Lithium-rich manganese-based cathode materials and their preparation methods, electrochemical devices

Abstract

This application provides a lithium-rich manganese-based cathode material, its preparation method, and an electrochemical device. The lithium-rich manganese-based cathode material includes a substrate material and a coating layer. The coating layer includes a lithium hexafluorozirconate coating layer located on the surface of the substrate material and a fluoride coating layer located on the side of the lithium hexafluorozirconate coating layer away from the substrate material. The chemical formula of the substrate material is Li(Li₂)₃. x Mn a Ni 1‑a‑ b Al b )O 2‑δ Where 0.05≤x≤0.33, 0

Description

Technical Field

[0001] This application relates to the field of new energy technology, specifically to a lithium-rich manganese-based cathode material and its preparation method, as well as an electrochemical device. Background Technology

[0002] With the rapid growth in demand for electric vehicles and large-scale energy storage, the development of high-energy-density and long-cycle-life lithium-ion battery cathode materials has become a current research hotspot. The specific capacity of traditional layered oxides (such as LiCoO2 and NCM) is approaching its theoretical limit (approximately 200 mAh / g), making it difficult to meet the future demand for battery energy densities exceeding 500 Wh / kg. Against this backdrop, Li-rich Mn-based layered oxides (LRMOs), due to their unique anionic redox reaction mechanism, can provide high reversible specific capacity while also offering advantages such as low cost (low / cobalt-free) and high operating voltage, and are considered one of the optimal choices for next-generation high-energy lithium-ion battery cathode materials.

[0003] However, the practical application of lithium-rich manganese-based cathode materials still faces severe challenges. For example, during cycling, lithium-rich manganese-based cathode materials experience irreversible oxygen loss and layered-spinel phase transitions, leading to voltage decay and capacity degradation. Under high voltage, lithium-rich manganese-based cathode materials can also undergo interfacial side reactions such as oxidative decomposition with the electrolyte interface (e.g., sulfide solid electrolytes). Furthermore, the poor solid-solid interface contact between lithium-rich manganese-based cathode materials and the electrolyte interface results in high lithium-ion transport impedance, affecting rate performance. During lithium deintercalation and deintercalation, lattice expansion can induce electrode cracks, damaging interfacial stability. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above technical problems, this application provides a lithium-rich manganese-based cathode material.

[0005] In addition, this application also provides a method for preparing a lithium-rich manganese-based cathode material and an electrochemical device using the lithium-rich manganese-based cathode material.

[0006] In a first aspect, embodiments of this application provide a lithium-rich manganese-based cathode material, which includes a matrix material and a coating layer, comprising a lithium hexafluorozirconate coating layer located on the surface of the matrix material and a fluoride coating layer located on the side of the lithium hexafluorozirconate coating layer away from the matrix material. The chemical formula of the matrix material is Li(Li₂)₃. x Mn a Ni 1-a-b Al b )O 2-δ Where 0.05≤x≤0.33, 0 <a<0.6,0.1≤b≤0.25,0≤δ≤0.2。

[0007] Based on the first aspect, in some possible embodiments, the fluoride coating layer includes at least one of AlF3, TiF4, and ZrF4.

[0008] Based on the first aspect, in some possible embodiments, the mass percentage of the lithium hexafluorozirconate coating to the substrate material is 1.0wt% to 3.0wt%; and / or the mass percentage of the fluoride coating to the substrate material is 0.05wt% to 0.30wt%.

[0009] Secondly, this application provides a method for preparing a lithium-rich manganese-based cathode material. The method includes: mixing a manganese precursor, a lithium source, and an aluminum source, and performing a first sintering to obtain a matrix material; mixing the matrix material with a hexafluorozirconic acid solution and drying it, followed by a second sintering to react on the surface of the matrix material to generate a lithium hexafluorozirconate coating layer, thereby obtaining an intermediate material; and mixing the intermediate material with a fluoride and performing a third sintering to form a fluoride coating layer on the surface of the intermediate material, thereby obtaining a lithium-rich manganese-based cathode material.

[0010] Based on the second aspect, in some possible embodiments, the concentration of the hexafluorozirconic acid solution is 1.0 mol / L to 5.0 mol / L; and / or the mass / volume ratio of the matrix material to the hexafluorozirconic acid solution is 10 kg: (0.1 L to 1.0 L).

[0011] Based on the second aspect, in some possible embodiments, the fluoride includes at least one of AlF3, TiF4 and ZrF4; and / or the mass percentage of the fluoride to the matrix material is 0.05wt% to 0.30wt%.

[0012] Based on the second aspect, in some possible embodiments, the manganese-based precursor includes nickel manganese hydroxide (Ni). x Mn y (OH)2, where x+y=1, 0.2≤x<0.5.

[0013] Based on the second aspect, in some possible embodiments, the mass percentage of the aluminum source relative to the total mass of the manganese-based precursor, the lithium source, and the aluminum source is 0.05wt% to 0.5wt%; and / or the aluminum source includes at least one of aluminum hydroxide and aluminum oxide.

[0014] Based on the second aspect, in some possible embodiments, the drying temperature is 80℃~120℃; the conditions for the first sintering include: heating to 750℃~950℃ at a heating rate of 2℃ / min~3℃ / min and sintering for 10~15h; the conditions for the second sintering include: heating to 300℃~600℃ at a heating rate of 2℃ / min~3℃ / min and sintering for 2~5h; the conditions for the third sintering include: heating to 550℃~750℃ at a heating rate of 2℃ / min~3℃ / min and sintering for 7~12h.

[0015] Thirdly, embodiments of this application also provide an electrochemical device, the electrochemical device including a positive electrode sheet, the positive electrode sheet including a positive electrode material, the positive electrode material being the aforementioned lithium-rich manganese-based positive electrode material.

[0016] Compared to existing technologies, the lithium-rich manganese-based cathode material provided in this application adopts an innovative double-layer coating structure design. The lithium hexafluorozirconate coating layer can serve as a "fast ion conductor layer," while the fluoride coating layer can serve as a "barrier and protective layer." The two work synergistically to improve the rate performance of the lithium-rich manganese-based cathode material, effectively suppress the dissolution of manganese ions, reduce interfacial side reactions between the lithium-rich manganese-based cathode material and the electrolyte, and mitigate volume changes during cycling, thereby improving the cycle stability and structural stability of the lithium-rich manganese-based cathode material. The lithium-rich manganese-based cathode material provided in this application employs a unique double-coating structure, effectively alleviating problems such as cathode / electrolyte interface instability and manganese dissolution under high voltage. This allows the lithium-rich manganese-based cathode material to simultaneously possess advantages such as high capacity, excellent rate performance, and long cycle life, making it suitable for next-generation high-energy-density lithium-ion battery systems. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a lithium-rich manganese-based cathode material provided in an embodiment of this application.

[0018] Figure 2 This is a process flow diagram of a method for preparing a lithium-rich manganese-based cathode material according to an embodiment of this application.

[0019] Figure 3 These are scanning electron microscope (SEM) images of the lithium-rich manganese-based cathode materials in Examples 1, 3, and Comparative Example 1 of this application. Figure 3 Figure (a-1) is a scanning electron microscope image of the lithium-rich manganese-based cathode material in Comparative Example 1, magnified 10,000 times. Figure 3 Figure (a-2) shows a scanning electron microscope image of the lithium-rich manganese-based cathode material in Comparative Example 1, magnified 50,000 times. Figure 3Figure (b-1) is a scanning electron microscope image of the lithium-rich manganese-based cathode material in Example 1, magnified 10,000 times. Figure 3 Figure (b-2) is a scanning electron microscope image of the lithium-rich manganese-based cathode material in Example 1, magnified 50,000 times. Figure 3 Figure (c-1) is a scanning electron microscope image of the lithium-rich manganese-based cathode material in Example 3, magnified 10,000 times. Figure 3 Figure (c-2) is a scanning electron microscope image of the lithium-rich manganese-based cathode material in Example 3, magnified 50,000 times.

[0020] Figure 4 The graph shows the test results of the first discharge capacity and first efficiency of the batteries prepared with lithium-rich manganese-based cathode materials in Examples 1-6 and Comparative Examples 1-2 of this application.

[0021] Figure 5 The graph shows the high-temperature cycling performance test results of the batteries prepared by the lithium-rich manganese-based cathode materials in Examples 1-6 and Comparative Examples 1-2 of this application. Detailed Implementation

[0022] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.

[0023] Please see Figure 1 As shown, this application provides a novel lithium-rich manganese-based cathode material 100. The lithium-rich manganese-based cathode material 100 includes a substrate material 10 and a coating layer 20. The coating layer 20 includes a lithium hexafluorozirconate coating layer 21 located on the surface of the substrate material 10 and a fluoride coating layer 22 located on the side of the lithium hexafluorozirconate coating layer 21 away from the substrate material 10. The chemical formula of the substrate material 10 is Li(Li₂)₃. x Mn a Ni 1-a-b Al b )O 2-δ Where 0.05≤x≤0.33, 0 <a<0.6,0.1≤b≤0.25,0 ≤δ ≤0.2。

[0024] This application selects lithium-rich manganese-based layered oxides (LRMOs) as the matrix material. Specifically, the chemical formula of the matrix material is Li(Li)x Mn a Ni 1-a-b Al b )O 2-δ , where 0.05 ≤ x ≤ 0.33, 0 < a < 0.6, 0.1 ≤ b ≤ 0.25, 0 ≤ δ ≤ 0.2. This matrix material has a high specific capacity (up to 250 - 300 mAh / g), and at the same time has the advantages of low cost (low cobalt) and high working voltage (3.0 - 4.8 V vs. Li + / Li). The anions and cations of this matrix material can carry out redox reactions synergistically: during the insertion and extraction of lithium ions, not only transition metals (such as Mn and Ni) contribute to electron transfer, but also oxygen ions (O 2- ) in the lattice participate in the reversible oxidation reaction (O 2- → O - / O2 n- ), thereby effectively improving the capacity. The manganese-rich characteristic of the matrix material can also reduce costs and improve the thermal stability of the matrix material. Moreover, the matrix material is doped with Al element, which can optimize the lattice structure of the matrix material, improve the morphological uniformity of the matrix material particles at the same time, provide more channels for the diffusion of lithium ions, and increase the lithium ion diffusion rate. In addition, LRMOs can be applied to the all-solid-state battery (ASSBs) system. Based on the above advantages of LRMOs, the combination of LRMOs and solid electrolyte has broad prospects. Among them, the wide electrochemical window (greater than 5 V) of the solid electrolyte can inhibit the decomposition of the solid electrolyte under high voltage, and the non-flammable characteristic of the solid electrolyte can alleviate the thermal runaway risk caused by oxygen evolution in traditional liquid batteries.

[0025] To further improve the electrochemical performance and structural stability of the matrix material, a double coating layer is designed on the surface of the matrix material in this application. This double coating layer includes a lithium hexafluorozirconate coating layer and a fluoride coating layer.

[0026] Among them, the lithium hexafluorozirconate (Li2ZrF6) coating layer is located on the side of the overall coating layer closer to the matrix material. This lithium hexafluorozirconate coating layer has excellent lithium ion conduction performance (ionic conductivity greater than 10 -4 S / cm). The lithium hexafluorozirconate coating layer can effectively promote the rapid transport of lithium ions on the surface of the lithium-rich manganese-based cathode material particles and at the lithium-rich manganese-based cathode material / electrolyte interface by providing three-dimensional lithium ion channels, acting as a "fast ion conductor layer", thereby improving the rate performance of the lithium-rich manganese-based cathode material. At the same time, the strong electronegativity of Zr 4+ in the lithium hexafluorozirconate coating layer is beneficial to stabilizing the valence states of transition metals on the surface of the matrix material and improving the surface chemical stability of the lithium-rich manganese-based cathode material.

[0027] Furthermore, lithium hexafluorozirconate coatings possess unique advantages compared to other lithium-ion conductors. For instance, compared to oxide lithium-ion conductors (such as Li3PO4), Li2ZrF6, as a fluorophosphate, inherently exhibits better tolerance to HF and better chemical compatibility with fluoride coatings. While Li3PO4 can also perform lithium-ion transport, it suffers from poor stability in the acidic environment of HF, readily generating byproducts such as LiF, metal phosphates, or metal titanates, leading to increased interfacial impedance between the cathode and electrolyte. Secondly, compared to oxide solid electrolytes (such as those containing Ti...),... 4+ LLTO and Co-containing 4+ When LCO and LRMOs are charged to high voltages (>4.6V), the surface of LRMOs exhibits strong oxidizing properties, causing many oxide solid electrolytes to be oxidized and decomposed, resulting in a sharp increase in interfacial impedance. Meanwhile, the F in Li₂ZrF₆... - With its high electronegativity, Li₂ZrF₆ is difficult to further oxidize, thus exhibiting better high-voltage stability. Compared to sulfide electrolytes (such as LPS and LGPS), Li₂ZrF₆ has a wider electrochemical window and flame-retardant properties, while sulfide electrolytes have a narrow electrochemical window, undergo severe oxidative decomposition under high voltage, and are extremely sensitive to H₂O and O₂, reacting adversely with active oxygen released from the surface of LRMOs, making them unsuitable for use. Therefore, using lithium hexafluorozirconate as the inner layer has certain advantages.

[0028] The fluoride coating is located on the side of the overall coating away from the substrate material, which can effectively isolate the substrate material and the electrolyte / electrolyte. The fluoride coating has the following characteristics: (1) High chemical stability: The fluoride coating has high chemical stability, especially strong resistance to HF acid corrosion. The fluoride can preferentially react with trace amounts of HF in the electrolyte to form a stable interface to protect the substrate material, thereby reducing the dissolution of transition metals in the substrate material; (2) Wide electrochemical window: The fluoride is extremely stable at high voltage (above 4.5V) and is not easily oxidized and decomposed, which can provide long-lasting protection for lithium-rich manganese-based cathode materials; (3) Physical barrier effect: The fluoride can form a dense and uniform fluoride coating on the surface of the substrate material, which can effectively physically isolate the substrate material from direct contact with the electrolyte, thereby reducing side reactions and gas generation.

[0029] Specifically, the fluoride coating layer may include at least one of AlF3, TiF4, and ZrF4, all of which possess high chemical stability, a wide chemical window, and high structural stability. Further, AlF3 is preferred as the fluoride coating layer because it has one of the widest electrochemical windows among all fluorides (stable voltage can reach above 5.5V); AlF3 exhibits a strong thermodynamic tendency to react with HF, which can sustainably maintain the stability of the cathode / electrolyte interface environment; and AlF3 possesses high chemical stability (Al-F bond energy as high as 664 kJ·mol⁻¹). -1 It can effectively block direct contact between the matrix material and the electrolyte, and suppress transition metal ions (especially Mn). 2+ It can prevent the dissolution of electrolytes under high voltage and suppress the decomposition reaction of electrolytes. The AlF3 layer also has excellent mechanical strength, which can buffer the volume change of the matrix material during cycling. In addition, while providing optimal protection, AlF3 has extremely low raw material cost (Al and F elements are abundant) and simple synthesis process, perfectly balancing the requirements of performance, cost and scalability.

[0030] Furthermore, TiF4 and ZrF4 also have unique advantages: (1) TiF4 and ZrF4 can react with Li to generate lithium-containing fluoride fast ion conductors (fluoride coatings), giving the fluoride coatings both passivation and ion conduction functions; (2) compared to Al 3+ Ti 4+ and Zr 4+ The ionic radius is larger and the electronegativity is higher, which is more compatible with surface lattice oxygen (O). 2- (3) Ti has a stronger binding energy, which greatly inhibits oxygen loss; 4+ and Zr 4+ High valence states can better suppress transition metals (especially Mn) in the matrix material. 3+ The reduction and migration of ) slows down the transformation of the layered structure to the spinel phase, thereby delaying voltage decay.

[0031] Furthermore, the inner lithium hexafluorozirconate layer requires the protection of the outer fluoride layer. Without the fluoride coating, the lithium hexafluorozirconate coating layer, when exposed to high voltage or acidic electrolytes for extended periods, may be oxidized or corroded, leading to functional degradation. While the outer fluoride coating layer possesses high stability, its poor ionic conductivity, if directly applied to the substrate material, would severely hinder lithium-ion transport, resulting in a decrease in the capacity and rate performance of the lithium-rich manganese-based cathode material. Therefore, the inner lithium hexafluorozirconate layer and the outer fluoride layer together constitute an "acid-resistant buffer zone," acting as both an ion-conducting inner layer as a "buffer" and "transition," while effectively eliminating the corrosive effects of HF, reducing the dissolution of transition metals from the substrate material, and improving the stability of the substrate material. This synergistic design of a "high-conductivity lithium inner layer combined with a high-stability outer layer" achieves "unimpeded and safe" ion transport in the lithium-rich manganese-based cathode material.

[0032] In some embodiments, the mass percentage of the lithium hexafluorozirconate coating to the substrate material can be 1.0 wt% to 3.0 wt%, which is beneficial for effectively improving the conductivity of the lithium-rich manganese-based cathode material. This mass percentage can, exemplarily, be 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, or any value within the range of any two of the above values. The mass percentage can further be 1.5 wt% to 2.5 wt%.

[0033] In some embodiments, the mass percentage of the fluoride coating layer to the matrix material can be 0.5 wt% to 3.0 wt%, which is beneficial for balancing the stability and capacity performance of the lithium-rich manganese-based cathode material. This mass percentage can, exemplarily, be 0.05 wt%, 0.10 wt%, 0.15 wt%, 0.20 wt%, 0.25 wt%, 0.30 wt%, or any value within the range of any two of the above values. The mass percentage can further be 0.05 wt% to 0.20 wt%.

[0034] Compared with existing technologies, the lithium-rich manganese-based cathode material of this application adopts a unique lithium hexafluorozirconate-fluoride double coating structure, which effectively solves the key problems of interface instability and manganese dissolution in traditional lithium-rich manganese-based materials under high voltage, enabling the lithium-rich manganese-based material to have advantages such as high capacity, excellent rate performance and long cycle life.

[0035] Please see Figure 2 As shown in the figure, this application provides a method for preparing a lithium-rich manganese-based cathode material, which specifically includes the following steps:

[0036] Step S1: The manganese-based precursor, lithium source and aluminum source are mixed and sintered for the first time to obtain the matrix material.

[0037] Specifically, manganese-based precursors, lithium sources, and aluminum sources are batched using a high-speed mixer according to a specific Li / Me ratio, and mixed evenly to obtain a dry mixture. The dry mixture is then fed through a crucible and subjected to a first sintering under an inert or air atmosphere. After cooling and collection, the material is pulverized to obtain the matrix material Li(Li₂)₃. x Mn a Ni 1-a-b Al b )O 2-δ Where 0.05≤x≤0.33, 0 <a<0.6,0.1≤b≤0.25,0 ≤δ ≤0.2。

[0038] In some embodiments, the manganese precursor may include nickel manganese hydroxide (Ni). x Mn y (OH)2, where x+y=1, 0.2≤x<0.5.

[0039] In some embodiments, the lithium source may include at least one of lithium hydroxide, lithium carbonate, and lithium nitrate.

[0040] In some embodiments, the ratio of the number of moles of Li in the lithium source to the total number of moles of Me (including Ni and Mn) in the manganese-based precursor, Li:Me, can be (1.10~1.45):1, which is beneficial for providing a sufficient lithium source. Li:Me can exemplary be 1.10:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1, 1.35:1, 1.4:1, 1.45:1, or any value within the range of any two of the above values. Li:Me can further be (1.25~1.40):1.

[0041] In some embodiments, the aluminum source includes at least one of aluminum hydroxide and aluminum oxide.

[0042] In some embodiments, the mass percentage of the aluminum source relative to the total mass of the manganese-based precursor, lithium source, and aluminum source (i.e., dry mix) can be 0.05 wt% to 0.5 wt%. This is beneficial because while aluminum forms the matrix material, some aluminum remains on the surface to form an inert aluminum oxide coating layer. This, combined with the outer fluoride coating layer, further reduces direct contact between the matrix material and the electrolyte. This mass percentage can, exemplarily, be 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, or any value within the range of any two of the above values. A further mass percentage can be 0.05 wt% to 0.15 wt%.

[0043] In some embodiments, the conditions for the first sintering may include: heating to 750°C to 950°C at a heating rate of 2°C / min to 3°C / min and sintering for 10 to 15 hours. Slow heating facilitates the mutual diffusion and reaction of the raw materials at high temperatures, resulting in a matrix material with a well-developed crystal structure. The temperature for the first sintering can, for example, be 750°C, 800°C, 850°C, 900°C, 950°C, or any value within the range of any two of the above values. The time can, for example, be 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, or any value within the range of any two of the above values.

[0044] During the first sintering process, the amount of material added to the crucible is controlled at 1.5~3.0 kg / crucible. The material inside the crucible is heated synchronously, and the efficiency of sintering gas entry and exit is improved, thereby improving the uniformity of the first sintering. This is beneficial for the normal capacity performance during the charge and discharge process after the matrix material is subsequently prepared into a lithium-rich manganese-based cathode material.

[0045] In some embodiments, the median particle size Dv50 of the matrix material particles can be 5 μm to 10 μm.

[0046] Step S2: After mixing the matrix material with the hexafluorozirconic acid solution and drying it, a second sintering is performed to react on the surface of the matrix material to generate a lithium hexafluorozirconate coating layer, thus obtaining the intermediate material.

[0047] Specifically, the matrix material is mixed with a hexafluorozirconic acid solution. Residual lithium on the surface of the matrix material reacts in situ with the hexafluorozirconic acid solution to generate lithium hexafluorozirconate. The mixture of matrix material and hexafluorozirconic acid solution is then dried, and a wet coating process is used to initially form a lithium hexafluorozirconate coating layer. A second sintering and pulverization process is then performed under an inert atmosphere to form a complete lithium hexafluorozirconate coating layer on the surface of the matrix material, yielding the intermediate material [Li(Li x Mn a Ni 1-a- b Al b )O 2-δ ]@Li2ZrF3,0.05≤x≤0.33,0 <a<0.6,0.1≤b≤0.25,0 ≤δ≤0.2。

[0048] In some embodiments, the concentration of the hexafluorozirconic acid solution can be from 1.0 mol / L to 5.0 mol / L, which facilitates the uniform reaction of hexafluorozirconic acid with residual lithium on the surface of the substrate material to form a uniform and complete lithium hexafluorozirconate coating layer. The concentration of the hexafluorozirconic acid solution can, exemplarily, be 1.0 mol / L, 2.0 mol / L, 3.0 mol / L, 4.0 mol / L, 5.0 mol / L, or any value within the range of any two of the above values. The concentration of the hexafluorozirconic acid solution can further be from 2.0 mol / L to 4.0 mol / L.

[0049] Furthermore, the mass / volume ratio of the matrix material to the hexafluorozirconic acid solution can be 10 kg : (0.1 L ~ 1.0 L), which facilitates sufficient contact between the matrix material and the hexafluorozirconic acid solution, allowing for the in-situ reaction on the surface of the matrix material to generate a complete and uniformly thick lithium hexafluorozirconate coating. The mass / volume ratio of the matrix material to the hexafluorozirconic acid solution can, for example, be 10 kg : 0.25 L, 10 kg : 0.35 L, 10 kg : 0.45 L, 10 kg : 0.55 L, 10 kg : 0.65 L, 10 kg : 0.75 L, 10 kg : 0.85 L, 10 kg : 1.0 L, or any value within the range of any two of the above values. The mass / volume ratio of the matrix material to the hexafluorozirconic acid solution can further be 10 kg : (0.35 L ~ 0.75 L).

[0050] During the drying process of the mixture of matrix material and hexafluorozirconic acid solution, the drying temperature can be between 80°C and 120°C. This facilitates the in-situ reaction of hexafluorozirconic acid with residual lithium on the surface of the matrix material to form lithium hexafluorozirconate, thus fixing the lithium hexafluorozirconate onto the surface of the matrix material. The drying temperature can, exemplarily, be 80°C, 90°C, 100°C, 110°C, 120°C, or any value within the range of any two of the above values. The drying temperature can further be between 90°C and 110°C.

[0051] In some embodiments, the drying equipment may be an oven capable of constant temperature drying. It is understood that the drying equipment includes, but is not limited to, an oven; any equipment capable of drying may be used.

[0052] In some embodiments, the moisture content of the mixture of the dried matrix material and the hexafluorozirconic acid solution is 0 to 1 wt%.

[0053] The conditions for the second sintering may include: heating at a rate of 2℃ / min to 3℃ / min to 300℃~600℃ and sintering for 2~5 hours. A lower sintering temperature helps reduce fluorine volatilization in the lithium hexafluorozirconate coating and phase transformation of the matrix material, resulting in a more stable lithium hexafluorozirconate coating and improving the structural stability of the intermediate material. The temperature for the second sintering can, for example, be 300℃, 400℃, 500℃, 600℃, or any value within the range of any two of the above values; the time can, for example, be 2 hours, 3 hours, 4 hours, 5 hours, or any value within the range of any two of the above values.

[0054] During the second sintering process, the amount of material added to the crucible is controlled at 1.5~3.0 kg / crucible. The material inside the crucible is heated synchronously, and the efficiency of sintering gas entry and exit is improved, thereby improving the uniformity of the second sintering.

[0055] The process of wet coating followed by drying and then low-temperature sintering is beneficial for forming a uniform and stable lithium hexafluorozirconate coating layer, thereby improving the electronic and ionic conductivity of the substrate material and enhancing the rate performance of lithium-rich manganese-based cathode materials.

[0056] In some embodiments, the median particle size Dv50 of the intermediate material particles can be 7 μm to 9 μm.

[0057] Step S3: Mix the intermediate material and fluoride, and perform a third sintering to form a fluoride coating layer on the surface of the intermediate material, thereby obtaining a lithium-rich manganese-based cathode material.

[0058] Specifically, the intermediate material and fluoride are dry-mixed and coated using a high-speed mixer, and then sintered a third time under an inert atmosphere to form a fluoride coating layer on the surface of the intermediate material, resulting in a double-layer coated lithium-rich manganese-based cathode material [Li(Li x Mn a Ni 1-a-b Al b )O 2-δ @Li2ZrF3@fluoride, 0.05≤x≤0.33, 0 <a<0.6,0.1≤b≤0.25,0 ≤δ≤0.2。

[0059] In some embodiments, the fluoride may include at least one of AlF3, TiF4, and ZrF4. The fluoride may further be AlF3.

[0060] Furthermore, the mass percentage of fluoride to the matrix material can be 0.05wt% to 0.30wt%, which is beneficial for forming a uniform and dense fluoride coating layer, effectively protecting the matrix material, and also taking into account the high capacity of the lithium-rich manganese-based cathode material. The mass percentage of fluoride to the matrix material can, for example, be 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, or any value within the range of any two of the above values. The mass percentage of fluoride to the matrix material can further be 0.05wt% to 0.20wt%.

[0061] The conditions for the third sintering can include: heating to 550℃~750℃ at a heating rate of 2℃ / min~3℃ / min and sintering for 7~12 hours, which is beneficial to improve the bonding force between the fluoride coating layer and the intermediate material, and improve the stability of the fluoride coating layer. The temperature for the third sintering can, for example, be 300℃, 400℃, 500℃, 600℃, or any value within the range of any two of the above values, and the time can, for example, be 2 hours, 3 hours, 4 hours, 5 hours, or any value within the range of any two of the above values.

[0062] During the third sintering process, the amount of material added to the crucible is controlled at 1.5~3.0 kg / crucible. The material inside the crucible is heated synchronously, and the efficiency of sintering gas entry and exit is improved, thereby improving the uniformity of the third sintering.

[0063] In some embodiments, the median particle size Dv50 of the lithium-rich manganese-based cathode material can be 7 μm to 9 μm.

[0064] Compared with existing technologies, the preparation method of lithium-rich manganese-based cathode material in this application has the following advantages:

[0065] 1. By combining wet coating of lithium hexafluorozirconate with low-temperature sintering inner layer coating process, lithium hexafluorozirconate, a fast ion conductor with high ionic conductivity, is formed in situ on the surface of the substrate material. This can effectively improve the electronic conductivity and ionic conductivity of lithium-rich manganese-based cathode materials, thereby improving the rate performance of lithium-rich manganese-based cathode materials.

[0066] 2. By forming a fluoride coating as an outer layer, the excellent chemical and thermal stability of fluorides effectively prevents direct contact between the electrolyte and the substrate material, thereby reducing side reactions. Compared to traditional coating materials, the fluoride coating has better adhesion and is less likely to peel off from the material surface, thus providing long-term protection.

[0067] 3. Compared with the traditional single coating method, the double-layer coating process of this application improves and balances the performance of lithium-rich manganese-based cathode materials through a reasonably designed double coating structure, enabling the lithium-rich manganese-based cathode materials to maintain good cycle stability under high-rate discharge conditions.

[0068] 4. This application further improves the coating effect by optimizing the sintering temperature and time of the second and third sintering processes. While improving the cycle stability and lifespan of the lithium-rich manganese-based cathode material, it also improves the conductivity of the lithium-rich manganese-based cathode material, thereby further improving the overall performance of the lithium-rich manganese-based cathode material.

[0069] This application also provides an electrochemical device (e.g., a secondary battery) that includes a positive electrode plate, the positive electrode plate including a positive electrode material, wherein the positive electrode material is the aforementioned lithium-rich manganese-based positive electrode material.

[0070] Compared to existing technologies, the electrochemical device provided in this application embodiment has higher charge-discharge efficiency and rate performance, as well as higher capacity and cycle life, due to the application of the aforementioned lithium-rich manganese-based cathode material.

[0071] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of the application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically described are all conventional commercially available products or publicly disclosed.

[0072] Example 1

[0073] Step S1, Ni 0.3 Mn 0.7 Ni(OH)2, lithium carbonate, and Al(OH)3 are mixed by first adding half the mass of Ni into a high-speed mixer. 0.3 Mn 0.7 After adding Al(OH)2 and lithium carbonate, add the remaining half mass of Ni after adding Al(OH)3. 0.3 Mn 0.7 (OH)₂ and lithium carbonate were mixed and fed into a crucible (the amount of material added to the crucible was controlled at 1.5~3.0 kg / crucible). The mixture was then sintered for 12 hours at 900℃ under air atmosphere with a heating rate of 2℃ / min~3℃ / min. After cooling, the mixture was pulverized and sieved to obtain a matrix material Li(Li₂) with a median particle size Dv₅₀ of 5μm~10μm. 0.17 Mn 0.59 Ni 0.331 Al 0.1 O2, where the number of moles of Li in lithium carbonate is related to the number of Ni. 0.3 Mn0.7 The ratio of the total molar number of Me (including Ni and Mn) in Al(OH)2 is 1.30:1, and Al(OH)3 accounts for a significant portion of the total molar number of Ni. 0.3 Mn 0.7 The total mass percentage of (OH)2, lithium carbonate, and Al(OH)3 is 0.1 wt%.

[0074] Step S2: The matrix material is mixed with a 2 mol / L hexafluorozirconic acid solution at a ratio of 10 kg: 0.45 L. After drying in an oven at 120°C (the moisture content of the dried material is less than or equal to 1 wt%), the mixture is fed into a crucible (the amount of material added to the crucible is controlled at 1.5~3.0 kg / crucible). Under a nitrogen atmosphere, the temperature is increased to 450°C at a heating rate of 2°C / min~3°C / min for a second sintering for 3 hours. A lithium hexafluorozirconate coating layer is formed on the surface of the matrix material. After cooling, the mixture is pulverized and sieved to obtain an intermediate material [Li(Li x Mn a Ni 1-a-b Al b )O 2-δ @Li2ZrF3.

[0075] Step S3: The intermediate material and fluoride AlF3 are mixed using a high-speed mixer, wherein the mass percentage of AlF3 to the matrix material is 0.1 wt%. The mixture is then fed into a crucible (the amount of material added to the crucible is controlled at 1.5~3.0 kg / crucible), and sintered for a second time at 720℃ for 8 hours under air atmosphere at a heating rate of 2℃ / min~3℃ / min, forming a fluoride coating layer on the surface of the intermediate material. After cooling, the mixture is pulverized and sieved to obtain a lithium-rich manganese-based cathode material [Li(Li x Mn a Ni 1-a-b Al b )O 2-δ ]@Li2ZrF3@AlF3.

[0076] Example 2:

[0077] The difference from Example 1 is that the concentration of the hexafluorozirconic acid solution in step S2 is 5 mol / L. The preparation methods for the remaining lithium-rich manganese-based cathode materials are basically the same as in Example 1.

[0078] Example 3:

[0079] The difference from Example 1 is that the mass percentage of AlF3 to the matrix material in step S3 is 0.3 wt%. The preparation methods of the remaining lithium-rich manganese-based cathode materials are basically the same as those in Example 1.

[0080] Example 4:

[0081] The difference from Example 1 is that the fluoride in step S3 is ZrF4, and the resulting lithium-rich manganese-based cathode material is [Li(Li x Mn a Ni 1-a-b Al b )O 2-δ @Li2ZrF3@ZrF4. The preparation methods for the remaining lithium-rich manganese-based cathode materials are basically the same as in Example 1.

[0082] Example 5:

[0083] The difference from Example 1 is that the fluoride in step S3 is TiF4, and the resulting lithium-rich manganese-based cathode material is [Li(Li x Mn a Ni 1-a-b Al b )O 2-δ @Li2ZrF3@TiF4. The preparation methods for the remaining lithium-rich manganese-based cathode materials are basically the same as in Example 1.

[0084] Example 6:

[0085] The difference from Example 1 is that the second sintering temperature in step S2 is 600°C. The preparation methods for the remaining lithium-rich manganese-based cathode materials are basically the same as those in Example 1.

[0086] Comparative Example 1:

[0087] The difference from Example 1 is that steps S2 and S3 are omitted, and the uncoated matrix material obtained in step S1 is the lithium-rich manganese-based cathode material. The preparation methods for the remaining lithium-rich manganese-based cathode materials are basically the same as in Example 1.

[0088] Comparative Example 2:

[0089] The difference from Example 1 is that no aluminum source is added in step S1. The preparation methods for the remaining lithium-rich manganese-based cathode materials are basically the same as those in Example 1.

[0090] The lithium-rich manganese-based cathode materials obtained in Examples 1-6 and Comparative Examples 1-2 were subjected to the following tests.

[0091] 1. Scanning electron microscopy (SEM) test: Axia ChemiSEM (model) with high-resolution imaging capability was used to observe the microscopic morphology and structural characteristics of the material at magnification of 10,000x and 5,000Kx.

[0092] 2. Mn leaching: Refer to GB / T 37211-2018 Test method for leaching of metallic impurities in cathode materials for lithium-ion batteries.

[0093] 3. Particle size test: The particle size distribution Dv50 was tested using a Malvern 3000 particle size analyzer after internal ultrasonic dispersion for 5 minutes.

[0094] 4. Electrochemical performance testing:

[0095] Battery preparation: Lithium-rich manganese-based positive electrode material, polyvinylidene fluoride (PVDF), and conductive agent (such as acetylene black or conductive carbon black) are weighed in a certain proportion, and an appropriate amount of NMP is added to prepare a slurry. Next, the slurry is uniformly coated on aluminum foil and vacuum dried at 115℃±5℃ / 8h, then compacted and cut into discs. Simultaneously, lithium metal sheets are used as the negative electrode material. Finally, the entire assembly is transferred to a glove box and assembled into CR2025 specification coin cells.

[0096] The test steps for the first charge-discharge efficiency include: under normal temperature conditions of 25℃, the battery is charged at a constant current of 0.1C (nominal capacity of 150mAh / g) to 4.55V, and then charged at a constant voltage until the current drops to 0.05C, at which point charging is stopped, and the first charge capacity is recorded; then it is discharged at 0.1C to the cutoff voltage of 2.3V, and the first discharge capacity is recorded. The 0.1C specific capacity of the positive electrode material is calculated based on the first discharge capacity, and the first charge-discharge efficiency of the battery is calculated according to the following formula, i.e., the first efficiency: First charge-discharge efficiency = (first discharge capacity / first charge capacity) * 100%.

[0097] Charge and discharge capacity: Repeat the above charging and discharging process once, record the charging capacity twice and the discharging capacity twice, and calculate the 0.1C specific capacity of the lithium-rich manganese-based cathode material based on the second discharging capacity.

[0098] High-temperature cycle retention test: The test measures the capacity retention of the battery after 100 cycles at 45℃ with a charge / discharge current of 1C and a voltage range of 2.3V to 4.55V.

[0099] The test results of Examples 1-6 and Comparative Examples 1-2 are shown in Table 1 and 2. Figures 3 to 5 As shown.

[0100] Table 1

[0101]

[0102] The above results indicate that:

[0103] pass Figure 3Figure (a-2) shows that the surface of the uncoated matrix material (Comparative Example 1) is relatively clean, and the secondary particles are spherical. This indicates that the addition of aluminum source Al(OH)3 can optimize the crystal structure of the matrix material, resulting in better uniformity of the particle morphology. Through comparison... Figure 3 Figure (b-1) Figure 3 (b-2) Figure Figure 3 Figure (c-1) and Figure 3 Figure (c-2) shows that, compared to Example 3 (AlF3 coating amount of 0.30wt%), the lithium-rich manganese-based cathode material in Example 1 (AlF3 coating amount of 0.10wt%) has fewer small particles on its surface, more uniform coating, and a more suitable coating amount.

[0104] Combined with Table 1 and Figures 4 to 5 As can be seen, compared with Comparative Examples 1 and 2, the substrate material doped with Al(OH)3 in Example 1, with Li2ZrF6 and AlF3 coatings on the inner and outer layers respectively, resulted in a battery with a first discharge capacity of 228.4 mAh / g and a first-time efficiency of 90.2% at 0.1C, significantly higher than Comparative Examples 1-2 (Comparative Example 1: 0.1C first discharge 220.1 mAh / g, first-time efficiency 88.4%; Comparative Example 2: 0.1C first discharge 218.5 mAh / g, first-time efficiency 86.7%). This is because the presence of Al in the substrate material optimizes the crystal structure and improves the uniformity of the substrate material particle morphology, providing more channels for lithium-ion diffusion and increasing the lithium-ion diffusion rate. In addition, the inner Li2ZrF6 coating mainly plays a role in fast ion conduction and structural stability, while Zr... 4+ The strong electronegativity of Mn can stabilize the Mn-O bond and inhibit Mn 3+ The Jahn-Teller distortion causes Mn 2+ The dissolution rate decreases. The outer AlF3 coating provides chemical stability and mechanical protection at the cathode / electrolyte interface. The high chemical stability of AlF3 (Al-F bond energy of 664 kJ / mol) effectively blocks contact between the substrate material and the electrolyte, reducing HF erosion of the substrate material and dissolution of transition metals within it. Furthermore, it fixes surface lattice oxygen in the lithium-rich manganese-based cathode material through strong Al-O bonds, reducing oxygen release during charging. The synergistic effect of the dual coating layers promotes lithium-ion diffusion and migration within the electrode material, reduces electrode polarization, and improves the battery's charge / discharge efficiency and rate performance. Simultaneously, as a physical barrier, it effectively reduces side reactions between the substrate material and the electrolyte, slowing down structural collapse and dissolution of active materials during charge / discharge, thereby improving the cycle life of the lithium-rich manganese-based cathode material.

[0105] Based on Example 3, Example 1 moderately adjusted the AlF3 coating amount. In Example 1, the lithium-rich manganese-based cathode material better balanced the protective effect of the fluoride coating layer with the specific capacity and lithium-ion transport of the lithium-rich manganese-based cathode material, reducing interface impedance and battery polarization. The charge-discharge capacity, first efficiency and high-temperature cycle stability of the battery prepared by the lithium-rich manganese-based cathode material in Example 1 are better.

[0106] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A lithium-rich manganese-based cathode material, characterized in that, It includes a matrix material and a coating layer. The coating layer includes a lithium hexafluorozirconate coating layer on the surface of the matrix material and a fluoride coating layer on the side of the lithium hexafluorozirconate coating layer away from the matrix material. The fluoride coating layer includes at least one of AlF3, TiF4, and ZrF4. The chemical formula of the matrix material is Li(Li x Mn a Ni 1-a-b Al b )O 2-δ , where 0.05 ≤ x ≤ 0.33, 0 < a < 0.6, 0.1 ≤ b ≤ 0.25, 0 ≤ δ ≤ 0.2, and the mass percentage of the fluoride coating layer to the matrix material is 0.05 wt% - 0.30 wt%.

2. The lithium-rich manganese-based cathode material as described in claim 1, characterized in that, The mass percentage of the lithium hexafluorozirconate coating to the matrix material is 1.0wt% to 3.0wt%.

3. A method for preparing a lithium-rich manganese-based cathode material, characterized in that, include: The manganese-based precursor, lithium source, and aluminum source are mixed and subjected to a first sintering to obtain the matrix material; The matrix material is mixed with a hexafluorozirconic acid solution and dried, and then subjected to a second sintering to react on the surface of the matrix material to form a lithium hexafluorozirconate coating layer, thus obtaining an intermediate material. as well as The intermediate material and fluoride are mixed and sintered for the third time. The fluoride includes at least one of AlF3, TiF4 and ZrF4. The mass percentage of the fluoride to the matrix material is 0.05wt% to 0.30wt% to form a fluoride coating layer on the surface of the intermediate material, thereby obtaining the lithium-rich manganese-based cathode material.

4. The preparation method according to claim 3, characterized in that, The concentration of the hexafluorozirconic acid solution is 1.0 mol / L to 5.0 mol / L; and / or The mass / volume ratio of the matrix material to the hexafluorozirconic acid solution is 10 kg: (0.1 L~1.0 L).

5. The preparation method according to claim 3, characterized in that, The manganese-based precursor includes nickel manganese hydroxide (Ni). x Mn y (OH)2, where x+y=1, 0.2≤x<0.

5.

6. The preparation method according to claim 3, characterized in that, The mass percentage of the aluminum source relative to the total mass of the manganese-based precursor, the lithium source, and the aluminum source is 0.05 wt% to 0.5 wt%; and / or The aluminum source includes at least one of aluminum hydroxide and aluminum oxide.

7. The preparation method according to claim 3, characterized in that, The drying temperature is 80℃~120℃; The conditions for the first sintering include: heating to 750℃~950℃ at a heating rate of 2℃ / min~3℃ / min and sintering for 10~15h; The conditions for the second sintering include: heating to 300℃~600℃ at a heating rate of 2℃ / min~3℃ / min and sintering for 2~5 hours; The conditions for the third sintering include: heating to 550℃~750℃ at a heating rate of 2℃ / min~3℃ / min and sintering for 7~12 hours.

8. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material, the positive electrode material being a lithium-rich manganese-based positive electrode material as described in any one of claims 1 to 2 or a lithium-rich manganese-based positive electrode material prepared by the method for preparing a lithium-rich manganese-based positive electrode material as described in any one of claims 3 to 7.

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