At the Battery 2030+ Annual Conference held in Turin, Italy on 7–8 May 2025, Jonas Fechner from the MEET Battery Research Center at the University of Münster — a member of the CIRCUBATT consortium — presented findings on how resistance behaviour in two widely used cathode chemistries, lithium iron phosphate (LFP) and nickel manganese cobalt oxide (NMC811), varies with temperature and state of charge (SOC). The research was conducted together with Markus Börner and Martin Winter, also from MEET at the University of Münster, with Markus Börner equally a member of the CIRCUBATT consortium. The work is conducted within the framework of the CIRCUBATT project (Horizon Europe grant no. 101192383), a partner of the Battery 2030+ community.
The research addresses a fundamental challenge in battery science: performance loss and aging in batteries are strongly linked to increasing internal resistance, yet resistance behaviour varies substantially depending on operating conditions. Understanding these dependencies is essential for application-specific material selection, optimised charging strategies, and informed second-life battery assessment.
Why Resistance Characterisation Matters for Battery Lifecycle Management
Batteries in real-world applications operate across a wide range of cycling rates, SOC windows, and temperatures. These variables do not affect LFP and NMC811 equally. A robust characterisation methodology that captures resistance behaviour across all three dimensions is a prerequisite for accurate material selection at the design stage and reliable end-of-life assessment for second-life applications.
The MEET team developed and applied an EIS-coupled pulse protocol specifically designed to:
- Provide early resistance analysis for resistance-related aging detection
- Predict cathode material performance across operating conditions
- Support better material selection, optimised charging protocol design, and improved second-life potential assessment
Experimental Setup and Protocol
The study tested LFP and NMC811 composite cathodes using a three-electrode PAT-cell format at three temperatures: 0°C, 20°C, and 40°C.
The EIS-coupled pulse test protocol included:
- EIS and pulse testing from 100% to 0% SOC
- EIS pulses applied at 5% SOC intervals
- EIS of reference electrode (RE) versus working electrode (WE) for ohmic resistance (R₀) and charge-transfer resistance (R₁) analysis
- 10x 2C pulse for DC internal resistance (DCiR) analysis
This combined approach allows resistance components to be resolved both spectrally (via EIS) and dynamically (via pulse testing), providing a more complete picture of cathode behaviour than either method alone.
Key Findings from EIS Evaluation
Temperature-Dependent Impedance Behaviour
The EIS results reveal clear and consistent temperature dependencies for both chemistries:
- Increasing temperature reduces R₀ for both LFP and NMC811 across all SOC regions.
- At 0°C, LFP shows lower R₀ and R₁ compared to NMC811, indicating superior electrochemical performance in cold operating environments.
- At 20°C and 40°C, NMC811 demonstrates lower R₀ and R₁ in the mid-SOC region compared to LFP, indicating better performance in ambient to warm conditions at these charge states.
SOC-Dependent Impedance Behaviour
SOC also plays a significant and chemistry-specific role:
- LFP maintains a lower R₁ below 15% SOC compared to NMC811.
- Lowest R₀ and R₁ values for both chemistries are achieved between 90% and 15% SOC.
- At low SOCs, R₁ rises sharply for both chemistries, but NMC811 shows a significantly steeper increase than LFP.
This divergence at low SOC has direct implications for applications involving deep discharge cycles, where NMC811’s resistance penalty becomes substantially larger.
Pulse Evaluation Results
The pulse evaluation — using 2C discharge pulses and DC internal resistance analysis — corroborates and extends the EIS findings:
- R₀ increases as temperature decreases for both chemistries.
- NMC811 shows steeper R₀ and R₁ increases at extreme SOCs compared to LFP.
- R₁ increase is more pronounced at low SOCs for both chemistries.
- DCiR trends are consistent with R₀ values derived from EIS, validating the complementary methodology.
- NMC811 shows a steady decline in mean discharge voltage during 2C pulses, with a sharp drop at approximately 15–20% SOC.
The consistency between pulse and EIS results strengthens confidence in the EIS-coupled protocol as a reliable predictor of dynamic performance.
Methodological Contribution
Short pulse testing yields performance metrics that more accurately reflect real-world application conditions than standard characterisation approaches. Voltage-drop evaluation during pulse testing provides a critical cross-validation of EIS results, creating a complementary and robust dual methodology. This has practical implications for how battery testing protocols are designed — both for new cell qualification and for <a href=”https://circubatt-project.eu/battery-second-life-value-chain-cambridge-workshop-2026/”>second-life fitness assessment</a>.
Implications for First and Second Life Battery Applications
The findings carry direct relevance for lifecycle-aware battery design and second-life decision-making within CIRCUBATT’s broader circular economy framework:
- NMC811 is better suited for operation at ambient to elevated temperatures, particularly within mid-range SOC windows.
- LFP demonstrates superior performance in low-temperature environments and in applications involving frequent cycling at or near extreme SOCs.
Considering the full range of operating conditions — cycling profiles, temperature exposure, and SOC windows — is essential for reducing resistance-related aging and extending second-life viability. This work directly supports CIRCUBATT’s goal of developing <a href=”https://circubatt-project.eu/ai-digital-tools-battery-lifetimes/”>lifecycle-aware battery management frameworks</a> that account for real-world operating diversity, enabling more accurate end-of-life assessment and more effective second-life deployment strategies. It also connects to the broader question of <a href=”https://circubatt-project.eu/smart-ebike-battery-design-lifespan-repair/”>how battery design choices made early in a product’s life</a> determine how far that battery can go after its first use.
What Comes Next
The MEET team identifies two directions for future work:
- Long-term cycling investigations to observe how resistance behaviour evolves with aging under the tested conditions
- Investigation of other electrode materials beyond LFP and NMC811
About CIRCUBATT
CIRCUBATT is a Horizon Europe project (grant no. 101192383) developing integrated, end-to-end solutions for circular battery value chain innovation. The project covers the full battery lifecycle — from sustainable battery design and AI-enhanced lifecycle management to second-life applications and advanced recycling — with the goal of reducing Europe’s reliance on critical raw materials and advancing its circular economy transition. Learn more about how the EU Batteries Regulation is shaping this transition.