Zinc-Ion Capacitors Working at Extreme Conditions

Abstract

Combing advantages of both Zn anode and carbon cathodes, zinc ion capacitors (ZICs) hold great potentials for electrical vehicles and grid storage. To meet practical applications, high-mass-loading electrodes and harsh environment need to be considered when designing energy storage devices. For one, high-loading electrodes bring simultaneously the dense packing of active materials in limited space and the reduction of inactive components, leading to lower production cost and higher energy densities at the cell level compared with thin electrodes. That is why active mass loadings must be no less than 10 mg cm−2 for practical applications and typical values for commercial energy storage devices are 10-20 mg cm-2. However, this is not the case in most research papers with typical loadings of only 1-4 mg cm-2. On the other hand, low and high temperature environment will be encountered in not only extreme regions like North Pole and outer space but also residential areas with ever-changing climate. As such, it is critical to develop cells working in a wide-temperature range of −30 °C–50 °C for most human habitats and a broader range from −50 °C to 70 °C for military uses. Strangely, those two important factors are often ignored in the development of ZICs. In this work, we demonstrate workable ZICs under extreme conditions through the incorporation of activated carbon, aqueous binder and concentrated electrolyte. First, with highly exposed surface area and enriched oxygen, nitrogen dopants, the activated carbon manifests large electrical double layer capacitance and Faradic pseudocapacitance. Second, sodium alginate-based aqueous binder shows better electrolyte wettability than the commonly used polymer binder, resulting in much improved capacitance. Third, highly concentrated electrolyte enables large zinc stripping/plating efficiency, long life cycles as well as low frozen temperature due to reduced hydrogen bonding interaction of water. Three keys combined unlock ZICs with a large capacitance of 436 F g−1 (capacity: 200 mAh g-1), ultrafast kinetics, ultralong cycles, ultrahigh loadings (10 mg cm-2), and wide-temperature cycling (-60 oC ~ 60 oC), resulting in a maximum energy density of 134.8 Wh kg−1 and power density of 118.4 kW kg−1 based on AC electrode, which lies among the best performance level for carbon-based ZICs.