Reactivity of Li[sub y][Ni[sub x]Co[sub 1−2x]Mn[sub x]]O[sub 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, 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. 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 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 4.2 V) and EC/DEC solvent or 1 M EC/DEC until approximately 170°C, compared to a 140°C onset temperature for 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 with is significantly worse for samples charged to 4.4 V. By contrast, samples with 0.35, 0.45, or 0.5 show almost identical excellent thermal stability at both 4.2 and 4.4 V.