Positive and negative electrode interface cooperative processing method of LTO-LMFP all-solid-state battery

Abstract

The invention discloses a positive and negative electrode interface cooperative processing method of an LTO-LMFP all-solid-state battery. The method comprises the following steps: preparing a lithium titanate negative electrode material by adopting a solid phase method or a hydrothermal method; mixing the prepared lithium titanate powder with a lithium phosphate precursor according to a certain proportion; after mixing, carrying out heat treatment on the mixture to promote the lithium phosphate to uniformly form a coating layer on the surfaces of the lithium titanate particles; a coprecipitation method or a solid-phase method is adopted to prepare the lithium manganese iron phosphate positive electrode material, so that the interface impedance is obviously reduced, and the physical contact and chemical compatibility between the electrode material and a sulfide solid electrolyte are effectively improved through a lithium phosphate coated lithium titanate negative electrode and a Mg-doped manganese phosphate coated lithium manganese iron phosphate positive electrode. The lithium phosphate and manganese phosphate coating layer is used as an interface buffer layer and can fill interface gaps, increase the effective contact area and provide a more stable ion transmission channel, so that the interface impedance between the positive electrode and the negative electrode and the solid electrolyte is greatly reduced, and rapid migration of lithium ions is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a method for collaboratively processing the positive and negative electrode interfaces of an LTO-LMFP all-solid-state battery. Background Art

[0002] Traditional lithium-ion batteries primarily use liquid organic electrolytes, which pose risks of leakage, flammability, and thermal runaway under extreme conditions such as overcharging, over-discharging, and short-circuiting, severely impacting battery safety. Furthermore, liquid electrolytes are prone to decomposition at high temperatures or during long-term cycling, leading to performance degradation and shortened battery life. To address these issues, all-solid-state battery technology has emerged.

[0003] All-solid-state batteries replace liquid electrolytes and separators with solid-state electrolytes, fundamentally eliminating the risks of leakage and combustion and significantly improving battery safety. At the same time, solid-state electrolytes have greater electrochemical stability and can be used with higher energy density electrode materials, such as lithium metal anodes, further increasing the battery's energy density. However, the industrialization of all-solid-state batteries still faces many challenges, one of the most critical bottlenecks being the interface between the solid-state electrode and the solid-state electrolyte.

[0004] Specifically, the limited contact area between the solid-state electrode and the solid-state electrolyte results in high interfacial impedance, hindering lithium-ion transmission and thus affecting the battery's rate performance. Furthermore, during the charge and discharge process, the volume change of the electrode material may cause the interface to detach, forming voids, further deteriorating the interfacial contact and accelerating battery capacity decay. At the same time, side reactions may occur between the electrode material and the solid-state electrolyte, generating a high-impedance interfacial layer, further hindering lithium-ion transmission and reducing the battery's cycle stability.

[0005] At present, research on the interface problems of all-solid-state batteries mainly focuses on the optimization of a single electrode or a single interface. For example, by surface coating or doping the positive or negative electrode materials, or optimizing the composition and morphology of the solid electrolyte, the interface performance can be improved. However, these single optimization strategies are often difficult to fully solve the complex interface compatibility issues between the positive and negative electrodes and the solid electrolyte. Especially under the requirements of high energy density and long cycle life, interfacial side reactions and interfacial impedance are still the key factors restricting the performance improvement of all-solid-state batteries.

[0006] Therefore, developing a processing method that can simultaneously and synergistically optimize the positive and negative electrode interfaces is of great significance for promoting the commercial application of all-solid-state batteries. Summary of the Invention

[0007] The object of the present invention is to provide a method for collaboratively processing the positive and negative electrode interfaces of an LTO-LMFP all-solid-state battery to solve the problems raised in the above background technology.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for collaboratively processing the positive and negative electrode interfaces of an LTO-LMFP all-solid-state battery, comprising the following steps:

[0009] S1. Prepare lithium titanate negative electrode material by solid phase method or hydrothermal method;

[0010] S2, mixing the prepared lithium titanate powder and lithium phosphate precursor in a certain proportion;

[0011] S3. After mixing, heat-treating the mixture to promote the uniform formation of a coating layer of lithium phosphate on the surface of the lithium titanate particles;

[0012] S4. preparing a lithium manganese iron phosphate positive electrode material by a co-precipitation method or a solid phase method, and introducing Mg doping during the preparation process;

[0013] S5, mixing the Mg-doped lithium manganese iron phosphate powder and the manganese phosphate precursor in a certain proportion;

[0014] S6, performing heat treatment after mixing, so that the manganese phosphate forms a uniform coating layer on the surface of the lithium manganese iron phosphate particles;

[0015] S7. Lithium sulfide, phosphorus pentasulfide, and lithium chloride are mixed according to a stoichiometric ratio, ball-milled under an inert atmosphere, and then heat-treated to obtain a lithium sulfur phosphorus chloride solid electrolyte powder with high ionic conductivity.

[0016] Preferably, in step S1, lithium carbonate and titanium dioxide are mixed in a stoichiometric ratio, ground evenly, and then sintered at a high temperature to obtain lithium titanate powder. The sintering temperature is controlled at 800-950° C., and the sintering time is 8-12 hours.

[0017] Preferably, in step S2, the mixing method may be wet mixing, such as ball milling or ultrasonic dispersion, or dry mixing.

[0018] Preferably, in step S3, the heat treatment temperature is 400-700°C, the time is 2-5 hours, and the thickness of the coating layer is controlled by adjusting the amount of lithium phosphate precursor and the heat treatment conditions, and the coating thickness is several nanometers to tens of nanometers.

[0019] Preferably: in step S4, the lithium source, manganese source, iron source and phosphorus source are mixed in a stoichiometric ratio, and an appropriate amount of magnesium source is added. The mixture undergoes coprecipitation, drying, pre-sintering and main sintering steps to obtain Mg-doped lithium manganese iron phosphate powder. The sintering temperature is 600-800°C and the sintering time is 5-10 hours.

[0020] Preferably, the doping amount of Mg is 0.5% to 5% of the total molar amount of lithium manganese iron phosphate.

[0021] Preferably, in step S6, the heat treatment temperature is 300-600°C, the time is 1-3 hours, and the coating thickness is several nanometers to tens of nanometers.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. Significantly Reduced Interfacial Impedance: The use of lithium phosphate-coated lithium titanate anodes and Mg-doped manganese phosphate-coated lithium manganese iron phosphate cathodes effectively improves the physical contact and chemical compatibility between the electrode materials and the sulfide solid electrolyte. The lithium phosphate and manganese phosphate coatings act as interfacial buffer layers, filling interfacial voids, increasing the effective contact area, and providing more stable ion transport channels. This significantly reduces the interfacial impedance between the positive and negative electrodes and the solid electrolyte, promoting rapid lithium ion migration.

[0024] 2. Effectively inhibiting interfacial side reactions: The lithium phosphate coating effectively isolates the lithium titanate negative electrode from direct contact with the sulfide solid electrolyte, preventing irreversible chemical reactions between the two. Similarly, the manganese phosphate coating protects the lithium iron manganese phosphate positive electrode from electrolyte corrosion. This synergistic interfacial protection mechanism fundamentally inhibits side reactions between the positive and negative electrodes and the solid electrolyte, reducing the formation of high-impedance interfacial products, thereby ensuring long-term interfacial stability and extending the battery's cycle life.

[0025] 3. Significantly improved rate performance: Due to the significant reduction in interfacial impedance and the optimization of the lithium-ion transmission path, the present invention enables lithium ions to shuttle more rapidly between the electrode and the electrolyte during the charge and discharge process. This directly manifests as a significant improvement in the battery's rate performance, that is, the battery can be charged and discharged rapidly at higher current densities, meeting the strict requirements of high-power output applications such as electric vehicles.

[0026] 4. Significantly Improved Cycling Stability: By effectively inhibiting interfacial side reactions and maintaining the integrity of the interface structure, the present invention can significantly slow the rate of battery capacity decay. The stable interface ensures that the structure of the electrode material and solid electrolyte is not damaged during long-term charge and discharge cycles, thereby significantly extending the service life of the all-solid-state battery and improving the battery's reliability and cost-effectiveness.

[0027] 5. Enhanced battery safety: The present invention utilizes a solid-state electrolyte, fundamentally eliminating the safety hazards of conventional liquid batteries, such as electrolyte leakage and combustion. Furthermore, by optimizing the positive and negative electrode interfaces, side reactions that could lead to thermal runaway are further suppressed, resulting in a more intrinsically safe all-solid-state battery fabricated by the present invention.

[0028] 6. Broaden the applicability of materials: The synergistic processing method proposed in this invention provides an effective solution for matching lithium titanate negative electrode and lithium manganese iron phosphate positive electrode with sulfide solid electrolyte, providing new ideas and technical support for the future development and application of more high-energy density, high-safety electrode materials and solid electrolyte systems. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0030] The present invention provides a technical solution:

[0031] 1. Preparation of LTO negative electrode material and Li3PO4 coating

[0032] 1.1 Preparation of LTO negative electrode materials

[0033] Lithium titanate (Li4Ti5O12, LTO) anode materials are prepared using conventional solid-phase or hydrothermal methods. For example, lithium carbonate (Li2CO3) and titanium dioxide (TiO2) are mixed in a stoichiometric ratio, ground uniformly, and then sintered at high temperature to produce LTO powder. The sintering temperature is typically controlled between 800 and 950°C, and the sintering time is 8 to 12 hours.

[0034] 1.2 Li3PO4 coating of LTO negative electrode

[0035] The prepared LTO powder is mixed with a lithium phosphate (Li3PO4) precursor (such as lithium dihydrogen phosphate or a lithium phosphate aqueous solution) in a specific proportion. The mixing method can be wet mixing (such as ball milling or ultrasonic dispersion) or dry mixing. After mixing, the mixture is heat treated, typically at a temperature of 400-700°C for 2-5 hours, to promote the uniform formation of a Li3PO4 coating on the surface of the LTO particles. The thickness of the coating can be controlled by adjusting the amount of Li3PO4 precursor and the heat treatment conditions, with the preferred coating thickness ranging from several nanometers to tens of nanometers.

[0036] The present invention coats LTO (lithium titanate) anode material with Li3PO4 (lithium phosphate). Li3PO4, an excellent lithium ion conductor, forms a uniform and dense coating on the surface of the LTO anode. This coating has the following functions:

[0037] Improve interface compatibility: The Li3PO4 coating layer can effectively improve the physical contact between the LTO negative electrode and the sulfide solid electrolyte, fill the interface gaps, increase the effective contact area, and thus reduce the interface impedance.

[0038] Inhibition of side reactions: The Li3PO4 coating layer can isolate the direct contact between the LTO negative electrode and the sulfide solid electrolyte, effectively inhibiting the chemical side reactions between the two, reducing the generation of high-impedance interface products, and thus maintaining the long-term stability of the interface.

[0039] Stable interface structure: During the charge and discharge process, the volume change of the LTO negative electrode is relatively small. Combined with the stability of the Li3PO4 coating layer, it can effectively maintain the integrity of the interface structure, avoid interface detachment, and ensure the smooth transmission of lithium ions.

[0040] 2. Preparation of LMFP cathode materials, Mg doping and manganese phosphate coating

[0041] 2.1 Preparation and Mg doping of LMFP cathode materials

[0042] Lithium manganese iron phosphate (LiMn1-xFexPO4, LMFP) cathode materials are prepared using a coprecipitation or solid-phase method, with Mg doping introduced during the preparation process. For example, a lithium source (such as lithium acetate), a manganese source (such as manganese acetate), an iron source (such as ferric acetate), and a phosphorus source (such as phosphoric acid) are mixed in a stoichiometric ratio, and an appropriate amount of a magnesium source (such as magnesium acetate) is added. The electrochemical performance of the material is optimized by adjusting the Mg doping level (typically 0.5% to 5% of the total molar weight of LMFP metal). The mixture undergoes coprecipitation, drying, pre-sintering, and main sintering to obtain Mg-doped LMFP powder. The sintering temperature is typically between 600 and 800°C, and the sintering time is 5 to 10 hours.

[0043] 2.2 Manganese phosphate coating of LMFP positive electrode

[0044] Mg-doped LMFP powder is mixed with a manganese phosphate precursor (e.g., a manganese phosphate solution) in a specific ratio. After mixing, the mixture is heat-treated at a temperature typically between 300°C and 600°C for 1 to 3 hours to form a uniform coating of manganese phosphate on the surface of the LMFP particles. The thickness of the coating is also controllable, with a preferred thickness ranging from several nanometers to tens of nanometers.

[0045] The present invention uses a treatment method combining Mg doping with manganese phosphate coating on LMFP (lithium manganese iron phosphate) cathode materials. This composite treatment aims to comprehensively improve the electrochemical performance and interfacial stability of the LMFP cathode:

[0046] Mg doping modification: By introducing an appropriate amount of Mg into the LMFP lattice, the crystal structure of LMFP can be optimized, improving its electronic conductivity and lithium-ion diffusion kinetics. The introduction of Mg helps stabilize the lattice structure and reduce structural strain during charge and discharge, thereby improving the cycling stability of LMFP.

[0047] Manganese phosphate coating: Based on Mg doping, the surface of the LMFP cathode is coated with manganese phosphate. The manganese phosphate coating has the following advantages:

[0048] Improved interface stability: The manganese phosphate coating can effectively protect the LMFP positive electrode from the corrosion of the sulfide solid electrolyte, inhibit the occurrence of interfacial side reactions, and reduce the increase of interfacial impedance.

[0049] Improve ion transfer efficiency: The manganese phosphate coating itself may have a certain lithium ion conductivity, or can provide a more stable ion transfer channel, thereby promoting the rapid migration of lithium ions at the interface between the positive electrode and the solid electrolyte.

[0050] Enhanced structural stability: The coating layer can enhance the structural integrity of LMFP particles and reduce particle breakage or interface detachment caused by volume changes during the cycle.

[0051] 3. Preparation of sulfide solid electrolyte

[0052] The present invention preferably uses a sulfide solid electrolyte, such as Li6PS5Cl. Li6PS5Cl can be prepared by solid-phase synthesis. Li2S, P2S5, and LiCl are mixed in a stoichiometric ratio, ball-milled under an inert atmosphere, and then heat-treated (e.g., sintered at 500-600°C for several hours) to obtain a Li6PS5Cl solid electrolyte powder with high ionic conductivity.

[0053] 4. Assembly of all-solid-state batteries

[0054] 4.1 Preparation of electrode sheets

[0055] The LTO negative electrode sheet is made by mixing Li3PO4-coated LTO negative electrode powder, a conductive agent (such as carbon black), and a binder (such as PVDF or PTFE) in a certain proportion, coating it on a current collector (such as copper foil), and compacting it after drying. The LMFP positive electrode sheet is made by mixing Mg-doped and manganese phosphate-coated LMFP positive electrode powder, a conductive agent, and a binder in a certain proportion, coating it on a current collector (such as aluminum foil), and compacting it after drying.

[0056] 4.2 Battery Assembly

[0057] The prepared LTO negative electrode sheet, sulfide solid electrolyte layer and LMFP positive electrode sheet are stacked in the order of negative electrode / solid electrolyte / positive electrode. The solid electrolyte layer can be formed by pressing the solid electrolyte powder into a thin sheet or by slurry coating. During the assembly process, it is necessary to carry out in an inert atmosphere glove box to avoid contact between the materials and moisture and oxygen in the air. After stacking is completed, the battery is cold-pressed or hot-pressed to ensure close contact between the layers, reduce the interfacial impedance, and finally form a complete all-solid-state battery.

[0058] 5. Performance Testing

[0059] Electrochemical performance tests, including charge-discharge cycle performance, rate performance, and electrochemical impedance spectroscopy (EIS), were conducted on the assembled all-solid-state batteries to verify the effectiveness of the proposed interface co-processing method. The expected results show that compared to batteries without interface co-processing, the interfacial impedance of the batteries of the present invention is significantly reduced, and the rate performance and cycling stability are greatly improved.

[0060] The core innovation of this invention lies in the coordinated processing of LTO negative electrode and LMFP positive electrode. The advantages of this coordinated strategy are:

[0061] Comprehensive suppression of side reactions: By simultaneously optimizing the positive and negative electrode interfaces, side reactions between the electrodes and the sulfide solid electrolyte can be effectively suppressed from both ends, forming a stable interface, thereby significantly reducing the irreversible capacity loss inside the battery.

[0062] Significantly improved rate performance: The Li3PO4 coating of the LTO negative electrode and the Mg doping and manganese phosphate coating of the LMFP positive electrode both help reduce the impedance of their respective interfaces and promote the rapid transport of lithium ions. The coordinated optimization of the positive and negative electrode interfaces makes the transmission path of lithium ions in the entire battery system smoother, thereby significantly improving the battery's rapid charge and discharge capabilities (rate performance).

[0063] Significantly improved cycling stability: By inhibiting side reactions and stabilizing the interface structure, this invention can effectively slow down battery capacity decay and extend battery life. The coordinated treatment of the positive and negative electrode interfaces ensures the stability and reliability of battery performance over long-term cycling.

[0064] The electrolyte used in this invention is a sulfide solid electrolyte, such as Li6PS5Cl. Sulfide solid electrolytes have high ionic conductivity and are key materials for achieving high-rate all-solid-state batteries. The interface co-processing method of this invention effectively addresses the interfacial compatibility issues between sulfide solid electrolytes and electrode materials, fully unleashing their performance.

[0065] In summary, the present invention effectively solves the key problems of high interface impedance and serious side reactions in all-solid-state batteries by synergistically treating the LTO negative electrode and LMFP positive electrode with Li3PO4 coating, Mg doping, and manganese phosphate coating, significantly improving the battery's rate performance and cycle stability, and providing a new technical approach for the development of high-performance and high-safety all-solid-state batteries.

[0066] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for collaboratively processing the positive and negative electrode interfaces of an LTO-LMFP all-solid-state battery, characterized in that: The following steps are involved: S1. Prepare lithium titanate negative electrode material by solid phase method or hydrothermal method; S2, mixing the prepared lithium titanate powder and lithium phosphate precursor in a certain proportion; S3. After mixing, heat-treating the mixture to promote the uniform formation of a coating layer of lithium phosphate on the surface of the lithium titanate particles; S4. preparing a lithium manganese iron phosphate positive electrode material by a co-precipitation method or a solid phase method, and introducing Mg doping during the preparation process; S5, mixing the Mg-doped lithium manganese iron phosphate powder and the manganese phosphate precursor in a certain proportion; S6, performing heat treatment after mixing, so that the manganese phosphate forms a uniform coating layer on the surface of the lithium manganese iron phosphate particles; S7. Lithium sulfide, phosphorus pentasulfide, and lithium chloride are mixed according to a stoichiometric ratio, ball-milled under an inert atmosphere, and then heat-treated to obtain a lithium sulfur phosphorus chloride solid electrolyte powder with high ionic conductivity.

2. The method for collaboratively processing the positive and negative electrode interfaces of an LTO-LMFP all-solid-state battery according to claim 1, characterized in that: In step S1, lithium carbonate and titanium dioxide are mixed according to a stoichiometric ratio, ground evenly, and then sintered at a high temperature to obtain lithium titanate powder. The sintering temperature is controlled at 800-950° C., and the sintering time is 8-12 hours.

3. The method for collaboratively processing the positive and negative electrode interfaces of an LTO-LMFP all-solid-state battery according to claim 1, wherein: In step S2, the mixing method can be wet mixing, such as ball milling and ultrasonic dispersion, or dry mixing.

4. The method for collaboratively processing the positive and negative electrode interfaces of an LTO-LMFP all-solid-state battery according to claim 1, characterized in that: In step S3, the heat treatment temperature is 400-700° C., the time is 2-5 hours, and the thickness of the coating layer is controlled by adjusting the amount of lithium phosphate precursor and the heat treatment conditions. The coating thickness is several nanometers to tens of nanometers.

5. The method for collaboratively processing the positive and negative electrode interfaces of an LTO-LMFP all-solid-state battery according to claim 1, characterized in that: In step S4, a lithium source, a manganese source, an iron source and a phosphorus source are mixed in a stoichiometric ratio, and an appropriate amount of a magnesium source is added. The mixture undergoes coprecipitation, drying, pre-sintering and main sintering steps to obtain Mg-doped lithium manganese iron phosphate powder. The sintering temperature is 600-800° C. and the sintering time is 5-10 hours.

6. The method for collaboratively processing the positive and negative electrode interfaces of an LTO-LMFP all-solid-state battery according to claim 5, characterized in that: The doping amount of Mg is 0.5% to 5% of the total molar amount of lithium manganese iron phosphate.

7. The method for co-processing the positive and negative electrode interfaces of an LTO-LMFP all-solid-state battery according to claim 1, characterized in that: In the step S6, the heat treatment temperature is 300-600° C., the time is 1-3 hours, and the coating thickness is several nanometers to tens of nanometers.