Dual-interface engineered SnO₂/Sn₄P₃@C heterojunctions: built-in electric field-driven fast kinetics for highly reversible lithium storage

The practical application of SnO₂ anodes in lithium-ion batteries is fundamentally constrained by cascading challenges of structural degradation and kinetic limitations. We demonstrate a dual-interface engineering strategy through precisely controlled gas-phase phosphorization, constructing SnO₂/Sn₄P₃ heterojunctions tightly encapsulated within hierarchical carbon frameworks (SnO₂/Sn₄P₃@C, SOPC). The SnO₂/Sn₄P₃ heterojunction generates a built-in electric field, reducing charge transfer resistance and activation energy (UPS work function: 2.91 eV) and guides LiF-rich SEI formation, while the dual-carbon confinement buffers mechanical strain and ensures the structural stability with long-term cycling at high current density. These features enable hybrid storage kinetics with capacitive dominance at high rates and stable faradaic reactions at low currents. The SOPC anode achieves exceptional cyclability with capacities of 954.8 mA h g^-1 after 600 cycles at 1 A g^-1 and 118.9 mA h g^-1 after 3000 cycles at 20 A g^-1. Full cells paired with LiFePO₄ demonstrate practical viability. This work establishes a universal interfacial engineering strategy for high-performance alloying/conversion anodes, bridging atomic-scale electronic modulation to scalable battery systems.