Enhanced Stability of Coated Carbon Electrode for Li‐O₂ Batteries and Its Limitations

Abstract

Li‐O2 batteries are promising next‐generation energy storage systems because of their exceptionally high energy density (≈3500 W h kg−1). However, to achieve stable operation, grand challenges remain to be resolved, such as preventing electrolyte decomposition and degradation of carbon, a commonly used air electrode in Li‐O2 batteries. In this work, using in situ differential electrochemical mass spectrometry, it is demonstrated that the application of a ZnO coating on the carbon electrode can effectively suppress side reactions occurring in the Li‐O2 battery. By probing the CO2 evolution during charging of 13C‐labeled air electrodes, the major sources of parasitic reactions are precisely identified, which further reveals that the ZnO coating retards the degradation of both the carbon electrode and electrolyte. The successful suppression of the degradation results in a higher oxygen efficiency, leading to enhanced stability for more than 100 cycles. Nevertheless, the degradation of the carbon electrode is not completely prevented by the coating, because the Li2O2 discharge product gradually grows at the interface between the ZnO and carbon, which eventually results in detachment of the ZnO particles from the electrode and subsequent deterioration of the performance. This finding implies that surface protection of the carbon electrode is a viable option to enhance the stability of Li‐O2 batteries; however, fundamental studies on the growth mechanism of the discharge product on the carbon surface are required along with more effective coating strategies.

Nonmacrocyclic Iron(II) Soluble Redox Mediators Leading to High-Rate Li–O 2 Battery

“…1,2 The rechargeable lithium-oxygen (Li-O 2 ) battery is an ideal candidate owing to its high theoretical energy density, compared with that of gasoline. [3][4][5][6] Despite the significant progress in enhancing the capacity and cycling stability in recent years, [7][8][9][10][11][12][13][14][15][16][17][18] the rate performance of Li-O 2 battery, to date, is quite limited to usually <0.5× A× g −1 cathode , which is a challenge, especially, for high energy conversion applications. 4,5 In Li-O 2 battery, the energy is stored via the oxygen evolution reaction (OER) process and released via the oxygen reduction reaction (ORR) process, both of which occur on the cathode.…”

“…20,21 For the achievement of high capacity, sp 2 carbon materials with large specific surface area, suitable pore structure and high conductivity are the most commonly used cathodes. [22][23][24] For improving cycling stability, usually, two categories of electrocatalysts have been developed, that is, the heterogeneous catalysts decorated on carbon-based cathode [12][13][14][15][16][24][25][26] and the soluble redox mediators employed in electrolyte. [7][8][9][10][11]18,[27][28][29][30][31] With heterogeneous catalysts, the insulated Li 2 O 2 product of the ORR process densely deposits on the cathode surface, leading to separation of the catalytic sites from the Li 2 O 2 surface exposed to the electrolyte.…”

Recent Progress on Catalysts for the Positive Electrode of Aprotic Lithium-Oxygen Batteries †

“…The composite of nano ZnO particles with a carbon coating was reported for the protection of carbon surface defects and the suppression of side reactions between carbon and Li 2 O 2 . By using isotope labeling method, they found a significant decrease in carbon dioxide releasing after the ZnO decorating [109]. Thus, a prolonged cycling life of 100 cycles was presented by this stabilized carbon positive electrode.…”

Strategies Toward Stable Nonaqueous Alkali Metal–O2 Batteries

“…Besides Al 2 O 3 , other inert metal‐oxide coatings were developed. Kang et al intensively investigated the stability of ZnO coated carbon cathode by using in situ differential electrochemical mass spectrometry (in situ DEMS) with labeled isotopic 13 C air electrode and 12 C TEGDME‐based electrolyte . With ZnO coating, the CO 2 evolution at charge was significantly retarded to 4.2 V. Meanwhile, the extent of oxygen evolution was one time higher, and the amount of CO 2 decreased about ≈60% compared with the pristine air electrode.…”