Inorganic metal oxide electrochromic materials have good application prospects for energy-saving windows in buildings and smart display applications. Therefore, the development of electrochromic films with good cycling stabilities, fast color-change response times, and high coloring efficiencies has attracted considerable attention. In this study, nanoflake Li-doped NiO electrochromic films were prepared using a hydrothermal method, and the films exhibited superior electrochromic performances in the LiOH electrolyte. Li⁺ ions doping increased the ion transmission rates of the NiO films, and effectively promoted the transportation of ions from the electrolyte into NiO films. Meanwhile, the nanoflake microstructure caused the NiO films to have larger specific surface areas, providing more active sites for electrochemical reactions. It was determined that the NiO-Li20% film exhibited an ultra-fast response in the LiOH electrolyte (coloring and bleaching times reached 3 and 1.5 s, respectively). Additionally, the coloration efficiency was 62.1 cm² C⁻¹, and good cycling stability was maintained beyond 1500 cycles. Finally, the simulation calculation results showed that Li doping weakened the adsorption strengths of the NiO films to OH⁻, which reduced the generation and decomposition of NiOOH and helped to improve the cycling stabilities of the films. Therefore, the research presented in this article provides a strategy for designing electrochromic materials in the future.