Lignin polymer composite sulfide electrolyte and preparation method thereof, and all-solid-state lithium metal battery

Abstract

The present application belongs to the technical field of all-solid-state batteries, and relates to a lignin polymer composite sulfide electrolyte, a preparation method thereof and an all-solid-state lithium metal battery. A lignin polymer is obtained by mixing and reacting thioctic acid, polyethylene glycol diacrylate, a lithium salt and lignin, wherein the reaction temperature is 130-140 DEG C, and the reaction time is 0.5-2 h; wherein the lignin is enzymatic lignin and / or alkali lignin; and the lignin is used in an amount of 3-55% of the mass sum of thioctic acid and polyethylene glycol diacrylate. The lignin polymer can be used as an electrolyte additive of an all-solid-state lithium metal battery, and enables a sulfide-based lithium metal all-solid-state battery to operate stably under a significantly reduced stacking pressure, and also enables significant inhibition of lithium dendrite growth during repeated lithium deposition and dissolution.

Description

Technical Field

[0001] This invention relates to the field of all-solid-state battery technology, and more specifically, to a lignin polymer composite sulfide electrolyte and its preparation method, and an all-solid-state lithium metal battery. Background Technology

[0002] With the increasing demand for high-energy-density and safer rechargeable batteries from grid-scale energy storage, electric vehicles, and portable electronic devices, all-solid-state batteries have emerged as a promising direction for next-generation high-performance energy storage technology. However, all-solid-state batteries typically rely on applying relatively high stacking stress to maintain stable operation, which poses a significant obstacle to their practical application.

[0003] This pressure dependence becomes particularly pronounced when lithium metal is used as the anode to maximize the energy density of all-solid-state batteries. The use of lithium metal introduces significant chemical-mechanical instabilities at the electrode-electrolyte interface, making the interfacial contact highly sensitive to external mechanical constraints. The necessity of high stacking pressure stems from the non-uniform compressive stress generated during lithium deposition in all-solid-state lithium metal batteries. Appropriate external pressure (10–70 MPa) can suppress dendrite growth and maintain tight solid-solid interface contact, thereby achieving stable cycling. To reduce stacking pressure, researchers have proposed various strategies, including constructing functional interlayers, modifying sulfide electrolytes, and designing lithium alloy anodes. While these strategies improve cycling performance at lower pressures, they each have inherent limitations: introducing interlayers increases manufacturing complexity, and chemically modifying sulfide electrolytes often involves solvent treatment, which can induce side reactions, leave solvent residues, and reduce ionic conductivity. Therefore, achieving long-term stable cycling at practically low stacking pressures at room temperature without compromising the inherent advantages of sulfide electrolytes remains a key unsolved challenge in the field of all-solid-state lithium metal batteries.

[0004] Sulfide-based all-solid-state batteries suffer from significant volume mismatch and inherently poor interfacial adhesion, challenges that are exacerbated under real-world low-pressure operation. During lithium stripping and deposition, the rigid sulfide electrolyte cannot adapt to the spatially non-uniform interfacial stress generated at the lithium / solid-state electrolyte interface. This non-uniform stress distribution promotes void formation, interfacial debonding, and ion transport path failure, further exacerbating local electric field concentration and accelerating dendritic lithium growth. This coupled electrochemical-mechanical instability triggers degradation of the lithium / solid-state electrolyte interface and the composite cathode, ultimately leading to premature battery failure under reduced mechanical constraints. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects and deficiencies of the above-mentioned technical problems and provide a lignin polymer that can be used as an electrolyte additive for all-solid-state lithium metal batteries, enabling sulfide-based lithium metal all-solid-state batteries to operate robustly under significantly reduced stacking pressure, and also significantly suppressing lithium dendrite growth during repeated lithium deposition and dissolution processes.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution:

[0007] A lignin polymer, wherein the lignin polymer is obtained by reacting lipoic acid, polyethylene glycol diacrylate, lithium salt and lignin at a reaction temperature of 130~140℃ and a reaction time of 0.5~2h;

[0008] Wherein, the lignin is enzymatically hydrolyzed lignin and / or alkali lignin;

[0009] The amount of lignin used is 3% to 55% of the total mass of thioctic acid and polyethylene glycol diacrylate.

[0010] The lignin polymer of the present invention can be used as an electrolyte additive for all-solid-state lithium metal batteries to resist lithium dendrite growth, reduce the stacking pressure required for stable cycling of sulfide solid-state batteries, and enable sulfide-based lithium metal all-solid-state batteries to operate robustly under significantly reduced stacking pressure.

[0011] Lignin is an abundant renewable biomass resource in nature, with wide-ranging sources. Statistics show that the paper industry produces approximately 50 million tons of lignin annually, most of which is treated as waste, resulting in significant resource waste. As one of the most important structural components of plant cell walls, lignin's basic structural unit is an aromatic compound composed of phenylpropane (C9) units. It mainly includes three typical monomer types: syringyl (S-lignin), guaiacyl (G-lignin), and p-coumaric acid (H-lignin). It possesses a unique three-dimensional network macromolecular structure and is rich in various functional groups, such as phenolic hydroxyl groups, alcoholic hydroxyl groups, ether bonds, and carbon-carbon double bonds. These abundant chemical groups provide numerous reaction sites for the chemical modification of lignin, enabling its application in composite materials through physical or chemical methods. This can reduce costs while further improving the mechanical properties and thermal stability of materials, which is of great significance for the high-value utilization of biomass materials.

[0012] Enzymatically hydrolyzed lignin is a product extracted from plant materials through enzymatic hydrolysis. Alkali lignin is a product extracted from plant materials after dissolving them in an alkaline solution. Both enzymatically hydrolyzed lignin and alkali lignin use phenylpropane units as their basic framework, linked by ether bonds and carbon-carbon bonds, and commonly contain characteristic functional groups such as methoxy, phenolic hydroxyl, and alcoholic hydroxyl groups. Due to the presence of aromatic rings and polar groups within their molecules, both exhibit similar surface activity and adsorption properties. These active groups not only determine the solubility and surface characteristics of lignin but also provide multiple reaction sites for its chemical modification.

[0013] This invention provides a method for preparing lignin polymers based on enzymatically hydrolyzed lignin and / or alkali lignin and lipoic acid. This method enables the production of lignin polymers without the need for initiators or solvents. It involves introducing enzymatically hydrolyzed lignin and / or alkali lignin into lipoic acid, using polyethylene glycol diacrylate as a crosslinking agent for lipoic acid, and simultaneously introducing lithium salts to allow Li... + The lignin polymer coordinates the hydroxyl groups on the enzymatic hydrolysis lignin and / or alkali lignin with the carboxyl groups on the polylipoic acid side chains, bridging the enzymatic hydrolysis lignin and / or alkali lignin with lipoic acid via lithium salts to form an elastomer with self-healing properties. This lignin polymer possesses inherent self-healing capabilities to balance fluctuating interfacial stresses during repeated lithium deposition and stripping processes, and significantly inhibits lithium dendrite growth during repeated lithium deposition and dissolution.

[0014] Moreover, lignin polymers can improve the interfacial contact between the electrolyte and the positive and negative electrodes, forming an adaptive interface. This can alleviate the volume expansion of the electrodes during battery cycling to some extent, thereby allowing the composite electrolyte to maintain good interfacial contact under low stacking pressure. Ultimately, this results in the solid-state battery being able to cycle stably under low pressure conditions.

[0015] This invention synthesizes lignin polymer elastomers in a solvent-free and initiator-free manner, avoiding the risks of inducing side reactions in sulfide electrolytes, leaving solvent residues, and reducing ionic conductivity.

[0016] Preferably, the molar ratio of thioctic acid to polyethylene glycol diacrylate is (9~10):1, and the amount of lithium salt used is 20%~25% of the total mass of thioctic acid and polyethylene glycol diacrylate.

[0017] Preferably, the amount of lignin used is 20% to 40% of the total mass of thioctic acid and polyethylene glycol diacrylate.

[0018] Preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0019] The present invention also protects the use of the lignin polymer as an electrolyte additive for reducing the cycling stacking stress of all-solid-state lithium metal batteries.

[0020] The lignin polymer of the present invention can resist lithium dendrite growth, reduce the stacking pressure required for stable cycling of sulfide solid-state batteries, and enable sulfide-based lithium metal all-solid-state batteries to operate robustly under significantly reduced stacking pressure. Therefore, it can be used as an electrolyte additive for all-solid-state lithium metal batteries.

[0021] Preferably, in the application, the cycle stacking pressure of the all-solid-state lithium metal battery is 5~40MPa.

[0022] Preferably, the cycle stacking pressure of the all-solid-state lithium metal battery is 5~8MPa.

[0023] The present invention also protects a lignin polymer composite sulfide electrolyte, comprising the lignin polymer and the sulfide electrolyte described above, wherein the lignin polymer accounts for 4 to 12% of the mass percentage of the lignin polymer in the lignin polymer composite sulfide electrolyte.

[0024] Preferably, the lignin polymer in the lignin polymer composite sulfide electrolyte is 5-7% by mass.

[0025] Preferably, the sulfide electrolyte is Li6PS5Cl.

[0026] The present invention also protects a method for preparing the lignin polymer composite sulfide electrolyte according to any of the above claims, comprising the following steps: mixing the lignin polymer and the sulfide electrolyte, heating and melting, and grinding to obtain the lignin polymer composite sulfide electrolyte.

[0027] This invention also protects an all-solid-state lithium metal battery comprising the lignin polymer composite sulfide electrolyte described in any of the preceding claims.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention discloses a lignin polymer, which is obtained by mixing and reacting lipoic acid, polyethylene glycol diacrylate, lithium salt and enzymatically hydrolyzed lignin and / or alkali lignin, and can be used as an electrolyte additive for all-solid-state lithium metal batteries, enabling sulfide-based lithium metal all-solid-state batteries to operate robustly under significantly reduced stacking pressure, and can also significantly inhibit lithium dendrite growth during repeated lithium deposition and dissolution processes. Attached Figure Description

[0029] Figure 1 The images shown are of the lignin polymers of Examples 1 and 3, and the polymer of Comparative Example 2. The image of the lignin polymer of Example 1 is shown below. Figure 1 As shown in (a) above, a physical image of the lignin polymer of Example 3 is shown below. Figure 1 As shown in (b) of the figure, a physical image of the polymer of Comparative Example 2 is shown. Figure 1 As shown in (c) in the figure.

[0030] Figure 2 The stress-strain curves are for the lignin polymers of Examples 1 and 3 and the polymer of Comparative Example 2.

[0031] Figure 3 The all-solid-state lithium metal batteries of Example 1 and Comparative Example 1 of this invention were tested at a pressure of 5 MPa, a rate of 0.3C, and a concentration of 11 mg·cm⁻¹. -2 Long-cycle performance test under heavy load.

[0032] Figure 4 The all-solid-state lithium metal battery of Comparative Example 1 of this invention was tested at a pressure of 5 MPa, a rate of 0.3C, and a concentration of 11 mg·cm⁻¹. -2 The specific capacity / voltage curve under load.

[0033] Figure 5 The all-solid-state lithium metal battery of Example 1 of this invention was tested at a pressure of 5 MPa, a rate of 0.3C, and a capacitance of 11 mg·cm⁻¹. -2 The specific capacity / voltage curve under load.

[0034] Figure 6 Example 1 and Comparative Example 1 of the present invention were compared at 0.6 mA·cm. -2 Cycling diagram of assembled lithium-lithium symmetric battery at current density.

[0035] Figure 7 The critical current density diagrams of lithium-lithium symmetric batteries in Examples 1 and 3 and Comparative Example 1 of the present invention are shown in the form of a step size of 0.1 mA·cm. -2 ). Detailed Implementation

[0036] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0037] The enzymatically hydrolyzed lignin was purchased from Shandong Longli Biotechnology Co., Ltd. (LIG-I type, residual sugar content ≤5.0%, ash content ≤5.0%, moisture content ≤14.0%, phenolic hydroxyl content ≥3.0%, lignin content ≥80%).

[0038] Polyethylene glycol diacrylate, manufactured by Shanghai Macklin, brand name P816110, with an average molecular weight of 575, containing 400-600 ppm MEHQ stabilizer (hydroquinone monomethyl ether).

[0039] Li6PS5Cl, VGCF (vapor-grown carbon fiber reinforcement), LiNi 0.88Co 0.55 Mn 0.55 O2 (NCM88) was purchased from GRINM (Guangdong) New Materials Technology Research Institute.

[0040] Example 1

[0041] A lignin polymer is obtained by mixing and reacting 1g of lipoic acid, 0.3g of polyethylene glycol diacrylate, 0.3g of lithium bis(trifluoromethanesulfonyl)imide, and 0.5g of enzymatically hydrolyzed lignin at a reaction temperature of 135℃ for 1h. The amount of enzymatically hydrolyzed lignin is 38% of the total mass of lipoic acid and polyethylene glycol diacrylate, the molar ratio of lipoic acid to polyethylene glycol diacrylate is 9.3:1, and the amount of lithium bis(trifluoromethanesulfonyl)imide is 23% of the total mass of lipoic acid and polyethylene glycol diacrylate.

[0042] The preparation method of the above-mentioned lignin polymer is as follows: Each component is preheated at 135 °C for 20 minutes until a homogeneous melt-flowing mixture is obtained. The melt is then magnetically stirred at 135 °C for 1 hour, and then cooled to room temperature to obtain the block polymer TPLE. A physical image of the lignin polymer is shown below. Figure 1 As shown in (a) above. The lignin polymer was melted at 135 °C to a fluid state, and its viscosity at this temperature was measured to be 6.0 Pa·s using a rotational viscometer at a speed of 30 rpm.

[0043] A lignin polymer composite sulfide electrolyte comprises the aforementioned lignin polymer and sulfide electrolyte Li6PS5Cl, wherein the mass percentage of the lignin polymer in the lignin polymer composite sulfide electrolyte is 5%.

[0044] A method for preparing a lignin polymer composite sulfide electrolyte is as follows: The aforementioned synthesized blocky lignin polymer and Li6PS5Cl powder are placed in a mortar at a mass ratio of 5:95. The mixture is preheated at 135 °C for 20 minutes to allow the lignin polymer to transition to a fluid state. The mixture is then ground for 15 minutes to ensure uniform dispersion of the lignin polymer within the sulfide electrolyte particles, thus forming the lignin polymer composite sulfide electrolyte.

[0045] An all-solid-state lithium metal battery comprising the aforementioned lignin polymer composite sulfide electrolyte.

[0046] A method for preparing an all-solid-state lithium metal battery is as follows:

[0047] The all-solid-state battery was assembled in an argon-filled glove box, where H2O and O2 levels were below 0.1 ppm.

[0048] Preparation of NCM88 composite cathode: 30 mg Li6PS5Cl, 1 mg VGCF, 70 mg LiNi0.88 Co 0.55 Mn 0.55 O2 (NCM88) was added to a mortar and ground for 10 minutes to obtain an NCM88 composite cathode.

[0049] For the full cell, approximately 110 mg of the aforementioned lignin polymer composite sulfide electrolyte was first pressed in a custom PTFE mold at 127 MPa for 3 seconds to form an electrolyte sheet with a diameter of 10 mm. On one side of the electrolyte sheet, 12 to 13 mg of an NCM88-based composite cathode was spread and further compacted at 300 MPa for 1 minute, resulting in an NCM88 cathode surface loading of approximately 12 mg·cm⁻¹. -2 Then, lithium metal foil is laminated onto the other side of the electrolyte sheet to form the negative electrode, completing the assembly of the battery mold. The assembled PTFE mold is placed into a stainless steel battery casing to obtain an all-solid-state lithium metal battery.

[0050] Examples 2-4

[0051] A lignin polymer is obtained by reacting lipoic acid, polyethylene glycol diacrylate, lithium bis(trifluoromethanesulfonyl)imide, and enzymatically hydrolyzed lignin at a reaction temperature of 135°C for 1 hour. The preparation method of each lignin polymer is the same as in Example 1.

[0052] The dosage of each component is shown in Table 1 below.

[0053] Table 1

[0054]

[0055] A physical image of the lignin polymer in Example 3 is shown below. Figure 1 As shown in (b) of the diagram.

[0056] The lignin polymers of Examples 2-4 were melted at 135°C to a fluid state. The viscosities of the lignin polymers of Examples 2-4 at this temperature were tested using a rotational viscometer with a rotation speed of 30 rpm and were 1.9 Pa·s, 3.2 Pa·s, and 8.5 Pa·s, respectively.

[0057] A lignin polymer composite sulfide electrolyte comprises the aforementioned lignin polymer and sulfide electrolyte Li6PS5Cl, wherein the lignin polymer accounts for 5% of the lignin polymer composite sulfide electrolyte by mass. The preparation method of the lignin polymer composite sulfide electrolyte is the same as that in Example 1.

[0058] An all-solid-state lithium metal battery includes the above-mentioned lignin polymer composite sulfide electrolyte. The preparation method of the all-solid-state lithium metal battery is the same as that in Example 1.

[0059] Examples 5-6

[0060] A lignin polymer, identical to the lignin polymer of Example 1.

[0061] A lignin polymer composite sulfide electrolyte comprises the aforementioned lignin polymer and sulfide electrolyte Li6PS5Cl, wherein the mass percentages of the lignin polymer in the lignin polymer composite sulfide electrolyte are 7% and 10%, respectively. The preparation method of the lignin polymer composite sulfide electrolyte is the same as that in Example 1.

[0062] An all-solid-state lithium metal battery includes the above-mentioned lignin polymer composite sulfide electrolyte. The preparation method of the all-solid-state lithium metal battery is the same as that in Example 1.

[0063] Comparative Example 1

[0064] An all-solid-state lithium metal battery, which differs from Example 1 in that the solid electrolyte used is Li6PS5Cl.

[0065] Comparative Example 2

[0066] A polymer is obtained by reacting 1g of lipoic acid, 0.3g of polyethylene glycol diacrylate and 0.3g of lithium bis(trifluoromethanesulfonyl)imide at a reaction temperature of 135°C for 1 hour.

[0067] The preparation method of the above polymer is the same as that in Example 1, and the actual image of the polymer is shown below. Figure 1 As shown in (c) in the figure.

[0068] That is, the polymer does not contain enzymatically hydrolyzed lignin.

[0069] A polymer composite sulfide electrolyte comprises the above-mentioned polymer and the sulfide electrolyte Li6PS5Cl, wherein the polymer accounts for 5% of the polymer composite sulfide electrolyte by mass. The preparation method of the polymer composite sulfide electrolyte is the same as that in Example 1.

[0070] A solid-state lithium metal battery is prepared in a way that differs from that in Example 1 in the preparation method of the electrolyte: 110 mg of polymer composite sulfide electrolyte is loaded into a PTFE mold and cold-pressed at 382 MPa to obtain a dense electrolyte sheet with a diameter of 10 mm.

[0071] Comparative Example 3

[0072] A lignin polymer, identical to the lignin polymer of Example 1.

[0073] A lignin polymer composite sulfide electrolyte comprises the aforementioned lignin polymer and sulfide electrolyte Li6PS5Cl, wherein the mass percentage of the lignin polymer in the lignin polymer composite sulfide electrolyte is 20%. The preparation method of the lignin polymer composite sulfide electrolyte is the same as that in Example 1.

[0074] Comparative Example 4

[0075] A lignin polymer, identical to the lignin polymer of Example 1.

[0076] A lignin polymer composite sulfide electrolyte comprises the aforementioned lignin polymer and sulfide electrolyte Li6PS5Cl, wherein the lignin polymer accounts for 3% of the mass percentage of the lignin polymer composite sulfide electrolyte. The preparation method of the lignin polymer composite sulfide electrolyte is the same as that in Example 1.

[0077] Performance testing

[0078] (1) Stress-strain measurements were performed on the lignin polymers of Examples 1 and 3 and the polymer of Comparative Example 2 at room temperature on a universal testing machine (UTM 6103) equipped with a 100 N force sensor, with the clamp rising at a speed of 50 mm / min. -1 The test results are as follows: Figure 2 As shown in Table 2.

[0079] Table 2

[0080]

[0081] like Figure 2 As shown, the lignin polymer of Example 1 exhibits the most balanced mechanical properties, withstanding over 300% strain and a maximum stress of 0.8 MPa, thus demonstrating high toughness and strong load-bearing capacity. In contrast, the lignin polymer of Example 3 exhibits moderate mechanical strength and elongation (stress = 0.26 MPa at 400% strain), while the polymer of Comparative Example 2, which does not contain enzymatically hydrolyzed lignin, exhibits significantly poorer mechanical strength with a maximum stress of 0.08 MPa.

[0082] (2) Long-term cycle testing: Tests were conducted at room temperature (25°C) using a LAND CT2001A battery testing system and a NEWARE battery testing system, with a voltage window of 2.5 to 4.3 V. The all-solid-state lithium metal batteries of Example 1 and Comparative Example 1 were subjected to constant current charge-discharge tests at stacking pressures of approximately 5 MPa, 13 MPa, 25 MPa, and 38 MPa, respectively. The test results are as follows: Figures 3-5 As shown in Table 3. Figure 3The all-solid-state lithium metal batteries of Example 1 and Comparative Example 1 of this invention were tested at a pressure of 5 MPa, a rate of 0.3C, and a concentration of 11 mg·cm⁻¹. -2 Long-cycle performance test under heavy load. Figure 4 The all-solid-state lithium metal battery of Comparative Example 1 of this invention was tested at a pressure of 5 MPa, a rate of 0.3C, and a concentration of 11 mg·cm⁻¹. -2 The specific capacity / voltage curve under load. Figure 5 The all-solid-state lithium metal battery of Example 1 of this invention was tested at a pressure of 5 MPa, a rate of 0.3C, and a capacitance of 11 mg·cm⁻¹. -2 The specific capacity / voltage curve under load.

[0083] Table 3

[0084]

[0085] From Table 3 above, Figure 3 and Figure 5 As can be seen, under a stacking pressure of approximately 5 MPa, the capacity of the battery in Example 1 remained at 77% after 100 cycles and at 70% after 200 cycles. The battery in Example 1 exhibited a stable charge-discharge curve and a capacity of 139.8 mAh·g. -1 High discharge capacity. From Table 3 above... Figure 4 It can be seen that the discharge specific capacity of the comparative sample 1 battery is low, and it shows obvious overcharging behavior during cycling, resulting in low charge and discharge efficiency.

[0086] To investigate the role of lignin polymers, the following constant current lithium stripping and deposition measurements and critical current density (CCD) tests were performed:

[0087] (3) Constant current lithium stripping and deposition measurement:

[0088] 110 mg of the lignin polymer composite sulfide electrolyte powder obtained in Example 1 was loaded into a PTFE mold and cold-pressed at 382 MPa to obtain a dense electrolyte sheet with a diameter of 10 mm. Two lithium metal foils (10 mm in diameter and 40 μm in thickness) were then placed on either side of the sheet and further pressed at 30 MPa to ensure good interfacial contact, thus preparing a lithium-lithium symmetric battery. The lithium-lithium symmetric battery was cycle-tested on a LAND battery testing system at 0.6 mA·cm⁻¹. -2 Constant current lithium stripping and deposition measurements were performed.

[0089] 110 mg of Li6PS5Cl sulfide electrolyte powder was loaded into a PTFE mold and cold-pressed at 382 MPa to obtain a dense electrolyte sheet with a diameter of 10 mm. Two lithium metal foils (10 mm in diameter and 40 μm in thickness) were then placed on either side of the sheet and further pressed at 30 MPa to ensure good interfacial contact, thus preparing a lithium-lithium symmetric battery. The lithium-lithium symmetric battery was cycle-tested on a LAND battery testing system at 0.6 mA·cm⁻¹. -2 Constant current lithium stripping and deposition measurements were performed.

[0090] Figure 6 The lithium-lithium symmetric batteries of Example 1 and Comparative Example 1 of this invention are at 0.6 mA·cm -2 Cycling diagram of assembled lithium-lithium symmetric battery at current density.

[0091] from Figure 6 As can be seen, the lithium-lithium symmetric battery prepared with Li6PS5Cl sulfide electrolyte in Comparative Example 1 experienced soft breakdown at approximately 30 hours, followed by complete lithium dendrite penetration and battery failure before 100 hours. In contrast, the lithium-lithium symmetric battery prepared with the lignin polymer composite sulfide electrolyte in Example 1 maintained stable cycling for 1300 hours at the same current density without any soft short circuit. The reduced polarization and extended lifetime indicate that the lignin polymer composite sulfide electrolyte alleviates interfacial stress accumulation and promotes more uniform lithium deposition, thereby suppressing dendrite nucleation and propagation under high current conditions, achieving higher operating current density and significantly extended cycle life.

[0092] (4) Critical current density (CCD) test:

[0093] 110 mg of the lignin polymer composite sulfide electrolyte powder obtained in each example was loaded into a PTFE mold and cold-pressed at 382 MPa to obtain a dense electrolyte sheet with a diameter of 10 mm. Two lithium metal foils (10 mm in diameter and 40 μm in thickness) were then placed on either side of the sheet and further pressed at 30 MPa to ensure good interfacial contact, thus preparing a lithium-lithium symmetric battery. The lithium-lithium symmetric battery was tested on a LAND battery testing system, and the critical current density was gradually increased from 0.1 to 3.0 mA·cm⁻¹. -2 The determination is made until battery failure, with a step size of 0.1 mA·cm. -2 .

[0094] 110 mg of Li6PS5Cl sulfide electrolyte powder was loaded into a PTFE mold and cold-pressed at 382 MPa to obtain a dense electrolyte sheet with a diameter of 10 mm. Two lithium metal foils (10 mm in diameter and 40 μm in thickness) were then placed on either side of the sheet and further pressed at 30 MPa to ensure good interfacial contact, thus preparing a lithium-lithium symmetric battery. The lithium-lithium symmetric battery was tested on a LAND battery testing system, and the critical current density was determined by gradually increasing the applied current density from 0.1 to 3.0 mA·cm⁻¹. -2 The determination is made until battery failure, with a step size of 0.1 mA·cm. -2 .

[0095] Figure 7 The critical current density diagrams of lithium-lithium symmetric batteries in Examples 1 and 3 and Comparative Example 1 of the present invention are shown in the form of a step size of 0.1 mA·cm. -2 ).

[0096] The test results of the critical current density for the remaining embodiments and comparative examples are shown in Table 4.

[0097] Table 4

[0098]

[0099] The dendrite suppression capability of the composite electrolyte was evaluated using the critical current density (CCD) in a lithium-lithium symmetric battery. A higher CCD value indicates a stronger ability of the electrolyte to resist dendrite growth. The lithium-lithium symmetric battery prepared with the Li6PS5Cl sulfide electrolyte had a CCD of 0.6 mA·cm⁻¹. -2 This reflects its localization of Li + Limited mechanical resilience due to flux concentration and void-induced interfacial instability. Increasing the content of enzymatically hydrolyzed lignin within the lignin polymer can significantly improve CCD. Specifically, the CCD of Example 3 can reach 1.0 mA·cm⁻¹. -2 The CCD in Example 1 was further improved to 2.1 mA·cm. -2 Compared to the lithium-lithium symmetric battery with the Li6PS5Cl sulfide electrolyte in Comparative Example 1, these properties enable the composite electrolyte to better adapt to interfacial stress and maintain close contact during lithium deposition and stripping. Long-term lithium stripping and deposition tests further confirm the significant inhibitory effect of the solid electrolyte with lignin polymer composite on lithium dendrite growth during repeated lithium deposition and dissolution.

[0100] These results collectively demonstrate that the co-incorporation of a lignin- and lipoic acid-mediated dynamic network significantly improves the mechanical resilience of lignin polymers. Figure 3-7The outstanding performance of both full-cell and lithium-lithium symmetric batteries is related to the excellent toughness and elasticity of the lignin polymers used in the examples. This superior elasticity and toughness, combined with the sulfide solid electrolyte, endows the electrolyte with the ability to resist lithium dendrite growth, enabling its successful application in lithium metal solid-state batteries. Furthermore, the lignin polymer can improve the interfacial contact between the electrolyte and the positive and negative electrodes, forming an adaptive interface. This alleviates the volume expansion of the electrodes during battery cycling to some extent, thereby allowing the composite electrolyte to maintain good interfacial contact even under low stacking pressure. Ultimately, this results in the solid-state battery being able to cycle stably under low pressure conditions.

[0101] As can be seen from the above data, the lignin polymer of this invention is an elastomer with high mechanical properties. Compared with traditional sulfide solid-state batteries that require high stacking pressure to maintain stability, the lignin polymer of this invention enables the composite sulfide electrolyte to operate stably in low-pressure solid-state batteries, achieving an initial discharge specific capacity of 139 mAh·g at a low pressure of 5 MPa. -1 Furthermore, it maintains 77% capacity after 100 cycles and reaches 70% capacity retention after 200 cycles.

[0102] Compared to traditional sulfide solid-state lithium metal batteries, which commonly exhibit soft short circuits or even hard short circuits during cycling, the lignin polymer of this invention enables the composite sulfide electrolyte to resist the growth of lithium dendrites on the negative electrode side, ensuring stable operation in lithium metal solid-state batteries at 0.6 mA·cm⁻¹. -2 The current density was constant for 1300 hours of cycling.

[0103] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. The use of a lignin polymer as an electrolyte additive to reduce the cycling stacking pressure of an all-solid-state lithium metal battery, wherein the cycling stacking pressure of the all-solid-state lithium metal battery is 5~40 MPa; The lignin polymer is obtained by mixing and reacting lipoic acid, polyethylene glycol diacrylate, lithium salt and lignin at a reaction temperature of 130~140℃ and a reaction time of 0.5~2h. in, The lignin is enzymatically hydrolyzed lignin and / or alkali lignin; The amount of lignin used is 38% to 40% of the total mass of lipoic acid and polyethylene glycol diacrylate; the molar ratio of lipoic acid to polyethylene glycol diacrylate is (9 to 10): 1; and the amount of lithium salt used is 20% to 25% of the total mass of lipoic acid and polyethylene glycol diacrylate. The electrolyte is a lignin polymer composite sulfide electrolyte, which includes the lignin polymer and the sulfide electrolyte, and the mass percentage of the lignin polymer in the lignin polymer composite sulfide electrolyte is 4~12%.

2. The use according to claim 1, characterized in that, The lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

3. The use according to claim 1, characterized in that, The cycle stacking pressure of the all-solid-state lithium metal battery is 5~8MPa.

4. The use according to claim 1, characterized in that, The sulfide electrolyte is Li6PS5Cl.

5. The use according to claim 1, characterized in that, The preparation method of the lignin polymer composite sulfide electrolyte includes the following steps: mixing the lignin polymer and the sulfide electrolyte, heating and melting, and grinding to obtain the lignin polymer composite sulfide electrolyte.

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