Dual Energy Storages by Sequential “Rocking Chair” and “Dual Ion” Processes of LiFe_0.6Mn_0.4PO₄/Carbon Modified Graphite Flakes

Abstract

Metal oxide coatings are regarded as a very efficient way to inhibit electrolyte decomposition and consequently improve the cyclability of high voltage cathode materials for high-energy-density batteries. However, the cathode capacities inevitably decrease due to the electrochemically inert nature of the coating agents. To address this common issue, herein we provide a new design of a 5 V cathode material for dual ion batteries, i.e., a graphite flakes (GF)-based composite cathode using amorphous carbon as well as homogeneously distributed LiFe 0.6 Mn 0.4 PO 4 fine particles as both the electrochemically active material and the coating agent with the aim to enhance cyclic capacity and cyclability simultaneously. Electrochemical evaluations evidence that dual energy storages by the sequential "rocking chair" process of cation Li + and the "dual ion" process of cation Li + /anion PF 6 − endow the composite cathode with capacity enhancements of ∼8% and ∼11% compared with those of GF and TiO 2 /carbon modified GF, respectively. Meanwhile, the capacity retention reaches 85% after 1000 charge/discharge cycles, exhibiting excellent cyclability. Furthermore, improvements in electrolyte−electrode interfacial compatibility, thermodynamics, and dynamics by the LiFe 0.6 Mn 0.4 PO 4 /carbon modification are demonstrated. Multiple coordinative functions generated between the matrix GF and the coating agent are the basis of the simultaneous enhancements in the cyclic capacity and cyclability. This superior dual energy storage strategy may be extended to other high voltage cathode materials to improve cyclic capacity and cyclability simultaneously.