Pretreatment method of solid electrolyte and method for measuring residual lithium value on surface of solid electrolyte
By treating garnet solid electrolytes with a mixed solvent of isopropanol/water and a surfactant, the problem of residual lithium value error caused by hydrolysis reaction was solved, and the accurate determination of residual lithium value was achieved, thus improving the accuracy and reliability of battery material evaluation.
Patent Information
- Application Number
- CN202511784788.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-02-06
AI Technical Summary
In the prior art, when measuring the residual lithium value of garnet solid electrolytes, the hydrolysis reaction with water causes the measured residual lithium value to include both the initial residual lithium and the lithium impurities newly added by the reaction, resulting in an overestimation of the value and misjudgment, which affects the evaluation of battery performance.
Solid electrolytes are treated with isopropanol or a mixture of isopropanol and water (mass ratio 1-2:8-9) and surfactants. The solution is filtered through a needle filter to form a hydrolysis-resistant clear solution, which is then accurately determined by hydrochloric acid titration to avoid hydrolysis.
It improves the accuracy and repeatability of residual lithium determination, ensuring that the measured values are closer to the true residual lithium level of the material, and supports the accurate evaluation of battery materials.
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Figure CN121475835A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of battery material testing technology, specifically to a pretreatment method for solid electrolytes and a method for determining the residual lithium value on their surface. Background Technology
[0002] Garnet solid electrolyte (chemical formula: Lithium hydroxide (LLZO) is a key material for developing all-solid-state batteries, but it is unstable in the atmosphere and its surface reacts with water and carbon dioxide to form lithium hydroxide (LiOH) and lithium carbonate (LiOH). Residual lithium layers, such as those found on the surface, significantly increase interfacial impedance, leading to deterioration in battery performance. To improve battery performance, researchers are working to reduce surface residual lithium through material modification. Therefore, accurately measuring the residual lithium content has become a crucial step in material development.
[0003] Conventional methods use water as a solvent to dissolve and extract residual lithium for titration. However, garnet electrolytes themselves undergo hydrolysis with water, continuously generating new LiOH. This results in the final measured "residual lithium value" actually including both the initial residual lithium of the material and lithium impurities newly added during the reaction, leading to inflated results and misjudgments, thus misleading material research and evaluation. Summary of the Invention
[0004] In view of this, this application provides a method for determining the residual lithium value on the surface of a solid electrolyte, thereby solving at least one of the above-mentioned technical problems.
[0005] To achieve the above objectives, in a first aspect, this application provides a pretreatment method for a solid electrolyte, wherein the solid electrolyte comprises lithium lanthanum zirconium oxide, and the pretreatment method comprises: obtaining a residual lithium reference value in the solid electrolyte, wherein the residual lithium reference value is the mass percentage of lithium ions in the solid electrolyte; adding the solid electrolyte to a solvent to obtain a hydrolysis-resistant suspension, wherein, for the residual lithium reference value being less than 1%, the solvent comprises isopropanol, and for the residual lithium reference value being greater than or equal to 1% and less than 3%, the solvent comprises isopropanol and water, wherein the mass ratio of water to isopropanol is 1~2:8~9; and separating the hydrolysis-resistant suspension to obtain a hydrolysis-resistant clear solution.
[0006] Based on the first aspect, in some possible implementations, obtaining the residual lithium reference value in the solid electrolyte includes: adding the solid electrolyte to water to obtain an easily hydrolyzable suspension; separating the easily hydrolyzable suspension to obtain an easily hydrolyzable clear solution; and titrating the easily hydrolyzable clear solution with hydrochloric acid to obtain the residual lithium reference value in the solid electrolyte.
[0007] Based on the first aspect, in some possible implementations, adding a solid electrolyte to water to obtain an easily hydrolyzable suspension includes: weighing a solid electrolyte, adding it to water, stirring, and then allowing it to stand to obtain the easily hydrolyzable suspension, wherein the mass concentration of the solid electrolyte is 0.05 g / mL to 0.2 g / mL.
[0008] Based on the first aspect, in some possible implementations, separating the easily hydrolyzable suspension to obtain the easily hydrolyzable clear liquid includes: using a needle filter to filter the easily hydrolyzable suspension to obtain the easily hydrolyzable clear liquid, wherein the needle filter includes a filter membrane with a pore size not exceeding 0.22 μm.
[0009] Based on the first aspect, in some possible implementations, titrating the easily hydrolyzable clear liquid with hydrochloric acid includes: using potentiometric titration to titrate the easily hydrolyzable clear liquid with hydrochloric acid of a concentration of 0.01~0.05 mol / L.
[0010] Based on the first aspect, in some possible implementations, separating the hydrolysis-resistant suspension to obtain the hydrolysis-resistant clear liquid includes: filtering the hydrolysis-resistant suspension using a needle filter to obtain the hydrolysis-resistant clear liquid, the needle filter comprising at least one filter membrane with a pore size not exceeding 0.22 μm.
[0011] Based on the first aspect, in some possible implementations, the needle filter comprises two filter membranes connected in series.
[0012] Based on the first aspect, in some possible implementations, for the residual lithium reference value being greater than or equal to 1% and less than 3%, the solvent further includes a surfactant, which is a silane coupling agent or Tween.
[0013] Based on the first aspect, in some possible implementations, the mass ratio of the surfactant to the solid electrolyte is 1:1 to 10.
[0014] Secondly, this application provides a method for determining the residual lithium value on the surface of a solid electrolyte, comprising: providing a hydrolysis-resistant solution from the pretreatment method of the solid electrolyte described above, and titrating the hydrolysis-resistant solution with hydrochloric acid to obtain a residual lithium value in the solid electrolyte.
[0015] In this application, a reference value (by mass percentage) of residual lithium ions in a solid electrolyte (lithium lanthanum zirconium oxide) is first obtained as a quantitative basis for subsequent pretreatment. Then, solvents are selected according to this reference value to prepare hydrolysis-resistant suspensions: isopropanol is used when the reference value is less than 1%, and a mixed solvent of water:isopropanol = 1–2:8–9 is used when the reference value is greater than or equal to 1% and less than 3%. Subsequently, the suspensions are separated to obtain a hydrolysis-resistant clear solution. Since the solvent selection is clearly driven by the reference value, the mismatch in treatment intensity caused by empirical solvent use is avoided, improving the consistency of pretreatment for different batches of samples. Using isopropanol when the residual lithium is low reduces sample contact with water, thereby reducing the risk of introducing new lithium species through hydrolysis. Using isopropanol as the main component with only a small amount of water when the residual lithium is between 1% and 3% helps to form a stable treatment system while limiting hydrolysis. Separating the suspension to obtain a clear solution allows for timely decoupling of the solid and liquid phases, reducing subsequent reactions and interference from particles on subsequent measurements. Therefore, the resulting hydrolysis-resistant solution can more accurately reflect the original state of the sample, and the accuracy, repeatability and comparability of the pretreatment process are improved accordingly. Attached Figure Description
[0016] Figure 1 This is a flowchart illustrating a method for pretreating a solid electrolyte and a method for determining the residual lithium value on its surface, provided in an embodiment of this application. Detailed Implementation
[0017] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description in order to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.
[0018] In related technologies, the conventional method for determining the residual lithium content of garnet solid electrolytes uses water as a solvent to dissolve and extract the residual lithium, followed by titration. However, garnet electrolytes themselves undergo hydrolysis with water, continuously generating new lithium hydroxide. This results in the final measured "residual lithium value" actually including both the initial residual lithium of the material and the lithium impurities newly added by the reaction, leading to inflated results and misjudgments, thus misleading material research and evaluation.
[0019] Based on this, this application improves the pretreatment method of solid electrolyte to achieve the purpose of inhibiting hydrolysis, thereby facilitating accurate and repeatable quantification of residual lithium in the subsequent process.
[0020] Please see Figure 1Based on this, one embodiment of this application provides a pretreatment method for solid electrolytes, the pretreatment method comprising: Step 1 (S1): Obtain the reference value of residual lithium ions in the solid electrolyte. The solid electrolyte is a garnet solid electrolyte, and the reference value of residual lithium ions is the percentage of lithium ions by mass in the solid electrolyte.
[0021] In some embodiments, obtaining a reference value for residual lithium ions in a solid electrolyte includes: adding the solid electrolyte to water to obtain an easily hydrolyzable suspension; separating the easily hydrolyzable suspension to obtain an easily hydrolyzable clear solution; and titrating the easily hydrolyzable clear solution with hydrochloric acid to obtain a reference value for residual lithium in the solid electrolyte. To reduce hydrolysis errors, the entire process controls the contact time with water, temperature, and degree of air exposure of the solution, and uses potentiometric titration to identify the equivalent point.
[0022] Specifically, 5 g to 10 g of solid electrolyte is weighed and added to 50 mL to 100 mL of water. After stirring for 3 to 6 minutes (preferably 5 minutes), the mixture is allowed to stand for 1 to 3 minutes to obtain an easily hydrolyzable suspension. The mass concentration of the solid electrolyte is 0.05 g / mL to 0.2 g / mL. The easily hydrolyzable suspension is filtered using a needle filter with a pore size not exceeding 0.22 μm to obtain an easily hydrolyzable clear solution. Potentiometric titration is then performed using a solution with a concentration of 0.01 to 0.05 mol·L⁻¹. -1 The residual lithium value in the solid electrolyte was obtained by titrating the easily hydrolyzed clear solution with hydrochloric acid.
[0023] In other embodiments, obtaining a reference value for residual lithium ions in a solid electrolyte includes: rapid estimation in a non-aqueous or water-controlled system, for example, dispersing the sample in isopropanol or isopropanol / acetonitrile and performing potentiometric titration with a standard acid (such as HCl-isopropanol or formic acid-isopropanol system) to obtain an approximate residual lithium value; or using an ion-selective electrode ( Approximate values can be obtained by conductivity titration; or by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The Li content in the extract was rapidly screened. This method was used to determine the solvent composition required for subsequent pretreatment and whether a surfactant needed to be added.
[0024] Step 2 (S2): Add the solid electrolyte to the solvent to obtain a hydrolysis-resistant suspension. For residual lithium reference values less than 1%, the solvent includes isopropanol; for residual lithium reference values greater than or equal to 1% and less than 3%, the solvent includes isopropanol and water, with a water:isopropanol mass ratio of 1-2:8-9 (i.e., isopropanol:water = 8-9:1-2).
[0025] For residual lithium reference values greater than or equal to 1% and less than 3%, the solvent also includes a surfactant, which is a silane coupling agent or Tween. The mass ratio of surfactant to solid electrolyte is 1:1 to 10. Preferably, the surfactant is first dissolved in isopropanol, and then a measured amount of water is added to form a homogeneous mixed solvent, thereby improving powder wetting and dispersion and inhibiting surface hydrolysis.
[0026] Step 3 (S3): Separate the hydrolysis-resistant suspension to obtain the hydrolysis-resistant clear solution.
[0027] In some embodiments, separating the hydrolysis-resistant suspension includes filtering the hydrolysis-resistant suspension using a needle filter with a pore size not exceeding 0.22 μm to obtain a hydrolysis-resistant clear solution. Since water is introduced during subsequent titration, selecting an appropriate membrane pore size ensures the filtrate is clear and the titration baseline is stable. The needle filter has two membranes connected in series, and the membrane material includes polyethersulfone (PES) or polyvinylidene fluoride (PVDF) to ensure chemical compatibility with the isopropanol / water system and to obtain a clear filtrate.
[0028] In other embodiments, separating the hydrolysis-resistant suspension includes using other separation methods, such as rotary centrifugation (5000–10000 r / min, 2–5 min), pressure filtration, or membrane separation, to obtain a clear primary filtrate, which, if necessary, is further polished and filtered through a 0.22 μm needle filter to obtain a hydrolysis-resistant clear solution.
[0029] In this application, a mixed system consisting of a surfactant and isopropanol / water is introduced to achieve stable dissolution and determination of ≤3% (mass fraction) residual lithium. When the isopropanol:water ratio is 8:2, the influence of water on the lattice and surface of the garnet material is significantly reduced; the surfactant forms an adsorption layer on the powder surface and improves wetting and dispersion, which can further suppress hydrolysis side reactions and the regeneration of LiOH, thereby enabling accurate and repeatable quantitative determination of residual lithium.
[0030] Based on this, one embodiment of this application also provides a method for determining the residual lithium value on the surface of a solid electrolyte, comprising: Step 4 (S4): Provide a hydrolysis-resistant solution from the pretreatment method of the solid electrolyte in Step 3.
[0031] Step 5 (S5): Titrate the hydrolysis resistant solution with hydrochloric acid to obtain the residual lithium value in the solid electrolyte.
[0032] Specifically, using hydrochloric acid of known concentration as the titrant, potentiometric titration was performed on the hydrolysis-resistant solution under continuous stirring, and the "potential / volume (E–V)" or "pH / volume (pH–V)" curves were recorded in real time. The soluble alkaline lithium species in the hydrolysis-resistant solution mainly originated from LiOH and... Dissolution.
[0033] During potentiometric titration, hydrochloric acid first neutralizes the hydrolysis-resistant solution. and put Transform into The first equivalent point appears ( Continue adding hydrochloric acid until Transform into A second equivalent point appears ( Stop the titration.
[0034] In terms of amount of substance, to The amount of acid consumed is exactly equal to the amount of lithium (as Li) in the solution, n(Li) = C HCl ×V2, and then combined with the sample weighing mass, the residual lithium value X = M(Li) × n(Li) is calculated as follows, where M(Li) = 6.94. Furthermore, blank correction and parallel sample retesting are employed to ensure accuracy.
[0035] In this application, (1) a mixed solution of isopropanol / water / surfactant is used to reduce the reaction between the solid electrolyte and water, thereby improving the accuracy of residual lithium content determination; (2) a principle and method for selecting a suitable dissolution / extraction system based on the properties of the solid electrolyte and the reference value of residual lithium is provided, thereby taking into account both dissolution efficiency and material stability; (3) a needle filter is simpler than traditional vacuum filtration, and when combined with a 0.22 μm double-layer filter membrane, it can effectively remove fine particles, optimize the filtration method, and improve the accuracy and repeatability of the test; (4) the selected solvent system minimizes the reaction with the material itself, suppresses the secondary generation of alkaline lithium species while ensuring titration sensitivity, improves measurement reliability, and helps to accurately evaluate and quickly screen the application performance of solid electrolytes in batteries.
[0036] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the present application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically mentioned are all conventional commercially available products or open-source materials.
[0037] 1) Pretreatment: Accurately weigh m grams (5–8 g) of garnet solid electrolyte (i.e., lithium lanthanum zirconium oxide), add it to 100 mL of pure water, stir for about 5 min, let stand for 1–3 min, and filter through a syringe filter with a pore size not exceeding 0.22 μm to obtain a hydrolysis-resistant clear solution. The total volume of the hydrolysis-resistant clear solution is denoted as [missing information]. (Usually 100 mL), take 5–10 mL of the hydrolyzable supernatant for titration, and record the sample volume. The dilution factor is... Then, the residual lithium reference value X was obtained by titration with (0.01~0.05) mol / L standard HCl.
[0038] Specifically, titration with standard HCl containing For hydrolyzable solutions, record the E–V (or pH–V) curves, and two equivalent points will appear: Neutralization And The equivalent point. Continue The equivalent point (total equivalent point).
[0039] The quantitative relationship of the amount of substance: .thus: Molecular weight of lithium carbonate Mass fraction of lithium carbonate .
[0040] Molecular weight of lithium hydroxide Mass fraction of lithium hydroxide .
[0041] Lithium Residual Reference Value The experimental data obtained from the three measurements are shown in Table 1 below: Table 1: Experimental data obtained from three measurements Since garnet solid electrolytes undergo hydrolysis in pure water, the residual lithium reference value X_Li(%) actually includes the initial residual lithium in the garnet solid electrolyte and the lithium impurities newly added during the reaction, resulting in a higher reference value compared to the actual residual lithium on the material surface. However, X_Li(%) can still serve as an "upper limit reference" for solvent system selection and process parameter setting, used for grading (X<1% select isopropanol; 1%≤X<3% select isopropanol / water with added surfactant), so as to obtain a more accurate residual lithium measurement value in subsequent hydrolysis-resistant systems.
[0042] Specifically, if X < 1%, pure isopropanol is selected; if 1% ≤ X < 3%, Tween (the mass ratio of surfactant to solid electrolyte is 1:1 to 10) is added to a system of water:isopropanol = 2:8 to prepare a solvent to dissolve / extract the residual lithium of the garnet solid electrolyte and obtain a hydrolysis-resistant solution.
[0043] 2) Determination of residual lithium in hydrolyzable solution 2.1 Take (5-10) mL of the hydrolysis-resistant clarified solution from step 1) and titrate it with (0.01~0.05) mol / L HCl to obtain the residual lithium value. For residual lithium reference value X less than 1%, the test results of different solvent components are shown in Table 2. The component content in each solvent is a mass ratio, and the same applies below: Table 2: Residual lithium values (X<1% samples, comparison of different solvent systems) It can be found that reducing the water content (1:9) or using pure isopropanol directly can significantly reduce the positive deviation caused by hydrolysis; in the 1:9 or "2:8 + Tween" system, the range is reduced to 0.0007, and the repeatability is better than the 2:8 system with higher water content, indicating that moderately reducing the water content and introducing surfactants can help improve the stability and accuracy of the data.
[0044] 2.2 Take 5–10 mL of the hydrolysis-resistant clarified solution from step 1) and titrate it with (0.01–0.05) mol / L HCl to obtain the residual lithium value. For the residual lithium reference value X greater than 1 and less than 3, the test results for different solvent components are shown in Table 3: Table 3: Residual lithium values (for samples with 1% ≤ X < 3%, comparison with or without surfactant addition) It can be observed that after introducing Tween under the condition of water:isopropanol=2:8, the average measured value decreased from 0.1892% to 0.1840%, and the range decreased from 0.0034 to 0.0030. This indicates that the surfactant improved the wetting and dispersion of the powder and inhibited the secondary reaction, resulting in a lower and more robust measured value that is closer to the true residual lithium level of the material.
[0045] Comparative Example 1 For residual lithium reference values X greater than 1 and less than 3, pure water and ethanol were used as solvents, and the other steps were the same as in Example 1. The results are shown in Table 4. Table 4: Comparative Results (Pure Water and Ethanol Systems) It can be observed that the measured values in the pure water and ethanol systems are significantly higher and fluctuate greatly (ranges of 0.147 and 0.201, respectively). Compared with the isopropanol / water / surfactant hydrolysis resistant system proposed in this application (see Tables 2 and 3), the values and dispersion are significantly unfavorable, indicating that the traditional solvent system is prone to problems such as hydrolysis or insufficient wetting, making it difficult to obtain true and reliable residual lithium results.
[0046] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.
Claims
1. A pretreatment method for a solid electrolyte, wherein the solid electrolyte comprises lithium lanthanum zirconium oxide, characterized in that, The preprocessing method includes: Obtain a reference value for residual lithium ions in the solid electrolyte, wherein the reference value for residual lithium ions is the mass percentage of lithium ions in the solid electrolyte; A solid electrolyte is added to a solvent to obtain a hydrolysis-resistant suspension. For a residual lithium reference value of less than 1%, the solvent includes isopropanol. For a residual lithium reference value of greater than or equal to 1% and less than 3%, the solvent includes isopropanol and water, and the mass ratio of water to isopropanol is 1-2:8-9. The hydrolysis-resistant suspension is separated to obtain a hydrolysis-resistant clear solution.
2. The preprocessing method as described in claim 1, characterized in that, Obtaining the residual lithium reference value in the solid electrolyte includes: A solid electrolyte is added to water to obtain an easily hydrolyzable suspension; the easily hydrolyzable suspension is separated to obtain an easily hydrolyzable clear solution; the easily hydrolyzable clear solution is titrated with hydrochloric acid to obtain a reference value for residual lithium in the solid electrolyte.
3. The preprocessing method as described in claim 2, characterized in that, Adding solid electrolytes to water to obtain easily hydrolyzable suspensions includes: Weigh out a solid electrolyte, add it to water and stir, then let it stand to obtain the easily hydrolyzable suspension, wherein the mass concentration of the solid electrolyte is 0.05 g / mL to 0.2 g / mL.
4. The preprocessing method as described in claim 2, characterized in that, Separating the easily hydrolyzed suspension to obtain an easily hydrolyzed clear solution includes: The easily hydrolyzable suspension is filtered using a needle filter to obtain the easily hydrolyzable clear solution, wherein the needle filter comprises a filter membrane with a pore size not exceeding 0.22 μm.
5. The preprocessing method as described in claim 2, characterized in that, Titration of the easily hydrolyzable supernatant with hydrochloric acid includes: Potentiometric titration was performed using a concentration of 0.01–0.05 mol·L⁻¹. -1 The hydrochloric acid was used to titrate the easily hydrolyzed clear solution.
6. The preprocessing method as described in claim 1, characterized in that, Separating the hydrolysis-resistant suspension to obtain a hydrolysis-resistant clear solution includes: The hydrolysis-resistant suspension is filtered using a needle filter to obtain the hydrolysis-resistant clear liquid, wherein the needle filter comprises at least one filter membrane with a pore size not exceeding 0.22 μm.
7. The pretreatment method as described in claim 6, characterized in that, The needle filter has two filter membranes connected in series.
8. The preprocessing method as described in claim 1, characterized in that, For residual lithium reference values greater than or equal to 1% and less than 3%, the solvent also includes a surfactant, which is a silane coupling agent or Tween.
9. The pretreatment method as described in claim 8, characterized in that, The mass ratio of the surfactant to the solid electrolyte is 1:1 to 10.
10. A method for determining the residual lithium value on the surface of a solid electrolyte, characterized in that, include: Provide a hydrolysis-resistant clear solution in the pretreatment method of the solid electrolyte according to any one of claims 1 to 9; The residual lithium in the solid electrolyte is determined by titrating the hydrolysis-resistant solution with hydrochloric acid.