Sequential Effect of Dual-Layered Hybrid Graphite Anodes on Electrode Utilization During Fast-Charging Li-Ion Batteries.

To recharge lithium-ion batteries quickly and safely while avoiding capacity loss and safety risks, a novel electrode design that minimizes cell polarization at a higher current is highly desired. This work presents a dual-layer electrode (DLE) technology via sequential coating of two different anode materials to minimize the overall electrode resistance upon fast charging. Electrochemical impedance spectroscopy and distribution of relaxation times analysis revealed the dynamic evolution of electrode impedances in synthetic graphite (SG) upon a change in the state of charge (SOC), whereas the natural graphite (NG) maintains its original impedance regardless of SOC variation. This disparity dictates the sequence of the NG and SG coating layers within the DLE, considering the temporal SOC gradient developed upon fast charging. Simulation and experimental results suggest that DLE positioning NG and SG on the top (second-layer) and bottom (first-layer), respectively, can effectively reduce the overall resistance at a 4 C-rate (15-min charging), demonstrating two times higher capacity retention (61.0%) over 200 cycles than its counterpart with reversal sequential coating, and is higher than single-layer electrodes using NG or NG/SG binary mixtures. Hence, this study can guide the combinatorial sequence for multi-layer coating of various active materials for a lower-resistivity, thick-electrode design.