In-situ graphene-coated carbon microsphere as high initial coulombic efficiency anode for superior Na/K-ion full cell

Hard carbon (HC), the most prospective anode material for sodium-ion batteries (SIBs) and potassium ion batteries (PIBs), still suffers a low initial Coulombic efficiency (ICE) and terrible rate performance, hindering commercial applications. In this study, spray drying-direct pyrolysis is used to prepare low-surface-area hard [email protected] carbon microspheres (HCG) as a high ICE anode for SIBs and PIBs. Such a tactic utilizes in-situ coating graphene instead of traditional long-term pretreatment to inhibit starch foaming, greatly reducing the preparation time and energy consumption. Benefiting from abundant mesopores, ordered microcrystalline structure and 3D conductive network, the obtained HCG for the SIBs anode delivers a high ICE and an excellent specific capacity of 343 mAh g−1 at 0.1C. Moreover, the HCG displays remarkable K storage capacity (292 mAh g−1 at 0.1C, 102 mAh g−1 at 8C) and ultra-high ICE (76.4% at 0.1C), one of the highest values in present carbon-based anodes. When matched with cathodes, the SIBs and PIBs full cells deliver exceptional energy densities of 240 and 210 W·h kg−1, respectively. Importantly, the kinetics analysis reveals HCG possesses better rate performance in PIBs than in SIBs ascribed to the higher insertion potential and larger diffusion coefficient in the plateau region. In addition, the mechanism analysis shows that there are similar behaviors for the storage of Na and K in HCG. This work not only provides an efficient and scalable preparation carbon-based anode strategy from the perspective of low energy consumption but also expands the practical material library for SIBs/PIBs.