Interrogation of the Reaction Mechanism in a Na–O₂ Battery Using In Situ Transmission Electron Microscopy

Abstract

Critical factors that govern the composition and morphology of discharge products are largely unknown for Na− O 2 batteries. Here we report a reversible oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) process in a sodium−oxygen battery observed using in situ environmental-transmission electron microscopy (TEM) experiment. The reaction mechanism and phase evolution are probed using in situ electron diffraction and TEM imaging. The reversible ORR and OER cycling lies upon the nanosized copper clusters that were formed in situ by sodiation of CuS. In situ electron diffraction revealed the formation of NaO 2 initially, which then disproportionated into orthorhombic and hexagonal Na 2 O 2 and O 2 . Na 2 O 2 was the major final ORR product that uniformly covered the whole wire-shape cathode. This uniform product morphology largely increased the application feasibility of Na− O 2 batteries in industry. In the following OER process, the Na 2 O 2 transformed to NaO 2 , which resulted in volume expansion at first, and then the NaO 2 decomposed to sodium ions and O 2 gas. Galvanostatic charge/discharge profiles of CuS in real Na− O 2 cells revealed a maximum capacity over 3 mAh cm −2 with a discharge cutoff voltage of 1.8 V and high cycling stability. The nanosized copper catalyst plays a dominating role in controlling the morphology, chemical composition of discharge products, and reversibility of this Na−O 2 battery. Our finding shines light on the exploration of effective catalysts for the Na−O 2 battery.

In situ TEM visualization of single atom catalysis in solid-state Na–O2 nanobatteries

“…The plateau voltages of the rst discharge curves were slightly higher than in the following cycles, which may be attributed to the sodiation process of the electrode materials. 31 The discharge voltages of the battery with an SA-Co/rGO cathode at all cycles were higher than 2 V, which is close to the theoretical discharge voltage of Na 2 O 2 (2.33 V). 32,33 The main charge plateau was at $4 V, in good agreement with the reported decomposition voltage of Na 2 O 2 .…”

“…32 The slight slope in the charge process between 2.5 and 3.5 V may correspond to the decomposition of NaO x . 31 These results indicate the higher catalytic activity and stability of the SA-Co/rGO cathode than that of rGO in coin cell Na-O 2 batteries. Furthermore, cycling tests (Fig.…”

Unraveling the reaction mechanisms of electrode materials for sodium‐ion and potassium‐ion batteries by in situ transmission electron microscopy

“…[77,78] Insights into the reaction of those metal-air batteries via in situ TEM, including the mechanism of the products formation and dynamic changes along the reactions, is of great urgency. [79,80] The copper-based catalyst used in the Na-O 2 battery has been reported by Gu et al [81] 8C-F). The decomposition of instable NaO 2 phase into Na 2 O 2 and O 2 is also identified by in situ TEM analysis.…”

3D Ag@C Cloth for Stable Anode Free Sodium Metal Batteries

“…By virtue of enticing theoretical capacity (1165 mAh g −1 ), desirable redox potential (–2.71 V vs SHE) and materials abundance, sodium metal anode (SMA) [ 1 ] would substantially boost energy density and feasibility of conventional sodium ion batteries (SIBs). [ 2 ] Furthermore, SMA also plays as an indispensable component for many novel Na‐S/Se/Te, [ 3 ] Na‐P, [ 4 ] Na‐O 2 , [ 5 ] Na‐CO 2 , [ 6 ] and Na‐Br/I systems. [ 7 ] For these reasons, SMA chemistry is currently an important research area for building advanced sodium ion batteries (SIBs).…”