Within an all-solid inorganic layout for an electrochromic device with tungsten trioxide acting as main electrochromic layer, there are a few possible electrochromic complementary materials that can act as the ionic storage layer, and among them nickel oxide has always attracted considerable interest. We analysed nickel oxide deposited by thermal evaporation to test the suitability of such a layer for use in an all-solid inorganic electrochromic device. Samples were analysed with X-ray photoelectron spectroscopy and electrochemical techniques, cyclic voltammetry and chronoamperometry with simultaneous monitoring of the optical properties of the samples. The characterisation deals with the activation potential ranges, the amount of inserted charge, colouration efficiency and optical and electrical compatibility with the tungsten trioxide layers. All these analyses provided criteria for the relation between the electrochromic properties of the thin films of nickel oxide and the deposition parameters employed, and opened a way to obtain cost-effective all-solid inorganic electrochromic devices.