Method for investigating electric expansion and electric shrinkage strain of nano metal electrode plate in electrolyte

Abstract

The invention discloses a method for investigating the electric expansion and electric shrinkage strain of a nano-metal electrode plate in an electrolyte, which comprises the following steps of: constructing a block nano-metal model by utilizing a first principle, and performing energy optimization on the model in directions of three coordinate axes x, y and z under a Cartesian three-dimensional coordinate system, determining parameters when the nano metal plate is constructed, so that the subsequent electrode plate model is in the most stable state; the method comprises the following steps: constructing a multi-layer nano-metal electrode plate model with different layer numbers according to the same surface, selecting an electrolyte environment of sodium halide as environmental parameters of the model, setting the required number of external charges, and then performing energy optimization to obtain the most stable energy structure of the nano-metal electrode plate under the selected metal, the selected number of external charges and the selected layer number; the real strain of a certain metal electrode plate is calculated, real strain diagrams of different charges under different layers of the metal are drawn, and the strain types of the metal material are classified according to the shape of a strain curve.

Description

Technical Field

[0001] The present invention relates to the field of computational materials physics and chemistry, and particularly to a method for investigating the electrostrictive strain of nano metal electrode plates in electrolytes. Background Art

[0002] The electrochemically actuated phenomenon refers to the elongation and compression movement of an electrode as the voltage changes. Currently, the electrochemically actuated phenomenon has been found in materials such as organic substances, metals, and ceramics. Electrochemically actuated devices manufactured based on the electrochemically actuated phenomenon have been widely used in the fields of robotics, display devices, and medical applications due to their low operating voltage, large strain, ability to work in electrolyte solutions, and strong cycle stability. Also, because various types of materials exhibit the electrochemically actuated phenomenon, electrochemically actuated devices based on various types of materials are being widely explored.

[0003] Nanorobots are one of the many applications of electrochemically actuated devices: in the medical field, nanorobots can reach areas of the human body that are difficult to access for surgical operations. Due to the limitations of nanorobots, it is of strategic value to explore the performance of electrochemically actuated devices at ultra-low voltages. Currently, the operating voltages of various electrochemically actuated devices invented by researchers range from 0.01 V to 1 V and exhibit a strain of about 0.5%. However, it is still a huge challenge to establish an ultra-low voltage environment suitable for actuators in actual experiments because most experiments are conducted in a low voltage environment of macroscopic materials and our experimental techniques for the strain of microscopic materials under low charges are poorly understood. Therefore, computational simulation is a recommended method for exploring the relationship between charge and strain in nanoscale electrode plates. Computer simulation can more conveniently create an ideal low-charge environment for the desired nano metal electrode plate by designing parameters such as the number of charges and material structure. Therefore, this technology is of great significance for helping us find the low-charge strain law of nano metal electrode plates. However, if the computational simulation environment is too ideal, it will be difficult to reproduce this ideal environment in reality; so sometimes the reproduction of simulation results in reality is a trend prediction. Summary of the Invention

[0004] In view of the above-mentioned defects of the prior art, the technical problems to be solved by the present invention are the difficulty in constructing a low-charge environment for nano metal electrode plates and the lack of information on the strain properties of nano metal electrode plates. The present invention provides a method for investigating the electrostrictive strain of nano metal electrode plates in electrolytes, and for the first time, successfully investigates the strain of various materials at the nanoscale and under low external charges and provides information on metal materials with relevant properties.

[0005] To achieve the above object, the present invention provides a nano - metal electrode plate dissolved in an electrolyte, and the electrode plate exhibits electro - dilation or electro - contraction phenomena. Specifically, an external charge is applied to the electrode plate to cause it to expand in the stretching direction, or an external charge is applied to the electrode plate to cause it to contract in the stretching direction.

[0006] Further, the electrolyte includes a strong electrolyte, and the electrolyte is a sodium halide electrolyte.

[0007] In another preferred embodiment of the present invention, a method for investigating the electro - dilation and electro - contraction strain of a nano - metal electrode plate in an electrolyte is provided, including the following steps:

[0008] S1. Use the first - principle to construct a bulk nano - metal model, and perform energy optimization on the model in the x, y, and z three - axis directions of the Cartesian three - dimensional coordinate system to determine the parameters for constructing the nano - metal plate so that the subsequent electrode plate model is in the most stable state;

[0009] S2. According to the parameters obtained in S1, construct multi - layer nano - metal electrode plate models with different numbers of layers on the same surface. The environmental parameters of the model are selected as the electrolyte environment of sodium halide, and the required number of external charges is set. Then, perform energy optimization to obtain the energy - most - stable structure of the nano - electrode plate under the selected metal, number of external charges, and number of layers. Obtain the atomic distances between two selected crystal directions of the nano - metal thin film in this crystal direction, which can be used to obtain the true strain compared with the distances between two identical specific atoms in this crystal direction of the bulk material in S1;

[0010] S3. According to the parameters obtained in S1 and S2, calculate the true strain of a certain metal electrode plate and draw the true - strain diagram of the metal with different numbers of layers and different charges. According to the true - strain diagram of the metal with different numbers of layers and different charges, that is, the shape of the strain curve, classify the strain types of the metal materials.

[0011] Further, in S2, according to the parameters obtained in S1, construct multi - layer nano - metal electrode plate models with different numbers of layers on the same surface. The environmental parameters of the model are selected as the electrolyte environment of sodium halide, and the required number of external charges is set. Then, perform energy optimization to obtain the energy - most - stable structure of the nano - electrode plate under the selected metal, number of external charges, and number of layers, specifically including the following steps:

[0012] S21. Construct a bulk nanometal model from S1 using first principles. Select two mutually perpendicular crystal directions as the tensile directions. Subsequently, determine the single-layer surface formed by these two crystal directions from the bulk nanometal obtained from S1. To construct an N-layer surface, place the previously intercepted single layer on the xy plane of the Cartesian three-dimensional coordinate system, with the two selected crystal directions coinciding with the x-axis and y-axis, and then stack (N - 1) such single layers along the z-axis. The distance between two adjacent single layers is obtained from the structure and parameters of the bulk nanometal, and the relative position of two adjacent single layers is determined by the structure of the bulk nanometal. Thus, a multi-layer nanometal thin film is obtained.

[0013] S22. Add an external charge and an electrolyte environment of sodium halide to the N-layer nanometal thin film. Thus, a nanometal electrode plate model with a selected charge number and a selected surface layer number of N is obtained. This model is energy-optimized in the xy directions of the Cartesian three-dimensional coordinate system to determine the true strain of the two mutually perpendicular crystal directions selected in S21.

[0014] Further, add an external charge of ±0.1 - 0.5∣e∣, and the sodium halide is one or more of NaF, NaCl, NaBr, and NaI, and the concentration of the sodium halide is 0.3 - 2M.

[0015] Further, in step S21, a vacuum layer is provided between the atomic layers of the metal thin film to ensure that the interaction between two multi-layer thin films is sufficiently small.

[0016] Further, the thickness of the vacuum layer is

[0017] Further, the parameters of the energy optimization are specifically set as follows: the k-point is 20×20×1, and the cut-off energy is 598.4 eV. The energy differences between two consecutive iteration steps of the electron cloud density, atomic or ionic coordinates, and lattice constants are 27.2×10 - 9 eV, 27.2×10 -8 eV, and 27.2×10 -7 eV.

[0018] Further, in step S2, the nanometal electrode plate is stretched in the two selected directions and an external charge is applied.

[0019] In another preferred embodiment of the present invention, an application of a method for examining the electrostriction strain of a nanometal electrode plate in an electrolyte is provided. The (001) surfaces of metals Rh, Al, Pt, and Ir exhibit electrostriction strain, while the (001) surfaces of metals Mo and W exhibit electrocontraction strain.

[0020] Technical effects

[0021] 1. A method provided by the present invention for investigating the electrostrictive strain of a nano-metal electrode plate in an electrolyte, for the first time proposes a property classification of the nano-metal electrode plate with high possibility and wide applicability. The method provided by the present invention can test various pure metals and has a wide range of applications.

[0022] 2. The method provided by the present invention will facilitate the subsequent research on electrode strain; provide research examples for the research of nanorobots and other devices that require ultra-low voltages. Under the conditions of different voltages and electrode thicknesses, the empirical electrode strain formula obtained from the strain curve will help to design various parameters of the electrochemically actuated device and accelerate its industrialization process. This also provides a new direction for the strain research of other non-metallic materials: the method is simple and easy to operate, the results of its investigation are verified in many aspects, and sometimes it is a trend prediction when reproducing the simulation results in reality; this also has certain guiding significance for guiding the experimental design of difficult-to-realize experimental environments using first-principles calculations in the future.

[0023] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the drawings to fully understand the purpose, features and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the Ir bulk model in Example 1 of the present invention;

[0025] Figure 2 is the multi-layer Ir(001) surface electrode plate model in Example 1 of the present invention, taking 7 layers as an example, and indicating the stretching direction;

[0026] Figure 3 is the true strain diagram related to the thickness of the multi-layer Ir(001) surface electrode plate and the applied charge in Example 1 of the present invention;

[0027] Figure 4 is the W bulk model in Example 2;

[0028] Figure 5 is the multi-layer W(001) surface electrode plate model in Example 2, taking 7 layers as an example, and indicating the stretching direction;

[0029] Figure 6 is the true strain diagram related to the thickness of the multi-layer W(001) surface electrode plate and the applied charge in Example 2;

[0030] Figure 7 According to the specific embodiment, it is found that the metal Rh, Al, Pt and the Ir(001) surface are electrostrictive strains;

[0031] Figure 8 According to the specific embodiment, it is found that the metal Mo and the W(001) surface are electrostrictive strains;

[0032] Figure 9 It is a true strain diagram related to the thickness of the multi-layer Au(111) surface electrode plate and the applied charge in the comparative example. Specific embodiments

[0033] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] In the following description, specific details such as specific internal programs and technologies are presented for the purpose of illustration rather than limitation, so as to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, the detailed descriptions of well-known systems, devices, circuits and methods are omitted to avoid unnecessary details from interfering with the description of the present invention.

[0035] The present invention provides a nano-metal electrode plate dissolved in an electrolyte solution. The electrode plate exhibits electrostriction or electrostretch phenomenon. Specifically, an external charge is applied to the electrode plate to expand the electrode plate in the stretching direction, or an external charge is applied to the electrode plate to shrink the electrode plate in the stretching direction. Among them, the nano-metal electrode plate has a particularly small thickness compared to the ordinary electrode plate, which is about the thickness of several atoms stacked up.

[0036] The electrolyte solution includes a strong electrolyte, and the electrolyte is a sodium halide electrolyte.

[0037] In another preferred embodiment of the present invention, a method for examining the electrostriction and electrostretch strain of a nano-metal electrode plate in an electrolyte solution is provided, including the following steps:

[0038] S1. Use the first principle to construct a bulk nano-metal model, and perform energy optimization on the three coordinate axes x, y, and z of the model in the Cartesian three-dimensional coordinate system to determine the parameters for constructing the nano-metal plate so that the subsequent electrode plate model is in the most stable state;

[0039] S2. According to the parameters obtained in S1, construct multi-layer nano-metal electrode plate models with different numbers of layers on the same surface. The environmental parameters of the model are selected as the electrolyte environment of sodium halide, and the required number of applied charges is set. Then, energy optimization is performed to obtain the most stable energy structure of the nano-electrode plate under the selected metal, number of applied charges, and number of layers; the recommended number of charges is ±0.1~0.5∣e∣; specifically, it includes the following steps:

[0040] S21. Construct a bulk nanometal model from S1 using first principles. Select two mutually perpendicular crystal directions as the tensile directions. Subsequently, determine the monolayer surface formed by these two crystal directions from the bulk nanometal obtained from S1. To construct an N - layer surface, place the previously intercepted monolayer on the xy - plane of the Cartesian three - dimensional coordinate system, with the two selected crystal directions coinciding with the x - axis and y - axis, and then stack (N - 1) such monolayers along the z - axis. The distance between two adjacent monolayers is obtained from the structure and parameters of the bulk nanometal, and the relative position of two adjacent monolayers is determined by the structure of the bulk nanometal. It is recommended that N be an odd number 2k + 1. In this way, one monolayer can be placed on the plane z = 0 first, and then 2k monolayers can be symmetrically placed with respect to the plane z = 0. Thus, a multi - layer nanometal thin film is obtained.

[0041] S22. Add an external charge and an electrolyte environment of sodium halide to the N - layer nanometal thin film. Thus, a nanometal electrode plate model with a selected charge number and a selected surface layer number of N is obtained. This model is energy - optimized in the xy two - axis directions of the Cartesian three - dimensional coordinate system to determine the true strain of the two mutually perpendicular crystal directions selected in S21. The added external charge is ±0.1~0.5∣e∣, and the sodium halide is one or more of NaF, NaCl, NaBr, and NaI. The concentration of the sodium halide is 0.3~2M, preferably 0.5~1M. The preferred sodium halide is NaCl, and the electrolyte environment should remain unchanged. In a specific embodiment, the electrolyte is a 1M aqueous solution of NaCl. Since NaCl is a strong electrolyte, strong electrolyte aqueous solutions similar thereto (such as a 0.5M aqueous solution of NaF, etc.) should also fall within the scope of protection of this patent. Thus, a nanometal electrode plate model with a selected charge number and a selected surface layer number of N is obtained. This model is energy - optimized in the xy two - axis directions of the Cartesian three - dimensional coordinate system to determine the true strain of the two mutually perpendicular crystal directions selected in S21, that is, ln (the distance between two specific atoms selected in this crystal direction of the nanometal thin film in S22 / the distance between two identical specific atoms selected in this crystal direction of the bulk material in S21).

[0042] S3. According to the parameters obtained from S1 and S2, calculate the true strain of a certain metal electrode plate and draw a true strain diagram of the metal with different charges at different numbers of layers. Classify the strain types of the metal material according to the shape of the strain curve (i.e., the true strain diagram of the metal with different charges at different numbers of layers). According to the shape of the strain curve, the strain types of the metal material are divided into electro - expansive strain and electro - contractive strain. The meanings of the type names are that applying more external charges causes the electrode plate to expand and contract laterally.

[0043] Further, in step S21, a vacuum layer is provided between the atomic layers of the metal thin film to ensure that the interaction between two multi - layer thin films is sufficiently small. The thickness of the vacuum layer is Preferably, the thickness of the vacuum layer is 100 Bohr (the default length unit in the jdftx software, approximately ); the key parameters for energy optimization are set as follows: the k-point is 20×20×1, the cut-off energy is 598.4 eV, and the energy differences between two consecutive iteration steps of the electron cloud density, atomic or ionic coordinates, and lattice constant are 27.2×10 -9 eV, 27.2×10 -8 eV, and 27.2×10 -7 eV.

[0044] In another preferred embodiment of the present invention, an application of a method for investigating the electrostriction strain of a nano-metal electrode plate in an electrolyte is provided. The (001) planes of metals Rh, Al, Pt, and Ir exhibit electrostriction strain, while the (001) planes of metals Mo and W exhibit electrostriction strain.

[0045] The following will illustrate a method for investigating the electrostriction strain of a nano-metal electrode plate in an electrolyte according to the present invention with specific examples.

[0046] Example 1

[0047] The embodiment of the present invention provides a design method for investigating the strain type of an Ir(001)-plane nano-electrode plate immersed in a 1M NaCl electrolyte, which specifically includes the following operations:

[0048] (1) Manually construct an Ir bulk model in a Cartesian three-dimensional coordinate system, as shown in Figure 1 . Since an infinitely large bulk needs to be simulated, the first-principles open-source calculation software JDFTx based on the Joint Density Functional Theory (JDFT) method is used. The designed bulk model is infinitely expanded using periodic boundary conditions (PBC), and energy optimization is performed in the x, y, and z coordinate axes. The key parameters for energy optimization are set as follows: the parameter of the exchange-correlation function is selected as gga-PBE; the pseudopotential of the Ir element is the GBRV ultrasoft pseudopotential; the k-point is set to 20×20×20; the energy cut-off threshold is 598 eV. The energy differences between two consecutive iteration steps of the electron cloud density, atomic or ionic coordinates, and lattice constant are 27.2×10 -9 eV, 27.2×10 -8 eV, and 27.2×10 -7 eV.

[0049] (2) To investigate the strain type of the Ir(001) surface, the

[100] crystal orientation and the

[010] crystal orientation are selected as the tensile directions. Based on the most energy-stable bulk structure obtained in (1), multi-layer Ir(001) surface electrode plate models with different numbers of layers are constructed. The single layer of the (001) surface intercepted from the bulk model is placed flat on the xy plane of the Cartesian three-dimensional coordinate system, and the

[100] crystal orientation and the

[010] crystal orientation coincide with the x-axis and y-axis. Then, a specific number of single layers are stacked along the z-axis, as shown in Figure 2 ; among them, each single layer of the electrode plate model has only 1 atom to reduce the required computing power, and the N-layer electrode plate also has only N atoms. The number of electrode plate layers is selected as 7, 9, 11, 13, and 15 layers; the externally applied charge number of the electrode plate takes values of ±0.1, ±0.2, and ±0.3|e|; the electrolyte adopts the SaLSA (spherical homogeneous liquid sensitivity hypothesis) continuous model, and the set concentration is 1M Na + and Cl - . Energy optimization is to perform system relaxation in the xy two coordinate axis directions under the Cartesian three-dimensional coordinate system using self-consistent calculations. The K-point is selected as 20×20×1; the parameters such as the selection of the pseudopotential, the selection of the exchange-correlation functional, the cut-off energy, the electron cloud density, the atomic or ionic coordinates, and the energy difference between two consecutive iteration steps of the lattice constant are the same as in step (1).

[0050] (3) Determine the true strain of the selected

[100] crystal orientation and

[010] crystal orientation in the most energy-stable structure in step (2), where the positions of the crystal orientations are as shown in Figure 2 ; draw the true strain diagrams of different charges at different numbers of layers of the Ir(001) surface electrode plate, as shown in Figure 3 ; the abscissa of the strain diagram selects the true strain, and the ordinate selects the charge surface density. Different colors represent the number of layers of the electrode plate - which means that the thicknesses of the electrode plates of different colors are different; among them, the selection of the charge surface density parameter should be derived from the surface model rather than the bulk model. Since the strain curve shape of Ir is a concave curve, the Ir(001) surface electrode plate is electrostrictive strain, that is, applying an external charge to the electrode plate will cause the electrode plate to expand along the tensile direction, which is the most common electrode plate strain type.

[0051] Example 2:

[0052] The embodiment of the present invention provides a design method for investigating the strain type of a W(001) surface nano-electrode plate immersed in a 1M NaCl electrolyte, which specifically includes the following operations:

[0053] (1) Manually construct a W bulk model under the Cartesian three-dimensional coordinate system, as shown in Figure 4As shown. Since the crystal structure of W is different from that of Ir, when constructing the bulk model, it is not possible to blindly copy the model, but it depends on the specific metal. The bulk model is optimized for energy in the x, y, and z coordinate directions. The key parameters for energy optimization are set as follows: the parameter of the exchange-correlation function is selected as gga-PBE; the pseudopotential of the Ir element is the GBRV ultrasoft pseudopotential; the k-point is set to 20×20×20; the energy cutoff threshold is 598 eV. The energy differences between two consecutive iteration steps of the electron cloud density, atomic or ionic coordinates, and lattice constant are 27.2×10 - 9 eV, 27.2×10 -8 eV, and 27.2×10 -7 eV.

[0054] (2) To investigate the strain type of the W(001) surface, the

[100] crystal direction and the

[010] crystal direction are selected as the tensile directions. According to the most energy-stable bulk structure obtained in (1), multilayer W(001) surface electrode models with different numbers of layers are constructed. The single layer of the (001) surface intercepted from the bulk model is placed flat on the xy plane of the Cartesian three-dimensional coordinate system. The

[100] crystal direction and the

[010] crystal direction coincide with the x-axis and y-axis, and then single layers of a specific number of layers are stacked along the z-axis, as Figure 5 shown. The number of layers of the electrode plate is selected as 7, 9, 11, 13, and 15 layers; the externally applied charge number of the electrode plate takes values of ±0.1, ±0.2, and ±0.3|e|; the electrolyte adopts the SaLSA (spherical homogeneous liquid sensitivity assumption) continuous model, and the set concentration is 1M Na + and Cl - . Energy optimization is to perform system relaxation in the xy two coordinate directions of the Cartesian three-dimensional coordinate system using self-consistent calculations. The k-point is selected as 20×20×1; the selection of pseudopotentials, the selection of exchange-correlation functionals, the cutoff energy, the electron cloud density, the energy differences between two consecutive iteration steps of atomic or ionic coordinates, and lattice constants are the same as in step (1).

[0055] (3) The most energy-stable structure in step (2) can determine the true strain of the selected

[100] crystal direction and

[010] crystal direction. The positions of the crystal directions are as Figure 5 shown. Plot the true strain diagrams of different charges for different numbers of layers of the W(001) surface electrode plate, as Figure 6 shown. The abscissa of this strain diagram selects the true strain, the ordinate selects the charge surface density, and different colors represent the number of layers of the electrode plate - which means that the thicknesses of the electrode plates of different colors are different; among them, the selection of the charge surface density parameter should be derived from the surface model rather than the bulk model. Since the shape of the strain curve of W is a convex curve, the W(001) surface electrode plate is electrostrictive strain, that is, applying an external charge to the electrode plate will cause the electrode plate to shrink along the tensile direction, which is an uncommon electrode plate strain type.

[0056] According to the specific embodiments provided by the present invention, it is found that the (001) surfaces of metals Rh, Al, Pt, and Ir are electrostrictive strains, as Figure 7 shown; the (001) surfaces of metals Mo and W are electrostriction strains, as Figure 8 shown. The relevant property information of these materials is protected by this patent.

[0057] Comparative example:

[0058] Referring to Example 1, an electrode plate model of Au(111) surface was constructed and its strain characteristics were calculated. See the literature Optimizing nanoporous metallic actuators through multiscale calculations and machine learning. The difference is that the electrode material in this comparative example is different from that in Example 1. The calculated results are as Figure 9 shown. It can be seen that the curve characteristics are consistent with those in Example 1.

[0059] The present invention uses the JDFTx software based on the combined density functional theory to perform high-throughput calculations on the strain process of nano-metal electrode plates, and for the first time invented a design method for investigating the electrostrictive and electrostriction strains of nano-metal electrode plates in electrolytes. This will help us reveal the strain law under low charges and has important research value. The electrochemical actuation phenomenon is an important research direction in the electrochemical field and the mechanical field. This invention provides ideas for studying the strain of nano-metals and also provides a new direction for the research of other metals in a low-voltage environment, and also has certain guiding significance for the future design of experiments using first-principles calculations to guide.

[0060] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations according to the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A nano-metal electrode plate dissolved in an electrolyte, characterized in that: The electrode plate exhibits an electrical expansion phenomenon or an electrical contraction phenomenon. Specifically, applying an external charge to the electrode plate causes the electrode plate to expand along the stretching direction, or applying an external charge to the electrode plate causes the electrode plate to shrink along the stretching direction.

2. A nano-metal electrode plate dissolved in an electrolyte according to claim 1, characterized in that: The electrolyte includes a strong electrolyte, and the electrolyte is a sodium halide electrolyte.

3. A method for investigating the electrical expansion and contraction strain of a nano-metal electrode plate in an electrolyte, characterized in that: The following steps are involved: S1, constructing a bulk nanometal model using the first principles, and optimizing the energy of the model in the xyz coordinate axis directions in a Cartesian three-dimensional coordinate system, so as to determine the parameters for constructing the nanometal plate so that the subsequent electrode plate model is in the most stable state; S2, constructing a multilayer nano-metal electrode plate model with different numbers of layers on the same surface according to the parameters obtained in S1, selecting a sodium halide electrolyte environment as the environmental parameter of the model, and setting the required external charge number, and then performing energy optimization to obtain the most energy stable structure of the nano-electrode plate under the selected metal, external charge number and number of layers, and obtaining the atomic distance of the nano-metal film on two selected crystal directions selected on the crystal direction, and obtaining the true strain; S3, based on the parameters obtained by S1 and S2, calculates the true strain of a metal electrode plate and draws the true strain diagram of the metal with different numbers of layers and different charges. According to the true strain diagram of the metal with different numbers of layers and different charges, that is, the shape of the strain curve, the strain type of the metal material is classified.

4. A method for investigating the electrical expansion and contraction strain of a nano-metal electrode plate in an electrolyte according to claim 3, characterized in that: S2, constructing a multilayer nano-metal electrode plate model with different numbers of layers on the same surface according to the parameters obtained in S1, selecting a sodium halide electrolyte environment as the environmental parameter of the model, and setting the required external charge number, and then performing energy optimization to obtain the most energy stable structure of the nano-electrode plate under the selected metal, external charge number and number of layers, specifically comprising the following steps: S21, construct a bulk nanometal model from S1 using the first principles, select two mutually perpendicular crystal directions as stretching directions, and then determine the single-layer surface formed by these two crystal directions from the bulk nanometal calculated in S1. To construct an N-layer surface, the single layer intercepted previously is placed flat on the xy plane of the Cartesian three-dimensional coordinate system, the two selected crystal directions coincide with the x-axis and the y-axis, and then (N-1) such single layers are stacked along the z-axis; the distance between two adjacent single layers is obtained by the structure and parameters of the bulk nanometal, and the relative position of the two adjacent single layers is determined by the structure of the bulk nanometal; thus, a multi-layer nanometal film is obtained; S22, adding external charges and sodium halide electrolyte environment to N layers of nanometal films; thereby obtaining a nanometal electrode plate model with a selected charge number and a selected number of surface layers of N, and the model is energy optimized in the xy coordinate axis directions in a Cartesian three-dimensional coordinate system to determine the true strains of the two mutually perpendicular crystal directions selected in S21.

5. A method for investigating the electrical expansion and contraction strain of a nano-metal electrode plate in an electrolyte according to claim 4, characterized in that: The added external charge is ±0.1-0.5|e|, the sodium halide is one or more of NaF, NaCl, NaBr, and NaI, and the concentration of the sodium halide is 0.3-2M.

6. A method for investigating the electrical expansion and contraction strain of a nano-metal electrode plate in an electrolyte according to claim 4, characterized in that: In step S21, a vacuum layer is provided between the atomic layers of the metal film to ensure that the interaction between the two multilayer films is sufficiently small.

7. A method for investigating the electrical expansion and contraction strain of a nano-metal electrode plate in an electrolyte according to claim 6, characterized in that: The thickness of the vacuum layer is 8. A method for investigating the electrical expansion and contraction strain of a nano-metal electrode plate in an electrolyte according to claim 4, characterized in that: The parameters of energy optimization are specifically set as K point 20×20×1 and cutoff energy 598.4 eV, where the energy differences of two consecutive iterations of electron cloud density, atomic or ion coordinates, and lattice constant are 27.2×10 -9 eV, 27.2×10 -8 eV and 27.2×10 -7 eV.

9. A method for investigating the electrical expansion and contraction strain of a nano-metal electrode plate in an electrolyte according to claim 3, characterized in that: In step S2, the nano-metal electrode plate is stretched in two selected directions and external charges are applied.

10. Application of the method for examining the electrical expansion and contraction strain of a nano-metal electrode plate in an electrolyte as claimed in any one of claims 3 to 9, characterized in that: The (001) surfaces of metals Rh, Al, Pt and Ir are electrically dilatant strain, while the (001) surfaces of metals Mo and W are electrically contractive strain.

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