Probing the 3-step Lithium Storage Mechanism in CH3NH3PbBr3 Perovskite Electrode by Operando-XRD Analysis

Organic-inorganic hybrid materials have gradually become one of the most actively studied research fields due to their fascinating properties. The reaction between lithium and organic-inorganic halide perovskite has just recently been proposed. However, the exact mechanisms taking place in this electrode material have not been fully elucidated, yet. To shed light on these processes an operando-X-ray diffraction study has been performed and is reported herein. According to our results the lithiation of CH3NH3PbBr3 entails three reaction steps, distinguishable during the initial galvanostatic lithiation for different Li-ion molar content x: (1) the initial Li+ insertion into the perovskite phase in which pure perovskite and lithiated phases coexist (0 <1), (2) the perovskite conversion reaction leading to the formation of metallic lead (1 <2), and finally, (3) the alloying of lithium with the metallic lead previously formed. In more detail, for x>0.3, the formation of a Li-x:CH3NH3PbBr3 phase with distinctive X-ray diffraction peaks is clearly detected, which coexists with the pristine material, till abruptly both phases disappear at x similar to 1 and CH3NH3Br and Pb metal are formed. It is shown that this conversion reaction is an irreversible process. The proposed mechanism for lithium storage gives a complete perspective of the complex structural environment involving the use of perovskite materials as electrodes for Li-ion batteries.