Li-O2 batteries, with an impressive theoretical specific energy of 3600 Wh kg-1, face challenges such as low discharge capacity, high charging overpotential, instability caused by singlet oxygen, and the shuttle effect, where soluble catalysts migrate to the anode, leading to degradation and lithium loss. An optimal strategy would incorporate three types of soluble additives: a catalyst to increase the discharge capacity, a redox mediator to lower the charging overpotential, and a scavenger to neutralize singlet oxygen. However, combining multiple additives poses compatibility issues and does not fully address the shuttle effect. To tackle these issues, we propose a multifunctional long-chain catalyst molecule equipped with a superoxide scavenger, redox mediator, and quencher for singlet oxygen. The long-chain structure anchors the molecule, preventing it from diffusing to the anode. Following this strategy, we designed P-TEMPO-TPA by grafting 2,2,6,6-tetramethyl-1-piperoxyl (TEMPO) and triphenylamine (TPA) onto a long-chain backbone. This molecule promotes Li2O2 formation, increasing the discharge capacity by 35 times and reducing singlet oxygen-driven side reactions. The soluble long-chain catalyst lowers the charging voltage to 3.65 V, extending the cycle life to 350 cycles (0.3 mAh cm-2) and 100 cycles (1.2 mAh cm-2). The long-chain design effectively mitigates the shuttle effect, paving the way for high-performance Li-O2 batteries.
Li et al. (Tue,) studied this question.