A positive electrode material, a preparation method and application thereof

Abstract

This invention provides a cathode material, its preparation method, and its application, relating to the fields of electrochemistry and new energy materials technology. The preparation method includes: first, dissolving an electrophilic reagent in an aprotic solvent free of active hydrogen to obtain an electrophilic reagent solution; then, mixing the cathode active material with the electrophilic reagent solution, causing the electrophilic reagent to react with nucleophilic sites on the surface of the cathode material, thereby generating a solid electrophilic interface layer in situ on the surface of the cathode active material. This solid electrophilic interface layer is firmly bonded to the cathode substrate, can achieve uniform coating on the surface of particles with complex morphologies, and possesses electronic insulation and ion conduction properties. It can both prevent electron conduction between cathode active material particles, suppress side reactions at the cathode-electrolyte interface, prevent transition metal dissolution and lattice oxygen loss, significantly improve the operating voltage window of the all-solid-state battery, and ensure smooth lithium-ion transport, thus improving the electrochemical performance of the all-solid-state battery.

Description

Technical Field

[0001] This invention relates to the field of electrochemistry and new energy materials technology, and in particular to a cathode material, its preparation method and application. Background Technology

[0002] Lithium-rich manganese-based cathode materials (xLi₂MnO₃·(1-x)LiMO₂) have attracted much attention due to their high specific capacity and are key cathode materials for realizing high-energy-density all-solid-state lithium batteries. However, when in direct contact with high-ionic-conductivity sulfide solid electrolytes (such as Li₆PS₅Cl, LPSC), their capacitance drops above 4.2 V (vs. Li₂MnO₃·(1-x)LiMO₂). + Severe interfacial side reactions occur at the operating voltage of solid-state batteries (SSE / Li). These interfacial side reactions include the oxidative decomposition of the solid electrolyte, the loss of lattice oxygen from the cathode material surface, and the dissolution of transition metal ions, leading to a sharp increase in interfacial impedance, rapid capacity decay, and battery failure, which severely limits the operating voltage window and cycle life of all-solid-state batteries.

[0003] To address the aforementioned technical challenges, existing technologies typically employ vapor deposition methods such as atomic layer deposition (ALD) or magnetron sputtering, along with mechanical hybrid coating methods, to modify the surface of cathode materials to construct a protective layer. However, vapor deposition methods are expensive, complex, and time-consuming, and struggle to achieve uniform coating on irregular cathode material particles, hindering large-scale industrial applications. Mechanical hybrid coating methods suffer from weak adhesion between the coating layer and the substrate, uneven coating thickness, susceptibility to detachment, and long processing times. They also fail to effectively suppress interfacial side reactions in the long term, offering limited protection for the cathode material and ultimately reducing the battery's electrochemical performance.

[0004] Therefore, this invention is proposed. Summary of the Invention

[0005] This invention provides a cathode material, its preparation method, and its application. The preparation process of this cathode material is simple, efficient, and low-cost, effectively suppressing the occurrence of interfacial side reactions and improving the interfacial compatibility and electrochemical stability between the cathode material and the solid electrolyte.

[0006] In a first aspect, the present invention provides a method for preparing a positive electrode material, comprising: first dissolving an electrophilic reagent in an aprotic solvent free of active hydrogen to obtain an electrophilic reagent solution; then mixing a positive electrode active material with the electrophilic reagent solution to allow the electrophilic reagent to undergo an electrophilic reaction with nucleophilic sites on the surface of the positive electrode material, thereby generating a solid electrophilic interface layer with electronic insulation and ion conduction properties in situ on the surface of the positive electrode active material.

[0007] In the preparation of the cathode material of this invention, an electrophilic reagent is introduced. The electrophilic reagent molecules form a tight "nucleophilic-electrophilic pair" with the nucleophilic sites (such as lattice oxygen) on the surface of the cathode active material, resulting in an electrophilic reaction. This process extracts electrons and lithium ions from the surface of the cathode active material and undergoes electrochemical reduction and decomposition. The decomposition products (such as LiF, organic lithium salts, etc.) are deposited in situ on the surface of the cathode active material to form a thin and dense solid electrophilic interface layer. This solid electrophilic interface layer has the characteristics of electronic insulation and ion conduction. It can suppress the cathode-electrolyte interface side reactions between active oxygen and electrolyte in the cathode active material, prevent transition metal dissolution and lattice oxygen loss, significantly improve the operating voltage window of the all-solid-state battery, and ensure smooth lithium ion transport. Furthermore, the solid electrophilic interface layer is generated in situ, and it is firmly bonded to the cathode substrate, achieving uniform coverage on the surface of particles with complex morphologies, effectively avoiding detachment and uneven coverage.

[0008] In the above technical solution, an aprotic solvent without active hydrogen is used to dissolve the electrophilic reagent. The reason is that this invention has found that when a solvent containing active hydrogen (such as ethanol, methanol, propanol, isopropanol, etc.) is used to dissolve the electrophilic reagent, the electrophilic reagent (such as acid anhydride compounds) will directly react with the solvent containing active hydrogen to generate ester compounds, making it difficult to achieve the expected coating purpose, reducing the protection effect on the cathode material, and thus leading to a decrease in the electrochemical performance of the all-solid-state battery.

[0009] Preferably, the electrophilic reaction is carried out at room temperature.

[0010] Furthermore, the thickness of the solid electrophilic interface layer is 1-50 nm, preferably 10 nm. The preparation method of the present invention can obtain a solid electrophilic interface layer of the above thickness. By controlling the thickness of the solid electrophilic interface layer within the above reasonable range, it is possible not only to ensure a good uniform coating effect, but also to reduce battery impedance, avoid the interface layer from affecting electron conduction, and improve the electrochemical performance of the battery.

[0011] Furthermore, when the positive electrode active material is mixed with the electrophilic reagent solution, the mass of the electrophilic reagent is 0.5-5% of the mass of the positive electrode active material.

[0012] Furthermore, the concentration of the electrophilic reagent solution is 10-50 mg / mL.

[0013] This invention has found that excessively high concentrations of the electrophilic reagent solution and excessive amounts of the electrophilic reagent relative to the positive electrode active material result in an excessively thick solid electrophilic interface layer, increasing battery impedance; conversely, insufficient concentrations lead to an uneven solid electrophilic interface layer, affecting the coating effect. Therefore, controlling the concentration of the electrophilic reagent solution and the amount of the electrophilic reagent relative to the positive electrode active material within the aforementioned range can help form a solid electrophilic interface layer with a thickness within this range. This solid electrophilic interface layer can not only effectively suppress the interfacial side reactions between the positive electrode and the electrolyte, but also does not affect electron conduction, effectively improving the electrochemical performance of the battery.

[0014] Furthermore, the electrophilic reagent is a fluorinated compound with strong electrophilic properties, and it contains a strong electron-withdrawing group, which can react with O on the surface of metal oxides. 2- A reaction occurs.

[0015] Preferably, the fluorinated compound includes at least one or more of difluoromaleic anhydride, trifluoroacetic anhydride, tetrafluorosuccinic anhydride, pentafluoropropionic anhydride, trifluoromethanesulfonic anhydride, and trifluoroacetylfluoride.

[0016] More preferably, the fluorinated compound includes trifluoroacetyl fluoride and at least one or more selected from difluoromaleic anhydride, trifluoroacetic anhydride, tetrafluorosuccinic anhydride, pentafluoropropionic anhydride, and trifluoromethanesulfonic anhydride. When a fluorinated compound composed of trifluoroacetyl fluoride and the other compounds mentioned above is selected as the electrophilic agent, the stringent requirements of trifluoroacetyl fluoride on experimental conditions can be reduced, the coating effect can be significantly improved, and the side reactions at the positive electrode-electrolyte interface can be effectively suppressed.

[0017] Furthermore, the aprotic solvent includes at least one or more of anhydrous n-hexane, anhydrous cyclohexane, and anhydrous n-decane. This invention has found that using the above-mentioned aprotic solvent to dissolve electrophilic reagents can effectively prevent the electrophilic reagents from reacting with them, ensuring a thorough and complete reaction between the electrophilic reagents and the positive electrode active material, thus providing more effective protection for the positive electrode active material and improving the electrochemical performance of all-solid-state batteries.

[0018] Furthermore, the positive electrode active material includes at least one or more of lithium-rich manganese-based positive electrode materials, lithium cobalt oxide positive electrode materials, lithium iron phosphate positive electrode materials, and ternary positive electrode materials.

[0019] The preferred lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, where M is a transition metal and 0 < x < 1.

[0020] Furthermore, the mixing is carried out by mechanical grinding, the steps of which include: slowly adding the electrophilic reagent solution to the positive electrode active material at a rate of 1-5 mL / min, while simultaneously performing mechanical grinding, so that the electrophilic reagent solution and the positive electrode active material are fully wetted and mixed, and grinding is performed until the aprotic solvent is completely evaporated.

[0021] In the above technical solution, the electrophilic reagent and the positive electrode active material are mixed by slowly adding them dropwise at the specific rate, which ensures the safety and uniformity of the reaction. This invention has found that if the two are directly mixed in large quantities, a violent exothermic reaction will occur, leading to uneven reaction and preventing the formation of a dense, uniform interface layer, thus reducing the protective coating effect on the positive electrode material.

[0022] Preferably, the mechanical grinding refers to manual grinding using a mortar and pestle. Since the electrophilic reaction between the electrophilic reagent and the positive electrode active material is a spontaneous electrophilic reaction, if a one-pot process such as ductile iron is used, a violent and rapid reaction will occur during the raw material addition stage, leading to uneven reaction and difficulty in achieving the desired coating effect. This reduces the protective effect on the positive electrode material, and consequently, the electrochemical performance of the all-solid-state battery declines.

[0023] Preferably, the grinding time is 5-10 minutes. Controlling the grinding time within this range can effectively make the electrophilic reagent react more uniformly with the positive electrode active material, thereby improving the coating effect.

[0024] Preferably, the mixing is carried out under an inert atmosphere, specifically in an inert atmosphere glove box (both water and oxygen content <0.1 ppm).

[0025] Furthermore, the mechanical grinding process further includes: vacuum drying the product obtained by mechanical grinding at room temperature to 60 °C for 2-12 h to remove residual aprotic solvent.

[0026] The cathode material of the present invention does not require high-temperature sintering during preparation, which greatly reduces energy consumption. Furthermore, when it undergoes electrophilic reaction under mechanical grinding, it only requires a few minutes (5-10 min) of grinding reaction, which can effectively reduce reaction time and improve reaction efficiency.

[0027] In some optional embodiments of the present invention, the method for preparing the positive electrode material includes the following steps: (1) Dissolve the electrophilic reagent in an aprotic solvent that does not contain active hydrogen to form an electrophilic reagent solution with a concentration of 10-50 mg / mL; (2) In an inert atmosphere glove box (water and oxygen content both <0.1 ppm), at room temperature, the electrophilic reagent solution is slowly added dropwise to the positive electrode active material at a rate of 1-5 mL / min, while simultaneously performing manual grinding for 5-10 min to ensure that the electrophilic reagent solution is fully wetted and mixed with the positive electrode active material and that an electrophilic reaction occurs. The mass of the electrophilic reagent is 0.5-5% of the mass of the positive electrode active material. (3) The powder obtained after grinding is vacuum dried at room temperature to 50-60 °C for 2-12 h to completely remove residual aprotic solvent and obtain surface-modified cathode material.

[0028] Preferably, the electrophilic reagent is difluoromaleic anhydride or trifluoroacetic anhydride, the aprotic solvent is anhydrous n-hexane or anhydrous n-decane, and the positive electrode active material is Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2.

[0029] In one optional embodiment of the present invention, the method for preparing the positive electrode material includes the following steps: (1) Dissolve difluoromaleic anhydride in anhydrous n-hexane to form an electrophilic reagent solution with a concentration of 10 mg / mL; (2) In an inert atmosphere glove box (water and oxygen content both <0.1 ppm), at room temperature, the electrophilic reagent solution was slowly added dropwise to the Li at a rate of 3 mL / min. 1.2 Mn 0.54 Ni 0.13 Co 0.13 In O2, the material is simultaneously hand-ground for 5 minutes to ensure that the electrophilic reagent solution is fully impregnated and mixed with the positive electrode active material and that an electrophilic reaction occurs. The mass of the electrophilic reagent is Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 0.5% of the mass of O2; (3) The powder obtained after grinding is vacuum dried at room temperature to 50 °C for 6 h to completely remove residual aprotic solvent and obtain surface-modified cathode material.

[0030] In a second aspect, the present invention provides a cathode material prepared by the above-described preparation method.

[0031] A third aspect of the present invention provides a cathode material prepared by the above-described preparation method or the application of the above-described cathode material in the preparation of an all-solid-state battery.

[0032] The beneficial effects of the cathode material, its preparation method, and its application provided by this invention include at least the following: This invention utilizes an electrophilic reagent to undergo an electrophilic reaction with nucleophilic sites on the surface of the cathode active material, thereby depositing a thin and dense solid electrophilic interface layer in situ on the surface of the cathode active material. This solid electrophilic interface layer is firmly bonded to the cathode substrate and can achieve uniform coating and coverage on the surface of particles with complex morphologies. It has the characteristics of electronic insulation and ion conduction, which can prevent electron conduction between cathode active material particles, suppress side reactions at the cathode-electrolyte interface, prevent transition metal dissolution and lattice oxygen loss, significantly improve the working voltage window of the all-solid-state battery, and ensure smooth lithium ion transport, thereby improving the electrochemical performance of the all-solid-state battery. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in this 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 this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is a SEM image of the LMNO cathode material.

[0035] Figure 2 This is a SEM image of LMNO@DFMA-0.5% prepared in Example 1.

[0036] Figure 3 This is a charge-discharge diagram of Comparative Example 1 and Example 1 during the first week. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0039] The materials and equipment used in the following embodiments and comparative examples are as follows: Lithium-rich manganese-based cathode material: Li 1.2 Mn 0.54 Ni 0.13 Co0.13 O2 (LMNO) is in powder form with a particle size (D50) of 3-5 μm. SEM images of the LMNO cathode material are shown below. Figure 1 As shown, it can be purchased directly or prepared using the following methods of the present invention: Mn(NO3)2, Ni(NO3)2, and Co(NO3)2 were weighed according to a stoichiometric ratio of 0.54:0.13:0.13 and dissolved in deionized water. NaOH and ammonia were added with stirring, and the pH was controlled between 10 and 12. The precursor Mn was generated through a co-precipitation reaction. 0.54 Ni 0.13 Co 0.13 (OH)₂ precipitate was filtered, washed, and dried to obtain precursor powder. The precursor powder was then thoroughly mixed and ground with lithium source Li₂CO₃ at a stoichiometric ratio (Li:transition metal ≈ 1.2:1) to ensure homogeneity. The mixture was calcined at 900°C for 12 hours in an oxygen atmosphere, and after natural cooling, ground and sieved to obtain Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2.

[0040] The sulfide solid electrolyte, Li6PS5Cl (LPSC), can be purchased directly or prepared using the following method of the present invention: The raw materials were accurately weighed according to the stoichiometric ratio of Li6PS5Cl (Li2S:P2S5:LiCl = 3:0.5:1) and mixed to obtain a mixed powder. The mixed powder was placed in a zirconia ball mill jar with a ball-to-material mass ratio of approximately 1:40 and a rotation speed of 300 r / min for 12 hours (changing direction every hour) to obtain a precursor powder. The precursor powder was pressed into tablets and placed in a sealed quartz crucible. Under a nitrogen atmosphere, the temperature was increased to 500℃ at a rate of 5℃ / min and held for 12 hours. The sintered product was ground and passed through a 200-mesh sieve to obtain Li6PS5Cl.

[0041] All operations for assembling the molded battery were carried out in an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), using lithium-indium alloy (Li-In) as the negative electrode to prepare an all-solid-state battery.

[0042] Example 1 This embodiment provides a method for preparing a cathode material, which uses difluoromaleic anhydride (DFMA) for interface modification. The steps include: (1) In a glove box, 100 mg of DFMA electrophilic reagent was dissolved in 10 mL of anhydrous n-hexane to form an electrophilic reagent solution with a concentration of 10 mg / mL; (2) Weigh 5.0 g of powdered LMNO cathode material into an agate mortar. Using a pipette, slowly add 2.5 mL of the above electrophilic reagent solution (equivalent to 25 mg of DFMA, accounting for 0.5% of the mass of LMNO cathode material) at a rate of 3 mL / min. An electrophilic reaction will occur at room temperature. During the addition process, perform gentle and continuous manual grinding. Grind 3 times after each addition of reagent to ensure that the solution and powder are fully mixed. After grinding for 5 min, the anhydrous n-hexane solvent will completely evaporate, and the powder will return to a dry state. (3) The powder obtained after grinding was transferred to a vacuum drying oven and dried at 50°C for 6 h to completely remove the residual solvent, thus obtaining the surface-modified LMNO cathode material, denoted as LMNO@DFMA-0.5%, and its SEM image is shown below. Figure 2 As shown, Figure 2 It can be observed that a dense coating layer (solid electrophilic interface layer) is generated on the surface of the positive electrode active material particles after interface modification treatment. This solid electrophilic interface layer is uniform and has a thickness of 10 nm.

[0043] This embodiment also provides an all-solid-state battery, the preparation method of which includes: thoroughly mixing LMNO@DFMA and LPSC in a mortar at a mass ratio of 70:30 to prepare a positive electrode composite. Taking 20 mg of the positive electrode composite, pressing it into a positive electrode sheet with a diameter of 10 mm under a pressure of 360 MPa. Pressing 80 mg of LPSC powder into an electrolyte layer under the same pressure. Finally, using lithium indium alloy as the negative electrode, assembling an all-solid-state battery, and then conducting electrochemical performance tests.

[0044] Example 2 This embodiment provides a method for preparing a cathode material, which uses trifluoroacetic anhydride (TFAA) for interface modification, and the steps include: (1) In a glove box, 300 mg of TFAA electrophilic reagent was dissolved in 10 mL of anhydrous n-hexane to form an electrophilic reagent solution with a concentration of 30 mg / mL; (2) Weigh 5.0 g of powdered LMNO cathode material into an agate mortar, and slowly add 1.67 mL of the above electrophilic reagent solution (equivalent to 50 mg of TFAA, accounting for 1.0% of the mass of LMNO cathode material) dropwise at a rate of 3 mL / min using a pipette. An electrophilic reaction will occur at room temperature. During the dropwise addition, perform gentle and continuous manual grinding, grinding 3 times after each drop of reagent is added, so that the solution and powder are fully wetted and mixed. After grinding for 5 min, the anhydrous n-hexane solvent will completely evaporate, and the powder will return to a dry state. (3) The powder obtained after grinding was transferred to a vacuum drying oven and dried at 50 °C for 6 h to completely remove the residual solvent, and the surface-modified LMNO cathode material was obtained, denoted as LMNO@TFAA-1%. A solid electrophilic interface layer was formed on the surface of the cathode material. The solid electrophilic interface layer was uniform and had a thickness of 16 nm.

[0045] This embodiment also provides an all-solid-state battery, the preparation method of which is the same as that in Embodiment 1.

[0046] Example 3 This embodiment is basically the same as embodiment 1, except that in step (2), the mass of DFMA is adjusted to 2.0% of the mass of LMNO cathode material.

[0047] The cathode material obtained in this embodiment is denoted as LMNO@DFMA-2%. A solid electrophilic interface layer is formed on the surface of this cathode material. This solid electrophilic interface layer is uniform and has a thickness of 15 nm.

[0048] Example 4 This embodiment is basically the same as Embodiment 3, except that the concentration of the electrophilic reagent solution prepared by DFMA in step (1) is adjusted to 50 mg / mL. The obtained cathode material is denoted as LMNO@DFMA-2%-50. A solid electrophilic interface layer is formed on the surface of the cathode material. The solid electrophilic interface layer is uniform and has a thickness of 45 nm.

[0049] Example 5 This embodiment is basically the same as embodiment 1, except that the mass of DFMA in step (2) is adjusted to 5.0% of the mass of LMNO cathode material.

[0050] The cathode material obtained in this embodiment is denoted as LMNO@DFMA-5%. A solid electrophilic interface layer is formed on the surface of this cathode material. This solid electrophilic interface layer is uniform and has a thickness of 50 nm.

[0051] Example 6 This embodiment is basically the same as that of embodiment 1, except that the aprotic solvent in step (1) is replaced by anhydrous n-decane in equal volume of anhydrous n-hexane, the electrophilic reagent is replaced by DFMA in step (2), and the mass of TFAA in step (2) is adjusted to 2.0% of the mass of LMNO cathode material.

[0052] The cathode material obtained in this embodiment is denoted as LMNO@TFAA-2%. A solid electrophilic interface layer is formed on the surface of this cathode material. This solid electrophilic interface layer is uniform and has a thickness of 22 nm.

[0053] Example 7 This embodiment is basically the same as embodiment 3, except that in step (2), the LMNO cathode material and electrophilic reagent solution are mixed in large quantities at once instead of being added slowly.

[0054] The cathode material obtained in this embodiment is denoted as LMNO@DFMA-2%-mixed. A solid electrophilic interface layer is formed on the surface of this cathode material. This solid electrophilic interface layer is non-uniform and has a thickness of 30 nm.

[0055] Comparative Example 1 This comparative example provides a cathode material that has not undergone any interface modification treatment, denoted as Pristine LMNO.

[0056] In the preparation of solid-state batteries, LMNO and LPSC were directly mixed according to the method of Example 1, and then the solid-state batteries were prepared according to the same steps as in Example 1.

[0057] Comparative Example 2 This comparative example is basically the same as Example 3, except that the solvent is anhydrous ethanol, that is, step (1) is: dissolve 100 mg of DFMA electrophilic reagent in 10 mL of anhydrous ethanol to form an electrophilic reagent solution with a concentration of 10 mg / mL.

[0058] The cathode material obtained in this comparative example is denoted as LMNO@DFMA-2%-anhydrous ethanol.

[0059] Comparative Example 3 This comparative example provides a cathode material using a traditional mechanical mixing and coating method, the steps of which include: Weigh 5.0 g of powdered LMNO cathode material and directly add 25 mg of pre-ground lithium fluoride (LiF) nanoparticles (the mass of the LiF nanoparticles is 0.5% of the mass of the LMNO cathode material, and its particle size is D50 = 50 nm). Mechanically mix and grind in a mortar for 30 min to attempt to form a LiF coating layer on the LMNO surface. The resulting cathode material is denoted as LMNO+LiF-mixed.

[0060] The method for preparing all-solid-state batteries is the same as in Example 1.

[0061] The all-solid-state batteries assembled in the above embodiments and comparative examples were tested under the following conditions: test temperature 25°C, voltage window 2.0-4.8 V (vs. Li). + / Li). The results are shown in Table 1. Electrochemical performance test graphs of the all-solid-state batteries prepared in Example 1 and Comparative Example 1 are shown in... Figure 3 As shown.

[0062] As shown in Table 1, compared with the unmodified sample (Comparative Example 1), the cathode materials prepared by the method of the present invention (Examples 1-7) exhibit a significantly improved first-cycle coulombic efficiency. This indicates that the in-situ generated interface layer effectively suppresses the occurrence of side reactions at the cathode-electrolyte interface during the first charge, reducing irreversible capacity loss.

[0063] The battery corresponding to Pristine LMNO exhibited the fastest capacity decay, with a capacity retention of only 60.2% after 100 cycles. The LMNO+LiF-mixed battery showed slightly improved cycle stability compared to the Pristine LMNO battery, but the effect was limited, with a capacity retention of only 63.6% after 100 cycles. However, the batteries in Examples 1-7, treated with electrophilic agents, demonstrated excellent cycle stability, especially the battery corresponding to LMNO@DFMA-0.5%, which achieved a capacity retention of 88.2% after 100 cycles. The lower charge / discharge capacities of Examples 4 and 5 compared to Examples 3 and 1 were due to the larger amount of electrophilic agent used, resulting in an excessively thick solid electrophilic interface layer on the positive electrode surface, thus increasing impedance.

[0064] In Comparative Example 2, anhydrous ethanol was used as the solvent. It reacts directly with DFMA to form ester compounds, which leads to an increase in battery impedance and greatly reduces the protection effect on the positive electrode material, resulting in a significantly lower electrochemical performance than in Example 3.

[0065] In summary, the above long-cycle test results fully demonstrate that the solid electrophilic interface layer constructed using the method of this invention can effectively and continuously protect the cathode material and prevent the continuous occurrence of interfacial side reactions, thereby significantly improving the cycle life of the battery.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that, include: First, dissolve the electrophilic reagent in an aprotic solvent that does not contain active hydrogen to obtain an electrophilic reagent solution; The positive electrode active material is then mixed with the electrophilic reagent solution, so that the electrophilic reagent reacts with the nucleophilic sites on the surface of the positive electrode material to generate a solid electrophilic interface layer with electronic insulation and ion conduction properties in situ on the surface of the positive electrode active material.

2. The method for preparing the cathode material according to claim 1, characterized in that, The thickness of the solid electrophilic interface layer is 1-50 nm.

3. The method for preparing the cathode material according to claim 1 or 2, characterized in that, When the positive electrode active material is mixed with the electrophilic reagent solution, the mass of the electrophilic reagent is 0.5-5% of the mass of the positive electrode active material; Preferably, the concentration of the electrophilic reagent solution is 10-50 mg / mL.

4. The method for preparing the cathode material according to any one of claims 1-3, characterized in that, The electrophilic reagent is a fluorine-containing compound with strong electrophilic properties; Preferably, the fluorinated compound includes at least one or more of difluoromaleic anhydride, trifluoroacetic anhydride, tetrafluorosuccinic anhydride, pentafluoropropionic anhydride, trifluoromethanesulfonic anhydride, and trifluoroacetylfluoride.

5. The method for preparing the cathode material according to any one of claims 1-3, characterized in that, The aprotic solvent includes at least one or more of anhydrous n-hexane, anhydrous cyclohexane, and anhydrous n-decane.

6. The method for preparing the cathode material according to any one of claims 1-3, characterized in that, The positive electrode active material includes at least one or more of lithium-rich manganese-based positive electrode materials, lithium cobalt oxide positive electrode materials, lithium iron phosphate positive electrode materials, and ternary positive electrode materials.

7. The method for preparing the cathode material according to any one of claims 1-3, characterized in that, The mixing is performed by mechanical grinding, and the steps include: slowly adding the electrophilic reagent solution dropwise to the positive electrode active material while mechanically grinding, so that the electrophilic reagent solution and the positive electrode active material are fully wetted and mixed, and grinding is performed until the aprotic solvent is completely evaporated; Preferably, the mechanical grinding time is 5-10 minutes; Preferably, the mixing is carried out under an inert atmosphere; Preferably, the electrophilic reagent solution is added slowly at a rate of 1-5 mL / min.

8. The method for preparing the cathode material according to claim 7, characterized in that, The mechanical grinding process further includes: vacuum drying the product obtained by mechanical grinding at room temperature to 60 °C for 2-12 h to remove residual aprotic solvent.

9. The cathode material prepared by the preparation method according to any one of claims 1-8.

10. The application of the cathode material prepared by the preparation method according to any one of claims 1-8 or the cathode material according to claim 9 in the preparation of all-solid-state batteries.

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