Graphite negative electrode coated with PVDF-based composite coating as well as preparation method and application of graphite negative electrode

Abstract

The invention discloses a graphite negative electrode coated with a PVDF (polyvinylidene fluoride)-based composite coating as well as a preparation method and application of the graphite negative electrode. The graphite negative electrode comprises a graphite pole piece and a composite coating which is coated on the graphite pole piece and is formed by PVDF and BaTiO3, the graphite pole piece is obtained by coating a current collector with mixed slurry formed by graphite, a binder, a conductive agent and deionized water. According to the invention, the compact and uniform composite coating is coated on the surface of the graphite negative plate to form a stable negative electrode / electrolyte interface, so that the interface impedance is reduced, and ion transmission under a fast charge condition is promoted, thereby improving the fast charge cycle stability and rate capability.

Description

Technical Field

[0001] The invention belongs to the field of lithium-ion battery material technology, specifically relating to a graphite anode coated with a PVDF-based composite coating, its preparation method, and its application. Background Technology

[0002] With the increasing demand for fast charging technology in electric vehicles and energy storage systems, traditional graphite anodes often exhibit problems such as limited lithium-ion diffusion, unstable electrode interfaces, and rapid cycle degradation under high-rate charging conditions, severely affecting the fast-charging performance of batteries. Research shows that the small interlayer spacing of graphite materials limits the lithium diffusion rate under high-current conditions, posing a challenge to achieving high-rate charging. Summary of the Invention

[0003] To address the aforementioned issues, the present invention aims to provide a PVDF-based composite coating-coated graphite anode, its preparation method, and its application. By coating the surface of the graphite anode sheet with a dense and uniform composite coating, a stable anode / electrolyte interface is formed, reducing interface impedance and promoting ion transport under fast charging conditions, thereby improving fast charging cycle stability and rate performance.

[0004] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: A PVDF-based composite coating-coated graphite anode includes a graphite electrode sheet and a composite coating of PVDF and BaTiO3 coated on the graphite electrode sheet; the graphite electrode sheet is obtained by coating a current collector with a mixed slurry of graphite, binder, conductive agent and deionized water.

[0005] Furthermore, in the composite coating, the mass percentage of PVDF and BaTiO3 is 80~90%:10~20%.

[0006] Furthermore, the current collector is a copper foil.

[0007] Furthermore, the adhesive is at least one of styrene-butadiene rubber and carboxymethyl cellulose.

[0008] Furthermore, the conductive agent is at least one of conductive carbon black and single-walled carbon nanotubes.

[0009] Furthermore, the mass percentages of the graphite, binder, and conductive agent are 91%:4%:5%.

[0010] The present invention also provides a method for preparing the above-mentioned PVDF-based composite coating-coated graphite anode, comprising the following steps: (1) Thoroughly mix graphite, binder, conductive agent and deionized water to obtain slurry, then coat the slurry onto the current collector, and dry it to obtain graphite electrode sheet; (2) First, BaTiO3 is ultrasonically dispersed in NMP, then PVDF is added and thoroughly mixed to obtain a slurry. Finally, the slurry is coated on a graphite electrode and dried to obtain a graphite negative electrode.

[0011] This invention also provides an application of the above-mentioned graphite anode in the preparation of lithium-ion batteries.

[0012] Compared with the prior art, the present invention has the following advantages and positive effects: (1) Significantly improves the interfacial stability of graphite anode under fast charging conditions This invention introduces a composite coating with PVDF as the matrix and functional inorganic fillers on the surface of a graphite anode, thereby constructing a stable interfacial transition layer between the anode active material and the electrolyte. This composite coating can effectively buffer the interfacial stress concentration and side reactions caused by high current density during fast charging, and promote the formation of a more uniform, dense and stable SEI film, thus significantly improving the stability of the anode interface.

[0013] (2) Reduce polarization during fast charging and improve rate charging and discharging performance. The functional fillers introduced into the composite coating can regulate the dielectric and interfacial properties of the coating. While ensuring the mechanical strength and adhesion of the coating, they can shorten the diffusion path of lithium ions on the negative electrode surface, reduce the interfacial charge transfer impedance, and exhibit lower polarization and better rate performance under medium and high rate conditions.

[0014] (3) Suppress the risk of lithium deposition and improve the safety of fast charging. This invention homogenizes the current density distribution on the negative electrode surface through a composite coating, improves the uniformity of lithium-ion flux, effectively reduces local overpotential, thereby suppressing the risk of lithium dendrites or metallic lithium deposition and enhancing safety during fast charging.

[0015] (4) Improve cycle life and capacity retention Because the composite coating can maintain a stable interface structure during cycling, reducing the continuous decomposition of the electrolyte and the consumption of active lithium, the fast-charging graphite anode of the present invention exhibits higher capacity retention and coulombic efficiency under long-cycle conditions, which is beneficial to extending the service life of lithium-ion batteries. Attached Figure Description

[0016] Figure 1 Impedance spectra of NCM811 / graphite full cells before (a) and after 50 cycles (b), where GR+PVDF+BTO represents Example 1, GR represents Comparative Example 1, and GR+PVDF represents Comparative Example 2.

[0017] Figure 2 Cyclic voltammetry plots of NCM811 / graphite full cells at scan rates of 0.1 mV (a) and 0.5 mV (b).

[0018] Figure 3 The charge-discharge curves of the NCM811 / graphite full cell at 0.1C(a), 0.5C(b), 1C(c), and 2C(d) are shown.

[0019] Figure 4 The graph (a) shows the performance of the NCM811 / graphite full cell after 200 cycles at 0.5C, and the corresponding coulombic efficiency graph (b).

[0020] Figure 5 The graph (a) shows the rate performance test results of the NCM811 / graphite full cell, and the corresponding coulombic efficiency graph (b) shows the results.

[0021] Figure 6 The VT plot is shown during the GITT test of the NCM811 / graphite full cell.

[0022] Figure 7 The T-LgD plot is shown during the GITT test of the NCM811 / graphite full cell. Detailed Implementation

[0023] The following is a detailed description of the preferred embodiments of the present invention, which does not constitute any limitation on the present invention. That is, the present invention is not limited to the following embodiments, and all common variations or alternative compounds in this technical field are included within the scope defined by the claims of this application.

[0024] Example

[0025] 1. Preparation of graphite electrode sheets: A slurry was prepared by mixing graphite (91 wt%), conductive carbon black (4.85 wt%), carbon nanotubes (0.15 wt%), styrene-butadiene rubber (2.5 wt%), carboxymethyl cellulose (1.5 wt%), and an appropriate amount of deionized water. The slurry was then coated onto copper foil and dried in an oven at 80 ℃ for 60 min, followed by drying in a vacuum drying oven at 120 ℃ for 300 min to obtain graphite electrode sheets.

[0026] 2. Preparation of graphite anode: BaTiO3 (1 wt%) was first ultrasonically dispersed in NMP (90 wt%), then PVDF (9 wt%) was added and thoroughly mixed to obtain a slurry. Finally, the slurry was coated onto a graphite electrode sheet and dried in an oven at 80 ℃ for 60 min, and then dried in a vacuum drying oven at 120 ℃ for 300 min to obtain a graphite anode.

[0027] Comparative Example 1 Preparation of graphite electrode sheets: A slurry was prepared by mixing graphite (91 wt%), conductive carbon black (4.85 wt%), carbon nanotubes (0.15 wt%), styrene-butadiene rubber (2.5 wt%), carboxymethyl cellulose (1.5 wt%), and an appropriate amount of deionized water. The slurry was then coated onto copper foil and dried in an oven at 80 ℃ for 60 min, followed by drying in a vacuum drying oven at 120 ℃ for 300 min to obtain graphite electrode sheets.

[0028] Comparative Example 2 1. Preparation of graphite electrode sheets: A slurry was prepared by mixing graphite (91 wt%), conductive carbon black (4.85 wt%), carbon nanotubes (0.15 wt%), styrene-butadiene rubber (2.5 wt%), carboxymethyl cellulose (1.5 wt%), and an appropriate amount of deionized water. The slurry was then coated onto copper foil and dried in an oven at 80 ℃ for 60 min, followed by drying in a vacuum drying oven at 120 ℃ for 300 min to obtain graphite electrode sheets.

[0029] 2. Preparation of graphite anode: PVDF (10 wt%) was ultrasonically dispersed in NMP (90 wt%) and thoroughly mixed to obtain a slurry. The slurry was then coated onto a graphite electrode and dried in an 80 ℃ oven for 60 min, followed by drying in a 120 ℃ vacuum drying oven for 300 min to obtain a graphite anode.

[0030] Performance testing: The graphite negative electrode (Example 1, Comparative Example 1 and Comparative Example 2) was cut to a diameter of 14 mm using a punching machine, and then pressed into a sheet under a pressure of 400 kg. Finally, the counter electrode sheet was assembled in a glove box filled with Ar gas in the following order: positive electrode shell, positive electrode sheet (active material is NCM811), separator, electrolyte, negative electrode sheet (i.e., graphite negative electrode), gasket, and negative electrode shell.

Claims

1. A graphite anode coated with a PVDF-based composite coating, characterized in that, The graphite negative electrode includes a graphite electrode sheet and a composite coating of PVDF and BaTiO3 coated on the graphite electrode sheet. The graphite electrode sheet is obtained by coating a current collector with a mixed slurry formed of graphite, binder, conductive agent and deionized water.

2. The graphite negative electrode according to claim 1, characterized in that, In the composite coating, the mass percentage of PVDF and BaTiO3 is 80~90%:10~20%.

3. The graphite negative electrode according to claim 1, characterized in that, The current collector is a copper foil.

4. The graphite negative electrode according to claim 1, characterized in that, The adhesive is at least one of styrene-butadiene rubber and carboxymethyl cellulose.

5. The graphite negative electrode according to claim 1, characterized in that, The conductive agent is at least one of conductive carbon black and single-walled carbon nanotubes.

6. The graphite negative electrode according to claim 1, characterized in that, The mass percentages of the graphite, binder, and conductive agent are 91%:4%:5%.

7. The method for preparing the graphite anode according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Thoroughly mix graphite, binder, conductive agent and deionized water to obtain slurry, then coat the slurry onto the current collector, and dry it to obtain graphite electrode sheet; (2) First, BaTiO3 is ultrasonically dispersed in NMP, then PVDF is added and thoroughly mixed to obtain a slurry. Finally, the slurry is coated on a graphite electrode and dried to obtain a graphite negative electrode.

8. The application of the graphite anode according to any one of claims 1-7 or the graphite anode prepared by the preparation method according to claim 8, characterized in that, It is used to manufacture lithium-ion batteries.

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