CN116083005A - Composite binder and preparation method and application thereof - Google Patents

Abstract

The invention discloses a composite binder, a preparation method and application thereof, which are prepared by mixing polyacrylic acid and an alkaline polymer, wherein the mass ratio of the polyacrylic acid to the alkaline polymer is 40:1-40:4, and the mixing is physical blending. The composite binder disclosed by the invention can be suitable for huge volume change of a silicon-based material in the charge-discharge process to a certain extent, and can also improve charge transfer between active particles and a conductive agent, so that the cycle and rate performance of a lithium ion battery are improved. Compared with a chemical polymerization method with a relatively complicated preparation process and a reaction degree not easy to control, the PAA-based adhesive is obtained by compounding PAA and an alkaline polymer in a certain proportion by adopting a physical blending method, and the preparation method has the advantages of simple process, safety, environmental protection, low cost and the like, and is suitable for large-scale commercial production and practical application.

Description

Composite binder and preparation method and application thereof

Technical Field

The invention belongs to the technical field of lithium ion batteries, relates to a composite binder, and in particular relates to a composite binder prepared based on a physical blending method, and a preparation method and application thereof.

Background

Polyacrylic acid (PAA) is a water-soluble high molecular polymer, and the molecular chain contains rich and uniformly distributed carboxyl groups, can form strong hydrogen bonding with active materials and current collectors, and is easy to modify; in addition, the PAA has the advantages of better electrochemical stability, electrolyte compatibility, safety, no toxicity, low cost and the like, so the PAA is considered as an ideal silicon-based negative electrode binder, and is expected to realize the commercial application of high-capacity silicon negative electrodes. However, the elasticity and chain mobility of the linear PAA homopolymer are poor, and the PAA is generally required to be modified by grafting small molecules, soft polymers or crosslinked polymers to form a crosslinked three-dimensional network structure, and the mechanical strength and mobility of the three-dimensional network structure are improved, so that the huge volume change of the silicon-based material in the lithium intercalation and deintercalation process is relieved, and the structural integrity of the electrode is maintained.

For a silicon-based anode system, the silicon-based material can react with lithium in the first lithium intercalation process to generate a large amount of irreversible products, so that lithium loss is more serious than that of a traditional graphite electrode. In order to improve the first coulombic efficiency of the silicon-based negative electrode, one of the prior art is to perform pre-lithiation treatment on the silicon-based material. The principle of prelithiation is mainly that silicon-based materials and metallic lithium react under certain conditions to generate substances such as silicate, lithium oxide and the like so as to reduce the loss of active lithium. Although the pre-lithiated silicon-based negative electrode material has a certain lithium supplementing effect, the bonding performance of the PAA binder is seriously affected due to the fact that some alkaline substances inevitably remain in the pre-lithiation process, and the problems of negative electrode material dropping, poor cycle performance and the like are caused. Therefore, improving the alkali resistance of the PAA binder is of great significance in achieving commercialization of silicon-based cathodes.

Disclosure of Invention

In order to solve the problems, the invention provides a composite binder based on a physical blending method, which not only can adapt to huge volume change of a silicon-based material in a charging and discharging process to a certain extent, but also can improve charge transfer between active particles and a conductive agent, thereby improving the cycle and multiplying power performance of a lithium ion battery; in addition, the composite adhesive has certain alkali resistance, can be suitable for a pre-lithiated silicon-based material system, has simple synthesis process and low cost, and is suitable for large-scale commercial production and practical application.

The invention also provides a preparation method and application of the composite binder.

In order to achieve the above purpose, the present invention adopts the following technical scheme:

firstly, the invention provides a composite adhesive, which is prepared by mixing polyacrylic acid and an alkaline polymer, wherein the mass ratio of the polyacrylic acid to the alkaline polymer is 40:1-40:4, and the mixing is physical blending.

In the invention, a polyacrylic acid (PAA) based composite binder is prepared and compounded by PAA and alkaline polymer through a simple physical blending method.

PAA is a water-soluble high molecular polymer, and the molecular chain contains rich and uniformly distributed carboxyl groups. The PAA system is adopted as the binder of the silicon-based anode material, firstly, the PAA has excellent adhesion performance, and can form a strong hydrogen bond with the silicon-based material and the current collector; secondly, the carboxyl on the PAA chain has high density and is easy to modify; thirdly, the PAA has good electrochemical stability and electrolyte compatibility, and is safe, nontoxic and low in cost.

The high-capacity pre-lithiated silicon-based negative electrode material can seriously influence the bonding performance of PAA due to the residue of alkaline substances, so that the problems of negative electrode material dropping, poor cycle performance and the like are caused. In order to solve the problems, the invention enhances the alkali resistance of PAA-based binders by introducing polymers which contain basic functional groups and can form hydrogen bonds with PAA, such as Polyaniline (PANI), polyethyleneimine (PEI), polyacrylamide (PAM), chitosan (CTS) and the like, thereby effectively inhibiting the falling-off of active materials in the circulation process and keeping the integrity of electrode structures. On the other hand, the N element in the alkaline polymer has lone pair electrons, and can be subjected to complexing decomplexing reaction with lithium ions under the action of an electric field, so that the rapid migration of the lithium ions is facilitated, and the rate performance of the battery is improved.

As a preferred embodiment of the present invention, the basic polymer includes one or more combinations of polyaniline, polyethyleneimine, polyacrylamide, or chitosan.

As a preferred embodiment of the present invention, the molecular weight of the polyacrylic acid is 20-60w.

As a preferable scheme of the invention, the solid content of the composite binder is 2-5%.

Secondly, the invention provides a preparation method of the composite adhesive, which comprises the following steps:

1) Weighing polyacrylic acid and a solvent, placing the polyacrylic acid and the solvent in a container, and stirring to fully dissolve the polyacrylic acid and the solvent to obtain a colorless transparent polyacrylic acid solution;

2) Weighing an alkaline polymer, adding the alkaline polymer into the polyacrylic acid solution obtained in the step 1), stirring and dispersing for a period of time, and then placing the mixture in an oil bath for continuous stirring to obtain a uniform polyacrylic acid-based composite binder solution.

As a preferable scheme of the invention, in the step 1), the solvent is DMSO or water, the stirring temperature is 15-35 ℃, and the stirring time is 4-6h.

As a preferred embodiment of the present invention, in step 2), after the addition of the basic polymer, stirring is performed at 15 to 35℃for 4 to 6 hours, and then stirring is performed in an oil bath at 50 to 70℃for 1 to 3 hours.

Finally, the invention provides application of the composite binder, which is applied to the field of lithium ion batteries, wherein the negative electrode material of the lithium ion battery is a mixture of a pre-lithiated silicon-based material and graphite, and the mass ratio of the pre-lithiated silicon-based material to the graphite is 1:9-4:6.

As a preferable scheme of the invention, the addition amount of the composite binder is 5-10%.

Compared with the prior art, the invention has the following beneficial effects:

1) The composite binder disclosed by the invention can be suitable for huge volume change of a silicon-based material in the charge-discharge process to a certain extent, and can also improve charge transfer between active particles and a conductive agent, so that the cycle and rate performance of a lithium ion battery are improved.

2) Compared with a chemical polymerization method with a relatively complicated preparation process and a reaction degree not easy to control, the PAA-based adhesive is obtained by compounding PAA and an alkaline polymer in a certain proportion by adopting a physical blending method, and the preparation method has the advantages of simple process, safety, environmental protection, low cost and the like, and is suitable for large-scale commercial production and practical application.

Drawings

Fig. 1 is an SEM photograph of the PAA-PANI composite binder prepared in example 1.

Fig. 2 shows the room temperature rate performance of example 1 using PAA-PANI as binder.

Fig. 3 is a graph showing the normal temperature 0.2C cycle performance of example 1 using PAA-PANI as binder.

Detailed Description

In order to facilitate understanding of the technical means, the creation characteristics, the achievement of the objects and the effects achieved by the present invention, the present invention is further described below with reference to specific examples, but the following examples are only preferred examples of the present invention, not all of which are described in detail below. Based on the examples in the embodiments, those skilled in the art can obtain other examples without making any inventive effort, which fall within the scope of the invention. The experimental methods in the following examples are conventional methods unless otherwise specified, and materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

In the invention, the pre-lithiated silicon-based material is pre-lithiated silicon oxide and is commercially available.

Example 1

This example provides for the preparation of a composite binder comprising:

0.31g of polyacrylic acid (PAA) and 10g of DMSO solvent were weighed into a beaker and stirred at 25℃for 6 hours to dissolve completely, giving a colorless transparent PAA-DMSO solution. Then 0.0232g of Polyaniline (PANI) was added to the PAA-DMSO solution, and dispersed with stirring at 25℃for 4 hours, and then placed in an oil bath at 50℃with stirring for 1 hour, to obtain a uniform PAA-PANI composite binder solution. SEM pictures of PAA-PANI composite binders are shown in FIG. 1, and the PAA-PANI composite is formed by stacking uniform wafers, and no obvious phase separation occurs, which indicates that PAA and PANI form a homogeneous composite after physical blending.

To test the ionic conductivity of the binder, the PAA-PANI solution prepared in this example was slowly poured into a polytetrafluoroethylene mold to uniformly distribute it, and then transferred to a forced air drying oven to dry at 70℃for 12 hours to form a transparent PAA-PANI film having a thickness of 100. Mu.m. Before testing, the adhesive film is soaked in electrolyte for 12 hours in a glove box, then is clamped between two stainless steel gaskets to be assembled into a pair of paired blocking button cells, and the electrochemical impedance spectrum test is carried out on the cells, wherein the frequency range is 2M-0.1 Hz, and the amplitude is 10mV. The bulk resistance of the binder is determined according to the Z' intercept of the Nyquist curve in the high frequency range, and the room temperature ion conductivity of the PAA-PANI binder is calculated to be 3.60 multiplied by 10 ^-5 S/cm。

In order to characterize the electrochemical performance of the binder, the mixture of pre-lithium silicon oxide and graphite is used as a negative electrode material, the PAA-PANI compound prepared in the embodiment is used as the binder, and the negative electrode material is prepared according to the mass ratio: conductive agent carbon black: binder=91:2:7 was prepared as a negative electrode tab. And (3) taking the pole piece as a working electrode and the lithium piece as a counter electrode, and assembling the button half-cell. And then, carrying out normal-temperature rate performance test on the assembled half battery, carrying out charging and discharging at different rates from 0.05C, 0.1C, 0.2C and 0.5C to 1.0C, cycling for 5 weeks at each rate, and finally carrying out charging and discharging test at 0.05C, wherein the result is shown in figure 2, the specific discharge capacity of the electrode at 0.5C reaches 305mAh/g, the specific discharge capacity at 1.0C still has 206mAh/g, which is 58% and 39% of the initial specific discharge capacity respectively, and the specific discharge capacity of the electrode can be restored to about 365mAh/g after the charging and discharging cycles are carried out at the rate of 0.05C. Further, a charge-discharge cycle performance test at room temperature of 0.2C was performed, and as a result, see FIG. 3, the initial specific capacity was 402mAh/g, and the capacity retention rate was 67% at 100 cycles.

Example 2

This example provides for the preparation of a composite binder comprising:

0.465g polyacrylic acid (PAA) and 15g DMSO solvent were weighed into a beaker and stirred at 25℃for 6 hours to dissolve completely, yielding a colorless transparent PAA-DMSO solution. Then, 0.03g of Polyethylenimine (PEI) was added to the PAA-DMSO solution, and the mixture was stirred and dispersed at 25℃for 4 hours, and then placed in an oil bath at 50℃and stirred for 1 hour, to obtain a uniform PAA-PEI composite binder solution.

A PAA-PEI adhesive film was prepared and tested for ionic conductivity in the same manner as in example 1. According to the obtained alternating current impedance spectrum, the room temperature ionic conductivity of the PAA-PEI binder is calculated to be 9.14X10 ^-6 S/cm。

A button half cell using PAA-PEI as a silicon-based negative electrode binder was assembled by the same method as in example 1, and normal temperature magnification and 0.2C cycle performance were tested. The specific discharge capacity of the electrode at the 0.5C multiplying power is 139mAh/g, the specific discharge capacity at the 1.0C multiplying power is 60mAh/g, which is 27% and 12% of the initial specific discharge capacity respectively, and after the charge-discharge cycle is carried out at the multiplying power of 0.05C, the specific discharge capacity of the electrode is recovered to about 315 mAh/g. Further, the capacity retention rate at room temperature of 0.2C charge-discharge cycle for 100 weeks was 62%.

Example 3

This example provides for the preparation of a composite binder comprising:

0.62g of polyacrylic acid (PAA) and 20g of DMSO solvent were weighed into a beaker and stirred at 25℃for 6 hours to dissolve completely, giving a colorless transparent PAA-DMSO solution. Then 0.05g of Polyacrylamide (PAM) was added to the PAA-DMSO solution, and the mixture was stirred and dispersed at 25℃for 4 hours, and then placed in an oil bath at 50℃and stirred for 1 hour, to obtain a uniform PAA-PAM composite binder solution.

The same procedure as in example 1 was usedThe PAA-PAM adhesive film was prepared and tested for ionic conductivity. According to the obtained alternating current impedance spectrum, the room temperature ionic conductivity of the PAA-PAM binder is calculated to be 1.26x10 ^-5 S/cm。

A button half cell using PAA-PAM as a silicon-based negative electrode binder was assembled by the same method as in example 1, and room temperature magnification and 0.2C cycle performance were tested. The specific discharge capacity of the electrode at the 0.5C multiplying power is 200mAh/g, the specific discharge capacity at the 1.0C multiplying power is 105mAh/g, which are 40% and 21% of the initial specific discharge capacity respectively, and after the charge-discharge cycle is carried out at the multiplying power of 0.05C, the specific discharge capacity of the electrode is recovered to about 335 mAh/g. Further, the capacity retention rate at room temperature of 0.2C charge-discharge cycle for 100 weeks was 60%.

Example 4

This example provides for the preparation of a composite binder comprising:

0.31g of polyacrylic acid (PAA) and 20g of DMSO solvent were weighed into a beaker and stirred at 35℃for 6 hours to dissolve completely, thus obtaining a colorless transparent PAA-DMSO solution. 0.0232g of Chitosan (CTS) was then added to the PAA-DMSO solution, dispersed with stirring at 25℃for 4 hours, and then placed in an oil bath at 70℃with stirring for 1 hour to obtain a uniform PAA-CTS composite binder solution.

A PAA-CTS adhesive film was prepared in the same manner as in example 1, and ion conductivity was measured. According to the obtained alternating current impedance spectrum, the room temperature ionic conductivity of the PAA-CTS binder is calculated to be 1.42 multiplied by 10 ^-5 S/cm。

A button half cell using PAA-CTS as a silicon-based material binder was assembled by the same method as in example 1, and room temperature magnification and 0.2C cycle performance were tested. The specific discharge capacity of the electrode at the 0.5C multiplying power is 280mAh/g, the specific discharge capacity at the 1.0C multiplying power is 190mAh/g, which are 55% and 37% of the initial specific discharge capacity respectively, and after the charge-discharge cycle is carried out at the multiplying power of 0.05C, the specific discharge capacity of the electrode is restored to about 350 mAh/g. Further, the capacity retention rate at room temperature of 0.2C charge-discharge cycle for 100 weeks was 64%.

Comparative example 1

Preparation by the same method as in example 1The pure PAA binder film was tested for ionic conductivity. According to the obtained alternating current impedance spectrum, the room temperature ionic conductivity of the PAA adhesive is calculated to be 8.35 multiplied by 10 ^-6 S/cm。

A button half cell using PAA as a silicon-based negative electrode binder was assembled by the same method as in example 1, and room temperature magnification and 0.2C cycle performance were tested. The specific discharge capacity of the electrode at the 0.5C multiplying power is 57mAh/g, the specific discharge capacity at the 1.0C multiplying power is 4mAh/g, the specific discharge capacity is only 13% and 0.9% of the initial specific discharge capacity respectively, and after the electrode is subjected to charge-discharge circulation at the multiplying power of 0.05C, the specific discharge capacity of the electrode is recovered to about 255 mAh/g. Further, the capacity retention rate at room temperature of 0.2C charge-discharge cycle for 100 weeks was only 25%.

While the invention has been described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and additions may be made without departing from the scope of the invention. Equivalent embodiments of the present invention will be apparent to those skilled in the art having the benefit of the teachings disclosed herein, when considered in the light of the foregoing disclosure, and without departing from the spirit and scope of the invention; meanwhile, any equivalent changes, modifications and evolution of the above embodiments according to the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims (9)

1. The composite adhesive is characterized by being prepared by mixing polyacrylic acid and an alkaline polymer, wherein the mass ratio of the polyacrylic acid to the alkaline polymer is 40:1-40:4, and the mixing is physical blending.

2. The composite binder of claim 1 wherein the basic polymer comprises one or more of polyaniline, polyethylenimine, polyacrylamide, or chitosan.

3. A composite adhesive according to claim 1, wherein the polyacrylic acid has a molecular weight of 20-60w.

4. A composite binder according to claim 1, wherein the composite binder has a solids content of 2-5%.

5. A method of preparing a composite adhesive according to any one of claims 1 to 4, comprising the steps of:

1) Weighing polyacrylic acid and a solvent, placing the polyacrylic acid and the solvent in a container, and stirring to fully dissolve the polyacrylic acid and the solvent to obtain a colorless transparent polyacrylic acid solution;

2) Weighing an alkaline polymer, adding the alkaline polymer into the polyacrylic acid solution obtained in the step 1), stirring and dispersing for a period of time, and then placing the mixture in an oil bath for continuous stirring to obtain a uniform polyacrylic acid-based composite binder solution.

6. The method of preparing a composite adhesive according to claim 5, wherein in step 1), the solvent is DMSO or water, the stirring temperature is 15-35 ℃, and the stirring time is 4-6h.

7. The method for preparing a composite binder according to claim 1, wherein in the step 2), after the addition of the basic polymer, stirring is performed for 4 to 6 hours at 15 to 35 ℃ and then stirring is performed for 1 to 3 hours in an oil bath at 50 to 70 ℃.

8. The use of a composite binder according to any one of claims 1 to 4, wherein the composite binder is used in the field of lithium ion batteries, the negative electrode material of the lithium ion battery is a mixture of a pre-lithiated silicon-based material and graphite, and the mass ratio of the pre-lithiated silicon-based material to the graphite is 1:9-4:6.

9. The use of a composite binder according to claim 8, wherein the composite binder is added in an amount of 5-10%.

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