Cathode materials: A key challenge for lithium ion batteries

Magnesium-ion batteries (MIBs) are promising candidates for large-scale energy storage applications owing to their high volumetric capacity, low cost, and no dendritic hazards. However, the development of the MIBs is restricted owing to the obstacles of incompatibility between Mg metal and conventional electrolytes as well as the lack of suitable cathode materials with fast ion reaction kinetics, which lead to low working voltage, poor rate performance and unsatisfied cycling stability. In this work, a magnesium-ion based dual-ion battery (Mg-DIB) is constructed, using 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) as organic anode, expanded graphite (EG) with high potential and fast anion diffusion kinetics as cathode, and ionic liquid as electrolyte. The PTCDI was demonstrated to go through threefold coordination mechanism and hydrogen bond formation during Mg-ion insertion, which shows good insolubility in organic electrolytes and good structural stability. As a result, the Mg-DIB was demonstrated to exhibit a reversible discharge capacity of 57.7 ​mAh g−1 at 2C in the voltage range of 1–4 ​V, and good cycling stability with capacity retention of 95.7% after 500 cycles at 5C, which present a new way to design high-performance MIBs and other energy storage devices.