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

Abstract

The invention belongs to the technical field of solid-state batteries, and provides a coated lithium-rich manganese-based positive electrode material as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing a lithium salt, a manganese salt, a cobalt salt and a nickel salt, carrying out a co-precipitation reaction, and sintering to obtain the lithium-rich manganese-based positive electrode material LRMO; the LRMO and the coating agent are mixed and subjected to ball milling, and the mass ratio of the LRMO to the coating agent is 100: (5-30). The invention also discloses the coated lithium-rich manganese-based positive electrode material prepared by the method and an all-solid-state battery, and the positive electrode of the battery comprises the coated lithium-rich manganese-based positive electrode material. The structural stability and interface compatibility of the LRMO are optimized by adjusting the content of the coating agent and the parameters of the ball milling process. The obtained coated positive electrode material can effectively stabilize Li-O-Li configuration, inhibit lattice oxygen release and transition metal dissolution, improve the interface matching with electrolyte, and significantly improve the cycle capacity retention ratio and voltage attenuation characteristic of the all-solid-state battery.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of solid-state batteries, in particular to a coated lithium-rich manganese-based positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] With the increasing demand for high energy density and long cycle life of full solid-state batteries in the new energy field, lithium-rich manganese-based positive electrode materials (LRMO) have a "Li2MnO3-LiMO2 (M is Ni, Co, etc.)" layered solid solution structure, a theoretical specific capacity of more than 250 mAh / g, and excellent voltage platform, becoming one of the core candidates for full solid-state battery positive electrode materials, and is widely considered as a key direction to break through the energy density bottleneck of traditional lithium-ion batteries.

[0003] However, LRMO has unavoidable technical defects in the actual application of full solid-state batteries: first, during the charging and discharging cycle process, it is prone to irreversible structural transformation from "layered to spinel to rock salt phase", accompanied by the release of a large amount of lattice oxygen and the dissolution of transition metal ions (Mn 2+ , Co 3+ , etc.), which directly leads to rapid cycle capacity decay and significant voltage decay of the battery, severely restricting the service life of the battery; second, the residual alkaline substances (such as LiOH, Li2CO3) on the surface of LRMO are prone to interface side reactions with sulfide solid-state electrolytes (such as LPSC, LPS, etc.), generating high-impedance products, leading to a sharp increase in interface impedance, significantly reducing ion transport kinetics, and thus affecting the rate performance and energy output efficiency of the full solid-state battery.

[0004] To solve the above problems, related technologies often use oxide coating (such as Al2O3, TiO2) or carbon-based coating to modify LRMO, but all have obvious limitations: the mechanical matching of oxide coating with LRMO matrix is poor, and cracks are easily generated due to volume changes during the cycle process, which cannot long-term inhibit side reactions; carbon-based coating can improve electronic conductivity, but has limited inhibitory effect on lattice oxygen release, and the chemical compatibility of carbon materials with sulfide solid-state electrolytes is insufficient, which easily exacerbates the interface impedance problem. In addition, the current modification methods often require multiple high-temperature treatments or rely on complex equipment such as magnetron sputtering, which is complicated, high in cost, and difficult to precisely control the thickness and uniformity of the coating layer, with poor adaptability, making it difficult to meet the needs of full solid-state battery mass production.

[0005] Therefore, developing a modification technology that can form a uniform and dense coating layer in situ, solve the two core problems of "structural instability" and "interface incompatibility" of LRMO, and has a simple process and is easy to industrialize, has become a key demand to promote the practicality of lithium-rich manganese-based positive electrode materials in full solid-state batteries. SUMMARY

[0006] The present disclosure provides a coated lithium-rich manganese-based positive electrode material and a preparation method and application thereof, to at least solve the above technical problems in the prior art.

[0007] According to a first aspect of the present disclosure, a preparation method of a coated lithium-rich manganese-based positive electrode material is provided, comprising the following steps: S1: mixing lithium salt, manganese salt, cobalt salt and nickel salt to perform a co-precipitation reaction, and then sintering to obtain a lithium-rich manganese-based positive electrode material Li 1.2 Ni x Co y Mn z O2 (LRMO), wherein x = 0.10-0.13, y = 0.09-0.13, z = 0.54-0.61, and x+y+z = 0.8; S2: mixing the lithium-rich manganese-based positive electrode material Li 1.2 Ni x Co y Mn z O2 with a coating agent and ball milling to obtain the coated lithium-rich manganese-based positive electrode material; the mass ratio of the lithium-rich manganese-based positive electrode material Li 1.2 Ni x Co y Mn z 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.

[0008] Specifically, the above-mentioned coating agent is a low-melting-point coating agent, and its core advantages are as follows: (1) The key feature of the low-melting-point coating agent is that the melting point is lower than the structural stability temperature of the LRMO (to avoid the phase transition of the LRMO layered structure), and it can quickly melt under the frictional heat energy of high-energy ball milling, without the need for an additional high-temperature sintering step, and a uniform coating layer is directly formed on the surface of the LRMO particles. Compared with the prior art (such as Al2O3, TiO2, and other oxide coatings), the traditional high-melting-point coating agent needs to be separately heat-treated to form a coating layer, which not only has a complicated process, but also easily leads to the agglomeration or structural damage of the LRMO particles; while the low-melting-point coating agent can realize in-situ melting and coating through the frictional heat generated in the ball milling process, which simplifies the process while ensuring the close combination of the coating layer and the LRMO matrix, and avoids the peeling off of the coating layer during the cycling process. (2) The low-melting-point coating agent uniformly covers the surface of the LRMO after melting, and forms a continuous and dense coating layer after cooling, which physically isolates the LRMO and the electrolyte, inhibits the release of lattice oxygen and the dissolution of transition metal ions, and blocks the irreversible transformation of "layered phase → spinel phase → rock salt phase". In addition, the decomposition products of the Zr-based coating agent can form stable Zr-O-Mn / Co / Ni coordination bonds with the surface of the LRMO, while avoiding the direct reaction of the residual alkali (LiOH, Li2CO3) on the surface of the LRMO with the sulfide electrolyte, reducing the interfacial impedance; and the Zr-based coating agent itself has ion conduction characteristics, which can build an efficient lithium ion transport channel and improve the ion transport kinetics. (3) The amount of the low-melting-point coating agent is controllable, which can form an effective protective layer while avoiding excessive occupation of the active material proportion, and guarantee the high-capacity advantage of the LRMO; the raw materials of the coating agent are easy to obtain, and the preparation process only needs conventional equipment such as a ball mill, without the need for complex instruments such as a magnetron sputtering, and the process parameters are easy to quantitatively control, which is suitable for large-scale production.

[0009] The proportion of the coating agent directly determines the coating effect and battery performance. The range of 5-30wt% is derived based on the balance of 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 the LRMO particles after melting, avoiding the side reactions caused by the exposed area; (2) ensuring the proportion of active material: LRMO is the core source of battery capacity, and the coating agent is a non-active material. A proportion of ≤30wt% can avoid a significant decrease in capacity caused by a low proportion of active material; (3) optimizing the interface impedance: the coating layer formed by the Zr-based coating agent in the above range can minimize the interface side reactions between LRMO and electrolyte, and the ion conduction characteristics of the coating agent itself can reduce the interface impedance and improve the cycle stability of the battery. If the proportion of the coating agent is too high, i.e., exceeds 30wt%, the proportion of active material LRMO will be significantly reduced, directly leading to a decrease in battery discharge capacity; a too thick coating layer will hinder the transmission of lithium ions between LRMO and electrolyte, resulting in a decrease in ionic conductivity and a deterioration in rate performance; an excessive amount of coating agent is prone to accumulate on the surface of the particles, leading to agglomeration of LRMO particles and further deteriorating the electrochemical performance. If the proportion of the coating agent is too low, i.e., less than 5wt%, a continuous coating layer cannot be formed, and there are a large number of exposed areas that cannot effectively isolate LRMO and electrolyte; the exposed areas will still release lattice oxygen, dissolve transition metals, and cause interface side reactions, leading to rapid cycle capacity decay and severe voltage decay of the battery; the discontinuous coating layer cannot prevent the reaction between residual alkali on the surface of LRMO and electrolyte, and the generation of high impedance products will significantly increase the interface impedance.

[0010] In a preferred embodiment, the coating agent is selected from at least one of Zr(SO4)2, Zr(NO3)4.

[0011] In a preferred embodiment, the lithium-rich manganese-based positive electrode material Li 1.2 Ni x Co y Mn z The mass ratio of Li2MnO2 to the coating agent is 100:20-28.

[0012] In an implementable embodiment, the lithium salt is selected from at least one of lithium hydroxide, lithium chloride, lithium carbonate, lithium oxalate, and lithium nitrate.

[0013] In an implementable embodiment, the manganese salt is selected from at least one of manganese sulfate, manganese nitrate, manganese carbonate, and manganese acetate.

[0014] In an implementable embodiment, the cobalt salt is selected from at least one of cobalt sulfate, cobalt nitrate, cobalt carbonate, and cobalt acetate.

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

[0016] In an implementation, 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.

[0017] In an implementation, the lithium-rich manganese-based positive electrode material Li 1.2 Ni x Co y Mn z O2, the total molar amount of manganese ions in the manganese salt, cobalt ions in the cobalt salt, and nickel ions in the nickel salt is 0.8 mol.

[0018] In an implementation, step S1 mixes the lithium salt, the manganese salt, the cobalt salt, the nickel salt, the precipitant, and the complexing agent to perform the coprecipitation reaction.

[0019] Specifically, the precipitant is selected from at least one of oxalic acid, ammonium bicarbonate, ammonium carbonate, and ammonium dihydrogen phosphate.

[0020] The core function of the precipitant is to react with Li + , Ni 2+ , Co 2+ , and Mn 2+ ions in the solution to generate stable solid coprecipitation, providing a molecularly mixed raw material basis for the formation of the LRMO layered structure in subsequent sintering.

[0021] Specifically, the complexing agent is selected from at least one of ammonia, ethylenediamine, diethylenetriamine, citric acid, tartaric acid, and ethylenediaminetetraacetic acid.

[0022] The core function of the complexing agent is to form stable complexes with transition metal ions such as Ni 2+ , Co 2+ , etc., to slow down the reaction rate with the precipitant, and to avoid precursor particle agglomeration and uneven particle size caused by excessive local ion concentration.

[0023] Specifically, the molar ratio of the precipitant to the lithium salt is 0.00556-0.01:1.

[0024] Specifically, the molar ratio of the complexing agent to the lithium salt is 0.0667-0.12:1.

[0025] Specifically, step S1 dissolves the lithium salt, the manganese salt, the cobalt salt, and the nickel salt in a solvent, and adds the precipitant and the complexing agent to form a mixed solution.

[0026] Specifically, the solvent is selected from water.

[0027] Specifically, the amount of lithium salt added is 0.5-0.9 mol relative to 100 mL of water.

[0028] Specifically, the conditions of the co-precipitation reaction include: under an inert atmosphere, at a temperature of 40-50°C, a rotation speed of 300-500 rpm, and for 4-6 h.

[0029] In an embodiment, the sintering conditions of step S1 include: under an inert atmosphere, pre-sintering at a temperature of 400-600°C for 2-4 h, and sintering at a temperature of 800-1000°C for 5-7 h.

[0030] In a preferred embodiment, the sintering conditions of step S1 include: under an inert atmosphere, pre-sintering at a temperature of 500°C for 3 h, and sintering at a temperature of 900°C for 6 h.

[0031] In an embodiment, the ball-to-material ratio of the ball milling of step S2 is 15-18:1.

[0032] In a preferred embodiment, the ball-to-material ratio of the ball milling of step S2 is 15-16:1.

[0033] In an embodiment, the ball milling process of step S2 includes: under an inert atmosphere, at a rotation speed of 700-1000 rpm for 25-35 min, followed by standing for 8-12 min; the above steps are repeated for 12-24 cycles.

[0034] Specifically, the inert atmosphere is any one of dry argon or helium, wherein the water content is ≤0.1 ppm and the oxygen content is ≤0.1 ppm. Preferably, argon is used as the protective atmosphere, which can effectively prevent the low-melting-point coating agent from undergoing hydrolysis or oxidation reactions, thereby ensuring the integrity of the coating layer.

[0035] In a preferred embodiment, the above steps are repeated for 16-18 cycles.

[0036] Specifically, under the above conditions, the frictional heat generated during the ball milling process ensures that the low-melting-point coating agent melts and partially decomposes, while avoiding phase transitions of the LRMO layered structure. In addition, high-energy ball milling can not only ensure grinding efficiency to achieve sufficient dispersion of the low-melting-point coating agent, but also avoid excessive grinding that damages the structure of the LRMO particles, thereby forming a uniform coating layer with a thickness of 8-20 nm on the surface of the LRMO. By adjusting the coating content and ball milling process parameters, the structural stability and interface compatibility of the coated lithium-rich manganese-based positive electrode material can be further optimized. The coated lithium-rich manganese-based 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 decay characteristics of the full solid-state battery.

[0037] 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.

[0038] In one embodiment, the thickness of the coating layer is 8~20 nm.

[0039] In one embodiment, the discharge specific capacity of the coated lithium-rich manganese-based cathode material is 209~293 mAh·g. -1 .

[0040] In a preferred embodiment, the discharge specific capacity of the coated lithium-rich manganese-based cathode material is 275~293 mAh·g. -1 .

[0041] 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.

[0042] According to one possible implementation of this disclosure, at least the following beneficial effects are achieved: 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.

[0043] 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.

[0044] In addition, the disclosure takes into account the high capacity advantage of the lithium-rich manganese-based material and the industrial feasibility of the preparation process. On the one hand, by optimizing the amount of coating agent and process parameters, the first circle discharge capacity of the coated lithium-rich manganese-based positive electrode material is close to the theoretical high capacity level of the lithium-rich manganese-based material while avoiding excessive reduction of the active material proportion. On the other hand, the preparation process uses conventional equipment such as ball milling and heat treatment, the coating agent raw material is easy to obtain, and the process parameters are easy to quantify and control. Without complex equipment such as magnetron sputtering or cumbersome processes such as multiple coating, it is beneficial to reduce production costs and improve production efficiency, and lays a material foundation for the large-scale application of high-energy-density all-solid-state batteries.

[0045] It should be understood that the content described in this part is not intended to identify key or important features of the embodiments of the disclosure, nor is it used to limit the scope of the disclosure. Other features of the disclosure will become readily apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0046] The above and other objects, features and advantages of the exemplary embodiments of the present disclosure will be more apparent from the following detailed description read in conjunction with the accompanying drawings, in which several embodiments of the present disclosure are shown by way of example, and in which: In the drawings, identical or corresponding reference numerals indicate identical or corresponding parts.

[0047] Figure 1 The SEM-EDS spectrum of the coated lithium-rich manganese-based positive electrode material Zr-LRMO-1 in Example 1 of the disclosure is shown; Figure 2 The XRD spectrum of the coated lithium-rich manganese-based positive electrode material prepared in Examples 1-6 of the disclosure is shown; Figure 3 The SEM image of the coated lithium-rich manganese-based positive electrode material prepared in Examples 1-6 of the disclosure is shown; Figure 4 The first circle charge-discharge curve of the all-solid-state battery prepared from the coated lithium-rich manganese-based positive electrode material of Example 1 of the disclosure is shown; Figure 5 The rate performance curve of the all-solid-state battery prepared from the coated lithium-rich manganese-based positive electrode material of Example 1 of the disclosure is shown; Figure 6 The I-T curve of the symmetric battery prepared from the coated lithium-rich manganese-based positive electrode material of Example 1 of the disclosure and the lithium ion conductivity and electronic conductivity test results are shown. Wherein (a) is the I-T curve and the lithium ion conductivity test results; (b) is the I-T curve and the electronic conductivity test results. DETAILED DESCRIPTION

[0048] In order to make the purposes, characteristics and advantages of the present disclosure more obvious and easy to understand, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present disclosure.

[0049] The purpose of the present disclosure is to solve the problems of structural instability, serious voltage decay, transition metal ion dissolution and high interface impedance of lithium-rich manganese-based positive electrode material Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 (LRMO) existing in all-solid-state batteries, as well as the defects of complex process and insufficient adaptability of existing modification technologies, and to provide a low-melting-point substance in-situ coated lithium-rich manganese-based positive electrode material applicable to all-solid-state batteries, a preparation method and application thereof.

[0050] The following will be specifically described through examples.

[0051] Example 1 In this embodiment, a coated lithium-rich manganese-based positive electrode material Zr-LRMO-1 is prepared as follows: (1) 0.5 mol of lithium hydroxide, 0.042 mol of nickel sulfate, 0.0375 mol of cobalt sulfate and 0.254 mol of manganese sulfate were sequentially added to 100 mL of deionized water, and then 5 mL of oxalic acid and 10 mL of ammonia water with a concentration of 6 mol / L were added dropwise at a rate of 1 mL / min. The temperature was raised to 40℃ under a nitrogen atmosphere, and the co-precipitation reaction was carried out at a rotation speed of 300 rpm for 4 h to obtain a lithium-rich manganese precursor.

[0052] (2) The lithium-rich manganese precursor was pre-sintered at a temperature of 500℃ for 3 h under a nitrogen atmosphere, and then sintered at a temperature of 900℃ for 6 h to obtain a lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.1 Co 0.09 Mn 0.61 O2.

[0053] (3) In a ball milling tank containing an inert atmosphere, 1.0 g of lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.1 Co 0.09 Mn 0.61O2, 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.

[0054] 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 sample morphology. 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.

[0055] Example 2 This embodiment prepares a coated lithium-rich manganese-based cathode material Zr-LRMO-2, as detailed below: (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.

[0056] (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 Co0.09 Mn 0.59 O2.

[0057] (3) In a ball mill tank containing inert atmosphere, 1.0 g of lithium-rich manganese-based positive material Li 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 sequentially added. Milling was carried out at a speed of 700 rpm for 30 min, followed by 10 min of rest, and the process was repeated for 18 cycles. Finally, a coated lithium-rich manganese-based positive material Zr-LRMO-2 was obtained, with an average particle size of 7.0 μm.

[0058] Example 3 In this example, a coated lithium-rich manganese-based positive material Zr-LRMO-3 was prepared as follows: (1) In 100 mL of deionized water, 0.7 mol of lithium hydroxide, 0.0595 mol of nickel sulfate, 0.0665 mol of cobalt sulfate and 0.341 mol of manganese sulfate were sequentially added. Then, 5 mL of oxalic acid and 10 mL of ammonia water with a concentration of 6 mol / L were added dropwise at a rate of 1 mL / min, and the temperature was raised to 43°C under a nitrogen atmosphere. The co-precipitation reaction was carried out at a speed of 500 rpm for 4 h, and a lithium-rich manganese precursor was obtained.

[0059] (2) The lithium-rich manganese precursor was pre-sintered at a temperature of 500°C for 3 h under a nitrogen atmosphere, and then sintered at a temperature of 900°C for 6 h. A lithium-rich manganese-based positive material Li 1.2 Ni 0.102 Co 0.114 Mn 0.584 O2.

[0060] (3) In a ball mill tank containing inert atmosphere, 1.0 g of lithium-rich manganese-based positive material Li 1.2 Ni 0.102 Co 0.114 Mn 0.584 O2, 0.24 g of Zr(NO3)4 and 19.22 g of ball milling beads were sequentially added. Milling was carried out at a speed of 700 rpm for 30 min, followed by 10 min of rest, and the process was repeated for 17 cycles. Finally, a coated lithium-rich manganese-based positive material Zr-LRMO-3 was obtained, with an average particle size of 8.9 μm.

[0061] Example 4 In this example, a coated lithium-rich manganese-based positive material Sn-LRMO-1 was prepared as follows: (1) 0.6 mol lithium chloride, 0.06 mol nickel sulfate, 0.06 mol cobalt sulfate and 0.28 mol manganese sulfate were sequentially added into 100 mL deionized water, then 5 mL oxalic acid and 10 mL ammonia water with a concentration of 6 mol / L were added dropwise at a rate of 1 mL / min, and the temperature was raised to 45°C under a nitrogen atmosphere, and co-precipitation reaction was carried out at a rotation speed of 400 rpm for 5 h to obtain a lithium-rich manganese precursor.

[0062] (2) The lithium-rich manganese precursor was pre-sintered at a temperature of 500°C for 3 h under a nitrogen atmosphere, and then sintered at a temperature of 900°C for 6 h to obtain a lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.12 Co 0.12 Mn 0.56 O2.

[0063] (3) In a ball mill tank containing an inert atmosphere, 1.0 g of the lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.12 Co 0.12 Mn 0.56 O2, 0.05 g of SnSO4 and 17.01 g of ball milling beads were sequentially added. Ball milling was carried out at a rotation speed of 700 rpm for 30 min, followed by standing for 10 min, and the process was repeated for 12 cycles to finally obtain a coated lithium-rich manganese-based positive electrode material Sn-LRMO-1 with an average particle size of 4.6 μm.

[0064] Example 5 A coated lithium-rich manganese-based positive electrode material Sn-LRMO-2 was prepared in this example as follows: (1) 0.9 mol lithium chloride, 0.099 mol nickel sulfate, 0.099 mol cobalt sulfate and 0.405 mol manganese nitrate were sequentially added into 100 mL deionized water, then 5 mL oxalic acid and 10 mL ammonia water with a concentration of 6 mol / L were added dropwise at a rate of 1 mL / min, and the temperature was raised to 50°C under a nitrogen atmosphere, and co-precipitation reaction was carried out at a rotation speed of 500 rpm for 6 h to obtain a lithium-rich manganese precursor.

[0065] (2) The lithium-rich manganese precursor was pre-sintered at a temperature of 500°C for 3 h under a nitrogen atmosphere, and then sintered at a temperature of 900°C for 6 h to obtain a lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0066] (3) In a ball mill tank containing an inert atmosphere, 1.0 g of the lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54Li2.2Mn0.4Ni0.2Co0.2O2, 0.3 g of SnS2, and 23.40 g of ball milling beads. Milling was performed at a rotation speed of 700 rpm for 30 min, followed by 10 min of rest. This process was repeated for 12 cycles, and finally, a coated lithium-rich manganese-based positive electrode material Sn-LRMO-2 was obtained, with an average particle size of 5.2 μm.

[0067] Example 6 In this example, a coated lithium-rich manganese-based positive electrode material Sn-LRMO-3 was prepared as follows: (1) 0.7 mol of lithium chloride, 0.063 mol of nickel sulfate, 0.077 mol of cobalt sulfate, and 0.327 mol of manganese nitrate were sequentially added to 100 mL of deionized water, followed by dropwise addition of 5 mL of oxalic acid and 10 mL of ammonia water with a concentration of 6 mol / L at a rate of 1 mL / min. The co-precipitation reaction was performed at a rotation speed of 470 rpm for 4.6 h under a nitrogen atmosphere, and the temperature was raised to 41 °C. A lithium-rich manganese precursor was obtained.

[0068] (2) The lithium-rich manganese precursor was pre-sintered at a temperature of 500 °C for 3 h under a nitrogen atmosphere, and then sintered at a temperature of 900 °C for 6 h. A lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.108 Co 0.132 Mn 0.56 O2.

[0069] (3) In a ball milling tank containing an inert atmosphere, 1.0 g of the lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.108 Co 0.132 Mn 0.56 O2, 0.1 g of SnSO4, and 18.70 g of ball milling beads were sequentially added. Milling was performed at a rotation speed of 700 rpm for 30 min, followed by 10 min of rest. This process was repeated for 12 cycles, and finally, a coated lithium-rich manganese-based positive electrode material Sn-LRMO-3 was obtained, with an average particle size of 7.8 μm.

[0070] Comparative Example 1 In this comparative example, a coated lithium-rich manganese-based positive electrode material Zr-LRMO-C1 was prepared. The difference between this comparative example and Example 1 is that the addition ratio of Zr(SO4)2 in this comparative example was 40 wt%, i.e., 0.4 g of Zr(SO4)2 was added in step (3), and the rest was the same as in Example 1. The average particle size of Zr-LRMO-C1 was 12.5 μm.

[0071] Comparative Example 2 A coated lithium-rich manganese-based positive electrode material Zr-LRMO-C2 was prepared in the present comparative example, which was different from Example 1 in that the addition ratio of Zr(SO4)2 was 1wt% in the present comparative example, that is, 0.01g of Zr(SO4)2 was added in step (3), and the rest was the same as Example 1. The average particle size of Zr-LRMO-C2 was 10.8μm.

[0072] Comparative Example 3 A coated lithium-rich manganese-based positive electrode material Zr-LRMO-C3 was prepared in the present comparative example, which was different from Example 1 in that the rotation speed of ball milling in step (3) was 300rpm in the present comparative example, and the rest was the same as Example 1. The average particle size of Zr-LRMO-C3 was 15.2μm.

[0073] Comparative Example 4 A coated lithium-rich manganese-based positive electrode material Zr-LRMO-C4 was prepared in the present comparative example, which was different from Example 1 in that the rotation speed of ball milling in step (3) was 1500rpm in the present comparative example, and the rest was the same as Example 1. The average particle size of Zr-LRMO-C4 was 2.1μm.

[0074] Test Example 1. The crystal structure of the coated lithium-rich manganese-based positive electrode materials prepared in Examples 1-6 was tested by X-ray diffraction test (XRD), and the results are shown in Figure 2 . Figure 2 It is shown that the diffraction peaks of the positive electrode materials of Examples 1-6 are all highly consistent with the peak position of the standard card, without obvious deviation or shift, which proves that the coating process does not destroy the layered crystal structure of LRMO, and the layered structure is the core basis of the high capacity of LRMO (guaranteeing the embedding / extraction channel of lithium ions). There is no additional impurity phase peak, which proves that the coating agent exists in the form of amorphous or extremely thin crystalline layer (thickness 8-20nm, XRD has low sensitivity to thin / amorphous materials and cannot be detected); the coating process does not cause phase change of LRMO or generate other impurity phases, and the material has high purity. The peak shape and strength of the diffraction peaks of the positive electrode materials of each example are basically consistent, which indicates that the layered structure of LRMO remains stable under different coating agent amounts and ball milling parameters, and proves that the process parameters of the present disclosure have good compatibility and will not destroy the crystal structure due to parameter adjustment.

[0075] 2. The microstructure of the coated lithium-rich manganese-based positive electrode materials prepared in Examples 1-6 was tested by scanning electron microscope, and the results are shown in Figure 3 . Figure 3 It is shown that the particle size of Example 1 ( Figure 3 a) is uniform, has good dispersibility, and has no obvious agglomeration; the surface is slightly densified, and there is no exposed rough area. The particle size of Example 2 ( Figure 3The particle size of b) is close to that of Example 1, the surface is more compact, and there is no local accumulation; the dispersibility is still good. Example 3 ( Figure 3 c) has a small amount of small particles attached to large particles, but does not form large-scale agglomeration; the surface coating layer is complete. Example 4 ( Figure 3 d) has slightly larger particle size, and the surface feels slightly rough, but there are no exposed areas, because the melting point of the Sn-based coating agent is slightly different from that of the Zr-based one, and the spreading after melting is slightly weaker, resulting in a slightly rough surface morphology, but an effective coating layer is still formed. Example 5 ( Figure 3 e) has a thicker and more compact layer on the surface of the particles, and there is slight agglomeration in some areas, which is due to the use of the coating agent close to the upper limit, and the accumulation in some areas after melting, resulting in slight agglomeration, but the integrity of the coating layer is not damaged, and still meets the performance requirements. Example 6 ( Figure 3 f) has slightly poor particle dispersibility, with a small amount of small particle agglomeration; the surface has locally exposed rough areas. In summary, when the coating agent dosage is 20-28wt% and the ball milling speed is 700rpm (Examples 1 and 2), the morphology is best (uniform particles, good dispersibility, and continuous coating layer).

[0076] 3. Assemble the all-solid-state battery: (1) Mix the coated lithium-rich manganese-based positive electrode material prepared in Examples 1-6 and Comparative Examples 1-4 with LIC electrolyte and VGCF conductive agent in a mass ratio of 60:35:5, place them in a ball milling jar, and mill them at a speed of 250 rpm for 4 cycles of "forward rotation for 30 min - stop for 10 min - reverse rotation for 30 min - stop for 10 min", to obtain a uniformly mixed composite positive electrode material. (2) Use a 10mm diameter mold to assemble the battery: weigh 100mg of LPSC powder into the mold, shake it flat, and apply pressure to the pointer until it is slightly moving, and then press it for 1min to form a dense electrolyte layer. Take about 4-6mg of the composite positive electrode material prepared in step (1), add 2-4% PFPE as a binder, dry roll it into a film, and punch it into a 10mm diameter positive electrode sheet, place it on one side of the electrolyte layer, apply a pressure of 250MPa for 5min to form a good interface. Finally, evenly spread 10mm of indium sheet and 3-6mg of lithium sheet on the other side of the solid electrolyte, apply pressure to the pointer until it is slightly moving, and then remove it from the press to the glove box, cover it with an outer stainless steel frame, and tighten the screws to 7-9N·m using a torque wrench, and the battery is complete.

[0077] The first circle charge-discharge performance and rate performance of the full solid-state battery prepared by the positive electrode material of Examples 1-6 and Comparative Examples 1-4 were tested. The first circle charge-discharge performance test: in a constant temperature environment of 25°C, transverse flow charge-discharge was carried out at a current density of 0.1C, the voltage interval was set to 1.5-4.0V, the voltage-capacity curve of the charge / discharge process was recorded, and the first circle capacity and coulombic efficiency were calculated. The rate performance test: the same batch of batteries were cycled for several cycles at different current densities in turn, the discharge specific capacity at each rate was recorded, and the cycle number-capacity curve was drawn; finally, the capacity recovery ability of the battery was verified at 0.1C.

[0078] The test results of the full solid-state battery of Example 1 are shown in Figure 4 and Figure 5 , Figure 4 is the first circle charge-discharge curve, it can be seen that the first circle discharge capacity is 292.04mAh / g, close to the theoretical capacity, indicating that the Zr(SO4)2coating does not block the lithium ion transmission channel and completely retains the high capacity characteristics of the lithium-rich material; the first circle coulombic efficiency is 92.1%, which proves that the coating layer effectively isolates the LRMO and the sulfide electrolyte, reduces the capacity loss caused by the reaction of surface residual alkali and electrolyte, transition metal dissolution and other side reactions. Figure 5 is the rate performance curve, it can be seen 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. It proves that the Zr-based coating layer not only provides a physical barrier, but also builds an efficient lithium ion transmission channel (reduces the interface impedance), so that the material can still work stably at high current.

[0079] The test results of the charge-discharge specific capacity and coulombic efficiency of the full solid-state battery prepared by the positive electrode material of each example and comparative example are shown in Table 1.

[0080] Table 1

[0081] Table 1 shows that the performance of the Zr-based coated positive electrode material (Zr-LRMO-1 / -2 / -3) is the best, which is because the interface compatibility and ion conductivity of the Zr-based coating agent are better, which can effectively inhibit the side reaction and at the same time retain high capacity. The performance of the Sn-based coated positive electrode material (Sn-LRMO-1 / -2 / -3) is the second, because the melting point and chemical stability of the Sn-based coating agent are weaker than Zr-based in matching with LRMO / electrolyte, which leads to an increase in side reactions and greater capacity loss. The performance of the material of the comparative example (Zr-LRMO-C1 / -C2 / -C3 / -C4) is the worst, because the out-of-control coating process of the comparative example material leads to the failure to form an effective coating layer, which leads to severe side reactions between LRMO and electrolyte, and a significant decay of capacity and coulombic efficiency.

[0082] 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.

[0083] Formula for calculating ionic conductivity: σ i =

[0084] 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.

[0085] Formula for calculating electronic conductivity: σ =

[0086] 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.

[0087] 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.

[0088] 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.

[0089] Table 2

[0090] Table 2 shows that the ion and electron conductivity of the Zr-based coating material (Zr-LRMO-1 / -2 / -3) is overall higher than that of the Sn-based (Sn-LRMO-1 / -2 / -3) and the comparative examples (Zr-LRMO-C1 / -C2 / -C3 / -C4), which is the core kinetic basis for its high rate performance and high cycle capacity. The conductivity difference between the examples and the comparative examples again verifies that the process parameters such as the amount of coating agent 5-30wt%, the ball milling speed 700-1000rpm are necessary conditions to ensure the conductivity.

[0091] The above through the systematic electrochemical performance test of the coated lithium-rich manganese-based positive electrode material of examples 1-6 and comparative examples 1-4, the results show that: using the low melting point coating agent in-situ coating method of the disclosure, the Zr(SO4)2coated LRMO positive electrode material prepared in the preferred process parameter range shows excellent electrochemical performance in the full solid-state battery, including high first cycle coulomb efficiency, higher lithium ion conductivity and electronic conductivity, and good interface compatibility. In the comparative examples, due to the too high or too low coating content, the ball milling process parameters deviate from the preferred range, resulting in a significant decrease in performance, further verifying the rationality of the process parameter range and the necessity of the key technical features of the disclosure. The disclosure provides an effective material design and preparation path for the practical application of lithium-rich manganese-based positive electrode materials with high stability and high interface compatibility in full solid-state batteries.

[0092] It should be understood that the various forms of flow shown above can be reordered, added, or deleted steps. For example, each step described in the disclosure can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions of the disclosure can be achieved, which is not limited herein.

[0093] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the disclosure, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0094] The above is only a specific embodiment of the disclosure, but the protection scope of the disclosure is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the disclosure. Therefore, the protection scope of the disclosure should be subject to the protection 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.

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, lithium carbonate, lithium oxalate, and lithium nitrate; The manganese salt is selected from at least one of manganese sulfate, manganese nitrate, manganese carbonate, and manganese acetate; The cobalt salt is selected from at least one of cobalt sulfate, cobalt nitrate, cobalt carbonate, and cobalt acetate; The nickel salt is selected from at least one of nickel sulfate, nickel nitrate, nickel carbonate, 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 at least one of oxalic acid, ammonium bicarbonate, ammonium carbonate, and ammonium dihydrogen phosphate. 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 preparation method according to claim 1, characterized in that, The ball-to-material ratio in step S2 is 15-18:

1.

7. The preparation method according to claim 1, characterized in that, The ball milling process described 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; repeating the above steps for 12-24 cycles.

8. The coated lithium-rich manganese-based cathode material prepared by the preparation method according to any one of claims 1 to 7, 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.

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

10. 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 8 to 9.

Images