High-Capacity Hard Carbon Synthesized from Macroporous Phenolic Resin for Sodium- and Potassium-Ion Battery

Hard carbon powders are synthesized by heat-treating macroporous phenolic-resin at different temperatures. We study influences of the temperatures on the structures and electrode properties of the hard carbon samples in nonaqueous Na and K cells. X-ray diffraction and scattering data of the samples confirm the decreased interlayer distance between sp2-carbon sheets and the expanded internal pores at the raised temperatures from 1100 to 1500 oC. Reversible capacities in Na cells increase with raising the heat-treatment temperature. A hard carbon sample carbonized at 1500 oC delivers the largest capacities of 386 and 336 mAh g-1 in Na and K cells, respectively.