Organic/inorganic hybrid quaternary ionogel electrolyte with low lithium-ion association and uniform lithium flux for lithium secondary batteries

Abstract

High-energy-density lithium secondary batteries require high-voltage electrolyte. Ionic liquids with wide electrochemical window have been regarded as promising electrolyte candidate for high-safety electrochemical devices. However, the solvation state of lithium ions severely restricts the conductivity due to the sluggish kinetics of lithium-ion cluster. Moreover, the leakage risk also impedes its practical application. Here, we propose to mitigate the above issues by designing organic/inorganic hybrid quaternary ionogel electrolyte (PSIL). The key to our strategy is promoting the dissociation of Li (TFSI)2− cluster and increasing the percentage of free Li+ in the ionogel electrolyte. The amorphous matrix formed by PEO and SiO2 increases the interaction between Li+ and PEO, reducing the association of Li (TFSI)2− cluster. And then, the synergistic transportation of lithium ions by PEO and ionic liquid promises the high conductivity of PSIL. As a result, the ionogel electrolyte shows a high conductivity of 1.50 ×10−3 S•cm−1at 20 ℃. The impressive electrochemical performance with LiFePO4 cathode indicates the high compatibility with the electrode. The ex-situ SEM and molecular dynamic simulation both demonstrate the uniform transportation of lithium ions during the electrochemical process and indicate the successful design for the quaternary ionogel electrolyte.