High rate and long cycle life porous carbon nanofiber paper anodes for potassium-ion batteries

Potassium-ion batteries (KIBs) are an emerging energy storage technology for low cost and large scale applications. However, they suffer from insufficient cycle life and poor rate capability caused by the large K ions. In this paper, these problems are circumvented by using free-standing porous carbon nanofiber (CNF) paper anodes. Excellent electrochemical performance was demonstrated with an extremely high rate capability retaining 100 mA h g(-1) at the current rate of 7.7 A g(-1), a high reversible capacity of 270 mA h g(-1) and a very low decay rate of 0.01% per cycle over 1200 cycles, which are much better than those of previously reported anode materials in KIBs and even in most sodium-ion batteries. The superior performance is attributed to the unique structure of CNFs, in which the porous structure can effectively alleviate the volume expansion induced by the insertion of large K ions. Considering the abundance and widespread distribution of potassium in the Earth's crust, the encouraging results make KIBs a strong competitor to Na-ion batteries as an alternative energy storage technology to Li-ion batteries.