Rational regulation ultra-microporous structure size for enhanced potassium ion storage performance

•Microporous carbon controlled by physical method was first used as anode materials for potassium ion hybrid capacitors with high energy density and high power density.•The optimized SROM-15 delivers an excellent reversible capacity of 264.2 mA h g − 1 at 100 mA g − 1 after 100 cycles.•Amorphous carbon materials with adsorption and intercalation mechanism possess higher specific capacity and faster reaction kinetics. The traditional views consider that the interlayer spacing is the major factor controlling battery performance due to the intercalation mechanism, but we find that the pore size of porous carbon in potassium ion storage is the most important factor determining battery electrochemical performance, because the adsorption mechanism occupies the leading position in the process of contributing energy. Herein, we prepare the short-range order ultra-microporous carbon (SROM) through physical grinding following a pyrolysis method. The optimized SROM-15 as anodes in the potassium-ion batteries delivers a remarkable reversible capacity of 264.2 mA h g − 1 at 100 mA g − 1 after 100 cycles, superior rate capacity (149.1 mA h g − 1 at 5 A g − 1), and excellent cycling life. The electrochemical properties of SROM-15 are better than most reported carbon materials. This experiment has demonstrated that when the pore size is adjusted to 0.84 nm, the specific capacity and K+ diffusion coefficient of SROM are the largest. In addition, the potassium-ion hybrid capacitors fabricated using SROM-15 anodes and corn stalk-derived activated carbons cathodes display outstanding specific energy of 50.6 W h kg−1 at specific power of 4500 W kg−1. The amorphous carbon materials with adsorption and intercalation mechanism possess remarkable cyclic stability for potassium ion storage. [Display omitted]