In‐Depth Analysis of the Degradation Mechanisms of High‐Nickel, Low/No‐Cobalt Layered Oxide Cathodes for Lithium‐Ion Batteries

Abstract A rational compositional design of high‐nickel, cobalt‐free layered oxide materials for high‐energy and low‐cost lithium‐ion batteries would be expected to further propel the widespread adoption of electric vehicles (EVs), yet a composition with satisfactory electrochemical properties has yet to emerge. The previous work has demonstrated a promising LiNi 0.883 Mn 0.056 Al 0.061 O 2 (NMA‐89) composition that outperformed high‐nickel, cobalt‐containing analogs in cycling stability and maintained a comparable rate performance and thermal stability. Herein, the capacity fading mechanism of NMA‐89 in a pouch full cell with a 4.2 V cutoff is compared to that of its cobalt‐containing analogs. The results reveal that particle cracking in LiNi 0.89 Mn 0.055 Co 0.055 O 2 (NMC‐89) and LiNi 0.883 Co 0.053 Al 0.064 O 2 (NCA‐89) leads to a loss of active material and an increase in surface area, thereby exacerbating structural and surface instabilities, accelerating impedance and polarization growth, and ultimately reducing their capacity retentions. LiNi 0.89 Mn 0.044 Co 0.042 Al 0.013 Mg 0.011 O 2 (NMCAM‐89) and NMA‐89 experience subdued surface reactions and maintain spherical particle structures, both of which are conducive to their capacity retentions during long‐term cycling. This investigation offers insights into how specific transition‐metal ions dictate the electrochemical stability of high‐Ni layered oxide cathode materials, highlights the benefit of Mn‐Al combination in NMA‐89, and presents potential strategies to further enhance the performance of this novel class of cathode materials.