Electrochromic performance of Ni oxide thin films intercalated with Li⁺ ions

Porous Ni oxide thin films were deposited on unheated ITO/glass substrates by sputtering in argon-oxygen. The as-deposited thin films have a cubic NiO structure and still exhibit such a structure after 10,000 electrochemical cycles in 1 M LiClO₄ in propylene carbonate in the range between 2.0 and 4.1 V vs Li/Li⁺. Electrochromic performance showed a rapid drop of charge density over the first hundreds of cycles and subsequently a very slow decrease. The charge density was 87% of the initial one after 1,000 cycles and 82% after 10,000 cycles, indicating an extremely slow decay after 1,000 cycles. Optical modulation was also slightly decreased after 10,000 cycles, which is due to the drop of charge density