Quantitative Porosity Engineering of Carbon Electrode in Lithium-Oxygen Batteries with Cell-Level Gravimetric Energy...

Lithium-oxygen batteries (LOBs) offer an extremely high theoretical energy density; however, their practical realization depends strongly on the design of porous carbon positive electrodes. Most prior efforts have emphasized material design while overlooking the role of the electrolyte stored within pores, leaving the design principles for achieving practical high-energy-density LOBs unclear. In the present study, through simulations, it is quantitatively demonstrated that while increasing pore volume initially improves energy density, it eventually plateaus due to increasing electrolyte demand. The simulations indicate that reduced electrolyte volumes and optimized mass loading of the positive electrode are crucial for maximizing energy density. Experimental validation with systematically tuned carbon electrodes in pouch-type LOBs with realistic mass-loadings supports these findings. While large pore volumes enhance capacity, they require excessive electrolyte, ultimately counter-balancing energy density. Conversely, lowering electrolyte volumes in highly porous electrodes leads to incomplete filling, increased impedance, enhanced parasitic reactions, and poor cycling stability. As a result, by tailoring the pore structure, electrodes capable of delivering cell-level energy density exceeding 1500 Wh kg^-1 and maintaining stable cycling under capacity-limited conditions are demonstrated. This work redefines the role of pore engineering in LOB electrodes, highlighting its crucial contribution to achieving practical, high-energy, and long-lasting LOBs.