A highly transparent ion conducting film enabling a visual electrochromic battery

Abstract

Electrochromic (EC) batteries realize the visualization of the energy level by naked eye and exhibit great potential in various applications including smart windows and wearable electronics. However, limited by the unstable electrolyte and the lack of matching EC electrodes, EC batteries with high working voltage window and energy density still remain a remarkable challenge. Herein, a highly transparent ion-conducting film (ICF) is employed to develop a rechargeable EC battery. The ICF exhibits extremely high optical transparency (over 85% in visible range) and ionic conductivity (σ = 0.46 mS cm⁻¹). In addition, we fabricated a complementary electrochromic battery (ICF-ECB) based on ICF by assembling the spinel Li₄Ti₅O₁₂ (LTO) as the EC layer and LiMn₂O₄ (LMO) as a matching counter electrode. Benefiting from the electrochemically stable ICF and battery-type electrochromic materials, the ICF-ECB delivers a high energy storage performance with an operating voltage of 3.0 V and stable discharging platform at 2.5 V. Impressively, the ICF-ECB demonstrates a high areal power/energy density (2.2 W m⁻², 0.14 W h m⁻²) and excellent cycling stability with 61.2% of its initial optical modulation after 200 cycles. Moreover, the resultant ICF-ECB exhibits an obvious and reversible color transition between yellowish-brown (discharge state) and dark blue (charged state), which endows the capacity of sufficient real-time information on the energy level and work status of the device. It is envisioned that the use of ICF to fabricate the multifunctional EC batteries provides new approach to develop intelligent electronic devices.