Defects and sulfur-doping design of porous carbon spheres for high-capacity potassium-ion storage

Heteroatom-doping had been demonstrated to effectively improve the capacitive energy storage of hard carbon in potassium ion batteries (KIBs). However, the external defects introduced during doping process are responsible to alter the microstructure of carbon host. But there is a scarcity of systematic in-depth understanding the comprehensive effects of defects and heteroatoms in hard carbon for K storage performance. Herein, a series of porous carbon microspheres in different defects level and S-doping amount (SPCS) were simply synthesized under different carbonization temperatures. It was found that various microstructural features of SPCS exhibited different trends with the change of carbonization temperature. Moreover, the depth of the K-ion insertion reaction, the additional oxidation-reduction reaction, and the adsorption process of K-ion on active sites can be enhanced by regulating the S-doping amount and defect level. Specially, the best SPCS can obtain a prominent reversible charging capacity of 435.1 mA h g−1 at 50 mA g−1 over 100 cycles. In addition, in-situ XRD characterization reveals that its lattice structure undergoes a disordered transformation without expansion of interlayer spacing during the K-ions insertion process. This work demonstrates that rational regulation of doping engineering is of great significance for obtaining high-performance carbon anodes for KIBs.