CN110890545A - A kind of PEDOT:PSS/CMC composite binder and its preparation method and application - Google Patents

Abstract

The invention relates to the field of lithium ion batteries, and discloses a PEDOT (PolyEthyleneEther phosphate)/PSS (Polybutylece carbonate)/CMC (CMC) composite binder as well as a preparation method and application thereof. The composite binder comprises crosslinked poly 3, 4-ethylenedioxythiophene, polystyrene sulfonate/hydroxymethyl cellulose (PEDOT: PSS/CMC); the preparation raw materials comprise PEDOT, PSS and CMC with the mass ratio of (0.1-10) to 1. When the composite binder is used for preparing the silicon-based cathode of the lithium ion battery, functional groups in the binder can be effectively bonded with silicon, so that the bonding force with a silicon-based material is improved, a more stable SEI film can be formed, the direct contact between the SEI film and an electrolyte is reduced, the amount of byproducts is reduced, and the overall structure of an electrode is more stable. The silicon-based negative electrode of the lithium ion battery prepared by the binder can keep complete appearance after circulation, and is beneficial to improving the circulation stability of the battery.

Description

A kind of PEDOT:PSS/CMC composite binder and its preparation method and application

technical field

The invention belongs to the technical field of negative electrode materials for lithium ion batteries, and in particular relates to a PEDOT:PSS/CMC composite binder and a preparation method and application thereof.

Background technique

In recent years, with the rapid development of the new energy industry, lithium-ion batteries have been widely used in the fields of electronic products, power batteries and energy storage due to their advantages of high energy density and long cycle life. However, with the continuous improvement of battery performance requirements for electric vehicles and hybrid vehicles, the development of high-power and high-energy-density lithium-ion batteries has become an urgent problem to be solved. The anode and cathode materials of lithium-ion batteries are closely related to the performance of the battery. At present, the energy density of commercial graphite anode materials has reached the bottleneck, and it is difficult to have room for improvement, while silicon-based anode materials have the advantages of high theoretical specific capacity (Si: 4200mAh·g ^-1 ), low lithium intercalation potential and abundant reserves. , is considered to be the most potential anode material for next-generation lithium-ion batteries that can replace graphite anodes.

Silicon-based anodes provide capacity through the process of alloying and dealloying with lithium ions during the charging and discharging process, and this process will generate huge volume expansion (about 300%), resulting in many problems, such as: 1. Huge volume expansion will lead to the crushing and pulverization of silicon-based material particles; 2. A large number of pulverized materials will peel off from the current collector, resulting in capacity decay and poor cycle performance; 3. Repeated volume changes during charging and discharging will cause the material The SEI film (solid electrolyte interfacial film) on the particle surface is constantly broken and reconstructed, which will consume a large amount of active lithium and reduce the capacity retention rate and Coulombic efficiency.

In order to solve the problem of structural instability during the cycle of silicon-based materials, researchers have carried out a series of studies and explorations in the past decade. The current research focus has gradually shifted from modifying active materials to optimizing the overall structure of the electrode, and improving the performance of the binder has become the key to optimizing the electrode structure. The ideal binder used in silicon-based materials should have good adhesion, Excellent mechanical properties, stable electrochemical properties and other performance conditions. At present, a large number of polymer binders have been developed and explored, including poly3,4-ethylenedioxythiophene: polystyrene sulfonate (PEDOT:PSS), polyacrylic acid (PAA), polyimide (PI) , hydroxymethyl cellulose (CMC), sodium alginate, etc. These studies have improved the physical properties of the binder to improve the electrode structure and improve the cycle performance of the battery. Further research shows that by forming an optimized mutual cross-linking structure between the electrode material and the binder, the irreversible structural changes of the electrode structure can be prevented and the electrode structure can be kept in a stable state. The synergistic effect between binders can effectively improve the connection between electrode materials and binders. Therefore, the development of new composite binders has important research on improving the structural stability of silicon-based electrodes and their electrical applications. significance.

SUMMARY OF THE INVENTION

A first aspect of the present invention provides a composite binder comprising poly-3,4-ethylenedioxythiophene in a cross-linked state: polystyrene sulfonate/hydroxymethyl cellulose (PEDOT: PSS/CMC).

According to an embodiment of the present invention, the raw materials for preparing the composite binder include PEDOT:PSS and CMC in a mass ratio of (0.1-10):1. Preferably, the mass ratio of PEDOT:PSS and CMC may be (0.5-5):1; as an example, the mass ratio of PEDOT:PSS and CMC may be 0.1:1, 0.5:1, 1:1, 2:1, 5:1.

According to an embodiment of the present invention, the composite binder contains ester groups and hydroxyl groups.

According to an embodiment of the present invention, the composite binder may be a liquid. For example, the composite binder contains PEDOT:PSS/CMC in a cross-linked state and a solvent; preferably, the mass concentration of PEDOT:PSS/CMC in the cross-linked state is 1-5wt%, such as 1.5-4wt% , exemplarily, the mass concentration is 2wt%. Wherein, the solvent can be at least one of water, dimethylformamide and glycerol, preferably water. Further, the composite binder may also contain uncrosslinked PEDOT:PSS and/or CMC.

A second aspect of the present invention provides a method for preparing the above-mentioned PEDOT:PSS/CMC composite binder. The preparation method includes the following steps: mixing and crosslinking a PEDOT:PSS solution and a CMC solution to obtain the PEDOT:PSS/CMC composite binder. binder.

Preferably, the preparation method comprises the following steps:

(1) respectively prepare PEDOT:PSS solution and CMC solution;

(2) The PEDOT:PSS solution and the CMC solution are mixed under stirring conditions, and the PEDOT:PSS/CMC composite binder is obtained through a cross-linking reaction.

According to an embodiment of the present invention, the weight percentage of PEDOT:PSS in the PEDOT:PSS solution is greater than 0 and less than or equal to 20wt%; preferably 1-15wt%, more preferably 2-8wt%; exemplary Ground, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%.

According to an embodiment of the present invention, the weight percentage of CMC in the CMC solution is greater than 0 and less than or equal to 20 wt %; preferably 1-15 wt %, more preferably 2-8 wt %; exemplarily, 2 wt % %, 3wt%, 4wt%, 5wt%, 6wt%.

According to an embodiment of the present invention, the preparation process of the PEDOT:PSS solution includes: at 20-30° C., adding the PEDOT:PSS solid powder to a solvent under stirring conditions to prepare a PEDOT:PSS solution. Wherein, the stirring time is 1-12h, preferably 3-8h, exemplarily, stirring is 4h, 5h, 6h. Wherein, the stirring speed is 200-800 rpm, preferably 300-500 rpm, exemplarily, the stirring speed is 400 rpm, 500 rpm.

According to an embodiment of the present invention, the preparation process of the CMC solution includes: at 20-30° C., adding the CMC solid powder to a solvent under stirring conditions to prepare a CMC solution. Wherein, the stirring time is 1-12h, preferably 3-8h, exemplarily, stirring is 4h, 5h, 6h. Wherein, the stirring speed is 200-800 rpm, preferably 300-500 rpm, exemplarily, the stirring speed is 400 rpm, 500 rpm.

According to an embodiment of the present invention, the solvent used for the preparation of the PEDOT:PSS solution and the CMC solution can be at least one of water, dimethylformamide and glycerol, preferably water.

According to an embodiment of the present invention, in step (2), the mixing specifically includes: mixing the PEDOT:PSS solution and the CMC solution of the same concentration, and stirring, to obtain the PEDOT:PSS/CMC composite binder .

According to an embodiment of the present invention, the volume ratio when the PEDOT:PSS solution and the CMC solution are mixed is (10-1000):100; more preferably (20-500):100, for example, the volume ratio is 10:100, 20 :100, 100:100, 250:100, 400:100, 500:100.

According to an embodiment of the present invention, in step (2), the stirring time is 10-24h, preferably 12-18h, and exemplarily, the stirring time is 12h, 15h, 16h.

According to an embodiment of the present invention, in step (2), the stirring speed is 200-800 rpm, preferably 300-500 rpm, exemplarily, the stirring speed is 400 rpm.

According to an embodiment of the present invention, in step (2), the temperature of the cross-linking reaction is room temperature, such as 20-40°C, or 20-30°C, exemplarily, the temperature is 25°C.

The PEDOT:PSS/CMC composite binder prepared by the present invention is based on the characteristic of the cross-linking reaction between PEDOT:PSS and CMC. By controlling the mixing ratio and giving a certain reaction time, the interaction between PEDOT:PSS and CMC can be fully generated. The cross-linking reaction forms stable bonds, thereby improving the mechanical properties of the adhesive.

The third aspect of the present invention provides the PEDOT:PSS/CMC composite binder obtained by the above preparation method.

A fourth aspect of the present invention provides the use of the above-mentioned PEDOT:PSS/CMC composite binder in a lithium ion battery. Preferably, it is used to prepare silicon-based negative electrodes for lithium ion batteries.

A fifth aspect of the present invention provides a silicon-based negative electrode for a lithium ion battery, the silicon-based negative electrode comprising a silicon-based negative electrode material with a mass ratio of (3-8):1 and the PEDOT:PSS/CMC composite binder , wherein, the quality of the PEDOT:PSS/CMC composite binder is based on the solute (the solute includes crosslinked PEDOT:PSS/CMC, and/or uncrosslinked PEDOT:PSS, and/or uncrosslinked PEDOT:PSS CMC) quality meter. Preferably, the mass ratio is (3.5-7.5):1, such as 4:1 or 7:1. Preferably, the silicon-based negative electrode does not include a conductive agent, and the conductive agent may be a conductive agent known in the art.

Wherein, the silicon-based negative electrode material is at least one of silicon, silicon monoxide and silicon carbon material.

A sixth aspect of the present invention provides a method for preparing the above-mentioned silicon-based negative electrode for a lithium ion battery, the preparation method comprising the steps of: mixing a silicon-based material, the PEDOT:PSS/CMC composite binder and a solvent (such as deionized water) ) uniformly mixed to obtain electrode slurry; and then coating the electrode slurry on the surface of the current collector and drying.

Wherein, the current collector is selected from at least one of copper foil, thin-film copper, nickel foil and foamed nickel, preferably copper foil.

Wherein, both the coating method and the drying method can adopt the methods known in the art.

A seventh aspect of the present invention provides a lithium ion battery, the lithium ion battery contains the above-mentioned PEDOT:PSS/CMC composite binder and/or the above-mentioned silicon-based negative electrode.

The inventors unexpectedly found that after cross-linking and compounding PEDOT:PSS with excellent electrical conductivity and a certain viscosity with CMC, its adhesiveness was significantly improved, and the electrical conductivity was still excellent. The reason is that PEDOT:PSS and CMC will form ester bonds after cross-linking, which enhances the intermolecular bonding force and thus enhances the cohesiveness of the adhesive.

Compared with the silicon-based anode prepared with the traditional binder, the cycle stability of the silicon-based anode prepared with the PEDOT:PSS/CMC composite binder is significantly improved. The reason is that there are a large number of hydroxyl groups in the composite binder. , ester group and other functional groups can strengthen the bonding force with silicon-based materials and improve the stability of electrode structure; on the other hand, the composite binder forms a uniform coating on the surface of silicon-based materials, which can achieve efficient ion and Electron conduction, the formation of a more stable SEI film reduces the direct contact with the electrolyte, reduces the amount of by-products, and makes the overall structure of the electrode more stable, thereby improving battery performance.

Beneficial effects of the present invention:

1. The present invention prepares a kind of composite binder by cross-linking and compounding PEDOT:PSS and CMC, which has better mechanical properties and electrical conductivity than traditional binders;

2. When the above-mentioned composite binder is used to prepare the silicon-based negative electrode of the lithium ion battery, the functional groups in the binder can be effectively bonded to the silicon, thereby improving the bonding force with the silicon-based material and improving the structural stability;

3. In the preparation process of the above-mentioned lithium-ion battery silicon-based negative electrode, the use of conductive agent is cancelled, so that the binder can form a uniform coating on the surface of the silicon-based material, avoiding the separation of the active material and the conductive agent, which leads to the instability of the electrode structure. The problem;

4. Compared with the silicon-based negative electrode prepared by using the PEDOT:PSS/CMC composite binder, the use of the composite binder is beneficial to the charge-discharge performance of the silicon-based negative electrode and improves its performance. Conductive properties.

5. The present invention provides a preparation method of the above-mentioned composite binder, and the preparation method has the characteristics of easy operation, green environmental protection and the like.

Description of drawings

Fig. 1 is the infrared spectrum of the composite binder prepared in Example 1 of the present invention.

FIG. 2 is a scanning electron microscope image of the silicon-based negative electrode sheet prepared in Example 1 of the present invention before being cycled.

3 is a scanning electron microscope image of the silicon-based negative electrode sheet prepared in Example 1 of the present invention after being cycled for 20 weeks.

FIG. 4 is an electrochemical performance diagram of the silicon-based negative electrode prepared in Example 1 of the present invention.

FIG. 5 is an electrochemical performance diagram of the silicon-based negative electrode prepared in Example 2 of the present invention.

6 is a scanning electron microscope image of the silicon base plate prepared in Comparative Example 1 of the present invention before cycling.

FIG. 7 is a scanning electron microscope image of the silicon base plate prepared in Comparative Example 1 of the present invention after being cycled for 20 weeks.

8 is a graph showing the electrochemical performance of the silicon-based negative electrode prepared in Comparative Example 1 of the present invention.

FIG. 9 is a scanning electron microscope image of the silicon base plate prepared in Comparative Example 2 of the present invention before cycling.

FIG. 10 is a scanning electron microscope image of the silicon base plate prepared in Comparative Example 2 of the present invention before cycling.

11 is a graph showing the electrochemical performance of the silicon-based negative electrode prepared in Comparative Example 2 of the present invention.

Detailed ways

The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following examples are only for illustrating and explaining the present invention, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the intended protection scope of the present invention.

Unless otherwise stated, the starting materials and reagents used in the following examples are commercially available or can be prepared by known methods.

Example 1

(1) Weigh 1 g of PEDOT:PSS powder and 1 g of CMC powder using an electronic balance, dissolve PEDOT:PSS powder and CMC powder in 50 mL of deionized water, respectively, to prepare a PEDOT:PSS solution and CMC with a mass percentage of 2wt%. solution. Solution preparation conditions: stirring at 25°C for 4 h, and the stirring speed is 400 rpm.

(2) Mix the two solutions in step (1) at a volume ratio of 1:1, and stir at 25° C. for 12 hours, with a stirring speed of 400 rpm, to prepare a PEDOT:PSS/CMC composite bond with a concentration of 2wt% agent;

(3) Mix the silicon-based material with the PEDOT:PSS/CMC composite binder in a mass ratio of 8:2 (the mass ratio of the silicon-based material to the solute in the binder), grind it evenly, and adjust the viscosity with deionized water. A negative electrode slurry was obtained. Use a scraper to evenly coat the negative electrode slurry on the copper foil, dry it under vacuum at 80°C, cut the piece, and roll it to obtain a silicon-based negative electrode piece;

(4) In an argon atmosphere glove box, metal lithium is used as the counter electrode, the electrolyte is 1 mol/L LiPF ₆ , and the electrolyte solvent is ethylene carbonate (EC)/dimethyl carbonate (DMC)/methyl carbonate Ethyl ester (EMC) (volume ratio of 1:1:1) solution, the separator is polypropylene film, and the above-mentioned silicon-based negative electrode sheet is assembled into a button battery, and its electrochemical performance is tested.

Fig. 1 is the infrared spectrum of the composite binder prepared in Example 1. It can be seen from Figure 1 that there are a large number of hydroxyl groups in the composite binder and the formation of ester groups.

2 and 3 are SEM photographs of the silicon-based negative electrode sheet prepared in Example 1 before cycling and after cycling for 20 weeks. It can be seen from Figures 2 and 3 that there are a large number of silicon particles on the pole piece before the cycle. The silicon particles are spherical, with a particle size of 50-100nm, and are evenly distributed on the pole piece. The particles are connected with each other by a binder. The silicon particles in the wafer also agglomerated, but the surface of the pole piece was flat without large-scale cracks and fragmentation, and the overall structure of the electrode remained intact.

FIG. 4 shows the electrochemical properties of the silicon-based negative electrode prepared in Example 1. It can be seen from Fig. 4 that its first charge-discharge performance is excellent, with a coulombic efficiency of 80.78% in the first week, and its discharge specific capacity can still reach 1106mAh·g ^-1 after 100 cycles of battery cycling.

Example 2

(1) Weigh 1 g of PEDOT:PSS powder and 1 g of CMC powder using an electronic balance, dissolve PEDOT:PSS powder and CMC powder in 50 mL of deionized water, respectively, to prepare a PEDOT:PSS solution and CMC with a mass percentage of 2wt%. solution. Solution preparation conditions: stirring at 25°C for 4 h, and the stirring speed is 400 rpm.

(2) Mix the two solutions in step (1) at a volume ratio of 2:1, and stir at 25° C. for 12 h with a stirring speed of 400 rpm, to prepare a PEDOT:PSS/CMC composite bond with a concentration of 2wt% agent;

(3) Mix the silicon-based material with the above-mentioned PEDOT:PSS/CMC composite binder in a mass ratio of 8:2 (the mass ratio of the silicon-based material to the solute in the binder material), grind it evenly, and adjust it with deionized water. viscosity to obtain a negative electrode slurry. Use a scraper to evenly coat the negative electrode slurry on the copper foil, dry it under vacuum at 80°C, cut the piece, and roll it to obtain a silicon-based negative electrode piece;

(4) In an argon atmosphere glove box, metal lithium is used as the counter electrode, the electrolyte is 1 mol/L LiPF ₆ , and the electrolyte solvent is ethylene carbonate (EC)/dimethyl carbonate (DMC)/methyl carbonate Ethyl ester (EMC) (volume ratio of 1:1:1) solution, the separator is polypropylene film, and the above-mentioned silicon-based negative electrode sheet is assembled into a button battery, and its electrochemical performance is tested.

Figure 5 shows the electrochemical properties of the silicon-based negative electrode prepared in Example 2. It can be seen from Figure 5 that its first charge-discharge performance is excellent, with a coulombic efficiency of 81% in the first week. After the battery is cycled for 100 weeks, its discharge specific capacity It can still reach 760mAh·g ^-1 .

Example 3

(1) Weigh 1 g of PEDOT:PSS powder and 1 g of CMC powder using an electronic balance, dissolve PEDOT:PSS powder and CMC powder in 50 mL of deionized water, respectively, to prepare a PEDOT:PSS solution and CMC with a mass percentage of 2wt%. solution. Solution preparation conditions: stirring at 25°C for 4 h, and the stirring speed is 400 rpm.

(2) Mix the two solutions in step (1) in a volume ratio of 5:1, and stir at 25° C. for 12 hours, with a stirring speed of 400 rpm, to prepare a PEDOT:PSS/CMC composite bond with a concentration of 2wt% agent;

(3) Mix the silicon-based material with the above-mentioned PEDOT:PSS/CMC composite binder in a mass ratio of 8:2 (the mass ratio of the silicon-based material to the solute in the binder material), grind it evenly, and adjust it with deionized water. viscosity to obtain a negative electrode slurry. Use a scraper to evenly coat the negative electrode slurry on the copper foil, dry it under vacuum at 80°C, cut the piece, and roll it to obtain a silicon-based negative electrode piece;

(4) In an argon atmosphere glove box, metal lithium is used as the counter electrode, the electrolyte is 1 mol/L LiPF ₆ , and the electrolyte solvent is ethylene carbonate (EC)/dimethyl carbonate (DMC)/methyl carbonate Ethyl ester (EMC) (volume ratio of 1:1:1) solution, the separator is a polypropylene film, and the above-mentioned silicon-based negative electrode sheet is assembled into a button battery.

Example 4

(1) Weigh 1 g of PEDOT:PSS powder and 1 g of CMC powder using an electronic balance, dissolve PEDOT:PSS powder and CMC powder in 50 mL of deionized water, respectively, to prepare a PEDOT:PSS solution and CMC with a mass percentage of 2wt%. solution. Solution preparation conditions: stirring at 25°C for 4 h, and the stirring speed is 400 rpm.

(2) Mix the two solutions in step (1) at a volume ratio of 0.5:1, and stir at 25°C for 12 hours, with a stirring speed of 400 rpm, to prepare a PEDOT:PSS/CMC composite bond with a concentration of 2wt% agent;

(3) Mix the silicon-based material with the above-mentioned PEDOT:PSS/CMC composite binder in a mass ratio of 8:2 (the mass ratio of the silicon-based material to the solute in the binder material), grind it evenly, and adjust it with deionized water. viscosity to obtain a negative electrode slurry. Use a scraper to evenly coat the negative electrode slurry on the copper foil, dry it under vacuum at 80°C, cut the piece, and roll it to obtain a silicon-based negative electrode piece;

(4) In an argon atmosphere glove box, metal lithium is used as the counter electrode, the electrolyte is 1 mol/L LiPF ₆ , and the electrolyte solvent is ethylene carbonate (EC)/dimethyl carbonate (DMC)/methyl carbonate Ethyl ester (EMC) (volume ratio of 1:1:1) solution, the separator is a polypropylene film, and the above-mentioned silicon-based negative electrode sheet is assembled into a button battery.

Example 5

(1) Weigh 1 g of PEDOT:PSS powder and 1 g of CMC powder using an electronic balance, dissolve PEDOT:PSS powder and CMC powder in 50 mL of deionized water, respectively, to prepare a PEDOT:PSS solution and CMC with a mass percentage of 2wt%. solution. Solution preparation conditions: stirring at 25°C for 4 h, and the stirring speed is 400 rpm.

(2) Mix the two solutions in step (1) at a volume ratio of 0.1:1, and stir at 25°C for 12 hours, with a stirring speed of 400 rpm, to prepare a PEDOT:PSS/CMC composite bond with a concentration of 2wt% agent;

(3) Mix the silicon-based material with the above-mentioned PEDOT:PSS/CMC composite binder in a mass ratio of 8:2 (the mass ratio of the silicon-based material to the solute in the binder material), grind it evenly, and adjust it with deionized water. viscosity to obtain a negative electrode slurry. Use a scraper to evenly coat the negative electrode slurry on the copper foil, dry it under vacuum at 80°C, cut the piece, and roll it to obtain a silicon-based negative electrode piece;

(4) In an argon atmosphere glove box, metal lithium is used as the counter electrode, the electrolyte is 1 mol/L LiPF ₆ , and the electrolyte solvent is ethylene carbonate (EC)/dimethyl carbonate (DMC)/methyl carbonate Ethyl ester (EMC) (volume ratio of 1:1:1) solution, the separator is a polypropylene film, and the above-mentioned silicon-based negative electrode sheet is assembled into a button battery.

Comparative Example 1

(1) Weigh 1 g of PEDOT:PSS powder using an electronic balance, dissolve the PEDOT:PSS powder in 50 mL of deionized water to prepare a 2 wt% PEDOT:PSS solution as a binder.

Solution preparation conditions: stirring at 25°C for 4 h, and the stirring speed is 400 rpm.

(2) Mix the silicon-based material with the above-mentioned binder in a mass ratio of 8:2 (the mass ratio of the silicon-based material to the solute in the binder material), grind it uniformly, and adjust the viscosity with deionized water to obtain a negative electrode slurry . Use a scraper to evenly coat the negative electrode slurry on the copper foil, dry it under a vacuum condition of 80°C, cut the piece, and roll it to obtain the battery silicon-based negative electrode piece;

(3) In an argon atmosphere glove box, metal lithium is used as the counter electrode, the electrolyte is LiPF ₆ of 1 mol/L, and the electrolyte solvent is ethylene carbonate (EC)/dimethyl carbonate (DMC)/methyl carbonate Ethyl ester (EMC) (volume ratio of 1:1:1) solution, the separator is polypropylene film, and the above-mentioned silicon-based negative electrode sheet is assembled into a button battery, and its electrochemical performance is tested.

FIG. 6 and FIG. 7 are scanning electron microscope pictures of the silicon base sheet prepared in Comparative Example 1 before and after 20 cycles of cycling. It can be seen from Figures 6 and 7 that there are a large number of silicon particles on the pole piece before the cycle. The silicon particles are spherical, with a particle size of 50-100nm, and are evenly distributed on the pole piece. The particles are connected with each other by a binder. The silicon particles in the sheet also agglomerated and the surface of the pole piece was cracked and broken.

Figure 8 shows the electrochemical performance of the silicon-based anode prepared in Comparative Example 1. It can be seen from Figure 8 that the first charge-discharge performance is excellent, and the Coulombic efficiency in the first week reaches 82%, but the cycle performance is poor, and the discharge specific capacity is 315mAh·g ^-1 after 100 cycles of cycling.

Comparative Example 2

(1) Weigh 1 g of CMC powder using an electronic balance, dissolve the CMC powder in 50 mL of deionized water to prepare a CMC solution with a mass percentage of 2 wt %, and use it as a binder.

CMC solution preparation conditions: stirring at 25° C. for 4 h, and the stirring speed is 400 rpm.

(2) Mix the silicon-based material with the above-mentioned binder in a mass ratio of 8:2 (the mass ratio of the silicon-based material to the solute in the binder material), grind it uniformly, and adjust the viscosity with deionized water to obtain a negative electrode slurry . Use a scraper to evenly coat the negative electrode slurry on the copper foil, dry it under a vacuum condition of 80°C, cut the piece, and roll it to obtain the battery silicon-based negative electrode piece;

(3) In an argon atmosphere glove box, metal lithium is used as the counter electrode, the electrolyte is LiPF ₆ of 1 mol/L, and the electrolyte solvent is ethylene carbonate (EC)/dimethyl carbonate (DMC)/methyl carbonate Ethyl ester (EMC) (volume ratio of 1:1:1) solution, the separator is polypropylene film, and the above-mentioned silicon-based negative electrode sheet is assembled into a button battery, and its electrochemical performance is tested.

9 and 10 are SEM photographs of the silicon-based negative electrode sheet prepared in Comparative Example 1 before cycling and after cycling for 20 weeks. It can be seen from Figures 9 and 10 that there are a large number of silicon particles on the pole piece before the cycle. The silicon particles are spherical, with a particle size of 50-100nm, and are evenly distributed on the pole piece. The particles are connected with each other by a binder. The silicon particles in the sheet also agglomerated, and the surface of the pole piece had large-area cracks and severe fragmentation.

Figure 11 shows the electrochemical performance of the silicon-based anode prepared in Comparative Example 2. It can be seen from Figure 11 that its first charge-discharge performance is excellent, with a Coulombic efficiency of 82% in the first week, but the cycle performance is poor, and the discharge after 50 cycles The specific capacity is only 300mAh·g ^-1 .

It can be seen from the comparison of Figures 3, 7 and 10 that the morphology of the silicon-based electrode sheet prepared using the PEDOT:PSS/CMC composite binder remains more complete after cycling and exhibits better structural stability.

It can be seen from Figures 4, 5, 8, and 11 that the silicon-based anode prepared with the PEDOT:PSS/CMC composite binder has better electrochemical performance, which is comparable to the silicon-based anode prepared with traditional CMC and PEDOT:PSS binders. Compared with the negative electrode, although there is little difference in the Coulombic efficiency in the first week, the cycle stability has been greatly improved.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. a composite binder, it is characterized in that, described composite binder comprises the poly-3,4-ethylene dioxythiophene of cross-linked state: polystyrene sulfonate/hydroxymethyl cellulose (PEDOT:PSS /CMC); Preferably, the preparation raw materials of the composite binder include PEDOT:PSS and CMC in a mass ratio of (0.1-10):1; Preferably, the composite binder contains ester groups and hydroxyl groups. 2. composite binder according to claim 1, is characterized in that, described composite binder is liquid, and contains PEDOT:PSS/CMC and solvent of cross-linked state in described composite binder; Preferably, the mass concentration of the cross-linked PEDOT:PSS/CMC is 1-5wt%; Preferably, the solvent is at least one of water, dimethylformamide, and glycerol; Preferably, the composite binder further contains uncrosslinked PEDOT:PSS and/or CMC. 3. according to the preparation method of the described composite binder of claim 1 and 2, it is characterized in that, described preparation method comprises the following steps: by PEDOT:PSS solution and CMC solution mixed crosslinking, obtain described PEDOT:PSS/CMC composite binder; Preferably, the preparation method comprises the following steps: (1) respectively prepare PEDOT:PSS solution and CMC solution; (2) The PEDOT:PSS solution and the CMC solution are mixed under stirring conditions, and the PEDOT:PSS/CMC composite binder is obtained through a cross-linking reaction. 4. the preparation method of composite binder according to claim 3, is characterized in that, in the described PEDOT:PSS solution, the weight percentage that PEDOT:PSS shares is greater than 0 and less than or equal to 20wt%; The weight percentage content of CMC in the CMC solution is greater than 0 and less than or equal to 20wt%; Preferably, the preparation process of the PEDOT:PSS solution includes: adding the PEDOT:PSS solid powder to a solvent under stirring conditions at 20-30° C. to prepare a PEDOT:PSS solution; Preferably, the preparation process of the CMC solution includes: at 20-30° C., adding the CMC solid powder to the solvent under stirring conditions to prepare the CMC solution; Preferably, the solvent used for the preparation of the PEDOT:PSS solution and the CMC solution can be at least one of water, dimethylformamide, and glycerol. 5. according to the preparation method of the described composite binder of claim 3 or 4, it is characterized in that, in step (2), described mixing specifically comprises: the PEDOT of described same concentration: PSS solution and CMC solution are mixed, and to stir; Preferably, the volume ratio when the PEDOT:PSS solution and the CMC solution are mixed is (10-1000): 100; Preferably, the stirring time is 10-24h, and the stirring speed is 200-800rpm; Preferably, the temperature of the cross-linking reaction is room temperature. 6. The PEDOT:PSS/CMC composite binder obtained according to the preparation method of any one of claims 3-5. 7. Use of the PEDOT:PSS/CMC composite binder according to claim 1 or 2 in a lithium ion battery; preferably, it is used to prepare a silicon-based negative electrode for a lithium ion battery. 8. A silicon-based negative electrode, wherein the silicon-based negative electrode comprises a silicon-based negative electrode material with a mass ratio of (3-8): 1 and the PEDOT:PSS/CMC composite binder described in claim 1 or 2 , wherein, the quality of the PEDOT:PSS/CMC composite binder is in terms of solid matter mass; Preferably, no conductive agent is included in the silicon-based negative electrode; Preferably, the silicon-based negative electrode material is at least one of silicon, silicon monoxide and silicon carbon materials. 9. The preparation method of the lithium ion battery silicon-based negative electrode according to claim 8, wherein the preparation method comprises the steps of: bonding the silicon-based material, the PEDOT:PSS/CMC composite described in claim 1 or 2 The agent and the solvent are evenly mixed to obtain electrode slurry; then the electrode slurry is coated on the surface of the current collector and dried; Preferably, the current collector is selected from at least one of copper foil, thin-film copper, nickel foil and nickel foam. 10 . A lithium ion battery, characterized in that, the lithium ion battery contains the PEDOT:PSS/CMC composite binder according to claim 1 or 2 and/or the silicon-based negative electrode according to claim 8 .

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