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Defining measurement standards for new battery technologies

The need

Lithium-ion (Li-ion) batteries occupy centre-stage among modern energy storage technologies, due to their high energy and power capacities, with low relative volume and weight. Li-ion batteries are projected to play a key role in global decarbonisation of energy – as energy storage devices for hybrid and electric vehicles, and in combination with renewable energy sources for grid energy storage.

As the UK transitions to the use of renewable energy, the long-term environmental sustainability and international competitiveness of many industrial sectors – especially the automotive industry – will depend on robust and precise measurement techniques for Li-ion batteries. Emerging energy storage technologies, such as sodium-ion batteries, supercapacitors and all-solid-state lithium-ion batteries, depend equally on accurate measurement for their rapid development. Our recent Energy Transition Report summarised essential measurement requirements of the UK battery industry.

In parallel to the £274m government investment in battery research from the Faraday Battery Challenge, NPL is combining expertise from multiple scientific disciplines to develop metrology for high energy density batteries. Our work will underpin new developments in battery science, encompassing support to industrial development of materials and devices as well as protocols to guide measurements in fundamental academic research.

The impact

Through an internal cross-theme project on high energy density batteries, we have marshalled a multidisciplinary team to support measurement standardisation across electrochemical, chemical and electrical characterisation techniques.

Our team initiated a collaboration with a UK-based energy materials development company (Deregallera, Caerphilly) through the Analysis for Innovators programme (A4I). We developed advanced test protocols for rapid screening of new electrode materials for Deregallera, using a combination of three-electrode electrochemical measurements and in situ Raman spectroscopy. The results allowed the company to make important strategic decisions on investment in their materials research programme, significantly accelerating their product development cycle.  

Within our ongoing research:

  • We are investigating reliable reference electrodes for materials characterisation and electrode parameterisation. This work supports in situ electrochemical diagnostics for reliable, reproducible and representative electrochemical investigation of materials used in energy storage devices, and recently yielded an open access review paper on the use of reference electrodes in Li-ion battery analysis.
  • We are developing best practice in advanced “operando” techniques – characterisation measurements conducted dynamically while the cell is charging and discharging – using Raman and IR spectroscopy as well as dimensional and thermal metrology. These measurements equip designers of novel energy storage materials to identify critical limiting processes, such as irreversible chemical changes which lead to capacity fade and electrode failure.
  • Using novel techniques and instrumentation, we are conducting in situ and in-line measurements of dimensional characteristics of battery components, such as electrodes and coatings, for quality control and defect detection of surface roughness, form and geometrical thickness.
  • Through simulation, we are assessing the performance of different cell configurations prior to lab implementation, allowing streamlined design of battery cell configurations optimised for different in situ and operando measurement techniques. Our work so far has guided improved cell design for operando Raman spectroscopy measurements on commercial samples.
  • We are implementing quality procedures and preparing a Good Practice Guide focusing on safe, optimal cell setup for robust battery electrode testing, especially considering the impact on electrochemical impedance spectroscopy (EIS) measurements of mechanical force applied during cell assembly and during electrode manufacturing (calendering process). This work is supported by simulation-led cell assembly protocols designed to eliminate perturbations in three-electrode EIS measurement.
  • We are developing new impedance reference standards and battery artefacts to underpin more reliable and reproducible EIS measurements for commercial Li-ion cells. In future it is planned to extend this work to modules and packs, in order to provide faster and more reliable diagnosis of state-of-charge and state-of-health.
  • Using techniques including time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), gas adsorption surface area analysis (“BET method”) and nuclear magnetic resonance (NMR) spectroscopy, we are developing robust and accurate protocols for ex situ metrology to assess local variations in battery electrode chemistry at different stages of operation.
  • We are investigating the use of advanced fibre optic temperature sensors to monitor the temperature inside battery cells and in the confined space of battery modules and packs. The 10 metre-long sensors can report the temperature every 5 mm, yielding the equivalent of thousands of thermocouples on a single fibre.
  • Using advanced data fusion approaches and innovative data handling methods, we are merging data obtained from multiple measurement sources to better understand heat generation in batteries, supporting more accurate definition of safe operating envelopes for charge and discharge current. We are also using trend analysis and other advanced time series analytics to quantify degradation rates under different conditions.

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The opportunity to interact with NPL scientists and utilise the advanced measurement techniques [they] are developing has been transformational for Deregallera’s energy storage materials research programme, […] saving tens of thousands of pounds and shaving months off research programmes.

Dr Peter Curran, Head of Materials Research - Deregallera Ltd