Preparation method of composite solid electrolyte coated modified positive electrode material

Abstract

The invention belongs to the technical field of lithium battery positive electrode material preparation, and discloses a preparation method of a composite solid electrolyte coated modified positive electrode material capable of reducing surface residual lithium, and the preparation method comprises the following steps: mixing and stirring a positive electrode material matrix, a compound HO-R-OH and dichloromethane, and introducing phosgene for reaction, and then stirring and heating until the dichloromethane is completely volatilized to obtain the product. According to the method, synthesis and coating of an organic polymer, reduction and in-situ conversion of residual lithium on the surface and synthesis and coating of an inorganic ion conductor are simultaneously realized only through a one-pot method, and the complex chemical reaction is completed through simple synthesis steps, so that the generation process is greatly simplified, and the raw material conversion rate is increased. And by reducing residual lithium on the surface of the positive electrode material, the interface side reaction is effectively inhibited, the interface ion transmission is improved, the internal cracks of the material are inhibited, and the electrochemical performance of the positive electrode material can be comprehensively improved through the synergistic effect of the composite coating layer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of preparation of lithium battery positive electrode materials, and particularly relates to a preparation method of a composite solid electrolyte coated modified positive electrode material. BACKGROUND

[0002] To meet the requirements of high energy density and large-scale energy storage for electric vehicles, it is urgent to develop high-performance electrode materials for lithium-ion batteries. In recent years, high-nickel positive electrode materials have been widely studied due to their inherent high reversible capacity and are considered as one of the most promising positive electrode materials. By further increasing the proportion of nickel element, the layered positive electrode material can achieve higher reversible capacity and higher working potential. However, high-nickel positive electrode materials have a lot of problems in practical application, such as serious positive electrode / electrolyte interface side reactions, and at high voltage, cation mixing caused by the similar radius between Ni 2+ (0.069 nm) and Li + (0.076 nm), and the formation and propagation of surface micro-cracks during charging and discharging, which will seriously deteriorate the electrochemical performance of high-nickel positive electrode materials. In addition, the surface residual lithium formed during the preparation of the positive electrode material is also considered to be the source of gas generation.

[0003] Surface modification is considered as a simple and effective strategy to effectively prevent the above-mentioned unwanted side reactions and thus improve the electrochemical performance. The current coating materials include oxides, fluorides and phosphates, however, these modified materials are electrochemically inert and have poor ionic conductivity. In comparison, lithium ion conductors with excellent ionic conductivity and chemical stability can both protect the positive electrode material and improve the interface ion transmission.

[0004] Solid-state electrolytes can be divided into two categories: organic solid-state electrolytes and inorganic solid-state electrolytes. The use of elastic organic electrolytes as a coating layer can effectively release the anisotropic stress of the positive electrode material and relieve the internal contact failure of the electrode caused by strain, while inorganic electrolytes have more excellent ionic conductivity. Therefore, the use of a composite electrolyte coating layer can comprehensively improve the electrochemical performance of the positive electrode material.

[0005] However, the above method can synthesize a composite coating layer, but the coating layer is a multilayer structure, the uniform mixing of the organic phase and the inorganic phase is not achieved, and it is difficult to play the synergistic effect of the two. And the organic coating layer and the inorganic coating layer are synthesized in multiple steps, the process is complex, the raw material utilization rate is low. In addition, the synthesis process of the composite coating layer does not eliminate the residual lithium on the surface of the positive electrode material, and the gas generation problem cannot be solved from the root.

[0006] As disclosed in Chinese patent application document CN118782763A, a composite solid electrolyte coated modified positive electrode material and its preparation method and application are disclosed, which cannot remove the residual lithium on the surface of the positive electrode material during the coating process, and the residual lithium is still between the positive electrode material and the coating layer after coating. The low ionic conductivity of the residual lithium is not conducive to the transmission of lithium ions on the surface.

[0007] Therefore, the synthesis and coating of the composite solid electrolyte on the surface of the positive electrode material are realized, and the in-situ conversion of the residual lithium on the surface is simultaneously realized. Not only can the gas production caused by the residual lithium on the surface be avoided, but also the residual lithium can be in-situ converted into inorganic electrolyte. Moreover, the synergistic effect of the organic and inorganic electrolytes is utilized to maximize the electrochemical performance of the positive electrode material. SUMMARY The technical problem to be solved by the present application is to overcome the deficiencies and defects mentioned in the above background art, and to provide a preparation method of a composite solid electrolyte coated modified positive electrode material. The in-situ synthesis and coating of the organic solid electrolyte on the surface of the positive electrode material are realized at the same time, and the residual lithium on the surface is converted into an inorganic ion conductor, finally forming an organic / inorganic composite coating layer, and improving the cycle stability and rate performance of the positive electrode material.

[0008] To solve the above technical problems, the technical solution provided by the present application is as follows: A preparation method of a composite solid electrolyte coated modified positive electrode material, comprising the following steps: (1) mixing, stirring and introducing phosgene (COCl2) into the positive electrode material matrix, compound HO-R-OH and dichloromethane (solvent) to react; R is an alkyl group with a carbon chain length <10; (2) after stirring and heating the reacted material until the dichloromethane is completely volatilized, it is obtained.

[0009] The above preparation method further comprises the following in step (1): the positive electrode material matrix comprises any one of lithium iron phosphate, lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobaltate, lithium nickel manganate, lithium nickel cobalt manganate and lithium nickel cobalt aluminumate.

[0010] Further, 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] Further, in step (1), the mass ratio of the compound HO-R-OH to the positive electrode material matrix is 0.1-10:100.

[0012] Further, in step (1), the mass ratio of the dichloromethane to the positive electrode material matrix is 0.5-5:1.

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

[0014] Further, in step (1), the gas flow rate of the phosgene is 0.01-1 L / min. The following chemical reaction occurs in step (1) to obtain the 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 <10. The reaction product HCl reacts with the residual lithium on the surface of the positive electrode material as follows to obtain the inorganic ion conductor LiCl: HCl + LiOH → LiCl + H2O. 2HCl + Li2CO3→ 2LiCl + H2O + CO2.

[0015] As can be seen, the polymerization reaction product HCl obtained during the preparation of the organic polymer can further react with the residual lithium (LiOH, Li2CO3) on the surface of the positive electrode material to obtain the inorganic ion conductor LiCl, thereby achieving the reduction and in-situ conversion of the residual lithium on the surface, and greatly reducing the content of the residual lithium on the surface of the positive electrode material.

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

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

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

[0019] Compared with the prior art, the present application has the following advantages: 1. The preparation method of the present application simultaneously realizes the synthesis and coating of the organic polymer, the reduction and in-situ conversion of the residual lithium on the surface, and the synthesis and coating of the inorganic ion conductor through one-pot method, thereby greatly simplifying the generation process and improving the raw material conversion rate.

[0020] 2. The preparation method of the present application further uses the polymerization reaction product HCl as a reactant to in-situ convert the residual lithium on the surface into the inorganic lithium ion conductor LiCl, thereby reducing the residual lithium on the surface of the positive electrode material, effectively inhibiting the interface side reaction, improving the interface ion transmission, and inhibiting the 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. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0022] Figure 1 The performance curve of 100 cycles at 10C of the lithium ion button cell assembled by the positive electrode material prepared in Example 1 and Comparative Example 1 at 25℃. DETAILED DESCRIPTION

[0023] In order to facilitate the understanding of the present application, the present application will be described more fully and specifically below in conjunction with the drawings of the specification and preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0024] Unless otherwise defined, all the professional terms used below have the same meaning as generally understood by those skilled in the art. The professional terms used in this paper are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application.

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

[0026] Example 1: A composite solid electrolyte coated modified positive electrode material, and the preparation method is as follows: (1) Take 100 g LiNi 0.9 Co 0.05 Mn 0.05 O2, 1 g ethylene glycol, 50 g dichloromethane, pour into a beaker for stirring, the stirring speed is 500 r / min, and pass in phosgene, the gas flow rate is 0.1 L / min, the stirring time is 5 min; (2) Stir and heat the reacted material, the stirring speed is 500 r / min, the temperature is 60℃, the heating time is 2 h, after the dichloromethane is completely volatilized, the composite solid electrolyte coated modified positive electrode material is obtained.

[0027] Example 2: A composite solid electrolyte coated modified positive electrode material, and the preparation method is as follows: (1) Take 200 g LiNi 0.9 Co 0.05 Mn 0.05Pour O2, 1 g ethylene glycol, and 50 g dichloromethane into a beaker and stir at a speed of 500 r / min. Add phosgene at a gas flow rate of 0.1 L / min and stir for 5 min. (2) The reacted material was stirred and heated at a speed of 500 r / min and a temperature of 60 °C for 2 h until the dichloromethane was completely volatilized to obtain a composite solid electrolyte coated modified positive electrode material.

[0028] Example 3: A composite solid electrolyte coated modified positive electrode material, the preparation method of which is as follows: (1) Weigh 50 g LiNi 0.9 Co 0.05 Mn 0.05 Pour O2, 1 g ethylene glycol, and 50 g dichloromethane into a beaker and stir at a speed of 500 r / min. Add phosgene at a gas flow rate of 0.1 L / min and stir for 5 min. (2) The reacted material was stirred and heated at a speed of 500 r / min and a temperature of 60 °C for 2 h until the dichloromethane was completely volatilized to obtain a composite solid electrolyte coated modified positive electrode material.

[0029] Example 4: A composite solid electrolyte coated modified positive electrode material, the preparation method of which is as follows: (1) Weigh 100 g LiNi 0.9 Co 0.05 Mn 0.05 Pour O2, 0.5 g ethylene glycol, and 50 g dichloromethane into a beaker and stir at a speed of 500 r / min. Add phosgene at a gas flow rate of 0.1 L / min and stir for 5 min. (2) The reacted material was stirred and heated at a speed of 500 r / min and a temperature of 60 °C for 2 h until the dichloromethane was completely volatilized to obtain a composite solid electrolyte coated modified positive electrode material.

[0030] Example 5: A composite solid electrolyte coated modified positive electrode material, the preparation method of which is as follows: (1) Weigh 100 g LiNi 0.9 Co 0.05 Mn 0.05 Pour O2, 1 g propylene glycol, and 50 g dichloromethane into a beaker and stir at a speed of 500 r / min. Add phosgene at a gas flow rate of 0.1 L / min and stir for 5 min. (2) After the reaction, the material is stirred and heated at a speed of 500 r / min and a temperature of 60 DEG C for 2 h, until the dichloromethane is completely volatilized, to obtain the composite solid electrolyte coated modified positive electrode material.

[0031] Example 6: A composite solid electrolyte coated modified positive electrode material is prepared by the following method: (1) 100 g of LiNi 0.9 Co 0.05 Mn 0.05 O2, 1 g of 1,2-butanediol, and 50 g of dichloromethane are poured into a beaker for stirring at a speed of 500 r / min, and phosgene is introduced at a gas flow rate of 0.1 L / min for 5 min of stirring; (2) After the reaction, the material is stirred and heated at a speed of 500 r / min and a temperature of 60 DEG C for 2 h, until the dichloromethane is completely volatilized, to obtain the composite solid electrolyte coated modified positive electrode material.

[0032] Example 7: A composite solid electrolyte coated modified positive electrode material is prepared by the following method: (1) 100 g of LiNi 0.9 Co 0.05 Mn 0.05 O2, 1 g of 1,5-pentanediol, and 50 g of dichloromethane are poured into a beaker for stirring at a speed of 500 r / min, and phosgene is introduced at a gas flow rate of 0.1 L / min for 5 min of stirring; (2) After the reaction, the material is stirred and heated at a speed of 500 r / min and a temperature of 60 DEG C for 2 h, until the dichloromethane is completely volatilized, to obtain the composite solid electrolyte coated modified positive electrode material.

[0033] Example 8: A composite solid electrolyte coated modified positive electrode material is prepared by the following method: (1) 100 g of LiNi 0.9 Co 0.05 Mn 0.05 O2, 1 g of ethylene glycol, and 50 g of dichloromethane are poured into a beaker for stirring at a speed of 500 r / min, and phosgene is introduced at a gas flow rate of 0.1 L / min for 20 min of stirring; (2) After the reaction, the material is stirred and heated at a speed of 500 r / min and a temperature of 60 DEG C for 2 h, until the dichloromethane is completely volatilized, to obtain the composite solid electrolyte coated modified positive electrode material.

[0034] Comparative Example 1: An uncoated modified positive electrode material, without any treatment to the positive electrode material LiNi 0.9 Co 0.05 Mn 0.05 O2.

[0035] Comparative Example 2: An organic polymer electrolyte coated modified positive electrode material, prepared as follows: (1) Take 200 g LiNi 0.9 Co 0.05 Mn 0.05 O2, 50 g of deionized water; (2) Pour the above mixture into a beaker and stir at a speed of 500 r / min for 5 min; (3) Filter the above mixture and dry at 150 °C for 10 h to reduce the residual lithium on the surface of the material; (4) Take 100 g of the dried material, 1 g of ethylene glycol, and 50 g of dichloromethane and pour them into a beaker and stir at a speed of 500 r / min while passing in phosgene at a flow rate of 0.1 L / min for 5 min; (5) Stir and heat the reacted material at a speed of 500 r / min and a temperature of 60 °C for 2 h, and after the dichloromethane is completely volatilized, an organic polymer electrolyte coated modified positive electrode material is obtained.

[0036] Comparative Example 3: An inorganic chloride electrolyte coated modified positive electrode material, prepared as follows: (1) Take 100 g LiNi 0.9 Co 0.05 Mn 0.05 O2, 50 g of deionized water, and measure 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) Filter the above mixture and dry at 150 °C for 10 h to remove the deionized water, and obtain an inorganic chloride electrolyte coated modified positive electrode material.

[0037] Residual lithium and performance test: The positive electrode materials prepared in the above examples and comparative examples were subjected to residual lithium test, and were respectively assembled into 2025 lithium half-batteries for electrochemical performance test. Among them, 14 mm lithium sheet was used as the negative electrode; polyethylene was used as the separator; 1 M LiPF6 / EC:DMC:EMC (1:1:1) solution was used as the electrolyte. At 25℃, direct current resistance test, rate performance and cycle performance test were carried out by using a battery test cabinet, the test voltage interval was 2.8-4.3 V, the test rate was 0.1 C-10 C, and the nominal capacity was 200 mAh g -1 ; the test results are as follows.

[0038] Table 1 Test results of examples 1-8 and comparative examples 1-3

[0039] From the test results of examples 1-8 and comparative examples 1-3 and the attached Figure 1 , it can be seen that the scheme of in-situ synthesis of organic and inorganic composite electrolyte on the surface of the positive electrode material can significantly reduce the direct current impedance of the battery, improve the first coulomb efficiency, and improve the rate performance and cycle stability compared with the uncoated sample and the sample coated with single electrolyte. As shown in Figure 1 , the capacity retention rate of example 1 coated with composite electrolyte was as high as 87.0% after 100 cycles at 10C, while that of comparative example 1 was only 56.8%.

Claims

1. A method for preparing a composite solid electrolyte-coated modified positive electrode material, characterized by, The steps include: (1) The cathode material matrix, the compound HO-R-OH and dichloromethane are mixed and stirred, and phosgene is introduced to react; wherein R is an alkyl group with a carbon chain length of less than 10; (2) Stir and heat the reacted materials until the dichloromethane is completely volatilized to obtain the product.

2. The production method according to claim 1, characterized by, In step (1), the positive electrode material matrix includes any one of lithium iron phosphate, lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobaltate, lithium nickel manganate, lithium nickel cobalt manganate 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 method of claim 1, wherein the step of forming the first and second layers is performed by a process selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. In step (1), the mass ratio of the compound HO-R-OH to the positive electrode material matrix is ​​0.1-10:

100.

5. The method of claim 1, wherein the step of forming the first and second layers is performed by a process selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. In step (1), the mass ratio of dichloromethane to the positive electrode material matrix is ​​0.5-5:

1.

6. The method of claim 1, wherein In step (1), the stirring speed is 300-1000 r / min, and the stirring time is 1-100 min.

7. The method of claim 1, wherein In step (1), the gas flow rate of the phosgene introduced is 0.01-1 L / min.

8. The method of claim 1, wherein In step (2), the rotation speed of the stirring heating is 300-1000 r / min.

9. The method of claim 1, wherein In step (2), the stirring and heating temperature is 50-200°C.

10. The production method according to any one of claims 1 to 9, characterized by, In step (2), the stirring and heating time is 1-5 h.

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