Method for measuring particle size of lithium salt
By using a non-polar organic solvent as the dispersion medium in a low dew point drying environment, the problem of lithium salts being hygroscopic and soluble was solved, achieving high precision and repeatability in lithium salt particle size measurement and expanding the application of laser particle size analyzers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI XUANYI NEW ENERGY DEV CO LTD
- Filing Date
- 2026-03-26
- Publication Date
- 2026-05-29
AI Technical Summary
In the existing technology, lithium salts such as lithium bromide are difficult to measure accurately due to their hygroscopic and soluble properties, which affects the performance of sulfide solid electrolyte materials.
In a dry environment with a dew point ≤ -45℃, non-polar organic solvents such as n-heptane, n-dodecane, and n-undecane are used as dispersion media, and a laser particle size analyzer is used to measure the particle size of lithium salt suspensions to prevent moisture absorption and dissolution, thus ensuring measurement accuracy.
It achieves accuracy and repeatability in lithium salt particle size measurement, with a relative standard deviation (RSD) of <2%, and is suitable for particle size measurement of highly hygroscopic lithium salts, expanding the application range of laser particle size analyzers and making them applicable to other easily soluble materials.
Smart Images
Figure CN122108870A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of materials measurement technology, and more specifically, to a method for measuring the particle size of lithium salts. Background Technology
[0002] With the continuous development of new energy technologies, all-solid-state lithium batteries have attracted much attention due to their advantages such as high energy density and high safety. Among them, sulfide solid electrolytes, due to their good ionic conductivity and processability, have gradually become the first choice for many lithium battery companies in the all-solid-state battery technology route. In the synthesis of sulfide solid electrolytes, lithium bromide (LiBr) is one of the important raw materials, and its physical properties have a significant impact on the performance of the final product. Particle size is an important parameter affecting the performance of lithium bromide in many aspects, including its participation in reactions, dispersibility, mixing uniformity, and reaction kinetics. Especially in the preparation of sulfide electrolyte materials with high requirements for uniformity and low porosity, precise control of lithium bromide particle size is crucial.
[0003] However, there are currently no publicly available patents or literature reports on particle size testing methods for lithium bromide. The main reason for this situation is that lithium bromide is highly hygroscopic and easily soluble in water and ethanol, making most of the dispersion media required for conventional particle size testing unsuitable. This physical characteristic greatly increases the difficulty of particle size measurement and limits its application in actual production control. Summary of the Invention
[0004] The main objective of this application is to provide a method for measuring the particle size of lithium bromide, in order to solve the problem in the prior art that the particle size of lithium salt powder, represented by lithium bromide, cannot be accurately measured due to its hygroscopic and soluble properties.
[0005] To achieve the above objectives, according to one aspect of this application, a method for measuring lithium salt particle size is provided, comprising the following steps:
[0006] Step S1: Obtain the lithium salt powder to be tested;
[0007] Step S2: Under the condition that the dew point of the measuring environment is ≤-45℃, the lithium salt powder is dispersed in a dispersion medium to form a lithium salt suspension; the particle size of the lithium salt in the lithium salt suspension is measured using a particle size measuring device; wherein, the dispersion medium is selected from at least one of n-heptane, n-dodecane, n-undecane, n-decane, n-hexane, toluene, xylene, anisole, and butyl butyrate.
[0008] Furthermore, the lithium salt powder is lithium halide, lithium sulfide, or lithium carbonate.
[0009] Furthermore, the lithium salt powder has a water content ≤100ppm and a purity ≥99.9%.
[0010] Furthermore, the particle size of the lithium salt powder is 0~100μm and is not 0.
[0011] Furthermore, the lithium salt powder is lithium bromide, lithium chloride, or lithium sulfide.
[0012] Further, the lithium salt powder is lithium bromide, and the dispersion medium is at least one selected from n-heptane, n-undecane, anisole, and butyl butyrate; preferably, the dispersion medium is a mixture of n-heptane and butyl butyrate.
[0013] Furthermore, the lithium salt powder is lithium chloride, and the dispersion medium is at least one of n-heptane, anisole, and butyl butyrate; preferably, the dispersion medium is n-heptane or anisole.
[0014] Furthermore, the lithium salt powder is lithium sulfide, and the dispersion medium is at least one of n-heptane, anisole, and butyl butyrate; preferably, the dispersion medium is n-heptane or anisole.
[0015] Furthermore, the lithium salt powder is lithium carbonate, and the dispersion medium is n-heptane and water.
[0016] Furthermore, the weight ratio of lithium salt powder to dispersion medium is 1:(1000~3000).
[0017] Furthermore, the dew point of the measured environment is ≤-50℃.
[0018] Furthermore, the atmosphere of the measurement environment is an inert atmosphere.
[0019] Furthermore, the weight ratio of lithium salt powder to dispersion medium is 1:(1500~2500).
[0020] Furthermore, the dew point of the measured environment is ≤-55℃.
[0021] Furthermore, the atmosphere of the measurement environment was an argon atmosphere.
[0022] Furthermore, the particle size measurement device is a laser particle size analyzer.
[0023] Furthermore, dispersion includes ultrasonic dispersion and magnetic stirring.
[0024] Furthermore, the measurement conditions for the laser particle size analyzer include: powder refractive index of 1.3~1.8, solvent refractive index of 1.3~1.6, absorptivity of 0.08~0.12%, shading of 5~12%, and sample cell rotation speed of 1800~3000 rpm.
[0025] Furthermore, the ultrasonic dispersion time is 1~30 min.
[0026] Furthermore, the magnetic stirring speed is 500~3000 rpm.
[0027] Furthermore, the relative standard deviation (RSD) of the measurement method is <2%.
[0028] Compared with the prior art, this application has the following beneficial effects:
[0029] The lithium salt particle size measurement method provided in this application is particularly suitable for particle size measurement of easily hygroscopic / easily soluble samples. This method is mainly aimed at inorganic salt powders such as lithium salts, which are easily hygroscopic and soluble in water or alcohol solvents. Under controlled drying conditions and with the selection of suitable solvents, it can effectively prevent the sample from absorbing moisture, agglomerating, or dissolving before measurement, ensuring the accuracy and repeatability of the measurement results; the measurement RSD is <2%. This application solves the problem of dependence on polar solvents in existing particle size analysis by selecting specific weakly polar organic solvents such as n-heptane, n-dodecane, n-undecane, n-decadecane, n-hexane, toluene, xylene, anisole, and butyl butyrate as dispersion media. This expands the applicability of laser particle size analyzer technology to inorganic salts and other sensitive materials. The method is also applicable to other salts or highly hygroscopic powder materials with similar physicochemical properties. Furthermore, the measurement method can be mainly completed using a laser particle size analyzer, exhibiting good operability and potential for easy industrial application. Attached Figure Description
[0030] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:
[0031] Figure 1 This is a graph showing the particle size distribution of lithium bromide measured in Example 1 of this application;
[0032] Figure 2 This is a graph showing the particle size distribution of lithium chloride measured in Example 2 of this application;
[0033] Figure 3 This is a graph showing the particle size distribution of lithium sulfide measured in Example 3 of this application.
[0034] Figure 4 This is a graph showing the particle size distribution of lithium carbonate measured in Example 4 of this application. Detailed Implementation
[0035] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.
[0036] In existing technologies, lithium salt powders, such as lithium bromide, are prone to moisture absorption and dissolution, making accurate measurement of their particle size distribution difficult. Currently, the most widely used particle size analyzer is the laser particle size analyzer, but it requires a suitable liquid-phase dispersion medium for sample preparation. Traditional aqueous or alcohol-based dispersants can cause lithium salts to dissolve or undergo chemical changes, thus affecting test accuracy. Therefore, how to screen a dispersion medium compatible with lithium salts that can effectively disperse particles without triggering physical or chemical reactions is one of the key problems this application aims to solve.
[0037] Therefore, according to one aspect of this application, a method for measuring the particle size of lithium bromide powder is provided, comprising the following steps:
[0038] To achieve the above objectives, according to one aspect of this application, a method for measuring the particle size of lithium bromide is provided, comprising the following steps:
[0039] Step S1: Obtain the lithium salt powder to be tested;
[0040] Step S2: Under the condition that the dew point of the measuring environment is ≤-45℃, the lithium salt powder is dispersed in a dispersion medium to form a lithium salt suspension; the particle size of the lithium salt in the lithium salt suspension is measured using a particle size measuring device; wherein, the dispersion medium is selected from at least one of n-heptane, n-dodecane, n-undecane, n-decane, n-hexane, toluene, xylene, anisole, and butyl butyrate.
[0041] This application first ensures that the dew point of the measurement environment is ≤-45℃, for example, by completing the measurement process in a dry room with a specific dew point or inert atmosphere-protected glove box to prevent lithium salt from absorbing moisture or reacting. This application addresses the hygroscopic and soluble characteristics of lithium salt by screening for dispersion media highly suitable for lithium salts, such as at least one of alkanes including n-heptane, n-dodecane, n-undecane, n-decadecane, and n-hexane, as well as toluene, xylene, anisole, and butyl butyrate. This type of dispersion media has good compatibility with the physicochemical properties of lithium salts, does not chemically react with lithium salts, does not dissolve lithium salts, and has moderate viscosity, which helps to uniformly disperse lithium salt particles; the measured particle size distribution values include D... 10 D 50 and D 90 value.
[0042] The particle size measurement method provided in this application is highly suitable for measuring the particle size of highly hygroscopic and water-soluble lithium salt powders. By using a strictly humidity-controlled environment and combining it with a non-polar or weakly polar organic solvent (such as n-heptane, anisole, and lipid compounds) as a dispersion medium, it effectively suppresses the hygroscopic deliquescence, solvent dissolution, and particle agglomeration behavior of sensitive lithium salts such as lithium bromide before testing. This achieves high-precision and high-reproducibility characterization of the true particle size distribution, with a measurement RSD < 2%. This method not only solves the long-standing technical bottleneck of "inability to disperse and stabilize" in the particle size detection of inorganic salt powders, but also significantly expands the applicability of laser particle size analysis technology in hygroscopic and reactive functional materials (such as lithium salts, sodium salts, magnesium salts, and other highly hygroscopic inorganic powders). The entire operation process mainly relies on conventional laser particle size analyzer equipment, requiring no complex pretreatment or specialized instruments. It has advantages such as simple steps, controllable cost, and strong compatibility, providing a practical and standardized testing solution for the quality control and process optimization of sensitive powders in fields such as new energy materials, solid electrolytes, and desiccants.
[0043] In some specific embodiments, the lithium salt powder has a water content ≤100ppm and a purity ≥99.9%; the particle size is 0~100μm and not zero. Because lithium salts (especially LiBr and LiCl) have extremely strong hygroscopic properties, their surfaces readily absorb environmental moisture, forming a hydrated layer or causing local dissolution. This leads to changes in particle surface tension and increased capillary force, resulting in irreversible agglomeration. Pre-drying the lithium salt powder to a water content ≤100ppm (preferably ≤50ppm) effectively eliminates the surface water film, ensuring that the particles exist in their "intrinsic form" in a non-polar dispersion medium. This significantly reduces the tendency to agglomerate, improves dispersion uniformity, and thus greatly enhances measurement repeatability and data reliability, with the RSD stabilizing below 2%.
[0044] In some specific embodiments, the lithium salt powder is lithium halide (LiX, where X is a halogen), lithium sulfide (Li2S), or lithium carbonate (Li2CO3). The measurement method of this application is most effective for lithium bromide, lithium chloride, and lithium sulfide, especially lithium bromide. Since LiBr, LiCl, and Li2S are all highly hygroscopic and water-soluble lithium salts with extremely high solubility in alcohols, traditional methods are not applicable; for example, water is unsuitable. Li2CO3 is slightly soluble but has weak hygroscopicity, so water can be used as a dispersion medium. The core advantage of the measurement method of this application lies in "inhibiting dissolution + inhibiting hygroscopicity," which is particularly irreplaceable for "dual-high" (high hygroscopicity + high solubility) substances such as LiBr / LiCl / Li2S, and provides high accuracy in particle size measurement results.
[0045] In some specific embodiments, the dispersion medium is a mixture of alkane solvents and lipid solvents. Although a single nonpolar solvent (such as n-heptane) cannot dissolve lithium salts, it has high surface tension and weak wettability. A small amount of polar groups can be introduced to moderately reduce the interfacial tension, enhance the wetting and spreading ability on the lithium salt surface, and at the same time maintain the overall nonpolar environment to avoid dissolution. For example, n-heptane + butyl butyrate form a synergistic dispersion system, which both inhibits dissolution (lithium bromide and butyl butyrate exhibit dissolution) and improves dispersion kinetics.
[0046] In some specific embodiments, when the lithium salt powder is lithium bromide and the dispersion medium is at least one of n-heptane, n-undecane, anisole, and butyl butyrate, D 10 RSD% < 1.1, D 50 RSD% < 1.9, D 90 The RSD% is <0.95; preferably, the dispersion medium is a mixture of n-heptane and butyl butyrate, D 10 RSD% < 0.2, D 50 RSD% < 0.1, D 90 The RSD% is less than 0.015.
[0047] In some specific embodiments, when the lithium salt powder is lithium chloride and the dispersion medium is at least one of n-heptane, anisole, and butyl butyrate, D 10 RSD% < 1.9, D 50 RSD% < 1.9, D 90 RSD% < 2.3; preferably, the dispersion medium is n-heptane or anisole, D 10 RSD% < 1.82, D 50 RSD% < 1.65, D 90 The RSD% is <2.0; more preferably, the dispersion medium is n-heptane, D 10 RSD% < 0.9, D 50 RSD% < 1.2, D 90 The RSD% is less than 0.7.
[0048] In some specific embodiments, when the lithium salt powder is lithium sulfide and the dispersion medium is at least one of n-heptane, anisole, and butyl butyrate, D 10 RSD% < 2.3, D 50 RSD% < 1.45, D 90 RSD% < 1.6; preferably, the dispersion medium is n-heptane or anisole, D 10 RSD% < 1.5, D 50 RSD% < 0.7, D 90 The RSD% is <1.6; more preferably, the dispersion medium is anisole, D 10RSD% < 0.5, D 50 RSD% < 0.7, D 90 The RSD% is less than 0.9.
[0049] In some specific embodiments, when the lithium salt powder is lithium carbonate and the dispersion medium is n-heptane and / or water, D 10 RSD% < 0.4, D 50 RSD% < 1.1, D 90 RSD% < 1.1; preferably, the dispersion medium is water, D 10 RSD% < 0.1, D 50 RSD% < 0.9, D 90 The RSD% is <0.5. For lithium carbonate, although it is slightly soluble in water, it has weak hygroscopicity. In addition to the specific dispersion medium selected in this application, water can also be used as the dispersion medium, and the accuracy of lithium salt particle size detection is also high.
[0050] This application selects a more suitable dispersion medium based on the characteristics of each lithium salt powder, thereby giving full play to the advantages of each dispersion medium and improving the dispersion effect. Using the above-mentioned mixed solvent system as the dispersion medium can significantly improve the dispersion stability and the consistency of light-blocking, and improve the detection accuracy.
[0051] In some specific implementations, the sample sampling range should preferably be 20-50 mg, and the solvent volume should preferably be 70-100 mL. Selecting the above ratio range corresponds to a light-blocking degree of 8-12%, so that the sensitivity and linear response of the laser particle size analyzer reach the optimal range. Under this ratio, the system can simultaneously meet the dual requirements of "high signal-to-noise ratio" and "low agglomeration", ensuring a stable and continuous testing process.
[0052] In some specific embodiments, the dew point of the measuring environment is ≤-50℃, more preferably ≤-55℃, and in more extreme dry environments, the dew point is ≤-60℃. By strictly controlling the dew point of the measuring environment and ensuring an extremely dry environment, the hygroscopic absorption and dissolution of lithium salt powder can be avoided, thereby ensuring more accurate detection results from the subsequent laser particle size analyzer. Specifically, lithium bromide begins to absorb moisture significantly when the dew point is above -45℃, and the moisture absorption rate decreases significantly at a dew point of -50℃; at a dew point of -55℃, the probability of water molecules migrating to the particle surface approaches zero, achieving the testing prerequisite of "zero hydration layer formation"; a dew point ≤-50℃ ensures that there is no visible moisture absorption during the entire testing process; a dew point ≤-55℃ further eliminates the micro-disturbance of "trace water" on the particle surface, thereby ensuring highly accurate particle size measurement.
[0053] In some specific implementations, the measurement environment is an inert atmosphere, such as an argon atmosphere. An inert atmosphere prevents certain lithium salts from reacting with oxygen or water, or from absorbing moisture, ensuring the dryness of the lithium salt powder during the measurement process and thus guaranteeing high accuracy of the test results. For example, in addition to moisture absorption, lithium salts such as Li₂S are easily oxidized by oxygen, and LiBr may slowly decompose to generate Br₂ in the presence of trace amounts of oxygen. Argon, as an inert protective gas, isolates oxygen and moisture, forming a "double barrier" that prevents both oxidation and deliquescence, which is especially crucial for highly reactive lithium salts (such as Li₂S) to ensure accurate test results.
[0054] In some specific embodiments, the particle size measurement device is a laser particle size analyzer, such as a Malvern laser particle size analyzer. More specifically, the measurement conditions of the laser particle size analyzer include: powder refractive index of 1.3~1.8, solvent refractive index of 1.3~1.6, absorptivity of 0.08~0.12%, light-blocking degree of 5~12%, sample cell rotation speed of 1800~3000 rpm, and the use of red and blue lasers for testing, with a red wavelength of 632.8 nm and a blue wavelength of 470 nm. By optimizing the measurement conditions, particle agglomeration or rapid sedimentation can be prevented while maintaining a high degree of light blocking, thereby significantly improving the sensitivity, accuracy, and repeatability of particle size measurement.
[0055] In some specific embodiments, the dispersion process can employ ultrasonic dispersion combined with magnetic stirring; specifically, the ultrasonic dispersion time is 1–30 min; and the magnetic stirring speed is 500–3000 rpm. This application optimizes the ultrasonic time and stirring speed to achieve a system dynamic balance. Ultrasonic dispersion breaks up hard agglomerates, while stirring maintains suspension, avoiding sedimentation-induced secondary agglomeration; thus achieving uniform and stable dispersion of lithium salt particles in a non-polar medium, obtaining D... 50 D 90 The particle size results show small fluctuations and good reproducibility.
[0056] In some specific implementations, the relative standard deviation (RSD) of the measurement method is <2%. In particle size distribution, D 10 Reflects the proportion of small particles and is sensitive to trace impurities or precursor residues; D 50 It is the median particle size, which is directly related to reaction kinetics; D 90 Large particle tails can affect sintering density. The measurement method in this application, through controlling sample drying, drying environment, uniform dispersion, and accurate measurement, ensures that the measured particle size RSD is significantly lower than industry standard (typically >5%). This demonstrates that the measurement method in this application can achieve industrial-grade quality control, fully meeting the stringent requirements for raw material consistency in solid-state battery materials.
[0057] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.
[0058] The raw materials used in the embodiments of this application are all existing technologies and are commercially available.
[0059] Example 1
[0060] Taking lithium bromide as an example, particle size was tested using n-heptane, n-undecane, anisole, butyl butyrate, and a mixed solution of n-heptane and butyl butyrate (volume ratio, n-heptane: butyl butyrate = 99:1) as the dispersion medium.
[0061] Step S1: In a dry room with a dew point of -50℃, at room temperature, the lithium bromide sample amount is 50mg (purity 99.9%), and the solvent volume is 70mL (the solvent needs to be dehydrated beforehand, with a water content of <5ppm). An ultrasonic probe is inserted into a glass beaker, and ultrasonic mixing (frequency 25kHz, power 1000W) is used for 2 minutes, while simultaneously using magnetic stirring at approximately 1000rpm to obtain a homogeneous suspension.
[0062] Step S2: Inject the suspension into the circulation tank of the Malvern laser particle size analyzer (model 3000+ultra). Set the powder refractive index to 1.784 and the absorptivity to 0.1. The solvent refractive index varies depending on the solvent; specifically, n-heptane is 1.397, n-undecane is 1.417, anisole is 1.516, and butyl butyrate is 1.406. The refractive index of the mixed solvent of n-heptane and butyl butyrate is set to 1.397.
[0063] Step S3: Set the shading level to above 5%, the sample cell rotation speed to 2500 rpm, and keep all operating parameters within the instrument's recommended range;
[0064] Step S4: Each experiment is conducted three times consecutively, with three parallel samples, and the RSD coefficient is calculated for each. The particle size test results are expressed as the effective particle size D. 10 (μm), median particle size D 50 (μm) and the limiting particle size D 90 (μm) represents the particle size. Specific particle size test results are shown in Table 1, and the particle size distribution curves are shown in... Figure 1 As shown.
[0065] Example 2
[0066] Taking lithium chloride as an example, particle size was tested using a mixed solution of n-heptane, anisole, and butyl butyrate (volume ratio of n-heptane: butyl butyrate = 9:1) as the dispersion medium.
[0067] Step S1: In a dry room with a dew point of -50℃, at room temperature, take 50mg of lithium chloride (99.9% purity) and 70ml of solvent (the solvent needs to be pre-dehydrated, with a water content of <5ppm). Insert an ultrasonic probe into a glass beaker and use an ultrasonic mixer (frequency 25kHz, power 1000W) to sonicate for 2 minutes, while simultaneously using magnetic stirring at approximately 800rpm to obtain a homogeneous suspension.
[0068] Step S2: Inject the suspension into the circulation tank of the Malvern laser particle size analyzer (model 3000+ultra). Set the powder refractive index to 1.381 and the absorptivity to 0.1. The solvent refractive index varies depending on the solvent, with n-heptane at 1.397, anisole at 1.516, and butyl butyrate at 1.406. The refractive index of the mixed solvent of n-heptane and butyl butyrate is set to 1.397.
[0069] Step S3: Set the shading level to above 5%, the sample cell rotation speed to 2500 rpm, and keep all operating parameters within the instrument's recommended range;
[0070] Step S4: Perform three parallel tests independently for each formulation and calculate the RSD coefficient. Particle size test results are expressed as effective particle size D. 10 (μm), median particle size D 50 (μm) and the limiting particle size D 90 (μm) represents the particle size. Specific particle size test results are shown in Table 2, and the particle size distribution curves are shown below. Figure 2 As shown.
[0071] Example 3
[0072] Taking lithium sulfide as an example, particle size was tested using n-heptane, anisole, and butyl butyrate as dispersion media.
[0073] Step S1: In a dry room with a dew point of -50℃, at room temperature, the lithium sulfide sample amount is 20mg (purity 99.9%), and the solvent volume is 70ml (the solvent needs to be dehydrated beforehand, with a water content of <5ppm). Insert an ultrasonic probe into a glass beaker and use an ultrasonic mixer (frequency 25kHz, power 1000W) for 1 minute, while using magnetic stirring at a speed of approximately 500rpm, to obtain a homogeneous suspension.
[0074] Step S2: Inject the suspension into the circulation tank of the Malvern laser particle size analyzer (model 3000+ultra), set the powder refractive index to 1.55 and the absorptivity to 0.1; the solvent refractive index varies depending on the solvent, with n-heptane at 1.397, anisole at 1.516, and butyl butyrate at 1.406.
[0075] Step S3: Set the shading level to above 5%, the sample cell rotation speed to 2500 rpm, and keep all operating parameters within the instrument's recommended range;
[0076] Step S4: Perform three parallel tests independently for each formulation and calculate the RSD coefficient. Particle size test results are expressed as effective particle size D. 10 (μm), median particle size D 50 (μm) and the limiting particle size D 90 (μm) represents the particle size. Specific particle size test results are shown in Table 1, and the particle size distribution curves are shown in... Figure 3 As shown.
[0077] Example 4
[0078] Taking lithium carbonate as an example, particle size was tested using n-heptane and water as dispersion media respectively.
[0079] Step S1: In a dry room with a dew point of -50℃, at room temperature, the lithium sulfide sample amount is 20mg (purity 99.9%), and the solvent volume is 70ml (the solvent needs to be dehydrated beforehand, with a water content of <5ppm). Insert an ultrasonic probe into a glass beaker and use an ultrasonic mixer (frequency 25kHz, power 1000W) for 5 minutes, while using magnetic stirring at a speed of approximately 800rpm, to obtain a homogeneous suspension.
[0080] Step S2: Inject the suspension into the circulation tank of the Malvern laser particle size analyzer (model 3000+ultra), set the powder refractive index to 1.55 and the absorptivity to 0.1; the solvent refractive index varies depending on the solvent, with n-heptane at 1.397 and water at 1.333;
[0081] Step S3: Set the shading level to above 5%, the sample cell rotation speed to 2500 rpm, and keep all operating parameters within the instrument's recommended range;
[0082] Step S4: Perform three parallel tests independently for each formulation and calculate the RSD coefficient. Particle size test results are expressed as effective particle size D. 10 (μm), median particle size D 50 (μm) and the limiting particle size D 90 (μm) represents the particle size. Specific particle size test results are shown in Table 1, and the particle size distribution curves are shown in... Figure 4 As shown.
[0083] Comparative Example 1
[0084] The difference between Comparative Example 1 and Example 1 is that the dew point temperature in step S1 was replaced with room temperature (40% humidity, 25°C); the other steps are the same. The particle size measurement results are shown in Table 5.
[0085] Comparative Example 2
[0086] The difference between Comparative Example 2 and Example 1 is that the solvent in step S1 was replaced with isobutyl isobutyrate, isoamyl isovalerate, butyl acetate, n-butanol, isopropanol, methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, diethyl ether, and oleic acid, respectively; the other steps were the same. The particle size measurement results are shown in Table 6.
[0087] Table 1
[0088]
[0089] As shown in Table 1, in the lithium bromide particle size test, due to the slight solubility of butyl butyrate and lithium bromide in the dispersion medium of Example 1, the dissolution rate was greatly accelerated with the assistance of ultrasound, thus making it impossible to measure the particle size. The n-heptane, anisole, n-undecane, and n-heptane / butyl butyrate used in this application as dispersion media for lithium bromide all had RSDs below 2%; the n-heptane / butyl butyrate mixed solvent showed better stability and dispersion effect.
[0090] Table 2
[0091]
[0092] As shown in Table 2, in the lithium chloride particle size test, since lithium chloride is insoluble in butyl butyrate, the test results of several solvents are relatively stable with the assistance of ultrasound. The third RSD coefficients of D10 and D50 are both less than 2.3%; especially n-heptane has the smallest RSD.
[0093] Table 3
[0094]
[0095] As shown in Table 3, in the lithium sulfide particle size test, since lithium sulfide is also insoluble in butyl butyrate, the test results of several solvents were relatively stable with the aid of ultrasound. The RSD results indicate that anisole showed the best stability for testing lithium sulfide; and the particle size distribution diagram shows that the results obtained with n-heptane are closer to a normal distribution.
[0096]
[0097] Table 4
[0098] As shown in Table 4, in the particle size detection of lithium carbonate, since lithium carbonate is stable and does not react with water, water can be used as a solvent. The test results are smaller than those obtained by organic solvents and are closer to the true value. However, it is not suitable for anhydrous testing environments. The organic solvent selected in this application can detect the particle size of lithium carbonate relatively accurately in anhydrous environments, and the RSD% is less than 1.1.
[0099] Table 5
[0100]
[0101] As shown in Table 5, the particle size of Comparative Example 1 was measured at room temperature or room temperature. When the ambient humidity was high, the detection error increased significantly. For lithium salts with strong hygroscopicity and high water solubility, the moisture content of the detection environment must be strictly controlled at a dew point ≤ -45℃.
[0102] Table 6
[0103]
[0104] As shown in Table 6, the polar aprotic solvents used in Comparative Example 2, such as isobutyl isobutyrate alkyl to dimethyl sulfoxide, can dissolve lithium salts such as lithium bromide and lithium chloride under ultrasonic assistance, making them undetectable. Diethyl ether is volatile and continuously evaporates during ultrasonication, making stable dispersion impossible, resulting in extremely poor reproducibility. Although oleic acid and other solvents are inert and do not dissolve in any lithium salts, their high viscosity prevents dispersion.
[0105] The lithium salt particle size detection method provided in this application has the following advantages:
[0106] (1) Material stability protection: The wet process isolates air and moisture through an inert dispersion medium (such as anhydrous organic solvent), effectively avoiding the hygroscopic deliquescence, oxidation or hydrolysis of materials such as lithium bromide (LiBr) and lithium sulfide (Li2S), and ensuring the chemical properties remain stable during the test.
[0107] (2) High-precision dispersion control: Combining ultrasonic treatment and stirring, the wet method can significantly suppress the electrostatic agglomeration and van der Waals adsorption of particles, and is especially suitable for the true particle size characterization of nano-sized lithium sulfide (Li2S) and lithium chloride (LiCl).
[0108] (3) Wide dynamic range measurement: Wet laser diffraction technology covers the particle size range of 0.01~2000um, accurately analyzing the multi-scale distribution characteristics of sulfide / halide electrolytes (such as micron-sized LiBr and submicron-sized Li2S mixed system).
[0109] (4) Improved operational safety: The wet method fixes the sample in the liquid phase, avoiding the toxic dust such as Li2S and LiBr generated by the dry method airflow dispersion, reducing the risk of laboratory exposure and meeting occupational health and safety standards.
[0110] (5) Process adaptability optimization: The wet test environment (such as solvent dispersion state) directly simulates the solid electrolyte slurry preparation process, and the obtained particle size data can guide the optimization of electrode coating uniformity and ion transport performance.
[0111] (6) Compatibility with highly reactive materials: For oxygen / water sensitive materials such as lithium sulfide (Li2S), the wet process supports testing in an inert medium (such as mineral oil) in a container without the need for complex inert gas protection equipment.
[0112] (7) Reduce mechanical damage error: Wet low-speed dispersion avoids the breakage of brittle particles (such as LiCl crystals) caused by high-speed airflow in dry dispersion, and truly reflects the original particle size distribution.
Claims
1. A method for measuring the particle size of lithium salts, characterized in that, The measurement method includes the following steps: Step S1: Obtain the lithium salt powder to be tested; Step S2: Under the condition that the dew point of the measuring environment is ≤-45℃, the lithium salt powder is dispersed in a dispersion medium to form a lithium salt suspension; the particle size of the lithium salt in the lithium salt suspension is measured using a particle size measuring device; wherein, the dispersion medium is selected from at least one of n-heptane, n-dodecane, n-undecane, n-decane, n-hexane, toluene, xylene, anisole, and butyl butyrate.
2. The method for measuring lithium salt particle size according to claim 1, characterized in that, The lithium salt powder is lithium halide, lithium sulfide, or lithium carbonate. And / or, the lithium salt powder has a water content ≤100ppm and a purity ≥99.9%; And / or, the particle size of the lithium salt powder is 0~100μm and not 0.
3. The method for measuring lithium salt particle size according to claim 2, characterized in that, The lithium salt powder is lithium bromide, lithium chloride, or lithium sulfide.
4. The method for measuring lithium salt particle size according to claim 3, characterized in that, The lithium salt powder is lithium bromide, and the dispersion medium is at least one of n-heptane, n-undecane, anisole, and butyl butyrate. Preferably, the dispersion medium is a mixture of n-heptane and butyl butyrate.
5. The method for measuring lithium salt particle size according to claim 3, characterized in that, The lithium salt powder is lithium chloride, and the dispersion medium is at least one of n-heptane, anisole, and butyl butyrate. Preferably, the dispersion medium is n-heptane or anisole.
6. The method for measuring lithium salt particle size according to claim 3, characterized in that, The lithium salt powder is lithium sulfide, and the dispersion medium is at least one of n-heptane, anisole, and butyl butyrate; preferably, the dispersion medium is n-heptane or anisole. And / or, the lithium salt powder is the lithium carbonate, and the dispersion medium is the n-heptane and / or water.
7. The method for measuring the particle size of lithium salts according to any one of claims 1 to 6, characterized in that, The weight ratio of the lithium salt powder to the dispersion medium is 1:(1000~3000). And / or, the dew point of the measurement environment is ≤-50°C; And / or, the atmosphere of the measurement environment is an inert atmosphere.
8. The method for measuring the particle size of lithium salts according to any one of claims 1 to 7, characterized in that, The weight ratio of the lithium salt powder to the dispersion medium is 1:(1500~2500). And / or, the dew point of the measurement environment is ≤-55℃; And / or, the atmosphere of the measurement environment is an argon atmosphere.
9. The method for measuring the particle size of lithium salts according to any one of claims 1 to 8, characterized in that, The particle size measuring device is a laser particle size analyzer; and / or, the dispersion includes ultrasonic dispersion and magnetic stirring.
10. The method for measuring lithium salt particle size according to claim 9, characterized in that, The measurement conditions of the laser particle size analyzer include: powder refractive index of 1.3~1.8, solvent refractive index of 1.3~1.6, absorptivity of 0.08~0.12%, shading of 5~12%, and sample cell rotation speed of 1800~3000 rpm; And / or, the ultrasonic dispersion time is 1~30 min; And / or, the magnetic stirring speed is 500~3000 rpm; And / or, the relative standard deviation (RSD) of the measurement method is <2%.