From a microscopic perspective, during the use of lithium-ion batteries, irreversible electrochemical reactions such as electrolyte decomposition, active material deactivation, and positive and negative electrode structure collapse lead to a reduction in the number of lithium ions inserted and extracted, resulting in a decrease in capacity.
Especially under high voltage and high temperature conditions, the surface of highly delithiated cathode materials readily reacts with the electrolyte. For example, the reaction activity of NCM811 with the electrolyte in the charging state is much greater than that of NCM111. Therefore, the higher the charge/discharge voltage and the higher the temperature, the faster the capacity of lithium-ion batteries decreases.
From a macro perspective, how do we accurately measure current, voltage, and temperature, and effectively manage thermal, power, and energy? How do we assess the lifespan of high-energy-density lithium-ion batteries and extend their service life? Undoubtedly, battery management systems play a crucial role.
Exploring solutions from different dimensions
Regarding the issue of rapid lifespan degradation in high-energy-density lithium-ion batteries such as NCM811, current industry solutions mainly focus on aspects such as materials, electrolytes, separators, and battery management systems.
In terms of materials, the surface of NCM811 particles can be modified to improve its various properties. Since different electrolyte additives result in different degrees and rates of battery polarization, using an electrolyte that reduces parasitic reactions within the battery can improve the cycle life and safety of high-energy-density lithium-ion batteries.
By applying a multifunctional composite coating of ceramics and polymers, Penghui Power has improved the stability and safety of high-energy-density lithium-ion batteries under high temperature and high pressure. In addition, Penghui Power has developed a special process system and electrolyte for silicon-carbon anodes, which has improved the battery's initial efficiency to 86% or more, solved the problem of rapid degradation in the first 50 weeks, and improved the battery's capacity and test life.
At the battery management system level, Professor Wei Xuezhe, Vice Dean of the School of Automotive Engineering at Tongji University, proposed a battery pack optimization design method based on an electro-thermal-lifespan coupling model. This method can perform impedance measurement and capacity estimation on individual battery cells, collecting data across multiple spatial and temporal dimensions. Simultaneously, this design ensures battery pack consistency and achieves multi-factor, multi-physical field coupling. According to Professor Wei, this is the third-generation battery management system centered on lifespan estimation, prediction, and management (the first-generation system focused on individual cell safety monitoring, and the second-generation system on SOC estimation). This system possesses complete series-parallel connection methods, balancing methods, and thermal management methods, effectively managing the lifespan degradation of high-energy-density lithium-ion batteries.
