High performance all-solid-state electrochromic device based on LixNiOy layer with gradient Li distribution

In the complementary electrochromic devices (ECDs), nickel oxide (NiOx) is the mostly studied material as counter electrode for its neutral brown color and relatively large coloration efficiency. However, there exist some obstacles that limit the utilization of NiOx counter electrode in ECDs due to the poor transparency in the bleached state and inadequate ion storage capacity. Here, a new type of counter electrode LixNiOy layers has been investigated, and LixNiOy-based all-solid-state inorganic ECD has been successfully fabricated by magnetron sputtering. The prepared ECD exhibits excellent electrochromic performance with an optical contrast of 72.8% at 550 nm, and desirable response time with 13 s and 3.5 s for coloring and bleaching process, respectively. Furthermore, the advantages of LixNiOy-based ECDs have been demonstrated due to the gradient distribution of Li element in the LixNiOy layer. The LixNiOy layer in the proposed ECD shows a Li-rich surface, which can provide more Li ions for the coloration process. Meanwhile, the bottom of LixNiOy layer is Li-poor, which can accommodate more ions during the bleaching reaction. This structure shows superiority over the traditional NiOx-based structure, as well as some other structures. Hence, our work guided a promising new structure for the electrochromic practical application and commercial mass production. (C) 2019 Elsevier Ltd. All rights reserved.