Unlocking the Potential of Ni-rich NCM811 Cathodes: Chlorine Substitution as a Pathway to Prevent Oxygen Release and Transition-Metal Dissolution

Abstract

Ni-rich materials offer high capacity and energy density and are widely used as mainstream cathodes in advanced lithium-ion batteries (LIBs) for electric vehicles. However, their long-term stability is often limited by structural degradation and oxygen evolution during delithiation. Herein, we systematically investigate the effects of sulfur (S) and chlorine (Cl) anion doping on the structural stability, electronic properties, and transition metal (TM) dissolution behavior of Ni0.8Co0.1Mn0.1O2 (NCM811) using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Structural analysis reveals that pristine NCM811 undergoes pronounced oxygen evolution under delithiation, while S-doping accelerates TM layer instability, particularly at high states of delithiation. In contrast, Cl-doping effectively suppresses oxygen release, preserves TM framework integrity, and stabilizes the surface lattice. Electronic structure analysis indicates that Cl substitution mitigates oxygen and TM overoxidation and favors a more stable Ni3+/Ni4+ redox couple, whereas S-doping destabilizes the TM environment and promotes dissolution. Kinetic studies further show that Cl incorporation significantly increases the energy barriers for superoxide (O_2^- ) formation and O2 evolution, thereby impeding oxygen-related degradation pathways. AIMD simulations confirm that Cl-doping prevents Ni migration and dissolution at both surface and subsurface regions, unlike pristine and S-doped systems. Collectively, these insights demonstrate that Cl-doping enhances the structural and electrochemical stability of Ni-rich NCM811, offering a viable design strategy for high-performance LIB cathodes with improved durability and extended cycle life.