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

Abstract

Samples of the layered cathode material, Li[NixCo1−2xMnx]O2Li[NixCo1−2xMnx]O2 (x=0.1,(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+.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 LiPF6LiPF6 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 Li0.5[Ni0.1Co0.8Mn0.1]O2Li0.5[Ni0.1Co0.8Mn0.1]O2 (x=0.1,(x=0.1, 4.2 V) and EC/DEC solvent or 1 M LiPF6LiPF6 EC/DEC until approximately 170°C, compared to a 140°C onset temperature for LiCoO2LiCoO2 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[NixCo1−2xMnx]O2Li[NixCo1−2xMnx]O2 with x=0.1x=0.1 is significantly worse for samples charged to 4.4 V. By contrast, samples with x=0.2,x=0.2, 0.35, 0.45, or 0.5 show almost identical excellent thermal stability at both 4.2 and 4.4 V. © 2005 The Electrochemical Society. All rights reserved.