Study of specific phase degradation of blended cathodes by high resolution in sitz synchrotron diffraction
M.S.D. Darma, M. Lang, K. Nikolowski, M. Knapp, V. Liebau, F. Fauth, H. Ehrenberg
2014
Recent development for Li ion battery commercialization is to use a blended system which consists of at least two types of cathode materials. Here we study a blended cathode system from a commercial cell consisting of a LiNiCoMnO 2 (NCM), LiNiCoAlO 2 (NCA) and LiMn 2 O 4 (LMO) mixture. In situ XRD for fresh and fatigued cathodes have been measured to follow structural change during cycling. From in situ XRD pattern, we can determine : (1) weight fraction (2) selective activity and (3) lattice
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... rameter of each phase during cycling. Based on the results, specific phase degradation in this cathode is discussed. Sample Preparation, Fatigued Protocol and Morphology Fatigue protocol Cathode morphology by SEM LMO, BoL NCA, BoL NCM, BoL Cycling condition BoL CL25 Number of cycling -1600 cycles Temperatur 25 °C 25 °C Charge/Discharge Rate -1C/2C Total Capacity Loss -13.5% 16.6 16.7 16.8 NCM 3.55 V 3.69 V 3.72 V Intensity [arb.unit] 2θ [degree] 110 NCA E = 29.9 keV NCM and NCA can be distinguished from their different electrochemical ativity: NCA actives below 3.72 V, NCM does not. NCM and NCA identification dQ vs E of individual component of composite cathode Sample preparation Cathode Separator Anode In situ cell Ex situ coin cell Cathode vs. Li Cell opening Washing, Cleaning, Stamping Primary particle ~100-500 nm Secondary particle ~ µm range NCM, CL25 LMO, CL25 NCA, BoL No significant morphology change of CL25 cathode compared to BoL cathode Cathodes from fresh (BoL) and fatigued cells are studied At room temperature cycling, degradation of our composite cathode is related to NCM and NCA phases. For NCM, origin of capacity loss is due to inactive phase at partially lithiated state (~30% NCM is inactive). No inactive NCA phase is found, however it is observed from XRD pattern that NCA of fatigued cathode is less active than fresh cathode. Lattice parameter evolution of fresh and fatigued battery reveals that LMO phase is not degraded. To get more understanding of degradation mechanism, surface sensitive analysis will be performed. ESR experiment wil also be performed to investigate the reason for decreasing lattice parameter c of NCA at higher potential which might be related to capacity loss of NCA. Summary and Outlook 4.9 5.0 5.1 Intensity [arb.unit] 2θ [degree] CL25 B
doi:10.5445/ir/220097896
fatcat:xzwyixnavbd3hmpzywwsnlxsmy