Composite binder composition as well as preparation method and application thereof

Abstract

The invention provides a composite binder composition as well as a preparation method and application thereof. The composite binder composition comprises water and a solid organic matter dispersed in the water, the solid organic matter comprises modified tamarind polysaccharide and a rubber polymer, and the weight ratio of the modified tamarind polysaccharide to the rubber polymer is (1-3): 1. By combining the modified tamarind polysaccharide and the rubber polymer, the excellent performance of the obtained composite binder composition in the preparation process of the aqueous lithium ion battery is realized. Wherein the modified tamarind polysaccharide has good rigidity, and the rubber polymer endows the composite binder composition with good elasticity and adhesive force to a current collector. By accurately controlling the proportion of the two, a polymer network which is good in performance, has a three-dimensional interpenetrating structure and takes soft, hard and elastic plasticity into account can be formed, and the cycling stability and the energy density of corresponding aqueous lithium ions are finally improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aqueous lithium-ion batteries, in particular, to a composite binder composition, its preparation method and application. BACKGROUND

[0002] The mainstream power battery in the current market, lithium-ion battery, is mainly composed of lithium iron phosphate and graphite. However, it is quite challenging to further improve the energy density based on the existing material system. In this context, silicon-based materials as the potential of lithium-ion battery anode are increasingly prominent. Silicon has attracted widespread attention due to its high theoretical specific capacity of 4200 mAh·g -1 , extensive natural resources and environmental friendliness. However, silicon undergoes significant volume expansion during repeated charge and discharge, ranging from 300% to 400%, which leads to the collapse of the electrode structure, damage to the conductive network, continuous destruction and reconstruction of the solid electrolyte interface (SEI) film, and further causes electrolyte loss and capacity decay, greatly limiting the electrochemical performance of silicon-based materials in practical applications.

[0003] The binder plays a crucial role in this scenario. During battery application, the binder interacts with the surface of silicon particles, effectively alleviating the volume expansion of silicon and maintaining the integrity of the electrode. In particular, the polymer binder plays a decisive role in improving the mechanical stability of the electrode. During the preparation of the electrode, an ideal binder can ensure the uniform dispersion of active materials and conductive agents in the solvent and achieve effective bonding, firmly adhering to the surface of the metal copper current collector. Traditional commercial binders, such as polyvinylidene fluoride (PVDF), interact with silicon particles through van der Waals forces, but their effect on limiting silicon particle expansion is not significant, and they require the use of organic solvents N-methyl pyrrolidone (NMP) during preparation, which is dangerous, environmentally unfriendly and costly. In contrast, water-based polymer binders, with hydrophilic groups such as -COOH, -OH, and -NH2, form hydrogen bonds and / or covalent bonds with the Si-OH on the surface of silicon powder, significantly enhancing the interfacial adhesion with silicon particles.

[0004] In recent years, researchers have found that by designing high-performance binders, the fragmentation problem of silicon electrodes can be effectively alleviated, and their cycle performance can be stabilized. However, most of the current experiments are carried out at a relatively low active material loading (≤1 mg / cm 2 ), which is different from the high energy density conditions required in practical applications (about 3 mg / cm 2) is far from the original. Under high loading, the volume expansion of silicon materials is more intense, which puts higher requirements on maintaining the stability of the electrode. Specifically: (1) With the increase of the active material loading in the positive and negative active layers, the binder based solely on hydrogen bonds cannot resist the cracking of high-areal-capacity silicon negative electrodes, and adjusting the mechanical properties of the binder is an important way to solve the above problems; (2) At present, highly elastic binders allow the pulverized silicon particles to condense together again during the cycle, but due to the lack of mechanical stiffness, elastic binders alone cannot solve the problem of silicon negative electrode expansion; (3) Binders with high stiffness, such as polyaniline and polyacrylic acid, can effectively constrain the volume change of silicon particles, thereby achieving controllable electrode expansion, but high stiffness makes it easier to break under critical stress, especially under high mass loading.

[0005] Based on this, how to reasonably design the elastic / rigid matching relationship of each component in the binder composition so that the electrodes prepared therefrom, especially the silicon negative electrode, can have better cycle stability at high loads has become a major difficulty and hot spot that needs to be urgently solved in the current lithium-ion battery field. Summary of the Invention

[0006] The main purpose of the present invention is to provide a composite binder composition, a preparation method and application thereof, so as to solve the problem in the prior art that it is difficult to establish a good elastic / rigid matching relationship between the components of the binder for aqueous lithium-ion batteries, and thus it is impossible to prepare an electrode sheet that can achieve both high energy density and long cycle stability.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a composite adhesive composition, comprising water and solid organic matter dispersed in the water, wherein the solid organic matter comprises modified tamarind polysaccharide and a rubber-like polymer, and the weight ratio of the modified tamarind polysaccharide to the rubber-like polymer is (1 to 3):1.

[0008] Furthermore, the glass transition temperature of the modified tamarind polysaccharide is 140°C to 200°C; and / or the glass transition temperature of the rubber-based polymer is -20°C to -25°C.

[0009] Furthermore, the modified tamarind polysaccharide is acrylic acid-modified tamarind polysaccharide, and the structure of the tamarind polysaccharide contains acryloyloxy groups; based on the total weight of the modified tamarind polysaccharide as 100%, the content of the acryloyloxy groups is 30% to 50%, preferably 40% to 50%; and / or the rubber-like polymer is selected from one or more of styrene-butadiene rubber, hydrogenated styrene-butadiene rubber, nitrile rubber and polyurethane rubber.

[0010] Furthermore, the solid content of the composite adhesive composition is 3 wt% to 10 wt%.

[0011] The second aspect of the present invention provides a method for preparing the above-mentioned composite adhesive composition, comprising: step S1, preparing tamarind polysaccharide and water into a tamarind polysaccharide solution, adding a modified monomer to the tamarind polysaccharide solution to obtain a mixed solution; step S2, sequentially subjecting the mixed solution to a first stirring and a second stirring to obtain a mixed slurry, wherein the mixed slurry includes modified tamarind polysaccharide; step S3, adding a rubber polymer to the mixed slurry, and obtaining a composite adhesive composition after a third stirring.

[0012] Furthermore, in step S1, the modified monomer is acrylic acid and / or acrylic acid salt, and the weight ratio of the modified monomer to tamarind polysaccharide is (2-4):7; preferably, the weight ratio of the modified monomer to tamarind polysaccharide is (3-4):7.

[0013] Furthermore, in step S2, the speed of the first stirring is 80±20 rpm, and the time is 30 min to 60 min; the time of the second stirring is 10 h to 20 h, and the second stirring is carried out at 60°C to 90°C; and / or, in step S3, the speed of the third stirring is 80±20 rpm, and the time is 30±5 min, and the third stirring is carried out at 25±2°C.

[0014] The third aspect of the present invention provides an application of the above-mentioned composite binder composition as a binder in the field of aqueous lithium-ion batteries to prepare an active material layer, wherein the active material layer is a positive electrode active material layer and / or a negative electrode active material layer. The above-mentioned composite binder composition is mixed with a conductive agent, an active material and oxalic acid to obtain an active material slurry; the active material slurry is sequentially coated and in-situ polymerized to obtain an active material layer.

[0015] Furthermore, the weight ratio of the composite binder composition, the conductive agent and the active material is 1:1:(3-4); based on the total weight of the composite binder composition as 100%, the added amount of oxalic acid is 5%-10%.

[0016] Furthermore, the in-situ polymerization is achieved by heating the coated current collector, and the heating temperature is 140° C. to 150° C. and the heating time is 0.8 h to 1 h.

[0017] By applying the technical solution of the present invention, by combining modified tamarind polysaccharide with a rubber-like polymer, the resulting composite binder composition achieves excellent performance in the preparation process of aqueous lithium-ion batteries. The modified tamarind polysaccharide has good rigidity, while the rubber-like polymer imparts good elasticity and adhesion to the current collector to the composite binder composition. By precisely controlling the ratio of the two, a high-performance, three-dimensional interpenetrating polymer network with both soft and hard elastic-plastic properties can be formed when the active material layer is subsequently used as a binder, ultimately improving the cycling stability and energy density of the corresponding aqueous lithium-ion battery. DETAILED DESCRIPTION

[0018] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0019] As described in the background art, the binders for aqueous lithium-ion batteries in the prior art have the problem of difficulty in establishing a good elastic / rigidity matching relationship between the components, and thus it is impossible to prepare an electrode sheet that can achieve both high energy density and long cycle stability, and the corresponding lithium-ion battery performance is also poor. In order to solve the above technical problems, the first aspect of the present invention provides a composite binder composition comprising water and a solid organic matter dispersed in the water, wherein the solid organic matter comprises a modified tamarind polysaccharide and a rubber-like polymer, and the weight ratio of the modified tamarind polysaccharide to the rubber-like polymer is (1-3):1.

[0020] By combining modified tamarind polysaccharide with a rubber-like polymer, the present invention achieves excellent performance in the preparation of aqueous lithium-ion batteries using the resulting composite binder composition. Specifically, the rigidity of the modified tamarind polysaccharide provides mechanical support for the binder composition, resisting the expansion pressure of the positive and / or negative electrode material particles during battery application and preventing damage to the electrode structure. The elasticity of the rubber-like polymer acts as a buffering mechanism, absorbing the stress generated by the volume change of the active material and preventing its separation from the binder, conductive agent, and current collector, thereby improving the cycling stability and overall mechanical strength of the electrode.

[0021] By precisely controlling the ratio of the two, a polymer network with good performance, a three-dimensional interpenetrating structure, and both soft and hard elastic and plastic properties can be formed when it is subsequently used as a binder to prepare the active material layer, ultimately improving the cycle stability and energy density of the corresponding aqueous lithium ion.

[0022] Furthermore, the glass transition temperature of the modified tamarind polysaccharide is 140°C to 200°C. In other words, the modified tamarind polysaccharide used in the present invention has good rigidity, which helps the binder composition in which it is used to prepare the active material layer to more effectively form a stable three-dimensional network structure, thereby improving the integrity and stability of the electrode structure. The glass transition temperature of the preferred rubber polymer is -20°C to -25°C, which means that the rubber polymer has excellent elasticity, and then is compounded with the above-mentioned rigid modified tamarind polysaccharide as a binder composition and polymerized in the application to form a well-structured three-dimensional network, which more effectively absorbs and relieves the stress generated by the volume change of the positive and negative electrode material particles, thereby improving the conductivity and cycle stability of the electrode.

[0023] In several preferred embodiments, a modified tamarind polysaccharide film with a thickness of 2 mm was prepared by coating and drying, and the elongation at break of the modified tamarind polysaccharide film was 80% to 150%. A rubber polymer film with a thickness of 2 mm was prepared by coating and drying, and the elongation at break of the rubber polymer was 160% to 180%. In other words, the modified tamarind polysaccharide provided by the present invention, when used as a component of a binder composition and applied to the active material layer, can provide better support for the positive and negative electrodes, reducing the breakage and detachment of the corresponding electrode sheets at high areal capacity, thereby improving the battery's cycling stability and energy density. The high elasticity of the rubber polymer enables the binder composition to be used to prepare the active layer, enabling more effective stress absorption and providing good deformation recovery, thereby enhancing the stability of the electrode structure after multiple charge and discharge cycles, and thus increasing the cycle life of the resulting aqueous lithium-ion battery.

[0024] Furthermore, the modified tamarind polysaccharide is acrylic acid-modified tamarind polysaccharide, and its structure contains acryloyloxy groups. Acryloyloxy groups are introduced onto the surface of the tamarind polysaccharide through an esterification reaction. During this process, the tamarind polysaccharide reacts with acrylic acid to form a hard polymer, TAA. The carboxylic acid groups of the acrylic acid react with the hydroxyl groups of the polysaccharide to form ester bonds, releasing water molecules. The double bonds of the acrylic acid remain in the resulting ester structure, meaning that the final esterified product incorporates acryloyloxy groups as side chains, i.e., the modified tamarind polysaccharide. This modification method and the preferred choice of the corresponding modifying monomers enhance the chemical stability of the modified polysaccharide through the ester bonds formed by the esterification reaction. This also facilitates stronger chemical bonding with the functional groups on the surface of the electrode material when used as a binder to prepare the active material layer. Furthermore, the presence of the acryloyloxy groups facilitates in-situ polymerization of the modified tamarind polysaccharide when it is subsequently used as a component of a binder composition to prepare the active material layer. Especially in the compounding process with soft, rubbery polymers, the acryloxy group helps to form a more uniform 3D interpenetrating network structure, providing effective stress buffering and mechanical support for the resulting electrode sheet.

[0025] Based on the above, the preferred acryloyloxy content is 30% to 50% based on the total weight of the modified tamarind polysaccharide as 100%, based on considerations for the balance of chemical bonding during the modification process. If the acryloyloxy content in the modified tamarind polysaccharide is too high, it may become too rigid, affecting its interaction with the rubber polymer elastomer during the subsequent in-situ polymerization process; while if the content is too low, it may weaken the bonding properties, affecting the subsequent bonding in the active material layer. A more preferred content of 40% to 50% allows the modified tamarind polysaccharide to provide rigid support in the binder composition while better cooperating with the rubber polymer to maintain the stability and elasticity of the active material layer obtained by subsequent polymerization, thereby improving the overall performance of the battery.

[0026] The rubber polymer is preferably selected from one or more of styrene-butadiene rubber (SBR), hydrogenated styrene-butadiene rubber (HBR), nitrile rubber (NBR), and polyurethane rubber. In several preferred embodiments, the rubber polymer is HBR, and the HBR has a degree of hydrogenation of 90±5%. The HBR with this degree of hydrogenation used in the present invention exhibits improved oxidative stability and electrolyte compatibility, and can be used as a binder component to maintain more stable performance during battery cycling, thereby better maintaining the structural integrity and electrochemical performance of the electrodes and lithium-ion batteries.

[0027] To balance the viscosity and dispersibility of the resulting composite binder composition, ensuring it provides both enhanced bonding strength and excellent processability during application, the composite binder composition preferably has a solids content of 3 to 10 wt%. This solids content allows the modified tamarind polysaccharide and rubber-based polymer to better leverage their rigidity and flexibility, forming an active material layer with enhanced bonding and elasticity after subsequent polymerization, thereby improving the overall performance of the battery in which it is incorporated.

[0028] The second aspect of the present invention provides a method for preparing the above-mentioned composite adhesive composition, comprising: step S1, preparing tamarind polysaccharide and water into a tamarind polysaccharide solution, adding a modified monomer to the tamarind polysaccharide solution to obtain a mixed solution; step S2, sequentially subjecting the mixed solution to a first stirring and a second stirring to obtain a mixed slurry, wherein the mixed slurry includes modified tamarind polysaccharide; step S3, adding a rubber polymer to the mixed slurry, and obtaining a composite adhesive composition after a third stirring.

[0029] With respect to the above-mentioned composite binder composition, the present invention accordingly provides an efficient preparation method thereof, the core of which is to mix tamarind polysaccharide with a modified monomer to prepare a modified tamarind polysaccharide, and then add a rubber-like polymer to form a composite binder with a specific structure and performance. The above-mentioned method provided by the present invention can effectively control the uniformity and structural stability of the formed composite binder while preparing a composite binder composition with excellent performance. In particular, the chemical reaction between the tamarind polysaccharide and the modified monomer in steps S1 and S2, and the sufficient physical mixing between the modified tamarind polysaccharide and the rubber-like polymer in step S3, each step is coordinated in order, which significantly improves the uniformity and processability of the obtained composite binder composition, so that it exhibits excellent performance in the subsequent process of preparing a high-load electrode material.

[0030] In several typical embodiments, the modified monomer in step S1 is acrylic acid and / or acrylic acid salt, and the weight ratio of the modified monomer to tamarind polysaccharide is (2-4):7. That is to say, acrylic acid and / or acrylic acid salt is used as a modified monomer to form a chemical bond with the hydroxyl group of tamarind polysaccharide through an esterification reaction to generate modified tamarind polysaccharide. By preferably setting the weight ratio of the modified monomer to tamarind polysaccharide to (2-4):7, the esterification reaction can be carried out more efficiently, the rigidity of the modified tamarind polysaccharide obtained can be improved, and then in the subsequent process of preparing the active material layer as a binder component, a stronger mechanical support can be provided, thereby improving the overall structural stability of the electrode sheet obtained in the end. More preferably, the weight ratio of the modified monomer to tamarind polysaccharide is (3-4):7. Under this ratio, the esterification reaction is more gentle and controllable, reducing the increase in viscosity that may be caused by excessive acrylic acid and the decrease in the dispersion performance of the subsequent composition slurry system. At the same time, the modified tamarind polysaccharide is more tightly bound to the rubber polymer, forming a more stable three-dimensional network structure during the subsequent in situ polymerization process, thereby significantly enhancing the cyclic stability of the high-load electrode.

[0031] In order to make the mixing of tamarind polysaccharide and modified monomer more uniform, promote the more complete esterification reaction, and reduce the reaction heterogeneity caused by local overheating or insufficient stirring, it is preferred that in step S2, the speed of the first stirring is 80±20rpm, and the time is 30min~60min. Furthermore, for the second stirring, it is preferred that the time is 10h~20h, and the second stirring is carried out at 60℃~90℃. Such reaction conditions are conducive to the formation of a modified tamarind polysaccharide with a more complete and stable structure, while also improving the reaction efficiency and product purity of the process of obtaining the modified tamarind polysaccharide, further improving the performance stability of the composite binder.

[0032] In step S3, the third stirring is preferably performed at a speed of 80±20 rpm, for a duration of 30±5 minutes, and at a temperature of 25±2°C. These mixing and stirring conditions facilitate uniform dispersion of the rubber-like polymer, promote its stable bonding with the modified tamarind polysaccharide, and improve the adaptability and resistance of the resulting binder composition to electrode material expansion when used as a binder in the active material layer, ultimately enhancing the various performance characteristics of the aqueous lithium-ion battery system.

[0033] The third aspect of the present invention provides an application of the above-mentioned composite binder composition as a binder in the field of aqueous lithium-ion batteries to prepare an active material layer, wherein the active material layer is a positive electrode active material layer and / or a negative electrode active material layer. The above-mentioned composite binder composition is mixed with a conductive agent, an active material and oxalic acid to obtain an active material slurry; the active material slurry is sequentially coated and in-situ polymerized to obtain an active material layer.

[0034] The above-mentioned composite binder composition provided by the present invention includes a rigid binder, namely modified tamarind polysaccharide, and an elastic binder, namely a rubber-like polymer. The advantages of the two are combined to synergistically form a composition system. Through the above-mentioned application process, a soft and hard elastic-plastic support layer with a three-dimensional interpenetrating structure can be formed in the active material layer. Among them, "hard" refers to the high rigidity of the plastic, which provides a framework to withstand expansion and maintain the integrity of the electrode, and "soft" refers to the high elasticity of the elastomer, which acts as a buffer and is not easy to break under high force. In the process of in situ polymerization, the hard polymer of modified tamarind polysaccharide is woven into the soft polymer network of the rubber-like polymer, thereby successfully constructing a directional three-dimensional interpenetrating bonding network for high surface capacity electrodes. Specifically:

[0035] Under the catalysis of oxalic acid, the liquid modified tamarind polysaccharide monomer undergoes self-polymerization to form a hard TAA-PAA polymer (i.e., tamarind polysaccharide-polyacrylic acid cross-linked polymer). When the modified tamarind polysaccharide swells in the elastic hydrogel formed by the rubber polymer, it polymerizes in situ within the rubber polymer system to form a 3D composite binder structure. In other words, while the active material layer is forming, the modified tamarind polysaccharide and the soft rubber polymer polymerize in situ to form a three-dimensional network composite binder. The network polymer layer formed by in situ polymerization not only has covalent bonds, hydrogen bonds, and electrostatic interactions with the positive / negative electrode active materials, but also has interaction forces generated by mechanical interlocking. From a microstructural perspective, the hard portion of the modified tamarind polysaccharide acts as a skeleton, bearing the internal stress generated by the volume change of the positive / negative electrode materials and restraining their impact on the electrodes; the soft portion of the rubber polymer acts as a buffer, alleviating the deformation caused by the volume change of the positive / negative electrode materials and preventing their separation from materials such as the binder and conductive agent. The synergy between soft and hard polymers stabilizes the overall structure of the electrode, playing a key role in highly loaded electrodes. Furthermore, the application process of the composite binder composition of the present invention, by incorporating the concept of in-situ polymerization, not only further strengthens the bond between the binder and the active material, resulting in a more uniform distribution of the active material, a more stable electrode structure, and improved battery performance, but also simplifies the overall process of binder material synthesis and electrode plate fabrication.

[0036] In practical applications, the process of obtaining the active material slurry preferably also includes mixing the composite binder composition, the conductive agent, and the active material to obtain an intermediate slurry; adding oxalic acid to the intermediate slurry, and stirring for 5 to 10 minutes to obtain the active material slurry. The refinement of this process promotes the thorough mixing of the modified tamarind polysaccharide with the active material and the conductive agent. The timing of adding oxalic acid and the selection of the corresponding stirring time further optimize the subsequent in-situ polymerization process, so that the formed TAA-PAA polymer can be more evenly distributed between the active material particles, forming a denser and more stable network structure, and ultimately significantly improving the cycle stability and energy density of the battery.

[0037] The active material layer is preferably a negative electrode active material layer, and more preferably, the negative electrode active material is nanosilicon powder. The composite binder composition provided by the present invention is better adapted for nanosilicon powder as a negative electrode active material. The synergistic effect of the hard polymer and the soft polymer in the resulting negative electrode active material layer can effectively control the volume expansion of the nanosilicon powder during charge and discharge, reduce internal stress in the silicon electrode, and prevent structural damage, thereby significantly improving the cycle stability and energy density of lithium-ion batteries containing silicon-based negative electrodes.

[0038] Furthermore, in order to optimize the composition of the electrode slurry and more effectively improve the mechanical stability and electrochemical performance of the resulting active material layer, the weight ratio of the composite binder composition, the conductive agent, and the active material is preferably 1:1:(3-4). Also, during the in-situ polymerization process, oxalic acid is used as a catalyst. Its appropriate use can promote the in-situ polymerization of the modified tamarind polysaccharide, forming a more stable bonding network structure, while avoiding side reactions and electrode performance degradation caused by excessive oxalic acid. On this basis, an oxalic acid addition of 5% to 10% is preferred, which can more effectively increase the speed and efficiency of the polymerization reaction under high loading conditions, thereby enhancing the structural stability and electrochemical performance of the active material layer.

[0039] In several typical embodiments, in-situ polymerization is achieved by heating the coated current collector, and the heating temperature is 140°C to 150°C for 0.8h to 1h. Within the above temperature range, the polymerization reaction of the modified tamarind polysaccharide is carried out efficiently, forming a more stable 3D network structure with the rubber polymer, while not causing polymer degradation due to excessively high temperature or incomplete reaction due to excessively low temperature. The above heating time can promote the full polymerization reaction, so that the composite binder composition can more evenly and tightly wrap the active material particles, forming a more stable active material layer, and ultimately improving the cycle stability and energy density of the resulting aqueous lithium-ion battery.

[0040] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0041] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0042] Example 1

[0043] A method for preparing a composite adhesive composition:

[0044] (1) Preparation of modified tamarind polysaccharide: Tamarind polysaccharide powder was completely dissolved in deionized water at room temperature to obtain a tamarind polysaccharide solution. Modified monomer acrylic acid was added to the obtained tamarind polysaccharide solution to obtain a mixed solution. During the addition, the weight ratio of modified monomer acrylic acid to tamarind polysaccharide in the solution was controlled to be 2:7.

[0045] (2) The obtained mixed solution was magnetically stirred at room temperature at a speed of 80 rpm for 40 minutes, i.e., the first stirring, so that the added acrylic acid could be completely dissolved. The reaction system was then stirred at 80°C for 15 hours to obtain a mixed slurry. During this process, tamarind polysaccharide and acrylic acid underwent an esterification reaction to form a hard polymer TAA. The carboxylic acid group of acrylic acid reacted with the hydroxyl group of polysaccharide to form an ester bond, while releasing water molecules. The double bond of acrylic acid was retained in the obtained ester structure, i.e., an acryloyloxy group was introduced as a side chain into the final esterified product, i.e., modified tamarind polysaccharide.

[0046] Wherein, based on the total weight of the obtained modified tamarind polysaccharide as 100%, the content of the acryloyloxy group in its structure is 30%; the glass transition temperature T of the obtained modified tamarind polysaccharide is g The modified tamarind polysaccharide was dissolved by stirring, and then coated on a polytetrafluoroethylene plate and dried to prepare a film with a thickness of 2 mm. The elongation at break of the film was tested according to GB / T 528-2012, and the result was 80%.

[0047] (3) Select glass transition temperature T g A rubber polymer, hydrogenated styrene-butadiene rubber (HSBR) at -20°C and a degree of hydrogenation of 90%, was dissolved by stirring, then coated onto a polytetrafluoroethylene plate and dried to produce a 2mm thick film. The resulting film was tested for elongation at break according to GB / T 528-2012, yielding a result of 180%. The HSBR was added to the mixed slurry containing modified tamarind polysaccharide in a specific proportion, and the mixture was stirred at 80 rpm for 30 minutes at 25°C (i.e., room temperature) to produce a composite adhesive composition.

[0048] The obtained composite adhesive composition includes water and modified tamarind polysaccharide and HSBR dispersed therein, with a solid content of 5wt%. Meanwhile, the weight ratio of the modified tamarind polysaccharide to the HSBR is 3:1.

[0049] A method for preparing a silicon negative electrode active layer:

[0050] The composite binder composition, nano-silicon powder, and conductive carbon black were mixed in deionized water at a mass ratio of 3:1:1 to form a uniform intermediate slurry. Oxalic acid was then added and stirred for 5 minutes to obtain an active material slurry. The oxalic acid was added in an amount of 5% based on the total weight of the composite binder composition (100%).

[0051] The active material slurry is coated on at least one side of the negative electrode current collector and heated at 140°C for 1 hour to achieve in-situ polymerization, forming an active material layer on the surface of the negative electrode current collector to produce an electrode sheet. During this process, the esterified product of modified tamarind polysaccharide is embedded in the HSBR emulsion. Heat-catalyzed polymerization is then performed to produce a TAA / HSBR composite polymer with interpenetrating network properties.

[0052] Example 2

[0053] A method for preparing a composite adhesive composition:

[0054] (1) Preparation of modified tamarind polysaccharide: Tamarind polysaccharide powder was completely dissolved in deionized water at room temperature to obtain a tamarind polysaccharide solution. Modified monomer acrylic acid was added to the obtained tamarind polysaccharide solution to obtain a mixed solution. During the addition, the weight ratio of modified monomer acrylic acid to tamarind polysaccharide in the solution was controlled to be 3:7.

[0055] (2) The resulting mixed solution was magnetically stirred at 80 rpm for 30 minutes at room temperature, i.e., the first stirring step, to allow the added acrylic acid to completely dissolve. The reaction system was then stirred at 60°C for 20 hours to obtain a mixed slurry. During this process, tamarind polysaccharide and acrylic acid underwent an esterification reaction to form a hard polymer, TAA, i.e., modified tamarind polysaccharide.

[0056] Wherein, based on the total weight of the obtained modified tamarind polysaccharide as 100%, the content of the acryloyloxy group in its structure is 40%; the glass transition temperature T of the obtained modified tamarind polysaccharide is g The obtained modified tamarind polysaccharide was dissolved by stirring, and then coated onto a polytetrafluoroethylene plate and dried to prepare a film with a thickness of 2 mm. The obtained film was tested for elongation at break according to GB / T 528-2012, and the result was 100%.

[0057] (3) Select glass transition temperature T g A rubber polymer, hydrogenated styrene-butadiene rubber (HSBR) at -20°C and a degree of hydrogenation of 90%, was dissolved by stirring, then coated onto a polytetrafluoroethylene plate and dried to prepare a 2 mm thick film. The resulting film was tested for elongation at break according to GB / T 528-2012, yielding a result of 180%. The HSBR was then added to the mixed slurry containing modified tamarind polysaccharide in a specific proportion, and the mixture was stirred at 80 rpm for 30 minutes at 25°C (i.e., room temperature) to produce a composite adhesive composition.

[0058] The obtained composite adhesive composition includes water and modified tamarind polysaccharide and HSBR dispersed therein, with a solid content of 3wt%. Meanwhile, the weight ratio of the modified tamarind polysaccharide to the HSBR is 2:1.

[0059] A method for preparing a silicon negative electrode active layer:

[0060] The composite binder composition, nano-silicon powder, and conductive carbon black were mixed in deionized water at a mass ratio of 3:1:1 to form a uniform intermediate slurry. Oxalic acid was then added and stirred for 8 minutes to obtain an active material slurry. The oxalic acid was added in an amount of 7% based on the total weight of the composite binder composition (100%).

[0061] The active material slurry is coated on at least one side of the negative electrode current collector, and the coated current collector is heated at 140° C. for 1 hour to achieve in-situ polymerization, forming an active material layer on the surface of the negative electrode current collector, thereby obtaining an electrode sheet.

[0062] Example 3

[0063] A method for preparing a composite adhesive composition:

[0064] (1) Preparation of modified tamarind polysaccharide: Tamarind polysaccharide powder was completely dissolved in deionized water at room temperature to obtain a tamarind polysaccharide solution. Modified monomer acrylic acid was added to the obtained tamarind polysaccharide solution to obtain a mixed solution. During the addition, the weight ratio of modified monomer acrylic acid to tamarind polysaccharide in the solution was controlled to be 4:7.

[0065] (2) The resulting mixed solution was magnetically stirred at 80 rpm for 60 minutes at room temperature, i.e., the first stirring step, to allow the added acrylic acid to completely dissolve. The reaction system was then stirred at 90°C for 10 hours to obtain a mixed slurry. During this process, tamarind polysaccharide and acrylic acid underwent an esterification reaction to form a hard polymer, TAA, i.e., modified tamarind polysaccharide.

[0066] Wherein, based on the total weight of the obtained modified tamarind polysaccharide as 100%, the content of the acryloyloxy group in its structure is 50%; the glass transition temperature T of the obtained modified tamarind polysaccharide is g The obtained modified tamarind polysaccharide was dissolved by stirring, and then coated onto a polytetrafluoroethylene plate and dried to prepare a film with a thickness of 2 mm. The obtained film was tested for elongation at break according to GB / T 528-2012, and the result was 150%.

[0067] (3) Select glass transition temperature T gA rubber polymer, hydrogenated styrene-butadiene rubber (HSBR) having a temperature of -20°C and a degree of hydrogenation of 90%, was dissolved by stirring, then coated onto a polytetrafluoroethylene plate and dried to prepare a 2 mm thick adhesive film. The resulting film was tested for elongation at break according to GB / T 528-2012, and the result was 180%. The HSBR was added to the mixed slurry containing modified tamarind polysaccharide obtained above in a specific proportion, and the mixture was stirred for a third time at 80 rpm for 30 minutes at 25°C (i.e., room temperature) to obtain a composite adhesive composition.

[0068] The obtained composite adhesive composition comprises water, modified tamarind polysaccharide and HSBR dispersed therein, with a solid content of 10 wt %. Meanwhile, the weight ratio of the modified tamarind polysaccharide to the HSBR is 1:1.

[0069] A method for preparing a silicon negative electrode active layer:

[0070] The composite binder composition, nano-silicon powder, and conductive carbon black were mixed in deionized water at a mass ratio of 4:1:1 to form a uniform intermediate slurry. Oxalic acid was then added to the mixture and stirred for 10 minutes to obtain an active material slurry. The oxalic acid was added in an amount of 10% based on the total weight of the composite binder composition (100%).

[0071] The active material slurry is coated on at least one side of the negative electrode current collector, and the coated current collector is heated at 150° C. for 0.8 h to achieve in-situ polymerization, forming an active material layer on the surface of the negative electrode current collector, thereby obtaining an electrode sheet.

[0072] Example 4

[0073] A method for preparing a composite adhesive composition:

[0074] The only difference between this embodiment and embodiment 1 is that in step (1), the weight ratio of the modified monomer acrylic acid to the tamarind polysaccharide in the solution is changed to 1:7.

[0075] At this time, based on the total weight of the modified tamarind polysaccharide as 100%, the content of the acryloyloxy group in its structure is 15%; the glass transition temperature T of the modified tamarind polysaccharide is 15%. g The obtained modified tamarind polysaccharide was dissolved by stirring, and then coated onto a polytetrafluoroethylene plate and dried to prepare a film with a thickness of 2 mm. The obtained film was tested for elongation at break according to GB / T 528-2012, and the result was 70%.

[0076] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0077] Example 5

[0078] A method for preparing a composite adhesive composition:

[0079] The only difference between this embodiment and embodiment 1 is that in step (1), the weight ratio of the modified monomer acrylic acid to the tamarind polysaccharide in the solution is changed to 1:1.

[0080] At this time, based on the total weight of the modified tamarind polysaccharide as 100%, the content of the acryloyloxy group in its structure is 70%; the glass transition temperature T of the modified tamarind polysaccharide is 100%. g The modified tamarind polysaccharide was dissolved by stirring, and then coated on a polytetrafluoroethylene plate and dried to prepare a film with a thickness of 2 mm. The elongation at break of the film was tested according to GB / T 528-2012, and the result was 160%.

[0081] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0082] Example 6

[0083] A method for preparing a composite adhesive composition:

[0084] The only difference between this embodiment and embodiment 1 is that in step (2), the speed of the first stirring is changed to 150 rpm and the time is changed to 10 min; at the same time, the time of the second stirring is changed to 5 h and the temperature is changed to 100°C.

[0085] At this time, based on the total weight of the modified tamarind polysaccharide as 100%, the content of the acryloyloxy group in its structure is 30%; the glass transition temperature T of the modified tamarind polysaccharide is 200 nm. g The modified tamarind polysaccharide was dissolved by stirring, and then coated on a polytetrafluoroethylene plate and dried to prepare a film with a thickness of 2 mm. The elongation at break of the film was tested according to GB / T 528-2012, and the result was 75%.

[0086] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0087] Example 7

[0088] A method for preparing a composite adhesive composition:

[0089] The only difference between this embodiment and embodiment 1 is that in step (2), the speed of the first stirring is changed to 50 rpm and the time is changed to 100 min; at the same time, the time of the second stirring is changed to 30 h and the temperature is changed to 50°C.

[0090] At this time, based on the total weight of the modified tamarind polysaccharide as 100%, the content of the acryloyloxy group in its structure is 30%; the glass transition temperature T of the modified tamarind polysaccharide is 200 nm. g The modified tamarind polysaccharide was dissolved by stirring, and then coated on a polytetrafluoroethylene plate and dried to prepare a film with a thickness of 2 mm. The elongation at break of the film was tested according to GB / T 528-2012, and the result was 70%.

[0091] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0092] Example 8

[0093] A method for preparing a composite adhesive composition:

[0094] The only difference between this embodiment and embodiment 1 is that in step (3), the type of hydrogenated styrene butadiene rubber (HSBR) is changed, specifically: the glass transition temperature T is selected g HSBR having a temperature of -10°C and a degree of hydrogenation of 70% was used as a rubber polymer, which was dissolved by stirring, then coated onto a polytetrafluoroethylene plate and dried to prepare a 2 mm thick film. The resulting film was tested for elongation at break according to GB / T 528-2012, and the result was 70%.

[0095] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0096] Example 9

[0097] A method for preparing a composite adhesive composition:

[0098] The only difference between this embodiment and embodiment 1 is that in step (3), the rotation speed of the third stirring is changed to 50 rpm and the time is changed to 60 min.

[0099] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0100] Example 10

[0101] A method for preparing a composite adhesive composition:

[0102] The only difference between this embodiment and embodiment 1 is that in step (3), the rotation speed of the third stirring is changed to 150 rpm and the time is changed to 10 minutes.

[0103] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0104] Example 11

[0105] A method for preparing a composite binder composition:

[0106] The difference between this example and Example 1 is that the solid content of the modified tamarind polysaccharide and HSBR in the obtained composite binder composition is changed to 1 wt%, while the weight ratio remains unchanged.

[0107] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0108] Example 12

[0109] A method for preparing a composite binder composition:

[0110] The difference between this example and Example 1 is that the solid content of the modified tamarind polysaccharide and HSBR in the obtained composite binder composition is changed to 15 wt%, while the weight ratio remains unchanged.

[0111] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0112] Comparative Example 1

[0113] A method for preparing a composite binder composition:

[0114] The difference between this comparative example and Example 1 is that the tamarind polysaccharide is not modified, but is directly prepared into a binder composition with the same solid content as in Example 1 by mixing the unmodified tamarind polysaccharide with HSBR.

[0115] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0116] Comparative Example 2

[0117] A method for preparing a composite binder composition:

[0118] The difference between this comparative example and Example 1 is that an equal weight of polyurethane is used instead of HSBR, and is mixed with the modified tamarind polysaccharide in Example 1 to prepare a binder composition with the same solid content as in Example 1.

[0119] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0120] Comparative Example 3

[0121] A method for preparing a composite binder composition:

[0122] The difference between this comparative example and Example 1 is that the weight ratio of the modified tamarind polysaccharide and HSBR in the obtained composite binder composition is changed to 5:1.

[0123] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0124] Comparative Example 4

[0125] A method for preparing a composite adhesive composition:

[0126] The only difference between this comparative example and Example 1 is that the weight ratio of the modified tamarind polysaccharide and HSBR in the obtained composite adhesive composition is changed to 1:2.

[0127] A method for preparing a silicon negative electrode active layer: consistent with Example 1.

[0128] Test Method

[0129] Mechanical properties of electrode sheet: tested according to GB / T 528-2012.

[0130] Battery sample preparation and performance test: A lithium sheet was used as the positive electrode, the electrode sheet containing the negative electrode active layer obtained in each embodiment and comparative example was used as the negative electrode, and 1M LiPF6+EC / DEC (1:1) v / v+10wt% FEC was used as the electrolyte to assemble a water-based lithium-ion battery sample with a capacity of 3800mAh / g. At 100mA·g -1 The battery samples were tested at a charge and discharge current density of 1.5 g, and the full charge electrode expansion rate (%), first charge specific capacity (mAh·g -1 ) and the 300th charge capacity (mAh g -1 ). Among them, the lower the fully charged electrode expansion rate, the smaller the volume change experienced by the active material inside the electrode when the battery is fully charged, and the higher the cycle stability of the corresponding battery sample.

[0131] The above test results are shown in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] From the above description, it can be seen that the above-mentioned embodiment of the present invention realizes the preparation of a composite adhesive composition with excellent performance. The obtained composite adhesive composition includes a rigid binder, namely modified tamarind polysaccharide, and an elastic binder, namely a rubber polymer, which synergistically form a composition system. The obtained composite adhesive composition is used as a binder to prepare an active material layer, and then an electrode sheet is obtained, and finally a battery sample is prepared. Because the composite adhesive composition can form a soft and hard elastic-plastic support layer with a three-dimensional interpenetrating structure in the active material layer, it can effectively improve the mechanical properties of the electrode sheet, as well as the energy density and cycle stability of the aqueous lithium-ion battery sample.

[0136] Among them, for each embodiment, specifically: by comparing Examples 4 and 5 with Examples 1 to 3, it can be seen that the preferred weight ratio of the modified monomer to the tamarind polysaccharide is (2 to 4): 7, which can improve the rigidity and toughness of the obtained modified tamarind polysaccharide, and then provide stronger mechanical support in the subsequent process of preparing the active material layer as a binder component, thereby improving the overall structural stability of the final electrode sheet.

[0137] Further comparison of Examples 2 and 3 with Example 1 shows that when a substantially identical preparation method is employed, the preferred weight ratio of the modified monomer to the tamarind polysaccharide is (3-4):7, which enables a tighter bonding of the modified tamarind polysaccharide and the rubber-like polymer, forming a more stable three-dimensional network structure during the subsequent in situ polymerization process (i.e., the various physical and chemical properties of the modified tamarind polysaccharide are more effectively improved), thereby significantly enhancing the cycle stability of the high-load electrode.

[0138] By comparing Examples 6 and 7 with Example 1, it can be seen that the conditions of the first stirring and the second stirring in step S2 are preferred, which are conducive to the formation of a modified tamarind polysaccharide with a more complete and stable structure, while also improving the reaction efficiency and product purity of the process of obtaining the modified tamarind polysaccharide, further improving the performance stability of the composite binder.

[0139] By comparing Example 8 with Example 1, it can be seen that the preferred rubber polymer is hydrogenated styrene butadiene rubber, and the degree of hydrogenation of the hydrogenated styrene butadiene rubber is 90±5%, which can maintain more stable performance during the battery cycle, thereby better maintaining the structural integrity and electrochemical properties of the electrode and the lithium-ion battery.

[0140] By comparing Examples 9 and 10 with Example 1, it can be seen that by optimizing the third stirring conditions, the resulting binder composition can be further improved in terms of adaptability and resistance to the expansion of the electrode material when used as a binder for the active material layer, thereby ultimately improving the various performances of the aqueous lithium-ion battery system.

[0141] By comparing examples 11 and 12 with example 1, it can be seen that the solid content (i.e. the total content of modified tamarind polysaccharide and HSBR) of the composite adhesive composition is preferably 3wt% to 10wt%, which can better play the rigid / flexible characteristics of the modified tamarind polysaccharide and the rubber polymer, form a more active material layer with better adhesion and elasticity after subsequent polymerization, and further improve the overall performance of the battery.

[0142] It should be noted that the terms "first", "second", and the like in the description and claims of the application are used for distinguishing between similar objects and do not necessarily have to follow an ordinal or chronological sequence. The terms are used interchangeably and are not used to denote any sequence or chronology unless specified otherwise.

[0143] The preferred embodiments of the application described above are intended to be illustrative only and the application is not limited to the embodiments described. Numerous modifications and variations are possible in light of the above teachings without departing from the scope of the application. The scope of the application is defined by the claims.

Claims

1. A composite binder composition comprising water and solid organic matter dispersed in the water, characterized in that: The solid organic matter includes modified tamarind polysaccharide and a rubber-like polymer, and the weight ratio of the modified tamarind polysaccharide to the rubber-like polymer is (1-3):

1.

2. The composite adhesive composition according to claim 1, characterized in that The glass transition temperature of the modified tamarind polysaccharide is 140° C. to 200° C.; and / or the glass transition temperature of the rubber-like polymer is -20° C. to -25° C.

3. The composite adhesive composition according to claim 1 or 2, characterized in that The modified tamarind polysaccharide is acrylic acid-modified tamarind polysaccharide, and the modified tamarind polysaccharide contains acryloyloxy groups in its structure; based on the total weight of the modified tamarind polysaccharide as 100%, the content of the acryloyloxy groups is 30% to 50%, preferably 40% to 50%; And / or, the rubber polymer is selected from one or more of styrene-butadiene rubber, hydrogenated styrene-butadiene rubber, nitrile rubber and polyurethane rubber.

4. The composite adhesive composition according to any one of claims 1 to 3, characterized in that The solid content of the composite adhesive composition is 3 wt% to 10 wt%.

5. A method for preparing the composite adhesive composition according to any one of claims 1 to 4, characterized in that: include: Step S1, preparing tamarind polysaccharide and water to form a tamarind polysaccharide solution, and adding a modified monomer to the tamarind polysaccharide solution to obtain a mixed solution; Step S2, the mixed solution is sequentially stirred by a first stirring step and a second stirring step to obtain a mixed slurry, wherein the mixed slurry includes the modified tamarind polysaccharide; Step S3, adding the rubber polymer to the mixed slurry, and obtaining the composite adhesive composition after a third stirring.

6. The method for preparing the composite adhesive composition according to claim 5, wherein: In step S1, the modified monomer is acrylic acid and / or acrylic acid salt, and the weight ratio of the modified monomer to the tamarind polysaccharide is (2-4):7; Preferably, the weight ratio of the modified monomer to the tamarind polysaccharide is (3-4):

7.

7. The method for preparing the composite adhesive composition according to claim 5 or 6, characterized in that: In step S2, the first stirring speed is 80±20 rpm, and the time is 30 min to 60 min; the second stirring time is 10 h to 20 h, and the second stirring is performed at 60° C. to 90° C.; And / or, in step S3, the third stirring is performed at a rotation speed of 80±20 rpm, a time of 30±5 min, and a temperature of 25±2°C.

8. A use of the composite binder composition according to any one of claims 1 to 4 as a binder in the field of aqueous lithium-ion batteries to prepare an active material layer, wherein the active material layer is a positive electrode active material layer and / or a negative electrode active material layer, characterized in that: mixing the composite binder composition according to any one of claims 1 to 4 with a conductive agent, an active material, and oxalic acid to obtain an active material slurry; The active material slurry is sequentially coated and in-situ polymerized to obtain the active material layer.

9. The use according to claim 8, characterized in that The weight ratio of the composite binder composition, the conductive agent and the active material is 1:1:(3-4); Based on the total weight of the composite adhesive composition being 100%, the added amount of the oxalic acid is 5% to 10%.

10. The use according to claim 8 or 9, characterized in that: The in-situ polymerization is achieved by heating the coated current collector, and the heating temperature is 140° C. to 150° C., and the heating time is 0.8 h to 1 h.

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