Carbamate structural unit-containing sodium carboxymethyl cellulose derivative aqueous binder and preparation method and application thereof

Abstract

The invention relates to the technical field of binders, in particular to a sodium carboxymethyl cellulose derivative water-based binder containing a carbamate structural unit as well as a preparation method and application of the sodium carboxymethyl cellulose derivative water-based binder. The preparation method of the sodium carboxymethyl cellulose derivative water-based binder containing the carbamate structural unit comprises the following steps: adding a cross-linking agent isocyanate monomer A and a solvent into a sodium carboxymethyl cellulose water solution, and carrying out thermal polymerization reaction at a certain temperature to obtain the water-based binder. The high-reactivity isocyanate cross-linking agent is introduced, so that the CMC is converted from a linear structure to a net structure, meanwhile, carbamate groups in the structure can form certain hydrogen bond interaction, and the mechanical property, the adhesive property, the stability and the electrochemical property of the adhesive can be effectively improved. The method can better adapt to the volume expansion of Si particles.

Description

Technical Field

[0001] The present invention relates to the technical field of binders, and particularly to an aqueous binder based on a sodium carboxymethyl cellulose derivative containing a urethane structural unit, and a preparation method and application thereof. Background Art

[0002] Silicon negative electrode materials are an important type of material in lithium-ion batteries. Compared with traditional graphite negative electrodes, silicon has a higher theoretical specific capacity. The theoretical specific capacity of silicon is as high as 3579 mAh / g, while that of graphite is 372 mAh / g. Therefore, silicon negative electrodes have the potential to provide higher energy density, thereby improving the overall performance of the battery, especially in application fields such as electric vehicles and large-scale energy storage. However, during the charge and discharge process of lithium-ion batteries, the silicon negative electrode material undergoes a huge volume change, about 300% or so. This volume expansion and contraction will cause the contact failure between the negative electrode material and the electrolyte and the electrode current collector, thereby leading to capacity decay, a decline in cycle performance, and even mechanical damage to the battery.

[0003] Related research shows that a suitable binder can not only buffer the stress during the expansion of silicon particles, but also improve the electron transfer between silicon and the current collector, achieving a more stable electrode structure. In addition, the update of the binder does not change the existing battery preparation process, its dosage proportion is extremely small and the cost is low, and it is more easily accepted by the market. Therefore, designing and developing high-performance binders that are more compatible with high specific capacity silicon-based negative electrodes has become an important topic in related fields of research. Summary of the Invention

[0004] The purpose of the present invention is to propose an aqueous binder based on a sodium carboxymethyl cellulose derivative containing a urethane structural unit, and a preparation method and application thereof, aiming at the above-mentioned deficiencies of the existing technology.

[0005] The first object of the present invention is to provide a preparation method of an aqueous binder based on a sodium carboxymethyl cellulose derivative containing a urethane structural unit. By adding a cross-linking agent isocyanate monomer A and a solvent to an aqueous solution of sodium carboxymethyl cellulose and carrying out a thermal polymerization reaction at a certain temperature, the aqueous binder can be prepared.

[0006] Further, the concentration of the aqueous solution of sodium carboxymethyl cellulose is 0.01 - 0.10 g / mL.

[0007] Further, the monomer A accounts for 1 - 10 mol% of the aqueous solution of sodium carboxymethyl cellulose.

[0008] Further, the monomer A is one or more of hexamethylene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, and dimethylbiphenyl diisocyanate.

[0009] Further, the time of the thermal polymerization reaction is 1 to 3 h, and the temperature is 70 to 90 °C.

[0010] The second object of the present invention is to provide a carboxymethyl cellulose sodium derivative-based aqueous binder containing a urethane structural unit prepared by the preparation method as described above.

[0011] The third object of the present invention is to provide a negative electrode material for a lithium-ion battery, including the carboxymethyl cellulose sodium derivative-based aqueous binder containing a urethane structural unit as described above.

[0012] The third object of the present invention is to provide a preparation method for the negative electrode material for a lithium-ion battery as described above, including the following steps: Weigh a certain mass of silicon powder and conductive additive, add them to the aqueous solution of the aqueous binder as described in claim 7, stir evenly, coat them on a copper foil, and dry to obtain a prepared electrode for standby.

[0013] Further, the particle size of the silicon powder is 60 to 100 nm; the conductive additive is one or more of acetylene black, Ketjen black, Super P, and carbon nanotubes; the mass ratio of the silicon powder, the conductive additive, and the aqueous binder is 50 to 70:30 to 20:20 to 10.

[0014] Further, the stirring time is 6 to 12 h, the drying temperature is 60 to 120 °C, and the drying time is 10 to 15 h.

[0015] The beneficial effects brought by the technical solution provided by the present invention are: 1. The present invention introduces a highly reactive isocyanate crosslinking agent to achieve the structural transformation of CMC from linear to network, and at the same time, the urethane groups in the structure can form certain hydrogen bond interactions, which can effectively improve the mechanical properties, adhesion properties, stability, and electrochemical properties of the binder. It enables better adaptation to the volume expansion of Si particles.

[0016] 2. The synthesis conditions of the preparation method of the carboxymethyl cellulose sodium derivative-based aqueous binder containing a urethane structural unit provided by the present invention are simple, and the reaction solvent is environmentally friendly and non-toxic. The binder is a modified material based on commercial carboxymethyl cellulose sodium, with low cost.

[0017] 3. The method of in-situ preparing the electrode in the present invention omits the post-treatment steps of the polymer, which is simple and convenient. Description of the Drawings

[0018] Figure 1 Comparison of the peel performance of the binders obtained in Example 1, Example 2, and Comparative Example 1; Figure 2Cyclic voltammogram of the secondary lithium battery prepared with the binder obtained in Example 1 at a scan rate of 0.05 mV; Figure 3 Battery cycle performance graph of the silicon anode lithium battery prepared with the binders obtained in Example 1 and Comparative Example 1 at a current density of 0.5C.

[0019] Figure 4 Battery cycle performance graph of the silicon-carbon anode lithium battery prepared with the binders obtained in Example 5 and Comparative Example 1 at a current density of 0.5C.

[0020] Figure 5 Battery cycle performance graph of the hard carbon anode lithium battery prepared with the binders obtained in Example 6 and Comparative Example 1 at a current density of 0.5C. Detailed implementation method

[0021] The following are specific examples of the present invention and in combination with the attached drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these examples.

[0022] The present invention provides a preparation method of a water-based covalently cross-linked polymer binder containing phosphonic acid groups, which includes the following steps: Dissolve the commercial binder sodium carboxymethylcellulose CMC in deionized water, then add an isocyanate monomer A as a cross-linking agent, and add acetone as a solvent, and carry out a cross-linking polymerization reaction at a certain temperature to obtain the covalently cross-linked network binder.

[0023] In the present invention, the concentration of sodium carboxymethylcellulose is 0.01~0.10 g / mL, preferably 0.01~0.05 g / mL, and more preferably 0.02 g / mL.

[0024] In the present invention, the monomer A is one of hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI), and dimethylbiphenyl diisocyanate (TODI). It accounts for 1~10 mol% of sodium carboxymethylcellulose, preferably 1~5 mol%, and more preferably 3 mol%.

[0025] In the present invention, the thermal polymerization time is 1~3 h, preferably 2 h; the polymerization temperature is 70~90°C, preferably 80°C.

[0026] Preparation method of silicon anode, including the following steps: Weigh a certain mass of silicon powder and conductive additive into an aqueous solution of a sodium carboxymethylcellulose derivative-based water-based binder containing a urethane structural unit, stir evenly and then coat it on a copper foil for drying to obtain a prepared electrode for standby.

[0027] In the present invention, the particle size of the silicon powder is 60 - 100 nm, more preferably 80 nm; the mass ratio of the silicon powder, the conductive additive and the aqueous binder is 50 - 70:30 - 20:20 - 10, preferably 60 - 70:20:20 - 10, and more preferably 60:20:20.

[0028] In the present invention, the stirring time is 6 - 12 h, preferably 7 - 10 h, and more preferably 8 - 9 h; the drying temperature is 60 - 120 °C, preferably 70 - 110 °C, and more preferably 80 - 100 °C; the drying time is 10 - 15 h, preferably 12 h.

[0029] Example 1 Dissolve 0.2000 g of sodium carboxymethylcellulose in 10 mL of deionized water. Separately, dissolve 0.0090 g of diphenylmethane diisocyanate in 1 mL of acetone solution and pour it into the CMC aqueous solution, where the molar ratio of sodium carboxymethylcellulose monomer to diphenylmethane diisocyanate is 100:3. Then, react the reaction system at a polymerization temperature of 80 °C for 2 h, and finally obtain an aqueous binder solution of sodium carboxymethylcellulose derivatives containing urethane structural units for standby.

[0030] The preparation method of the corresponding silicon negative electrode material for lithium-ion batteries is as follows: Take 0.1200 g of silicon powder and 0.0400 g of Super P in an aqueous solution containing 0.0400 g of aqueous binder, stir well for 8 h to obtain a uniformly dispersed slurry, then uniformly coat the slurry onto the surface of a 9-μm copper foil through a coater, dry it at 100 °C for 12 h, and finally cut it into circular electrode sheets with a radius of 7.5 mm for standby.

[0031] Example 2 Dissolve 0.2000 g of sodium carboxymethylcellulose in 10 mL of deionized water. Separately, dissolve 0.0150 g of diphenylmethane diisocyanate in 1 mL of acetone solution and pour it into the CMC aqueous solution, where the molar ratio of sodium carboxymethylcellulose monomer to diphenylmethane diisocyanate is 100:5. Then, react the reaction system at a polymerization temperature of 80 °C for 2 h, and finally obtain an aqueous binder solution of sodium carboxymethylcellulose derivatives containing urethane structural units for standby.

[0032] The preparation method of the negative electrode material for the lithium-ion battery in this case is as follows: Take 0.1200 g of silicon powder (SIC material, hard carbon material) and 0.0400 g of Super P in an aqueous solution containing 0.0400 g of the above-mentioned aqueous binder, stir well for 8 h to obtain a uniformly dispersed slurry, then uniformly coat the slurry onto the surface of a 9-μm copper foil through a coater, dry at 100 °C for 12 h, and finally cut it into circular electrode sheets with a radius of 7.5 mm for standby.

[0033] Example 3 Dissolve 0.2000 g of sodium carboxymethylcellulose in 10 mL of deionized water. Separately, dissolve 0.0090 g of dimethylbiphenyl diisocyanate in 1 mL of acetone solution and pour it into the CMC aqueous solution, where the molar ratio of sodium carboxymethylcellulose monomer to dimethylbiphenyl diisocyanate is 100:3. Then, react the reaction system at a polymerization temperature of 80 °C for 2 h, and finally obtain an aqueous binder solution of sodium carboxymethylcellulose derivatives containing urethane structural units for standby.

[0034] The preparation method of the negative electrode material of the lithium-ion battery corresponding to this case is as follows: Take 0.1200 g of silicon powder and 0.0400 g of Super P in an aqueous solution containing 0.0400 g of the above-mentioned aqueous binder, stir well for 8 h to obtain a uniformly dispersed slurry, then uniformly coat the slurry onto the surface of a 9-μm copper foil through a coater, dry at 100 °C for 12 h, and finally cut it into circular electrode sheets with a radius of 7.5 mm for standby.

[0035] Example 4 Dissolve 0.2000 g of sodium carboxymethylcellulose in 10 mL of deionized water. Separately, dissolve 0.0150 g of dimethylbiphenyl diisocyanate in 1 mL of acetone solution and pour it into the CMC aqueous solution, where the molar ratio of sodium carboxymethylcellulose monomer to dimethylbiphenyl diisocyanate is 100:5. Then, react the reaction system at a polymerization temperature of 80 °C for 2 h, and finally obtain an aqueous binder solution of sodium carboxymethylcellulose derivatives containing urethane structural units for standby.

[0036] The preparation method of the negative electrode material of the lithium-ion battery corresponding to this case is as follows: Take 0.1200 g of silicon powder and 0.0400 g of Super P in an aqueous solution containing 0.0400 g of the above-mentioned aqueous binder, stir well for 8 h to obtain a uniformly dispersed slurry, then uniformly coat the slurry onto the surface of a 9-μm copper foil through a coater, dry at 100 °C for 12 h, and finally cut it into circular electrode sheets with a radius of 7.5 mm for standby.

[0037] Example 5 Prepare a water-based binder solution of sodium carboxymethyl cellulose derivatives containing urethane structural units according to the process steps of Example 1 for later use.

[0038] The preparation method of the corresponding silicon-carbon negative electrode material for lithium-ion batteries is as follows: Take 0.1200 g of silicon-carbon material and 0.0400 g of Super P and place them in an aqueous solution containing 0.0400 g of the water-based binder. Stir well for 8 h to obtain a uniformly dispersed slurry. Then, evenly coat the slurry onto the surface of a 9-μm copper foil through a coater, dry it at 100 °C for 12 h, and finally cut it into circular electrode sheets with a radius of 7.5 mm for later use.

[0039] Example 6 Prepare a water-based binder solution of sodium carboxymethyl cellulose derivatives containing urethane structural units according to the process steps of Example 1 for later use.

[0040] The preparation method of the corresponding hard-carbon negative electrode material for lithium-ion batteries is as follows: Take 0.1200 g of hard-carbon material and 0.0400 g of Super P and place them in an aqueous solution containing 0.0400 g of the water-based binder. Stir well for 8 h to obtain a uniformly dispersed slurry. Then, evenly coat the slurry onto the surface of a 9-μm copper foil through a coater, dry it at 100 °C for 12 h, and finally cut it into circular electrode sheets with a radius of 7.5 mm for later use.

[0041] Control Example 1 Dissolve 0.4000 g of sodium carboxymethyl cellulose in 20 mL of deionized water for later use.

[0042] The preparation method of the negative electrode material for the lithium-ion battery corresponding to this case is as follows: Take 0.1200 g of silicon powder and 0.0400 g of Super P and place them in an aqueous solution containing 0.0400 g of the above polymer. Stir well for 8 h to obtain a uniformly dispersed slurry. Then, evenly coat the slurry onto the surface of a 9-μm copper foil through a coater, dry it at 100 °C for 12 h, and finally cut it into circular electrode sheets with a radius of 7.5 mm for later use.

[0043] Transfer the processed electrode sheets to a glove box for the assembly of coin cells.

[0044] The battery components were stacked in sequence in an argon glove box (H2O / O2 < 0.1 ppm): the negative electrode case, shrapnel, gasket, lithium foil counter electrode, separator (Celgard 2400PP film), negative electrode sheet, gasket, and positive electrode case, and an appropriate amount of electrolyte was dropped between each step. The electrolyte used was 1 M LiPF6 dissolved in EC / DEC (volume ratio 1:1) with the addition of 10% FEC film-forming additive. The assembled battery was placed in an incubator at 25 °C for 12 h to allow the electrolyte to fully infiltrate.

[0045] Figure 1 This is a comparison of the stripping properties of the aqueous binders used in Example 1, Example 2, and Comparative Example 1. From Figure 1 it can be seen that compared with Example 2 and Comparative Example 1, the stripping strength of Example 1 was significantly improved. This was due to the introduction of an appropriate amount of cross-linking agent, which promoted the interaction between the binder chain segments, and the network structure constructed by the dynamic and static cross-linking methods enhanced the binding ability of the aqueous binder; Figure 2 This is a cyclic voltammogram of the secondary lithium battery prepared in Example 1 at a scan rate of 0.05 mV / s. From Figure 2 it can be obtained that during multiple scans, lithium ion insertion / extraction peaks appeared at 0.01 V, 0.19 V and 0.37 V, 0.53 V respectively in the silicon material, indicating that the aqueous covalent cross-linked binder material of Example 1 did not affect the lithium ion insertion / extraction process in the battery and could stably exist in the electrochemical window of 0.01 - 1.5 V; Figure 3 This is a comparison chart of the cycling results of the silicon anode lithium batteries prepared in Example 1, Example 3, and Comparative Example 1 at a current density of 2.1 A / g. From Figure 3 it can be seen that after 200 cycles, the battery corresponding to Example 1 still had a discharge specific capacity of 1339.7 mAh / g. Compared with Example 3 and Comparative Example 1, it showed excellent cycling performance.

[0046] Figure 4 This is a comparison chart of the cycling results of the silicon-carbon anode lithium batteries prepared in Example 5 and Comparative Example 1 at a current density of 2.1 A / g. From Figure 4 it can be seen that after 300 cycles, the battery corresponding to Example 5 could release a higher discharge specific capacity compared with Comparative Example 1, showing excellent cycling performance.

[0047] Figure 5 This is a comparison chart of the cycling results of the hard carbon anode lithium batteries prepared in Example 6 and Comparative Example 1 at a current density of 2.1 A / g. From Figure 5 it can be seen that after 800 cycles, the battery corresponding to Example 6 could release a higher discharge specific capacity compared with Comparative Example 1, showing excellent cycling performance.

[0048] Where not otherwise involved, the prior art shall apply.

[0049] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and not for limiting the scope of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications, supplements, or use similar means for substitution to the described specific embodiments, but will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a carboxymethyl cellulose sodium derivative-based aqueous binder containing a urethane structural unit, characterized in that, The aqueous binder can be prepared by adding a crosslinking agent, isocyanate monomer A, and a solvent to an aqueous solution of sodium carboxymethylcellulose and carrying out a thermal polymerization reaction at a certain temperature.

2. The preparation method according to claim 1, characterized in that, The concentration of the aqueous solution of sodium carboxymethylcellulose is 0.01 - 0.10 g / mL.

3. The preparation method according to claim 1, characterized in that, The monomer A accounts for 1 - 10 mol% of the aqueous solution of sodium carboxymethylcellulose.

4. The preparation method according to claim 1, characterized in that, The monomer A is one or more of hexamethylene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, and dimethylbiphenyl diisocyanate.

5. The preparation method according to claim 1, characterized in that, The time for the thermal polymerization reaction is 1 - 3 h, and the temperature is 70 - 90 °C.

6. An aqueous binder based on sodium carboxymethylcellulose derivatives containing urethane structural units prepared by the preparation method according to any one of claims 1 - 5.

7. A negative electrode material for a lithium-ion battery, characterized in that, An aqueous binder based on sodium carboxymethylcellulose derivatives comprising the urethane structural units as claimed in claim 6.

8. A method for preparing the anode material of a lithium-ion battery as described in claim 7, characterized in that, Comprising the following steps: Weigh a certain mass of silicon powder and a conductive additive, add them to the aqueous solution of the aqueous binder as claimed in claim 7, stir evenly, coat the mixture on a copper foil, and dry it to obtain a prepared electrode sheet.

9. The preparation method according to claim 8, characterized in that, The particle size of the silicon powder is 60 - 100 nm; the conductive additive is one or more of acetylene black, Ketjen black, Super P, and carbon nanotubes; the mass ratio of the silicon powder, the conductive additive, and the aqueous binder is 50 - 70:30 - 20:20 - 10.

10. The preparation method according to claim 8, characterized in that, The stirring time is 6 - 12 h, the drying temperature is 60 - 120 °C, and the drying time is 10 - 15 h.

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