A method of anionically intercalating a graphite electrode

Abstract

The application discloses a method for anion local embedding of a graphite electrode, which forms a limited electrochemical cell on the surface of the graphite electrode by using an electrochemical probe with a tip aperture of several hundred nanometers to tens of microns, and promotes anion embedding of the graphite electrode in an electrolyte by applying an electrode potential; wherein the electrochemical probe is obtained by drawing a glass or quartz capillary tube by using a P-2000 laser drawing instrument, the electrochemical probe is characterized by a hollow conical tube, and an electrolyte solution is filled in the electrochemical probe; the method can construct a micro-area electrochemical cell in any area of the graphite electrode material to embed anion into the electrode material, and has the characteristics of controllable reaction area, small reaction area, simple operation and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemistry, and in particular relates to a method for locally embedding anions into a graphite electrode. Background Art

[0002] Energy crises and environmental challenges are forcing humanity to seek new energy alternatives to traditional fossil fuels. In recent years, renewable energy sources such as solar and wind power have garnered widespread attention. However, renewable energy sources are intermittent and cannot output energy continuously and stably. Electrochemical energy storage systems, with lithium-ion batteries being a prime example, enable controllable energy conversion. However, traditional lithium-ion batteries have limitations in terms of environmental friendliness, safety, and energy density. Therefore, developing environmentally friendly, high-performance energy storage systems and promoting further advancements in battery technology are crucial for efficient energy utilization.

[0003] In recent years, dual-ion batteries (DIBs) have attracted widespread attention due to their high operating voltage and environmentally friendly properties. Unlike traditional lithium-ion batteries, which rely on the intercalation and deintercalation of cations between the positive and negative electrode materials to achieve charge and discharge, DIBs allow both positive and negative ions to intercalate and deintercalate within the electrode materials, resulting in a high discharge voltage platform. However, the dual-ion batteries currently published still have problems such as unsatisfactory cycle stability, low actual specific capacity, and poor rate performance. See the articles "Sui, Y.; Liu, C.; Masse, RC; Neale, ZG; Atif, M.; AlSalhi, M.; Cao, G., Dual-ion batteries: The emerging alternative rechargeable batteries. Energy Storage Materials 2020, 25, 1-32." and "Ou, X.; Gong, D.; Han, C.; Liu, Z.; Tang, Y., Advances and Prospects of Dual-Ion Batteries. Advanced Energy Materials 2021, 11(46).".

[0004] Traditional battery performance testing methods can only obtain macroscopic statistical average data, while the microstructure and electrochemical processes of electrode materials have a decisive influence on battery performance. However, there are currently few reports on the controlled anion insertion / extraction in micro-regions of electrode material surfaces for dual-ion batteries. Therefore, constructing a micro-region battery reaction system and studying the anion insertion / extraction process in electrode materials under confined conditions is of great significance for understanding the anion diffusion mechanism in electrode materials and promoting the further development of dual-ion batteries. Summary of the Invention

[0005] In response to the shortcomings of the prior art, the present invention aims to provide a method for locally embedding anions into a graphite electrode. The method comprises filling a hollow capillary probe having a tip opening with a diameter in the micrometer or nanometer range with an electrolyte solution containing a specific type of anion. Under the action of capillary tension, the internal solution can form microdroplets at the probe tip. A translation stage is used to control the probe to approach the surface of the graphite electrode material. When the droplets at the probe tip contact the surface of the graphite electrode material, a microelectrochemical cell with an aperture equivalent to the probe can be formed on the graphite surface. By adjusting the electrochemical parameters such as the voltage and current applied to the system, the embedding and extraction of anions in the electrolyte into the microregion inside the graphite electrode material can be controlled. The method is simple to operate, has a controllable electrochemical reaction area, is highly repeatable, and can significantly improve the efficiency of electrode material screening and reaction parameter optimization for dual-ion battery systems.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A method for locally embedding anions into a graphite electrode uses an electrochemical probe with a tip aperture ranging from several hundred nanometers to several tens of micrometers to form a confined electrochemical cell on the surface of the graphite electrode. An electrode potential is applied to the electrochemical probe to promote the embedding of anions in the electrolyte solution into the graphite electrode. The electrochemical probe is a hollow tube filled with an electrolyte solution.

[0008] A method for localized embedding of anions into a graphite electrode, comprising the following steps:

[0009] Step 1: Fill the hollow electrochemical probe with electrolyte solution and fix the electrochemical probe on the z-axis translation stage so that it moves synchronously with the translation stage. Insert the Ag / AgCl electrode as the reference electrode or counter electrode into the tail of the electrochemical probe. Fix the graphite electrode on the xy-axis translation stage and use it as the working electrode.

[0010] Step 2: Manually adjust the position of the z-axis translation stage so that the tip of the electrochemical probe is close to the surface of the graphite electrode, and observe the relative position between the two with the help of a 45° inclined microscope. Stop manual adjustment when the probe tip is 3 to 10 mm away from the electrode surface. Then use a program step to control the translation stage to move downward at a constant speed within a step speed range of 0.2 to 5 μm / s close to the surface of the graphite electrode. Apply a constant voltage of 0.1 to 2 V between the graphite electrode and the Ag / AgCl electrode through the electrochemical workstation. When the droplet at the probe tip contacts the surface of the graphite electrode, the two electrodes are connected to generate a current response signal. When the current change exceeds the set threshold of 20pA, the instrument receives the current feedback signal and controls the probe to stop moving. A confined micro-electrochemical cell with an aperture equivalent to the tip of the electrochemical probe is formed on the surface of the graphite electrode.

[0011] Step 3: Apply cyclic voltammetry scanning potential or constant voltage potential to the working electrode, and the electrolyte anions filled in the electrochemical probe are locally embedded in the electrode material under the action of the electric field.

[0012] The electrochemical probe described in step one is made of a capillary drawn by a P-2000 laser drawing instrument, that is, a hollow conical structure tube with a tip opening diameter of 200nm to 90μm obtained by drawing the capillary using a CO2 laser drawing instrument. The capillary material includes a glass tube or a quartz tube, and the outer diameter of the capillary is 1mm and the inner diameter is 0.5mm or 0.7mm.

[0013] The electrolyte solution in step 1 is a soluble salt solution containing the following types of anions, the anions in the salt solution include F - 、Cl - Br - , I - 、SO4 2- 、HSO4 - 、SO3 2- 、HSO3 - 、ClO4 - PF6 - 、NO3 - 、ZnCl4 2- 、AlCl4 - TFSI - 、FSI - The solvent in the salt solution includes H2O, PC, EC / DEC; the anion concentration is 0.1M~10M.

[0014] The graphite electrode in step 1 includes pyrolytic graphite, highly oriented pyrolytic graphite, graphite felt, graphite rod, natural graphite, artificial synthetic graphite, amorphous graphite, and graphene, preferably highly oriented pyrolytic graphite.

[0015] The counter electrode in step 1 includes an Ag / AgCl electrode, a Pt electrode, and a Pd-H electrode.

[0016] The step three is specifically:

[0017] 3.1. First, perform a cyclic voltammetric scan on the working electrode at a constant scan rate of 0.5 V / s to 10 V / s, preferably 5 V / s, to determine the insertion / extraction potential of anions in the graphite electrode. The constant scan rate is 0.5 V / s to 10 V / s, preferably 5 V / s. The cyclic voltammetric scan range is -1 V to 3.0 V. The oxidation peak of the cyclic voltammetric scan corresponds to the insertion potential of anions in graphite, and the reduction peak corresponds to the extraction potential of anions in graphite.

[0018] 3.2. The working electrode is then continuously subjected to variable potential or constant potential scanning to allow the anions to be embedded in the electrode material. The variable potential scanning adopts linear sweep voltammetry (LSV) or cyclic voltammetry (CV). The potential scanning interval is the +0.5V and -0.5V ranges corresponding to the oxidation peak and reduction peak of the cyclic voltammetry curve. The scanning direction is from low potential to high potential. The scan rate is set to 0.5V / s to 10V / s, preferably 5V / s or 1V / s; the number of cycles is set to 500 to 5000; the applied potential of the constant potential scanning is set to the potential corresponding to the CV oxidation peak or a potential more positive than the oxidation peak, and the constant potential scanning time is set to 0.5h to 5h.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The confined electrochemical cell system constructed using a hollow conical electrochemical probe has the characteristics of small reaction area and controllable reaction area, and can perform micron or nanoscale anion embedding on any graphite electrode material.

[0021] 2. Combined with the xyz-axis translation stage, the electrochemical probe can quickly construct a micro-area electrochemical cell at each point on the electrode surface. The hollow structure of the electrochemical probe is conducive to the rapid filling of the electrolyte solution. This anion embedding method is easy to operate and highly efficient.

[0022] 3. It can be used to reveal the relationship between the surface composition and structure of the electrode and the anion embedding process. The micro-electrochemical cell is scanned with wide potential cyclic voltammetry to obtain the oxidation / reduction peaks corresponding to the embedding / de-embedding of anions in graphite. When the electrode potential is more positive than the anion embedding potential, the anions are embedded in the graphite. The anions can be embedded in the graphite by using constant potential, constant current, linear sweep voltammetry or cyclic voltammetry. The range of anion embedding in the graphite is related to the size of the micro-electrochemical cell, realizing the localized embedding of anions at specific sites on the electrode.

[0023] In summary, the present invention is flexible and efficient, enabling the localized embedding of anions within the electrode material. This method can be further used for high-throughput screening of electrode materials in dual-ion batteries and further guide the design and optimization of battery systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the anion localized embedding graphite electrode system of the present invention.

[0025] Figure 2 For the characterization of electrochemical probes; Figure 2 (A) is an optical photograph of the probe side view. Figure 2(B)-(D) are probes of various pore sizes characterized by scanning electron microscopy.

[0026] Figure 3 The CV scan results of different types of anions embedded in HOPG are 2M ZnSO4 (anion: SO4 2- )、2M ZnCl2(anion: ZnCl4 2- )、3M NaCl (anion: Cl - ).

[0027] Figure 4 This is the result of 500 cyclic voltammetry scans of 1M ZnSO4 solution on the HOPG surface at a scan rate of 0.5V / s, where the diameter of the microdroplet is about 40μm.

[0028] Figure 5 This is the linear sweep voltammetry result of 1M ZnSO4 solution on the HOPG surface at a scan rate of 1V / s for 900 cycles, where the diameter of the microdroplet is about 15μm.

[0029] Figure 6 The HOPG electrode characterized by time of flight secondary ion mass spectrometry (TOF-SIMS) was charged by linear sweep voltammetry. - distributed within it. Figure 6 (A) in the equation is S - Three-dimensional distribution diagram inside HOPG; Figure 6 (B) in the sentence is S - Distribution diagram along the XZ section inside HOPG;

[0030] Figure 6 (C) in the sentence is S - Distribution diagram along the YZ cross section inside HOPG. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely explained below in conjunction with the drawings in the embodiments of the present invention. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the present invention.

[0032] Example 1

[0033] Reference Figure 1 The test bench on which the present invention is based is an existing device, including an xy-axis translation stage 1 and a z-axis translation stage 8 above it, a graphite electrode 3 is fixed on the xy-axis translation stage, an electrochemical probe 5 is fixed on the z-axis translation stage 8, a reference electrode 5 is inserted into the tail of the electrochemical probe, and the reference electrode 5 is connected to the current collector 2 below the graphite electrode 3 through a wire and an ammeter 6.

[0034] The method of localized embedding of anions into a graphite electrode in this embodiment is specifically as follows:

[0035] Step 1: Fix a capillary electrochemical probe filled with 1M ZnSO4 electrolyte solution on the z-axis translation stage, insert an Ag / AgCl electrode into the tail of the capillary probe, and fix highly oriented pyrolytic graphite (HOPG) on the xy-axis translation stage. The Ag / AgCl electrode serves as the counter electrode and the HOPG serves as the working electrode.

[0036] Preparation of electrochemical probe described in step 1

[0037] Capillary probes with nanometer or micrometer tip apertures are prepared using a P-2000 laser drawer. A glass capillary with an outer diameter of 1 mm and an inner diameter of 0.5 mm is fixed on the laser drawer. The CO2 laser emitted by the drawer heats the middle of the capillary. The drawing parameters of the laser drawer are set as follows: Line 1: HEAT 250FIL 3VEL 20DEL 250PUL 0; Line 2: HEAT 320FIL 4VEL 20DEL 255PUL 0. A capillary probe with a tip opening diameter of 20 μm can be obtained. Figure 2 A is a side view of the prepared probe. It can be seen that the probe body is a hollow tube structure and the probe tip is a tapered structure. By adjusting the drawing parameters of the laser drawing instrument, tapered capillary probes with various tip opening diameters can be obtained, such as Figure 2 As shown in BD, 1M ZnSO4 solution is then poured into the probe. Under the action of surface tension, the solution in the probe can form a droplet at the probe tip that is equivalent to the probe pore diameter.

[0038] Step 2: Manually adjust the position of the z-axis translation stage to gradually move the electrochemical probe toward the HOPG surface. Observe the relative position between the probe tip and the graphite electrode surface using a 45° inclined microscope. Control the probe to stop 3 to 10 mm from the HOPG surface. Then, apply a working voltage of +1.0 V (vs Ag / AgCl) to the working electrode. Set the z-axis translation stage to move downward at a constant speed of 1 μm / s toward the HOPG surface. When the droplet at the probe tip contacts the HOPG surface, the working electrode and the counter electrode connect to each other, generating a current step signal. The instrument receives current feedback and controls the probe to stop moving. The droplet acts as a microelectrochemical cell connecting the working electrode and the probe.

[0039] Step 3: Apply cyclic voltammetry scanning potential or constant voltage potential to the working electrode, and the electrolyte anions filled in the probe are locally embedded in the electrode material under the action of the electric field.

[0040] 3.1, Determine SO4 in ZnSO4 solution by cyclic voltammetry scanning 2-Insertion and extraction potential in HOPG. After the graphite working electrode is connected to the electrochemical probe, a single cyclic voltammetry scan is performed on the working electrode at a scan rate of 5V / s in the potential range of 0-1.2V (vsAg / AgCl). The oxidation peak and reduction peak potentials of the cyclic voltammetry curve correspond to the SO4 2- The potentials for insertion (~0.8 V vs Ag / AgCl) and extraction (~0.5 V vs Ag / AgCl), such as Figure 3 The midpoint is shown by the dashed line.

[0041] 3.2 Cyclic voltammetry scans promote anion embedding into HOPG electrodes

[0042] After the electrochemical probe, the microdroplets of the electrolyte solution and the HOPG electrode were connected to each other to form an electrochemical cell, a cyclic voltage of 0 to 1.2 V (vs Ag / AgCl) was applied to the HOPG working electrode, the number of scans was set to 500, and the cyclic voltammetry scan rate was set to 0.5 V / s. Figure 4 The corresponding cyclic voltammetry scanning image shows that with the increase of scanning number, the intensity of oxidation / reduction peak of cyclic voltammetry curve gradually decreases, indicating that SO4 2- It gradually saturates inside the HOPG electrode.

[0043] Characterization of anion intercalation into graphite electrodes by time-of-flight secondary ion mass spectrometry (TOF-SIMS)

[0044] After the linear voltammetric scan charging of the HOPG electrode surface is completed, the electrochemical probe is patterned on the electrochemical scanning area of ​​the HOPG surface, and the residual salt solution on the surface of the HOPG electrode is rinsed with deionized water. The sample is then transferred to the chamber of the time-of-flight secondary ion mass spectrometer. The electrochemical scanning area is re-positioned with the help of the patterned mark, and the target area is continuously bombarded with an ion source. The S element-related signals at different sample depths are collected to obtain S - Distribute information within HOPG.

[0045] Example 2

[0046] This embodiment differs from the first embodiment in that linear sweep voltammetry (LSV) is used instead of cyclic voltammetry to promote anion embedding into the HOPG electrode. In this embodiment, a forward linear sweep voltammetry (LSV) of 0 to 1.2 V (vsAg / AgCl) is used, the number of cycles is set to 900, and the scan rate is set to 1 V / s.

[0047] Figure 5 The linear sweep voltammetry image corresponding to the scanning process of 0 to 900 circles in the embodiment of the present invention is shown. As the number of scanning circles increases, the peak intensity of the linear sweep voltammetry curve gradually decreases, indicating that SO4 2-It gradually saturates inside the HOPG electrode.

[0048] Figure 6 This is a three-dimensional distribution diagram of the S element inside the HOPG electrode material obtained by characterizing the time-of-flight secondary ion mass spectrometry (TOF-SIMS) corresponding to the embodiment of the present invention. It can be seen that the S element is distributed along the columnar shape inside the HOPG, indicating that the S element is embedded in the HOPG electrode under the action of the electric field.

[0049] Example 3

[0050] The difference between this embodiment and the first embodiment is that 2M ZnCl2 is used as the electrolyte solution. The corresponding cyclic voltammetry characteristic curve is as follows: Figure 3 As shown by the dotted line in the middle, the forward linear sweep voltammetry (LSV) method of 0-1.3V (vsAg / AgCl) was used in this embodiment, the number of cycles was set to 2000 times, and the sweep rate was set to 1V / s. In this embodiment, ZnCl4 2- Intercalation occurs in the HOPG electrode material.

[0051] Example 4

[0052] The present embodiment is different from the first embodiment in that 3M Zn(TFSI)2 / EMC is used as the electrolyte, pyrolytic graphite is used as the working electrode, and linear sweep voltammetry (LSV) of 0-1.8V (vsAg / AgCl) is used. The number of cycles is set to 500 and the sweep rate is set to 1V / s. In this embodiment, TFSl - Intercalation occurs in the graphite electrode material.

[0053] Example 5

[0054] The difference between this embodiment and the first embodiment is that 3M NaCl is used as the electrolyte solution. The corresponding cyclic voltammetry characteristic curve is as follows: Figure 3 As shown by the solid line, in this embodiment, cyclic voltammetry (CV) at 0-1.2 V is used, the number of cycles is set to 1000 times, and the scan rate is set to 2 V / s. In this embodiment, Cl - Embedded in HOPG electrode material.

Claims

1. A method for localized embedding of anions into a graphite electrode, characterized in that: An electrochemical probe with a tip aperture of several hundred nanometers to several tens of micrometers is used to form a confined electrochemical cell on the surface of a graphite electrode. An electrode potential is applied to the electrochemical probe to promote the insertion of anions in the electrolyte solution into the graphite electrode. The electrochemical probe is a hollow tube filled with an electrolyte solution. The specific steps include: Step 1: Fill the hollow electrochemical probe with electrolyte solution and fix the electrochemical probe on the z-axis translation stage so that it moves synchronously with the translation stage. Insert the Ag / AgCl electrode as the reference electrode or counter electrode into the tail of the electrochemical probe. Fix the graphite electrode on the xy-axis translation stage and use it as the working electrode. Step 2: Manually adjust the z-axis translation stage position so that the electrochemical probe tip approaches the graphite electrode surface, and observe the relative position between the two with the help of a 45° inclined microscope. Stop manual adjustment when the probe tip is 3 to 10 mm away from the electrode surface. Then, use a program to step the stage downward at a constant speed within the step speed range of 0.2 to 5 μm / s to approach the graphite electrode surface. Apply a constant voltage of 0.1 to 2 V between the graphite electrode and the Ag / AgCl electrode using the electrochemical workstation. When the droplet at the probe tip contacts the graphite electrode surface, the two electrodes communicate with each other and generate a current response signal. When the current change exceeds the set threshold of 20 pA, the instrument receives the current feedback signal and controls the probe to stop moving. A confined micro-electrochemical cell with an aperture equivalent to the electrochemical probe tip is formed on the graphite electrode surface. Step 3: Apply cyclic voltammetry scanning potential or constant voltage potential to the working electrode, and the electrolyte anions filled in the probe are locally embedded in the electrode material under the action of the electric field.

2. The method for localized anion embedding in a graphite electrode according to claim 1, characterized in that: The electrochemical probe in step 1 is formed by drawing a capillary using a P-2000 laser drawing instrument.

3. The method for localized anion embedding in a graphite electrode according to claim 2, characterized in that: A hollow conical structure tube with a tip opening diameter of 200 nm to 90 μm is obtained by drawing a capillary using a CO2 laser drawing instrument. The capillary material includes a glass tube and a quartz tube. The outer diameter of the capillary is 1 mm and the inner diameter is 0.5 mm or 0.7 mm.

4. The method for localized anion embedding in a graphite electrode according to claim 1, characterized in that: The electrolyte solution in step 1 is a soluble salt solution containing the following types of anions, the anions in the salt solution include F - 、Cl - Br - , I - 、SO4 2- 、HSO4 - 、SO3 2- 、HSO3 - 、ClO4 - PF6 - 、NO3 - 、ZnCl4 2- 、AlCl4 - TFSI - or FSI - The solvent in the salt solution includes H2O or PC; the anion concentration is 0.1 M~10 M.

5. The method for localized anion embedding in a graphite electrode according to claim 1, characterized in that: The graphite electrode in step 1 is highly oriented pyrolytic graphite.

6. The method for localized anion embedding in a graphite electrode according to claim 1, characterized in that: The counter electrode in step 1 includes an Ag / AgCl electrode, a Pt electrode or a Pd-H electrode.

7. The method for localized anion intercalation into a graphite electrode according to claim 1, wherein: The step three is specifically: 3.

1. First, determine the insertion / extraction potential of anions in the graphite electrode by performing a cyclic voltammetric scan on the working electrode at a constant scan rate of 0.5 V / s to 10 V / s; the cyclic voltammetric scan range is -1 V to 3.0 V. The oxidation peak in the cyclic voltammetric scan corresponds to the insertion potential of anions in graphite, and the reduction peak corresponds to the extraction potential of anions in graphite; 3.

2. The working electrode is then continuously subjected to variable potential or constant potential scanning to allow the anions to be embedded in the electrode material. The variable potential scanning adopts linear sweep voltammetry or cyclic voltammetry. The potential scanning interval is the +0.5 V and -0.5 V range corresponding to the oxidation peak and reduction peak of the cyclic voltammetry curve. The scanning direction is from low potential to high potential. The scan rate is set to 0.5 V / s ~ 10 V / s; the number of cycles is set to 500 ~ 5000; the applied potential of the constant potential scanning is set to the potential corresponding to the CV oxidation peak or a potential more positive than the oxidation peak, and the constant potential scanning time is set to 0.5 h ~ 5 h.

8. The method for localized anion intercalation into a graphite electrode according to claim 7, wherein: The sweep rate was set to 5 V / s or 1 V / s.

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