From Pouch-Cell Swelling to Rock-Salt Reconstruction: A Multimodal Mechanistic Framework for 6C Fast-Charging Degradation of NCM

Abstract

Fast-charging capability is essential for lithium–ion batteries, but performance loss in practical pouch cells often arises from coupled electrochemical–mechanical processes that are hard to identify by conventional postmortem methods. Here, we establish a multiscale, workflow-driven diagnosis that connects nondestructive cell inspection to electrode- and material-level signatures using identical Li(Ni,Co,Mn)O2 (NCM)–based pouch cells subjected to 90 cycles under 1C/0.2C and 6C/0.2C protocols. Under the aggressive 6C/0.2C regime, the cell exhibits rapid capacity decay, retaining only ~47% of its initial capacity at the 90th cycle, accompanied by severe macroscopic swelling and a disproportionate shift of charge capacity into the constant-voltage (CV) step, accounting for over 90% of the total charge capacity, which is attributable to markedly increased polarization. X-ray computed tomography (CT) reveals internal void development and stack disruption without disassembly. Cross-sectional SEM and transmission electron microscopy (TEM) further show that fast charging accelerates mechanical damage in polycrystalline (PC) NCM and promotes near-surface reconstruction toward rock-salt–like domains, while X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) capture concomitant loss of layered ordering and intensified cathode–electrolyte interphase (CEI) chemical evolution. Material-level degradation is quantitatively reflected in a reduction of the XRD I(003)/I(104) ratio from 1.1 (pristine) to 0.9 (6C/0.2C). This study offers a practical framework to identify failure modes and guide durable fast-charge pouch cell design. Copyright © 2026 Seoyeong Kim et al. International Journal of Energy Research published by John Wiley & Sons Ltd.