Ultrafast and Stable Lithium Storage Enabled by the Electric Field Effect in Layer-Structured Tablet-Like NH4TiOF3 Mesocrystals.

Abstract

Design and synthesis of advanced electrode materials with fast and stable ion storage are of importance for energy storage applications. Herein, we propose that introducing the heterogeneous interface in layer-structured mesocrystals is an efficient way to greatly improve the rate capability and cycle stability of lithium-ion battery (LIB) devices. NH4TiOF3 mesocrystals were employed as a typical model system to demonstrate the idea. The NH4TiOF3 mesocrystals were obtained via the hydrothermal reaction, and the NH4TiOF3/TiO2 interfaces were generated through calcining at different temperatures under an argon atmosphere. Phase composition, microstructure, and chemical analyses show that the as-prepared NH4TiOF3 mesocrystals possess "tablet-like" morphology, and the formation of the NH4TiOF3/TiO2 interface can be controlled by the calcination temperature. When evaluated as the anode for LIBs, the optimized sample (NH4TiOF3 calcined at 250 °C, NTF-250) shows excellent, fast, and stable lithium storage properties. Specifically, the NTF-250 electrode holds a reversible capacity of 159.5 mA h g-1 after 200 cycles at 0.2 A g-1. At a high current density of 20 A g-1, the electrode still maintains a reversible capacity of 89.6 mA h g-1 and reaches a reversible capacity of 128.6 mA h g-1 at a current density of 1 A g-1 after 2000 cycles. Theoretical and experimental studies show that the synergistic effects of the heterogeneous NH4TiOF3/anatase TiO2 interface in the layer-structured NH4TiOF3 mesocrystals lead to the upgraded electrochemical properties. Especially, the local build-in electric field induced by the nonuniform distribution of charge across the NH4TiOF3/anatase TiO2 interface facilitates the charge transport during the charging and discharging cycling. The current electrode design strategy paves a new way in boosting stable ion storage and thus is of great interest in energy storage and conversion.