The search for efficient anodic electrochromic materials is essential to the development of electrochromic devices, such as smart windows. Magnetron-sputtered lithium-nickeltungsten mixed oxides are good candidates to tackle this issue; however, they display a complicated microstructure, making it difficult to pinpoint the origin of their electro-optical properties. Herein, by exploring the Li2O-NiO-WO3 phase diagram, we obtained a new phase, Li2Ni2W2O9, that crystallizes in the orthorhombic Pbcn space group. This material can reversibly uptake/release 0.75 Li + (31 mAh.g-1) when cycled between 2.5 and 5.0 V vs Li + /Li. Moreover, through operando optical microscopy, we show that this new phase is electrochromic, and access crucial information about the diffusion-limited insertion of lithium at the single-particle-scale. This study sets the ground for future syntheses of electrochemically active materials crystallizing in the ramsayite structure, and details how the electrochromic properties of battery materials can be used to shed some light on their electrochemical mechanisms.