A high-rate and high-efficiency molten-salt sodium–oxygen battery. Issue 11 (27th September 2022)

• Record Type: Journal Article
• Authors: Zhu, Yun Guang; Leverick, Graham; Accogli, Alessandra; Gordiz, Kiarash; Zhang, Yirui; Shao-Horn, Yang
• Is Part Of: Energy & environmental science. Volume 15:Issue 11(2022)
• Page Start: 4636
• Page End: 4646
• Publication Date: 2022-09-27
• Subjects: Energy conversion -- Periodicals; Fuel switching -- Periodicals; Environmental sciences -- Periodicals; Environmental chemistry -- Periodicals; 333.79
• DOI: 10.1039/d2ee01774a
• Languages: English
• ISSNs: 1754-5692

Abstract

Abstract : A molten-salt Na–O2 battery featuring a liquid Na negative electrode and Ni positive electrode was found to form Na2 O2 on discharge, enabled by nitrate redox where NO3 − is reduced to Na2 O and NO2 −, then reactions with O2 produce Na2 O2 and reform NO3 − . Abstract : Alkali metal–oxygen batteries can provide greater specific energy than Li-ion batteries but often suffer from low power density, cycleability, and energy efficiency due to the sluggish kinetics of the oxygen electrode and parasitic reactions at both the oxygen and alkali metal electrodes. In this study, we demonstrated a molten-salt Na–O2 battery operating at 443 K with high areal energy (33 mW h cm −2 geo ) and power densities (19 mW cm −2 geo ), with high energy efficiency (∼90% at 5 mA cm −2 geo ), and stable cycling (400 cycles with no capacity loss). Raman, pressure tracking and titration measurements were used to show that the dominant discharge product is Na2 O2 . Moreover, the redox activity of nitrate anions in the molten salt was found to be critical to enable the formation of Na2 O2 . Through 18 O-labeling experiments as well as discharging Na–Ar cells, we demonstrated that the discharge reaction occurs via the electrochemical reduction of NaNO3 to Na2 O and NaNO2, where chemical reactions with O2 lead to the formation of Na2 O2 from Na2 O, and the regeneration of NaNO3 from NaNO2 .