Enhancing high-rate plateau capacity of hard carbons by TiC-mediated closed pore formation and heterojunction engineering for sodium-ion batteries

Fast-charging sodium-ion batteries with high energy density require hard carbons anodes that combine high low-voltage plateau capacity and rapid Na⁺ kinetics. However, simultaneously achieving these properties remains a critical challenging. Here, we utilize MXene as a structural modulator to create the closed-pore structure of hard carbons, enhancing Na storage while constructing TiC/C heterojunctions to accelerate Na⁺ transport. Unlike pure glucose-derived carbon, the MXene/TiC-embedded precursor induces curved graphite lattices and a moderately increased graphitization degree during carbonization, promoting formation of closed pores for dense sodium cluster storage. The resulting glucose/MXene-derived hard carbons (GM-HCs) exhibits a high reversible capacity of 381.4 mAh g^-1 at 0.1C. Moreover, GM-HCs demonstrate remarkable low-voltage plateau capacity at high rate, retaining 124.9 mAh g^-1 at 20C. Density functional theory (DFT) calculations confirm reduced Na⁺ diffusion barriers and enhanced electronic conductivity in hard carbons with TiC/C heterojunctions. When paired with a Na₃V₂O₂(PO₄)₂F cathode, GM-HCs-based full cells deliver high energy density and stable cycling, retaining 95.2 % capacity after 400 cycles. This work presents a dual strategy by creation of closed pores and construction of heterojunctions to simultaneously enhance plateau capacity and Na⁺ migration, advancing the development of high-performance sodium-ion battery anodes.