Lithium–oxygen batteries face an energy-power trade-off due to sluggish O2 transport and pore clogging by Li2O2. Simulations show that reducing tortuosity via interconnected macropores enhances oxygen mobility. A freestanding graphene electrode having interconnected macropores with low tortuosity delivers >2500 mAh g−1, stable lean-electrolyte cycling, and high-rate performance, providing a practical strategy to improve both energy and power in LOBs.
Abstract
The energy–power trade-off in lithium–oxygen batteries (LOBs) arises from sluggish oxygen (O2) transport in the porous positive electrode and pore clogging by lithium peroxide (Li2O2). While increasing porosity enhances electrolyte accessibility and Li2O2 storage, it also increases electrolyte demand, compromising the overall energy density of the cell and necessitating alternative strategies to boost power capabilities without sacrificing energy density. In this study, theoretical simulations of O2 transport reveal that reducing tortuosity by improving pore interconnectivity has a more significant impact on O2 transport than porosity itself. Based on this insight, a freestanding graphene-based electrode with a highly interconnected macroporous network is fabricated via a non-solvent-induced phase separation approach using polyacrylonitrile (PAN) as a carbon scaffold and polyethylene oxide (PEO) as a sacrificial porogen. The selective decomposition of PEO creates spatially interconnected macropores, effectively reducing tortuosity. The resulting electrode enables LOB cells to achieve >2500 mAh g−1 at 1.0 mA cm−2 under lean-electrolyte conditions. Stable cycling at 4 mAh cm−2 is maintained with only 3.25 g Ah−1 electrolyte, and high-rate performance persists over 90 cycles at 1.5 mA cm−2. This work demonstrates a robust strategy to simultaneously improve energy and power performance in practical LOBs through rational electrode architecture.
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