Revealing the closed pore formation of waste wood-derived hard carbon for advanced sodium-ion battery.

Although the closed pore structure plays a key role in contributing low-voltage plateau capacity of hard carbon anode for sodium-ion batteries, the formation mechanism of closed pores is still under debate. Here, we employ waste wood-derived hard carbon as a template to systematically establish the formation mechanisms of closed pores and their effect on sodium storage performance. We find that the high crystallinity cellulose in nature wood decomposes to long-range carbon layers as the wall of closed pore, and the amorphous component can hinder the graphitization of carbon layer and induce the crispation of long-range carbon layers. The optimized sample demonstrates a high reversible capacity of 430 mAh g at 20 mA g (plateau capacity of 293 mAh g for the second cycle), as well as good rate and stable cycling performances (85.4% after 400 cycles at 500 mA g). Deep insights into the closed pore formation will greatly forward the rational design of hard carbon anode with high capacity.