Using NH4VO3 as both the precursor and oxidizing agent, polyaniline (PANI) is in situ synthesized within NH4V4O10 (NVO) crystal interlayers via a one-step hydrothermal method. The expanded lattice spacing, abundant oxygen vacancies and reduced electrostatic attraction endow the NVO/PANI cathode with an enhanced capacity of 350 mA h g-1 at 0.1 A g-1, as well as 87% capacity retention after 500 cycles at 1 A g-1.