Method for improving anion storage capacity of graphite through low-temperature oxygen inhibition

Abstract

The invention discloses a method for improving the anion storage capacity of graphite through low-temperature oxygen inhibition. The method comprises the following steps: uniformly mixing graphite powder, a conductive agent and a binder in proportion to obtain electrode slurry; coating a conductive current collector with the electrode slurry, and performing vacuum drying to obtain a graphite electrode; the method comprises the following steps: by taking a graphite electrode as a working electrode, a carbon rod electrode as a counter electrode and an Ag / AgCl electrode as a reference electrode, respectively carrying out electrochemical performance tests under normal-temperature and low-temperature conditions in a sulfuric acid aqueous solution, thereby completing the improvement of the anion storage capacity of the graphite. The low-temperature oxygen inhibition strategy in the invention greatly reduces the occurrence of oxygen evolution side reaction, so that the graphite electrode can efficiently embed anions at a higher potential, the voltage window is widened, the coulombic efficiency and stability of the electrode are improved, and the method has important reference value for research and development of low-temperature and high-voltage batteries, and has wide application prospects. Or the method can become an important link for constructing an extreme low-temperature energy storage system in the future.

Description

Technical Field

[0001] This invention belongs to the field of anion batteries, specifically relating to a method for improving the anion storage capacity of graphite by low-temperature oxygen suppression. Background Technology

[0002] With the continuous growth of global energy demand and increasing emphasis on environmental protection, the development of efficient and sustainable energy storage technologies has become an urgent priority. Against this backdrop, anion batteries, as a novel energy storage system, have attracted widespread attention. While traditional lithium-ion batteries have achieved great success in consumer electronics and electric vehicles, they face challenges such as limited resources, high costs, and room for improvement in safety performance. Anion batteries utilize the insertion and extraction of anions in electrode materials to store and convert energy. Compared to traditional lithium-ion batteries, they offer advantages such as potentially high energy density, abundant resource reserves, and good environmental friendliness. Furthermore, the materials used in anion batteries are relatively widely available and inexpensive, helping to reduce energy storage costs and promote large-scale energy storage applications, such as grid energy storage. However, research on anion batteries is still in its early stages and faces many challenges, such as improving the stability and conductivity of electrode materials, optimizing electrolyte systems, and enhancing battery cycle life and rate performance. Therefore, in-depth research into the principles, materials, and performance of anion batteries is of great significance for promoting the development of energy storage technologies and achieving sustainable energy utilization.

[0003] Among electrode materials for aqueous anion exchange batteries, graphite has received widespread attention due to its high operating voltage, good conductivity, low cost, and environmental friendliness, making it the most commonly used cathode material. Graphite has a typical two-dimensional layered structure, which allows anions (HSO4) to... - ClO4 - PF4 - ,Br - Cl - (etc.) Intercalation into the graphite layers. However, in aqueous anion batteries, the potential for anion intercalation is more positive than the potential for oxygen evolution reaction. The strong oxygen evolution reaction makes it difficult to fully utilize the capacity of anion intercalation and reduces the energy density of the electrode. Furthermore, continuous bubble precipitation will damage the stability of the electrode, causing severe volume expansion of graphite and even structural collapse. Summary of the Invention

[0004] This invention is proposed to suppress the oxygen evolution reaction of graphite, increase the working voltage of graphite anion intercalation, and make more efficient use of the anion storage capacity of graphite. Its purpose is to provide a method for low-temperature oxygen suppression to improve the energy density of graphite.

[0005] This invention is achieved through the following technical solution: A method for enhancing the anion storage capacity of graphite by low-temperature oxygen suppression includes the following steps: S1. Preparation of graphite electrodes; S2, Optimization of electrochemical performance at room temperature: The electrochemical performance of a graphite electrode as the working electrode, along with a counter electrode and a reference electrode, was optimized at room temperature in an aqueous sulfuric acid solution. The conditions for optimizing the room-temperature electrochemical performance are: temperature 20 ℃ ~ 25 ℃; voltage window 0 ~ 2.1 V vs. Ag / AgCl; S3, Low-temperature electrochemical performance optimization: The low-temperature electrochemical performance of the graphite electrode as the working electrode, along with the counter electrode and reference electrode, was optimized in sulfuric acid aqueous solution to improve the capacity of graphite to store anions. The conditions for optimizing the low-temperature electrochemical performance are: temperature -100 ℃ ~ 0 ℃; voltage window 0 ~ 2.1 V vs. Ag / AgCl.

[0006] In the above technical solution, the method for preparing the graphite electrode is as follows: graphite powder, conductive agent and binder are mixed uniformly in proportion to obtain electrode slurry, the electrode slurry is coated on conductive current collector, and the graphite electrode is obtained after drying.

[0007] In the above technical solution, the conductive agent is any one of CNT, Ketjen black, Acetylene black or SuperP; the binder is any one of PVDF, CMC, PTFE or LA; and the conductive current collector is any one of titanium foil, titanium mesh, carbon cloth, carbon paper, graphite paper or graphite felt.

[0008] In the above technical solution, the mass ratio of graphite powder, conductive agent and binder is 5:4:1, 6:3:1, 7:2:1 or 8:1:1.

[0009] In the above technical solution, the drying conditions are vacuum drying at 80 ℃ for 24 h.

[0010] In the above technical solution, the graphite loading in the dried graphite electrode is 1 mg cm⁻¹. -2 ~ 50 mgcm -2 .

[0011] In the above technical solution, the graphite electrode is prepared by cutting graphite foil or graphite paper of appropriate size and using it directly as the graphite electrode.

[0012] In the above technical solution, the counter electrode in steps S2 and S3 is a carbon rod electrode or a platinum sheet electrode, and the reference electrode is an Ag / AgCl electrode.

[0013] In the above technical solution, the concentration of the sulfuric acid aqueous solution in steps S2 and S3 is 4 mol / L. -1 ~17mol L -1 .

[0014] The low-temperature oxygen suppression strategy of this invention effectively widens the voltage window of graphite (from 0~1.6 vs. Ag / AgCl to 0~2.1 vs. Ag / AgCl), allowing the capacity of anion intercalation that is masked by the oxygen evolution reaction in the high potential region to be released, improving the coulombic efficiency by 26.8%, while reducing the damage of the oxygen evolution reaction to the electrode and improving the electrode stability.

[0015] The beneficial effects of this invention are: This invention provides a method for enhancing the anion storage capacity of graphite by suppressing oxygen at low temperatures. Under low-temperature conditions, the oxygen evolution reaction of the electrode is suppressed, so that the anion insertion capacity of the electrode dominates at high potential. This broadens the voltage window of graphite and improves the stability of the electrode, providing a reference for the development and theoretical research of high-performance water-based high-voltage cathodes. Attached Figure Description

[0016] Figure 1 This is an optical photograph of the graphite electrode prepared in Example 1 of the present invention; Figure 2 This is the X-ray diffraction pattern of the graphite electrode prepared in Example 1 of the present invention; Figure 3 The graphite electrode prepared in Example 1 of this invention exhibits cyclic voltammetric polarization curves at room temperature and low temperature. Figure 4 The electrochemical performance and charge-discharge curves of the graphite electrode prepared in Example 1 of this invention at room temperature and low temperature are shown in Figure a (a is the constant current charge-discharge capacity graph of the graphite electrode at room temperature; b is the constant current charge-discharge curve graph of the graphite electrode at room temperature; c is the constant current charge-discharge capacity graph of the graphite electrode at low temperature; d is the constant current charge-discharge curve graph of the graphite electrode at low temperature). Figure 5 These are performance optimization diagrams of the graphite electrode prepared in Example 1 of the present invention at room temperature and low temperature (a is the graphite electrode potential optimization diagram at room temperature and low temperature; b is the graphite electrode coulombic efficiency optimization diagram at room temperature and low temperature).

[0017] For those skilled in the art, other related figures can be obtained from the above figures without any creative effort. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0019] Example A method for enhancing the anion storage capacity of graphite by low-temperature oxygen suppression includes the following steps: S1. Preparation of graphite electrodes; Graphite powder, conductive agent (Super P), and binder (PVDF) were uniformly mixed at a mass ratio of 8:1:1 and thoroughly mixed using a planetary ball mill at 300 rpm for 24 h to obtain a black electrode slurry. This slurry was then coated onto a carbon cloth current collector and vacuum dried at 80 ℃ for 24 h to obtain a graphite loading of 14 mg / cm². -2 Graphite electrodes; S2, Optimization of electrochemical performance at room temperature: A graphite electrode was used as the working electrode, along with a carbon rod electrode as the counter electrode and an Ag / AgCl electrode as the reference electrode, at a concentration of 4.0 mol / L. –1 Optimization of electrochemical performance at room temperature in sulfuric acid aqueous solution; The conditions for optimizing the room-temperature electrochemical performance were: a temperature of 20°C; a voltage window of 0–1.6 V vs. Ag / AgCl, at 2.8 mA cm⁻¹. -2 7 mA cm -2 14 mA cm -2 28 mA cm -2 70 mA cm -2 Perform constant current charge and discharge five times at a current density; S3, Low-temperature electrochemical performance optimization: The low-temperature electrochemical performance of the graphite electrode as the working electrode, along with the counter electrode and reference electrode, was optimized in sulfuric acid aqueous solution to improve the capacity of graphite to store anions. The conditions for optimizing the low-temperature electrochemical performance are: temperature -40℃; voltage window of 0~2.1 V vs. Ag / AgCl, respectively at 2 mA cm⁻¹. -2 5 mA cm -2 10 mA cm -2 20 mA cm -2 50 mA cm -2 100 mA cm -2 The constant current charge and discharge cycle was performed 5 times at the specified current density.

[0020] The graphite electrode prepared in Example 1 was tested and characterized: I. Morphological characteristics: The macroscopic morphology of the graphite electrode prepared in Example 1 was observed by optical photography. Figure 1The area coated with graphite slurry in the graphite electrode appears dark black, and no obvious breakage or falling off is observed in the area loaded with active material when the electrode is bent, proving that the graphite is stably attached to the conductive substrate.

[0021] II. X-ray diffraction pattern test: X-ray diffraction spectroscopy was performed on the graphite electrode prepared in Example 1 to investigate its phase composition. Figure 2 Obvious diffraction peaks were observed at 26.5°, 44.5°, 54.7° and 77.4°, corresponding to the (002), (101), (004) and (110) crystal planes of graphite, proving that the active material of the electrode prepared by the present invention is graphite.

[0022] III. Electrochemical Performance Testing: Cyclic voltammetric polarization curves were tested on the graphite electrode prepared in Example 1. Figure 3 As shown, lowering the temperature can significantly suppress the oxygen evolution reaction of graphite, thus broadening the maximum potential for storing anions in graphite from 1.6 V vs. Ag / AgCl to 2.1 V vs. Ag / AgCl.

[0023] IV. Constant Current Charge-Discharge Test: The graphite electrode prepared in Example 1 was subjected to constant current charge-discharge testing. Figure 4 As shown, under normal temperature conditions, graphite electrodes cannot reach higher potentials due to the limitation of the oxygen evolution reaction, while under low temperature conditions, the hydrogen evolution reaction of graphite is suppressed, allowing the potential to break through to higher levels. Figure 5 The specific optimization of graphite electrode performance under room temperature and low temperature conditions is shown. Low temperature inhibits oxygen evolution reaction, which expands the voltage window by 0.5 V and improves coulombic efficiency by 26.8%. Low temperature reduces the damage to the electrode caused by the continuous generation of bubbles due to oxygen evolution reaction, and improves the stability of graphite electrode.

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0025] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for enhancing the anion storage capacity of graphite by low-temperature oxygen suppression, characterized in that: Includes the following steps: S1. Preparation of graphite electrodes; S2, Optimization of electrochemical performance at room temperature: The electrochemical performance of a graphite electrode as the working electrode, along with a counter electrode and a reference electrode, was optimized at room temperature in an aqueous sulfuric acid solution. The conditions for optimizing the room-temperature electrochemical performance are: temperature 20 ℃ ~ 25 ℃; voltage window 0 ~ 2.1 V vs. Ag / AgCl, 0.5 ~ 100 mA cm⁻¹ -2 Cycling at current density 1 to 100 times; S3, Low-temperature electrochemical performance optimization The graphite electrode with optimized electrochemical performance at room temperature was used as the working electrode, and its low-temperature electrochemical performance was optimized in sulfuric acid aqueous solution along with the counter electrode and reference electrode to improve the capacity of graphite to store anions. The conditions for optimizing the low-temperature electrochemical performance are: temperature -100 ℃ ~ 0 ℃; voltage window 0~2.1 V vs. Ag / AgCl, 0.5~100 mA cm⁻¹ -2 Cycle 1 to 100 times at current density.

2. The method for improving the anion storage capacity of graphite by low-temperature oxygen suppression according to claim 1, characterized in that: The graphite electrode is prepared by uniformly mixing graphite powder, conductive agent and binder in a certain proportion to obtain an electrode slurry, coating the electrode slurry onto a conductive current collector, and drying it to obtain a graphite electrode.

3. The method for improving the anion storage capacity of graphite by low-temperature oxygen suppression according to claim 2, characterized in that: The conductive agent is any one of CNT, Ketjen black, Acetylene black, or Super P; the binder is any one of PVDF, CMC, PTFE, or LA; and the conductive current collector is any one of titanium foil, titanium mesh, carbon cloth, carbon paper, graphite paper, or graphite felt.

4. The method for improving the anion storage capacity of graphite by low-temperature oxygen suppression according to claim 2, characterized in that: The mass ratio of the graphite powder, conductive agent, and binder is 5:4:1, 6:3:1, 7:2:1, or 8:1:

1.

5. The method for improving the anion storage capacity of graphite by low-temperature oxygen suppression according to claim 2, characterized in that: The drying conditions were vacuum drying at 80 °C for 24 h.

6. The method for improving the anion storage capacity of graphite by low-temperature oxygen suppression according to claim 2, characterized in that: The graphite loading in the dried graphite electrode is 1 mg cm⁻¹. -2 ~50 mg cm -2 .

7. The method for improving the anion storage capacity of graphite by low-temperature oxygen suppression according to claim 1, characterized in that: The graphite electrode is prepared by cutting graphite foil or graphite paper to a suitable size and using it directly as the graphite electrode.

8. The method for improving the anion storage capacity of graphite by low-temperature oxygen suppression according to claim 1, characterized in that: In steps S2 and S3, the counter electrode is a carbon rod electrode or a platinum sheet electrode, and the reference electrode is an Ag / AgCl electrode.

9. The method for improving the anion storage capacity of graphite by low-temperature oxygen suppression according to claim 1, characterized in that: The concentration of the sulfuric acid aqueous solution in steps S2 and S3 is 4 mol / L. -1 ~17 mol L -1 .

Images