CN112310399A

CN112310399A - Lithium ion battery silicon negative electrode binder and electrode preparation method and application thereof

Info

Publication number: CN112310399A
Application number: CN202011160049.5A
Authority: CN
Inventors: 王艳; 黄韦博; 郑洪河
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2020-10-27
Filing date: 2020-10-27
Publication date: 2021-02-02

Abstract

A lithium ion battery silicon cathode binder and a preparation method and application of an electrode thereof. The lithium ion battery silicon cathode binder is prepared from the following components in a mass ratio of 10-1:1-10 of polyvinylidene fluoride and polyvinyl alcohol. The adhesive provided by the invention can be used as a silicon negative electrode adhesive of a lithium ion battery, so that irreversible lithium consumption of the electrode can be effectively inhibited on the basis of improving the overall adhesion of the electrode.

Description

Lithium ion battery silicon negative electrode binder and electrode preparation method and application thereof

Technical Field

The invention relates to a binder, in particular to a silicon cathode binder of a lithium ion battery, belonging to the technical field of lithium ion batteries.

Background

With the development of new energy automobiles, development of negative electrode materials with high specific energy, high power and long service life has become one of the research hotspots of lithium ion batteries. Silicon has been widely noticed because of its high theoretical specific capacity (4200mAh/g), low discharge voltage, abundant reserves, low price and other advantages. However, the silicon has a large volume effect (> 300%) after charging and discharging, which causes pulverization of silicon particles and even shedding of the silicon particles from a current collector to lose electrochemical activity, so that the cycling stability of the silicon particles is poor, and the commercial application of the silicon negative electrode is limited. Therefore, the volume expansion of the buffering silicon in the lithium embedding process is improved, the cycling stability of the silicon cathode is improved, and the buffering silicon cathode is a main attack direction for overcoming the defects of silicon-based materials.

The binder is an important component of the electrode, and its main function is to connect the electrode active material, the conductive agent, and the current collector. The choice of binder can significantly affect the electrochemical performance of the electrode. PVDF is the most widely used oily binder, has good chemical stability, thermal stability, mechanical properties, processability and dispersibility, and can show good electrochemical properties in the conventional carbon material electrode. However, with the development of silicon-based materials, PVDF has not been able to meet the current application needs.

Disclosure of Invention

In order to solve the above-described problems, an object of the present invention is to provide a binder that can effectively suppress irreversible lithium consumption of an electrode while improving the adhesion of the entire electrode.

In order to achieve the technical purpose, the invention provides a silicon cathode binder of a lithium ion battery, which consists of polyvinylidene fluoride and polyvinyl alcohol in a mass ratio of 10-1: 1-10.

In one embodiment of the present invention, the lithium ion battery silicon negative electrode binder is formed by adding polyvinylidene fluoride and polyvinyl alcohol into a solvent.

In one embodiment of the present invention, the solvent used is N-methylpyrrolidone (NMP).

In one embodiment of the present invention, the mass concentration of the solution formed by adding polyvinylidene fluoride and polyvinyl alcohol to the solvent is 1 wt% to 20 wt%.

The invention also provides a lithium ion battery silicon cathode which contains the lithium ion battery silicon cathode binder.

The invention also provides a preparation method of the silicon cathode of the lithium ion battery, which comprises the following steps:

dissolving polyvinylidene fluoride and polyvinyl alcohol in a solvent, and uniformly mixing to obtain a binder solution;

adding silicon and a conductive agent into a binder solution to be uniformly dispersed to obtain electrode slurry; wherein the mass ratio of the silicon to the conductive agent to the binder is 7-9: 1-2: 1-2;

and coating the electrode slurry on a copper current collector, drying, pressing, cutting and drying to obtain the silicon cathode.

In one embodiment of the present invention, the silicon includes pure silicon, silicon dioxide, and silicon monoxide. The adopted conductive agent is selected from one or more of conductive carbon black, acetylene black, carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, graphene and graphene oxide.

In one embodiment of the invention, the temperature of drying is 110 ℃ to 130 ℃ (preferably 120 ℃) and the time of drying is 15h to 17h (preferably 16 h).

The invention also provides a lithium ion battery which comprises the silicon cathode of the lithium ion battery.

According to the lithium ion battery silicon cathode binder, PVDF and PVA are compounded to serve as the silicon cathode binder, the excellent mechanical property and dispersion property of PVDF are reserved, meanwhile, the hydroxyl in PVA, the oxygen-containing functional group on the surface of the active material and the hydrogen bond formed by fluorine in PVDF act to further improve the overall adhesion of the electrode, and therefore the volume expansion of silicon is effectively relieved. When the PVDF/PVA composite binder is applied to the silicon cathode of the lithium ion battery, the first reversible specific capacity can reach 3309mAh/g, which is 702mAh/g higher than that of the silicon cathode using PVDF as the binder, and the first coulombic efficiency is improved by 17%. After the silicon cathode obtained by the silicon cathode binder provided by the invention is cycled for 150 circles at 0.5C, the specific capacity of 1095mAh/g still exists, and the capacity of the silicon cathode using single PVDF as the binder is rapidly reduced to 50mAh/g after the silicon cathode is cycled for 30 circles.

Drawings

Fig. 1 is a scanning electron micrograph of the negative electrodes in example 1 and comparative example 1.

Fig. 2 is a first cyclic voltammogram of the negative electrodes in example 1 and comparative example 1.

Fig. 3 is a first charge and discharge curve of the negative electrodes in example 1 and comparative example 1.

Fig. 4 is a graph showing cycle performance of the negative electrodes in example 1 and comparative example 1.

Detailed Description

A silicon negative electrode binder is a mixture of PVDF and PVA, and specifically comprises the following steps:

s1, uniformly mixing PVDF and PVA in a solvent (NMP) to obtain a binder solution. Wherein the mass concentration of the binder solution is 1-20 wt%.

S2, uniformly dispersing silicon (pure silicon, silicon dioxide and silicon monoxide) and a conductive agent (a mixture of one or more of conductive carbon black, acetylene black, carbon fibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene and graphene oxide) in a binder solution to obtain the electrode slurry. Wherein the mass ratio of the silicon to the conductive agent to the binder is 7-9: 1-2: 1-2.

S3: and coating the electrode slurry on a copper current collector, drying, pressing, cutting and drying (vacuum at 120 ℃ for 16h) to obtain the silicon negative plate.

Example 1

The embodiment provides a silicon anode binder, which is prepared by the following steps:

s1, dissolving 2.1g of PVA and 0.9g of PVDF in 97g of NMP to prepare a 3% PVA-PVDF mixed solution as an electrode binder.

S2, adding 0.7g of silicon and 0.15g of conductive agent into 5g of 3% PVA-PVDF solution, and uniformly dispersing to obtain electrode slurry;

and S3, coating the electrode slurry on a copper current collector, drying, pressing, cutting and drying to obtain the silicon negative plate.

The silicon negative electrode is used for preparing a lithium ion battery.

Example 2

This example provides a silicon negative electrode binder, and an electrode preparation method thereof, which are substantially the same as those of example 1 except that: the mass ratio of PVA to PVDF was 3: 7.

Example 3

This example provides a silicon negative electrode binder, and an electrode preparation method thereof, which are substantially the same as those of example 1 except that: the mass ratio of PVA to PVDF was 5: 5.

Example 4

This example provides a silicon negative electrode binder, and an electrode preparation method thereof, which are substantially the same as those of example 1 except that: the mass ratio of PVA to PVDF was 6: 4.

Example 5

This example provides a silicon negative electrode binder, and an electrode preparation method thereof, which are substantially the same as those of example 1 except that: the mass ratio of PVA to PVDF was 8: 2.

Example 6

This example provides a silicon negative electrode binder, and an electrode preparation method thereof, which are substantially the same as those of example 1 except that: the mass ratio of PVA to PVDF was 9: 1.

Comparative example 1

This comparative example provides a silicon anode binder, and an electrode preparation method thereof, which are substantially the same as example 1 except that: PVDF alone was used as the binder.

Comparative example 2

This comparative example provides a silicon anode binder, and an electrode preparation method thereof, which are substantially the same as comparative example 1 except that: DMF is selected as the solvent.

Comparative example 3

This example provides a silicon negative electrode binder, and an electrode preparation method thereof, which are substantially the same as those of example 3 except that: polyacrylic acid (PAA) was used instead of PVA, with N, N-Dimethylformamide (DMF) as solvent.

Comparative example 4

This example provides a silicon negative electrode binder, and an electrode preparation method thereof, which are substantially the same as those of example 2 except that: PAA was used instead of PVA and DMF was used as solvent.

Electrochemical performance tests of the assembled battery using the electrodes obtained in examples 1 to 6 and comparative examples 1 to 4 as a negative electrode and metallic lithium as a counter electrode are shown in table 1 (1C ═ 4200 mAh/g).

TABLE 1

Fig. 1 is a scanning electron micrograph of the negative electrodes in example 1 and comparative example 1, and it can be seen that the distribution of nano silicon spheres is more uniform in example 1 than in comparative example 1.

Fig. 2 is a first cyclic voltammogram of the negative electrodes in example 1 and comparative example 1. Comparative example 1 has a significant reduction peak in the voltage range of 1.8-1.2V, whereas example 1 has only a small reduction peak in this voltage range, indicating that the irreversible lithium consumption of example 1 is significantly lower than that of comparative example 1.

Fig. 3 is a first charge and discharge curve of the negative electrodes in example 1 and comparative example 1. It can be seen that the polarization of example 1 is significantly less than that of comparative example 1. The first reversible capacity of example 1 was 3309mAh/g, and the first coulombic efficiency was 86%. While comparative example 1 had a first reversible capacity of 2607mAh/g and a first coulombic efficiency of 69%. The first significant increase in coulombic efficiency of example 1 is consistent with the results of fig. 2.

Fig. 4 is a graph showing cycle performance of the negative electrodes in example 1 and comparative example 1. It can be seen that the cycling stability of example 1 is significantly better than that of comparative example 1. After 150 cycles at 0.5C, example 1 maintained a reversible capacity of 1095mAh/g, whereas comparative example 1 rapidly dropped to 50mAh/g after 30 cycles.

Compared with the comparative example, the invention has the advantages that the PVDF and the PVA are compounded to be used as the silicon cathode binder and used for the lithium ion battery, so that the advantages of the PVDF (good chemical stability, thermal stability, mechanical property, processability and dispersibility) are retained, and the serious irreversible lithium consumption of the PVDF in the first-turn charging process is effectively relieved. In addition, PVA contains abundant hydroxyl groups, and can form hydrogen bonds with F in PVDF and oxygen-containing functional groups on the surface of an active material, so that the overall stability of the electrode is further improved, and the cycling stability of the electrode is obviously improved.

The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. The lithium ion battery silicon cathode binder consists of polyvinylidene fluoride and polyvinyl alcohol in a mass ratio of 10-1: 1-10.

2. The silicon negative binder of claim 1, wherein the silicon negative binder is formed by adding polyvinylidene fluoride and polyvinyl alcohol to a solvent.

3. The silicon negative electrode binder for lithium ion batteries according to claim 2, wherein the solvent is N-methylpyrrolidone.

4. The silicon negative electrode binder of the lithium ion battery as claimed in claim 2, wherein the mass concentration of the solution formed by adding polyvinylidene fluoride and polyvinyl alcohol to the solvent is 1-20 wt%.

5. A silicon negative electrode for a lithium ion battery comprising the silicon negative electrode binder for a lithium ion battery according to any one of claims 1 to 4.

6. The method for preparing the silicon negative electrode of the lithium ion battery according to claim 5, which comprises the following steps:

and coating the electrode slurry on a copper current collector, drying, pressing, cutting and drying to obtain the silicon cathode of the lithium ion battery.

7. The method of claim 6, wherein the silicon comprises pure silicon, silicon dioxide, or silicon monoxide.

8. The preparation method according to claim 6, wherein the conductive agent is selected from one or more of conductive carbon black, acetylene black, carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, graphene, and graphene oxide.

9. The preparation method according to claim 6, wherein the drying temperature is 110-130 ℃ and the drying time is 15-17 h.

10. A lithium ion battery comprising the lithium ion battery silicon negative electrode of claim 5.