A Comparison Between the High Temperature Electrode /Electrolyte Reactions of Li[sub x]CoO[sub 2] and Li[sub x]Mn[sub 2]O[sub 4]

Accelerating rate calorimetry (ARC) is used to compare the reactions between (4.2 V) or (4.2 V) and an equal mass of 1 M (ethylene carbonate/diethyl carbonate) electrolyte. The ARC results show that under these conditions, the self-heating rates and hence thermal power are significantly larger for than for This result is not consistent with the results of oven exposure tests on 18650 size cells using the same materials, where higher temperatures are needed to initiate thermal runaway for cells with cathodes. The amount of reaction heat generated by the reaction of with 1 M electrolyte is independent of the electrode/electrolyte mass ratio (at least for the first reaction process), while that generated by the reaction of with electrolyte increases with electrolyte amount. ARC experiments using an approximate 1:6 electrolyte to electrode mass ratio, which mirrors the conditions found in 18650 cells, demonstrate that is much more reactive than as is observed in commercial cells. The work presented here suggests that the safety of Li-ion cells using cathodes can be improved by decreasing the positive electrode porosity. © 2001 The Electrochemical Society. All rights reserved.