Carbon dioxide assist for non-aqueous sodium–oxygen batteries

Abstract

We report a novel non-aqueous Na-air battery that utilizes a gas mixture of CO 2 and O 2 . The battery exhibits a high specific energy of 6500-7000 Whkg −1 (based on the carbon mass) over a range of CO 2 feed compositions. The energy density achieved is higher, by 200% to 300%, than that obtained in pure oxygen. Ex-situ FTIR and XRD analysis reveal that Na 2 O 2 , Na 2 C 2 O 4 and Na 2 CO 3 are the principal discharge products. The Na-CO 2 /O 2 and Mg-CO 2 /O 2 battery platforms provide a promising, new approach for CO 2 capture and generation of electrical energy.

CO2/oxalate cathodes as safe and efficient alternatives in high energy density metal–air type rechargeable batteries

“…Interestingly, in some electrolytes based on ionic liquids, it is the CO 2 that gets reduced to oxalate and O 2 does not formally participate in reactions 14 . Selective reduction of CO 2 to oxalate from ambient air through a catalyst 16 and simultaneous reduction of O 2 to peroxide is also possible, potentially allowing for a rechargeable Li-air battery by eliminating the presence of carbonates.…”

“…A primary battery with Na anode and CO 2 /oxalate cathode has recently been realized by Das et al 14 as an unexpected byproduct of Na-(O 2 +CO 2 ) battery experiments, observing that oxygen admixture to CO 2 can act as a catalyst for the produc-tion of oxalate salts during discharge in appropriately chosen ionic liquid electrolytes while no oxide or carbonate discharge products are formed. The voltage of this battery (≈2.25 V, OCV) is about 18% smaller than that of an analogous Na-(O 2 +CO 2 )/(peroxide+carbonate+oxalate) battery presented in the same work (≈2.75 V, OCV, see Fig.…”

“…1 of Ref. 14) or that of a Na-O 2 /(peroxide) battery (2.6 V, theoretical OCV). This experimental result indicates the feasibility of metal-air type batteries with CO 2 /oxalate cathodes, and also indicates that oxalate formation may be similarly energetic as peroxide formation when proper catalysts and electrolytes are used.…”

“…Such reactions would lead to the elimination of practical rechargeablity 12 , though for a primary, non-rechargeable battery, the addition of large amounts of CO 2 (≈ 20-80%) in the gas feed, as an assist to O 2 , leads to 2-3 fold increase of the realizable energy density of such primary batteries 13,14 . The carbonates produced from a mix of O 2 and CO 2 feed require very large overpotentials during the charging, at least as long as no catalyst will be found to reduce this overpotential to a practical value 10 .…”

“…Due to these features, oxalates are significantly safer discharge products than peroxides. Oxalates are also known to be easily and quantitatively oxidizable to CO 2 , in both aqueous and organic electrolytes on various types of electrodes, including graphite 14,16,24,26 . Thus, reversible electrochemistries can be based on CO 2 /oxalate conversions.…”