Controlling Lithium Deposition of Hollow Carbon Nanospheres via Lithiophilic-ZnO and Lithiophobic-TiO₂ Engineering for Lithium Metal Anodes in Secondary Batteries

Lithium metal is regarded as a highly potential anode material owing to its exceptional energy density. However, it faces several challenges, including irregular lithium dendrite growth, volume changes during cycling, and low Coulombic efficiency. Among various solutions, hollow carbon spheres (HCSs) have been highlighted for their ability to provide a stable space for lithium deposition and to accommodate volume changes. However, the identical nature of the inner and outer carbon linings in HCSs and the migration of Li ions along the lithiophilic carbon shell pose some challenges, because dendrites can form outside the carbon shell, thereby degrading battery performance. To overcome these challenges, this study proposes a novel HCS structure in which ZnO seeds are introduced into the empty space of the HCS and the carbon shell is composited with TiO₂. ZnO, with higher lithiophilicity than carbon, preferentially facilitates uniform lithium deposition within the inner space of the carbon shell. Simultaneously, the carbon shell combined with lithiophobic TiO₂ reduces the lithiophilicity of the shell, successfully suppressing Li dendrite formation caused by the movement of Li ions along the outer carbon shell. This dual-functional design suppresses Li dendrites, significantly enhancing electrochemical and cycle performance. The morphology and elemental dispersion of the proposed HCS structure were confirmed using SEM, TEM, and TEM-EDS. Electrochemical analysis revealed that the proposed material exhibited a low nucleation overpotential and maintained approximately 100% Coulombic efficiency even after 500 cycles, demonstrating excellent cycling performance.