Preparation method of composite solid electrolyte coated modified positive electrode material

Abstract

The application belongs to the technical field of preparation of lithium battery positive electrode materials, and discloses a preparation method of composite solid electrolyte coated modified positive electrode material with reduced surface residual lithium, comprising the following steps: mixing, stirring and reacting positive electrode material matrix, compound HO-R-OH and dichloromethane by introducing phosgene, and then stirring and heating until the dichloromethane is completely volatilized to obtain the product. The method simultaneously realizes the synthesis and coating of organic polymers, the reduction and in-situ conversion of surface residual lithium, and the synthesis and coating of inorganic ion conductors through one-pot method. The above complex chemical reactions are completed through simple synthesis steps, greatly simplifying the generation process and improving the raw material conversion rate. By reducing the surface residual lithium of the positive electrode material, the interface side reaction is effectively inhibited, the interface ion transmission is improved, the internal crack of the material is inhibited, and the synergistic effect of the composite coating layer can comprehensively improve the electrochemical performance of the positive electrode material.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery cathode material preparation technology, and particularly relates to a method for preparing a composite solid electrolyte coated modified cathode material. Background Technology

[0002] To meet the requirements of high energy density and large-scale energy storage in electric vehicles, the development of high-performance electrode materials for lithium-ion batteries is urgently needed. In recent years, high-nickel cathode materials have been extensively studied due to their inherent high reversible capacity and are considered one of the most promising cathode materials. By further increasing the proportion of nickel, layered cathode materials can achieve even higher reversible capacity and higher operating potential. However, high-nickel cathode materials face numerous challenges in practical applications, such as severe cathode / electrolyte interface side reactions and the degradation of nickel content at high voltages. 2+ (0.069 nm) and Li + The similar radii (0.076 nm) leading to cation mixing, and the formation and propagation of surface microcracks during charge and discharge, severely degrade the electrochemical performance of high-nickel cathode materials. Furthermore, residual lithium formed on the surface during cathode material preparation is also considered a source of gas generation.

[0003] Surface modification is considered a simple and effective strategy to prevent the aforementioned undesirable side reactions, thereby improving electrochemical performance. Currently used coatings include oxides, fluorides, and phosphates; however, these modified materials are electrochemically inert and have poor ionic conductivity. In contrast, lithium-ion conductors with excellent ionic conductivity and chemical stability can both protect the cathode material and improve interfacial ion transport.

[0004] Solid electrolytes can be divided into two categories: organic solid electrolytes and inorganic solid electrolytes. Using an elastic organic electrolyte as a coating layer can effectively release the anisotropic stress of the cathode material and alleviate strain-induced internal electrode contact failure, while inorganic electrolytes exhibit superior ionic conductivity. Therefore, using a composite electrolyte coating layer can comprehensively improve the electrochemical performance of the cathode material.

[0005] However, while the above methods can synthesize composite coatings, the coatings are multi-layered structures, failing to achieve a uniform mixture of organic and inorganic phases, thus hindering their synergistic effect. Furthermore, the synthesis of both organic and inorganic coatings involves multiple steps, resulting in complex processes and low raw material utilization. In addition, the composite coating synthesis process does not eliminate residual lithium on the cathode material surface, failing to address the gas generation problem at its root.

[0006] For example, Chinese patent application document CN118782763A discloses a composite solid electrolyte coated modified cathode material and its preparation method and application. However, the coating process cannot remove residual lithium on the surface of the cathode material. After coating, the residual lithium is still between the cathode material and the coating layer. The low ionic conductivity of the residual lithium is not conducive to the transport of lithium ions on the surface.

[0007] Therefore, by synthesizing and coating composite solid electrolytes on the surface of cathode materials and simultaneously achieving in-situ conversion of residual lithium on the surface, gas generation caused by residual lithium on the surface can be avoided, and residual lithium can be converted into inorganic electrolytes in situ. Furthermore, by utilizing the synergistic effect of organic and inorganic electrolytes, the electrochemical performance of cathode materials can be maximized. Summary of the Invention The technical problem to be solved by this invention is to overcome the shortcomings and defects mentioned in the background art above, and to provide a method for preparing a composite solid electrolyte-coated modified cathode material. While achieving in-situ synthesis and coating of organic solid electrolyte on the surface of the cathode material, residual lithium on the surface is converted into an inorganic ionic conductor, ultimately forming an organic / inorganic composite coating layer, thereby improving the cycle stability and rate performance of the cathode material.

[0008] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A method for preparing a composite solid electrolyte-coated modified cathode material includes the following steps: (1) The positive electrode material matrix, compound HO-R-OH and dichloromethane (solvent) are mixed and stirred, and phosgene (COCl2) is introduced to carry out the reaction; wherein R is an alkyl group with a carbon chain length of <10; (2) Stir and heat the reacted material until the dichloromethane is completely volatilized to obtain the product.

[0009] In the above preparation method, further, in step (1), the positive electrode material matrix includes any one of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0010] Furthermore, in step (1), the compound HO-R-OH includes at least one of ethylene glycol, propylene glycol, 1,2-butanediol and 1,5-pentanediol.

[0011] Furthermore, in step (1), the mass ratio of the compound HO-R-OH to the positive electrode material matrix is ​​0.1-10:100.

[0012] Furthermore, in step (1), the mass ratio of dichloromethane to the cathode material matrix is ​​0.5-5:1.

[0013] Further, in step (1), the stirring rotation speed is 300-1000 r / min, and the stirring duration is 1-100 min.

[0014] Further, in step (1), the gas flow rate of the introduced phosgene is 0.01-1 L / min The following chemical reaction occurs in step (1) to obtain an organic polymer: nHO-R-OH + nCOCl2→ -[RO-COO]- n + 2nHCl, wherein 100<n<1000000>0, and R is an alkyl group with a carbon chain length of <10; HCl, the reaction product of the above reaction, reacts with residual lithium on the surface of the positive electrode material according to the following reaction to obtain inorganic ionic conductor LiCl: HCl+LiOH→LiCl+H2O; 2HCl+Li2CO3→2LiCl+H2O+CO2.

[0015] It can be seen that HCl, the polymerization product obtained during preparation of the organic polymer, can further react with residual lithium (LiOH, Li2CO3) on the surface of the positive electrode material to obtain inorganic ionic conductor LiCl, which realizes reduction and in-situ conversion of surface residual lithium and greatly reduces the content of residual lithium on the surface of the positive electrode material.

[0016] Further, in step (2), the rotation speed of the stirring and heating is 300-1000 r / min.

[0017] Further, in step (2), the temperature of the stirring and heating is 50-200 °C.

[0018] Further, in step (2), the duration of the stirring and heating is 1-5 h.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. In the preparation method of the present invention, synthesis and coating of organic polymers, reduction and in-situ conversion of surface residual lithium, and synthesis and coating of inorganic ionic conductors are simultaneously achieved only through a one-pot method. The above complex chemical reactions are completed through simple synthesis steps, which greatly simplifies the production process and improves the raw material conversion rate.

[0020] 2. In the preparation method of the present invention, HCl, which is a polymerization product, is further used as a reactant to convert surface residual lithium into inorganic lithium ionic conductor LiCl in situ, so as to reduce surface residual lithium of the positive electrode material, effectively inhibit interface side reactions, improve interface ion transport, inhibit internal cracks of the material, and the synergistic effect of the composite coating layer can comprehensively improve the electrochemical performance of the positive electrode material. Description of Drawings

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The figures show the performance curves of lithium-ion coin cells assembled with the cathode materials prepared in Example 1 and Comparative Example 1 at 100 cycles at 10C, at 25 °C. Detailed Implementation

[0023] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0024] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0025] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0026] Example 1: A composite solid electrolyte-coated modified cathode material is prepared by the following method: (1) Weigh 100 g LiNi 0.9 Co 0.05 Mn 0.05 O2, 1 g ethylene glycol, and 50 g dichloromethane were poured into a beaker and stirred at 500 r / min. Phosgene was introduced at a flow rate of 0.1 L / min and the stirring time was 5 min. (2) Stir and heat the reacted material at a speed of 500 r / min and a temperature of 60 ℃ for 2 h until the dichloromethane is completely volatilized to obtain the composite solid electrolyte coated modified cathode material.

[0027] Example 2: A composite solid electrolyte-coated modified cathode material is prepared by the following method: (1) Weigh 200 g LiNi 0.9 Co 0.05 Mn 0.05O2, 1 g ethylene glycol, and 50 g dichloromethane were poured into a beaker and stirred at 500 r / min. Phosgene was introduced at a flow rate of 0.1 L / min and the stirring time was 5 min. (2) Stir and heat the reacted material at a speed of 500 r / min and a temperature of 60 ℃ for 2 h until the dichloromethane is completely volatilized to obtain the composite solid electrolyte coated modified cathode material.

[0028] Example 3: A composite solid electrolyte-coated modified cathode material is prepared by the following method: (1) Weigh 50 g of LiNi 0.9 Co 0.05 Mn 0.05 O2, 1 g ethylene glycol, and 50 g dichloromethane were poured into a beaker and stirred at 500 r / min. Phosgene was introduced at a flow rate of 0.1 L / min and the stirring time was 5 min. (2) Stir and heat the reacted material at a speed of 500 r / min and a temperature of 60 ℃ for 2 h until the dichloromethane is completely volatilized to obtain the composite solid electrolyte coated modified cathode material.

[0029] Example 4: A composite solid electrolyte-coated modified cathode material is prepared by the following method: (1) Weigh 100 g LiNi 0.9 Co 0.05 Mn 0.05 O2, 0.5 g ethylene glycol, and 50 g dichloromethane were poured into a beaker and stirred at 500 r / min. Phosgene was introduced at a flow rate of 0.1 L / min and the stirring time was 5 min. (2) Stir and heat the reacted material at a speed of 500 r / min and a temperature of 60 ℃ for 2 h until the dichloromethane is completely volatilized to obtain the composite solid electrolyte coated modified cathode material.

[0030] Example 5: A composite solid electrolyte-coated modified cathode material is prepared by the following method: (1) Weigh 100 g LiNi 0.9 Co 0.05 Mn 0.05 O2, 1 g propylene glycol, and 50 g dichloromethane were poured into a beaker and stirred at 500 r / min. Phosgene was introduced at a flow rate of 0.1 L / min and the stirring time was 5 min. (2) Stir and heat the reacted material at a speed of 500 r / min and a temperature of 60 ℃ for 2 h until the dichloromethane is completely volatilized to obtain the composite solid electrolyte coated modified cathode material.

[0031] Example 6: A composite solid electrolyte-coated modified cathode material is prepared by the following method: (1) Weigh 100 g LiNi 0.9 Co 0.05 Mn 0.05 O2, 1 g of 1,2-butanediol, and 50 g of dichloromethane were poured into a beaker and stirred at 500 r / min. Phosgene was also introduced at a flow rate of 0.1 L / min for 5 min. (2) Stir and heat the reacted material at a speed of 500 r / min and a temperature of 60 ℃ for 2 h until the dichloromethane is completely volatilized to obtain the composite solid electrolyte coated modified cathode material.

[0032] Example 7: A composite solid electrolyte-coated modified cathode material is prepared by the following method: (1) Weigh 100 g LiNi 0.9 Co 0.05 Mn 0.05 O2, 1 g of 1,5-pentanediol, and 50 g of dichloromethane were poured into a beaker and stirred at 500 r / min. Phosgene was also introduced at a flow rate of 0.1 L / min for 5 min. (2) Stir and heat the reacted material at a speed of 500 r / min and a temperature of 60 ℃ for 2 h until the dichloromethane is completely volatilized to obtain the composite solid electrolyte coated modified cathode material.

[0033] Example 8: A composite solid electrolyte-coated modified cathode material is prepared by the following method: (1) Weigh 100 g LiNi 0.9 Co 0.05 Mn 0.05 O2, 1 g ethylene glycol, and 50 g dichloromethane were poured into a beaker and stirred at 500 r / min. Phosgene was introduced at a flow rate of 0.1 L / min and the stirring time was 20 min. (2) Stir and heat the reacted material at a speed of 500 r / min and a temperature of 60 ℃ for 2 h until the dichloromethane is completely volatilized to obtain the composite solid electrolyte coated modified cathode material.

[0034] Comparative Example 1: An uncoated and modified cathode material, not the cathode material LiNi 0.9 Co 0.05 Mn 0.05 O2 is not subject to any processing.

[0035] Comparative Example 2: An organic polymer electrolyte-coated modified cathode material is prepared by the following method: (1) Weigh 200 g LiNi 0.9 Co 0.05 Mn 0.05 O2, 50 g deionized water; (2) Pour the above mixture into a beaker and stir at a speed of 500 r / min for 5 min; (3) The above mixture was filtered and dried at 150 °C for 10 h to reduce residual lithium on the material surface; (4) Weigh 100 g of dried material, 1 g of ethylene glycol and 50 g of dichloromethane into a beaker and stir at 500 r / min. Phosgene is introduced at a flow rate of 0.1 L / min and the stirring time is 5 min. (5) Stir and heat the reacted material at a speed of 500 r / min and a temperature of 60 ℃ for 2 h until the dichloromethane is completely volatilized to obtain the positive electrode material with organic polymer electrolyte coating modification.

[0036] Comparative Example 3: An inorganic chloride electrolyte-coated modified cathode material is prepared by the following method: (1) Weigh 100 g LiNi 0.9 Co 0.05 Mn 0.05 O2, 50 g deionized water, and 10 ml of 1 mol / L HCl; (2) Pour the above mixture into a beaker and stir at a speed of 500 r / min for 5 min; (3) The above mixture was filtered and dried at 150 °C for 10 h to remove deionized water, and an inorganic chloride electrolyte-coated modified cathode material was obtained.

[0037] Residual lithium and performance testing: The cathode materials prepared in the above examples and comparative examples were subjected to residual lithium testing, and then assembled into 2025 pairs of lithium half-cells for electrochemical performance testing. A 14 mm lithium sheet was used as the negative electrode; polyethylene was used as the separator; and a 1 M LiPF6 / EC∶DMC∶EMC (1:1:1) solution was used as the electrolyte. DC internal resistance, rate performance, and cycle performance were tested at 25 °C using a battery testing cabinet. The test voltage range was 2.8–4.3 V, the test rate was 0.1 C–10 C, and the nominal capacity was 200 mAh g⁻¹. -1 The test results are as follows.

[0038] Table 1 Test results of Examples 1-8 and Comparative Examples 1-3

[0039] The test results from Examples 1-8 and Comparative Examples 1-3 above, and the appendix Figure 1 As can be seen, the method proposed in this invention for simultaneously synthesizing organic and inorganic composite electrolytes in situ on the surface of the cathode material can significantly reduce the DC impedance of the battery, improve the initial coulombic efficiency, and enhance rate performance and cycle stability compared to uncoated samples and samples coated with a single electrolyte. Figure 1 As shown, Example 1, coated with composite electrolyte, maintained a capacity retention of up to 87.0% after 100 cycles at 10C, while Comparative Example 1 only maintained 56.8%.

Claims

1. A method for preparing a composite solid electrolyte-coated modified cathode material, characterized in that, Includes the following steps: (1) The positive electrode material matrix, compound HO-R-OH and dichloromethane are mixed and stirred, and phosgene is introduced to carry out the reaction. The resulting polymerization product HCl is further reacted with residual lithium on the surface of the positive electrode material to obtain the inorganic ionic conductor LiCl; wherein R is an alkyl group with a carbon chain length of <10; the mass ratio of compound HO-R-OH to the positive electrode material matrix is ​​0.1-10:100; the mass ratio of dichloromethane to the positive electrode material matrix is ​​0.5-5:1; the gas flow rate of the introduced phosgene is 0.01-1 L / min; (2) Stir and heat the reacted material until the dichloromethane is completely volatilized to obtain the product.

2. The preparation method according to claim 1, characterized in that, In step (1), the cathode material matrix includes any one of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

3. The preparation method according to claim 1, characterized in that, In step (1), the compound HO-R-OH includes at least one of ethylene glycol, propylene glycol, 1,2-butanediol and 1,5-pentanediol.

4. The preparation method according to claim 1, characterized in that, In step (1), the stirring speed is 300-1000 r / min and the stirring time is 1-100 min.

5. The preparation method according to claim 1, characterized in that, In step (2), the stirring and heating speed is 300-1000 r / min.

6. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the stirring and heating is 50-200 ℃.

7. The preparation method according to any one of claims 1-6, characterized in that, In step (2), the stirring and heating time is 1-5 h.

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