Is Cobalt in Li‐Rich Layered Oxides for Li‐Ion Batteries Necessary?

Abstract

Abstract Cobalt is considered an essential element for layered cathode active materials supporting enhanced lithium‐ion conductivity and structural stability. Herein, we investigated the influence of Co concentration on the physicochemical properties and electrochemical performance of lithium‐rich layered oxides (LRLOs) with different Co content (Li1.2Ni0.2‐x/2Mn0.6‐x/2CoxO2, x=0, 0.04, and 0.08). Though the presence of Co grants structural stability to LRLOs, superior long‐term cycling stability is achieved with the Co‐free LRLO retaining 88.1 % of the initial specific capacity (vs. 75.9 % of Li1.2Ni0.16Mn0.56Co0.08O2) after 300 galvanostatic cycles at 250 mA g−1 (1 C). The chemical stability on the surface of LRLOs containing Co declines faster, indicating a higher bulk structural stability not being the primary determinant of the LRLOs’ cycling performance. Ex‐situ investigations indicate that the superior cycling stability of Co‐free LRLO is obtained by reducing the Mn‐related redox at discharge, which contributes to the large degree of polarization and low energy efficiency. Finally, the full‐cell configured with the optimized LRLO as cathode and graphite anode delivers an energy density of 464 Wh kg−1 at C/10, and 74.4 % and 94.3 % of retention in discharge specific capacity and average voltage at the 1000th cycle, demonstrating the applicability of Co‐free LRLO for sustainable LIBs.