A C8P monolayer with cross-sp-hybridized phosphorus atoms and ultrahigh energy density as a K-ion battery anode

Abstract

K-ion batteries (KIBs) are promising alternatives to Li-ion batteries due to the abundant availability of K and the similar chemical attributes of K and Li. However, the development of KIBs is significantly hindered by the lack of viable anode materials. Herein we propose a novel C-rich C₈P monolayer featuring cross-sp-hybridized P atoms, identified by swarm-intelligence structural prediction. Its high stability shows strong synthesis potential and application feasibility. As an anode material for K-ion batteries (KIBs), C₈P offers a K storage capacity of up to 1662 mA h g⁻¹, about eight times larger than that of commercial graphite. Additionally, it exhibits a low diffusion barrier of 0.24 eV and a low average open-circuit voltage of 0.34 V, ensuring high-rate performance and safety. The α-C₇PN and β-C₇PN monolayers, isostructural to C₈P, also show desirable properties for KIBs. Comprehensive analysis indicates that their attractive properties can be attributed to their unique bonding pattern, planar configuration, and inherent metallicity. Our work presents a feasible strategy for the design of 2D carbon-anode materials for KIBs.