KOH-activated hard carbon spheres with enhanced pseudo-capacitance for superior low-temperature electrochemical performance of Li-ion batteries

The intercalation-type graphite anode with a diffusion-controlled storage mechanism has fundamental limitations for low-temperature performance. Pseudo-capacitance has fast reaction kinetics and is not controlled by diffusion. Therefore, pseudo-capacitance may improve the low-temperature performance of lithium-ion batteries. In this work, hard carbon spheres (HCSs) are prepared by carbonizing polymer, and KOH-activated hard carbon spheres (K-HCSs) are also prepared to optimize their structure. Compared with the HCSs anode, the K-HCSs anode exhibits a higher initial specific capacity of 118 mAh g⁻¹ at − 20 ℃. Moreover, the K-HCSs anode demonstrates a high capacity of 75 mAh g⁻¹ after 300 cycles with a current density of 0.5 A g⁻¹ at − 20 ℃. CV results display that the K-HCSs anode has higher pseudo-capacitance (79.76%) than the HCSs anode (78.13%) at − 20 ℃. The enhanced pseudo-capacitance can be ascribed to the abundant defects of K-HCSs.