Cationic Defect-Modulated Li-Ion Migration in High-Voltage Li-Metal Batteries

Li metal exhibits high potential as an anode material for next-generation high-energy density batteries. However, the nonuniform transport of Li⁺ ions causes Li-dendrite growth at the metal electrode, leading to severe capacity decay and a short cycling life. In this study, negatively charged lithiophilic sites (such as cationic metal vacancies) were used as hosts to regulate the atomic-scale Li⁺-ion deposition in Li-metal batteries (LMBs). As a proof of concept, three-dimensional (3D) carbon nanofibers (CNFs) decorated with negatively charged TiNbO₄ grains (labeled CNF/nc-TNO) were confirmed to be promising Li hosts. Cationic vacancies caused by the carbothermal reduction of Nb⁵⁺ and Ti⁴⁺ ions generated a negatively charged fiber surface and strong electrostatic interactions that guided the Li⁺-ion flux to the shadowed areas underneath the fiber and throughout the fibrous mat. Consequently, circumferential Li-metal plating was observed in the CNF/nc-TNO host, even at a high current density of 10 mA cm^-2. Moreover, CNF/nc-TNO asymmetric cells delivered a significantly more robust and stable Coulombic efficiency (CE) (99.2% over 380 cycles) than cells comprising electrically neutral CNFs without cationic defects (which exhibits rapid failure after 20 cycles) or Cu foil (which exhibits rapid CE decay, with a CE of 87.1% after 100 cycles). Additionally, CNF/nc-TNO exhibited high stability and low-voltage hysteresis during repeated Li plating/stripping (for over 4000 h at 2 mA cm^-2) with an areal capacity of 2 mAh cm^-2. It was further paired with high-voltage LiNi_0.8Co_0.1Mn_0.1 (NCM811) cathodes, and the full cells showed long-term cycling (220 cycles) with a CE of 99.2% and a steady rate capability.