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4-methyl-2- [(2,2,3,3,4,4,5,5-octafluoropentyl)oxy]-1,3,2-dioxaphosphinane with the oxidation number of phosphorous (III) is used as an oxidative additive (OA) to a standard carbonate-based electrolyte for the high-voltage Li-ion cells with the overlithiated layered oxide Li 1.20 Ni 0.18 Mn 0.53 Co 0.09 O 2 (OLO) as a positive electrode. Electrochemical stability of electrolytes with and without OA is compared by linear sweep voltammetry, and characteristics of coin half and full cells are examined by means of cycling tests and electrochemical impedance spectroscopy. Presence of OA in electrolyte mixture provides noticeable improvement in Coulombic efficiency, capacity retention, and rate properties of the cells, most likely, through the formation of an interface layer on the OLOsurface due to the decomposition of OA. Morphology of OLO after cycling with OA-containing electrolyte is investigated by scanning electron microscopy and the presence of amorphous coating is observed; 31 P NMR analysis reveals that the products by the oxidation of OA are present on the cathode's surface. Differential scanning calorimetry data point out the substantially improved thermal stability of the OLO cathode after cycling in OA-containing electrolyte. Therefore, substituted dioxaphosphinanes may be considered as a promising structural pattern for design of new additives for the development of high-voltage electrolytes.

The thermal stability of lithium‐rich layered oxide with the composition Li(Li1/6Ni1/6Co1/6Mn1/2)O2−xFx (x=0.00 and 0.05) is evaluated for use as a cathode material in lithium‐ion batteries. Thermogravimetric analysis, evolved gas analysis, and differential scanning calorimetry show that, upon fluorine doping, degradation of the lithium‐rich layered oxides commences at higher temperatures and the exothermic reaction is suppressed. Hot box tests also reveal that the prismatic cell with the fluorine‐doped powder does not explode, whereas that with the undoped one explodes at about 135 °C with a sudden temperature increase. XRD analysis indicates that fluorine doping imparts the lithium‐rich layered oxide with better thermal stability by mitigating oxygen release at elevated temperatures that cause an exothermic reaction with the electrolyte. The origin of the reduced oxygen release from the fluorinated lithium‐rich layered oxide is also discussed.

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