Synergistic effect of fluorinated solvent and Mg2+ enabling 4.6 V LiCoO2 performances

Increasing the charging cut-off potential of lithium cobalt oxide (LiCoO2, LCO) can effectively improve the energy density of the lithium-ion batteries, which are the mainstream energy storage devices used in 3C electronic products. However, the continuous decomposition of the electrolyte and dissolution of Co from the electrode will occur at high-potential operation, which deteriorate the performances of LCO. Here, a cathode-electrolyte interface (CEI) layer containing MgF2 is constructed to enhance the electrochemical stability of LCO at 4.6 V (vs. Li+/Li). The Mg2+ added to the cathode gradually releases into the electrolyte during cycling, which forms a stable MgF2-rich protective layer. In addition, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) is added to the electrolyte acting as a F source to increase the content of MgF2 in the CEI layer. The MgF2-rich CEI layer effectively suppresses the decomposition of electrolyte components and the dissolution of Co of LCO, which makes the Li||LiCoO2 (Li||LCO) cell cycled stably at 3∼4.6 V (vs. Li+/Li) in 200 cycles with a retention of 83.9%.