Investigation of Li_1.17Ni_0.20Mn_0.53Co_0.10O₂ as an Interesting Li- and Mn-Rich Layered Oxide Cathode Material through Electrochemistry, Microscopy, and In Situ Electrochemical Dilatometry

Despite their high capacity, Li- and Mn-rich layered oxide cathode materials suffer from capacity fading during prolonged cycling when cycled to potentials higher than 4.5 V vs. Li⁺/Li. In the work reported herein, we have synthesized the Li- and Mn-rich Li_1.17Ni_0.20Mn_0.53Co_0.10O₂ cathode material by using a sol-gel method. The composition and structure are analyzed by ICP, XRD, SEM, and TEM. During testing in half-cells between 2.5 and 4.6 V vs. Li⁺/Li at 20 mA g⁻¹, the initial capacity of about 165 mAh g⁻¹ increases during cycling, reaching about 200 mAh g⁻¹ after 30 cycles. The capacity then slowly fades, reaching 188 mAh g⁻¹ after 120 cycles. Also, a high average discharge potential of 3.8 V is obtained, which decreases to 3.6 V after 120 cycles. This study leads to new insights about the effect of Ni concentration on the stability of the Li- and Mn- rich cathode materials. The in situ electrochemical dilatometry (ECD) study demonstrates an irreversible process during the 1^st cycle, which can be related to the activation of Li₂MnO₃. During subsequent cycles, the electrodes’ thickness does not change, which reflects a morphological stabilization, in contrast to the continuous electrochemical instability of these materials upon cycling.