The widespread adoption of wind and solar energy generation is limited by the lack of cheap, efficient, stable, and safe energy storage systems. Aqueous lithium-ion batteries, combining the high efficiency and cycling stability of intercalation materials with the low cost and flammability of aqueous electrolytes, are potentially an excellent solution to the stationary energy storage problem. In this work, four iron based phosphate polyanion compounds were evaluated as anode materials for an aqueous lithium-ion battery. Constant current cycling of these materials in deoxygenated aqueous electrolyte closely matched organic half-cell cycling data and previous literature results, indicating the stability of the aqueous electrolyte and the materials under these conditions. When dissolved oxygen was present in the aqueous electrolyte, all four iron phosphate materials had low coulombic efficiency which was attributed to a parasitic oxygen reduction in the electrolyte. Of the novel iron phosphate/LMO full cell pairings, deoxygenated aqueous Li₃Fe₂(PO₄)₃/LiMn₂O₄ cells achieved good capacity retention over 100 cycles while maintaining excellent round trip energy efficiency.