Interface-reinforced solid-state electrochromic Li-ion batteries enabled by in-situ liquid-solid transitional plastic glues

The electrochromic Li-ion batteries (ELIBs) combine the functions of electrochromism and energy storage, realizing the display of energy-storage levels by visual signals. However, the accompanying interfacial issues including physical contact and (electro)chemical stability should be taken into account when the conventional liquid/gel electrolytes are replaced with solid-state counterparts. Herein, the in-situ liquid-solid transitional succinonitrile (SCN) plastic glues are constructed between electrodes and poly(ethylene oxide) (PEO) polymer electrolytes, enabling an interface-reinforced solid-state ELIB. Specifically, the liquid SCN precursor can adequately wet electrode/PEO interfaces at high temperature, while it returns back to solid state at room temperature, leading to seamless interfacial contact and smooth ionic transfer without changing the solid state of the device. Moreover, the SCN interlayer suppresses the direct contact of PEO with electrodes containing high-valence metal ions, evoking the improved interfacial stability by inhibiting the oxidation of PEO. Therefore, the resultant solid-state ELIB with configuration of LiMn2O4/SCN-PEO-SCN/WO3 delivers an initial discharge capacity of 111 mA h g−1 along with a capacity retention of 88.3% after 200 cycles at 30 °C. Meanwhile, the electrochromic function is integrated into the device by distinguishing its energy-storage levels through distinct color changes. This work proposes a promising solid-state ELIB with greatly reinforced interfacial compatibility by introducing in-situ solidified plastic glues.