Molecular dynamics simulation analysis method for pyrolysis mechanism of binder for hot-pressed electrode foil

Abstract

The invention discloses a molecular dynamics simulation analysis method for a pyrolysis mechanism of a binder for a hot-pressed electrode foil. The molecular dynamics simulation analysis method comprises the following steps: constructing a molecular model on simulation software; performing energy minimization and geometric optimization on the molecular model; establishing an ethyl cellulose model with a periodic boundary condition, and performing annealing treatment on the box; obtaining an ethyl cellulose model in a stable state; a simulation result is obtained; and performing data analysis on the simulation result. According to the molecular dynamics simulation analysis method for the pyrolysis mechanism of the binder for the hot-pressed electrode foil, based on molecular dynamics simulation, the influence of different variables on binder pyrolysis can be effectively revealed by accurately controlling factors such as the heating rate, the heat preservation time and different temperatures, and the thermal stability of the binder is improved. And a certain theoretical basis is laid for a hot-pressing electrode foil degreasing process, so that research and explanation on a microscopic mechanism level can be carried out for perfecting a macroscopic binder pyrolysis experiment phenomenon.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of aluminum electrolytic capacitor anode materials, and in particular relates to a molecular dynamics simulation analysis method for the pyrolysis mechanism of a binder for hot-pressed electrode foil. Background Art

[0002] Electrode foil is a key material for the production of aluminum electrolytic capacitors. Its performance determines the capacity, loss, life, reliability and size of the capacitor. The traditional preparation of electrode foil relies on electrochemical corrosion to improve its specific capacity. The electrode foil prepared by this method is not only close to the theoretical limit of the specific capacity of the capacitor, but also produces a large amount of acid in the corrosion process, which will bring serious environmental pollution problems. Therefore, a new type of electrode foil has emerged - hot-pressed electrode foil. Its preparation technology is based on the idea of ​​additive manufacturing. After mixing aluminum powder and binder, it is coated on the surface of the aluminum base and sintered to form a "sandwich" structure with only aluminum powder stacked. The introduction of this hot-pressed electrode foil preparation technology solves the barriers of the above traditional electrode foil preparation technology and reduces environmental pollution.

[0003] Whether the pyrolysis of the binder is complete during the preparation of hot-pressed electrode foil will affect the formation of sintering necks between aluminum powders, which has a great impact on the specific capacitance of the capacitor. At present, most studies use experimental methods to explore the pyrolysis of binders by changing the heating rate, pyrolysis atmosphere and insulation time. However, due to the lack of research and explanation of the macroscopic experimental phenomena at the microscopic mechanism level, it is impossible to examine the physical and chemical evolution process in the experiment, making it difficult to truly reflect the pyrolysis mechanism of the binder under different heating rates, insulation time and sintering environment.

[0004] With the rapid development of computer technology, the application areas of molecular dynamics simulation technology have gradually broadened: it can not only simulate the physical and chemical changes of molecular structure at the atomic level, but also systematically analyze the properties of organic matter and complex chemical reaction mechanisms from a microscopic perspective.

[0005] Therefore, a molecular dynamics simulation analysis method for the pyrolysis mechanism of the binder for hot-pressed electrode foil needs to be developed in this field, which lays a certain theoretical foundation for the degreasing process of hot-pressed electrode foil. Summary of the invention

[0006] The purpose of the present invention is to provide a molecular dynamics simulation analysis method for the pyrolysis mechanism of a binder for hot-pressed electrode foil. Based on molecular dynamics simulation, by precisely controlling factors such as the heating rate, the holding time, and different temperatures, the influence of different variables on the pyrolysis of the binder can be effectively revealed, which lays a certain theoretical foundation for the degreasing process of the hot-pressed electrode foil, and further can provide a microscopic mechanism-level research explanation for the macroscopic binder pyrolysis experimental phenomenon.

[0007] To achieve the above object, the present invention provides a molecular dynamics simulation analysis method for the pyrolysis mechanism of a binder for hot-pressed electrode foil, comprising the following steps:

[0008] Step S1, constructing a molecular model on simulation software;

[0009] Step S2, performing energy minimization and geometry optimization on the molecular model constructed in step S1;

[0010] Step S3, establishing a box of appropriate size in the simulation software, placing ethyl cellulose in the box, establishing an ethyl cellulose model with periodic boundary conditions, and performing annealing treatment on the box;

[0011] Step S4, using the molecular dynamics simulation software Lammps to relax the ethyl cellulose model established in step S3 to minimize the energy, and finally obtain the ethyl cellulose model in a stable state;

[0012] Step S5, using the molecular dynamics simulation software Lammps to set appropriate force field function ReaxFF and parameters for the box established in step S4, to obtain simulation results;

[0013] Step S6: By performing data analysis on the simulation results obtained in step S5, the pyrolysis reaction path of the ethyl cellulose is determined according to the number of fragments after the reaction, the evolution law of the weight percentage of different products and the change of the structure of the ethyl cellulose.

[0014] Preferably, in step S1, the ethyl cellulose model is established using Materials Studio simulation software to construct a long-chain polymer with β-anhydroglucose as a unit; and the ethyl cellulose long chain is established using the Build Polymer module.

[0015] Preferably, step S2 specifically comprises relaxing the ethyl cellulose model established in step S1 using Lammps to minimize its energy; during the relaxation process, an NVT ensemble is selected to ensure stability, a Berendsen thermostat with a damping constant of 100 is used to maintain the system temperature, and the force field selects the ReaxFF force field function.

[0016] Preferably, in step S2, the NVT ensemble is selected to minimize the energy of the molecular model constructed in step S1, wherein N, V, and T represent the number of atoms, volume, and temperature in the simulation system, respectively, and the initial values ​​of these three parameters are set and kept unchanged in the simulation;

[0017] Forcite was used to perform geometry optimization on the molecular model constructed in step S1.

[0018] Preferably, step S4 specifically includes changing the step size to change the heating rate, and using the jump command to achieve simulation of different target temperatures.

[0019] Preferably, in step S5, a suitable force field function ReaxFF is set, whose total energy E total The composition description is as follows:

[0020] E total =E bond +E over +E under +E lp +E tors +E H-bond +E vdWaals +E Coulomb +E val ;

[0021] Among them, E bond 、E over 、E under 、E lp and E tors They are bond energy, overmatch energy, undermatch energy, lone pair energy and torsion angle energy;

[0022] In addition, E H-bond 、E vdWaals 、E val and E Coulomb They represent hydrogen bond energy, van der Waals energy, valence bond angle energy and Coulomb energy respectively.

[0023] Preferably, the force field function ReaxFF calculates the bond order B by the distance r between atoms. ij , the specific expression is,

[0024]

[0025] Among them, p b1 、p b2 represents the bond order of the σ bond, p b3 、p b4 represents the bond order of a single π bond, p b5 、p b6 represents the bond order of the double π bond; r ij represents the distance between atom i and atom j; The distance representing the equilibrium bond length of the σ bond; The distance representing the equilibrium bond length of the π bond; The distance representing the balanced bond length of the double π bond.

[0026] Preferably, in step S5, NVT ensemble average calculation is performed to obtain corresponding physical quantities.

[0027] Preferably, in step S6, the species file and the bonds file are calculated during the pyrolysis process, and the species file and the bonds file are post-processed using a python script to obtain characteristic products of the pyrolysis of the binder and a regular evolution diagram of the products as the temperature changes, and perform data analysis on the simulation results.

[0028] The present invention adopts the molecular dynamics simulation analysis method of the pyrolysis mechanism of the hot pressed electrode foil binder, and the beneficial effects are as follows:

[0029] (1) Since the main component of the binder is ethyl cellulose, the present invention analyzes the breakage of the chemical bonds in the molecule under different pyrolysis conditions by simulating and calculating the pyrolysis stability of the ethyl cellulose model, and analyzes the pyrolysis law of ethyl cellulose from a microscopic perspective, thereby systematically revealing the pyrolysis mechanism of the binder and reducing the number of experiments, cost and time of experiments;

[0030] (2) The present invention can not only quickly and accurately obtain physical quantities such as potential energy, temperature, kinetic energy and pressure during the pyrolysis of ethyl cellulose through the established theoretical model, but also obtain species files and bonds files, so as to systematically understand the characteristic reactions and products of pyrolysis, provide a new method for exploring the microscopic behavior of pyrolysis of ethyl cellulose, and provide theoretical support for designing a more efficient hot-pressing electrode foil degreasing process. It has significant industrial application prospects and reduces the high cost and difficulty of experimental implementation.

[0031] (3) The present invention provides a method for simulating the thermal decomposition mechanism and its influencing mechanism of the binder for hot-pressed electrode foil using molecular dynamics. In the simulation process, the NVT ensemble (constant number of atoms, volume and temperature) is first selected to ensure the stability of the system. By selecting a reasonable time step (such as 0.25fs) and using the Reaxff potential function, the dynamic behavior of the thermal decomposition of ethyl cellulose under the reaction force field is simulated;

[0032] (4) The present invention uses Lammps software for molecular dynamics simulation, which supports large-scale parallel computing, is suitable for nanoscale simulation, and can effectively improve simulation efficiency; the force field function ReaxFF can effectively capture the changes in bonds at the ionic level, making it a valuable tool for reflecting atomic changes in complex systems.

[0033] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The flowchart of the embodiment of the molecular dynamics simulation analysis method of the pyrolysis mechanism of the binder for hot pressed electrode foil of the present invention;

[0035] Figure 2The structure diagram of ethyl cellulose in the embodiment of the molecular dynamics simulation analysis method of the pyrolysis mechanism of the binder for hot-pressed electrode foil of the present invention;

[0036] Figure 3 This is a diagram showing the structure of ethyl cellulose after relaxation, which is an example of a molecular dynamics simulation analysis method for the pyrolysis mechanism of a binder for hot-pressed electrode foil according to the present invention;

[0037] Figure 4 The pyrolysis state diagram of ethyl cellulose in the embodiment of the molecular dynamics simulation analysis method of the pyrolysis mechanism of the binder for hot-pressed electrode foil of the present invention; wherein, (a) is the pyrolysis state diagram at 1200K; (b) is the pyrolysis state diagram at 1600K; (c) is the pyrolysis state diagram at 2000K; (d) is the pyrolysis state diagram at 2600K;

[0038] Figure 5 This is a diagram showing the evolution of gas, tar and carbon during the pyrolysis process in an embodiment of a molecular dynamics simulation analysis method for the pyrolysis mechanism of a binder for hot-pressed electrode foil of the present invention;

[0039] Figure 6 This is a distribution diagram of ethyl cellulose thermal decomposition products at different target temperatures in an embodiment of the molecular dynamics simulation analysis method for the thermal decomposition mechanism of the binder for hot-pressed electrode foil of the present invention. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0041] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0042] like Figure 1 As shown, the molecular dynamics simulation analysis method for the pyrolysis mechanism of the binder for hot pressing electrode foil comprises the following steps:

[0043] Step S1, constructing a molecular model on simulation software.

[0044] The ethyl cellulose model was established using Materials Studio simulation software to construct a long-chain polymer with β-anhydroglucose as a unit. The ethyl cellulose long chain was established using the Build Polymer module.

[0045] Step S2: performing energy minimization and geometry optimization on the molecular model constructed in step S1.

[0046] The NVT ensemble is selected to minimize the energy of the molecular model constructed in step S1, where N, V, and T represent the number of atoms, volume, and temperature in the simulation system, respectively. The initial values ​​of these three parameters are set and kept unchanged in the simulation.

[0047] Forcite was used to perform geometry optimization on the molecular model constructed in step S1.

[0048] The ethyl cellulose model established in step S1 was relaxed using Lammps to minimize its energy. During the relaxation process, the NVT ensemble was selected to ensure stability, the system temperature was maintained by a Berendsen thermostat with a damping constant of 100, and the potential function was the ReaxFF potential function.

[0049] Step S3, creating a box of appropriate size in the simulation software, placing ethyl cellulose in the box, creating an ethyl cellulose model with periodic boundary conditions, and annealing the box.

[0050] The choice of periodic boundary conditions ensures that ethyl cellulose will not be affected by the box boundaries during the pyrolysis process, thus better simulating the pyrolysis behavior in the actual environment.

[0051] Step S4: Use the molecular dynamics simulation software Lammps to relax the ethyl cellulose model established in step S3 to minimize the energy, and finally obtain the ethyl cellulose model in a stable state.

[0052] Changing the step size changes the heating rate, and using the jump command to simulate different target temperatures.

[0053] Step S5, using the molecular dynamics simulation software Lammps to set appropriate force field function ReaxFF and parameters for the box established in step S4, perform NVT ensemble average calculation to obtain corresponding physical quantities, and obtain simulation results.

[0054] The selected force field function ReaxFF can effectively capture the changes in bonds at the ionic level, making it a valuable tool for reflecting atomic changes in complex systems. total The composition description is as follows:

[0055] E total =E bond +E over +E under +E lp +E tors +E H-bond +E vdWaals +E Coulomb +E val ;

[0056] Among them, E bond 、E over 、E under 、E lp and E torsThey are bond energy, overmatch energy, undermatch energy, lone pair energy and torsion angle energy.

[0057] In addition, E H-bond 、E vdWaals 、E val and E Coulomb They represent hydrogen bond energy, van der Waals energy, valence bond angle energy and Coulomb energy respectively.

[0058] The force field function ReaxFF is designed to capture the breaking and joining of bonds in molecular reactions, allowing the description of the bond order, bond distance and bond dissociation energy of the atomic structure. The force field function ReaxFF calculates the bond order B through the distance r between atoms. ij , the specific expression is,

[0059]

[0060] Among them, p b1 、p b2 represents the bond order of the σ bond, p b3 、p b4 represents the bond order of a single π bond, p b5 、p b6 Represents the bond order of the double π bond. ij Represents the distance between atom i and atom j. The distance representing the equilibrium bond length of the σ bond. The distance representing the equilibrium bond length of a π bond. The distance representing the equilibrium bond length of a double π bond. Generally speaking, during the preliminary model building process, the bond order is initially randomly generated based on certain constraints. The bond order is known before the calculation and changes continuously as the environment changes.

[0061] Step S6: By performing data analysis on the simulation results obtained in step S5, the pyrolysis reaction path of the ethyl cellulose is determined according to the number of fragments after the reaction, the evolution law of the weight percentage of different products and the change of the structure of the ethyl cellulose.

[0062] The species files and bonds files in the pyrolysis process are calculated, and the species files and bonds files are post-processed using Python scripts to obtain the characteristic products of the binder pyrolysis and the evolution diagram of the products with temperature changes, and the simulation results are analyzed.

[0063] Example

[0064] The molecular dynamics simulation analysis method for the pyrolysis mechanism of the binder for hot pressing electrode foil comprises the following steps:

[0065] Step S1, using Materails Studio software to establish β-anhydroglucose units, and using the Build Polymer module to establish an ethyl cellulose long chain with a degree of polymerization of 35, such as Figure 2 As shown, there are 6 long chains with a degree of polymerization of 35.

[0066] Step S2: Use Forcite to perform geometric optimization.

[0067] Step S3, establishing an AC box through the Amorphous Cell module, placing the above 6 ethyl cellulose long chains into the AC box, establishing an ethyl cellulose model with periodic boundary conditions, and then annealing the AC box.

[0068] Step S4: According to the actual situation, the model in step S3 is imported into Lammps for energy minimization (total relaxation time 50ps). The relaxation result is as follows: Figure 3 As shown, the density of the AC box is 0.1g / ml, and the length, width and height of the outer box are box.

[0069] Step S5, set the force field function ReaxFF, and set the temperature range to 300K-3000K, the time step to 0.25fs, the entire simulation process to 250ps, output the atomic position information and thermodynamic information of the system for analysis every 1000 steps, and set the initial temperature to 300K. Figure 3-Figure 4 shown.

[0070] Step S6: Set periodic boundary conditions for the simulation system so that it will not fly out of the set range during the calculation process. After a cyclic calculation of time step t+△t, Dump obtains the atomic coordinates of the system.

[0071] Calculate the species file and bonds file during the pyrolysis process. Use the python script to post-process the species file and bonds file to obtain the characteristic products of the pyrolysis of the binder and the evolution diagram of the products with temperature changes, such as Figure 5-Figure 6 shown.

[0072] This embodiment shows that the efficiency of binder pyrolysis can be changed by changing the heating rate and different target temperatures, which is expected to reduce the residual rate of the binder in the actual degreasing process and improve the specific capacity of the hot-pressed electrode foil.

[0073] Therefore, the present invention adopts the molecular dynamics simulation analysis method of the pyrolysis mechanism of the binder for hot-pressed electrode foil. Based on molecular dynamics simulation, by precisely controlling factors such as the heating rate, holding time and different temperatures, it can effectively reveal the influence of different variables on the pyrolysis of the binder, and lay a certain theoretical foundation for the degreasing process of the hot-pressed electrode foil, and further can provide a microscopic mechanism-level research explanation for the experimental phenomenon of macroscopic binder pyrolysis.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A molecular dynamics simulation analysis method for the pyrolysis mechanism of a binder for hot pressed electrode foil, characterized in that: The following steps are involved: Step S1, constructing a molecular model on simulation software; Step S2, performing energy minimization and geometry optimization on the molecular model constructed in step S1; Step S3, establishing a box of appropriate size in the simulation software, placing ethyl cellulose in the box, establishing an ethyl cellulose model with periodic boundary conditions, and performing annealing treatment on the box; Step S4, using the molecular dynamics simulation software Lammps to relax the ethyl cellulose model established in step S3 to minimize the energy, and finally obtain the ethyl cellulose model in a stable state; Step S5, using the molecular dynamics simulation software Lammps to set appropriate force field function ReaxFF and parameters for the box established in step S4, to obtain simulation results; Step S6: By performing data analysis on the simulation results obtained in step S5, the pyrolysis reaction path of the ethyl cellulose is determined according to the number of fragments after the reaction, the evolution law of the weight percentage of different products and the change of the structure of the ethyl cellulose.

2. The molecular dynamics simulation analysis method for the pyrolysis mechanism of the hot-pressed electrode foil binder according to claim 1, characterized in that: In step S1, the Materials Studio simulation software is used to establish an ethyl cellulose model, and a long-chain polymer with β-anhydroglucose as a unit is constructed; and the ethyl cellulose long chain is established through the Build Polymer module.

3. The molecular dynamics simulation analysis method for the pyrolysis mechanism of the hot-pressed electrode foil binder according to claim 1, characterized in that: Specifically, step S2 uses Lammps to relax the ethyl cellulose model established in step S1 to minimize its energy; during the relaxation process, the NVT ensemble is selected to ensure stability, and the system temperature is maintained by a Berendsen thermostat with a damping constant of 100, and the force field selects the ReaxFF force field function.

4. The molecular dynamics simulation analysis method for the pyrolysis mechanism of the hot-pressed electrode foil binder according to claim 3, characterized in that: In step S2, the NVT ensemble is selected to minimize the energy of the molecular model constructed in step S1, where N, V, and T represent the number of atoms, volume, and temperature in the simulation system, respectively. The initial values ​​of these three parameters are set and kept unchanged in the simulation; Forcite was used to perform geometry optimization on the molecular model constructed in step S1.

5. The molecular dynamics simulation analysis method for the pyrolysis mechanism of the hot-pressed electrode foil binder according to claim 1, characterized in that: Step S4 specifically includes changing the step size to change the heating rate, and using the jump command to achieve simulation of different target temperatures.

6. The molecular dynamics simulation analysis method for the pyrolysis mechanism of the hot-pressed electrode foil binder according to claim 1, characterized in that: In step S5, a suitable force field function ReaxFF is set, whose total energy E total The composition description is as follows: AND total =And bond +E over +E under +E lp +E tors +E H-bond +E vdWaals +E Coulomb +E val ; Among them, E bond 、E over 、E under 、E lp and E tors They are bond energy, overmatch energy, undermatch energy, lone pair energy and torsion angle energy; In addition, E H-bond 、E vdWaals 、E val and E Coulomb They represent hydrogen bond energy, van der Waals energy, valence bond angle energy and Coulomb energy respectively.

7. The molecular dynamics simulation analysis method for the pyrolysis mechanism of the hot-pressed electrode foil binder according to claim 6, characterized in that: The force field function ReaxFF calculates the bond order B through the distance r between atoms. ij , the specific expression is, Among them, p b1 、p b2 represents the bond order of the σ bond, p b3 、p b4 represents the bond order of a single π bond, p b5 、p b6 represents the bond order of the double π bond; r ij represents the distance between atom i and atom j; The distance representing the equilibrium bond length of the σ bond; The distance representing the equilibrium bond length of the π bond; The distance representing the balanced bond length of the double π bond.

8. The molecular dynamics simulation analysis method for the pyrolysis mechanism of the hot-pressed electrode foil binder according to claim 7, characterized in that: In step S5, NVT ensemble average calculation is performed to obtain corresponding physical quantities.

9. The molecular dynamics simulation analysis method for the pyrolysis mechanism of the hot-pressed electrode foil binder according to claim 1, characterized in that: In step S6, the species file and the bonds file in the pyrolysis process are calculated, and the species file and the bonds file are post-processed using a python script to obtain characteristic products of the pyrolysis of the binder and a regular evolution diagram of the products with temperature changes, and perform data analysis on the simulation results.

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