Li-ion technology is a fast growing and the most promising battery technology nowadays. Despite the advantages of the Li-ion batteries, there are major technical and financial challenges remaining that limit their application. The Li-ion battery is a non-linear and a time-variable system, whose internal electrochemical processes are almost impossible to be observed directly. The complicated electrochemical processes occurring in the battery lead to a battery degradation and decreasing of its performance. Moreover, the battery degradation may lead to malfunction or even more serious consequences like fire, a failure of an expensive equipment and even in the worst case casualties. Therefore, the determination of the Li-ion battery condition and lifetime is one of the major tasks, which should be solved for the successful using of the Li-ion batteries. The solving of these major tasks improves safety, reliability and performance of the Li-ion batteries and increases attractiveness of the Li-ion technology for an application. Unfortunately, the non-observability of the electrochemical processes in the battery does not allow direct measurements of the battery lifetime and only estimation of this parameter is possible.
Nowadays, the monitoring of Li-ion cell degradation is performed by considering such characteristic as the state of health (SoH). The existing SoH estimation methods are usually divided into four approaches, including direct assessment approach, data driven approach, adaptive approach and differential curves analysis approach. The detailed classification of the SoH estimation methods, which can be found in literature is given below.
The detailed analysis of the mentioned methods for the SoH estimation showed that:
- There is not the best SoH estimation method, which can be used in any systems. All currently existing methods have advantages and disadvantages, which should be considered during selection of the SoH estimation for the realisation in the battery management system;
- The SoH estimation method should be selected by taking into account the design of the battery system, application and operation conditions;
- A compromise between the accuracy of the estimation and the resources needed should be always found.
Text by Dr. Kirill Murashko