Mechanistic insights into the dry prelithiated WO3 thin films in electrochromic devices

While the dry prelithiation method has been extensively applied in WO3-based electrochromic devices, the insight of prelithiated WO3 films is still ambiguous. Herein, the electrochromic and electrochemical performance of the WO3 films prepared by an in situ dry prelithiation method is investigated. The deposited lithium is calculated to be separated into 47.8% 'active lithium' and 52.2% 'dead lithium'. On one hand, the enhancement of the electrochemical cycling stability and charge density can be ascribed to the preactivation of 'active lithium', which enlarges the surface area for ion transporting. On the other, the irreversible formation of 'dead lithium zone' in the prelithiated WO3 films originates from 'dead lithium seed', leading to the detriment of optical properties. This work further provides a profound insight into the implication of prelithiated lithium on the electrochemical and electrochromic properties of the WO3 films.