New insight in the electrochemical behaviour of stainless steel electrode in water-in-salt electrolyte

Aqueous electrolytes containing a very high concentration of salt are useful for improving the performance of aqueous rechargeable batteries. These electrolytes, which contain a higher mole concentration of salt than that of water, have only a small amount of free water. Consequently, the electrochemical stability window of various electrodes in such electrolytes is wider than the predicted thermodynamic value of 1.23 V. Moreover, the formation of a solid electrolyte interphase on the negative electrode surface also contributes to the larger electrochemical stability window. In this work, we found that a redox wave corresponding to the electrochemical reduction of bis(trifluoromethylsulfonyl)imide anions in a highly concentrated (21 molal) solution of lithium bis (trifluoromethylsulfonyl)imide is barely observed when the potential range that the electrode is cycled is limited to between 0 and - 1.8 V.