Modified lithium-rich manganese-based material and preparation method therefor, and positive electrode sheet and secondary battery

Abstract

Provided in the present application are a modified lithium-rich manganese-based material and a preparation method therefor, and a positive electrode sheet and a secondary battery. The modified lithium-rich manganese-based material comprises a matrix, and a first coating layer, a second coating layer and a third coating layer sequentially arranged on the matrix; the matrix comprises a lithium-rich manganese-based material doped with an element M; the first coating layer comprises a lithium oxide containing an element M; the second coating layer comprises a metal phosphate and a solid electrolyte; and the third coating layer comprises a nano metal oxide.

Description

Modified lithium-rich manganese-based materials and their preparation methods, positive electrode sheets and secondary batteries Technical Field

[0001] This application relates to the field of battery technology, and in particular to a modified lithium-rich manganese-based material and its preparation method, a positive electrode sheet, and a secondary battery. Background Technology

[0002] Lithium-ion batteries are widely used in 3C products, energy storage systems, and power batteries due to their advantages such as high energy density, long cycle life, and good rate performance. The cathode material, as the core component of a lithium-ion battery, is the source of active lithium ions and directly determines the battery's energy density. It is also a key factor affecting the battery's power density, cycle life, and safety performance.

[0003] Lithium-rich manganese-based materials have become a popular cathode material due to their advantages such as high discharge specific capacity, high energy density, and high safety. However, the poor thermal stability of traditional lithium-rich manganese-based materials leads to significant deterioration in their storage performance, cycle performance, and gas generation under high-temperature conditions, severely limiting their commercial application. Summary of the Invention

[0004] Based on this, according to various embodiments of this application, a modified lithium-rich manganese-based material and its preparation method, a positive electrode sheet, and a secondary battery are provided. The technical solution is as follows:

[0005] In a first aspect, this application provides a modified lithium-rich manganese-based material, comprising a matrix and a first coating layer, a second coating layer and a third coating layer sequentially disposed on the matrix;

[0006] The matrix comprises a lithium-rich manganese-based material doped with element M, wherein element M includes one or more of Nb, Sn, Ta and Sb;

[0007] The first coating layer comprises lithium oxide containing the element M;

[0008] The second coating layer comprises a metal phosphate salt and a solid electrolyte, wherein the metal ions in the metal phosphate salt have a chemical valence greater than 1, and the solid electrolyte contains lithium ions;

[0009] The third coating layer comprises nano-metal oxides.

[0010] In some embodiments, the matrix is ​​expressed as: (1-x)Li₂MnO₃·xLiNi a Mn b Co c M dO2, where 0 <x<1,a+b+c=1,0.30≤a<0.80,0.30≤b<0.80,c≥0,0<d≤0.05。

[0011] In some embodiments, the metal phosphate salt includes one or more of cobalt phosphate, manganese phosphate, nickel phosphate, magnesium phosphate, aluminum phosphate, and cerium phosphate.

[0012] In some embodiments, the solid electrolyte includes one or more of lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium lanthanum zirconate, and lithium lanthanum titanate.

[0013] In some embodiments, the mass ratio of the metal phosphate salt to the solid electrolyte is 1:(0.80 to 1.20).

[0014] In some embodiments, the nano-metal oxide includes one or more of TiO2, ZrO2, Al2O3, WO3, CeO2, and ZnO.

[0015] In some embodiments, the average particle size of the nano-metal oxide is 10 nm to 100 nm.

[0016] In some embodiments, the specific surface area of ​​the nano-metal oxide is 0.1 m². 2 / g~200m 2 / g.

[0017] In some embodiments, the mass ratio of the substrate, the first coating layer, the second coating layer, and the third coating layer is 100:(0.05-0.6):(0.05-0.6):(0.05-0.2).

[0018] A second aspect of this application provides a method for preparing the modified lithium-rich manganese-based material as described above, comprising the following steps:

[0019] A first intermediate is obtained by mixing a lithium-rich manganese-based precursor, a lithium source, and a dopant and performing a first sintering.

[0020] The first intermediate, metal phosphate salt, and solid electrolyte are mixed and then subjected to a second sintering process to obtain the second intermediate.

[0021] The second intermediate and nano-metal oxide are mixed and then subjected to a third sintering process to obtain the modified lithium-rich manganese-based material.

[0022] In some embodiments, the expression for the lithium-rich manganese-based precursor is: Ni e Mn f Co g (OH)2 or Ni e Mn f Cog CO3, where e+f+g=1, 0.30≤e<0.80, 0.30≤f<0.80, g≥0.

[0023] In some embodiments, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium fluoride, lithium nitrate, lithium sulfate, lithium acetate, and lithium oxalate.

[0024] In some embodiments, the dopant includes one or more of oxides, fluorides, hydroxides, carbonates, sulfates, oxalates, acetates, and ethoxides containing the element M.

[0025] In some embodiments, the molar ratio of the transition metal element in the lithium-rich manganese-based precursor to the lithium element in the lithium source is 1:(1.10 to 1.50).

[0026] In some embodiments, the mass ratio of the lithium-rich manganese-based precursor to the dopant is 100:(0.05 to 0.60).

[0027] In some embodiments, the sintering temperature of the first sintering is 850°C to 950°C, the sintering time is 5h to 15h, and the sintering atmosphere is an oxidizing atmosphere.

[0028] In some embodiments, the ratio of the mass of the first intermediate to the total mass of the metal phosphate salt and the solid electrolyte is 100:(0.05 to 0.6).

[0029] In some embodiments, the mass ratio of the metal phosphate salt to the solid electrolyte is 1:(0.80 to 1.20).

[0030] In some embodiments, the mass ratio of the second intermediate to the nano-metal oxide is 100:(0.05 to 0.2).

[0031] In some embodiments, the sintering temperature of the second sintering is 650°C to 800°C, the sintering time is 3h to 6h, and the sintering atmosphere is an oxidizing atmosphere.

[0032] In some embodiments, the sintering temperature of the third sintering is 300℃~500℃, the sintering time is 3h~6h, and the sintering atmosphere is an oxidizing atmosphere.

[0033] In a third aspect, this application provides a positive electrode sheet comprising the modified lithium-rich manganese-based material as described above, or the modified lithium-rich manganese-based material prepared by the method described above.

[0034] In a fourth aspect, this application provides a secondary battery, including the positive electrode plate as described above. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the disclosed drawings without creative effort.

[0036] Figure 1 is a schematic diagram of the structure of the modified lithium-rich manganese-based material in one embodiment;

[0037] Figure 2 is a schematic flowchart of the preparation method of the modified lithium-rich manganese-based material in one embodiment;

[0038] Figure 3 is a surface electron microscope image of the modified lithium-rich manganese-based material in Example 1;

[0039] Figure 4 is a cross-sectional electron microscope image of the modified lithium-rich manganese-based material of Example 1;

[0040] Figure 5 shows the surface electron microscope image of the modified lithium-rich manganese-based material of Comparative Example 1.

[0041] Figure 6 is a cross-sectional electron microscope image of the modified lithium-rich manganese-based material of Comparative Example 1.

[0042] Figure 7 is a comparison of the total capacity of the modified lithium-rich manganese-based materials of Example 1 and Comparative Example 1.

[0043] Figure 8 is a comparison of the all-electric high-temperature storage performance at 60°C of the modified lithium-rich manganese-based materials of Example 1 and Comparative Example 1.

[0044] Figure 9 is a comparison of the all-electric high-temperature cycling performance at 60°C of the modified lithium-rich manganese-based materials of Example 1 and Comparative Example 1.

[0045] Figure 10 is a comparison of the all-electric high-temperature gas generation performance at 60°C of the modified lithium-rich manganese-based materials of Example 1 and Comparative Example 1.

[0046] Reference numerals: 10, 20, 30, 31, 32, 40.

[0047] Details of one or more embodiments of this application are set forth in the following description, and other features, objects, and advantages of this application will become apparent from the specification and its claims. Detailed Implementation

[0048] To facilitate understanding of this application, the following detailed description is provided in conjunction with specific embodiments. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0049] 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. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0050] In this application, "and / or" means any and all combinations of one or more of the related listed items. "At least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two, three, etc., unless otherwise expressly and specifically defined. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise expressly and specifically defined.

[0051] When a numerical range is disclosed in this application, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed in this application should be understood to include any and all subranges to which they are included.

[0052] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0053] In this application, "above" or "below" includes the number itself. For example, "below 1" includes 1.

[0054] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0055] In this application, room temperature refers to indoor temperature, normal temperature, or general temperature. Generally, room temperature can be any of the following temperature ranges: 23℃±2℃, 25℃±5℃, or 20℃±5℃.

[0056] the term

[0057] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0058] Particle size: For spherical particles, particle size refers to the diameter of the spherical particle. For non-spherical particles, particle size usually refers to the equivalent particle size (generally referred to as particle size), which can be obtained by observation using a scanning electron microscope (SEM) or by measurement using a laser particle size analyzer. The equivalent particle size means that when a particle has a physical property that is the same as or similar to that of a homogeneous spherical particle, the diameter of the actual particle is represented by the diameter of the spherical particle. Unless otherwise stated or contradictory, the particle size in this application refers to the equivalent particle size.

[0059] Particle size distribution parameter: In the particle size distribution curve, the particle size corresponding to the cumulative particle size distribution percentage reaching N% is called the DN particle size. This indicates that particles smaller than this size account for N% of all particles, where N = 0–100. When N = 100, the D100 particle size represents the particle size corresponding to the cumulative particle size distribution percentage reaching 100%. When N = 50, the D50 particle size is the particle size corresponding to the cumulative particle size distribution percentage reaching 50%, representing the median particle size, indicating that particles smaller and larger than this size each account for 50%. For example, a D50 particle size of 1 mm means that particles smaller than 1 mm and particles larger than 1 mm each account for 50% of all particles. The DN particle size can be measured using a laser particle size analyzer.

[0060] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0061] Traditional lithium-rich manganese-based materials suffer from poor thermal stability, leading to significant deterioration in their storage performance, cycle performance, and gas generation under high-temperature conditions. Therefore, a method to effectively improve the high-temperature performance of lithium-rich manganese-based materials is urgently needed. To address these issues, industry, academia, and research institutions have proposed several optimization methods, mainly in the following three aspects: (1) improving the structural stability of the material through doping modification; (2) optimizing the surface element distribution and morphology of the material through post-treatment; and (3) improving the interfacial stability of the material through coating treatment. However, these solutions have not been very effective in improving the high-temperature performance of lithium-rich manganese-based materials, and there is still a significant gap before commercial application.

[0062] Based on this, in the first aspect of this application, a modified lithium-rich manganese-based material is provided to solve the problem of poor thermal stability of traditional lithium-rich manganese-based materials, giving it outstanding advantages in high-temperature storage, high-temperature cycling and high-temperature gas production, while also ensuring that the capacity and rate performance of the material are further improved.

[0063] In some embodiments, the modified lithium-rich manganese-based material includes a matrix and a first coating layer, a second coating layer and a third coating layer disposed sequentially on the matrix.

[0064] The matrix includes a lithium-rich manganese-based material doped with element M, wherein element M includes one or more of Nb, Sn, Ta and Sb;

[0065] The first coating layer includes lithium oxide containing element M;

[0066] The second coating layer includes a metal phosphate salt and a solid electrolyte. The metal ions in the metal phosphate salt have a chemical valence greater than 1, and the solid electrolyte contains lithium ions.

[0067] The third coating layer consists of nano-metal oxides.

[0068] Compared with traditional technologies, the modified lithium-rich manganese-based material provided in this application has at least the following beneficial effects: (1) Through the doping modification of the matrix and the synergistic effect of the three-layer coating structure, the internal structure of the crystal is stabilized, the surface structure of the material is strengthened, and the formation of through cracks in the modified lithium-rich manganese-based material is avoided, effectively suppressing its structural collapse and oxygen release during charging and discharging; (2) The ionic conductivity of the material is improved, and the Li-... +(2) Improve the diffusion and migration speed between the material and the electrolyte, thereby enhancing the charge-discharge capacity, cycle performance and rate performance of the material; (3) Improve the wettability of the material surface with the electrolyte, reduce the polarization of the material during the charge-discharge process, thereby enhancing the cycle performance and rate performance of the material; (4) Improve the thermal stability of the material, effectively improve the storage performance and cycle performance of the material under high temperature conditions, and reduce the problem of high temperature gas generation. Therefore, the modified lithium-rich manganese-based material provided in this application has the characteristics of stable surface structure, excellent electrochemical performance and high cycle stability. It can significantly improve the thermal stability and high temperature resistance of the material on the basis of improving the capacity and rate performance of the material, making it outstanding in high temperature storage, high temperature cycling and suppression of high temperature gas generation, and very suitable as a commercial battery cathode material.

[0069] Please refer to Figure 1, which is a structural schematic diagram of a modified lithium-rich manganese-based material in one embodiment. As shown in Figure 1, the modified lithium-rich manganese-based material includes a substrate 10, and a first coating layer 20, a second coating layer 30, and a third coating layer 40 sequentially disposed on the substrate 10.

[0070] Among them, element M, as a high-valence cation, not only does it dope inside the matrix 10, but also exists on the surface of the matrix 10 in the form of lithium oxide, forming the first coating layer 20. This can increase the size of the primary particles and reduce the specific surface area. Compared with the three transition metal elements Mn, Co, and Ni, element M has a larger ionic radius, and the binding energy of the M-O bond is stronger than that of the Mn-O, Co-O, and Ni-O bonds. Therefore, some M elements enter the transition metal sites in the crystal structure, which not only expands the Li interlayer spacing but also benefits Li... + It can be extracted and can also be used with O. 2- This allows for the formation of stronger chemical bonds to suppress the loss of lattice oxygen, stabilize the material structure, and improve the material's cycle performance and rate capability. Meanwhile, some M elements that do not enter the crystal structure exist as lithium oxides at grain boundaries and on the surface of the matrix 10, which is beneficial to Li... + It can facilitate the insertion and extraction of electrolytes and reduce electrolyte erosion, further stabilizing the material structure and thus improving the material's cycle performance.

[0071] Optionally, the substrate 10 includes a lithium-rich manganese-based material doped with element M, wherein element M is selected from one or more of Nb, Sn, Ta and Sb.

[0072] As an example, element M can be selected from any one of Nb, Sn, Ta, and Sb, or from at least two of the aforementioned high-valence metal elements, such as Nb and Sn, Nb and Ta, Nb and Sb, Sn and Ta, Sn and Sb, Ta and Sb, and combinations of Nb, Sn, and Ta. Further optionally, element M may include one or more of Nb and Sn.

[0073] Optionally, the expression for matrix 10 is: (1-x)Li₂MnO₃·xLiNi a Mn b Co c M d O2, where 0 <x<1,a+b+c=1,0.30≤a<0.80,0.30≤b<0.80,c≥0,0<d≤0.05。

[0074] Understandably, a, b, c, d, and x represent the number of atoms of the corresponding element or the number of molecules of the corresponding compound molecule. By adjusting the values ​​of a, b, c, d, and x, the content of element M in matrix 10 can be controlled, ensuring a high content of element Mn and a low content of element Co, thereby improving the electrochemical performance of the material while reducing the material cost.

[0075] As an example, x can take values ​​of 0.01, 0.02, 0.05, 0.08, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, 0.95, or 0.99; a can take values ​​of 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, or 0.80. The value of b can be 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, or 0.80; the value of c can be 0, 0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, or 0.29; the value of d can be 0.01, 0.02, 0.03, 0.04, or 0.05, and can further be selected as 0. <d≤0.01。

[0076] Optionally, the first coating layer 20 comprises a lithium oxide containing element M; wherein the lithium oxide containing element M includes one or more of lithium niobium oxide, lithium tin oxide, lithium tantalum oxide, and lithium antimony oxide. Further optionally, the lithium oxide containing element M includes one or more of lithium niobium oxide and lithium tin oxide.

[0077] After forming a first coating layer 20 on the surface of the substrate 10, a second coating layer 30 is formed on the surface of the first coating layer 20. This further reduces the direct contact between the electrolyte and the material, lowers the possibility of structural collapse during battery cycling, and thus improves the structural stability of the material. The second coating layer 30 includes a metal phosphate salt 31 and a solid electrolyte 32. The metal phosphate salt 31 contains alternating metal cations and phosphate ions forming a three-dimensional network structure, which is Li + The insertion / extraction of Li provides a three-dimensional ion diffusion channel, thereby accelerating the Li-3D ion diffusion process. +Transmission efficiency; PO4 3- O 2- The electronegativity is stronger, and transition metals and PO4 are more reactive. 3- The chemical bonds between them are stronger than those between transition metals and lattice oxygen, which can suppress oxygen release from modified lithium-rich manganese-based materials during battery charging and discharging. Solid electrolyte 32 contains lithium ions, whose main function is to enter the three-dimensional network structure formed by the metal phosphate salt, stabilizing this network structure and simultaneously improving the ionic conductivity of the material, thereby increasing the Li-to-metal conductivity. + The diffusion and transfer rates between the modified lithium-rich manganese-based material and the electrolyte.

[0078] Optionally, the metal phosphate salt 31 includes one or more of cobalt phosphate (Co3(PO4)2), manganese phosphate (Mn3(PO4)2), nickel phosphate (Ni3(PO4)2), magnesium phosphate (Mg3(PO4)2), aluminum phosphate (AlPO4), and cerium phosphate (CePO4), and may further be selected as one or more of cobalt phosphate (Co3(PO4)2), aluminum phosphate (AlPO4), and cerium phosphate (CePO4).

[0079] By using the aforementioned metal phosphate salt 31, a three-dimensional porous network structure can be constructed on the surface of the first coating layer 20, thereby improving the Li + While improving transmission efficiency, it also greatly inhibits the corrosion of materials by the electrolyte. Meanwhile, PO4 3- It has strong covalent interactions with transition metal ions, which can suppress the release of lattice oxygen and help enhance the thermal stability of the material.

[0080] Optionally, the solid electrolyte 32 includes one or more of lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), lithium lanthanum zirconate (LLZO), and lithium lanthanum titanate (LLTO), and is further optionally one or more of lithium aluminum titanium phosphate (LATP) and lithium lanthanum zirconate (LLZO).

[0081] Using the aforementioned solid electrolyte 32 can improve the ionic conductivity of the material and accelerate the Li... + This improves the transmission efficiency, thereby enhancing the capacity and rate performance of the material, and also stabilizes the three-dimensional network structure formed by the phosphate metal salt 31, thereby improving the structural stability of the material.

[0082] Optionally, the mass ratio of metal phosphate salt 31 to solid electrolyte 32 is 1:(0.80 to 1.20), for example 1:0.80, 1:0.85, 1:0.90, 1:0.95, 1:1.00, 1:1.05, 1:1.10, 1:1.15 or 1:1.20, and further optionally 1:1.

[0083] By controlling the mass ratio of metal phosphate salt 31 to solid electrolyte 32, the synergistic effect of the two can be improved, which promotes the formation of a more stable three-dimensional network structure in the second coating layer 30, thereby further improving the charge-discharge capacity, rate performance and cycle performance of the material.

[0084] After the first coating layer 20 and the second coating layer 30 are sequentially disposed on the surface of the substrate 10, a third coating layer 40 is also disposed on the surface of the second coating layer 30. The nano-metal oxides in the third coating layer 40 have the characteristics of good chemical stability and high thermal stability, which significantly improves the high-temperature performance of the material. At the same time, they also have the characteristics of large specific surface area, loose and porous, and strong hydrophilicity, which makes the material surface have good wettability with electrolyte. This can reduce the stress between primary particles of the material, reduce the small changes in structure and volume of the material during battery cycling, reduce the polarization of the material during battery charging and discharging, thereby improving the cycle performance, rate performance and high-temperature performance of the material.

[0085] Optionally, the nano-metal oxide in the third coating layer 40 includes one or more of TiO2, ZrO2, Al2O3, WO3, CeO2 and ZnO, and may further be one or more of TiO2, ZrO2 and Al2O3.

[0086] Optionally, the average particle size of the nano-metal oxide is 10 nm to 100 nm, such as 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, and further optionally 20 nm to 60 nm.

[0087] Optionally, the specific surface area of ​​the nano-metal oxide is 0.1 m². 2 / g~200m 2 / g, for example 0.1m 2 / g、1m 2 / g、5m 2 / g, 10m 2 / g、20m 2 / g、40m 2 / g、60m 2 / g、80m 2 / g, 100m 2 / g、120m 2 / g, 140m 2 / g、160m 2 / g、180m 2 / g or 200m 2 / g, further optional to 40m 2 / g~120m 2 / g.

[0088] Optionally, the mass ratio of the substrate 10, the first coating layer 20, the second coating layer 30, and the third coating layer 40 is 100:(0.05~0.6):(0.05~0.6):(0.05~0.2).

[0089] As an example, the mass ratio of the substrate 10 to the first covering layer 20 can be 100:0.05, 100:0.1, 100:0.15, 100:0.2, 100:0.25, 100:0.3, 100:0.35, 100:0.4, 100:0.45, 100:0.5, 100:0.55, or 100:0.6, further preferably 100:(0.1 to 0.3), and even more preferably 100:0.2; the mass ratio of the substrate 10 to the second covering layer 30 can be 100:0.05, 100:0.1, 100:0.15, 100:0.2, 100:0.05, 100:0.0 ... The mass ratio of the substrate 10 to the third covering layer 40 can be 0.25, 100:0.3, 100:0.35, 100:0.4, 100:0.45, 100:0.5, 100:0.55 or 100:0.6, further selectable as 100:(0.1 to 0.3), and even further selectable as 100:0.2; the mass ratio of the substrate 10 to the third covering layer 40 can be 100:0.05, 100:0.08, 100:0.1, 100:0.12, 100:0.15, 100:0.18 or 100:0.2, further selectable as 100:(0.08 to 0.12), and even further selectable as 100:0.1.

[0090] By controlling the mass ratio of the substrate 10, the first coating layer 20, the second coating layer 30, and the third coating layer 40, it is possible to ensure that the material has a suitable concentration of doping element M and form a stable and perfect three-layer coating structure, which makes the material's structural stability, electrochemical performance, and high-temperature resistance performance even better.

[0091] Optionally, the first covering layer 20, the second covering layer 30 and the third covering layer 40 can each be partially covered or completely covered independently.

[0092] In some examples, the first coating layer 20, the second coating layer 30, and the third coating layer 40 are all fully coated. That is, the first coating layer 20 is loaded on all surfaces of the substrate 10 to form a continuous film structure, the second coating layer 30 is loaded on all surfaces of the first coating layer 20 to form a continuous film structure, and the third coating layer 40 is loaded on all surfaces of the second coating layer 30 to form a continuous film structure. This results in a more significant improvement in the structural stability, long-cycle performance, and high-temperature performance of the material.

[0093] In some examples, at least one of the first coating layer 20, the second coating layer 30, and the third coating layer 40 is partially coated and forms a dispersed island structure, which can improve the structural stability, cycling performance, and high-temperature performance of the material while reducing the material preparation cost.

[0094] Understandably, this application does not impose any particular limitation on the D50 particle size of the modified lithium-rich manganese-based material. Compared with the unmodified lithium-rich manganese-based material of the same particle size, the discharge specific capacity, rate performance, and cycle stability of the modified lithium-rich manganese-based material can be significantly improved after doping modification with high-valence cations and three-layer coating treatment.

[0095] Optionally, the D50 particle size of the modified lithium-rich manganese-based material is 1 μm to 20 μm, for example, 1 μm, 5 μm, 10 μm, 15 μm, or 20 μm. More preferably, the D50 particle size of the modified lithium-rich manganese-based material is 3 μm to 15 μm, and modified lithium-rich manganese-based materials within this D50 particle size range exhibit superior electrochemical performance, thermal stability, and high-temperature resistance.

[0096] Optionally, the thickness of the first coating layer 20, the second coating layer 30 and the third coating layer 40 are each independently 10nm to 200nm, for example 10nm, 20nm, 40nm, 60nm, 80nm, 100nm, 120nm, 140nm, 160nm, 180nm or 200nm.

[0097] Understandably, the D50 particle size of the modified lithium-rich manganese-based material can be measured by a laser particle size analyzer, and the thicknesses of the first coating layer 20, the second coating layer 30, and the third coating layer 40 can be observed by a transmission electron microscope (TEM).

[0098] In a second aspect, this application provides a method for preparing a modified lithium-rich manganese-based material, used to prepare the modified lithium-rich manganese-based material as described above.

[0099] Please refer to Figure 2, which is a schematic flowchart of a method for preparing a modified lithium-rich manganese-based material in one embodiment. As shown in Figure 2, the method for preparing the modified lithium-rich manganese-based material includes the following steps:

[0100] S1: Mix lithium-rich manganese-based precursor, lithium source and dopant, and perform first sintering to obtain first intermediate;

[0101] S2: Mix the first intermediate, metal phosphate salt and solid electrolyte, and perform a second sintering to obtain the second intermediate;

[0102] S3: Mix the second intermediate and nano-metal oxide, and perform a third sintering to obtain a modified lithium-rich manganese-based material.

[0103] Understandably, the first intermediate includes a matrix and a first coating layer loaded on the matrix, the second intermediate includes a matrix and a first coating layer and a second coating layer sequentially loaded on the matrix, and the modified lithium-rich manganese-based material includes a matrix and a first coating layer, a second coating layer and a third coating layer sequentially loaded on the matrix. The composition and thickness of the matrix, the first coating layer, the second coating layer and the third coating layer are as described in the first aspect of this application, and will not be repeated here.

[0104] This application utilizes a three-stage sintering process to achieve doping modification and three-layer coating of lithium-rich manganese-based materials. This process effectively stabilizes the surface structure of the material and significantly improves its thermal stability and high-temperature resistance, while enhancing its charge / discharge capacity and rate performance. This results in a modified lithium-rich manganese-based material with stable surface structure, excellent electrochemical performance, and high cycle stability. Furthermore, the three-stage sintering process is simple, efficient, and low-cost, facilitating large-scale production and promoting the commercial application of modified lithium-rich manganese-based materials.

[0105] Optionally, the expression for the lithium-rich manganese-based precursor is: Ni e Mn f Co g (OH)2 or Ni e Mn f Co g CO3, where e+f+g=1, 0.30≤e<0.80, 0.30≤f<0.80, g≥0.

[0106] The aforementioned lithium-rich manganese-based precursors are selected from hydroxides or carbonates containing nickel, cobalt, and manganese. e, f, and g represent the number of atoms of the corresponding elements in the entire precursor molecule. By controlling the values ​​of e, f, and g, a high Mn content and a low Co content can be ensured, which is beneficial for reducing raw material costs.

[0107] Optionally, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium fluoride, lithium nitrate, lithium sulfate, lithium acetate, and lithium oxalate, and may further be lithium carbonate.

[0108] Optionally, the dopant includes one or more of oxides, fluorides, hydroxides, carbonates, sulfates, oxalates, acetates, and ethoxides containing element M, and is further optionally an oxide containing element M. As an example, oxides containing element M include, but are not limited to, Nb₂O₅, SnO₂, Ta₂O₅, or Sb₂O₅.

[0109] Understandably, the raw materials for the aforementioned lithium-rich manganese-based precursor, lithium source, and dopant can contain bound water, such as lithium hydroxide monohydrate, or they can be waterless, such as anhydrous lithium carbonate. This application does not impose any particular limitation on this.

[0110] Optionally, the molar ratio of the transition metal element in the lithium-rich manganese-based precursor to the lithium element in the lithium source is 1:(1.10 to 1.50), for example 1:1.10, 1:1.15, 1:1.20, 1:1.25, 1:1.30, 1:1.35, 1:1.40, 1.45 or 1.50, and further optionally 1.30.

[0111] By controlling the molar ratio of transition metal elements in the lithium-rich manganese-based precursor to lithium elements in the lithium source, the lithium content in the material can be increased, which is beneficial to improving the charge / discharge capacity and rate performance of the material.

[0112] Optionally, the mass ratio of lithium-rich manganese-based precursor to dopant is 100:(0.05 to 0.60), for example 100:0.05, 100:0.10, 100:0.15, 100:0.20, 100:0.25, 100:0.30, 100:0.35, 100:0.40, 100:0.45, 100:0.50, 100:0.55 or 100:0.60, further preferably 100:(0.10 to 0.30), and even more preferably 100:0.20.

[0113] Optionally, the sintering temperature of the first sintering is 850℃~950℃, the sintering time is 5h~15h, and the sintering atmosphere is an oxidizing atmosphere. As an example, the sintering temperature of the first sintering can be 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃; the sintering time of the first sintering can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, or 15h; and the sintering atmosphere of the first sintering can be an air atmosphere or an oxygen atmosphere.

[0114] By controlling the sintering temperature, sintering time, and sintering atmosphere of the first sintering, some high-valence metal cations can enter the crystal structure as stably as possible, and some high-valence metal cations exist in the form of lithium oxides at the grain boundaries or on the surface. At the same time, it ensures that the matrix forms a lithium-rich manganese base matrix structure with high crystallinity and low spinel impurity content.

[0115] Optionally, after the first sintering, the method further includes the following step: sieving the first sintered product to obtain a first intermediate.

[0116] Optionally, the mass ratio of the first intermediate to the total mass of the metal phosphate salt and the solid electrolyte is 100:(0.05 to 0.6), for example 100:0.05, 100:0.1, 100:0.15, 100:0.2, 100:0.25, 100:0.3, 100:0.35, 100:0.4, 100:0.45, 100:0.5, 100:0.55 or 100:0.6, further optionally 100:(0.1 to 0.3), and even more preferably 100:0.2.

[0117] Optionally, the mass ratio of the metal phosphate salt to the solid electrolyte is 1:(0.80 to 1.20), for example 1:0.80, 1:0.85, 1:0.90, 1:0.95, 1:1.00, 1:1.05, 1:1.10, 1:1.15 or 1:1.20, and further optionally 1:1.

[0118] Optionally, the sintering temperature of the second sintering is 650℃~800℃, the sintering time is 3h~6h, and the sintering atmosphere is an oxidizing atmosphere. As an example, the sintering temperature of the second sintering can be 650℃, 680℃, 700℃, 720℃, 740℃, 760℃, 780℃, or 800℃; the sintering time of the second sintering can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h; and the sintering atmosphere of the second sintering can be an air atmosphere or an oxygen atmosphere.

[0119] Optionally, after the second sintering, the method further includes the following step: sieving the second sintering product to obtain a second intermediate.

[0120] Optionally, the mass ratio of the second intermediate to the nano-metal oxide is 100:(0.05 to 0.2), for example 100:0.05, 100:0.08, 100:0.1, 100:0.12, 100:0.15, 100:0.18 or 100:0.2, further preferably 100:(0.08 to 0.12), and even more preferably 100:0.1.

[0121] Optionally, the sintering temperature of the third sintering is 300℃~500℃, the sintering time is 3h~6h, and the sintering atmosphere is an oxidizing atmosphere. As an example, the sintering temperature of the third sintering can be 300℃, 320℃, 350℃, 380℃, 400℃, 420℃, 450℃, 480℃, or 500℃; the sintering time of the third sintering can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h; and the sintering atmosphere of the third sintering can be an air atmosphere or an oxygen atmosphere.

[0122] Optionally, after the third sintering, the following step is also included: sieving the third sintering product to obtain a modified lithium-rich manganese-based material.

[0123] In a third aspect, this application provides a positive electrode sheet comprising the modified lithium-rich manganese-based material described in the first aspect of this application, or the modified lithium-rich manganese-based material prepared by the method described in the second aspect of this application.

[0124] Based on the above-mentioned modified lithium-rich manganese-based materials, the positive electrode sheet has high capacity, good rate performance, excellent cycle performance and good thermal stability, and has outstanding advantages in high-temperature storage, high-temperature cycling and suppression of high-temperature gas generation.

[0125] Optionally, the positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. As an example, the positive current collector has two surfaces opposite each other along the thickness direction, and the positive active layer is disposed on at least one of the two opposite surfaces of the positive current collector.

[0126] Optionally, the positive electrode current collector may be a metal foil or a composite current collector. As an example, the metal foil used as the positive electrode current collector may be aluminum foil. The composite current collector used as the positive electrode current collector includes a polymer layer and a metal layer formed on at least one surface of the polymer layer; the polymer layer is made of materials including, but not limited to, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polystyrene (PS); the metal layer is made of materials including, but not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys.

[0127] Optionally, the positive electrode active layer includes a positive electrode material, which includes the modified lithium-rich manganese-based material described in the first aspect of this application, or the modified lithium-rich manganese-based material prepared by the method described in the second aspect of this application. It is understood that the positive electrode material may be used alone, i.e., the modified lithium-rich manganese-based material described above may be used alone, or two or more may be used in combination, i.e., the modified lithium-rich manganese-based material described above may be used in combination with at least one of the positive electrode materials known in the art. As an example, the positive electrode material includes, but is not limited to: lithium transition metal oxides, lithium phosphates with an olivine structure, and their respective modified compounds. Among them, lithium transition metal oxides include, but are not limited to: lithium cobalt oxides, such as LiCoO2; lithium nickel oxides, such as LiNiO2; lithium manganese oxides, such as LiMnO2 or LiMn2O4; lithium nickel cobalt oxides; lithium manganese cobalt oxides; lithium nickel manganese oxides; lithium nickel cobalt manganese oxides, such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333 LiNi0.5 Co 0.2 Mn 0.3 O2(NCM 523 LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM 211 LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM 622 LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 Lithium nickel cobalt aluminum oxides, such as LiNi 0.85 Co 0.15 Al 0.05 O2; and modified compounds of the aforementioned lithium transition metal oxides. Lithium phosphates with an olivine structure include, but are not limited to: lithium iron phosphate (LiFePO4, LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate (LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0128] Optionally, the positive electrode active layer includes a binder, which includes one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0129] Optionally, the positive electrode active layer includes a conductive agent, which includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon quantum dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] Optionally, the preparation method of the positive electrode sheet includes the following steps: dispersing the positive electrode material, conductive agent and binder in a solvent (e.g., N-methylpyrrolidone) to obtain a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and obtaining the positive electrode sheet after drying, cold pressing and cutting processes.

[0131] In a fourth aspect, this application provides a secondary battery including the positive electrode sheet described in the third aspect of this application.

[0132] Understandably, a secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. During the charging and discharging process, active ions (such as Li)... + Na +The ion-carrying electrode repeatedly inserts and de-emits between the positive and negative electrodes. The diaphragm, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, located between the positive and negative electrodes, mainly conducts active ions.

[0133] Optionally, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector. As an example, the negative current collector has two surfaces opposite each other along the thickness direction, and the negative active layer is disposed on at least one of the two opposite surfaces of the negative current collector.

[0134] Optionally, the negative electrode current collector may be a metal foil or a composite current collector. As an example, the metal foil used as the negative electrode current collector may be copper foil or lithium foil. The composite current collector used as the negative electrode current collector includes a polymer layer and a metal layer formed on at least one surface of the polymer layer; the polymer layer is made of materials including, but not limited to, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polystyrene (PS); the metal layer is made of materials including, but not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys.

[0135] Optionally, the negative electrode active layer includes a negative electrode material, which can be a negative electrode material known in the art. As examples, negative electrode materials include, but are not limited to: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate; silicon-based materials include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys; tin-based materials include one or more of elemental tin, tin oxide compounds, and tin alloys.

[0136] Optionally, the negative electrode active layer includes a binder, which includes one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0137] Optionally, the negative electrode active layer includes a conductive agent, which includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0138] Optionally, the electrolyte includes one or more of liquid electrolytes, gel electrolytes, and all-solid electrolytes.

[0139] Optionally, the liquid electrolyte includes an electrolyte salt and an organic solvent. The electrolyte salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. The organic solvent includes one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0140] This application does not impose any particular restrictions on the material of the separator in the secondary battery; separators with good chemical and mechanical stability known in the art can be selected. As an example, the separator material includes one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film; when the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0141] Alternatively, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0142] Optionally, the secondary battery includes an outer packaging for encapsulating the aforementioned electrode components and electrolyte. The outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. Alternatively, the outer packaging of the secondary battery can be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0143] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0144] The following description is further illustrated with specific embodiments and comparative examples. Unless otherwise specified, the raw materials involved in the following specific embodiments and comparative examples are all commercially available. Unless otherwise specified, the instruments used are all commercially available. Unless otherwise specified, the processes involved are conventionally selected by those skilled in the art.

[0145] Example 1

[0146] Please refer to Table 1. The preparation method of the modified lithium-rich manganese-based material in this embodiment is as follows:

[0147] (1) Preparation of the first intermediate: Weigh the lithium-rich manganese-based precursor, lithium source and dopant respectively, mix them evenly using a high-speed rotary mixer to obtain the first mixture; place the first mixture in an atmosphere tube furnace for the first sintering, and then sieve to obtain the first intermediate;

[0148] The expression for the lithium-rich manganese-based precursor is Ni. 0.35 Mn 0.65 (OH)2, the lithium source is lithium carbonate (Li2CO3);

[0149] The molar ratio of transition metal elements in the lithium-rich manganese-based precursor to lithium elements in the lithium source is 1:1.38.

[0150] The dopant is Nb2O5, and the mass ratio of lithium-rich manganese-based precursor to dopant is 100:0.2;

[0151] The first sintering process specifically involves heating the temperature to 900°C at a rate of 3°C / min in an air atmosphere, sintering at 900°C for 12 hours, and then naturally cooling it to room temperature.

[0152] The first intermediate includes a matrix and a first coating layer supported on the matrix, and the matrix is ​​expressed as: 0.38Li₂MnO₃·0.62LiNi 0.56 Mn 0.44 Nb 0.0023 O2.

[0153] (2) Preparation of the second intermediate: Weigh the first intermediate, metal phosphate salt and solid electrolyte respectively, and mix them evenly using a high-speed rotating mixer to obtain the second mixture; place the second mixture in an atmosphere tube furnace for second sintering to form a second coating layer with a three-dimensional porous network structure on the surface of the first intermediate, and then sieve to obtain the second intermediate;

[0154] Among them, the metal phosphate salt is cobalt phosphate, and the solid electrolyte is lithium aluminum titanium phosphate (LATP);

[0155] The mass ratio of the first intermediate, the metal phosphate salt, and the solid electrolyte is 100:0.2:0.2;

[0156] The second sintering process involves heating the temperature to 725°C at a rate of 3°C / min in air, sintering at 725°C for 4 hours, and then naturally cooling to room temperature.

[0157] (3) Preparation of modified lithium-rich manganese-based materials: weigh the first intermediate and nano metal oxide respectively, mix them evenly using a high-speed rotating mixer to obtain a third mixture; place the third mixture in an atmosphere tube furnace for third sintering to form a third coating layer on the surface of the first intermediate, and then sieve to obtain modified lithium-rich manganese-based materials.

[0158] Among them, the nano-metal oxide is nano-TiO2 with an average particle size of 20 nm and a specific surface area of ​​55 m². 2 / g;

[0159] The mass ratio of the first intermediate to the nano-metal oxide is 100:0.1;

[0160] The third sintering process involves heating the temperature to 425°C at a rate of 3°C / min in air, sintering at 425°C for 5 hours, and then naturally cooling it to room temperature.

[0161] Example 2

[0162] This embodiment is basically the same as Embodiment 1, except that: in step (1), the dopant is SnO2 of equal mass, and the resulting matrix is ​​expressed as 0.38Li2MnO3·0.62LiNi 0.56 Mn 0.44 Sn 0.0018 O2, the sintering temperature of the first sintering is 930℃.

[0163] Example 3

[0164] This embodiment is basically the same as embodiment 1, except that in step (2), the metal phosphate salt is aluminum phosphate of equal mass, and the sintering temperature of the second sintering is 750℃.

[0165] Example 4

[0166] This embodiment is basically the same as embodiment 1, except that: in step (2), the phosphate metal salt is cerium phosphate of equal mass, the solid electrolyte is lithium lanthanum zirconate (LLZO) of equal mass, and the sintering temperature of the second sintering is 700℃.

[0167] Example 5

[0168] This embodiment is basically the same as embodiment 1, except that:

[0169] In step (2), the sintering temperature of the second sintering is 700℃;

[0170] In step (3), the nano-metal oxide selected is an equal mass of nano-ZrO2 with an average particle size of 60 nm and a specific surface area of ​​68 m². 2 / g, the sintering temperature of the third sintering is 500℃.

[0171] Example 6

[0172] This embodiment is basically the same as embodiment 1, except that:

[0173] In step (2), the sintering temperature of the second sintering is 700℃;

[0174] In step (3), the nano-metal oxide selected is an equal mass of nano-Al2O3 with an average particle size of 20 nm and a specific surface area of ​​110 m². 2 / g, the sintering temperature of the third sintering is 450℃.

[0175] Example 7

[0176] This embodiment is basically the same as Embodiment 1, except that in step (1), the mass ratio of the lithium-rich manganese-based precursor to the dopant Nb2O5 is 100:0.6, and the resulting matrix is ​​expressed as 0.38Li2MnO3·0.62LiNi 0.56 Mn 0.44 Nb 0.0068 O2.

[0177] Example 8

[0178] This embodiment is basically the same as that of embodiment 1, except that in step (2), the mass ratio of the first intermediate, cobalt phosphate and LATP is 100:0.6:0.6.

[0179] Example 9

[0180] This embodiment is basically the same as that of embodiment 1, except that in step (3), the mass ratio of the second intermediate to nano TiO2 is 100:0.2.

[0181] Example 10

[0182] This embodiment is basically the same as embodiment 1, except that:

[0183] In step (1), the mass ratio of lithium-rich manganese-based precursor to dopant Nb₂O₅ is 100:0.6, and the resulting matrix is ​​expressed as 0.38Li₂MnO₃·0.52LiNi 0.67 Mn 0.52 Nb 0.0068 O2;

[0184] In step (2), the mass ratio of the first intermediate, cobalt phosphate, and LATP is 100:0.6:0.6;

[0185] In step (3), the mass ratio of the second intermediate to nano-TiO2 is 100:0.2.

[0186] Comparative Example 1

[0187] The preparation method of the modified lithium-rich manganese-based material in this comparative example is as follows:

[0188] (1) Preparation of the first intermediate: Same as step (1) in Example 1.

[0189] (2) Preparation of modified lithium-rich manganese-based material: The matrix and solid electrolyte are weighed separately and mixed evenly using a high-speed rotating mixing device to obtain a second mixture; the second mixture is placed in an atmosphere tube furnace for a second sintering to coat the surface of the first intermediate with a second coating layer having a three-dimensional porous network structure, and then screened to obtain the modified lithium-rich manganese-based material.

[0190] The solid electrolyte is lithium aluminum titanium phosphate (LATP), and the mass ratio of the first intermediate to LATP is 100:0.2.

[0191] The second sintering process involves heating the temperature to 500°C at a rate of 3°C / min in an air atmosphere, sintering at 500°C for 4 hours, and then naturally cooling to room temperature.

[0192] Comparative Example 2

[0193] The preparation method of the modified lithium-rich manganese-based material in this comparative example is as follows:

[0194] (1) Preparation of the first intermediate: Same as step (1) in Example 1.

[0195] (2) Preparation of modified lithium-rich manganese-based materials: The matrix and nano metal oxides were weighed separately and mixed evenly using a high-speed rotating mixing device to obtain a second mixture; the second mixture was placed in an atmosphere tube furnace for a second sintering to form a third coating layer on the surface of the first intermediate, and then sieved to obtain modified lithium-rich manganese-based materials.

[0196] Among them, the nano-metal oxide is nano-TiO2 with an average particle size of 20 nm and a specific surface area of ​​50 m². 2 / g;

[0197] The mass ratio of the first intermediate to the nano-metal oxide is 100:0.1;

[0198] The second sintering process involves heating the temperature to 425°C at a rate of 3°C / min in an air atmosphere, sintering at 425°C for 5 hours, and then naturally cooling it to room temperature.

[0199] Comparative Example 3

[0200] The preparation method of the modified lithium-rich manganese-based material in this comparative example is as follows:

[0201] (1) Preparation of the first intermediate: Same as step (1) in Example 1.

[0202] (2) Preparation of the second intermediate: without adding metal phosphate salt and solid electrolyte, the first intermediate is directly subjected to a second sintering, and the sintering conditions are the same as those in step (2) of Example 1;

[0203] (3) Preparation of modified lithium-rich manganese-based materials: without adding nano metal oxides, the second intermediate is directly subjected to third sintering, and the sintering conditions are the same as those in step (3) of Example 1.

[0204] Comparative Example 4

[0205] The preparation method of the modified lithium-rich manganese-based material in this comparative example is as follows:

[0206] (1) Preparation of the first intermediate: Without adding dopants, weigh the lithium-rich manganese-based precursor and lithium source, mix them evenly using a high-speed rotary mixer to obtain the first mixture; place the first mixture in an atmosphere tube furnace for the first sintering, and sieve to obtain the first intermediate;

[0207] The expression for the lithium-rich manganese-based precursor is Ni. 0.35 Mn 0.65 (OH)2, the lithium source is lithium carbonate (Li2CO3);

[0208] The molar ratio of transition metal elements in the lithium-rich manganese-based precursor to lithium elements in the lithium source is 1:1.38.

[0209] The first intermediate is a matrix without a first coating layer on its surface, and its formula is: 0.38Li₂MnO₃·0.62LiNi 0.56 Mn 0.44 O2;

[0210] The first sintering process involves heating the temperature to 900°C at a rate of 3°C / min in air, sintering at 900°C for 12 hours, and then naturally cooling it to room temperature.

[0211] (2) Preparation of the second intermediate: Same as step (2) in Example 1;

[0212] (3) Modified lithium-rich manganese-based material: without adding nano metal oxides, the second intermediate is directly subjected to a third sintering, and the sintering conditions are the same as those in step (3) of Example 1.

[0213] Comparative Example 5

[0214] The preparation method of the modified lithium-rich manganese-based material in this comparative example is as follows:

[0215] (1) Preparation of the first intermediate: Without adding dopants, weigh the lithium-rich manganese-based precursor and lithium source, mix them evenly using a high-speed rotary mixer to obtain the first mixture; place the first mixture in an atmosphere tube furnace for the first sintering, and sieve to obtain the first intermediate;

[0216] The expression for the lithium-rich manganese-based precursor is Ni. 0.35 Mn 0.65 (OH)2, the lithium source is lithium carbonate (Li2CO3);

[0217] The molar ratio of transition metal elements in the lithium-rich manganese-based precursor to lithium elements in the lithium source is 1:1.38.

[0218] The first intermediate is a matrix without a first coating layer on its surface, and its formula is: 0.38Li₂MnO₃·0.62LiNi 0.56 Mn 0.44 O2;

[0219] The first sintering process involves heating the temperature to 900°C at a rate of 3°C / min in air, sintering at 900°C for 12 hours, and then naturally cooling it to room temperature.

[0220] (2) Preparation of the second intermediate: without adding metal phosphate salts and solid electrolytes, the matrix is ​​directly subjected to a second sintering, and the sintering conditions are the same as those in step (2) of Example 1;

[0221] (3) Modified lithium-rich manganese-based materials: Same as step (3) in Example 1.

[0222] Test case

[0223] 1. Physicochemical tests of modified lithium-rich manganese-based materials:

[0224] (1) BET specific surface area: Following the GB / T 13390-2008 standard, "Determination of Specific Surface Area of ​​Metal Powders - Nitrogen Adsorption Method", the BET surface area was measured using a Beijing Bestech 3H-2000A surface area analyzer. The results are shown in Table 2. The test conditions were: 4g-8g of sample was placed in a U-shaped sample tube, degassed at 150℃ for 20min, the adsorbate ratio was He:N2 = 4:1, and the BET specific surface area of ​​the reference substance was 9.6m². 2 / g.

[0225] (2) Powder compaction density: The powder resistivity and compaction density were tested using a Yuaneng Technology PRCD 1100 powder resistivity and compaction density meter. The results are shown in Table 2. The test conditions were as follows: 1g to 2g of sample was loaded into the sample stage and a pressure holding test was performed for 15s under compaction loads of 20MPa, 40MPa, 60MPa, 80MPa and 100MPa respectively.

[0226] (3) Surface morphology: The surface morphology was characterized by field emission scanning electron microscopy (SEM) of Thermo Fisher Scientific Helios NanoLab; Argon ion polishing technology (also known as CP section polishing technology) was used to bombard the cross section of the modified lithium-rich manganese-based material to obtain a flat and precise polished cross section, and the results were captured by SEM. The results are shown in Figures 3 to 6.

[0227] 2. Button test:

[0228] The modified lithium-rich manganese-based materials of each embodiment and comparative example were used as positive electrode materials. SuperP was used as the conductive agent, and PVDF-5130 was used as the binder. The positive electrode slurry was prepared by dispersing the positive electrode material, conductive agent, and binder in an organic solvent at a mass ratio of 94:3:3. The positive electrode slurry was then coated onto aluminum foil, and after drying, cold pressing, and cutting, the positive electrode sheet was obtained. Using lithium metal sheet as the negative electrode, a 1M LiPF6 solution was used as the electrolyte, and ethylene carbonate (EC) and dimethyl carbonate (DMC) were used as the solvent in a volume ratio of 1:1. Coin cell CR2032 batteries were assembled for evaluation and testing (coin cell capacity standard 230mAh / g). The test conditions were as follows: activation was performed at 0.1C charge and discharge under high temperature of 45℃ and voltage range of 2.0V to 4.65V; then, discharge was performed at 0.1C rate under normal temperature of 25℃ and voltage range of 2.5V to 4.65V; and then discharge was performed at 0.33C / 0.5C rate under voltage range of 2.5V to 4.55V.

[0229] 3. Full electrical test:

[0230] The modified lithium-rich manganese-based materials of Example 1 and Comparative Example 1 were used as positive electrode materials, with SuperP as the conductive agent and PVDF-5130 as the binder. Positive electrode sheets were prepared according to a mass ratio of positive electrode material, conductive agent, and binder of 96.2:2:1.8. The negative electrode material was graphite, with SuperP as the conductive agent and CMC / SBR as the binder. Negative electrode sheets were prepared according to a mass ratio of negative electrode material, conductive agent, and binder of 96.5:0.5:3. A 120mm×200mm stacked soft-pack battery was formed by assembling positive electrode sheets, negative electrode sheets, and a lithium-rich manganese-based battery-specific electrolyte. The soft-pack battery underwent full-charge testing (full-charge capacity standard 210mAh / g). It was subjected to 0.1C charge-discharge at 45℃ and a voltage range of 2.0V–4.60V to complete the corresponding formation and capacity determination. At 25℃ and a voltage range of 2.0V–4.45V, it underwent 0.1C / 0.33C rate charge-discharge testing. At 45℃ and a voltage range of 2.0V–4.45V, it underwent 0.33C high-temperature cycling testing. Finally, at 60℃ and a voltage range of 2.0V–4.45V, it underwent 1C full-charge high-temperature storage and 28-day gas generation testing. The results are shown in Figures 7–10.

[0231] 4. Test Result Analysis:

[0232] As shown in Figures 3-6, compared to the modified lithium-rich manganese-based material of Comparative Example 1, the primary particles on the surface of the modified lithium-rich manganese-based material of Example 1 are finer, with a distinct coating layer and a smoother surface. Table 2 shows that, compared to the modified lithium-rich manganese-based materials of Examples 1-10, the BET specific surface area and powder compaction density of the modified lithium-rich manganese-based materials of Examples 1-10 are slightly increased, with the BET specific surface area reaching 1.22 m². 2 / g~1.40m 2 / g, the powder compaction density reaches 2.55g / cc~2.62g / cc, which is beneficial to optimizing its electrochemical performance.

[0233] Modified lithium-rich manganese-based materials were assembled into button cells. After being fully activated at high temperatures of 2.0V to 4.65V, the electrochemical performance of the button cells in Examples 1 to 10 at different current densities (0.1C, 0.33C, and 0.5C) was as follows: the specific capacity at 0.1C reached 242.5mAh / g to 250mAh / g, the specific capacity at 0.33C reached 214.5mAh / g to 229.6mAh / g, the specific capacity at 0.5C reached 209.3mAh / g to 225.6mAh / g, the 0.5C / 0.1C rate capability reached 86.31% to 90.06%, and the capacity retention rate after 50 cycles reached 97.28% to 98.35%. The discharge specific capacity of Examples 1-10 is generally higher than that of Comparative Examples 1-5, with a difference of nearly 20 mAh / g in 0.5C discharge specific capacity. The capacity retention rate after 50 cycles is significantly increased, demonstrating that the modified lithium-rich manganese-based material has higher discharge specific capacity, better rate performance, and better cycle stability through the synergistic effect of high-valence cation doping modification and multilayer coating structure.

[0234] The modified lithium-rich manganese-based material of Example 1 exhibits the best overall electrical performance in the button cell. The modified lithium-rich manganese-based material of Comparative Example 1 was prepared using a common two-stage sintering process. As shown in Table 3 and Figures 7-10, after fully activating the modified lithium-rich manganese-based materials of Example 1 and Comparative Example 1 at different current densities (0.1C, 0.33C), the total discharge capacity of Example 1 is 6-9 mAh / g higher than that of the Comparative Example. With a capacity retention rate ≥80%, Example 1 can be stored at 60°C for 350 days, while Comparative Example 1 only lasts 180-200 days. With a capacity retention rate ≥80%, Example 1 can cycle at 60°C for 1500 days, while Comparative Example 1 lasts approximately 600 days. The total gas production of Example 1 at 60°C for 28 days is only 6.36 mL / Ah, approximately 5 mL / Ah lower than that of Comparative Example 1. This demonstrates that the modified lithium-rich manganese-based material of Example 1, through the synergistic effect of high-valence cation doping modification and multilayer coating structure, effectively improves the material's discharge specific capacity, high-temperature storage performance, and high-temperature cycling performance, while significantly reducing the high-temperature gas generation problem. Therefore, the modified lithium-rich manganese-based material provided in this application can effectively improve the material's thermal stability and high-temperature resistance, thereby enhancing the safety of battery use.

[0235] Table 1. Comparison of preparation processes for modified lithium-rich manganese-based materials Note: Substance 1 is a dopant, and amount 1 is the mass ratio of precursor to dopant; Substance 2 is a metal phosphate salt, and amount 2 is the mass ratio of matrix to metal phosphate salt; Substance 3 is a solid electrolyte, and amount 3 is the mass ratio of matrix to solid electrolyte; Substance 4 is a nano-metal oxide, and amount 4 is the mass ratio of intermediate to nano-metal oxide; " / " indicates that no corresponding substance was added and no sintering treatment was performed, and "-" indicates that no corresponding substance was added but sintering treatment was performed.

[0236] Table 2. Comparison of physicochemical properties and electrochemical performance of modified lithium-rich manganese-based materials and coin cells.

[0237] Table 3. Comparison of electrochemical performance of all-electric components

[0238] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0239] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A modified lithium-rich manganese-based material, characterized in that, It includes a substrate, and a first covering layer, a second covering layer, and a third covering layer disposed sequentially on the substrate; The matrix comprises a lithium-rich manganese-based material doped with element M, wherein element M includes one or more of Nb, Sn, Ta, and Sb; The first coating layer comprises lithium oxide containing the element M; The second coating layer comprises a metal phosphate salt and a solid electrolyte, wherein the metal ions in the metal phosphate salt have a chemical valence greater than 1, and the solid electrolyte contains lithium ions; The third coating layer comprises nano-metal oxides.

2. The modified lithium-rich manganese-based material as described in claim 1, characterized in that, The matrix is ​​expressed as: (1-x)Li₂MnO₃·xLiNi a Mn b Co c M d O2, where 0 <x<1,a+b+c=1,0.30≤a<0.80,0.30≤b<0.80,c≥0,0<d≤0.05。 3. The modified lithium-rich manganese-based material as described in claim 1, characterized in that, One or more of the following conditions must be met: (1) The metal phosphate salt includes one or more of cobalt phosphate, manganese phosphate, nickel phosphate, magnesium phosphate, aluminum phosphate and cerium phosphate; (2) The solid electrolyte includes one or more of lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium lanthanum zirconate and lithium lanthanum titanate; (3) The mass ratio of the metal phosphate salt to the solid electrolyte is 1:(0.80~1.20).

4. The modified lithium-rich manganese-based material as described in claim 1, characterized in that, One or more of the following conditions must be met: (1) The nano-metal oxide includes one or more of TiO2, ZrO2, Al2O3, WO3, CeO2 and ZnO; (2) The average particle size of the nano-metal oxide is 10 nm to 100 nm; (3) The specific surface area of ​​the nano-metal oxide is 0.1 m². 2 / g~200m 2 / g.

5. The modified lithium-rich manganese-based material according to any one of claims 1 to 4, characterized in that, The mass ratio of the substrate, the first coating layer, the second coating layer, and the third coating layer is 100:(0.05~0.6):(0.05~0.6):(0.05~0.2).

6. A method for preparing a modified lithium-rich manganese-based material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: A first intermediate is obtained by mixing a lithium-rich manganese-based precursor, a lithium source, and a dopant and performing a first sintering. The first intermediate, metal phosphate salt, and solid electrolyte are mixed and then subjected to a second sintering process to obtain the second intermediate. The second intermediate and nano-metal oxide are mixed and then subjected to a third sintering process to obtain the modified lithium-rich manganese-based material.

7. The method for preparing the modified lithium-rich manganese-based material as described in claim 6, characterized in that, One or more of the following conditions must be met: (1) The expression for the lithium-rich manganese-based precursor is: Ni e Mn f Co g (OH)2 or Ni e Mn f Co g CO3, where e+f+g=1, 0.30≤e<0.80, 0.30≤f<0.80, g≥0.

8. The method for preparing the modified lithium-rich manganese-based material as described in claim 7, characterized in that, One or more of the following conditions must be met: (1) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium fluoride, lithium nitrate, lithium sulfate, lithium acetate and lithium oxalate; (2) The dopant includes one or more of the following: oxides, fluorides, hydroxides, carbonates, sulfates, oxalates, acetates and ethanolates containing the element M; (3) The molar ratio of the transition metal element in the lithium-rich manganese-based precursor to the lithium element in the lithium source is 1:(1.10~1.50); (4) The mass ratio of the lithium-rich manganese-based precursor to the dopant is 100:(0.05 to 0.60).

9. The method for preparing the modified lithium-rich manganese-based material as described in claim 8, characterized in that, The sintering temperature of the first sintering is 850℃~950℃, the sintering time is 5h~15h, and the sintering atmosphere is an oxidizing atmosphere.

10. The method for preparing the modified lithium-rich manganese-based material according to any one of claims 7 to 9, characterized in that, One or more of the following conditions must be met: (1) The ratio of the mass of the first intermediate to the total mass of the metal phosphate salt and the solid electrolyte is 100:(0.05~0.6); (2) The mass ratio of the metal phosphate salt to the solid electrolyte is 1:(0.80~1.20); (3) The mass ratio of the second intermediate to the nano metal oxide is 100:(0.05~0.2).

11. The method for preparing the modified lithium-rich manganese-based material as described in claim 10, characterized in that, The second sintering temperature is 650℃~800℃, the sintering time is 3h~6h, and the sintering atmosphere is an oxidizing atmosphere.

12. The method for preparing the modified lithium-rich manganese-based material as described in claim 10, characterized in that, The sintering temperature of the third sintering is 300℃~500℃, the sintering time is 3h~6h, and the sintering atmosphere is an oxidizing atmosphere.

13. A positive electrode plate, characterized in that, It includes the modified lithium-rich manganese-based material as described in any one of claims 1 to 6, or the modified lithium-rich manganese-based material prepared by the method described in any one of claims 7 to 12.

14. A secondary battery, characterized in that, Including the positive electrode sheet as described in claim 13.

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