Composite positive electrode material for solid-state lithium battery as well as preparation method and application of composite positive electrode material

Abstract

The invention relates to the technical field of solid-state lithium battery positive electrode materials, in particular to a composite positive electrode material for a solid-state lithium battery and a preparation method and application of the composite positive electrode material. The composite positive electrode material comprises a lithium-rich manganese-based positive electrode material and a Li-Al-Ti-O layer coated on the surface of the lithium-rich manganese-based positive electrode material through an atomic layer deposition technology; the lithium-rich manganese-based positive electrode material is micron-sized and meets the condition that D50 is greater than or equal to 1 mu m and less than or equal to 10 mu m, the thickness of a Li-Al-Ti-O layer is 1-10 nm, and the Li-Al-Ti-O layer comprises the following elements in atomic percent: 1-30 at% of Li, 5-40 at% of Al, 5-40 at% of Ti and the balance of O; the Li-Al-Ti-O layer simultaneously plays triple roles of an ion transmission bridge, a physical contact enhancement layer and a chemical isolation layer, the specific capacity of the all-solid-state battery assembled by adopting the composite positive electrode material is remarkably improved, and the capacity retention ratio is greater than or equal to 98.5% after 100 times of circulation at room temperature of 0.5 DEG C.

Description

Technical Field

[0001] This invention relates to the field of solid-state lithium battery cathode material technology, and in particular to a composite cathode material for solid-state lithium batteries, its preparation method, and its application. Background Technology

[0002] Lithium-rich manganese-based cathode materials (xLi₂MnO₃•(1-x)LiMO₂, where M represents Ni, Co, Mn, etc.) are considered key cathode materials for next-generation high-energy-density lithium-ion batteries due to their high specific capacity (>250 mAh / g) and high operating voltage. However, in liquid batteries, lithium-rich manganese-based cathode materials face challenges such as interfacial side reactions, transition metal dissolution, and voltage decay.

[0003] Existing technologies employ atomic layer deposition (ALD) to deposit coatings such as Al2O3 and ZrO3 on the surface of cathode materials to improve interfacial stability. This approach is designed for the "solid-liquid interface" characteristics of liquid batteries. Through in-depth research, this invention reveals that directly applying surface modification strategies from liquid batteries to solid-state batteries has limited effectiveness and may even be counterproductive. This is because the "solid-solid interface" of solid-state batteries differs fundamentally from that of liquid batteries: First, the physical contact mechanisms differ: liquid electrolytes can flow and fill pores, while the contact between the solid electrolyte and the cathode is rigid, exhibiting inherent contact resistance and prone to "contact delamination"; Second, the ion transport paths differ: ions in liquid systems can bypass the electrolyte, while ion transport in solid systems is strictly limited to the solid-solid contact point, especially at the micrometer scale; Third, the interfacial stability requirements differ: local coating defects in liquid systems can be compensated for by the electrolyte, while any coating defect in a solid system becomes a "hotspot" for side reactions.

[0004] Therefore, there is an urgent need for a cathode modification scheme specifically designed for the solid-solid interface characteristics of solid-state batteries. This scheme must address the three major technical challenges unique to solid-state batteries: ion transport, physical contact, and interface stability. Summary of the Invention

[0005] Based on the background technology, this invention provides a composite cathode material for solid-state lithium batteries, its preparation method, and its application, aiming to solve the inherent problems of poor physical contact at the solid-solid interface, limited ion transport, and severe interfacial side reactions in solid-state batteries.

[0006] To achieve the above objectives, the main technical solutions adopted by the present invention are as follows.

[0007] On one hand, the present invention proposes a composite cathode material for solid-state lithium batteries, comprising a lithium-rich manganese-based cathode material and a Li-Al-Ti-O layer coated on its surface by atomic layer deposition technology; the lithium-rich manganese-based cathode material is micron-sized and its D50 satisfies: 1μm≤D50≤10μm, the Li-Al-Ti-O layer has a thickness of 1-10nm and the atomic percentages of each element in the Li-Al-Ti-O layer are: Li 1at%-30at%, Al 5at%-40at%, Ti 5at%-40at%, with the balance being O.

[0008] By using atomic layer deposition technology, this invention coats the surface of lithium-rich manganese-based cathode material with a Li-Al-Ti-O layer (hereinafter referred to as LATO layer). The LATO layer plays a triple role as an ion transport bridge, a physical contact enhancement layer, and a chemical isolation layer: (1) The LATO layer is constructed by atomic layer deposition technology. It is continuous and ultra-thin, completely covering the primary particle surface and secondary particle grain boundaries of the lithium-rich manganese-based cathode material. It can fill the microscopic gaps between the cathode and the solid electrolyte, transforming the unfavorable "point contact" into an effective "surface contact". During cycling, it acts as a stress buffer layer to prevent contact peeling, thus solving the physical contact problem unique to solid batteries; (2) As a lithium-ion conductor, LATO establishes a dedicated ion transport channel at the solid-solid interface, overcoming the defects of traditional insulating coatings that hinder and block ion transport, and improving the ion transport performance of the solid-solid interface; (3) The LATO layer is constructed by atomic layer deposition technology. It is uniform, continuous, dense, and free of pinholes, which can meet the extreme requirements of solid batteries for interface density. It helps to play an effective chemical isolation layer role and avoid the formation of "hot spots" by local side reactions.

[0009] Therefore, when the composite cathode material of the present invention is used in solid-state lithium batteries, it produces a significant synergistic effect: it significantly reduces the interface impedance, effectively suppresses voltage decay and capacity decay during cycling, prevents interface contact failure, and significantly improves the capacity retention rate of solid-state lithium batteries.

[0010] Furthermore, the lithium-rich manganese-based cathode material is a polycrystalline secondary microsphere, and the Li-Al-Ti-O layer is an amorphous, non-crystalline structure. The amorphous, non-crystalline Li-Al-Ti-O layer completely covers the primary particle surface and secondary particle grain boundaries of the lithium-rich manganese-based cathode material.

[0011] In this technical solution, a lithium-rich manganese-based cathode material with a polycrystalline secondary micron-sphere structure is used as the coating substrate. On the one hand, it can buffer volume changes and has good crack resistance after coating. On the other hand, the rough surface is conducive to uniform film formation, which can be directly coated and is not easy to agglomerate. No granulation is required after coating, which helps to simplify the coating process.

[0012] In this technical solution, the amorphous LATO layer is a continuous Li + Compared with crystalline LATO, the diffusion channel is more adapted to the surface morphology of lithium-rich manganese-based cathode materials and has no grain boundary defects. Therefore, the coating layer has high room temperature ionic conductivity and good interfacial stability. Moreover, its good elastic modulus can buffer the volume change of lithium-rich manganese-based cathode materials, which helps to improve the interfacial peeling condition after long cycling.

[0013] Furthermore, the D50 of the lithium-rich manganese-based cathode material satisfies: 1μm ≤ D50 ≤ 5μm, specifically 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2... .9μm, 3.0μm, 3.1μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, 4.0μm, 4.1μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5.0 μm, etc.; the thickness of the Li-Al-Ti-O layer is 3-7 nm.

[0014] The dimensions of lithium-rich manganese-based cathode materials and the thickness of the LATO layer need to be optimized synergistically. In this technical solution, the D50 of the lithium-rich manganese-based cathode material is limited to 1-5 μm, and the thickness of the LATO layer is limited to 3-7 nm. The lithium-rich manganese-based cathode material that meets the above requirements, combined with the LATO layer, can balance ion / electron transport, resulting in better performance of the composite cathode material.

[0015] Furthermore, impedance spectroscopy fitting using the four-probe method determined that the lithium-ion conductivity σ of the Li-Al-Ti-O layer at 25℃ is ≥2.5×10⁻⁶. -6 S•cm -1 .

[0016] On the other hand, the present invention proposes a method for preparing a composite cathode material for solid-state lithium batteries, comprising the following steps: S1 provides micron-scale lithium-rich manganese-based cathode materials; S2. Using atomic layer deposition technology, a Li-Al-Ti-O layer is deposited on the surface of a micron-sized lithium-rich manganese-based cathode material.

[0017] Further, the specific operation of step S1 is as follows: Lithium source, nickel source, manganese source and cobalt source are dissolved in solvent according to the target stoichiometric ratio and stirred evenly to obtain a mixed salt solution; under constant temperature stirring at 55-80℃, an alkaline precipitant is slowly added dropwise to the mixed salt solution to adjust the pH value of the reaction system to 9-14, and the co-precipitation reaction is carried out for 12-24 h to obtain a precipitate; the precipitate is filtered, washed and dried to obtain a precursor powder; the precursor powder and lithium source are mixed according to the stoichiometric ratio, and sintered at low temperature at 300-500℃ and high temperature at 700-950℃ respectively, and then naturally cooled to room temperature to obtain a lithium-rich manganese-based cathode material with a microstructure of polycrystalline secondary microspheres; In this technical solution, the lithium source is selected from at least one of lithium acetate, lithium carbonate, lithium hydroxide, and lithium nitrate; the nickel source is selected from at least one of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate; the manganese source is selected from at least one of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate; and the cobalt source is selected from at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate. In this technical solution, the solvent is water, ethanol, or a mixture of water and ethanol in any volume ratio; In this technical solution, the preferred temperature for the coprecipitation reaction is 60-70℃, specifically 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃, 70℃, etc.; the preferred stirring rate is 600-800 rpm, specifically 600 rpm, 610 rpm, 620 rpm, 630 rpm, 640 rpm, 650 rpm, 660 rpm, 670 rpm, 680 rpm, 690 rpm, etc. The rpm values ​​are 700 rpm, 710 rpm, 720 rpm, 730 rpm, 740 rpm, 750 rpm, 760 rpm, 770 rpm, 780 rpm, 790 rpm, 800 rpm, etc.; the pH value of the system is preferably 9-11, such as 9, 9.5, 10, 10.5, 11, etc.; the coprecipitation reaction time is preferably 15-20 h, such as 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, etc. In this technical solution, the washing process involves sequentially washing with deionized water and ethanol, with each solvent used for 3-5 washes. In this technical solution, the drying temperature is 80-100℃, such as 80℃, 85℃, 90℃, 95℃, 100℃, etc.; the drying time is 8-12h, such as 8h, 9h, 10h, 11h, 12h, etc. In this technical solution, the atmosphere for low-temperature sintering and high-temperature sintering is an air atmosphere or an oxygen atmosphere. The low-temperature sintering time is 3-6 hours with a heating rate of 3-6℃ / min, and the high-temperature sintering time is 10-20 hours with a heating rate of 3-8℃ / min.

[0018] Furthermore, in step S2, during deposition, an aluminum source, a lithium source, an oxygen source, and a titanium source are sequentially introduced into each deposition cycle for deposition. By controlling the deposition temperature, deposition chamber pressure, and pulse times of various source materials, an amorphous LATO layer of a specific thickness is uniformly deposited on the surface of a lithium-rich manganese-based cathode material. When the deposition temperature is 100-300℃, the deposition chamber pressure is 0.5-3 Torr, and the pulse times of the aluminum, lithium, oxygen, and titanium sources in a single deposition cycle are 100-300 ms, 3-30 deposition cycles are performed to obtain an amorphous LATO layer with a thickness of 1-10 nm. Preferably, the deposition temperature is 220-280℃, and the deposition chamber... The pressure is 0.8-1.5 Torr, and the pulse time of the aluminum source, lithium source, oxygen source, and titanium source in a single deposition cycle is 150-250 ms, respectively. After 10-20 deposition cycles, an amorphous and non-crystalline LATO layer with a thickness of 3-7 nm is obtained. More preferably, the deposition temperature is 250℃, the pressure in the deposition chamber is 1 Torr, and the pulse time of the aluminum source, lithium source, oxygen source, and titanium source in a single deposition cycle is 200 ms, respectively. After 15 deposition cycles, an amorphous and non-crystalline LATO layer with a thickness of about 5 nm is obtained. Preferably, the aluminum source is trimethylaluminum, the lithium source is at least one of lithium tert-butoxide, lithium isopropoxide, lithium hexamethyldisilamine, and lithium cyclopentadiene, the oxygen source is at least one of high-purity water vapor and ozone, and the titanium source is at least one of alkoxy titanium (such as tetrabutyl titanate, methyl titanate, tetraethoxy titanium, tetraisopropoxy titanium, etc.) and titanium halide (such as titanium trichloride, titanium tetrachloride, etc.).

[0019] Furthermore, in step S2, during deposition, each element is subjected to adsorption and pressure holding after the pulse, and the adsorption and pressure holding time is not less than 5 seconds. The adsorption and pressure holding is mainly to promote the penetration of each element into the interparticle gaps to cover the secondary particle grain boundaries as much as possible, so that the LATO layer coating is more continuous and uniform; the effect is better if the adsorption and pressure holding time is 10 seconds or more.

[0020] In addition, the present invention also proposes a solid-state battery using the above-mentioned composite cathode material for solid-state lithium batteries as the cathode.

[0021] Furthermore, an all-solid-state battery is constructed using a sulfide solid electrolyte as the electrolyte, and the all-solid-state battery retains ≥98.5% of its capacity after 100 cycles at room temperature and 0.5C.

[0022] Compared with existing technologies, this invention solves the inherent problems of poor physical contact, limited ion transport, and severe interfacial side reactions in solid-state batteries by coating the surface of lithium-rich manganese-based cathode material with a LATO layer. The LATO layer simultaneously functions as an ion transport bridge, a physical contact enhancement layer, and a chemical isolation layer. When the resulting composite cathode material is used in solid-state lithium batteries, it helps to comprehensively improve the performance of solid-state lithium batteries, especially the discharge specific capacity and long-cycle capacity retention. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a TEM image of the solid-state lithium battery composite cathode material obtained in Example 1.

[0025] Figure 2 The image shows a comparison of the electrochemical impedance spectra of the solid-state batteries assembled in Example 1 and Comparative Examples 1-3.

[0026] Figure 3 This is a comparison chart of the cycle performance of solid-state batteries assembled in Example 1 and Comparative Examples 1-3.

[0027] Figure 4 The image shows a comparison of the interface morphology of the solid-state batteries assembled in Example 1 and Comparative Example 2 after cycling. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0029] All chemical raw materials used in the following examples and comparative examples are commercially available, and all apparatus and operations involved are conventional in the art.

[0030] Example 1

[0031] The composite cathode material for solid-state lithium batteries was prepared according to the following steps: S1. 0.5Li₂MnO₃•0.5LiMO₂ was synthesized by co-precipitation method. Manganese, nickel, and cobalt sources (molar ratio 4:1:1) were dissolved in deionized water according to the target stoichiometric ratio and stirred at 600 r / min to obtain a mixed salt solution. Under constant temperature stirring at 60℃, an alkaline precipitant Na2CO3 solution (2...) was slowly added dropwise to the mixed salt solution. The pH of the reaction system was adjusted to 11 using NH3•H2O solution (mol / L) and co-precipitation reaction for 18 h to form a precipitate, which is a metal precursor. The precipitate was filtered and washed three times each with deionized water and ethanol, and then dried in an oven at 100℃ for 12 h to obtain precursor powder. The precursor powder was mixed with lithium source Li2CO3 (Li to M molar ratio of 1.4:1), and under air atmosphere, the temperature was first raised to 500℃ at a rate of 5℃ / min and sintered at 500℃ for 5 h. Then, the temperature was raised to 900℃ at a rate of 5℃ / min and sintered at 900℃ for 15 h. After natural cooling to room temperature, a lithium-rich manganese-based cathode material with a D50 of 5 μm was obtained. S2. An atomic layer deposition technique is used to deposit a LATO layer on the surface of a lithium-rich manganese-based cathode material. Using the lithium-rich manganese-based cathode material obtained in the previous step as a substrate, ozone was used as the oxygen source, lithium tert-butoxide as the lithium source, trimethylaluminum as the aluminum source, and tetrabutyl titanate as the titanium source. The aluminum source, lithium source, oxygen source, and titanium source were sequentially introduced for deposition at a deposition temperature of 250°C and a chamber pressure maintained at 1 Torr. In each deposition cycle, each pulse for each metal source lasted for 200 ms, and the pressure was maintained for 10 s during the adsorption phase. After each metal source pulse, nitrogen was used to purge for 20 s to remove unreacted residues and ensure self-limiting growth. A total of 15 cycles were performed to finally obtain a LATO layer with a thickness of about 5 nm. The atomic percentages of each element in the LATO layer were: Li 15 at%, Al 25 at%, Ti 25 at%, and the balance being O.

[0032] like Figure 1 As shown: In the obtained composite cathode material, clear lattice fringes can be observed inside the lithium-rich manganese-based cathode material, with an interlayer spacing of approximately 0.476 nm, indicating a hexagonal crystal system. The (003) plane of the space group or the (001) plane of the monoclinic C / 2m space group; a uniform, continuous, pinhole-free LATO coating layer with a thickness of about 5 nm can be observed on the surface of the lithium-rich manganese-based cathode material, which covers the primary particle surface and secondary particle grain boundaries of the lithium-rich manganese-based cathode material.

[0033] Example 2

[0034] Compared with Example 1, step S1 remains unchanged, but the deposition cycle in step S2 is adjusted from 15 times to 3 times. The deposition conditions are: deposition temperature 220°C, deposition chamber pressure 1.5 Torr, and pulse time 250 ms. All other conditions remain the same as in Example 1. The LATO coating thickness of the obtained composite cathode material is approximately 1 nm.

[0035] Example 3

[0036] Compared with Example 1, step S1 remains unchanged, but the deposition cycle in step S2 is adjusted from 15 cycles to 10 cycles. The deposition conditions are: deposition temperature 280°C, deposition chamber pressure 0.8 Torr, and pulse time 150 ms. All other conditions remain the same as in Example 1. The LATO coating thickness of the obtained composite cathode material is approximately 3 nm.

[0037] Example 4

[0038] Compared with Example 1, step S1 remains unchanged, but the deposition cycle in step S2 is adjusted from 15 to 20 times. The deposition conditions are: deposition temperature 240°C, deposition chamber pressure 1.2 Torr, and pulse time 210 ms. All other conditions remain the same as in Example 1. The LATO coating thickness of the obtained composite cathode material is approximately 7 nm.

[0039] Example 5

[0040] Compared with Example 1, step S1 remains unchanged, but the deposition cycle in step S2 is adjusted from 15 to 30 times. The deposition conditions are: deposition temperature 220°C, deposition chamber pressure 0.9 Torr, and pulse time 180 ms. All other conditions remain the same as in Example 1. The LATO coating thickness of the obtained composite cathode material is approximately 10 nm.

[0041] Example 6

[0042] Compared with Example 1, the stirring rate during the co-precipitation reaction in step S1 was adjusted from 600 rpm to 800 rpm, and the co-precipitation reaction time was adjusted from 18 h to 15 h. Finally, a lithium-rich manganese-based cathode material with a D50 of 1 μm was obtained. All other aspects remained the same as in Example 1.

[0043] Example 7

[0044] Compared with Example 1, the stirring rate during the co-precipitation reaction in step S1 was adjusted from 600 rpm to 700 rpm, the pH value of the system was adjusted from 11 to 10, and the co-precipitation reaction time was adjusted from 18 h to 20 h. Finally, a lithium-rich manganese-based cathode material with a D50 of 3 μm was obtained. All other aspects remained the same as in Example 1.

[0045] Example 8

[0046] Compared with Example 1, the temperature of the co-precipitation reaction in step S1 was adjusted from 60°C to 80°C, and the co-precipitation reaction time was adjusted from 18h to 20h. Finally, a lithium-rich manganese-based cathode material with a D50 of 10μm was obtained. All other aspects were the same as in Example 1.

[0047] Example 9

[0048] Compared with Example 1, step S1 is the same, but the atomic percentage of each element in the LATO layer formed in step S2 is different. Specifically, the atomic percentage of each element in the LATO layer is: Li 30at%, Al 5at%, Ti 5at%, with the balance being O. The rest are consistent with Example 1.

[0049] Example 10

[0050] Compared with Example 1, step S1 is the same, but the atomic percentage of each element in the LATO layer formed in step S2 is different. Specifically, the atomic percentage of each element in the LATO layer is: Li 1at%, Al 40at%, Ti 40at%, with the balance being O. The rest are consistent with Example 1.

[0051] Example 11

[0052] Compared with Example 1, step S1 is the same, but the holding time of the adsorption stage in step S2 is adjusted from 10s to 5s, and the rest is consistent with Example 1.

[0053] Example 12

[0054] Compared with Example 1, step S1 is the same, except that pressure holding is not performed during the adsorption stage in step S2, and the rest is consistent with Example 1.

[0055] Comparative Example 1 Manganese, nickel, and cobalt sources (molar ratio 4:1:1) were dissolved in deionized water according to the target stoichiometric ratio and stirred at 600 rpm to obtain a mixed salt solution. Under constant temperature stirring at 60°C, alkaline precipitant Na₂CO₃ solution (2 mol / L) and NH₃•H₂O solution were slowly added dropwise to the mixed salt solution to adjust the pH of the reaction system to 11. The co-precipitation reaction proceeded for 18 hours to form a precipitate, which is a metal precursor. The precipitate was filtered and then... The precursor powder was then washed three times each with deionized water and ethanol, and then dried in an oven at 100°C for 12 hours to obtain the precursor powder. The precursor powder was mixed with lithium source Li2CO3 (Li to M molar ratio of 1.4:1), and under an air atmosphere, the temperature was first raised to 500°C at a heating rate of 5°C / min and sintered at 500°C for 5 hours. Then, the temperature was raised to 900°C at a heating rate of 5°C / min and sintered at 900°C for 15 hours. Finally, the mixture was naturally cooled to room temperature to obtain lithium-rich manganese-based cathode material.

[0056] Comparative Example 2 The composite cathode material for solid-state lithium batteries was prepared according to the following steps: S1. 0.5Li₂MnO₃•0.5LiMO₂ was synthesized by co-precipitation method. Manganese, nickel, and cobalt sources (molar ratio 4:1:1) were dissolved in deionized water according to the target stoichiometric ratio and stirred at 600 rpm to obtain a mixed salt solution. Under constant temperature stirring at 60°C, alkaline precipitant Na₂CO₃ solution (2 mol / L) and NH₃•H₂O solution were slowly added dropwise to the mixed salt solution to adjust the pH of the reaction system to 11. The co-precipitation reaction proceeded for 18 hours to form a precipitate, which is a metal precursor. The precipitate was filtered and then... The precursor powder was then washed three times each with deionized water and ethanol, and then dried in an oven at 100°C for 12 hours to obtain the precursor powder. The precursor powder was mixed with lithium source Li2CO3 (Li to M molar ratio of 1.4:1), and under an air atmosphere, the temperature was first raised to 500°C at a heating rate of 5°C / min and sintered at 500°C for 5 hours. Then, the temperature was raised to 900°C at a heating rate of 5°C / min and sintered at 900°C for 15 hours. Finally, the temperature was naturally cooled to room temperature to obtain lithium-rich manganese-based cathode material. S2. An Al2O3 layer is deposited on the surface of a lithium-rich manganese-based cathode material using atomic layer deposition (ALD) technology. Using the lithium-rich manganese-based cathode material obtained in the previous step as a substrate, ozone as an oxygen source, and trimethylaluminum as a metal source, the deposition temperature was controlled at 250℃, the chamber pressure was maintained at 1 Torr, the pulse lasted for 200ms in each deposition cycle, and the pressure was maintained for 10s during the adsorption stage; nitrogen was used to purge for 20s after each metal source pulse to remove unreacted residues, and an Al2O3 layer with a thickness of about 5nm was obtained after 15 cycles.

[0057] Comparative Example 3 The composite cathode material for solid-state lithium batteries was prepared according to the following steps: S1. 0.5Li₂MnO₃•0.5LiMO₂ was synthesized by co-precipitation method. Manganese, nickel, and cobalt sources (molar ratio 4:1:1) were dissolved in deionized water according to the target stoichiometric ratio and stirred at 600 rpm to obtain a mixed salt solution. Under constant temperature stirring at 60°C, alkaline precipitant Na₂CO₃ solution (2 mol / L) and NH₃•H₂O solution were slowly added dropwise to the mixed salt solution to adjust the pH of the reaction system to 11. The co-precipitation reaction proceeded for 18 hours to form a precipitate, which is a metal precursor. The precipitate was filtered and then... The precursor powder was then washed three times each with deionized water and ethanol, and then dried in an oven at 100°C for 12 hours to obtain the precursor powder. The precursor powder was mixed with lithium source Li2CO3 (Li to M molar ratio of 1.4:1), and under an air atmosphere, the temperature was first raised to 500°C at a heating rate of 5°C / min and sintered at 500°C for 5 hours. Then, the temperature was raised to 900°C at a heating rate of 5°C / min and sintered at 900°C for 15 hours. Finally, the temperature was naturally cooled to room temperature to obtain lithium-rich manganese-based cathode material. S2. Using the sol-gel method, a LATO layer with the same chemical composition as in Example 1 is deposited on the surface of the lithium-rich manganese-based cathode material. Using the lithium-rich manganese-based cathode material obtained in the previous step as a substrate, the LATO layer was coated by the sol-gel method: LiNO3, Al(NO3)3•9H2O, and Ti(OCH2CH2CH2CH3)4 were first dissolved in anhydrous ethanol according to the required stoichiometric ratio and stirred for 30 min to ensure homogenization. Then, the cathode material was added and stirred for 2 h. After drying in a forced-air environment at 80 °C, it was calcined at 400 °C for 5 h in an air atmosphere and then naturally cooled to room temperature.

[0058] Comparative Example 4 Compared with Example 1, step S1 remains unchanged, while in step S2, Li is deposited on the surface of the lithium-rich manganese-based cathode material using atomic layer deposition technology. 0.33 La 0.56 During the deposition of the TiO3 layer, a lanthanum source, a lithium source, an oxygen source, and a titanium source were sequentially introduced. The lanthanum source was lanthanum nitrate, the lithium source was lithium tert-butoxide, the oxygen source was ozone, and the titanium source was n-butyl titanate. All other aspects were consistent with those in Example 1.

[0059] Comparative Example 5 Compared with Example 1, step S1 remains unchanged, while in step S2, Li3V is deposited on the surface of the lithium-rich manganese-based cathode material using atomic layer deposition technology. 0.6 PO 19 During deposition, a vanadium source, a lithium source, an oxygen source, and a phosphorus source are sequentially introduced. The vanadium source is vanadium pentaethoxy, the lithium source is lithium tert-butoxide, the oxygen source is ozone, and the phosphorus source is trimethyl phosphate. The rest are consistent with those in Example 1.

[0060] Comparative Example 6 Compared with Example 1, step S1 remains unchanged, while in step S2, Li is deposited on the surface of the lithium-rich manganese-based cathode material using atomic layer deposition technology. 1.0 Mn 0.12 O 1.7 During the deposition of the layer, manganese source, lithium source and oxygen source are sequentially introduced, wherein the manganese source is manganese acetylacetone, the lithium source is lithium tert-butoxide, and the oxygen source is ozone, and the rest are consistent with Example 1.

[0061] Comparative Example 7 Compared with Example 1, step S1 remains unchanged. In step S2, an atomic layer deposition technique is used to deposit a LiNbO3 layer on the surface of the lithium-rich manganese-based cathode material. During deposition, a niobium source, a lithium source, and an oxygen source are introduced sequentially. The niobium source is niobium pentaethoxy, the lithium source is lithium tert-butoxide, and the oxygen source is ozone. All other steps are consistent with Example 1.

[0062] The products obtained from each embodiment and comparative example were used as cathode materials, and composite cathodes were assembled according to a mass ratio of cathode material, electrolyte (LiPSC), and conductive agent (carbon nanotubes) of 60:37:3. During the solid-state lithium battery assembly process, 100 mg of electrolyte was first transferred to a PEEK cylinder and held at 2T pressure for 2 min, then 15 mg of the composite cathode material was added and held at 4T pressure for 2 min; on the other side, lithium-indium alloy was added, and also held at 2T pressure for 2 min; finally, the assembled battery was sealed in a stainless steel casing and subjected to approximately 2T pressure for electrical performance testing; the entire assembly process was carried out in an argon-filled glove box. Electrical performance tests were conducted at 2.0-4.8V (vs. Li). + Within the voltage range of / Li), the initial discharge specific capacity at 0.1C and the discharge specific capacity and capacity retention rate after 100 cycles at 0.5C were tested. The specific measurement results are shown in Table 1.

[0063]

[0064] As shown in Table 1 and Figures 1-4 As shown in the following: Compared with Comparative Example 1, Examples 1-12 show that, compared with lithium-rich manganese-based cathode materials without any coating layer, the presence of the LATO coating layer helps to solve the problems of poor physical contact at the solid-solid interface, limited ion transport, and severe interfacial side reactions in solid-state batteries. The resulting composite cathode material can achieve high specific capacity and capacity retention when used in solid-state lithium batteries.

[0065] Furthermore, a comparison of the test results of Example 1 and Comparative Example 3 shows that the LATO coating layer obtained by atomic layer deposition (ALD) in this invention significantly improves both discharge specific capacity and capacity retention compared to the coating layer of the same composition obtained by the gel method. This is likely because the LATO coating layer obtained by ALD is thin, continuously and uniformly distributed, and completely covers the primary particle surface and secondary particle grain boundaries of the lithium-rich manganese-based cathode material. This maximizes the triple function of the ion transport bridge, physical contact enhancement layer, and chemical isolation layer, resulting in a more significant improvement in electrochemical performance. It is worth noting that a comparison of the test results of Examples 1, 11, and 12 shows that during ALD deposition, adsorption and holding pressure are performed after each element pulse for at least 5 seconds, preferably at least 10 seconds. This promotes the penetration of each element into the secondary particle gaps to cover the secondary particle grain boundaries as much as possible, making the LATO coating more continuous and uniform, effectively promoting the triple function of the LATO coating layer.

[0066] Furthermore, a comparison of the test results of Example 1 with those of Comparative Examples 2 and 4-7 shows that when the surface of the lithium-rich manganese-based cathode material is coated with an Al2O3 layer, it cannot enhance ion transport, which is detrimental to improving the specific capacity. Moreover, although it can enhance physical contact and act as a chemical isolation layer to some extent, improving cycle stability, the interface contact deteriorates severely after long cycles, while the interface contact in Example 1 remains tight (e.g., ...). Figure 4 As shown); when the surface of the lithium-rich manganese-based cathode material is coated with an Al2O3 layer and a Li2O3 layer... 0.33 La 0.56 TiO3 layer, Li3V 0.6 PO 19 Layer, Li 1.0 Mn 0.12 O 1.7 While the specific capacity is improved to varying degrees when using layers or LiNbO3 layers, the improvement is not as significant as that of the present invention, and the improvement effect on capacity retention is incomparable to that of the present invention.

[0067] like Figure 2 As shown: The solid-state battery obtained in Example 1 has the lowest impedance. The solid-state batteries obtained in Comparative Examples 1, 2, and 3 have significantly higher impedances than those in Example 1, indicating severe interfacial reactions and poor ion conduction efficiency. Figure 3 As shown, the solid-state battery obtained in Example 1 has a capacity of nearly 185 mAh / g and is durable, with a capacity retention rate of 98.5% after 100 cycles; while Comparative Examples 1-3 have lower capacity and decay rapidly, and their performance is far inferior to that of Example 1.

[0068] In addition, a comparison of the test results from Examples 1-5 shows that when the thickness of the LATO coating layer is 1-10 nm, the resulting composite cathode material can achieve higher specific capacity and capacity retention when used in solid-state lithium batteries; the preferred thickness of the LATO coating layer is 3-7 nm, and particularly preferably 5 nm. A comparison of the test results from Examples 1, 6, 7, and 8 shows that, with a LATO layer thickness of 5 nm, the performance of the composite cathode material is also related to the size of the lithium-rich manganese-based cathode material. A high specific capacity and capacity retention can be obtained when the D50 of the lithium-rich manganese-based cathode material is 1-10 μm; the preferred D50 is 1-5 μm, and particularly preferably 5 μm. Therefore, a proper match between the particle size of the lithium-rich manganese-based cathode material and the thickness of the LATO coating layer can balance ion / electron transport, and is more helpful in solving the problems of poor physical contact at the solid-solid interface, limited ion transport, and severe interfacial side reactions in solid-state batteries.

[0069] In summary, the composite cathode material proposed in this invention, consisting of a lithium-rich manganese-based cathode material and a Li-Al-Ti-O layer coated on its surface using atomic layer deposition technology, can significantly reduce interface impedance, effectively suppress voltage and capacity decay during cycling, prevent interface contact failure, and significantly improve the specific capacity and capacity retention of solid-state lithium batteries.

[0070] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples.

Claims

1. A composite cathode material for solid-state lithium batteries, characterized in that: The cathode material includes a lithium-rich manganese-based cathode material and a Li-Al-Ti-O layer coated on its surface using atomic layer deposition technology. The lithium-rich manganese-based cathode material is micron-sized and has a D50 that satisfies: 1μm≤D50≤10μm. The Li-Al-Ti-O layer has a thickness of 1-10nm and the atomic percentages of each element in the Li-Al-Ti-O layer are: Li 1at%-30at%, Al 5at%-40at%, Ti 5at%-40at%, with the balance being O.

2. The composite cathode material for solid-state lithium batteries according to claim 1, characterized in that: The lithium-rich manganese-based cathode material is a polycrystalline secondary microsphere, and the Li-Al-Ti-O layer is an amorphous, non-crystalline structure. The amorphous, non-crystalline Li-Al-Ti-O layer completely covers the primary particle surface and secondary particle grain boundaries of the lithium-rich manganese-based cathode material.

3. The composite cathode material for solid-state lithium batteries according to claim 1, characterized in that: The D50 of the lithium-rich manganese-based cathode material satisfies: 1μm≤D50≤5μm, and the thickness of the Li-Al-Ti-O layer is 3-7nm.

4. The composite cathode material for solid-state lithium batteries according to claim 1, characterized in that: The lithium-ion conductivity σ of the Li-Al-Ti-O layer at 25℃ was determined by impedance spectroscopy fitting using the four-probe method to be ≥2.5×10⁻⁶. -6 S•cm -1 .

5. A method for preparing a composite cathode material for solid-state lithium batteries as described in any one of claims 1-4, characterized in that: The following steps are included: S1 provides micron-scale lithium-rich manganese-based cathode materials; S2. Using atomic layer deposition technology, a Li-Al-Ti-O layer is deposited on the surface of a micron-sized lithium-rich manganese-based cathode material.

6. The method for preparing the composite cathode material for solid-state lithium batteries according to claim 5, characterized in that: The specific operation of step S1 is as follows: Lithium source, nickel source, manganese source, and cobalt source are dissolved in a solvent according to the target stoichiometric ratio and stirred evenly to obtain a mixed salt solution; under constant temperature stirring at 55-80℃, an alkaline precipitant is slowly added dropwise to the mixed salt solution to adjust the pH value of the reaction system to 9-14, and the co-precipitation reaction is carried out for 12-24 h to obtain a precipitate; the precipitate is filtered, washed, and dried to obtain a precursor powder; the precursor powder is mixed with lithium source according to the stoichiometric ratio, and sintered at low temperature at 300-500℃ and high temperature at 700-950℃ respectively, and then naturally cooled to room temperature to obtain the final product; Preferably, the lithium source is selected from at least one of lithium acetate, lithium carbonate, lithium hydroxide, and lithium nitrate; the nickel source is selected from at least one of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate; the manganese source is selected from at least one of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate; and the cobalt source is selected from at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate. Preferably, the solvent is water, ethanol, or a mixture of water and ethanol; Preferably, the temperature of the coprecipitation reaction is 60-70℃, the stirring rate is 600-800rpm, the pH value of the system is 9-11, and the coprecipitation reaction time is 15-20h. Preferably, the washing process involves washing with deionized water and ethanol sequentially, with each solvent used for 3-5 washes. Preferably, the drying temperature is 80-100℃ and the drying time is 8-12h; Preferably, the atmosphere for both low-temperature sintering and high-temperature sintering is an air atmosphere or an oxygen atmosphere, the low-temperature sintering time is 3-6 hours and the heating rate is 3-6℃ / min, the high-temperature sintering time is 10-20 hours and the heating rate is 3-8℃ / min.

7. The method for preparing the composite cathode material for solid-state lithium batteries according to claim 5, characterized in that: In step S2, during deposition, an aluminum source, a lithium source, an oxygen source, and a titanium source are sequentially introduced into each deposition cycle for deposition. Preferably, the deposition temperature is 100-300℃, the pressure in the deposition chamber is 0.5-3 Torr, and the pulse time of the aluminum source, lithium source, oxygen source and titanium source in a single deposition cycle is 100-300ms, and 3-30 deposition cycles are performed. Preferably, the deposition temperature is 220-280℃, the pressure in the deposition chamber is 0.8-1.5 Torr, and the pulse time of the aluminum source, lithium source, oxygen source and titanium source in a single deposition cycle is 150-250ms, and 10-20 deposition cycles are performed. Preferably, the deposition temperature is 250℃, the pressure in the deposition chamber is 1 Torr, and the pulse time of the aluminum source, lithium source, oxygen source and titanium source in a single deposition cycle is 200ms, and 15 deposition cycles are performed. Preferably, the aluminum source is trimethylaluminum, the lithium source is at least one of lithium tert-butoxide, lithium isopropoxide, lithium hexamethyldisilamide, and lithium cyclopentadiene, the oxygen source is at least one of high-purity water vapor and ozone, and the titanium source is at least one of alkoxytitanium and titanium halide.

8. The method for preparing the composite cathode material for solid-state lithium batteries according to claim 7, characterized in that: In step S2, during deposition, each element is subjected to adsorption and pressure holding after the pulse, and the adsorption and pressure holding time is not less than 5 seconds. Preferably, the adsorption and pressure holding time is not less than 10 seconds.

9. A solid-state battery using the composite cathode material for solid-state lithium batteries as described in any one of claims 1-4 as the cathode.

10. The solid-state battery according to claim 9, characterized in that: A solid-state battery is constructed using a sulfide solid electrolyte as the electrolyte. After 100 cycles at room temperature and 0.5C, the capacity retention rate of the solid-state battery is ≥98.5%.

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