Protecting lithium anode with ionic liquid modified poly(vinylidene fluoride) single ion conducting separators for iodide-assisted lithium oxygen batteries

Redox mediators (RMs) have been reported to effectively promote the sluggish decomposition of discharge products in Li-O2 batteries (LOBs), however, the attack of the oxidized RMs and other harmful species remains challenging to Li anodes. Herein, an ionic liquid modified sulfonated poly(vinylidene fluoride) (MSP) single lithium-ion conducting membrane was fabricated, which only allows the transfer of Li+ and blocks the passthrough of anions and other molecules. The ionic liquid modification apparently strengthened the conductivity of the membrane without losing its impermeability and ionic selectivity. The utility of the MSP separator significantly extended the cycle life of the LOB in comparison to the cell using a glass fiber separator, from 60 to 210 rounds at the 1.0 A g−1 and the capacity of 1000 mAh g−1. The rate performance was obviously enhanced from 44, 31 and 23 cycles to152, 129 and 107 cycles at the rates of 2.0, 3.0 and 5.0 A g−1, respectively. The full-discharge capacity was also enlarged from 3700 to 17,000 mAh g−1. The MSP separator enables the iodide-assisted cathode process and improves the deposition/dissolution of the Li anode, which are essential for the performance enhancement of aprotic LOBs.