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

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.