Solar-thermal conversion is the most direct strategy of solar energy utilization, and spinel-type transition metal
oxides as photo-thermal conversion (PTC) materials have attracted great attention because of their attractive
optical property and durable stability under strong sunlight or harsh temperature condition. Supercapacitors are
important electrochemical energy storage devices, but sluggish ionic mobility and freezing of electrolytes at low
temperatures directly lead to low or even no capacitance. Herein, we report an effective strategy to recover the
charge storage ability of sandwich-type supercapacitors by employing a series of spinel-type PTC coatings. Under
solar irradiation, these PTC coatings can effectively capture sunlight and convert it into thermal energy, thereby
increasing the actual operation temperature of supercapacitor devices. At low ambient temperatures ( 20 and
30 C), the devices coated with Cu1.5Mn1.5O4 film showed the highest temperature increase (about 60 C)
because of the best PTC effect. Consequently, a significant capacitance improvement was achieved (from close to
zero up to desirable values), thus enabling the devices to work well at such low ambient temperatures. This works
offers a highly effective method to improve low-temperature performance of supercapacitors and, simultaneously,
endows a new application of spinel-type PTC coatings for supporting electrochemical energy storage devices.