Storage mechanism of K in hydrogen-substituted graphdiyne as a superior anode

Potassium ion batteries (KIBs) have attracted great attention as promising alternatives to traditional lithium ion batteries. Seeking a proper anode material is a great challenge, due to the larger size of the K ion. We have proposed hydrogen-substituted graphdiyne (HsGDY) as the potential anode of KIBs by performing first principles calculations with molecular dynamic simulations. The adsorption mechanism and electrochemical properties of single-layer and bulk HsGDY were analyzed. With K-loading, HsGDY becomes a conductor with good conductivity along the stacking direction of the carbon layers. We found that no clusters of K were formed at high concentrations of K, due to the special adsorption mechanism around the edge of the holes in HsGDY. The specific capacity due to the K intercalation can reach 1094 mA h g-1 with a volume expansion of less than 30%. There was also a proper voltage profile with an average open circuit voltage of 0.38 V. The diffusion rate along the direction of the stacking layers was incredibly fast, with a diffusion barrier of 0.14 eV. The storage of K in HsGDY with a high concentration and a fast diffusion rate with high thermodynamic stability demonstrates the potential ability of HsGDY to be used as an excellent anode of KIBs.