Positive electrode active material and all-solid-state battery

Abstract

The application relates to the technical field of batteries, and discloses a positive electrode active material and a full-solid-state battery, wherein the positive electrode active material comprises a lithium-rich manganese-based material, the content of nickel elements in a surface layer region of the lithium-rich manganese-based material is higher than that in an internal region, the content of cobalt elements in the surface layer region is lower than that in the internal region, the surface layer region comprises a first surface far away from the internal region and a second surface close to the internal region, the content of nickel elements gradually decreases along a thickness direction from the first surface to the second surface, and the content of cobalt elements gradually increases along the thickness direction from the first surface to the second surface; the lithium-rich manganese-based material further comprises first doping elements and second doping elements; the first doping elements comprise at least one of W, Nb and Mo elements, and the second doping elements comprise at least one of Mg, Na and K elements. The application controls the distribution of nickel and cobalt elements in specific regions of the lithium-rich manganese-based material in the positive electrode active material, and simultaneously introduces doping elements, so that the conductivity, capacity and structural stability of the positive electrode active material are improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a positive electrode active material and an all-solid-state battery. Background Technology

[0002] Lithium-rich manganese-based cathode materials are highly promising high-energy-density cathode materials in the field of lithium-ion batteries. Their core advantage lies in the ability to achieve ultra-high capacity output through the participation of lattice oxygen in redox reactions. However, problems such as poor cycle performance and severe voltage decay have greatly limited their large-scale and commercial applications, becoming a key technological bottleneck that urgently needs to be overcome.

[0003] To improve the cycle stability and suppress voltage decay of lithium-rich manganese-based materials, existing technologies often employ modification methods such as doping and coating to regulate their performance. While these methods alleviate the aforementioned defects to some extent, problems still remain to be solved. The Li₂MnO₃ component in lithium-rich manganese-based cathode materials is chemically inert before activation, and the materials contain a large amount of highly oxidized Mn. 4+ Mn 4+ Its strong electron localization makes it difficult to participate in electron conduction, causing the material itself to act like a "semiconductor" or even an "insulator". When applied to solid-state batteries, this can lead to limited capacity utilization and poor cycle stability.

[0004] To address the aforementioned issues of poor conductivity, capacity performance, and cycling stability, existing technologies typically introduce Co into lithium-rich manganese-based materials. However, while Co contributes to higher conductivity and charging capacity, it also leads to severe oxygen loss. The lack of oxygen disrupts the stable octahedral coordination structure of the transition metal in lithium-rich manganese-based materials, causing the transition metal to migrate to the lithium layer during subsequent charge-discharge cycles. This results in an irreversible phase transition, ultimately leading to a significant decrease in the material's cycling performance.

[0005] To address the cycling performance issues arising from the introduction of Co into lithium-rich manganese-based materials, existing technologies have attempted to optimize and improve the cathode material by appropriately increasing the Ni concentration. However, the increase in Ni content inevitably leads to a decrease in material capacity, making it impossible to achieve a good balance between high capacity and excellent cycling performance, and thus failing to meet the comprehensive performance requirements of cathode materials in practical applications. Summary of the Invention

[0006] In view of this, in order to solve the problem of severe oxygen loss and capacity decay in existing lithium-rich manganese-based materials, which makes it difficult for batteries to simultaneously achieve good cycle performance and capacity performance, this application provides a positive electrode active material and an all-solid-state battery containing the positive electrode active material.

[0007] According to an embodiment of the present application, in a first aspect, the present application provides a positive electrode active material, including a lithium-rich manganese-based material, the lithium-rich manganese-based material includes a surface layer region and an internal region, the surface layer region is a region from the surface of the lithium-rich manganese-based material to an internal depth of L nm, and the internal region is the remaining region of the lithium-rich manganese-based material except the surface layer region, where 300 ≤ L ≤ 400; The mass content of nickel element in the surface layer region is denoted as m1%, and the mass content of nickel element in the internal region is denoted as m2%, and m1 > m2; The mass content of cobalt element in the surface layer region is denoted as n1%, and the mass content of cobalt element in the internal region is denoted as n2%, and n1 < n2; The surface layer region includes a first surface and a second surface arranged opposite to each other, the first surface is arranged away from the internal region, the second surface faces the internal region and is in contact with the surface of the internal region. In the surface layer region, along the direction from the first surface to the second surface, the mass content of the nickel element decreases in sequence, and the mass content of the cobalt element increases in sequence; The lithium-rich manganese-based material further includes a first doping element and a second doping element; the first doping element includes at least one of W, Nb, and Mo elements, and the second doping element includes at least one of Mg, Na, and K elements.

[0008] Optionally, the internal region and the surface layer region independently include a substance with the chemical formula xLi2MnO3·(1 x)Li e Q 1-e Ni a Co b Mn c M d O2, where 0 < x < 1, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 < d < 0.7, 0 < e < 1, M includes the first doping element; Q includes the second doping element.

[0009] As an optional implementation manner, along the direction from the first surface to the second surface, for any depth t nm and (t + 1) nm in the surface layer region, the mass content of the nickel element satisfies: 0.0065% ≤ X t -X t+1 ≤ 0.0092%, where X t is the mass content of the nickel element in the lithium-rich manganese-based material at a distance of t nm from the first surface along the direction from the first surface to the second surface, and X t+1The mass content of nickel in the lithium-rich manganese-based material at a distance of (t+1) nm from the first surface along the direction from the first surface to the second surface, where 0≤t≤L-1.

[0010] As an optional implementation, along the direction from the first surface to the second surface, for any depth t nm and (t+1) nm within the surface region, the mass content of cobalt satisfies: 0.0062% ≤ C t+1 -C t ≤0.0095%, where C t+1 C represents the mass content of cobalt in a lithium-rich manganese-based material at a distance of (t+1) nm from the first surface along the direction from the first surface to the second surface. t The mass content of cobalt in the lithium-rich manganese-based material at a distance t nm from the first surface along the direction from the first surface to the second surface, where 0 ≤ t ≤ L-1.

[0011] In an optional implementation, in the surface region, the mass ratio of nickel to cobalt on the first surface is (1.5~2.3):1, and the mass ratio of nickel to cobalt on the second surface is (0.8~1.2):1.

[0012] In an optional implementation, the mass ratio of nickel to cobalt in the internal region is (0.8~1.2):1.

[0013] In an optional embodiment, in the lithium-rich manganese-based material, the ratio of the total mass of cobalt and nickel to the mass of manganese is 1:(1.5~2).

[0014] As an optional implementation, the mass content of the first dopant element is 0.03% to 1% based on the total mass of the lithium-rich manganese-based material.

[0015] As an optional implementation, the mass content of the second dopant element is 0.01% to 0.8% based on the total mass of the lithium-rich manganese-based material.

[0016] In an optional implementation, the lithium-rich manganese-based material comprises secondary particles formed by the agglomeration of primary particles.

[0017] In an optional embodiment, the positive electrode active material further includes a composite layer that coats at least a portion of the surface of the lithium-rich manganese-based material; the composite layer includes LiCoO2 and Li3BO3.

[0018] As an optional implementation, the mass content of Li3BO3 is 440ppm to 4400ppm based on the total mass of the positive electrode active material, and / or the mass content of LiCoO2 is 520ppm to 5500ppm.

[0019] In one optional embodiment, the average particle size of the primary particles of the lithium-rich manganese-based material is 200 nm to 500 nm.

[0020] In some alternative embodiments, the thickness of the composite layer is denoted as H, which satisfies: 10nm ≤ H ≤ 50nm.

[0021] In some optional embodiments, the average particle size of the secondary particles of the lithium-rich manganese-based material is denoted as D, which satisfies: 1μm≤D≤3μm.

[0022] Furthermore, in some alternative implementations, the following condition is satisfied: 20≤D / (2H)≤140.

[0023] In some optional embodiments, the compacted density of the positive electrode active material powder is 3.0 g / cm³. 3 ~3.3g / cm 3 .

[0024] In some optional embodiments, the specific surface area of ​​the positive electrode active material is 2m². 2 / g~3m 2 / g.

[0025] In some optional embodiments, the powder conductivity of the positive electrode active material is 1.0 × 10⁻⁶ under a pressure of 48 MPa to 55 MPa. -6 S / cm ~ 9.0 × 10 -5 S / cm.

[0026] In some optional embodiments, the X-ray diffraction pattern of the positive electrode active material has diffraction peaks in the range of 2θ diffraction angles of 20° to 23°.

[0027] In some optional embodiments, the X-ray diffraction pattern of the positive electrode active material further includes a (003) characteristic peak and a (104) characteristic peak, wherein the 2θ diffraction angle of the (003) characteristic peak is 18°~20° and the 2θ diffraction angle of the (104) characteristic peak is 44°~45°; the peak intensity of the (003) characteristic peak is K1 and the peak intensity of the (104) characteristic peak is K2, satisfying: K1 / K2>2.1.

[0028] Secondly, this application provides an all-solid-state battery, the all-solid-state battery including a positive electrode sheet, the positive electrode sheet including the positive electrode active material described in the first aspect.

[0029] In some alternative embodiments, the all-solid-state battery further includes a negative electrode, which comprises an indium metal layer and / or a lithium metal layer.

[0030] Furthermore, in some alternative embodiments, the negative electrode includes an indium metal layer and a lithium metal layer.

[0031] In some alternative embodiments, the all-solid-state battery further includes a solid electrolyte layer, which includes a halide solid electrolyte layer and / or a sulfide solid electrolyte layer.

[0032] Furthermore, in some optional embodiments, the solid electrolyte layer includes a halide solid electrolyte layer and a sulfide solid electrolyte layer.

[0033] In some optional embodiments, when the solid electrolyte layer comprises a halide solid electrolyte layer and a sulfide solid electrolyte layer, the mass ratio of the halide solid electrolyte layer to the sulfide solid electrolyte layer is (20~60):(40~80).

[0034] The technical solution of this application has the following advantages: 1. The positive electrode active material provided in this application contains lithium-rich manganese-based materials. Introducing cobalt into these materials can, on the one hand, improve the performance of the cathode by using Co... 3+ / Co 4+ Redox couples form highly efficient small-polarization electronic conduction channels, significantly improving the electronic conductivity of the material. On the other hand, Co... 3+ / Co 4+ The 3d band structure of the redox couple and the oxygen anion (O 2- The 2p bands of the two atoms partially overlap, which can promote the growth of oxygen anions (O). 2- Cobalt participates in charge transfer reactions, that is, it can activate the redox reaction of lattice oxygen, contributing a higher charging capacity. Furthermore, cobalt can accelerate the electrochemical activation process of the Li2MnO3 component in lithium-rich manganese-based materials, contributing a higher capacity to the material more quickly, thereby improving the capacity performance of the positive electrode active material. This application introduces Ni into lithium-rich manganese-based materials. On the one hand, Ni... 2+ / Ni 4+ The reduction potential of the two-electron reduction couple is higher than that of Mn. 3+ / Mn 4+ The single-electron reduction potential allows Ni to preferentially undergo reduction during charging and discharging, thereby inhibiting the migration of manganese to the lithium layer after charging and discharging. This prevents the structural phase transition caused by manganese migration. On the other hand, Ni... 2+ / Ni 4+Two-electron reduction pairs can also preferentially provide charge compensation, delaying dependence on the redox reaction of oxygen anions, thereby protecting the stability of lattice oxygen and suppressing oxygen escape.

[0035] This application designs a lithium-rich manganese-based material divided into a surface region near the material surface and an internal region away from the material surface. The design also features a higher nickel content in the surface region than in the internal region, and a lower cobalt content in the internal region than in the surface region. Increasing the nickel content near the material surface while decreasing the cobalt content helps reduce oxygen loss from the material surface, stabilizes the material structure, and, when applied to all-solid-state batteries, can specifically address the core problems faced by traditional homogeneous lithium-rich manganese-based cathode materials in solid-state systems, such as poor interfacial stability, slow ion transport kinetics, and severe voltage decay. This allows the cathode active material to simultaneously possess multiple advantages in structure, interface, and electrochemical performance. Meanwhile, this application further specifies that the mass content of nickel decreases sequentially and the mass content of cobalt increases sequentially along the direction from the surface to the interior in the surface region. On the one hand, this enables the nickel content in the surface region to be higher than that in the interior region, and the cobalt content in the surface region to be lower than that in the interior region, thereby reducing the cobalt content on the material surface and increasing the nickel content on the material surface. This achieves high conductivity and high capacity while reducing oxygen loss and stabilizing the material structure. On the other hand, the gradient change of nickel and cobalt can effectively avoid stress concentration caused by rapid changes in content. The gradient change of nickel and cobalt makes the lattice parameters of the surface region change continuously from the first surface to the second surface, which can effectively avoid the problems of lattice mismatch and interface stress concentration that occur when the element content changes drastically. Furthermore, the gradient change of nickel and cobalt can also construct a continuous lithium-ion diffusion channel, reduce the diffusion resistance of lithium ions, and thus improve the rate performance of the material.

[0036] Secondly, the surface region in this application is a lithium-rich manganese-based material with a depth L of 300 nm to 400 nm from the surface to the interior. The size of the surface region, within the range of nm, is controlled by the depth L, thereby controlling the gradient changes in nickel and cobalt elements. Firstly, this ensures a relatively high nickel content and a relatively low cobalt content in the second surface of the surface region, while maintaining adequate amounts of cobalt and nickel within the material. This allows the lithium-rich manganese-based material to maintain high conductivity and capacity while effectively suppressing oxygen loss. Secondly, it ensures a suitable depth in the surface region, achieving specific nickel and cobalt content in specific areas of the material. Furthermore, it ensures a continuous gradient change in the mass content of nickel and cobalt in the surface region, resulting in continuous changes in lattice parameters. This effectively reduces lattice mismatch and interfacial stress concentration caused by abrupt changes in lattice parameters, improving the stability of the material structure and promoting the construction of continuous lithium-ion diffusion channels. Thirdly, the appropriate depth of the surface region enhances its protective effect on the internal regions, reducing side reactions between the internal regions with higher cobalt content and the electrolyte. This effectively suppresses oxygen loss and manganese transfer, improving the structural stability of the lithium-rich manganese-based material and consequently enhancing the structural stability of the positive electrode active material.

[0037] Furthermore, this application introduces specific first and second doping elements into the transition metal sites and lithium sites of the lithium-rich manganese-based material, respectively. The high-valence ions corresponding to the first doping element have extremely strong electron-withdrawing capabilities, such as W... 6+ 、Nb 5+ Mo 6+ Mo 5+ The first dopant can form very strong WO, Nb-O, and Mo-O bonds with oxygen, greatly improving the stability of lattice oxygen and raising the oxygen evolution barrier. Furthermore, the strong chemical bond formed between the first dopant and oxygen can stabilize the TM-O bond between the transition metal (TM) and oxygen in lithium-rich manganese-based materials, inhibiting overall structural collapse and thus improving the overall structural stability of the lithium-rich manganese-based materials. The second dopant has an ionic radius close to that of lithium and preferentially incorporates into lithium sites in lithium-rich manganese-based materials, forming strong chemical bonds such as Mg-O, Na-O, and KO bonds. This can lock oxygen at oxygen sites during deep delithiation, preventing oxygen loss caused by the sliding of metal elements from transition metal sites to oxygen sites, thereby suppressing the irreversible phase transition from layered structure to spinel phase in lithium-rich manganese-based materials. The first and second doping elements work synergistically, with the second doping element acting as a support at the lithium site and the first doping element acting as a migration inhibitor at the transition metal site. Together, they achieve multi-level synergistic stability of the bulk structure of lithium-rich manganese-based materials, effectively improving the cycle stability and capacity performance of the positive electrode active material when applied to batteries. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the structure of the positive electrode active material in Example 1 of this application; In the figure, 1 represents lithium-rich manganese-based material; 1-1 represents the surface region; 1-11 represents the first surface; 1-12 represents the second surface; 1-2 represents the internal region; and 2 represents the composite layer.

[0040] Figure 2 This is a field emission electron microscope image of the positive electrode active material of Example 1 of this application.

[0041] Figure 3 This is a scanning electron microscope image of the grain cross-section of the positive electrode active material of Example 1 of this application.

[0042] Figure 4 yes Figure 3 The scanning electron microscope images of the grain profiles correspond to the EDS line scan data of Ni and Co elements.

[0043] Figure 5 yes Figure 3 The scanning electron microscope images of the grain profiles correspond to the EDS line scan data of Mn, W, and Mg elements.

[0044] Figure 6 This is the X-ray diffraction (XRD) pattern of the positive electrode active material of Example 1 of this application.

[0045] Figure 7 This is a schematic diagram of the all-solid-state battery of Embodiment 1 of this application; In the diagram, 3 represents the positive electrode layer; 3-1 represents the positive electrode active material; 3-2 represents the halide solid electrolyte; 3-3 represents the vapor-grown carbon fiber (VGCF); 4 represents the solid electrolyte layer; 4-1 represents the halide solid electrolyte layer; 4-2 represents the sulfide solid electrolyte layer; 5 represents the negative electrode layer; 5-1 represents the indium metal layer; and 5-2 represents the lithium metal layer. Detailed Implementation

[0046] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0047] It should be noted in the description of this application that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, the technical features involved in the different embodiments of this application described below may be combined with each other as long as they do not conflict with each other.

[0048] To address the problem of severe oxygen loss and capacity decay in lithium-rich manganese-based materials in related technologies, which makes it difficult for batteries to simultaneously achieve good cycle performance and capacity performance, this application proposes the following solution.

[0049] In a first aspect, this application provides a positive electrode active material, including a lithium-rich manganese-based material, wherein the lithium-rich manganese-based material includes a surface region and an internal region, the surface region being the region from the surface of the lithium-rich manganese-based material to an internal depth of L nm, and the internal region being the remaining regions of the lithium-rich manganese-based material other than the surface region, wherein 300≤L≤400; The mass content of nickel in the surface region is denoted as m1, and the mass content of nickel in the inner region is denoted as m2, where m1 > m2. The mass content of cobalt in the surface region is denoted as n1%, and the mass content of cobalt in the inner region is denoted as n2%, where n1 < n2. The surface region includes a first surface and a second surface disposed opposite to each other. The first surface is disposed away from the inner region, and the second surface faces the inner region and is in contact with the surface of the inner region. In the surface region, along the direction from the first surface to the second surface, the mass content of nickel decreases sequentially, and the mass content of cobalt increases sequentially. The lithium-rich manganese-based material further includes a first doping element and a second doping element; the first doping element includes at least one of W, Nb, and Mo, and the second doping element includes at least one of Mg, Na, and K.

[0050] The positive electrode active material provided in this application contains lithium-rich manganese-based materials. Introducing cobalt into these materials can, on the one hand, improve the performance of the cathode by using Co... 3+ / Co 4+ Redox couples form highly efficient small-polarization electronic conduction channels, significantly improving the electronic conductivity of the material. On the other hand, Co... 3+ / Co4+ The 3d band structure of the redox couple and the oxygen anion (O 2- The 2p bands of the two atoms partially overlap, which can promote the growth of oxygen anions (O). 2- Cobalt participates in charge transfer reactions, that is, it can activate the redox reaction of lattice oxygen, contributing a higher charging capacity. Furthermore, cobalt can accelerate the electrochemical activation process of the Li2MnO3 component in lithium-rich manganese-based materials, contributing a higher capacity to the material more quickly, thereby improving the capacity performance of lithium-rich manganese-based materials.

[0051] However, this study found that while the introduction of cobalt activates the oxygen capacity of lithium-rich manganese-based materials, it also disrupts the originally stable oxygen protection structure, making it easier for oxygen to escape from the oxygen sites in the delithiated state. This leads to severe oxygen loss, and the lack of oxygen disrupts the stable octahedral coordination structure of the transition metal Mn in the lithium-rich manganese-based materials, causing Mn to migrate to the lithium layer during subsequent charge-discharge cycles, triggering an irreversible phase transition and ultimately resulting in a significant decrease in the material's cycle performance. To address this, this application introduces Ni into the lithium-rich manganese-based materials. On the one hand, Ni... 2+ / Ni 4+ The reduction potential of the two-electron reduction couple is higher than that of Mn. 3+ / Mn 4+ The single-electron reduction potential allows Ni to preferentially undergo reduction during charging and discharging, thereby inhibiting the migration of manganese to the lithium layer after charging and discharging. This suppresses the structural phase transition induced by manganese migration. On the other hand, Ni... 2+ / Ni 4+ Two-electron reduction pairs can also preferentially provide charge compensation, delaying dependence on the redox reaction of oxygen anions, thereby protecting the stability of lattice oxygen and suppressing oxygen escape.

[0052] This application also found that excessive increases in nickel content inevitably lead to a decrease in the capacity of lithium-rich manganese-based materials, and that oxygen loss in lithium-rich manganese-based materials typically occurs first on the surface and then extends into the matrix. To address this, this application designs a lithium-rich manganese-based material with a surface region close to the material surface and an internal region far from the surface. Furthermore, the application designs that the nickel content in the surface region is higher than that in the internal region, while the cobalt content in the internal region is lower than that in the surface region. Increasing the nickel content near the material surface while decreasing its cobalt content helps reduce oxygen loss from the material surface, stabilizes the material structure, and, when applied to all-solid-state batteries, can specifically solve the core problems faced by traditional homogeneous lithium-rich manganese-based cathode materials in solid-state systems, such as poor interfacial stability, slow ion transport kinetics, and severe voltage decay. This allows the cathode active material to possess multiple advantages in terms of structure, interface, and electrochemical performance. Meanwhile, this application further specifies that the mass content of nickel decreases sequentially from the surface to the interior in the surface region, while the mass content of cobalt increases sequentially. On the one hand, this allows for a higher nickel content in the surface region compared to the interior region, and a lower cobalt content in the surface region compared to the interior region. This reduces the cobalt content on the material surface and increases the nickel content, achieving high conductivity and high capacity while minimizing oxygen loss and stabilizing the material structure. On the other hand, the gradient change in nickel and cobalt effectively avoids stress concentration caused by rapid changes in content. The gradient change in nickel and cobalt ensures a continuous change in lattice parameters from the first surface to the second surface in the surface region, effectively avoiding lattice mismatch and interface stress concentration problems that occur when element content changes drastically. Furthermore, the gradient change in nickel and cobalt can also construct continuous lithium-ion diffusion channels, reducing lithium-ion diffusion resistance and thus improving the rate performance of the material.

[0053] Secondly, the surface region in this application is the area between the surface and the internal depth L of the lithium-rich manganese-based material, ranging from 300 nm to 400 nm. By controlling the size of the surface region through the depth L, the gradient changes in nickel and cobalt elements are controlled. Firstly, this ensures that the nickel content in the second surface of the surface region is relatively high, and the cobalt content is relatively low, while simultaneously ensuring that the material contains relatively appropriate amounts of cobalt and nickel. This allows the lithium-rich manganese-based material to effectively suppress oxygen loss while maintaining its advantages of high conductivity and high capacity. Secondly, it ensures that the surface region has a suitable depth, allowing specific nickel and cobalt content to be present in specific areas of the material. The cobalt content is carefully controlled. Simultaneously, ensuring a continuous gradient in the mass content of both nickel and cobalt in the surface region allows for continuous variation in lattice parameters. This effectively reduces lattice mismatch and interfacial stress concentration caused by abrupt changes in lattice parameters, improving the stability of the material structure and promoting the construction of continuous lithium-ion diffusion channels. Thirdly, a suitable depth in the surface region enhances its protective effect on the internal region, reducing side reactions between the internal region (with a relatively higher cobalt content) and the electrolyte. This effectively suppresses oxygen loss and manganese transfer, improving the structural stability of lithium-rich manganese-based materials and consequently enhancing the structural stability of the positive electrode active material.

[0054] Furthermore, this application introduces specific first and second doping elements into the transition metal sites and lithium sites of the lithium-rich manganese-based material, respectively. The high-valence ions corresponding to the first doping element have extremely strong electron-withdrawing capabilities, such as W... 6+ 、Nb 5+ Mo 6+ Mo 5+ The first dopant can form very strong WO, Nb-O, and Mo-O bonds with oxygen, greatly improving the stability of lattice oxygen and raising the oxygen evolution barrier. Furthermore, the strong chemical bond formed between the first dopant and oxygen can stabilize the TM-O bond between the transition metal (TM) and oxygen in lithium-rich manganese-based materials, inhibiting overall structural collapse and thus improving the overall structural stability of the lithium-rich manganese-based materials. The second dopant has an ionic radius close to that of lithium and preferentially incorporates into lithium sites in lithium-rich manganese-based materials, forming strong chemical bonds such as Mg-O, Na-O, and KO bonds. This can lock oxygen at oxygen sites during deep delithiation, preventing oxygen loss caused by the sliding of metal elements from transition metal sites to oxygen sites, thereby suppressing the irreversible phase transition from layered structure to spinel phase in lithium-rich manganese-based materials. The first and second doping elements work synergistically, with the second doping element acting as a support at the lithium site and the first doping element acting as a migration inhibitor at the transition metal site. Together, they achieve multi-level synergistic stability of the bulk structure of lithium-rich manganese-based materials, effectively improving the cycle stability and capacity performance of the positive electrode active material when applied to batteries.

[0055] This application also found that if the mass content of cobalt in the surface region is higher than or equal to the mass content of cobalt in the internal region, and the mass content of nickel in the surface region is lower than or equal to the mass content of nickel in the internal region, then the cobalt content in the internal region is relatively too low and the nickel content is relatively too high, while the nickel content in the surface region is relatively too low and the cobalt content is relatively too high. The cobalt content in the internal region is insufficient to improve the material's conductivity and capacity. Furthermore, the relatively high nickel content in the internal region can actually lead to a decrease in the material's capacity, thus hindering the improvement of the conductivity and capacity performance of the lithium-rich manganese-based material in the positive electrode active material. Consequently, when applied to batteries, this is detrimental to improving the battery's interfacial impedance, capacity performance, cycle stability, and rate performance. Conversely, the relatively high cobalt content and relatively low nickel content in the surface region can lead to severe oxygen loss on the material surface, resulting in poor material structural stability and consequently, poor cycle stability when applied to batteries.

[0056] This application also found that if the depth L of the surface region is less than 300 nm, firstly, it leads to a decrease in nickel content and an excessively rapid increase in cobalt content, making the lattice parameters of the surface region prone to abrupt changes, resulting in lattice mismatch and stress concentration, thus deteriorating the structural stability of the material; secondly, it leads to insufficient protection of the internal region by the surface region, making the material in the internal region prone to side reactions with the electrolyte, affecting the performance of lithium-rich manganese-based materials. Conversely, if the depth L of the surface region is greater than 400 nm, it leads to an excessively large surface region, resulting in a relatively high nickel content in the material, a decrease in the capacity of the positive electrode active material, and an excessively large surface region, which leads to faster changes in lattice parameters, which is not conducive to improving the structural stability of the material.

[0057] It should be noted that the mass content of nickel in the surface region (m1%), the mass content of nickel in the inner region (m2%), the mass content of cobalt in the surface region (b1%), and the mass content of cobalt in the inner region (b2%) can be obtained by energy dispersive X-ray spectroscopy (EDS).

[0058] In this application, m1% refers to the average mass content of nickel in the surface region based on the total mass of the surface region; m2% refers to the average mass content of nickel in the internal region based on the total mass of the internal region; n1% refers to the average mass content of cobalt in the surface region based on the total mass of the surface region; and n2% refers to the average mass content of cobalt in the internal region based on the total mass of the internal region.

[0059] Optionally, in some embodiments, the mass content m2% of nickel element in the internal region is 8% - 12%.

[0060] Optionally, in some embodiments, the mass content n2% of cobalt element in the internal region is 8% - 12%.

[0061] In the present application, the mass content m1% of nickel element and the mass content n1% of cobalt element in the surface region are not specifically limited. As long as the mass content of nickel element on the first surface in the surface region is 8% - 12%, the mass content of cobalt element is 8% - 12%, and along the direction from the first surface to the second surface, the mass content of nickel element decreases in sequence, and the mass content of cobalt element increases in sequence, then m1 > m2 and n1 < n2 can be satisfied.

[0062] It should be noted that the depth L of the surface region from the surface to the internal depth of the lithium-rich manganese-based material can be obtained by combining field emission electron microscopy with EDS energy spectrum test. Exemplarily, the depth L can be, for example, 300nm, 310nm, 320nm, 330nm, 340nm, 350nm, 360nm, 370nm, 380nm, 390nm, 400nm, etc. or a value within the range composed of any two of the above values.

[0063] Optionally, the internal region and the surface region independently include a substance with the chemical formula xLi2MnO3·(1 x)Li e Q 1-e Ni a Co b Mn c M d O2, where 0 < x < 1, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 < d < 0.7, 0 < e < 1, M includes a first doping element; Q includes a second doping element.

[0064] In some embodiments, along the direction from the first surface to the second surface, for any depth t nm and (t + 1) nm in the surface region, the mass content of nickel element satisfies: 0.0065% ≤ X t -X t+1 ≤ 0.0092%, where X t is the mass content of nickel element in the lithium-rich manganese-based material at a distance of t nm from the first surface along the direction from the first surface to the second surface, X t+1The mass content of nickel at a distance of (t+1) nm from the first surface along the direction from the first surface to the second surface, where 0 ≤ t ≤ L-1. Thus, this application further limits the change in the mass content of nickel in the lithium-rich manganese-based material per unit nanometer depth to 0.0065%~0.0092%, to control the rate of decrease in nickel mass content from the first surface to the second surface, thereby controlling the continuous change in the internal lattice parameters of the material. This avoids abrupt changes in cell parameters due to rapid changes in nickel content, preventing the generation of huge lattice mismatch stresses caused by abrupt changes in cell parameters, thereby stabilizing the structure of the lithium-rich manganese-based material and further improving the structural stability of the positive electrode active material. Simultaneously, controlling the rate of change of nickel content also ensures the enrichment of nickel on the surface, creating a difference between the surface nickel content and the nickel content in the bulk phase. This further suppresses oxygen loss on the material surface and ensures that the surface reactivity is sufficient to support the improvement of high-rate performance.

[0065] It should be noted that the mass content X of nickel in the lithium-rich manganese-based material at a distance t nm from the first surface along the direction from the first surface to the second surface is... t The mass content X of nickel in the lithium-rich manganese-based material at a distance of (t+1) nm from the first surface along the direction from the first surface to the second surface. t+1 The mass content of nickel in lithium-rich manganese-based materials can be obtained by EDS testing at any location in the surface region at a depth of t nm and a depth of (t+1) nm. For example, the X... t -X t+1 For example, it can be 0.0065%, 0.0070%, 0.0075%, 0.0080%, 0.0085%, 0.0090%, 0.0092%, etc., or a value within the range of any two of the above values. For instance, t can be 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 399, etc., or a value within the range of any two of the above values.

[0066] In some embodiments, along the direction from the first surface to the second surface, for any depth t nm and (t+1) nm within the surface region, the mass content of cobalt satisfies: 0.0062% ≤ C t+1 -C t ≤0.0095%, where C t+1 C represents the mass content of cobalt in a lithium-rich manganese-based material at a distance of (t+1) nm from the first surface along the direction from the first surface to the second surface. tThe mass content of cobalt in the lithium-rich manganese-based material at a distance t nm from the first surface along the direction from the first surface to the second surface is defined as 0 ≤ t ≤ L⁻¹. Thus, this application further controls the change in the mass content of cobalt in the lithium-rich manganese-based material per unit nanometer depth to be 0.0062%~0.0095%, thereby controlling the rate of increase of cobalt content from the first surface to the second surface in the surface region. On the one hand, by maintaining a suitable rate of change in cobalt content, the reasonable continuous change of lattice parameters is further controlled, reducing the occurrence of lattice abrupt changes. This more effectively avoids the generation of huge lattice mismatch stress inside the material caused by lattice abrupt changes. Combined with the change in nickel content, this improves the structural stability of the lithium-rich manganese-based material and avoids the generation of lattice mismatch stress as a crack initiation source in subsequent practical applications. This avoids the damage to the material structure caused by lattice mismatch stress during repeated deformation of the material due to repeated insertion and extraction of lithium ions during battery charging and discharging, and thus avoids the rapid capacity decay caused by the reaction between the material and the electrolyte after structural damage. On the other hand, by controlling the rate of change of cobalt content in the surface region, sufficient cobalt is ensured inside the material to improve conductivity and capacity, while the cobalt content on the surface is kept low to reduce oxygen loss. This is more conducive to improving the material's interface stability, ion transport kinetics, and electrochemical performance, and thus helps to achieve high capacity performance, high rate performance, and long cycle stability of the battery.

[0067] It should be noted that the mass content C of cobalt in the lithium-rich manganese-based material at a distance t nm from the first surface along the direction from the first surface to the second surface is... t The mass content C of cobalt in the lithium-rich manganese-based material at a distance of (t+1) nm from the first surface along the direction from the first surface to the second surface. t+1 The mass content of cobalt can be obtained by EDS testing at any location in the surface region at a depth of (t+1) nm and at a depth of t nm. For example, the C... t+1 -C t For example, it can be 0.0062%, 0.0065%, 0.0070%, 0.0075%, 0.0080%, 0.0085%, 0.0090%, 0.0095%, etc., or a value within the range of any two of the above values. For instance, t can be 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 399, etc., or a value within the range of any two of the above values.

[0068] In some embodiments, in the surface region, the mass ratio of nickel to cobalt on the first surface is (1.5~2.3):1, and the mass ratio of nickel to cobalt on the second surface is (0.8~1.2):1. This ensures that the first and second surfaces in the surface region have specific mass ratios of nickel and cobalt, resulting in a higher nickel content and a lower cobalt content in the surface region compared to the interior region. This effectively improves the material's conductivity and ensures high-capacity performance, while further suppressing the release of lattice oxygen and the dissolution of manganese ions, thus further enhancing the structural stability of the positive electrode active material.

[0069] It should be noted that the mass ratio of nickel to cobalt in the first surface and the mass ratio of nickel to cobalt in the second surface can both be obtained by EDS testing. For example, the mass ratio of nickel to cobalt in the first surface can be 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, or a value within any two of the above values; the mass ratio of nickel to cobalt in the second surface can be 0.8:1, 0.9:1, 2.0:1, 2.1:1, 2.2:1, or a value within any two of the above values.

[0070] In some embodiments, the mass ratio of nickel to cobalt in the internal region is (0.8~1.2):1. This ensures that the lithium-rich manganese-based material contains a sufficient amount of cobalt, further improving the material's conductivity and more effectively promoting high-capacity performance. Simultaneously, introducing an appropriate amount of nickel to match the cobalt content further stabilizes the material structure while reducing the impact of nickel on the material's capacity.

[0071] It should be noted that the mass ratio of nickel to cobalt in the internal region can be obtained by EDS testing. For example, the mass ratio of nickel to cobalt in the internal region can be 0.8:1, 0.9:1, 2.0:1, 2.1:1, 2.2:1, or a value within any two of the above ranges.

[0072] In some embodiments, in the lithium-rich manganese-based material, the ratio of the total mass of cobalt and nickel to the mass of manganese is 1:(1.5~2).

[0073] In this application, the ratio of the total mass content of cobalt and nickel to the mass of manganese in both the surface and internal regions of the lithium-rich manganese-based material is within the range of 1:(1.5~2). The ratio of the total mass content of cobalt and nickel to the mass of manganese in the surface and internal regions can be the same or different, and those skilled in the art can choose according to their needs.

[0074] It should be noted that the ratio of the total mass of cobalt and nickel to the mass of manganese in the lithium-rich manganese-based material can be obtained by inductively coupled plasma optical emission spectrometry (ICP). The ICP testing method refers to GB / T30902-2014 "Determination of Impurity Elements in Inorganic Chemical Products - Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES)". For example, the ratio of the total mass of cobalt and nickel to the mass of manganese can be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, or a value within any two of the above ranges.

[0075] In some embodiments, the mass content of the first dopant element is 0.03% to 1% based on the total mass of the lithium-rich manganese-based material. This further improves the stability of lattice oxygen, raises the oxygen evolution barrier, and is more conducive to improving the structural stability of the positive electrode active material. Simultaneously, it avoids the impact of excessive inert elements on the material's capacity caused by an excessively high doping content of the first dopant element, thus ensuring the material has a high capacity and further improving the battery's capacity performance and cycle stability.

[0076] It should be noted that the mass content of the first dopant element in the lithium-rich manganese-based material can be obtained by inductively coupled plasma atomic emission spectrometry (ICP). For example, the mass content of the first dopant element in the lithium-rich manganese-based material can be 0.03%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or a value within any two of the above ranges.

[0077] In some embodiments, the mass content of the second dopant element is 0.01% to 0.8% based on the total mass of the lithium-rich manganese-based material. This further prevents the slippage of transition metal sites and oxygen loss in the material, more effectively suppresses irreversible phase transitions, and avoids the impact of excessive dopant content on the material's capacity performance. This further improves the structural stability of the positive electrode active material while ensuring high specific capacity output and excellent cycle performance.

[0078] It should be noted that the mass content of the second dopant element in the lithium-rich manganese-based material can be obtained by ICP testing. For example, the mass content of the second dopant element in the lithium-rich manganese-based material can be 0.01%, 0.03%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or a value within any two of the above ranges.

[0079] In some alternative embodiments, the lithium-rich manganese-based material comprises secondary particles formed by the agglomeration of the primary particles.

[0080] Optionally, the lithium-rich manganese-based material may also include primary particles.

[0081] In some embodiments, the positive electrode active material further includes a composite layer, which coats at least a portion of the surface of the lithium-rich manganese-based material; the composite layer comprises LiCoO2 and Li3BO3. Thus, by coating the lithium-rich manganese-based material with a composite layer containing LiCoO2 and Li3BO3, direct contact between the lithium-rich manganese-based material and external materials can be isolated, especially direct contact between the lithium-rich manganese-based material and the battery electrolyte, effectively suppressing side reactions such as manganese dissolution and electrolyte decomposition, and improving the ionic and electronic conductivity of the positive electrode active material, thereby further improving the battery's capacity performance, rate performance, and cycle stability. The electronic conductivity of LiCoO2 is approximately 10⁻⁶. -3 ~10 -2 The S / cm ratio is 4-6 orders of magnitude higher than that of lithium-rich manganese-based materials. Li3BO3 is a lithium-ion conductor, and the two work synergistically to accelerate lithium-ion diffusion at the cathode surface and electrolyte interface, reducing voltage polarization during charging and discharging, and improving the battery's actual output voltage and energy density. Simultaneously, the high conductivity enables uniform charging and discharging reactions, avoiding excessively high local overpotentials, further reducing transition metal dissolution and oxygen escape, alleviating side reactions at the cathode / electrolyte interface, and further extending battery cycle life. Secondly, a small portion of the boron in the composite layer forms strong chemical bonds (BO bonds) with the oxygen on the material surface, making the composite layer tightly bonded to the lithium-rich manganese-based material, less prone to detachment under long-term cycling stress. Furthermore, the BO bonds further anchor oxygen, further preventing oxygen loss, improving both material conductivity and battery cycle performance. In addition, the Li3BO3 in the composite layer is an acidic glass phase, which can react with residual lithium (LiOH, Li2CO3) on the surface of lithium-rich manganese-based materials. At the same time, the composite layer can prevent lithium-rich manganese-based materials from contacting air and carbon dioxide, thus avoiding the formation of new residual lithium. This effectively reduces residual lithium on the material surface and is more conducive to improving the cycle stability and rate performance of the battery.

[0082] Furthermore, in some embodiments, the mass content of Li3BO3 is 440ppm to 4400ppm, based on the total mass of the positive electrode active material. This further improves the ionic conductivity of the positive electrode active material, accelerates the diffusion of lithium ions on the positive electrode surface and at the electrolyte interface, reduces voltage polarization during charging and discharging, and further enhances the actual output voltage and energy density of the battery, thus improving the battery's rate performance and cycle stability. Secondly, a sufficient mass content of Li3BO3 provides enough boron (B) to form boron bonds with oxygen (O) on the surface of the lithium-rich manganese-based material, increasing the tightness of the bond between the composite layer and the lithium-rich manganese-based material, further preventing oxygen loss from the lithium-rich manganese-based material, and further improving the battery's cycle performance. Moreover, a sufficient content of Li3BO3 can more fully react with LiOH and Li2CO3 on the surface of the lithium-rich manganese-based material, and further prevent the formation of new residual lithium. In addition, the mass content of Li3BO3 is in the range of 440ppm to 4400ppm. While achieving the above-mentioned effects, it can also avoid the increase in the proportion of inactive materials in the cathode material due to excessive Li3BO3 in the positive electrode active material, thereby avoiding the impact of excessive Li3BO3 on the volumetric energy density of the positive electrode.

[0083] It should be noted that the mass content of Li3BO3 in the positive electrode active material can be obtained by ICP testing. For example, the mass content of Li3BO3 in the positive electrode active material can be, for example, 440ppm, 500ppm, 100ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4400ppm, or a value within any range of two of the above values.

[0084] Furthermore, in some embodiments, the mass content of LiCoO2 is 520ppm to 5500ppm based on the total mass of the positive electrode active material. This is more conducive to improving the electronic conductivity of the positive electrode active material, constructing a fast electron conduction channel, further reducing the electron transport impedance in the positive electrode active material, further promoting the uniformity of charge-discharge reactions under high conductivity, more conducive to avoiding excessively high local overpotentials, transition metal dissolution, and oxygen escape, and more conducive to extending the cycle life of the battery. Moreover, a specific content of LiCoO2 can better synergistically block direct contact between the lithium-rich manganese-based material and the battery electrolyte with Li3BO3, further suppressing side reactions between the lithium-rich manganese-based material and external materials, and better blocking contact between the lithium-rich manganese-based material and air or carbon dioxide, further suppressing the generation of residual alkaline substances on the surface of the lithium-rich manganese-based material. In addition, the mass content of LiCoO2 is in the range of 520ppm to 5500ppm. While achieving the above effects, it can also avoid the increase in the proportion of inactive materials in the cathode material due to the excessive content of LiCoO2 in the cathode active material, and avoid the impact of excessive LiCoO2 on the volumetric energy density of the cathode.

[0085] It should be noted that the mass content of LiCoO2 in the positive electrode active material can be obtained by ICP testing. For example, the mass content of LiCoO2 in the positive electrode active material can be, for example, 520ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 5000ppm, 5500ppm, etc., or a value within the range of any two of the above values.

[0086] In some optional embodiments, the average particle size of the primary particles in the lithium-rich manganese-based material is 200 nm to 500 nm. This ensures that lithium ions have a suitable transport path in the lithium-rich manganese-based material, improves the material's kinetic performance, and helps to fully utilize its capacity. At the same time, the appropriately sized primary particles can also effectively suppress oxygen escape and transition metal dissolution in the lithium-rich manganese-based material, thereby improving the stability of the positive electrode active material.

[0087] This study found that if the average particle size of the primary particles in lithium-rich manganese-based materials is less than 200 nm, the specific surface area of ​​the materials will increase, increasing the risk of oxygen escape and transition metal dissolution. This will cause the structure of the positive electrode active material to collapse during cycling, which is detrimental to improving the cycling stability of the positive electrode active material. If the average particle size of the primary particles in lithium-rich manganese-based materials is greater than 500 nm, it will increase the lithium-ion transport path, which will hinder the electrochemical kinetics of the materials and prevent the capacity from being fully utilized, thus affecting the capacity performance of the battery.

[0088] It should be noted that the average particle size of the primary particles of the lithium-rich manganese-based material can be obtained by field emission electron microscopy. For example, the average particle size of the primary particles of the lithium-rich manganese-based material can be 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc., or a value within any two of the above values.

[0089] In some embodiments, the thickness of the composite layer is denoted as H, satisfying: 10nm ≤ H ≤ 50nm. This ensures that the composite layer coating the surface of the lithium-rich manganese-based material has sufficient thickness, effectively isolating the lithium-rich manganese-based material from external environments, further effectively isolating it from the electrolyte, further suppressing side reactions between the material and the electrolyte, effectively isolating it from direct contact with air and carbon dioxide, and further suppressing the formation of residual alkali on the material surface. Furthermore, a sufficiently thick composite coating layer can further improve the ionic and electronic conductivity of the positive electrode active material, thus further improving the capacity performance, rate performance, and cycle stability of the battery containing the positive electrode active material. Simultaneously, a composite layer thickness H within the range of 10nm to 50nm can also prevent excessive thickness from increasing the migration path of lithium ions in the positive electrode active material, thereby ensuring lower ionic impedance, further improving the rate performance of the battery, and preventing an increase in the proportion of inactive materials in the composite layer within the positive electrode active material, thus further ensuring higher energy density of the battery.

[0090] This study found that if the thickness H of the composite layer is less than 10 nm, discontinuous coating is likely to occur, which cannot effectively prevent direct contact between the lithium-rich manganese-based material and the electrolyte. Interfacial side reactions (such as Mn dissolution and electrolyte decomposition) will still occur. Furthermore, it cannot prevent direct contact between the lithium-rich manganese-based material and air or carbon dioxide. New residual alkali is easily generated on the exposed surface of the lithium-rich manganese-based material, affecting the cycle performance of the positive electrode active material. In addition, if the thickness of the composite layer is too low, it cannot effectively improve the ionic conductivity and electronic conductivity of the positive electrode active material. The capacity utilization, rate performance and cycle stability of the positive electrode active material when applied to the battery are limited. If the thickness of the coating layer is higher than 50 nm, the migration path of lithium ions in the positive electrode active material will be significantly prolonged, the ionic impedance of the battery will increase sharply, and the rate performance will deteriorate. At the same time, if the thickness of the composite layer is too thick, the proportion of inactive material in the positive electrode active material will increase, and the volumetric energy density of the battery will decrease.

[0091] It should be noted that the thickness H of the composite layer can be obtained by transmission electron microscopy. For example, the thickness H of the composite layer can be 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, or a value within any two of the above values.

[0092] In some embodiments, the average particle size of the secondary particles in the lithium-rich manganese-based material is denoted as D, satisfying: 1μm ≤ D ≤ 3μm. Secondary particles within this size range can reduce pulverization or cracking problems that may be caused by small particles in the material, thereby improving the mechanical strength and structural stability of the positive electrode active material. At the same time, it avoids problems such as excessively large secondary particle sizes leading to excessively long ion transport paths, resulting in low utilization of active sites within the material, and consequently, low capacity and poor rate performance. Secondary single-crystal particles, due to their single-crystal structure, can withstand greater stress and exhibit better stability during multiple charge-discharge cycles, reducing battery degradation.

[0093] It should be noted that the average particle size D of the secondary particles in the lithium-rich manganese-based material can be obtained by observation and testing using a field emission electron microscope. For example, the average particle size D of the secondary particles in the lithium-rich manganese-based material can be, for example, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, or a value within any two of the above ranges.

[0094] Furthermore, in some embodiments, the following condition is satisfied: 20 ≤ D / (2H) ≤ 140. Thus, the relationship between the average particle size of the secondary particles of the lithium-rich manganese-based material and the thickness of the composite layer, D / (2H), is maintained within the range of 20 to 140. This results in excellent mechanical compatibility between the composite layer and the lithium-rich manganese-based material, significantly reducing internal stress generated in the positive electrode active material during battery cycling. It also ensures that the composite layer is uniform, dense, and thin, effectively suppressing the dissolution of transition metal ions and blocking interfacial side reactions between the lithium-rich manganese-based material and the electrolyte, while also effectively suppressing the increase in interfacial impedance.

[0095] This study found that if the relationship between the average particle size of the secondary particles in the lithium-rich manganese-based material and the thickness of the composite layer, D / (2H), is less than 20, it indicates that the average particle size of the secondary particles in the lithium-rich manganese-based material is too small and the thickness of the composite layer is too thick. This leads to a deterioration in the diffusion kinetics of lithium ions in the positive electrode active layer, a sharp increase in the impedance of the positive electrode active material, and consequently, a deterioration in the rate performance of the battery. Furthermore, due to the significant difference in physical properties between the composite layer and the lithium-rich manganese-based material, when the composite layer is too thick and the average particle size of the secondary particles is too small, the internal stress generated by the insertion / extraction of lithium ions in the positive electrode during battery cycling will be high, easily leading to structural damage to the composite layer and affecting the structural stability of the positive electrode active material, thus hindering the improvement of battery cycle stability. Conversely, if the average particle size of the lithium-rich manganese-based material is too small, it will lead to a decrease in the active material's density and overall performance. The decrease in the proportion of the material affects the capacity performance of the battery. If the relationship between the average particle size of the secondary particles of the lithium-rich manganese-based material and the thickness of the composite layer, D / (2H), is higher than 140, it means that the average particle size of the secondary particles of the lithium-rich manganese-based material is too large and the thickness of the composite layer is too thin. Insufficient thickness makes it impossible to form a continuous and effective coating layer, thus failing to effectively block the direct contact between the positive electrode active material and the solid electrolyte. At the same time, during the charging and discharging process, the mechanical strength of the thin composite layer is insufficient, and it is very easy to break and fail in the early stage of cycling, which cannot effectively improve the cycle and rate performance of the positive electrode active material. In addition, the thin composite layer requires extremely high uniformity and precision in the preparation process. Slight process fluctuations may lead to poor coating of some particles in the positive electrode active material, resulting in poor consistency and repeatability of battery performance, which is not conducive to large-scale production.

[0096] For example, the relationship between the average particle size D of the secondary particles of the lithium-rich manganese-based material and the thickness H of the composite layer, D / (2H), can be, for example, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, or a value within the range of any two of the above values.

[0097] In some embodiments, the compacted density of the positive electrode active material powder is 3.0 g / cm³. 3 ~3.3g / cm3 This ensures tight and uniform contact within the positive electrode active material, which helps alleviate localized stress concentration during subsequent applications, protects the grain integrity of the positive electrode active material, and prevents grain boundary cracking from blocking ion transport channels. Simultaneously, it avoids excessively high powder compaction density, which could lead to overly tight internal material contact, hindering ion diffusion, causing excessive internal stress in the electrode, deteriorating structural stability, and resulting in uneven current distribution during energization. This application controls the powder compaction density of the positive electrode active material to be within 3.0 g / cm³. 3 ~3.3g / cm 3 Within this range, it can further maintain stable ion transport channels and low interface impedance, which is more conducive to improving the cycle stability and rate performance of the battery.

[0098] It should be noted that the compacted density of the positive electrode active material powder can be measured using a compaction density meter. The specific test method refers to GB / T 44330-2024 "Determination of Compacted Density of Powder for Lithium-ion Battery Positive Electrode Materials". During the test, a pressure of 5 tons is applied, the inner diameter of the mold is 12 mm, and the applied pressure is 376.69 MPa. For example, the compacted density of the positive electrode active material powder can be, for instance, 3.0 g / cm³. 3 3.1g / cm 3 3.2g / cm 3 3.3g / cm 3 Values ​​equal to or within the range of any two of the above values.

[0099] In some embodiments, the specific surface area of ​​the positive electrode active material is 2m². 2 / g~3m 2 / g. This ensures an appropriate contact area between the positive electrode active layer and the electrolyte, allowing more active sites to participate in the reaction and thus maximizing the material's capacity. Simultaneously, it avoids the occurrence of more side reactions caused by excessively large specific surface areas of the positive electrode active material, further improving the structural stability of the positive electrode active material. Furthermore, a specific surface area within the aforementioned range also results in a suitable powder compaction density, more effectively improving lithium-ion transport efficiency, enhancing the structural stability of the positive electrode active material, further reducing internal stress and interfacial impedance of the electrode, and further improving the rate performance and cycle performance of the battery.

[0100] It should be noted that the specific surface area of ​​the positive electrode active material can be calculated by analyzing the nitrogen adsorption-desorption curve. The test method for specific surface area refers to GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method". For example, the specific surface area of ​​the positive electrode active material may be 2.0 m². 2 / g、2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.6m 2 / g, 2.7m 2 / g, 2.8m 2 / g, 2.9m 2 / g, 3.0m 2 / g or values ​​within the range of any two of the above values.

[0101] In some embodiments, the powder conductivity of the positive electrode active material is 1.0 × 10⁻⁶ under a pressure of 48 MPa to 55 MPa. -6 S / cm ~ 9.0 × 10 -5 S / cm. Thus, the powder conductivity of the positive electrode active material, within a specific range, enables a more uniform electrochemical reaction within the positive electrode, avoids localized lithium delithiation transitions, reduces lattice distortion of the positive electrode active material, and effectively reduces side reactions between the positive electrode sheet containing the positive electrode active material and the electrolyte, reducing the dissolution of transition metals and the escape of lattice oxygen. This maintains the structural stability of the positive electrode active material and is more conducive to improving the cycle stability of the battery.

[0102] It should be noted that the powder conductivity of the positive electrode active material under a pressure of 48MPa to 55MPa can be obtained by testing using the four-probe method, with the testing method referring to GB / T 30835-2014 "Carbon Composite Lithium Iron Phosphate Positive Electrode Materials for Lithium-ion Batteries". For example, under a pressure of 48MPa to 55MPa, the powder conductivity of the positive electrode active material can be, for example, 1.0 × 10⁻⁶. -6 S / cm, 5.0×10 -6 S / cm, 1.0×10 -5 S / cm, 1.5×10 -5 S / cm, 2.0×10 -5 S / cm, 2.5×10 -5 S / cm, 3.0×10 -5 S / cm, 3.5×10 -5 S / cm, 4.0×10 -5 S / cm, 4.5×10 -5 S / cm, 5.0×10 -5 S / cm, 5.5×10 -5 S / cm, 6.0×10 -5 S / cm, 6.5×10 -5 S / cm, 7.0×10 -5S / cm, 7.5×10 -5 S / cm, 8.0×10 -5 S / cm, 9.0×10 -5 S / cm or values ​​within the range of any two of the above values.

[0103] In some embodiments, the X-ray diffraction pattern of the positive electrode active material exhibits diffraction peaks in the range of 2θ diffraction angles from 20° to 23°. Thus, the presence of well-crystallized lithium-rich manganese-based materials in the positive electrode active material provides structural assurance for its long-cycle stability and high-rate performance.

[0104] The X-ray diffraction pattern of the positive electrode active material provided in this application shows that the diffraction peaks in the range of 2θ diffraction angle 20°~23° belong to superlattice diffraction peaks.

[0105] In some embodiments, the X-ray diffraction pattern of the positive electrode active material further includes a (003) characteristic peak and a (104) characteristic peak, wherein the 2θ diffraction angle of the (003) characteristic peak is 18°~20° and the 2θ diffraction angle of the (104) characteristic peak is 44°~45°; the peak intensity of the (003) characteristic peak is K1 and the peak intensity of the (104) characteristic peak is K2, satisfying: K1 / K2>2.1.

[0106] In the X-ray diffraction pattern of the positive electrode active material provided in this application, the (003) characteristic peak is a diffraction peak generated by the (003) crystal plane, which is a crystal plane in which Li layers and transition metal layers are arranged alternately and orderly; the (004) characteristic peak is a diffraction peak generated by the (004) crystal plane, which is a crystal plane in which transition metal and lithium metal are mixed and arranged. In the X-ray diffraction pattern of the positive electrode active material, when the ratio K1 / K2 of the peak intensity of the (003) characteristic peak to the peak intensity of the (004) characteristic peak is greater than 2.1, the diffraction peak of the (004) crystal plane is lower, indicating that the probability of lithium-nickel mixing phenomenon in the positive electrode active material during battery operation is low, or even almost non-existent, thereby avoiding the influence of lithium-nickel mixing on lithium-ion intercalation and deintercalation, which is beneficial to improving the specific capacity, initial efficiency and cycle stability of the battery. Furthermore, in the X-ray diffraction pattern of the positive electrode active material provided in this application, the ratio of the peak intensity of the (003) characteristic peak to the peak intensity of the (104) characteristic peak, K1 / K2, is greater than 2.1, and the peak intensity of the (004) characteristic peak is relatively low, which also indicates that the introduction of the second dopant element into the lithium-rich manganese-based material did not cause lithium-nickel mixing phenomenon.

[0107] For example, the 2θ diffraction angle of the characteristic peak (003) can be, for example, 18.0°, 18.2°, 18.4°, 18.6°, 18.8°, 19.0°, 19.2°, 19.4°, 19.6°, 19.8°, 20.0°, or a value within the range of any two of the above values; the 2θ diffraction angle of the characteristic peak (104) can be, for example, 44.0°, 44.1°, 44.2°, 44.3°, 44.4°, 44.5°, 44.6°, 44.7°, 44.8°, 44.9°, 45.0°, or a value within the range of any two of the above values.

[0108] For example, the ratio K1 / K2 of the peak intensity of the (003) characteristic peak and the peak intensity of the (104) characteristic peak can be, for example, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, or a value within the range of any two of the above values.

[0109] Secondly, this application provides an all-solid-state battery, which includes a positive electrode sheet comprising the positive electrode active material described in the first aspect. Thus, the all-solid-state battery provided by this application contains a specific positive electrode active material, which can effectively improve the capacity performance, rate performance, and cycle stability of the all-solid-state battery.

[0110] In some embodiments, the all-solid-state battery includes a negative electrode, which includes an indium metal layer and / or a lithium metal layer.

[0111] Furthermore, in some embodiments, the negative electrode is an indium metal layer and a lithium metal layer.

[0112] In some embodiments, the all-solid-state battery further includes a solid electrolyte layer, which includes a halide solid electrolyte layer and / or a sulfide solid electrolyte layer.

[0113] Furthermore, in some embodiments, the solid electrolyte layer is a halide solid electrolyte layer and a sulfide solid electrolyte layer.

[0114] In some embodiments, when the solid electrolyte layer comprises a halide solid electrolyte layer and a sulfide solid electrolyte layer, the mass ratio of the halide solid electrolyte layer to the sulfide solid electrolyte layer is (20~60):(40~80).

[0115] For example, the mass ratio of the halide solid electrolyte layer to the sulfide solid electrolyte layer can be, for example, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, or a value within the range of any two of the above values.

[0116] Example 1 This embodiment provides a method for preparing an all-solid-state battery, including the following steps: (1) Preparation of positive electrode active material ① Preparation of hydroxide precursor powder: Nickel sulfate, cobalt sulfate, manganese sulfate, and magnesium sulfate were mixed with deionized water in a Ni:Co:Mn:Mg molar ratio of 0.13:0.13:0.54:0.014 to prepare mixed solution A. The total concentration of metal ions in mixed solution A was 2 mol / L.

[0117] Nickel sulfate, cobalt sulfate, manganese sulfate, and magnesium sulfate were mixed with deionized water in a Ni:Co:Mn:Mg molar ratio of 0.217:0.043:0.54:0.014 to prepare mixed solution B. The total concentration of metal ions in mixed solution B was 2 mol / L.

[0118] A mixed solution C was prepared by mixing NaOH, NH3·H2O, sodium tungstate, and deionized water, wherein the concentration of NaOH was 4 mol / L, the concentration of ammonia was 0.4 mol / L, and the concentration of sodium tungstate was 0.0059 mol / L.

[0119] A certain amount of deionized water was added to the reactor, and the pH was adjusted to 11.5 using ammonia and sodium hydroxide at a concentration ratio of 1:10. Mixed solutions A and C were added to the reactor containing the base solution using a peristaltic pump to carry out the first coprecipitation reaction, controlling the pH of the first coprecipitation reaction at 11.5 to obtain the precursor intermediate. Mixed solution B was then slowly pumped into mixed solution A using a peristaltic pump to obtain a metal salt mixed solution D with continuously varying elemental concentrations. The metal salt mixed solution D and mixed solution C were then added concurrently to the reactor containing the precursor intermediate to carry out the second coprecipitation reaction, controlling the pH of the second coprecipitation reaction at 11.5. The products obtained from the second coprecipitation reaction were then sequentially separated, washed, and dried to obtain hydroxide precursor powder.

[0120] ② The hydroxide precursor powder obtained in step ① and lithium hydroxide are thoroughly mixed in a mixer at a molar ratio of 1:1.47 to obtain a mixture. The mixture is placed in an air atmosphere and heated to 500℃ at a heating rate of 1℃ / min and held for 5h. Then, it is heated to 900℃ at a heating rate of 2℃ / min and held for sintering for 20h to obtain lithium-rich manganese-based material.

[0121] ③ Mix the lithium-rich manganese-based material, cobalt boride and lithium hydroxide thoroughly according to the formula. Then place the thoroughly mixed material in an air atmosphere and calcine it at 600℃ for 10 hours to obtain the positive electrode active material.

[0122] The structural schematic diagram of the positive electrode active material obtained in this embodiment is as follows: Figure 1 As shown, by Figure 1 As can be seen, the positive electrode active material prepared in this embodiment includes a lithium-rich manganese-based material 1 and a composite layer 2 coated on the surface of the lithium-rich manganese-based material 1. The lithium-rich manganese-based material 1 includes a surface region 1-1 and an inner region 1-2. The surface region 1-1 is the region from the surface of the lithium-rich manganese-based material 1 to the interior with a depth of L nm. The inner region 1-2 is the remaining region of the lithium-rich manganese-based material 1 excluding the surface region 1-1, where L = 350 nm. The surface region 1-1 has a first surface 1-11 and a second surface 1-12 disposed opposite to each other. The first surface 1-11 is disposed away from the inner region 1-2, and the second surface 1-12 is disposed towards the inner region 1-2 and is in contact with the outer surface of the inner region 1-2.

[0123] In the positive electrode active material, the lithium-rich manganese-based material consists of secondary particles formed by the agglomeration of primary particles. The average particle size of the primary particles is 300 nm, and the average particle size of the secondary particles is 2 μm. The chemical formula of the internal region of the lithium-rich manganese-based material is 0.47Li₂MnO₃·0.53Li 0.967 Mg 0.033 Ni 0.304 Co 0.304 Mn 0.386 W 0.0055 In the surface region of the lithium-rich manganese-based material, the mass content of nickel decreases sequentially from the first surface to the second surface, while the mass content of cobalt increases sequentially. Along the thickness direction from the first surface to the second surface, the mass content of nickel per nanometer of surface thickness, based on the total mass per unit nanometer thickness of the surface region, satisfies: X t -X t+1 =0.0076%~0.0080%, where, X t X represents the mass content of nickel in a lithium-rich manganese-based material at an arbitrary distance t nm from the first surface along the thickness direction from the first surface to the second surface. t+1Let C represent the mass content of nickel in the lithium-rich manganese-based material at a distance of (t+1) nm from the first surface along the thickness direction from the first surface to the second surface, where 0 ≤ t ≤ 349. Along the thickness direction from the first surface to the second surface, in the surface region per nanometer thickness, based on the total mass per unit nanometer thickness of the surface region, the mass content of cobalt satisfies: C t+1 -C t =0.0077%~0.0081%, where, C t+1 C represents the mass content of cobalt in a lithium-rich manganese-based material at a distance of (t+1) nm from the first surface along the thickness direction from the first surface to the second surface. t Let t be the mass content of cobalt in the lithium-rich manganese-based material at any distance t nm from the first surface along the thickness direction from the first surface to the second surface, where 0 ≤ t ≤ 349. The mass ratio of nickel to cobalt on the first surface is 1.8:1, and the mass ratio of nickel to cobalt on the second surface is 1:1. In the internal region, the mass ratio of nickel to cobalt remains 1:1, and the mass content of nickel (m2%) and cobalt (n2%) in the internal region is 8.9%. In the lithium-rich manganese-based material, the ratio of the total mass of cobalt and nickel to the mass of manganese is 1:1.9. In the surface region, the mass content of nickel decreases sequentially from the first surface to the second surface. The mass content of nickel on the second surface of the surface region is equal to the mass content of nickel in the inner region. Therefore, the average mass content of nickel in the surface region, m1%, is greater than the mass content of nickel in the inner region, m2%, which satisfies the condition: m1 > m2. In the surface region, the mass content of cobalt increases sequentially from the first surface to the second surface. The mass content of cobalt on the second surface of the surface region is equal to the mass content of cobalt in the inner region. Therefore, the average mass content of cobalt in the surface region, n1%, is less than the mass content of cobalt in the inner region, n2%, which satisfies the condition: n1 < n2.

[0124] The lithium-rich manganese-based material also includes a first dopant element and a second dopant element. The first dopant element is W, and the second dopant element is Mg. Based on the total mass of the lithium-rich manganese-based material, the mass content of W is 0.5%, and the mass content of Mg is 0.4%. The composite layer in the positive electrode active material is composed of LiCoO2 and Li3BO3. Based on the total mass of the positive electrode active material, the mass content of Li3BO3 is 2340 ppm, the mass content of LiCoO2 is 3680 ppm, and the thickness H of the composite layer is 34 nm.

[0125] Figure 2 This is a field emission electron microscope (FET) image of the positive electrode active material provided in this embodiment. Figure 2It can be seen that the positive electrode active material provided in this embodiment is a secondary particle formed by the agglomeration of primary particles.

[0126] Figure 3 This is a scanning electron microscope image of the grain cross-section of the positive electrode active material provided in this embodiment. Figure 4 In accordance with Figure 3 Data graphs of Ni and Co elements obtained by EDS line scanning of the straight lines in the scanning electron microscope image. Figure 5 In accordance with Figure 3 The data graph of Mn, W, and Mg elements obtained by EDS linear scanning of the straight lines in the scanning electron microscope image is from... Figures 3-5 It can be seen that the cobalt content in the surface region of the lithium-rich manganese-based material inside the positive electrode active material shows an increasing trend from the surface to the interior. The cobalt content in the interior region is relatively uniform and higher than that in the surface region. On the other hand, the nickel content in the surface region shows a decreasing trend from the surface to the interior. The nickel content in the interior region is relatively uniform and lower than that in the surface region. The contents of Mn, W, and Mg are uniformly distributed in the lithium-rich manganese-based material.

[0127] Figure 6 The figure shows the X-ray diffraction (XRD) pattern of the positive electrode active material provided in this embodiment. As can be seen from the figure, the characteristic diffraction peak (002) of the lithium-rich manganese-based positive electrode material appears at 21.52°, indicating that the lithium-rich manganese-based positive electrode material has been successfully prepared. The characteristic diffraction peaks (003) and (104) appear at 18.69° and 44.70°, respectively. The relative intensity ratio of the characteristic diffraction peaks (003) and (104) is 2.336, which indicates that there is almost no cation mixing in the lithium-rich manganese-based positive electrode material, which makes the lithium ion transport channel unobstructed and is conducive to improving the rate performance of the material.

[0128] (2) Preparation of positive electrode mixture The positive electrode active material obtained in step (1) and the halide electrolyte Li3YBr 5.7 F 0.3 Conductive agent and vapor-grown carbon fiber (VGCF) are mixed at a mass ratio of 65:30:5 to obtain the positive electrode mixture.

[0129] (3) Preparation of negative electrode sheet The negative electrode is composed of stacked indium metal sheets and lithium metal sheets. The lithium metal layer is 50µm thick. The indium metal sheet with a thickness of 100µm is rolled down to a thickness of 50µm using a roller press. The indium metal sheet is then sliced ​​by a slicing machine. The indium metal sheet and lithium metal sheet after being rolled down by the roller press are stacked together to obtain the negative electrode.

[0130] (4) Preparation of solid electrolyte layer The solid electrolyte layer comprises two types of electrolyte layers stacked together: a halide electrolyte layer and a sulfide electrolyte layer. The halide electrolyte in the halide electrolyte layer is Li3YBr. 5.7 F 0.3 The sulfide electrolyte in the sulfide electrolyte layer is Li 5.5 PS 4.5 Cl 1.5 Furthermore, halide solid electrolytes account for 40% of the total mass percentage of the solid electrolyte layer, and sulfide electrolytes account for 60% of the total mass percentage of the solid electrolyte layer.

[0131] (4) Preparation of all-solid-state secondary batteries The positive electrode mixture obtained in step (2) is ground and placed in a mold (with an inner diameter of 10 mm). It is then pressed into sheets using a tablet press with a pressure of 2 tons to obtain the positive electrode sheet. Subsequently, the halide solid electrolyte from step (4) is placed in the mold battery sleeve and placed above the positive electrode mixture. The sleeve is then placed in the tablet press and pressed into sheets with a pressure of 2 tons to press the halide solid electrolyte into sheets. Then, the sulfide electrolyte from step (4) is added to the mold battery sleeve and placed above the halide sheet. The sleeve is placed in the tablet press and a pressure of 2 tons is applied to it to press the sulfide electrolyte into sheets. Subsequently, the negative electrode sheet prepared in step (3) is placed in the sleeve. The mold battery sleeve is placed in a pressure controllable device, and a certain pressure is applied by a torque wrench to ensure the assembled all-solid-state secondary battery.

[0132] Figure 7 This is a schematic diagram of an all-solid-state battery. As shown in the diagram, the all-solid-state battery includes, in sequence, a positive electrode layer 3, a solid electrolyte layer 4, and a negative electrode layer 5. The positive electrode layer 1 is composed of a positive electrode active material 3-1, a halide solid electrolyte 3-2, and vapor-grown carbon fiber (VGCF) 3-3. The solid electrolyte layer 4 is composed of a halide solid electrolyte layer 4-1 and a sulfide solid electrolyte layer 4-2. The halide solid electrolyte layer 4-1 is positioned closer to the positive electrode 3, and the sulfide solid electrolyte layer 4-2 is positioned further away from the positive electrode 3. The negative electrode layer 5 is composed of an indium metal layer 5-1 and a lithium metal layer 5-2. The indium metal layer 5-1 is positioned closer to the solid electrolyte layer 4, and the lithium metal layer 5-2 is positioned further away from the solid electrolyte layer 4.

[0133] The preparation methods and parameter settings of the remaining embodiments and comparative examples are basically the same as those of Example 1-1. The differences are shown in Tables 1 and 2. Tables 1-2 only show the differences in the relevant parameters of the prepared products compared to Example 1. When the product parameters change, the preparation process can be adjusted adaptively accordingly. In Tables 1 and 2, L represents the depth of the surface region from the surface to the interior of the lithium-rich manganese-based material, in nm; m1 represents the mass content of nickel in the surface region; m2 represents the mass content of nickel in the interior region; n1 represents the mass content of cobalt in the surface region; n2 represents the mass content of cobalt in the interior region; X t Indicates: the mass content of nickel in the lithium-rich manganese-based material at a distance t nm from the first surface along the direction from the first surface to the second surface; X t+1 Indicates: the mass content of nickel in the lithium-rich manganese-based material at a distance of (t+1) nm from the first surface along the direction from the first surface to the second surface; C t+1 Indicates: the mass content of cobalt in the lithium-rich manganese-based material at a distance of (t+1) nm from the first surface along the direction from the first surface to the second surface; C t The following values ​​represent the mass content of cobalt in the lithium-rich manganese-based material at a distance of t nm from the first surface along the direction from the first surface to the second surface; h represents the mass content of the first dopant element based on the total mass of the lithium-rich manganese-based material; j represents the mass content of the second dopant element based on the total mass of the lithium-rich manganese-based material; k represents the mass content of Li3BO3 based on the total mass of the positive electrode active material; l represents the mass content of LiCoO2 based on the total mass of the positive electrode active material; H represents the thickness of the composite layer in nm; D represents the average particle size of the secondary particles of the lithium-rich manganese-based material in μm; K1 / K2 represents the ratio of the peak intensity of the characteristic peak (003) to the peak intensity of the characteristic peak (104).

[0134] Table 1

[0135] Table 2

[0136] In addition to the differences in Tables 1 and 2, some embodiments and comparative examples also differ from Embodiment 1 in the following ways: The difference between Example 8 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.967 Mg 0.033 Ni 0.306 Co 0.306 Mn 0.386 W 0.00033 O2.

[0137] The difference between Example 9 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.967 Mg 0.033 Ni 0.306 Co 0.306 Mn 0.386 W 0.0110 O2.

[0138] The difference between Example 10 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.967 Mg 0.033 Ni 0.306 Co 0.306 Mn 0.386 W 0.00011 O2.

[0139] The difference between Example 11 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.967 Mg 0.033 Ni 0.304 Co 0.304 Mn 0.376 W 0.0166 O2.

[0140] The difference between Example 12 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.999 Mg 0.001 Ni 0.306 Co 0.306 Mn 0.384 W 0.00546 O2.

[0141] The difference between Example 13 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.934 Mg 0.066 Ni 0.306 Co 0.306 Mn 0.383 W 0.00546 O2.

[0142] The difference between Example 14 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.9996 Mg 0.0004 Ni 0.306 Co 0.306 Mn 0.383 W 0.00547O2.

[0143] The difference between Example 15 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.9 Mg 0.1 Ni 0.306 Co 0.306 Mn 0.383 W 0.00552 O2.

[0144] The difference between Example 26 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.965 Na 0.035 Ni 0.305 Co 0.305 Mn 0.388 Nb 0.00537 O2, with Nb as the first dopant and Na as the second dopant.

[0145] The difference between Example 27 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.963 K 0.037 Ni 0.306 Co 0.306 Mn 0.386 Mo 0.00541 O2, with Mo as the first dopant and K as the second dopant.

[0146] The difference between Comparative Example 1 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.967 Mg 0.033 Ni 0.304 Co 0.304 Mn 0.386 W 0.00546 O2.

[0147] The difference between Comparative Example 2 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li₂MnO₃·0.53Li 0.967 Mg 0.033 Ni 0.304 Co 0.304 Mn 0.386 W 0.00546 O2.

[0148] The difference between Comparative Example 3 and Example 1 is that the chemical formula of the internal region in the lithium-rich manganese-based material is: 0.47Li2MnO3·0.53LiNi 0.306 Co 0.306 Mn0.387 O2.

[0149] Test example: The all-solid-state batteries provided in the above embodiments and comparative examples were tested as follows: (1) Measurement of gram capacity: At 25°C, the all-solid-state batteries provided in the above embodiments and comparative examples were charged to 4.2V at 0.1C, charged at a constant voltage to 0.025C, allowed to stand for 5 minutes, and then discharged to 1.9V at 0.1C. The discharge specific capacity was recorded. The discharge specific capacity is the electrochemical energy released when discharging from 4.2V to 1.9V under 0.1C conditions.

[0150] (2) First test of Coulomb efficiency: At 25°C, the all-solid-state batteries provided in the above embodiments and comparative examples were charged to 4.2V at 0.1C, and then charged at a constant voltage to 0.025C. After standing for 5 minutes, they were discharged to 1.9V at 0.1C. The discharge capacity and charge capacity of the first cycle were recorded. The first coulombic efficiency was calculated using the formula: First coulombic efficiency = (first cycle discharge capacity / first cycle charge capacity) × 100%.

[0151] (3) Capacity retention test: At 25°C, the all-solid-state batteries provided in the above embodiments and comparative examples were charged at 1C to 4.2V, charged at constant voltage to 0.025C, and then left to stand for 5 minutes before being discharged at 1C to 1.9V. This process was repeated 200 times. The discharge capacity at the first cycle and the discharge capacity at the 200th cycle were measured, and the capacity retention rate after 200 cycles was calculated, i.e., the capacity retention rate after 200 cycles = (discharge capacity at the 200th cycle / discharge capacity at the first cycle) × 100%.

[0152] (4) Ratio performance testing: The nominal specific capacity is 200mAh / g, the test voltage is 1.9V~4.2V, the test temperature is 45℃, and the performance is tested at charge / discharge rates of 1C / 0.1C. The rate performance (%) of 1C / 0.1C is calculated using the formula: discharge specific capacity at 1C rate / discharge specific capacity at 0.1C rate × 100%.

[0153] The test results are shown in Table 3.

[0154] Table 3

[0155] As can be seen from Tables 1-3, this application introduces lithium-rich manganese-based materials into the positive electrode active material. In the surface region of the lithium-rich manganese-based material, the mass content of nickel is controlled to decrease sequentially from the direction away from the interior region to the direction closer to the interior region, while the mass content of cobalt is sequentially increased sequentially from the direction away from the interior region to the direction closer to the interior region. The nickel content in the surface region is higher than that in the interior region, and the cobalt content in the surface region is lower than that in the interior region. This improves the conductivity and capacity performance of the positive electrode active material. At the same time, increasing the nickel content near the material surface and reducing its cobalt content helps to reduce oxygen loss from the material surface and stabilize the material structure. This allows the positive electrode active material to have multiple advantages in structure, interface and electrochemical performance, thereby improving the battery's capacity performance, cycle stability and rate performance.

[0156] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A positive electrode active material, comprising a lithium-rich manganese-based material, characterized in that, The lithium-rich manganese-based material includes a surface region and an internal region. The surface region is the area from the surface of the lithium-rich manganese-based material to an internal depth of L nm. The internal region is the remaining area of ​​the lithium-rich manganese-based material excluding the surface region, wherein 300≤L≤400. The mass content of nickel in the surface region is denoted as m1, and the mass content of nickel in the inner region is denoted as m2, where m1 > m2. The mass content of cobalt in the surface region is denoted as n1%, and the mass content of cobalt in the inner region is denoted as n2%, where n1 < n2. The surface region includes a first surface and a second surface disposed opposite to each other. The first surface is disposed away from the inner region, and the second surface faces the inner region and is in contact with the surface of the inner region. In the surface region, along the direction from the first surface to the second surface, the mass content of nickel decreases sequentially, and the mass content of cobalt increases sequentially. The lithium-rich manganese-based material further includes a first doping element and a second doping element; the first doping element includes at least one of W, Nb, and Mo, and the second doping element includes at least one of Mg, Na, and K.

2. The positive electrode active material according to claim 1, characterized in that, Along the direction from the first surface to the second surface, for any depth t nm and (t+1) nm within the surface region, the mass content of nickel satisfies: 0.0065% ≤ X t -X t+1 ≤0.0092%, where X t X represents the mass content of nickel in a lithium-rich manganese-based material at a distance t nm from the first surface along the direction from the first surface to the second surface. t+1 The mass content of nickel in the lithium-rich manganese-based material at a distance of (t+1) nm from the first surface along the direction from the first surface to the second surface, where 0≤t≤L-1; And / or, along the direction from the first surface to the second surface, for any depth t nm and (t+1) nm within the surface region, the mass content of the cobalt element satisfies: 0.0062% ≤ C t+1 -C t ≤0.0095%, where C t+1 C represents the mass content of cobalt in a lithium-rich manganese-based material at a distance of (t+1) nm from the first surface along the direction from the first surface to the second surface. t The mass content of cobalt in the lithium-rich manganese-based material at a distance t nm from the first surface along the direction from the first surface to the second surface, where 0 ≤ t ≤ L-1; And / or, in the surface region, the mass ratio of nickel to cobalt on the first surface is (1.5~2.3):1, and the mass ratio of nickel to cobalt on the second surface is (0.8~1.2):

1.

3. The positive electrode active material according to claim 1, characterized in that, In the internal region, the mass ratio of nickel to cobalt is (0.8~1.2):1; And / or, in the lithium-rich manganese-based material, the ratio of the total mass of cobalt and nickel to the mass of manganese is 1:(1.5~2).

4. The positive electrode active material according to claim 1, characterized in that, Based on the total mass of the lithium-rich manganese-based material, the mass content of the first dopant element is 0.03%~1%; And / or, based on the total mass of the lithium-rich manganese-based material, the mass content of the second dopant element is 0.01% to 0.8%.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that, The lithium-rich manganese-based material includes secondary particles formed by primary particle agglomeration. And / or, the positive electrode active material further includes a composite layer, the composite layer covering at least a portion of the surface of the lithium-rich manganese-based material; the composite layer includes LiCoO2 and Li3BO3; Preferably, based on the total mass of the positive electrode active material, the mass content of Li3BO3 is 440ppm to 4400ppm, and / or the mass content of LiCoO2 is 520ppm to 5500ppm.

6. The positive electrode active material according to claim 5, characterized in that, The average particle size of the primary particles of the lithium-rich manganese-based material is 200 nm to 500 nm. And / or, the thickness of the composite layer is denoted as H, and the average particle size of the secondary particles of the lithium-rich manganese-based material is denoted as D, satisfying at least one of the following conditions: (a) 10nm ≤ H ≤ 50nm; (b) 1μm≤D≤3μm; (c) 20≤D / (2H)≤140.

7. The positive electrode active material according to claim 1, characterized in that, The compacted density of the positive electrode active material powder is 3.0 g / cm³. 3 ~3.3g / cm 3 ; And / or, the specific surface area of ​​the positive electrode active material is 2m². 2 / g~3m 2 / g; And / or, under a pressure of 48 MPa to 55 MPa, the powder conductivity of the positive electrode active material is 1.0 × 10⁻⁶. -6 S / cm ~ 9.0 × 10 -5 S / cm.

8. The positive electrode active material according to claim 1, characterized in that, The X-ray diffraction pattern of the positive electrode active material shows diffraction peaks in the range of 2θ diffraction angles of 20° to 23°. And / or, the X-ray diffraction pattern of the positive electrode active material further includes a (003) characteristic peak and a (104) characteristic peak, wherein the 2θ diffraction angle of the (003) characteristic peak is 18°~20° and the 2θ diffraction angle of the (104) characteristic peak is 44°~45°; the peak intensity of the (003) characteristic peak is K1 and the peak intensity of the (104) characteristic peak is K2, satisfying: K1 / K2>2.

1.

9. An all-solid-state battery, characterized in that, The all-solid-state battery includes a positive electrode, which includes the positive electrode active material according to any one of claims 1 to 8.

10. The all-solid-state battery according to claim 9, characterized in that, The all-solid-state battery further includes a negative electrode, which comprises an indium metal layer and / or a lithium metal layer; preferably, the negative electrode comprises an indium metal layer and a lithium metal layer. And / or, the all-solid-state battery further includes a solid electrolyte layer, the solid electrolyte layer including a halide solid electrolyte layer and / or a sulfide solid electrolyte layer, preferably, the solid electrolyte layer including a halide solid electrolyte layer and a sulfide solid electrolyte layer; Preferably, when the solid electrolyte layer comprises a halide solid electrolyte layer and a sulfide solid electrolyte layer, the mass ratio of the halide solid electrolyte layer to the sulfide solid electrolyte layer is (20~60):(40~80).

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