Structural evolution and cycle enhancement of LiFe0.5Mn0.5PO4 nanofibers as cathode materials for aqueous lithium-ion batteries

Aqueous lithium-ion batteries (ALIBs) attract increasing research attention as large-scale energy storage technique, because of their high safety and cost effectiveness. Searching new electrode materials is crucial to gain high energy density of ALIBs. LiFexMn1-xPO4 with high voltage plateau and high theoretical capacity, is promising cathode candidate for ALIBs, yet the electrochemical performance and reaction mechanism in ALIBs have not been explored. Herein, combined electrochemical investigation and spectroscopic study show that the manganese element dissolved from LiFe0.5Mn0.5PO4, leading to further structural degradation and dramatic capacity fading during cycling in conventional 2 M Li2SO4 electrolyte. By applying 30 m LiTFAC aqueous electrolyte, in which the free water content is reduced, the Mn dissolution of LiFe0.5Mn0.5PO4 is significantly suppressed. The synthesized LiFe0.5Mn0.5PO4 nanofiber cathode exhibits a specific capacity of 121.6 mAh g-1 over 100 cycles with a high capacity retention of 94%. In addition, LiFe0.5Mn0.5PO4 nanofiber cathode shows excellent rate performance as well in 30 m LiTFAC aqueous electrolyte, a capacity of 70.9 mAh g-1 at 10 C can be achieved over 100 cycles. This study demonstrates the promising application potential of LiFexMn1-xPO4 as cathode material for ALIBs with high energy density.