Critical Deterioration Roots of Ni-Rich Cathode during Long-Term Cycling: Material Degradation, Diffusion Limit or Interfacial Instability?

Severe performance deterioration in long-term cycling is a long-standing challenge for practical applications of high-energy-density Ni-rich LiNi_1-x-yMn_xCo_yO₂ (NMC, x+y < 0.5) cathodes at high potentials (>4.3V vs. Li/Li⁺). Great efforts have correlated the performance deterioration to many physical observations, while the critical deterioration roots of Ni-rich cathode during long-term cycling are not well elaborated. Herein, we perform a systematic and in-depth investigation to probe the critical contributions from observed deterioration roots of Ni-rich LiNi_0.83Mn_0.1Co_0.07O₂ cathode in full cells with graphite anode after 1000 cycles at different upper potentials. Intriguingly, the severe capacity retention in electrochemical evaluation of recovered cathode half cells is contrail to the insignificant structural changes and transition metal loss via post-mortem characterizations of bulk material. GITT tests unveils that chemical diffusion limit is the dominant deterioration root of Ni-rich cathode at high potential. The severe chemical diffusion of Li⁺ is strongly correlated to the exacerbated surface reconstructions at the cathode surface. Our study suggests that stabilizing the cathode interface and mitigating the surface reconstructions is the most crucial for enabling long lifespan of Ni-rich cathodes at high potentials.