What types of lithium battery models are there?
There are two ways to model the lithium battery model, one is to carry out a large number of experiments on the battery, accumulate experimental data, simulate the collected data, and summarize the law of change of the lithium-ion battery; the other It is to study the micro-behavior of lithium-ion batteries. Through the description of the micro-behavior, with the help of computer means, a theoretical model is established. Commonly used lithium battery models mainly include internal resistance model, equivalent circuit model, genetic algorithm model, neural network model and electrochemical model.
1. The internal resistance model of the lithium battery model
The internal resistance model is the simplest battery model, usually used to predict the capacity of the battery. Generally speaking, battery capacity varies with voltage and internal resistance. Since the voltage will change differently under different discharge currents, researchers have tried to establish the relationship between internal resistance and capacity. However, the internal resistance is not an intrinsic value, and the internal resistance model requires a lot of experimental data. For example, the maximum capacity of the battery changes at different temperatures, the output voltage of the battery changes at different current rates, and the internal resistance of the battery changes at different temperatures. According to the data obtained from the experiment, the internal resistance of the battery is used to determine the capacity of the battery according to the different use environment of the battery, so the model is closer to a database.
Because the battery will reflect some of the characteristics of resistance and capacitance under the action of current, v.Johsonl6.] et al. proposed that it can be used Equivalent circuit to build a battery model to simulate the dynamic and static performance of the battery. The basic equivalent circuit of a lithium-ion battery, where V and V represent the open circuit voltage and output voltage of the battery, R is the internal resistance of the battery, and the RG parallel circuit simulates the external characteristics of the battery.
3. The genetic algorithm model of the lithium battery model
The lithium ion battery model based on the genetic algorithm can generally analyze the experimental data, solve the equation and other methods to establish the model to simulate the battery characteristic. But because the chemical reaction inside the battery is very complicated, it is difficult to find a suitable function to describe the battery model. The genetic algorithm is easy to calculate, and the output function is very flexible, and it can be used to build a lithium battery pack model.
4. The neural network model of the lithium battery model
The feasibility of using the neural network algorithm to build the battery model is studied, the lithium-ion battery model is established, and the successful prediction of the electric vehicle The remaining power of the battery.
Combined use of neural network algorithm and fuzzy algorithm, taking advantage of each other to make up for the shortcomings of the two algorithms, used to estimate the remaining capacity of the lithium-ion battery, and improve the estimation accuracy of a single algorithm.
5. The electrochemical model of the lithium battery model
The electrochemical model is a model established based on the basic chemical principles of the battery. The principle model of the lithium ion battery is based on the research basis of west in 1982 Gradually established. When studying porous electrodes composed of fibrous active material particles, West established a quasi-two-dimensional porous electrode model, assuming that the solution phase in the battery is a binary solution system, defaulting the diffusion coefficient to a constant, and the solid phase diffusion process is The control step, the electrochemical process is ignored. Since the lithium battery is also a porous electrode system, when studying the Li:LiClO4:TIS2 battery model, a similar processing method was adopted. Considering the structure of the battery, the structure of the diaphragm was introduced into the model. The results of Mao et al.'s research show that the thinner the separator, the more power the battery can release. However, because this model is not a true battery model, it only studies the principle of a single electrode, and does not model the battery as a whole, so the model cannot fully simulate the chemical characteristics of the battery. In the above models, it is assumed that the lithium ion intercalation process is infinitely fast, so there is an electrochemical equilibrium system at the electrode/electrolyte interface. In other words, the OCP (Open Circuit Potential) particle surface concentration of the battery is related to the concentration of the nearby electrolyte.
When Doyle was studying Li:PEO3LiCF3SO3:TiS2 batteries, he established a true battery model based on the porous electrode model. The Butler-Walmer equation is used to describe the electrochemical reaction that occurs on each electrode, and Fick's law is used to describe the diffusion phenomenon of lithium particles inside the electrode, and the diffusion coefficient is assumed to be a constant. When a chemical reaction occurs, the volume of the battery is The change is ignored. At the battery diaphragm, lithium ions pass through the diaphragm to form a layer of SEI film, which simplifies the film into a film resistance. The battery model does not consider the occurrence of side reactions. On the basis of , Fuller  et al. established an equation describing the chemical characteristics of lithium-ion batteries under the dilute solution theory, and established a general lithium-ion battery model. The study of Fuller et al. explained the relationship between the open circuit potential ocP and SOC of the battery. The work is of great significance. The study shows that the relationship between OCP and SOc curve is non-linear, and the relationship between current density and the curve is very close. The greater the rate of change of the OCP and soc curves, the more uniform the current density distribution. Then Nalin and Giacomo et al. used the finite element method to solve the chemical model of the lithium-ion battery on the basis of the predecessors, and compared the solved model with the actual battery discharge characteristics.
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