A conjugated poly(p-phenylene) anode with Na-solvent co-insertion enables high-rate and low-temperature Na-ion batteries

Abstract

The Na+-solvent co-intercalation in graphite anode features fast kinetics and high reversibility, which provides the opportunities to design high-rate and long-life Na-ion batteries (NIBs) with low cost. However, graphite anode suffers from relatively low specific capacity of around 100 mAh g−1. Herein, we report that a conjugated polymer of poly(p-phenylene) (PPP) can also function as the host material for the co-insertion of ether-Na+, forming a ternary polymer insertion compound (t-PIC), which realizes a high reversible capacity of 179 mAh g−1 with an initial Coulombic efficiency of 87.9 % at 0.05 A/g, excellent rate performance (93.9 mAh g−1 at 227 C) as well as 14,000 stable cycles. The fast kinetics of the Na+-ether co-insertion also enables PPP to operate well at not only low temperatures (i.e., −70 °C) but also a high areal capacity (3.7 mAh cm−2) with stable cyclability. The results of experiments and theoretical simulation suggest that the co-insertion of solvent and Na+ in the PPP electrode requires high cathodic stability of electrolyte solvents. Our findings pave the way to develop high-performance polymer anode materials working with Na+-solvent co-insertion reaction for sustainable NIBs.