阅读说明：本技术 一种导电聚合物用于固态电解质界面膜的可行性测试方法 (Feasibility testing method for conductive polymer used for solid electrolyte interface film ) 是由 毕可东 胡斌 于 2021-07-27 设计创作，主要内容包括：本发明提供一种导电聚合物用于固态电解质界面膜的可行性测试方法,包括：步骤10)构建采用待测导电聚合物作为固态电解质界面膜的锂离子电池模型；步骤20)利用分子动力学对锂离子电池模型进行热力学弛豫；步骤30)利用分子动力学对锂离子电池模型进行模拟充电；步骤40)根据锂离子电池模型中锂离子的运动轨迹,得到锂离子电池模型的扩散系数,从而确定待测导电聚合物作为固态电解质界面膜的可行性。本发明导电聚合物用于固态电解质界面膜的可行性测试方法,可以测试导电聚合物作为人工电解质界面膜的性能。(The invention provides a feasibility test method for a conductive polymer used for a solid electrolyte interface film, which comprises the following steps: step 10), constructing a lithium ion battery model adopting a conductive polymer to be tested as a solid electrolyte interface film; step 20) carrying out thermodynamic relaxation on the lithium ion battery model by utilizing molecular dynamics; step 30) utilizing molecular dynamics to carry out simulated charging on the lithium ion battery model; and step 40) obtaining the diffusion coefficient of the lithium ion battery model according to the movement track of lithium ions in the lithium ion battery model, thereby determining the feasibility of the conductive polymer to be tested as a solid electrolyte interface film. The feasibility test method of the conducting polymer used for the solid electrolyte interface film can test the performance of the conducting polymer used as the artificial electrolyte interface film.)

1. A method for testing the feasibility of a conductive polymer for use in a solid electrolyte interface membrane, comprising the steps of:

step 10), constructing a lithium ion battery model adopting a conductive polymer to be tested as a solid electrolyte interface film;

step 20) carrying out thermodynamic relaxation on the lithium ion battery model by utilizing molecular dynamics;

step 30) utilizing molecular dynamics to carry out simulated charging on the lithium ion battery model;

and step 40) obtaining the diffusion coefficient of the lithium ion battery model according to the movement track of lithium ions in the lithium ion battery model, thereby determining the feasibility of the conductive polymer to be tested as a solid electrolyte interface film.

2. The method for testing the feasibility of the conductive polymer for the solid electrolyte interface film according to claim 1, wherein in the step 10), the model of the lithium ion battery constructed comprises a graphite negative electrode, an electrolyte solution and the solid electrolyte interface film; the graphite negative electrode is a graphite layer formed by stacking eight layers of graphene in a surface mode, and the eight layers of graphene are provided with armchairs; the electrolyte solution comprises ethylene carbonate molecules and lithium hexafluorophosphate molecules, and the concentration of the electrolyte solution is 1M; the solid electrolyte interface film is of a conductive polymer film-like structure.

3. The method of claim 2 wherein one of the dangling carbon atoms on both left and right edges of the graphite negative electrode is randomly functionalized and the other dangling carbon atom is completely graft-covered with hydrogen atoms.

4. The method for testing the feasibility of a conductive polymer for a solid electrolyte interface membrane according to claim 1, wherein said step 20) comprises in particular:

equilibrating for 2ns at a temperature of 20K using a canonical ensemble; the temperature is then raised from 20K to 320K at intervals of every 50K/ns in 6ns and equilibrated at 320K for 2ns under a regular ensemble.

5. The method for testing the feasibility of a conductive polymer for a solid electrolyte interface membrane according to claim 1, wherein said step 30) comprises in particular:

in isothermal isobaric systemTo sum up, the intensity is applied along the z-axis direction of the lithium ion battery model asOf the electric field of (a).

6. The method for testing the feasibility of a conductive polymer for a solid electrolyte interface membrane according to claim 1, wherein said step 40) comprises in particular:

step 401) calculating to obtain the mean square displacement of lithium ions in the lithium ion battery model by using the formula (1):

in the formula, N represents the number of lithium ions and the vector r_i(t) represents the position of the ith particle at time t, r_i(0) Indicating the position of the ith particle at the time of initiation,<·>represents an ensemble average;

step 402), calculating the diffusivity of the lithium ion battery model by using the formula (2):

step 403), if the diffusivity of the lithium ion battery model is not less than the diffusivity of a conventional lithium ion battery, the conductive polymer to be tested is feasible for being used as a solid electrolyte interface film, otherwise, the conductive polymer to be tested is not feasible.

Technical Field

The invention belongs to the technical field of lithium ion battery solid electrolyte membranes, and particularly relates to a feasibility test method for a conductive polymer used for a solid electrolyte interface membrane.

Background

In recent years, the demand for lithium ion batteries has increased year by year in the fields of mobile portable devices and new energy automobiles. At present, the lithium ion battery generally adopts liquid electrolyte to conduct ions, and organic electrolyte is easy to cause accidents such as liquid leakage, electrode corrosion, combustion and explosion, and has great potential safety hazard.

Nowadays, there are a series of problems restricting the development of lithium ion battery technology, and the problem of solid electrolyte interface film (SEI) is particularly important. When the lithium ion battery is charged and discharged for the first time, a small amount of polar aprotic solvent in the electrolyte generates a reduction decomposition reaction after part of electrons are obtained on the surface of a negative electrode, and the reduction decomposition reaction is combined with lithium ions to generate an interface film with the thickness of about 100-120nm, and the film is called a solid electrolyte interface film (SEI). A solid electrolyte interface film (SEI) is generally formed at a solid-liquid phase interface between an anode material and an electrolyte. When the lithium ion battery is charged, lithium ions are removed from the positive active material, penetrate through the diaphragm after entering the electrolyte, then enter the electrolyte, and finally are embedded into the layered gap of the negative carbon material, so that the lithium ions complete a complete lithium removal-lithium embedding process. At this time, electrons return from the anode along the outer end and enter the carbon material of the cathode. Electrons, a solvent in the electrolyte, and lithium ions undergo an oxidation-reduction reaction, and solvent molecules receive the electrons and then combine with the lithium ions to form a solid electrolyte interface film (SEI) and generate gases such as H2, CO, and CH2 ═ CH 2. As the thickness of the solid electrolyte interface film (SEI) increases until electrons cannot penetrate, a passivation layer is formed, inhibiting the progress of the redox reaction of the electrolyte. The solid electrolyte interface film (SEI) is complex and diverse in physical composition, and its physical composition varies depending on the electrolyte composition, and generally consists of lithium oxide (Li2O), lithium fluoride (LiF), lithium chloride (LiCl), lithium carbonate (Li2CO3), LiCO2-R, alkoxide, and non-conductive polymer, and is a multi-layered structure, and one side near the electrolyte is porous and one side near the electrode is dense. However, the solid electrolyte interface film is very easy to fall off, crack and cyclically regenerate, and active lithium ions in the lithium ion battery are continuously consumed, so that the cycle life of the lithium ion battery is reduced. In view of the need for high cycle life of lithium ion batteries, artificial solid electrolyte interfacial films have become a focus of research.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the feasibility test method for the conductive polymer used for the solid electrolyte interface film is provided, and the performance of the conductive polymer used as the artificial electrolyte interface film can be tested.

In order to solve the above technical problems, the present invention provides a method for testing the feasibility of a conductive polymer for a solid electrolyte interface film, comprising the following steps:

step 10), constructing a lithium ion battery model adopting a conductive polymer to be tested as a solid electrolyte interface film;

step 20) carrying out thermodynamic relaxation on the lithium ion battery model by utilizing molecular dynamics;

step 30) utilizing molecular dynamics to carry out simulated charging on the lithium ion battery model;

and step 40) obtaining the diffusion coefficient of the lithium ion battery model according to the movement track of lithium ions in the lithium ion battery model, thereby determining the feasibility of the conductive polymer to be tested as a solid electrolyte interface film.

As a further improvement of the embodiment of the present invention, in the step 10), the constructed lithium ion battery model includes a graphite negative electrode, an electrolyte solution, and a solid electrolyte interface film; the graphite negative electrode is a graphite layer formed by stacking eight layers of graphene in a surface mode, and the eight layers of graphene are provided with armchairs; the electrolyte solution comprises ethylene carbonate molecules and lithium hexafluorophosphate molecules, and the concentration of the electrolyte solution is 1M; the solid electrolyte interface film is of a conductive polymer film-like structure.

As a further improvement of the embodiment of the invention, one suspended carbon atom on the left edge and the right edge of the graphite negative electrode is randomly functionalized, and the other suspended carbon atom is completely grafted and covered by hydrogen atoms.

As a further improvement of the embodiment of the present invention, the step 20) specifically includes:

equilibrating for 2ns at a temperature of 20K using a canonical ensemble; the temperature is then raised from 20K to 320K at intervals of every 50K/ns in 6ns and equilibrated at 320K for 2ns under a regular ensemble.

As a further improvement of the embodiment of the present invention, the step 30) specifically includes:

applying an intensity of as follows along the z-axis direction of the lithium ion battery model under an isothermal and isobaric ensembleOf the electric field of (a).

As a further improvement of the embodiment of the present invention, the step 40) specifically includes:

step 401) calculating to obtain the mean square displacement of lithium ions in the lithium ion battery model by using the formula (1):

in the formula, N represents the number of lithium ions and the vector r_i(t) represents the position of the ith particle at time t, r_i(0) Indicating the position of the ith particle at the time of initiation,<·>represents an ensemble average;

step 402), calculating the diffusivity of the lithium ion battery model by using the formula (2):

step 403), if the diffusivity of the lithium ion battery model is not less than the diffusivity of a conventional lithium ion battery, the conductive polymer to be tested is feasible for being used as a solid electrolyte interface film, otherwise, the conductive polymer to be tested is not feasible.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects: the feasibility test method for the conductive polymer used for the solid electrolyte interface film provided by the embodiment of the invention comprises the following steps of firstly constructing a lithium ion battery model adopting the conductive polymer to be tested as the solid electrolyte interface film; then, carrying out thermodynamic relaxation and simulated charging on the lithium ion battery model by utilizing molecular dynamics; and finally, obtaining the diffusion coefficient of the lithium ion battery model according to the movement track of lithium ions in the lithium ion battery model, thereby determining the feasibility of the conductive polymer to be tested as a solid electrolyte interface film. The method provided by the embodiment of the invention can be used for testing the performance of the conductive polymer as the artificial electrolyte interface film, can provide a design approach for further developing and designing a novel artificial solid electrolyte interface film, and provides a theoretical basis for later-stage development of the artificial solid electrolyte interface film.

Drawings

FIG. 1 is a flow chart of a method for testing the feasibility of a conducting polymer for use in a solid electrolyte interface membrane according to an embodiment of the present invention;

FIG. 2 is a diagram of a component model of a lithium ion battery; (i) is lithium ion, (ii) is hexafluorophosphate ion, (iii) is ethylene carbonate, (iv) is polythiophene chain, (v) is graphite cathode, (vi) is lithium ion battery model;

fig. 3(a) is a schematic diagram of a model before charging the lithium ion battery, and fig. 3(b) is a schematic diagram of a model after charging the lithium ion battery;

fig. 4 is a schematic diagram of Mean Square Displacement (MSD) of lithium ions in a battery model at temperatures of 300K, 400K and 500K, respectively.

Detailed Description

The technical solution of the present invention will be explained in detail below.

An embodiment of the present invention provides a method for testing feasibility of a conductive polymer for a solid electrolyte interface film, as shown in fig. 1, comprising the following steps:

and step 10) constructing a lithium ion battery model adopting the conductive polymer to be tested as a solid electrolyte interface film.

And 20) carrying out thermodynamic relaxation on the lithium ion battery model by utilizing molecular dynamics.

And step 30) utilizing molecular dynamics to carry out simulated charging on the lithium ion battery model.

And step 40) obtaining the diffusion coefficient of the lithium ion battery model according to the movement track of lithium ions in the lithium ion battery model, thereby determining the feasibility of the conductive polymer to be tested as a solid electrolyte interface film.

The method provided by the embodiment of the invention is used for constructing a half-cell model comprising a negative electrode, electrolyte and a conductive polymer type solid electrolyte interface film, and characterizing the capability of lithium ions penetrating through the solid electrolyte interface film by calculating the diffusion rate of the lithium ions. The method provided by the embodiment of the invention predicts the feasibility of the conductive polymer used as the interface film of the solid electrolyte of the lithium ion battery by using a molecular dynamics simulation method, neglects the electron transfer of the oxidation-reduction reaction in the lithium ion charging and discharging process in the calculation process, and saves a large amount of simulation calculation resources. The method provided by the embodiment of the invention can be used for testing the performance of the conducting polymer as the artificial electrolyte interface film, so that the conducting polymer type solid electrolyte interface film can be screened.

Preferably, in the step 10), the model of the lithium ion battery constructed includes a graphite negative electrode, an electrolyte solution and a solid electrolyte interface film.

The step 10) specifically comprises the following steps: an electrolyte solution of concentration 1M was established in Materials studio software from 30 lithium hexafluorophosphate (LiPF) dissolved in 350 Ethylene Carbonate (EC) molecules₆) And (4) molecule formation.

The graphite cathode is a graphite layer formed by stacking eight layers of graphene in a face-to-face manner, and the eight layers of graphene all have armchair edges. Preferably, one of the dangling carbon atoms on the left and right edges of the graphite negative electrode is randomly functionalized by a hydroxyl group and a carboxyl group to improve the stability thereof. Preferably, to avoid the effects of edge unsaturation, the dangling carbon atoms on the other side are completely graft-covered by hydrogen atoms.

The conductive polymer takes polythiophene as an example, a single polythiophene chain comprises 10 thiophene monomers, the artificial solid electrolyte interface structure is a polythiophene film structure constructed by using ten polythiophene chains by using an Amorphous Cell module of Materials Studio, and the specific space size isFinally, an initial nano lithium ion battery model comprising a graphite cathode, a polythiophene artificial solid electrolyte interface film (A-SEI) and an electrolyte solution is constructed, as shown in FIG. 2, the space size of the lithium ion battery model isIn addition, a two-layer graphene model is placed next to the electrolyte at the z-axis direction edge of the lithium ion battery model to prevent unreasonable movement of electrolyte molecules from causing erroneous results.

Preferably, the method further comprises the following steps between the step 10) and the step 20): the initially constructed lithium ion battery model was optimized for configuration using PACKMOL to obtain a reasonable geometry.

Preferably, the step 20) specifically includes:

a regular ensemble (NVT) was used to balance 2ns at a temperature of 20K to remove unreasonable singularities in the model. The temperature was then raised from 20K to 320K at intervals of every 50K/ns in 6ns and equilibrated at 320K for 2ns under NVT. During thermodynamic relaxation, a Nose-Hoover thermostat and barostat were used to maintain temperature and pressure during molecular dynamics simulations. Periodic boundary conditions are applied in the x and y directions and reflective boundary conditions are applied in the z direction.

Preferably, the step 30) specifically includes:

applying an intensity of 1 in a z-axis direction of a lithium ion battery model under an isothermal and isobaric ensemble (NPT) Of the electric field of (a).

As shown in fig. 3, the distribution of the various particles was 10ps upon application of an electric field. Lithium ions move from the electrolyte solution to the negative electrode due to the applied external electric field, and the PF₆ ^-The ions move in the opposite direction. In the electrolyte solution, lithium ions are surrounded by EC molecules, and the movement of the ions pushes the EC molecules to do translational motion. Whereas the external electric field effects only cause a slight rotational movement of the EC molecules, since the interaction between the EC dipole moment and the electric field is very weak. No lithium ions were present in the graphite negative electrode sheet before the electric field was applied to the lithium ion battery model. However, when an external electric field is applied for 100ps, 30 lithium ions are stored in the graphite layer. Initially, due to lithium salt (LiPF)₆) Completely dissolved in EC solvent, hence PF₆ ^-The ions are distributed throughout the electrolyte solution. But under the action of an external electric field, the PF₆ ^-The ions migrate to the other side of the graphite cathode. This situation indicates that the electrolyte solution is slightly polarized. Simulation is carried out toAt 100ps, lithium ions in the system were all stored in the graphite negative electrode layer, which marks the end of the battery charging process. When lithium ions gradually enter the graphite layer, the interval between the graphite negative electrode layers becomes large and the graphite layer shape becomes wavy. Once the lithium ions reach the negative electrode and are reduced between the graphite layers, these cations remain stationary in the layers. During charging, the number of lithium ions reaching the graphite negative electrode steadily increases, and therefore, a pseudo ion current can be obtained in a steady state. In order to ensure that lithium ions in the electrolyte solution completely penetrate through the polythiophene layers and enter the graphite layers, the simulation system is simulated for 400ps under the action of an external electric field.

Preferably, the step 40) specifically includes:

step 401) the diffusivity (D) of the particles indicates the rate of spatial movement of the particles, and the diffusivity can be derived from the Mean Square Displacement (MSD) of the particles. Mean Square Displacement (MSD) is an index of deviation of the spatial position of lithium ions from a reference position with time. Calculating the mean square displacement of lithium ions in the lithium ion battery model by using the formula (1):

in the formula, N represents the number of lithium ions and the vector r_i(t) represents the position of the ith particle at time t, r_i(0) Indicating the position of the ith particle at the time of initiation,<·>represents ensemble averaging.

Step 402), calculating the diffusivity of the lithium ion battery model by using the formula (2):

in order to obtain accurate results, three independent simulations of mean-square-shift time-dependent data of lithium ion migration were performed, followed by further averaging. The diffusivity of lithium ions is derived from the data of the variation of the mean square displacement of the ensemble with time.

Step 403), if the diffusivity of the lithium ion battery model is not less than the diffusivity of a conventional lithium ion battery, the conductive polymer to be tested is feasible for being used as a solid electrolyte interface film, otherwise, the conductive polymer to be tested is not feasible.

The mean square shift of lithium ions across the polythiophene artificial solid electrolyte interface film (a-SEI) can distinguish three different kinetic forms: elastic movement in a short time, entrapment movement in the middle time, and diffusion in a long time. As shown in FIG. 4, the diffusivity of lithium ions in the interfacial matrix of the polythiophene artificial solid electrolyte was 2.7X 10 at 300K temperature by extracting the diffusivity of lithium ions from the slope of the mean square displacement MSD diffusion state^-11m²S, 3.5X 10 at 400K^-11m²At a temperature of 500K, is 6.2X 10^-10m²And s. The lithium ion diffusivity calculated by the method is slightly higher than the diffusivity of lithium ions in polyethylene oxide (PEO) of a solid electrolyte interface layer of a common lithium ion battery. Therefore, the diffusion movement of lithium ions in nano lithium ion batteries demonstrates the feasibility of using polythiophene as an artificial solid electrolyte interface film (a-SEI).

The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are intended to further illustrate the principles of the invention, and that various changes and modifications may be made without departing from the spirit and scope of the invention, which is also intended to be covered by the appended claims. The scope of the invention is defined by the claims and their equivalents.