Driving range is a key indicator that people consider when purchasing new energy vehicles, and it is also an important factor for relevant departments to consider when formulating policies. Therefore, new energy vehicle manufacturers prefer high-energy-density lithium batteries. With the help of these three factors, high-energy-density lithium batteries are gradually becoming the mainstream.
However, under current technological conditions, high-energy-density lithium batteries experience rapid lifespan degradation, and the cycle life of lithium batteries does not match the mileage life of the vehicle, nor does the calendar life of lithium batteries match the service life of the vehicle. This poses many challenges to the promotion of new energy vehicles.
Why do high-energy-density lithium batteries experience faster lifespan degradation?
From a microscopic perspective, during the use of lithium batteries, irreversible electrochemical reactions occur inside, such as electrolyte decomposition, active material deactivation, and collapse of the positive and negative electrode structures, leading to a reduction in the number of lithium ions inserted and extracted, which in turn causes a decrease in capacity.
Especially under high voltage and high temperature conditions, the highly delithiated cathode surface readily reacts with the electrolyte. For example, the reactivity of NCM811 with the electrolyte during charging is much greater than that of NCM111. Therefore, the higher the charge/discharge voltage and the higher the temperature, the faster the lithium battery capacity decreases.
From a macro perspective, how to accurately measure current, voltage, and temperature, and effectively manage thermal, power, and energy? How to perceive the lifespan status of high-energy-density lithium batteries and extend their service life? Undoubtedly, the battery management system plays 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 materials, electrolytes, separators, and battery management systems.
In terms of materials, the performance of NCM811 can be improved by modifying the surface of the particles. Since different electrolyte additives result in different degrees and rates of polarization in the battery, 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 Energy has improved the stability and safety of high-energy-density lithium-ion batteries under high temperature and high pressure. In addition, Penghui Energy has also developed a process system and electrolyte specifically for silicon-carbon anodes, which has increased the battery's initial efficiency to 86% or more, solved the problem of rapid degradation in the first 50 weeks of battery life, and improved the battery's capacity and experimental life.
At the battery management system level, Professor Wei Xuezhe, Vice Dean of the School of Automotive Studies at Tongji University, proposed a battery pack optimization design method based on an "electric-thermal-lifetime" coupled model. This method can perform impedance measurement and capacity estimation on individual battery cells, and collect data from multiple spatial and temporal dimensions. Simultaneously, this design ensures the consistency of the battery pack and achieves multi-factor and multi-physical field coupling. According to Professor Wei, this is the third-generation battery management system (the first-generation system focuses on individual cell safety monitoring, and the second-generation system focuses on SOC estimation) with lifetime estimation, prediction, and management as its core. This management system has complete series-parallel connection schemes, equalization schemes, and thermal management schemes, which can effectively manage the lifetime degradation of high-energy-density lithium-ion batteries.
Driven by market demand, battery companies such as Sandon New Energy, Guoxuan High-Tech, and Penghui Energy have all begun to invest in high-energy-density lithium-ion batteries. Material companies like Shanshan Group have also followed suit, making corresponding arrangements in the upstream sector. The industry's exploration of the lifespan degradation problem of high-energy-density lithium-ion batteries will undoubtedly benefit the development of the lithium-ion battery industry and the further promotion of new energy vehicles.
