Over the past decades, many scientific discoveries in material science have allowed Li-ion batteries to become the most effective way to store energy in portable devices. However, their implementation in more demanding applications such as long range electrical vehicles requires an increase of their energy density [1]. The quest towards better performances is exploring alternative technologies, such as the Lithium-Oxygen (Li-O₂) technology, which offers a very high theoretical capacity [1]. Non-aqueous Li-O₂ batteries lie on the overall electrochemical reaction: 2 Li + O_{2 (g)} ↔ Li₂O₂ (± 2 e^-), which enlists the reversible uptake and removal of one mole of dioxygen every 53.6 Ah (corresponding to 2 moles of electron). Although the reaction is simple, mastering the Li-O₂ chemistry remains an enormous challenge. This calls for a better understanding of fundamental mechanism of the overall chemistry. It involves the monitoring of gaseous species which requires the development of unconventional tools enabling an accurate investigation of these battery systems.

This need was an impetus to design a new electrochemical cell as reported herein. It integrates a pressure sensor enabling to accurately monitor with high reproducibility and sensitivity in operando pressure changes during charge/discharge without disturbing the cell system [2]. Its friendly use is demonstrated by quantifying the amount of parasitic reaction in Li-O₂ cells based on a carbon cathode with various electrolytes frequently encountered in the literature, such as LiTFSI in DME, DEGDME and TEGDME; LiNO₃ in DMA [3], and LiClO₄ in DMSO. Through this comparative study based on pneumatic data, we were able to easily observe the phenomena currently limiting the performances of Li-O₂ batteries such as electrolyte instability, oxidation of the carbon electrode and the role of impurity contamination [4]. Moreover, aging of such cells was investigated, showing for all systems a formatting process occurring during the first cycles, hence the importance of the set-up reported herein enabling easy gas monitoring over unlimited number of cycles.

Finally, this technology is directly transferable to the study of every material whose electrochemical behavior enlists gas uptake and release such as Li-rich layered compounds [5], organic electrode materials and other metal-air batteries.

1          P. G. Bruce, S. A. Freunberger, L. J. Hardwick and J.-M. Tarascon, Nat. Mater., 2012, 11, 19–29.

2          F. Lepoivre, A. Grimaud, D. Larcher and J.-M. Tarascon, Submitted to JES, 2015.

3          V. Giordani, W. Walker, V. S. Bryantsev, J. Uddin, G. V. Chase and D. Addison, J. Electrochem. Soc., 2013, 160, A1544–A1550.

4          K. U. Schwenke, S. Meini, X. Wu, H. A. Gasteiger and M. Piana, Phys. Chem. Chem. Phys., 2013, 15, 11830.

5          E. McCalla, A. S. Prakash, E. Berg, M. Saubanère, A. M. Abakumov, D. Foix, B. Klobes, M.-T. Sougrati, G. Rousse, F. Lepoivre and others, J. Electrochem. Soc., 2015, 162, A1341–A1351.