Coated lithium-rich manganese-based positive electrode material, and preparation method and application thereof

Abstract

The present disclosure belongs to the technical field of solid-state batteries, and provides a coated lithium-rich manganese-based positive electrode material and a preparation method and application thereof. The preparation method comprises: mixing lithium salt, manganese salt, cobalt salt and nickel salt to perform a co-precipitation reaction, and sintering to obtain a lithium-rich manganese-based positive electrode material LRMO; mixing the LRMO with a coating agent and ball milling to obtain the same, and the mass ratio of the two is 100:5-30. The present disclosure also discloses a coated lithium-rich manganese-based positive electrode material prepared according to the above method, and a full solid-state battery, wherein the positive electrode of the battery comprises the above coated lithium-rich manganese-based positive electrode material. By adjusting the content of the coating agent and the ball milling process parameters, the structural stability and interface compatibility of the LRMO are optimized. The obtained coated positive electrode material can effectively stabilize the Li-O-Li configuration, inhibit the release of lattice oxygen and the dissolution of transition metals, and at the same time improve the interface matching with the electrolyte, thereby significantly improving the cycle capacity retention rate and voltage attenuation characteristics of the full solid-state battery.

Description

Technical Field

[0001] This disclosure relates to the field of solid-state battery technology, and in particular to a coated lithium-rich manganese-based cathode material, its preparation method, and its application. Background Technology

[0002] With the increasing demand for high-energy-density, long-cycle-life all-solid-state batteries in the new energy field, lithium-rich manganese-based cathode materials (LRMO) have become one of the core candidates for all-solid-state battery cathode materials due to their layered solid solution structure of "Li2MnO3-LiMO2 (M is Ni, Co, etc.)", which has a theoretical specific capacity of over 250mAh / g and an excellent voltage platform. They are widely regarded as a key direction for breaking through the energy density bottleneck of traditional lithium-ion batteries.

[0003] However, LRMO has unavoidable technical drawbacks in practical applications of all-solid-state batteries: Firstly, it is prone to irreversible structural transformation from layered to spinel to rock salt phase during charge-discharge cycles, accompanied by the large release of lattice oxygen and transition metal ions (Mn). 2+ Co 3+ The dissolution of LRMO (such as LiOH and Li2CO3) directly leads to rapid decay of battery cycle capacity and significant voltage decay, severely restricting battery life. Secondly, alkaline substances (such as LiOH and Li2CO3) remaining on the surface of LRMO are prone to undergo interfacial side reactions with sulfide solid electrolytes (such as LPSC and LPS) to generate high-resistivity products, which leads to a sharp increase in interfacial impedance, significantly reducing ion transport kinetics and thus affecting the rate performance and energy output efficiency of all-solid-state batteries.

[0004] To address these issues, related technologies often employ oxide coating (such as Al2O3 and TiO2) or carbon-based coating to modify LRMO. However, both methods have significant limitations: oxide coatings exhibit poor mechanical compatibility with the LRMO matrix, are prone to cracking due to volume changes during cycling, and cannot effectively suppress side reactions in the long term; while carbon-based coatings can improve electronic conductivity, their inhibitory effect on lattice oxygen release is limited, and the chemical compatibility between carbon materials and sulfide solid electrolytes is insufficient, easily exacerbating interfacial impedance problems. Furthermore, current modification methods often require multiple high-temperature treatments or rely on complex equipment such as magnetron sputtering, resulting in cumbersome processes, high costs, and difficulty in precisely controlling the coating thickness and uniformity, leading to poor adaptability and making it difficult to meet the demands of large-scale production of all-solid-state batteries.

[0005] Therefore, developing a modification technology that can form a uniform and dense coating layer in situ, solve the two core problems of LRMO "structural instability" and "interface incompatibility", and is simple and easy to industrialize has become a key requirement to promote the practical application of lithium-rich manganese-based cathode materials in all-solid-state batteries. Summary of the Invention

[0006] This disclosure provides a coated lithium-rich manganese-based cathode material, its preparation method, and its application, in order to at least solve the above-mentioned technical problems existing in the prior art.

[0007] According to a first aspect of this disclosure, a method for preparing a coated lithium-rich manganese-based cathode material is provided, comprising the following steps:

[0008] S1: Lithium salt, manganese salt, cobalt salt, and nickel salt are mixed and subjected to a co-precipitation reaction, followed by sintering to obtain lithium-rich manganese-based cathode material Li. 1.2 Ni x Co y Mn z O2 (LRMO), where x=0.10~0.13, y=0.09~0.13, z=0.54~0.61, x+y+z=0.8;

[0009] S2: The lithium-rich manganese-based cathode material Li 1.2 Ni x Co y Mn z O2 and a coating agent are mixed and ball-milled to obtain the coated lithium-rich manganese-based cathode material; the lithium-rich manganese-based cathode material Li 1.2 Ni x Co y Mn z The mass ratio of O2 to the coating agent is 100:5~30, and the coating agent is selected from at least one of SnS2, SnSO4, Zr(SO4)2, and Zr(NO3)4.

[0010] Specifically, the above-mentioned coating agent is a low-melting-point coating agent, whose core advantages are: (1) The key characteristic of the low-melting-point coating agent is that its melting point is lower than the structural stability temperature of LRMO (avoiding the phase transformation of the LRMO layered structure), and it can melt rapidly under the action of frictional heat energy of high-energy ball milling, without the need for additional high-temperature sintering steps, and directly form a uniform coating layer on the surface of LRMO particles. Compared with existing technologies (such as Al2O3, TiO2 and other oxide coatings): traditional high-melting-point coating agents require separate high-temperature heat treatment to form a coating layer, which is not only cumbersome, but also easily leads to LRMO particle agglomeration or structural damage; while the low-melting-point coating agent can achieve in-situ melting coating through frictional heat generation during the ball milling process, simplifying the process while ensuring the tight bonding between the coating layer and the LRMO matrix, and avoiding the coating layer falling off during the cycle. (2) After melting, the low-melting-point coating agent uniformly covers the surface of LRMO. After cooling, it forms a continuous and dense coating layer, which physically isolates LRMO from the electrolyte, inhibits the release of lattice oxygen and the dissolution of transition metal ions, and blocks the irreversible transformation of "layered → spinel → rock salt phase". In addition, the decomposition products of Zr-based coating agent can form stable Zr-O-Mn / Co / Ni coordination bonds with the surface of LRMO, while avoiding the direct reaction between residual alkali (LiOH, Li2CO3) on the surface of LRMO and sulfide electrolyte, thus reducing interfacial impedance. Furthermore, the Zr-based coating agent itself has ion conduction characteristics, which can build an efficient lithium-ion transport channel and improve ion transport kinetics. (3) The amount of low-melting-point coating agent can be controlled, which can avoid excessive occupation of the active material ratio while forming an effective protective layer, thus ensuring the high capacity advantage of LRMO. The raw materials of the coating agent are readily available, and the preparation process only requires conventional equipment such as ball mills, without the need for complex instruments such as magnetron sputtering. The process parameters are easy to quantify and control, making it suitable for large-scale production.

[0011] The proportion of coating agent directly determines the coating effect and battery performance. The range of 5~30wt% is derived from the balance between effective coating and capacity retention, which can produce the following effects: (1) Forming a continuous and dense coating layer: When the proportion is greater than or equal to 5wt%, the coating agent can completely cover the surface of LRMO particles after melting, avoiding side reactions caused by exposed areas; (2) Ensuring the proportion of active material: LRMO is the core source of battery capacity. The coating agent is an inactive material. The proportion ≤30wt% can avoid a significant decrease in capacity caused by an excessively low proportion of active material; (3) Optimizing interface impedance: The coating layer formed by Zr-based coating agent within the above range can minimize the interface side reactions between LRMO and electrolyte. At the same time, its own ion conduction characteristics can reduce interface impedance and improve battery cycle stability. If the proportion of the coating agent is too high, exceeding 30 wt%, the proportion of the active material LRMO will be significantly reduced, directly leading to a decrease in battery discharge capacity. An excessively thick coating layer will hinder the transport of lithium ions between LRMO and the electrolyte, resulting in reduced ionic conductivity and poorer rate performance. Excessive coating agent tends to accumulate on the particle surface, causing LRMO particle agglomeration and further deteriorating electrochemical performance. If the proportion of the coating agent is too low, below 5 wt%, a continuous coating layer cannot be formed, resulting in a large number of exposed areas that cannot effectively isolate LRMO from the electrolyte. Exposed areas will still experience lattice oxygen release, transition metal dissolution, and interfacial side reactions, leading to rapid capacity decay and severe voltage drop. A discontinuous coating layer cannot prevent the reaction between residual alkali on the LRMO surface and the electrolyte, resulting in the formation of high-resistivity products and a significant increase in interfacial impedance.

[0012] In a preferred embodiment, the coating agent is selected from at least one of Zr(SO4)2 and Zr(NO3)4.

[0013] In a preferred embodiment, the lithium-rich manganese-based cathode material Li 1.2 Ni x Co y Mn z The mass ratio of O2 to the coating agent is 100:20~28.

[0014] In one embodiment, the lithium salt is selected from at least one of lithium hydroxide, lithium chloride, lithium carbonate, lithium oxalate, and lithium nitrate.

[0015] In one embodiment, the manganese salt is selected from at least one of manganese sulfate, manganese nitrate, manganese carbonate, and manganese acetate.

[0016] In one embodiment, the cobalt salt is selected from at least one of cobalt sulfate, cobalt nitrate, cobalt carbonate, and cobalt acetate.

[0017] In one embodiment, the nickel salt is selected from at least one of nickel sulfate, nickel nitrate, nickel carbonate, and nickel acetate.

[0018] In one embodiment, the molar ratio of lithium ions in the lithium salt, manganese ions in the manganese salt, cobalt ions in the cobalt salt, and nickel ions in the nickel salt is 1:0.45~0.51:0.075~0.11:0.083~0.11.

[0019] In one possible embodiment, relative to 1 mol of the lithium-rich manganese-based cathode material Li 1.2 Ni x Co y Mn z The total molar amount of O2, manganese ions in manganese salt, cobalt ions in cobalt salt, and nickel ions in nickel salt is 0.8 mol.

[0020] In one embodiment, step S1 involves mixing lithium salt, manganese salt, cobalt salt, nickel salt with a precipitant and a complexing agent to carry out the coprecipitation reaction.

[0021] Specifically, the precipitant is selected from at least one of oxalic acid, ammonium bicarbonate, ammonium carbonate, and ammonium dihydrogen phosphate.

[0022] The core function of a precipitant is to react with Li in the solution. + Ni 2+ Co 2+ Mn 2+ Ionic reactions generate stable solid coprecipitates, providing a molecular-level mixing basis for subsequent sintering to form the LRMO layered structure.

[0023] Specifically, the complexing agent is selected from at least one of ammonia, ethylenediamine, diethylenetriamine, citric acid, tartaric acid, and ethylenediaminetetraacetic acid.

[0024] The core function of complexing agents is to react with Ni 2+ Co 2+ The transition metal ions form stable complexes, which slows down their reaction rate with the precipitant and avoids precursor particle agglomeration and uneven particle size caused by excessively high local ion concentration.

[0025] Specifically, the molar ratio of the precipitant to the lithium salt is 0.00556 to 0.01:1.

[0026] Specifically, the molar ratio of the complexing agent to the lithium salt is 0.0667 to 0.12:1.

[0027] Specifically, in step S1, lithium salt, manganese salt, cobalt salt, and nickel salt are dissolved in a solvent, and a precipitant and a complexing agent are added dropwise to form a mixture.

[0028] Specifically, the solvent is selected from water.

[0029] Specifically, the amount of lithium salt added is 0.5~0.9 mol relative to 100 mL of water.

[0030] Specifically, the conditions for the coprecipitation reaction include: reacting at a temperature of 40-50°C and a rotation speed of 300-500 rpm for 4-6 hours under an inert atmosphere.

[0031] In one embodiment, the sintering conditions in step S1 include: pre-sintering at a temperature of 400~600℃ for 2~4 hours under an inert atmosphere, followed by sintering at 800~1000℃ for 5~7 hours.

[0032] In a preferred embodiment, the sintering conditions in step S1 include: pre-sintering at 500°C for 3 hours in an inert atmosphere, followed by sintering at 900°C for 6 hours.

[0033] In one embodiment, the ball-to-material ratio in step S2 is 15-18:1.

[0034] In a preferred embodiment, the ball-to-material ratio in step S2 is 15-16:1.

[0035] In one embodiment, the ball milling process in step S2 includes: reacting at a speed of 700-1000 rpm for 25-35 minutes under an inert atmosphere, followed by standing for 8-12 minutes; the above steps are repeated for 12-24 cycles.

[0036] Specifically, the inert atmosphere is either dry argon or helium, with a water content ≤0.1 ppm and an oxygen content ≤0.1 ppm. Argon is preferred as the protective atmosphere to effectively prevent hydrolysis or oxidation of the low-melting-point coating agent, ensuring the integrity of the coating layer.

[0037] In a preferred embodiment, the above steps are repeated 16 to 18 times.

[0038] Specifically, under the aforementioned conditions, the frictional heat generated during ball milling ensures the melting and partial decomposition of the low-melting-point coating agent, while preventing phase transitions in the LRMO layered structure. Furthermore, high-energy ball milling ensures efficient dispersion of the low-melting-point coating agent while avoiding over-milling that could damage the LRMO particle structure, thus forming a uniform coating layer with a thickness of 8–20 nm on the LRMO surface. By adjusting the coating content and ball milling process parameters, the structural stability and interfacial compatibility of the coated lithium-rich manganese-based cathode material can be further optimized. This coated material effectively stabilizes the "Li-O-Li" configuration, suppresses lattice oxygen release and transition metal dissolution, and improves interfacial compatibility with the electrolyte, significantly enhancing the cycle capacity retention and voltage decay characteristics of all-solid-state batteries.

[0039] According to a second aspect of this disclosure, a coated lithium-rich manganese-based cathode material prepared according to the above-described preparation method is provided, including a lithium-rich manganese-based cathode material Li 1.2 Ni x Co y Mn z O2, where x = 0.10~0.13, y = 0.09~0.13, z = 0.54~0.61, x+y+z = 0.8, and Li coated on the lithium-rich manganese-based cathode material. 1.2 Ni x Co y Mn z The outer coating of O2.

[0040] In one embodiment, the thickness of the coating layer is 8~20 nm.

[0041] In one embodiment, the discharge specific capacity of the coated lithium-rich manganese-based cathode material is 209~293 mAh·g. -1 .

[0042] In a preferred embodiment, the discharge specific capacity of the coated lithium-rich manganese-based cathode material is 275~293 mAh·g. -1 .

[0043] According to a third aspect of this disclosure, an all-solid-state battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises the aforementioned coated lithium-rich manganese-based positive electrode material.

[0044] According to one possible implementation of this disclosure, at least the following beneficial effects are achieved:

[0045] This disclosure significantly improves the cycle stability and voltage retention of lithium-rich manganese-based cathode materials. This improvement is mainly due to the selection of low-melting-point coating agents and the precisely controlled in-situ coating process—by controlling the amount of coating agent added, combined with the ball milling speed and an appropriate ball-to-material ratio, the coating agent melts and decomposes during heat treatment and forms a uniform and dense coating layer in situ, effectively suppressing lattice oxygen release, transition metal dissolution, and irreversible phase transition from layered to spinel to rock salt phase during the charge and discharge process of lithium-rich manganese-based materials.

[0046] Meanwhile, this disclosure effectively enhances the interfacial compatibility and ion transport kinetics between lithium-rich manganese-based cathode materials and sulfide solid electrolytes. By constructing the coating layer, direct reaction between residual alkali on the surface of the lithium-rich manganese-based material and the sulfide electrolyte is avoided, while the coating layer itself provides a highly efficient lithium-ion transport channel. This advantage is primarily attributed to the chemical compatibility between the coating layer and the sulfide electrolyte, as well as the precise control of the uniformity and density of the coating layer through the ball milling process.

[0047] Furthermore, this disclosure balances the high capacity advantage of lithium-rich manganese-based materials with the industrial feasibility of the preparation process. On the one hand, by optimizing the amount of coating agent and process parameters, an effective protective layer is formed while avoiding an excessive reduction in the proportion of active material, enabling the first-cycle discharge capacity of the coated lithium-rich manganese-based cathode material to approach the theoretical high capacity level of lithium-rich manganese-based materials. On the other hand, the preparation process uses conventional equipment such as ball milling and heat treatment, the coating agent raw materials are readily available, and the process parameters are easy to quantify and control. It eliminates the need for complex equipment such as magnetron sputtering or cumbersome processes of multiple coatings, which helps to reduce production costs and improve production efficiency, laying a material foundation for the large-scale application of high-energy-density all-solid-state batteries.

[0048] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0049] The above and other objects, features, and advantages of this disclosure will become readily apparent from the following detailed description of exemplary embodiments, taken in conjunction with the accompanying drawings. Several embodiments of this disclosure are illustrated in the drawings by way of example and not limitation, in which:

[0050] In the accompanying drawings, the same or corresponding reference numerals indicate the same or corresponding parts.

[0051] Figure 1 The SEM-EDS spectrum of the coated lithium-rich manganese-based cathode material Zr-LRMO-1 in Embodiment 1 of this disclosure is shown;

[0052] Figure 2 The XRD spectra of the coated lithium-rich manganese-based cathode materials prepared in Examples 1-6 of this disclosure are shown;

[0053] Figure 3 SEM images of the coated lithium-rich manganese-based cathode materials prepared in Examples 1-6 of this disclosure are shown;

[0054] Figure 4 The diagram shows the first charge-discharge curve of an all-solid-state battery prepared from the coated lithium-rich manganese-based cathode material of Embodiment 1 of this disclosure;

[0055] Figure 5 The rate performance curve of an all-solid-state battery prepared by the coated lithium-rich manganese-based cathode material of Embodiment 1 of this disclosure is shown.

[0056] Figure 6The diagram shows the IT curve and the test results of lithium-ion conductivity and electronic conductivity of the symmetric battery prepared by the coated lithium-rich manganese-based cathode material of Embodiment 1 of this disclosure; wherein, (a) is the IT curve and the test results of lithium-ion conductivity; and (b) is the IT curve and the test results of electronic conductivity. Detailed Implementation

[0057] To make the objectives, features, and advantages of this disclosure more apparent and understandable, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0058] The purpose of this disclosure is to address the challenges of lithium-rich manganese-based cathode materials, specifically Li... 1.2 Mn 0.54 Co 0.13 Ni 0.13 To address the problems of structural instability, severe voltage decay, transition metal ion dissolution, and high interfacial impedance in all-solid-state batteries, as well as the shortcomings of existing modification technologies such as complex processes and insufficient adaptability, this paper proposes an in-situ coating of low-melting-point materials with lithium-rich manganese-based cathode materials applicable to all-solid-state batteries, along with its preparation method and application.

[0059] The following examples illustrate this in detail.

[0060] Example 1

[0061] This embodiment prepares a coated lithium-rich manganese-based cathode material Zr-LRMO-1, as detailed below:

[0062] (1) 0.5 mol lithium hydroxide, 0.042 mol nickel sulfate, 0.0375 mol cobalt sulfate and 0.254 mol manganese sulfate were added sequentially to 100 mL of deionized water. Then, 5 mL of oxalic acid and 10 mL of ammonia solution with a concentration of 6 mol / L were added dropwise at a rate of 1 mL / min. The mixture was heated to 40 °C under a nitrogen atmosphere and co-precipitated at a speed of 300 rpm for 4 h to obtain a lithium-rich manganese precursor.

[0063] (2) The lithium-rich manganese precursor was pre-sintered at 500°C for 3 hours under a nitrogen atmosphere, and then sintered at 900°C for 6 hours to obtain the lithium-rich manganese-based cathode material Li. 1.2 Ni 0.1 Co 0.09 Mn 0.61 O2.

[0064] (3) In a ball mill jar containing an inert atmosphere, 1.0 g of lithium-rich manganese-based cathode material Li was added sequentially. 1.2 Ni 0.1 Co 0.09 Mn 0.61 O2, 0.2 g of Zr(SO4)2, and 18.0 g of ball milling beads were used. The mixture was ball milled at 700 rpm for 30 min, followed by a 10 min resting time. This process was repeated 16 times to obtain the coated lithium-rich manganese-based cathode material Zr-LRMO-1 with an average particle size of 3.8 μm.

[0065] The scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) spectra of the above-mentioned coated lithium-rich manganese-based cathode material Zr-LRMO-1 are as follows: Figure 1 As shown, the top left image is the SEM morphology of LRMO particles coated with Zr(SO4)2 (where Ch 1 is the "Channel 1" signal of the scanning electron microscope (SEM), corresponding to the secondary electron signal channel of the SEM, which is the core signal source for observing the morphology of the sample. This SEM morphology image was obtained through this channel). It can be seen that the particles exhibit a complete polygonal / plate-like structure, with no obvious rough pores or breakage marks on the surface, and clear edges with bright borders. This indicates that the structure of the LRMO particles was not destroyed during the ball milling coating process (the layered structure is intact, avoiding premature phase transition); the bright borders are the continuous coating layer formed after the Zr(SO4)2 melts, with no exposed areas, meeting the design requirement of physically isolating LRMO from the electrolyte. The top right, bottom left, and bottom right images are EDS elemental distribution maps, corresponding to different elements. It can be seen that the distribution areas of O (top right), S (bottom left), and Zr (bottom right) completely overlap with the particle outlines in the SEM morphology image; the elemental signals (white bright spots) are uniformly distributed on the particle surface, with no local deficiencies / enrichments. This directly proves that Zr(SO4)2 was successfully coated on the LRMO surface; the uniform distribution of O, S, and Zr indicates that the coating agent was completely dispersed and did not agglomerate after melting, and the coating layer thickness was uniform; the simultaneous presence and consistent distribution of O, S, and Zr are consistent with the chemical formula of Zr(SO4)2, proving that the coating agent did not undergo component decomposition.

[0066] Example 2

[0067] This embodiment prepares a coated lithium-rich manganese-based cathode material Zr-LRMO-2, as detailed below:

[0068] (1) 0.8 mol lithium hydroxide, 0.088 mol nickel nitrate, 0.0599 mol cobalt sulfate and 0.393 mol manganese sulfate were added sequentially to 100 mL of deionized water. Then, 5 mL of oxalic acid and 10 mL of ammonia solution with a concentration of 6 mol / L were added dropwise at a rate of 1 mL / min. The temperature was raised to 47 °C under a nitrogen atmosphere and the co-precipitation reaction was carried out at a speed of 350 rpm for 4.3 h to obtain a lithium-rich manganese precursor.

[0069] (2) The lithium-rich manganese precursor was pre-sintered at 500°C for 3 hours under a nitrogen atmosphere, and then sintered at 900°C for 6 hours to obtain the lithium-rich manganese-based cathode material Li. 1.2 Ni 0.132 Co 0.09 Mn 0.59 O2.

[0070] (3) In a ball mill jar containing an inert atmosphere, 1.0 g of lithium-rich manganese-based cathode material Li was added sequentially. 1.2 Ni 0.132 Co 0.09 Mn 0.59 O2, 0.28 g of Zr(NO3)4, and 20.48 g of ball milling beads were used. The mixture was ball milled at 700 rpm for 30 min, followed by a 10 min resting time. This process was repeated 18 times to obtain the coated lithium-rich manganese-based cathode material Zr-LRMO-2 with an average particle size of 7.0 μm.

[0071] Example 3

[0072] This embodiment prepares a coated lithium-rich manganese-based cathode material Zr-LRMO-3, as detailed below:

[0073] (1) 0.7 mol lithium hydroxide, 0.0595 mol nickel sulfate, 0.0665 mol cobalt sulfate and 0.341 mol manganese sulfate were added sequentially to 100 mL of deionized water. Then, 5 mL of oxalic acid and 10 mL of ammonia solution with a concentration of 6 mol / L were added dropwise at a rate of 1 mL / min. The mixture was heated to 43 °C under a nitrogen atmosphere and co-precipitated at a speed of 500 rpm for 4 h to obtain a lithium-rich manganese precursor.

[0074] (2) The lithium-rich manganese precursor was pre-sintered at 500°C for 3 hours under a nitrogen atmosphere, and then sintered at 900°C for 6 hours to obtain the lithium-rich manganese-based cathode material Li. 1.2 Ni 0.102 Co 0.114 Mn 0.584 O2.

[0075] (3) In a ball mill jar containing an inert atmosphere, 1.0 g of lithium-rich manganese-based cathode material Li was added sequentially. 1.2 Ni0.102 Co 0.114 Mn 0.584 O2, 0.24 g of Zr(NO3)4, and 19.22 g of ball milling beads were used. The mixture was ball milled at 700 rpm for 30 min, followed by a 10 min resting time. This process was repeated 17 times to obtain the coated lithium-rich manganese-based cathode material Zr-LRMO-3 with an average particle size of 8.9 μm.

[0076] Example 4

[0077] This embodiment prepares a coated lithium-rich manganese-based cathode material Sn-LRMO-1, as detailed below:

[0078] (1) 0.6 mol lithium chloride, 0.06 mol nickel sulfate, 0.06 mol cobalt sulfate and 0.28 mol manganese sulfate were added sequentially to 100 mL of deionized water. Then, 5 mL of oxalic acid and 10 mL of ammonia solution with a concentration of 6 mol / L were added dropwise at a rate of 1 mL / min. The mixture was heated to 45 °C under a nitrogen atmosphere and co-precipitated at a speed of 400 rpm for 5 h to obtain a lithium-rich manganese precursor.

[0079] (2) The lithium-rich manganese precursor was pre-sintered at 500°C for 3 hours under a nitrogen atmosphere, and then sintered at 900°C for 6 hours to obtain the lithium-rich manganese-based cathode material Li. 1.2 Ni 0.12 Co 0.12 Mn 0.56 O2.

[0080] (3) In a ball mill jar containing an inert atmosphere, 1.0 g of lithium-rich manganese-based cathode material Li was added sequentially. 1.2 Ni 0.12 Co 0.12 Mn 0.56 O2, 0.05 g SnSO4, and 17.01 g of ball milling beads were used. The mixture was ball milled at 700 rpm for 30 min, followed by a 10 min resting time. This process was repeated 12 times to obtain the coated lithium-rich manganese-based cathode material Sn-LRMO-1 with an average particle size of 4.6 μm.

[0081] Example 5

[0082] This embodiment prepares a coated lithium-rich manganese-based cathode material Sn-LRMO-2, as detailed below:

[0083] (1) 0.9 mol lithium chloride, 0.099 mol nickel sulfate, 0.099 mol cobalt sulfate and 0.405 mol manganese nitrate were added sequentially to 100 mL of deionized water. Then, 5 mL of oxalic acid and 10 mL of ammonia solution with a concentration of 6 mol / L were added dropwise at a rate of 1 mL / min. The mixture was heated to 50 °C under a nitrogen atmosphere and co-precipitated at a speed of 500 rpm for 6 h to obtain a lithium-rich manganese precursor.

[0084] (2) The lithium-rich manganese precursor was pre-sintered at 500°C for 3 hours under a nitrogen atmosphere, and then sintered at 900°C for 6 hours to obtain the lithium-rich manganese-based cathode material Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0085] (3) In a ball mill jar containing an inert atmosphere, 1.0 g of lithium-rich manganese-based cathode material Li was added sequentially. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, 0.3 g SnS2, and 23.40 g of ball milling beads were used. The mixture was ball milled at 700 rpm for 30 min, followed by a 10 min resting time. This process was repeated 12 times to obtain the coated lithium-rich manganese-based cathode material Sn-LRMO-2 with an average particle size of 5.2 μm.

[0086] Example 6

[0087] This embodiment prepares a coated lithium-rich manganese-based cathode material Sn-LRMO-3, as detailed below:

[0088] (1) 0.7 mol lithium chloride, 0.063 mol nickel sulfate, 0.077 mol cobalt sulfate and 0.327 mol manganese nitrate were added sequentially to 100 mL of deionized water. Then, 5 mL of oxalic acid and 10 mL of ammonia solution with a concentration of 6 mol / L were added dropwise at a rate of 1 mL / min. The mixture was heated to 41 °C under a nitrogen atmosphere and co-precipitated at a speed of 470 rpm for 4.6 h to obtain a lithium-rich manganese precursor.

[0089] (2) The lithium-rich manganese precursor was pre-sintered at 500°C for 3 hours under a nitrogen atmosphere, and then sintered at 900°C for 6 hours to obtain the lithium-rich manganese-based cathode material Li. 1.2 Ni 0.108 Co 0.132 Mn 0.56 O2.

[0090] (3) In a ball mill jar containing an inert atmosphere, 1.0 g of lithium-rich manganese-based cathode material Li was added sequentially. 1.2 Ni 0.108 Co0.132 Mn 0.56 O2, 0.1 g SnSO4, and 18.70 g of ball milling beads were used. The mixture was ball milled at 700 rpm for 30 min, followed by a 10 min resting time. This process was repeated 12 times to obtain the coated lithium-rich manganese-based cathode material Sn-LRMO-3 with an average particle size of 7.8 μm.

[0091] Comparative Example 1

[0092] This comparative example prepared a coated lithium-rich manganese-based cathode material Zr-LRMO-C1. The difference from Example 1 is that the addition ratio of Zr(SO4)2 in this comparative example is 40wt%, that is, 0.4g of Zr(SO4)2 is added in step (3), and the rest is the same as in Example 1. The average particle size of Zr-LRMO-C1 is 12.5μm.

[0093] Comparative Example 2

[0094] This comparative example prepared a coated lithium-rich manganese-based cathode material Zr-LRMO-C2. The difference from Example 1 is that the addition ratio of Zr(SO4)2 in this comparative example is 1wt%, that is, 0.01g of Zr(SO4)2 is added in step (3), and the rest is the same as in Example 1. The average particle size of Zr-LRMO-C2 is 10.8μm.

[0095] Comparative Example 3

[0096] This comparative example prepared a coated lithium-rich manganese-based cathode material Zr-LRMO-C3. The difference from Example 1 is that the ball milling speed in step (3) of this comparative example is 300 rpm, and the rest is the same as in Example 1. The average particle size of Zr-LRMO-C3 is 15.2 μm.

[0097] Comparative Example 4

[0098] This comparative example prepared a coated lithium-rich manganese-based cathode material Zr-LRMO-C4. The difference from Example 1 is that the ball milling speed in step (3) of this comparative example is 1500 rpm, and the rest is the same as in Example 1. The average particle size of Zr-LRMO-C4 is 2.1 μm.

[0099] Test case

[0100] 1. The crystal structure of the coated lithium-rich manganese-based cathode materials prepared in Examples 1-6 was tested using X-ray diffraction (XRD), and the results are as follows: Figure 2 As shown. Figure 2The diffraction peaks of the cathode materials in Examples 1-6 all highly coincide with the peak positions of the standard card, with no significant shift or deviation. This proves that the coating process did not destroy the layered crystal structure of LRMO, which is the core basis for LRMO's high capacity (ensuring lithium-ion insertion / extraction channels). The absence of additional impurity phase peaks indicates that the coating agent exists as an amorphous or extremely thin crystalline layer (thickness 8-20 nm; XRD has low sensitivity to thin / amorphous materials and cannot detect it). The coating process did not cause a phase transition in LRMO or generate other impurity phases, resulting in high material purity. The diffraction peak shapes and intensities of the cathode materials in each example are basically consistent, indicating that the layered structure of LRMO remains stable under different coating agent dosages and ball milling parameters. This proves that the process parameters disclosed herein have good compatibility and will not damage the crystal structure due to parameter fine-tuning.

[0101] 2. The microstructure of the coated lithium-rich manganese-based cathode materials prepared in Examples 1-6 was tested using scanning electron microscopy, and the results are as follows: Figure 3 As shown. Figure 3 As shown, Example 1 ( Figure 3 a) The particles are uniform in size, well-dispersed, and without obvious agglomeration; the surface exhibits slight densification, with no exposed rough areas. Example 2 ( Figure 3 The particle size of (b) is close to that of Example 1, with a denser surface and no localized accumulation; the dispersibility remains good. Example 3 ( Figure 3 c) A small number of small particles adhered to large particles, but no large-scale agglomeration was formed; the surface coating layer was intact. Example 4 ( Figure 3 The particle size of (d) is slightly larger, and the surface roughness is slightly stronger, but there are no exposed areas. This is because the melting point of the Sn-based coating agent is slightly different from that of the Zr-based one, and its spreadability is slightly weaker after melting, resulting in a slightly rougher surface morphology, but an effective coating layer is still formed. Example 5 ( Figure 3 (e) A thicker, denser layer forms on the surface of the particles, with slight local agglomeration. This is because the amount of coating agent is close to the upper limit, and some areas accumulate after melting, leading to slight agglomeration. However, this does not damage the integrity of the coating layer and still meets the performance requirements. Example 6 ( Figure 3 f) has slightly poor particle dispersibility and a small number of small particles agglomerate; there are localized rough areas exposed on the surface. In summary, the morphology is best (uniform particles, good dispersibility, and continuous coating layer) when the amount of coating agent is 20~28wt% and the ball milling speed is 700rpm (Examples 1 and 2).

[0102] 3. Assembly of all-solid-state batteries: (1) The coated lithium-rich manganese-based cathode materials prepared in Examples 1-6 and Comparative Examples 1-4 were mixed with LIC electrolyte and VGCF conductive agent at a mass ratio of 60:35:5, respectively, and placed in a ball mill jar. The mixture was ball-milled at a speed of 250 rpm for 30 min forward rotation - 10 min stop - 30 min reverse rotation - 10 min stop for 4 cycles to obtain a uniformly mixed composite cathode material. (2) Using a mold with a diameter of 10 mm, the batteries were assembled in sequence: 100 mg of LPSC powder was weighed and placed in the mold. After leveling, pressure was applied until the pointer moved slightly. The mixture was statically pressed for 1 min to form a dense electrolyte layer. About 4-6 mg of the composite cathode material obtained in step (1) was taken, and 2-4% of PFPE was added as a binder. The mixture was dry-rolled into a film and then punched into a cathode sheet with a diameter of 10 mm. The sheet was placed on one side of the electrolyte layer and subjected to a pressure of 250 MPa for 5 min to form a good interface. Finally, evenly spread the 10mm indium sheet and the cut 3~6mg lithium sheet on the other side of the solid electrolyte, pressurize until the pointer moves slightly, wait for 30 seconds, remove it from the pressurization device to the outside of the glove box, put on the outer stainless steel frame, and use a torque wrench to tighten the outer shell screws to 7~9 N·m to complete the battery encapsulation.

[0103] The first-cycle charge-discharge performance and rate performance of all-solid-state batteries prepared with the cathode materials of Examples 1-6 and Comparative Examples 1-4 were tested. First-cycle charge-discharge performance test: Under a constant temperature environment of 25℃, the batteries were charged and discharged at a current density of 0.1C, with the voltage range set from 1.5 to 4.0V. The voltage-capacity curves during the charging / discharging process were recorded, and the first-cycle capacity and coulombic efficiency were calculated. Rate performance test: The same batch of batteries were cycled several times at different current densities. The discharge specific capacity was recorded at each rate, and the cycle number-capacity curve was plotted. Finally, the battery was returned to 0.1C to verify its capacity recovery capability.

[0104] The test results of the all-solid-state battery in Example 1 are as follows: Figure 4 and Figure 5 As shown, Figure 4 The first charge-discharge curve shows that the first discharge capacity is 292.04 mAh / g, which is close to the theoretical capacity. This indicates that the Zr(SO4)2 coating did not block the lithium-ion transport channels and fully preserved the high capacity characteristics of the lithium-rich material. The first coulombic efficiency is 92.1%, which proves that the coating layer effectively isolates LRMO from the sulfide electrolyte and reduces capacity loss caused by side reactions such as surface residual alkali reaction with electrolyte and transition metal dissolution. Figure 5 The rate performance curve shows that even at 5C (high current), the battery can still maintain a certain capacity; after returning to 0.1C, the capacity basically recovers to the initial level. This proves that the Zr-based coating not only provides a physical barrier, but also builds an efficient lithium-ion transport channel (reducing interface impedance), enabling the material to work stably under high current.

[0105] The test results of charge / discharge specific capacity and coulombic efficiency of all-solid-state batteries prepared with cathode materials of each embodiment and comparative example are shown in Table 1.

[0106] Table 1

[0107]

[0108] Table 1 shows that the Zr-based coated cathode material (Zr-LRMO-1 / -2 / -3) exhibits the best performance. This is because the Zr-based coating agent has better interfacial compatibility and ion conductivity, effectively suppressing side reactions while retaining high capacity. The Sn-based coated cathode material (Sn-LRMO-1 / -2 / -3) performs second best because the Sn-based coating agent has a weaker melting point, chemical stability, and LRMO / electrolyte matching degree compared to the Zr-based one, leading to increased side reactions and greater capacity loss. The comparative material (Zr-LRMO-C1 / -C2 / -C3 / -C4) performs the worst because the uncontrolled coating process in the comparative material prevents the formation of an effective coating layer, resulting in severe side reactions between LRMO and the electrolyte, and a significant decrease in capacity and coulombic efficiency.

[0109] 4. Accurately weigh 100 mg of the composite cathode powder prepared in Part 3 of the test example and place it in a mold cavity with an inner diameter of 10 mm. Then, cover the upper and lower surfaces of the powder with a 10 mm diameter carbon-coated aluminum foil as electrodes for electron conduction and lithium-ion blocking. Finally, maintain a pressure of 250 MPa for 10 min to complete the integrated molding and interface contact optimization of the symmetrical battery (blocking electrode). Connect the assembled battery to an electrochemical workstation and perform IT curve testing under constant voltage.

[0110] Formula for calculating ionic conductivity: σ i =

[0111] Where, σ i Ω is the ionic conductivity, in mS / cm; L is the thickness of the electrolyte sheet, in cm; R is the impedance, in Ohm; r is the radius of the electrode sheet, in cm.

[0112] Formula for calculating electronic conductivity: σ =

[0113] Where σ is the electronic conductivity, in units of S / cm; L is the thickness of the electrolyte sheet, in units of cm; I is the current, in units of A; U is the voltage, in units of V; and r is the radius of the electrode sheet, in units of cm.

[0114] The ionic conductivity and electronic conductivity of the symmetric battery prepared by the coated cathode material in Example 1 were tested using the above method. The test results are as follows: Figure 6 As shown. Figure 6 In the figure, the IT curve of lithium-ion conductivity ( Figure 6 As shown in (a), the current gradually decreases over time and eventually stabilizes (current approaches 0), reflecting the strong transport capability of lithium ions. The IT curve of electronic conductivity (…) Figure 6 As shown in (b), the current gradually decreases over time and then stabilizes, with a relatively high final stable current, demonstrating excellent electron transport capability. In summary, the coated cathode material of Example 1 possesses both good lithium-ion conductivity and excellent electronic conductivity.

[0115] Meanwhile, the ionic conductivity and electronic conductivity of the symmetric batteries prepared by the coated cathode materials of Examples 1-6 and Comparative Examples 1-4 were tested using the above method, and the test results are shown in Table 2.

[0116] Table 2

[0117]

[0118] Table 2 shows that the ionic and electronic conductivity of the Zr-based coated material (Zr-LRMO-1 / -2 / -3) is generally higher than that of the Sn-based (Sn-LRMO-1 / -2 / -3) and the comparative example (Zr-LRMO-C1 / -C2 / -C3 / -C4), which is the core kinetic basis for its high rate performance and high cycle capacity. The difference in conductivity between the examples and the comparative examples further verifies that process parameters such as coating agent dosage of 5~30wt% and ball milling speed of 700~1000rpm are necessary conditions to ensure conductivity.

[0119] The above systematic electrochemical performance tests on the coated lithium-rich manganese-based cathode materials of Examples 1-6 and Comparative Examples 1-4 show that the Zr(SO4)2-coated LRMO cathode materials prepared using the in-situ coating method of the low-melting-point coating agent disclosed in this invention, within the preferred process parameter range, exhibit excellent electrochemical performance in all-solid-state batteries, including high first-cycle coulombic efficiency, high lithium-ion conductivity and electronic conductivity, and good interfacial compatibility. In contrast, the comparative examples showed a significant performance decline due to excessively high or low coating content and deviations from the preferred ball milling process parameters, further verifying the rationality of the process parameter range and the necessity of the key technical features of this disclosure. This disclosure provides an effective material design and preparation path for the practical application of highly stable, highly interfacially compatible lithium-rich manganese-based cathode materials in all-solid-state batteries.

[0120] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this disclosure can be achieved, and this is not limited herein.

[0121] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0122] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for preparing a coated lithium-rich manganese-based cathode material, characterized in that, Includes the following steps: S1: Lithium salt, manganese salt, cobalt salt, and nickel salt are mixed and subjected to a co-precipitation reaction, followed by sintering to obtain lithium-rich manganese-based cathode material Li. 1.2 Ni x Co y Mn z O2, among which, x=0.10~0.13, y=0.09~0.13, z=0.54~0.61, x+y+z=0.8; S2: The lithium-rich manganese-based cathode material Li 1.2 Ni x Co y Mn z O2 and a coating agent are mixed and ball-milled to obtain the coated lithium-rich manganese-based cathode material; the lithium-rich manganese-based cathode material Li 1.2 Ni x Co y Mn z The mass ratio of O2 to the coating agent is 100:5~30, and the coating agent is selected from at least one of SnS2, SnSO4, Zr(SO4)2, and Zr(NO3)4; the ball-to-material ratio of the ball mill is 15~18:1; the ball milling process includes: reacting at a speed of 700~1000 rpm for 25~35 min under an inert atmosphere, followed by standing for 8~12 min; the above steps are repeated for 12~24 cycles.

2. The preparation method according to claim 1, characterized in that, In step S1, the lithium salt is selected from at least one of lithium hydroxide, lithium chloride, and lithium nitrate; The manganese salt is selected from at least one of manganese sulfate, manganese nitrate, and manganese acetate; The cobalt salt is selected from at least one of cobalt sulfate, cobalt nitrate, and cobalt acetate; The nickel salt is selected from at least one of nickel sulfate, nickel nitrate, and nickel acetate; The molar ratio of lithium ions in lithium salts, manganese ions in manganese salts, cobalt ions in cobalt salts, and nickel ions in nickel salts is 1:0.45~0.51:0.075~0.11:0.083~0.

11.

3. The preparation method according to claim 1, characterized in that, Step S1 involves mixing lithium salt, manganese salt, cobalt salt, nickel salt with a precipitant and a complexing agent to carry out the coprecipitation reaction; The precipitant is selected from oxalic acid; The complexing agent is selected from at least one of ammonia, ethylenediamine, diethylenetriamine, citric acid, tartaric acid, and ethylenediaminetetraacetic acid; The molar ratio of the precipitant to the lithium salt is 0.00556~0.01:1, and the molar ratio of the complexing agent to the lithium salt is 0.0667~0.12:

1.

4. The preparation method according to claim 1, characterized in that, The conditions for the coprecipitation reaction include: under an inert atmosphere, at a temperature of 40-50°C and a rotation speed of 300-500 rpm for 4-6 hours.

5. The preparation method according to claim 1, characterized in that, The sintering conditions described in step S1 include: pre-sintering at a temperature of 400~600℃ for 2~4 hours under an inert atmosphere, followed by sintering at 800~1000℃ for 5~7 hours.

6. The coated lithium-rich manganese-based cathode material prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The coated lithium-rich manganese-based cathode material includes lithium-rich manganese-based cathode material Li 1.2 Ni x Co y Mn z O2, where x = 0.10~0.13, y = 0.09~0.13, z = 0.54~0.61, x+y+z = 0.8, and Li coated on the lithium-rich manganese-based cathode material. 1.2 Ni x Co y Mn z The outer coating of O2.

7. The coated lithium-rich manganese-based cathode material according to claim 6, characterized in that, The thickness of the coating layer is 8~20nm.

8. An all-solid-state battery, characterized in that, The all-solid-state battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes the coated lithium-rich manganese-based positive electrode material as described in any one of claims 6 to 7.

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