Sandwich-like Prussian blue/graphene oxide composite films as ion-sieves for fast and uniform Li ionic flux in highly stable Li metal batteries

Abstract

The uncontrollable growth of lithium dendrites caused by inhomogeneous Li deposition greatly hinders the practical applications of Li metal batteries. Herein, an ionic sieve-type composite separator (PB/GO@PP) for highly stable Li metal batteries was constructed by coating of sandwich-like Prussian blue/graphene oxide composite films on the commercial PP separator via a facile vacuum infiltration approach. The PB nanospheres with unique open-framework structure and narrow pore window, ensure the PB/GO@PP separator into an ionic sieve to promote homogenous Li ionic flux. Moreover, the PB could act as spacers to prevent GO nanosheets from stacking, leading to porous structure for fast Li-ion transport. With further assistance of GO nanosheets, the PB/GO@PP separator exhibits improved mechanical strength to alleviate the volume change of Li metal electrodes. Due to the synergistic effects of PB nanospheres and GO nanosheets, the PB/GO@PP separator can effectively regulate uniform Li deposition and suppress Li dendrite growth, resulting in a high Coulombic efficiency (98%) and an ultralong cycling life (500 h) at a current density of 1 mA cm−2. Importantly, the Li|LiFePO4 full cells with PB/GO@PP separators deliver significantly enhanced rate capacity and cycling stability. These results demonstrate that modification of separators with PB/GO layer can be a compelling strategy to improve the long-time electrochemical stability of Li metal batteries.