Engineering of nanonetwork-structured carbon to enable high-performance potassium-ion storage

Potassium-ion batteries (KIBs) have been developed as an emerging electrochemical energy storage device due to the low cost and abundant resource of potassium. However, they suffer insufficient cyclability and poor rate capability caused by the large K⁺, severely limits their further applications. Herein, a nanonetwork-structured carbon (NNSC) is reported to address the issue. Cycling stability with very low decay rate of 0.004% per cycle over 2000 cycles and excellent rate capability (i.e., 261 mAh g^-1 at 100 mA g^-1 and 108 mAh g^-1 at 5000 mA g^-1) are achieved. The superior performance is attributed to the unique structure of NNSC, in which the three-dimensional interconnected hierarchical porous structure with hollow nanosphere as network units not only can effectively alleviate the volume expansion induced by the insertion of large K⁺, but also can offer fast pathways for K⁺ diffusion. In addition, the local graphitized carbon shell of NNSC can promote conductivity of material and reduce the resistance to K⁺ transportation. Thus, the NNSC has great potential in developing stable-structure and high-rate electrodes for next generation KIBs.