Kinetics Manipulation for Improved Solid Electrolyte Interphase and Reversible Na Storage

Minimizing the irreversibility during the first cycle in carbon anodes is crucial to the energy density and lifespan of Na-ion batteries (NIBs). However, the underlying mechanism of the irreversible capacity, especially combined with the kinetics and interface, is still incompletely understood. Herein, we discovered that poor kinetics and strong polarization will drive the Na+ residual at the interface as pseudo-dead Na to trigger electrolyte decomposition and form extra SEI, thus sacrificing the initial Coulombic efficiency (ICE). Manipulating defect concentration is, therefore, developed to improve the kinetics, reduce the diffusion barrier of Na+, and lower the Fermi energy of the anode to impede the pseudo-dead Na and extra SEI formation, thereby ensuring high ICE and even capacity. This study proposes a complementary view on the understanding of initial irreversibility and interface evolution influenced by Na+ kinetics, which provides guidance for defect chemistry and engineering for future design of carbon anodes toward high-performance NIBs.