Lignin derivative composite binder as well as preparation method and application of silicon-based negative electrode plate of lignin derivative composite binder

Abstract

The invention discloses a lignin derivative composite binder and a preparation method and application of a silicon-based negative electrode plate thereof, and belongs to the technical field of battery materials. The lignin derivative composite binder is prepared by the following preparation method: polyacrylic acid and polyethylene glycol grafted modified lignin are subjected to heating reaction in a solvent to obtain the lignin derivative composite binder, wherein the weight of the polyethylene glycol grafted modified lignin is 5-55% of the total weight of the polyacrylic acid and the polyethylene glycol grafted modified lignin, and the reaction temperature of the heating reaction is 70-170 DEG C. The lignin derivative composite binder disclosed by the invention is prepared by carrying out heating reaction on polyacrylic acid and polyethylene glycol grafted modified lignin in a solvent. The lignin derivative composite binder disclosed by the invention can be used for improving the cycle performance and rate capability of an electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and more specifically, to a lignin derivative composite binder, a preparation method and application thereof for a silicon-based negative electrode sheet. Background Art

[0002] With the rapid development of the new energy vehicle industry, the demand for power batteries is also increasing continuously, and the demand for high-energy-density lithium-ion batteries is also growing. Although lithium-ion batteries have made remarkable progress in the field of energy storage, the energy density of their electrode materials is still limited to a certain extent. In order to further improve the energy storage capacity of lithium-ion batteries, scientific researchers are constantly exploring new electrode materials and innovative technical means in order to achieve high-energy-storage-density lithium-ion batteries in practical applications. They strive to find and optimize electrode materials with higher energy density. Silicon-based materials are highly expected by the majority of scientific researchers because of their excellent high theoretical specific capacity, and it is considered that they are expected to become the ideal negative electrode material for high-energy-density lithium-ion batteries.

[0003] However, during the charge and discharge process of the battery, problems such as large volume expansion, active material pulverization, and unstable solid electrolyte interface film will occur in silicon-based materials. In order to promote the wide application of silicon-based materials in the field of lithium-ion batteries, scientific researchers are actively researching and exploring effective ways to solve these problems.

[0004] The binder plays a significant role in maintaining the integrity of the electrode structure and the conductive network. Therefore, starting from the binder to solve problems such as the volume effect of silicon-based materials is the simplest and lowest-cost method. The adhesion and mechanical properties of traditional binders are not suitable for the volume effect of silicon-based materials, and it is difficult to maintain the long-cycle stability of the electrode. Therefore, it is necessary to develop new binders, such as three-dimensional cross-linked binders, self-healing binders, conductive binders, etc. Therefore, developing multifunctional three-dimensional binders is expected to comprehensively solve the cycle stability problem of silicon-based negative electrodes in lithium-ion batteries.

[0005] Developing new silicon-based negative electrode binders has become a current research hotspot, and a series of binders have been successfully designed. However, the process of constructing a three-dimensional cross-linked network structure for these binders is complex, and it is difficult to repair when reaching the strength limit, resulting in a sharp decline in electrochemical performance. At the same time, the low conductivity of silicon-based materials requires the addition of more conductive agents to ensure the coverage of the conductive network. Excessive addition of conductive agents will cause the cycle stability of high-active material loading electrodes, thus unable to achieve high-energy-density lithium-ion batteries.

[0006] The prior art discloses a preparation method and application of a lignin aqueous composite battery binder and its silicon-based negative electrode sheet. The preparation method of the silicon-based negative electrode sheet based on the lignin aqueous battery binder includes the following steps: dissolving polyacrylic acid, sulfonated lignin, sodium thiooctanoate, silicon-based active material and conductive material in water, mixing evenly to obtain a negative electrode slurry, then scraping the negative electrode slurry onto a substrate, and finally obtaining the negative electrode sheet by high-temperature drying and thermal esterification. The silicon-based negative electrode sheet based on the lignin aqueous binder has strong adhesion, effectively inhibits the volume effect of the silicon-based negative electrode sheet during charge and discharge, and improves the cycle performance of the silicon-based negative electrode sheet. At a current density of 0.2 A / g, after 100 cycles, the prepared silicon monoxide electrode still retains a discharge specific capacity of 1192 mAh / g. However, its cycle performance is still relatively low and needs to be further improved. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiency that the improvement of the cycle performance of the existing negative electrode binder for lithium-ion batteries is still relatively low, and to provide a lignin derivative composite binder, which can not only significantly improve the cycle performance of the battery, but also improve the rate performance of the battery.

[0008] Another object of the present invention is to provide a negative electrode slurry for a lithium-ion battery.

[0009] Another object of the present invention is to provide a negative electrode sheet for a lithium-ion battery.

[0010] Another object of the present invention is to provide a lithium-ion battery.

[0011] The above objects of the present invention are achieved by the following technical solutions:

[0012] A lignin derivative composite binder is prepared by the following preparation method: heating and reacting polyacrylic acid and polyethylene glycol graft-modified lignin in a solvent to obtain a lignin derivative composite binder; wherein, the weight of the polyethylene glycol graft-modified lignin is 5-55% of the total weight of polyacrylic acid and polyethylene glycol graft-modified lignin, and the reaction temperature of the heating reaction is 70-170 °C.

[0013] Lignin has multi-functional group characteristics and a natural three-dimensional skeleton structure. By grafting and modifying to introduce polyethylene glycol segments, the phenolic hydroxyl groups of lignin can be converted into alcoholic hydroxyl groups, improving the activity of lignin hydroxyl groups.

[0014] The flexible and controllable three-dimensional network lignin is constructed by using the elastic polymer polyethylene glycol (PEG) as the cross-linking chain, and the three-dimensional structure binder with high ionic conductivity is prepared by compounding with the rigid polymer polyacrylic acid. The problem of low reactivity of functional groups caused by the cohesion of lignin is solved by cross-linking network functionalized lignin. At the same time, the curling and straightening of the PEG covalent cross-linking chain can also assist in stress dissipation and the elastic expansion and contraction of the cross-linking network. The continuous ether bonds on PEG are also beneficial to the directional transport of lithium ions, which also has a positive effect on improving the rate performance of the SiO electrode and the lithium ion transport barrier caused by problems such as thickness at high load. Therefore, the lignin derivative composite binder of the present invention can improve the cycle performance and rate performance of lithium ion batteries.

[0015] Lignin belongs to renewable biological resources, which can save resources and energy to a certain extent and respond to the goal of green sustainable development.

[0016] Polyacrylic acid can be obtained commercially or prepared by self-making.

[0017] Polyacrylic acid can be synthesized by thermal-initiated free radical polymerization.

[0018] Preferably, the solvent can be 1,4-dioxane.

[0019] In the present invention, the weight of polyethylene glycol graft-modified lignin can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% of the total weight of polyacrylic acid and polyethylene glycol graft-modified lignin.

[0020] In the present invention, the reaction temperature of the heating reaction can be 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C.

[0021] Preferably, the weight of polyethylene glycol graft-modified lignin is 10-30% of the total weight of polyacrylic acid and polyethylene glycol graft-modified lignin.

[0022] A slightly smaller weight percentage of polyethylene glycol graft-modified lignin in the total weight of polyacrylic acid and polyethylene glycol graft-modified lignin is more beneficial to improving the cycle performance and rate performance of the silicon-based anode lithium ion battery.

[0023] Preferably, the reaction temperature of the heating reaction is 100-165°C. A higher reaction temperature of the heating reaction is beneficial to the thermal esterification reaction of polyacrylic acid and polyethylene glycol graft-modified lignin, and the obtained binder is beneficial to improving the cycle performance and rate performance of the silicon-based anode lithium ion battery.

[0024] Preferably, the reaction time of the heating reaction can be 6-10 h.

[0025] Preferably, the preparation method of the polyethylene glycol grafted modified lignin comprises the following steps: heating lignin and polyethylene glycol in concentrated sulfuric acid to obtain the polyethylene glycol grafted modified lignin.

[0026] Concentrated sulfuric acid plays a catalytic and dehydrating role in this process. Concentrated sulfuric acid is a strong acid that can significantly reduce the activation energy of the reaction and accelerate the cross-linking reaction between lignin and PEG. It can promote the formation of ether bonds (-C-O-C-) through protonation, making the active sites of the reactants more susceptible to nucleophilic attack. A large number of hydroxyl (-OH) groups are contained in the lignin molecule, and concentrated sulfuric acid can protonate these hydroxyl groups, making them more likely to react with other molecules. In addition, concentrated sulfuric acid has strong dehydrating properties and can remove the water in the reaction system, thus promoting the reaction to proceed in the direction of forming cross-linked products. The dehydration effect helps to form stable ether bonds and further promotes the formation of a cross-linked network.

[0027] Preferably, after the reaction is completed, the reactants can be dropped into water to form a flocculent precipitate. The precipitate is centrifuged and washed with water multiple times, and then dried in a vacuum oven to obtain the polyethylene glycol grafted modified lignin.

[0028] Preferably, the lignin is alkali lignin.

[0029] Preferably, the mass ratio of the lignin to the polyethylene glycol is 1:(4 - 6).

[0030] Preferably, in the preparation method of the polyethylene glycol grafted modified lignin, the heating reaction time is 4 - 5 h, and the heating reaction temperature is 150 - 160 °C.

[0031] The present invention also protects a negative electrode paste for a lithium-ion battery, which comprises a negative electrode active material, a conductive agent, and a negative electrode binder, and the negative electrode binder is the lignin derivative composite binder described in any one of the above.

[0032] The negative electrode active material can be silicon monoxide or silicon.

[0033] In the preparation of the negative electrode paste for a lithium-ion battery, the negative electrode active material SiO and the conductive agent conductive carbon black can be mixed in a certain mass ratio, and an appropriate mass is weighed into an agate ball milling jar. The volume of the material does not exceed 1 / 2 of the ball milling jar, and the SiO and conductive carbon black mixture is ball milled at a certain rotation speed. Then, the active material: conductive agent: binder is used to prepare the negative electrode paste for a lithium-ion battery according to a certain mass ratio.

[0034] Among them, the ball milling treatment can not only reduce the particle size of SiO to make it more delicate, but also help the conductive carbon black to be evenly distributed on the surface of SiO, thus constructing an efficient conductive network.

[0035] In the negative electrode paste, the mass fraction of the conductive agent in the negative electrode paste can be 10-20%.

[0036] The present invention also protects a silicon-based negative electrode sheet for a lithium-ion battery, which includes a negative electrode current collector and a negative electrode active material layer provided on the surface of the negative electrode current collector. The negative electrode active material layer is obtained by drying the above-mentioned negative electrode paste for a lithium-ion battery.

[0037] The present invention also protects a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator provided between the positive electrode sheet and the negative electrode sheet, and an electrolyte. The negative electrode sheet is the above-mentioned negative electrode sheet for a lithium-ion battery.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] The present invention discloses a lignin derivative composite binder, which is prepared by heating and reacting polyacrylic acid and polyethylene glycol graft-modified lignin in a solvent. The polyethylene glycol graft-modified lignin is a flexible and controllable three-dimensional network lignin constructed with an elastic polymer polyethylene glycol as a cross-linking chain. Further reacting with a rigid polymer polyacrylic acid to prepare a high-ion-conductive three-dimensional structure lignin derivative composite binder. The introduction of lignin can improve the rate performance, and the polyethylene glycol grafted on lignin helps to synergistically enable the rapid directional transmission of lithium ions by lignin, so that the rate performance and long cycle performance at a high current density of the silicon-based negative electrode lithium-ion battery are significantly improved. Brief Description of the Drawings

[0040] Figure 1 It is a 180° peeling performance diagram of negative electrode sheets prepared with different binders.

[0041] Figure 2 It is for 0.5Ag -1 Cycling diagram of batteries prepared with different binders at a current density.

[0042] Figure 3 It is a rate diagram of batteries prepared with different binders.

[0043] Figure 4 It is an impedance diagram of batteries prepared with different binders after cycling 5 times. Detailed Embodiments

[0044] The following further illustrates the present invention in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventional raw material reagents purchased.

[0045] Alkali lignin is provided by Zhejiang Jiefa Technology Co., Ltd.

[0046] Example 1

[0047] A lignin derivative composite binder is prepared by the following preparation method:

[0048] Preparation of polyethylene glycol grafted modified lignin (LPEG):

[0049] The acrylic acid monomer is passed through a chromatography column to remove the inhibitor. 50 g of purified acrylic acid and 100 g of deionized water are placed in a three-necked flask, and 0.25 g of ammonium persulfate (APS) is added as a thermal initiator. Under a nitrogen atmosphere and at a reaction temperature of 60 °C, high-speed stirring reaction is carried out for 3 h to obtain high-viscosity polyacrylic acid. The product is cut into pieces, then washed with water many times and freeze-dried to obtain polyacrylic acid.

[0050] 5 g of alkali lignin and 25 g of polyethylene glycol are placed in a flask. After the lignin is completely dispersed in the polyethylene glycol, 200 μL of concentrated sulfuric acid is added at 160 °C and reacted for 4 h. The reactant is dropped into 2 L of deionized water to form a flocculent precipitate. After centrifugation, the precipitate is washed with deionized water many times, and then dried in a vacuum oven at 60 °C to obtain polyethylene glycol grafted modified lignin (LPEG).

[0051] The polyacrylic acid and polyethylene glycol grafted modified lignin are compounded and dissolved in 1,4-dioxane according to a ratio of 9:1 to prepare a binder solution. After stirring evenly, heating and drying reaction is carried out at 150 °C for 8 hours to obtain a lignin derivative composite binder with high ionic conductivity. At this time, the weight of the polyethylene glycol grafted modified lignin is 10% of the total weight of the polyacrylic acid and the polyethylene glycol grafted modified lignin.

[0052] Preparation of the negative electrode paste: The negative electrode active material SiO and conductive carbon black are mixed at a mass ratio of 7:2, and the SiO and conductive carbon black mixture is ball-milled at a rotation speed of 400 r / min for 10 h. The negative electrode paste is prepared according to a mass ratio of negative electrode active material: conductive agent: binder of 7:2:1.

[0053] Preparation of the negative electrode sheet: After the negative electrode paste is stirred for 5 - 6 h to be fully mixed evenly, the negative electrode paste is blade-coated to obtain a wet electrode with an active material loading of 1.0 mg cm -2 The wet electrode is placed in a blast drying oven at 60 °C for 1 - 2 h to remove most of the solvent, and then dried in a vacuum drying oven at 80 °C for 10 h to completely remove the residual solvent. The dried electrode sheet is cut into electrode sheets with a diameter of 12 mm using a slicing machine.

[0054] Preparation of the lithium-ion battery: Using polypropylene as the battery separator, containing 1 mol of LiPF 6, A mixed electrolyte of ethylene carbonate:diethyl carbonate with 10 wt% fluoroethylene carbonate and 1 wt% vinylene carbonate is used as the battery electrolyte, where the volume ratio of ethylene carbonate to diethyl carbonate is 1:1. The assembly of CR2032 coin-type half-cells is carried out in a glove box filled with argon.

[0055] Example 2

[0056] A lignin derivative composite binder is prepared by the following preparation method:

[0057] Polyacrylic acid and polyethylene glycol graft-modified lignin are compounded and dissolved in 1,4-dioxane at a ratio of 9:1 to prepare a binder solution. After stirring evenly, it is heated and dried at 80 °C for 8 hours to obtain a lignin derivative composite binder with high ionic conductivity. The weight of polyethylene glycol graft-modified lignin is 10% of the total weight of polyacrylic acid and polyethylene glycol graft-modified lignin.

[0058] The difference from Example 1 is that the reaction temperature of the heating reaction is 80 °C.

[0059] The rest is the same as in Example 1 and will not be elaborated here.

[0060] Example 3

[0061] A lignin derivative composite binder is prepared by the following preparation method:

[0062] Polyacrylic acid and polyethylene glycol graft-modified lignin are compounded and dissolved in 1,4-dioxane at a ratio of 7:3 to prepare a binder solution. After stirring evenly, it is heated and dried at 80 °C for 8 hours to obtain a lignin derivative composite binder with high ionic conductivity.

[0063] The difference from Example 1 is that the weight of polyethylene glycol graft-modified lignin is 30% of the total weight of polyacrylic acid and polyethylene glycol graft-modified lignin. The reaction temperature of the heating reaction is 80 °C.

[0064] The rest is the same as in Example 1 and will not be elaborated here.

[0065] Example 4

[0066] A lignin derivative composite binder is prepared by the following preparation method:

[0067] Polyacrylic acid and polyethylene glycol graft-modified lignin are compounded and dissolved in 1,4-dioxane at a ratio of 5:5 to prepare a binder solution. After stirring evenly, it is heated and dried at 80 °C for 8 hours to obtain a lignin derivative composite binder with high ionic conductivity.

[0068] The difference from Example 1 is that the weight of polyethylene glycol graft-modified lignin is 50% of the total weight of polyacrylic acid and polyethylene glycol graft-modified lignin. The reaction temperature for the heating reaction is 80 °C.

[0069] The rest is the same as in Example 1 and will not be elaborated here.

[0070] Comparative Example 1

[0071] A silicon-based anode binder for lithium-ion batteries is prepared by the following method: Polyacrylic acid is dissolved in 1,4-dioxane to prepare a binder solution. After stirring evenly, it is dried for 8 hours to obtain binder PAA.

[0072] The preparation method of polyacrylic acid is the same as that of polyacrylic acid in Example 1.

[0073] Comparative Example 2

[0074] A silicon-based anode binder for lithium-ion batteries is prepared by the following method: Polyacrylic acid and polyethylene glycol are compounded and dissolved in 1,4-dioxane in a ratio of 9:1 to prepare a binder solution. After stirring evenly, it is dried at 80 °C for 8 hours to obtain a lignin derivative composite binder with high ionic conductivity.

[0075] The rest is the same as in Example 1 and will not be elaborated here.

[0076] Result Detection

[0077] The binders of Examples 2 to 4 and Comparative Examples 1 to 2 above are respectively used to prepare lithium-ion battery anode sheets by the same method as in Example 1, and the following mechanical property tests are carried out. The test method is: For the 180° peel test, a microcomputer-controlled electronic universal testing machine CMT6203 from Shenzhen Sansi Experimental Instrument Co., Ltd. is used. The electrode sheet is cut into a rectangle of 50 mm × 18 mm, and a 3M tape with a width of 18 mm is adhered to the coated surface of the electrode sheet, and a 180° peel test is carried out at a peel rate of 100 mm min -1 .

[0078] The test results are as Figure 1 shown:

[0079] The maximum bonding strength of the binder in Example 2 is 4.0 N. When the ratio of polyacrylic acid to polyethylene glycol graft-modified lignin reaches 9:1, the multi-level and multi-faceted synergistic effect enables it to achieve the maximum bonding strength of 4.0 N, and during the battery cycling process, the electrode material is not likely to fall off. The bonding strength of Comparative Example 1 is 3.5 N.

[0080] The effect of network-structured alkali lignin on improving the bonding strength was demonstrated by the peel strength test. The addition of polyethylene glycol graft-modified lignin can increase the elasticity and toughness of the material, contribute to stress dissipation and network resilience, but an increase in its content will reduce the stress of the composite material. As can be seen from the attached drawings, the peel strength of the electrode sheet in Example 2 was significantly improved. In Example 2, a stable bonding interface can be formed, providing multi-directional binding sites, thereby enhancing the bonding strength. And during the battery cycling process, the electrode material is not likely to fall off either.

[0081] The lithium-ion batteries were respectively prepared from the binders of Examples 2 to 4 and Comparative Examples 1 to 2 by the same method as in Example 1, and the following performance tests were carried out:

[0082] (1) Constant current charge and discharge test: The constant current charge and discharge test is to record the cycle performance and rate performance data of the battery under a constant current density. The Neware charge and discharge test system was used to test the cycle performance and rate performance of the battery. The test conditions of the battery were at a constant temperature of 25 °C. The battery needed to be static for 10 h before cycling, and was activated for one cycle with a small current, and then the constant current charge and discharge test was carried out.

[0083] Cycle performance: Each example was subjected to a constant current charge and discharge test at a current density of 0.5 A g -1 .

[0084] The specific test results of the cycle performance of each example and comparative example are shown in Table 1 and Figure 2 as follows:

[0085] Table 1

[0086] Group Number of cycles <![CDATA[Discharge specific capacity (mAh g -1 )]]> Example 1 500 1053.73 Example 2 500 682.99 Example 3 500 321.65 Example 4 370 78.01 Comparative Example 1 200 418.82

[0087] The specific test results of the rate performance of each example and comparative example are shown in Table 2 and Figure 3 as follows:

[0088] Table 2

[0089]

[0090] After thermal esterification crosslinking, the electrode prepared from the binder of Example 1 still had a capacity of 788.21 mAh g -1 at a current density of 1 A g -1 . When the current density returned to 0.2 A g -1 again, the electrode prepared from the binder of Example 1 still had a capacity of 1739.98 mAh g -1 , indicating that the electrodes of the examples of the present invention have excellent rate performance.

[0091] The charge-discharge cycle test results show that the lignin derivative composite binder of the embodiments of the present invention has excellent cycle performance and rate performance. Under the stepped current density, the discharge specific capacity decreases less; in constant current charge-discharge, at a high current density of 0.5 Ag -1 it maintains a long cycle with a high specific capacity.

[0092] It can be seen from Example 1 and Example 2 that in Example 1, a high-temperature thermal esterification cross-linking reaction is adopted, and the discharge specific capacity is higher. This is because after thermal esterification cross-linking, polyacrylic acid and polyethylene glycol graft-modified lignin form a stronger covalent cross-linking network. The covalent-non-covalent cross-linking network formed by the binder in Example 1 has higher structural stability than the hydrogen bond cross-linking network formed by the binder in Example 2, thereby improving the cycle life and electrochemical performance of the electrode.

[0093] It can be seen from Examples 2 to 4 that in the preparation method of the lignin-based binder, the weight of polyethylene glycol graft-modified lignin is 10-30% of the total weight of polyacrylic acid and polyethylene glycol graft-modified lignin, and the prepared lignin derivative composite binder has more excellent cycle performance and rate performance.

[0094] For the SiO electrode prepared with the binder of non-crosslinked lignin in Comparative Example 1, at a current density of 0.5 Ag -1 it can only cycle 200 times and has a capacity of only 418.82 mAh g -1 At a current density of 1 Ag -1 it has a capacity of only 146 mAh g -1 This may be because there is no three-dimensional skeleton support of lignin, and it is also difficult to maintain the integrity of the electrode sheet, resulting in the contact failure of the conductive network in the rapid change rate test. The SiO electrode in Comparative Example 2 also has too poor rate performance.

[0095] It can be seen that lignin has the function of improving the rate performance. At the same time, introducing the lithium-conducting segment PEG helps to synergistically promote the rapid directional transport of lithium ions by lignin, thereby obtaining higher and more stable rate performance.

[0096] (2) Ionic conductivity, interfacial impedance and ion diffusion rate

[0097] Electrochemical impedance test: The electrochemical impedance test is to apply a sinusoidally varying cross-linked perturbation voltage to the electrode to make the voltage of the electrode change according to the sine wave law, so as to obtain an impedance spectrum diagram, and then study the dynamics and ion diffusion mechanism of the electrode. The test is carried out using an electrochemical workstation. At room temperature, a sinusoidal alternating voltage with an amplitude of 5 mV is applied to the battery in the frequency range of 0.01 Hz to 100 kHz.

[0098] Electrochemical impedance tests were carried out on different binder half-cells, and the test results are asFigure 4 As shown. Figure 4 It can be seen that after five cycles, Example 1 has the smallest impedance, which is 30.29Ω for Example 1, 45.58Ω for Example 2, and 63.45Ω for Comparative Example 1, indicating that the binder has a good wetting effect on the electrolyte. The slope of the oblique line in the medium and low frequency regions of Example 1 and Example 2 is higher than that of Comparative Example 1, indicating that the electrode can maintain the stability of the electrode and the integrity of the conductive network during the cycle, and a stable SEI is generated, which has a better charge transfer effect. The introduction of polyethylene glycol grafted modified lignin also increases the diffusion rate of ions and ionic conductivity, thereby reducing impedance.

[0099] It can be seen that the ionic conductivity and ion diffusion rate of the embodiment of the present invention are significantly improved, and the electrode prepared therefrom has a smaller interface impedance.

[0100] It can be seen from the above results that the lignin derivative composite binder of the present invention has certain mechanical properties, reduces the volume effect during the charge and discharge process of the SiO negative electrode, and promotes the transmission of lithium ions while maintaining the integrity of the conductive network, so that its rate performance and long cycle performance at high current density are significantly improved.

[0101] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A lignin derivative composite binder, characterized in that: The composite binder is prepared by the following preparation method: polyacrylic acid and polyethylene glycol grafted modified lignin are heated in a solvent for reaction to obtain a lignin derivative composite binder; wherein the weight of the polyethylene glycol grafted modified lignin is 5-55% of the total weight of the polyacrylic acid and polyethylene glycol grafted modified lignin, and the reaction temperature of the heating reaction is 70-170°C.

2. The lignin derivative composite binder according to claim 1, characterized in that: The weight of the polyethylene glycol grafted modified lignin is 10-30% of the total weight of the polyacrylic acid and the polyethylene glycol grafted modified lignin.

3. The lignin derivative composite binder according to claim 1, characterized in that: The reaction temperature of the heating reaction is 100-165°C.

4. The lignin derivative composite binder according to claim 1, characterized in that: The preparation method of the polyethylene glycol grafted modified lignin comprises the following steps: heating lignin and polyethylene glycol in concentrated sulfuric acid for reaction to obtain the polyethylene glycol grafted modified lignin.

5. The lignin derivative composite binder according to claim 4, characterized in that: The lignin is alkali lignin.

6. The lignin derivative composite binder according to claim 4, characterized in that: The mass ratio of the lignin to the polyethylene glycol is 1:(4-6).

7. The lignin derivative composite binder according to claim 4, characterized in that: In the preparation method of polyethylene glycol grafted modified lignin, the heating reaction time is 4 to 5 hours and the heating reaction temperature is 150 to 160°C.

8. A negative electrode slurry for a lithium ion battery, characterized in that: The invention comprises a negative electrode active material, a conductive agent and a negative electrode binder, wherein the negative electrode binder is the lignin derivative composite binder according to any one of claims 1 to 7.

9. A negative electrode sheet for a lithium-ion battery, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, wherein the negative electrode active material layer is obtained by drying the negative electrode slurry of the lithium ion battery according to claim 8.

10. A lithium ion battery, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet, a separator arranged between the positive electrode sheet and the negative electrode sheet, and an electrolyte, wherein the negative electrode sheet is the negative electrode sheet of the lithium ion battery as claimed in claim 9.

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