Fast-Ion Conductor Coating Strategy Modified LiMn2O4 for Rocking-Chair Lithium-Ion Capacitors

Abstract

Spinel LiMn₂O₄, with reversible capacity provided by earth-abundant Mn redox couple, highlights its attractiveness as a faradic cathode material due to its low cost, environmental friendliness, and unique three-dimensional Li⁺ diffusion channels. However, the surface degradation and Mn dissolution of LiMn₂O₄ are generally considered to be harmful and detrimental to achieving a long cycle life. Herein, a LiMn₂O₄ covered by LiTaO₃ featuring as a fast-ion conductivity was synthesized and employed as a rocking-chair lithium-ion-capacitor cathode materials. As a result, the 3TaLMO with the optimal coating thickness displayed low impedance, the highest lithium-ion diffusion rate, and excellent cycling stability (half-cell, 80.90% capacity retention rate after 2000 cycles, at 0.3 A g^–1). After further assembly into rocking-chair lithium-ion capacitor (LIC) with activated carbon, it achieves a high energy density (394.5 W h kg^–1), high power density (90 kW kg^–1), and an excellent long cycle life (77.27% of the initial capacity after 2000 cycles at 1.0 A g^–1). The excellent electrochemical performance is mainly attributed to the excellent structural stability and fast-ion transfer characteristics of this coating composite structure. This modification strategy brings LMO one step closer to realizing a long cycle life faradic cathode material for rocking-chair LICs.