Grégory Gachot

Boron esters as tunable anion carriers for non-aqueous batteries electrochemistry.

Compounds like LiF, Li(2)O, and Li(2)O(2) have considerable importance in batteries; the first two are ubiquitous in the protective SEI at the negative electrode, or the result of conversion reactions with fluorides and oxides. The latter, Li(2)O(2,) forms from oxygen reduction in the much vaunted Li/air batteries. Mastering their solubility in Li-based electrolytes is viewed as essential for further progress in battery safety, lifetime, or capacity. Aprotic solvents cannot provide the H-bonds necessary to their dissolution, and simple practical solutions have yet to materialize. Here we disclose a novel and large family of boron esters of general formula Y-C((CH(2)O)(Z(1)O)(Z(2)O))B whose Lewis acidity stems from geometrical constraint and can be tuned via electron affinity either by Y = CH(3) --> Y = NO(2) or Z(1,2) = CH(2) --> Z(1,2) = CO so as to partially or fully dissolve the above compounds both in battery solvent EC/DMC and in DMF. The extreme simplicity of synthesis and variability of these boron-based anion carriers, where the exchange rate is fast, are not only a valuable addition to coordination science but also a step forward to improve present battery systems.

Comprehensive Insights into the Reactivity of Electrolytes Based on Sodium Ions

We report a systematic investigation of Na-based electrolytes that comprise various NaX [X=hexafluorophosphate (PF6 ), perchlorate (ClO4 ), bis(trifluoromethanesulfonyl)imide (TFSI), fluorosulfonyl-(trifluoromethanesulfonyl)imide (FTFSI), and bis(fluorosulfonyl)imide (FSI)] salts and solvent mixtures [ethylene carbonate (EC)/dimethyl carbonate (DMC), EC/diethyl carbonate (DEC), and EC/propylene carbonate (PC)] with respect to the Al current collector stability, formation of soluble degradation compounds, reactivity towards sodiated hard carbon (Nax -HC), and solid-electrolyte interphase (SEI) layer formation. Cyclic voltammetry demonstrates that the stability of Al is highly influenced by the nature of the anions, solvents, and additives. GC-MS analysis reveals that the formation of SEI telltales depends on the nature of the linear alkyl carbonates and the battery chemistry (Li(+) vs. Na(+) ). FTIR spectroscopy shows that double alkyl carbonates are the main components of the SEI layer on Nax -HC. In the presence of Na salts, EC/DMC and EC/DEC presented a higher reactivity towards Nax -HC than EC/PC. For a fixed solvent mixture, the onset temperature follows the sequence NaClO4

Gas chromatography/Fourier transform infrared/mass spectrometry coupling: a tool for Li-ion battery safety field investigation

As electric vehicles may have a positive impact on global warming, worldwide endeavour is devoted to improving the performance, durability and safety of Li-ion batteries considered as the most promising technology. To help the characterisation and identification of volatile compounds released upon batteries ageing or during a system malfunction-induced thermal event, we implemented the coupling of the gas chromatography (GC) technique with mass spectrometry (MS) and Fourier transform infrared (FTIR) analytical tools. Through two detailed examples related to the thermal runaway phenomenon and the battery swelling, this paper provides evidence that the complementarities of these techniques allow us to detect and then accurately identify a vast array of volatile molecules ensuing from electrochemically/chemically driven electrolyte degradation. Hence, this GC/FTIR/MS equipment will be powerful in studying the impact of new electrolyte molecules on the battery functioning or safety and in assessing its degradation state after long-term or unexpected premature capacity loss.

Paving the Way for K-Ion Batteries: Role of Electrolyte Reactivity through the Example of Sb-Based Electrodes

Developing potassium-ion batteries remains a challenge so far due to the lack of efficient electrolytes. Moreover, the high reactivity of K metal and the use of half-cells may greatly alter both the electrochemical performance and the solid electrolyte interphase formation. Here, it is shown that in K metal/Sb half-cells, Coulombic efficiency improvement is achieved by the addition of fluoroethylene carbonate + vinylene carbonate to propylene carbonate (PC), the replacement of PC by ethylene carbonate/diethyl carbonate, and the replacement of KPF6 by potassium bis(fluorosulfonyl)imide. Surprisingly, however, storage of cells containing K metal leads to the coloration of K metal, separators, and Sb electrodes, whereas no change occurs for cells prepared without K metal. These results demonstrate that for all electrolytes, the high electrolyte reactivity with K metal also influences the Sb/electrolyte interface via a cross-talk mechanism. This observation is supported by gas chromatography/mass spectrometry analysis of electrolytes and X-ray photoelectron spectroscopy analysis of Sb electrodes. In summary, these results indicate that the search for efficient electrolytes for potassium-ion batteries must be carried out in full cells if one wants to obtain meaningful correlations between electrochemical performance and electrode/electrolyte interfacial properties. Overall, the results presented here are also likely to benefit the development of other emerging Na- and Mg-ion cell chemistries.