Improved Na+/K+ Storage Properties of ReSe2–Carbon Nanofibers Based on Graphene Modifications

With the rapid development of electronic equipment and the emergence of electric and hybrid electric vehicles in recent years, it has become necessary to investigate energy storage materials with high efficiency, the existence of alternative and abundant resources, and the environment-friendliness [ 1 , 2 , 3 ]. Owing to the characteristics of the high energy density and broad voltage range, lithium-ion batteries (LIBs) have gained considerable attention since their development [ 4 , 5 , 6 , 7 ]. However, the limited distribution of lithium resources in the earth has hindered their widespread applications in grid energy storage system [ 8 , 9 , 10 ]. As promising alternatives to LIBs, sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs) have attracted considerable interest owing to the abundance of sodium/potassium sources and their low prices [ 7 , 11 , 12 , 13 , 14 ]. In addition, NIBs and KIBs have redox voltages which are closer to Na + /Na (− 2.71 V vs. normal hydrogen electrode) and K + /K (− 2.93 V) to that of Li + /Li (− 3.04 V) [ 15 , 16 , 17 ]. Nevertheless, Na + (1.02 Å) and K + (1.38 Å) have larger radii than Li + (0.76 Å), which means that they are more likely to induce sluggish reaction kinetics and massive volume expansions, thus resulting in poor rate performances and unstable circulation [ 13 , 18 , 19 ]. Moreover, graphite has a capacity of 372 mAh g −1 in LIBs, exhibits a low capacity in KIBs (279 mAh g −1 ), but cannot be used in NIBs. Therefore, the need to identify electrode materials with larger physical spaces to adapt Na + /K + fuel cells is imminent.