Compared with the pure WO3 film, the Ti doped tungsten oxide film has no change in the color change amplitude. While the coloring and fading response speeds are obviously increased. And the amount of charge stored in the reaction is increased. Moreover, after a plurality of cycles, the current decay becomes small, the cycle stability increases, and the film cycle life increases. In addition, WO3 is converted from a monoclinic system to a cubic system. And at the same time, Ti4+ ions suppress grain growth to make the degree of crystallization lowered.
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Furthermore, in the injection process of lithium ion, compared with the transformation of WO3 film from monoclinic phase to cubic phase, the cubic phase of WO3: Ti film has no change in crystal structure before and after discoloration. In other words, the lattice strain caused by discoloration is reduced, and the energy barrier to be overcome is reduced. Also, the degree of change of roughness is also small, so the cycle performance of Ti doped WO3 thin film is better than that of the undoped WO3 film.
