Effect of the External Pressure on Li-Ion Pouch Cell at High C-Rate Conditions
Authors: Lee Ha Eun , Jo Hyeonseong , Kim Seong Su 
Published: December 2024

Rechargeable Lithium-ion batteries (LIBs) are the power source used widely in portable electronic devices and are becoming increasingly important in the automotive industry applications. LIBs need to be high-energy, safe, and cost-effective to address the demand for large driving ranges of batteries in electric vehicles (EVs) and hybrid electric vehicles (HEV). Therefore, technologies for extending the cycle life of LIBs and solving component degradation problems are required. Recently, the recharging time for batteries in EVs is longer compared to the refueling time for gasoline-powered vehicles which prevents the widespread adoption of battery-powered EVs into the transportation sector. In that perspective, achieving fast charge has been considered as one of the most important directions for the progression of EVs in the market and it can possibly lead to increased customer acceptability by reducing charging time. However, fast charging of LIBs makes them susceptible to lithium plating and induces high temperatures, and the decomposition of electrolytes results in thermal runaway and explosion. Thus, understanding capacity fades and improving cell stability for long cycle life at a high C-rate are critical for designing LIBs. It has been known that external pressure has a positive influence on Li-ion pouch cell capacity fading during aging experiments. Nonetheless, the effect of external pressure under high C-rate conditions is not well understood and has not been extensively covered in many studies. Even in some of the research conducted experiments under high C-rate conditions, the concept of normalized capacity has been introduced, leading to studies that do not account for the initial capacity drop [1,2].

This work analyzed the effect of external pressure on the battery’s sustainability under high C-rate conditions. The interrelationship of mechanical pressure and the electrochemical performance was investigated using 1.05 Ah graphite/NMC622 stacked LIBs. The charging speed was set to 1,5 and 10C-rates in the constant current/constant voltage (CC-CV) mode to test fast charging conditions. The pressure and thickness changes were analyzed using the pressure measurement system and 3-dimensional digital image correlation (3D-DIC). Also, the post-mortem analysis conducted to confirm the morphology of each cell component and internal resistance under fast charging conditions were analyzed using scanning electron microscopy (SEM) analysis and electrochemical impedance spectroscopy (EIS), respectively. The results demonstrate the negative influence of the external pressure was confirmed initial cycling stage increases the internal resistance which lowers the ionic conductivity. Overall, we propose that innovative pressurizing strategies to maximize cell cyclability and pressure sensing results could provide a non-destructive diagnostic approach to support the advancement of fast-charging battery technologies. This research highlights the significance of external active pressurization in systems operating at high C-rates.

Reference

[1] Mussa, A.S., et al., Effects of external pressure on the performance and ageing of single-layer lithium-ion pouch cells. Journal of Power sources, 2018. 385: p. 18-26

[2] Chen, F., et al., Air and PCM cooling for battery thermal management considering battery cycle life. Applied Thermal Engineering, 2020. 173: p. 115154

Figure 1