Large-scale reactive molecular dynamics simulation method for analyzing interface product of lithium ion battery

Abstract

The invention relates to a large-scale reactive molecular dynamics simulation method for analyzing a lithium ion battery interface product, and the method specifically comprises the steps: building a lithium ion battery atomic scale model, setting simulation conditions, carrying out reactive molecular dynamics simulation under the preset simulation conditions, and analyzing the interface product generated by simulation. And a reaction network is constructed, so that identification and analysis of an interface product formed between the electrolyte and the electrode of the lithium ion battery are realized. Compared with the prior art, the ReaxFF force field is combined with the electrochemical kinetics method, the electrochemical behavior of the battery is simulated more truly, and the practicability and accuracy of the model are enhanced. According to the method, the reaction network is automatically extracted from the MD track by using the ReacNetGeneraa tor, reaction paths and quantity can be extracted from a large amount of atomic coordinate data, the reaction matrix is generated, the interface product formed in the battery is efficiently identified and analyzed, and a powerful tool is provided for understanding the interface reaction mechanism of the battery.

Description

Technical Field

[0001] The invention relates to the technical field of electrochemical simulation, and in particular to a large-scale reactive molecular dynamics simulation method for analyzing interface products of lithium-ion batteries. Background Art

[0002] The interface products formed during the charge and discharge process of lithium-ion batteries are important components that affect battery performance, stability and safety. Current experimental test characterization methods such as SEM and XPS are not sufficient to fully analyze the formation and evolution of interface products. Atomic simulation is a good advanced research method. Ab Initio Molecular Dynamics (AIMD) simulation can be used for atomic-scale simulation research, but AIMD is limited to small systems (about hundreds of atoms) and the time scale is relatively short, usually limited to the picosecond range, which is not conducive to large-scale and long-term research on the interface evolution process of lithium-ion batteries. Using classical molecular dynamics (MD) simulation can greatly expand the simulation system scale and time scale of atomic simulation, which can reach the scale of hundreds of thousands of atoms and hundreds of nanoseconds. However, the accuracy of MD simulation is heavily dependent on the classical force field that describes the interaction between atoms.

[0003] Therefore, there is an urgent need to develop a method with high accuracy that can accurately study the interface products of lithium-ion batteries. Summary of the invention

[0004] The purpose of the present invention is to provide a large-scale reactive molecular dynamics simulation method for analyzing the interface products of lithium-ion batteries in order to overcome the defects of the above-mentioned prior art. By combining the ReaxFF force field with the electrochemical kinetics method, the electrochemical behavior of the battery can be simulated more realistically by dynamically adjusting the electronegativity of atoms and considering the influence of the voltage applied by the electrodes.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] The present invention provides a large-scale reactive molecular dynamics simulation method for analyzing interface products of lithium-ion batteries, the method comprising: building an atomic-scale model of a lithium-ion battery, setting simulation conditions, performing reactive molecular dynamics simulation under preset simulation conditions, analyzing interface products generated by the simulation, and constructing a reaction network to achieve identification and analysis of interface products formed between an electrolyte and an electrode of a lithium-ion battery;

[0007] The simulation conditions are: using ReaxFF force field to simulate the interaction between atoms; using implicit degree of freedom electrochemical kinetics method to simulate the electrochemical driving force generated by applying external voltage to the metal electrode.

[0008] Furthermore, the lithium-ion battery model includes a positive electrode atomic layer, an electrolyte layer and a negative electrode atomic layer constructed in sequence from top to bottom, the electrolyte molecules are filled between the negative electrode atomic layer and the positive electrode atomic layer, and a pure repulsive force perpendicular to the positive electrode surface is introduced to prevent the electrolyte molecules from reacting with the positive electrode atoms;

[0009] The atoms in the negative electrode atomic layer and the positive electrode atomic layer are fixed in position during the reactive molecular dynamics simulation to prevent the atoms from drifting.

[0010] Furthermore, the ReaxFF force field uses bond length, bond order or bond energy relationships to achieve a smooth transition between bonded and non-bonded systems.

[0011] Furthermore, the implicit degree of freedom electrochemical kinetics method is specifically as follows: firstly, the electronegativity of atoms in the two electrodes is enhanced, and then the atomic electrochemical potential χ*i is determined.

[0012] Furthermore, the formula used to enhance the electronegativity of atoms in the two electrodes is:

[0013] χ *i = x 0i ±Φ i / 2

[0014] Among them, χ 0i and Φ i are the atomic electronegativity after charge balance and the atomic electrochemical potential of atom i, respectively.

[0015] Furthermore, the calculation formula of the atomic electrochemical potential is:

[0016]

[0017] Where k is the effective diffusion rate; R ij represents the distance between atoms i and j; ω(Rij) is the local weighting function, which is used to indicate whether two atoms are considered to be part of the same metal cluster; η is the relaxation rate; F(Wi) is the switching function, and Wi is the total number of coordinated metal atoms of atom i.

[0018] Furthermore, when an atom separates from other metal atoms, F(Wi) will start to relax, causing a voltage difference between the metal atoms in the electrode;

[0019] If the atom detaches from the electrode, the electronegativity of the atom returns to its original value χ0i.

[0020] Furthermore, the LAMMPS software package is used to perform reaction molecular dynamics simulation under preset temperature and simulation conditions, so that the electrolyte molecules will form interface products on the battery electrodes through chemical reactions.

[0021] Furthermore, the ReacNetGenerator network generator is used for the interface products generated by the simulation, and the connectivity of atoms at each moment is determined based on the coordinates and bond sequences, and then the type of substance is detected based on the atomic connectivity.

[0022] Furthermore, a simplified molecular input line input specification is used for indexing to ensure the uniqueness of the detected species, and then the reaction paths and quantities in the entire trajectory are calculated. After generating the reaction matrix, a force-oriented algorithm is used to construct the reaction network.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] 1. The present invention combines the ReaxFF force field with the electrochemical kinetics method. During the simulation process, the ReaxFF force field is used to describe the reactive interactions between atoms, and the implicit degree of freedom electrochemical kinetics (EChemDID) method is combined to simulate the electrochemical driving force of the external voltage on the electrode. By dynamically adjusting the electronegativity of atoms and considering the influence of the voltage applied to the electrode, the electrochemical behavior of the battery can be simulated more realistically. This innovative combination enables the simulation to not only accurately describe the reaction process, but also simulate the effects of electrochemical drive, enhancing the practicality and accuracy of the model.

[0025] 2. The present invention is based on the automatic analysis of interface products of ReacNetGenerator. ReacNetGenerator is used to automatically extract reaction networks from MD trajectories, and reaction paths and quantities can be extracted from a large amount of atomic coordinate data, and a reaction matrix can be generated. Through this automated analysis method, the interface products formed in the battery can be efficiently identified and analyzed, and their changes during the entire simulation process can be calculated. It not only improves the efficiency of data processing, but also ensures the comprehensive analysis of reaction paths and products, providing a powerful tool for understanding the interface reaction mechanism of the battery.

[0026] 3. The present invention introduces a pure repulsive force between the electrode and the electrolyte molecules to prevent the electrolyte molecules from reacting with the electrode atoms, thereby being able to more accurately study the interaction between the electrolyte and the electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A flowchart of a large-scale reactive molecular dynamics simulation method for analyzing interfacial products of lithium-ion batteries;

[0028] Figure 2 This is a structural diagram of the atomic scale model of the lithium-ion battery in Example 1. DETAILED DESCRIPTION

[0029] The specific implementation methods of the present invention are described in detail below through examples. These examples are implemented on the premise of the scheme described in the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following examples.

[0030] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. Any features such as structure / module name, control mode, algorithm, process or composition ratio not clearly described in this technical solution are regarded as common technical features disclosed in the prior art.

[0031] Example 1

[0032] This embodiment provides a large-scale reactive molecular dynamics simulation method for analyzing lithium-ion battery interface products, such as Figure 1 As shown, the following steps are included:

[0033] S1: Build an atomic scale model of a lithium-ion battery, such as Figure 2 As shown in the figure, from top to bottom, it includes the positive electrode lithium atomic layer, electrolyte layer and negative electrode atomic layer constructed in sequence; the electrolyte molecules are filled between the negative electrode atomic layer and the positive electrode atomic layer, and a pure repulsive force perpendicular to the positive electrode surface is introduced to prevent the electrolyte molecules from reacting with the positive electrode atoms. The periodic boundary conditions are only applied in the lateral dimensions of x and y. The negative electrode atoms and positive electrode atoms at the bottom of the atomic model are fixed during the reaction molecular dynamics simulation of the lithium battery charge and discharge cycle process to avoid atomic drift in the lithium-ion battery model.

[0034] S2: Set the simulation conditions and use the ReaxFF force field to simulate the interactions between atoms. The ReaxFF force field uses bond length, bond order, or bond energy relationship to achieve a smooth transition between bonded and non-bonded systems, allowing reactions to occur during molecular dynamics simulations. The specific process is as follows: During the MD simulation, the bond order is updated at each iteration, and the calculation of the system potential energy takes the bond order into account. The ReaxFF force field also considers non-bonded interactions between each pair of atoms, including van der Waals terms and Coulomb terms. During the MD simulation, the qeq / shielded method is used for charge balance.

[0035] The implicit degree of freedom electrochemical kinetics method is used to simulate the electrochemical driving force generated by applying an external voltage to the metal electrode. In the EChemDID simulation, the χ *i = x 0i ±Φ i / 2 enhances the atomic electronegativity of atoms in the two electrodes, where χ0i and Φi are the atomic electronegativity of charge balance and the atomic electrochemical potential of atom i, respectively. During MD simulations, the atomic electrochemical potential χ*i can be immediately determined using the following formula:

[0036]

[0037] Where k is the effective diffusion rate; R ij represents the distance between atoms i and j; ω(Rij) is a local weighting function used to indicate whether two atoms are considered to be part of the same metal cluster; η is the relaxation rate; F(Wi) is a switching function, where Wi is the total number of coordinated metal atoms of atom i. When an atom separates from other metal atoms, F(Wi) turns on relaxation, causing a voltage difference to be generated between the metal atoms in the electrode; if the atom detaches from the electrode, the electronegativity of the atom returns to its original value χ0i.

[0038] S3: Reactive molecular dynamics simulation, using the LAMMPS software package to perform reactive molecular dynamics simulation under preset temperature and simulation conditions, so that the electrolyte molecules will form interface products on the battery electrodes through chemical reactions.

[0039] S4: Analyze the interface products and construct the reaction network. The simulated interface products use the ReacNetGenerator network generator to automatically extract the reaction network from the MD trajectory containing the atomic coordinates, read the MD trajectory file, and then determine the connectivity of the atoms at each moment based on the coordinates and bond sequence. Then, based on the atomic connectivity, detect the type of substance, including molecules and free radicals.

[0040] The simplified molecular input line specification (SMILES) was used for indexing to ensure the uniqueness of the detected species, and then the reaction paths and quantities in the entire trajectory were calculated. After the reaction matrix was generated, the reaction network was constructed using a force-oriented algorithm.

[0041] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A large-scale reactive molecular dynamics simulation method for analyzing lithium-ion battery interface products, characterized in that: The method comprises: constructing an atomic scale model of a lithium ion battery, setting simulation conditions, performing reactive molecular dynamics simulation under preset simulation conditions, analyzing interface products generated by the simulation, and constructing a reaction network to realize identification and analysis of interface products formed between an electrolyte and an electrode of the lithium ion battery; The simulation conditions are: using ReaxFF force field to simulate the interaction between atoms; using implicit degree of freedom electrochemical kinetics method to simulate the electrochemical driving force generated by applying external voltage to the metal electrode.

2. A large-scale reactive molecular dynamics simulation method for analyzing lithium-ion battery interface products according to claim 1, characterized in that: The lithium-ion battery model includes a positive electrode atomic layer, an electrolyte layer and a negative electrode atomic layer constructed in sequence from top to bottom, electrolyte molecules are filled between the negative electrode atomic layer and the positive electrode atomic layer, and a pure repulsive force perpendicular to the positive electrode surface is introduced to prevent the electrolyte molecules from reacting with the positive electrode atoms; The atoms in the negative electrode atomic layer and the positive electrode atomic layer are fixed in position during the reactive molecular dynamics simulation to prevent the atoms from drifting.

3. The large-scale reactive molecular dynamics simulation method for analyzing lithium-ion battery interface products according to claim 1, characterized in that: The ReaxFF force field uses bond length, bond order or bond energy relationships to achieve a smooth transition between bonded and non-bonded systems.

4. The large-scale reactive molecular dynamics simulation method for analyzing lithium-ion battery interface products according to claim 1, characterized in that: The implicit degree of freedom electrochemical kinetics method is specifically as follows: firstly, the electronegativity of atoms in the two electrodes is enhanced, and then the atomic electrochemical potential χ*i is determined.

5. A large-scale reactive molecular dynamics simulation method for analyzing lithium-ion battery interface products according to claim 4, characterized in that: The formula used to enhance the electronegativity of atoms in the two electrodes is: x *i =x 0i ±Φ i / 2 Among them, χ 0i and Φ i are the atomic electronegativity after charge balance and the atomic electrochemical potential of atom i, respectively.

6. A large-scale reactive molecular dynamics simulation method for analyzing lithium-ion battery interface products according to claim 4, characterized in that: The calculation formula of the atomic electrochemical potential is: Where k is the effective diffusion rate; R ij represents the distance between atoms i and j; ω(Rij) is the local weighting function, which is used to indicate whether two atoms are considered to be part of the same metal cluster; η is the relaxation rate; F(Wi) is the switching function, and Wi is the total number of coordinated metal atoms of atom i.

7. A large-scale reactive molecular dynamics simulation method for analyzing lithium-ion battery interface products according to claim 6, characterized in that: When an atom separates from other metal atoms, F(Wi) will start to relax, causing the metal atoms in the electrode to generate a voltage difference; If the atom detaches from the electrode, the electronegativity of the atom returns to its original value χ0i.

8. The large-scale reactive molecular dynamics simulation method for analyzing lithium-ion battery interface products according to claim 1, characterized in that: The LAMMPS software package is used to perform reaction molecular dynamics simulation under preset temperature and simulation conditions, so that the electrolyte molecules will form interface products on the battery electrodes through chemical reactions.

9. The large-scale reactive molecular dynamics simulation method for analyzing lithium-ion battery interface products according to claim 1, characterized in that: The ReacNetGenerator network generator is used for the interface products generated by the simulation, and the connectivity of atoms at each moment is determined based on the coordinates and bond sequences, and then the type of substance is detected based on the atomic connectivity.

10. A large-scale reactive molecular dynamics simulation method for analyzing lithium-ion battery interface products according to claim 9, characterized in that: A simplified molecular input line input specification is used for indexing to ensure the uniqueness of the detected species. The reaction paths and quantities in the entire trajectory are calculated. After the reaction matrix is ​​generated, a force-oriented algorithm is used to construct the reaction network.

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