The electrochemical behaviors and lithium-storage mechanism of LiCoO2 in a broad voltage window (1.0−4.3 V) are studied by charge−discharge cycling, XRD, XPS, Raman, and HRTEM. It is found that the reduction mechanism of LiCoO2 with lithium is associated with the irreversible formation of metastable phase Li1+x
CoII IIIO2−y
and then the final products of Li2O and Co metal. During the charging process, the Li2O/Co mixture can be oxidized into CoO, and then the Li2O/CoO mixture can result in the formation of Co3O4 in the higher-voltage region. Li
x
CoO
y
is the final product when the active material is charged to 4.3 V. During the subsequent cycles, the lithium uptake/release reactions are related to the reversible conversion of Co ↔ CoO ↔ Co3O4 ↔ Li
x
CoO
y
.
We prepare a series of two-dimensional (2D) tin-based perovskite (RNH 2 ) 2 SnBr 4 with different carbon chains. All of them have extra-large Stokes shifts, broad emission, and ultralong PL lifetimes. The PLQYs of (C 8 H 17 NH 2 ) 2 SnBr 4 and (OAm) 2 SnBr 4 powders reach up to 54 and 60%, respectively. Density functional theory calculations and experimental results reveal that the properties of 2D Sn-based perovskites may originate from self-trapped excitons, which result from excited-state structural deformation. The results show that the [SnBr 6 ] 4− octahedron distorted by the carbon chain with arrangement distortion changes the photophysical properties of 2D tinbased perovskite. Furthermore, (OAm) 2 SnBr 4 powders are used to engineer UV pumped light-emitting diodes. This work provides new strategies for the preparation of environmentally friendly perovskite materials.
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