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The overall electrochemical performance of carbon anodes for potassium-ion batteries (PIBs) is considerably restricted by their poor cyclic property and rate capability issues. Herein, we report a water chestnut-derived slope-dominated carbon anode through moderate-temperature pyrolysis at 900 °C, which manifests a high initial reversible capacity of 253.2 mAh g–1 at a current density of 100 mA g–1, remarkable rate property of 134.8 mAh g–1 at 1000 mA g–1, and impressive cycling performance of 220.5 mAh g–1 at 100 mA g–1 after 1000 cycles. When assembled with the potassiated 3,4,9,10-perylene-tetracarboxylic acid dianhydride cathode, the initial reversible capacity reaches 124.3 mAh g–1 at 25 mA g–1, and 84.7% of the capacity is maintained even after 300 cycles at 50 mA g–1. The improved potassium storage properties could be ascribed to the disordered microstructure with relatively larger oxygen-containing defect concentration, high specific surface area, and stochastically oriented short graphene nanosheets. Density functional theory calculations illustrate that oxygen doping can effectively alter the charge density distribution of carbon and facilitate the adsorption of K+ on water chestnut-derived carbon, which boosts potassium ion storage. This work would provide a promising avenue to design and synthesize slope-dominated carbon materials for low-cost PIBs with excellent rate and cycling properties and high safety.

Hierarchical porous carbon nanofibers with intimately coupled Co-based ultrasmall nanoparticles and a carbon substrate are prepared by a universal strategy, exhibiting improved potassium storage properties.