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 BC 3, BC 2 O, and BCO 2 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 Na 3 V 2 (PO 4 ) 3 for SIB and K 0.45 Mg 0.1 Fe 0.1 Mn 0.8 O 2 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.