Nonlinear Frequency Analysis of Lithium-ion Batteries

锂离子电池模型用于各种目的，包括电池系统的设计，状态的估计，如温度和充电状态，以及控制（非）充电电流。模型的特征仍然是一个开放式的问题。一种常见的方法是电化学阻抗谱（EIS），它假设电池在其线性运行状态下表现。然而，电池本质上是非线性系统，例如在开路电压和充电状态之间具有非线性关系，以及非线性动力学。当电池暴露在中等到较高幅度的激励电流中时，其电压和温度响应的非线性变得明显。因此，仅基于线性假设的电池模型表征会导致模型退化。有必要在模型参数化中包括非线性操作制度，以便更好地描述整体行为，包括在线性制度中未触发的现象。例如，用于分析电池随时间退化的传统EIS实验通常会忽略这一信息，这意味着无法深入了解潜在的行为。为了在更大范围内分析电池的行为，频率响应分析必须扩展到非线性系统。这包括多变量傅立叶分析，与通常的线性系统分析相比，获得的光谱解释更具挑战性。此外，电池模型本身的参数往往是电池状态的函数，在分析中不能认为是时不变的。该项目与法拉第研究所多尺度建模快速启动项目密切相关，旨在回答如何将频率分析扩展到电池背景下的非线性系统，如何保持时域模型结构与非线性频率响应之间的关系，以及如何在频域分析中包括参数函数依赖于状态的问题。在这些领域的突破将大大改善，更有效和更通用的电池模型表征程序。这将反过来导致在设计阶段更可靠的行为推断（包括性能和降解模型），并且，从相对简单的实验室测量中，对影响商用电池降解的现象有了新的见解。如果有足够的测试通道，后者可以扩展到对许多细胞的性能和退化进行高通量研究。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最近才探索的一种新方法，由Murbach等人(1)于2018年使用非线性EIS （NLEIS）和Nina Harting等人(2)于2017年使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开放式的问题，可以通过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 Electrochem。系统工程学报。2018 (11):A2758-A2765。(2) Harting, Wolff, Röder, Krewer，“锂离子电池的非线性频率响应分析（NFRA）”，电化学学报，2017年第2卷，第133-139页，ISSN 0013-4686。与EPSRC的战略和研究领域保持一致本项目由EPSRC外部资助，因此不属于任何特定的研究领域。由法拉第研究所资助。法拉第培训基金参考文件（FITG030-B）。法拉第Grant参考EP/S514901/1。任何涉及的公司或合作者，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