Surface modification method of LLZO solid electrolyte powder

Abstract

The invention relates to the technical field of solid electrolyte, in particular to a surface modification method of LLZO solid electrolyte powder, which comprises the following steps: carrying out surface chemical analysis on original LLZO powder to obtain a lithium carbonate index for representing the surface impurity content of the LLZO powder; determining the qualification of the original powder based on the lithium carbonate index; qualified original powder and the modified precursor solution are mixed and react under preset conditions, a uniform gel coating layer is formed on the surface of the powder, and gel-coated intermediate powder is obtained; characterizing the gel coated intermediate powder to obtain a coating quality index, and judging the coating qualification based on the coating quality index; performing heat treatment on the qualified gel coated intermediate powder to obtain surface modified LLZO powder; and performing electrochemical performance test on the surface modified LLZO powder to obtain a performance evaluation index, and judging the qualification of surface modification. The electrochemical stability of the LLZO powder is improved.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte technology, and more particularly to a method for surface modification of LLZO solid electrolyte powder. Background Technology

[0002] Solid-state lithium batteries are considered a core development direction for next-generation energy storage technology due to their potential high energy density and inherent safety. Among numerous solid electrolyte materials, LLZO has attracted much attention due to its high room-temperature ionic conductivity, good thermodynamic stability to lithium metal, and wide electrochemical window. However, LLZO still faces severe interfacial challenges in practical applications, largely stemming from its powder surface characteristics. First, the lithium element in LLZO is chemically extremely reactive. When the powder is exposed to air, it reacts rapidly with H2O and CO2, forming insulating Li2CO3 and LiOH layers on its surface. This insulating layer severely hinders the transport of lithium ions between electrolyte particles, leading to a significant decrease in overall ionic conductivity and a substantial increase in the interfacial impedance between the electrolyte and the electrode. Second, even under inert atmosphere treatment, the solid-solid contact between LLZO and the lithium metal anode remains unsatisfactory, exhibiting poor interfacial wettability, high contact resistance, and is prone to inducing uneven growth and penetration of lithium dendrites during cycling. Furthermore, when LLZO comes into direct contact with high-voltage cathode materials (such as LiCoO2, NCM, etc.), harmful interdiffusion and side reactions occur at the interface, forming a high-resistivity intermediate phase, which deteriorates the long-cycle performance of the battery.

[0003] Chinese Patent Application Publication No. CN118336097A discloses a method for preparing LLZO solid electrolyte material, including the preparation of lithium lanthanum zirconium oxide powder material, which involves mixing raw materials such as lithium hydroxide monohydrate, lanthanum oxide and zirconium dioxide to form a wet mixture, and then drying, pre-calcining, grinding and high-temperature sintering to obtain sample powder; and the preparation of LLZO solid electrolyte sheet, which involves weighing an appropriate amount of sample powder and obtaining LLZO solid electrolyte material through steps such as pressing and sintering.

[0004] However, the existing technology has the following problems: it does not consider passivating or protecting the highly active surface through surface modification, resulting in the continuous and uncontrollable generation of Li2CO3 from the prepared LLZO powder during subsequent storage, transportation, and any air exposure before battery assembly. This not only causes the material properties to degrade significantly over time, but also leads to poor batch-to-batch performance consistency and low repeatability of the final battery products, seriously affecting the reliability of their industrial applications. Summary of the Invention

[0005] Therefore, the present invention provides a surface modification method for LLZO solid electrolyte powder to overcome the problem that the material properties of LLZO solid electrolyte powder will significantly degrade over time due to the lack of consideration for surface modification in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for surface modification of LLZO solid electrolyte powder, comprising: Step S1: Perform surface chemical analysis on the original LLZO powder to obtain the lithium carbonate index, which is used to characterize the content of surface impurities. Step S2: Based on the comparison result between the lithium carbonate index and the preset threshold, determine the qualification of the original powder. If it is unqualified, determine the pretreatment strategy of the original powder based on the difference between the lithium carbonate index and the preset threshold. Step S3: Mix the qualified raw powder with the modified precursor solution and react under preset conditions to form a uniform gel coating layer on the powder surface to obtain gel-coated intermediate powder. The preset conditions include stirring at a preset stirring speed and a preset heating program for a preset duration under an inert atmosphere. Step S4: The coating quality index is obtained by characterizing the intermediate powder coated by the gel, and the qualification of the coating is determined based on the comparison result between the coating quality index and the preset quality index. If the coating is unqualified, the stirring speed and heating rate in step S3 are adjusted based on the coefficient of variation of the coating layer thickness. Step S5: Heat-treat the qualified gel-coated intermediate powder to crystallize the coating layer and allow limited interfacial interdiffusion with the LLZO matrix surface to form a chemically bonded composite interfacial layer, thereby obtaining surface-modified LLZO powder. Step S6: Perform electrochemical performance testing on the surface-modified LLZO powder obtained in step S5, obtain the performance evaluation index, and determine the qualification of surface modification based on the comparison result of the performance evaluation index and the preset evaluation index. If the surface modification is not qualified, reduce the heat treatment temperature of step S5 or increase the coating reaction time of step S3 based on the ionic conductivity and critical current density.

[0007] Furthermore, the lithium carbonate index R is the ratio of the sum of the intensities of the two characteristic peaks of lithium carbonate asymmetric stretching vibration and lithium carbonate out-of-plane bending vibration to the intensity of the internal standard peak.

[0008] Furthermore, in step S2, the original powder is determined to be unqualified based on the comparison result that the lithium carbonate index is greater than or equal to a preset threshold, and the pretreatment strategy of the original powder is determined based on the difference between the lithium carbonate index and the preset threshold.

[0009] Further, in step S2, the pretreatment strategy for the raw powder is determined based on the difference between the lithium carbonate index and a preset threshold, including: If the difference in lithium carbonate index is less than the preset difference, the pretreatment strategy for the original powder is determined to be to automatically execute the thermal cleaning procedure. If the difference in lithium carbonate index is greater than or equal to the preset difference, the pretreatment strategy for the original powder is determined to be an automatic thermal cleaning and mechanical activation combined process. The lithium carbonate index difference is the difference between the lithium carbonate index and a preset threshold.

[0010] Furthermore, the process of step S3 includes: Step S31: Prepare the modified precursor solution; Step S32: Under the protection of an inert atmosphere and with stirring, the qualified raw powder is added to the precursor solution to form a uniform suspension and mixed to make the precursor uniformly adsorbed on the surface of the powder particles. Step S33: Introduce a hydrolysis medium into the suspension system and adjust the reaction temperature to promote the hydrolysis-condensation reaction of the surface-adsorbed precursors, thereby forming a uniform amorphous gel coating layer in situ on the powder surface. Step S34: The reaction system is subjected to solid-liquid separation, and the obtained solid product is washed and preliminarily dried to obtain an intermediate powder with a gel layer on the surface.

[0011] Furthermore, in step S4, based on the comparison result that the coating quality index is less than the preset quality index, the coating is determined to be unqualified, and the preset condition parameters of step S3 are adjusted based on the coating layer thickness variation coefficient.

[0012] Furthermore, the coating quality index is determined based on the coating coverage rate and the coating layer thickness uniformity index.

[0013] Furthermore, in step S4, based on the condition that the coefficient of variation of the coating thickness is greater than or equal to the first preset coefficient of variation and less than the second preset coefficient of variation, it is determined to increase the preset stirring speed in step S3. Based on the condition that the coefficient of variation of the coating thickness is greater than or equal to the second preset coefficient of variation, it is determined that, while increasing the preset stirring speed, the heating rate of the hydrolysis-condensation reaction in step S3 should be reduced simultaneously.

[0014] Furthermore, the adjustment range of the preset stirring speed in step S3 is positively correlated with the difference in the coefficient of variation, wherein the difference in the coefficient of variation is the difference between the coefficient of variation of the coating layer thickness and the first preset coefficient of variation.

[0015] Furthermore, step S6 includes the following process: The ionic conductivity and critical current density were obtained by electrochemical performance testing of surface-modified LLZO powder. The performance evaluation index is calculated based on ionic conductivity and critical current density. Compare the performance evaluation index with the preset evaluation index; The surface modification is deemed unqualified based on the comparison result that the performance evaluation index is less than the preset evaluation index. The heat treatment temperature of step S5 is reduced based on the condition that the ionic conductivity is less than the preset conductivity, or the coating reaction time is increased based on the condition that the critical current density is less than the preset current density.

[0016] Compared with the prior art, the beneficial effects of the present invention are that by introducing quantitative criteria such as lithium carbonate index, coating quality index, and performance evaluation index, the present invention realizes full-process monitoring of raw material purity, coating process and final performance, fundamentally solving the problems of batch instability and uncontrollable modification effect caused by traditional open-ring process, and ensuring high consistency and reliability of material performance.

[0017] Furthermore, this invention intelligently matches different intensity pretreatment strategies based on the degree of lithium carbonate exceeding the standard, achieving targeted and efficient removal of raw material impurities; it accurately diagnoses the cause of uneven coating by using the coefficient of variation of coating thickness, and adjusts the stirring speed and heating rate of S3 accordingly, ensuring the uniformity and quality of the coating from the source.

[0018] Furthermore, this invention forms a uniform, dense, and chemically bonded composite interface layer on the surface of LLZO particles through in-situ gel coating in step S3 and controlled heat treatment in step S5. This interface layer effectively blocks subsequent side reactions between LLZO and air, stabilizing material properties. Simultaneously, the optimized interface significantly reduces interfacial impedance and enhances its ability to suppress lithium dendrites, thereby comprehensively improving the ionic conductivity and cycle stability of the modified LLZO powder. Attached Figure Description

[0019] Figure 1 This is a flowchart of the surface modification method for LLZO solid electrolyte powder according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the process of determining the qualification of the original powder based on the lithium carbonate index in an embodiment of the present invention. Figure 3 This is a flowchart illustrating the process of determining the qualification of a coating based on a coating quality index, as described in an embodiment of the present invention. Figure 4 This is a flowchart illustrating the process of determining the pass / failability of surface modification based on a performance evaluation index, as described in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0021] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0022] It should be noted that the data in this embodiment are all derived from a comprehensive analysis and evaluation of historical test data and corresponding historical test results from the three months prior to this test. Those skilled in the art will understand that the determination of the above-mentioned parameters for any single item in this invention can be achieved by selecting the value with the highest percentage based on the data distribution as the preset standard parameter, using weighted summation to obtain the value as the preset standard parameter, substituting each historical data point into a specific formula and using the value obtained from that formula as the preset standard parameter, or other selection methods, as long as the invention can clearly define different specific situations in the single-item judgment process through the obtained values.

[0023] Please see Figure 1 The diagram shown is a flowchart of the surface modification method for LLZO solid electrolyte powder according to an embodiment of the present invention. The surface modification method for LLZO solid electrolyte powder according to an embodiment of the present invention includes: Step S1: Perform surface chemical analysis on the original LLZO powder to obtain the lithium carbonate index, which is used to characterize the content of surface impurities. Step S2: Based on the comparison result between the lithium carbonate index and the preset threshold, determine the qualification of the original powder. If it is unqualified, determine the pretreatment strategy of the original powder based on the difference between the lithium carbonate index and the preset threshold. Step S3: Mix the qualified raw powder with the modified precursor solution and react under preset conditions to form a uniform gel coating layer on the powder surface to obtain gel-coated intermediate powder. The preset conditions include stirring at a preset stirring speed and a preset heating program for a preset duration under an inert atmosphere. Step S4: The coating quality index is obtained by characterizing the intermediate powder coated by the gel, and the qualification of the coating is determined based on the comparison result between the coating quality index and the preset quality index. If the coating is unqualified, the stirring speed and heating rate in step S3 are adjusted based on the coefficient of variation of the coating layer thickness. Step S5: Heat-treat the qualified gel-coated intermediate powder to crystallize the coating layer and allow limited interfacial interdiffusion with the LLZO matrix surface to form a chemically bonded composite interfacial layer, thereby obtaining surface-modified LLZO powder. Step S6: Perform electrochemical performance testing on the surface-modified LLZO powder obtained in step S5, obtain the performance evaluation index, and determine the qualification of surface modification based on the comparison result of the performance evaluation index and the preset evaluation index. If the surface modification is not qualified, reduce the heat treatment temperature of step S5 or increase the coating reaction time of step S3 based on the ionic conductivity and critical current density.

[0024] Specifically, in step S1, a Fourier transform infrared spectrometer is used to perform surface chemical analysis on the original LLZO powder to identify and read the intensity of characteristic peaks located near the asymmetric stretching vibration and out-of-plane bending vibration of lithium carbonate.

[0025] Specifically, the lithium carbonate index R is the ratio of the sum of the intensities of the two characteristic peaks of lithium carbonate asymmetric stretching vibration and lithium carbonate out-of-plane bending vibration to the intensity of the internal standard peak, wherein the internal standard peak is the Zr-O vibration peak of the LLZO matrix.

[0026] Understandably, LLZO is extremely unstable in air, and its surface rapidly reacts with H2O and CO2 to form an impurity layer primarily composed of Li2CO3. This is the most significant and common reason for its extremely high interfacial impedance and performance degradation. Therefore, directly quantifying the Li2CO3 content is the most direct and relevant indicator for evaluating raw material quality. Determining the qualification of the raw powder based on the lithium carbonate index enables quantitative screening of raw material conditions and precise matching of pretreatment strategies.

[0027] Please see Figure 2 As shown, it is a flowchart of the process for determining the qualification of the original powder based on the lithium carbonate index in an embodiment of the present invention; Specifically, in step S2, the original powder is determined to be unqualified based on the comparison result that the lithium carbonate index is greater than or equal to a preset threshold, and the pretreatment strategy of the original powder is determined based on the difference between the lithium carbonate index and the preset threshold. Based on the comparison results showing that the lithium carbonate index is less than a preset threshold, the original powder is deemed qualified and a coating operation is performed.

[0028] In this embodiment of the invention, the preset threshold is determined based on the application performance requirements of the original LLZO powder and the subsequent modification process window, and its value is in the range of 0.15 to 0.35, preferably 0.25.

[0029] Specifically, in step S2, the pretreatment strategy for the raw powder is determined based on the difference between the lithium carbonate index and a preset threshold, including: If the difference in lithium carbonate index is less than the preset difference, the pretreatment strategy for the original powder is determined to be to automatically execute the thermal cleaning procedure. If the difference in lithium carbonate index is greater than or equal to the preset difference, the pretreatment strategy for the original powder is determined to be an automatic thermal cleaning and mechanical activation combined process. The lithium carbonate index difference is the difference between the lithium carbonate index and a preset threshold.

[0030] In this embodiment of the invention, the preset difference value is 0.10, but the value is not limited to this. Those skilled in the art can adjust the value according to actual needs.

[0031] Specifically, the thermal cleaning process is as follows: The original LLZO powder with excessive lithium carbonate index is placed in a tube furnace under an inert atmosphere or vacuum, and heat-treated by a preset heating program (e.g., heating to 500-700°C at a rate of 2-5°C / min), and held at this temperature for 1-3 hours, so that most of the lithium carbonate impurities on the surface are thermally decomposed into lithium oxide and carbon dioxide gas. Then, it is cooled to room temperature under the protection of an inert atmosphere to obtain qualified LLZO powder with significantly reduced surface impurities. The combined process of thermal cleaning and mechanical activation is as follows: First, the original LLZO powder is subjected to thermal cleaning treatment with parameters similar to those mentioned above to remove the main lithium carbonate impurities; then, the thermally cleaned powder is treated in an inert atmosphere-protected mechanical activation device (such as a planetary ball mill or a high-energy vibration mill) with specific grinding media (such as zirconia balls) at a speed of 200-400 rpm for 2-4 hours. The residual surface impurity layer is further removed by mechanical force, the powder surface is activated and its dispersibility is improved, thereby obtaining LLZO powder with a uniform and qualified surface condition.

[0032] Specifically, when the lithium carbonate index difference is less than a preset difference, the powder is heated to a first preset temperature and held at that temperature for a first preset time under a high-purity argon atmosphere. When the lithium carbonate index difference is greater than or equal to a preset difference, the powder is heated to a second preset temperature and held at that temperature for a second preset time under a high-purity argon atmosphere, and then immediately subjected to mechanical ball milling under an inert atmosphere.

[0033] In this embodiment of the invention, the first preset temperature ranges from 450°C to 550°C, and the first preset duration ranges from 1 to 3 hours. Preferably, the first preset temperature is 500°C and the first preset duration is 2 hours. The second preset temperature ranges from 500°C to 600°C, and the second preset duration ranges from 2 to 4 hours. Preferably, the second preset temperature is 550°C and the second preset duration is 3 hours. A planetary ball mill is used for mechanical ball milling, and the ball milling parameters include a ball-to-material ratio of 3:1, a rotation speed of 200 rpm, and a ball milling time of 1 hour.

[0034] Understandably, the purpose is to gently remove any loose reactive layer (such as Li2O) that may remain after thermal cleaning and activate the powder surface to increase its reactivity, thus providing a better interface for subsequent gel coating, rather than to significantly refine the powder particle size.

[0035] Specifically, step S3 includes the following process: Step S31: Prepare the modified precursor solution; Step S32: Under the protection of an inert atmosphere and with stirring, the qualified raw powder is added to the precursor solution to form a uniform suspension and mixed to make the precursor uniformly adsorbed on the surface of the powder particles. Step S33: Introduce a hydrolysis medium into the suspension system and adjust the reaction temperature to promote the hydrolysis-condensation reaction of the surface-adsorbed precursors, thereby forming a uniform amorphous gel coating layer in situ on the powder surface. Step S34: The reaction system is subjected to solid-liquid separation, and the obtained solid product is washed and preliminarily dried to obtain an intermediate powder with a gel layer on the surface.

[0036] Specifically, in step S31, the preparation process of the modified precursor solution involves dissolving or dispersing a lithium source compound and a metal source compound selected from at least one of Al, Ti, Ta, Nb, Si, B, or P in a composite solvent composed of alcohols, organic acids, and chelating agents to form a clear and stable modified precursor solution. The total molar concentration of the metal source compound is controlled within the range of 0.05 mol / L to 0.5 mol / L, and the mass ratio of the total molar amount of metal elements to the mass of the LLZO powder to be modified is controlled within the range of 0.005 to 0.02.

[0037] In step S32, the prepared precursor solution is transferred to a three-necked flask equipped with mechanical stirring, temperature control, and argon inlet / outlet. High-purity argon gas (purity >99.999%) is continuously introduced to displace and maintain an inert atmosphere within the reactor. Stirring is started and the rotation speed is set to 500 rpm. Subsequently, under continuous stirring, the pretreated LLZO powder (e.g., 10.0 g by mass, average particle size D50 = 1.0 μm) that passed the test in step S2 is slowly and batch-wise added to the precursor solution through a feeding funnel. The feeding time is controlled within 15–20 minutes to prevent powder agglomeration. After the feeding is complete, the system is heated to 35 °C and maintained at this temperature, and stirring is continued at 500 rpm for 120 minutes. This mixing process aims to fully disperse the LLZO particles to form a uniform suspension and drive the precursor molecules to uniformly adsorb onto the surface of the powder particles through physical and chemical interactions.

[0038] In step S33, under argon protection and a constant temperature of 35°C, a mixed solution of deionized water and anhydrous ethanol (water to ethanol volume ratio of 1:9, total water volume of 120% of the theoretically required stoichiometric amount for complete hydrolysis) is slowly added dropwise to the suspension obtained in step S32 through a constant-pressure dropping funnel. The dropping rate is controlled at 1.0 mL / min. After the water is added, the temperature of the reaction system is slowly increased to 60°C at a rate of 0.5°C / min and maintained at this temperature for 180 minutes. During this process, the trimethyl borate and lithium acetate precursors adsorbed on the surface of the LLZO particles undergo controlled hydrolysis and condensation reactions, generating an amorphous lithium boron oxide gel in situ on the particle surface, which gradually crosslinks to form a continuous and uniform coating layer, thus avoiding the formation of independent precipitated particles in the bulk solution phase.

[0039] In step S34, after the reaction is complete, the entire reaction system is cooled to room temperature. Under argon protection, using corrosion-resistant centrifuge tubes, the mixture is centrifuged at 8000 rpm for 10 minutes, and the supernatant is carefully removed to complete solid-liquid separation. Next, a dispersion-centrifugation washing procedure is used, with anhydrous ethanol as the washing agent, to thoroughly wash the obtained solid product three times to remove any unreacted precursors, byproducts, and residual solvent. The washed wet filter cake is transferred to a vacuum drying oven and dried at 60 °C and -0.095 MPa for 12 hours. Finally, an LLZO intermediate powder with a uniformly coated amorphous Li3BO3 gel layer is obtained. This powder is a loose, pale white solid and is used in subsequent heat treatment steps.

[0040] Please see Figure 3 As shown, it is a flowchart of determining the qualification of the coating based on the coating quality index in an embodiment of the present invention; Specifically, in step S4, based on the comparison result that the coating quality index is less than the preset quality index, the coating is determined to be unqualified, and the preset condition parameters of step S3 are adjusted based on the coating layer thickness variation coefficient. Based on the comparison result that the coating quality index is greater than or equal to the preset quality index, the coating is determined to be qualified.

[0041] Specifically, the coating quality index is determined based on the coating coverage rate and the coating thickness uniformity index. The coating quality index = first weighting coefficient × coating coverage rate / coverage rate threshold + second weighting coefficient × uniformity index threshold / coating thickness uniformity index, where the first weighting coefficient is 0.6, the coverage rate threshold is 95%, the second weighting coefficient is 0.4, and the uniformity index threshold is 5.0.

[0042] The coating coverage rate was obtained through scanning electron microscopy (SEM) image analysis. First, the gel-coated intermediate powder was ultrasonically dispersed in anhydrous isopropanol, then dropped onto a silicon wafer and dried to obtain a well-dispersed monolayer particle sample. Subsequently, gold sputtering was performed to enhance conductivity. Using a field emission scanning electron microscope (FET), at least 30 well-dispersed individual particles were randomly selected at an accelerating voltage of 5 kV and a magnification of 100,000x, and high-resolution secondary electron images were acquired. Professional image analysis software (such as ImageJ) was used to perform thresholding and binarization on each image, converting the grayscale image into a black-and-white binary image. White areas represent the highly conductive coating layer, and black areas represent the exposed LLZO matrix or coating defects. The software automatically calculated the percentage of white pixels (coated areas) to the total pixels (area within the particle outline) in each particle image, which is the coating coverage rate of that particle. Finally, the coating coverage rate was calculated as the arithmetic mean of the coverage rates of all statistically analyzed particles.

[0043] The coating thickness uniformity index was obtained through cross-sectional analysis using transmission electron microscopy (TEM). First, the gel-coated intermediate powder was mixed with epoxy resin and cured to prepare an insert. Then, using ultrathin slicing technology with a diamond scalpel, it was cut into ultrathin slices approximately 80 nanometers thick and transferred onto a copper mesh support film to obtain TEM cross-sectional samples. At least 30 particles with clear cross-sections and intact coatings were randomly selected and imaged using TEM at 200,000x magnification. In each high-resolution TEM image, at least 10 measurement points were selected at equal intervals along the coating contour of a single particle. Image analysis software was used to accurately measure the coating thickness perpendicular to the particle surface at each point. All thickness data for all measured particles were statistically analyzed, and the overall average thickness and overall standard deviation were calculated. The coating thickness uniformity index is the reciprocal of the coating thickness coefficient of variation, where the coefficient of variation is calculated as (standard deviation of coating thickness / average thickness) × 100%.

[0044] In this embodiment of the invention, the preset quality index is 0.9, but the value is not limited to this. Those skilled in the art can adjust the value according to actual needs.

[0045] Specifically, in step S4, based on the condition that the coefficient of variation of the coating thickness is greater than or equal to the first preset coefficient of variation and less than the second preset coefficient of variation, it is determined to increase the preset stirring speed in step S3. Based on the condition that the coefficient of variation of the coating thickness is greater than or equal to the second preset coefficient of variation, it is determined that, while increasing the preset stirring speed, the heating rate of the hydrolysis-condensation reaction in step S3 should be reduced simultaneously.

[0046] In this embodiment of the invention, the first preset coefficient of variation is 20%, and the second preset coefficient of variation is 30%, but the above values ​​are not limited to these, and those skilled in the art can adjust the above values ​​according to actual needs.

[0047] Specifically, the adjustment range of the preset stirring speed in step S3 is positively correlated with the difference in the coefficient of variation. If the difference in the coefficient of variation is less than the preset difference in the coefficient of variation, the stirring speed is increased to the corresponding value using the first speed adjustment coefficient of 1.2. If the difference in the coefficient of variation is greater than or equal to the preset difference in the coefficient of variation, the stirring speed will be increased to the corresponding value using the second speed adjustment factor of 1.5. The coefficient of variation difference is the difference between the coefficient of variation of the coating layer thickness and the first preset coefficient of variation.

[0048] In this embodiment of the invention, the preset coefficient of variation difference is 5%, but this value is not limited to this. Those skilled in the art can adjust this value according to actual needs.

[0049] Please see Figure 4 As shown, it is a flowchart of the present invention for determining the passability of surface modification based on the performance evaluation index; Specifically, step S6 includes the following process: The ionic conductivity and critical current density were obtained by electrochemical performance testing of surface-modified LLZO powder. The performance evaluation index is calculated based on ionic conductivity and critical current density. Compare the performance evaluation index with the preset evaluation index; Based on the comparison result that the performance evaluation index is less than the preset evaluation index, the surface modification is deemed unqualified. Based on the condition that the ionic conductivity is less than the preset conductivity, the heat treatment temperature of step S5 is reduced, or the coating reaction time of step S3 is increased based on the condition that the critical current density is less than the preset current density. The surface modification is deemed qualified based on the comparison results where the performance evaluation index is greater than or equal to the preset evaluation index.

[0050] In this embodiment of the invention, the heat treatment temperature of step S5 is reduced based on the difference between the preset conductivity and the ionic conductivity, and the adjustment range of the heat treatment temperature is 550 ℃ to 650 ℃; the coating reaction time of step S3 is increased based on the difference between the preset current density and the critical current density, and the adjustment range of the coating reaction time is 120 minutes to 240 minutes. The specific adjustment range is not limited, as long as the adjustment range is positively correlated with the difference.

[0051] Specifically, the performance evaluation index is calculated using the following formula: ; In the formula, P is the performance evaluation index. It is the ionic conductivity. To preset the conductivity, set The critical current density, To preset the current density, set 0.5 mA / cm 2 .

[0052] In this embodiment of the invention, the preset evaluation index is 0.9, but this value is not limited to this. Those skilled in the art can adjust the value according to actual needs.

[0053] Specifically, in step S5, the heat treatment process is as follows: the qualified coated gel intermediate powder is evenly spread in an alumina crucible and placed in a tube furnace. Under the protection of a high-purity argon atmosphere with a flow rate of 150 mL / min, the temperature is first raised to 350 °C at 3 °C / min and held for 90 minutes to completely remove residual solvents and organic groups from the gel layer; then the temperature is raised to the core heat treatment temperature of 600 °C at 4 °C / min and held for 180 minutes to allow the amorphous gel layer to fully crystallize and undergo controllable interfacial interdiffusion with the LLZO matrix surface to form a chemically bonded composite interface layer; after the heat treatment is completed, the powder is naturally cooled to room temperature in the furnace, and after gentle grinding and sieving, the surface-modified LLZO powder is obtained. Example

[0054] Step S1: Perform surface chemical analysis on the original LLZO powder to obtain the lithium carbonate index, which is used to characterize the content of surface impurities. The lithium carbonate index was measured to be 0.38. Step S2: Based on the comparison result of the lithium carbonate index of 0.38 and the preset threshold of 0.25, the original powder is determined to be unqualified. The difference in lithium carbonate index is 0.13. The pretreatment strategy for the original powder is to automatically execute a combined process of thermal cleaning and mechanical activation. Step S3: Mix the qualified raw powder with the modified precursor solution and react under the conditions of stirring speed of 500 rpm, heating rate of 0.5 ℃ / min and reaction time of 180 minutes to form a uniform gel coating layer on the powder surface and obtain gel-coated intermediate powder. In step S4, the coating quality index is obtained by characterizing the intermediate powder coated by the gel. The coating quality index is 0.82. Based on the comparison between the coating quality index of 0.82 and the preset quality index of 0.9, the coating is determined to be unqualified. The stirring speed and heating rate in step S3 are adjusted based on the coefficient of variation of the coating layer thickness.

[0055] In this embodiment, the coefficient of variation of the coating thickness was measured to be 25%. Based on the condition that the coefficient of variation of the coating thickness is greater than or equal to the first preset coefficient of variation of 20% and less than the second preset coefficient of variation of 30%, it was determined to increase the stirring speed in step S3. The adjusted stirring speed was 750 rpm. Example

[0056] Step S1: Perform surface chemical analysis on the original LLZO powder to obtain the lithium carbonate index, which is used to characterize the content of surface impurities. The lithium carbonate index was measured to be 0.38. Step S2: Based on the comparison result of the lithium carbonate index of 0.38 and the preset threshold of 0.25, the original powder is determined to be unqualified. The difference in lithium carbonate index is 0.13. The pretreatment strategy for the original powder is to automatically execute a combined process of thermal cleaning and mechanical activation. Step S3: Mix the qualified raw powder with the modified precursor solution and react under the conditions of stirring speed of 750 rpm, heating rate of 0.5 ℃ / min and reaction time of 180 minutes to form a uniform gel coating layer on the powder surface and obtain gel-coated intermediate powder. Step S4: The coating quality index is obtained by characterizing the intermediate powder coated with the gel. If the coating quality index is 0.9, the coating is deemed qualified. Step S5 involves heat-treating the qualified gel-coated intermediate powder. The heat treatment process is as follows: the qualified gel-coated intermediate powder is evenly spread in an alumina crucible and placed in a tube furnace. Under the protection of a high-purity argon atmosphere with a flow rate of 150 mL / min, the temperature is first raised to 350 °C at 3 °C / min and held for 90 minutes to completely remove residual solvents and organic groups from the gel layer. Then, the temperature is raised to the core heat treatment temperature of 600 °C at 4 °C / min and held for 180 minutes to form a chemically bonded composite interface layer. After the heat treatment, the powder is naturally cooled to room temperature in the furnace and then gently ground and sieved to obtain surface-modified LLZO powder. Step S6: Electrochemical performance testing was performed on the surface-modified LLZO powder obtained in step S5. The ionic conductivity was 0.8 × 10⁻⁶. -3 The critical current density is 0.45 mA / cm², and the measured performance evaluation index is 0.85. Based on the comparison between the performance evaluation index of 0.85 and the preset evaluation index of 0.9, the surface modification is deemed unqualified. Based on the ionic conductivity and critical current density, the heat treatment temperature of step S5 is reduced or the coating reaction time of step S3 is increased.

[0057] In this embodiment, the adjusted core heat treatment temperature is 590 °C, and the adjusted coating reaction time is 186 minutes. Example

[0058] Step S1: Perform surface chemical analysis on the original LLZO powder to obtain the lithium carbonate index, which is used to characterize the content of surface impurities. The lithium carbonate index was measured to be 0.38. Step S2: Based on the comparison result of the lithium carbonate index of 0.38 and the preset threshold of 0.25, the original powder is determined to be unqualified. The difference in lithium carbonate index is 0.13. The pretreatment strategy for the original powder is to automatically execute a combined process of thermal cleaning and mechanical activation. Step S3: Mix the qualified raw powder with the modified precursor solution and react under the conditions of stirring speed of 750 rpm, heating rate of 0.5 ℃ / min and reaction time of 180 minutes to form a uniform gel coating layer on the powder surface and obtain gel-coated intermediate powder. Step S4: The coating quality index is obtained by characterizing the intermediate powder coated with the gel. If the coating quality index is 0.9, the coating is deemed qualified. Step S5 involves heat-treating the qualified gel-coated intermediate powder. The heat treatment process is as follows: the qualified gel-coated intermediate powder is evenly spread in an alumina crucible and placed in a tube furnace. Under the protection of a high-purity argon atmosphere with a flow rate of 150 mL / min, the temperature is first raised to 350 °C at 3 °C / min and held for 90 minutes to completely remove residual solvents and organic groups from the gel layer. Then, the temperature is raised to the core heat treatment temperature of 590 °C at 4 °C / min and held for 186 minutes to form a chemically bonded composite interface layer. After the heat treatment, the powder is naturally cooled to room temperature in the furnace and then gently ground and sieved to obtain surface-modified LLZO powder. Step S6: Electrochemical performance testing was performed on the surface-modified LLZO powder obtained in step S5. The ionic conductivity was 1.02 × 10⁻⁶. -3 The surface modification is qualified based on the comparison between the performance evaluation index of 1.02 and the preset evaluation index of 0.9, with a current density of 0.51 mA / cm² and a critical current density of 0.51 mA / cm².

[0059] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for surface modification of LLZO solid electrolyte powder, characterized in that, include: Step S1: Perform surface chemical analysis on the original LLZO powder to obtain the lithium carbonate index, which is used to characterize the content of surface impurities. Step S2: Based on the comparison result between the lithium carbonate index and the preset threshold, determine the qualification of the original powder. If it is unqualified, determine the pretreatment strategy of the original powder based on the difference between the lithium carbonate index and the preset threshold. Step S3: Mix the qualified raw powder with the modified precursor solution and react under preset conditions to form a uniform gel coating layer on the powder surface to obtain gel-coated intermediate powder. The preset conditions include stirring at a preset stirring speed and a preset heating program for a preset duration under an inert atmosphere. Step S4: The coating quality index is obtained by characterizing the intermediate powder coated by the gel, and the qualification of the coating is determined based on the comparison result between the coating quality index and the preset quality index. If the coating is unqualified, the stirring speed and heating rate in step S3 are adjusted based on the coefficient of variation of the coating layer thickness. Step S5: Heat-treat the qualified gel-coated intermediate powder to crystallize the coating layer and allow limited interfacial interdiffusion with the LLZO matrix surface to form a chemically bonded composite interfacial layer, thereby obtaining surface-modified LLZO powder. Step S6: Perform electrochemical performance testing on the surface-modified LLZO powder obtained in step S5, obtain the performance evaluation index, and determine the qualification of surface modification based on the comparison result of the performance evaluation index and the preset evaluation index. If the surface modification is not qualified, reduce the heat treatment temperature of step S5 or increase the coating reaction time of step S3 based on the ionic conductivity and critical current density.

2. The surface modification method for LLZO solid electrolyte powder according to claim 1, characterized in that, The lithium carbonate index R is the ratio of the sum of the intensities of the two characteristic peaks of lithium carbonate asymmetric stretching vibration and lithium carbonate out-of-plane bending vibration to the intensity of the internal standard peak.

3. The surface modification method for LLZO solid electrolyte powder according to claim 2, characterized in that, In step S2, the original powder is determined to be unqualified based on the comparison result that the lithium carbonate index is greater than or equal to a preset threshold, and the pretreatment strategy of the original powder is determined based on the difference between the lithium carbonate index and the preset threshold.

4. The surface modification method for LLZO solid electrolyte powder according to claim 3, characterized in that, In step S2, a pretreatment strategy for the raw powder is determined based on the difference between the lithium carbonate index and a preset threshold. include, If the difference in lithium carbonate index is less than the preset difference, the pretreatment strategy for the original powder is determined to be to automatically execute the thermal cleaning procedure. If the difference in lithium carbonate index is greater than or equal to the preset difference, the pretreatment strategy for the original powder is determined to be an automatic thermal cleaning and mechanical activation combined process. The lithium carbonate index difference is the difference between the lithium carbonate index and a preset threshold.

5. The surface modification method for LLZO solid electrolyte powder according to claim 4, characterized in that, The process of step S3 includes: Step S31: Prepare the modified precursor solution; Step S32: Under the protection of an inert atmosphere and with stirring, the qualified raw powder is added to the precursor solution to form a uniform suspension and mixed to make the precursor uniformly adsorbed on the surface of the powder particles. Step S33: Introduce a hydrolysis medium into the suspension system and adjust the reaction temperature to promote the hydrolysis-condensation reaction of the surface-adsorbed precursors, thereby forming a uniform amorphous gel coating layer in situ on the powder surface. Step S34: The reaction system is subjected to solid-liquid separation, and the obtained solid product is washed and preliminarily dried to obtain an intermediate powder with a gel layer on the surface.

6. The surface modification method for LLZO solid electrolyte powder according to claim 5, characterized in that, In step S4, based on the comparison result that the coating quality index is less than the preset quality index, the coating is determined to be unqualified, and the preset condition parameters of step S3 are adjusted based on the coating layer thickness variation coefficient.

7. The surface modification method for LLZO solid electrolyte powder according to claim 6, characterized in that, The coating quality index is determined based on the coating coverage rate and the coating layer thickness uniformity index.

8. The surface modification method for LLZO solid electrolyte powder according to claim 7, characterized in that, In step S4, based on the condition that the coefficient of variation of the coating thickness is greater than or equal to the first preset coefficient of variation and less than the second preset coefficient of variation, it is determined to increase the preset stirring speed in step S3. Based on the condition that the coefficient of variation of the coating thickness is greater than or equal to the second preset coefficient of variation, it is determined that, while increasing the preset stirring speed, the heating rate of the hydrolysis-condensation reaction in step S3 should be reduced simultaneously.

9. The surface modification method for LLZO solid electrolyte powder according to claim 8, characterized in that, The adjustment range of the preset stirring speed in step S3 is positively correlated with the difference in the coefficient of variation, wherein the difference in the coefficient of variation is the difference between the coefficient of variation of the coating layer thickness and the first preset coefficient of variation.

10. The surface modification method for LLZO solid electrolyte powder according to claim 9, characterized in that, The process of step S6 includes: The ionic conductivity and critical current density were obtained by electrochemical performance testing of surface-modified LLZO powder. The performance evaluation index is calculated based on ionic conductivity and critical current density. Compare the performance evaluation index with the preset evaluation index; The surface modification is deemed unqualified based on the comparison result that the performance evaluation index is less than the preset evaluation index. Based on the condition that the ionic conductivity is less than the preset conductivity, the heat treatment temperature of step S5 is reduced, or the coating reaction time of step S3 is increased based on the condition that the critical current density is less than the preset current density.

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