Robust NaO₂ Electrochemistry in Aprotic Na–O₂ Batteries Employing Ethereal Electrolytes with a Protic Additive

Abstract

Aprotic metal-oxygen batteries, such as Li-O2 and Na-O2 batteries, are of topical research interest as high specific energy alternatives to state-of-the-art Li-ion batteries. In particular, Na-O2 batteries with NaO2 as the discharge product offer higher practical specific energy with better rechargeability and round-trip energy efficiency when compared to Li-O2 batteries. In this work, we show that the electrochemical deposition and dissolution of NaO2 in Na-O2 batteries is unperturbed by trace water impurities in Na-O2 battery electrolytes, which is desirable for practical battery applications. We find no evidence for the formation of other discharge products such as Na2O2·H2O. Furthermore, the electrochemical efficiency during charge remains near ideal in the presence of trace water in electrolytes. Although sodium anodes react with trace water leading to the formation of a high-impedance solid electrolyte interphase, the increase in discharge overpotential is only ∼100 mV when compared to cells employing nominally anhydrous electrolytes.

Sodium Peroxide Dihydrate or Sodium Superoxide: The Importance of the Cell Configuration for Sodium–Oxygen Batteries

“…Ortiz‐Vitoriano et al discovered that even when the water content is as high as 6000 ppm, NaO 2 is still the major discharge product except when exposing NaO 2 to air. [3c,16] It is very unlikely that the GC cell has a huge amount of water (≫6000 ppm) from the air before discharge but the peroxide‐based product is observed at the beginning of the discharge. Nevertheless, the formation of the peroxide‐based product requires water either from the air atmosphere or the decomposition of the solvent.…”

Ion Pairing Limits Crystal Growth in Metal–Oxygen Batteries

“…4c for the cells shows that the discharge is a 1e -/O 2 process, which is clearly indicative of the formation of NaO 2 14,39,49 . In addition, both X-ray diffraction and Raman spectroscopy confirm that NaO 2 is the only observable discharge product 39 (supplementary Figs. S6 and S7).…”

Electrolyte Additives for Room‐Temperature, Sodium‐Based, Rechargeable Batteries

“…The effect of H 2 O as an additive to liquid electrolytes and its accompanying role on the stripping/plating performance of sodium metal was recently studied . The addition of 500 ppm of H 2 O to N ‐methyl‐ N ‐propylpyrrolidinium bis(fluorosulfonyl)imide promoted the decomposition of the bis(fluorosulfonyl)imide (FSI) anion, leading to the formation of a more regular SEI layer on sodium metal with lower polarization and smooth in morphology …”

“…The effect of H 2 Oa sa na dditive to liquid electrolytes and its accompanying role on the stripping/plating performance of sodiumm etal was recently studied. [70,71] The addition of 500 ppm of H 2 Ot oN-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide promoted the decomposition of the bis(fluorosulfonyl)imide (FSI) anion, leadingt ot he formation of am ore regularS EI layer on sodium metal with lower polarization and smooth in morphology. [71] Inspired by the analogues use of Li 2 S n ÀLiNO 3 in the LiÀSb attery,L ia nd co-workers evaluated sodium polysulfide( Na 2 S 6 ) alone and as ac oadditive with sodium nitrate (NaNO 3 )i n ether-based electrolyte.…”