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

Hard carbon is synthesized by heat-treating macroporous phenolic resin at different temperatures. We study influences of temperature on the structures and electrode properties of the hard carbon in 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 °C. Reversible capacities in Na cells increase with an increase in the heat-treatment temperature. Hard carbon carbonized at 1500 °C delivers the largest capacities of 386 and 336 mAh g–1 at 10 mA g–1 in Na and K cells, respectively.