Positive electrode active material and lithium ion secondary battery

Abstract

The invention discloses a positive electrode active material and a lithium ion secondary battery. The positive electrode active material comprises a lithium-rich manganese-based material, a first coating layer and a second coating layer, the first coating layer comprises a first fast ion conductor and coats part of the surface of the lithium-rich manganese-based material; the second coating layer comprises a first region and a second region which are connected with each other, the first region coats the lithium-rich manganese-based material which is not coated by the first coating layer, and the first region comprises lithium halide or a compound formed by the lithium halide and a second fast ion conductor; and the second region is coated with the first coating layer and comprises a compound formed by lithium halide and the first fast ion conductor or a compound formed by lithium halide, the first fast ion conductor and the second fast ion conductor. The two coating layers are closely connected in space and function, rapid ion / electron continuous transmission, stable interface chemistry and lasting physical protection are jointly achieved, and the rate capability and the cycling stability of the battery are improved while high-capacity exertion of the lithium-rich manganese-based material is guaranteed.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a positive electrode active material and a lithium-ion secondary battery. Background Technology

[0002] Currently, the continuous improvement of energy density of lithium-ion secondary batteries as high-energy storage carriers is the core direction of industrial development. Li-rich manganese-based (LRM) materials are regarded as one of the candidate active materials for the next generation of high-energy-density batteries due to their theoretical specific capacity of over 250 mAh / g. However, LRM materials still have a series of inherent defects in practical applications, such as (1) structural instability: LRM materials are prone to irreversible phase transitions during charging and discharging, leading to continuous capacity decay; (2) severe interfacial side reactions: LRM materials are prone to oxygen escape under high voltage, causing the electrolyte or solid electrolyte to be oxidized, generating an unstable interfacial phase, which further aggravates impedance growth and capacity decay; (3) poor ionic / electronic conductivity: LRM materials have poor intrinsic ionic and electronic conductivity, and a passivation layer is easily formed on the surface, resulting in a significant increase in interfacial impedance. Summary of the Invention

[0003] In view of this, the technical problem to be solved by this application is to overcome the problems of unstable structure, serious interfacial side reactions and poor ion / electron conductivity of existing lithium-rich manganese-based materials, and to provide a lithium-rich manganese-based material with good structural stability, high interfacial compatibility with electrolyte and fast ion conduction, as well as a method for preparing the same, and a lithium-ion secondary battery containing the lithium-rich manganese-based material.

[0004] To achieve the above objectives, this application adopts the following technical solution.

[0005] According to an embodiment of this application, in a first aspect, a positive electrode active material is provided, comprising a core and a coating layer; the core comprises a lithium-rich manganese-based material, and the coating layer comprises a first coating layer and a second coating layer; the first coating layer comprises a first fast ion conductor, and the first coating layer covers a portion of the surface of the lithium-rich manganese-based material; the second coating layer comprises a first region and a second region interconnected, the first region covers the lithium-rich manganese-based material not covered by the first coating layer, the first region comprising lithium halide or a complex formed by lithium halide and a second fast ion conductor; the second region covers the first coating layer, the second region comprising a complex formed by lithium halide and the first fast ion conductor, or the second region comprising a complex formed by lithium halide, the first fast ion conductor, and the second fast ion conductor.

[0006] In some alternative embodiments, the halogen content is 4%-65% based on the mass of the second coating layer, and the halogen includes at least one of Cl, Br, and F.

[0007] In some alternative embodiments, the thickness of the second coating layer is 10 nm to 150 nm.

[0008] Furthermore, in some optional embodiments, the thickness of the second coating layer is 80nm-120nm.

[0009] In some alternative implementations, the thickness of the first coating layer is 10 nm to 50 nm.

[0010] Furthermore, in some alternative embodiments, the thickness of the first coating layer is 20nm-40nm.

[0011] In some optional embodiments, the general chemical formula of the lithium-rich manganese-based material is Li. 1+x Ni a Co b Mn c D d O e D includes at least one of the elements Al, Ti, Zr, Ta, Nb, Mo, W, F, Cl, and Br, with 0.1≤x≤0.5, 0.1≤a≤0.3, 0.1≤b≤0.3, 0.5≤c≤0.8, 0.01≤d≤0.2, and 2≤e≤3.

[0012] Furthermore, in some optional embodiments, the lithium-rich manganese-based material includes Al, Zr, and F elements, with the mass content of Al element being 500-3000 ppm, the mass content of Zr element being 500-3000 ppm, and the mass content of F element being 1500-12000 ppm, based on the mass of the positive electrode active material.

[0013] In some alternative embodiments, the first fast ion conductor and the second fast ion conductor each independently comprise Li7La3Zr. 2-y E y O 12 Li 1+z Al z Ti 2-z (PO4)3, Li3PS4, Li7P3S 11 Li2ZrO3, Li4Ti5O 12 At least one of the following, wherein E includes at least one of Al, Ga, Ta, and Nb, 0 ≤ y ≤ 0.6, and 0.05 ≤ z ≤ 0.2.

[0014] In some alternative embodiments, the lithium halide includes at least one of LiCl, LiBr, and LiF.

[0015] Furthermore, in some optional embodiments, the first coating layer is Li7La3Zr. 2-y E y O 12 The first region in the second coating layer is Li4PS4F, and the second region in the second coating layer is Li4PS4F-Li8La3Zr. 2-y E y O 12 F, where E includes at least one of Al, Ga, Ta, and Nb, and 0 ≤ y ≤ 0.6.

[0016] In some optional embodiments, the XPS F 1S spectrum of the positive electrode active material has characteristic peaks at 683eV-684eV and 685.5eV-687.5eV.

[0017] In some optional embodiments, the particle size Dv50 of the positive electrode active material is 0.5 μm-9 μm.

[0018] In some alternative embodiments, the particle size distribution SPAN value of the positive electrode active material is 0.5-2.

[0019] In some alternative embodiments, the positive electrode active material includes secondary particles formed by the agglomeration of primary particles, wherein the average particle size of the primary particles is 0.2 μm-1.0 μm.

[0020] In some optional embodiments, the specific surface area of ​​the positive electrode active material is 1 m². 2 / g-4m 2 / g.

[0021] In some optional embodiments, the positive electrode active material has an ionic conductivity of 10 at 25°C. -8 S / cm-10 -6 S / cm.

[0022] According to an embodiment of this application, in a second aspect, a lithium-ion secondary battery is also provided, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector in the thickness direction, the positive active layer including the positive active material described in the first aspect of this application.

[0023] In some alternative embodiments, the lithium-ion secondary battery includes any one of all-solid-state batteries, semi-solid-state batteries, and liquid batteries.

[0024] The technical solution of this application has the following advantages:

[0025] The positive electrode active material provided in this application includes a core and a coating layer. The core includes a lithium-rich manganese-based material, and the coating layer includes a first coating layer and a second coating layer. The first coating layer includes a first fast ion conductor and covers a portion of the surface of the lithium-rich manganese-based material. The second coating layer includes a first region and a second region that are interconnected. The first region covers the lithium-rich manganese-based material that is not covered by the first coating layer. The first region includes lithium halide or a complex formed by lithium halide and a second fast ion conductor. The second region covers the first coating layer. The second region includes a complex formed by lithium halide and the first fast ion conductor, or the second region includes a complex formed by lithium halide, the first fast ion conductor, and the second fast ion conductor.

[0026] This application constructs a partially encapsulated first coating layer containing a first fast ion conductor on the surface of a lithium-rich manganese-based material. This ensures the continuity of ion channels while retaining sufficient electronic conduction pathways. The partially encapsulated structure effectively alleviates interfacial stress, thereby synergistically improving the ion and electron transport kinetics and structural stability of the lithium-rich manganese-based material. The lattice structure and chemical environment of the first coating layer also promote the in-situ, dense growth of the second coating layer, significantly improving the compatibility between the active material and the solid electrolyte. Simultaneously, by introducing lithium halides into the second coating layer, interfacial chemistry can be modulated, impedance reduced, and a dense and strongly bonded physical barrier formed through the in-situ chemical bonding of lithium halides with the first / second fast ion conductors. This effectively inhibits the dissolution of transition metals in the active material, reduces interfacial side reactions, and prevents electrolyte diffusion into the positive electrode. The two coating layers are spatially and functionally closely integrated, jointly achieving rapid continuous ion / electron transport, stable interfacial chemistry, and durable physical protection. Ultimately, while ensuring the high capacity of the lithium-rich manganese-based material, the rate performance and cycle stability of the battery are significantly improved.

[0027] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the specific embodiments of this application, the drawings used in the description of the specific embodiments 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.

[0029] Figure 1 This is a schematic diagram of the structure of the positive electrode active material in one embodiment of this application; Figure 2 This is a SEM image of a lithium-rich manganese-based material in one embodiment of this application; Figure 3 This is a SEM image of the positive electrode active material precursor in one embodiment of this application; Figure 4 This is a SEM image of the positive electrode active material in one embodiment of this application; Figure 5 This is an XPS F1S spectrum of the positive electrode active material in one embodiment of this application. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] Currently, research has attempted to improve the electrochemical performance of lithium-rich manganese-based materials through surface coating. For example, physical coating (using materials such as Al2O3 and SiO2) can suppress interfacial side reactions to some extent, while chemical coating (using materials such as Li3PO4 and Li2ZrO3) can enhance interfacial contact and improve cycle stability. However, these methods still have significant limitations. Physical coatings often have weak adhesion and are prone to detachment, making it difficult to maintain the coating effect during long-term cycling. Chemical coatings often rely on high-temperature sintering, which can easily cause structural damage to the lithium-rich manganese-based material and unnecessary interfacial side reactions. Especially in all-solid-state battery systems, lithium-rich manganese-based materials, in addition to high capacity and high structural stability, must also meet several stringent requirements, such as close interfacial contact with the solid electrolyte, excellent interfacial compatibility, and high ionic conductivity. Existing single coating strategies cannot comprehensively address these performance requirements, resulting in unsatisfactory performance of lithium-rich manganese-based materials in practical applications of solid-state batteries.

[0033] To address the problems of structural instability, severe interfacial side reactions, and low ionic / electronic conductivity in lithium-rich manganese-based materials in related technologies, this application proposes the following solutions.

[0034] According to a first aspect, this application provides a positive electrode active material, including a core and a coating layer; the core includes a lithium-rich manganese-based material, and the coating layer includes a first coating layer and a second coating layer; the first coating layer includes a first fast ion conductor, and the first coating layer covers a portion of the surface of the lithium-rich manganese-based material; the second coating layer includes a first region and a second region connected to each other, the first region covers the lithium-rich manganese-based material not covered by the first coating layer, the first region includes lithium halide or a complex formed by lithium halide and a second fast ion conductor; the second region covers the first coating layer, the second region includes a complex formed by lithium halide and the first fast ion conductor, or the second region includes a complex formed by lithium halide, the first fast ion conductor, and the second fast ion conductor.

[0035] This application research found that by using a first fast ion conductor to coat part of the surface of a lithium-rich manganese-based material to form a partially coated first coating layer, the first coating layer has at least the following functions: (1) reducing interfacial ion transport resistance: the fast ion conductor has high lithium-ion conductivity, which can significantly reduce the migration barrier of lithium ions from the positive electrode active material to the solid electrolyte, ensuring the continuity of the ion channel and improving ion transport efficiency; (2) maintaining electronic conduction pathways: the uncoated positive electrode active material area can retain electronic conduction pathways, ensuring that electron transport is not blocked, thereby taking into account both ion conduction and electronic conduction, and preventing the problems caused by traditional fully coated layers. (3) Alleviating material stress concentration: The non-fully coated structure has the ability to allow local elastic deformation of the active material, which can buffer the interface stress caused by the volume change of the active material during charging and discharging, and effectively disperse the pressure during the high-voltage process of solid-state battery assembly, thereby helping to maintain the structural integrity of the material and improve the electrochemical stability of the battery; (4) Providing a guarantee for the continuous and dense growth of the second coating layer: The lattice structure and chemical environment of the first coating layer can provide good nucleation sites for the in-situ growth of the second coating layer, effectively promoting the continuous growth of the dense second coating layer.

[0036] The dense structure of the second coating layer can perform at least the following functions: (1) Forming an interface barrier and suppressing side reactions: The dense second coating layer can effectively block the direct contact between lithium-rich manganese-based materials and solid electrolytes, prevent the dissolution of transition metals in active materials, improve structural stability, and at the same time block the diffusion of solid electrolytes into the active materials, preventing local short circuits; (2) Regulating interface chemistry and reducing interface impedance: Lithium halide in the second coating layer, as a stable phase at the interface between active materials and active materials, conductive agents, and binders, has high ionic conductivity and low interface energy, which can enhance the contact tightness between active materials and conductive agents, thereby maintaining a good conductive path; at the same time, the chemical composition of the second coating layer (such as Li4PS4F) has good lattice matching with sulfide / oxide solid electrolytes, which can further reduce interface impedance and achieve efficient continuous ion transport; (3) Strong interface bonding and not easy to fall off: The second coating layer is grown in situ, which can achieve seamless interface bonding, for example, through chemical reaction Li3PS4+ The LiF→Li4PS4F pair forms a new phase at the interface, achieving chemical bonding rather than physical adhesion, thereby effectively improving the compatibility of the active material with the solid electrolyte.

[0037] In summary, this application constructs a partially encapsulated first coating layer containing a first fast ion conductor on the surface of a lithium-rich manganese-based material. This ensures the continuity of ion channels while retaining sufficient electronic conduction pathways. Furthermore, the characteristics of this partially encapsulated structure effectively alleviate interfacial stress, thereby synergistically improving the ion and electron transport kinetics and structural stability of the lithium-rich manganese-based material. The lattice structure and chemical environment of the first coating layer also promote the in-situ, dense growth of the second coating layer, significantly improving the compatibility between the active material and the solid electrolyte. Simultaneously, by introducing lithium halides into the second coating layer, interfacial chemistry can be modulated, impedance reduced, and a dense and strongly bonded physical barrier formed through the in-situ chemical bonding of lithium halides with the first / second fast ion conductors. This effectively suppresses the dissolution of transition metals in the active material, reduces interfacial side reactions, and prevents electrolyte diffusion into the positive electrode. The two coating layers are spatially and functionally closely integrated, jointly achieving rapid continuous ion / electron transport, stable interfacial chemistry, and durable physical protection. Ultimately, while ensuring the high capacity of the lithium-rich manganese-based material, the rate performance and cycle stability of the battery are significantly improved.

[0038] For example, see Figure 1 , Figure 1This is a schematic diagram of the structure of a positive electrode active material in one embodiment of this application, wherein a refers to a lithium-rich manganese-based material, b refers to a first coating layer, the first coating layer covers part of the surface of the lithium-rich manganese-based material (i.e., dot-like coating), c refers to a second coating layer, the second coating layer includes a first region and a second region that are connected to each other, the first region covers the lithium-rich manganese-based material that is not covered by the first coating layer, and the second region covers the first coating layer.

[0039] In one embodiment, the coating rate of the first coating layer is 1%-50% based on the surface area of ​​the lithium-rich manganese-based material. This application research found that if the coating rate of the first coating layer is too low (less than 1%), it is difficult to form continuous ion transport channels, resulting in a high lithium-ion migration barrier and an inability to effectively improve interfacial ion transport efficiency. Simultaneously, an insufficient first coating layer cannot buffer the volume changes of the active material during charging and discharging, nor the external pressure during solid-state battery assembly, which is detrimental to maintaining the structural stability of the material. Furthermore, as the nucleation substrate for the second coating layer, an insufficient coating rate of the first coating layer cannot provide enough nucleation sites for the in-situ growth of the second coating layer, affecting the dense growth of the second coating layer. Conversely, if the coating rate of the first coating layer is too high (more than 50%), the electronic conductivity pathway of the lithium-rich manganese-based material is severely blocked, restricting the rate performance of the material. At the same time, the elastic buffering capacity of the incompletely coated structure is also weakened, and the stress of the material during cycling and assembly cannot be effectively released, making the interface prone to cracking and peeling, which in turn damages the structural integrity and long-term cycle stability of the battery.

[0040] It should be noted that the coverage rate of the first coating layer can be obtained through XPS-HRTEM-BET characterization testing. Specifically, elemental analysis of the material surface is performed using X-ray photoelectron spectroscopy (XPS) to obtain the signal intensity ratio of coating layer characteristic elements (such as La and Zr) to core characteristic elements (such as Ni and Mn), which allows for a preliminary calculation of the surface coverage ratio. Further analysis of cross-sectional elemental distribution using high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) allows for direct observation and statistical analysis of the length proportion of the coating region. In addition, specific surface area (BET) testing and coating layer mass increment data are used in conjunction with the theoretical density model of the coating material for calculation verification. For example, the coverage rate of the first coating layer may be 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or a value within the range of any two of the above values.

[0041] For example, see Figure 2 and Figure 3, Figure 2 This is a SEM image of a lithium-rich manganese-based material (i.e., without a coating layer) in one embodiment of this application. Figure 3 This is a SEM image of the positive electrode active material precursor (lithium-rich manganese-based material and first coating layer) in one embodiment of this application. The images are compared... Figure 2 and Figure 3 It can be seen that, Figure 3 The primary particle surface of the lithium-rich manganese-based material has a large number of clear dot-like protrusions or attachments. The number of dot-like protrusions or attachments on each primary particle is between 5 and 100. This indicates that the first coating layer exists in a discontinuous and incomplete "dot-like coating" form on part of the surface of the lithium-rich manganese-based material.

[0042] Please continue reading Figure 4 , Figure 4 This is a SEM image of the positive electrode active material in one embodiment of this application. (Comparison is needed for accurate translation.) Figure 3 and Figure 4 It can be seen that, Figure 4 The surface morphology of primary particles in lithium-rich manganese-based materials has undergone significant changes, with previously clearly visible dot-like coatings (such as...) Figure 3 The material (as shown) is covered by a continuous, uniform film, with small bumps visible on the surface in localized areas. The film corresponds to a lithium halide layer or a dense composite layer formed by the reaction of lithium halide with a second fast-ion conductor, while the localized bumps may be related to interfacial chemical bonding and localized growth of the coating layer. This morphological feature indicates that the dense second coating layer achieves complete coverage of both the first coating layer and the surface of the lithium-rich manganese-based material not covered by the first coating layer.

[0043] In some embodiments, the halogen content is in the range of 4%-65% based on the mass of the second coating layer, and the halogen includes at least one of Cl, Br, and F. In this way, not only can the interfacial chemistry be effectively controlled and the interfacial impedance be reduced, but also strong interfacial bonding force can be ensured, which can significantly improve the chemical compatibility and interfacial stability between the positive electrode active material and the solid electrolyte.

[0044] If the halogen content in the second coating layer is less than 4%, it will be difficult to achieve the above-mentioned effect. On the contrary, when the halogen content in the second coating layer exceeds 65%, the excess halogen may locally agglomerate, destroying the uniformity and density of the coating layer, and even inducing additional interfacial side reactions, which will degrade the chemical stability and ion transport performance of the interface. On the other hand, excess halogen will crowd out the loading sites of fast ion conductors, destroy the conductive network they construct, and cause the electron transport resistance to rise sharply.

[0045] It should be noted that the mass content of halogen elements in the second coating layer can be determined by ion milling cross-section polishing. Scanning electron microscope Energy dispersive spectrometer (CP) SEM The halogen content is obtained by characterization in conjunction with EDS (Enhanced Digital Substances). For example, the mass content of halogen elements can be 4%, 8%, 12%, 16%, 20%, 24%, 28%, 32%, 36%, 40%, 44%, 48%, 52%, 56%, 60%, 65%, etc., or values ​​within the range of any two of the above values.

[0046] In some implementations, the thickness of the first coating layer is controlled to be 10 nm. Within a 50nm range, while constructing continuous ion transport channels, sufficient exposed surface of the positive electrode active material can be maintained to sustain the electronic conductivity network. Furthermore, its incompletely encapsulated structure alleviates interfacial stress caused by volume changes in the active material, thus achieving a balance between high ion conduction efficiency and electrode structural integrity. In particular, when the thickness of the first coating layer is further controlled to 20nm... At a thickness between 40 nm and 50 nm, the high conductivity of the fast ion conductor and the mechanical buffering function of the coating layer on the positive electrode active material can be better synergistically utilized, thereby further optimizing the ion transport kinetics and cycle stability at the interface. If the thickness of the first coating layer is less than 10 nm, it is difficult to form a continuous and effective ion transport path, and the mechanical buffering effect on the positive electrode active material is weak. If the thickness of the first coating layer is greater than 50 nm, the difference in thermal expansion or volume change behavior between the coating layer and the positive electrode active material increases, making it more prone to internal stress accumulation during long-term cycling, leading to cracking of the coating layer or peeling off from the surface of the active material, which in turn destroys the interface stability and the continuity of ion transport.

[0047] It should be noted that the thickness of the first coating layer can be determined by CP. The thickness of the first coating layer is obtained through SEM characterization. Specifically, section polishing (CP) technology can be used to prepare the cross-section of the coated cathode material particles to obtain a smooth cross-section with a clear interface. Then, the actual thickness of the first coating layer is observed and measured at high magnification using a scanning electron microscope (SEM). To improve the accuracy of the measurement, this application combines image analysis software to statistically analyze the thickness data from more than five random fields of view, and takes the average of the thickness data as the final thickness value of the first coating layer. For example, the thickness of the first coating layer can be 10nm, 12.5nm, 15nm, 17.5nm, 20nm, 22.5nm, 25nm, 27.5nm, 30nm, 32.5nm, 35nm, 37.5nm, 40nm, 42.5nm, 45nm, 47.5nm, 50nm, or a value within any two of the above ranges.

[0048] In some implementations, the thickness of the second coating layer is controlled to be 10 nm. Within a 150 nm range, the coating layer can provide sufficient space for halogen elements (such as F and Cl) to form stable phases like LiF and LiCl in situ at the interface, while also maintaining a reasonable ion migration path length. This allows the halogen elements to effectively regulate interfacial chemistry, reducing interfacial impedance, and also forms a continuous and dense physical barrier to suppress transition metal dissolution and side reactions. Specifically, when the thickness of the second coating layer is controlled at 80 nm... Between 120 nm and 120 nm, the chemical regulation effect of halogens and the physical barrier effect of dense coating can achieve better synergy, thereby maintaining good high-rate performance while further improving interface stability and cycle life. If the thickness of the second coating layer is less than 10 nm, it is difficult to form a complete and continuous interface protective layer, the chemical regulation effect of halogens is insufficient, and the suppression effect on side reactions is limited. If the thickness of the second coating layer is greater than 150 nm, it will significantly prolong the migration path of lithium ions in the coating layer, and may increase the interface stress due to the mismatch between the thermal expansion behavior and the positive electrode active material, causing the coating layer to crack or peel off during long-term cycling, thereby damaging the electrochemical performance of the battery.

[0049] It should be noted that the thickness of the second coating layer can be determined by CP. The thickness of the second coating layer is obtained through SEM characterization. Specifically, section polishing (CP) technology can be used to prepare the cross-section of the coated cathode material particles to obtain a smooth cross-section with a clear interface. Then, the actual thickness of the second coating layer is observed and measured at high magnification using a scanning electron microscope (SEM). To improve the accuracy of the measurement, this application combines image analysis software to statistically analyze the thickness data from more than five random fields of view, and takes the average value of the thickness data as the final thickness value of the second coating layer. For example, the thickness of the second coating layer can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, etc., or a value within any two of the above ranges.

[0050] In some embodiments, the general chemical formula of the lithium-rich manganese-based material is Li. 1+x Ni a Co b Mn c D d O eD includes at least one of the elements Al, Ti, Zr, Ta, Nb, Mo, W, F, Cl, and Br, with 0.1≤x≤0.5, 0.1≤a≤0.3, 0.1≤b≤0.3, 0.5≤c≤0.8, 0.01≤d≤0.2, and 2≤e≤3. Controlling the excess lithium (x ≥ 0.1) provides a sufficient source of lithium for insertion and extraction, which is fundamental to achieving high specific capacity. However, excessive lithium (x>0.5) can easily lead to an increase in residual lithium compounds and enhanced interfacial alkalinity, thus deteriorating cycle performance. Furthermore, controlling the doping amount of element D allows for multi-dimensional stabilization and regulation of the bulk structure of lithium-rich manganese-based materials.

[0051] Furthermore, in some embodiments, Al is doped into the lithium-rich manganese-based material, and the mass content of Al is controlled to be within 500 g / L based on the mass of the positive electrode active material. Between 3000ppm, Al can be ensured 3+ As a structural stabilizer, it appropriately replaces Ni / Mn sites, enhancing crystal framework stability and effectively suppressing lattice oxygen release during cycling. This prevents insufficient structural stabilization and insignificant oxygen release suppression due to excessively low Al content (<500ppm), and also prevents Al content exceeding 3000ppm from causing Al... 3+ Excessive occupation of active sites leads to a significant decrease in reversible capacity.

[0052] Meanwhile, by doping Zr into the lithium-rich manganese-based material, and controlling the Zr content at 500 g / L based on the mass of the positive electrode active material, the Zr content is controlled to be within the range of 500 g / L. Between 3000ppm, Zr can be ensured 4+ A suitable amount enters the Li layer of the crystal lattice to form a strong Zr O bonds stabilize the layered structure and suppress lattice distortion during charging and discharging; they prevent limited lattice stabilization due to excessively low Zr content (<500ppm) and also prevent Zr content from causing excessive Zr degradation (>3000ppm). 4+ It accumulates at grain boundaries, forming an inactive phase and reducing the electrochemical performance of the material.

[0053] Furthermore, by doping lithium-rich manganese-based materials with sulfur (F) and controlling the F content at 1500 g / L based on the mass of the positive electrode active material, the method of measurement is further improved. Between 12000ppm, F can be ensured - Partially replaces O 2- , forming a strong F M (M refers to metal) bonds firmly bind lattice oxygen, suppressing irreversible release of lattice oxygen under high voltage, thereby improving the structural stability and high-voltage cycling performance of the material; preventing insufficient lattice oxygen binding due to low F content (<1500ppm), which would fail to meet the requirements of high-voltage operation, and also preventing lattice distortion or the formation of unstable fluorides induced by high F content (>12000ppm), which would affect the chemical stability of the interface.

[0054] It should be noted that the mass content of Al, Zr, and F elements in lithium-rich manganese-based materials can be determined by ion milling cross-section polishing. Scanning electron microscope Energy dispersive spectrometer (CP) SEM The content of Al can be obtained by characterization in conjunction with EDS (Enhanced Microscopy and Degradation). For example, the mass content of Al can be 500 ppm, 750 ppm, 1000 ppm, 1250 ppm, 1500 ppm, 1750 ppm, 2000 ppm, 2250 ppm, 2500 ppm, 2750 ppm, 3000 ppm, or values ​​within any two of the above ranges; the mass content of Zr can be 500 ppm, 750 ppm, 1000 ppm, 1250 ppm, 1500 ppm, 1750 ppm, etc. The values ​​may be 2000ppm, 2250ppm, 2500ppm, 2750ppm, 3000ppm, or any value within the range of any two of the above values; the mass content of element F may be, for example, 1500ppm, 2550ppm, 3600ppm, 4650ppm, 5700ppm, 6750ppm, 7800ppm, 8850ppm, 9900ppm, 10950ppm, 12000ppm, or any value within the range of any two of the above values.

[0055] In some embodiments, the first fast ion conductor and the second fast ion conductor each independently comprise Li7La3Zr. 2-y E y O 12 Li 1+z Al z Ti 2-z (PO4)3, Li3PS4, Li7P3S 11 Li2ZrO3, Li4Ti5O 12 At least one of the following, wherein E includes at least one of Al, Ga, Ta, and Nb, 0 ≤ y ≤ 0.6, and 0.05 ≤ z ≤ 0.2.

[0056] For example, the lithium halide includes at least one of LiCl, LiBr, and LiF.

[0057] In some embodiments, the first coating layer is Li7La3Zr. 2-y E y O 12 (abbreviated as LLZO), the first region in the second coating is Li4PS4F, and the second region in the second coating layer is Li4PS4F-Li8La3Zr. 2-y E y O 12 F, where E includes at least one of Al, Ga, Ta, and Nb, and 0 ≤ y ≤ 0.6. The cubic garnet-type LLZO used in this application has three-dimensional interconnected tetrahedral-octahedral lithium-ion migration channels. Its grain boundary resistance is significantly lower than that of other LLZO morphologies such as tetragonal phase, nanoparticles, or lamellar / amorphous structures, enabling the construction of a highly efficient three-dimensional ion transport network, thereby significantly improving the rate performance of the battery. Furthermore, the stability of its cubic phase structure can be maintained by doping the cubic garnet-type LLZO with appropriate elements, effectively suppressing the transformation to other crystal phases (such as tetragonal phase) during high temperatures or cycling, thus ensuring the cycling stability of lithium-rich manganese-based materials. Moreover, the cubic garnet-type LLZO also possesses high ionic conductivity and a wide electrochemical window (0.6 V vs. Li). + The presence of Li and its excellent chemical inertness not only meet the rapid charge and discharge requirements of high-voltage lithium-rich manganese-based materials, but also prevent direct contact between components such as lithium halides and the matrix, thus preventing the dissolution of transition metals and the corrosion of lithium-rich manganese-based materials by halide ions. This ensures the chemical and electrochemical stability of the interface while achieving efficient ion transport.

[0058] Meanwhile, when the second coating includes orthorhombic Li4PS4F, it can construct a highly efficient lithium-ion fast transport channel with high ionic conductivity. Moreover, the strong bond formed between F and P in the Li4PS4F structure and the stable chemical bonds between Li and O and P can jointly enhance the bonding strength of the interface. At the same time, Li4PS4F can also effectively suppress oxygen release, transition metal dissolution and electrolyte decomposition. Among them, the F element, with its high electronegativity, can form a strong FM bond with the transition metal (M is the transition metal), further suppressing metal ion migration. In addition, the stable chemical properties of Li4PS4F itself also make it less prone to side reactions with the electrolyte, thereby significantly improving the stability of the interface and electrochemical compatibility.

[0059] In some embodiments, the XPS F1S spectrum of the positive electrode active material exhibits characteristic peaks at 683 eV-684 eV and 685.5 eV-687.5 eV. As an example, such as... Figure 5 As shown, the F 1s spectrum of the positive electrode active material shows characteristic peaks at 683.7 eV (peak 2) and 686.1 eV (peak 1), corresponding to the Li-F bond and the transition metal, respectively. Fluorine bonds, such as Mn F, Ni The presence of F indicates that halogens not only exist in the form of LiF, but also form stable chemical bonds with the transition metals on the surface of the positive electrode active material, thus confirming that the second coating layer is a chemically bonded interface protective layer.

[0060] In some embodiments, the positive electrode active material includes secondary particles, which are agglomerated from primary particles, and the average particle size of the primary particles is 0.2 μm-1.0 μm. This is achieved by controlling the average particle size of the primary particles to be uniformly distributed within the range of 0.2 μm. Within the 1.0 μm range, it is beneficial to shorten and homogenize the diffusion path of lithium ions in the solid phase, while promoting the formation of dense and stable agglomerates within the secondary particles, thereby improving the compaction density and charge transport uniformity of the material. If the average particle size of the primary particles is less than 0.2 μm, their higher specific surface area will exacerbate interfacial side reactions, and the contact resistance between particles may increase; if the average particle size of the primary particles is greater than 1.0 μm, the diffusion path of lithium ions within the particles will be too long, leading to increased polarization, limited capacity utilization, and potentially affecting the compaction density and mechanical stability of the electrode.

[0061] It should be noted that the term "primary particle," also known as a primary particle, refers to the original particles formed during material preparation. These particles exist independently in a single-crystal state and do not physically contact or chemically bond with adjacent particles. The average particle size of primary particles can be obtained through statistical electron microscopy (SEM). The specific testing method involves selecting representative scanning electron microscope (SEM) or transmission electron microscope (TEM) images, randomly selecting no fewer than 100 independent primary particles from the images, and using professional image analysis software (such as Nano Measure) to measure the particle size of each particle individually and calculate the arithmetic mean. This arithmetic mean is then used as the average particle size of the primary particles.

[0062] For example, the average particle size of a primary particle may be 0.2 μm, 0.28 μm, 0.36 μm, 0.44 μm, 0.52 μm, 0.6 μm, 0.68 μm, 0.76 μm, 0.84 μm, 0.92 μm, 1.0 μm, or a value within the range of any two of the above values.

[0063] In some implementations, the particle size Dv50 of the positive electrode active material is controlled to be 0.5 μm. A particle size between 9 μm and 9 μm can effectively improve the compaction density of the electrode while ensuring good material processing performance, and optimize the transport paths of ions and electrons within the electrode, thereby improving the volumetric energy density and rate performance of the battery. If the particle size Dv50 of the positive electrode active material is less than 0.5 μm, the specific surface area of ​​the material is too large, which can easily aggravate interfacial side reactions and is not conducive to electrode processing and improving compaction density. If the particle size Dv50 of the positive electrode active material is greater than 9 μm, the diffusion path of lithium ions within the particles is significantly prolonged, aggravating polarization and limiting capacity utilization at high rates, while also potentially affecting the uniform distribution and structural stability of the active material in the electrode.

[0064] It is understood that the particle size Dv50 of the positive electrode active material refers to the particle size corresponding to a cumulative volume distribution percentage of 50%, that is, the volume content of particles smaller than or equal to this size accounts for 50% of the total particle volume. The Dv50 test method can refer to standard GB / T19077-2016 / ISO 13320:2009, and is performed using a laser particle size analyzer (Malvern MasterSize 3000). For example, the particle size Dv50 of the positive electrode active material can be 0.5μm, 1.5μm, 2.5μm, 3.5μm, 4.5μm, 5.5μm, 6.5μm, 7.5μm, 8.5μm, 9.0μm, or a value within any two of the above ranges.

[0065] In some embodiments, the particle size distribution (SPAN) of the positive electrode active material is controlled to be within 0.5. Within a range of 2, a denser particle packing can be achieved while maintaining material processing performance, thus improving the electrode compaction density. A relatively concentrated and suitable particle size distribution also allows for a more sufficient and uniform contact area between the active material and the coating layer, thereby improving ion transport efficiency at the interface. If the SPAN value is less than 0.5, it indicates that the particle size distribution is too concentrated, which may lead to large gaps during particle packing, thus affecting the compaction density. If the SPAN value is greater than 2, it indicates that the particle size distribution is too wide, and the filling between large and small particles is not coordinated, which is also not conducive to forming a dense and stable electrode structure. Furthermore, too many small particles may exacerbate side reactions, or too many large particles may prolong the ion migration path, thus affecting the overall electrochemical performance.

[0066] It should be noted that the particle size distribution SPAN value is a key parameter characterizing the uniformity of the active material particle size in the electrode material. Its calculation formula is: SPAN = (D90 - D10) / D50, where D10, D50, and D90 are cumulative particle size distribution parameters based on volume, representing the particle size values ​​corresponding to volume fractions of 10%, 50%, and 90%, respectively, on the cumulative particle distribution curve. A smaller SPAN value indicates a more concentrated distribution of particle size in the system, meaning better particle uniformity. For example, the particle size distribution SPAN value of the positive electrode active material can be 0.50 μm, 0.65 μm, 0.80 μm, 0.95 μm, 1.10 μm, 1.25 μm, 1.40 μm, 1.55 μm, 1.70 μm, 1.85 μm, 2.00 μm, or values ​​within any two of the above ranges.

[0067] In some embodiments, the specific surface area of ​​the positive electrode active material is 1 m². 2 / g-4m 2 / g, a moderate specific surface area can provide more lithium-ion insertion / extraction active sites and a shorter diffusion path, which helps to improve the initial capacity and high-rate charge and discharge performance of the battery, and can also maintain the structural integrity of the material to ensure the long-cycle performance of the battery.

[0068] For example, the specific surface area of ​​the positive electrode active material can be, for instance, 1.0 m². 2 / g, 1.3m 2 / g, 1.6m 2 / g、m 2 / g、m 2 / g, 2.5m 2 / g, 2.8m 2 / g, 3.1m 2 / g, 3.4m 2 / g, 3.7m 2 / g, 4.0m 2 / g or a value within the range of any two of the above values. Specific surface area is measured using the nitrogen adsorption method according to standard GB / T 19587-2017.

[0069] In some embodiments, the ionic conductivity of the positive electrode active material is controlled to be 10 at 25°C. -8 S / cm-10 -6S / cm ensures that the material maintains high ionic conductivity while guaranteeing efficient electron transport between active material particles, thereby reducing polarization resistance within the electrode and improving capacity retention and cycle stability at high rates. Ionic conductivity testing can be performed according to standard GB / T30835-2014, using a KLA R50 four-probe resistivity meter to test the intrinsic ionic conductivity of the material. For example, the ionic conductivity of the positive electrode active material at 25°C could be, for instance, 1.0 × 10⁻⁶. -8 S / cm, 2.0×10 -8 S / cm, 3.0×10 -8 S / cm, 5.0×10 -8 S / cm, 7.0×10 -8 S / cm, 1.0×10 -7 S / cm, 2.0×10 -7 S / cm, 3.0×10 -7 S / cm, 5.0×10 -7 S / cm, 7.0×10 -7 S / cm, 1.0×10 -6 S / cm or values ​​within the range of any two of the above values.

[0070] In some embodiments, the method for preparing the positive electrode active material according to the first aspect of this application includes the following steps: S1. Obtain lithium-rich manganese-based materials; S2. The lithium-rich manganese-based material is mixed with a solution containing a first fast ion conductor, dried and then calcined to obtain a precursor. The precursor has a portion of the surface of the lithium-rich manganese-based material coated with a first fast ion conductor. The mass ratio of the lithium-rich manganese-based material to the first fast ion conductor is 100:1-1000:1. S3. The precursor obtained in S2 is mixed with lithium halide or lithium halide with a second fast ion conductor, and then heated to 120℃-180℃ and kept at that temperature for at least 1 hour for heat treatment to obtain the positive electrode active material.

[0071] As an example, coprecipitation can be used. A high-temperature solid-state sintering method is used to prepare lithium-rich manganese-based materials. Specifically, this involves: a co-precipitation reaction is carried out in a reactor using an aqueous solution containing a mixed metal salt of Ni, Co, and Mn; an aqueous solution of sodium hydroxide; and a salt solution containing at least one dopant element (selected from Al, Ti, Zr, Ta, Nb, Mo, W, F, Cl, and Br, preferably Al, Zr, and F). After the reaction, the mixture is filtered, washed, and dried to obtain a precipitate. Subsequently, the precipitate is mixed uniformly with a lithium salt and calcined in a furnace under an atmosphere in stages. The calcination procedure is as follows: heating from room temperature to 500°C. 600℃ and hold for 5 hours, then continue to raise the temperature to 800℃. The material was heated to 900℃ and held for 12 hours, and then naturally cooled to room temperature to obtain lithium-rich manganese-based material.

[0072] Subsequently, the prepared lithium-rich manganese-based material was mixed with a solution containing the first fast ion conductor, dried, and then subjected to a process at 800°C. Calcination at 1000℃ for 12 hours allows the first fast ion conductor precursor to fully crystallize and form a stable interface with a portion of the lithium-rich manganese-based material, thus initially constructing a first coating layer with dual ion and electron conduction functions. Subsequently, natural cooling to room temperature helps alleviate thermal stress caused by sudden temperature changes, preventing microcracks or interface delamination between the first coating layer and the lithium-rich manganese-based material due to differences in thermal expansion behavior, thereby maintaining the integrity of the first coating layer and its bonding strength with the lithium-rich manganese-based material. During this process, the mass ratio of the lithium-rich manganese-based material to the first fast ion conductor is controlled at 100:1. A ratio of 1000:1 allows the first fast ion conductor to coat part of the surface of the lithium-rich manganese-based material in a discontinuous, dotted, or island-like manner, forming a partially coated first layer. The remaining part of the lithium-rich manganese-based material surface remains exposed, thus establishing a fast ion transport channel while preserving a continuous electronic conduction pathway, ultimately resulting in a precursor with part of its surface coated with the first fast ion conductor.

[0073] If the calcination temperature is too low or the time is insufficient, the first fast ion conductor precursor will not crystallize sufficiently and the interfacial bonding will be weak; if the calcination temperature is too high, it may cause structural damage or over-sintering of lithium-rich manganese-based materials.

[0074] If the mass ratio of lithium-rich manganese-based material to the first fast ion conductor is too high (i.e., too few first fast ion conductors), it will lead to discontinuous coating and insufficient ion channel construction; if the mass ratio of lithium-rich manganese-based material to the first fast ion conductor is too low (i.e., too many first fast ion conductors), it is easy to form a complete or excessively thick coating layer, thereby hindering electron transport and increasing interfacial stress.

[0075] Finally, a precursor partially coated with a first fast ion conductor is mixed with lithium halide or lithium halide with a second fast ion conductor, and then subjected to a process at 120°C. A heat treatment process is performed at 180°C for at least 1 hour. This process allows lithium halide, or lithium halide and a second fast ion conductor, to form a dense second coating layer on the precursor surface through an in-situ chemical reaction. Specifically, when the second fast ion conductor and the first fast ion conductor are the same substance, i.e., only lithium halide is added, the lithium halide reacts with the exposed lithium-rich manganese-based material surface to form a metallic coating layer. Halogenated bonds (such as Mn) F, Ni The first region is dominated by lithium halides (F), and lithium halides can also react with the fast ion conductors of the first coating layer (e.g., Li3PS4 reacts with LiF to generate Li4PS4F), thereby forming a chemically bonded second region on the first coating layer. When the second fast ion conductor and the first fast ion conductor are different substances, that is, when lithium halides and the second fast ion conductor are added at the same time, during the heat treatment process, lithium halides react with the second fast ion conductor and the exposed lithium-rich manganese-based material to form the first region. At the same time, lithium halides react with the second fast ion conductor and the first fast ion conductor in the first coating layer to generate a complex containing lithium halides, the first fast ion conductor, and the second fast ion conductor in situ, which constitutes the second region.

[0076] The above-mentioned mild heat treatment process can prevent high temperature damage to the lithium-rich manganese-based material, promote the chemical bonding and uniform distribution of halogens at the interface, and achieve continuous connection between the first and second regions. After the reaction is completed, natural cooling can help maintain the stability of the interface structure generated in situ, and finally obtain a positive electrode active material with a complete double-layer coating structure. In this way, the synergistic effect of interface chemical regulation, continuous ion transport and physical barrier protection can be achieved, thereby improving the rate performance and long-cycle stability of the battery.

[0077] According to a second aspect of this application, a lithium-ion secondary battery is also provided, comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector in the thickness direction, characterized in that the positive active layer comprises the positive active material described in the first aspect of this application.

[0078] In some embodiments, the lithium-ion secondary battery includes any one of all-solid-state batteries, semi-solid-state batteries, and liquid batteries.

[0079] It should be noted that when the first fast ion conductor and the second fast ion conductor are Li 1+z Al z Ti 2-z When (PO4)3 (0.05≤z≤0.2) is present, it is suitable for liquid batteries. The electrolyte in the liquid battery includes a non-aqueous solvent, a lithium salt, and additives. The non-aqueous solvent includes at least one of cyclic carbonates, linear carbonates, and linear carboxylic acid esters. The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, lithium difluorodioxalate phosphate, lithium bis(oxalate borate), lithium 4,5-dicyano-2-trifluoromethyl-imidazolium lithium, lithium bis(pentafluoroethylsulfonyl)imino, and lithium tri(trifluoromethylsulfonyl)methyl. The additives include at least one of nitrile compounds, vinylene carbonate, and 1,3-propenesulfonyl lactone.

[0080] The present application will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Where specific experimental steps or conditions are not specified in the embodiments and comparative examples, they can be performed according to the conventional experimental steps or conditions described in the literature in the art. Reagents or instruments used, unless otherwise specified, are all commercially available conventional reagent products.

[0081] Example 1 This embodiment provides a method for preparing an all-solid-state battery, including the following steps: Step 1: Preparation of positive electrode active material (1) Preparation of lithium-rich manganese-based materials 1) Prepare a mixed salt solution of NiSO4, CoSO4, and MnSO4, and a mixed alkaline solution of NaOH and NH3·H2O for later use. The total concentration of metal ions in the mixed salt solution is 2 mol / L. 2+ :Co 2+ :Mn 2+ The molar ratio is 0.17:0.17:0.66, the molar concentration of NaOH is 4 mol / L, and the molar concentration of NH3·H2O is 0.2 mol / L.

[0082] A certain amount of deionized water was added to the reactor. The above mixed salt solution was pumped into the reactor at a feed rate of 100-250 ml / h using a peristaltic pump. The stirring speed was controlled at 700-1200 rpm, the circulating water temperature was 40-80℃, and the alkaline feed rate was adjusted using a three-stage speed control to control the pH of the solution system at 12.0. The feeding time was 18-40 h. After the reaction was completed, the obtained slurry was subjected to solid-liquid separation, followed by centrifugal washing with deionized water, and then dried at 80-150℃ for 15-30 h to obtain the lithium-rich manganese-based material precursor.

[0083] 2) Mix the lithium-rich manganese-based material precursor prepared in step 1) with LiOH·H2O, controlling the molar ratio n(Li):n(Me)=1.5:1, where Me is a metal such as Ni, Co, or Mn. After mixing evenly, place the mixture in a muffle furnace, first heat it to 500℃-600℃ at a rate of 1-5℃ / min, hold it at that temperature for 5h, then heat it to 800℃-900℃ at a rate of 1-5℃ / min, hold it at that temperature for 12h, and then cool it naturally to room temperature to obtain the lithium-rich manganese-based material.

[0084] (2) Preparation of precursors for positive electrode active materials The lithium-rich manganese-based material prepared in step (1) is combined with Li7La3Zr2O 12After being mixed evenly at a mass ratio of 650:1, the mixture was placed in an atmosphere furnace for calcination. The calcination procedure was as follows: the temperature was first raised to 900℃ from room temperature and held for 12 hours, and then naturally cooled to room temperature to obtain a positive electrode active material precursor with a first coating layer.

[0085] (3) Preparation of positive electrode active material After the positive electrode active material precursor obtained in step (2) is mixed with LiF at a mass ratio of 500:1, it is calcined. The calcination procedure is as follows: first, the temperature is raised to 120℃-180℃ and maintained for 1-5 hours, then it is naturally cooled to room temperature, and then the material is ground and sieved to obtain the positive electrode active material.

[0086] Step 2: Preparation of the positive electrode sheet The positive electrode active material obtained in the first step, lithium phosphorus sulfur chlorine and conductive carbon black were dry mixed in an inert atmosphere with a mass ratio of 60:30:10 and a humidity of less than 1ppm to obtain a mixture. The mixture was then ball-milled at 400rpm for 3h. After ball milling, it was hot-rolled at 100℃ and 15MPa to obtain a positive electrode sheet with a thickness of 120μm.

[0087] Step 3: Preparation of the negative electrode First, the lithium metal block is cut into small pieces and pressed into initial lithium cakes using a hydraulic press in an inert atmosphere glove box. Then, initial lithium strips are obtained through rolling. Subsequently, under sealed inert atmosphere conditions, a precision twin-roll calender is used to roll the initial lithium strips to the thin lithium strips required for the mold battery, with the rolling pressure controlled at 50. The pressure is 80 MPa, and the thickness tolerance is controlled at about 1 μm. Finally, the surface of the obtained lithium strip is polished to make its surface roughness not exceed 0.1 μm, thus obtaining the negative electrode sheet.

[0088] Step 4: Preparation of solid electrolyte membrane Lithium, phosphorus, sulfur, and chlorine were mixed with polytetrafluoroethylene at a mass ratio of 6:1 and then rolled to obtain a solid electrolyte membrane with a thickness of 45 μm. The positive electrode sheet and the solid electrolyte membrane prepared in the second step were hot-pressed at 180℃ and 8 MPa to obtain a composite positive electrode-solid electrolyte layer.

[0089] Step 5: Fabrication of all-solid-state batteries The positive electrode sheet prepared in the second step, the solid electrolyte layer prepared in the fourth step, and the negative electrode sheet prepared in the third step are stacked sequentially to obtain an all-solid-state battery.

[0090] Example 16 The difference between this embodiment and Example 1 lies in the preparation of the positive electrode active material: The positive electrode active material precursor was prepared according to the same method as in Example 1. The positive electrode active material precursor was mixed with LiF and Li3PS4 at a mass ratio of 6500:13:10 and then calcined. The calcination procedure was as follows: first, the temperature was raised to 120℃-180℃ and held for 1-5 hours, then naturally cooled to room temperature, and then the material was ground and sieved to obtain the positive electrode active material.

[0091] The rest of the content is the same as in Example 1.

[0092] Example 17 This embodiment provides a method for preparing a liquid battery, including the following steps: The positive electrode active material was prepared according to the same method as in Example 1. Then, under the conditions of 25°C and normal pressure, the positive electrode active material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in N-methylpyrrolidone solvent at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The positive electrode slurry was coated on both sides of an aluminum foil. After drying and rolling, a positive electrode active material layer was formed on both sides of the aluminum foil to obtain a positive electrode sheet. Then, the positive electrode sheet was punched into small discs with a diameter of 12 mm using a film die. After drying and weighing, it was assembled into a CR2430 coin cell in a glove box under an Ar protective atmosphere using a CR2025 coin cell case, with a Li metal disc as the negative electrode, and an electrolyte (composed of 1.2 mol / L LiPF6, with DMC and FEC as solvents, and a volume ratio of DMC to FEC of 3:7) was injected.

[0093] Comparative Example 1 A positive electrode active material precursor was prepared using the same method as in Example 1. Then, this precursor was reacted with LiF and Li7La3Zr2O. 12 After being mixed evenly at a mass ratio of 6500:13:10, the mixture was calcined. The calcination procedure was as follows: the temperature was first raised to 900℃ from room temperature and held for 12 hours, followed by natural cooling to room temperature to obtain the positive electrode active material, which includes a core lithium-rich manganese-based material and a coating layer on the surface of the core. The coating layer is composed of LiF and Li7La3Zr2O. 12 The complex, namely Li8La3Zr2O 12 F.

[0094] The rest of the content is the same as in Example 1.

[0095] The preparation methods of Examples 2-15 are basically the same as those of Example 1. The differences are shown in Tables 1-2.

[0096] Table 1

[0097] Table 2

[0098] I. Performance Testing of All-Solid-State Batteries 1. Ratio Performance Test At 45℃, the battery is charged at a constant current rate of 0.1C to a voltage of 4.2V, then charged at a constant voltage of 4.2V to a current of 0.02mA. After resting for 10 minutes, it is discharged at a constant current rate of 0.1C to a voltage of 1.9V. The capacity at this point is recorded as the discharge capacity at the 0.1C rate. After resting for 10 minutes, the battery is charged at a constant current rate of 1C to a voltage of 4.2V, then charged at a constant voltage of 4.2V to a current of 0.02mA. After resting for 10 minutes, it is discharged at a constant current rate of 1C to a voltage of 1.9V. The capacity at this point is recorded as the discharge capacity at the 1C rate. The ratio of the discharge capacity at the 1C rate to the discharge capacity at the 0.1C rate is the 1C rate performance.

[0099] 2. Cyclic performance test At 45℃, the battery was charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V until the current equals 0.02mA. It was then discharged at a discharge rate of 1C to 1.9V, and this charge-discharge cycle was repeated 300 times. The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 300th cycle were measured. 300 The capacity retention rate after 300 cycles is Q = Q 300 / Q1×100%.

[0100] 3. Mass energy density test At 45℃, the formed all-solid-state batteries were charged to 4.2V at a constant current of 0.33C, left to stand for 10 minutes, and then discharged at a constant current of 0.1C to the cutoff voltage of 1.9V (5 batteries per group) to obtain the energy of the all-solid-state batteries. The mass energy density (Wh / Kg) of the all-solid-state battery = specific capacity (mAh / g) × average discharge voltage (V).

[0101] II. Performance Testing of Liquid Batteries 1. Ratio Performance Test At 25℃, the full battery is charged at a constant current rate of 0.1C to a voltage of 4.6V, then charged at a constant voltage of 4.6V to a current of 0.02mA. After resting for 10 minutes, it is discharged at a constant current rate of 0.1C to a voltage of 2V. The capacity at this point is recorded as the discharge capacity at the 0.1C rate. After resting for 10 minutes, it is charged at a constant current rate of 1C to a voltage of 4.6V, then charged at a constant voltage of 4.6V to a current of 0.02mA. After resting for 10 minutes, it is discharged at a constant current rate of 1C to a voltage of 2V. The capacity at this point is recorded as the discharge capacity at the 1C rate. The ratio of the discharge capacity at the 1C rate to the discharge capacity at the 0.1C rate is the 1C rate performance.

[0102] 2. Cyclic performance test At 25°C, the full battery was charged at a constant current of 1C to 4.6V, then charged at a constant voltage of 4.6V until the current equals 0.02mA. It was then discharged at a discharge rate of 1C to 2V, and this charge-discharge cycle was repeated 300 times. The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 300th cycle were measured. 300 The capacity retention rate after 300 cycles is Q = Q 300 / Q1×100%.

[0103] 3. Mass energy density test At 25°C, the formed liquid batteries were charged at a constant current of 0.1C to 4.8V, left to stand for 10 minutes, and then discharged at a constant current of 0.1C to the cutoff voltage of 2.0V (5 batteries per group) to obtain the energy of the liquid batteries. The mass energy density (Wh / kg) of the liquid battery = specific capacity (mAh / g) × average discharge voltage (V).

[0104] The test results are shown in Table 3.

[0105] Table 3

[0106] As can be seen from Tables 1-3, this application, by constructing a non-fully coated first coating layer containing a first fast ion conductor on the surface of lithium-rich manganese-based materials, can ensure the continuity of ion channels while retaining a sufficient number of electronic conduction pathways. Furthermore, the characteristics of this non-fully coated structure effectively alleviate interfacial stress, thereby synergistically improving the ion and electron transport kinetics and structural stability of the lithium-rich manganese-based materials. The lattice structure and chemical environment of the first coating layer can also promote the in-situ, dense growth of the second coating layer, significantly improving the compatibility between the active material and the solid electrolyte. Simultaneously, by introducing lithium halides into the second coating layer, interfacial chemistry can be controlled, impedance reduced, and a dense and strongly bonded physical barrier formed through the in-situ chemical bonding of lithium halides with the first / second fast ion conductors. This effectively inhibits the dissolution of transition metals in the active material, reduces interfacial side reactions, and prevents electrolyte diffusion into the positive electrode. Thus, it jointly achieves rapid continuous ion / electron transport, stable interfacial chemistry, and durable physical protection, significantly improving the rate performance and cycle stability of the battery while ensuring the high capacity of the lithium-rich manganese-based material.

[0107] 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 application.

Claims

1. A positive electrode active material, comprising a core and a coating layer; characterized in that, The core comprises a lithium-rich manganese-based material, and the coating layer comprises a first coating layer and a second coating layer; The first coating layer includes a first fast ion conductor, and the first coating layer covers a portion of the surface of the lithium-rich manganese-based material; The second coating layer includes a first region and a second region that are interconnected. The first region coats a lithium-rich manganese-based material that is not coated by the first coating layer. The first region includes lithium halide or a complex formed by lithium halide and a second fast ion conductor. The second region coats the first coating layer. The second region includes a complex formed by lithium halide and a first fast ion conductor, or the second region includes a complex formed by lithium halide, a first fast ion conductor, and a second fast ion conductor.

2. The positive electrode active material according to claim 1, characterized in that, Based on the surface area of ​​the lithium-rich manganese-based material, the coating rate of the first coating layer is 1%-50%; And / or, based on the mass of the second coating layer, the mass content of the halogen element is 4%-65%, and the halogen element includes at least one of Cl, Br, and F; And / or, the thickness of the second coating layer is 10nm-150nm; And / or, the thickness of the first coating layer is 10nm-50nm.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The general chemical formula of the lithium-rich manganese-based material is Li. 1+x Ni a Co b Mn c D d O e D includes at least one of the elements Al, Ti, Zr, Ta, Nb, Mo, W, F, Cl, and Br, with 0.1≤x≤0.5, 0.1≤a≤0.3, 0.1≤b≤0.3, 0.5≤c≤0.8, 0.01≤d≤0.2, and 2≤e≤3; And / or, the first fast ion conductor and the second fast ion conductor each independently comprise Li7La3Zr 2-y E y O 12 Li 1+z Al z Ti 2-z (PO4)3, Li3PS4, Li7P3S 11 Li2ZrO3, Li4Ti5O 12 At least one of the following, wherein E includes at least one of Al, Ga, Ta, and Nb, 0 ≤ y ≤ 0.6, and 0.05 ≤ z ≤ 0.2; And / or, the lithium halide includes at least one of LiCl, LiBr, and LiF.

4. The positive electrode active material according to claim 3, characterized in that, The first coating layer is Li7La3Zr 2- y E y O 12 The first region in the second coating layer is Li4PS4F, and the second region in the second coating layer is Li4PS4F-Li8La3Zr. 2-y E y O 12 F, where E includes at least one of Al, Ga, Ta, and Nb, and 0 ≤ y ≤ 0.

6.

5. The positive electrode active material according to claim 1 or 2, characterized in that, The lithium-rich manganese-based material includes Al, Zr and F elements. Based on the mass of the positive electrode active material, the mass content of Al element is 500-3000 ppm, the mass content of Zr element is 500-3000 ppm, and the mass content of F element is 1500-12000 ppm. And / or, the thickness of the first coating layer is 20nm-40nm; And / or, the thickness of the second coating layer is 80nm-120nm.

6. The positive electrode active material according to claim 1, characterized in that, The XPS F 1S spectrum of the positive electrode active material shows characteristic peaks at 683eV-684eV and 685.5eV-687.5eV.

7. The positive electrode active material according to claim 1, characterized in that, The particle size Dv50 of the positive electrode active material is 0.5μm-9μm; And / or, the particle size distribution SPAN value of the positive electrode active material is 0.5-2; And / or, the positive electrode active material includes secondary particles, which are formed by the aggregation of primary particles, and the average particle size of the primary particles is 0.2μm-1.0μm.

8. The positive electrode active material according to claim 1, 2, 4, 6 or 7, characterized in that, The specific surface area of ​​the positive electrode active material is 1m². 2 / g-4m 2 / g; And / or, the positive electrode active material has an ionic conductivity of 10 at 25°C. -8 S / cm-10 -6 S / cm.

9. A lithium-ion secondary battery, comprising a positive electrode sheet, said positive electrode sheet comprising a positive current collector and a positive active layer disposed on at least one surface of the positive current collector in the thickness direction, characterized in that, The positive electrode active layer comprises the positive electrode active material according to any one of claims 1-8.

10. The lithium-ion secondary battery according to claim 9, characterized in that, The lithium-ion secondary battery includes any one of the following: all-solid-state battery, semi-solid-state battery, and liquid battery.

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