Surface-modified lithium-rich cathode material, cathode sheet and preparation method and application thereof

Abstract

The present application relates to a kind of surface modified lithium-rich positive electrode material, positive electrode sheet and its preparation method and application.The surface modified lithium-rich positive electrode material includes: lithium-rich positive electrode material matrix, lithium salt coating layer generated by in-situ reaction and spinel structure transition layer;Spinel structure transition layer is between lithium-rich positive electrode material matrix and lithium salt coating layer;Lithium salt coating layer is generated by in-situ reaction of aluminum salt and lithium raw material;Wherein, lithium raw material includes lithium oxide and / or material that can generate lithium oxide by thermal decomposition, and the lithium salt coating layer is generated by in-situ reaction of lithium oxide and aluminum salt;Spinel structure transition layer and the lattice of lithium salt coating layer on the surface of lithium-rich manganese-based positive electrode material matrix contain Al element with concentration gradient distribution, and form Al-O bond by combining with O element.The present application makes lithium-rich positive electrode material not only have excellent lattice oxygen stability at high voltage by surface modification, also show good lithium ion diffusion capacity and electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage materials technology, and in particular to a surface-modified lithium-rich cathode material, cathode sheet, its preparation method and application. Background Technology

[0002] In recent years, the development of industries such as electric vehicles, electric ships, and electric aircraft has placed higher demands on lithium-ion batteries, making the need for high-energy-density, long-life, low-cost, and highly safe lithium-ion batteries increasingly urgent. Cathode materials for lithium-ion batteries are key materials for improving battery energy density, and solid-state batteries are the main way to achieve high-energy-density batteries. Therefore, developing high-energy-density lithium-ion battery cathode materials and realizing solid-state lithium batteries are particularly important.

[0003] Lithium-rich manganese-based layered oxides (LRMs) possess unique redox processes, enabling them to deliver discharge capacities exceeding 300 mAh / g, making them a promising material. However, the low compaction density, voltage hysteresis, severe voltage decay, and safety concerns of LRMs limit their commercial application. Irreversible redox processes in LRMs lead to transition metal migration and a decrease in the valence state of transition metals after cycling, considered a primary cause of voltage decay. Furthermore, irreversible oxygen release from the LRM surface can cause severe side reactions between the cathode and electrolyte, impacting battery safety and cycle stability.

[0004] To date, researchers have employed numerous methods to address the aforementioned challenges of lithium-rich manganese-based cathode materials. For instance, optimizing the local structure and charge compensation mechanism through compositional optimization, as well as coating and doping modifications, are common and effective methods. Compared to cobalt-containing lithium-rich manganese-based cathode materials, cobalt-free lithium-rich manganese-based cathode materials exhibit better voltage decay and cycle stability. Furthermore, constructing a surface coating protective layer can reduce side reactions between the cathode material surface and the electrolyte. Coating materials include oxides, lithium-ion conductors, phosphates, sulfides, and fluorides. Additionally, doping with foreign elements can regulate the local oxygen environment, suppress transition metal migration, and stabilize the crystal lattice structure. Doping elements such as cations (Al2O3, Al ... 3+ Ti 4+ 、Nb 5+ La 5+ Mg 2 + ), anion (S) 2- BO4 5- PO4 3- SO4 2- )wait.

[0005] Currently, methods for surface modification of lithium-rich manganese-based cathode materials include surface coating, surface element doping, and surface structure rearrangement. However, using any single modification method can hardly completely solve the problems of severe oxygen release and voltage decay on the surface. While combining these methods can improve the results, it is still difficult to achieve the desired effect, and it inevitably leads to complicated preparation processes and serious energy consumption issues.

[0006] In addition, lithium-rich manganese-based cathode materials are one of the preferred cathode materials in solid-state batteries. However, due to interface problems such as solid-solid contact, the difference in the ability of lithium-rich cathode materials to conduct lithium ions leads to the existence of an interface space charge layer between them. This seriously affects the rapid transport of lithium ions and the capacity utilization of the material, thus limiting the practical application of lithium-rich cathode materials in solid-state batteries.

[0007] In summary, current traditional surface modification of lithium-rich cathode materials cannot completely solve the problems of severe oxygen release and voltage decay on the surface. Furthermore, when applied to solid-state batteries, they cannot be used due to significant obstacles to lithium-ion transport at the interface between the lithium-rich cathode material and the solid electrolyte, as well as the poor material kinetics and low capacity of lithium-rich manganese-based cathode materials in solid-state batteries.

[0008] Therefore, there is an urgent need for a lithium-rich cathode material that can combine high energy density, good cycle stability, low voltage decay, and high safety in lithium-ion batteries, and to realize its application in solid-state lithium batteries. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing technologies by providing a surface-modified lithium-rich cathode material, cathode sheet, its preparation method, and applications. The surface-modified lithium-rich cathode material of this invention features a spinel structure transition layer formed through an in-situ reaction between the lithium-rich cathode material matrix and the lithium salt coating layer. A layered-spinel heterostructure is formed between the lithium-rich cathode material matrix and the substrate, achieving optimized adjustment of the surface structure of the lithium-rich cathode material. This effectively improves the interface problem between the lithium-rich cathode material and the solid electrolyte, and significantly improves the electrochemical performance of the cathode material. When used in lithium-ion batteries, it exhibits excellent high-voltage cycle stability, excellent rate performance, long cycle life, high specific capacity, and high energy density.

[0010] To achieve the above objectives, in a first aspect, embodiments of the present invention provide a surface-modified lithium-rich cathode material, comprising:

[0011] Lithium-rich cathode material matrix, lithium salt coating layer generated through in-situ reaction, and spinel structure transition layer;

[0012] The spinel structure transition layer is located between the lithium-rich cathode material matrix and the lithium salt coating layer;

[0013] The lithium salt coating layer is generated by in-situ reaction of aluminum salt with lithium raw material; wherein, the lithium raw material includes lithium oxide and / or materials that can generate lithium oxide through thermal decomposition, and the lithium salt coating layer is generated by in-situ reaction of the lithium oxide with aluminum salt;

[0014] The spinel structure transition layer and lithium salt coating layer on the surface of the lithium-rich manganese-based cathode material contain Al elements with a concentration gradient distribution, which combine with O elements to form Al-O bonds.

[0015] Preferably, the lithium-rich cathode material matrix is ​​a lithium-rich manganese-based cathode material with the chemical formula: xLi2MnO3·(1-x)LiTMO2; wherein, 0≤x≤1, and TM is one or more of Ni, Co, Mn, Al, Zn, Mg, Zr, and Cr.

[0016] Preferably, the aluminum salt includes one or more of aluminum sulfate, aluminum silicate, and aluminum sulfide;

[0017] The lithium raw materials include one or more of lithium oxide, lithium carbonate, lithium hydroxide, and lithium acetate.

[0018] The lithium salt coating layer accounts for 0.1wt%-1wt% of the total mass of the lithium-rich cathode material, and the lithium salt coating layer includes one or more of lithium sulfate, lithium silicate, and lithium sulfide.

[0019] Preferably, the general chemical formula of the spinel structure transition layer is: Li4Al y M z Mn 5-y-z O 12 Wherein, 0 < y ≤ 1, 0 ≤ z ≤ 1, and y + z ≤ 1; M includes one or more of Ni, Co, Zn, Mg, Zr, and Cr, and the thickness of the spinel structure transition layer is less than or equal to 4 nm.

[0020] Preferably, the Al element accounts for 0.1%-1% of the total atomic percentage of the lithium-rich manganese-based cathode material.

[0021] In a second aspect, embodiments of the present invention provide a method for preparing the surface-modified lithium-rich cathode material described in the first aspect above, comprising:

[0022] Lithium raw materials, lithium-rich cathode material matrix precursors, and aluminum salts are mixed and ball-milled according to the required mass ratio.

[0023] The product obtained by ball milling was sintered at 800℃-900℃ for 5-12 hours to obtain the surface-modified lithium-rich cathode material.

[0024] Preferably, the lithium raw material includes one or more of lithium oxide, lithium carbonate, lithium hydroxide, and lithium acetate;

[0025] The chemical formula of the lithium-rich cathode material matrix precursor is Ni. a Co b Mn c M 1-a-b-c CO3, where 0≤a≤0.45, 0≤b≤0.16, 0.39≤c≤1;

[0026] The aluminum salts include one or more of aluminum sulfate, aluminum silicate, and aluminum sulfide.

[0027] Prior to the high-temperature sintering, the process further includes: pre-firing the product obtained from the ball milling at a temperature below 800°C.

[0028] Preferably, the chemical formula of the lithium-rich cathode material matrix precursor is Ni. m Mn 1-m CO3, 0.25≤m≤0.45.

[0029] Thirdly, embodiments of the present invention provide a positive electrode sheet, comprising: the surface-modified lithium-rich positive electrode material described in the first aspect above, or the surface-modified lithium-rich positive electrode material prepared by the preparation method described in the second aspect above.

[0030] Fourthly, embodiments of the present invention provide a lithium battery, comprising: the surface-modified lithium-rich cathode material described in the first aspect above, or the surface-modified lithium-rich cathode material prepared by the preparation method described in the second aspect above, or the cathode sheet described in the third aspect above;

[0031] The lithium battery includes any one of the following: liquid lithium-ion battery, liquid metal lithium battery, hybrid solid-liquid lithium-ion battery, hybrid solid-liquid metal lithium battery, in-situ solidified lithium battery, solid lithium-ion battery, and solid metal lithium battery.

[0032] The surface-modified lithium-rich cathode material provided in this invention has a lithium salt coating layer formed through an in-situ reaction on the surface of the lithium-rich cathode material substrate, and a spinel structure transition layer formed through an in-situ reaction between the lithium-rich cathode material substrate and the lithium salt coating layer, thereby forming a layered-spinel heterostructure between the lithium-rich cathode material substrates. The surface-modified lithium-rich cathode material of this invention combines surface aluminum doping, surface rearrangement, and interface coating, achieving optimized adjustment of the surface structure of the lithium-rich cathode material, effectively improving the interface problem between the lithium-rich cathode material and the solid electrolyte, and significantly improving the electrochemical performance of the cathode material. When used in lithium-ion batteries, the lithium-rich cathode material of this invention exhibits advantages such as excellent high-voltage cycle stability, excellent rate performance, long cycle life, high specific capacity, and high energy density. Attached Figure Description

[0033] Figure 1 Transmission electron microscope (TEM) images of the cathode materials of Embodiment 1 and Comparative Example 1 of the present invention;

[0034] Figure 2 These are scanning transmission electron microscope (STEM) images of the cathode materials of Embodiment 1 and Comparative Example 1 of the present invention;

[0035] Figure 3 The X-ray diffraction (XRD) pattern corresponds to the cathode material in Embodiment 1 of the present invention;

[0036] Figure 4 The above are X-ray photoelectron spectroscopy (XPS) spectra of the cathode materials of Example 1 and Comparative Example 1 of the present invention.

[0037] Figure 5 The above are electrochemical data graphs of the cathode materials in Example 1 and Comparative Example 1 of this invention.

[0038] Figure 6 This is a comparison and structural schematic diagram of the voltage decay of the positive electrode material in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0039] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0040] This invention provides a surface-modified lithium-rich cathode material, comprising: a lithium-rich cathode material matrix, a lithium salt coating layer generated through an in-situ reaction, and a spinel structure transition layer. The spinel structure transition layer is located between the lithium-rich cathode material matrix and the lithium salt coating layer.

[0041] The lithium-rich cathode material matrix is ​​a lithium-rich manganese-based cathode material with the chemical formula: xLi₂MnO₃·(1-x)LiTMO₂; where 0≤x≤1, and TM is one or more of Ni, Co, Mn, Al, Zn, Mg, Zr, and Cr. Preferably, the lithium-rich manganese-based cathode material contains nickel, such as Li. 1.15 Ni 0.30 Mn 0.55 O2, Li 1.2 Ni 0.13 Co 0.13 Mn0 .54 O2, Li 1.2 Ni 0.2 Mn 0.6 O2, etc. More preferably, the lithium-rich manganese-based cathode material contains nickel but not cobalt. Using cobalt-free lithium-rich manganese-based cathode material can greatly reduce costs, and as verified by the embodiments of the present invention, its first-cycle discharge specific capacity can reach the discharge specific energy of cobalt-containing lithium-rich manganese-based cathode material, so that the cobalt-free lithium-rich manganese-based cathode material can meet the requirements of high specific energy while saving costs.

[0042] The lithium salt coating layer is located on the surface of the lithium-rich cathode material substrate and is formed by the in-situ reaction of aluminum salt with lithium raw material. The lithium raw material includes lithium oxide and / or materials that can generate lithium oxide through thermal decomposition. The lithium salt coating layer is formed by the in-situ reaction of lithium oxide with aluminum salt. The aluminum salt includes one or more of aluminum sulfate, aluminum silicate, and aluminum sulfide, preferably aluminum sulfate. The lithium raw material includes one or more of lithium oxide, lithium carbonate, lithium hydroxide, and lithium acetate, preferably lithium carbonate.

[0043] The lithium salt coating includes one or more of lithium sulfate, lithium silicate, and lithium sulfide. The lithium salt coating accounts for 0.1wt%-1wt% of the total mass of the lithium-rich cathode material, specifically any value within this range, such as 0.1wt%, 0.2wt%, 0.3wt%, 0.5wt%, 0.6wt%, 0.8wt%, or 1wt%. When the lithium salt coating content is within this range, a suitable coating thickness can be achieved, reducing side reactions between the cathode material and the electrolyte. Excessive coating thickness leads to capacity decay, while insufficient coating thickness weakens the coating effect. When used in liquid lithium-ion batteries, the lithium salt coating not only effectively prevents the electrode material from directly contacting the electrolyte, but also has good stability against lattice oxygen under high voltage. When used in solid-state lithium batteries, such as in-situ solid-state lithium batteries, the lithium salt coating can form a lithium-ion transport bridge between the cathode material and the electrolyte, thereby effectively improving the ion transport path and enhancing the lithium-ion diffusion capability of lithium-rich manganese-based cathode materials in solid-state batteries, thus achieving better capacity utilization.

[0044] The preferred lithium salt coating layer is lithium sulfate. Besides functioning as a lithium salt, the coating layer also contains aggregated sulfate anions. The aggregation of these sulfate polyanions on the surface exhibits strong SO bonding ability, thus mitigating irreversible oxygen release and transition metal migration. This results in the coated lithium-rich cathode material exhibiting better cycle stability and voltage decay rate, making it more suitable for liquid lithium-ion batteries and solid-state batteries. The inventors discovered that constructing a sulfate-rich polyanion environment on the surface of lithium-rich manganese-based cathode materials can stabilize the local oxygen environment, thereby reducing surface oxygen release. Combined with the formation of a spinel structure on the surface, a stable structure and three-dimensional ion diffusion channels are obtained, which effectively stabilize the surface of the lithium-rich manganese-based cathode material.

[0045] The general chemical formula for the spinel structure transition layer is: Li₄Al y M z Mn 5-y-z O 12 Wherein, 0 < y ≤ 1, 0 ≤ z ≤ 1, and y + z ≤ 1; M includes one or more of Ni, Co, Zn, Mg, Zr, and Cr, and the thickness of the spinel transition layer is less than or equal to 4 nm, and can be any value within the above range, such as 1 nm, 2 nm, 3 nm, 4 nm, etc. Because an excessively thick spinel transition layer can lead to a decrease in material capacity and average voltage, sacrificing the material's specific energy, this invention can control the thickness of the spinel transition layer within the above range by controlling process parameters such as raw material ratio and sintering temperature.

[0046] During the in-situ formation of the lithium-rich cathode material matrix, spinel structure transition layer, and lithium salt coating layer through the reaction between lithium raw materials, lithium-rich cathode material matrix precursors, and aluminum salts, surface doping of aluminum atoms occurs on the surface of the lithium-rich cathode material matrix. The spinel structure transition layer and lithium salt coating layer on the surface of the lithium-rich manganese-based cathode material matrix contain Al elements with a concentration gradient distribution, gradually decreasing in concentration from the surface to the matrix core. Gradient doping helps stabilize the surface crystal structure, reduces surface structure collapse, and better maintains structural rigidity. According to the atomic molar ratio, the Al element accounts for 0.1%-1% of all atoms in the lithium-rich manganese-based cathode material, and can be any value within this range, such as 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.008, 0.009, and 0.01. When the aluminum content in the surface doping is within the above-mentioned range, the stability of the surface lattice oxygen and structure can be achieved. Excessive doping will lead to a decrease in the specific capacity of the material. The formation of nano-layer Al doping on the surface of the lithium-rich cathode material matrix can combine with O elements on the surface of the lithium-rich cathode material to form Al-O bonds with strong binding energy, thereby effectively stabilizing the surface lattice oxygen and avoiding phase transitions and other problems caused by lattice oxygen loss.

[0047] The surface-modified lithium-rich cathode material of this invention achieves a three-in-one effect of aluminum doping, surface rearrangement, and interfacial coating on the surface of lithium-rich manganese-based cathode materials. Aluminum doping stabilizes the surface crystal structure, reducing structural changes and maintaining structural rigidity. The spinel structure formed after surface rearrangement accelerates lithium-ion diffusion, improving the rate performance of the lithium-rich manganese-based cathode material. Furthermore, compared to layered structures, the spinel structure better confines surface lattice oxygen, reducing surface oxygen release. When applied to liquid lithium batteries, the surface coating effectively reduces side reactions between the cathode material and the electrolyte. When applied to solid-state lithium batteries, the lithium salt coating forms a lithium-ion transport bridge between the cathode material and the electrolyte, effectively improving the ion transport path and enhancing the lithium-ion diffusion capacity of the lithium-rich manganese-based cathode material in solid-state batteries, resulting in better capacity utilization.

[0048] This invention also provides a method for preparing surface-modified lithium-rich manganese-based cathode materials. This method allows for the simple surface modification of lithium-rich manganese-based cathode materials by using aluminum salts, such as aluminum sulfate, with a lithium-rich cathode material matrix precursor and lithium raw materials during high-temperature sintering. This invention achieves the formation of a lithium-rich manganese-based cathode material matrix, a surface lithium salt coating layer, and a spinel heterostructure through an in-situ reaction between the two via a one-step sintering process involving the lithium-rich manganese-based cathode material precursor, lithium raw materials, and aluminum salts. Furthermore, it results in a gradient doping of aluminum atoms on the cathode material surface, thus obtaining a surface-modified lithium-rich cathode material. This preparation method achieves the combined effects of surface element doping, surface reconstruction, and surface coating in a single simple synthesis step, reducing operational steps while achieving multiple benefits. The preparation process is simple and suitable for large-scale production. Through surface element doping, structural rearrangement, and surface coating, the cycle stability and voltage decay rate of the lithium-rich cathode material are significantly improved, and the relevant kinetic properties and thermal stability of the material are also significantly enhanced.

[0049] The present invention also provides a positive electrode sheet comprising a surface-modified lithium-rich positive electrode material. Due to the special structure and composition of the surface of the lithium-rich positive electrode material of the present invention, it exhibits excellent high-voltage cycle stability, excellent rate performance, long cycle life, high specific capacity, and high energy density when applied to existing liquid lithium-ion batteries. When applied to solid-state batteries, especially in-situ solid-state lithium batteries, it can further enhance the ion transport capability of the battery, thereby increasing the specific capacity and energy density, resulting in a solid-state battery with excellent safety performance.

[0050] This invention also provides a method for preparing a surface-modified lithium-rich cathode material, which mainly includes the following steps:

[0051] Step 1: Mix and ball-mill the lithium raw material, lithium-rich cathode material matrix precursor, and aluminum salt according to the required mass ratio.

[0052] Lithium raw materials include one or more of the following: lithium oxide, lithium carbonate, lithium hydroxide, and lithium acetate.

[0053] Aluminum salts include one or more of aluminum sulfate, aluminum silicate, and aluminum sulfide.

[0054] The chemical formula of the lithium-rich cathode material matrix precursor is Ni a Co b Mn c M 1-a-b-c CO3, wherein 0 ≤ a ≤ 0.45, 0 ≤ b ≤ 0.16, and 0.39 ≤ c ≤ 1. Furthermore, the lithium-rich cathode material matrix precursor is preferably a material containing Ni but not Co, and the preferred chemical formula is Ni. m Mn 1-m CO3, 0.25≤m≤0.45.

[0055] The required mass ratios of the above-mentioned raw materials can be calculated by reverse calculation based on the desired product. Those skilled in the art will know how to perform this calculation.

[0056] For example, in a preferred embodiment of the present invention, lithium carbonate is used as the lithium raw material, and Ni is used as the precursor for the lithium-rich cathode material matrix. 0.35 Mn 0.65 The required mass ratio of CO3 to aluminum sulfate is [0.4-0.45]:1:[0.001-0.01]. When the ratio of these three components is controlled within this range, it ensures not only complete reaction between the lithium raw material and the aluminum salt to obtain the surface-coated lithium salt layer, but also that the lithium raw material reacts with the precursor to form the target lithium-rich cathode material matrix. Furthermore, it enables the formation of a spinel structure transition layer of suitable nanometer thickness between the lithium salt coating layer and the lithium-rich cathode material matrix, and achieves a suitable proportion of aluminum atom surface doping. Excessive or insufficient lithium raw material content leads to the formation of impurity phases in the lithium-rich manganese-based cathode material, while excessive aluminum salt content affects the material's specific capacity, and insufficient aluminum salt content prevents the formation of a good lithium salt surface coating. The specific raw materials selected vary depending on the desired product, and the mass ratio range of the raw materials used can be calculated by those skilled in the art using commonly used industry techniques.

[0057] In a preferred embodiment, the ball milling equipment of the present invention uses polyurethane balls, and the milling speed is 200-300 rpm. Of course, those skilled in the art will understand that ball milling is a commonly used technique in the industry, and they can select the specific ball milling equipment, milling media, milling speed, etc., according to actual needs without any creative effort.

[0058] Step 2: The product obtained by ball milling is sintered at 800℃-900℃ for 5-12 hours to obtain a surface-modified lithium-rich cathode material.

[0059] Specifically, sintering can be carried out using a tube furnace. The high-temperature sintering temperature is 800-900℃, but can be any value within this range, such as 800℃, 820℃, 860℃, 880℃, or 900℃. Too high a sintering temperature will result in excessively large primary particles of the cathode material, affecting capacity utilization; too low a sintering temperature will result in poor crystallinity of the lithium-rich material, thus affecting its electrochemical performance. The sintering time is 5-12 hours, and can be any value within this range, such as 5h, 6h, 7h, 8h, 9h, 10h, 11h, or 12h. Furthermore, prior to high-temperature sintering, the product obtained from the ball milling process can be pre-sintered at a temperature below 800℃.

[0060] The preparation process of this invention is simple, achieving elemental doping, surface reconstruction, and surface coating of the lithium-rich cathode material substrate through a single sintering step. This method enables the formation of an effective protective layer on the cathode material surface. The preparation process is not only simple and easy to operate, but also achieves excellent material properties.

[0061] The surface-modified lithium-rich cathode material prepared by the present invention can be used as a lithium battery cathode and applied in various energy storage devices.

[0062] A positive electrode sheet is prepared by using a surface-modified lithium-rich positive electrode material prepared according to conventional processes. For example, the positive electrode material of this invention is mixed with a conductive additive (Super P) and a binder (polyvinylidene fluoride) at a mass ratio of 96:2:2, and an appropriate amount of organic solvent (N-methylpyrrolidone) is added to form a uniformly dispersed slurry. Finally, the slurry is uniformly coated onto an aluminum foil current collector using a doctor blade and dried in an oven to obtain the positive electrode sheet.

[0063] The surface-modified lithium-rich cathode material obtained by this invention has high energy density, good structural stability and excellent cycle performance. It can be applied to lithium batteries, lithium battery packs or lithium battery modules, including liquid lithium-ion batteries, liquid lithium metal batteries, hybrid solid-liquid lithium-ion batteries, hybrid solid-liquid lithium metal batteries, in-situ solidified lithium batteries, solid lithium-ion batteries and solid lithium metal batteries. It is widely used in consumer electronics, electric vehicles, large-scale energy storage and other fields, and also has good application prospects in large-scale energy storage systems.

[0064] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0065] The reagents and materials used in the following examples and comparative examples, including electrolytes, electrolyte additives, and lithium metal anodes, are all commercially available conventional reagent products and can also be prepared using conventional methods. Where specific experimental steps or conditions are not specified in the examples, they should be performed according to conventional experimental procedures or conditions in the art.

[0066] Example 1

[0067] This embodiment prepares lithium sulfate-coated lithium-rich manganese-based cathode material Li. 1.15 Ni 0.30 Mn 0.55O2 (written as xLi2MnO3·(1-x)LiTMO2) is in the form of 0.35Li2MnO3·0.65LiNi 0.546 Mn 0.453 O2).

[0068] Step 1: Add 10 grams of Ni 0.35 Mn 0.65 CO3 precursor, 4.15 g lithium carbonate and 28.3 mg aluminum sulfate were added to a ball mill jar, and polyurethane balls were added as milling beads at a volume ratio of 1:1. The mixture was then milled in a planetary ball mill at 200 rpm for 3 hours and then sieved.

[0069] Step 2: Place the powder obtained in Step 1 into a crucible and then into a muffle furnace. First, heat the crucible to 350℃ at a heating rate of 5℃ / min and hold for 5 hours. Then, heat the crucible to 700℃ at a heating rate of 5℃ / min and hold for 15 hours. Finally, heat the crucible to 860℃ at a heating rate of 5℃ / min and hold for 5 hours to obtain lithium sulfate-coated lithium-rich manganese-based cathode material Li. 1.15 Ni 0.30 Mn 0.55 O2. Testing showed that the lithium sulfate coating content was 0.3 wt%, and calculations showed that Al accounted for 0.2% of all atoms in the lithium-rich manganese-based cathode material.

[0070] The material obtained in Example 1 was characterized by transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). 1.15 Ni 0.30 Mn 0.55 The morphological structure and specific composition of O2 are as follows: Figure 1-4 As shown. For ease of indicating the corresponding materials in the figure, ANLRM is used to denote the lithium-rich manganese-based cathode material Li after surface modification in Example 1 of this invention. 1.15 Ni 0.30 Mn 0.55 O2. Meanwhile, NLRM is used to denote the lithium-rich manganese-based cathode material of Comparative Example 1 of this invention.

[0071] Example 2

[0072] This embodiment prepares lithium sulfate-coated lithium-rich manganese-based cathode material Li. 1.15 Ni 0.30 Mn 0.55 O2 (written as xLi2MnO3·(1-x)LiTMO2) is in the form of 0.35Li2MnO3·0.65LiNi 0.546 Mn 0.453 O2).

[0073] Step 1: Add 10 grams of Ni 0.35 Mn 0.65 CO3 precursor, 4.15 g of lithium carbonate and 56.6 mg of aluminum sulfate were added to a ball mill jar, and polyurethane balls were added as milling beads at a volume ratio of 1:1. The mixture was then milled in a planetary ball mill at 200 rpm for 3 hours and then sieved.

[0074] Step 2: Place the powder obtained in Step 1 into a crucible and then into a muffle furnace. First, heat the material to 350℃ at a heating rate of 5℃ / min and hold for 5 hours. Then, heat the material to 700℃ at a heating rate of 5℃ / min and hold for 15 hours. Finally, heat the material to 860℃ at a heating rate of 5℃ / min and hold for 5 hours to obtain lithium sulfate-coated lithium-rich manganese-based cathode material Li. 1.15 Ni 0.30 Mn 0.55 O2. Testing showed that the lithium sulfate coating content was 0.6 wt%, and calculations showed that Al atoms accounted for 0.4% of all atoms in the lithium-rich manganese-based cathode material.

[0075] Example 3

[0076] This embodiment prepares lithium sulfate-coated lithium-rich manganese-based cathode material Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 (written as xLi2MnO3·(1-x)LiTMO2) is in the form of 0.5Li2MnO3·0.5LiNi 0.33 Co 0.33 Mn 0.33 O2).

[0077] Step 1: Add 10 grams of Ni 0.16 Co 0.16 Mn 0.68 CO3 precursor, 4.125 g of lithium carbonate and 28.3 mg of aluminum sulfate were added to a ball mill jar, and polyurethane balls were added as milling beads at a volume ratio of 1:1. The mixture was then milled in a planetary ball mill at 200 rpm for 3 hours and then sieved.

[0078] Step 2: After placing the powder obtained in Step 1 into a crucible, place it in a muffle furnace. First, heat the furnace to 350℃ at a heating rate of 5℃ / min and hold for 5 hours. Then, heat the furnace to 700℃ at a heating rate of 5℃ / min and hold for 15 hours. Finally, heat the furnace to 860℃ at a heating rate of 5℃ / min and hold for 5 hours to obtain lithium sulfate-coated lithium-rich manganese-based cathode material Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54O2. Testing showed that the lithium sulfate coating content was 0.3 wt%, and calculations showed that Al atoms accounted for 0.17 wt% of all atoms in the lithium-rich manganese-based cathode material.

[0079] Example 4

[0080] Lithium sulfate-coated lithium-rich manganese-based cathode material Li 1.2 Ni 0.2 Mn 0.6 O2 (written as xLi2MnO3·(1-x)LiTMO2) is in the form of 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.5 O2).

[0081] Step 1: Add 10 grams of Ni 0.25 Mn 0.75 CO3 carbonate precursor, 4.21 g lithium carbonate and 28.3 mg aluminum sulfate were added to a ball mill jar, and polyurethane balls were added as milling beads at a volume ratio of 1:1. The mixture was then milled in a planetary ball mill at 200 rpm for 3 hours and then sieved.

[0082] Step 2: Take the powder obtained in Step 1, place it in a crucible, and then place it in a muffle furnace. First, heat the furnace to 350℃ at a heating rate of 5℃ / min and hold for 5 hours. Then, heat the furnace to 700℃ at a heating rate of 5℃ / min and hold for 15 hours. Finally, heat the furnace to 860℃ at a heating rate of 5℃ / min and hold for 5 hours to obtain lithium sulfate-coated lithium-rich manganese-based cathode material Li. 1.2 Ni 0.2 Mn 0.6 O2. Testing showed that the lithium sulfate coating content was 0.3 wt%, and calculations showed that Al atoms accounted for 0.18% of all atoms in the lithium-rich manganese-based cathode material.

[0083] Comparative Example 1

[0084] Step 1: Add 10 grams of Ni 0.35 Mn 0.65 The CO3 precursor and 4.15 g of lithium carbonate were added to a ball mill jar, and polyurethane balls were added as milling beads at a volume ratio of 1:1. The mixture was then milled in a planetary ball mill at 200 rpm for 3 hours and then sieved.

[0085] Step 2: Place the powder obtained in Step 1 into a crucible and then into a muffle furnace. First, heat the crucible to 350℃ at a heating rate of 5℃ / min and hold for 5 hours. Then, heat the crucible to 700℃ at a heating rate of 5℃ / min and hold for 15 hours. Finally, heat the crucible to 860℃ at a heating rate of 5℃ / min and hold for 5 hours to obtain the original uncoated lithium-rich manganese-based cathode material Li. 1.15 Ni 0.30 Mn0.55 O2.

[0086] Comparative Example 2

[0087] Step 1: Add 10 grams of Ni 0.16 Co 0.16 Mn 0.68 The CO3 precursor and 4.125 g of lithium carbonate were added to a ball mill jar, and polyurethane balls were added as milling beads at a volume ratio of 1:1. The mixture was then milled in a planetary ball mill at 200 rpm for 3 hours and then sieved.

[0088] Step 2: Place the powder obtained in Step 1 into a crucible and then into a muffle furnace. First, heat the crucible to 350℃ at a heating rate of 5℃ / min and hold for 5 hours. Then, heat the crucible to 700℃ at a heating rate of 5℃ / min and hold for 15 hours. Finally, heat the crucible to 860℃ at a heating rate of 5℃ / min and hold for 5 hours to obtain the original uncoated lithium-rich manganese-based cathode material Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0089] Comparative Example 3

[0090] Step 1: Add 10 grams of Ni 0.25 Mn 0.75 The CO3 precursor and 4.21 g of lithium carbonate were added to a ball mill jar, and polyurethane balls were added as milling beads at a volume ratio of 1:1. The mixture was then milled at 200 rpm for 3 hours in a planetary ball mill and then sieved.

[0091] Step 2: Place the powder obtained in Step 1 into a crucible and then into a muffle furnace. Heat the crucible to 350℃ at a heating rate of 5℃ / min and hold for 5 hours. Then heat the crucible to 700℃ at a heating rate of 5℃ / min and hold for 15 hours. Finally, heat the crucible to 860℃ at a heating rate of 5℃ / min and hold for 5 hours to obtain the original uncoated lithium-rich manganese-based cathode material Li. 1.2 Ni 0.2 Mn 0.6 O2.

[0092] The cathode materials of the above-obtained embodiments and comparative examples were characterized.

[0093] Performance parameter characterization:

[0094] (I) Morphological characteristics:

[0095] like Figure 1-2 As shown, the surface morphology of the cathode materials prepared in Example 1 and Comparative Example 1 was characterized using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). Figure 1Figure a is a TEM image of Comparative Example 1, and Figure b is a TEM image of Example 1. Figure 2 Figure a shows the STEM image of Comparative Example 1, and Figure b shows the STEM image of Example 1. As can be seen from the figures, compared to the original material surface, the crystal lattice structure of the lithium-rich manganese-based cathode material treated with aluminum sulfate transforms into a spinel structure, with a spinel structure thickness of approximately 2-4 nm. Figure 1 As shown in Figure b, the outermost layer of the material in Embodiment 1 of the present invention has an amorphous coating layer.

[0096] (II) Composition Characterization:

[0097] The lithium salt coating amount in Example 1 of this invention is only 0.3 wt%, which is too small to be characterized using conventional methods. To confirm the composition of the coating material of the surface-modified lithium-rich cathode material, the lithium sulfate coating amount in Example 1 was increased to 5 wt%, i.e., 10 g Ni. 0.35 Mn 0.65 CO3 carbonate precursor, 4.15 g lithium carbonate, and 471.66 mg aluminum sulfate were prepared using the same process and characterized by XRD. The results are as follows: Figure 3 As shown, characteristic peaks of lithium sulfate (2θ = 22.2°) and aluminum oxide (2θ = 43.4°) appeared in the synthesized sample, which indicates that the reaction products of aluminum salt and lithium raw materials in Example 1 of this invention are lithium sulfate and aluminum oxide.

[0098] The surfaces of the cathode materials in Example 1 and Comparative Example 1 were analyzed using X-ray photoelectron spectroscopy (XPS), and the results are as follows: Figure 4 As shown. From Figure 4 As can be seen from a, compared to the uncoated lithium-rich manganese-based cathode material Li... 1.15 Ni 0.30 Mn 0.55 O2 (NLRM in the figure), surface-modified lithium-rich manganese-based cathode material Li 1.15 Ni 0.30 Mn 0.55 A new Al-O peak appeared at 73 eV for O2 (ANLRM in the figure), which proves that aluminum is doped on the surface; Figure 4 In b, the S2p spectra at different etching times also prove the existence of a sulfate coating layer on the surface, while combining with... Figure 4 The shift in the S2p peak position in c and 4d proves that the lithium-rich manganese-based cathode material after surface modification is coated with a layer of lithium sulfate. Therefore, combined with XPS, TEM, and STEM results, it is proved that alumina exists in the form of surface doping of the cathode material, and the lithium sulfate cathode material exists in the form of a surface coating layer.

[0099] (III) Electrochemical performance testing:

[0100] Electrochemical tests were performed on each example and comparative example:

[0101] All examples and comparative examples were prepared as half-cells. The specific button cell manufacturing steps are as follows:

[0102] (1) Liquid lithium-ion batteries were prepared using the cathode materials obtained in Examples 1-4 and Comparative Examples 1-3 according to the following steps:

[0103] Electrode preparation: A slurry was prepared according to the ratio of positive electrode material: Super P: polyvinylidene fluoride (PVDF) = 95:2.5:2.5, and then coated onto a 20µm thick aluminum foil to produce a positive electrode sheet with an areal density of 4-5 mg / cm³. 2 .

[0104] Battery Assembly: Button batteries were assembled using R2032 button battery casings. The positive electrode was obtained by coating lithium sulfate-rich manganese-based positive electrode materials from Examples 1-4 and Comparative Examples 1-3, with metallic lithium as the negative electrode. A polyethylene (PE) separator coated with alumina was used. 80 μL of commercially available high-voltage lithium-rich electrolyte was added to obtain the button battery. The commercially available high-voltage lithium-rich electrolyte consisted of a 1 mol / L mixture of lithium hexafluorophosphate (LiPF6)@ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DEC volume ratio 1:1).

[0105] (2) The cathode materials obtained in Example 1 and Comparative Example 1 were used to prepare an in-situ solid-state lithium-ion battery according to the following steps:

[0106] Following the preparation process of the positive electrode sheet in (1) above, the positive electrode materials of Example 1 and Comparative Example 1 were used to prepare positive electrode sheets as positive electrodes for lithium batteries. Metallic lithium was used as the negative electrode, and an alumina-coated PE separator was used. A button cell case of R2032 was used to assemble solid-state batteries. A polymerization precursor solution was injected into the battery case. The polymerization precursor solution included: butyl acrylate monomer, lithium salt LiTFSi, additive lithium difluorooxalate borate (LiDFOB) + succinate at 40 wt% of solvent mass, and initiator azobisisobutyl (AIBN) at 0.5 wt% of solvent mass. Specifically, the butyl acrylate monomer was 80 μL, the lithium salt LiTFSi was 0.8 mol / L, the additive was 0.2 mol / L, and the initiator was 0.5 wt%. The assembled button cell was heated in a 60°C oven for 24 h to polymerize and obtain an in-situ solid-state battery.

[0107] Electrochemical charge-discharge tests were conducted on lithium-ion batteries composed of the cathode materials of the embodiments and comparative examples of the present invention:

[0108] 1) 1C Cycling Performance Test at 30℃: The coin cells of the liquid batteries assembled with the cathode materials in Examples 1-4 and Comparative Examples 1-3 were tested using a blue electric current meter. The prepared coin cells were placed in a high-temperature oven at 30℃ for charge-discharge testing, with a voltage range of 2.0V-4.8V. Two cycles of 0.1C charge-discharge activation were performed, followed by constant current charge-discharge at 1C for 500 cycles. Data on parameters such as initial discharge capacity, initial coulombic efficiency, discharge capacity at the 500th cycle, capacity retention rate at the 500th cycle, and voltage retention rate were obtained. Table 1 shows the electrochemical performance of the liquid lithium-ion batteries assembled with cathode materials in each example and comparative example at 1C current density at 30℃.

[0109] Table 1: Electrochemical performance at 1C current density at 30℃.

[0110]

[0111] Figure 5 The figures shown are electrochemical data graphs of the cathode materials in Example 1 and Comparative Example 1 of this invention. Figure 6 This is a comparison and structural schematic diagram of the voltage decay of the positive electrode material in Embodiment 1 and Comparative Example 1 of the present invention.

[0112] Combination Figure 5 and Figure 6 As shown in Table 1, it can be seen that the initial discharge capacity of the cathode materials in Examples 1 and 2 at 0.1C is 280 mAh / g and 283 mAh / g, respectively, while the initial discharge capacity of the cathode material in Comparative Example 1 at 0.1C is 270 mAh / g (as shown in Table 1). Figure 5 a) It is evident that the coated cathode material exhibits a higher initial discharge capacity at 0.1C, with Examples 1 and 2 showing increases of 10 mAh / g and 13 mAh / g, respectively, compared to Comparative Example 1. The initial discharge capacities of Examples 1-2 at 1C are 230 mAh / g and 226 mAh / g, while Comparative Example 1 is 220 mAh / g. This demonstrates that the discharge specific capacity of the aluminum sulfate-coated lithium-rich manganese-based cathode material of the present invention is increased by 10 mAh / g and 6 mAh / g, respectively. Regarding the initial coulombic efficiency, Examples 1-2 are 86.4% and 84.71%, respectively, both higher than the 84% of Comparative Example 1. Furthermore, at 30°C and a 1C current density, after 500 cycles between 2.0V and 4.8V, the capacity retention rates of the cathode materials in Examples 1-2 are 93.58% and 90.83%, respectively, while that of Comparative Example 1 is only 87.5% (e.g., ...). Figure 5 (b) It is evident that the aluminum sulfate-coated lithium-rich manganese-based cathode material exhibits superior capacity retention at a high voltage of 4.8V compared to the uncoated material. Furthermore, the materials in Examples 1-2 show voltage decay rates of 0.28 mV / cycle and 0.42 mV / cycle after 500 cycles, respectively, while Comparative Example 1 shows 0.58 mV / cycle (e.g., ...). Figure 5 c. Figure 6 As can be seen, the voltage decay rate of the uncoated material in Comparative Example 1 is 0.3 mV / cycle higher than that of the lithium-rich material coated with aluminum sulfate in Example 1, which is 51.7% higher. Therefore, the lithium-rich manganese-based cathode material coated with aluminum sulfate exhibits very low voltage decay. After 500 cycles, the specific energy retention rate of Example 1 is 90%, while that of Comparative Example 1 is only 80.5% after 1500 cycles, representing a 9.5% improvement in specific energy retention. Examples 1-2 of the present invention exhibit lower voltage decay and higher specific capacity after 500 cycles, thus demonstrating higher energy density. The modified material in Example 1 still exhibits a discharge specific energy (calculated based on the active material) of 734 Wh / kg after 500 stable cycles at a 1C cycling rate, while the discharge specific energy of Comparative Example 1 is only 633 Wh / kg. Example 1 is 101 Wh / kg higher than Comparative Example 1. After long-term cycling following lithium sulfate coating, the material of this invention still possesses a very high energy density, which greatly enhances the market competitiveness of lithium-rich manganese-based cathode materials. A comparison of Examples 1-2 and Comparative Example 1 shows that the surface-modified lithium-rich manganese-based cathode material of this invention exhibits excellent high-voltage cycling stability and low voltage decay. This is because the lithium sulfate surface modification creates a stable local oxygen environment on the material surface, reducing irreversible oxygen release and improving structural stability. Therefore, the lithium-rich manganese-based material prepared using this method exhibits excellent high-voltage cycling stability, high specific capacity, and high energy density, which significantly enhances its market competitiveness.

[0113] Example 3 uses 0.3 wt% lithium sulfate to coat lithium-rich manganese-based cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, Li, a lithium-rich manganese-based cathode material in Comparative Example 2 1.2 Ni 0.13 Co 0.13 Mn 0.54O2 does not have a lithium sulfate coating. It can be seen that the cathode material of Example 3 has an initial discharge capacity of 296 mAh / g at 0.1C, while the cathode material of Comparative Example 2 has an initial discharge capacity of 290 mAh / g at 0.1C, indicating that the coated cathode material has a higher initial discharge capacity at 0.1C. The initial discharge capacity of Example 3 at 1C is 248 mAh / g, while that of Comparative Example 2 is 250 mAh / g. In terms of initial coulombic efficiency, Example 3 is 85.09%, while Comparative Example 2 is 80%, showing that Example 3 is significantly higher than Comparative Example 3. Furthermore, at 30°C and a 1C current density, after 500 cycles between 2.0V and 4.8V, the capacity retention rate of the cathode material of Example 3 is 88.57%, while that of Comparative Example 2 is only 74.76%. Therefore, the aluminum sulfate-coated lithium-rich manganese-based cathode material Li... 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 exhibits superior capacity retention at a high voltage of 4.8V compared to the uncoated material, exceeding it by approximately 13.81%. Furthermore, the voltage decay rate of the cathode material in Example 3 after 500 cycles is 0.88 mV / cycle, while that in Comparative Example 2 is 1 mV / cycle. This demonstrates that the voltage decay rate of the uncoated lithium sulfate material in Comparative Example 2 is 0.12 mV / cycle higher than that in Example 2, indicating a significant voltage decay. Therefore, the lithium sulfate-coated lithium-rich manganese-based cathode material Li... 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 exhibits very low voltage decay. A comparison of Example 3 and Comparative Example 2 shows that, using different lithium-rich manganese-based cathode material substrates, the surface-modified lithium-rich manganese-based cathode material of this invention still demonstrates excellent high-voltage cycle stability, low voltage decay, and superior electrochemical performance.

[0114] Example 4 uses 0.3 wt% lithium sulfate to coat lithium-rich manganese-based cathode material Li 1.2 Ni 0.2 Mn 0.6 O2, Li, a lithium-rich manganese-based cathode material in Comparative Example 3 1.2 Ni 0.2 Mn 0.6O2 lacks a lithium sulfate coating. It can be seen that the cathode material of Example 4 has an initial discharge capacity of 269.32 mAh / g at 0.1C, while the cathode material of Comparative Example 3 has an initial discharge capacity of 257 mAh / g at 0.1C. The initial discharge capacity of Example 4 at 1C is 217.9 mAh / g, while that of Comparative Example 3 is 207.8 mAh / g, showing that the initial discharge capacities of Example 4 at both 0.1C and 1C are significantly higher than those of Comparative Example 3. Furthermore, after 500 cycles at 30°C and a 1C current density between 2.0V and 4.8V, the capacity retention rate of the cathode material of Example 4 is 88.08%, while that of Comparative Example 3 is only 81.44%. Therefore, the lithium-rich manganese-based cathode material Li coated with aluminum sulfate exhibits good performance. 1.2 Ni 0.2 Mn 0.6 O2 exhibits superior capacity retention at a high voltage of 4.8V compared to the uncoated material. Furthermore, the cathode material of Example 4 shows a voltage decay rate of 0.64 mV / cycle after 500 cycles, while Comparative Example 3 shows 0.65 mV / cycle. The comparison between Example 4 and Comparative Example 3 demonstrates that, even with different lithium-rich manganese-based cathode material substrates, the surface-modified lithium-rich manganese-based cathode material of this invention still exhibits excellent high-voltage cycle stability, low voltage decay, and superior electrochemical performance.

[0115] 2) Rate discharge performance test at 30℃: The button cells assembled with the positive electrode materials in Example 1 and Comparative Example 1 were tested using a Blue Electric Tester. The voltage range was 2.0V-4.8V, and constant current charging and discharging was performed at a current of 1C. Constant current discharge cycles were performed for 5 cycles at currents of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C respectively, and the discharge cutoff voltage was 2.0V.

[0116] Table 2 shows the rate performance of liquid lithium-ion batteries assembled with cathode materials of Example 1 and Comparative Example 1, tested at 30°C.

[0117]

[0118] The specific data for the rate performance tests of the cathode materials in Example 1 and Comparative Example 1 are as follows. Figure 5As shown in Figure d, the specific capacities of Example 1 after 5 cycles of constant current discharge at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C were 275 mAh / g, 258 mAh / g, 241 mAh / g, 226 mAh / g, 206 mAh / g, and 185 mAh / g, respectively. In contrast, the specific capacities of Comparative Example 1 after 5 cycles of constant current discharge at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C were 264 mAh / g, 249 mAh / g, 231 mAh / g, 213 mAh / g, 196 mAh / g, and 169 mAh / g, respectively. It can be seen that the difference in specific capacity between the cathode materials of Example 1 and Comparative Example 1 gradually increases with increasing current density. At current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C, Example 1 exhibits a specific capacity that is 9-13 mAh / g higher than that of Comparative Example 1. At a current density of 5C, Example 1 exhibits a specific capacity that is 16 mAh / g higher than that of Comparative Example 1. This demonstrates that at high rates, the lithium-rich cathode material of the present invention, after being coated with lithium sulfate, has a higher specific capacity, better rate performance, and better voltage retention.

[0119] 3) First-cycle discharge specific capacity and coulombic efficiency test of 0.1C in-situ solid-state battery at 30℃: The button batteries assembled with the positive electrode materials in Example 1 and Comparative Example 1 were tested using a blue electric tester. The prepared button batteries were placed in a high-temperature oven at 30℃ for charge and discharge tests, with a voltage range of 2.0V-4.8V. The batteries were activated by 0.1C charge and discharge for two cycles to obtain the first discharge capacity and the first coulombic efficiency.

[0120] Table 3 shows the discharge capacity test data of the in-situ solid-state lithium-ion batteries assembled with cathode materials in Example 1 and Comparative Example 1.

[0121] 0.1C discharge capacity mAh / g 1C discharge capacity mAh / g Example 1 272 229 Comparative Example 1 259 214

[0122] After assembling the cathode materials obtained in Example 1 and Comparative Example 1 into an in-situ solid-state battery, the initial discharge capacity of Example 1 at 0.1C was 272 mAh / g, while that of the cathode material in Comparative Example 1 was 259 mAh / g. This shows that the coated cathode material has a higher initial discharge capacity of 13 mAh / g at 0.1C. The in-situ solid-state battery obtained in Example 1 had an initial discharge capacity of 229 mAh / g at 1C, while that of Comparative Example 1 was 214 mAh / g. Therefore, the aluminum sulfate-coated lithium-rich manganese-based cathode material of this invention has a 15 mAh / g higher discharge specific capacity. Based on the in-situ solid-state batteries assembled from the cathode materials of Example 1 and Comparative Example 1, the surface-modified lithium-rich manganese-based cathode material of the present invention still exhibits very good specific capacity when applied to solid-state batteries. This is because the lithium sulfate coating of the present invention and the cathode material matrix can form a more robust lithium-ion transport channel, and the lithium-ion interface conduction between the cathode material and the solid electrolyte is enhanced, enabling the modified lithium-rich manganese-based cathode material to have better lithium-ion diffusion ability in solid-state batteries, thereby achieving higher capacity.

[0123] This demonstrates that the surface-modified lithium-rich cathode material of the present invention combines surface aluminum doping, surface rearrangement, and interfacial coating, achieving optimized adjustment of the surface structure of the lithium-rich cathode material. This effectively improves the interfacial problem between the lithium-rich cathode material and the solid electrolyte, significantly enhancing the electrochemical performance of the cathode material. When used in lithium-ion batteries, the lithium-rich cathode material of the present invention exhibits excellent high-voltage cycle stability, superior rate performance, long cycle life, high specific capacity, and high energy density.

[0124] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A surface-modified lithium-rich cathode material, characterized in that, The surface-modified lithium-rich cathode material includes: Lithium-rich cathode material matrix, lithium salt coating layer generated through in-situ reaction, and spinel structure transition layer; The spinel structure transition layer is located between the lithium-rich cathode material matrix and the lithium salt coating layer; The lithium salt coating layer is generated by in-situ reaction of aluminum salt with lithium raw material; wherein, the lithium raw material includes lithium oxide and / or materials that can generate lithium oxide through thermal decomposition, and the lithium salt coating layer is generated by in-situ reaction of the lithium oxide with aluminum salt; The spinel structure transition layer and lithium salt coating layer on the surface of the lithium-rich cathode material matrix contain Al elements with a concentration gradient distribution, which combine with O elements to form Al-O bonds.

2. The surface-modified lithium-rich cathode material according to claim 1, characterized in that, The lithium-rich cathode material matrix is ​​a lithium-rich manganese-based cathode material with the chemical formula: xLi2MnO3·(1-x)LiTMO2; Where 0≤x≤1, and TM is one or more of Ni, Co, Mn, Al, Zn, Mg, Zr, and Cr.

3. The surface-modified lithium-rich cathode material according to claim 1, characterized in that, The aluminum salts include one or more of aluminum sulfate, aluminum silicate, and aluminum sulfide. The lithium raw materials include one or more of lithium oxide, lithium carbonate, lithium hydroxide, and lithium acetate. The lithium salt coating layer accounts for 0.1wt%-1wt% of the total mass of the lithium-rich cathode material, and the lithium salt coating layer includes one or more of lithium sulfate, lithium silicate, and lithium sulfide.

4. The surface-modified lithium-rich cathode material according to claim 1, characterized in that, The general chemical formula of the spinel structure transition layer is: Li4Al y M z Mn 5-y-z O 12 Wherein, 0 < y ≤ 1, 0 ≤ z ≤ 1, and y + z ≤ 1; M includes one or more of Ni, Co, Zn, Mg, Zr, and Cr, and the thickness of the spinel structure transition layer is less than or equal to 4 nm.

5. The surface-modified lithium-rich cathode material according to claim 1, characterized in that, The Al element accounts for 0.1%-1% of the total atomic percentage of the lithium-rich cathode material.

6. A method for preparing a surface-modified lithium-rich cathode material according to any one of claims 1-5, characterized in that, The preparation method includes: Lithium raw materials, lithium-rich cathode material matrix precursors, and aluminum salts are mixed and ball-milled according to the required mass ratio. The product obtained by ball milling was sintered at 800℃-900℃ for 5-12 hours to obtain the surface-modified lithium-rich cathode material.

7. The preparation method according to claim 6, characterized in that, The lithium raw materials include one or more of lithium oxide, lithium carbonate, lithium hydroxide, and lithium acetate. The chemical formula of the lithium-rich cathode material matrix precursor is Ni. a Co b Mn c TM 1-a-b-c CO3, wherein 0≤a≤0.45, 0≤b≤0.16, 0.39≤c≤1; TM is one or more of Al, Zn, Mg, Zr, and Cr; The aluminum salts include one or more of aluminum sulfate, aluminum silicate, and aluminum sulfide. Prior to the high-temperature sintering, the process further includes: pre-firing the product obtained from the ball milling at a temperature below 800°C.

8. The preparation method according to claim 7, characterized in that, The chemical formula of the lithium-rich cathode material matrix precursor is Ni. m Mn 1-m CO3, 0.25≤m≤0.

45.

9. A positive electrode sheet, characterized in that, The positive electrode sheet comprises: the surface-modified lithium-rich positive electrode material according to any one of claims 1-5, or the surface-modified lithium-rich positive electrode material prepared by the preparation method according to any one of claims 6-8.

10. A lithium battery, characterized in that, The lithium battery includes the surface-modified lithium-rich cathode material according to any one of claims 1-5, or the surface-modified lithium-rich cathode material obtained by the preparation method according to any one of claims 6-8, or the cathode sheet according to claim 9. The lithium battery includes any one of the following: liquid lithium-ion battery, liquid metal lithium battery, hybrid solid-liquid lithium-ion battery, hybrid solid-liquid metal lithium battery, in-situ solidified lithium battery, solid lithium-ion battery, and solid metal lithium battery.

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