Evaluation of cyclic aging tests of prismatic automotive LiNiMnCoO2-Graphite cells considering influence of homogeneity and anode overhang. (August 2018)

• Record Type: Journal Article
• Authors: Lewerenz, Meinert; Sauer, Dirk Uwe
• Is Part Of: Journal of energy storage. Volume 18(2018)
• Page Start: 421
• Page End: 434
• Publication Date: 2018-08
• Subjects: CDA capacity difference analysis -- FCE full cycle equivalents -- DVA differential voltage analysis -- DOD depth-of-discharge -- HLD homogeneity of lithium distribution -- OCV open circuit voltage -- SOC state-of-charge; Shallow cycling -- Anode overhang -- Pressure -- Homogeneity of lithium distribution -- SOC dependency; Energy storage -- Periodicals; Energy storage -- Research -- Periodicals; 621.3126
• DOI: 10.1016/j.est.2018.06.003
• Languages: English
• ISSNs: 2352-152X

Abstract

Graphical abstract: Highlights: Capacity fade in compressed cells is lowest around 50% SOC and increases to 0% and 100% SOC, respectively. Capacity trend strongly depends on anode potential and pressure. Lithium distribution occurs in distinct SOCs or follows Gaussian distribution. Inhomogeneities remain stable for low potential difference on the anode. Capacity difference and dV/dQ are good methods to measure homogeneity. Abstract: Cyclic aging tests of 20 compressed prismatic automotive Li(NiMnCo)O2 |Graphite cells are evaluated. The shallow cyclic aging tests are conducted around five average SOCs with respect to the anode. The cells are cycled at two DODs and two C-rates. The irreversible capacity loss is evaluated by the slope of the near-linear part at the end of aging test. The homogeneity of lithium distribution (HLD) is associated with peak height of differential voltage analysis (DVA) and to capacity difference analysis (CDA). The evaluations of DVA, CDA and capacity fade curve are depending mainly on the average SOC and hardly on DOD or C-rate. The trends correlate with the volume expansion originated from the graphite. The highest HLD and the lowest capacity fade are reached around 50% SOC where hardly any additional volume expansion occurs. In the SOC regions with high volume expansion of the graphite the HLD reduces dramatically and the capacity fade rises towards 0% and 100%, respectively. Due to smeared characteristics in DVA, capacity loss cannot be directly separated into shares related to anode overhang, HLD, loss of active material and residual irreversible losses. The combination of cell compression and high gradients of volume expansion during shallow cycling is found to be the root cause for the flattening of DVA curves.