A lithium-rich manganese-based material and a lithium-ion secondary battery

Abstract

The application provides a lithium-rich manganese-based material and a lithium ion secondary battery; the lithium-rich manganese-based material comprises a lithium-rich manganese-based core doped with Ru elements and Nb elements, and a coating layer covering at least part of the surface of the lithium-rich manganese-based core, wherein the coating layer comprises lithium cobaltate and glassy boride. The lithium-rich manganese-based material of the application is doped with Ru elements and Nb elements in the lithium-rich manganese-based core; the Ru elements participate in the regulation of the conduction band through the d orbit, thereby reducing the migration energy barrier of active ions and improving the electronic conductivity; the Nb elements stabilize the lattice structure through strong covalent bonds, thereby reducing micro-cracks and phase changes in the cycle. Meanwhile, the lithium cobaltate in the coating layer forms a conductive interface by reacting with residual alkali on the surface of the material, thereby promoting the transmission of active ions; the glassy boride enhances the mechanical strength of the coating layer and inhibits crack propagation. The lithium-rich manganese-based material has the advantages of high capacity, high rate performance and long cycle life, and can improve the capacity, rate performance and cycle performance of the lithium ion secondary battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion secondary battery technology, and particularly relates to a lithium-rich manganese-based material and a lithium-ion secondary battery. Background Technology

[0002] Lithium-ion batteries (LIBs) have been widely used in portable electronic devices (such as smartphones and laptops), electric vehicles (EVs), and large-scale energy storage systems (ESS) due to their high energy density and long cycle life. With the increasing demands for range, safety, and cost control from downstream applications, developing cathode materials that combine high energy density, low cost, and excellent cycle stability has become a core research direction in the lithium-ion battery field. Lithium-rich manganese-based cathode materials are considered a potential core material for next-generation high-energy-density lithium-ion batteries because their theoretical capacity is significantly higher than that of traditional ternary materials and lithium iron phosphate (LFP), and they benefit from abundant manganese resources and do not rely on expensive nickel and cobalt elements.

[0003] However, lithium-ion batteries based on existing lithium-rich manganese-based materials cannot simultaneously achieve high capacity, high rate performance, and long cycle life. Summary of the Invention

[0004] This invention provides a lithium-rich manganese-based material, which has the advantages of high capacity, high rate performance and long cycle life, and can improve the capacity, rate performance and cycle performance of lithium-ion secondary batteries.

[0005] The present invention also provides a lithium-ion secondary battery, which has high capacity, excellent rate performance and cycle performance.

[0006] The first aspect of the present invention provides a lithium-rich manganese-based material, comprising a lithium-rich manganese-based core doped with Ru and Nb, and a coating layer covering at least a portion of the surface of the lithium-rich manganese-based core, the coating layer comprising lithium cobalt oxide and glassy boride.

[0007] The lithium-rich manganese-based material as described above, wherein, based on the lithium-rich manganese-based material, the Ru element doping amount is 4000-5000 ppm; and / or, based on the lithium-rich manganese-based material, the Nb element doping amount is 4000-5000 ppm; and / or, the glassy boride includes B element, and based on the lithium-rich manganese-based material, the B element mass content is 290-800 ppm.

[0008] In the lithium-rich manganese-based material described above, the coating layer has a coverage rate of 70-90% on the surface of the lithium-rich manganese-based core; and / or,

[0009] The mass ratio of lithium cobalt oxide to glassy boride is (1000-10000):(5-100); and / or,

[0010] The melting point of the glassy boride is not lower than 1000℃, preferably 1000-2300℃; and / or,

[0011] The glassy boride includes at least one of CoB, NiB, B6Si, TiB2, and ZrB2; and / or,

[0012] The chemical formula of the lithium-rich manganese-based core is x(Li₂MnO₃)·(1-x)(LiM p Ru q Nb t O2); wherein M includes at least one of Ni, Co, and Mn, 0.98≤p<1, 0<q≤0.01, 0<t≤0.01.

[0013] In the lithium-rich manganese-based material described above, the average thickness of the coating layer is 0.1-3 nm; and / or,

[0014] The ratio of the radius of the lithium-rich manganese-based core to the thickness of the coating layer is (1000-5000):1.

[0015] The lithium-rich manganese-based material as described above, wherein, in the XRD pattern, the full width at half maximum (FWHM) of the diffraction peak (104) of the lithium-rich manganese-based material is 0.228-0.35; and / or,

[0016] In the XRD pattern, the diffraction intensity ratio of the diffraction peak (003) to the diffraction peak (104) of the lithium-rich manganese-based material is 1.6-2.0; and / or,

[0017] The pH of the lithium-rich manganese-based material is 10.5-12; and / or,

[0018] The residual alkali content of the lithium-rich manganese-based material is 700-1500 ppm.

[0019] The lithium-rich manganese-based material as described above, wherein the lithium-rich manganese-based material comprises primary particles, the average particle size of which is 0.1-0.7 μm; and / or,

[0020] The lithium-rich manganese-based material has a particle size Dv90 of 6-9 μm, a particle size Dv10 of 1-2 μm, and a particle size Dv50 of 1-5 μm, preferably Dv50 of 3-4 μm; and / or,

[0021] The Span value of the lithium-rich manganese-based material is 0.5-2, preferably 0.8-1.5; and / or,

[0022] The specific surface area of ​​the lithium-rich manganese-based material is 1-4 m².2 / g; and / or,

[0023] The conductivity of the lithium-rich manganese-based material is ≥10. -6 S / cm; and / or,

[0024] The resistivity of the lithium-rich manganese-based material is ≤10. 6 Ω·cm.

[0025] In the lithium-rich manganese-based material described above, the glassy borides are distributed in an island-like pattern on the surface of the lithium-rich manganese-based core.

[0026] The lithium-rich manganese-based material as described above, wherein the coating layer comprises a first coating layer close to the lithium-rich manganese-based core and a second coating layer away from the lithium-rich manganese-based core, wherein the first coating layer comprises the lithium cobalt oxide and the second coating layer comprises the glassy boride; or the first coating layer comprises the glassy boride and the second coating layer comprises the lithium cobalt oxide.

[0027] A second aspect of the present invention provides a lithium-ion secondary battery, 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 a positive active material; the positive active material including the lithium-rich manganese-based material described in the first aspect above.

[0028] The lithium-ion secondary battery described above includes any one of all-solid-state batteries, semi-solid-state batteries, and liquid batteries.

[0029] The lithium-rich manganese-based material of this invention incorporates Ru and Nb elements into its lithium-rich manganese-based core. Ru participates in conduction band modulation through its d orbitals, lowering the migration barrier for active ions (such as lithium ions) and simultaneously improving electronic conductivity. Nb stabilizes the crystal structure through strong covalent bonds, reducing microcracks and phase transitions during cycling. Simultaneously, the lithium cobalt oxide in the coating layer reacts with residual alkali on the material surface to form a conductive interface, promoting active ion transport; the glassy boride enhances the mechanical strength of the coating layer, inhibiting crack propagation. The synergistic effect of these factors gives the lithium-rich manganese-based material advantages such as high capacity, high rate performance, and long cycle life, thereby improving the capacity, rate performance, and cycle performance of lithium-ion secondary batteries. Attached Figure Description

[0030] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0031] Figure 1 This is a SEM image of the lithium-rich manganese-based material provided in Embodiment 1 of the present invention;

[0032] Figure 2 This is a SEM image of the lithium-rich manganese-based material provided in Comparative Example 1 of the present invention;

[0033] Figure 3 This is a SEM image of the lithium-rich manganese-based material provided in Comparative Example 2 of the present invention;

[0034] Figure 4 This is a SEM image of the lithium-rich manganese-based material provided in Comparative Example 3 of the present invention.

[0035] Figure 5 This is a cross-sectional EDS image of the lithium-rich manganese-based material provided in Embodiment 1 of the present invention;

[0036] Figure 6 The XRD patterns of lithium-rich manganese-based materials of Example 1 and Comparative Examples 1-3 of this invention are shown below.

[0037] Figure 7 Charge-discharge curves of liquid batteries prepared from lithium-rich manganese-based materials in Example 1 and Comparative Examples 1-3 of this invention.

[0038] Figure 8 The cycling curves are for the liquid batteries prepared from lithium-rich manganese-based materials in Example 1 and Comparative Examples 1-3 of this invention.

[0039] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0041] In order to enable existing lithium-ion batteries to achieve high capacity, excellent rate performance and long cycle life at the same time, the inventors conducted in-depth research and found that the main reason for the poor performance of current batteries is that existing lithium-ion batteries often use lithium-rich manganese-based materials as cathode materials. However, such materials face multiple technical bottlenecks in practical applications, including insufficient structural stability, poor interface compatibility and oxygen release risk.

[0042] To address the aforementioned issues, the inventors attempted to surface-coat or dope lithium-rich manganese-based materials. During this process, they discovered that while doping with transition metals (such as titanium) can improve initial capacity or structural stability to some extent, it is difficult to sustainably suppress oxygen release during cycling. Furthermore, traditional coatings, if lacking sufficient ion or electron transport capabilities, are prone to forming new interfacial impedances, which in turn leads to a decrease in rate performance and cycling efficiency.

[0043] Based on this, the inventors proposed the lithium-rich manganese-based material of the present invention with the goal of maintaining the high capacity of lithium-rich manganese-based materials while also taking into account voltage retention, structural stability and interface compatibility during cycling.

[0044] The first aspect of the present invention provides a lithium-rich manganese-based material, comprising a lithium-rich manganese-based core doped with Ru and Nb, and a coating layer covering at least a portion of the surface of the lithium-rich manganese-based core, the coating layer comprising lithium cobalt oxide and glassy boride.

[0045] It should be noted that the lithium-rich manganese-based core has a layered structure.

[0046] Glassy borides refer to amorphous borides, which have a structural characteristic of short-range order and long-range disorder.

[0047] The lithium-rich manganese-based material provided by this invention has the advantages of high capacity, high rate performance, and long cycle life, and can improve the capacity, rate performance, and cycle performance of lithium-ion secondary batteries. The reason is:

[0048] On the one hand, doped Ru, in a high-valence or variable-valence state, participates in the electronic structure reconstruction of the transition metal layer, which helps to enhance the covalent interaction of the transition metal-oxygen bond and improve charge compensation behavior. Doped Nb, due to its high valence state and strong bond energy, can enhance lattice oxygen stability and suppress irreversible oxygen release at high charging potentials, thereby mitigating the phase transition degradation common in lithium-rich manganese-based materials. The synergistic doping of Ru and Nb simultaneously addresses electronic structure regulation and framework stabilization at the lattice scale, making it less prone to irreversible layer-to-spinel or rock-salt phase transitions during high-voltage delithiation in lithium-rich manganese-based materials. While maintaining a high average discharge voltage and cycle reversibility, the lithium cobalt oxide coating possesses good lithium-ion insertion / extraction compatibility, thus avoiding the formation of additional migration barriers and improving the ion transport efficiency of lithium-rich manganese-based materials. The boron in the glassy borides of the coating enhances the interfacial bonding between the coating and the lithium-rich manganese-based core through transition metal-OB bonding, effectively suppressing coating peeling and microcrack propagation during cycling. Simultaneously, the glassy borides themselves exhibit good chemical inertness and mechanical compliance, mitigating local stress concentration induced by surface reconstruction during high-voltage cycling. Furthermore, their short-range ordered and long-range disordered structural characteristics facilitate the formation of a continuous stress buffer network on the particle surface and absorb local strain during charge-discharge volume changes, further enhancing the structural stability of lithium-rich manganese-based materials.

[0049] The testing methods for the doping elements in the lithium-rich manganese-based core and the types of materials in the coating layer in this invention are as follows:

[0050] Lithium-rich manganese-based materials were characterized using profiled EDS (energy dispersive spectroscopy) and EPMA (electron probe microanalysis): profiled EDS was used to determine the types of dopants in the lithium-rich manganese-based core, and EPMA was used to analyze the types of materials in the coating layer.

[0051] In one specific embodiment, based on lithium-rich manganese-based materials, the Ru doping amount is 4000-5000 ppm. Controlling the Ru doping amount within the range of 4000-5000 ppm suppresses oxygen release, phase transition expansion, and voltage decay during charging and discharging while maintaining the integrity of the layered lattice structure, thereby balancing doping enhancement and structural integrity.

[0052] For example, based on lithium-rich manganese-based materials, the Ru doping amount is 4000ppm, 4100ppm, 4200ppm, 4300ppm, 4400ppm, 4500ppm, 4600ppm, 4700ppm, 4800ppm, 4900ppm or 5000ppm, or a range of any two of these values.

[0053] In one specific embodiment, based on lithium-rich manganese-based materials, the Nb doping amount is 4000-5000 ppm. Controlling the Nb doping amount within the range of 4000-5000 ppm suppresses oxygen release, phase transition expansion, and voltage decay during charging and discharging while maintaining the integrity of the layered lattice structure, thus achieving a balance between doping enhancement and structural integrity.

[0054] For example, based on lithium-rich manganese-based materials, the doping amount of Nb is 4000ppm, 4100ppm, 4200ppm, 4300ppm, 4400ppm, 4500ppm, 4600ppm, 4700ppm, 4800ppm, 4900ppm or 5000ppm, or a range of any two of these values.

[0055] In one specific embodiment, the glassy boride includes element B, and based on lithium-rich manganese-based materials, the mass content of element B is 20-800 ppm. Within this range, the mass content of element B can provide both interface passivation and mechanical buffering, while maintaining low transmission impedance, thus balancing the cycle stability and rate performance of lithium-ion secondary batteries.

[0056] For example, based on lithium-rich manganese-based materials, the mass content of element B is 20ppm, 290ppm, 300ppm, 350ppm, 400ppm, 450ppm, 500ppm, 550ppm, 600ppm, 650ppm, 700ppm or 800ppm, or a range of any two of these values.

[0057] In this invention, the doping amounts of Ru and Nb elements and the mass content of B element in the lithium-rich manganese-based material were detected by ICP-MS.

[0058] In one specific embodiment, the coating layer has a coverage rate of 70-90% on the surface of the lithium-rich manganese-based core. Within this range, the coating rate ensures that most of the active interfaces are synergistically protected by lithium cobalt oxide and glassy boride, while retaining certain ion transport channels. This reduces electrolyte erosion and side reactions, suppresses polarization increase, and thus improves the cycle stability and rate performance of the lithium-ion secondary battery.

[0059] For example, the coating layer has a coating percentage of 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, or 90% on the surface of the lithium-rich manganese-based core, or a range of any two of these values.

[0060] In this invention, the coating ratio refers to the percentage of the surface area of ​​the coating layer on the lithium-rich manganese-based core.

[0061] The coating rate testing method in this invention is as follows:

[0062] Scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) was used to calculate the coverage area of ​​the coating layer on the surface of the lithium-rich manganese-based core using image analysis software, thus obtaining the coating efficiency.

[0063] In one specific embodiment, the mass ratio of lithium cobalt oxide to glassy boride is 2000:1 to 10:1. Within this range, the lithium cobalt oxide forms a continuous or semi-continuous lithium-conducting phase, while the glassy boride is dispersed therein as a small amount of reinforcing phase. The lithium cobalt oxide improves interfacial lithium-ion migration, while the glassy boride enhances the thermal stability and mechanical integrity of the coating layer. The two work synergistically to balance the rate performance and cycle stability of the lithium-ion secondary battery.

[0064] For example, the mass ratio of lithium cobalt oxide to glassy boride is 200:1, 20:1, 10:1, 1000:1, 100:1, 50:1 or 2000:1, or a range of any two of these values.

[0065] The mass ratio of lithium cobalt oxide to glassy boride in this invention is calculated by converting ICP content.

[0066] In one specific embodiment, the melting point of the glassy boride is not lower than 1000°C, preferably 1000-2300°C. Glassy borides with the above melting point can withstand the coating sintering temperature and maintain structural stability, thus still playing an interface enhancement role after high-temperature treatment, ensuring the cycle stability of the lithium-ion secondary battery.

[0067] For example, the melting point of the glassy boride is 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃, 1600℃, 1700℃, 1800℃, 1900℃, 2000℃, 2100℃, 2200℃, 2300℃ or above, or a range consisting of any two of these values.

[0068] The melting point of the glassy boride of the present invention was tested by scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

[0069] In one specific embodiment, the glassy boride includes at least one of CoB, NiB, B6Si, TiB2, and ZrB2. These substances possess excellent thermal stability and interfacial compatibility, enabling them to co-construct a high-temperature resistant, low-side-reaction coating layer with lithium cobalt oxide, thereby improving the cycle stability of lithium-ion secondary batteries.

[0070] When the glassy boride is a mixture of the aforementioned substances, the present invention does not specifically limit the proportion of each specific substance in the mixture.

[0071] In one specific embodiment, the chemical formula of the lithium-rich manganese-based core is x(Li₂MnO₃)·(1-x)(LiM p Ru q Nb t O2); wherein M includes at least one of Ni, Co, and Mn, 0.98≤p<1, 0<q≤0.01, 0<t≤0.01. The above-mentioned lithium-rich manganese-based core ensures that Ru and Nb enter the layered lattice in trace amounts, enhancing structural stability and suppressing phase transitions and oxygen release during cycling, thereby improving the cycle performance of lithium-ion secondary batteries.

[0072] For example, p is 0.98, 0.982, 0.984, 0.986, 0.988, 0.99, 0.992, 0.994, 0.996, 0.998, or 0.999, or a range of any two of these values.

[0073] For example, q is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009 or 0.01, or a range of any two of these values.

[0074] For example, t is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009 or 0.01, or a range of any two of these values.

[0075] In one specific embodiment, the average thickness of the coating layer is 0.1-3 nm. By controlling the average thickness of the coating layer to 0.1-3 nm, the coating layer has the ability to continuously cover the core surface without affecting the lithium-ion migration path, ensuring a low interface impedance, thereby balancing the cycle performance and rate performance of the lithium-ion secondary battery.

[0076] Transmission electron microscopy (TEM) was used to image and analyze the cross-section of lithium-rich manganese-based materials. Ten different locations were selected on the TEM images, and the vertical distance from the outer edge of the coating layer to the edge of the core interface was measured using image analysis software. The average value of multiple measurements was taken as the average thickness of the coating layer.

[0077] The ratio of the core radius to the coating thickness of the lithium-rich manganese-based core was statistically calculated.

[0078] For example, the average thickness of the coating layer is 0.1 nm, 0.3 nm, 0.5 nm, 0.7 nm, 0.9 nm, 1.1 nm, 1.3 nm, 1.5 nm, 1.7 nm, 1.9 nm, 2.1 nm, 2.3 nm, 2.5 nm, 2.7 nm, 2.9 nm, or 3 nm, or a range of any two of these values.

[0079] In one specific embodiment, the radius of the lithium-rich manganese-based core to the thickness of the coating layer is (1000-5000):1. This range ensures that the coating layer forms a continuous thin protective shell on the surface of the lithium-rich manganese-based core, suppressing surface structure reconstruction, microcrack propagation, and electrolyte erosion during cycling, while also ensuring unobstructed electron or ion channels. This achieves a synergistic match between the high capacity of the lithium-rich manganese-based core and the low impedance protection of the coating layer, thereby improving the cycle stability, voltage retention, and rate performance of the lithium-ion secondary battery.

[0080] For example, the ratio of the radius of the lithium-rich manganese-based core to the thickness of the coating layer is 1000:1, 1500:1, 2000:1, 2500:1, 3000:1, 3500:1, 4000:1, 4500:1 or 5000:1, or a range of any two of these values.

[0081] To further improve the crystal order, layered structure integrity and surface chemical state of lithium-rich manganese-based materials, the half-peak width of the (104) peak, the (003) / (104) intensity ratio, pH and residual alkali content were controlled.

[0082] In one specific embodiment, the full width at half maximum (FWHM) of the diffraction peak (104) of the lithium-rich manganese-based material in the XRD pattern is 0.228-0.35. Within this FWHM range, the lithium-rich manganese-based material exhibits moderate crystallinity and grain uniformity, which is more conducive to stabilizing the lithium insertion / extraction process.

[0083] For example, in the XRD pattern, the full width at half maximum (FWHM) of the diffraction peak (104) of the lithium-rich manganese-based material is 0.228, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34 or 0.35, or a range of any two of these values.

[0084] In one specific embodiment, the diffraction intensity ratio of the diffraction peak (003) to the diffraction peak (104) of the lithium-rich manganese-based material in the XRD pattern is 1.6-2.0. Within this range, the layered structure of the lithium-rich manganese-based material exhibits better orientation and lower cation mixing, which is more conducive to reducing lithium-ion diffusion resistance and suppressing phase transitions.

[0085] For example, in the XRD pattern, the diffraction intensity ratio of the diffraction peak (003) to the diffraction peak (104) of the lithium-rich manganese-based material is 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95 or 2.0, or a range consisting of any two of these values.

[0086] In one specific embodiment, the pH of the lithium-rich manganese-based material is 10.5-12. Within this pH range, side reactions are suppressed while the surface retains a certain level of reactivity.

[0087] For example, the pH of the lithium-rich manganese-based material is 10.5, 10.6, 10.7, 10.8, 10.9, 11, 11.1, 11.2, 11.3, 11.4, 11.5 or 12, or a range of any two of these values.

[0088] The pH testing method for the lithium-rich manganese-based material in this invention is as follows:

[0089] The pH of the lithium-rich manganese-based material was measured using a pH meter (pHS-25 type pH meter). 1g of the lithium-rich manganese-based material was weighed and added to a reaction flask. 10mL of high-purity water was added to the reaction flask, and the mixture was heated to boiling for 15min. After cooling to room temperature, the mixture was separated into layers. The upper clear layer was taken, and the pH value of the lower slurry was measured using a pH meter.

[0090] In one specific embodiment, the residual alkali content of the lithium-rich manganese-based material is 700-1500 ppm. Within this range, the residual alkali content can reduce the consumption of electrolyte by residual LiOH, Li2CO3, etc., and the thickening of the interfacial film, thereby suppressing the increase in impedance.

[0091] For example, the residual alkali content of the lithium-rich manganese-based material is 700ppm, 800ppm, 900ppm, 1100ppm, 1200ppm, 1300ppm, 1400ppm or 1500ppm, or a range of any two of these values.

[0092] The method for testing the residual alkali content of lithium-rich manganese-based materials in this invention is as follows:

[0093] At 25℃, 30g of lithium-rich manganese-based material was placed in 100g of water, stirred thoroughly, and then filtered to obtain a lithium-rich manganese-based material solution. The solution was titrated with hydrochloric acid standard solution, and the residual alkali content of the lithium-rich manganese-based material solution was calculated based on the results.

[0094] When all the above parameters are within the above range, the layered main structure of the lithium-rich manganese-based material is orderly, the surface alkalinity residue is low, and the electrode / electrolyte side reactions are weakened, thereby improving the cycle life of lithium-ion secondary batteries, reducing polarization, and improving high-rate performance.

[0095] In one specific embodiment, the lithium-rich manganese-based material includes primary particles with an average particle size of 0.1-0.7 μm. Controlling the primary particle size within this range ensures sufficient exposure of active sites while reducing diffusion resistance and cycle stress caused by excessively large grains, thereby improving the rate performance and cycle life of the lithium-ion secondary battery.

[0096] For example, the average particle size of the primary particles is 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm or 0.7 μm, or a range of any two of these values.

[0097] The method for testing the average particle size of primary particles in this invention is as follows:

[0098] On the surface or cross-section of the positive electrode active layer, the particle size of all primary particles in the SEM image taken at 1000x magnification using a scanning electron microscope is measured and counted. If the number of primary particles in a single image is insufficient, multiple images can be taken until the number of observed primary particles is accumulated to 800. The arithmetic mean of the particle sizes of these 800 primary particles is then calculated, and the result is the average particle size of the primary particles.

[0099] In one specific embodiment, the lithium-rich manganese-based material has a particle size Dv90 of 6-9 μm, a particle size Dv10 of 1-2 μm, and a particle size Dv50 of 1-5 μm, preferably a particle size Dv50 of 3-4 μm. By limiting the particle sizes Dv90, Dv10, and Dv50 to the above ranges, the lithium-rich manganese-based material exhibits a more uniform particle size distribution, achieving a balance between compaction density and electrolyte wetting, as well as lithium-ion diffusion channels, thereby improving the volumetric energy density and rate performance of the lithium-ion secondary battery.

[0100] For example, the particle size Dv90 of the lithium-rich manganese-based material is 6 μm, 6.3 μm, 6.6 μm, 6.9 μm, 7.2 μm, 7.5 μm, 7.8 μm, 8.1 μm, 8.4 μm, 8.7 μm or 9 μm, or a range of any two of these values.

[0101] For example, the particle size Dv10 of the lithium-rich manganese-based material is 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2 μm, or a range consisting of any two of these values.

[0102] For example, the particle size Dv50 of the lithium-rich manganese-based material is 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, or a range of any two of these values.

[0103] The particle size Dv10 of lithium-rich manganese-based materials refers to the particle size on the particle size distribution curve of lithium-rich manganese-based materials when the volume of the smallest particle size accounts for 10% of the total volume.

[0104] The particle size Dv50 of lithium-rich manganese-based materials refers to the particle size on the particle size distribution curve of lithium-rich manganese-based materials when the volume of the smallest particle size accounts for 50% of the total volume.

[0105] The particle size Dv90 of lithium-rich manganese-based materials refers to the particle size on the particle size distribution curve of lithium-rich manganese-based materials when the volume of the smallest particle size accounts for 90% of the total volume.

[0106] The testing methods for the particle sizes Dv90, Dv10, and Dv50 of the lithium-rich manganese-based material of this invention are as follows:

[0107] The positive electrode active layer was scraped off from the positive electrode sheet, and then washed with NMP to obtain solid particulate products. The particle size Dv90, Dv10 and Dv50 of the lithium-rich manganese-based material were then measured by a laser particle size analyzer.

[0108] In one specific embodiment, the Span value of the lithium-rich manganese-based material is 0.5-2, preferably 0.8-1.5. A Span value within this range indicates that the lithium-rich manganese-based material has a concentrated particle size distribution, which can reduce side reactions caused by fine powder and uneven transport caused by coarse particles, thereby improving the uniformity of electrode film formation and ultimately enhancing the cycle stability and rate performance of the lithium-ion secondary battery.

[0109] For example, the Span value of the lithium-rich manganese-based material is 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9 or 2, or a range of any two of these values.

[0110] Span = (Dv90 - Dv10) / Dv50.

[0111] In one specific embodiment, the specific surface area of ​​the lithium-rich manganese-based material is 1-4 m². 2 / g. Within this specific surface area range, sufficient interfacial contact is ensured while suppressing interfacial side reactions, thereby improving the rate performance and cycle stability of lithium-ion secondary batteries.

[0112] For example, the specific surface area of ​​the lithium-rich manganese-based material is 1m². 2 / g, 1.3m 2 / g, 1.5m 2 / g, 1.8m 2 / g、2m 2 / g, 2.3m 2 / g, 2.5m 2 / g, 2.8m 2 / g、3m 2 / g、3.3m 2 / g, 3.5m 2 / g, 3.8m 2 / g or 4m 2 / g, or a range consisting of any two of these values.

[0113] In one specific embodiment, the conductivity of the lithium-rich manganese-based material is ≥10. -6 S / cm. Within this range, electron transport can be guaranteed and polarization reduced, while impedance growth and voltage decay can be suppressed, thereby improving the cycle stability and rate performance of lithium-ion secondary batteries.

[0114] For example, the conductivity of lithium-rich manganese-based materials is 1×10⁻⁶. -6 S / cm, 2×10 -6 S / cm, 3×10 -6 S / cm, 4×10 -6 S / cm, 5×10 -6 S / cm, 6×10 -6 S / cm, 7×10 -6 S / cm, 8×10 -6 S / cm, 9×10 -6 S / cm or higher, or a range consisting of any two of these values.

[0115] In this invention, the electrical conductivity of the lithium-rich manganese-based material refers to the powder electrical conductivity.

[0116] The conductivity of the lithium-rich manganese-based material of this invention was measured using the four-probe method according to standard GB / T 30836-2014.

[0117] In one specific embodiment, the resistivity of the lithium-rich manganese-based material is ≤10. 6 Within this range, sufficient electron conductivity can be guaranteed, polarization losses during charging and discharging can be reduced, thereby improving the rate performance and cycle stability of lithium-ion secondary batteries.

[0118] For example, the resistivity of lithium-rich manganese-based materials is 1×10⁻⁶. 6 Ω·cm, 9×10 5 Ω·cm, 8×10 5 Ω·cm, 7×10 5 Ω·cm, 6×10 5 Ω·cm, 5×10 5 Ω·cm, 4×10 5 Ω·cm, 3×10 5 Ω·cm, 2×10 5 Ω·cm, 1×10 5 Ω·cm or less, or a range consisting of any two of these values.

[0119] The resistivity of the lithium-rich manganese-based material of this invention was measured using the four-probe method according to standard GB / T 30836-2014.

[0120] In one specific embodiment, the glassy boride is distributed in an island-like pattern on the surface of the lithium-rich manganese-based core. The island-like distribution of the glassy boride can form a highly stable amorphous framework locally, buffering volume changes and surface stress during charging and discharging, while also ensuring migration channels for lithium ions and electrons. This reduces interfacial impedance and suppresses the spread of side reactions, thereby improving the cycle life and rate performance of the lithium-ion secondary battery.

[0121] In one specific embodiment, the coating layer includes a first coating layer close to the lithium-rich manganese-based core and a second coating layer away from the lithium-rich manganese-based core. The first coating layer includes lithium cobalt oxide, and the second coating layer includes a glassy boride; or the first coating layer includes a glassy boride, and the second coating layer includes lithium cobalt oxide. When the first coating layer is a glassy boride and the second coating layer is lithium cobalt oxide, adhesion and crack resistance are enhanced, and the lithium cobalt oxide maintains good electrochemical compatibility. When the first coating layer is lithium cobalt oxide and the second coating layer is a glassy boride, a conductive interface for lithium-ion migration is established first, and then the glassy boride provides an additional barrier. Both of these cases achieve synergy between interface protection and transport optimization, thereby maintaining the high capacity output and long-term cycling reliability of the lithium-rich manganese-based material while suppressing voltage decay, mitigating surface reconstruction, and reducing residual alkali side reactions.

[0122] This invention does not specifically limit the preparation method of lithium-rich manganese-based materials. In one embodiment, the preparation method of lithium-rich manganese-based materials includes the following steps:

[0123] 1) A mixture is obtained by mixing a metal salt solution and an alkaline solution; the metal salt solution contains Ni. 2+ Co 2+ Mn 2+ Ru 3+ 、Nb 5+ The mixture was adjusted to pH 7.5-9, and the precursor was obtained after the reaction.

[0124] 2) The above precursor is mixed with a lithium source and then sintered to obtain a lithium-rich manganese-based core.

[0125] Specifically, the temperature is first increased to 500-600℃ at a rate of 1-3℃ / min and held for 300-500min; then increased to 750-950℃ at a rate of 1-5℃ / min and held for 600-800min; finally, increased to 800-1200℃ at a rate of 1-3℃ / min and held for 300-700min. 500-600℃ is the melting temperature of the lithium source, which is conducive to lithium source diffusion and uniform distribution of lithium-rich manganese-based precursors; 750-950℃ is the main stage for the formation of the layered structure of lithium-rich manganese-based materials, determining their primary particle size, lithium-nickel mixing, and other properties; 800-100℃ further stabilizes the layered structure and makes the material size more uniform.

[0126] 3) After mixing the lithium-rich manganese-based core with a cobalt source and glassy boride, a coating treatment is performed to obtain lithium-rich manganese-based materials.

[0127] The present invention does not specifically limit the alkaline solution; for example, it can be a mixture of NaOH and NH3·H2O.

[0128] The present invention does not specifically limit the cobalt source, for example, it can be one of Co(OH)2, CoOOH, and Co3O4.

[0129] The present invention does not specify the mass ratio of cobalt source to glassy boride, for example it can be (50-400):1.

[0130] The present invention does not specify the ratio of precursor to lithium source. For example, the ratio of the total number of moles of metal ions in the lithium source to the total number of moles in the precursor is 1.62:1.

[0131] The present invention does not specifically limit the conditions of the coating treatment. For example, the coating treatment temperature is 670-800℃, the coating treatment time is 600-1000min, and the heating rate of the coating treatment is 1-5℃ / min.

[0132] During the coating process, the cobalt source and residual alkali react to generate lithium cobalt oxide, which diffuses on the surface of the lithium-rich manganese-based core and also drives the uniform diffusion of glassy borides on the surface of the lithium-rich manganese-based core. At the same time, the O bonds between the glassy borides and the surface of the lithium-rich manganese-based core form transition metal-OB bonds, achieving strong bonding.

[0133] A second aspect of the present invention provides a lithium-ion secondary battery, comprising 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 a positive active material; the positive active material including the lithium-rich manganese-based material of the first aspect. This lithium-ion secondary battery exhibits high capacity, excellent rate performance, and cycle performance.

[0134] It is conceivable that, in addition to the aforementioned lithium-rich manganese-based material, the positive electrode active layer also includes conductive agents and binders.

[0135] This invention does not specifically limit the material of the positive electrode current collector; it can be any material conventional in the art. For example, the material of the positive electrode current collector can be either aluminum foil or nickel foil.

[0136] This invention does not specifically limit the type of conductive agent; it can be any material conventional in the art. For example, the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber.

[0137] This invention does not specifically limit the type of adhesive, which can be a conventional material in the art. For example, the adhesive can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0138] This invention does not specifically limit the preparation method of the positive electrode sheet. In one embodiment, the positive electrode sheet can be prepared by a method including the following steps:

[0139] The lithium-rich manganese-based material of the present invention is dispersed with a conductive agent and a binder in an N-methylpyrrolidone (NMP) solvent and thoroughly stirred to form a uniform positive electrode slurry. The positive electrode slurry is uniformly coated on a positive electrode current collector, and after drying, rolling and slitting, a positive electrode sheet is obtained.

[0140] This invention does not impose specific limitations on the amount of lithium-rich manganese-based materials, conductive agents, and binders, which can be adjusted according to actual conditions.

[0141] As can be imagined, the lithium-ion secondary battery of the present invention, in addition to the above-mentioned positive electrode, also includes a negative electrode, an electrolyte, and a separator.

[0142] The present invention does not specifically limit the structure of the negative electrode sheet. In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least a portion of the surface of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, a binder, and a conductive agent.

[0143] This invention does not specifically limit the material of the negative electrode current collector; it can be any conventional material in the art. For example, the negative electrode current collector can be any of copper foil, nickel foam, or copper foam.

[0144] This invention does not specifically limit the type of negative electrode active material, and it can be any negative electrode active material commonly used in batteries. For example, the negative electrode active material can be selected from at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrodes), tin-based negative electrode materials (mainly including tin and tin alloys).

[0145] This invention does not specifically limit the type of binder; it can be any binder commonly used in battery negative electrodes. For example, the binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0146] This invention does not specifically limit the type of conductive agent; it can be any conductive agent commonly used in the negative electrode of batteries. For example, the conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene.

[0147] This invention does not specifically limit the preparation method of the negative electrode sheet. In one embodiment, the negative electrode sheet can be prepared by a method including the following steps:

[0148] The negative electrode active material, conductive agent, and binder are dispersed in deionized water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, a negative electrode sheet is obtained.

[0149] This invention does not impose specific limits on the amount of negative electrode active material, conductive agent, and binder, and these amounts can be adjusted according to actual conditions.

[0150] This invention does not specifically limit the composition of the electrolyte, which may include one or more solvents commonly used in current battery electrolytes, as well as lithium salts commonly used in current battery electrolytes. For example, the solvent may include at least one of ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, and γ-butyrolactone; the lithium salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0151] This invention does not specifically limit the material of the separator; it can be any separator material commonly used in batteries. For example, the separator can be selected from any of the following: polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven fabric separator, and separator with ceramic coating.

[0152] This invention does not specifically limit the method of battery preparation. In one embodiment, the battery can be prepared by a method including the following steps:

[0153] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are wound or stacked to obtain a bare cell, which is then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried, electrolyte is injected into the dried battery. After the battery is placed, formed, and resealed, the lithium-ion secondary battery is completed.

[0154] In one specific embodiment, the lithium-ion secondary battery includes any one of all-solid-state batteries, semi-solid-state batteries, and liquid batteries.

[0155] When the lithium-ion secondary battery is an all-solid-state battery, the present invention does not strictly limit the selection of the solid electrolyte, and may include one or more of polymer solid electrolyte, oxide solid electrolyte, halide solid electrolyte, and sulfide solid electrolyte.

[0156] The present invention will be further described below through specific embodiments.

[0157] Example 1

[0158] The preparation method of the lithium-rich manganese-based material in this embodiment includes the following steps:

[0159] 1) Prepare mixed salt solutions of NiSO4, CoSO4, MnSO4, Ru2(SO4)3, and Nb2(SO4)5, and a mixed alkaline solution of NaOH and NH3·H2O, respectively, for later use. The total metal ion concentration of the mixed salt solutions is 2 mol / L. 2+ Co 2+ Mn 2+ Ru 3+ 、Nb 5+ The molar ratio of the two compounds was 0.125:0.125:0.74:0.05:0.05, the molar concentration of NaOH was 3 mol / L, and the molar concentration of NH3·H2O was 0.2 mol / L. 7 L of deionized water was added to the reactor, and the mixed salt solution was pumped into the reactor at a rate of 175 mL / h using a peristaltic pump. The stirring speed was controlled at 1000 rpm, the circulating water temperature was 55℃, and the feed rate of the mixed alkali solution was adjusted using a three-stage speed control to maintain the pH of the solution system at 7.5. The feeding time was 30 h. The flow of the mixed salt and mixed alkali solutions was then stopped, the stirring speed was adjusted to 200 rpm, and the reaction was allowed to proceed for 24 h. The reaction system was then subjected to solid-liquid separation. The obtained solid was washed by centrifugation with deionized water and dried at 120℃ for 24 h to obtain the precursor Ni. 12.5 Co 12.5 Mn 74 Ru0.5 Nb 0.5 (OH)2.

[0160] 2) The mixture of the above precursor and LiOH·H2O was placed in a muffle furnace and sintered. The material was then removed and ground to obtain a lithium-rich manganese-based core of 0.62(Li2MnO3)*0.38(LiNi). 0.329 Co 0.329 Mn 0.315 Ru 0.0135 Nb 0.0135 O2). The molar ratio of lithium ions to metal ions in the precursor in LiOH·H2O is 1.62:1, and the metal ions in the precursor include Ni. 2+ Co 2+ Mn 2+ Ru 3+ 、Nb 5+ .

[0161] The specific steps of the sintering process are as follows: first, raise the temperature to 500℃ (T1) at 1℃ / min and hold it at that temperature for 300min (t1); then raise the temperature to 850℃ (T2) at 2℃ / min and hold it at that temperature for 600min (t2); then raise the temperature to 1000℃ (T3) at 1℃ / min and hold it at that temperature for 300min (t3).

[0162] 3) After uniformly mixing 100g of the above-mentioned lithium-rich manganese-based core with 4g of Co(OH)2 and 0.06g of glassy CoB, the mixture is placed in a muffle furnace for coating treatment to obtain lithium-rich manganese-based material 0.62(Li2MnO3)*0.38(LiNi) 0.329 Co 0.329 Mn 0.315 Ru 0.0135 Nb 0.0135 O2)@LCO@CoB. The coating treatment was performed at a temperature of 670℃ for 600 min at a heating rate of 2℃ / min. Some parameters of the preparation method are shown in Table 3.

[0163] Examples 2-37 and Comparative Examples 1-5 are basically the same as Example 1, with the differences shown in Table 1 A, 1B, 1C, 1D, 2A, 2B, 3A, 3B.

[0164] Experimental Example 1

[0165] 1. The doping elements and coating materials in the lithium-rich manganese-based core of the examples and comparative examples were tested. The doping amounts of Ru and Nb elements and the mass content of B element in the lithium-rich manganese-based materials of the examples and comparative examples were tested. The results are shown in Tables 1A, 1B, 1C, and 1D. The coating rate (abbreviated as coating rate), the mass ratio of lithium cobalt oxide to glassy boride, the melting point of glassy boride, the coating thickness, and the ratio of the radius of the lithium-rich manganese-based core to the thickness of the coating layer (abbreviated as radius to thickness ratio) of the lithium-rich manganese-based materials of the examples and comparative examples were tested. XRD, pH, and residual alkali content of the lithium-rich manganese-based materials were tested. The average particle size, particle size Dv90, particle size Dv10, particle size Dv50, specific surface area, conductivity, and resistivity of the primary particles of the lithium-rich manganese-based materials were tested. The results are shown in Tables 2A and 2B. Scanning electron microscopy was performed on the lithium-rich manganese-based materials of Example 1 and Comparative Examples 1-3. The results are shown in the figure. Figure 1-4 .

[0166] Depend on Figure 1 It can be seen that the lithium-rich manganese-based material in Example 1 has a near-single-crystal morphology, the surface powder is LCO (lithium cobalt oxide), and the island-like white spots are glassy boride CoB. From Figure 2 It can be seen that the primary particles of the lithium-rich manganese-based material without Ru and Nb doping (Comparative Example 1) are relatively large. Figure 3 It can be seen that the surface of the lithium-rich manganese-based material in Comparative Example 2 does not contain powdery lithium cobalt oxide. From Figure 4 It can be seen that the surface of the lithium-rich manganese-based material in Comparative Example 3 does not have island-shaped white spots CoB.

[0167] Figure 5 This is a cross-sectional EDS image of the lithium-rich manganese-based material provided in Example 1, by... Figure 5 It can be seen that the doping elements Ru and Nb are uniformly distributed in the core of the lithium-rich manganese-based material.

[0168] Figure 6 The XRD patterns of lithium-rich manganese-based materials in Example 1 and Comparative Examples 1-3 are shown below. Figure 6 It can be seen that in Comparative Example 1, which is not doped with Ru and Nb, the (003) crystal plane peak is shifted to the right, at 18.73~18.75°. The other three samples doped with Ru and / or Nb have (003) crystal planes shifted to the left, at 18.61~18.65°. This is because the dopant element -O bond is formed in the lattice, and its large ionic radius causes the c-axis to expand, which is shown in XRD as the diffraction peak shifting to a lower angle (2θ decreases). The lithium-rich manganese-based materials of Example 1 and Comparative Examples 1-3 show a spinel phase peak at 35.5°, which is the peak of the spinel phase LCO formed by low-temperature coating of Co(OH)2. Comparative Example 2 is not coated with Co(OH)2, so it does not show this peak.

[0169] 2. Testing Methods

[0170] 1) Test methods for doping elements and coating material types in lithium-rich manganese-based cores

[0171] Lithium-rich manganese-based materials were characterized using profiled EDS (energy dispersive spectroscopy) and EPMA (electron probe microanalysis): profiled EDS was used to determine the types of dopants in the lithium-rich manganese-based core, and EPMA was used to analyze the types of materials in the coating layer.

[0172] 2) Test methods for the doping amounts of Ru and Nb elements and the mass content of B element in lithium-rich manganese-based materials

[0173] ICP-MS was used for detection.

[0174] 3) Test methods for the coating ratio (abbreviated as coating ratio), the mass ratio of lithium cobalt oxide to glassy boride, and the melting point of glassy boride in lithium-rich manganese-based materials.

[0175] Scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) was used to calculate the coverage area of ​​the coating layer on the surface of the lithium-rich manganese-based core using image analysis software, thus obtaining the coating efficiency.

[0176] Melting point was determined by scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

[0177] The mass ratio of lithium cobalt oxide to glassy boride was calculated using ICP content conversion.

[0178] 4) Test methods for average coating thickness and the ratio of the radius of the lithium-rich manganese-based core to the coating thickness.

[0179] Transmission electron microscopy (TEM) was used to image and analyze the cross-section of lithium-rich manganese-based materials. Ten different locations were selected on the TEM images, and the vertical distance from the outer edge of the coating layer to the edge of the core interface was measured using image analysis software. The average value of multiple measurements was taken as the average thickness of the coating layer.

[0180] The ratio of the core radius to the coating thickness of the lithium-rich manganese-based core was statistically calculated.

[0181] 5) Test methods for pH and residual alkali

[0182] pH: The pH of the lithium-rich manganese-based material was measured using a pH meter (pHS-25 type pH meter). 1g of the lithium-rich manganese-based material was weighed and added to the reaction flask. 10mL of high-purity water was added to the reaction flask, and the mixture was heated to boiling for 15min. After cooling to room temperature, the mixture was separated into layers. The upper clear layer was taken, and the pH value of the lower slurry was measured using a pH meter.

[0183] Residual alkali content: At 25℃, 30g of lithium-rich manganese-based material was placed in 100g of water, stirred thoroughly, and filtered to obtain a lithium-rich manganese-based material solution. The solution was titrated with hydrochloric acid standard solution, and the residual alkali content of the lithium-rich manganese-based material solution was calculated based on the results.

[0184] 6) Test methods for the average particle size, particle size Dv90, particle size Dv10, particle size Dv50, specific surface area, conductivity, and resistivity of primary particles in lithium-rich manganese-based materials.

[0185] Average particle size of primary particles: On the surface or cross-section of the positive electrode active layer, the particle size of all primary particles in the SEM image taken at 1000x magnification using a scanning electron microscope is measured and counted. If the number of primary particles in a single image is insufficient, multiple images can be taken until the number of observed primary particles reaches 800. The arithmetic mean of the particle sizes of these 800 primary particles is then calculated, and the result is the average particle size of the primary particles.

[0186] Particle sizes Dv90, Dv10, and Dv50 of lithium-rich manganese-based materials: The positive electrode active layer was scraped off from the positive electrode sheet, and then washed with NMP to obtain solid particulate products. The particle sizes Dv90, Dv10, and Dv50 of the lithium-rich manganese-based materials were then measured using a laser particle size analyzer.

[0187] Specific surface area of ​​lithium-rich manganese-based materials: determined by nitrogen adsorption method, that is, by measuring the amount of adsorbate such as nitrogen in lithium-rich manganese-based materials (samples to be tested) under different relative pressures, the specific surface area of ​​lithium-rich manganese-based materials is calculated using the BET equation.

[0188] Electrical conductivity of lithium-rich manganese-based materials: measured using the four-probe method according to standard GB / T 30836-2014.

[0189] The resistivity of lithium-rich manganese-based materials was measured using the four-probe method according to standard GB / T 30836-2014.

[0190] Table 1A

[0191]

[0192] Table 1B

[0193]

[0194] Table 1C

[0195]

[0196] Table 1D

[0197]

[0198] Table 2A

[0199]

[0200] Table 2B

[0201]

[0202] Table 3A

[0203]

[0204] Table 3B

[0205]

[0206] Experimental Example 2

[0207] 1. The lithium-rich manganese-based materials of the examples and comparative examples were prepared into mold batteries, and the charging capacity, discharging capacity, first efficiency, and cycle performance were tested. The lithium-rich manganese-based materials of the examples and comparative examples were prepared into liquid batteries, and the charge-discharge curves, rate performance, and capacity retention were tested. The results are shown in Tables 4A and 4B.

[0208] The method for preparing an all-solid-state battery includes the following steps:

[0209] (1) Preparation of positive electrode sheet: Under inert atmosphere, the prepared lithium-rich manganese-based material, lithium phosphorus sulfur chlorine and conductive carbon black were dry-mixed at a mass ratio of 60:30:10 (humidity <1ppm) to obtain a mixture. The mixture was placed in a ball mill and ball-milled at 400 rpm for 3 hours. After ball milling, it was hot-rolled at 100℃ and 15MPa to produce a positive electrode sheet with a thickness of 120μm.

[0210] (2) Preparation of negative electrode: A lithium metal foil with a thickness of 45 μm is polished to make its surface roughness Ra≤0.1 μm to obtain a negative electrode.

[0211] (3) Composite positive electrode-solid electrolyte layer: Lithium, phosphorus, sulfur, chlorine and polytetrafluoroethylene (PTFE) are mixed at a mass ratio of 6:1 and rolled to form a solid electrolyte membrane with a thickness of 45 μm. The resulting positive electrode sheet and the solid electrolyte membrane are hot-pressed at 180°C and 8 MPa to obtain the composite positive electrode-solid electrolyte layer.

[0212] (4) Assembly of all-solid-state batteries:

[0213] By stacking the composite positive electrode-solid electrolyte layer and the negative electrode in sequence, an all-solid-state battery is obtained.

[0214] The method for preparing a liquid battery includes the following steps:

[0215] (1) Preparation of the positive electrode sheet: Lithium-rich manganese-based material, Super P, and PVDF were mixed in a mass ratio of 8:1:1, and NMP was added to prepare a positive electrode slurry. The positive electrode slurry was coated on both sides of an aluminum foil, and after drying and rolling, a positive electrode sheet was obtained. The areal density of the positive electrode sheet was 25 mg / cm³. 2 .

[0216] (2) Preparation of the negative electrode sheet: Graphite, Super P, and SBR were mixed in a mass ratio of 8:1:1, and deionized water was added to prepare a negative electrode slurry. The negative electrode slurry was coated on both sides of a copper foil, and after drying and rolling, a negative electrode sheet was obtained. The areal density of the negative electrode sheet was 12 mg / cm³. 2 .

[0217] (3) Preparation of liquid batteries

[0218] The positive electrode, separator, and negative electrode are stacked sequentially to assemble a battery cell; the separator used is made of PP / PE material; the assembled battery cell is placed in a battery casing, electrolyte is injected, and it is sealed to obtain a liquid lithium-ion battery. The solvent in the electrolyte includes DMC and FEC in a mass ratio of 3:7, and the concentration of LiPF6 in the electrolyte is 1.2 mol / L.

[0219] 2. Testing Methods

[0220] 1) Test methods for charging capacity, discharging capacity, first-efficiency performance, and cycle performance of mold batteries

[0221] (1) 0.1C discharge capacity test:

[0222] The test environment temperature was 45℃±1℃. The charge / discharge method is as follows:

[0223] a) High-rate charging: 0.1C, until voltage ≥ 4.2V; b) Constant-voltage charging: 4.2V, until current ≤ 0.02mA; c) Rest for 10min; d) High-rate discharging: 0.1C, until voltage ≤ 1.9V, record the battery's first discharge capacity C0; e) Rest for 10min. First-cycle efficiency = 0.1C discharge capacity / 0.1C charge capacity.

[0224] (2) Capacity retention test during 1C cycle:

[0225] k) High-rate charging: 1C, until the voltage ≥ 4.2V; l) Constant-voltage charging: 4.2V, until the current ≤ 0.02mA; m) Let stand for 10min; n) High-rate discharging: 1C, until the voltage ≤ 1.9V, and record the battery's discharge capacity C1 at this time; o) Let stand for 10min;

[0226] Repeat step (2) 100 times and record the battery discharge capacity C2 at this time.

[0227] Calculate using the following formula:

[0228] Capacity retention rate after 100 cycles = C2 / C1 × 100%.

[0229] 1C / 0.1C discharge capacity ratio = C1 / C0 × 100%.

[0230] 2) Test methods for charge-discharge curves, rate performance, and cycle performance of liquid batteries

[0231] Charge-discharge curves: The liquid batteries prepared above were subjected to charge-discharge tests. The test environment temperature was 25℃±1℃, the test voltage was 2-4.8V, and the test condition was 0.1C. The tests were completed according to the specified charge-discharge regime, and charge-discharge curves were obtained. The charge-discharge curves of the liquid batteries in Examples 1 and Comparative Examples 1-3 are shown below. Figure 7 .

[0232] Depend on Figure 7 It can be seen that the liquid battery in Example 1 has the best capacity performance.

[0233] Rate performance: The battery was charged and discharged at 25℃ using a battery charge and discharge tester. The charge and discharge regime was as follows: constant current charging at 0.2C to 4.25V, then constant voltage charging at 4.25V until the current decreased to 0.02C, followed by resting for 5 minutes, and then constant current discharging at 0.2C to 2.5V. The discharge capacity Q was recorded. 0.2c After resting for 5 minutes, charge with a constant current of 0.2C to 4.25V, then switch to a constant voltage of 4.25V to charge until the current decreases to 0.02C. After resting for 5 minutes, discharge with a constant current of 3C to 2.5V, and record the discharge capacity Q. 3c The capacity retention rate can be calculated using the following formula:

[0234] 3C discharge rate capacity retention rate = Q 3c / Q 0.2c ×100%.

[0235] Cyclic performance: The capacity retention of each battery was tested. The specific test method was as follows: at 25℃, the battery was charged at a constant current rate of 1C to 4.6V, then charged at a constant voltage of 4.6V until the current ≤0.02mA, followed by discharging at a discharge rate of 1C to 2V, and then allowed to stand for 10 minutes. This was repeated 100 times as one cycle. The discharge capacity Q1 at the first cycle and Q2 at the 100th cycle were measured. 100 The capacity retention rate of the battery after 100 cycles is calculated based on the test data.

[0236] Capacity retention rate (%) = Q 100 / Q1×100%.

[0237] The cycling curves of the liquid batteries in Examples 1 and 1-3 are shown below. Figure 8 .

[0238] 3) Test methods for discharge capacity, cycle performance, and rate performance of all-solid-state batteries

[0239] Discharge capacity: The assembled all-solid-state battery was tested for 0.1C discharge capacity at a test environment temperature of 45℃±1℃. The specific test method was as follows: constant current charging at 0.1C rate until the voltage ≥4.2V, then constant voltage charging at 4.2V until the current ≤0.02mA, and after standing for 10min, constant current discharge at 0.1C rate until the voltage ≤1.9V, and after standing for 10min again, the discharge capacity of the battery was calculated based on the discharge curve.

[0240] Cyclic performance: The capacity retention of each battery was tested. The specific test method was as follows: at 25℃, the battery was charged at a constant current rate of 1C to 4.6V, then charged at a constant voltage of 4.6V until the current ≤0.02mA, followed by discharging at a discharge rate of 1C to 2V, and then allowed to stand for 10 minutes. This was repeated 100 times as one cycle. The discharge capacity Q1 at the first cycle and Q2 at the 100th cycle were measured. 100 The capacity retention rate of the battery after 100 cycles is calculated based on the test data.

[0241] Capacity retention rate (%) after 100 cycles = Q 100 / Q1×100%.

[0242] Rate performance: The battery was charged and discharged at 25℃ using a battery charge and discharge tester. The charge and discharge regime was as follows: constant current charging at 0.2C to 4.25V, then constant voltage charging at 4.25V until the current decreased to 0.02C, followed by resting for 5 minutes, and then constant current discharging at 0.2C to 2.5V. The discharge capacity Q was recorded. 0.2c After resting for 5 minutes, charge with a constant current of 0.2C to 4.25V, then switch to a constant voltage of 4.25V to charge until the current decreases to 0.02C. After resting for 5 minutes, discharge with a constant current of 3C to 2.5V, and record the discharge capacity Q. 3c The capacity retention rate can be calculated using the following formula:

[0243] 3C discharge rate capacity retention rate = Q 3c / Q 0.2c ×100%.

[0244] Table 4A

[0245]

[0246] Table 4B

[0247]

[0248] As shown in Tables 4A and 4B, compared with the comparative example, the lithium-ion secondary battery made from the lithium-rich manganese-based material of the present invention has excellent capacity, rate performance and cycle performance.

[0249] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A lithium-rich manganese-based material, characterized in that, The core comprises a lithium-rich manganese-based core doped with Ru and Nb, and a coating layer covering at least a portion of the surface of the lithium-rich manganese-based core, the coating layer comprising lithium cobalt oxide and glassy boride.

2. The lithium-rich manganese-based material according to claim 1, characterized in that, Based on the lithium-rich manganese-based material, the Ru element doping amount is 4000-5000 ppm; and / or, based on the lithium-rich manganese-based material, the Nb element doping amount is 4000-5000 ppm; and / or, the glassy boride includes B element, and based on the lithium-rich manganese-based material, the B element mass content is 290-800 ppm.

3. The lithium-rich manganese-based material according to claim 1 or 2, characterized in that, The coating layer has a coating rate of 70-90% on the surface of the lithium-rich manganese-based core; and / or, The mass ratio of lithium cobalt oxide to glassy boride is (1000-10000):(5-100); and / or, The melting point of the glassy boride is not lower than 1000℃, preferably 1000-2300℃; and / or, The glassy boride includes at least one of CoB, NiB, B6Si, TiB2, and ZrB2; and / or, The chemical formula of the lithium-rich manganese-based core is x(Li₂MnO₃)·(1-x)(LiM p Ru q Nb t O2); wherein M includes at least one of Ni, Co, and Mn, 0.98≤p<1, 0<q≤0.01, 0<t≤0.

01.

4. The lithium-rich manganese-based material according to any one of claims 1-3, characterized in that, The average thickness of the coating layer is 0.1-3 nm; and / or, The ratio of the radius of the lithium-rich manganese-based core to the thickness of the coating layer is (1000-5000):

1.

5. The lithium-rich manganese-based material according to any one of claims 1-4, characterized in that, In the XRD pattern, the full width at half maximum (FWHM) of the diffraction peak (104) of the lithium-rich manganese-based material is 0.228–0.35; and / or, In the XRD pattern, the diffraction intensity ratio of the diffraction peak (003) to the diffraction peak (104) of the lithium-rich manganese-based material is 1.6-2.0; and / or, The pH of the lithium-rich manganese-based material is 10.5-12; and / or, The residual alkali content of the lithium-rich manganese-based material is 700-1500 ppm.

6. The lithium-rich manganese-based material according to any one of claims 1-5, characterized in that, The lithium-rich manganese-based material comprises primary particles with an average particle size of 0.1-0.7 μm; and / or, The lithium-rich manganese-based material has a particle size Dv90 of 6-9 μm, a particle size Dv10 of 1-2 μm, and a particle size Dv50 of 1-5 μm, preferably Dv50 of 3-4 μm; and / or, The Span value of the lithium-rich manganese-based material is 0.5-2, preferably 0.8-1.5; and / or, The specific surface area of ​​the lithium-rich manganese-based material is 1-4 m². 2 / g; and / or, The conductivity of the lithium-rich manganese-based material is ≥10. -6 S / cm; and / or, The resistivity of the lithium-rich manganese-based material is ≤10. 6 Ω·cm.

7. The lithium-rich manganese-based material according to any one of claims 1-6, characterized in that, The glassy borides are distributed in an island-like pattern on the surface of the lithium-rich manganese-based core.

8. The lithium-rich manganese-based material according to any one of claims 1-6, characterized in that, The coating layer includes a first coating layer close to the lithium-rich manganese-based core and a second coating layer away from the lithium-rich manganese-based core. The first coating layer includes the lithium cobalt oxide, and the second coating layer includes the glassy boride; or the first coating layer includes the glassy boride, and the second coating layer includes the lithium cobalt oxide.

9. A lithium-ion secondary battery, comprising a positive electrode sheet, the 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, the positive active layer comprising a positive active material; characterized in that, The positive electrode active material includes the lithium-rich manganese-based 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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