Modeling Cyclic Capacitive Loading of Thin-Film Batteries

Abstract

Previous modeling of thin-film batteries has primarily looked at simple discharge loads. This work examines modeling of midfrequency dynamic loads with large variation in current during repetitive loading cycles, a type of loading that is very common in microelectromechanical system (MEMS) applications. Here we show an extension of traditional modeling of thin-film batteries to account for switching and capacitive loading representing piezoelectric or electrostatic microactuation. This model captures behavior at both fast and slow timescales, including effects of short-duration, high-current spikes. We show validation of the model and introduce a cycle projection scheme that allows for over 94% reduction in numerical calculations over a full battery discharge which includes over a million cycles. © The Author(s) 2017. 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: 10.1149/2.1141702jes] All rights reserved.Manuscript submitted October 6, 2016; revised manuscript received December 2, 2016. Published January 5, 2017.Limitations of available power sources, such as batteries, place significant constraints on design of engineered systems at many scales, from vehicles to microelectromechanical systems (MEMS).1 Battery modeling can be used to help navigate these limitations, and many different modeling approaches have been developed. 2,3 This work focuses on adapting existing modeling approaches to capture cyclic, capacitive loading (i.e. repeated charging of a load that behaves approximately like a capacitor) of thin-film batteries, a loading which is very common in, for example, MEMS applications. Additionally, for small-scale systems, all-solid-state batteries are an attractive alternative to more traditional liquid electrolyte constructs in that sealing of the liquid electrolyte is avoided, 4 generally providing better size and assembly compatibility with micromachined devices. These solid electrolytes typically have lower ionic conductivities, but the effects of this are mitigated by the reduced thickness at which these thin films can be deposited.5 Various studies have looked at the different properties of various battery chemistries and configurations, [5][6][7][8][9][10][11][12] which is still a very active area of research. However, modeling of cyclic capacitive loads seems to be lacking in the literature.Understanding the implications of cyclic loading on batteries is important. There have been mixed reports on the broader loading category of intermittent loads on batteries at various scales. Several reports have indicated that loading conditions can have substantial effects on the battery output ability. Fuller et al.13 discussed different relaxation phenomena in lithium-ion insertion batteries. Feeney et al.14 recently demonstrated, on a specific primary Li-ion battery...

An advanced all-solid-state Li-ion battery model

“…This suggests that the spacecharge layers in this particular ASSB do not have a large influence on the static (DC) discharge curves and, thus, on the overall performance, which has also been concluded by others [26,42]. However, this might be different for ASSB that are used in, for example, applications in which mid-to-high frequency dynamic loads are applied, such as microelectromechanical systems (MEMS) [16].…”

“…Earlier work on electrochemical ASSB modelling has been performed, in which moderately good agreement between the measurements and simulations has been reported [11,12]. Based on this work, where usually only DC (dis)charges profiles are applied, modelling efforts have also been performed in which highly dynamic battery loads were applied [16]. These dynamic load profiles are very common in microelectromechanical systems (MEMS) [17].…”