Improved thermal stability of Li-rich layered oxide by fluorine doping

Abstract: Thermal stability of Lithium-rich layered oxide with the composition Li(Li1/6Ni1/6Co1/6Mn1/2)O2-xFx (x=0.00 and 0.05) was evaluated for use as a cathode material in lithium ion batteries. Thermogravimetric analysis, evolved gas analysis, and differential scanning calorimetry showed 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 revealed that the prismatic cell with the fluorine-doped powder did not explode, while that with undoped one exploded at ~135°C with a sudden temperature increase. X-ray diffraction analysis indicated that fluorine doping imparts the lithium-rich layered oxide with better thermal stability by mitigating the oxygen release at elevated temperatures that causes the exothermic reaction with electrolyte. The origin of the reduced oxygen release from the fluorinated lithium-rich layered oxide was also discussed.