Constructing Hard Carbon Submicron Spheres with Boron Doping as Advanced Anode Materials toward Enhanced Sodium and Potassium-Ion Storage

Heteroatom doping and morphology modulation are recognized as effective strategies for improving the electrochemical properties of hard carbon materials. In this study, boron-doped hard carbon submicrometer spheres (BHC-1200) were prepared through a hydrothermal treatment followed by a high-temperature carbonization route, serving as dual-functional anodes for both sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). X-ray diffraction characterization reveals expanded interlayer spacing for BHC-1200, while X-ray photoelectron spectroscopy further confirms the successful doping of boron through the identification of BC3, BC2O, and BCO2 configurations, which contribute to enhanced defects and improved electrical conductivity. Benefiting from boron doping and a spherical morphology, BHC-1200 exhibits exceptional electrochemical properties in both SIBs and PIBs. As a SIB anode, BHC-1200 demonstrates a reversible specific capacity of 342.7 mAh g–1 at 0.03 A g–1, and possesses a capacity retention of 91.6% after 1000 cycles at 1.0 A g–1. In addition, BHC-1200 also delivers a high reversible specific capacity (361.1 mAh g–1 at 0.03 A g–1) and a competitive cycling stability when used as an anode for PIBs. Full cell tests paired BHC-1200 as an anode with Na3V2(PO4)3 for SIB and K0.45Mg0.1Fe0.1Mn0.8O2 for PIB as cathodes display stable cycling performance, highlighting BHC-1200′s potential for practical energy storage applications. This work establishes a straightforward heteroatom-doping strategy for carbon anodes, balancing high capacity, rate capability, and cyclability in postlithium battery systems.