Nonlinear Frequency Analysis of Lithium-ion Batteries

描述研究背景，包括潜在影响锂离子电池模型用于各种目的，包括电池系统的设计、温度和充电状态等状态的估计，以及(放电)充电电流的控制。模型的特征仍然是一个无限期的问题。一种常见的方法是电化学阻抗谱(EIS)，它假设电池在其线性工作状态下工作。然而，电池本质上是非线性系统，例如具有开路电压和荷电状态之间的非线性关系以及非线性动力学。当电池暴露在中等到更高幅度的励磁电流中时，电压和温度响应中的非线性变得明显。因此，仅基于线性假设的电池模型表征会导致模型退化。为了更好地描述整体行为，有必要在模型参数化中包括非线性运行机制，以包括在线性机制中未被触发的现象。例如，用于分析电池随时间退化的传统EIS实验通常忽略了这些信息，这意味着错过了对潜在行为的洞察。要分析电池在更广泛范围内的行为，频率响应分析必须扩展到非线性系统。这包括多变量傅里叶分析，与通常的线性系统分析相比，对所获得的频谱的解释更具挑战性。此外，电池模型本身的参数通常是电池状态的函数，在分析中不能被认为是时不变的。目的与目的本项目与Faraday Institution多尺度建模快速启动项目紧密结合，试图回答如何在电池环境中将频率分析扩展到非线性系统，如何保持时域模型结构和非线性频率响应之间的关系，以及如何在频域分析中包含参数对状态的函数依赖性。这些领域的突破将大大改进电池模型的表征程序，使其更高效、更通用。这反过来将导致在设计阶段对行为进行更可靠的外推(包括性能和退化建模)，并通过相对简单的实验室测量，对影响商业可用电池退化的现象有新的见解。后者可以扩展到高通量研究一些电池的性能和退化，如果有足够的测试通道来进行这项工作。研究方法的新颖性实验应用于锂离子电池的非线性频率分析是一种新的方法，只是最近探索的一种新方法，Murbach等人(1)在2018年用非线性EIS(1)，Nina Harting等人(2)在2017年用非线性频率响应分析(NFRA)。锂离子电池内部的非线性仍然是一个无限制的问题，可以用NLEIS和NFRA等技术来探索。(1)Murbach、Hu、Schwartz，“锂离子电池的非线性电化学阻抗谱：实验方法、分析和初步发现”，.J电化学。SoC。2018年165(11)：A2758-A2765。(2)Harting，Wolff，Röder，Krewer.“锂离子电池的非线性频率响应分析(NFRA)”，电子工程学报，第248卷，2017年，第133-139页，ISSN 0013-4686。与EPSRC的战略和研究领域的结盟本项目是由EPSRC外部资助的，因此它不属于任何特定的研究领域。由法拉第研究所资助。法拉第培训拨款参考(FITG030-B)。Faraday Grant参考文献EP/S514901/1.任何参与的公司或合作者由David Howey监督

Description of the context of the research including potential impactLithium-ion battery models are used for a variety of purposes including the design of battery systems, the estimation of states such as temperature and state of charge, and the control of (dis)charging currents. Characterisation of models remains an open-ended issue. One common approach is electrochemical impedance spectroscopy (EIS) which assumes batteries behave in their linear regime of operation. However, batteries are inherently non-linear systems, for example having a non-linear relationship between open circuit voltage and state of charge, and non-linear kinetics. Non-linearities become evident in the voltage and temperature response when a battery is exposed to moderate to higher amplitude excitation currents. Therefore, battery model characterization based only on linear assumptions can lead to model degeneracy. It is necessary to include nonlinear operational regimes in model parameterisation in order to provide a better characterization of overall behaviour, to include phenomena not triggered in linear regimes. For example this information is commonly overlooked by traditional EIS experiments used to analyse battery degradation over time, which means that insights are missed into the underlying behaviour.To analyse battery behaviour in a wider range of regimes, frequency response analysis has to be extended to nonlinear systems. This includes a multivariable Fourier analysis, where the interpretation of the spectrum obtained is much more challenging compared to the usual analysis of linear systems. In addition, parameters of the battery model themselves are often functions of the battery states and cannot be considered time-invariant in the analysis.Aims & ObjectivesThis project, in close alignment with the Faraday Institution Multiscale Modelling Fast Start Project, seeks to answer the questions of how to extend frequency analysis to nonlinear systems in the context of batteries, how to preserve the relationship between time domain model structure and nonlinear frequency response, and how to include parameter functional dependence on states in the frequency domain analysis. Breakthroughs in these areas will lead to greatly improved, more efficient and more general characterisation procedures for battery models. This will in turn result in more reliable extrapolation of behaviour at design stage (including performance and degradation modelling), and, from relatively simple lab measurements, new insights into the phenomena that impact degradation in commercially available cells. The latter could be extended to a high-throughput study of performance and degradation in a number of cells if sufficient test channels are available to undertake this.Novelty of the research methodologyNonlinear frequency analysis experimentally applied to lithium-ion batteries is a new methodology only explored recently with nonlinear EIS (NLEIS) by Murbach et al (1) in 2018 and nonlinear frequency response analysis (NFRA) by Nina Harting et al (2) in 2017. The nonlinearities within a lithium-ion cell remain an open-ended problem which can be explored with NLEIS and NFRA amongst other techniques.(1) Murbach, Hu, Schwartz, "Nonlinear Electrochemical Impedance Spectroscopy of Lithium-Ion Batteries: Experimental Approach, Analysis, and Initial Findings", .J Electrochem. Soc. 2018 165(11): A2758-A2765.(2) Harting, Wolff, Röder, Krewer, "Nonlinear Frequency Response Analysis (NFRA) of Lithium-Ion Batteries", Electrochimica Acta, Volume 248, 2017, Pages 133-139, ISSN 0013-4686.Alignment to EPSRC's strategies and research areasThis project is funded externally to EPSRC therefore it does not fall within any specific research area. Funded by the Faraday Institution. Faraday Training grant reference (FITG030-B). Faraday Grant reference EP/S514901/1.Any companies or collaborators involvedSupervised by David Howey