Uncovering the hidden drivers of battery impedance changes

Understanding what happens inside a battery during operation is essential for improving performance, safety and lifetime. A new study, conducted within the NEMO framework, introduces two innovative measurement protocols that make it possible to distinguish between two key factors affecting battery impedance during high-current excitation: electrochemical processes and self-heating.

Using advanced Electrochemical Impedance Spectroscopy (EIS) and Nonlinear EIS (NLEIS) techniques, the researchers developed methods that exploit the different time scales of these phenomena. While electrochemical nonlinearities occur almost instantaneously, temperature-related effects develop more slowly. By separating these contributions, the new approach provides a more accurate picture of battery behaviour under demanding operating conditions.

The methods were tested on a lithium nickel manganese cobalt oxide (NMC) battery cell and successfully quantified the relative impact of thermal and electrochemical effects on impedance changes. The results revealed that, under certain conditions, impedance reductions are driven entirely by electrochemical processes, while at higher excitation levels both electrochemical and thermal contributions play a role.

The study also challenges a widely used assumption in battery diagnostics. Researchers found that the battery remained within a linear operating regime at voltage amplitudes up to 280 mV, significantly higher than the commonly accepted 20 mV threshold. This finding could help simplify future impedance measurements and expand the practical use of impedance-based diagnostic techniques.

Read the full study on Zenodo: Quantitative separation of thermal and electrochemical contributions in nonlinear EIS measurements

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Diagnostic approach reveals how temperature shapes battery aging in electric vehicles

As electric vehicles expand globally, understanding how batteries age under real-world conditions is essential for improving performance, safety, and durability. Within the NEMO project framework, researchers at Vrije Universiteit Brussel (VUB) investigated the degradation of 75 Ah NMC631 lithium-ion cells, focusing on the impact of temperature using a combined diagnostic approach based on incremental capacity analysis (ICA) and electrochemical impedance spectroscopy (EIS).

Cells were tested under identical cycling conditions while varying only the temperature, allowing a clear assessment of temperature-driven aging. The results show that lower temperatures significantly slow degradation, with cells maintaining stable electrochemical behavior and retaining over 90% state of health even after 1600 cycles. In contrast, higher temperatures accelerate aging and intensify internal changes.

The study reveals that multiple degradation mechanisms occur simultaneously, including lithium inventory loss, reduced conductivity, and active material degradation. It also shows that internal differences within cells grow over time, leading to distinct aging pathways—even under identical operating conditions.

By combining ICA and EIS, the researchers provide a more complete understanding of battery health, enabling clearer differentiation between gradual degradation and potential failure modes. This approach offers valuable insights for improving battery management systems, enhancing safety, and extending the lifetime of EV batteries.

Read the full study here.

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New model for predicting battery swelling under mechanical constraints

Lithium-ion batteries powering electric vehicles do not operate in isolation. Packed tightly into modules, they are subject to constant mechanical pressure, a design feature that improves stability and performance, but also introduces a hidden risk: as cells charge and discharge, they swell and contract, generating fluctuating internal stresses that can crack electrodes, deform separators, and trigger dangerous side reactions, including internal short circuits and thermal runaway.

To address this challenge, researchers within the NEMO project from Graz University of Technology (TUG) and Vrije Universiteit Brussel (VUB) have developed a novel P2D-based computational model that integrates lithium-ion transport dynamics with pressure-dependent parameters to accurately predict cell thickness changes under mechanical constraints — and does so without requiring real-time sensors during operation.

The model was validated against experimental data for a 1C discharge cycle at 0.164 MPa of external pressure. It achieved a mean absolute percentage error (MAPE) of just 6.87% in predicting cell thickness change — a strong result that demonstrates the model’s ability to bridge the gap between laboratory measurements and real-world battery pack conditions.

Crucially, unlike existing approaches that rely on embedded physical sensors or ignore mechanical boundary conditions altogether, this model is entirely simulation-based. It can therefore be integrated into battery management systems (BMS) and digital twin frameworks without hardware modifications, reducing cost and complexity.

This work, developed within the NEMO project framework, directly supports the development of next-generation battery management systems capable of accounting for mechanical stress in real time, improving safety assessment, extending battery lifetimes, and ultimately reducing the total cost of ownership of electric vehicles and stationary energy storage systems.

The full paper is available open access on Zenodo: https://zenodo.org/records/19554839

How mechanical deformation affects battery impedance responses

We are pleased to share that researchers from TUG – Graz University of Technology have published a new open-access scientific examining how mechanical deformation influences the electrochemical behaviour of lithium-ion batteries , a topic of growing importance for battery safety and performance in both automotive and stationary applications. The article, titled “Effects of Mechanical Deformation Depth and Size on the Electrochemical Impedance Response of Lithium-Ion Batteries”, is freely available online.

As interest in electrified transport and large-scale energy storage grows, understanding how batteries respond to mechanical stresses, such as impacts, compression, or structural deformation, is critical. Real-world battery systems encounter mechanical loads during vehicle use, vibration, installation, and packaging constraints, and these loads can alter internal cell behaviour in ways that affect both performance and safety.

In this study, the authors use electrochemical impedance spectroscopy (EIS) to analyse how different depths and sizes of mechanical deformation affect battery impedance responses. EIS is a widely used diagnostic technique in battery research that provides insights into internal resistance, charge transfer processes, and degradation mechanisms. By systematically varying mechanical deformation conditions and observing the resulting impedance spectra, the paper demonstrates that cell mechanical state can meaningfully influence impedance signatures, which has important implications for battery diagnostics, modelling, and real-time state assessment.

The findings highlight the need to consider mechanical effects alongside electrical and thermal factors in battery models and management systems. This is particularly relevant for applications where batteries are subject to repeated or unexpected mechanical stresses, for instance in automotive environments with road vibrations and crash scenarios, or in stationary systems where pack compression and thermal expansion occur over long lifetimes.

Understanding how mechanical deformation alters EIS responses also supports more robust implementations of diagnostic algorithms and state-of-health estimators that are used in battery management systems (BMS). By integrating such insights into advanced models, researchers and engineers can improve the reliability of battery condition monitoring and enhance safety margins in both design and operation.

The paper contributes to a broader effort across the research community to link physical deformation, internal electrochemistry, and observable electrical behaviour, making it a valuable reference for those working on battery modelling, diagnostics, and integrated BMS solutions.

Read the full article: https://zenodo.org/records/18594080

Bringing battery impedance diagnostics into the real world: opportunities and limits

Researchers involved in the EU-funded project NEMO have published a new peer-reviewed scientific paper in the Journal of Power Sources, addressing a critical challenge in modern battery management: the practical applicability of online Electrochemical Impedance Spectroscopy (EIS) for real-world battery systems.

The article “Practical considerations and limitations of online Electrochemical Impedance Spectroscopy for battery systems management” provides an in-depth and methodical analysis of how EIS-based diagnostics behave when moved from controlled laboratory conditions to operational battery electronics and embedded systems.

From theory to practice in battery electronics

Electrochemical Impedance Spectroscopy is widely recognised as a powerful tool for characterising battery behaviour, enabling insights into internal processes related to ageing, degradation, temperature effects, and state-of-health estimation. As such, EIS is often proposed as a key enabler for advanced battery electronics and next-generation battery management systems (BMS).

However, implementing EIS online and in real time introduces non-trivial constraints. The paper systematically examines these constraints, focusing on issues such as measurement accuracy under dynamic operating conditions, signal perturbations caused by load variations, hardware limitations, and the interpretability of impedance data when acquired during normal battery operation.

Rather than proposing EIS as a universal solution, the authors take a critical and evidence-based approach, clarifying when and how online EIS can provide reliable information and when it may lead to misleading conclusions if applied without sufficient safeguards or modelling support.

Relevance for NEMO and Advanced Battery Modelling

This contribution directly supports NEMO’s objective of developing next-generation models for advanced battery electronics, where accurate diagnostics must be tightly coupled with realistic system constraints. By identifying the boundaries of validity for online impedance measurements, the paper helps inform the design of robust battery models, control strategies, and electronic architectures that can operate safely and efficiently in real-world applications.

The publication is openly accessible: you can read it here: https://zenodo.org/records/18298276

Optimising real-time charging for e-micromobility devices

We are pleased to announce the publication of a new scientific article authored by researchers from the ETEC Department & MOBI Research Group at Vrije Universiteit Brussel (VUB), within the framework of the EU-funded NEMO project.

The paper, titled “Optimization of charging process for electric micromobility devices with real-time operation”, has been published in the peer-reviewed journal Results in Engineering (Elsevier) and is now openly available via Zenodo.

Advancing fast charging for e-micromobility

Electric micromobility, including e-bikes, electric scooters, and light-weight electric motorcycles, is a rapidly expanding segment of sustainable urban transport. However, fast charging these devices presents key technical challenges, particularly when operating within low-cost processors and limited cooling systems. Traditional optimisation algorithms often require high computational resources, making them impractical for real-time charging control in micromobility.

To address these barriers, the VUB team developed a novel optimised charging algorithm that integrates offline training with real-time operation. The algorithm leverages a balance between charging speed and battery thermal behavior, producing optimized policy maps based on a 1D electrothermal model and dynamic programming. Once trained offline, these maps can be efficiently interpolated on low-cost microcontrollers during real-time use.

Key results and performance improvements

Experimental validation on a 43 Ah battery demonstrated that the proposed strategy significantly improves charging performance compared with conventional constant-current approaches:

Charging time reduced by 8.5 %, without compromising battery temperature or state-of-charge profiles.
Robust stability across varying initial states of charge and environmental conditions.
Minimal execution time of ~0.44 ms on an 8-bit microcontroller, highlighting suitability for real-world low-cost applications.

These findings offer a significant step toward efficient, safe, and scalable charging strategies in the micromobility landscape, a critical enabler for broader adoption of electric transportation in urban environments.

EU funding and acknowledgements

This research was supported by the European Commission under the NEMO project. This paper is openly accessible and available through the Zenodo open repository.

Read the paper: https://zenodo.org/records/18174820