Method for reducing residual alkali on surface of high-nickel positive electrode material

Abstract

The present disclosure relates to the field of lithium-ion batteries. Disclosed is a method for reducing residual alkali on the surface of a high-nickel positive electrode material. The method comprises the following steps: uniformly stirring and mixing a gel containing polyethylene oxide and high-nickel positive electrode material particles, standing, and performing centrifugal separation to obtain a high-nickel positive electrode material and a lithium complex gel. According to the present disclosure, the gel containing polyethylene oxide is mixed with the high-nickel positive electrode material, residual alkali is efficiently removed by using polyethylene oxide having the property of complexing lithium ions, the process does not cause damage to the interior of high-nickel positive electrode material particles, the operation is simple, the gel can be subsequently recycled, and harmless treatment of a product is realized.

Description

A method for reducing residual alkali on the surface of high-nickel positive electrode material Technical Field

[0001] This article relates to the field of lithium-ion batteries, and in particular to a method for reducing residual alkali on the surface of high-nickel positive electrode materials. Background Art

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, are widely used in a wide range of fields, including consumer electronics, electric vehicles, and chemical energy storage. They are a research hotspot in the current new energy sector. With the rapid development of new energy vehicles, higher energy density requirements are being placed on lithium-ion batteries. As one of the key materials in lithium-ion batteries, the development of high-energy-density cathode materials has become a research focus.

[0003] Lithium nickel cobalt manganese oxide cathode materials are widely used cathode materials due to their high specific capacity, high energy density, low price, and environmental friendliness. Cathode materials are classified into different types based on their nickel content. As the nickel content increases, the energy density gradually increases, but the cycling stability weakens. High-nickel materials are sintered at lower temperatures, resulting in less volatilization of lithium salts. Consequently, excess lithium salts remain on the surface of the material in the form of oxides. Furthermore, the high nickel content can easily cause a mix of nickel and lithium, leading to lithium precipitation. The lithium remaining on the particle surface readily absorbs water and carbon dioxide from the air to form alkaline substances LiOH and Li2CO3. This can easily lead to a jelly-like slurry during the homogenization and coating processes of battery production, resulting in uneven coating and capacity decay. Furthermore, residual alkali reacts easily with the electrolyte at high temperatures to generate gas, causing battery bloating and posing a serious safety hazard.

[0004] To address the problem of high residual alkali on the surface of high-nickel positive electrode materials, the current common method is to wash the high-nickel materials with water. However, the water washing process is cumbersome, consumes a large amount of water resources, and generates a large amount of waste liquid. In addition, a certain amount of water will remain after washing, and the dissolved lithium will be precipitated again during the subsequent drying process, which does not completely remove the residual lithium. Water washing will also damage the structure of the high-nickel positive electrode material and reduce battery performance. Alternatively, an acid-containing solvent can be used to neutralize and remove the residual alkali on the surface of the high-nickel material, but this process is prone to generate a large amount of waste liquid, and the acid-containing ethanol solution will cause a certain amount of lithium dissolution in the high-nickel material, affecting the chemical properties of the high-nickel material.

[0005] Summary of the Invention

[0006] This article provides a method for reducing the residual alkali on the surface of high-nickel positive electrode materials to solve the technical problems of low efficiency of residual alkali removal on the surface of high-nickel positive electrode materials, multiple removal processes, easy lithium loss, and high waste emissions.

[0007] In order to solve the above technical problems, this article aims to provide a method for reducing the residual alkali on the surface of high-nickel positive electrode materials, comprising the following steps: stirring and mixing the gel containing polyethylene oxide and the high-nickel positive electrode material particles evenly, letting them stand, and centrifuging to obtain the gel of the high-nickel positive electrode material and the complexed lithium.

[0008] In this paper, polyethylene oxide and solvent are made into a gel. The solvent in the gel state does not affect the electrical properties of the high-nickel positive electrode material. The property of polyethylene oxide to complex lithium ions is utilized to dissolve the lithium salt on the surface of the high-nickel positive electrode material, thereby achieving efficient removal of residual alkali. The gel will not cause lithium dissolution of the high-nickel positive electrode material.

[0009] In one embodiment, the polyethylene oxide-containing gel is a gel containing 0.8 wt % to 6 wt % polyethylene oxide.

[0010] In one embodiment, the polyethylene oxide-containing gel is a gel containing 1 wt % to 4 wt % polyethylene oxide.

[0011] When the polyethylene oxide (PEO) content in the gel in this paper is too high or too low, if it is too high, the gel will have high viscosity and low mixing uniformity with the high-nickel positive electrode material, affecting the operation and residual alkali removal effect; if it is too low, it will not be enough to react with the residual alkali, resulting in poor residual alkali removal effect. In addition, when the PEO content in the gel is low, the viscosity of the gel formed is insufficient, and the effect of the solvent on the high-nickel positive electrode material may be enhanced. The solvent will cause a small amount of lithium dissolution, reducing the material capacity and cycle stability.

[0012] In one embodiment, the method for preparing the polyethylene oxide-containing gel is: dissolving polyethylene oxide in a solvent at 30-70° C. under stirring conditions to form a gel.

[0013] In one embodiment, the method for preparing the polyethylene oxide-containing gel is: dissolving polyethylene oxide in a solvent at 40-60° C. under stirring conditions to form a gel.

[0014] The low or high temperature of gel preparation in this paper will affect the viscosity of PEO gel. If the temperature is low, the viscosity of the gel will increase, which will reduce the mixing uniformity with the positive electrode material and affect the efficiency of residual alkali removal; if the temperature is high, the viscosity will decrease and the fluidity will increase, which will increase the corrosion of the solvent on the positive electrode material and reduce the cycle stability.

[0015] In one embodiment, the solvent is at least one of ethanol, acetonitrile, dimethylformamide, and anisole.

[0016] In one embodiment, the mass ratio of the polyethylene oxide-containing gel to the high-nickel positive electrode material particles is (1-4): (1-7).

[0017] In one embodiment, the mass ratio of the polyethylene oxide-containing gel to the high-nickel positive electrode material particles is (1-3): (2-5).

[0018] When the gel in this paper is mixed with high-nickel positive electrode materials, if there is more high-nickel positive electrode material, PEO cannot completely react with the residual alkali, affecting the removal efficiency; if there is less high-nickel positive electrode material, the residual alkali removal effect is better, but too much gel will also cause certain damage to the structure of the high-nickel positive electrode material, resulting in reduced cycle stability.

[0019] In one embodiment, the standing time is 30 min-60 min.

[0020] In one embodiment, the centrifugal speed is 1000 rpm-1200 rpm, and the centrifugal time is 15 min-30 min.

[0021] In one embodiment, the high nickel positive electrode material particles are LiNixCo y Mn z O2, where 0.6≤x<1, 0.1≤y≤0.2, 0.1≤Z≤0.2.

[0022] In one embodiment, the particle size of the high-nickel positive electrode material particles is 5-13 μm.

[0023] In one embodiment, the method further comprises the following steps: dissolving a lithium salt in an organic solvent to form an electrolyte, and mixing the complexed lithium gel with the electrolyte to form a gel electrolyte.

[0024] In one embodiment, the lithium salt is at least one of lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, and lithium dioxalatoborate, and the organic solvent is at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0025] In one embodiment, the concentration of lithium salt in the electrolyte is 0.1-3 mol / L, and the mass fraction of polyethylene oxide in the gel electrolyte is 1 wt%-20 wt%.

[0026] Compared with the existing technology, this article has the following beneficial effects:

[0027] 1. This article utilizes the property of polyethylene oxide to complex lithium ions. Polyethylene oxide is made into a gel state. When it is mixed with a high-nickel positive electrode material and allowed to stand, the solvent forms a gel state and will not corrode the positive electrode material to cause lithium dissolution. Polyethylene oxide can complex the lithium ions on the surface of the high-nickel positive electrode material and then dissolve the lithium salt, thereby achieving efficient removal of residual alkali. This process will not cause damage to the interior of the high-nickel positive electrode material particles, and the gel will not cause lithium dissolution of the high-nickel positive electrode material, so that the high-nickel positive electrode material has excellent electrochemical properties when used in the field of battery positive electrode materials.

[0028] 2. In this paper, the separation of high-nickel positive electrode material and gel can be achieved through centrifugation, which is simple to operate. The gel complexed with lithium ions can be subsequently recycled. The lithium absorbed by the gel can be used as a lithium supplement for the electrolyte to prepare a gel electrolyte, thus achieving harmless treatment of the product and avoiding the problem of excessive waste discharge. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of this document to clearly and completely describe the technical solutions in the embodiments of this document. Obviously, the embodiments described are only part of the embodiments of this document, not all of the embodiments. Based on the embodiments of this document, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this document.

[0030] Example 1

[0031] A method for reducing residual alkali on the surface of a high-nickel positive electrode material comprises the following steps:

[0032] (1) Polyethylene oxide (PEO) was dissolved in ethanol at 40°C under stirring to form a 1 wt% PEO gel;

[0033] (2) Add high nickel positive electrode particles LiNi into the gel in step (1) at a mass ratio of high nickel positive electrode particles to gel of 2:5. 0.8 Co 0.1 Mn 0.1 O2, the average particle size of high nickel cathode particles is 5 μm, stir to make the particles evenly dispersed in the gel, and let it stand for 30 min;

[0034] (3) centrifuging the gel obtained in step (2) at a speed of 1000 rpm for 20 min to separate the low residual alkali high nickel positive electrode material and the lithium complexed PEO gel;

[0035] (4) Lithium perchlorate is dissolved in dimethyl carbonate to form a 0.1 mol / L electrolyte, and PEO gel is immersed in the electrolyte to form a gel electrolyte, wherein the mass of polyethylene oxide is 5 wt% of the gel electrolyte.

[0036] Example 2

[0037] A method for reducing residual alkali on the surface of a high-nickel positive electrode material comprises the following steps:

[0038] (1) Polyethylene oxide (PEO) was dissolved in anisole at 50° C. under stirring to form a 4 wt % PEO gel;

[0039] (2) Add high nickel positive electrode particles LiNi into the gel of step (1) at a mass ratio of high nickel positive electrode particles to gel of 3:5. 0.8 Co 0.1 Mn 0.1 O2, the average particle size of high nickel cathode particles is 5 μm, stir to make the particles evenly dispersed in the gel, and let it stand for 40 min;

[0040] (3) centrifuging the gel obtained in step (2) at a speed of 1200 rpm for 15 min to separate the low residual alkali high nickel positive electrode material and the PEO gel complexed with lithium;

[0041] (4) Lithium perchlorate is dissolved in dimethyl carbonate to form a 0.5 mol / L electrolyte, and PEO gel is immersed in the electrolyte to form a gel electrolyte, wherein the mass of polyethylene oxide is 10 wt% of the gel electrolyte.

[0042] Example 3

[0043] A method for reducing residual alkali on the surface of a high-nickel positive electrode material comprises the following steps:

[0044] (1) Polyethylene oxide (PEO) was dissolved in dimethylformamide at 50°C under stirring to form a 2 wt% PEO gel;

[0045] (2) Add high nickel positive electrode particles LiNi into the gel in step (1) at a mass ratio of high nickel positive electrode particles to gel of 1:2. 0.8 Co 0.1 Mn 0.1 O2, the average particle size of high nickel cathode particles is 5 μm, the particles are stirred to be evenly dispersed in the gel, and then allowed to stand for 60 min;

[0046] (3) centrifuging the gel obtained in step (2) at a speed of 1000 rpm for 20 min to separate the low residual alkali high nickel positive electrode material and the lithium complexed PEO gel;

[0047] (4) Lithium perchlorate is dissolved in dimethyl carbonate to form a 1 mol / L electrolyte, and PEO gel is immersed in the electrolyte to form a gel electrolyte, wherein the mass of polyethylene oxide is 20 wt % of the gel electrolyte.

[0048] Example 4

[0049] A method for reducing residual alkali on the surface of a high-nickel positive electrode material, wherein each step and the reagents and process parameters used in each step are the same as those in Example 1, except that, in step (1), polyethylene oxide (PEO) is dissolved in ethanol at 40° C. under stirring conditions to form a 6 wt % PEO gel.

[0050] Example 5

[0051] A method for reducing residual alkali on the surface of a high-nickel positive electrode material, wherein each step and the reagents and process parameters used in each step are the same as those in Example 1, except that, in step (1), polyethylene oxide (PEO) is dissolved in ethanol at 40° C. under stirring conditions to form a gel containing 0.8 wt % PEO.

[0052] Example 6

[0053] A method for reducing residual alkali on the surface of a high-nickel positive electrode material, wherein each step and the reagents and process parameters used in each step are the same as those in Example 1, except that, in step (1), polyethylene oxide (PEO) is dissolved in ethanol at 30° C. under stirring to form a gel containing 6 wt % PEO.

[0054] Example 7

[0055] A method for reducing residual alkali on the surface of a high-nickel positive electrode material, wherein each step and the reagents and process parameters used in each step are the same as those in Example 1, except that, in step (1), polyethylene oxide (PEO) is dissolved in ethanol at 70° C. under stirring conditions to form a gel containing 6 wt % PEO.

[0056] Example 8

[0057] A method for reducing residual alkali on the surface of a high-nickel positive electrode material, wherein each step and the reagents and process parameters used in each step are the same as those in Example 1, except that in step (2), the mass ratio of the high-nickel positive electrode particles to the gel is 1:7.

[0058] Embodiment 9

[0059] A method for reducing residual alkali on the surface of a high-nickel positive electrode material, wherein each step and the reagents and process parameters used in each step are the same as those in Example 1, except that in step (2), the mass ratio of the high-nickel positive electrode particles to the gel is 4:1.

[0060] Comparative Example 1

[0061] A method for reducing residual alkali on the surface of a high-nickel positive electrode material comprises the following steps:

[0062] (1) 1 kg of high nickel positive electrode particles LiNi with an average particle size of 5 μm 0.8 Co0.1 Mn 0.1 Disperse O2 into 2 kg of clean water, stir and wash for 10 minutes at a stirring speed of 1000 r / min and a washing temperature of 35°C;

[0063] (2) After washing, the high-nickel positive electrode particles were separated from the water by filtration and dried under vacuum at 100° C. for 4 h to obtain the washed high-nickel positive electrode material.

[0064] Comparative Example 2

[0065] A method for reducing residual alkali on the surface of a high-nickel positive electrode material comprises the following steps:

[0066] (1) Polyethylene oxide (PEO) was dissolved in ethanol at 40° C. under stirring to form a 0.6 wt % PEO aqueous solution;

[0067] (2) Add high nickel positive electrode particles LiNi into the aqueous solution of step (1) at a mass ratio of high nickel positive electrode particles to 0.6 wt% PEO aqueous solution of 2:5. 0.8 Co 0.1 Mn 0.1 O2, the average particle size of high nickel cathode particles is 5 μm, stir to make the particles evenly dispersed in the aqueous solution, and let it stand for 30 minutes;

[0068] (3) After washing, the high-nickel cathode particles were separated from the water by filtration and dried under vacuum at 100°C for 4 h to obtain a high-nickel cathode material and a lithium-complexed PEO aqueous solution, respectively.

[0069] Performance testing

[0070] 1. The residual alkali of the high-nickel positive electrode materials obtained in the examples and comparative examples was detected by a potentiometric titrator, and the pH value was also detected. The test results are shown in Table 1 below.

[0071] 2. In order to detect the electrochemical properties of the high-nickel ternary positive electrode materials obtained in the examples and comparative examples, the high-nickel positive electrode material obtained in the examples or comparative examples, the binder polyvinylidene fluoride (PVDF), and the conductive agent SP were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1, stirred to form a slurry, and the slurry was coated on aluminum foil and dried to obtain a positive electrode sheet. Graphite was used as the negative electrode, and the positive electrode sheet, the negative electrode sheet, the gel electrolyte obtained in Example 1, and the diaphragm were assembled into a button battery in a glove box for charge, discharge, and cycle tests. Table 1 shows the performance test results of the examples and comparative examples.

[0072] Table 1 - Performance test results of the examples and comparative examples herein

[0073] Combining the performance test results of Examples 1-3 and Comparative Examples 1-2 in Table 1, it can be seen that Examples 1-3 can effectively reduce the residual alkali content on the surface of the high-nickel positive electrode material, and do not damage the structure of the high-nickel positive electrode material, and its electrochemical performance remains relatively good; while Comparative Example 1 adopts the traditional water washing and alkali reduction method, although it significantly reduces the surface residual alkali of the high-nickel positive electrode material, due to the sensitivity of the high-nickel positive electrode material itself to water, and the inevitable residue of washing water in the internal voids of the high-nickel positive electrode after drying, the electrochemical cycle performance of the high-nickel positive electrode material when used in the battery field has been significantly reduced; Comparative Example 2 uses a PEO-containing solution instead of PEO gel. Although it can also reduce the residual alkali amount, the solution will cause certain damage to the positive electrode material, resulting in lithium dissolution, thereby reducing the discharge capacity and cycle stability.

[0074] Combining the performance test results of Example 1 and Example 4-5 in Table 1, it can be seen that the PEO content in the gel of Example 4-5 is too high or too low. If it is too high, the gel will have high viscosity and low mixing uniformity with the positive electrode material. If it is too low, it will not be enough to react with the residual alkali, resulting in that Example 4 and Example 5 can remove the residual alkali but the effect is not as good as

[0075] In Example 1 and Example 5, the PEO content is relatively low, and the viscosity of the formed gel is insufficient. The effect of the solvent on the positive electrode material may be enhanced, and the solvent may cause a small amount of lithium dissolution, thereby reducing the material capacity and cycle stability.

[0076] Combining the performance test results of Example 1 and Examples 6-7 in Table 1, it can be seen that the preparation temperature of the gel in Example 6 and Example 7 is low or high, which will affect the viscosity of the PEO gel. The increase in viscosity at low temperature will reduce the mixing uniformity with the positive electrode material. The decrease in viscosity at high temperature increases the fluidity, increases the corrosion of the positive electrode material, and reduces the cycle stability.

[0077] Combining the performance test results of Example 1 and Examples 8-9 in Table 1, it can be seen that Example 8 has more positive electrode material and PEO cannot completely react with the residual alkali. Example 9 has less positive electrode material, so the residual alkali removal effect is better, but excessive gel will also cause certain damage to the material structure, resulting in reduced cycle stability.

[0078] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of this article in detail. It should be understood that the above descriptions are only specific embodiments of this article and are not intended to limit the scope of protection of this article.

Claims

1. A method for reducing residual alkali on the surface of high-nickel positive electrode materials, characterized in that: The method comprises the following steps: mixing the gel containing polyethylene oxide and high-nickel positive electrode material particles uniformly, standing the mixture, and centrifuging to obtain the high-nickel positive electrode material and the complex lithium gel.

2. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 1, characterized in that: The polyethylene oxide-containing gel is a gel containing 0.8 wt % to 6 wt % polyethylene oxide.

3. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 2, characterized in that: The polyethylene oxide-containing gel is a gel containing 1 wt% to 4 wt% polyethylene oxide.

4. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 1, characterized in that: The method for preparing the polyethylene oxide-containing gel is as follows: polyethylene oxide is dissolved in a solvent at 30-70° C. under stirring conditions to form a gel.

5. A method for reducing residual alkali on the surface of high-nickel positive electrode materials according to claim 4, characterized in that: The method for preparing the polyethylene oxide-containing gel is as follows: polyethylene oxide is dissolved in a solvent at 40-60° C. under stirring conditions to form a gel.

6. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 4 or 5, characterized in that: The solvent is at least one of ethanol, acetonitrile, dimethylformamide and anisole.

7. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 1, characterized in that: The mass ratio of the polyethylene oxide-containing gel to the high-nickel positive electrode material particles is (1-4): (1-7).

8. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 7, characterized in that: The mass ratio of the polyethylene oxide-containing gel to the high-nickel positive electrode material particles is (1-3): (2-5).

9. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 1, characterized in that: The standing time is 30min-60min.

10. A method for reducing residual alkali on the surface of high-nickel positive electrode materials according to claim 1, characterized in that: The centrifugal speed is 1000rmp-1200rmp, and the centrifugal time is 15min-30min.

11. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 1, characterized in that: The high nickel positive electrode material particles are LiNixCo y Mn z O2, where 0.6≤x<1, 0.1≤y≤0.2, 0.1≤Z≤0.

2.

12. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 1, characterized in that: The particle size of the high-nickel positive electrode material particles is 5-13 μm.

13. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 1, characterized in that: The method further comprises the following steps: dissolving lithium salt in an organic solvent to form an electrolyte, and mixing the complex lithium gel with the electrolyte to form a gel electrolyte.

14. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 13, characterized in that: The lithium salt is at least one of lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, and lithium dioxalatoborate; and the organic solvent is at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

15. A method for reducing residual alkali on the surface of a high-nickel positive electrode material according to claim 13, characterized in that: The concentration of lithium salt in the electrolyte is 0.1-3 mol / L, and the mass fraction of polyethylene oxide in the gel electrolyte is 1wt%-20wt%.

Images