Although vanadium-based materials are potential electrode materials for Li-ion batteries, the development of commonly known vanadium-based crystalline phases is hindered by their inferior cyclic performance. Unlike crystalline phases, the amorphous vanadium-based materials do not exhibit undesirable phase transformations during the charge/discharge process leading to poor cyclic performance. Herein, we demonstrate the influence of a reducing atmosphere on the structure of vanadate–phosphate (V2O5-P2O5) glass and its electrochemical properties as a lithium-ion battery cathode. By employing various characterization techniques, we unveil the influence of reducing atmosphere on valence state of vanadium ions and structure of V2O5-P2O5 glass. The V2O5-P2O5 glass, synthesized in a reducing atmosphere, exhibits an ultra-high specific capacity of 270 mAh g−1 with excellent capacity retention of ∼90% after 100 cycles. Moreover, a stable specific capacity of 220 mAh g−1 is delivered at a high current density of 85 mA g−1 after 300 cycles, corresponding to 80% capacity retention. Overall, the V2O5-P2O5 glass, synthesized in a reducing atmosphere, renders higher capacity, excellent rate performance and stable cyclic performance than the V2O5-P2O5 glass, synthesized in the air atmosphere. The current work provides a novel route to develop multi-valence transition metal oxide electrodes for Li-ion batteries.