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

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 Li_1.17Ni_0.25Mn_0.58O₂ 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 Li_1.17Ni_0.25Mn_0.58O₂ 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.

References

[1] C.S. Johnson, N. Li; C.Lefief, M.M. Thackeray, Electrochemistry Communications, 9, 787 (2007).

[2] T.A. Arunkumar, Y. Wu, A. Manthiram, Chemistry of Materials, 19, 3067 (2007).

[3] H.X. Li, L.Z. Fan, Electrochimica Acta, 113, 407 (2013).

[4] Y.K. Sun, M.J. Lee, C.S. Yoon, J. Hassoun, K. Amine, Advanced Materials, 24, 1192 (2012).