NH4V3O8·0.2H2O is synthesized by sodium dodecyl sulfonate (SDS) assisted hydrothermal method and its electrochemical performance is investigated. The as-prepared material is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared (IR) spectrum, differential scanning calorimetry and thermal gravimetry (DSC/TG), cyclic voltammetry (CV), and charge–discharge cycling test. The results show a pure NH4V3O8·0.2H2O phase with flake-like morphology is obtained and the average flake thickness is about 150nm. The NH4V3O8·0.2H2O electrode has a good lithium ion insertion/extraction ability with the highest discharge capacity of 225.9mAhg−1 during 1.8–4.0V versus Li at the constant current density of 15mAg−1. After 30 cycles, it still maintains a high discharge capacity of 209.4mAhg−1, demonstrating good cyclic stability. Interestingly, at the discharge process a new (NH4)Li x V3O8·0.2H2O compound is formed due to the new lithium ion from lithium metal anode.