High-performance coal-based hard carbons for sodium-ion storage enabled by Joule-heated rapid pyrolysis

Hard carbon materials are potentially used in sodium-ion battery anodes, yet their structure is complex and not easy to control. In this paper, a Joule-heated rapid pyrolysis is proposed for the preparation of hard carbon. The selected highly volatile bituminous coal-based hard carbon is affected by the Joule-heated explosion, where a large number of volatile components are instantly released, which reorganizes the microstructure of hard carbon, increases the layer spacing of carbon microcrystals, and obtains an expanded structure. This coal-based hard carbon exhibits high sodium ion storage capacity (274 mAh g-1), high ICE (80%), and remarkable cycling stability with 80% capacity retention for more than 1000 cycles. In addition, the coal-based hard carbon anode showed good capacity retention (40%) at an extremely low temperature (-40°C).