Electrochromic Corundum-like Compound Based on the Reversible (De)insertion of Lithium: Li2Ni2W2O9

The search for efficient anodic electrochromic materialsis essentialto the development of electrochromic devices, such as smart windows.Magnetron-sputtered lithium-nickel-tungsten mixed oxides are goodcandidates to tackle this issue; however, they display a complicatedmicrostructure, making it difficult to pinpoint the origin of theirelectro-optical properties. Herein, by exploring the Li2O-NiO-WO3 phase diagram, we obtained a newphase, Li2Ni2W2O9, thatcrystallizes in the orthorhombic Pbcn space group.This material can reversibly uptake/release 0.75 Li+ (31mA h center dot g(-1)) when cycled between 2.5 and 5.0 Vversus Li+/Li. Moreover, through operando optical microscopy, we show that this new phase is electrochromic,and crucial information can be accessed about the diffusion-limitedinsertion of lithium at the single-particle scale. This study setsthe ground for future syntheses of electrochemically active materialscrystallizing in the ramsayite structure and details how the electrochromicproperties of battery materials can be used to shed some light ontheir electrochemical mechanisms.

Automated summary

The search for efficient anodic electrochromic materials is crucial for the development of electrochromic devices, such as smart windows. In this study, a new phase, Li2Ni2W2O9, was obtained by exploring the Li2O-NiO-WO3 phase diagram. This new phase exhibits reversible lithium uptake/release and electrochromic properties, providing valuable insights into the diffusion-limited insertion of lithium and the electrochemical mechanisms of battery materials.