Confined Li metal storage in porous carbon frameworks promoted by strong Li-substrate interaction

Abstract

Li metal suffers from uncontrollable dendrite formation and huge volume changes during cycling, resulting in shortened cycle lifetimes. Porous carbon frameworks have been explored as host materials to store Li metal; however, the low pore utilization and uneven Li plating remain crucial issues. Herein, we demonstrate that a strong interaction between Li and substrate plays a critical role in enhancing pore utilization in the carbon framework electrodes, thus improving their cycle lifetimes. As a model architecture, we examine a Li storage process in a framework electrode consisting of porous carbon derived from metal-organic frameworks (MOFs) and a galvanically displaced Ag layer on a Cu substrate. The MOF-derived carbon framework electrode on the Agdeposited Cu substrate exhibits significantly better cycling stability (>250 cycles) than the electrode on bare Cu (140 cycles). In-operando synchrotron X-ray diffraction studies combined with microstructural characterizations reveal that the lithiophilic Ag on the substrate preferentially reacts with Li+ to form LixAg during the initial stage of Li plating and promotes confined Li storage in the carbon framework electrode while suppressing top plating. However, the Ag layer is found to lose its effectiveness when the thickness of the electrode exceeds a critical value. Based on simulation studies, the efficacy of lithiophilic layers toward improving pore utilization is discussed in terms of the kinetic competition between Li+ transport through porous channels and the interfacial reaction of Li+ with the substrate, which can provide a guideline for designing porous carbon frameworks with high capacity and long cycle lifetimes.