Efficient washing method of high-nickel ternary positive electrode material

Abstract

The invention discloses an efficient washing method of a high-nickel ternary positive electrode material, and belongs to the field of positive electrode materials of lithium ion batteries. The washing method comprises the following steps: (1) dispersing the high-nickel ternary positive electrode material in a washing solution composed of a solvent, boric acid and a high-valence transition metal salt, carrying out stirring and washing treatment, carrying out suction filtration on the obtained solution, and drying to obtain a solid product; and (2) carrying out segmented sintering treatment on the solid product in an oxidizing atmosphere. The ternary positive electrode material is washed with the composite washing liquid, so that residual alkali is efficiently reduced; meanwhile, high-valence transition metal salt is added into a washing solution, two-stage sintering is adopted after the high-valence transition metal salt is dried, and doping of high-valence transition metal can prevent lithium from being continuously dissolved out and stabilize and repair a surface crystal structure; therefore, residual alkali on the surface of the material is reduced, structural stability of the material is enhanced, and electrical properties of the material are not lost. In addition, the water washing method is short in time consumption and small in damage to the surface of the material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode materials, and particularly relates to an efficient water washing method for high-nickel ternary cathode materials. Background Technology

[0002] Due to their lower synthesis temperature, high-nickel ternary cathode materials exhibit lower lithium salt volatilization during synthesis compared to other materials. This results in excessive lithium compounds remaining on the material surface. These compounds readily react with moisture and carbon dioxide in the air to form lithium hydroxide and lithium carbonate, which accumulate on the surface and are commonly referred to as residual alkali. Excessive residual alkali increases the processing difficulty of ternary cathode materials. Furthermore, during battery operation, residual alkali can react harmfully with the electrolyte, generating hazardous gases that severely compromise normal battery operation. Therefore, reducing the residual alkali on the surface of high-nickel ternary cathode materials is crucial to ensuring their safe application.

[0003] In existing technologies, water washing is commonly used to reduce the residual lithium content on the surface of high-nickel ternary cathode materials. However, this method requires a large amount of water, is time-consuming, and has poor effectiveness. Furthermore, water washing can lead to capacity loss, damage to the surface structure, and decreased cycle performance of the high-nickel ternary cathode material. Additionally, during the post-processing of the water-washed high-nickel ternary cathode material, the small amount of alkaline oxides remaining on its surface continue to react with H2O and CO2 in the air to generate residual alkali, which also causes some damage to the material surface.

[0004] Therefore, solving the above problems is crucial for the efficient and safe application and long-term development of high-nickel ternary cathode materials. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide an efficient water washing method for high-nickel ternary cathode materials that can improve the washing rate of the material, enhance the surface structure stability of the material, and maintain the stability of the electrochemical performance of the material.

[0006] Technical solution: The efficient water washing method for high-nickel ternary cathode material of the present invention includes the following steps:

[0007] (1) Disperse the high-nickel ternary cathode material in a water washing solution composed of solvent, boric acid and high-valence transition metal salt, and perform stirring and water washing treatment. The resulting solution is filtered and dried to obtain a solid product.

[0008] (2) The solid product is subjected to segmented sintering in an oxidizing atmosphere, and after the process, a high-nickel ternary cathode material is obtained after water washing.

[0009] Further, in step (1), the general chemical formula of the high-nickel ternary cathode material is: Li 1+y (Ni a Co bMn 1-a-b- c Z c ) 1-y O2, where 0≤y≤0.2, 0.9≤a≤0.95, 0.01≤b≤0.1, 0≤c≤0.05, and Z is Al. 3+ Cr 3+ ,Sc 3+ Ga 3+ La 3+ Sm 3+ Ti 4+ Zr 4+ Nb 5+ W 6+ Mo 6+ One or more of them.

[0010] Furthermore, the solvent is composed of water and anhydrous alcohol in a volume ratio of 6-8:2-4. If the proportion of water is too high, the material surface will be severely damaged during the water washing process, and if the proportion of anhydrous ethanol is too high, the efficiency of removing residual alkali will be reduced.

[0011] Furthermore, the mass ratio of boric acid to high-nickel ternary cathode material is 0.5-5:100, preferably 1-2:100.

[0012] Furthermore, the mass ratio of the high-valence transition metal salt to the high-nickel ternary cathode material is 1-5:100, preferably 1-3:100.

[0013] Furthermore, the mass ratio of the high-nickel ternary cathode material to the washing solution is 1:1-5, preferably 1:1-3. The application of the washing solution can greatly improve the washing effect, which is efficient and causes little damage to the material surface. Among them, the surface doping of high-valence transition metals is an effective way to repair the surface structure of the material and prevent lithium dissolution. Through the composite application of each component, the washing effect is improved and the material structure is stabilized, and the electrochemical performance is kept stable.

[0014] Furthermore, the mass ratio of boric acid to high-valence transition metal salt is 1:1.5-3. Maintaining a suitable mass ratio can stably generate the target product in which the two elements work synergistically, thereby improving the structural stability of the material and enhancing its electrochemical performance. However, excessive boric acid can damage the surface structure of the material, while excessive high-valence transition metal salt can lead to an overly thick coating layer on the material surface, which will reduce the electrochemical performance of the material.

[0015] Furthermore, the high-valence transition metal salt is a molybdenum salt, preferably (NH4)2MoO4.

[0016] Furthermore, the parameters for the stirring and washing treatment are as follows: stirring speed 200-400 rpm / min, preferably 200-300 rpm / min, washing temperature 0-20℃, preferably 10-15℃, and washing time 5-20 min, preferably 5-10 min.

[0017] Furthermore, the drying conditions are: drying at 80-120℃ for 12-16 hours under vacuum.

[0018] Further, in step (2), the parameters for the segmented sintering treatment are: in a pure oxygen environment, first keep at 450-550℃ for 4-6 hours, then continue to raise the temperature to 700-760℃ and keep at that temperature for 4-8 hours.

[0019] Invention Principle: In this invention, the Li3BO3 generated from the reaction of LiOH and Li2CO3 on the surface of the high-nickel ternary cathode material with boric acid (H3BO3) forms a uniform Li3BO3 coating layer on the surface of the high-nickel ternary cathode material after sintering. This Li3BO3 coating layer prevents the high-nickel ternary cathode material from further reacting with H2O and CO2 in the air to generate residual alkali. Furthermore, during the second sintering process, boron ions and high-valence transition metal molybdenum ions diffuse into the particle surface and interior of the high-nickel ternary cathode material, thus forming uniform doping. The doping with boron and molybdenum ions improves the crystal structure stability of the high-nickel ternary material, effectively suppresses the dissolution of Ni and Co elements during charging and discharging, enhances the interfacial stability of the cathode material, and thereby improves the electrochemical performance of the high-nickel ternary material.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant effects: (1) In the water washing method of the high nickel cathode material of the present invention, the addition of a small amount of ethanol can reduce the degree of damage to the material by water. In addition, the addition of a small amount of boric acid makes the water washing solution weakly acidic, which can promote the maximum dissolution of surface LiOH and Li2CO3 in the washing solution, and at the same time improve the water washing speed. Furthermore, the residual alkali reacts with boric acid to generate Li3BO3, thereby effectively reducing the content of residual lithium; (2) In this invention, the boric acid washed with water continues to react with the small amount of residual, incompletely washed lithium oxide to generate Li3BO3, thereby inhibiting the generation of residual alkali; the water washing method of this invention can not only reduce the degree of damage to the material surface caused by water washing, but also generate a Li3BO3 coating layer on the material surface, thereby improving the surface stability of the material; (3) This invention uses a composite water washing solution to wash the ternary cathode material, thereby efficiently reducing residual alkali; at the same time, a high-valence transition metal salt is added to the water washing solution, and after drying it, a two-stage sintering is adopted. The doping of the high-valence transition metal can prevent the continued dissolution of lithium and stabilize and repair the surface crystal structure; thereby reducing the residual alkali on the material surface, enhancing the structural stability of the material, and without losing the electrical performance of the material; in addition, the water washing method of this invention is short in time and causes less damage to the material surface. Attached Figure Description

[0021] Figure 1 SEM image of high-nickel ternary cathode material before water washing;

[0022] Figure 2 Here is a SEM image of the cathode material prepared in Example 3;

[0023] Figure 3 The graphs show the 0.1C and 1C electrochemical curves of the cathode material prepared in Example 3. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings.

[0025] Example 1: The high-nickel ternary cathode material described in this example (chemical formula: LiNi) 0.9 Co 0.05 Mn 0.05 A highly efficient water washing method (O2) includes the following steps:

[0026] (1) The high-nickel ternary cathode material and the washing solution composed of deionized water, anhydrous alcohol, H3BO3 and (NH4)2MoO4 (wherein, the volume ratio of deionized water to anhydrous alcohol is 7:3, H3BO3 accounts for 1% of the mass of the high-nickel ternary cathode material, and (NH4)2MoO4 accounts for 1% of the mass of the high-nickel ternary cathode material, and the mass ratio of the high-nickel ternary cathode material to the washing solution is 1:1) are stirred and washed. The temperature of the mixed washing solution is controlled at 15℃, so that the high-nickel ternary cathode material is suspended in the washing solution. The stirring speed is 300 rpm / min and the washing time is 10 min to obtain solution A.

[0027] (2) The liquid A produced in step (1) is filtered to obtain solid product A. It is then dried at 100°C for 12 hours in a vacuum environment to obtain solid product B.

[0028] (3) Solid product B was kept at 450℃ for 4 hours in a pure oxygen environment, and then the temperature was increased to 740℃ and kept for 4 hours to obtain solid product C. The residual alkali value and electrochemical performance were measured.

[0029] Example 2: The high-nickel ternary cathode material described in this example (chemical formula: LiNi) 0.9 Co 0.05 Mn 0.05 A highly efficient water washing method (O2) includes the following steps:

[0030] (1) The high-nickel ternary cathode material and the washing solution composed of deionized water, anhydrous alcohol, H3BO3 and (NH4)2MoO4 (wherein, the volume ratio of deionized water to anhydrous alcohol is 7:3, H3BO3 accounts for 1% of the mass of the high-nickel ternary cathode material, and (NH4)2MoO4 accounts for 1.5% of the mass of the high-nickel ternary cathode material, and the mass ratio of the high-nickel ternary cathode material to the washing solution is 1:1) are stirred and washed. The temperature of the mixed washing solution is controlled at 15℃, so that the high-nickel ternary cathode material is suspended in the washing solution. The stirring speed is 300 rpm / min and the washing time is 10 min to obtain solution A.

[0031] (2) The liquid A produced in step (1) is filtered to obtain solid product A. It is then dried at 100°C for 12 hours in a vacuum environment to obtain solid product B.

[0032] (3) Solid product B was kept at 450℃ for 4 hours in a pure oxygen environment, and then the temperature was increased to 740℃ and kept for 4 hours to obtain solid product C. The residual alkali value and electrochemical performance were measured.

[0033] Example 3: The high-nickel ternary cathode material described in this example (chemical formula: LiNi) 0.9 Co 0.05 Mn 0.05 A highly efficient water washing method (O2) includes the following steps:

[0034] (1) The high-nickel ternary cathode material and the washing solution composed of deionized water, anhydrous alcohol, H3BO3 and (NH4)2MoO4 (wherein, the volume ratio of deionized water to anhydrous alcohol is 7:3, H3BO3 accounts for 1% of the mass of the high-nickel ternary cathode material, and (NH4)2MoO4 accounts for 2% of the mass of the high-nickel ternary cathode material, and the mass ratio of the high-nickel ternary cathode material to the washing solution is 1:1) are stirred and washed. The temperature of the mixed washing solution is controlled at 15℃, so that the high-nickel ternary cathode material is suspended in the washing solution. The stirring speed is 300 rpm / min and the washing time is 10 min to obtain solution A.

[0035] (2) The liquid A produced in step (1) is filtered to obtain solid product A. It is then dried at 100°C for 12 hours in a vacuum environment to obtain solid product B.

[0036] (3) Solid product B was kept at 450℃ for 4 hours in a pure oxygen environment, and then the temperature was increased to 740℃ and kept for 4 hours to obtain solid product C. The residual alkali value and electrochemical performance were measured.

[0037] The cathode material was characterized before and after water washing, and the results are shown in the figure. Figures 1-2 As shown in the figure, the surface of the material particles was rough before washing and contained a large amount of residual alkali; after washing, the surface of the material was smooth and the distribution of residual alkali was significantly reduced.

[0038] The 0.1C and 1C electrochemical curves of the cathode material prepared in Example 3 are shown below. Figure 3 As shown in the figure, the 0.1C and 1C discharge specific capacities of the material after washing with water according to the method of Example 3 are both improved.

[0039] Example 4: The high-nickel ternary cathode material described in this example (chemical formula: LiNi) 0.9 Co 0.05 Mn 0.05 A highly efficient water washing method (O2) includes the following steps:

[0040] (1) The high-nickel ternary cathode material and the washing solution composed of deionized water, anhydrous alcohol, H3BO3 and (NH4)2MoO4 (wherein, the volume ratio of deionized water to anhydrous alcohol is 7:3, H3BO3 accounts for 1% of the mass of the high-nickel ternary cathode material, and (NH4)2MoO4 accounts for 2.5% of the mass of the high-nickel ternary cathode material, and the mass ratio of the high-nickel ternary cathode material to the washing solution is 1:1) are stirred and washed. The temperature of the mixed washing solution is controlled at 15℃, so that the high-nickel ternary cathode material is suspended in the washing solution. The stirring speed is 300 rpm / min and the washing time is 10 min to obtain solution A.

[0041] (2) The liquid A produced in step (1) is filtered to obtain solid product A. It is then dried at 100°C for 12 hours in a vacuum environment to obtain solid product B.

[0042] (3) Solid product B was kept at 450℃ for 4 hours in a pure oxygen environment, and then the temperature was increased to 740℃ and kept for 4 hours to obtain solid product C. The residual alkali value and electrochemical performance were measured.

[0043] Example 5: The high-nickel ternary cathode material described in this example (chemical formula: LiNi) 0.9 Co 0.05 Mn 0.05 A highly efficient water washing method (O2) includes the following steps:

[0044] (1) The high-nickel ternary cathode material and the washing solution composed of deionized water, anhydrous alcohol, H3BO3 and (NH4)2MoO4 (wherein, the volume ratio of deionized water to anhydrous alcohol is 7:3, H3BO3 accounts for 1% of the mass of the high-nickel ternary cathode material, and (NH4)2MoO4 accounts for 3% of the mass of the high-nickel ternary cathode material, and the mass ratio of the high-nickel ternary cathode material to the washing solution is 1:1) are stirred and washed. The temperature of the mixed washing solution is controlled at 15℃, so that the high-nickel ternary cathode material is suspended in the washing solution. The stirring speed is 300 rpm / min and the washing time is 10 min to obtain solution A.

[0045] (2) The liquid A produced in step (1) is filtered to obtain solid product A. It is then dried at 100°C for 12 hours in a vacuum environment to obtain solid product B.

[0046] (3) Solid product B was kept at 450℃ for 4 hours in a pure oxygen environment, and then the temperature was increased to 740℃ and kept for 4 hours to obtain solid product C. The residual alkali value and electrochemical performance were measured.

[0047] Comparative Example 1: The difference from Example 1 is that (NH4)2MoO4 is not included in the washing solution in step (1).

[0048] Comparative Example 2: The difference from Example 1 is that in step (1), the washing solution does not contain H3BO3 and (NH4)2MoO4.

[0049] Comparative Example 3: The difference from Example 1 is that in step (1), the washing solution is deionized water.

[0050] Comparative Example 4: The difference from Example 3 is that in step (1), phosphoric acid is used instead of boric acid in the washing solution.

[0051] Comparative Example 5: The difference from Example 3 is that in step (1), Al(NO3)3·9H2O is used instead of (NH4)2MoO4 in the washing solution.

[0052] Comparative Example 6: The difference from Example 3 is that in step (1), H3BO3 in the washing solution accounts for 2% of the mass of the high-nickel ternary cathode material.

[0053] Comparative Example 7: The difference from Example 3 is that in step (1), H3BO3 in the washing solution accounts for 0.5% of the mass of the high-nickel ternary cathode material.

[0054] The composition of the washing solution in Examples 1-5 and Comparative Examples 1-7 is shown in Table 1.

[0055] In Examples 1-5 and Comparative Examples 1-7, the positive electrode material prepared from water was mixed with polyvinylidene fluoride (PVDF) and acetylene black in a ratio of 90:5:5 to form an electrode sheet. A lithium metal sheet was used as the negative electrode, PE (2500) was used as the separator, and a 1 mol / L lithium hexafluorophosphate solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC to DMC mass ratio of 2:1) was used as the electrolyte. The cells were assembled into button cells in an argon-filled glove box and their electrochemical performance was tested.

[0056] The electrochemical performance test conditions were as follows: charge / discharge voltage range of 2.7V-4.8V, test temperature of 25℃, and the battery cycle performance was tested at a rate of 1C after 3 cycles at 0.1C. The specific test results are shown in Table 2.

[0057] Table 1. Composition of the washing solutions in Examples 1-5 and Comparative Examples 1-7

[0058]

[0059]

[0060] Table 2 Performance test table of the cathode materials prepared in Examples 1-5 and Comparative Examples 1-7

[0061]

[0062] As shown in Table 2, Comparative Example 1 did not use molybdenum. The test results indicate that the effect of boron alone on improving the electrochemical performance of the material is not as good as the synergistic effect of molybdenum and boron.

[0063] Comparative Example 2 did not use boric acid and molybdenum salt. The test results showed that the residual alkali value of the material was too high, proving that boric acid and molybdenum salt are beneficial to reducing the residual alkali on the material surface.

[0064] Comparative Example 3 used only deionized water as a solvent. The test results showed that the residual alkali value of the material was too high and the electrochemical performance of the material was severely reduced, proving that using only deionized water as a solvent severely damaged the surface of the material.

[0065] Comparative Examples 4 and 5 replaced boron and molybdenum elements, respectively. The test data showed that the two elements work synergistically to improve the electrochemical performance of the material, reduce the residual alkali value, and maximize the material's performance.

[0066] Comparative Examples 6 and 7 increased and decreased the amount of boric acid added, respectively, proving that the addition of boric acid must be in an appropriate ratio.

[0067] Based on the embodiments and comparative examples, the roles of boron and molybdenum in this invention are summarized as follows: 1. They generate LiMoO4 to coat the material surface, preventing electrolyte corrosion, and also provide a lithium-ion conduction pathway; 2. A small amount of Mo... 6+ 3. By doping into the near-surface crystal structure of the material, it acts as a "pillar effect" to stabilize the crystal structure and prevent the dissolution of transition metals; 4. It generates a Li3BO3-B2O3 glass phase, which, as a coating layer, can reduce electrolyte erosion, isolate oxygen, and inhibit Mo. 6+ 4. Synergistic effect of molybdenum and boron: Lithium oxide, boron oxide and molybdenum oxide generate Li3MoBO6 with a NASICON-type fast ion conductor structure (reaction equation: 3Li2O+MoO3+B2O3+3 / 2O2→2Li3MoBO6), which can improve the lithium ion diffusion rate and thus improve the electrochemical performance of the material.

Claims

1. A highly efficient water washing method for high-nickel ternary cathode materials, characterized in that, Includes the following steps: (1) Disperse the high-nickel ternary cathode material in a water washing solution composed of solvent, boric acid and high-valence transition metal salt, and perform stirring and water washing treatment. The resulting solution is filtered and dried to obtain a solid product. (2) The solid product is subjected to segmented sintering in an oxidizing atmosphere, and after the process, a high-nickel ternary cathode material is obtained after water washing.

2. The water washing method according to claim 1, characterized in that, In step (1), the general chemical formula of the high-nickel ternary cathode material is: Li 1+y (Ni a Co b Mn 1-a-b-c Z c ) 1-y O2, where 0≤y≤0.2, 0.9≤a≤0.95, 0.01≤b≤0.1, 0≤c≤0.05, and Z is Al. 3+ Cr 3+ ,Sc 3+ Ga 3+ La 3+ Sm 3+ Ti 4+ Zr 4+ Nb 5+ W 6+ Mo 6+ One or more of them.

3. The water washing method according to claim 1, characterized in that, In step (1), the solvent is composed of water and anhydrous alcohol in a volume ratio of 6-8:2-4.

4. The water washing method according to claim 1, characterized in that, In step (1), the mass ratio of boric acid to high-nickel ternary cathode material is 0.5-5:

100.

5. The water washing method according to claim 1, characterized in that, In step (1), the mass ratio of the high-valence transition metal salt to the high-nickel ternary cathode material is 1-5:

100.

6. The water washing method according to claim 1, characterized in that, In step (1), the mass ratio of the high-nickel ternary cathode material to the washing solution is 1:1-5.

7. The water washing method according to claim 1, characterized in that, In step (1), the mass ratio of boric acid to high-valence transition metal salt is 1:1.5-3.

8. The water washing method according to claim 1, characterized in that, In step (1), the high-valence transition metal salt is a molybdenum salt.

9. The water washing method according to claim 1, characterized in that, In step (1), the parameters for the stirring and washing treatment are: stirring speed 200-400 rpm / min, washing temperature 0-20℃, and washing time 5-20 min.

10. The water washing method according to claim 1, characterized in that, In step (2), the parameters for the segmented sintering process are: in a pure oxygen environment, first hold at 450-550℃ for 4-6 hours, then continue to raise the temperature to 700-760℃ and hold for 4-8 hours.

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