Quasi-solid state rechargeable Na-CO₂ batteries with reduced graphene oxide Na anodes

Na-CO₂ batteries using earth-abundant Na and greenhouse gas CO₂ are promising tools for mobile and stationary energy storage, but they still pose safety risks from leakage of liquid electrolyte and instability of the Na metal anode. These issues result in extremely harsh operating conditions of Na-CO₂ batteries and increase the difficulty of scaling up this technology. We report the development of quasi-solid state Na-CO₂ batteries with high safety using composite polymer electrolyte (CPE) and reduced graphene oxide (rGO) Na anodes. The CPE of PVDF-HFP [poly(vinylidene fluoride-co-hexafluoropropylene)]-4% SiO₂/NaClO₄-TEGDME (tetraethylene glycol dimethyl ether) has high ion conductivity (1.0 mS cm^-1), robust toughness, a nonflammable matrix, and strong electrolyte-locking ability. In addition, the rGO-Na anode presents fast and nondendritic Na⁺ plating/stripping (5.7 to 16.5 mA cm^-2). The improved kinetics and safety enable the constructed rGO-Na/CPE/CO₂ batteries to successfully cycle in wide CO₂ partial pressure window (5 to 100%, simulated car exhaust) and especially to run for 400 cycles at 500 mA g^-1 with a fixed capacity of 1000 mA·hour g^-1 in pure CO₂. Furthermore, we scaled up the reversible capacity to 1.1 A·hour in pouch-type batteries (20 × 20 cm, 10 g, 232 Wh kg^-1). This study makes quasi-solid state Na-CO₂ batteries an attractive prospect.