Effects of citric acid treatment on the electrochemical properties of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode material

The influence of citric acid pre-activation on the electrochemical properties of cathode materials used in lithium batteries is investigated. During the citric acid pre-activation of the surface of coprecipitated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂, 13.37 wt.% of lithium is removed, mainly owing to the decomposition of the Li₂MnO₃. Electrochemical property tests indicate that the cycle performance and rate capability of the material are enhanced after citric acid pre-activation. The initial charge-discharge efficiency increases from 66.4% to 79.9%, while the capacity retention after 100 cycles at 0.5C increases from 84.85% to 90.81%. When the current density increases to 5C, the specific discharge capacity of the delithiated material is 108.9 mAh·g^-1, much higher than that (95.10 mAh·g^-1) before the treatment. This is caused by the formation of a spinel-like structure on the cathode surface, as citric acid removes some of the Li₂O in the Li₂MnO₃ phase. As a result, a channel for Li⁺ transmission is created and the impedance at the interface between the cathode material and the electrolyte is effectively reduced, facilitating the rapid transport of Li⁺ through the electrode interface.