Peanut Shell Hybrid Sodium Ion Capacitor with Extreme Energy - Power Rivals Lithium Ion Capacitors

This is the first report of a hybrid sodium ion capacitor (NIC) with the active materials in both the anode and the cathode being derived entirely from a single precursor: peanut shells, which are a green and highly economical waste globally generated at over 6 million tons per year. The electrodes push the envelope of performance, delivering among the most promising sodiation capacity - rate capability - cycling retention combinations reported in literature for each materials class. Hence the resultant NIC also offers a state-of-the-art cyclically stable combination of energy and power, not only in respect to previously published NICs but also as compared to Li ion capacitors (LICs). The ion adsorption cathode based on Peanut Shell Nanosheet Carbon (PSNC) displays a hierarchically porous architecture, a sheet-like morphology down to 15 nm in thickness, a surface area on par with graphene materials (up to 2396 m²g^-1) and high levels of oxygen doping (up to 13.51 wt%). Scanned from 1.5 - 4.2 V vs. Na/Na⁺ PSNC delivers a specific capacity of 161 mAhg^-1 at 0.1A g^-1 and 73 mAhg^-1 at 25.6 Ag^-1. A low surface area Peanut Shell Ordered Carbon (PSOC) is employed as an ion intercalation anode. PSOC delivers a total capacity of 315 mAhg^-1 with a flat plateau of 181 mAhg^-1 occurring below 0.1 V (tested at 0.1 Ag^-1), and is stable at 10,000 cycles (tested at 3.2 Ag^-1). The assembled NIC operates within a wide temperature range (0 - 65°C), yielding at room temperature (by active mass) 201, 76 and 50 Wh kg^-1 at 285, 8500 and 16500 W kg^-1, respectively. At 1.5 - 3.5 V, the hybrid device achieved 72% capacity retention after 10,000 cycles tested at 6.4 Ag^-1, and 88% after 100,000 cycles at 51.2 Ag^-1.