Improved electrochemical performances of li- and Mn-Rich layered oxides 0.4Li4/3Mn2/3O2·0.6LiNi1/3Co1/3Mn1/3O2 cathode material by Co3O4 coating

Abstract

High-capacity Li- and Mn-rich layered oxides are of special concern as cathode materials for lithium-ion batteries, but suffer from inferior cycling stability and low initial coulombic efficiency. Herein, Co3O4 coating has been proposed to improve the electrochemical performances of 0.4Li4/3Mn2/3O2·0.6LiNi1/3Co1/3Mn1/3O2 in a hydrothermal-assisted process. The Co3O4 coating could enhance the cycling stability, mitigate the phase transformation from layered to spinel-like structure and polarization. The 2% Co3O4 coated sample (LNMC-2) delivers capacity retention of 94.1% while only 70.3% for the pristine counterpart (LNMC-p) after 80cycles at 100mA g−1 in 2–4.8V. The discharge mid-voltage drops at 2.07mV per cycle for LNMC-2 in contrast to 5.38mV per cycle for LNMC-p. In addition, part of Co3O4 transforms to cubic phase LixCoyO active layer during initial discharge process, which improves the initial coulombic efficiencies from 71.74% to 74.9%, 80.18% and 84.99% for LNMC-p, LNMC-2, LNMC-5 and LNMC-10, respectively (at 20mA g−1 in 2–4.8V). Additionally, the rate capability is also improved after Co3O4 coating due to enhanced DLi+. Co3O4 coating, which combines the functions of protective layer and electrochemically active lithium-free insertion host, has been shown to be feasible and beneficial toward advanced Li- and Mn-rich layered oxides cathode materials for lithium-ion batteries.