Identifying compatibility of lithium salts with LiFePO4 cathode using a symmetric cell

The electrochemical performance of lithium-ion batteries is dominated by the interphase electrochemistry between the electrolyte and electrode materials . A multitude of efforts have been dedicated to the solid electrolyte interphase (SEI) formed on the anode. However, the interphase on the cathode, namely the cathode electrolyte interphase (CEI), is left aside, partially due to the fact that it is hard to single out the CEI considering the complicated anode-cathode inter-talk. Herein, a partially delithiated lithium iron phosphate (Li 0.25 FePO 4 ) electrode is used as the anode. Owing to a high voltage plateau (≈3.45 V vs. Li/Li + ), negligible reduction reactions of electrolyte occur on the L 0.25 FePO 4 anode. Therefore, the CEI can be investigated exclusively. Using a LiFePO 4 |Li 0.25 FePO 4 symmetric cell configuration, we scrutinize the compatibility of the electrolytes containing a wide spectrum of lithium salts , Li[(FSO 2 )(C m F 2m+1 SO 2 )N] (m = 0, 1, 2, 4), with the LiFePO 4 , in both cycling and calendar tests. It is found that the Li[(FSO 2 )( n -C 4 F 9 SO 2 )N] (LiFNFSI)-based electrolyte exhibits the highest compatibility with LiFePO 4 .