Highly conductive locally graphitized sheath on fibrous micro-Si anode for high-energy Li-ion battery

Silicon (Si) is a promising anode material for developing high-energy-density lithium-ion batteries, yet challenges remain in improving its mechanical stability and intrinsic conductivity. Therefore, reinforcing the Si by microstructuring and modulating the electronic structure, such as doping, is critical. However, the typical high-energy doping process compromises the fine engineering of porous structures, and such a trade-off inevitably hinders the establishment of an energy-efficient and facile protocol to produce highly conductive but volume-accommodating Si anodes. Herein, we report a one-pot synthesis route for fabricating nickel-doped fibrous microspherical Si anodes by exploiting simple galvanic replacement at a relatively low temperature in a scalable manner. The nickel dopant emerging from the reaction serves as an electronic booster and structural support for the Si framework. Furthermore, homogeneously distributed dopants catalyze the graphitization of carbon sheath in part which features mechanical stiffness and high ionic/electrical conductivity. Consequently, synergistic effects from the multifunctional dopant and mixed conducting sheath enable a stable and fast battery operation, achieving a quick stabilization of coulombic efficiency exceeding 99 %. Thus, the full-cell paired with the LiNi_0.6Co_0.2Mn_0.2O₂ cathode shows 80 % capacity retention after 250 cycles by preventing irreversible Li consumption. This work sheds light on the utilization of classical chemistry to prepare high-performing battery materials.