Crystallization-induced thickness tuning of carbon nanosheets for fast potassium storage

Carbon nanosheets (CNS) have garnered significant interest as anode materials for potassium-ion batteries (PIBs) due to the excellent potassium storage kinetics and rate performance. Moreover, tuning the thickness of CNS can enhance the potassium storage performance by exposing abundant surface active sites and shortening the K⁺ migration path. Herein, crystallization-induced thickness tuning of carbon nanosheets in polyvinyl pyrrolidone-potassium chloride (PVP-KCl) solution is reported to enhance the fast potassium storage. PVP with varying molecular weights is employed to induce the crystallization behavior of KCl, leading to the formation of KCl grains with controllable sizes. Concurrently, these KCl grains act as hard templates for dispersing the PVP molecules to fabricate carbon nanosheets on the surface during annealing. PVP with high molecular weight is beneficial for hindering ion migration to reduce crystal sizes, which can decrease the thickness of carbon nanosheets. The ultrathin structure exposes abundant potassium storage sites, endowing CNS with high reversible capacity (359.0 mAh/g at 100 mA/g). The reduction in the migration path of K⁺ ions facilitate rapid ion and electron transport kinetics, resulting in rate performance with a capacity of 181.9 mAh/g at 1 A/g. Our work extends the application of the crystallization-induced strategy for controllable designing carbon nanosheets, and puts forward some conceptions on improving the potassium storage performance of carbon anode materials.