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An aging model for a negative graphite electrode in a lithium-ion battery, for moderate currents up to 1C, is derived and fitted to capacity fade experimental data. The predictive capabilities of the model, using only four fitted parameters, are demonstrated at both 25 • C and 45 • C. The model is based on a linear combination of two current contributions: one stemming from parts of the graphite particles covered by an intact microporous solid-electrolyte-interface (SEI) layer, and one contribution from parts of the particles were the SEI layer has cracked due to graphite expansion. Mixed kinetic and transport control is used to describe the electrode kinetics. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0641506jes] All rights reserved.Manuscript submitted December 19, 2014; revised manuscript received February 6, 2015. Published March 10, 2015 Lithium-ion batteries are used in all sorts of electric devices such as mobile phones, lawn mowers, electrical scooters and electric cars. Common for all lithium-ion battery chemistries is that they suffer from aging phenomena over time. Degradation occurs during storage, but is further induced by battery cycling and higher temperatures. Life time degradation generally occurs due to various processes such as electrolyte decomposition, loss of active material and loss of cycleable lithium due to parasitic reactions. 1The most common negative electrode material in lithium-ion batteries is graphite. For cells deploying negative graphite electrodes, significant amounts of cycleable lithium is lost into forming the solidelectrolyte-interface (SEI) layer on the graphite surface. The initial SEI formation during the first "formation" cycles of the battery is most pronounced, but, depending on operation conditions, the SEI layer formation will continue during the whole lifetime of the battery. The SEI layer is not homogeneous, neither with regards to morphology nor composition. Cracks are known to form upon battery cycling, 2 and various chemical compounds have been observed.2,3 Experimental work has shown that for low currents (≤C/10) the long term capacity loss usually follows a t 1/2 dependence, and models in literature usually ascribes this dependence to a diffusion limitation through the SEI layer of a reacting species in the electrolyte that participates in forming the SEI layer. [4][5][6] This paper focuses on SEI formation on graphite at moderate load currents (≤1C) at both 25• C and 45• C. For these conditions it has been shown that the SEI formation is the main cause of battery degradation. 7Although not treated explicitly, the positive electrode material is assumed to be LiFePO 4 (LFP) since it has been seen that this positive electrode material does not suffer from nor cause significant degrada...

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An isothermal two-dimensional liquid phase model for the conservation of mass, momentum, and species in the anode of a direct methanol fuel cell ͑DMFC͒ is presented and analyzed. The inherent electrochemistry in the DMFC anode active layer is reduced to boundary conditions via parameter adaption. The model is developed for the case when the geometry aspect ratio is small, and it is shown that, under realistic operating conditions, a reduced model, which nonetheless describes all the essential physics of the full model, can be derived. The significant benefits of this approach are that physical trends become much more apparent than in the full model and that there is considerable reduction in the time required to compute numerical solutions, a fact especially useful for wide-ranging parameter studies. Such a study is then performed in terms of the three nondimensional parameters that emerge from the analysis, and we subsequently interpret our results in terms of the dimensional design and operating parameters. In particular, we highlight their effect on methanol mass transfer in the flow channel and on the current density. The results indicate the relative importance of mass-transfer resistance in both the flow channel and the adjacent porous backing.

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