Composite binder, method for preparing the same, negative electrode slurry, negative electrode, and battery

Abstract

The application relates to the technical field of battery materials, and discloses a composite binder, a preparation method thereof, negative electrode slurry, a negative electrode and a battery. The preparation method of the composite binder comprises the following steps: mixing sodium carboxymethyl cellulose, hyperbranched polyether amine, a catalyst and water, and making the sodium carboxymethyl cellulose and the hyperbranched polyether amine carry out an amidation reaction under the action of the catalyst to condense amino groups and carboxyl groups to form a semi-interpenetrating network structure polymer, to obtain a glue solution, and removing or not removing water in the glue solution to obtain the composite binder; the mass ratio of the sodium carboxymethyl cellulose and the hyperbranched polyether amine is 70-95:5-30; the hyperbranched polyether amine has a molecular weight of 500-5000, a molecular branching degree of greater than or equal to 0.4, and an amino group density of greater than or equal to 3 mmol / g. The composite binder prepared by the preparation method can improve the defects of a hard carbon negative electrode bonding system, such as insufficient peeling strength, easy material dropping in cycles and high interface impedance.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to composite binders and their preparation methods, negative electrode slurry, negative electrode, and battery. Background Technology

[0002] Hard carbon, with its disordered carbon layer structure, large interlayer spacing, abundant sodium storage sites, and low sodium intercalation potential, is currently the most commercially promising anode material for sodium-ion batteries. Among various hard carbon precursors, biomass raw materials (such as coconut shells, straw, rice husks, and nut shells) have become the mainstream choice for industrial hard carbon due to their wide availability, low cost, and high renewability.

[0003] Currently, the industrial production of hard carbon anodes commonly employs a water-based binder system of sodium carboxymethyl cellulose (CMC) combined with styrene-butadiene rubber (SBR). While this system is inexpensive and has good slurry processability, it exhibits two layers of peel strength defects when applied to biomass hard carbon: Inherent defects: The surface of biomass hard carbon has few polar sites, and CMC can only be anchored to it by forming sparse hydrogen bonds with a limited number of hydroxyl or carboxyl groups. This results in a low initial peeling force, which is much lower than that of artificial graphite anodes. The low initial peeling force makes the electrode prone to edge powdering and coating microcracks during subsequent rolling, slitting and battery assembly processes.

[0004] Further exacerbation occurs later: During charging and discharging, the hard carbon undergoes volume deformation, and the cyclic stress continues to act on the already weak bonding interface, further leading to the debonding of particles from the current collector, the shedding of active materials, and the cracking of the electrode, ultimately causing rapid capacity decay and a significant reduction in cycle life.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a composite binder and its preparation method, a negative electrode slurry, a negative electrode, and a battery. It aims to improve the shortcomings of hard carbon negative electrode bonding systems, such as insufficient peel strength, easy material shedding during cycling, and high interfacial impedance. This invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a composite adhesive, comprising: Sodium carboxymethyl cellulose, hyperbranched polyetheramine, catalyst and water are mixed. Under the action of the catalyst, the sodium carboxymethyl cellulose and the hyperbranched polyetheramine undergo an amidation reaction, and the amino and carboxyl groups condense to form a polymer with a semi-interpenetrating network structure to obtain a glue solution. The water in the glue solution is removed or not removed to obtain the composite adhesive. The mass ratio of sodium carboxymethyl cellulose to hyperbranched polyetheramine is 70~95:5~30; The hyperbranched polyetheramine has a number-average molecular weight of 500-5000, a degree of molecular branching ≥0.4, and an amino density ≥3 mmol / g; The mass ratio of the catalyst to the sodium carboxymethyl cellulose is 5~25:100.

[0007] In an optional embodiment, the mass ratio of water to sodium carboxymethyl cellulose is 50 to 200:1.

[0008] In an optional embodiment, the catalyst is selected from at least one of EDC•HCl and NHS.

[0009] In an optional embodiment, the catalyst comprises EDC·HCl and NHS, with the molar ratio of NHS to EDC·HCl being 1 to 1.2:1.

[0010] In an optional embodiment, the method of mixing sodium carboxymethyl cellulose, hyperbranched polyetheramine, catalyst, and water includes: Sodium carboxymethyl cellulose is dissolved in water and completely swollen to obtain a CMC solution; Hyperbranched polyetheramine was added to the CMC solution and stirred until homogeneous. Then, a catalyst was added, and after the reaction was complete, a composite binder was obtained.

[0011] Secondly, the present invention provides a composite adhesive prepared by any of the preparation methods described in the foregoing embodiments.

[0012] Thirdly, the present invention provides a negative electrode slurry comprising a composite binder as described in the foregoing embodiments and a negative electrode active material, wherein the negative electrode active material comprises hard carbon.

[0013] In optional embodiments, the material includes a negative electrode active material, a conductive agent, a composite binder, and water. The components, on a dry weight basis and by weight percentage, are: 92-96 parts of negative electrode active material, 2-4 parts of conductive agent, and 2-4 parts of composite binder. Optionally, the solid content of the negative electrode slurry is 45-50%.

[0014] In an optional embodiment, the negative electrode active material is hard carbon; and / or, the conductive agent is selected from at least one of carbon black, carbon nanotubes, and graphene.

[0015] Fourthly, the present invention provides a negative electrode, comprising a current collector and a negative electrode active layer loaded on the surface of the current collector, wherein the negative electrode active layer comprises a composite binder as described in the foregoing embodiments.

[0016] Fifthly, the present invention provides a battery comprising a negative electrode as described in the foregoing embodiments.

[0017] The present invention has the following beneficial effects: In summary, the method for preparing the composite binder provided by this invention, through partial condensation of sodium carboxymethyl cellulose (CMC) and hyperbranched polyetheramine (HPEA), can obtain a polymer with a semi-interpenetrating network structure. This significantly enhances the cohesive strength and anti-swelling ability of the binder layer and more effectively disperses mechanical stress throughout the entire three-dimensional network, avoiding localized bond failure. Furthermore, the stable three-dimensional network structure can suppress disordered growth of the SEI film, improve the initial coulombic efficiency, and the network framework effectively buffers volume changes, maintaining electrode structural integrity and improving cycle life. The ether bonds of HPEA provide additional sodium ion transport channels, reducing charge transfer impedance and improving rate performance. The method requires no organic solvents, has a mild pre-crosslinking step, requires no modification to existing coating equipment, uses a low amount of catalyst, has minimal impact on cost, and is easy to industrialize. Therefore, the composite binder prepared in the embodiments of this invention, when applied to the negative electrode of a battery, can effectively improve the electrochemical performance of the battery. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0020] Based on the existing problems with hard carbon anodes, the inventors considered the following: If linear polymer binders such as modified polyvinyl alcohol, polyethylene oxide, and sodium alginate are used, or modified with hyperbranched polyethyleneimine and linear polyetheramine, the following issues arise: linear polymers have fewer anchoring sites and poor stress dispersion; hyperbranched polyethyleneimine lacks flexible ether bonds, resulting in insufficient deformation buffering and ion conduction capacity; and conventional linear polyetheramines have limited effective anchoring sites. None of these methods can simultaneously improve the inertia of the biomass hard carbon interface and resist structural damage caused by cyclic deformation.

[0021] Therefore, the following technical solution of the present invention is proposed: This invention provides a method for preparing a composite adhesive, comprising: Sodium carboxymethyl cellulose, hyperbranched polyetheramine, catalyst and water are mixed. Under the action of the catalyst, the sodium carboxymethyl cellulose and the hyperbranched polyetheramine undergo an amidation reaction, and the amino and carboxyl groups condense to form a polymer with a semi-interpenetrating network structure to obtain a glue solution. The water in the glue solution is removed or not removed to obtain the composite adhesive. The mass ratio of sodium carboxymethyl cellulose to hyperbranched polyetheramine is 70~95:5~30; The hyperbranched polyetheramine has a number-average molecular weight of 500-5000, a degree of molecular branching ≥0.4, and an amino density ≥3 mmol / g; The mass ratio of the catalyst to the sodium carboxymethyl cellulose is 5~25:100.

[0022] The method for preparing the composite binder provided in this invention uses sodium carboxymethyl cellulose (CMC) as a linear polymer framework to provide basic film-forming properties and slurry rheology adjustment capabilities. Under the condition of a suitable amount of catalyst, some terminal amino groups of hyperbranched polyetheramine (HPEA) partially condense with the carboxyl groups of the CMC side chains, forming covalent cross-linking points. The unreacted amino groups remain in a free state and can form multiple hydrogen bonds with the polar groups (-OH, -COOH) on the surface of the hard carbon negative electrode active material and the current collector. The flexible ether bonds in the HPEA molecular framework buffer volume deformation and dissipate stress, while the ether oxygen atoms coordinate with sodium ions to construct auxiliary ion transport channels.

[0023] Compared to existing binder systems, the semi-interpenetrating network structure significantly enhances the cohesive strength and anti-swelling ability of the binder layer, and can more effectively disperse mechanical stress throughout the three-dimensional network, avoiding localized bond failure. The stable three-dimensional network structure can suppress the disordered growth of the SEI film, improve the initial coulombic efficiency, and the network skeleton effectively buffers volume changes, maintains the integrity of the electrode structure, and improves cycle life. The ether bonds of HPEA provide additional sodium ion transport channels, reduce charge transfer impedance, and improve rate performance. No organic solvents are required, the pre-crosslinking step is mild, no modification to existing coating equipment is needed, the amount of added catalyst is low, the impact on cost is minimal, and it is easy to industrialize. Therefore, the composite binder prepared in this embodiment can effectively improve the electrochemical performance of the battery when applied to the negative electrode.

[0024] It should be noted that the mass ratio of sodium carboxymethyl cellulose and hyperbranched polyetheramine should be within the range required by this invention. If the proportion of sodium carboxymethyl cellulose is too high, the electrode will become brittle. If the proportion of sodium carboxymethyl cellulose is too low, the bonding effect of the composite adhesive will be poor.

[0025] It should be noted that the selected hyperbranched polyetheramine has a molecular weight of 500-5000. This is because a molecular weight below 500 results in insufficient terminal amino groups and excessively short ether chain segments, limiting its deformation buffering capacity; while a molecular weight above 5000 leads to decreased water solubility, excessively high viscosity of the adhesive, and difficulty in controlling the crosslinking reaction. A molecular branching degree ≥0.4 is required because a branching degree below 0.4 results in a near-linear molecular structure, making it impossible to achieve the synergistic effect of three-dimensional multi-point anchoring. An amino group density ≥3 mmol / g is also required because an excessively low amino group density results in insufficient anchoring sites, making it difficult to simultaneously meet the dual requirements of crosslinking reaction and hydrogen bond anchoring.

[0026] Optionally, products meeting the requirements of hyperbranched polyetheramines with a molecular weight of 500-5000, a degree of branching ≥0.4, and an amino density ≥3mmol / g can be obtained through custom synthesis or by ordering from professional hyperbranched polymer R&D and manufacturing companies, such as Wuhan Hyperbranched Resin Technology Co., Ltd. and Weihai Chenyuan Molecular New Materials Co., Ltd. In addition, Xi'an Ruixi Biotechnology Co., Ltd. and Xi'an Qiyue Biotechnology Co., Ltd. also provide hyperbranched polyetheramine research reagents, whose parameters can be customized according to requirements.

[0027] Optionally, in some embodiments of the present invention, the number-average molecular weight of the hyperbranched polyetheramine is about 1800 to 3800, the degree of molecular branching is about 0.45 to 0.62, and the amino density is about 3.5 to 5.2 mmol / g.

[0028] Specifically, the preparation method of the composite adhesive is as follows: First, dissolve sodium carboxymethyl cellulose in water and stir at room temperature for 2-4 hours until it is completely swollen to obtain a CMC solution. Then, add HPEA to the CMC solution and stir until well mixed; Then, add the catalyst; After the materials are added, stir and react at 25~40℃ for 0.5~2 hours to obtain the composite adhesive.

[0029] During the reaction, carboxyl groups are activated under the action of a catalyst. As the reaction proceeds, the pH slowly rises, and the activated carboxyl groups undergo partial amidation crosslinking with the amino groups of HPEA, forming a composite adhesive with a semi-interpenetrating network structure. The degree of reaction is controlled by the amount of catalyst added. When the mass ratio of sodium carboxymethyl cellulose to hyperbranched polyetheramine is 70-95:5-30 and the mass ratio of catalyst to sodium carboxymethyl cellulose is 5-25:100, approximately 5-30% of the amino groups in HPEA can participate in crosslinking, while the remaining amino groups are retained for subsequent anchoring. Optionally, the mass ratio of water to sodium carboxymethyl cellulose is 50-200:1.

[0030] Optionally, the catalyst is selected from at least one of EDC•HCl (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride) and NHS (N-hydroxysuccinimide).

[0031] Preferably, the catalyst comprises EDC·HCl and NHS, with a molar ratio of NHS to EDC·HCl of 1 to 1.2:1 (e.g., 1:1, 1.1:1, or 1.2:1). During the reaction, the weak acidity of EDC·HCl causes the pH of the system to spontaneously decrease to 5.0 to 6.5, thereby activating the carboxyl groups. The combined use of NHS and EDC·HCl can further stabilize the activated intermediate and improve the efficiency of the amidation reaction.

[0032] Optionally, after obtaining the composite binder, the water can be removed or left unremoved. The composite binder without water removal is in a liquid state and can usually be applied directly to the negative electrode slurry without removal.

[0033] The composite binder provided in this invention is prepared using the method described in this invention. When applied to the negative electrode of a battery, this composite binder can improve the electrochemical performance of the battery.

[0034] The negative electrode slurry provided in this embodiment of the invention includes a composite binder and a negative electrode active material as provided in this embodiment of the invention, wherein the negative electrode active material includes hard carbon.

[0035] Furthermore, the negative electrode slurry includes a negative electrode active material, a conductive agent, a composite binder, and water. The components, on a dry weight basis and by weight percentage, are: 92-96 parts of negative electrode active material, 2-4 parts of conductive agent, and 2-4 parts of composite binder.

[0036] Optionally, to ensure better processing performance of the negative electrode slurry, the solid content of the negative electrode slurry is 45-50%.

[0037] Optionally, the negative electrode active material is hard carbon; and / or, the conductive agent is selected from at least one of carbon black, carbon nanotubes and graphene.

[0038] The negative electrode provided in this embodiment of the invention includes a current collector and a negative electrode active layer loaded on the surface of the current collector, wherein the negative electrode active layer includes the composite binder provided in this embodiment of the invention.

[0039] Specifically, the preparation method of the negative electrode includes: A negative electrode active material and a conductive agent are added to the composite binder in a liquid state, and the mixture is stirred in a high-speed mixer to obtain a uniform, agglomerated negative electrode slurry. In this step, water may or may not be added to ensure that the solid content of the obtained negative electrode slurry is 45-50%.

[0040] After obtaining the negative electrode slurry, it is uniformly coated on the surface of the negative electrode current collector with a coating density of 120-150 g / m². During the drying process, the pre-crosslinked network is further cured, and at the same time, the unreacted amino groups form hydrogen bonds with the hard carbon and foil surface, ensuring high bonding stability between the formed negative electrode active layer and the negative electrode current collector.

[0041] The battery provided in this embodiment of the invention includes a negative electrode provided in this embodiment. Because the battery includes the negative electrode provided in this invention, it exhibits excellent electrochemical performance.

[0042] Example 1 Sodium carboxymethyl cellulose was dissolved in deionized water and stirred at room temperature for 3 hours to obtain a CMC solution. The mass ratio of sodium carboxymethyl cellulose to deionized water was 1:100. Then, hyperbranched polyetheramine (hPEA-yne, an alkynyl-terminated hyperbranched polyetheramine from Xi'an Ruixi Biotechnology Co., Ltd., which, according to batch testing in this example, has a number-average molecular weight of approximately 2500, a molecular branching degree of approximately 0.51, and an amino density of approximately 4.8 mmol / g) was added to the CMC solution at a mass ratio of 80:20, and the mixture was stirred until homogeneous. Subsequently, EDC·HCl solid powder was added, with the mass ratio of EDC·HCl to sodium carboxymethyl cellulose being 15:100. After the addition was complete, the mixture was stirred and reacted at 25°C for 1 hour to obtain the adhesive solution (composite adhesive).

[0043] Hard carbon powder (D50 of 4.5μm) and conductive agent (carbon black Super P) were added to the adhesive solution in sequence, and deionized water was added to adjust the solid content of the slurry to 48%. The mixture was stirred at 4500 rpm for 90 min to obtain a uniformly dispersed negative electrode slurry. By weight, the adhesive solution (dry weight, i.e., the weight of the adhesive solution excluding water) was 3 parts, the hard carbon powder was 94 parts, and the conductive agent was 3 parts.

[0044] The slurry is evenly coated on the surface of copper foil with a coating density of 130 g / m², and then rolled and dried to obtain the negative electrode sheet.

[0045] Example 2 Sodium carboxymethyl cellulose was dissolved in deionized water and stirred at room temperature for 2 hours to obtain a CMC solution. The mass ratio of sodium carboxymethyl cellulose to deionized water was 1:200. Then, hyperbranched polyetheramine (hPEA-yne, an alkynyl-terminated hyperbranched polyetheramine from Xi'an Ruixi Biotechnology Co., Ltd., with a number-average molecular weight of approximately 3800, a degree of molecular branching of approximately 0.62, and an amino density of approximately 5.2 mmol / g, as determined by batch testing in this example) was added to the CMC solution at a mass ratio of 70:30, and the mixture was stirred until homogeneous. Subsequently, EDC•HCl solid powder was added, with a mass ratio of EDC•HCl to sodium carboxymethyl cellulose of 5:100. After the addition was complete, the mixture was stirred and reacted at 25°C for 1 hour to obtain the adhesive solution (composite binder).

[0046] Hard carbon powder (D50 of 5.0 μm) and conductive agent (carbon nanotubes CNT) were added to the adhesive solution in sequence, and deionized water was added to adjust the solid content of the slurry to 45%. The mixture was stirred at 4500 rpm for 90 min to obtain a uniformly dispersed negative electrode slurry. By weight, the adhesive solution (dry weight, i.e., the weight of the adhesive solution excluding water) was 4 parts, the hard carbon powder was 92 parts, and the conductive agent was 4 parts.

[0047] The slurry is evenly coated on the surface of copper foil with a coating density of 130 g / m², and then rolled and dried to obtain the negative electrode sheet.

[0048] Example 3 Sodium carboxymethyl cellulose was dissolved in deionized water and stirred at room temperature for 4 hours to obtain a CMC solution. The mass ratio of sodium carboxymethyl cellulose to deionized water was 1:50. Then, hyperbranched polyetheramine (Akoli's customized hyperbranched polyetheramine product, with a measured number-average molecular weight of approximately 1800, a molecular branching degree of approximately 0.45, and an amino density of approximately 3.5 mmol / g) was added to the CMC solution at a mass ratio of 95:5, and the mixture was stirred until homogeneous. Subsequently, EDC•HCl solid powder was added, with the mass ratio of EDC•HCl to sodium carboxymethyl cellulose being 25:100. After the addition was complete, the mixture was stirred and reacted at 25°C for 1 hour to obtain the adhesive solution (composite adhesive).

[0049] Hard carbon powder (D50 of 4.8 μm) and conductive agent (graphene) were added to the adhesive solution in sequence, and deionized water was added to adjust the solid content of the slurry to 50%. The mixture was stirred at 4500 rpm for 90 min to obtain a uniformly dispersed negative electrode slurry. By weight, the adhesive solution (dry weight, i.e., the weight of the adhesive solution excluding water) was 2 parts, the hard carbon powder was 96 parts, and the conductive agent was 2 parts.

[0050] The slurry is evenly coated on the surface of copper foil with a coating density of 130 g / m², and then rolled and dried to obtain the negative electrode sheet.

[0051] Comparative Example 1 Sodium carboxymethyl cellulose (CMC) was mixed with deionized water and stirred at room temperature for 3 hours to obtain a gel solution. Hard carbon powder (D50 of 4.5 μm) and conductive agent (carbon black Super P) were added sequentially to the CMC solution. The mixture was stirred at 4500 rpm for 90 min, and then styrene-butadiene rubber (SBR emulsion) was added to obtain a uniformly dispersed negative electrode slurry. The mass ratio of CMC to SBR dry powder was 1:2, which is calculated by weight as follows: 3 parts of the slurry excluding water, 95 parts of the hard carbon powder, and 2 parts of the conductive agent. A negative electrode slurry with the same solid content as in Example 1 was obtained.

[0052] The slurry is evenly coated on the surface of copper foil with a coating density of 130 g / m², and then rolled and dried to obtain the negative electrode sheet.

[0053] Comparative Example 2 This comparative example is basically the same as Example 1, except that: too much hyperbranched polyetheramine was added, and the mass ratio of CMC to hyperbranched polyetheramine was 60:40.

[0054] Comparative Example 3 This comparative example is basically the same as Example 1, except that the molecular weight of the hyperbranched polyetheramine used is too large, about 6000.

[0055] Comparative Example 4 This comparative example is basically the same as Example 1, except that the molecular branching of the polyetheramine used is too small, about 0.3.

[0056] Comparative Example 5 This comparative example is basically the same as Example 1, except that the amino density of the hyperbranched polyetheramine used is too small, about 2 mmol / g.

[0057] Comparative Example 6 This embodiment is basically the same as Embodiment 1, except that EDC•HCl solid powder was not added.

[0058] Experimental Example (1) Measure the bonding stability of the active layer of each negative electrode.

[0059] Peel strength test: The negative electrode sheets prepared in each embodiment and comparative example were cut into samples with a width of 20 mm and a length of 100 mm. The peel strength was tested by using a universal tensile testing machine with a peel speed of 50 mm / min using the 180° peel method. The average peel strength was recorded.

[0060] Record the test results in Table 1.

[0061] (2) Assemble the negative electrode sheets prepared in each embodiment and comparative example into a button cell and measure its electrochemical performance.

[0062] The assembly method of the button cell is as follows: the negative electrode sheets prepared in each embodiment and comparative example are punched into circular sheets with a diameter of 12mm, NFPP is used as the positive electrode, glass fiber membrane is used as the separator, 1M NaPF6 is dissolved in EC / DEC (volume ratio 1:1) as the electrolyte, and CR2032 button cells are assembled in an argon glove box.

[0063] Electrochemical performance was tested using the Blue Battery Testing System: First Coulomb efficiency: The ratio of the first charge specific capacity to the first discharge specific capacity was recorded when the first charge and discharge cycle was performed at a current density of 0.05C. Cyclic performance: 100 charge-discharge cycles were performed at a current density of 0.5C / 0.5C, and the capacity retention rate was recorded on the 100th cycle. Rate performance: Charged at current densities of 0.5C, 1C, 2C and 4C respectively, and the charging specific capacity at each rate was recorded.

[0064] Record the test results in Table 1.

[0065] Table 1 Test results for each embodiment and comparative example

[0066] As can be seen from Table 1, the active layer of the negative electrode sheet prepared in each embodiment of the present invention has better bonding stability, which is significantly better than that of the negative electrode sheet prepared by conventional binder (CMC); the electrochemical performance of the battery prepared in each embodiment of the present invention is also better, which is significantly better than that of the battery prepared by conventional binder (Comparative Example 1).

[0067] Comparing Comparative Example 2 with Example 1, Comparative Example 2 showed significantly worse peel strength and cycle capacity retention. This indicates that excessive addition of hyperbranched polyetheramine leads to an excess of amino groups in the crosslinking reaction. The excess HPEA failed to effectively participate in network construction. Instead, the excessive molecular chain entanglement and plasticizing effect weakened the cohesive strength of the adhesive layer. At the same time, the hydrogen bond anchoring sites of free amino groups and hard carbon surface tended to be saturated, making it impossible to further improve the bonding strength. Comparing Comparative Example 3 with Example 1, Comparative Example 3 showed significantly worse peel strength and cycle capacity retention. This indicates that the excessively large molecular weight of the hyperbranched polyetheramine used leads to decreased water solubility and excessively high adhesive viscosity. The penetration and uniform dispersion of HPEA molecular chains in the CMC network are hindered, the crosslinking reaction efficiency is reduced, and excessive ether chain segments may introduce additional free volume, weakening the compactness of the adhesive layer. As a result, the peel strength and electrochemical performance of the negative electrode sheet both decrease. Comparing Comparative Example 4 with Example 1, Comparative Example 4 showed significantly worse peel strength and cycle capacity retention. This indicates that when the branching of the polyetheramine used was too small, the molecular structure tended to be linear or slightly branched, and the terminal amino groups were distributed in one or two dimensions in space. It could not form a three-dimensional multi-point synergistic anchoring effect, and its ability to bond with hard carbon surfaces and current collectors was limited. Its peel strength was significantly lower than that of Example 1. Comparing Comparative Example 5 with Example 1, Comparative Example 5 showed significantly worse peel strength and cycle capacity retention. This indicates that when the amino density of the hyperbranched polyetheramine used is too small, there are insufficient active sites for anchoring and crosslinking in the polymer per unit mass. Even if some amino groups participate in amidation crosslinking, the number of amino groups remaining that can be used for hydrogen bond anchoring is limited, making it impossible to form a dense multi-point anchoring network on the hard carbon surface. This results in a significant decrease in both peel strength and cycle stability. Comparing Comparative Example 6 with Example 1, the peel strength and cycle capacity retention of Comparative Example 6 were significantly lower than those of Example 1. This indicates that the addition of EDC·HCl catalyst during the preparation of the composite adhesive can effectively promote the amidation crosslinking reaction of CMC and HPEA, forming a semi-interpenetrating network structure, and significantly improving the cohesive strength and cycle stability of the adhesive layer.

[0068] In summary, the method for preparing the composite binder provided by this invention, through partial condensation of sodium carboxymethyl cellulose (CMC) and hyperbranched polyetheramine (HPEA), can obtain a polymer with a semi-interpenetrating network structure. This significantly enhances the cohesive strength and anti-swelling ability of the binder layer and more effectively disperses mechanical stress throughout the entire three-dimensional network, avoiding localized bond failure. Therefore, the composite binder prepared by this invention, when applied to the negative electrode of a battery, can effectively improve the electrochemical performance of the battery.

[0069] Compared with the prior art, the present invention has the following advantages: 1. Significantly improved peel strength: The semi-interpenetrating network structure combined with the multi-point anchoring effect of HPEA improves the bonding force between the electrode and the current collector compared to the traditional CMC / SBR system.

[0070] 2. Enhanced electrochemical stability: The stable three-dimensional network structure can suppress the disordered growth of the SEI film and improve the initial coulombic efficiency. At the same time, the network framework effectively buffers volume changes, maintains the integrity of the electrode structure, and improves cycle life.

[0071] 3. Reduced interface impedance: HPEA's ether bonds provide additional sodium ion transport channels, reducing charge transfer impedance and improving rate performance.

[0072] 4. Strong process compatibility: No organic solvents are required, the pre-crosslinking step is mild, no modification to existing coating equipment is required, the amount of added catalyst is low, the impact on cost is small, and it is easy to industrialize.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a composite adhesive, characterized in that, include: Sodium carboxymethyl cellulose, hyperbranched polyetheramine, catalyst and water are mixed. Under the action of the catalyst, the sodium carboxymethyl cellulose and the hyperbranched polyetheramine undergo an amidation reaction, and the amino and carboxyl groups condense to form a polymer with a semi-interpenetrating network structure to obtain a glue solution. The water in the glue solution is removed or not removed to obtain the composite adhesive. The mass ratio of sodium carboxymethyl cellulose to hyperbranched polyetheramine is 70~95:5~30; The hyperbranched polyetheramine has a number-average molecular weight of 500-5000, a degree of molecular branching ≥0.4, and an amino density ≥3 mmol / g; The mass ratio of the catalyst to the sodium carboxymethyl cellulose is 5~25:

100.

2. The preparation method according to claim 1, characterized in that, The mass ratio of water to sodium carboxymethyl cellulose is 50~200:

1.

3. The preparation method according to claim 1, characterized in that, The catalyst is selected from at least one of EDC·HCl and NHS; Preferably, the catalyst comprises EDC·HCl and NHS, with the molar ratio of NHS to EDC·HCl being 1 to 1.2:

1.

4. The preparation method according to claim 1, characterized in that, Methods of mixing sodium carboxymethyl cellulose, hyperbranched polyetheramine, catalyst, and water include: The sodium carboxymethyl cellulose was dissolved in the water and completely swollen to obtain a CMC solution. The hyperbranched polyetheramine was added to the CMC solution and stirred until homogeneous. Then the catalyst was added, and after sufficient reaction, the composite binder was obtained.

5. A composite adhesive, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 4.

6. A negative electrode slurry, characterized in that, It includes the composite binder and negative electrode active material as described in claim 5, wherein the negative electrode active material includes hard carbon.

7. The negative electrode slurry according to claim 6, characterized in that, It includes a negative electrode active material, a conductive agent, the composite binder, and water; The components, on a dry weight basis and by weight percentage, are: 92-96 parts of the negative electrode active material, 2-4 parts of the conductive agent, and 2-4 parts of the composite binder; the negative electrode active material includes hard carbon. Optionally, the solid content of the negative electrode slurry is 45-50%.

8. The negative electrode slurry according to claim 7, characterized in that, The negative electrode active material is hard carbon; And / or, the conductive agent is selected from at least one of carbon black, carbon nanotubes and graphene.

9. A negative electrode, characterized in that, It includes a current collector and a negative electrode active layer loaded on the surface of the current collector, wherein the negative electrode active layer includes the composite binder as described in claim 5.

10. A battery, characterized in that, Includes the negative electrode as described in claim 9.

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