Water-based binder, preparation method thereof and application of water-based binder in lithium ion battery

Abstract

The invention discloses a water-based binder, a preparation method thereof and application of the water-based binder in a lithium ion battery, and belongs to the technical field of lithium ion battery materials. According to the invention, polyethyleneimine and glutaraldehyde-dopamine are utilized to synthesize a water-soluble polymer binder with excellent adhesion characteristics, an electrode material is prepared, and the peeling strength of a pole piece can reach 3.28 N. And when the surface loading capacity of the pole piece is 2.4-2.5 mg cm <-2 >, the specific capacity is 540.8 mAh g <-1 > after 100 cycles under the current density of 0.5 C. Meanwhile, an SEM structure and EIS data show that after the PEI-GA (0.2%)-DPA (9.8%) composite electrode is circulated, the whole electrode has the best integrity and the minimum impedance value.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery materials, and specifically relates to an aqueous binder and a preparation method thereof and application in lithium ion batteries. Background Art

[0002] Lithium-ion batteries have been widely used in electronics, electricity, lighting and many other fields due to their high energy density, clean and environmentally friendly, and portable advantages. However, the current commercialized graphite negative electrode still has the problem of low theoretical specific capacity, which restricts its performance improvement. Silicon-based materials have attracted much attention due to their ultra-high theoretical specific capacity and more stable voltage platform. However, silicon materials have low electrical conductivity and expand in volume during charging and discharging, causing the active material to fall off, crush, and continuously grow the solid electrolyte membrane, which seriously damages the performance of the battery. The addition of a binder can enhance electrode adhesion, improve electrode integrity, and increase battery cycle stability. This simple and direct method has great application potential in improving battery performance.

[0003] The preparation of traditional binders usually requires a large amount of organic solvents and additives to participate in the reaction. However, people currently have an urgent demand for high-safety, low-cost and high-efficiency lithium-ion battery materials, and need a new type of binder that is environmentally friendly and low-cost while ensuring good quality. Summary of the invention

[0004] In view of the above problems existing in the prior art, one technical problem to be solved by the present invention is to provide a water-based adhesive, which is obtained by cross-linking polyethyleneimine (PEI) glutaraldehyde (GA) and dopamine (DPA), and the electrode peeling strength reaches 3.28N. Another technical problem to be solved by the present invention is to provide a method for preparing a water-based adhesive, in which water is used as a solvent during the preparation to ensure that the prepared adhesive has good water solubility. Another technical problem to be solved by the present invention is to provide a lithium-ion battery using the above-mentioned adhesive.

[0005] Technical solution: In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] A water-based adhesive is obtained by cross-linking polyethyleneimine (PEI), glutaraldehyde (GA) and dopamine (DPA), wherein the mass proportions of polyethyleneimine, glutaraldehyde and dopamine are 85%-95%, 0.1%-0.3%, 4.9%-14.7% respectively, and the total mass proportion of the three substances is 100%.

[0007] The mass proportions of the aqueous binder, polyethyleneimine, glutaraldehyde and dopamine are 95%:0.1%:4.9%, 90%:0.2%:9.8% or 85%:0.3%:14.7%.

[0008] The molecular weight of the aqueous binder, polyethyleneimine, is 70,000.

[0009] The preparation method of the water-based adhesive comprises preparing a polydopamine solution, a polyethyleneimine solution and a glutaraldehyde solution, and then stirring and mixing the three solutions at room temperature to obtain the water-based adhesive.

[0010] In the preparation method of the aqueous binder, the mass concentrations of the dopamine solution, the polyethyleneimine solution and the glutaraldehyde solution are all 5wt.%.

[0011] The preparation method of the aqueous binder comprises the following steps: mixing dopamine hydrochloride powder with Tris hydrochloric acid in a dark place, stirring to obtain a uniformly mixed dopamine solution; and mixing deionized water with polyethyleneimine to obtain a polyethyleneimine solution.

[0012] The above aqueous binder is used in lithium-ion batteries, which use silicon-carbon negative electrodes.

[0013] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0014] (1) The present invention adopts polyethyleneimine (PEI), glutaraldehyde (GA) and dopamine (DPA) for cross-linking to synthesize a polymer binder with good adhesion, water solubility and high stability.

[0015] (2) When the addition amount of GA is 0.2% and the addition amount of DPA is 9.8%, the electrode electrochemical performance is the best. The peel strength of the prepared PEI-GA (0.2%)-DPA (9.8%) electrode is 3.28N, while the peel strength of the electrode prepared with PEI as the binder is only 1.33N.

[0016] (3) The SEM image after one hundred cycles shows that the composite silicon-carbon electrode prepared by the present invention has significantly fewer cracks and forms a uniform and dense SEI layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The infrared spectra of samples PEI, DPA and PEI-GA (0.2%)-DPA (9.8%);

[0018] Figure 2 This is the rate cycling characteristic diagram of the composite silicon-carbon electrode;

[0019] Figure 3 These are SEM images of silicon-carbon electrodes with different compositions before and after 100 cycles. DETAILED DESCRIPTION

[0020] The present invention is further illustrated below in conjunction with specific examples. The examples are implemented based on the technical solutions of the present invention. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0021] Example 1

[0022] A method for preparing a water-based binder comprises the following steps:

[0023] Mix 0.5 g of dopamine hydrochloride powder with 9.5 g of Tris hydrochloric acid solution in a dark place, stir in the dark, and obtain a uniformly mixed dopamine solution, which is stored in the dark and used immediately after preparation;

[0024] 18.0 g of deionized water was mixed with 2.0 g of polyethyleneimine (MW 70000, 50% in H2O) to form a polyethyleneimine solution with a mass fraction of 5 wt.%;

[0025] Mix 2.0 g of glutaraldehyde (50% in H2O) with 18.0 g of deionized water to prepare a 5 wt.% glutaraldehyde solution;

[0026] The polyethyleneimine solution, glutaraldehyde solution and dopamine solution were stirred for 30 minutes at an effective mass ratio of 95:0.1:4.9, 90:0.2:9.8 and 85:0.3:14.7 to obtain a uniformly mixed binder solution, which was labeled as PEI-GA (0.1%)-DPA (4.9%), PEI-GA (0.2%)-DPA (9.8%) and PEI-GA (0.3%)-DPA (14.7%), respectively, and stored in a cool place.

[0027] The infrared spectra of samples PEI, DPA and PEI-GA (0.2%)-DPA (9.8%) are shown in Figure 2. Figure 1 As shown. 3271cm -1 The absorption peak at 1654 cm is the NH stretching vibration peak. -1 The absorption peak at 2816cm is the NH bending vibration peak. -1 The absorption peak at 1294 cm is the stretching vibration peak of CH. -1 The absorption peak at 1603cm is the stretching vibration peak of CN. -1 The absorption peak at 1647 cm is attributed to the C=C vibration peak of the benzene ring. -1 An obvious absorption peak can be observed at 1297 cm-1, which is the C=N stretching vibration peak. The CN bending vibration peak is shifted and appears at 1297 cm-1. -1 The changes in the infrared spectrum, especially the formation of imine bonds (-C=N-), indicate that PEI-GA-DPA is successfully cross-linked.

[0028] The cycling performance of each binder was investigated at a current density of 0.5C. The specific capacities of Si-C@PVDF and Si-C@PEI electrodes after 100 cycles were 489.6 mAh g -1 and 412.0mAh g -1 Compared with pure PEI binder, the performance of PEI-GA (0.2%)-DPA (9.8%) binder cross-linked by imine bonds is improved. Under the same conditions, Si / C@PEI-GA-DPA electrode can still maintain 540.8 mAh g -1 The charge capacity.

[0029] Example 2

[0030] First, the silicon-carbon material, the cross-linking binder (PEI, PVDP, PEI-GA (0.1%)-DPA (0.9%), PEI-GA (0.2%)-DPA (9.8%), PEI-GA (0.3%)-DPA (0.7%)) and the conductive additive were mixed together in a ratio of 80:10:10 and stirred until the mixed material was muddy, with uniform color and no obvious separation and granularity;

[0031] Use a scraper to evenly apply the mixed slurry on the cut copper foil (8cm*20cm), with a blade thickness of 90-115μm. After natural ventilation for 2h, transfer the electrode to a vacuum drying oven and dry at 80℃ for 8h;

[0032] The electrode sheet was cut into a circular electrode sheet with a radius of 7 mm using a slicer. The active material surface loading of the Si-C electrode was about 2.4-2.5 mg cm -2 Then, the electrode was moved into a glove box with an argon atmosphere and placed for 6 hours before use.

[0033] For samples PEI, PVDF, PEI-GA (0.1%)-DPA (0.9%), PEI-GA (0.2%)-DPA (9.8%), and PEI-GA (0.3%)-DPA (0.7%), a 180° peeling test experiment was carried out using a tensile testing machine, and the tape used was 3M tape.

[0034] The results showed that the average peeling forces of the silicon-carbon electrodes of samples PEI, PVDF, PEI-GA (0.1%)-DPA (0.9%), PEI-GA (0.2%)-DPA (9.8%), and PEI-GA (0.3%)-DPA (0.7%) were 1.33N, 1.43N, 2.73N, 3.28N, and 2.40N, respectively. The adhesion force of the aqueous binder electrode of the present invention is greater than that of pure PEI (1.33N), indicating that the binder can adhere the active material to the current collector very well, thereby ensuring the stability of the electrode.

[0035] The cycle rate was 0.1C, 0.2C, 0.5C, 1C, 3C, 1C, 0.5C, 0.2C, 0.1C, and each rate was cycled five times. Figure 2 As shown in the figure, the electrode material of the present invention has good reversibility and cycle stability. It not only has high coulombic efficiency, but also can restore its specific capacity to the original cycle state after high rate (3C) discharge. When discharged at 3C, the specific capacity of Si-C@PEI-GA (0.2%)-DPA (9.8%) is 314.2 mAh g -1 , while the specific capacity of Si-C@PEI is only 172.7 mAhg at 3C discharge. -1 Compared with the first 0.1C cycle data, when the current was restored to 0.1C for rate charge and discharge, the capacity retention rate of the Si-C@PEI-GA (0.2%)-DPA (9.8%) electrode was as high as 99.15%, further showing the good reversible properties of the electrode.

[0036] Example 3

[0037] When using a CR2032 half-cell shell, it is necessary to ensure that the concentration of water and oxygen in the electrode does not exceed 1ppm in an argon environment in order to complete the battery-related assembly.

[0038] The electrode sheets (Si-C@PEI, Si-C@PVDP, Si-C@PEI-GA(0.1%)-DPA(0.9%), Si-C@PEI-GA(0.2%)-DPA(9.8%), Si-C@PEI-GA(0.3%)-DPA(0.7%)) and the diaphragm were placed in the center of the positive electrode shell of a CR-2032 button battery. 80 μL of electrolyte was dripped on the diaphragm, and a lithium sheet was placed in the center of the electrode shell. Be careful not to have any contact between the lithium sheet and the battery shell to prevent the battery from short circuiting. Finally, the negative electrode battery shell was covered with a 40-60 kg / cm 2 The battery is sealed with pressure, and the pressure is reduced after about 3 seconds. The battery is taken out and the battery open circuit voltage is checked with a miniature multimeter to determine whether the battery is short-circuited.

[0039] The battery was left to stand for 24 h before conducting relevant electrochemical tests to ensure that the electrolyte fully infiltrated the diaphragm and electrode sheets.

[0040] Table 1 shows the impedance values ​​of Si-C@PEI, Si-C@PVDF, Si-C@PEI-GA (0.1%)-DPA (0.9%), Si-C@PEI-GA (0.2%)-DPA (9.8%), and Si-C@PEI-GA (0.3%)-DPA (0.7%) composite silicon-carbon electrodes before and after cycling, describing the impedance characteristics of silicon-carbon electrodes before and after cycling. In the Si-C@PEI-GA (0.2%)-DPA (9.8%) electrode, a good initial electrochemical state is exhibited. As the cycle proceeds, the electrode structure changes. The more complete the electrode structure, the lower the impedance. It can be seen that the binder PEI-GA (0.2%)-DPA (9.8%) provides excellent performance in maintaining the integrity of the electrode structure.

[0041] Table 1 Impedance values ​​before and after different electrode cycles

[0042]

[0043] The morphological characteristics of PVDF, PEI, and PEI-GA-DPA composite silicon-carbon electrodes before and after cycling were tested. The microscopic morphology and structure were as follows: Figure 3 As shown, from left to right are PVDF, PEI, and PEI-GA-DPA. Figure 3 It can be seen that before the cycle, the three electrodes have similar microscopic morphology, the electrodes are uniform, and there are few agglomerations and clusters. The SEM image after 100 cycles is as follows Figure 3 As shown, the Si-C@PEI-GA (0.2%)-DPA (9.8%) electrode has significantly fewer cracks and forms a uniform and dense surface layer, further verifying the excellent bonding performance of the PEI-GA-DPA binder during cycling.

[0044] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A water-based binder, It is characterized in that It is obtained by cross-linking polyethyleneimine, glutaraldehyde and dopamine, wherein the weight proportions of polyethyleneimine, glutaraldehyde and dopamine are 85%-95%, 0.1%-0.3%, 4.9%-14.7% respectively, and the total weight proportion of the three substances is 100%.

2. The aqueous binder according to claim 1, It is characterized in that The mass proportions of polyethyleneimine, glutaraldehyde and dopamine are 95%:0.1%:4.9%, 90%:0.2%:9.8% or 85%:0.3%:14.7%.

3. The aqueous binder according to claim 1, It is characterized in that The molecular weight of the polyethyleneimine is 70,000.

4. A method for preparing the aqueous binder according to claim 1, It is characterized in that A dopamine solution, a polyethyleneimine solution and a glutaraldehyde solution were prepared, and then the three solutions were stirred and mixed at room temperature to obtain an aqueous binder solution.

5. A method for preparing the aqueous binder according to claim 4, It is characterized in that The mass concentrations of the dopamine solution, the polyethyleneimine solution and the glutaraldehyde solution are all 5 wt.%.

6. A method for preparing the aqueous binder according to claim 4, It is characterized in that Dopamine powder is mixed with Tris hydrochloric acid in a dark place, and stirred to obtain a uniformly mixed dopamine solution; deionized water is mixed with polyethyleneimine to obtain a polyethyleneimine solution.

7. Use of the aqueous binder according to claim 1 in lithium ion batteries.

8. Use of the aqueous binder according to claim 7 in lithium ion batteries, It is characterized in that The lithium ion battery adopts a silicon-carbon negative electrode.

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