Facile preparation of Hf₃N₄ thin films directly used as electrodes for lithium-ion storage

Transition-metal nitride thin-film electrodes are potential electrode materials for all-solid-state thin-film lithium-ion batteries. In this study, orthorhombic Hf₃N₄ thin-film electrodes applied in lithium-ion batteries were fabricated by the magnetron sputtering deposition of Hf followed by N₂ plasma immersion and post-annealing for the first time. This electrode material without additives such as binders and conductive agents exhibited a high specific capacity, high cycling stability, and excellent rate performance. At a current density of 0.1 A g^-1, the initial discharge capacity was 583.2 mA h g^-1 and the stable Coulombic efficiency was 96.6%. At a high current density of 2 A g^-1, the Hf₃N₄ thin-film electrodes could still provide a stable discharge capacity of about 260 mA h g^-1 and Coulombic efficiency close to 100%. By analyzing the cyclic voltammetry curves at different scan rates, it was found that the Li⁺ storage in Hf₃N₄ thin-film electrodes was mainly contributed by a pseudo-capacitance mechanism.