oxide. Layered nickel cobalt manganese oxide, which combines the advantages of lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide, has seen rapid development in recent years.

[0003] The most common method for synthesizing lithium nickel cobalt manganese oxide is the co-precipitation method, which is to pass alkaline solution into a nickel cobalt manganese mixed salt solution to continuously produce nickel cobalt manganese hydroxide. The precursor is then dried and mixed with lithium salt and calcined to obtain lithium nickel cobalt manganese oxide.

[0004] CN115215388A discloses a method for preparing a ternary cathode material and a ternary cathode material, which are used to improve the preparation efficiency and yield of the ternary cathode material. The method comprises: mixing a manganese salt and / or an aluminum salt with a nickel salt and a cobalt salt, and performing a coprecipitation reaction with an alkaline substance and a complexing agent in a solvent to obtain a coprecipitated slurry having a target median particle size; washing the coprecipitated slurry to obtain a ternary precursor slurry; mixing a lithium source with the ternary precursor slurry in an inert atmosphere to obtain a first mixture; drying the first mixture to obtain a second mixture; and subjecting the second mixture to a high-temperature sintering treatment to obtain the ternary cathode material.

[0005] CN105261737A discloses a method for preparing a ternary positive electrode material, which includes: step 1: uniformly mixing a salt ingredient and an alkali ingredient in a solution to form a mixed solution; step 2: precipitating the mixed solution in step 1 to form precursor grains, and controlling the nucleation and crystal growth rate of the co-precipitation reaction by adjusting parameters; step 3: washing and filtering the precursor grains formed in step 2, adding cation sites to the liquid phase for doping modification, and then drying; step 4: adding lithium to the dried raw materials, and then roasting, and then performing surface coating modification to obtain a finished ternary material.

[0006] In the above scheme, lithium ions cannot fully enter nickel cobalt manganese hydroxide, resulting in residual lithium on the surface of lithium nickel cobalt manganese oxide, affecting the cycle stability of the positive electrode material. In addition, the raw materials for the synthesis of nickel cobalt manganese hydroxide are mostly sulfates. The nickel cobalt manganese hydroxide after coprecipitation also contains a part of sulfur element, which needs to be removed by alkaline water washing. This step will produce a large amount of alkaline wastewater, which has a great impact on the environment. If this step is omitted, the sulfur impurity content will be too high, which is not conducive to the electrochemical performance of the positive electrode material.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The purpose of the present disclosure is to provide a composite ternary positive electrode material, its preparation method and application. The present disclosure uses an alkaline solution containing tin and calcium for alkaline washing, which can not only remove sulfur impurities, but also dope calcium and tin in the precursor. It is then modified with hydrofluoric acid to generate fluoride, which can separate the oxide from the electrolyte, reduce side reactions during the charge and discharge process, and thus significantly enhance the material's cycle performance.

[0010] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0011] In a first aspect, the present disclosure provides a method for preparing a composite ternary cathode material, the preparation method comprising the following steps:

[0012] (1) mixing a mixed salt solution of calcium salt and tin salt with an alkali solution to obtain a mixed solution;

[0013] (2) mixing the ternary precursor and the mixed solution, separating the solid and the liquid to obtain a solid material, slurrying the solid material, adding hydrofluoric acid, and reacting to obtain a composite ternary precursor;

[0014] (3) The composite ternary precursor is mixed with a lithium source, and sintered to obtain the composite ternary positive electrode material.

[0015] The present invention pre-prepares an alkaline solution containing calcium tin salt, and mixes it with a ternary precursor. While removing sulfur impurities, the calcium tin element can enter the nickel cobalt manganese hydroxide particles to form a co-doping. The two elements can not only stabilize the material structure, but also expand the lithium ion transmission channel, ultimately making the positive electrode material exhibit excellent cycle performance. Hydrofluoric acid is then used to modify its surface, so that the hydroxide on the surface is converted into fluoride. CaSnF6 has a negative thermal expansion effect and can produce gaps on the surface during lithium calcination, promoting the reaction of lithium ions with the internal nickel cobalt manganese hydroxide, which can reduce the residual lithium ions on the surface, reduce residual alkali, and improve cycle performance.

[0016] In one embodiment, the calcium salt in step (1) includes calcium chloride and / or calcium nitrate.

[0017] In one embodiment, the tin salt in step (1) includes tin chloride and / or tin nitrate.

[0018] In one embodiment, the total molar concentration of calcium salt and tin salt in the mixed salt solution of step (1) is 0.01 to 0.2 mol / L, for example, 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L or 0.2 mol / L.

[0019] In one embodiment, the molar ratio of calcium element to tin element in the mixed salt solution of step (1) is (0.8-1.2):1, for example: 0.8:1, 0.9:1, 1:1, 1.1:1 or 1.2:1, etc.

[0020] In one embodiment, the molar concentration of the alkali solution in step (1) is 2 to 10 mol / L, for example, 2 mol / L, 3 mol / L, 5 mol / L, 8 mol / L or 10 mol / L.

[0021] In one embodiment, the pH of the mixed solution in step (1) or (2) is ≥12.

[0022] In one embodiment, the ternary precursor in step (2) includes nickel-cobalt-manganese hydroxide.

[0023] In one embodiment, the solid-liquid ratio of the ternary precursor and the mixed solution in step (2) is 1:(2-5) kg / L, for example: 1:2 kg / L, 1:2.5 kg / L, 1:3 kg / L, 1:4 kg / L or 1:5 kg / L, etc.

[0024] The ternary precursor disclosed in the present invention can be a ternary precursor solid particle or a ternary precursor slurry. After the co-precipitation reaction, the ternary precursor does not need to be washed with alkali to remove sulfur, and can be directly filtered and washed with water before use, or the ternary precursor slurry can be directly used, which greatly simplifies the preparation process of the composite ternary material, saves costs and improves production efficiency.

[0025] In one embodiment, the slurrying in step (2) comprises mixing the solid material with deionized water.

[0026] In one embodiment, the solid-to-liquid ratio of the solid material and deionized water in step (2) is 1:(2-5) kg / L, for example: 1:2 kg / L, 1:2.5 kg / L, 1:3 kg / L, 1:4 kg / L or 1:5 kg / L, etc.

[0027] In one embodiment, the mass concentration of the hydrofluoric acid in step (2) is 30-40%, for example, 30%, 32%, 35%, 38% or 40%.

[0028] In one embodiment, the pH of the reaction in step (2) is 4 to 5, for example, 4, 4.2, 4.5, 4.8 or 5.

[0029] In one embodiment, the reaction temperature in step (2) is 100-150°C, for example, 100°C, 120°C, 130°C, 140°C or 150°C.

[0030] In one embodiment, the reaction time of step (2) is 10 to 30 minutes, for example, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes.

[0031] In one embodiment, the lithium source in step (3) includes lithium hydroxide and / or lithium carbonate.

[0032] In one embodiment, the temperature of the sintering treatment in step (3) is 600-1000°C, for example, 600°C, 700°C, 800°C, 900°C or 1000°C.

[0033] In one embodiment, the sintering treatment time in step (3) is 20 to 36 hours, for example, 20 hours, 25 hours, 30 hours, 32 hours or 36 hours.

[0034] In a second aspect, the present disclosure provides a composite ternary positive electrode material, which is prepared by the method described in the first aspect.

[0035] In a third aspect, the present disclosure provides a positive electrode plate, which comprises the composite ternary positive electrode material as described in the second aspect.

[0036] In a fourth aspect, the present disclosure provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet as described in the third aspect.

[0037] Compared with the prior art, the present disclosure has the following beneficial effects:

[0038] (1) The present invention uses an alkaline solution containing tin and calcium for alkaline washing, which can not only remove sulfur impurities, but also dope calcium and tin into the precursor. After modification with hydrofluoric acid, the generated fluoride can separate the oxide from the electrolyte, reduce the side reactions during the charge and discharge process, and thus significantly enhance the cycle performance of the material.

[0039] (2) The method disclosed in the present invention is applicable to various ternary positive electrode materials. The 0.1C discharge capacity of the NCM622 ternary positive electrode material can reach more than 183.8 mAh / g, and the capacity retention rate after 100 cycles can reach more than 97.52%. The 0.1C discharge capacity of the NCM811 ternary positive electrode material can reach more than 204 mAh / g, and the capacity retention rate after 100 cycles can reach more than 97.6%, showing good capacity performance and cycle performance.

[0040] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0041] The technical solution of the present disclosure is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0042] The ternary precursors used in the examples and comparative examples of the present disclosure were prepared by the following method:

[0043] A mixed solution of nickel, cobalt, and manganese salts, along with a sodium hydroxide solution and an ammonia solution, was added to a reactor via a precision metering pump at a constant flow rate. The pH was controlled at 11, and the reaction was allowed to proceed at 60°C with constant stirring. The stoichiometric ratio of nickel sulfate, cobalt sulfate, and manganese sulfate in the mixed solution was controlled, and the reaction was stopped when the particles reached 10 μm.

[0044] The concentration of the nickel-cobalt-manganese salt mixed solution is 1.0 mol / L, the concentration of the sodium hydroxide solution is 5 mol / L, the concentration of the ammonia water is 3 mol / L, and the solution flow rate is 100 mL / min.

[0045] The suspension is filtered and washed with water to obtain the ternary precursor (NCM622 precursor or NCM811 precursor).

[0046] Example 1

[0047] This embodiment provides a composite ternary cathode material, and the preparation method of the composite ternary cathode material is as follows:

[0048] (1) preparing a 0.08 mol / L mixed solution of calcium chloride and tin chloride, with a molar ratio of calcium ions to tin ions of 1:1, adding a sodium hydroxide solution with a concentration of 5 mol / L, and controlling the pH to 14;

[0049] (2) NCM622 precursor was added to the mixed solution at a solid-liquid ratio of 1:3 kg / L, stirred for 1 h, the product was filtered, deionized water was added at a solid-liquid ratio of 1:3 kg / L to prepare a slurry, 40 wt% HF was added, the pH was controlled to 4.2, and the mixture was stirred at 120 ° C for 20 min to obtain a composite ternary precursor;

[0050] (3) The composite ternary precursor is mixed with lithium carbonate according to Li / M=1.02, and sintered at 800° C. for 24 h to obtain the composite ternary positive electrode material.

[0051] Example 2

[0052] This embodiment provides a composite ternary cathode material, and the preparation method of the composite ternary cathode material is as follows:

[0053] (1) preparing a 0.01 mol / L mixed solution of calcium chloride and tin chloride, wherein the molar ratio of calcium ions to tin ions is 0.8:1, adding a sodium hydroxide solution, wherein the concentration of the sodium hydroxide solution is 2 mol / L, and controlling the pH to 12;

[0054] (2) NCM811 precursor was added to the mixed solution at a solid-liquid ratio of 1:2.5 kg / L, stirred for 1 h, the product was filtered, deionized water was added at a solid-liquid ratio of 1:2 kg / L to prepare a slurry, 35 wt% HF was added, the pH was controlled to 4, and the mixture was stirred at 150 ° C for 10 min to obtain a composite ternary precursor;

[0055] (3) The composite ternary precursor was mixed with lithium carbonate according to Li / M=1.02, and sintered at 600° C. for 36 h to obtain the composite ternary positive electrode material.

[0056] Example 3

[0057] This embodiment provides a composite ternary cathode material, and the preparation method of the composite ternary cathode material is as follows:

[0058] (1) preparing a 0.2 mol / L mixed solution of calcium chloride and tin chloride, wherein the molar ratio of calcium ions to tin ions is 1.2:1, adding a sodium hydroxide solution thereto, wherein the concentration of the sodium hydroxide solution is 10 mol / L, and controlling the pH to 15;

[0059] (2) NCM622 precursor was added to the mixed solution at a solid-liquid ratio of 1:5 kg / L, stirred for 1 h, the product was filtered, deionized water was added at a solid-liquid ratio of 1:4 kg / L to prepare a slurry, 30 wt% HF was added, the pH was controlled to 5, and the mixture was stirred at 100 ° C for 30 min to obtain a composite ternary precursor;

[0060] (3) The composite ternary precursor is mixed with lithium carbonate according to Li / M=1.02, and sintered at 1000° C. for 20 h to obtain the composite ternary positive electrode material.

[0061] Example 4

[0062] The only difference between this embodiment and embodiment 1 is that the molar ratio of calcium ions to tin ions is 0.5:1, and other conditions and parameters are exactly the same as those in embodiment 1.

[0063] Example 5

[0064] The only difference between this embodiment and embodiment 1 is that the molar ratio of calcium ions to tin ions is 1.5:1, and other conditions and parameters are exactly the same as those in embodiment 1.

[0065] Example 6

[0066] The only difference between this embodiment and embodiment 1 is that after the sodium hydroxide solution is added in step (1), the pH of the mixed solution is 11.5, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0067] Example 7

[0068] The only difference between this embodiment and embodiment 1 is that after adding hydrofluoric acid in step (2), the pH of the mixed solution is 3.5, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0069] Example 8

[0070] The only difference between this embodiment and embodiment 1 is that after adding hydrofluoric acid in step (2), the pH of the mixed solution is 5.5. Other conditions and parameters are exactly the same as those in embodiment 1.

[0071] Comparative Example 1

[0072] The only difference between this comparative example and Example 1 is that no calcium salt and tin salt are added, and sodium hydroxide solution is directly used for alkali washing. Other conditions and parameters are exactly the same as those in Example 1.

[0073] Comparative Example 2

[0074] The only difference between this comparative example and Example 1 is that no tin salt is added, and other conditions and parameters are exactly the same as those in Example 1.

[0075] Comparative Example 3

[0076] The only difference between this comparative example and Example 1 is that no calcium salt is added, and other conditions and parameters are exactly the same as those in Example 1.

[0077] Comparative Example 4

[0078] The only difference between this comparative example and Example 1 is that hydrofluoric acid is not added, and other conditions and parameters are exactly the same as those in Example 1.

[0079] Comparative Example 5

[0080] The only difference between this comparative example and Example 1 is that no sodium hydroxide solution is added, and other conditions and parameters are exactly the same as those in Example 1.

[0081] Performance testing:

[0082] The dried samples obtained in the examples and comparative examples were subjected to inductively coupled plasma spectroscopy (ICP) testing to determine the S element content in the materials. The positive electrode materials obtained in the examples and comparative examples were mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 90:5:5, and N-methylpyrrolidone (NMP) was used as a solvent. The mixture was evenly coated on aluminum foil, dried, and rolled to form a simulated battery positive electrode. The negative electrode was a metal lithium sheet, the diaphragm was Celgard2400, and the electrolyte was 1 mol / L LiPF6 / DMC+DEC (volume ratio of 1:1), forming a CR2025 type simulated battery. The charge and discharge voltage range was 3.0~4.5V, and the electrochemical performance data of the lithium-ion battery positive electrode material lithium nickel cobalt manganese oxide was obtained. The test results are shown in Table 1:

[0083] Table 1

[0084] As can be seen from Table 1, it can be obtained from Examples 1-3 that the sulfur content of the positive electrode material prepared by the method of the present disclosure can reach below 823 ppm, and the method is applicable to various ternary positive electrode materials. The 0.1C discharge capacity of the NCM622 ternary positive electrode material prepared can reach more than 183.8 mAh / g, and the capacity retention rate after 100 cycles can reach more than 97.52%. The 0.1C discharge capacity of the NCM811 ternary positive electrode material prepared can reach more than 204 mAh / g, and the capacity retention rate after 100 cycles can reach more than 97.6%, showing good capacity performance and cycle performance.

[0085] By comparing Example 1 with Examples 4-5, it can be seen that during the preparation of the composite ternary positive electrode material disclosed in the present invention, the molar ratio of calcium and tin will affect its performance. The molar ratio of calcium and tin is controlled at 0.8 to 1.2:1, and the performance of the composite ternary positive electrode material is better. If the amount of calcium added is too large and the tin content is excessive, the outer layer is coated with a mixture of calcium fluoride, tin and calcium fluoride. Calcium fluoride does not have a negative thermal expansion effect, thereby reducing the effect of widening the lithium ion channel, affecting the discharge capacity and cycle stability of the material to a certain extent. If the amount of tin added is too large, it will cause the same effect as adding too much calcium.

[0086] By comparing Example 1 and Example 6, it can be seen that in the preparation process of the composite ternary positive electrode material disclosed in the present invention, after the addition of sodium hydroxide solution, the pH of the mixed solution will affect its performance. By controlling the pH above 12, the performance of the composite ternary positive electrode material is better. If the pH is too low, the alkaline washing effect cannot be achieved, and the sulfur impurities in the material are difficult to fully remove.

[0087] By comparing Example 1 with Examples 7-8, it can be seen that during the preparation process of the composite ternary positive electrode material disclosed in the present invention, after adding hydrofluoric acid, the pH of the mixed solution will affect its performance. By controlling the pH at 4-5, the performance of the composite ternary positive electrode material is better. If the pH is too high, the amount of hydrofluoric acid added is small, and the surface fluoride is not completely generated. If the pH is too low, the amount of hydrofluoric acid added is too much, which will convert part of the nickel, cobalt and manganese hydroxides and reduce the electrochemical properties of the material.

[0088] From the comparison between Example 1 and Comparative Examples 1-3, it can be seen that the present disclosure pre-prepares an alkaline solution containing calcium tin salt and mixes it with the ternary precursor. While removing sulfur impurities, the calcium tin element can enter the nickel cobalt manganese hydroxide particles to form co-doping. The two elements can not only stabilize the material structure, but also expand the lithium ion transmission channel, ultimately making the positive electrode material exhibit excellent cycle performance.

[0089] From the comparison between Example 1 and Comparative Example 4, it can be seen that the present disclosure uses hydrofluoric acid to modify the surface of the precursor doped with calcium and tin, so that the hydroxide on the surface is converted into fluoride. CaSnF6 has a negative thermal expansion effect, which can produce gaps on the surface during lithium addition and calcination, promote the reaction of lithium ions with internal nickel, cobalt and manganese hydroxides, reduce the residual lithium ions on the surface, reduce residual alkali, and improve cycle performance.

[0090] From the comparison between Example 1 and Comparative Example 5, it can be seen that the present disclosure uses an alkaline solution containing tin and calcium for alkaline washing, which can not only dope calcium and tin into the precursor, but also remove sulfur impurities in the precursor during the alkaline washing process, thereby further improving the electrical properties of the material.

Claims

1. A method for preparing a composite ternary positive electrode material, comprising the following steps: (1) mixing a mixed salt solution of calcium salt and tin salt with an alkali solution to obtain a mixed solution; (2) mixing the ternary precursor and the mixed solution, separating the solid and the liquid to obtain a solid material, slurrying the solid material, adding hydrofluoric acid, and reacting to obtain a composite ternary precursor; (3) The composite ternary precursor is mixed with a lithium source, and subjected to sintering treatment to obtain the composite ternary positive electrode material.

2. The preparation method according to claim 1, wherein The calcium salt in step (1) includes calcium chloride and / or calcium nitrate.

3. The preparation method according to claim 1 or 2, wherein: The tin salt in step (1) includes tin chloride and / or tin nitrate.

4. The preparation method according to any one of claims 1 to 3, wherein The total molar concentration of calcium salt and tin salt in the mixed salt solution of step (1) is 0.01-0.2 mol / L.

5. The preparation method according to any one of claims 1 to 4, wherein: The molar ratio of calcium element to tin element in the mixed salt solution of step (1) is (0.8-1.2):

1.

6. The preparation method according to any one of claims 1 to 5, wherein: The molar concentration of the alkali solution in step (1) is 2 to 10 mol / L; Optionally, the pH of the mixed solution is ≥12.

7. The preparation method according to any one of claims 1 to 6, wherein: The ternary precursor in step (2) includes nickel-cobalt-manganese hydroxide.

8. The preparation method according to any one of claims 1 to 7, wherein: The solid-liquid ratio of the ternary precursor and the mixed solution in step (2) is 1:(2-5) kg / L.

9. The preparation method according to any one of claims 1 to 8, wherein: The slurrying in step (2) includes mixing the solid material with deionized water.

10. The preparation method according to any one of claims 1 to 9, wherein: The solid-to-liquid ratio of the solid material to deionized water in step (2) is 1:(2-5) kg / L.

11. The preparation method according to any one of claims 1 to 10, wherein: The mass concentration of the hydrofluoric acid in step (2) is 30-40%.

12. The preparation method according to any one of claims 1 to 11, wherein: The pH of the reaction in step (2) is 4-5.

13. The preparation method according to any one of claims 1 to 12, wherein: The reaction temperature in step (2) is 100-150°C.

14. The preparation method according to any one of claims 1 to 13, wherein: The reaction time of step (2) is 10 to 30 minutes.

15. The preparation method according to any one of claims 1 to 6, wherein: The lithium source in step (3) includes lithium hydroxide and / or lithium carbonate.

16. The preparation method according to any one of claims 1 to 15, wherein: The temperature of the sintering treatment in step (3) is 600-1000°C.

17. The preparation method according to any one of claims 1 to 16, wherein: The sintering time in step (3) is 20 to 36 hours.

18. A composite ternary positive electrode material prepared by the method according to any one of claims 1 to 17.

19. A positive electrode sheet comprising the composite ternary positive electrode material as claimed in claim 18.

20. A lithium ion battery comprising the positive electrode sheet according to claim 19.

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