291. High Temperature Testing of NMC/Graphite Cells for Rapid Cell Performance Screening and Studies of Electrolyte Degradation
LiNi0.5Mn0.3Co0.2O2/graphite cells with two different electrolytes underwent charge-discharge cycling at 70 ºC. The 70 ºC condition reduced the time it took for cells to lose significant capacity. Studies of the changes to the electrolyte after cycling by gas chromatography/mass spectrometry (GC/MS) and by Nuclear Magnetic Resonance spectroscopy (NMR) suggest that the same processes which cause cell failure and electrolyte degradation at 40 ºC and 55 ºC occur at 70 ºC, only at an accelerated rate. Transition metal dissolution from the positive electrode was tracked using X-ray fluorescence studies of the negative electrode after testing. Based on the confidence obtained that the same degradation processes were occurring; advanced graphites were screened in NMC811/graphite cells at 70 ºC. Differences in cell lifetime were apparent in weeks at 70 ºC while the same differences took much longer to observe at 40 ºC. It is our opinion that elevated temperature testing of Li-ion cells at 70 ºC is a viable rapid screening technique for advanced electrolytes and advanced electrode materials.