(a) Current density–time curves acquired by potential step measurement applied between 1.2 V and 3 V. The inset shows optical images of the electrochromic effect in the Li₄Ti₅O₁₂/FTO electrode at bleached and colored states. (b) Transmittance spectra of the Li₄Ti₅O₁₂/FTO electrode at (i) bleached and (ii) colored states. (c)In situtransmittance curves obtained during switched pulse potential cycling tests with wavelengths of 850 nm, 700 nm, 600 nm, 500 nm, and 400 nm.^[16]