An Ultra-Low-Temperature Alternating Current Filter.

Traditional alternating current filter based on aluminum electrolytic capacitors (AECs) suffer from abrupt drop of filtering capability at ultra-low temperatures (≤-30 °C), which greatly hinders the reliable working of electronics at extremely cold conditions. Herein, an ultra-low-temperature alternating current (AC) filter for the first time enabled by high-frequency supercapacitor based on covalently bonded hollow carbon onion-graphene hybrid structure is reported. It is found that the covalent bonding junctions enable high electronic conductivity and efficient ion adsorption/desorption behavior in the hybrid structure. Moreover, the hybrid structure owns positive curvature and shallows pores for fast ion diffusion kinetics. Consequently, the supercapacitor exhibits a record short resistor-capacitor time constant (τRC ) of 0.098 ms at 120 Hz at room temperature. Combining with low-melting-point electrolyte, the supercapacitor possesses excellent filtering capability and can output stable direct current signal with low fluctuation coefficients in a temperature range of -50 to 0 °C. More interestingly, the filter presents high negative phase angle, low dissipation factor, short τRC , and high capacitance retention below -30 °C, whereas AEC cannot work properly owing to its phase angle<45°. This work realizes the fabrication of an ultra-low-temperature AC filter, which presents a critical step forward for promoting the development of ultra-low-temperature electronics.