Composite ternary positive electrode material and preparation method and application thereof

Abstract

The application discloses a composite ternary positive electrode material and a preparation method and application thereof, and the preparation method comprises 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 a ternary precursor and the mixed solution, performing solid-liquid separation to obtain solid material, adding hydrofluoric acid to the solid material after slurry preparation, and performing 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. Alkaline washing is performed by using an alkaline solution containing tin and calcium, sulfur impurities can be removed, calcium and tin are doped in the precursor, and fluorides are generated by modification of hydrofluoric acid, so that oxides are separated from electrolyte, side reactions in the charging and discharging process are reduced, and therefore, the cycle performance of the material is significantly enhanced.

Description

Technical Field

[0001] This disclosure belongs to the field of lithium-ion battery technology, and relates to a composite ternary cathode material, its preparation method and application. Background Technology

[0002] Lithium-ion batteries are considered a new generation of green, high-energy batteries due to their high energy density, long lifespan, and low pollution, and are widely used in many fields such as mobile phones, digital cameras, computers, and electric vehicles. The cathode material, as a crucial component of lithium-ion batteries, determines the battery's final performance. Currently, the most researched cathode materials include lithium cobalt oxide, lithium manganese oxide, and layered lithium nickel cobalt manganese oxide. Among them, layered lithium nickel cobalt manganese oxide combines the advantages of lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide, and its development has been very rapid in recent years.

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

[0004] CN115215388A discloses a method for preparing a ternary cathode material and the ternary cathode material itself, which aims to improve the preparation efficiency and yield of ternary cathode materials. The method includes: mixing manganese salt and / or aluminum salt with nickel salt and cobalt salt, and co-precipitating them with an alkaline substance and a complexing agent in a solvent to obtain a co-precipitated slurry with a target median particle size; washing the co-precipitated 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 high-temperature sintering to obtain the ternary cathode material.

[0005] CN105261737A discloses a method for preparing a ternary cathode material, the method comprising: Step 1: mixing salt and alkali ingredients uniformly in a solution to form a mixed solution; Step 2: precipitating the mixed solution from Step 1 to form precursor grains, controlling the nucleation and crystal growth rate of the co-precipitation reaction by adjusting parameters; Step 3: adding cation sites to the liquid phase of the precursor grains formed in Step 2 after washing and filtration for doping modification, and then drying; Step 4: adding lithium to the dried raw material, then calcining, and then surface coating modification to obtain the finished ternary material.

[0006] In the above-described scheme, lithium ions cannot fully penetrate nickel cobalt manganese hydroxide, resulting in residual lithium on the surface of lithium nickel cobalt manganese oxide, which affects the cycle stability of the cathode material. Furthermore, the raw materials for synthesizing nickel cobalt manganese hydroxide often use sulfates, and the co-precipitated nickel cobalt manganese hydroxide still contains some sulfur, which needs to be removed by alkaline washing. This step generates a large amount of alkaline wastewater, which has a significant environmental impact. Omitting this step would result in excessively high sulfur impurity content, which is detrimental to the electrochemical performance of the cathode material. Summary of the Invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0008] The purpose of this disclosure is to provide a composite ternary cathode material, its preparation method, and its application. This disclosure uses an alkaline solution containing tin and calcium for alkaline washing, which can not only remove sulfur impurities, but also dope the precursor with calcium and tin. After modification with hydrofluoric acid, fluoride is generated, which can separate the oxide from the electrolyte, reduce side reactions during charging and discharging, and thus significantly enhance the cycle performance of the material.

[0009] To achieve this objective, the present disclosure adopts the following technical solution:

[0010] In a first aspect, this disclosure provides a method for preparing a composite ternary cathode material, the method comprising the following steps:

[0011] (1) Mix the mixed salt solution of calcium salt and tin salt with the alkaline solution to obtain a mixed solution;

[0012] (2) The ternary precursor and the mixed solution are mixed, and the solid material is obtained by solid-liquid separation. The solid material is pulped and hydrofluoric acid is added to react and obtain the composite ternary precursor.

[0013] (3) The composite ternary precursor is mixed with a lithium source and sintered to obtain the composite ternary cathode material.

[0014] This disclosure pre-prepares an alkaline solution containing calcium tin salt, which is then mixed with a ternary precursor. While removing sulfur impurities, the calcium tin elements can enter the nickel cobalt manganese hydroxide particles to form co-doped components. These two elements stabilize the material structure and expand the lithium-ion transport channels, ultimately resulting in excellent cycle performance of the cathode material. Hydrofluoric acid is then used to modify the surface, converting the surface hydroxides into fluorides. CaSnF6 exhibits a negative thermal expansion effect, which can create gaps on the surface during lithium addition and calcination, promoting the reaction between lithium ions and the internal nickel cobalt manganese hydroxide. This reduces residual lithium ions on the surface, decreases residual alkali, and improves cycle performance.

[0015] In one embodiment, the calcium salt in step (1) comprises calcium chloride and / or calcium nitrate.

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

[0017] In one embodiment, the total molar concentration of calcium salt and tin salt in the mixed salt solution in 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, etc.

[0018] In one embodiment, the molar ratio of calcium to tin in the mixed salt solution in step (1) is (0.8 to 1.2):1, for example: 0.8:1, 0.9:1, 1:1, 1.1:1 or 1.2:1, etc.

[0019] In one embodiment, the molar concentration of the alkaline 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, etc.

[0020] In one embodiment, the pH of the mixed solution in step (1) or (2) is ≥12.

[0021] In one embodiment, the ternary precursor in step (2) comprises nickel cobalt manganese hydroxide.

[0022] 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.

[0023] The ternary precursor described in this disclosure can be ternary precursor solid particles or 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 for use, or the ternary precursor slurry can be used directly. This greatly simplifies the preparation process of composite ternary materials, saves costs, and improves production efficiency.

[0024] In one embodiment, the pulping step (2) includes mixing solid materials with deionized water.

[0025] In one embodiment, the solid-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.

[0026] In one embodiment, the mass concentration of hydrofluoric acid in step (2) is 30-40%, for example: 30%, 32%, 35%, 38% or 40%, etc.

[0027] 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, etc.

[0028] In one embodiment, the reaction temperature in step (2) is 100 to 150°C, for example: 100°C, 120°C, 130°C, 140°C or 150°C.

[0029] In one embodiment, the reaction time in step (2) is 10 to 30 minutes, for example: 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes.

[0030] In one embodiment, the lithium source in step (3) includes lithium hydroxide and / or lithium carbonate.

[0031] In one embodiment, the sintering temperature in step (3) is 600 to 1000°C, for example: 600°C, 700°C, 800°C, 900°C or 1000°C.

[0032] In one embodiment, the sintering process in step (3) takes 20 to 36 hours, for example, 20 hours, 25 hours, 30 hours, 32 hours or 36 hours.

[0033] In a second aspect, this disclosure provides a composite ternary cathode material, which is prepared by the method described in the first aspect.

[0034] Thirdly, this disclosure provides a positive electrode sheet comprising the composite ternary positive electrode material as described in the second aspect.

[0035] Fourthly, this disclosure provides a lithium-ion battery comprising a positive electrode as described in the third aspect.

[0036] Compared with the prior art, this disclosure has the following beneficial effects:

[0037] (1) The present invention uses an alkaline solution containing tin and calcium for alkaline washing, which can not only remove sulfur impurities, but also dop calcium and tin in the precursor. After modification with hydrofluoric acid, fluoride is generated, which can separate the oxide from the electrolyte and reduce the side reactions during the charging and discharging process, thereby significantly enhancing the cycle performance of the material.

[0038] (2) The method described in this disclosure is applicable to various ternary cathode materials. The 0.1C discharge capacity of the NCM622 ternary cathode 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 cathode 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.

[0039] After reading and understanding the detailed description, other aspects can be understood. Detailed Implementation

[0040] The technical solutions of this disclosure will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0041] The ternary precursors used in the embodiments and comparative examples of this disclosure were all prepared by the following method:

[0042] A mixed solution of nickel, cobalt, and manganese salts, along with sodium hydroxide and ammonia solutions, was added to the reactor at a controlled flow rate using a precision metering pump. The pH was maintained at 11, and the reaction was carried out at 60°C with continuous 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 a length of 10 μm.

[0043] The nickel-cobalt-manganese salt mixed solution has a concentration of 1.0 mol / L, the sodium hydroxide solution has a concentration of 5 mol / L, the ammonia solution has a concentration of 3 mol / L, and the solution flow rate is 100 mL / min.

[0044] The suspension was filtered and washed with water to obtain the ternary precursor (NCM622 precursor or NCM811 precursor).

[0045] Example 1

[0046] This embodiment provides a composite ternary cathode material, and the preparation method of the composite ternary cathode material is as follows:

[0047] (1) Prepare a 0.08 mol / L mixed solution of calcium chloride and tin chloride, with a calcium to tin ion molar ratio of 1:1. Add sodium hydroxide solution to the solution, the concentration of which is 5 mol / L, and control the pH to 14.

[0048] (2) The NCM622 precursor was added to the mixed solution at a solid-liquid ratio of 1:3 kg / L, stirred for 1 h, filtered, and deionized water was added at a solid-liquid ratio of 1:3 kg / L to prepare the slurry. 40 wt% HF was added, the pH was controlled at 4.2, and the mixture was stirred at 120 °C for 20 min to obtain the composite ternary precursor.

[0049] (3) The composite ternary precursor is mixed with lithium carbonate at Li / M = 1.02 and sintered at 800°C for 24 hours to obtain the composite ternary cathode material.

[0050] Example 2

[0051] This embodiment provides a composite ternary cathode material, and the preparation method of the composite ternary cathode material is as follows:

[0052] (1) Prepare a 0.01 mol / L mixed solution of calcium chloride and tin chloride, with a calcium to tin ion molar ratio of 0.8:1. Add sodium hydroxide solution to the solution, the concentration of which is 2 mol / L, and control the pH to 12.

[0053] (2) The NCM811 precursor was added to the mixed solution at a solid-liquid ratio of 1:2.5 kg / L, stirred for 1 h, filtered, and deionized water was added at a solid-liquid ratio of 1:2 kg / L to prepare the slurry. 35 wt% HF was added, the pH was controlled at 4, and the reaction was stirred at 150℃ for 10 min to obtain the composite ternary precursor.

[0054] (3) The composite ternary precursor was mixed with lithium carbonate at Li / M = 1.02 and sintered at 600°C for 36 h to obtain the composite ternary cathode material.

[0055] Example 3

[0056] This embodiment provides a composite ternary cathode material, and the preparation method of the composite ternary cathode material is as follows:

[0057] (1) Prepare a 0.2 mol / L mixed solution of calcium chloride and tin chloride, with a calcium to tin ion molar ratio of 1.2:1. Add sodium hydroxide solution to the solution, the concentration of which is 10 mol / L, and control the pH to 15.

[0058] (2) Add NCM622 precursor to the mixed solution at a solid-liquid ratio of 1:5 kg / L, stir for 1 h, filter the product, add deionized water at a solid-liquid ratio of 1:4 kg / L to make slurry, add 30 wt% HF, control the pH to 5, stir at 100℃ for 30 min to obtain the composite ternary precursor.

[0059] (3) The composite ternary precursor is mixed with lithium carbonate at Li / M = 1.02 and sintered at 1000°C for 20 h to obtain the composite ternary cathode material.

[0060] Example 4

[0061] The only difference between this embodiment and Embodiment 1 is that the molar ratio of calcium to tin ions is 0.5:1; all other conditions and parameters are exactly the same as in Embodiment 1.

[0062] Example 5

[0063] The only difference between this embodiment and Embodiment 1 is that the molar ratio of calcium to tin ions is 1.5:1; all other conditions and parameters are exactly the same as in Embodiment 1.

[0064] Example 6

[0065] The only difference between this embodiment and Embodiment 1 is that after adding sodium hydroxide solution in step (1), the pH of the mixed solution is 11.5. Other conditions and parameters are exactly the same as in Embodiment 1.

[0066] Example 7

[0067] 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. Other conditions and parameters are exactly the same as in embodiment 1.

[0068] Example 8

[0069] 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 in embodiment 1.

[0070] Comparative Example 1

[0071] The only difference between this comparative example and Example 1 is that calcium and tin salts are not added, and sodium hydroxide solution is used directly for alkaline washing. All other conditions and parameters are exactly the same as in Example 1.

[0072] Comparative Example 2

[0073] The only difference between this comparative example and Example 1 is that no tin salt is added; all other conditions and parameters are exactly the same as in Example 1.

[0074] Comparative Example 3

[0075] The only difference between this comparative example and Example 1 is that no calcium salt was added; all other conditions and parameters are exactly the same as in Example 1.

[0076] Comparative Example 4

[0077] The only difference between this comparative example and Example 1 is that hydrofluoric acid is not added; all other conditions and parameters are exactly the same as in Example 1.

[0078] Comparative Example 5

[0079] The only difference between this comparative example and Example 1 is that sodium hydroxide solution is not added; all other conditions and parameters are exactly the same as in Example 1.

[0080] Performance testing:

[0081] The dried samples prepared in the examples and comparative examples were subjected to inductively coupled plasma (ICP) spectroscopy to determine the sulfur (S) content in the materials. The positive electrode materials prepared in the examples and comparative examples were mixed with conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) at a mass ratio of 90:5:5, using N-methylpyrrolidone (NMP) as a solvent. The mixture was then coated onto aluminum foil, dried, and rolled to form the positive electrode of a simulated battery. The negative electrode was a lithium metal sheet, the separator was Celgard 2400, and the electrolyte was 1 mol / L LiPF6 / DMC+DEC (volume ratio 1:1), forming a CR2025 type simulated battery. The charge / discharge voltage range was 3.0–4.5 V. The electrochemical performance data of the lithium-ion battery positive electrode material, lithium nickel cobalt manganese oxide, were obtained, and the test results are shown in Table 1.

[0082] Table 1

[0083]

[0084] As shown in Table 1, and based on Examples 1-3, the sulfur content of the cathode material prepared by the method described in this disclosure can reach below 823 ppm. Furthermore, the method is applicable to various ternary cathode materials. The 0.1C discharge capacity of the NCM622 ternary cathode material prepared can reach above 183.8 mAh / g, and the capacity retention rate after 100 cycles can reach above 97.52%. The 0.1C discharge capacity of the NCM811 ternary cathode material prepared can reach above 204 mAh / g, and the capacity retention rate after 100 cycles can reach above 97.6%, demonstrating excellent capacity and cycle performance.

[0085] A comparison of Examples 1 and 4-5 shows that the molar ratio of calcium to tin affects the performance of the composite ternary cathode material described in this disclosure. Controlling the molar ratio of calcium to tin to 0.8 to 1.2:1 results in a composite ternary cathode material with better performance. If the amount of calcium added is too large, the tin content will be excessive, and the outer coating will be a mixture of calcium fluoride, tin, and calcium fluoride. Calcium fluoride does not have a negative thermal expansion effect, thus reducing the effect of widening the lithium-ion channel and 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 have the same effect as adding too much calcium.

[0086] A comparison of Examples 1 and 6 shows that during the preparation of the composite ternary cathode material disclosed in this invention, the pH of the mixed solution after adding sodium hydroxide solution affects its performance. When the pH is controlled above 12, the composite ternary cathode material has better performance. If the pH is too low, the alkaline washing effect cannot be achieved, and sulfur impurities in the material are difficult to remove completely.

[0087] A comparison of Examples 1 and 7-8 shows that during the preparation of the composite ternary cathode material disclosed in this invention, the pH of the mixed solution after the addition of hydrofluoric acid affects its performance. Controlling the pH at 4-5 results in a composite ternary cathode material with better performance. If the pH is too high, the amount of hydrofluoric acid added is insufficient, and the surface fluoride formation is incomplete. If the pH is too low, the amount of hydrofluoric acid added is excessive, which will convert some nickel-cobalt-manganese hydroxide and reduce the electrochemical performance of the material.

[0088] As can be seen from the comparison between Example 1 and Comparative Examples 1-3, the present disclosure pre-prepared an alkaline solution containing calcium tin salt, which was then mixed with a ternary precursor. While removing sulfur impurities, the calcium tin elements could enter the nickel-cobalt-manganese hydroxide particles to form co-doping. The two elements could stabilize the material structure and expand the lithium-ion transport channels, ultimately enabling the cathode material to exhibit excellent cycle performance.

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

[0090] As can be seen from the comparison between Example 1 and Comparative Example 5, 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 cathode material, comprising the following steps: (1) Mix the mixed salt solution of calcium salt and tin salt with the alkaline solution to obtain a mixed solution; (2) The ternary precursor and the mixed solution are mixed, and the solid material is obtained by solid-liquid separation. The solid material is pulped and hydrofluoric acid is added to react and obtain the composite ternary precursor. (3) The composite ternary precursor is mixed with a lithium source and sintered to obtain the composite ternary cathode 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, wherein, The tin salt in step (1) includes tin chloride and / or tin nitrate.

4. The preparation method according to claim 1, wherein, The total molar concentration of calcium and tin salts in the mixed salt solution in step (1) is 0.01~0.2 mol / L.

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

1.

6. The preparation method according to claim 1, wherein, The molar concentration of the alkaline solution in step (1) is 2~10 mol / L.

7. The preparation method according to claim 1, wherein, The pH of the mixed solution in step (1) is ≥12.

8. The preparation method according to claim 1, wherein, The ternary precursor in step (2) includes nickel-cobalt-manganese hydroxide.

9. The preparation method according to claim 1, wherein, The solid-liquid ratio of the ternary precursor and the mixed solution in step (2) is 1:(2~5) kg / L.

10. The preparation method according to claim 1, wherein, The pulping process in step (2) involves mixing solid materials with deionized water.

11. The preparation method according to claim 10, wherein, The solid-liquid ratio of the solid material and deionized water in step (2) is 1:(2~5) kg / L.

12. The preparation method according to claim 1, wherein, The mass concentration of hydrofluoric acid in step (2) is 30-40%.

13. The preparation method according to claim 1, wherein, The pH of the reaction in step (2) is 4-5.

14. The preparation method according to claim 1, wherein, The reaction temperature in step (2) is 100~150℃.

15. The preparation method according to claim 1, wherein, The reaction time in step (2) is 10~30 min.

16. The preparation method according to claim 1, wherein, The lithium source in step (3) includes lithium hydroxide and / or lithium carbonate.

17. The preparation method according to claim 1, wherein, The sintering temperature in step (3) is 600~1000℃.

18. The preparation method according to claim 1, wherein, The sintering process in step (3) takes 20 to 36 hours.

19. A composite ternary cathode material prepared by the method described in any one of claims 1-18.

20. A positive electrode sheet comprising the composite ternary positive electrode material as described in claim 19.

21. A lithium-ion battery comprising the positive electrode as described in claim 20.

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