阅读说明：本技术 一种共混型聚乙烯醇基粘结剂及其制备方法和应用 (Blending type polyvinyl alcohol-based binder and preparation method and application thereof ) 是由 王艳 郑洪河 王玮 黄韦博 吕林泽 沈鸣 于 2021-07-20 设计创作，主要内容包括：本发明属于锂离子电池负极材料技术领域,公开了一种共混型聚乙烯醇基粘结剂及其制备方法和应用。本发明将质量分数为1～20％的聚乙烯醇水溶液与质量分数为1～20％的半乳甘露聚糖水溶液共混,即得到共混型聚乙烯醇基粘结剂。相对于单一聚乙烯醇粘接剂,采用该共混型粘结剂制备的复合膜的孔隙直径更小,孔径分布更均匀,且热稳定性更高,可以有效缓解硅负极循环过程中的开裂问题,且改变了聚乙烯醇粘结剂的物理特性,使其能够缓冲硅负极巨大的体积变化；同时还具有优异的导锂特性。本发明的粘结剂适用范围广,且成本低廉、原料易得、工艺简单、环境友好,易实现大规模生产。(The invention belongs to the technical field of lithium ion battery cathode materials, and discloses a blending type polyvinyl alcohol-based binder and a preparation method and application thereof. The invention blends 1-20% of polyvinyl alcohol aqueous solution and 1-20% of galactomannan aqueous solution by mass fraction to obtain the blending type polyvinyl alcohol-based binder. Compared with a single polyvinyl alcohol adhesive, the composite film prepared by the blending type adhesive has smaller pore diameter, more uniform pore size distribution and higher thermal stability, can effectively relieve the cracking problem of the silicon cathode in the circulating process, changes the physical characteristics of the polyvinyl alcohol adhesive and can buffer the huge volume change of the silicon cathode; and also has excellent lithium conducting property. The binder disclosed by the invention is wide in application range, low in cost, easy in raw material obtaining, simple in process, environment-friendly and easy to realize large-scale production.)

1. The preparation method of the blending type polyvinyl alcohol-based binder is characterized by comprising the following steps:

and blending the polyvinyl alcohol aqueous solution and the galactomannan aqueous solution to obtain the blended polyvinyl alcohol-based binder.

2. The preparation method of the blending type polyvinyl alcohol-based binder as claimed in claim 1, wherein the mass fraction of the polyvinyl alcohol aqueous solution is 1-20%.

3. The preparation method of the blending type polyvinyl alcohol-based binder as claimed in claim 1 or 2, wherein the mass fraction of the galactomannan aqueous solution is 1-20%.

4. The preparation method of the blending type polyvinyl alcohol-based binder as claimed in claim 1, wherein the weight ratio of the polyvinyl alcohol aqueous solution to the galactomannan aqueous solution is 0.5-10: 0.1 to 7.

5. The preparation method of the blending type polyvinyl alcohol-based binder as claimed in claim 2 or 4, wherein the pH of the galactomannan aqueous solution is 5-9.

6. The blending type polyvinyl alcohol-based binder prepared by the preparation method of the blending type polyvinyl alcohol-based binder as claimed in any one of claims 1 to 5.

7. The application of the blended polyvinyl alcohol-based binder as claimed in claim 6, wherein the blended polyvinyl alcohol-based binder is used in a negative electrode material of a lithium ion battery.

8. The use of the blended polyvinyl alcohol-based binder of claim 7, wherein the lithium ion battery negative electrode material comprises a silicon electrode, a graphite electrode, a silicon carbon electrode and a silicon oxide electrode.

Technical Field

The invention relates to the technical field of lithium ion battery cathode materials, in particular to a blending type polyvinyl alcohol-based binder and a preparation method and application thereof.

Background

The silicon has ultrahigh theoretical specific capacity (high temperature can reach 4200mAh/g) and high volume specific capacity (9786 mAh/cm)³) Low intercalation potential of lithium (<0.5V vs.Li/Li⁺) High storage and low pollution, and becomes one of the most potential next generation cathode materials. However, the volume expansion of the silicon cathode based on the lithium alloying mechanism is large, which causes the problems that silicon is easy to be pulverized and broken in the charging and discharging process, the interface film of the solid electrolyte is unstable, and the silicon is separated from the conductive network. These problems lead to rapid cycle capacity fading of the silicon cathode and poor large-current charge and discharge performance, and seriously restrict the industrial application of the silicon cathode.

Designing a functional binder is an important method for improving the electrochemical performance of the silicon cathode. Through research, the water-based binder is more suitable for a silicon negative electrode. The polyhydroxy polyvinyl alcohol polymer has good thermal stability and film forming property, and can form strong hydrogen bond action with hydroxyl functional groups on the silicon surface, so that the volume expansion of the silicon cathode can be buffered to a certain extent.

However, the single polyvinyl alcohol binder has the disadvantages of low viscosity, poor functionality and poor dispersibility of electrode materials, so that the electrochemical performance of the silicon negative electrode still has a great improvement space. The blending type binder can overcome the defect of a single binder, investigate the category and function of the blending material, the synergistic effect between the blending binders and the influence of the blending binder on the electrochemical performance of the silicon cathode, and has great significance for promoting the industrial application of the silicon cathode.

Disclosure of Invention

The invention aims to provide a blending type polyvinyl alcohol-based binder, a preparation method and application thereof, and solves the problems of the existing polyvinyl alcohol alone serving as the binder.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of a blending type polyvinyl alcohol-based binder, which comprises the following steps:

and blending the polyvinyl alcohol aqueous solution and the galactomannan aqueous solution to obtain the blended polyvinyl alcohol-based binder.

Preferably, in the preparation method of the blending type polyvinyl alcohol-based binder, the mass fraction of the polyvinyl alcohol aqueous solution is 1-20%.

Preferably, in the preparation method of the blending type polyvinyl alcohol-based binder, the mass fraction of the galactomannan aqueous solution is 1-20%.

Preferably, in the preparation method of the blended polyvinyl alcohol-based binder, the weight ratio of the polyvinyl alcohol aqueous solution to the galactomannan aqueous solution is 0.5-10: 0.1 to 7.

Preferably, in the preparation method of the blending type polyvinyl alcohol-based binder, the aqueous solution of galactomannan has a pH of 5 to 9.

The invention also provides a blended polyvinyl alcohol-based binder prepared by the preparation method of the blended polyvinyl alcohol-based binder.

The invention also provides application of the blending type polyvinyl alcohol-based binder in a lithium ion battery cathode material.

Preferably, in the application of the blended polyvinyl alcohol-based binder, the negative electrode material of the lithium ion battery comprises a silicon electrode, a graphite electrode, a silicon-carbon electrode and a silicon oxide electrode.

Through the technical scheme, compared with the prior art, the invention has the following beneficial effects:

(1) the adhesive has high viscosity, good stability and easy storage. The polyvinyl alcohol adhesive not only can be used as a thickening agent, but also greatly changes the physical characteristics of the polyvinyl alcohol adhesive, so that the polyvinyl alcohol adhesive can buffer the huge volume change of a silicon cathode; and the silicon negative electrode has excellent lithium-conducting property, overcomes the defect of poor lithium-conducting property of the traditional polymer binder, and can greatly improve the multiplying power of the silicon negative electrode.

(2) Compared with polyvinyl alcohol, the composite membrane prepared by the blending type binder has smaller pore diameter, more uniform pore size distribution and higher thermal stability. Therefore, the pole piece prepared by the blending type polyvinyl alcohol adhesive is more compact, and the cracking problem of the silicon negative pole in the circulating process can be effectively relieved.

(3) According to the invention, through a synergistic effect between the blending binders, the problems of difficult dissolution, easy agglomeration and poor stability of galactomannan are solved, the defects of poor mechanical property and low viscosity of polyvinyl alcohol are overcome, and the preparation method has an important significance for improving the cycle and rate performance of the silicon cathode.

(4) The binder is suitable for silicon electrodes, graphite electrodes, silicon-carbon electrodes, silicon oxide electrodes and other lithium ion battery electrodes, and has the advantages of low cost, easily available raw materials, simple process, environmental friendliness and easy realization of large-scale production.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.

FIG. 1 is an SEM image and an SEM image after charge and discharge cycles of silicon negative electrode sheets prepared in example 3 and comparative example 1;

wherein, (a) is an SEM image of the silicon negative pole piece of comparative example 1; (b) is SEM picture of the silicon cathode pole piece of the example 3; (c) is an SEM image of the silicon negative electrode plate of comparative example 1 after 300 charge-discharge cycles; (d) is an SEM picture of a silicon negative electrode plate after 300 charge-discharge cycles of example 3;

fig. 2 is a rate chart of button cells prepared in example 3, comparative example 1 and comparative example 2;

fig. 3 is a 0.5C cycle chart of button cells prepared in examples 1-4 and comparative example 1;

fig. 4 is a 0.5C cycle chart of button cells prepared in example 3 and comparative examples 1-2;

fig. 5 is a graph of the charge/discharge cycle at 0.5C/1C for the button cells prepared in example 6 and comparative example 3.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention provides a preparation method of a blending type polyvinyl alcohol-based binder, which comprises the following steps:

(1) dissolving polyvinyl alcohol in water at 20-100 ℃ to obtain a polyvinyl alcohol aqueous solution;

(2) dissolving galactomannan in water at 20-80 ℃, and adjusting the pH to 5-9 to obtain a galactomannan water solution;

(3) and (3) blending the polyvinyl alcohol aqueous solution obtained in the step (1) and the galactomannan aqueous solution obtained in the step (2) to obtain the blending type polyvinyl alcohol-based binder.

Preferably, in the preparation method of the blending type polyvinyl alcohol-based binder, the mass fraction of the polyvinyl alcohol aqueous solution in the step (1) is 1-20%.

Preferably, in the preparation method of the blending type polyvinyl alcohol-based binder, the mass fraction of the galactomannan aqueous solution in the step (2) is 1-20%.

Preferably, in the preparation method of the blended polyvinyl alcohol-based binder, the mass ratio of the polyvinyl alcohol aqueous solution and the galactomannan aqueous solution blended in the step (3) is 0.5-10: 0.1 to 7.

The invention also provides a blended polyvinyl alcohol-based binder prepared by the preparation method of the blended polyvinyl alcohol-based binder.

The invention also provides application of the blending type polyvinyl alcohol-based binder in a lithium ion battery cathode material.

Preferably, in the application of the blended polyvinyl alcohol-based binder, the negative electrode material of the lithium ion battery comprises a silicon electrode, a graphite electrode, a silicon-carbon electrode and a silicon oxide electrode.

Further preferably, in the application of the blending type polyvinyl alcohol-based binder, the silicon electrode is obtained by uniformly coating nano silicon powder, the blending type polyvinyl alcohol-based binder and conductive carbon black.

Example 1

The embodiment provides a blending type polyvinyl alcohol-based binder, and the preparation method comprises the following steps:

(1) weighing 1.2g of polyvinyl alcohol powder in 38.8g of water, heating in a water bath at 95 ℃ for 1h, completely dissolving to obtain a polyvinyl alcohol aqueous solution with the mass fraction of 3%, and standing for later use;

(2) weighing 0.5g galactomannan powder in 24.5g water, controlling pH to 6, heating in 80 deg.C water bath for 1h, dissolving completely to obtain galactomannan water solution with mass fraction of 2%, and standing for use;

(3) 0.67g of polyvinyl alcohol aqueous solution and 2g of galactomannan aqueous solution are blended to obtain the blending type polyvinyl alcohol-based binder.

The method for applying the adhesive to the lithium ion battery comprises the following steps: weighing 0.21g of nano silicon powder, 0.03g of conductive carbon black and 0.06g of blending type polyvinyl alcohol-based binder, homogenizing for 30min by using a high-speed shearing machine, coating the mixture on a copper foil to prepare a silicon cathode, taking a metal lithium sheet as a counter electrode, and taking the metal lithium sheet as a cathode material containing 1mol/L LiPF₆Ethylene carbonate/ethyl methyl carbonate/dimethyl carbonate/fluoroethylene carbonate in a volume ratio of 3:3:3:1 as an electrolyte, and assembled into a C2032 button cell in an argon-filled glove box.

Example 2

This example provides a blended polyvinyl alcohol-based binder, which is prepared and applied in the same manner as in example 1, except that the weight of the aqueous polyvinyl alcohol solution in step (3) is 1g, and the weight of the aqueous galactomannan solution is 1.5 g.

Example 3

This example provides a blended polyvinyl alcohol-based binder, which is prepared and applied in the same manner as in example 1, except that the weight of the aqueous polyvinyl alcohol solution in step (3) is 1.33g and the weight of the aqueous galactomannan solution is 1 g.

Example 4

This example provides a blended polyvinyl alcohol-based binder, which is prepared and applied in the same manner as in example 1, except that the weight of the aqueous polyvinyl alcohol solution in step (3) is 1.67g and the weight of the aqueous galactomannan solution is 0.5 g.

Example 5

This example provides a blended polyvinyl alcohol-based binder, which is prepared and applied in the same manner as in example 3, except that the aqueous galactomannan solution is replaced with galactomannan powder and blended with the aqueous polyvinyl alcohol solution in step (3).

Example 6

This example provides a blending type polyvinyl alcohol based binder, which is prepared in the same manner as in example 1, and the application method is different from that of example 1 in that a graphite negative electrode is replaced with a silicon negative electrode, wherein the graphite negative electrode comprises 0.96g of graphite, 0.01g of conductive carbon black, and 0.03g of the blending type polyvinyl alcohol based binder.

Example 7

This example provides a blended polyvinyl alcohol-based binder, which is similar to example 1 in the preparation method and application method, except that the mass fraction of the polyvinyl alcohol aqueous solution in step (1) is 10%, and the mass fraction of the galactomannan aqueous solution in step (2) is 7%.

Example 8

This example provides a blended polyvinyl alcohol-based binder, which is similar to example 2 in the preparation method and application method, except that the mass fraction of the polyvinyl alcohol aqueous solution in step (1) is 6%, and the mass fraction of the galactomannan aqueous solution in step (2) is 15%.

Example 9

This example provides a blended polyvinyl alcohol-based binder, which is similar to example 3 in the preparation method and application method, except that the mass fraction of the polyvinyl alcohol aqueous solution in step (1) is 16%, and the mass fraction of the galactomannan aqueous solution in step (2) is 17%.

Example 10

This example provides a blended polyvinyl alcohol-based binder, which is similar to example 4 in the preparation method and application method, except that the mass fraction of the polyvinyl alcohol aqueous solution in step (1) is 20%, and the mass fraction of the galactomannan aqueous solution in step (2) is 2%.

Example 11

This example provides a blended polyvinyl alcohol-based binder, which is similar to example 5 in the preparation method and application method, except that the mass fraction of the polyvinyl alcohol aqueous solution in step (1) is 11%, and the mass fraction of the galactomannan aqueous solution in step (2) is 20%.

Example 12

This example provides a blended polyvinyl alcohol-based binder, which is similar to example 6 in the preparation method and application method, except that the mass fraction of the polyvinyl alcohol aqueous solution in step (1) is 20%, and the mass fraction of the galactomannan aqueous solution in step (2) is 20%.

Comparative example 1

The comparative example provides a polyvinyl alcohol binder, the preparation method of which is:

weighing 1.2g of polyvinyl alcohol powder in 38.8g of water, heating in a water bath at 95 ℃ for 1h, and completely dissolving to obtain a polyvinyl alcohol aqueous solution with the mass fraction of 3%, namely the polyvinyl alcohol binder.

The application method was the same as in example 3, except that the blended type polyvinyl alcohol-based binder was replaced with a polyvinyl alcohol binder.

Comparative example 2

The comparative example provides a galactomannan binder, the method of preparation comprising:

weighing 0.5g of galactomannan powder in 24.5g of water, controlling the pH value to be 6, heating in water bath at 80 ℃ for 1h to obtain galactomannan water solution with the mass fraction of 2%, namely the galactomannan binder.

The application method was the same as in example 3, except that the blended polyvinyl alcohol based binder was replaced with a galactomannan binder.

Comparative example 3

The present comparative example provides a sodium carboxymethylcellulose-styrene butadiene rubber binder (pulsatilla), and the preparation method and application method thereof are the same as those of example 7, except that the blended type polyvinyl alcohol based binder is replaced with the sodium carboxymethylcellulose-styrene butadiene rubber binder.

The electrochemical performance test method comprises the following steps: the cells were cycled and rate tested by first cycling through 3 cycles with 0.05C (1C ═ 4.2A/g) and 5 cycles with 0.1C.

SEM characteristics were carried out on the original silicon negative electrode pieces prepared in example 3 and comparative example 1 and the electrode pieces after 300 charge-discharge cycles, and the results are shown in FIG. 1. The result shows that compared with the silicon cathode prepared by the polyvinyl alcohol binder, the silicon cathode prepared by the blending type polyvinyl alcohol-based binder has fewer pores, the whole electrode is more compact, and the cracking degree of the pole piece after charge-discharge circulation is smaller.

The button cells prepared in example 3, comparative example 1 and comparative example 2 were tested at a rate of 10C, and the results are shown in fig. 2. Compared with a silicon negative electrode prepared by a polyvinyl alcohol binder and a galactomannan binder, the silicon negative electrode prepared by the blended polyvinyl alcohol-based binder has obviously improved rate capability, and the capacity retention rate reaches more than 50% under the rate of 10 ℃.

The button cells prepared in examples 1-4 and comparative example 1 were cycled at 0.5C for 300 cycles, and the cycling results are shown in fig. 3. The results show that the mass ratio of polyvinyl alcohol to galactomannan in the blended polyvinyl alcohol-based binder of the present invention affects the cycle performance of silicon negative electrodes.

The button cells prepared in example 3 and comparative examples 1-2 were cycled at 0.5C for 300 cycles, and the cycling results are shown in fig. 4. The result shows that compared with the binder with a single component, the blending type binder disclosed by the invention can greatly improve the cycle performance of the silicon negative electrode.

The button cells prepared in example 6 and comparative example 3 were cycled at 0.5C charge/1C discharge with cycling results as shown in fig. 5. The results show that the button cell using the sodium carboxymethylcellulose-styrene butadiene rubber binder has capacity jump water after 25 cycles, and the button cell using the blended polyvinyl alcohol-based binder of the invention has 50 cycles of capacity still keeps stable. It is shown that the adhesive of the present invention provides better cycling stability than adhesives provided by the prior art.

The coulombic efficiencies of the button cells obtained in example 3 and example 5 for the first three rounds are shown in table 1.

TABLE 1 Coulomb efficiency for the first three turns of button cell

The results in table 1 show that the addition manner of galactomannan in the blended polyvinyl alcohol-based binder of the invention has an influence on the electrochemical performance of the silicon negative electrode, wherein the blended binder prepared by adding the galactomannan solution has higher coulombic efficiency.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.