Degradation of spinel lithium manganese oxides by low oxidation durability of LiPF6-based electrolyte at 60 °C

The manganese dissolution behavior of lithium hexafluorophosphate (LiPF6) dissolved in carbonate-based organic solvents is investigated by ex situ field emission scanning electron microscope (FE-SEM), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and inductively coupled plasma (ICP). It is found that the LiPF6 salt anions in the electrolytes are prone to oxidize upon contacting delithiated lithium manganese oxide with high oxidizing power and the electrons that evolved from the oxidation of anions are consumed in the reduction of tetravalent manganese ions to trivalent manganese ions at 60 °C. The generated trivalent manganese ions readily undergo a disproportion reaction and thereby release divalent manganese ions into the electrolytes, which leads to a capacity loss in the lithium manganese oxide cathode.

► A reasonable mechanism for Mn dissolution was demonstrated.
► Reduction of Mn4+ ions to Mn3+ ions by accepting electrons from PF6− anions
► LiPF6-based electrolytes lead to the considerable Mn dissolution at 60 °C.