Do you know the Lithium battery state of health assessment model?
259 2022-09-24
SOC is commonly used in energy storage battery and it is very important to identify the quality,cycle life of energy storage battery.The state of health of lithium batteries cannot be obtained by direct measurement, but can be obtained through model evaluation. The aging and health of batteries are affected by many factors. At present, the state of health evaluation models of lithium batteries mainly include electrochemical models and equivalent circuit models. and empirical models.

1. Electrochemical model

The electrochemical model analyzes the changes of the state of health of the battery during the operation process from the electrochemical reaction mechanism of the battery, and considers the influence of the aging factors of the battery on the internal and external state variables (temperature, current rate, cut-off voltage, etc.) of the battery. The research on electrochemical models of lithium batteries includes complex electrochemical models based on SEI mechanism models, electrochemical first-principles models, and single-factor and multi-factor comprehensive electrochemical models.

2. Equivalent circuit model

Equivalent circuit model From the perspective of battery electrical engineering, combined with a large number of state data analysis, the lithium battery is equivalent to a basic circuit model, and the circuit model is used to evaluate the state of health of the battery. There are three basic equivalent circuit models of lithium battery: Rint model, RC model and Thevenin model. PNGV model and GNL model are improved models based on Thevenin equivalent circuit model.

3. Empirical Models

The empirical model obtains the change of the battery performance state through a large number of experimental data analysis, fitting, trial and error, empirical formula and statistical processing, and summarizes the change rule of the battery state of health. There are mainly battery impedance empirical models and battery capacity estimation empirical models.
This part of the content can be found in this platform article for details:
It is not easy to understand lithium battery model research, this review is worth a look!

4. Difficulties in the study of the health status of lithium batteries

More and more attention is paid to the research on the health status and lifespan of lithium batteries. However, the research on the SOH of batteries is still in its infancy, mainly for the following three reasons.

4.1 The research period is long and the experimental conditions are strictly controlled
The cycle life of lithium batteries is long, and the aging test cycle of batteries is very long. During the test, the temperature, charge-discharge current, and charge-discharge cut-off voltage need to be strictly controlled, and the aging of the battery needs to be evaluated at regular intervals.
4.2 It is difficult to monitor and analyze the internal state of the battery
The SOH research of lithium batteries involves the internal state variables of the battery, such as the internal temperature, electrolyte concentration and internal resistance of the battery in the electrochemical model. It is very difficult to accurately monitor the internal state of the battery. It is also necessary to quantitatively analyze these state variables. This makes the SOH research of batteries difficult to solve.

4.3 Coupling of various influencing factors
The battery operating temperature, charge-discharge rate, and discharge depth are all factors that affect the aging and life of the battery, and these factors work together. The study of battery SOH requires the decoupling of various influencing factors. However, these factors are interrelated, the decoupling conditions are difficult to control, and it is difficult to perform decoupling analysis at present.

5. The significance of the research on the health status of lithium batteries
Battery SOH research is difficult and the progress is slow, but SOH research is of great value to the use, maintenance and evaluation of batteries, and can provide a basis and reference for planning, policy and industrial development, and is of great significance

5.1 Significance of battery management
The battery management system estimates the battery‘s state of charge and the remaining power is related to the battery‘s capacity. If the battery management system can grasp the aging law and health status of the battery, it will help it manage the battery‘s full life cycle.

5.2 Significance of battery use and maintenance
SOH research is conducive to mastering the factors affecting battery aging and providing theoretical guidance for battery use and maintenance. For the use and maintenance of batteries, understanding the factors affecting battery aging can reduce high and low temperature, overcharge and overdischarge, etc., which are harmful to battery use; knowing the current health status of the battery can help determine the inherent hidden dangers and life of the battery. Provides reference for battery maintenance and replacement.

5.3 Significance of battery economic evaluation
The accurate evaluation of SOH is of great significance to the economic evaluation of batteries. Different application scenarios, usage methods and maintenance methods of lithium batteries lead to differences in battery life and economic evaluations such as battery use costs and economic benefits. The battery aging model is established through SOH research to provide data support for analyzing the economics of batteries, and will provide effective assistance for corporate investment decisions, government policy formulation and industrial development planning.

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