A hard carbon material with free-standing porous structure and high contents of heteroatom functional groups is considered to be a potential anode for potassium-ion batteries (PIBs). Herein, a free-standing phosphorus/nitrogen cofunctionalized porous carbon monolith (denoted as PN-PCM) anode for PIBs is successfully fabricated via a supercritical CO2 foaming technology, followed by amidoximation, phosphorylation, and thermal treatment. Thanks to the synergistic effect of a three-dimensional macroporous open structure and high P/N contents of 6.19/5.74 at%, the PN-PCM anode delivers an excellent reversible specific capacity (396 mA h g–1 at 0.1 A g–1 after 300 cycles) with high initial Coulombic efficiency (63.6%), a great rate performance (168 mA h g–1 at 5 A g–1), and an ultralong cycling stability (218 mA h g–1 at 1 A g–1 after 3000 cycles). Theoretical calculations clarify that in a P/N cofunctionalized carbon, the P–C bonds devote more to enhancing the potassium storage via adsorption and improving electronic conductivity of carbon, while P–O bonds contribute more to enlarging the interlayer distance of carbon and reducing the ion diffusion barrier.
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Gong et al. (2020) studied this question.