Exploring High-Energy Li-I(r)on Batteries and Capacitors with Conversion-Type Fe₃O₄-rGO as the Negative Electrode

We report a microwave-assisted solvothermal process for the preparation of magnetite (Fe₃O₄, ca. 5 nm)-anchored reduced graphene oxide (rGO). It has been examined as a prospective conversion-type negative electrode for multiple energy storage applications, such as Li-ion batteries (LIBs) and Li-ion capacitors (LICs). A LiFePO₄/Fe₃O₄-rGO cell is constructed and capable of delivering an energy density of approximately 139 Wh kg⁻¹ with a notable cyclability (ca. 76 %) after 500 cycles. Prior to the fabrication of a LIB, the Fe₃O₄-rGO is electrochemically pretreated to eliminate the irreversible capacity loss. In addition to the LIB, a high-energy LIC is also fabricated by using the pre-lithiated Fe₃O₄-rGO composite as the anode and commercial activated carbon as the cathode. This LIC registered a maximum energy density of approximately 114 Wh kg⁻¹ with good cyclability. For both the LIB and LIC, the mass loading between the electrodes was adjusted based on the performance with metallic Li. The improved electrochemical performance of Fe₃O₄-rGO over existing materials is a promising development in the quest for novel, fast, low cost, and efficient energy storage systems without compromising the eco-friendliness.