Positive electrode active material and preparation method thereof, positive electrode and solid-state battery

Abstract

The invention provides a positive electrode active material and a preparation method thereof, a positive electrode and a solid-state battery, and particularly relates to the technical field of solid-state batteries. The positive electrode active material has a core-shell structure, and the core-shell structure comprises a core layer and a coating layer coating the core layer; the core layer is made of a lithium-rich manganese-based material; and the coating layer is made of a fast ion conductor and a halide solid electrolyte. The fast ion conductor in the coating layer of the positive electrode active material can improve the ionic conductivity of the surface layer of the positive electrode active material, promote rapid migration of lithium ions and assist in improving the initial coulombic efficiency. Meanwhile, the coating layer improves the chemical stability of the positive electrode active material, effectively inhibits the interface side reaction between the positive electrode body and the sulfide electrolyte, and relieves the structural degradation in the cycle process. The coating layer can also be used as a buffer layer to inhibit stress generated by volume shrinkage and expansion in charge and discharge cycles, maintain good contact of an electrode interface, and realize improvement of the electrochemical performance of the material.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and in particular to a positive electrode active material and its preparation method, a positive electrode, and a solid-state battery. Background Technology

[0002] With the booming development of the electric vehicle industry, cathode materials that combine higher safety, higher capacity, and lower cost are attracting increasing attention. Among currently commercially available cathode materials, such as lithium carbonate (Li₂CO₃), lithium manganese oxide (LiMnO₄), lithium iron phosphate (LiFePO₄), high-nickel lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt aluminum oxide (NCA), lithium-rich manganese-based oxides stand out due to their significant advantages such as high specific energy, low cost, and excellent thermal stability. However, this material has inherent defects such as low initial coulombic efficiency, poor cycle stability, and significant voltage decay, which greatly restricts its practical application in electric vehicles and portable electronic devices. Nevertheless, the strong market demand for high-energy-density rechargeable batteries continues to drive the research and optimization of lithium-rich manganese-based cathode materials.

[0003] Under the current technological framework, research on lithium-rich manganese-based cathode materials still faces key technological bottlenecks, namely, how to effectively address core issues such as low initial coulombic efficiency, poor cycle stability, and rapid voltage decay rate. Currently, the academic community widely adopts acid washing processes to reduce the residual lithium content in lithium-rich manganese-based materials. Although this method can significantly improve the initial electrochemical performance of the cathode material, the acid washing process easily induces oxygen defects and transition metal dissolution, leading to a decrease in structural and thermal stability, ultimately adversely affecting the capacity retention and cycle performance of the cathode material.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a positive electrode active material and its preparation method, a positive electrode and a solid-state battery, aiming to solve at least one of the above-mentioned technical problems in the prior art.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A first aspect of the present invention provides a positive electrode active material having a core-shell structure, the core-shell structure comprising a core layer and a coating layer covering the core layer; the core layer is a lithium-rich manganese-based material; the coating layer is made of a fast ion conductor and a halide solid electrolyte.

[0007] Furthermore, the chemical formula of the lithium-rich manganese-based material is Li 1+α (Mn 0.54 Ni 0.13 Co 0.13 )1-β Mg β O 2-β / 2 F β / 2 Where 0.1≤α≤0.5, 0<β≤0.03.

[0008] Preferably, the mass ratio of the lithium-rich manganese-based material, the fast ion conductor, and the halide solid electrolyte is 100:(0.5~1.5):(0.5~1.5).

[0009] Furthermore, the fast ion conductor includes at least one of Li3PO4, LiNbO3, Li3BO3, and Li2ZrO3.

[0010] Preferably, the halide solid electrolyte includes at least one of Li3YCl6, Li3InCl6, Li3ScCl6, Li3YbCl6, Li3TbCl6, Li3YBr6, and Li3GdBr6.

[0011] A second aspect of the present invention provides a method for preparing the aforementioned positive electrode active material, comprising the following steps: A. A transition metal carbonate precursor, lithium source, and MgF2 are mixed and ground to obtain a first mixture; the first mixture is subjected to a first sintering to obtain a lithium-rich manganese-based material semi-finished product; B. The lithium-rich manganese-based material semi-finished product is pickled and vacuum dried to obtain the lithium-rich manganese-based material. C. The lithium-rich manganese-based material, fast ion conductor, and halide solid electrolyte are mixed and ground to obtain a second mixture, and then the second mixture is subjected to a second sintering to obtain a positive electrode active material.

[0012] Furthermore, the transition metal carbonate precursor is Mn 0.54 Ni 0.13 Co 0.13 CO3.

[0013] Preferably, in step A, the molar ratio of the transition metal carbonate precursor, lithium source, and MgF2 is (1-β):(1+α):β; where 0.1≤α≤0.5, 0<β≤0.03; Preferably, the first sintering is carried out in an oxygen atmosphere.

[0014] Preferably, the first sintering process includes a sequential lithiation process and a doping process.

[0015] Preferably, the lithiation process involves heating to 400-600°C at a rate of 1-5°C / min and holding at that temperature for 3-7 hours to complete the lithiation.

[0016] Preferably, the doping process involves heating to 700-900°C at a rate of 1-5°C / min and holding at that temperature for 10-14 hours to complete the doping process.

[0017] Further, in step B, the pickling is performed using an acid solution, wherein the acid in the acid solution includes at least one of oxalic acid, sorbic acid, and citric acid.

[0018] Preferably, the concentration of the acid solution is 0.05~0.5M.

[0019] Preferably, the pickling time is 20-60 minutes.

[0020] Preferably, the process further includes deionized water washing after the acid washing, followed by vacuum drying.

[0021] Preferably, the vacuum drying temperature is 60~90℃.

[0022] Further, in step C, the mass ratio of the lithium-rich manganese-based material, the fast ion conductor, and the halide solid electrolyte is 100:(0.5~1.5):(0.5~1.5).

[0023] Preferably, the second sintering is carried out under inert gas protection.

[0024] Preferably, the inert gas includes at least one of nitrogen, helium, and argon.

[0025] Preferably, the second sintering process is carried out by heating the temperature to 400-600°C at a rate of 1-5°C / min and holding the temperature for 4-6 hours.

[0026] A third aspect of the present invention provides a positive electrode comprising a current collector and a positive electrode active material composition coated on the current collector; The positive electrode active material composition includes a positive electrode active material, a sulfide solid electrolyte, and a conductive agent; The positive electrode active material is the positive electrode active material described in the first aspect, or the positive electrode active material prepared by the preparation method described in the second aspect.

[0027] Further, the positive electrode active material composition is pressurized and molded, and the current collector is attached to obtain the positive electrode.

[0028] Preferably, the pressure for the pressurization molding is 120~150MPa.

[0029] Preferably, the current collector is made of steel sheet.

[0030] A fourth aspect of the present invention provides a solid-state battery, comprising a negative electrode, a sulfide solid electrolyte layer, and the positive electrode described in the third aspect.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects: The positive electrode active material provided by this invention uses a lithium-rich manganese-based material as the core layer, which can fully leverage its advantages of high specific energy and low cost. The fast ion conductor in the coating layer can improve the ionic conductivity of the surface layer of the positive electrode active material, promote the rapid migration of lithium ions, and help improve the initial coulombic efficiency. At the same time, the coating layer formed by the fast ion conductor and the halide solid electrolyte improves the chemical stability of the positive electrode active material, effectively suppresses the interfacial side reactions between the positive electrode body and the sulfide electrolyte, and alleviates structural degradation during cycling. In addition, the coating layer can also act as a buffer layer to suppress the stress caused by the volume contraction and expansion of the core layer during charge and discharge cycles, maintain good contact at the electrode interface, and thus effectively improve the problems of poor cycle stability and rapid voltage decay, thereby improving the electrochemical performance of the material.

[0032] In the preparation method provided by this invention, acid washing can effectively remove residual lithium on the surface of the semi-finished product, reduce interfacial side reactions, and improve initial electrochemical performance. Secondary sintering not only ensures a tight bond between the coating layer and the core material, forming a complete and uniform core-shell structure, but also optimizes the ion conductivity and interfacial compatibility of the coating layer through the sintering process. Finally, through a continuous process of "doping-removal-coating", a positive electrode active material with excellent initial coulombic efficiency, cycle stability, and structural stability is efficiently prepared. Moreover, the overall process is easy to scale up and has good prospects for industrial application.

[0033] The cathode and solid-state battery provided by this invention, given the advantages of the aforementioned cathode active materials, enable the prepared cathode and solid-state battery to also have good initial coulombic efficiency, better stability, and better cycle performance. This fully meets the core requirements of high-energy-density batteries in terms of safety, long lifespan, and large-scale production, laying a key foundation for their application in electric vehicles, portable electronic devices, and other fields. Attached Figure Description

[0034] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific 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 from these drawings without creative effort.

[0035] Figure 1 This is a SEM image of the positive electrode active material obtained in Example 1. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, 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. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0037] In the following, the terms “comprising,” “having,” and their cognates, which may be used in various embodiments of the invention, are intended only to indicate a particular feature, number, step, operation, element, component, or combination thereof, and should not be construed as excluding, firstly, the presence of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, or adding the possibility of one or more features, numbers, steps, operations, elements, components, or combinations thereof.

[0038] A first aspect of the present invention provides a positive electrode active material having a core-shell structure, the core-shell structure comprising a core layer and a coating layer covering the core layer; the core layer is a lithium-rich manganese-based material; the coating layer is made of a fast ion conductor and a halide solid electrolyte.

[0039] The positive electrode active material provided by this invention uses a lithium-rich manganese-based material as the core layer, which can fully leverage its advantages of high specific energy and low cost. The fast ion conductor in the coating layer can improve the ionic conductivity of the surface layer of the positive electrode active material, promote the rapid migration of lithium ions, and help improve the initial coulombic efficiency. At the same time, the coating layer formed by the fast ion conductor and the halide solid electrolyte improves the chemical stability of the positive electrode active material, effectively suppresses the interfacial side reactions between the positive electrode body and the sulfide electrolyte, and alleviates structural degradation during cycling. In addition, the coating layer can also act as a buffer layer to suppress the stress caused by the volume contraction and expansion of the core layer during charge and discharge cycles, maintain good contact at the electrode interface, and thus effectively improve the problems of poor cycle stability and rapid voltage decay, thereby improving the electrochemical performance of the material.

[0040] Furthermore, the chemical formula of the lithium-rich manganese-based material is Li 1+α (Mn 0.54 Ni 0.13 Co 0.13 ) 1-β Mg β O 2-β / 2 F β / 2 Where 0.1≤α≤0.5, 0<β≤0.03.

[0041] Typically, but not restrictively, α can be, for example, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5, or any value in the range of 0.1 to 0.5; β can be, for example, 0.01, 0.012, 0.015, 0.018, 0.02, 0.022, 0.025, 0.028, or 0.03, or any value in the range of 0 < β ≤ 0.03.

[0042] Mg doping can increase the interlayer spacing of the 003 crystal plane, reduce the resistance to lithium-ion transport, and at the same time, the bonding effect of Mg-O bonds can suppress the release of oxygen in the cathode phase structure, thereby improving the structural stability of the material and reducing the capacity loss in the first cycle. F doping can stabilize the cathode material structure and suppress the release of oxygen caused by irreversible phase transition by replacing some oxygen elements in the bulk phase of the material.

[0043] Preferably, the mass ratio of the lithium-rich manganese-based material, the fast ion conductor, and the halide solid electrolyte is 100:(0.5~1.5):(0.5~1.5).

[0044] Typical, but not limiting, mass ratios of the lithium-rich manganese-based material, the fast-ion conductor, and the halide solid electrolyte can be, for example, 100:0.5:0.5, 100:0.6:0.6, 100:0.7:0.7, 100:0.8:0.8, 100:0.9:0.9, 100:1.0:1.0, 100:1.1:1.1, 100:1.2:1.2, 100:1.3:1.3, 10 The ratio can be 0:1.4:1.4, 100:1.5:1.5, or any combination of values ​​within the range of 100:(0.5~1.5):(0.5~1.5); the ratio of fast ion conductor to halide solid electrolyte can be the same or different, for example, it can also be 100:0.5:1.0, 100:0.8:1.2, 100:1.0:0.7, 100:1.2:0.9, 100:1.5:1.0, etc.

[0045] Furthermore, the fast ion conductor includes at least one of Li3PO4, LiNbO3, Li3BO3, and Li2ZrO3. Coating the surface of the lithium-rich manganese-based cathode material with the fast ion conductor Li3PO4 not only improves the ionic conductivity of the cathode material surface and mitigates side reactions between the cathode material and the solid electrolyte, but also stabilizes the surface oxygen through the bonding effect of PO bonds, further enhancing the structural and thermal stability of the material.

[0046] Preferably, the halide solid electrolyte includes at least one of Li3YCl6, Li3InCl6, Li3ScCl6, Li3YbCl6, Li3TbCl6, Li3YBr6, and Li3GdBr6. Coating the surface of a lithium-rich manganese-based material with a halide solid electrolyte, due to its excellent ionic conductivity, high oxidation resistance, and chemical stability to the cathode material, can suppress interfacial problems between the cathode bulk and the sulfide electrolyte caused by side reactions.

[0047] Fast ion conductors and halide solid electrolytes serve as buffer layers, suppressing problems such as poor contact at the cathode / sulfide electrolyte interface caused by the contraction and expansion of the cathode material during battery charging and discharging, thus significantly improving the overall performance of all-solid-state batteries.

[0048] A second aspect of the present invention provides a method for preparing the aforementioned positive electrode active material, comprising the following steps: A. A transition metal carbonate precursor, lithium source, and MgF2 are mixed and ground to obtain a first mixture; the first mixture is subjected to a first sintering to obtain a lithium-rich manganese-based material semi-finished product; B. The lithium-rich manganese-based material semi-finished product is pickled and vacuum dried to obtain the lithium-rich manganese-based material. C. The lithium-rich manganese-based material, fast ion conductor, and halide solid electrolyte are mixed and ground to obtain a second mixture, and then the second mixture is subjected to a second sintering to obtain a positive electrode active material.

[0049] In the preparation method provided by this invention, acid washing can effectively remove residual lithium on the surface of the semi-finished product, reduce interfacial side reactions, and improve initial electrochemical performance. Secondary sintering not only ensures a tight bond between the coating layer and the core material, forming a complete and uniform core-shell structure, but also optimizes the ion conductivity and interfacial compatibility of the coating layer through the sintering process. Finally, through a continuous process of "doping-removal-coating", a positive electrode active material with excellent initial coulombic efficiency, cycle stability, and structural stability is efficiently prepared. Moreover, the overall process is easy to scale up and has good prospects for industrial application.

[0050] Furthermore, the transition metal carbonate precursor is Mn 0.54 Ni 0.13 Co 0.13 CO3. In this article, TM is an abbreviation for "Transition Metal". The molar amount of a transition metal refers to the total molar amount of all transition metals.

[0051] Preferably, in step A, the molar ratio of the transition metal carbonate precursor, lithium source, and MgF2 is (1-β):(1+α):β; where 0.1≤α≤0.5, 0<β≤0.03; Preferably, the first sintering is carried out in an oxygen atmosphere. The selection of an oxygen atmosphere for the first sintering is mainly to ensure the performance of the lithium-rich manganese-based material semi-finished product: First, it provides a sufficient oxygen source to help build a complete and orderly layered crystal structure and avoid lattice defects caused by oxygen deficiency; second, it stabilizes the high valence states of transition metals such as Mn and Ni through oxidation, preventing structural distortion or ion transport obstruction caused by their reduction; and third, it oxidizes reducing impurities such as CO that may be generated from the decomposition of transition metal carbonate precursors into harmless CO2, avoiding the generation of electrochemically inactive impurity phases, ensuring material purity, and laying a good foundation for subsequent modification treatment.

[0052] Preferably, the first sintering process includes a sequential lithiation process and a doping process. During the lithiation process, the lithium source reacts fully with the transition metal carbonate precursor to initially form a layered crystal structure of lithium-rich manganese-based material, and the high valence state of the transition metal is stabilized through oxidation. The doping process promotes the uniform doping of Mg and F elements into the initially crystallized lattice, while avoiding lattice defects or uneven distribution of dopant elements due to oxygen deficiency, thus ensuring that the optimization effect of doping on the material's structural stability and ion transport performance is effectively exerted.

[0053] Preferably, the lithiation process involves heating to 400-600°C at a rate of 1-5°C / min and holding at that temperature for 3-7 hours to complete the lithiation.

[0054] Typical, but not limiting, the heating rate of the lithiation process can be, for example, 1 °C / min, 1.5 °C / min, 2 °C / min, 2.5 °C / min, 3 °C / min, 3.5 °C / min, 4 °C / min, 4.5 °C / min, or 5 °C / min, or any rate within the range of 1 to 5 °C / min; the target temperature can be, for example, 400 °C, 420 °C, 440 °C, 460 °C, 480 °C, 500 °C, 520 °C, 540 °C, 560 °C, 580 °C, or 600 °C, or any temperature within the range of 400 to 600 °C; the holding time can be, for example, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, or 7 h, or any duration within the range of 3 to 7 h.

[0055] Preferably, the doping process involves heating to 700-900°C at a rate of 1-5°C / min and holding at that temperature for 10-14 hours to complete the doping process.

[0056] Typical, but not limiting, heating rates during the doping process can be, for example, 1 °C / min, 1.5 °C / min, 2 °C / min, 2.5 °C / min, 3 °C / min, 3.5 °C / min, 4 °C / min, 4.5 °C / min, or 5 °C / min, or any rate within the range of 1 to 5 °C / min; target temperatures can be, for example, 700 °C, 720 °C, 740 °C, 760 °C, 780 °C, 800 °C, 820 °C, 840 °C, 860 °C, 880 °C, or 900 °C, or any temperature within the range of 700 to 900 °C; holding times can be, for example, 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h, or 14 h, or any duration within the range of 10 to 14 h.

[0057] Further, in step B, the pickling is performed using an acid solution, wherein the acid in the acid solution includes at least one of oxalic acid, sorbic acid, and citric acid.

[0058] Preferably, the concentration of the acid solution is 0.05~0.5M.

[0059] Typical, but not limiting, acid solution concentrations can be, for example, 0.05 M, 0.08 M, 0.1 M, 0.15 M, 0.2 M, 0.25 M, 0.3 M, 0.35 M, 0.4 M, 0.45 M, or 0.5 M, or any concentration in the range of 0.05 to 0.5 M.

[0060] Preferably, the pickling time is 20-60 minutes.

[0061] Typical, but not limiting, pickling times can be, for example, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, or any duration within the range of 20 to 60 min.

[0062] Preferably, the process further includes deionized water washing after the acid washing, followed by vacuum drying.

[0063] Preferably, the vacuum drying temperature is 60~90℃.

[0064] Typical, but not limiting, vacuum drying temperatures may be, for example, 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, 82°C, 85°C, 88°C, or 90°C, or any temperature within the range of 60°C to 90°C.

[0065] Further, in step C, the mass ratio of the lithium-rich manganese-based material, the fast ion conductor, and the halide solid electrolyte is 100:(0.5~1.5):(0.5~1.5).

[0066] Typical, but not limiting, mass ratios of lithium-rich manganese-based materials, fast-ion conductors, and halide solid electrolytes can be, for example, 100:0.5:0.5, 100:0.6:0.6, 100:0.7:0.7, 100:0.8:0.8, 100:0.9:0.9, 100:1.0:1.0, 100:1.1:1.1, 100:1.2:1.2, 100:1.3:1.3, 100 The ratios can be any combination within the range of 1.4:1.4, 100:1.5:1.5, or 100:(0.5~1.5):(0.5~1.5); the amounts of fast ion conductor and halide solid electrolyte can be the same or different, for example, 100:0.5:1.5, 100:0.8:1.2, 100:1.0:0.7, 100:1.2:0.9, 100:1.5:1.0, etc.

[0067] Preferably, the second sintering is carried out under inert gas protection.

[0068] Preferably, the inert gas includes at least one of nitrogen, helium, and argon.

[0069] Preferably, the second sintering process is carried out by heating the temperature to 400-600°C at a rate of 1-5°C / min and holding the temperature for 4-6 hours.

[0070] Typical, but not limiting, the heating rate of the second sintering process can be, for example, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, or 5℃ / min, or any rate within the range of 1 to 5℃ / min; the target temperature can be, for example, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃, or 600℃, or any temperature within the range of 400 to 600℃; the holding time can be, for example, 4 h, 4.2 h, 4.5 h, 4.8 h, 5 h, 5.2 h, 5.5 h, 5.8 h, or 6 h, or any duration within the range of 4 to 6 h.

[0071] A third aspect of the present invention provides a positive electrode comprising a current collector and a positive electrode active material composition coated on the current collector; The positive electrode active material composition includes a positive electrode active material, a sulfide solid electrolyte, and a conductive agent; The positive electrode active material is the positive electrode active material described in the first aspect, or the positive electrode active material prepared by the preparation method described in the second aspect.

[0072] Further, the positive electrode active material composition is pressurized and molded, and the current collector is attached to obtain the positive electrode.

[0073] Preferably, the pressure for the pressurization molding is 120~150MPa.

[0074] Typically, but not limitingly, the pressure applied during the compression molding process can be, for example, 120 MPa, 122 MPa, 124 MPa, 126 MPa, 128 MPa, 130 MPa, 132 MPa, 134 MPa, 136 MPa, 138 MPa, 140 MPa, 142 MPa, 144 MPa, 146 MPa, 148 MPa, or 150 MPa, or any value within the range of 120 to 150 MPa.

[0075] Preferably, the current collector is made of steel sheet.

[0076] A fourth aspect of the present invention provides a solid-state battery, comprising a negative electrode, a sulfide solid electrolyte layer, and the positive electrode described in the third aspect.

[0077] The cathode and solid-state battery provided by this invention, given the advantages of the aforementioned cathode active materials, enable the prepared cathode and solid-state battery to also have good initial coulombic efficiency, better stability, and better cycle performance. This fully meets the core requirements of high-energy-density batteries in terms of safety, long lifespan, and large-scale production, laying a key foundation for their application in electric vehicles, portable electronic devices, and other fields.

[0078] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0079] The transition metal carbonate precursor used in the examples and comparative examples is Mn. 0.54 Ni 0.13 Co 0.13 CO3 is prepared as follows: a 2 M mixed sulfate solution is prepared by mixing MnSO4·H2O, NiSO4·6H2O, and CoSO4·7H2O in a molar ratio of Mn:Ni:Co = 0.54:0.13:0.13.

[0080] A 5 L continuous co-precipitation reactor was used, with 1 L of ultrapure water as the bottom solution. The reactor was set at a constant temperature of 55°C and a stirring speed of 800 rpm. The mixed sulfate solution and 2 M Na2CO3 precipitant were simultaneously pumped in at rates of 1.5 mL / min and 1.2-1.6 mL / min, respectively. 0.2 M NH3·H2O was added as a complexing agent to balance Mn. 2+ / Ni 2+ / Co 2+ Differences in coprecipitation kinetics.

[0081] The pH of the reaction system was maintained at 7.8 ± 1.0 using an online pH monitoring system for 20 h. After filtration, alternating washing with ultrapure water / ethanol, and vacuum drying at 100°C for 12 h, the transition metal carbonate precursor (Mn) was obtained. 0.54 Ni 0.13 Co 0.13 CO3).

[0082] Example 1 This embodiment provides a positive electrode active material, and the preparation method is as follows: 1. Mix the transition metal carbonate precursor, lithium source (Li₂CO₃, Li:TM = 1.4375), and dopant (MgF₂, Mg:TM = 1% molar ratio). Grind thoroughly in a mortar until homogeneous, ensuring high dispersion of each component, to obtain the first mixture.

[0083] 2. Place the first mixture in a 100 mL corundum crucible and put it into an oxygen atmosphere box furnace. Increase the temperature to 500 °C at 3 °C / min and hold for 5 h to complete lithiation and preliminary crystallization; continue to increase the temperature to 800 °C at 3 °C / min and hold for 12 h to promote the synthesis of lithium-rich manganese-based materials and uniform doping of Mg / F elements. After naturally cooling to room temperature, obtain the semi-finished lithium-rich manganese-based material.

[0084] 3. Add 50 g of lithium-rich manganese-based material semi-finished product to 0.1 M oxalic acid solution and stir magnetically for 0.5 h. After filtration, wash with 1000 mL of deionized water and dry under vacuum at 80 ℃ to obtain lithium-rich manganese-based material.

[0085] 4. The lithium-rich manganese-based material, fast ion conductor Li3PO4, and halide solid electrolyte Li3YCL6 were mixed at a mass ratio of 100:1:1 and thoroughly ground in a mortar until homogeneous, ensuring high dispersion of each component. The mixture was calcined at 500℃ for 5 h in an Ar atmosphere (heating rate 3℃ / min), followed by natural cooling to obtain the final positive electrode active material. Scanning electron microscopy (SEM) was performed on this positive electrode active material, and the results are as follows: Figure 1 As shown, from Figure 1It can be seen that the primary particles of the positive electrode are around 100nm in size, with smooth particle surfaces. The fast ion conductor Li3PO4 and the halide solid electrolyte Li3YCL6 material are uniformly coated on the surface of the positive electrode particles.

[0086] Comparative Example 1 This comparative example provides a positive electrode active material, and the preparation method is as follows: 1. Mix the transition metal carbonate precursor and the lithium source (Li2CO3, Li:TM=1.4375). Grind thoroughly in a mortar until homogeneous, ensuring high dispersion of each component, to obtain the first mixture.

[0087] 2. Same as the steps in Example 1.

[0088] 3. Same as the steps in Example 1.

[0089] 4. Omit this step and do not perform the wrapping.

[0090] Comparative Example 2 This comparative example provides a positive electrode active material. The difference from Example 1 is that step 4 is omitted and no coating is performed. The remaining steps are the same as in Example 1 and will not be repeated here.

[0091] Comparative Example 3 This comparative example provides a positive electrode active material, and the preparation method is as follows: 1. Mix the transition metal carbonate precursor and the lithium source (Li2CO3, Li:TM=1.4375). Grind thoroughly in a mortar until homogeneous, ensuring high dispersion of each component, to obtain the first mixture.

[0092] 2. Same as the steps in Example 1.

[0093] 3. Same as the steps in Example 1.

[0094] 4. Same as the steps in Example 1.

[0095] Comparative Example 4 This comparative example provides a positive electrode active material. Unlike Example 1, in step 4, only the fast ion conductor Li3PO4 is used for coating. The remaining steps are the same as in Example 1 and will not be repeated here.

[0096] Comparative Example 5 This comparative example provides a positive electrode active material. The difference from Example 1 is that in step 4, the lithium-rich manganese-based material is mixed with fast ion conductors Li3PO4 and Li3BO3 at a mass ratio of 100:0.5:0.5. The remaining steps are the same as in Example 1 and will not be repeated here.

[0097] Comparative Example 6 This comparative example provides a positive electrode active material. Unlike Example 1, in step 4, only the halide solid electrolyte Li3YCL6 is used for coating. The remaining steps are the same as in Example 1 and will not be repeated here.

[0098] Test Example 1 Assemble a solid-state battery according to the following steps: 1. The lithium-rich manganese-based cathode material and the sulfide solid electrolyte Li7P3S obtained in the examples and comparative examples were respectively used. 11 The sulfide solid electrolyte and the conductive agent VGCF were added together in a mortar at a mass ratio of 80:20:2 and ground. After thorough grinding, the sulfide solid electrolyte and the conductive agent were uniformly coated on the surface of the positive electrode particles to obtain the positive electrode active material composition.

[0099] 2. Take 0.01g of the positive electrode active material composition, pressurize it at 130MPa in a mold battery, and attach a steel sheet as a current collector; take the sulfide electrolyte Li7P3S 11 0.1g is placed on the surface of the positive electrode layer and pressed at 130MPa to form a solid-state molded battery; a lithium indium negative electrode (0.1g) is then placed on top of the electrolyte layer and pressed at 130MPa to form a solid-state molded battery, and a steel sheet is attached as a current collector; the battery bolts are tightened to obtain a solid-state molded battery.

[0100] Solid-state battery test conditions: Charge and discharge at 45℃ and at rates of 0.1C / 0.33C / 0.5C / 1C / 2C / 5C, with charge and discharge cutoff voltages of 4.25V~2.0V, and charge and discharge cycle tests are performed.

[0101] The obtained data are recorded in Tables 1, 2, and 3.

[0102] Table 1 Cell Capacity

[0103] Table 2 Discharge rates of each group of cells

[0104] Table 3. Cells in each group cycle 1CC / 1CD

[0105] As can be seen from Table 1, the capacity and initial efficiency of Comparative Example 1 are lower than those of Comparative Examples 2 and 3 with single doping or coating modification, and are far lower than those of other comparative examples and Example 1. This is mainly due to the improved stability of the bulk structure of the doped sample and the improved lithium conductivity and interface stability of the coating fast ion material or halide electrolyte. Combining Tables 2 and 3, the rate performance and cycle performance are improved by single doping or coating fast ion conductors. The best rate performance and cycle performance are achieved when the doping and fast ion conductor and halide electrolyte are combined and coated.

[0106] Comparing Example 1 and Comparative Example 2, it is shown that coating the lithium-rich manganese-based cathode material with the fast ion conductor Li3PO4 and the halide solid electrolyte increases the ionic conductivity of the cathode material surface, mitigates side reactions between the cathode material and the solid electrolyte, and the PO bond formation stabilizes the surface oxygen. The halide solid electrolyte coating provides fast lithium conduction capability, thereby improving the material's electrical performance. Comparing Example 1 and Comparative Example 3, it is shown that doping the lithium-rich manganese-based cathode material with Mg expands the 003 crystal plane interlayer spacing, reduces lithium-ion transport resistance, and the Mg-O bonding suppresses oxygen release from the cathode bulk phase structure, improving material structural stability and reducing first-cycle capacity loss. F doping replaces some oxygen in the bulk phase, stabilizing the cathode material structure and suppressing oxygen release due to irreversible phase transitions.

[0107] Example 2 This embodiment provides a positive electrode active material. The difference from Example 1 is that LiNbO3 is used to replace Li3PO4 in step 4. The other raw materials and preparation methods are the same as in Example 1, and will not be described again here.

[0108] Example 3 This embodiment provides a positive electrode active material. Unlike Example 1, in step 4, the lithium-rich manganese-based material is mixed with fast ion conductors Li3NbO3, Li3BO3, and halide solid electrolyte Li3YCl6 at a mass ratio of 100:0.5:0.5:1 and thoroughly ground in a mortar until homogeneous, ensuring high dispersion of each component. It is then calcined at 500°C for 5 hours in an Ar atmosphere (heating rate 3°C / min), and naturally cooled to obtain the final positive electrode active material. The remaining steps are the same as in Example 1 and will not be repeated here.

[0109] Example 4 This embodiment provides a positive electrode active material. The difference from Example 1 is that Li3InCl6 is used instead of Li3YCl6 in step 4. The other raw materials and preparation methods are the same as in Example 1, and will not be described again here.

[0110] Example 5 This embodiment provides a positive electrode active material. Unlike Example 1, in step 4, the lithium-rich manganese-based material is mixed with the fast ion conductor Li3PO4, the halide solid electrolyte Li3YCl6, and Li3InCl6 at a mass ratio of 100:1:0.5:0.5 and thoroughly ground in a mortar until homogeneous, ensuring high dispersion of each component. It is then calcined at 500°C for 5 hours in an Ar atmosphere (heating rate 3°C / min), and naturally cooled to obtain the final positive electrode active material. The remaining steps are the same as in Example 1 and will not be repeated here.

[0111] Example 6 This embodiment provides a positive electrode active material. Unlike Example 1, in step 4, the lithium-rich manganese-based material is mixed with fast ion conductors Li3PO4, LiNbO3, and halide solid electrolytes Li3YCl6 and Li3InCl6 at a mass ratio of 100:0.5:0.5:0.5:0.5 and thoroughly ground in a mortar until homogeneous, ensuring high dispersion of each component. The mixture is then calcined at 500°C for 5 hours in an Ar atmosphere (heating rate 3°C / min) and allowed to cool naturally to obtain the final positive electrode active material. The remaining steps are the same as in Example 1 and will not be repeated here.

[0112] Test Example 2 Following the method described in Test Example 1, solid-state batteries were assembled using the materials from Examples 2-6, and their electrochemical performance was tested. The obtained data are recorded in Tables 4, 5, and 6.

[0113] Table 4 Cell Capacity

[0114] Table 5 Discharge rates of each group of cells

[0115] Table 6. Cells in each group cycle 1CC / 1CD

[0116] As shown in Table 4, in Example 1, the fast ion conductor using Li3PO4 exhibited the highest initial efficiency and specific capacity. Replacing it with LiNbO3 (Example 2) resulted in a slight decrease in initial efficiency, indicating that its lithium conductivity was slightly inferior to Li3PO4. The dual fast ion conductor combination (Example 3) showed slightly lower specific capacity and initial efficiency, possibly due to the heterogeneous structure formed between Li3BO3 and Li3PO4 during sintering, affecting interfacial ion transport. Li3InCl6 (Example 4) performed slightly worse than Li3YCl6 when used alone, but its initial efficiency was slightly higher, indicating better interfacial stability with the cathode material. The dual halide electrolyte (Example 5) showed specific capacity and initial efficiency close to those of Example 1, indicating good synergistic effect between the two halides. The composite coating (Example 6) showed overall performance similar to Example 1, but slightly lower, possibly due to a slight increase in interfacial impedance between the various materials.

[0117] As shown in Table 5, the composite coating strategy (Example 6) exhibits the best rate performance, indicating that the synergistic coating of multiple materials can effectively improve ion transport capability and alleviate interface polarization. Li3InCl6 (Example 4) shows poor rate performance when used alone, possibly because its lithium conductivity is slightly weaker than that of Li3YCl6. The dual fast ion conductor (Example 3) performs slightly worse than Li3PO4 alone, possibly because the heterogeneous interface formed after Li3BO3 sintering affects ion migration.

[0118] As shown in Table 6, the composite coating (Example 6) exhibits the best cycle stability, indicating that the synergistic effect of multiple materials can effectively alleviate side reactions between the cathode and electrolyte, and improve interfacial stability. The dihalide (Example 5) performs excellently, demonstrating a good synergistic effect between Li3YCl6 and Li3InCl6 in terms of interfacial compatibility and ionic conductivity. The dual fast ion conductor (Example 3) shows slightly poorer cycle performance, possibly due to insufficient structural stability of Li3BO3 after sintering, leading to interfacial deterioration during long-term cycling.

[0119] Example 7 This embodiment provides a positive electrode active material. The difference from Embodiment 1 is that in step 4, the lithium-rich manganese-based material is mixed with the fast ion conductor Li3PO4 and the halide solid electrolyte Li3YCL6 at a mass ratio of 100:0.5:1.5. The remaining steps are the same as in Embodiment 1 and will not be repeated here.

[0120] Example 8 This embodiment provides a positive electrode active material. The difference from Embodiment 1 is that in step 4, the lithium-rich manganese-based material is mixed with the fast ion conductor Li3PO4 and the halide solid electrolyte Li3YCL6 in a mass ratio of 100:1.5:0.5. The remaining steps are the same as in Embodiment 1 and will not be repeated here.

[0121] Example 9 This embodiment provides a positive electrode active material. The difference from Embodiment 1 is that in step 4, the lithium-rich manganese-based material is mixed with the fast ion conductor Li3PO4 and the halide solid electrolyte Li3YCL6 at a mass ratio of 100:0.2:1. The remaining steps are the same as in Embodiment 1 and will not be repeated here.

[0122] Example 10 This embodiment provides a positive electrode active material. The difference from Embodiment 1 is that in step 4, the lithium-rich manganese-based material is mixed with the fast ion conductor Li3PO4 and the halide solid electrolyte Li3YCL6 at a mass ratio of 100:1:0.2. The remaining steps are the same as in Embodiment 1 and will not be repeated here.

[0123] Example 11 This embodiment provides a positive electrode active material. The difference from Embodiment 1 is that in step 4, the lithium-rich manganese-based material is mixed with the fast ion conductor Li3PO4 and the halide solid electrolyte Li3YCL6 in a mass ratio of 100:0.2:0.2. The remaining steps are the same as in Embodiment 1 and will not be repeated here.

[0124] Example 12 This embodiment provides a positive electrode active material. The difference from Embodiment 1 is that in step 4, the lithium-rich manganese-based material is mixed with the fast ion conductor Li3PO4 and the halide solid electrolyte Li3YCL6 in a mass ratio of 100:2:2. The remaining steps are the same as in Embodiment 1 and will not be repeated here.

[0125] Test Example 3 Following the method described in Test Example 1, solid-state batteries were assembled using the materials from Examples 7-12, and their electrochemical performance was tested. The obtained data are recorded in Tables 7, 8, and 9.

[0126] Table 7 Cell Capacity

[0127] Table 8 Discharge rate of each group of cells

[0128] Table 9. Cells in each group cycle 1CC / 1CD

[0129] As shown in Table 7, Examples 1, 7, and 8 exhibited the best capacity and first-efficiency performance, while Examples 9, 10, 11, and 12 showed a decrease in both capacity and first-efficiency performance. This indicates that within a certain range, the type and amount of composite coating can effectively improve ion transport capability and alleviate interfacial polarization. Combined with Table 8, the surface coating amount of the cathode material affects lithium conductivity, which in turn affects rate performance. Combined with Table 9, the surface coating amount of the cathode material affects lithium conductivity and impedance. The more coating, the greater the impedance and the worse the lithium conductivity. The less coating, the more side reactions occur between the cathode and the electrolyte, and the less stable the surface structure of the cathode material, thus affecting cycle performance.

[0130] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, 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, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A positive electrode active material, characterized in that, It has a core-shell structure, the core-shell structure including a core layer and a covering layer covering the core layer; The core layer is a lithium-rich manganese-based material; The coating material includes fast ion conductors and halide solid electrolytes.

2. The positive electrode active material according to claim 1, characterized in that, The chemical formula of the lithium-rich manganese-based material is Li 1+α (Mn 0.54 Ni 0.13 Co 0.13 ) 1-β Mg β O 2-β / 2 F β / 2 ; Where 0.1≤α≤0.5, 0<β≤0.03; Preferably, the mass ratio of the lithium-rich manganese-based material, the fast ion conductor, and the halide solid electrolyte is 100:(0.5~1.5):(0.5~1.5).

3. The positive electrode active material according to claim 1, characterized in that, The fast ion conductor includes at least one of Li3PO4, LiNbO3, Li3BO3, and Li2ZrO3; Preferably, the halide solid electrolyte includes at least one of Li3YCl6, Li3InCl6, Li3ScCl6, Li3YbCl6, Li3TbCl6, Li3YBr6, and Li3GdBr6.

4. A method for preparing the positive electrode active material according to any one of claims 1 to 3, characterized in that, Includes the following steps: A. A transition metal carbonate precursor, lithium source, and MgF2 are mixed and ground to obtain a first mixture; the first mixture is subjected to a first sintering to obtain a lithium-rich manganese-based material semi-finished product; B. The lithium-rich manganese-based material semi-finished product is pickled and vacuum dried to obtain the lithium-rich manganese-based material. C. The lithium-rich manganese-based material, fast ion conductor, and halide solid electrolyte are mixed and ground to obtain a second mixture, and then the second mixture is subjected to a second sintering to obtain a positive electrode active material.

5. The preparation method according to claim 4, characterized in that, The transition metal carbonate precursor is Mn 0.54 Ni 0.13 Co 0.13 CO3; Preferably, in step A, the molar ratio of the transition metal carbonate precursor, the lithium source, and MgF2 is (1-β):(1+α):β; Where 0.1≤α≤0.5, 0<β≤0.03; Preferably, the first sintering is carried out in an oxygen atmosphere; Preferably, the first sintering process includes a sequential lithiation process and a doping process; Preferably, the lithiation process involves heating to 400-600°C at a rate of 1-5°C / min and holding at that temperature for 3-7 hours to complete the lithiation. Preferably, the doping process involves heating to 700-900°C at a rate of 1-5°C / min and holding at that temperature for 10-14 hours to complete the doping process.

6. The preparation method according to claim 4, characterized in that, In step B, the pickling is performed using an acid solution, wherein the acid in the acid solution includes at least one of oxalic acid, sorbic acid, and citric acid. Preferably, the concentration of the acid solution is 0.05~0.5M; Preferably, the pickling time is 20-60 minutes; Preferably, the process further includes deionized water washing after the pickling, followed by vacuum drying; Preferably, the vacuum drying temperature is 60~90℃.

7. The preparation method according to any one of claims 4 to 6, characterized in that, In step C, the mass ratio of the lithium-rich manganese-based material, the fast ion conductor, and the halide solid electrolyte is 100:(0.5~1.5):(0.5~1.5). Preferably, the second sintering is carried out under inert gas protection; Preferably, the inert gas includes at least one of nitrogen, helium, and argon; Preferably, the second sintering process is carried out by heating the temperature to 400-600°C at a rate of 1-5°C / min and holding the temperature for 4-6 hours.

8. A positive electrode, characterized in that, Compositions including current collectors and positive electrode active materials coated on the current collectors; The positive electrode active material composition includes a positive electrode active material, a sulfide solid electrolyte, and a conductive agent; Wherein, the positive electrode active material is the positive electrode active material according to any one of claims 1 to 3, or the positive electrode active material prepared by the preparation method according to any one of claims 4 to 7.

9. The positive electrode according to claim 8, characterized in that, The positive electrode active material composition is pressurized and molded, and then attached to the current collector to obtain the positive electrode; Preferably, the pressure applied during the pressure molding process is 120~150MPa; Preferably, the current collector is made of steel sheet.

10. A solid-state battery, characterized in that, It includes a negative electrode, a sulfide solid electrolyte layer, and a positive electrode as described in claim 8 or 9.

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