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

Abstract

Aqueous lithium-ion batteries (ALIBs) attract increasing research attention as a large-scale energy storage technique, because of their high safety and cost effectiveness. Searching for new electrode materials is important to achieve high energy density in ALIBs. LiFe_xMn_1−xPO₄ with a high voltage plateau and theoretical capacity is a promising cathode candidate for ALIBs, yet the electrochemical performance and reaction mechanism in ALIBs have not been explored. Herein, combined electrochemical investigations and spectroscopic studies show that the Mn element dissolves from LiFe_0.5Mn_0.5PO₄, leading to further structural degradation and capacity fading during cycling in the conventional 2 M Li₂SO₄ electrolyte. By applying 30 m LiTFAC aqueous electrolyte, in which the free water content is reduced, the Mn dissolution from LiFe_0.5Mn_0.5PO₄ is significantly suppressed. The synthesized LiFe_0.5Mn_0.5PO₄ nanofiber cathode exhibits a specific capacity of 121.6 mA h g⁻¹ over 100 cycles with 94% capacity retention. In addition, the LiFe_0.5Mn_0.5PO₄ nanofiber cathode shows excellent rate performance as well in 30 m LiTFAC aqueous electrolyte; a capacity of 70.9 mA h g⁻¹ at 10C can be achieved over 300 cycles. This study demonstrates the promising application potential of LiFe_xMn_1−xPO₄ as a cathode material for ALIBs with high energy density.