Improving performances of cathode-electrolyte interphase via the potentiostatic reduction of lithium bis(fluorosulfonyl)imide additive

The low concentration electrolyte shows the advantages of low viscosity and low cost, but the formation of porous and soluble organic cathode-electrolyte interphase (CEI) limits its performance. Herein, the electrochemical performance of the low concentration electrolyte of 0.45 M LiPF6‑diethyl carbonate (DEC)/ ethylene carbonate (EC) (1:1, in volume ratio) is improved by 0.05 M bis(fluorosulfonyl)imide (LiFSI) additive, aided by the antecedent process of potentiostatic reduction at a low potential of 1.5 V. Results show that LiFSI is preferentially reduced via breaking the structure of FSI− anion to form a robust LiF-rich CEI on the surface of LiFePO4 (LFP) cathode, solving the problem that it is difficult to form inorganic LiF on the cathode surface. In the subsequent cycling of LFP/Li half-battery, the as-formed CEI inhibits the corrosion of aluminum collector, suppresses the excessive decomposition of the electrolyte and improves the diffusion of Li+, resulting in a much-enhanced cycle stability of the cathode. Therefore, the cyclic performance of the LFP/Li half-battery using the modified low concentration electrolyte with the antecedent process of potentiostatic reduction is on a par with that using the standard electrolyte (1.0 M LiPF6-DEC/EC). Compared with the traditional electrolyte engineering of constructing a LiF-rich CEI by the direct oxidation defluorination of fluorinated anions, this strategy needs a lower reaction energy and can play a positive role at a lower reaction potential. This work provides an effective way to construct LiF-rich CEI which helps to improve the performance of low concentration electrolytes.