A modified lignin lead-acid battery negative electrode paste and its preparation method

Abstract

This invention relates to the field of lead-acid battery technology, and discloses a modified lignin-based negative electrode paste for lead-acid batteries and its preparation method. The negative electrode paste comprises lead oxide powder, sulfuric acid solution, deionized water, modified lignin, barium sulfate, short fibers, humic acid, eugenol, acetylene black, graphene carbon nanotube composite material, and a surfactant. The modified lignin is obtained through oxidation, sulfonation, and metal ion chelation modification, with the metal ions including bismuth and antimony ions. The preparation method employs a dry-mixing-water-mixing staged process. This invention increases the active sites of lignin through oxidation and sulfonation, improves stability and imparts electrochemical activity through metal chelation, and, synergistically, enhances the antioxidant effect of eugenol and the conductive network of the graphene carbon nanotube composite material, significantly improving the battery's low-temperature performance, cycle life, and capacity retention.

Description

Technical Field

[0001] This invention relates to the field of lead-acid battery technology, and in particular to a modified lignin lead-acid battery negative electrode paste and its preparation method. Background Technology

[0002] Lead-acid batteries hold an irreplaceable position in communication backup power, renewable energy storage, and electric transportation due to their advantages such as low cost, high safety, long cycle life, and high recyclability. However, with the increasing application in cold regions and deep charge / discharge scenarios, the technical shortcomings of traditional negative electrode lead paste are becoming increasingly apparent. Sodium lignin sulfonate (lignin for short), as a key organic expander, can effectively inhibit the volume shrinkage of the negative electrode active material during charge and discharge. However, the phenolic hydroxyl groups in its molecular structure are easily oxidized in the electrolyte, and the hydrophilicity of the sulfonic acid groups makes it easy to dissolve and be lost during cycling, resulting in a decline in expansion function, gradual hardening of the negative electrode plate, and a significant decrease in low-temperature start-up performance and cycle life. In addition, in existing technologies, metal-based hydrogen evolution inhibitors are added directly in the form of oxides or salts, which are prone to hydrolysis and aggregation in the acidic environment of lead paste, resulting in poor dispersibility and difficulty in forming a uniform and effective hydrogen evolution inhibition layer on the lead surface. This leads to severe hydrogen evolution at the end of charging and aggravated battery water loss.

[0003] Therefore, there is an urgent need to develop a negative electrode lead paste technology that can stabilize organic swelling agents, synergistically suppress hydrogen evolution, and construct a highly efficient conductive network. Summary of the Invention

[0004] The purpose of this invention is to provide a modified lignin-based negative electrode paste for lead-acid batteries, in order to solve the problem in the prior art where the rapid dissolution of lignin in the negative electrode paste of lead-acid batteries leads to a decrease in effective active ingredients, resulting in reduced expansion function and cycle life.

[0005] The present invention also aims to provide a method for preparing a modified lignin lead-acid battery negative electrode paste, which is used to prepare a negative electrode paste with stable organic expanding agent, effective hydrogen evolution and high conductivity.

[0006] On one hand, this invention discloses a modified lignin-based lead-acid battery negative electrode paste, comprising the following raw materials in parts by weight: 1000 parts lead oxide powder, 100-180 parts sulfuric acid solution, 100-200 parts deionized water, 5-10 parts modified lignin, 10-20 parts barium sulfate, 0.5-1 part short fiber, 1-10 parts humic acid, 0.2-0.8 parts eugenol, 0.5-1 part acetylene black, 1-5 parts graphene carbon nanotube composite material, and 0.1-0.3 parts surfactant; Modified lignin includes oxidation and sulfonation reactions.

[0007] By employing the above technical solutions, this invention utilizes modified lignin as a functional additive. After oxidation treatment, the phenolic hydroxyl groups in its molecular structure are converted into quinone groups, accompanied by side chain breakage, increasing the content of active functional groups such as carboxyl groups and enhancing its chemical affinity with lead ions and lead sulfate surfaces. Subsequent sulfonation further introduces sulfonic acid groups, improving the solubility and dispersion stability of lignin, allowing it to form a uniformly distributed organic network in the lead paste matrix, effectively inhibiting the volume shrinkage and structural collapse of the negative electrode active material during charge-discharge cycles. Eugenol and lignin both belong to the phenolic natural products, and both contain phenolic hydroxyl and methoxy substituents in their molecular structures, which can construct a dual phenolic antioxidant network in the negative electrode lead paste. When the phenolic hydroxyl groups of modified lignin are oxidized to a quinone structure after capturing free radicals, eugenol can regenerate it by providing hydrogen atoms, and vice versa, forming a redox cycle that significantly extends the antioxidant protection period. Meanwhile, the allyl side chain of eugenol possesses hydrophobicity and steric hindrance effects, forming a complementary hydrophilic and hydrophobic structure with the hydrophilic sulfonic acid / carboxyl groups of modified lignin. Together, they construct a dense organic adsorption layer on the surface of lead particles. Lignin provides structural stability through strong adsorption of carboxyl groups, while eugenol provides interfacial lubrication through weak adsorption of methoxy groups and benzene rings, synergistically inhibiting the shrinkage of the specific surface area of ​​the active material. In addition, eugenol can also penetrate to the interface between humic acid and lead, preventing humic acid swelling agent clustering by reducing interfacial tension, thus ensuring the uniform dispersion of the porous structure of humic acid in the lead paste. Simultaneously, the lubricating effect of eugenol reduces friction between the active material and the separator during charging and discharging, synergistically extending cycle life. The graphene-carbon nanotube composite material, through the construction of a three-dimensional conductive network, not only significantly reduces electrode internal resistance and improves high-rate discharge performance, but its high specific surface area also provides abundant reaction sites for lead sulfate deposition and dissolution, synergistically improving the battery's low-temperature start-up capability and cycle life.

[0008] Lead oxide powder serves as the precursor and framework for the active material of the negative electrode; barium sulfate acts as a homocrystalline nucleating agent and anti-passivation agent. BaSO4 and PbSO4 have similar crystal structures, and BaSO4 acts as a seed crystal, providing heterogeneous nucleation sites, resulting in finer and more uniformly distributed PbSO4 crystals generated during discharge, preventing the formation of a dense passivation layer covering the lead surface; simultaneously, it remains stable in the lead paste, providing expansion space and preventing the active material from hardening and falling off due to volume changes during charge-discharge cycles; short fibers provide mechanical reinforcement and structural retention; humic acid functions similarly to lignin, forming a protective film on the surface of lead particles through adsorption, preventing the negative electrode plate from shrinking and hardening due to lead grain growth during formation and cycling; its loose organic layer structure increases the porosity of the lead paste, improving electrolyte wettability, thereby enhancing the battery's low-temperature start-up performance and charge acceptance; when used in conjunction with modified lignin, it can extend the working cycle of the expansion agent; acetylene black can construct a conductive network and an anti-passivation barrier. Although lead itself is conductive, the PbSO4 generated at the end of the discharge is an insulator that encapsulates unreacted lead nuclei, leading to passivation. Acetylene black particles form a three-dimensional conductive carbon network in the lead paste, providing an alternative pathway for electron transport and ensuring deep utilization of active materials. At the same time, their high specific surface area adsorption characteristics can prevent excessive growth of lead sulfate grains, inhibit irreversible sulfation, and improve high-rate discharge performance.

[0009] Preferably, the lead oxide powder has an oxidation degree of 70% to 75% and a particle size of ≤5μm.

[0010] Preferably, the surfactant includes OP-10 and sodium dodecyl sulfate.

[0011] Preferably, the modified lignin is prepared by the following method: A1. Dissolve lignin in deionized water, add oxidizing agent, and stir to react; A2. After adding concentrated sulfuric acid and sulfonating agent and stirring to react, the mixture is cooled to 20-30℃ and then salted out. After filtration and drying, oxidized sulfonated lignin is obtained.

[0012] Preferably, the oxidizing agent includes persulfate or peroxide.

[0013] More preferably, persulfates include sodium persulfate and potassium persulfate; peroxides include hydrogen peroxide.

[0014] Preferably, the amount of oxidant used is 5% to 20% of the wood content.

[0015] Preferably, the sulfonating agent includes one or more of chlorosulfonic acid, aminosulfonic acid, and sodium sulfite.

[0016] Preferably, the amount of sulfonating agent used is 30% to 80% of the wood quality.

[0017] Preferably, the stirring reaction in step A1 includes a temperature of 50-60°C and a reaction time of 30-60 min; the stirring reaction in step A2 includes a temperature of 50-60°C and a reaction time of 60-120 min.

[0018] Preferably, the modified lignin also includes a chelation reaction of metal ions; the metal ions include bismuth ions and antimony ions.

[0019] Preferably, the chelation reaction of metal ions includes the following steps: A3. Disperse oxidized sulfonated lignin in deionized water, add soluble salts of metal ions and coordination stabilizers, adjust the pH to 3.0-4.5, stir the reaction at 30-50℃ for 2-5 hours, and dry to obtain the final product.

[0020] Preferably, the coordination stabilizer includes citric acid and / or tartaric acid.

[0021] Preferably, the amount of soluble salt of metal ions added is 10% to 25% of the weight of oxidized sulfonated wood.

[0022] Preferably, the graphene-carbon nanotube composite material is prepared through the following steps: Concentrated sulfuric acid was added to a mixture of graphite powder, P2O5 and Na2S2O4. Potassium permanganate was slowly added in an ice bath. The mixture was stirred at 0-4°C for 4 hours. After the reaction was completed, the mixture was stirred at room temperature for 4-5 days. Hydrogen peroxide solution was added, and the mixture was centrifuged and washed until neutral to obtain a graphene oxide suspension. The graphene oxide suspension was sonicated for 2–4 hours, then hydroxylated carbon nanotubes and sodium ascorbate were added. The mixture was subjected to a hydrothermal reaction at 120–160 °C for 6–8 hours. After cooling, the mixture was washed and freeze-dried to obtain the final product.

[0023] On the other hand, the present invention also provides a preparation method, comprising the following steps: S1. Weigh out all the raw materials for the negative electrode paste of the modified lignin lead-acid battery and set aside. S2. Add lead oxide powder, modified lignin, barium sulfate, short fiber, humic acid, acetylene black and graphene carbon nanotube composite material into the paste mixing machine and dry mix first, then add surfactant, deionized water and eugenol and mix. S3. Add the sulfuric acid solution to the paste mixing machine while stirring.

[0024] Preferably, the dry stirring time is 10-20 min; the mixing time after adding deionized water is 5-15 min.

[0025] Preferably, the sulfuric acid solution has a mass percentage of 45% to 50%, and the acid addition time is 20 to 30 minutes.

[0026] The beneficial effects of this invention are: This invention utilizes lignin modified through both oxidation and sulfonation. By introducing abundant active functional groups such as carboxyl and sulfonic acid groups, it significantly enhances the chemical affinity of lignin with lead-active materials and the surface of lead sulfate, effectively suppressing electrode shrinkage and sulfation during charge and discharge. Furthermore, through metal ion chelation modification, specific metal elements are stably anchored in the lignin framework in a molecular-level dispersion using coordination chemistry, enabling controlled release during electrochemical cycling. This forms highly catalytically active sites on the negative electrode surface, significantly inhibiting hydrogen evolution and reducing electrolyte water loss. Simultaneously, a cross-linked network is constructed to prevent the dissolution and loss of organic additives in the electrolyte, fundamentally solving the technical bottlenecks of poor stability and short action cycle of traditional expansion agents. The phenolic hydroxyl aromatic compounds introduced into the formulation act as antioxidants, protecting the negative electrode active material from oxidative corrosion through a dual mechanism of free radical capture and metal ion complexation. Meanwhile, the three-dimensional conductive network constructed from graphene and carbon nanotubes significantly reduces electrode internal resistance, providing efficient electron transport channels and improving high-rate discharge performance. The preparation process employs a phased and paste-like procedure, using gradient control of solid-state premixing, aqueous dispersion, and acidification reaction to ensure uniform molecular-level distribution and interface optimization of each functional component within the lead paste matrix. Through the synergistic effect of the above structural design and process, the negative electrode lead paste obtained by this invention exhibits excellent capacity retention and charge acceptance under extreme low-temperature environments, significantly improving cycle life compared to traditional formulations. Furthermore, it effectively inhibits the softening and shedding of active materials, achieving a performance breakthrough and improved reliability of lead-acid batteries in wide-temperature-range, long-cycle application scenarios. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0028] A modified lignin-based lead-acid battery negative electrode paste comprises the following raw materials in parts by weight: 1000 parts lead oxide powder, 100-180 parts sulfuric acid solution, 100-200 parts deionized water, 5-10 parts modified lignin, 10-20 parts barium sulfate, 0.5-1 part short fiber, 1-10 parts humic acid, 0.2-0.8 parts eugenol, 0.5-1 part acetylene black, 1-5 parts graphene carbon nanotube composite material, and 0.1-0.3 parts surfactant; Modified lignin includes oxidation and sulfonation reactions.

[0029] By employing the above technical solutions, this invention utilizes modified lignin as a functional additive. After oxidation treatment, the phenolic hydroxyl groups in its molecular structure are converted into quinone groups, accompanied by side chain breakage, increasing the content of active functional groups such as carboxyl groups and enhancing its chemical affinity with lead ions and lead sulfate surfaces. Subsequent sulfonation further introduces sulfonic acid groups, improving the solubility and dispersion stability of lignin, allowing it to form a uniformly distributed organic network in the lead paste matrix, effectively inhibiting the volume shrinkage and structural collapse of the negative electrode active material during charge-discharge cycles. Eugenol and lignin both belong to the phenolic natural products, and both contain phenolic hydroxyl and methoxy substituents in their molecular structures, which can construct a dual phenolic antioxidant network in the negative electrode lead paste. When the phenolic hydroxyl groups of modified lignin are oxidized to a quinone structure after capturing free radicals, eugenol can regenerate it by providing hydrogen atoms, and vice versa, forming a redox cycle that significantly extends the antioxidant protection period. Meanwhile, the allyl side chain of eugenol possesses hydrophobicity and steric hindrance effects, forming a complementary hydrophilic and hydrophobic structure with the hydrophilic sulfonic acid / carboxyl groups of modified lignin. Together, they construct a dense organic adsorption layer on the surface of lead particles. Lignin provides structural stability through strong adsorption of carboxyl groups, while eugenol provides interfacial lubrication through weak adsorption of methoxy-benzene rings, synergistically inhibiting the shrinkage of the specific surface area of ​​the active material. In addition, eugenol can also penetrate to the interface between humic acid and lead, preventing humic acid swelling agent clustering by reducing interfacial tension, thus ensuring the uniform dispersion of the porous structure of humic acid in the lead paste. Simultaneously, the lubricating effect of eugenol reduces friction between the active material and the separator during charging and discharging, synergistically extending cycle life. The graphene-carbon nanotube composite material, through the construction of a three-dimensional conductive network, not only significantly reduces electrode internal resistance and improves high-rate discharge performance, but its high specific surface area also provides abundant reaction sites for lead sulfate deposition and dissolution, synergistically improving the battery's low-temperature start-up capability and cycle life.

[0030] Lead oxide powder serves as the precursor and framework for the active material of the negative electrode; barium sulfate acts as a homocrystalline nucleating agent and anti-passivation agent. BaSO4 and PbSO4 have similar crystal structures, and BaSO4 acts as a seed crystal, providing heterogeneous nucleation sites, resulting in finer and more uniformly distributed PbSO4 crystals generated during discharge, preventing the formation of a dense passivation layer covering the lead surface; simultaneously, it remains stable in the lead paste, providing expansion space and preventing the active material from hardening and falling off due to volume changes during charge-discharge cycles; short fibers provide mechanical reinforcement and structural retention; humic acid functions similarly to lignin, forming a protective film on the surface of lead particles through adsorption, preventing the negative electrode plate from shrinking and hardening due to lead grain growth during formation and cycling; its loose organic layer structure increases the porosity of the lead paste, improving electrolyte wettability, thereby enhancing the battery's low-temperature start-up performance and charge acceptance; when used in conjunction with modified lignin, it can extend the working cycle of the expansion agent; acetylene black can construct a conductive network and an anti-passivation barrier. Although lead itself is conductive, the PbSO4 generated at the end of the discharge is an insulator that encapsulates unreacted lead nuclei, leading to passivation. Acetylene black particles form a three-dimensional conductive carbon network in the lead paste, providing an alternative pathway for electron transport and ensuring deep utilization of active materials. At the same time, their high specific surface area adsorption characteristics can prevent excessive growth of lead sulfate grains, inhibit irreversible sulfation, and improve high-rate discharge performance.

[0031] In some embodiments, the oxidation degree of lead oxide powder is 70% to 75%, and the particle size is ≤5 μm. Controlling the lead oxide powder within a suitable oxidation degree range ensures sufficient PbO active sites on the lead powder surface to react with sulfuric acid, which is beneficial for forming a stable lead paste skeleton structure, while avoiding the decrease in specific surface area and reduced reactivity caused by excessive oxidation. At the same time, limiting the particle size to ≤5 μm ensures the fine dispersion of lead powder particles, increases the contact area with the electrolyte, improves the utilization rate of active materials, and helps to form a tight interfacial bond with additives such as modified lignin.

[0032] In some embodiments, the surfactant includes OP-10 and sodium dodecyl sulfate; the addition of surfactant can help emulsify and disperse eugenol.

[0033] In some embodiments, modified lignin is prepared by the following method: A1. Dissolve lignin in deionized water, add oxidizing agent, and stir to react; A2. After adding concentrated sulfuric acid and sulfonating agent and stirring to react, the mixture is cooled to 20-30℃ and then salted out. After filtration and drying, oxidized sulfonated lignin is obtained.

[0034] By employing a stepwise oxidation and sulfonation process to chemically modify lignin, the three-dimensional network structure of lignin is first opened by selective oxidation with an oxidant, increasing the carboxyl content. Subsequently, a sulfonating agent is introduced under acidic conditions to achieve electrophilic substitution reaction on the aromatic ring, thereby increasing the degree of sulfonation. Finally, the product is efficiently separated and purified by salting-out precipitation. The resulting oxidized sulfonated lignin exhibits excellent lead affinity, dispersion stability, and electrochemical activity, laying a structural foundation for subsequent functionalization modification.

[0035] In some embodiments, the oxidant includes persulfate and peroxide; persulfate includes sodium persulfate and potassium persulfate; peroxide includes hydrogen peroxide; the amount of oxidant used is 5% to 20% of the lignin mass; by selecting persulfate or peroxide as the oxidant, strong oxidizing free radical species are generated under mild conditions, which can effectively attack the side chains and ether bonds of lignin molecules and achieve functional group transformation; limiting the amount of oxidant to 5% to 20% of the lignin mass ensures that the oxidation reaction proceeds fully and oxidized lignin with high carboxyl content is obtained, while avoiding excessive oxidation that leads to excessively low molecular weight and structural damage, thus maintaining the film-forming properties and mechanical strength required for lignin as an expansion agent.

[0036] In some embodiments, the sulfonating agent includes one or more of chlorosulfonic acid, aminosulfonic acid, and sodium sulfite; the amount of sulfonating agent used is 30% to 80% of the lignin mass; chlorosulfonic acid and aminosulfonic acid are suitable for deep sulfonation to obtain products with high charge density, while sodium sulfite is suitable for nucleophilic substitution sulfonation under mild conditions; controlling the amount of sulfonating agent in the range of 30% to 80% can increase the degree of sulfonation of lignin, significantly improve solubility and compatibility with lead paste system, while retaining sufficient free phenolic hydroxyl groups for subsequent metal chelation modification.

[0037] In some embodiments, the stirring reaction in step A1 includes a temperature of 50–60°C and a reaction time of 30–60 min; the stirring reaction in step A2 includes a temperature of 50–60°C and a reaction time of 60–120 min; controlling the oxidation stage at 50–60°C for 30–60 min ensures the generation rate and reaction selectivity of oxidant free radicals, achieving appropriate ring opening of lignin molecules and introduction of carboxyl groups; controlling the sulfonation stage at 50–60°C for 60–120 min ensures the full progress of the sulfonation reaction and the structural uniformity of the product, while avoiding side reactions and product degradation caused by high temperature.

[0038] In some embodiments, the modified lignin further includes a metal ion chelation reaction; the metal ions include bismuth ions and antimony ions; the metal ion chelation reaction includes the following steps: A3. Disperse oxidized sulfonated lignin in deionized water, add soluble salts of metal ions and coordination stabilizers, adjust the pH to 3.0-4.5, stir the reaction at 30-50℃ for 2-5 hours, and dry to obtain the final product.

[0039] By adopting the above technical solutions, the sulfonated groups of oxidized lignin increase, resulting in higher solubility and better initial starting performance. However, due to dissolution loss, its capacity decays rapidly, leading to poor stability. Therefore, by chelating metal ions with oxidized sulfonated lignin, on the one hand, stable coordination complexes can be formed between carboxyl and phenolic hydroxyl groups and metal ions to construct a three-dimensional cross-linked network structure, significantly reducing the dissolution rate of lignin in the electrolyte and extending its operating cycle. On the other hand, the controlled release of metal ions can be achieved during electrochemical cycling, forming high hydrogen evolution overpotential nano-active sites or catalytic nucleation centers on the negative electrode surface in situ. This synergistically inhibits hydrogen evolution and improves the crystal morphology of lead sulfate, thereby enhancing the battery's cycle life and charging efficiency.

[0040] In some embodiments, the coordination stabilizer includes citric acid and / or tartaric acid; when citric acid or tartaric acid is selected as the coordination stabilizer, its polycarboxylic acid structure can form soluble complexes with bismuth ions, antimony ions, etc., effectively inhibiting the hydrolysis and precipitation of metal ions in acidic aqueous solutions with pH 3.0 to 2.5, and ensuring the single-phase homogeneity of the chelation reaction.

[0041] In some embodiments, the graphene-carbon nanotube composite material is prepared by the following steps: Concentrated sulfuric acid was added to a mixture of graphite powder, P2O5 and Na2S2O4. Potassium permanganate was slowly added in an ice bath. The mixture was stirred at 0-4°C for 4 hours. After the reaction was completed, the mixture was stirred at room temperature for 4-5 days. Hydrogen peroxide solution was added, and the mixture was centrifuged and washed until neutral to obtain a graphene oxide suspension. The graphene oxide suspension was sonicated for 2–4 hours, then hydroxylated carbon nanotubes and sodium ascorbate were added. The mixture was subjected to a hydrothermal reaction at 120–160 °C for 6–8 hours. After cooling, the mixture was washed and freeze-dried to obtain the final product.

[0042] By adopting the above technical solution, graphene oxide with a high degree of oxidation is first prepared by oxidation-reduction method, and abundant oxygen-containing functional groups are introduced to improve its water dispersibility. Then, it is thoroughly mixed with hydroxylated carbon nanotubes by ultrasonic dispersion. The reduction effect of sodium ascorbate during hydrothermal reduction is used to simultaneously achieve partial reduction of graphene oxide and surface modification of carbon nanotubes, and finally form a three-dimensional composite structure of graphene-coated carbon nanotubes. This structure combines the high conductivity of graphene and the high aspect ratio of carbon nanotubes, and constructs an efficient electron transport network and mechanical reinforcement framework in lead paste.

[0043] A preparation method comprising the following steps: S1. Weigh out all the raw materials for the negative electrode paste of the modified lignin lead-acid battery and set aside. S2. Add lead oxide powder, modified lignin, barium sulfate, short fiber, humic acid, acetylene black and graphene carbon nanotube composite material into the paste mixing machine and dry mix first, then add surfactant, deionized water and eugenol and mix. S3. Add the sulfuric acid solution to the paste mixing machine while stirring.

[0044] By adopting the above technical solutions, step S2 employs a two-stage mixing process: dry mixing followed by water mixing. Dry mixing ensures that the solid powder is fully dispersed and initially forms a uniform mixture, avoiding agglomeration when water is added later. Water mixing allows water-soluble or hydrophilic components such as modified lignin and humic acid to fully swell and disperse, forming a uniform paste precursor. Step S3 adopts a dynamic reaction mode of adding acid while stirring, controlling the gradual reaction between sulfuric acid and lead oxide powder to avoid local overheating and lead paste agglomeration. At the same time, it ensures the uniform formation of lead sulfate crystals and the stable control of lead paste viscosity, ultimately obtaining a negative electrode lead paste product with uniform structure and stable performance.

[0045] In some embodiments, the dry stirring time is 10–20 min; the mixing time after adding deionized water is 5–15 min; controlling the dry stirring time to 10–20 min ensures sufficient dispersion and initial interfacial contact between lead oxide powder and various additives, avoiding local performance differences caused by uneven mixing; controlling the water mixing time to 5–15 min allows the deionized water to fully wet the solid mixture, and the modified lignin and humic acid and other organic components to fully absorb water and swell, forming a uniform plastic paste, while avoiding excessive stirring that would cause the lead paste temperature to rise and harden prematurely.

[0046] In some embodiments, the sulfuric acid solution has a mass percentage of 45%–50%, and the acid addition time is 20–30 min. Using a 45%–50% concentration sulfuric acid solution as the reacting acid ensures the stoichiometric requirements for reacting with lead oxide powder to produce lead sulfate, while avoiding excessive heat release and local hardening of the lead paste caused by excessively high concentrations. Controlling the acid addition time to be completed uniformly within 20–30 min ensures the uniform release of reaction heat and the controllability of the lead paste temperature, which is conducive to forming a loosely structured lead paste skeleton with a reasonable pore distribution, providing good ion transport channels and mechanical strength for the active material after formation.

[0047] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0048] Preparation Example Preparation Example 1-1: A modified lignin was prepared by the following method: A1. Dissolve 1g of lignin in 30mL of deionized water, add 0.2g of sodium hydroxide solution and 0.1g of ammonium persulfate, and stir the mixture at 50℃ for 60min. A2. Add 0.5 mL of concentrated sulfuric acid and 0.4 g of sodium sulfite, stir and react at 50 °C for 100 min, cool to 25 °C, add 10 g of sodium chloride for salting out, filter and dry to obtain oxidized sulfonated lignin. Preparation Examples 1-2: A modified lignin was prepared by the following method: A1. Dissolve 1g of lignin in 30mL of deionized water, add 0.2g of sodium hydroxide solution and 0.1g of ammonium persulfate, and stir the mixture at 50℃ for 60min. A2. Add 0.5 mL of concentrated sulfuric acid and 0.4 g of sodium sulfite, stir and react at 50 °C for 100 min, cool to 25 °C, add 10 g of sodium chloride for salting out, filter and dry to obtain oxidized sulfonated lignin. A3. Disperse 1g of oxidized sulfonated lignin in 30mL of deionized water, add 0.2g of antimony trichloride and 0.15g of citric acid, adjust the pH to 3.5 with 0.1M dilute hydrochloric acid, stir and react at 40℃ for 4h, centrifuge, wash with deionized water until neutral, and dry at 60℃ to obtain the product.

[0049] Preparation Examples 1-3, a modified lignin, differed from Preparation Examples 1-2 only in that antimony trichloride was replaced with the same mass of bismuth citrate.

[0050] Preparation Examples 1-4, a modified lignin, differed from Preparation Examples 1-2 only in that the amount of bismuth citrate added was 0.05 g.

[0051] Preparation Example 2-1: A graphene-carbon nanotube composite material was prepared through the following steps: Add 120 mL of concentrated sulfuric acid to a mixture of 2 g graphite powder, 0.3 g P2O5 and 1 g Na2S2O4. Slowly add 10 g potassium permanganate in an ice bath. Stir the mixture at 2 °C for 4 h. After the reaction is complete, stir at room temperature for 4 days. Add 10 mL of 30% hydrogen peroxide solution and centrifuge and wash until neutral to obtain a graphene oxide suspension. A graphene-carbon nanotube composite material was obtained by sonicating 100 mL of 5 mg / mL graphene oxide suspension for 4 h, adding 0.15 g of hydroxylated carbon nanotubes and 0.12 g of sodium ascorbate, and carrying out a hydrothermal reaction at 140 °C for 6 h. After cooling, the mixture was washed with deionized water and freeze-dried.

[0052] Example Example 1: A modified lignin-based lead-acid battery negative electrode paste was prepared by the following method: S1. Weigh out all the raw materials for the negative electrode paste of the modified lignin lead-acid battery and set aside. Weigh out 1000 parts of lead oxide powder (oxidation degree 74%, particle size 3-5 μm), 150 parts of 50% sulfuric acid solution, 150 parts of deionized water, 8 parts of modified lignin prepared in Preparation Examples 1-2, 15 parts of barium sulfate, 0.7 parts of short fiber, 5 parts of humic acid, 0.5 parts of eugenol, 0.8 parts of acetylene black, 3 parts of graphene carbon nanotube composite material prepared in Preparation Example 2-1, and 0.2 parts of sodium dodecyl sulfate; S2. Add lead oxide powder, modified lignin, barium sulfate, short fiber, humic acid, acetylene black and graphene carbon nanotube composite material into the paste mixing machine and dry mix for 15 minutes. Then add sodium dodecyl sulfate, deionized water and eugenol and mix for 10 minutes. S3. Add 50% sulfuric acid solution to the paste mixing machine while stirring for 20 minutes to obtain a modified lignin lead-acid battery negative electrode paste.

[0053] Example 2: A modified lignin lead-acid battery negative electrode paste was prepared by the following method: S1. Weigh out all the raw materials for the negative electrode paste of the modified lignin lead-acid battery and set aside. Weigh out 1000 parts of lead oxide powder (oxidation degree 74%, particle size 3-5 μm), 100 parts of 50% sulfuric acid solution, 100 parts of deionized water, 5 parts of modified lignin prepared in Preparation Examples 1-2, 10 parts of barium sulfate, 0.5 parts of short fiber, 1 part of humic acid, 0.2 parts of eugenol, 0.5 parts of acetylene black, 1 part of graphene carbon nanotube composite material prepared in Preparation Example 2-1, and 0.1 parts of sodium dodecyl sulfate; S2. Add lead oxide powder, modified lignin, barium sulfate, short fiber, humic acid, eugenol, acetylene black and graphene carbon nanotube composite material into the paste mixing machine and dry mix for 15 minutes. Then add sodium dodecyl sulfate, deionized water and eugenol and mix for 10 minutes. S3. Add 50% sulfuric acid solution to the paste mixing machine while stirring for 20 minutes to obtain a modified lignin lead-acid battery negative electrode paste.

[0054] Example 3: A modified lignin-based lead-acid battery negative electrode paste was prepared by the following method: S1. Weigh out all the raw materials for the negative electrode paste of the modified lignin lead-acid battery and set aside. Weigh out 1000 parts of lead oxide powder (oxidation degree 74%, particle size 3-5 μm), 180 parts of 50% sulfuric acid solution, 200 parts of deionized water, 10 parts of modified lignin prepared in Preparation Examples 1-2, 20 parts of barium sulfate, 1 part of short fiber, 10 parts of humic acid, 0.8 parts of eugenol, 1 part of acetylene black, 5 parts of graphene carbon nanotube composite material prepared in Preparation Example 2-1, and 0.3 parts of sodium dodecyl sulfate; S2. Add lead oxide powder, modified lignin, barium sulfate, short fiber, humic acid, eugenol, acetylene black and graphene carbon nanotube composite material into the paste mixing machine and dry mix for 15 minutes. Then add sodium dodecyl sulfate, deionized water and eugenol and mix for 10 minutes. S3. Add 50% sulfuric acid solution to the paste mixing machine while stirring for 20 minutes to obtain a modified lignin lead-acid battery negative electrode paste.

[0055] Example 4: A modified lignin lead-acid battery negative electrode paste, which differs from Example 1 only in that the modified lignin prepared in Example 1-1 is replaced with the same mass of modified lignin.

[0056] Example 5: A modified lignin lead-acid battery negative electrode paste, which differs from Example 1 only in that the modified lignin prepared in Examples 1-3 is replaced with the same mass of modified lignin.

[0057] Comparative Example Comparative Example 1: A modified lignin lead-acid battery negative electrode paste, which differs from Example 1 only in that the amount of modified lignin added is 1 part.

[0058] Comparative Example 2: A modified lignin lead-acid battery negative electrode paste, which differs from Example 1 only in that the same mass of lignin is used to replace the modified lignin in Example 1.

[0059] Comparative Example 3, a modified lignin lead-acid battery negative electrode paste, differs from Example 1 only in that it does not contain eugenol.

[0060] Comparative Example 4, a modified lignin lead-acid battery negative electrode paste, differs from Example 1 only in that it does not contain graphene carbon nanotube composite material.

[0061] Comparative Example 5 is a modified lignin lead-acid battery negative electrode paste, which differs from Example 1 only in that the modified lignin prepared in Examples 1-4 is replaced with the same mass of modified lignin.

[0062] Performance testing: The negative electrode lead pastes prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were respectively made into negative electrode plates, which were then combined with positive electrode plates made according to the positive electrode plate lead paste formula and preparation process to prepare 20AH batteries of the same model. The following battery performance tests were then performed.

[0063] 1. Capacity test: After the battery is fully charged, use I... 10(A) Current discharge: The ambient temperature of the battery is kept at about 25°C. The change in current value during the discharge time should not exceed 1%. When the voltage of a single battery cell reaches 1.8V, stop the discharge and record the discharge time. Calculate the discharge capacity. 2. -40℃ Low Temperature Capacity Test: Place the fully charged battery in a -40℃ environment for 20 hours. The battery is then subjected to I... 10 (A) Discharge the battery with current. During the discharge process, the ambient temperature of the battery should be maintained at around -40℃. The change in current should not exceed 1%. When the voltage of a single battery cell reaches 1.8V, stop the discharge and record the discharge time. Calculate the discharge capacity. 3. Cycle life test: The ambient temperature around the battery is maintained at approximately 25°C. 1) Using I 10 (A) Discharge the battery cell voltage until it reaches 1.8V; 2) Limit the voltage to 2.35V / cell, with a 2.5I... 10 (A) Charge for 12 hours; 3) Repeat steps 1) and 2). When the discharge time in step 1) is less than 8 hours, the life test is terminated. 4. Capacity retention test: The capacity retention rate shall be tested in accordance with GB / T22199.1-2017. The results of the above performance tests are listed in Table 1.

[0064] Table 1 Performance test results

[0065] The data above show that Examples 1 and 5 demonstrate the optimal synergistic effect of oxidized sulfonated lignin chelated with antimony or bismuth, combined with eugenol and graphene carbon nanotube composites, resulting in a low-temperature capacity retention rate exceeding 47% and a cycle life exceeding 420 cycles. Example 4, lacking metal chelation modification, exhibits slightly weaker expansion agent stability and a slightly reduced cycle life. Comparative Examples 1-4 indicate that the absence of any component leads to performance degradation. In Comparative Example 1, the addition of 1 part of modified lignin resulted in reduced capacity and cycle life; in Comparative Example 2, the lack of lignin modification led to a decline in expansion function; in Comparative Example 3, the lack of eugenol reduced antioxidant properties; in Comparative Example 4, the lack of a conductive network caused a sharp deterioration in low-temperature performance; and in Comparative Example 5, the low amount of chelated metal ions resulted in reduced capacity and cycle life.

[0066] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A modified lignin-based lead-acid battery negative electrode paste, characterized in that, Including the following parts by weight of raw materials: 1000 parts lead oxide powder, 100-180 parts sulfuric acid solution, 100-200 parts deionized water, 5-10 parts modified lignin, 10-20 parts barium sulfate, 0.5-1 part short fiber, 1-10 parts humic acid, 0.2-0.8 parts eugenol, 0.5-1 part acetylene black, 1-5 parts graphene carbon nanotube composite material, and 0.1-0.3 parts surfactant; The modified lignin is prepared by oxidation and sulfonation reactions.

2. The modified lignin lead-acid battery negative electrode paste according to claim 1, characterized in that, The modified lignin is prepared by the following method: A1. Dissolve lignin in deionized water, add oxidizing agent, and stir to react; A2. After adding concentrated sulfuric acid and sulfonating agent and stirring to react, the mixture is cooled to 20-30℃ and then salted out. After filtration and drying, oxidized sulfonated lignin is obtained.

3. The modified lignin lead-acid battery negative electrode paste according to claim 2, characterized in that, The oxidant includes persulfate and peroxide; the amount of the oxidant used is 5% to 20% of the wood content.

4. The modified lignin lead-acid battery negative electrode paste according to claim 2, characterized in that, The sulfonating agent includes one or more of chlorosulfonic acid, aminosulfonic acid, and sodium sulfite; the amount of the sulfonating agent used is 30% to 80% of the wood quality.

5. The modified lignin lead-acid battery negative electrode paste according to claim 2, characterized in that, The stirring reaction in step A1 includes a temperature of 50–60°C and a reaction time of 30–60 min; the stirring reaction in step A2 includes a temperature of 50–60°C and a reaction time of 60–120 min.

6. The modified lignin lead-acid battery negative electrode paste according to claim 1, characterized in that, The modified lignin further includes a chelation reaction of metal ions; the metal ions include bismuth ions and antimony ions; the chelation reaction of metal ions includes the following steps: A3. Disperse oxidized sulfonated lignin in deionized water, add soluble salts of metal ions and coordination stabilizers, adjust the pH to 3.0-4.5, stir the reaction at 30-50℃ for 2-5 hours, and dry to obtain the final product.

7. The modified lignin lead-acid battery negative electrode paste according to claim 1, characterized in that, The graphene carbon nanotubes are prepared through the following steps: Concentrated sulfuric acid was added to a mixture of graphite powder, P2O5 and Na2S2O4. Potassium permanganate was slowly added in an ice bath. The mixture was stirred at 0-4°C for 4 hours. After the reaction was completed, the mixture was stirred at room temperature for 4-5 days. Hydrogen peroxide solution was added, and the mixture was centrifuged and washed until neutral to obtain a graphene oxide suspension. The graphene oxide suspension was sonicated for 2–4 hours, then hydroxylated carbon nanotubes and sodium ascorbate were added. The mixture was subjected to a hydrothermal reaction at 120–160 °C for 6–8 hours. After cooling, the mixture was washed and freeze-dried to obtain the final product.

8. A preparation method for preparing the modified lignin lead-acid battery negative electrode paste according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Weigh out all the raw materials for the negative electrode paste of the modified lignin lead-acid battery and set aside. S2. Add lead oxide powder, modified lignin, barium sulfate, short fiber, humic acid, acetylene black and graphene carbon nanotube composite material into the paste mixing machine and dry mix first, then add surfactant, deionized water and eugenol and mix. S3. Add the sulfuric acid solution to the paste mixing machine while stirring.

9. The preparation method according to claim 8, characterized in that, The dry stirring time is 10-20 minutes; the mixing time after adding deionized water is 5-15 minutes.

10. The preparation method according to claim 8, characterized in that, The sulfuric acid solution has a mass percentage of 45% to 50%, and the acid addition time is 20 to 30 minutes.

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