Journal
JOURNAL OF POWER SOURCES
Volume 269, Issue -, Pages 920-926Publisher
ELSEVIER
DOI: 10.1016/j.jpowsour.2014.07.051
Keywords
Lithium ion battery; Electrolyte; High voltage cathode; Ex-situ surface analysis
Funding
- BASF SE Scientific Network on Electro-chemistry and Batteries
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Layered Li(Ni1/3Co1/3Mn1/3)O-2 (NCM) materials have been investigated at high working potential and elevated temperature to correlate electrochemical performance with changes to the electrode interface. Graphite/NCM cells were cycled to either 4.2 or 4.5 V vs Li/Li+ at room temperature (25 degrees C) followed by moderately elevated temperature (55 degrees C). Cells cycled to 4.2 and 4.5 V have similar capacity retention, but the cells cycled to 4.5 V have poorer first cycle efficiency, efficiency upon cycling at 55 degrees C, and greater increases in cell resistance. Surface analyses indicate thicker surface films on the cathode after cycling to 4.5 V, compared to cycling at a lower voltage of 4.2 V. The thicker surface film on the cathode is the result of electrolyte oxidation to generate poly(ethylene carbonate) and lithium alkyl carbonates. Electrochemical impedance spectroscopy of three-electrode cells reveals that the cathode dominates the cell impedance and the cathode impedance is much greater for cells cycled to 4.5 V than cells cycled to 4.2 V. (C) 2014 Elsevier B.V. All rights reserved.
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