Atomic layer deposition regulating hydrated K2Ti6O13 nanobelts on graphene platform with accelerated solid solution potassiation for potassium ion capacitors

Abstract Potassium ion capacitors (PICs) represent a promising energy storage device with high energy and power densities for long stretches beyond the lithium and sodium storage chemistry of nowadays. As an analogous anode like lithium titanates, potassium titanates (KTO) are expected to be applied to PICs. Herein, hydrated KTO (K2Ti6O13) nanobelts were regulated on graphene nanosheets by a method of atomic layer deposition (ALD) coupled with hydrothermal potassiation. The close correlation of KTO to the underneath graphene nanosheets favors the electron transport, the interweaved structure facilitates the permeation of electrolyte ions, and the chemically (interlayer) adsorbed water endows KTO with larger interlayer spacing, synergistically giving rise to an accelerated solid solution potassiation mechanism. Based upon this, superior specific capacity and rate capability (87 mAh g−1@1 A g−1), as well as stability of the ALD KTO can be delivered, outperforming many performances of reported KTO anodes. The PICs exhibit simultaneously high energy/power densities (Max. 119.3 Wh kg−1@117.5 W kg−1, 4.7 kW kg−1@35.3 Wh kg−1) as well as good capacity retention after 4,000 cycles. Our work demonstrates the great performance of ALD KTO anode and the promising application of PICs, which propose a delicate methodology of high performance K+ storage anode materials.