A method for measuring the exchange current density of a crystal face

Abstract

The application discloses a kind of measurement methods of interfacial exchange current density, belong to electrochemical test field.The method for realizing of the present application is: using self-built three-electrode single particle electrochemical test system to measure the electrochemical impedance spectroscopy of multiple micron scale particles, obtain the current density of multiple single crystal particles;X-ray diffraction technique is used to obtain material crystal structure information;Using high-resolution transmission electron microscopy to measure the crystal face type of any exposed surface of single particle;The three-dimensional reconstruction of single crystal particle is carried out to obtain the geometric information of particle;Through crystal structure information, the crystal face type information of exposed surface and the angle information between each exposed surface, the crystal face type of all exposed surfaces is calibrated;According to the crystal face type of all exposed surfaces of multiple particles, the area of corresponding exposed surface and the current density of particle, the exchange current density of different crystal faces of crystal material is calculated.The present application can be used for the measurement of micron scale crystal material crystal face exchange current density, quantitative analysis of the electrochemical activity of material.

Description

A method for measuring crystal plane exchange current density Technical Field

[0001] This invention relates to a method for measuring crystal plane exchange current density, belonging to the field of electrochemical testing. Background Technology

[0002] Crystalline materials are widely used in electrochemical energy storage, electrocatalysis, and photoelectrochemistry. Taking lithium-ion batteries in electrochemical energy storage as an example, all commercially available cathode materials are currently crystalline. Due to the anisotropic nature of crystalline materials, the electrochemical activity varies significantly across different crystal facets. Most crystalline material particles expose multiple types of crystal facets, resulting in different electrochemical reaction characteristics on different exposed faces of the same particle. This phenomenon significantly affects the electrochemical reaction rate and lifecycle stability of the material. The exchange current density of crystal facets, as an intrinsic electrochemical kinetic parameter, is the most important parameter reflecting the electrochemical reactivity of a material. To design highly active and stable electroactive crystalline materials and improve material utilization efficiency, it is necessary to develop methods for measuring the exchange current density of crystal facets.

[0003] Taking the research of electrochemical energy storage materials as an example, electrochemical impedance spectroscopy, cyclic voltammetry, and Tafel curves have been developed for testing the exchange current density of materials. However, the developed exchange current density measurement methods can only measure macroscopic electrodes, reflecting the electrochemical reaction capability at the macroscopic electrode scale. Because it is difficult to simultaneously and accurately measure the geometric and electrochemical parameters of individual micrometer-scale particles, the measurement of exchange current density at even smaller crystal planes is impossible. Currently, electrochemical devices are increasingly widely used in various fields of social production. Besides electrochemical energy storage research, electrocatalysis and photoelectrochemistry research, as well as the development of corresponding crystal electrode materials, also require related technologies to measure the exchange current density of crystal planes. Summary of the Invention

[0004] To address the challenge of measuring crystal plane exchange current density using existing methods, the main objective of this invention is to provide a method for measuring crystal plane exchange current density. This method can simultaneously analyze the reactivity of multiple crystal planes in different electrochemical environments and quantify the intrinsic electrochemical reactivity of electroactive crystalline materials. Compared to traditional macroscopic electrode-scale exchange current density testing methods, this invention is applicable to smaller scales, provides highly quantifiable results, and more accurately describes the electrochemical activity of materials. By analyzing the relationship between the electrochemical environment and crystal plane electrochemical kinetic parameters, particle-scale structural optimization of the material can be performed, thereby improving its electrochemical performance.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] The present invention discloses a method for measuring crystal plane exchange current density, comprising the following steps:

[0007] The crystal structure information of the crystal material is obtained and analyzed by X-ray diffraction pattern, the unit cell parameters of the crystal material are obtained, and a database of standard inter-plane angles is established.

[0008] A single crystal particle is selected in a scanning electron microscope equipped with a rotatable sample stage and a robotic arm. High-resolution morphological images of the single crystal particle from multiple angles are acquired to obtain its morphological characteristics. A small portion of the single crystal particle is cut for transmission electron microscopy (TEM) sample preparation. The crystal plane type information of any exposed surface of the single crystal particle is obtained through high-resolution TEM images. The remaining portion of the single crystal particle is welded to a resin-coated tungsten needle to fabricate a single-particle microelectrode.

[0009] Electrochemical testing of a single-particle microelectrode was performed using a three-electrode single-particle electrochemical testing system to obtain the current density of the single crystal particle. The current density of the single crystal particle was acquired through a self-built three-electrode single-particle electrochemical testing system, which includes a single-particle three-electrode in-situ electrochemical cell, an electromagnetic shielding box, a vibration-isolated test bench, and an electrochemical workstation. The single-particle three-electrode electrochemical cell is placed in the electromagnetic shielding box and connected to the electrochemical workstation; the electromagnetic shielding box is grounded and placed on the vibration-isolated test bench. The single-particle three-electrode in-situ electrochemical cell includes a single-particle microelectrode, a top cover containing multiple pores, and a shell. The single-particle microelectrode is connected to the electrochemical testing equipment through the pores in the shell. Liquid and gas injection are achieved through pipes in the pores of the top cover. The in-situ electrochemical testing can be achieved by connecting the three-electrode in-situ electrochemical cell and the workstation using a three-electrode system. Electrochemical impedance spectroscopy (EIS) was performed on the single-crystal particles, and the EIS was fitted using an equivalent circuit to obtain the charge transfer resistance (Rc) of the single-crystal particles. CT According to the formula Calculate the current density (i) of the single crystal particle. 0(Particle) Where R is the gas constant, T is the temperature, n is the number of electrons transferred in the reaction, and F is the Faraday constant.

[0010] After the single-particle microelectrode completed electrochemical testing, it was cleaned and transferred to a scanning electron microscope. A focused ion beam was used to perform three-dimensional reconstruction of the single-crystal particle to obtain its geometric structure information. This geometric structure information includes the area of ​​each exposed surface of the single-crystal particle and the angle between each exposed surface.

[0011] The measured angles between exposed surfaces are compared with the established database of standard crystal plane angles. The exposed surfaces of known crystal plane types are used as reference surfaces to calibrate other crystal planes one by one, thereby obtaining the crystal plane types of all exposed surfaces of the single crystal particle.

[0012] Repeat the above steps for multiple single-crystal particles to obtain information on the current density, exposed surface area, and exposed surface crystal type of multiple single-crystal particles.

[0013] Based on the obtained information on the current density, exposed surface area, and exposed surface crystal type of the multiple single crystal particles, the formula is used. Calculate the exchange current density (i) for all crystal planes. 0(Facet) ), where the superscript i represents different crystal planes, n represents the number of crystal planes, and s represents the area of ​​the crystal plane.

[0014] As an improvement to the crystal plane exchange current density measurement method described in this invention, the three-electrode single-particle electrochemical testing system can perform all electrochemical testing items supported by the electrochemical workstation, realize the electrochemical signal acquisition of a single micron-scale active particle, test the thermodynamic parameters of the active particle, and analyze the electrode kinetic process of the active particle.

[0015] As an improvement to the crystal plane exchange current density measurement method described in this invention, the three-electrode single-particle electrochemical testing system can study a wide variety of electrochemical systems, including particle-solution, particle-gas, and particle-gas-solution electrochemical systems.

[0016] Beneficial effects:

[0017] 1. This invention provides a method for measuring the exchange current density of crystal planes. The test results are highly quantitative, enabling the measurement of exchange current densities on different crystal planes of crystalline materials. It establishes the relationship between the electrochemical reaction kinetics of crystal planes and the physical and chemical parameters of the crystal planes, providing a theoretical basis for subsequent material structure design. By exposing crystal planes with high exchange current densities, it enables fast charging and discharging of batteries, extending battery life. Furthermore, it facilitates the development of highly active, low-cost hydrogen evolution reaction electrode materials, achieving low-cost hydrogen production through water electrolysis.

[0018] 2. The present invention provides a method for measuring crystal plane exchange current density, employing a three-electrode single-particle electrochemical testing system, comprising a single-particle electrochemical cell for injecting and discharging gas and solution and isolating them from air, a shielded box, a vibration-isolated test bench, and an electrochemical workstation. This system enables high-precision electrochemical signal acquisition for various electrochemical systems, including particle-solution, particle-gas, and particle-gas-solution systems, and is used for the research and development of electrode materials for secondary ion batteries, room-temperature fuel cells, electrochemical sensor electrodes, and photoelectrochemical electrodes. Attached Figure Description

[0019] Figure 1 is a flowchart of the method for measuring the crystal plane exchange current density provided by the present invention and the exchange current densities of the six crystal planes of NMC811 obtained by testing.

[0020] Figure 2 shows the measured or calculated data of six NMC811 single crystal particles in the embodiment provided by the present invention.

[0021] Figure 3 is a schematic diagram of the single-particle microelectrode provided by the present invention and a partial enlarged view of its tip.

[0022] Wherein: 1-resin; 2-metallic tungsten needle; 3-NMC811 single crystal particles.

[0023] Figure 4 is a schematic diagram of the single-particle three-electrode in-situ electrochemical cell provided by the present invention.

[0024] Wherein: 4-quartz window; 5-top cover; 6-shell; 7-sealing gasket; 8-single-particle microelectrode; 9-counter electrode; 10-reference electrode; 11-sealing rubber ring; 12-fastening bolt; 13-gas and liquid pipeline.

[0025] Figure 5 is a schematic diagram of the three-electrode single-particle electrochemical testing system provided by the present invention.

[0026] Among them: 14-Aluminum alloy electromagnetic shielding box; 15-Grounding wire; 16-Electrochemical workstation; 17-Vibration isolation test bench; 18-Single particle three-electrode in-situ electrochemical cell. Detailed Implementation

[0027] The following uses lithium-ion batteries, specifically LiNi... 0.8 Co 0.1 Mn 0.1 The invention is further described in detail with reference to the embodiments and accompanying drawings of the O2(NMC811) single crystal cathode particle six crystal plane exchange current density measurement examples, but the implementation of the invention is not limited thereto.

[0028] As shown in Figure 1, a method for measuring crystal plane exchange current density according to this embodiment is described below.

[0029] S100 acquires the crystal structure information of the NMC811 single crystal cathode particle, obtains the unit cell parameters of the NMC811 single crystal cathode particle crystal, and establishes a database of standard crystal plane angles.

[0030] Specifically, X-ray diffraction (XRD) analysis was performed on NMC811 single-crystal powder particles. The unit cell parameters were extracted from the refined XRD pattern. The results showed that NMC811 belongs to the hexagonal crystal system, and the unit cell parameters of the NMC811 supercell are as follows: The corresponding XRD patterns and refinement point plots are shown in Figure 2a.

[0031] S200 obtains the crystal plane type information of any exposed surface of a single NMC811 single crystal particle.

[0032] Specifically, several particle images were captured from different angles using a scanning electron microscope (SEM) equipped with a rotatable sample stage, a focused ion beam (FIB), and a robotic arm to obtain the morphological characteristics of the individual NMC811 single crystal particle. A portion of the individual NMC811 single crystal particle was cut using the FIB for transmission electron microscopy (TEM) sample preparation. Note that the portion of the NMC811 single crystal particle cut should be as small as possible to avoid extensively damaging the original surface of the NMC811 single crystal particle and to avoid significantly affecting the original morphology of the NMC811 single crystal particle. The TEM sample was imaged using a high-resolution transmission electron microscope (HRTEM) to obtain the crystal plane type information of any exposed surface of the NMC811 single crystal particle. The HRTEM imaging should clearly record the position of the corresponding exposed surface of the NMC811 single crystal particle. Taking particle I in Figure 2 as an example, the crystal plane can be identified as (101) from the HRTEM, corresponding to the ρ plane of particle I.

[0033] S300 obtains the current density of the NMC811 single crystal particle.

[0034] Specifically, a single-particle microelectrode is fabricated in a SEM equipped with a FIB and a robotic arm. The single-particle microelectrode (Figure 3) consists of a tungsten needle 2 coated with resin 1 and an NMC811 single-crystal particle 3. The fabrication process of the single-particle microelectrode is as follows: First, the tip of the resin-coated tungsten needle is removed using the FIB to expose the metal; then, the NMC811 single-crystal particle 3 is welded to the robotic arm using the FIB, and the NMC811 single-crystal particle 3 is moved to the vicinity of the tip of the resin-coated tungsten needle; finally, the NMC811 single-crystal particle 3 is welded to the tip of the resin-coated tungsten needle to obtain the single-particle microelectrode. The single-particle microelectrode is assembled into a single-particle three-electrode in-situ electrochemical cell. A schematic diagram of the single-particle three-electrode in-situ electrochemical cell is shown in Figure 4, including a quartz window 4, a top cover 5, a shell 6, a sealing gasket 7, a single-particle microelectrode 8, a counter electrode 9, a reference electrode 10, a sealing rubber ring 11, fastening bolts 12, and a gas / liquid pipeline 13. The quartz window 4 and top cover 5 are sealed with sealant, and the shell 6 and top cover 5 are sealed with the sealing gasket 7. The single-particle microelectrode 8, counter electrode 9, and reference electrode 10 pass through the sealing rubber ring 11 and fastening bolts 12 for sealing and connection to the external circuit. Electrolyte is injected into the electrochemical cell through the liquid / gas injection pipeline 13. The single-particle three-electrode in-situ electrochemical cell is assembled into a single-particle three-electrode electrochemical testing platform for testing, and electrochemical impedance spectroscopy (EIS) is performed using a three-electrode connection method. The schematic diagram of the three-electrode electrochemical testing platform is shown in Figure 5, including an aluminum alloy electromagnetic shielding box 14, a grounding wire 15, an electrochemical workstation 16, a vibration isolation test bench 17, and a single-particle three-electrode in-situ electrochemical cell 18. The single-particle three-electrode in-situ electrochemical cell 18 is connected to the electrochemical workstation 16, and placed within the electromagnetic shielding box 14, which is grounded to 15. The electromagnetic shielding box 14 is then placed on the vibration isolation test bench 17. The charge transfer resistance (Rc) of the NMC811 single crystal particle is extracted from the EIS using an equivalent circuit model. CT ), through formula Calculate the current density (i) of the NMC811 single crystal particle. 0(Particle) Where R is the gas constant, T is the temperature, n is the number of electrons transferred in the reaction, and F is the Faraday constant. The EIS and equivalent circuit fitting curves of the NMC811 single crystal particles are shown in Figure 2b.

[0035] S400 acquires the geometric structure information of the NMC811 single crystal particle. The geometric structure information includes the area of ​​each exposed surface of the NMC811 single crystal particle and the angle between each exposed surface.

[0036] Specifically, the NMC811 single crystal particles, after electrochemical testing, were immersed in acetonitrile for cleaning to remove residual electrolyte. The NMC811 single crystal particles were then transferred to a SEM equipped with a fibrillated imager (FIB) for three-dimensional reconstruction. The area of ​​each exposed surface of a single NMC811 single crystal particle and the angle between each exposed surface were measured in the resulting three-dimensional image. The three-dimensional reconstructed image of the NMC811 single crystal particle is shown in Figure 2d.

[0037] S500 obtains the crystal plane type of all exposed surfaces of the NMC811 single crystal particle.

[0038] Specifically, the angles between exposed surfaces measured in S400 are compared with the standard inter-crystal plane angle database established in S100. Using the exposed surfaces of known crystal plane types obtained in S200 as reference samples, other crystal planes are successively calibrated to obtain other crystal plane types. The three-dimensional structure of the particle is reconstructed based on each calibrated exposed surface type and compared with the three-dimensional structure of the particle reconstructed by FIB. If the three-dimensional structures match, it proves that the calibrated crystal plane type is accurate. If they do not match, the crystal plane type calibration of the exposed surfaces is repeated. During the three-dimensional structure comparison, each crystal plane can move freely along the normal direction. The crystal plane type calibration results of the NMC811 single crystal particle are shown in Figure 2e.

[0039] The S600 acquires information on the current density, exposed surface area, and exposed surface crystal type of multiple NMC811 single crystal particles.

[0040] Specifically, the S100-S500 operation was repeated for the other five NMC811 single crystal particles, and the test results of the other five NMC811 single crystal particles are shown in Figure 2.

[0041] The S700 acquires exchange current density information for different crystal planes of the NMC811 material.

[0042] Specifically, the current density, crystal area, and exposed crystal type information of the multiple NMC811 single crystal particles obtained by S600 are substituted into the formula respectively. Solve the system of equations to calculate the exchange current density (i) on the crystal plane. 0(Facet) The superscript i represents different crystal planes, n represents the number of crystal planes, and s represents the area of ​​the crystal plane. Finally, the exchange current density of six crystal planes (003), (201), (104), (113), (102), and (101) of NMC811 cathode material was obtained, and the corresponding data are shown in Figure 1.

[0043] The exchange current density of six crystal planes of NMC811 cathode material was measured using the method of this invention. Based on the obtained exchange current density of the crystal planes, the correlation between the electrochemical kinetics of the material and the physical and chemical parameters of the material was established. By adopting the design concept of exposing crystal planes with larger exchange current densities, a high-rate lithium-ion battery cathode material was developed, which shortened the charging time of the battery and extended the service life of the battery.

[0044] According to the foregoing description, the embodiments described are merely illustrative of the technical solutions of the present invention and not intended to limit it. The present invention will be described in detail with reference to the foregoing embodiments. Those skilled in the art can still make modifications or equivalent substitutions to the specific implementations of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the pending claims. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

[0045] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for measuring crystal plane exchange current density, characterized in that, The process includes the following steps: Step 1: Obtain the crystal structure information of the material to obtain the unit cell parameters; Step 2: Select a single crystal particle in a scanning electron microscope equipped with a rotatable sample stage and a robotic arm, cut a small portion of the single crystal particle for transmission electron microscopy (TEM) sample preparation to obtain the crystal plane type information of any exposed surface of the single crystal particle; weld the remaining portion of the single crystal particle to a resin-coated tungsten needle to fabricate a single-particle microelectrode; Step 3: Perform electrochemical testing on the single-particle microelectrode using a three-electrode single-particle electrochemical testing system to obtain the current density of a single single crystal particle; Step 4: Perform three-dimensional reconstruction of the single crystal particle after electrochemical testing to obtain the geometric structure information of the single single crystal particle. Step 5: Based on the crystal structure information, the crystal plane type information of any exposed surface, and the angle information between each exposed surface, determine the crystal plane type of all exposed surfaces. Step 6: Repeat steps 1 to 5 to test multiple single crystal particles. Step 7: Calculate the exchange current density of different crystal planes of the crystal material from the crystal plane type of all exposed surfaces, the area of ​​the corresponding crystal plane, and the current density of the particles obtained from the tests of multiple single crystal particles, thus realizing the measurement of crystal plane exchange current density. The calculation method of the exchange current density of different crystal planes of the material in step 7 is based on the obtained information on the crystal plane type of all exposed surfaces of multiple single crystal particles, the area of ​​the corresponding crystal plane, and the current density of the particles, using the formula... Calculate the exchange current density for all crystal planes, where the superscript i represents different crystal planes, n represents the number of crystal planes, and s represents the area of ​​the crystal plane.

2. The method for measuring crystal plane exchange current density as described in claim 1, characterized in that: The method for measuring the current density of a single single-crystal particle in step three involves a three-electrode single-particle electrochemical testing system comprising a single-particle three-electrode in-situ electrochemical cell, an electromagnetic shielding box, a vibration-isolated test bench, and an electrochemical workstation. The single-particle three-electrode electrochemical cell is placed within the electromagnetic shielding box, and the single-particle three-electrode in-situ electrochemical cell is connected to the electrochemical workstation. The electromagnetic shielding box is grounded and placed on the vibration-isolated test bench. Electrochemical impedance spectroscopy is performed on the single-crystal particle, and the electrochemical impedance spectrum is fitted using an equivalent circuit to obtain the charge transfer resistance (R) of the single-crystal particle. CT According to the formula Calculate the current density (i) of the single crystal particles. 0（Particle） ); where R is the gas constant, T is the temperature, n is the number of electrons transferred in the reaction, and F is the Faraday constant.

3. The method for measuring crystal plane exchange current density as described in claim 1, characterized in that: The three-dimensional reconstruction method for single-crystal particles in step four involves cleaning the single-particle microelectrode after electrochemical testing and transferring it to a scanning electron microscope, where a focused ion beam is used to reconstruct the three-dimensional structure of the single-crystal particles.

4. The method for measuring crystal plane exchange current density as described in claim 1, characterized in that: In step five, the method for calibrating the crystal plane type of all exposed surfaces of a single micron-scale single crystal particle is as follows: establish a standard crystal plane angle database based on the obtained material cell parameters; use the exposed surfaces of known crystal plane types as reference surfaces, and calibrate other crystal planes one by one based on the obtained angle data between exposed surfaces.

5. The method for measuring crystal plane exchange current density as described in claim 2, characterized in that: The single-particle three-electrode electrochemical cell includes a quartz window, a top cover, a shell, a sealing gasket, a single-particle microelectrode, a counter electrode, a reference electrode, a sealing rubber ring, fastening bolts, and gas and liquid pipelines. The quartz window and top cover of the electrochemical cell are sealed by applying sealant, and the shell and top cover of the electrochemical cell are sealed by a sealing gasket. The single-particle microelectrode, counter electrode, and reference electrode pass through the sealing rubber ring and fastening bolts to achieve sealing and connection with the external circuit. The solution / gas is injected into the electrochemical cell through the liquid / gas injection pipelines.

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