Ruddlesden Popper 2D perovskites as Li-ion battery electrodes

Hybrid metal halide perovskites, typically known for their photovoltaic applications, have recently gained traction as a potential energy-storage material due to their promising gravimetric capacities as lithium-ion battery electrode materials. Here we investigate the effect of tuning the layering properties of the quasi two-dimensional Ruddlesden Popper (RP) layered perovskite series (BA)(2)(MA)(n-1)PbnX3n+1 (BA - butylammonium, MA - methylammonium, X - halide (I- and Br-)) from n = 1 to n = 4 and the equivalent bulk crystal structure MAPbX(3). The interaction between the insertion of lithium ions and the layering arrangement of the perovskite structure are studied electrochemically and compared to a reported three-stage energy storage mechanism in bulk perovskites. The layering structure that optimises both capacity and stability is determined to be n = 4, providing a compromise between the number of active layers and the lithium ion access between them provided by the BA organic chain, thus demonstrating initial and stabilised gravimetric capacities of 575.5 mA h g(-1) and 89.9 mA h g(-1) respectively. The effect of changing the halide within the perovskite structure is investigated and demonstrates a greater gravimetric capacity for the lighter bromide species compared to the commonly used iodide. Finally, high molarity electrolytes and tailored cut-off potentials are used to improve the stability of the RP layered perovskite electrodes.