Dispersing agent for garnet type solid electrolyte and preparation method thereof

Abstract

The invention relates to a dispersing agent for garnet type solid electrolyte and a preparation method thereof, a special powder dispersing agent for dispersing garnet type solid electrolyte (LLZO, Li7La3Zr2O12) in an ethanol or isopropanol system is a polycarboxylic acid-polyether colorless transparent viscous liquid copolymer, and the copolymer is anchored on the surface of powder particles through the strong adsorption effect of carboxyl, so that the dispersing agent can be used for dispersing the garnet type solid electrolyte (LLZO, Li7La3Zr2O12) in an ethanol or isopropanol system. Meanwhile, the polyether chain segment realizes solvent compatibility and steric hindrance effect, the preparation method for the dispersing agent is a controllable free radical polymerization method and specifically comprises dozens of specific steps and conditions, and the dispersing agent has the advantages that the grinding particle size of the garnet type solid electrolyte can be effectively reduced, stable dispersion of powder in slurry is realized, and the dispersing effect is good. Powder agglomeration is inhibited, and the grinding efficiency is improved, so that the mass production requirement of the high-safety solid-state lithium ion battery is met.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a dispersant for garnet-type solid electrolytes and its preparation method. Background Technology

[0002] Traditional commercial lithium-ion batteries use electrolytes with organic carbonate solvents, whose volatile and flammable properties pose safety hazards. All-solid-state lithium metal batteries (ASSLB) are considered the most promising next-generation energy storage devices due to their safety and potentially high energy density. Solid-state electrolytes, as a key component of solid-state batteries, are non-flammable and have good compatibility with metallic lithium, and have received widespread attention in recent years. Garnet-structured oxide solid electrolytes (Li7La3Zr2O) are a prime example. 12 LLZO has high room temperature conductivity (nearly 10). -3 S cm -1 With its advantages such as stability to lithium metal, wide electrochemical window (0-4V), and ability to be prepared in air, it is one of the candidates for solid electrolyte materials for next-generation high-safety solid-state batteries.

[0003] LLZO powder particle size, as a key structural parameter, has a decisive impact on its electrochemical performance. Reducing the particle size can significantly improve the dispersion uniformity of LLZO particles, promoting the preparation of ultrathin solid electrolyte layers; simultaneously, by shortening the ion transport path, it effectively enhances lithium-ion mobility, thereby optimizing the overall performance of solid-state batteries. In practical applications, such as when compounded with polymers (e.g., PEO) or used for surface coating of cathode materials, the particle size needs to be controlled within 200 nm to obtain optimal performance.

[0004] LLZO samples synthesized using a high-temperature solid-state method typically have primary particles ranging from 5 to 12 μm and exhibit significant agglomeration, making them unsuitable for solid-state electrolyte applications. Considering that LLZO reacts with water to form Li + / H + Ion exchange reactions cause material denaturation; therefore, isopropanol or anhydrous ethanol are often used as solvents in industrial production, employing sand milling processes to reduce powder particle size. Because nano-sized LLZO powder possesses extremely high surface energy, it is prone to soft agglomeration during sand milling, hindering further powder refinement. Therefore, it is necessary to add suitable dispersants during sand milling to inhibit particle agglomeration and sedimentation, thereby improving grinding efficiency and promoting effective reduction in powder particle size.

[0005] Dispersants are typically chemical additives, such as surfactants or polymers, whose main function is to promote the stable and uniform dispersion of solid particles in liquid or dispersion media, and to prevent their re-aggregation or sedimentation. They overcome agglomeration forces such as van der Waals attraction by adsorbing onto the particle surface, altering the particle's surface properties (e.g., reducing surface tension and increasing wettability), and generating electrostatic repulsion (charge stabilization) or steric hindrance (steric stability) between particles. Dispersants are widely used in coatings, inks, ceramics, pigments, pesticides, nanomaterial preparation, cosmetics, pharmaceuticals, and mineral processing (e.g., ball milling), and are key components for obtaining stable and uniform suspension systems (dispersions). Common dispersants include polyelectrolytes, polycarboxylates, phosphates, sulfonates, and various nonionic surfactants. However, existing common dispersants such as polyethylene glycol (PEG) and polyacrylic acid do not provide ideal dispersion effects for LLZO powder in ethanol / isopropanol systems, failing to meet its dispersion requirements. Although polyethylene glycol (PEG) exhibits good compatibility with ethanol / isopropanol solvents, the adsorption between its ether bonds (-O-) and the hydroxyl groups (Zr-OH) on the LLZO surface is weak, failing to inhibit the aggregation of nanoparticles. Polyacrylic acid (PAA), while capable of adsorbing La2+ groups on the LLZO surface through carboxylate groups (-COO-),... 3+ / Zr 4+ While forming strong coordination bonds, it undergoes deprotonation under alkaline conditions, leading to a sharp decrease in its solubility in ethanol / isopropanol. This makes it difficult for dispersant molecules to effectively migrate to the LLZO particle interface through the solvent medium. Furthermore, due to the strong alkalinity of LLZO, conventional ester-containing dispersants are prone to degradation, ultimately losing their dispersing effect.

[0006] To address the aforementioned issues, several publications have revealed methods, including CN119390965B, "Preparation Method of Ceramic Dispersant." However, this method has the following limitations: First, it employs a multi-step chemical synthesis route, involving numerous complex processes, high operational difficulty, and challenges in ensuring batch-to-batch product stability. Second, it utilizes large quantities of hazardous chemicals such as dichloromethane, triethylamine, bromoacetyl bromide, and tetrahydrofuran, posing risks of leakage, poisoning, and environmental pollution treatment, thus failing to meet the requirements of green chemistry development. Furthermore, the product's molecular structure has an excessively high ester bond ratio, making it prone to degradation in strongly alkaline media, leading to main chain breakage and loss of dispersion effect. CN104479068B, "Preparation Method of a Polycarboxylate-type Ceramic Dispersant," produces an aqueous solution containing a polymer dispersant; however, as mentioned earlier, LLZO reacts with water to form Li + / H +The ion exchange reaction dictates that the dispersant system must be strictly anhydrous. Furthermore, although this dispersant has good water solubility, its low solubility in the ethanol / isopropanol system hinders the movement of the dispersant to the particle surface through the solvent and limits the full extension of the dispersant molecular chains in the solvent medium, thus affecting the inhibition of aggregation. CN106589422B, "A method for preparing a superdispersant for titanium dioxide," firstly, the dispersant prepared therein is only suitable for organic carrier resin systems, exhibiting significant limitations in alcohol dispersion systems. Secondly, due to its rich ester bond functional groups in its molecular structure, this substance is prone to structural degradation in strongly alkaline environments. Therefore, this dispersant also cannot meet the dispersion requirements of LLZO in the ethanol / isopropanol system.

[0007] Therefore, it is of great significance to propose a dispersant for garnet-type solid electrolytes that combines strong affinity for alcohol solvents, strong powder binding, and high alkali resistance, and its preparation method, in order to address the dispersion problem of LLZO powder materials. Summary of the Invention

[0008] The objective of this invention is to overcome the shortcomings of the prior art and provide a dispersant for garnet-type solid electrolytes and its preparation method, which combines strong affinity for alcohol solvents and powder binding with high alkali resistance, and can be prepared simply without excessive investment.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A dispersant for garnet-type solid electrolytes, specifically designed for dispersing garnet-type solid electrolytes (LLZO, Li7La3Zr2O) in ethanol / isopropanol systems. 12 The powder dispersant is a colorless, transparent, viscous liquid copolymer of polycarboxylic acid and polyether. This copolymer is anchored to the surface of powder particles through the strong adsorption of its carboxyl groups. At the same time, its polyether segments achieve solvent compatibility and steric hindrance effect, thereby achieving stable dispersion of powder in slurry, inhibiting powder agglomeration and improving grinding efficiency.

[0011] The dispersant is prepared by controlled free radical polymerization.

[0012] Compared with the prior art, the present invention has the following advantages or effects:

[0013] This dispersant can significantly improve the dispersibility of LLZO powder, effectively enhancing dispersion stability and particle size control. In its polyether-polycarboxylic acid copolymer molecular structure, the acidic segments (-COOH) are anchored to the La groups on the LLZO surface through coordination. 3+ / Zr 4+Ether segments enhance alcohol solvent compatibility and promote molecular chain extension. Addressing the problem of reversible soft agglomeration and difficulty in reducing particle size caused by high surface energy when grinding LLZO powder in anhydrous alcohol solvents, this dispersant effectively inhibits agglomeration, significantly refines particle size, and overcomes the shortcomings of existing dispersants such as insufficient alcohol solubility, poor alkali resistance, and failure upon contact with water. Attached Figure Description

[0014] Figure 1 The following is a comparative image of sample a) Example 1 and b) Example 2 for a dispersant for garnet-type solid electrolytes according to the present invention.

[0015] Figure 2 This is a diagram showing the sedimentation of the dispersant after 0 hours of standing. Figure 2 The following are comparison images of the effects of the dispersant sedimentation experiment: a) after standing for 0 h, b) after standing for 1 h, c) after standing for 6 h, d) after standing for 12 h, e) after standing for 24 h, and f) after standing for 48 h.

[0016] Figure 3 SEM images of the sand-ground samples: a) blank, b) comparison images of Example 1 and c) Example 2.

[0017] Figure 4 The present invention provides a dispersant for garnet-type solid electrolytes and a schematic diagram of its preparation process.

[0018] The present invention will be further described in detail below with reference to the accompanying drawings. Detailed Implementation

[0019] like Figures 1-3 As shown, this is a dispersant for garnet-type solid electrolytes, specifically designed for dispersing garnet-type solid electrolytes (LLZO, Li7La3Zr2O) in ethanol / isopropanol systems. 12 The powder dispersant is a colorless, transparent, viscous liquid copolymer of polycarboxylic acid and polyether. This copolymer is anchored to the surface of powder particles through the strong adsorption of its carboxyl groups. At the same time, its polyether segments achieve solvent compatibility and steric hindrance effect, thereby achieving stable dispersion of powder in slurry, inhibiting powder agglomeration and improving grinding efficiency.

[0020] The dispersant of the present invention may further be

[0021] In the polycarboxylic acid-polyether copolymer, the carboxylic acid group (-COOH) reacts with the garnet-type solid electrolyte (LLZO, Li7La3Zr2O). 12 Metal ions (La) on the surface 3+ / Zr 4+The polyether segments form coordination bonds; the polyether segments promote the dissolution of the copolymer through strong solvation with ethanol / isopropanol solvents, causing the molecular chains to extend and generate steric hindrance to inhibit particle aggregation.

[0022] like Figure 4 As shown, the method for preparing the dispersant for any one of claims 1 to 2 is characterized by preparation by controlled free radical polymerization, and the specific process steps and conditions are as follows:

[0023] A. Pre-treat the polyether monomer and polycarboxylic acid monomer, remove the polymerization inhibitor from the monomer by vacuum distillation, and collect the treated monomers separately;

[0024] B. Dissolve 0.1–2 wt% of the initiator, representing the total mass of the monomers, in anhydrous ethanol;

[0025] C. Add a certain amount of anhydrous ethanol to the container, purge with nitrogen gas to replace dissolved oxygen in the solvent, then add a certain amount of polyether monomer and polycarboxylic acid monomer, and stir magnetically until completely dissolved;

[0026] D. Add 0.1–4 wt% of the chain transfer agent dodecyl mercaptan (TDDM) and continue stirring for 10 min;

[0027] E. Add the initiator solution and continue stirring for 10 minutes until well mixed;

[0028] F. Connect the container to the nitrogen protection system and continuously bubble nitrogen for 30 minutes to completely remove oxygen;

[0029] G. Heat the oil bath to 60-80℃, start timing, continuously monitor the reaction process, observe the polymer state, take a small sample of the reaction solution every 30 minutes, add cold diethyl ether and observe the polymer precipitation.

[0030] H. After reacting for 1 to 4 hours, the mixture is rapidly cooled to room temperature in a cold water bath, and a trace amount of hydroquinone, a polymerization inhibitor, is added to the reaction solution to terminate the reaction.

[0031] I. Slowly pour the reaction solution into 10 times its volume of cold ether, stir magnetically for 30 min to allow the polymer to precipitate completely, separate the copolymer by centrifugation, wash 3 times with cold ether, and vacuum dry at 40℃ for 24 h to remove ethanol solvent, to obtain a colorless, transparent, viscous liquid copolymer.

[0032] J. To ensure the dispersion stability of the dispersant in the solvent system, it is necessary to control the polymerization temperature and reaction time to keep the average molecular weight of the copolymer below 2000;

[0033] K. This polymerization reaction must be carried out in an environment where oxygen is strictly excluded. The presence of oxygen will cause the free radicals generated by the initiator to be quenched, thus preventing the chain growth reaction from continuing.

[0034] This method can be further...

[0035] The polyether monomer in step A is at least one of triethylene glycol divinyl ether (TEGDVE), ethylene glycol divinyl ether (DEGDVE), and 1,4-cyclohexanediethanol divinyl ether.

[0036] The polycarboxylic acid monomer in step A is at least one of acrylic acid (AA), maleic acid (MA), and itaconic acid (ITA).

[0037] The initiator in step B is at least one of azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), and potassium persulfate (KPS).

[0038] Example 1

[0039] In a three-necked flask, 100 ml of anhydrous ethanol was first added, and nitrogen was bubbled through for 10 min to remove oxygen. Then, 0.02 mol of pretreated acrylic acid and 0.02 mol of triethylene glycol divinyl ether monomer were added. After the monomers were fully dissolved by magnetic stirring, 0.25 wt% dodecyl mercaptan was added, and stirring continued for 10 min. Subsequently, a pre-prepared 0.2 wt% initiator solution was added, and the mixture was stirred for 10 min before being connected to a continuous nitrogen protection system and bubbled through for 30 min to remove oxygen. The system was placed in a 70°C oil bath to initiate the polymerization reaction. After 2 hours of reaction, the mixture was immediately cooled to room temperature in a cold water bath, and a trace amount of hydroquinone was added to terminate the reaction. Finally, the reaction solution was slowly poured into 10 times its volume of cold diethyl ether, and the copolymer was completely precipitated by magnetic stirring for 30 min. The precipitate was collected by centrifugation at 8000 rpm for 10 min, washed three times with cold diethyl ether, and then vacuum-dried at 40°C for 24 hours to obtain the target copolymer with a molecular weight of approximately 800. (Image shown). Figure 1 As shown in a.

[0040] Example 2

[0041] In a three-necked flask, 100 ml of anhydrous ethanol was first added, and nitrogen was bubbled through for 10 min to remove oxygen. Then, 0.04 mol of pretreated acrylic acid and 0.01 mol of triethylene glycol divinyl ether monomer were added. After the monomers were fully dissolved by magnetic stirring, 0.25 wt% dodecyl mercaptan was added, and stirring continued for 10 min. Subsequently, a pre-prepared 0.2 wt% initiator solution was added, and the mixture was stirred for 10 min before being connected to a continuous nitrogen protection system and bubbled through for 30 min to remove oxygen. The system was placed in a 65°C oil bath to initiate the polymerization reaction. After 4 h of reaction, the mixture was immediately cooled to room temperature in a cold water bath, and a trace amount of hydroquinone was added to terminate the reaction. Finally, the reaction solution was slowly poured into 10 times its volume of cold diethyl ether, and the copolymer was completely precipitated by magnetic stirring for 30 min. The precipitate was collected by centrifugation at 8000 rpm for 10 min, washed three times with cold diethyl ether, and then dried under vacuum at 40°C for 24 h to obtain the target copolymer with a molecular weight of approximately 1600. (Image shown). Figure 1 As shown in b.

[0042] The performance of the dispersant was evaluated using the following methods:

[0043] 1. Sedimentation experiment: 2g of LLZO powder (agglomerated powder without dispersant), 5wt% of various dispersants and 8g of isopropanol were added to a glass sample bottle. The mixture was first sonicated for 10min, then shaken in a shaker for 60min and allowed to stand. The sedimentation of the slurry after standing for different times was observed to compare the stabilizing effect of different dispersants on the LLZO suspension system.

[0044] 2. Sand Milling - Particle Size Testing: Micron-sized LLZO ceramic powder was wet-milled using a vertical sand mill. The experimental steps were as follows: First, an LLZO-isopropanol slurry with a solid content of 40% was prepared, and 5 wt% dispersant was added. After thorough mixing, the slurry was transferred to the vertical sand mill. The slurry was continuously milled at 2000 rpm for 4 hours. After milling, samples were immediately taken, ultrasonically dispersed in anhydrous ethanol, and then the particle size was tested using a laser particle size analyzer.

[0045] 3. SEM Testing: First, the milled sample was placed in a forced-air drying oven and dried overnight (approximately 12 hours) at 60°C. Then, it was transferred to a vacuum drying oven and dried for another 6 hours at the same temperature to completely remove residual solvent. Finally, scanning electron microscopy (SEM) was used to characterize the microstructure of the LLZO powder after the two-stage drying process, analyzing the particle dispersion and surface morphology.

[0046] After treatment with this dispersant, the powder dispersion performance is significantly improved. Among them, the dispersion stability and particle size control effect of Example 1 are better than those of Example 2.

[0047] Settlement test status as follows Figure 2 As shown, after standing for 1 hour, the blank control group began to show stratification; after standing for 6 hours, the polyacrylic acid group began to show stratification; after standing for 6 hours, the polyethylene glycol group also began to show stratification; while Examples 1 and 2 remained in a stable suspended state after standing for 24 and 48 hours, respectively, indicating that both examples could effectively inhibit powder sedimentation.

[0048] The particle size distribution data of the samples after sand milling are shown in Table 1. The D50 values ​​of the control sample, Example 1, and Example 2 are 1.180 μm, 0.152 μm, and 0.324 μm, respectively. This indicates that both dispersants can effectively reduce particle agglomeration, and the dispersant in Example 1 performs better than that in Example 2.

[0049] SEM results showed that the dispersant significantly affected the microstructure and dispersibility of the samples. The blank control sample exhibited irregular primary particle shapes and severe agglomeration; the sample in Example 1 showed a regular blocky morphology with uniform particle size distribution, demonstrating good dispersibility and no obvious agglomeration; the particle morphology of Example 2 was similar to that of Example 1, with smaller primary particle sizes, but still exhibited some degree of agglomeration. These morphological characteristics showed good consistency with the laser particle size analysis results, confirming that the dispersing effect of Example 1 was slightly better than that of Example 2.

[0050] The particle size distribution data of the samples after sand milling are shown in Table 1. The D50 values ​​of the control sample, Example 1, and Example 2 are 1.180 μm, 0.152 μm, and 0.324 μm, respectively. This indicates that both dispersants can effectively reduce particle agglomeration, and the dispersant in Example 1 performs better than that in Example 2.

[0051] Table 1. Grinding particle size distribution (2000 rpm, 4 h)

[0052]

[0053]

[0054] As described above, the present invention can be well implemented. The above embodiments are only the best implementations of the present invention, but the implementation of the present invention is not limited to the above embodiments. Other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are all included within the protection scope of the present invention.

Claims

1. A dispersant for garnet-type solid electrolytes, characterized in that... Garnet-type solid electrolytes (LLZO, Li7La3Zr2O) specifically designed for dispersing ethanol / isopropanol systems 12 The powder dispersant is a colorless, transparent, viscous liquid copolymer of polycarboxylic acid and polyether. This copolymer is anchored to the surface of powder particles through the strong adsorption of its carboxyl groups. At the same time, its polyether segments achieve solvent compatibility and steric hindrance effect, thereby achieving stable dispersion of powder in slurry, inhibiting powder agglomeration and improving grinding efficiency.

2. The dispersant according to claim 1, characterized in that... In the polycarboxylic acid-polyether copolymer, the carboxylic acid group (-COOH) reacts with the garnet-type solid electrolyte (LLZO, Li7La3Zr2O). 12 Metal ions (La) on the surface 3+ / Zr 4+ The polyether segments form coordination bonds; the polyether segments promote the dissolution of the copolymer through strong solvation with ethanol / isopropanol solvents, causing the molecular chains to extend and generate steric hindrance to inhibit particle aggregation.

3. A method for preparing the dispersant according to any one of claims 1 to 2, characterized in that... The preparation method is controlled free radical polymerization. The specific process steps and conditions are as follows: A. Pre-treat the polyether monomer and polycarboxylic acid monomer, remove the polymerization inhibitor from the monomer by vacuum distillation, and collect the treated monomers separately; B. Dissolve 0.1–2 wt% of the initiator, representing the total mass of the monomers, in anhydrous ethanol; C. Add a certain amount of anhydrous ethanol to the container, purge with nitrogen gas to replace dissolved oxygen in the solvent, then add a certain amount of polyether monomer and polycarboxylic acid monomer, and stir magnetically until completely dissolved; D. Add 0.1–4 wt% of the chain transfer agent dodecyl mercaptan (TDDM) and continue stirring for 10 min; E. Add the initiator solution and continue stirring for 10 minutes until well mixed; F. Connect the container to the nitrogen protection system and continuously bubble nitrogen for 30 minutes to completely remove oxygen; G. Heat the oil bath to 60℃~80℃, start timing, continuously monitor the reaction process, observe the polymer state, take a small sample of the reaction solution every 30 minutes, add cold diethyl ether and observe the polymer precipitation. H. After reacting for 1 to 4 hours, the mixture is rapidly cooled to room temperature in a cold water bath, and a trace amount of hydroquinone, a polymerization inhibitor, is added to the reaction solution to terminate the reaction. I. Slowly pour the reaction solution into 10 times its volume of cold diethyl ether, stir magnetically for 30 min to allow the polymer to precipitate completely, centrifuge for 10 min to collect the copolymer precipitate, and wash it three times with cold diethyl ether. Finally, vacuum dry at 40 °C for 24 h to completely remove residual solvent, obtaining a colorless, transparent, viscous liquid copolymer; J. To ensure the dispersion stability of the dispersant in the solvent system, it is necessary to control the polymerization temperature and reaction time to keep the average molecular weight of the copolymer below 2000; K. This polymerization reaction must be carried out in an environment where oxygen is strictly excluded. The presence of oxygen will cause the free radicals generated by the initiator to be quenched, thus preventing the chain growth reaction from continuing.

4. The method according to claim 3, characterized in that: The polyether monomer in step A is at least one of triethylene glycol divinyl ether (TEGDVE), ethylene glycol divinyl ether (DEGDVE), and 1,4-cyclohexanediethanol divinyl ether.

5. The method according to claim 3, characterized in that: The polycarboxylic acid monomer in step A is at least one of acrylic acid (AA), maleic acid (MA), and itaconic acid (ITA).

6. The method according to claim 3, characterized in that: The initiator in step B is at least one of azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), and potassium persulfate (KPS).

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