LiFePO4 − xNy thin-film electrodes coated on carbon fiber-modified current collectors for pseudocapacitors

• LiFePO4 − xNy thin films were sputter-deposited on micron carbon fibers (MCFs).
• MCFs only act as a three-dimensional current collector in this system.
• The pseudocapacitor exhibits a high specific capacitance.

LiFePO4 − xNy thin films were sputter-deposited on micron carbon fibers (MCFs) under a gas mixture of N2/Ar/H2 as electrode materials in pseudocapacitors. The MCFs were fabricated by thermal chemical vapor deposition on stainless steel substrates as current collectors. Various amounts of N2 were introduced by controlling the flow ratios of N2 to Ar/H2. The LiFePO4 − xNy thin films coated on the surfaces of MCFs were observed by field emission scanning electron microscopy. The electrochemical properties of the LiFePO4 − xNy thin films were characterized using cyclic voltammetry and charge–discharge processes. The LiFePO4 − xNy thin-film electrode deposited under the optimal N2 contents exhibited a high specific capacitance of 722 F/g at 1 A/g. Even at a current of 20 A/g, the electrode delivered a capacitance of 298 F/g. The pseudocapacitors using LiFePO4 − xNy thin-film electrodes showed no significant capacitance fading after 1000 cycles at 1 A/g. The results indicated that nitrogen doping improved the electrochemical performances of LiFePO4, demonstrating the potential of LiFePO4 − xNy as an active material in pseudocapacitors.