Expanded Graphite as a Superior Anion Host Carrying High Output Voltage (4.62 V) and High Energy Density for Lithium Dual-Ion Batteries

Abstract

The demand for safer, sustainable, and economical energy storage devices has motivated the development of lithium dual-ion batteries (Li_DIBs) for large-scale storage applications. For the Li_DIBs, expanded graphite (EG) cathodes are valuable as anion intercalation host frameworks to fabricate safer and more cost-effective devices. In this study, three different carbon cathode materials, including microwave-treated expanded graphite (MW-EG), ball-milled expanded graphite (BM-EG), and high-temperature-carbonized carbon nanoflakes (CNFs), were developed by different synthesis methods. Li_DIBs were configured by employing 4 M of LiPF6 in a dimethyl carbonate electrolyte and MW-EG/BM-EG/CNF as an anion host cathode. After 600 cycles, a Li-MW-EG Li_DIB exhibited a reversible capacity of 66.1 mAh/g with a high Coulombic efficiency of 96.2% at a current rate of 0.05 A/g and an outstanding average energy density of 298.97 Wh/kg (with an output voltage of 4.62 V). The remarkable electrochemical results are associated with (i) moderate structural defects with a very low ID/IG ratio (0.848), (ii) degree of graphitization, which improves the mechanical stability and conductivity, and (iii) large pore volume and pore diameter, easy facilitating the accumulation of PF6− ions. The energy density characteristics demonstrate the feasibility of utilizing MW-EG as a promising cathode for energy-related Li_DIB applications.