Reactivity of Li y [ Ni x Co1 − 2x Mn x ] O 2 ( x = 0.1 , 0.2, 0.35, 0.45, and 0.5; y = 0.3 , 0.5) with Nonaqueous Solvents and Electrolytes Studied by ARC

Samples of the layered cathode material, Li[Ni x Co 1 - 2 x Mn x ]O 2 (x = 0.1, 0.2, 0.35, 0.45, and 0.5), were synthesized at 900°C, fabricated into electrodes, and charged to both 4.2 and 4.4 V vs. Li/Li + . The charged electrode materials were rinsed to remove the electrolyte salt and then added, along with ethylene carbonate (EC)/diethyl carbonate (DEC) solvent or 1 M LiPF 6 EC/DEC, to stainless steel accelerating rate calorimetry (ARC) sample holders that were welded closed. ARC shows that there is no significant exothermic reaction between Li 0 . 5 [Ni 0 . 1 Co 0 . 8 Mn 0 . 1 ]O 2 (x = 0.1, 4.2 V) and EC/DEC solvent or 1 M LiPF 6 EC/DEC until approximately 170°C, compared to a 140°C onset temperature for LiCoO 2 charged to 4.2 V. As x increases from 0.1 to 0.2, the onset temperature for materials charged to 4.2 V does not change significantly, but the main exothermic peak shifts significantly to higher temperatures. However, the thermal stability of Li[Ni x Co 1 - 2 x Mn x ]O 2 with x = 0.1 is significantly worse for samples charged to 4.4 V. By contrast, samples with x = 0.2, 0.35, 0.45, or 0.5 show almost identical excellent thermal stability at both 4.2 and 4.4 V.