Evolution of interfacial electro-chemo-mechanics in high-energy-density NCM811||Si/C-composite Lithium-Ion pouch cells

Abstract

High-energy–density lithium-ion batteries (LIBs) are widely utilized as energy storage devices, but the electrodes undergo significant volume changes and the expansion of cells during operation, leading to irreversible stress accumulation within the batteries. The irreversible stress has a profound impact on battery performance. LIBs experience different pressure conditions after various cycle numbers, but there have been no reports on the relationship between pressure changes at different cycling stages (pressure stages) and the various composition of electrode–electrolyte interfacial (EEI) film in pouch cells. This paper investigates the impact of different pressure stages on the EEI film and electrical performance in 300 Wh kg⁻¹ NCM811||Si/C pouch cells under constant gap conditions. In practical applications, the dynamic internal pressure is monitored and quantified using self-generated in-situ pressure testing equipment, which is further correlated with the observed charging and discharging processes. A multi-stage cycling process is observed. In the first stage, the battery exhibits nearly reversible expansion. In the second stage, the maximum and minimum internal pressures increase uniformly, indicating a steady rise in irreversible pressure. In the third stage, the internal pressure of the battery rises rapidly, accompanied by a rapid decline in electrical performance. Additionally, other electrical parameters also exhibit a staged evolution pattern. It is found that with the increase of pressure, the main composition transformation of SEI film and the slow diffusion coefficient of Li⁺ may lead to the degradation of the battery. Ultimately, we proposed a capacity predictor based on normalized pressure in the AIMD model and validated it to diagnose the evolution of the Si/C anode, by integrating macroscopic and microscopic perspectives. This predictor achieves the minimum recorded error is a mere 0.33 %.