Enhanced Electrochemical Performance of Li1.17Ni0.25Mn0.58O2 Cathode Material for Lithium-Ion Battery Via Fluorine Doping and LiCrMnO4 Coating

Abstract

The layered lithium-enriched and manganese metal oxides are considered to be an attractive cathode with a high capacity of 250 mAh g-1 when charged above 4.5 V [1]. However, the irreversible loss of oxygen and undesirable dissolution of transition metal ions during charge/discharge process cause the poor cycling performance and unsatisfactory thermal stability [2]. Many strategies are applied to overcome the large irreversible capacity loss during the first cycle and the following-up capacity fading. Substitutions and surface coatings are considered to be effective ways to solve these problems [3,4].In this study, in order to improve the electrochemical performance of Li1.17Ni0.25Mn0.58O2 cathode material, fluorine doping and LiCrMnO4 coating were applied. F- is more electronegative thus fluorine substitution may change the energy bond between the transition metal ions and the anion. The spinel LiCrMnO4 with three-dimensional Li+ diffusion channels exhibits high electronic conductivity and the Cr3+ can be oxidated to Cr6+, which provides a higher capacity. Therefore, we synthesized the fluorine doping materials by the co-precipitation method followed by a high-temperature solid-state reaction. And the LiCrMnO4 coated Li1.17Ni0.25Mn0.58O2 was prepared by a chemical deposition method followed by a high-temperature calcination.The result reveals that irreversible loss of oxygen was reduced during the first charge and cycling performance was enhanced dramatically by fluorine doping and LiCrMnO4 coating. For fluorine substitution materials, the improvement in cycling performance was more visible at high temperature. For LiCrMnO4 coating materials, the rate capability was largely improved. The modified cathode materials exhibit excellent cycling stability.