Lignin inorganic oxide composite binder, preparation thereof and application of lignin inorganic oxide composite binder in hard carbon negative electrode

Abstract

The invention discloses a lignin-inorganic oxide composite binder, preparation thereof and application of the lignin-inorganic oxide composite binder in a hard carbon negative electrode. The preparation method comprises the following steps: firstly, carrying out quaternization modification on lignosulfonate to obtain quaternized lignosulfonate, and then utilizing the action of quaternary ammonium and sulfonate of the quaternized lignosulfonate, hydroxyl and inorganic oxyacid radicals of inorganic nano oxide and carboxyl and hydroxyl of sodium carboxymethyl cellulose to prepare the modified lignosulfonate. The lignin-inorganic oxide composite binder with the interpenetrating network structure is formed. According to the binder, sodium carboxymethyl cellulose serves as a hard phase to enhance the mechanical rigidity, quaternized lignosulfonate rich in flexible long chains serves as a soft phase to bear part of loads, and inorganic nano oxide rich in hydroxyl serves as a crosslinking point or physical filler to enhance the structural stability of the binder. Besides, a multi-network structure formed by hydrogen bond crosslinking not only endows the binder with an excellent ion transmission rate, but also helps to enhance the interfacial compatibility of the binder with an ester electrolyte, thereby significantly improving the rate capability and cycle performance of the hard carbon negative electrode.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion batteries, specifically relating to a lignin inorganic oxide composite binder, its preparation, and its application in hard carbon anodes. Background Technology

[0002] The key to the development of advanced sodium-ion batteries lies in constructing high-performance electrode materials and electrolyte systems, with the research and development of low-cost, high-performance anode materials being the core component. Hard carbon, due to its low cost and high specific capacity, has become one of the most commercially promising anode materials for sodium-ion batteries. Carbonate electrolytes, with their excellent high-voltage stability, economic practicality, and safety and reliability, have become the mainstream choice for commercial lithium / sodium-ion battery systems. However, in ester-based electrolytes, hard carbon anodes first form a solid electrolyte interphase (SEI) dominated by organic components, which has high solubility, leading to a significant decrease in the structural stability of the hard carbon anode, thus affecting rate performance and cycle performance.

[0003] Binders are a key component of battery electrodes, primarily functioning to fix active materials and conductive agents onto the current collector surface, preventing the active materials from detaching or peeling off during charging and discharging. Furthermore, binder molecules can form hydrogen bond networks and electrostatic interactions with oxygen-containing functional groups on the electrode material surface, achieving uniform dispersion and surface control of the electrode material. This significantly optimizes the SEI film formation process and improves the rate performance and cycle performance of hard carbon anodes. Currently, lithium / sodium-ion battery anode material systems commonly employ aqueous binders containing carboxyl or hydroxyl functional groups, such as sodium carboxymethyl cellulose and polyacrylic acid. These polymers can simultaneously achieve key functions such as rheological property regulation, particle dispersion, and interfacial adhesion in negative electrode slurry systems. However, their inherent characteristics still present technical bottlenecks that urgently need to be overcome: First, the hydroxyl and carboxyl functional groups enriched on their surface have poor compatibility with ester electrolytes, thus affecting the structural stability of the SEI film; second, the one-dimensional linear molecular structure is difficult to adapt to the significant volume changes caused by the long-term insertion and extraction of lithium / sodium ions in the negative electrode material, leading to a decrease in its cycle stability; third, its intrinsic ionic conductivity is low, hindering the rapid transport of ions in the electrode system, resulting in a sharp decrease in the battery capacity retention rate at high rates. Therefore, it is urgent to construct a multi-component synergistic composite bonding system through the optimized design of functional additive systems to comprehensively improve the overall performance of the electrode.

[0004] To address the aforementioned issues, inorganic nano-oxides (such as silicon dioxide and zinc oxide) are often used as functional reinforcing fillers in polymer-based composite materials due to their intrinsic properties, such as high reactivity and excellent thermal stability. These fillers can significantly improve the mechanical strength, thermal stability, and ionic conductivity of the composite materials. For example, Tian Zhenhua et al. (Journal of Shaanxi University of Science and Technology, 2022, 40(3):1-6,51) added zinc oxide as a crosslinking agent and sodium carboxymethyl cellulose as a dispersant to collagen hydrogel to prepare a collagen / sodium carboxymethyl cellulose / zinc oxide ternary composite hydrogel membrane with excellent thermal stability and mechanical properties. Zhang Li et al. (ACS Appl. Mater. Interfaces 2018, 10, 44463-44471) prepared a silicon-carbon anode material (SiO2 / TiO2@C) for lithium-ion batteries by using nano-SiO2 and TiO2 as active materials and combining them with sodium carboxymethyl cellulose and conductive carbon materials. The three-dimensional continuous conductive network constructed by the oxygen-containing groups on the surface of SiO2 and TiO2 interacting with sodium carboxymethyl cellulose and carbon materials through dynamic hydrogen bonding effectively suppressed the volume expansion of the nano-oxides. The resulting silicon-carbon anode exhibited excellent cycling performance (maintaining 590 mAh / g after 400 cycles at 1 A / g) and high rate performance (maintaining 410 mAh / g at 2 A / g). In addition, inorganic silicon oxide has also been used alone to modify the defects on the surface of hard carbon anodes, improving the compatibility of hard carbon anodes with ester electrolytes. For example, Zhang Guangxiang et al. (Angew. Chem. Int. Ed. 2025, 64, e202424028) used trimethylsilane solution to treat the surface of hard carbon anode, cleverly transforming the highly reactive oxygen-containing functional groups such as hydroxyl and carboxyl groups on the surface of hard carbon into an anion-anchored Si-O-Si layer, successfully inducing the formation of a uniform, dense and stable inorganic / organic hybrid SEI film on the surface of hard carbon. The resulting hard carbon anode exhibited excellent high-rate performance (maintaining 206.2 mAh / g at 500 mA / g) and cycling performance (maintaining 95.3 mAh / g after 1000 cycles) in ester electrolytes.

[0005] Lignosulfonate, as a bio-based environmentally friendly material, offers excellent thermal stability and mechanical flexibility through its three-dimensional network structure. Its abundant polar functional groups (such as sulfonic acid groups, carboxyl groups, and hydroxyl groups) can form multiple chemical bonds with conductive components, constructing a highly efficient ion-electron dual-conductivity network. This demonstrates broad application prospects in the field of aqueous binders for hard carbon anodes in sodium-ion batteries. Gond et al. (ACS Sustain. Chem. Eng., 2021, 12708-12717) first used sodium lignosulfonate as an aqueous binder for hard carbon anodes in sodium-ion batteries, finding a first-time coulombic efficiency of 91.13% and a reversible charge specific capacity of 257 mAh / g in ester electrolytes. However, sodium lignosulfonate exhibits low binding performance, and the prepared electrode cannot effectively buffer the volume deformation of the active material during long-term charge-discharge processes, resulting in poor cycle performance (only lasting a few dozen cycles). To compensate for the weak adhesion of sodium lignosulfonate when used alone, Jiao et al. (GreenChem., 2024, 26(11): 6643-6655) utilized the synergistic effect of multiple hydrogen bonds formed between the sulfonic acid groups, phenolic hydroxyl groups, and carboxyl groups in sodium lignosulfonate and the carboxyl and alcoholic hydroxyl groups in sodium carboxymethyl cellulose to construct a sodium lignosulfonate / sodium carboxymethyl cellulose composite binder system. The peel strength of the negative electrode was 5.88 N / cm, significantly higher than that of pure sodium lignosulfonate (2.18 N). The hard carbon negative electrode prepared by them exhibited a high reversible charging specific capacity of 348 mAh / g in ether-based electrolyte, significantly higher than that of pure sodium carboxymethyl cellulose (286 mAh / g). However, the composite of sodium lignosulfonate and sodium carboxymethyl cellulose was difficult to form a high-strength cross-linked structure, resulting in a decrease in the mechanical properties of the composite system. The mechanical peel strength of the electrode decreased by about 6.4% compared to pure sodium carboxymethyl cellulose (from 6.28 N / cm to 5.88 N / cm). In addition, its system still contains a large number of carboxyl groups, making it unsuitable for use in ester electrolyte systems.

[0006] In summary, existing lignin-based aqueous binders suffer from insufficient mechanical properties and poor compatibility with ester-based electrolytes, leading to decreased interfacial stability between the hard carbon anode and the ester-based electrolyte. This results in a reduction in reversible specific capacity (generally below 300 mAh / g) and accelerated degradation of cycle and rate performance, severely restricting the large-scale application of hard carbon anode materials. Summary of the Invention

[0007] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing a lignin-inorganic oxide composite binder.

[0008] This invention develops a lignin-inorganic oxide composite binder with excellent mechanical properties, good ionic conductivity, and affinity for ester electrolytes, based on the principle of synergistic crosslinking and electrostatic association between quaternized modified sodium lignin sulfonate, nano-oxides, and sodium carboxymethyl cellulose. First, lignin sulfonate is quaternized to obtain quaternized lignin sulfonate. Then, utilizing the synergistic effects (including electrostatic attraction and multiple hydrogen bonds) between the quaternary ammonium and sulfonate groups of the quaternized lignin sulfonate, the hydroxyl and inorganic oxyacid groups of the inorganic nano-oxides, and the carboxyl and hydroxyl groups of sodium carboxymethyl cellulose, a lignin-inorganic oxide composite binder with an interpenetrating network structure is formed. In this composite binder, sodium carboxymethyl cellulose acts as a hard phase to enhance mechanical rigidity, the flexible long-chain quaternized lignin sulfonate acts as a soft phase to bear part of the load, and the hydroxyl-rich inorganic nano-oxides act as crosslinking points or physical fillers to enhance the structural stability of the composite binder. Furthermore, the multi-network structure formed by hydrogen bonding not only endows the composite binder with excellent ion transport rate, but also helps to suppress the excessive exposure of polar groups such as hydroxyl and carboxyl groups, significantly enhancing its interfacial compatibility with ester electrolytes.

[0009] Another objective of this invention is to provide a lignin-inorganic oxide composite binder prepared by the above method. The multidimensional interpenetrating network structure of this binder promotes sodium ion transport in the hard carbon anode and forms a strong mechanical interlock at the interface between the hard carbon particles and the current collector, thereby significantly improving the rate performance and mechanical stability of the anode. Secondly, the positively charged quaternary ammonium cations in the binder attract fluoride ions from the electrolyte to accumulate on the surface of the hard carbon anode, promoting the formation of an SEI film rich in inorganic sodium fluoride, enhancing the interfacial compatibility between the hard carbon anode and the ester electrolyte, thus significantly improving the cycle performance of the hard carbon anode. Simultaneously, the negatively charged sulfonate, inorganic oxyacid, and carboxyl functional groups attract sodium ions from the electrolyte to accumulate on the electrode surface, promptly compensating for irreversible sodium loss during the initial charge-discharge process, which is beneficial for improving the reversible sodium storage capacity of the hard carbon anode.

[0010] The lignin inorganic oxide composite binder provided by this invention has a low content of polar functional groups such as hydroxyl, carboxyl and sulfonic acid groups, and its surface potential does not exceed -6.0mV.

[0011] Another object of the present invention is to provide the application of the above-mentioned lignin inorganic oxide composite binder in the hard carbon anode of sodium-ion batteries.

[0012] The lignin-inorganic oxide composite binder prepared using this invention, when used in hard carbon anodes, exhibits a mechanical peel strength of not less than 7.0 N / cm; in ester electrolytes, the first-cycle reversible sodium storage capacity at 20 mA / g is not less than 380 mAh / g. Particularly noteworthy is its reversible sodium storage capacity of not less than 140 mAh / g at 1000 mA / g, and its reversible sodium storage capacity after 1000 cycles is not less than 100 mAh / g.

[0013] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0014] In a first aspect, the present invention provides a method for preparing a lignin-inorganic oxide composite binder, comprising the following steps:

[0015] (1) Dissolve lignin sulfonate in water to prepare a solution, add an alkaline regulator to adjust the solution to alkalinity, heat and add a quaternizing reagent to react, and obtain a quaternized lignin sulfonate solution;

[0016] (2) Add inorganic nano-oxide to the quaternized lignin sulfonate solution obtained in step (1), disperse it evenly, heat it and add sodium carboxymethyl cellulose to carry out condensation crosslinking reaction. After the reaction is completed, the product is subjected to ultrasonic degassing treatment and lignin inorganic oxide composite binder is obtained by drying process.

[0017] The amounts of each reactant, by weight, are as follows:

[0018] 100 parts of lignin sulfonate;

[0019] 50-100 parts of quaternizing reagent;

[0020] 40-80 parts of inorganic nano-oxides;

[0021] Sodium carboxymethyl cellulose, 40-80 parts.

[0022] Preferably, the amounts of each reactant, by weight, are as follows:

[0023] 100 parts of lignin sulfonate;

[0024] 80-100 parts of quaternizing reagent;

[0025] 50-60 parts of inorganic nano-oxides;

[0026] Sodium carboxymethyl cellulose, 50-60 parts.

[0027] The weight parts of the quaternizing reagent can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, etc.

[0028] The inorganic nano-oxides can be present in weight parts of 40, 45, 55, 60, 65, 70, 75, 80, etc.

[0029] The sodium carboxymethyl cellulose can be in the following weight proportions: 40 parts, 45 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, 80 parts, etc.

[0030] Any other specific point value within the above numerical range can be selected, and will not be elaborated on here.

[0031] Preferably, the lignin sulfonate in step (1) includes at least one of sodium lignin sulfonate extracted by acid pulping or ammonium lignin sulfonate, sodium lignin sulfonate, calcium lignin sulfonate and magnesium lignin sulfonate obtained by sulfonation reaction using alkali lignin, enzymatically hydrolyzed lignin and organic solvent lignin as raw materials; more preferably, at least one of calcium lignin sulfonate and magnesium lignin sulfonate.

[0032] Preferably, the lignin sulfonate in step (1) is obtained by separation and purification using an ultrafiltration membrane with a molecular weight cutoff of 2000.

[0033] Preferably, the sulfonate content of the lignin sulfonate in step (1) is 1.0 to 2.0 mmol / g (e.g., 1.0 mmol / g, 1.2 mmol / g, 1.5 mmol / g, 1.8 mmol / g, 2.0 mmol / g, etc.). Any other specific point value within this range can be selected, and will not be elaborated here.

[0034] Preferably, the alkalinity regulator in step (1) is at least one of sodium hydroxide solution and potassium hydroxide solution.

[0035] Preferably, the solid mass concentration of the alkaline regulator in step (1) is 10-30% (e.g., 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, etc.). Any other specific value within this range can be selected, and will not be elaborated here.

[0036] Preferably, the alkalinity mentioned in step (1) refers to the pH of the solution being 9 to 12 (e.g., 9, 9.5, 10, 10.5, 11, 11.5, 12, etc.). Any other specific value within this range can be selected, and will not be elaborated here.

[0037] Preferably, the mass concentration of the lignin sulfonate solution prepared by dissolving it in water in step (1) is 20-30% (e.g., 20%, 22%, 25%, 28%, 30%, etc.). Any other specific value within this range can be selected, and will not be elaborated here.

[0038] Preferably, the heating temperature in step (1) is 70 to 90°C. The heating temperature can be 70°C, 75°C, 80°C, 85°C, 90°C, etc. Any other specific point value within this range can be selected, which will not be elaborated here.

[0039] Preferably, the quaternizing agent in step (1) includes at least one of hexadecyltrimethylammonium bromide, 2,3-epoxypropyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, and benzyltrimethylammonium chloride.

[0040] Preferably, the reaction time in step (1) is 2 to 8 hours (e.g., 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc.); more preferably, it is 4 to 6 hours; any other specific point value within the above range can be selected, and will not be described in detail here.

[0041] Preferably, the inorganic nano-oxide in step (2) includes at least one of nano-silica, nano-titanium dioxide, nano-zinc oxide and nano-alumina; more preferably, it includes at least one of nano-silica and nano-titanium dioxide.

[0042] Preferably, the degree of hydroxyl substitution of the inorganic nano-oxide in step (2) is 0.2 to 0.8 (e.g., 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, etc.). Any other specific point value within this range can be selected, and will not be described in detail here.

[0043] Preferably, the average molecular weight of sodium carboxymethyl cellulose in step (2) is 2000 to 10000 (e.g., 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, etc.); any other specific value within this range can be selected, and will not be described in detail here.

[0044] Preferably, the degree of carboxyl substitution of sodium carboxymethyl cellulose in step (2) is 0.4 to 0.8 (e.g., 0.4, 0.5, 0.6, 0.7, 0.8, etc.). Any other specific value within this range can be selected, and will not be described in detail here.

[0045] Preferably, after the inorganic nano-oxide in step (2) is added to the quaternized lignin sulfonate solution, it is dispersed evenly by ultrasonic treatment. The ultrasonic treatment time is 1 to 3 hours (e.g., 1.0 hours, 1.2 hours, 1.5 hours, 2.0 hours, 2.5 hours, 3.0 hours, etc.). Any other specific point value within this range can be selected, and will not be described in detail here.

[0046] Preferably, the ultrasonic degassing treatment time in step (2) is 0.2 to 1.0 h (e.g., 0.2 h, 0.4 h, 0.5 h, 0.6 h, 0.8 h, 1.0 h, etc.). Any other specific point value within this range can be selected, and will not be described in detail here.

[0047] Preferably, the temperature for heating in step (2) is 40 to 60°C (e.g., 40°C, 45°C, 50°C, 55°C, 60°C, etc.). Any other specific point value within this range can be selected, and will not be described in detail here.

[0048] Preferably, the condensation crosslinking reaction time in step (2) is 2 to 4 hours (e.g., 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, etc.). Any other specific point value within this range can be selected, and will not be described in detail here.

[0049] Preferably, the temperature of the ultrasonic degassing treatment in step (2) is 40 to 60°C (e.g., 40°C, 45°C, 50°C, 55°C, 60°C, etc.). Any other specific point value within this range can be selected, and will not be described in detail here.

[0050] Preferably, the drying process in step (2) includes at least one of spray drying and infrared drying.

[0051] Preferably, the drying temperature in step (2) is 100-120℃ (e.g., 100℃, 105℃, 110℃, 115℃, 120℃, etc.). Any other specific point value within this range can be selected, and will not be described in detail here.

[0052] Preferably, the preparation method of the lignin inorganic oxide composite binder includes the following steps:

[0053] (1) Dissolve lignin sulfonate in water to prepare a solution, add an alkaline regulator to adjust the pH of the solution to 9-12, heat to 70-90℃, add a quaternizing reagent to react, and obtain a quaternized lignin sulfonate solution.

[0054] (2) Add inorganic nano-oxide to the quaternized lignin sulfonate solution obtained in step (1), and sonicate it for 1 to 3 hours to make it uniformly dispersed. Heat it to 40 to 60°C and add sodium carboxymethyl cellulose to carry out condensation crosslinking reaction for 2 to 4 hours. After the reaction is completed, sonicate the product at 40 to 60°C for 0.2 to 1.0 hours to obtain lignin inorganic oxide composite gel emulsion. Finally, obtain lignin inorganic oxide composite binder by drying process.

[0055] Secondly, the present invention provides a lignin inorganic oxide composite binder prepared by the above preparation method.

[0056] Thirdly, the present invention provides the application of the above-mentioned lignin inorganic oxide composite binder in the hard carbon anode of sodium-ion batteries.

[0057] Sodium-ion battery electrolytes are mainly divided into two types: ester-based and ether-based. Compared to ester-based electrolytes, ether-based electrolytes have poor high-voltage stability and are expensive, making it difficult to meet the development requirements of low-cost, high-energy-density sodium-ion batteries. However, the electrochemical performance of hard carbon anodes in ester-based electrolytes, such as cycle stability, specific capacity, and coulombic efficiency, is significantly lower than that in ether-based electrolytes. This is mainly due to the poor compatibility between traditional binders and ester-based electrolytes. The lignin-inorganic oxide composite binder described in this invention has good compatibility with ester-based electrolytes, thereby significantly improving the electrochemical performance of hard carbon anodes in ester-based electrolytes.

[0058] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0059] (1) Mechanical properties: Through the synergistic effect of multiple hydrogen bonds and electrostatic attraction, the binder can achieve a synergistic improvement in bonding strength and mechanical properties, ensuring that the hard carbon anode can maintain excellent structural integrity during molding, long-term storage and cycling.

[0060] (2) Electrochemical performance: The low hydroxyl / carboxyl group characteristics of this binder effectively improve its interfacial compatibility with ester electrolytes, promoting the formation of a uniform and dense thin SEI film on the surface of the hard carbon anode, thereby significantly improving the long-term cycling stability of the hard carbon anode in ester electrolyte systems. Simultaneously, the unique interpenetrating network structure of this binder can significantly improve the rate performance of the hard carbon anode by reducing interfacial impedance, providing key support for the development of fast-charging hard carbon anodes. Furthermore, the strong adsorption properties of this binder for sodium ions can significantly improve the sodium storage capacity of the hard carbon anode, which has important application value for constructing high-capacity hard carbon anodes.

[0061] (3) Preparation process and cost: The lignin inorganic oxide composite binder developed in this invention has the advantages of simple preparation process, wide availability of raw materials and low cost, and has the potential for large-scale industrial application, thus providing an innovative solution for the development of low-cost, high-energy-density and long-cycle-life sodium-ion batteries. Attached Figure Description

[0062] Figure 1 The Fourier transform infrared spectrum of quaternized calcium lignin sulfonate, inorganic nano-silica, sodium carboxymethyl cellulose and their composite aqueous binder in Example 3 of the present invention.

[0063] Figure 2 The impedance AC curves of the hard carbon negative electrode in Example 3 and Comparative Example 1 of the present invention are shown.

[0064] Figure 3 The graphs show the rate performance test results of the hard carbon anodes in Example 3 and Comparative Example 1 of this invention.

[0065] Figure 4 The graphs show the cycle performance test results of the hard carbon negative electrode in Example 3 and Comparative Example 1 of this invention. Detailed Implementation

[0066] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0067] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0068] The lignin sulfonates described in the examples and comparative examples were obtained by separation and purification using an ultrafiltration membrane with a molecular weight cutoff of 2000.

[0069] Example 1

[0070] Weigh 100g of sodium lignosulfonate (sulfonate content 1.0mmol / g) and dissolve it in 400g of water. Adjust the pH of the solution to 9 with 20wt% sodium hydroxide reagent, heat to 70℃, add 50g of cetyltrimethylammonium bromide, react at a constant temperature for 2h, and then cool to room temperature to obtain a quaternized sodium lignosulfonate solution.

[0071] 40g of nano-zinc oxide (hydroxyl substitution degree 0.2) was weighed and added to the above-mentioned quaternized lignin sulfonate sodium solution. The solution was ultrasonically treated for 1 hour to ensure uniform dispersion. The temperature was then raised to 40℃, and 40g of sodium carboxymethyl cellulose (average molecular weight 5000, carboxyl substitution degree 0.4) was added to initiate a condensation crosslinking reaction for 2 hours. After the reaction was completed, the product was first subjected to ultrasonic degassing treatment at 40℃ for 0.2 hours, followed by spray drying at 110℃ to finally obtain a lignin inorganic oxide composite binder.

[0072] Example 2

[0073] Weigh 100g of ammonium lignosulfonate (sulfonate content 2.0mmol / g) and dissolve it in 233g of water. Adjust the pH of the solution to 12 with 20wt% sodium hydroxide reagent. Heat the reaction system to 90℃, add 100g of 2,3-epoxypropyltrimethylammonium chloride, and react at a constant temperature for 8h. Then cool to room temperature to obtain a quaternized ammonium lignosulfonate solution.

[0074] 80g of nano-alumina (hydroxyl substitution degree 0.8) was weighed and added to the above-mentioned quaternized lignin sulfonate ammonium solution. The mixture was ultrasonically treated for 2 hours to ensure uniform dispersion. The temperature was then raised to 60℃, and 80g of sodium carboxymethyl cellulose (average molecular weight 8000, carboxyl substitution degree 0.8) was added to initiate a condensation crosslinking reaction for 4 hours. After the reaction was completed, the product was first subjected to ultrasonic degassing treatment at 50℃ for 1.0 hour, followed by infrared drying at 120℃, ultimately yielding a lignin inorganic oxide composite binder.

[0075] Example 3

[0076] Weigh 100g of calcium lignosulfonate (sulfonate content 2.0mmol / g) and dissolve it in 400g of water. Adjust the pH of the solution to 9 with 20wt% sodium hydroxide reagent. Heat the reaction system to 70℃, add 80g of 3-chloro-2-hydroxypropyltrimethylammonium chloride, and react at a constant temperature for 4h. Then cool to room temperature to obtain a quaternized calcium lignosulfonate solution.

[0077] 80g of nano-silica (hydroxyl substitution degree 0.2) was weighed and added to the above-mentioned quaternized calcium lignin sulfonate solution. The mixture was ultrasonically treated for 1 hour to ensure uniform dispersion. The temperature was then raised to 40℃, and 50g of sodium carboxymethyl cellulose (average molecular weight 5000, carboxyl substitution degree 0.4) was added to initiate a condensation crosslinking reaction for 2 hours. After the reaction was completed, the product was first subjected to ultrasonic degassing treatment at 40℃ for 0.2 hours, followed by spray drying at 110℃ to finally obtain a lignin inorganic oxide composite binder.

[0078] Example 4

[0079] Weigh 100g of magnesium lignosulfonate (sulfonate content 2.0mmol / g) and dissolve it in 233g of water. Adjust the pH of the solution to 12 with 20wt% sodium hydroxide reagent. Heat the reaction system to 90℃, add 100g of benzyltrimethylammonium chloride, and react at a constant temperature for 8h. Then cool to room temperature to obtain a quaternized magnesium lignosulfonate solution.

[0080] 60g of nano-titanium dioxide (hydroxyl substitution degree 0.8) was weighed and added to the above-mentioned quaternized magnesium lignin sulfonate solution. The mixture was ultrasonically treated for 2 hours to ensure uniform dispersion. The temperature was then raised to 60℃, and 60g of sodium carboxymethyl cellulose (average molecular weight 8000, carboxyl substitution degree 0.8) was added to initiate a condensation crosslinking reaction for 4 hours. After the reaction was completed, the product was first subjected to ultrasonic degassing treatment at 50℃ for 1.0 hour, followed by infrared drying at 120℃, ultimately yielding a lignin inorganic oxide composite binder.

[0081] Example 5

[0082] Weigh 50g of calcium lignosulfonate and 50g of magnesium lignosulfonate (both with a sulfonate content of 1.5mmol / g) and dissolve them in 300g of water. Adjust the pH of the solution to 11 using 20wt% sodium hydroxide reagent. Heat the reaction system to 80℃, add 90g of 2,3-epoxypropyltrimethylammonium chloride, and react at a constant temperature for 5 hours. Then cool to room temperature to obtain a mixed solution of quaternized calcium lignosulfonate and quaternized magnesium lignosulfonate.

[0083] 50g of nano-silica (hydroxyl substitution degree 0.5) and 5g of nano-titanium dioxide (hydroxyl substitution degree 0.5) were weighed and added to the above-mentioned quaternized calcium lignosulfonate / quaternized magnesium lignosulfonate mixed solution. The mixture was ultrasonically treated for 1.5h to ensure uniform dispersion. The temperature was then raised to 50℃, and 55g of sodium carboxymethyl cellulose (average molecular weight 6500, carboxyl substitution degree 0.5) was added to initiate a condensation crosslinking reaction for 3h. After the reaction was completed, the product was first subjected to ultrasonic degassing treatment at 45℃ for 0.6h, followed by spray drying at 115℃ to finally obtain a lignin inorganic oxide composite binder.

[0084] Comparative Example 1 (compared to Example 3, sodium carboxymethyl cellulose was used directly as an aqueous binder)

[0085] Sodium carboxymethyl cellulose (average molecular weight 5000, degree of carboxyl substitution 0.4) was directly used as an aqueous binder for sodium-ion hard carbon anodes.

[0086] Comparative Example 2 (compared to Example 3, directly using unmodified calcium lignosulfonate, nano-silica, and sodium carboxymethyl cellulose for cross-linking composite)

[0087] Weigh 100g of calcium lignosulfonate (sulfonate content 2.0mmol / g) and dissolve it in 400g of water. Stir thoroughly until the calcium lignosulfonate is completely dissolved to obtain a calcium lignosulfonate solution.

[0088] 80g of nano-silica (hydroxyl substitution degree 0.2) was weighed and added to the above-mentioned calcium lignosulfonate solution. The solution was ultrasonically treated for 1 hour to ensure uniform dispersion. The temperature was then raised to 40℃, and 50g of sodium carboxymethyl cellulose (average molecular weight 5000, carboxyl substitution degree 0.4) was added to initiate a condensation crosslinking reaction for 2 hours. After the reaction was completed, the product was first subjected to ultrasonic degassing treatment at 40℃ for 0.2 hours, followed by spray drying at 110℃, ultimately yielding a lignin inorganic oxide composite binder based on calcium lignosulfonate.

[0089] Comparative Example 3 (compared to Example 3, sodium carboxymethyl cellulose and silica were directly crosslinked and composited).

[0090] 80g of nano-silica (hydroxyl substitution degree 0.2) was weighed and added to 400g of water. The mixture was ultrasonically treated for 1 hour to ensure uniform dispersion. The temperature was then raised to 40℃, and 50g of sodium carboxymethyl cellulose (average molecular weight 5000, carboxyl substitution degree 0.4) was added to initiate a condensation crosslinking reaction for 2 hours. After the reaction was complete, the product was first ultrasonically degassed at 40℃ for 0.2 hours, followed by spray drying at 110℃ to finally obtain the sodium carboxymethyl cellulose / nano-silica composite binder.

[0091] Comparative Example 4 (compared to Example 3, quaternized calcium lignosulfonate was used directly as an aqueous binder)

[0092] 100g of calcium lignosulfonate (sulfonate content 2.0mmol / g) was dissolved in 400g of water, and the pH of the solution was adjusted to 9 using 20wt% sodium hydroxide reagent. The reaction system was heated to 70℃, and 80g of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added. After reacting at a constant temperature for 4 hours, the mixture was cooled to room temperature to obtain a quaternized calcium lignosulfonate solution. Subsequently, the quaternized calcium lignosulfonate solution was spray-dried at 110℃ to finally obtain the quaternized calcium lignosulfonate binder.

[0093] Comparative Example 5 (compared to Example 3, quaternized calcium lignosulfonate and nano-silica were directly cross-linked and composited)

[0094] Weigh 100g of calcium lignosulfonate (sulfonate content 2.0mmol / g) and dissolve it in 400g of water. Adjust the pH of the solution to 9 with 20wt% sodium hydroxide reagent. Heat the reaction system to 70℃, add 80g of 3-chloro-2-hydroxypropyltrimethylammonium chloride, and react at a constant temperature for 4h. Then cool to room temperature to obtain a quaternized calcium lignosulfonate solution.

[0095] 80g of nano-silica (hydroxyl substitution degree 0.2) was weighed and added to the above-mentioned quaternized calcium lignosulfonate solution, and ultrasonically treated for 1h to ensure uniform dispersion. The temperature was raised to 40℃ and reacted for 2h. After the reaction was completed, the product was first ultrasonically degassed at 40℃ for 0.2h, and then spray-dried at 110℃ to finally obtain the quaternized calcium lignosulfonate / nano-silica composite binder.

[0096] Comparative Example 6 (compared to Example 3, quaternized calcium lignosulfonate and sodium carboxymethyl cellulose were directly cross-linked)

[0097] Weigh 100g of calcium lignosulfonate (sulfonate content 2.0mmol / g) and dissolve it in 400g of water. Adjust the pH of the solution to 9 with 20wt% sodium hydroxide reagent. Heat the reaction system to 70℃, add 80g of 3-chloro-2-hydroxypropyltrimethylammonium chloride, and react at a constant temperature for 4h. Then cool to room temperature to obtain a quaternized calcium lignosulfonate solution.

[0098] 50g of sodium carboxymethyl cellulose (average molecular weight 5000, degree of carboxyl substitution 0.4) was weighed and added to the above-mentioned quaternized calcium lignin sulfonate solution and mixed evenly. A condensation crosslinking reaction was carried out at 40℃ for 2 hours. After the reaction was completed, the product was first subjected to ultrasonic degassing treatment at 40℃ for 0.2 hours, followed by spray drying at 110℃, finally yielding a quaternized calcium lignin sulfonate / sodium carboxymethyl cellulose composite binder.

[0099] Results and Analysis:

[0100] The lignin oxide composite binder obtained in the examples was structurally characterized, and the surface charge characteristics of the aqueous binders obtained in the examples and comparative examples were tested. The electrochemical behavior of the hard carbon anode of a sodium-ion battery assembled with this binder was also studied. The results are shown in Table 1 and... Figures 1-4 .

[0101] Preparation of hard carbon anode for sodium-ion batteries: The binder, conductive carbon black, and hard carbon active particles from the examples and comparative examples were mixed in a mass ratio of 10:10:80 and uniformly coated onto a copper current collector to serve as the hard carbon anode for sodium-ion batteries. A 1 mol / L vinyl carbonate / diethyl carbonate (EC / DEC) electrolyte and Whatman glass fiber as the separator were assembled together into a CR2032 battery casing to obtain a sodium-ion symmetrical half-cell.

[0102] Structural characterization of the adhesive: The absorption positions of different chemical bonds or functional groups in the molecule were measured using Fourier transform infrared spectroscopy to determine the material structure. First, the sample was ground uniformly with an appropriate amount of spectroscopically pure potassium bromide powder. After drying in an infrared chamber, it was placed in a pressing mold and pressed into a thin sheet. The sheet was then fixed on a sample holder for measurement, with a scanning wavelength range of 4000–400 cm⁻¹. -1 .

[0103] The surface potential of the adhesive indirectly characterizes the number of negatively charged functional groups on the adhesive surface. The larger the negative value of the surface potential, the more negative charges (such as hydroxyl, carboxyl, and sulfonate groups) there are. The test is performed using a Zeta potential meter. A 0.1 g / L adhesive solution is prepared using deionized water. A small amount of the solution is then placed in the sample cell, and the Zeta potential value of the adhesive particle surface is automatically measured at 25°C. Data is collected five times for each test, and the average of the effective values ​​is taken.

[0104] The peel strength of the hard carbon anode was tested using a computer-controlled electronic universal testing machine (TSKL-10D). The test temperature was 25℃, the peel rate was set to 6 cm / min, and the average mechanical properties were taken as the final data.

[0105] Electrochemical performance testing of the hard carbon anode in sodium-ion batteries: Impedance performance testing was conducted using an electrochemical workstation (Bio-Logic VMP-3e), with a frequency range set from 0.01Hz to 100kHz and a voltage amplitude set to 5mV. Low-rate and high-rate first-cycle charge-discharge tests (low rate more clearly reflects the true sodium storage performance of the electrode material, while high rate more accurately reflects the structural stability of the electrode material), cycle performance tests, and rate performance tests were conducted using a Xinwei battery testing system (CT-4008-5V50mA-164). The constant current charge-discharge current densities set for the low-rate and high-rate first-cycle charge-discharge tests were 20mA / g and 1000mA / g, respectively. Figure 3 The charge and discharge current densities for the rate performance test were set to 20mA / g, 50mA / g, 100mA / g, 200mA / g, 400mA / g, 600mA / g, 800mA / g, and 1000mA / g, respectively. Each current density was cycled 5 times, and the average value was taken as the test result. Figure 4 The constant current charge-discharge current density set for the cyclic performance test was 1000 mA / g.

[0106] Table 1. Surface potential of the binder and test results of peel strength and electrochemical performance of the prepared hard carbon anode.

[0107]

[0108]

[0109] Table 1 Explanation:

[0110] The zeta potentials of the binders prepared in Examples 1-5 were all higher than -6.0 mV, while those in Comparative Examples 1-5 were all lower than -9.0 mV. This indicates that the density of negatively charged groups (such as hydroxyl, carboxyl, and sulfonic acid groups) in the binders of Examples 1-5 was significantly lower than that in Comparative Examples 1-5. The peel strength of the hard carbon anodes corresponding to Examples 1-5 were all higher than 7.3 N / cm, while the highest value in Comparative Examples 1-6 was only 6.0 N / cm. This indicates that the binders used in Examples 1-5 have superior bonding performance. Among them, the zeta potential of Example 3 was as high as -5.4 mV, and the peel strength of the hard carbon anode was as high as 8.4 N. In conventional ester-based electrolytes, the hard carbon anode using this binder exhibits a reversible sodium storage capacity of up to 399 mAh / g in the first cycle at a current density of 20 mA / g, and still maintains a reversible sodium storage capacity of 150 mAh / g at a current density of 1000 mA / g. Furthermore, it retains a reversible sodium storage capacity of 110 mAh / g after 1000 cycles, demonstrating a significant advantage over the binders in Comparative Examples 1-6. However, it should be noted that the Zeta potentials in Examples 2-3 are slightly lower than the corresponding values ​​in Comparative Example 6. The reasons are analyzed as follows:

[0111] Compared to Example 3, Comparative Example 1 used only sodium carboxymethyl cellulose (CMC) as an aqueous binder, which could not effectively shield or reduce the negatively charged carboxyl and hydroxyl functional groups in CMC (Zeta potential as low as -17.1 mV). This would catalyze the decomposition of ester electrolytes and damage the stability of the SEI film. Simultaneously, relying solely on CMC made it difficult to effectively construct a stable three-dimensional cross-linked network structure, resulting in a significant decrease in its bonding performance (the mechanical peel strength of the hard carbon anode was only 4.5 N / cm), easily leading to structural instability of the electrode material during long-term charge-discharge cycles. These defects ultimately resulted in a decrease in the first-cycle reversible sodium storage capacity of the hard carbon anode (319 mAh / g), a deterioration in rate performance (at a current density of 1000 mA / g, the reversible sodium storage capacity dropped to 61 mAh / g), and a worsening of cycle performance (at a current density of 1000 mA / g, the reversible sodium storage capacity after 1000 cycles was only 40 mAh / g).

[0112] Compared to Example 3, Comparative Example 2, which only used unquaternized calcium lignosulfonate, nano-silica, and sodium carboxymethyl cellulose for crosslinking, still resulted in an excessive number of residual hydroxyl and carboxyl functional groups in the composite system (Zeta potential as low as -14.0 mV), thereby catalyzing the decomposition of ester electrolytes and damaging the stability of the SEI film. Furthermore, due to insufficient crosslinking strength, the bonding performance of the composite binder was significantly reduced (the mechanical peel strength of the hard carbon anode was only 6.0 N / cm), making the electrode material prone to structural instability during long-term charge-discharge cycles. These defects ultimately led to a decrease in the first-cycle reversible sodium storage capacity of the hard carbon anode (365 mAh / g), a deterioration in rate performance (at a current density of 1000 mA / g, the reversible sodium storage capacity dropped to 120 mAh / g), and a deterioration in cycle performance (at a current density of 1000 mA / g, the reversible sodium storage capacity after 1000 cycles was only 87 mAh / g).

[0113] Compared to Example 3, Comparative Example 3 used only nano-silica and sodium carboxymethyl cellulose to construct a cross-linked composite system. Although the silanol groups of nano-silica and the carboxyl groups of sodium carboxymethyl cellulose can partially shield the system through hydrogen bonding, there are still a large number of residual silica and hydroxyl functional groups in the system. This causes the zeta potential of the composite binder to drop to -11.2 mV, which still catalyzes the decomposition of ester electrolytes and damages the stability of the SEI film. In addition, the intrinsic electronic insulation properties of both significantly increase the internal resistance of the electrode, exacerbating the irreversible consumption of sodium ions, resulting in a decrease in the first-cycle reversible specific capacity of the hard carbon anode to 350 mAh / g. In terms of mechanical properties, since both sodium carboxymethyl cellulose and nano-silica exhibit strong rigidity and lack of flexibility, the mechanical peel strength of the hard carbon anode prepared by the resulting composite binder is only 5.5 N / cm, which makes it difficult to maintain the stability of the electrode structure during long cycles. This leads to a deterioration in the rate performance of the hard carbon anode (the reversible sodium storage specific capacity is only 109 mAh / g at a current density of 1000 mA / g) and a deterioration in cycle performance (the capacity drops to 64 mAh / g after 1000 cycles at a current density of 1000 mA / g).

[0114] Compared to Example 3, when Comparative Example 4 directly used quaternized calcium lignosulfonate as an aqueous binder, although the quaternization modification could shield some of the phenolic hydroxyl functional groups on the calcium lignosulfonate and neutralize the negatively charged sulfonate groups, it could not effectively shield or reduce carboxyl and alcohol hydroxyl groups. This resulted in the number of negatively charged groups remaining at a high level (Zeta potential as low as -13.5 mV), still catalyzing the decomposition of ester electrolytes and damaging the stability of the SEI film. Simultaneously, the bonding performance of single quaternized calcium lignosulfonate was insufficient (the hard carbon anode peel performance was only 1.8 N), making it difficult to maintain the structural stability of the electrode material during long-term charge-discharge cycles. These defects ultimately led to a decrease in the first-cycle reversible sodium storage capacity of the hard carbon anode (330 mAh / g), a deterioration in rate performance (at a current density of 1000 mA / g, the reversible sodium storage capacity dropped to 116 mAh / g), and a decrease in cycle stability (at a current density of 1000 mA / g, only 49 mAh / g remained after 1000 cycles).

[0115] Compared to Example 3, Comparative Example 5 used only a composite of quaternized calcium lignosulfonate and nano-silica as a binder. Although the quaternary ammonium and sulfonate groups in quaternized calcium lignosulfonate can effectively shield the silica and silanol groups on the surface of nano-silica through hydrogen bonding and electrostatic attraction, the large number of residual carboxyl and hydroxyl functional groups in its molecules still cause the Zeta potential of the composite system to remain at a low level of -9.7 mV. This will catalyze the decomposition of ester electrolytes and damage the stability of the SEI film. In addition, since the adhesion between nano-silica and quaternized calcium lignosulfonate is poor, the composite of the two failed to significantly improve the adhesion performance (the peel strength of the hard carbon anode is only 3.8 N), making it difficult to maintain the structural stability of the electrode during long-term cycling. These defects ultimately lead to a significant reduction in the reversible sodium storage capacity of the hard carbon anode (initially 342 mAh / g), a decrease in rate performance (at a current density of 1000 mA / g, the reversible sodium storage capacity is only 85 mAh / g), and a deterioration in cycle stability (at a current density of 1000 mA / g, it decays to 52 mAh / g after 1000 cycles).

[0116] Compared to Example 3, Comparative Example 6 directly prepared a binder by chemically crosslinking quaternized calcium lignin sulfonate with CMC. The performance of this binder was significantly different from that of Comparative Examples 1-5. Test results showed that its Zeta potential was -5.2 mV, higher than that of Examples 2-3, indicating that the number of negatively charged oxygen-containing functional groups (such as carboxyl, hydroxyl, and sulfonic acid groups) on the binder surface was relatively small. This characteristic helps reduce the risk of electrolyte decomposition and maintain SEI film stability. Therefore, the cycling stability of the hard carbon anode using this binder (capacity retention of 80.91% after 1000 cycles at a current density of 1000 mA / g) was better than that of Example 3 (capacity retention of 70.67% after 1000 cycles at a current density of 1000 mA / g). However, due to the lack of nano-silica participation, the reversible sodium storage specific capacity (375 mAh / g) of the hard carbon anode using this binder was slightly lower than that of Example 3. Meanwhile, the lack of silica in the binder system results in low cross-linking strength, significantly reducing the peel strength of the hard carbon anode (only 4.1 N) and weakening the interfacial bonding between the active material and the current collector. This leads to a reversible sodium storage capacity of only 110 mAh / g at a high rate of 1000 mA / g.

[0117] Figure 1 The Fourier transform infrared (FTIR) spectroscopy analysis results of quaternized calcium lignin sulfonate, sodium carboxymethyl cellulose, nano-silica, and their composite aqueous binder in Example 3 of this invention are presented. Quaternized calcium lignin sulfonate is prepared through the quaternization reaction of calcium lignin sulfonate. In the FTIR spectra of calcium lignin sulfonate and quaternized calcium lignin sulfonate, the 1043 cm⁻¹... -1The absorption peak at 2945 cm⁻¹ is attributed to the SO stretching vibration of the sulfonic acid group. -1 The absorption peak at 1645 cm⁻¹ corresponds to the CH stretching vibration on the aromatic ring of lignin; compared with sodium lignin sulfonate, quaternized sodium lignin sulfonate shows an absorption peak at 1645 cm⁻¹. -1 1464cm -1 and 960cm -1 New characteristic absorption peaks appeared at 1090 cm⁻¹, attributed to the C=O, CN, and NH stretching vibrations in the quaternary ammonium salt, confirming that the quaternary ammonium groups have been successfully grafted onto the molecular backbone of calcium lignosulfonate; the infrared spectrum of nano-silica showed that at 1090 cm⁻¹... -1 The strong absorption peak at 800 cm⁻¹ corresponds to the asymmetric stretching vibration of Si-O-Si. -1 and 3420cm -1 The absorption peaks at these locations are attributed to the stretching vibrations of Si-O and Si-OH, respectively; the characteristic absorption peak of CMC appears at 1637 cm⁻¹. -1 (C=O stretching vibration of carboxymethyl group) and 1018 cm -1 (CO stretching vibration of alcohol hydroxyl group); in the infrared spectrum of the composite binder, the lignin benzene ring CH (~2945cm) is located at this position. -1 ) and nano-silica Si-O-Si (~1090cm) -1 The characteristic peaks are still visible. However, compared to the single spectra of quaternized calcium lignin sulfonate and sodium carboxymethyl cellulose, the characteristic peaks of carboxyl, hydroxyl, and sulfonate groups are not only significantly weaker in intensity but also show a marked shift. Meanwhile, the characteristic peak of quaternary ammonium salts (1645 cm⁻¹) is also significantly shifted. -1 1464cm -1 960cm -1 ) and the Si-O peak of nano-silica (800 cm⁻¹) -1 The ) disappeared in the spectrum. The above results indicate that intermolecular crosslinking and hydrogen bonding interactions occurred between quaternized calcium lignin sulfonate, nano-silica, and sodium carboxymethyl cellulose, successfully preparing a lignin / inorganic nano-oxide composite binder.

[0118] Figure 2The figures show the AC impedance curves of the hard carbon anodes corresponding to Example 3 and Comparative Example 1 of this invention. As can be seen from the curves, the semi-circular radius of the hard carbon anode corresponding to Example 3 is significantly smaller than that of Comparative Example 1. The slope of the straight line of the hard carbon anode corresponding to Example 3 is significantly greater than that of Comparative Example 1. This indicates that the hard carbon anode corresponding to the lignin / inorganic nano-oxide composite binder prepared by this invention has lower charge transfer impedance and ion diffusion impedance compared to commercial sodium carboxymethyl cellulose. This is mainly attributed to the unique interpenetrating network structure of this composite aqueous binder, which provides an efficient channel for the transport and diffusion of sodium ions. Simultaneously, the benzene rings on the calcium lignin sulfonate and conductive carbon black molecules construct a complete three-dimensional conductive network through the π-interpenetrating stacking effect, promoting rapid electron migration and thus significantly reducing the interfacial impedance of the hard carbon anode in ester electrolytes.

[0119] Figure 3 The rate performance test results of the hard carbon anodes using Example 3 and Comparative Example 1 are presented. In the current density range of 20–1000 mA / g, the specific capacities of the hard carbon anode of Example 3 were 396, 384, 368, 324, 201, 120, 139, and 117 mAh / g, respectively, significantly higher than those of Comparative Example 1. This is mainly due to the fact that the hard carbon anode of Example 3 not only has lower charge transfer resistance and ion diffusion resistance (e.g., ... Figure 2 Furthermore, its excellent interfacial compatibility with ester electrolytes promotes the formation of a solid electrolyte membrane (SEI) that is more conducive to sodium ion transport and diffusion.

[0120] Figure 4 The figures show the cycle performance test results of the hard carbon anodes from Example 3 and Comparative Example 1 of this invention. At a current density of 1000 mA / g, the hard carbon anode from Example 3 maintained a reversible charge specific capacity of 110 mAh / g after 1000 cycles, significantly better than the 40 mAh / g of Comparative Example 1. This is mainly attributed to the composite binder effectively reducing the exposure of hydroxyl and carboxyl functional groups, enhancing the interfacial compatibility between the hard carbon anode and the ester electrolyte, and simultaneously ensuring the structural stability of the hard carbon anode during long-term cycling with its excellent bonding properties and mechanical stability, thus collectively contributing to the excellent cycle performance of the anode.

[0121] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a lignin-inorganic oxide composite binder, characterized in that, Includes the following steps: (1) Dissolve lignin sulfonate in water to prepare a solution, adjust the pH to alkaline, heat and add quaternizing reagent to react, and obtain quaternized lignin sulfonate solution; (2) Add inorganic nano-oxide to the quaternized lignin sulfonate solution, disperse it evenly, heat it and add sodium carboxymethyl cellulose to carry out condensation crosslinking reaction, ultrasonic degassing treatment, and dry it to obtain lignin inorganic oxide composite binder.

2. The preparation method of the lignin inorganic oxide composite binder according to claim 1, characterized in that, The amounts of each reactant, by weight, are as follows: 100 parts of lignin sulfonate; 50-100 parts of quaternizing reagent; 40-80 parts of inorganic nano-oxides; 40-80 parts of sodium carboxymethyl cellulose; More preferably, the amounts of each reactant are as follows, by weight: 100 parts of lignin sulfonate; 80-100 parts of quaternizing reagent; 50-60 parts of inorganic nano-oxides; Sodium carboxymethyl cellulose, 50-60 parts.

3. The method for preparing a lignin-inorganic oxide composite binder according to claim 1 or 2, characterized in that, The sulfonate content of the lignin sulfonate in step (1) is 1.0–2.0 mmol / g; And / or, the lignin sulfonate in step (1) includes at least one of sodium lignin sulfonate extracted by acid pulping or ammonium lignin sulfonate, sodium lignin sulfonate, calcium lignin sulfonate and magnesium lignin sulfonate obtained by sulfonation reaction using alkali lignin, enzymatic hydrolysis lignin and organic solvent lignin as raw materials; more preferably at least one of calcium lignin sulfonate and magnesium lignin sulfonate. And / or, the quaternizing agent in step (1) includes at least one of hexadecyltrimethylammonium bromide, 2,3-epoxypropyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride and benzyltrimethylammonium chloride; And / or, the heating temperature in step (1) is 70–90°C; And / or, the reaction time in step (1) is 2 to 8 hours.

4. The method for preparing a lignin-inorganic oxide composite binder according to claim 1 or 2, characterized in that, The inorganic nano-oxide in step (2) includes at least one of nano-silica, nano-titanium dioxide, nano-zinc oxide and nano-alumina; more preferably at least one of nano-silica and nano-titanium dioxide. And / or, the degree of hydroxyl substitution of the inorganic nano-oxide in step (2) is 0.2 to 0.8; And / or, after the inorganic nano-oxides in step (2) are added to the quaternized lignin sulfonate solution, they are dispersed evenly by ultrasonic treatment for a period of 1 to 3 hours.

5. A method for preparing a lignin-inorganic oxide composite binder according to claim 1 or 2, characterized in that, The average molecular weight of the sodium carboxymethyl cellulose in step (2) is 2000-10000; And / or, the degree of carboxyl substitution of the sodium carboxymethyl cellulose in step (2) is 0.4 to 0.8; And / or, the temperature for heating in step (2) is 40–60°C; And / or, the time for the condensation crosslinking reaction in step (2) is 2 to 4 hours.

6. The method for preparing a lignin-inorganic oxide composite binder according to claim 1 or 2, characterized in that, The alkaline adjuster used in step (1) to adjust the pH to alkalinity is at least one of sodium hydroxide solution and potassium hydroxide solution; And / or, the solid mass concentration of the alkaline adjuster used in step (1) to adjust the pH to alkalinity is 10-30%; And / or, the alkalinity in step (1) refers to the pH of the solution being 9 to 12; And / or, the lignin sulfonate of step (1) is dissolved in water to prepare a solution with a mass concentration of 20-30%.

7. A method for preparing a lignin-inorganic oxide composite binder according to claim 1 or 2, characterized in that, The lignin sulfonate described in step (1) is obtained by separation and purification using an ultrafiltration membrane with a molecular weight cutoff of 2000; And / or, the ultrasonic degassing treatment in step (2) takes 0.2 to 1.0 hours; And / or, the temperature of the ultrasonic degassing treatment in step (2) is 40–60°C; And / or, the drying process in step (2) includes at least one of spray drying and infrared drying; the drying temperature in step (2) is 100-120°C.

8. A method for preparing a lignin-inorganic oxide composite binder according to claim 1 or 2, characterized in that, Includes the following steps: (1) Dissolve lignin sulfonate in water to prepare a solution, add an alkaline regulator to adjust the pH of the solution to 9-12, heat to 70-90℃, add a quaternizing reagent to react, and obtain a quaternized lignin sulfonate solution. (2) Add inorganic nano-oxide to the quaternized lignin sulfonate solution obtained in step (1), and sonicate it for 1-3 hours to make it uniformly dispersed. Heat it to 40-60℃ and add sodium carboxymethyl cellulose to carry out condensation crosslinking reaction for 2-4 hours. After the reaction is completed, sonicate the product at 40-60℃ for 0.2-1.0 hours to obtain lignin inorganic oxide composite gel emulsion. Finally, dry it to obtain lignin inorganic oxide composite binder.

9. A lignin-inorganic oxide composite binder obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the lignin inorganic oxide composite binder of claim 9 in the hard carbon anode of sodium-ion batteries.

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