Finding a needle in a haystack: mapping binders in battery anodes unlocks insights
Researchers at the University of Oxford have developed a new patent-pending staining and imaging process that allows previously “invisible” binders in lithium-ion battery anodes to be mapped and quantified. Binder holds together the different particles in an electrode and while making up only around 5% of an electrode, their distribution has a disproportionate impact on battery performance and manufacturability.
The technique, which is attracting considerable industry and academic interest, has multiple potential uses including, in the long-term, as a quality control technique and to optimise slurry mixing and electrode drying protocols on battery manufacturing lines. It is also helping to further the fundamental understanding of binder-mediated surface processes that critically affect the longevity and charging rate of Li-ion batteries.
Binders – a critical component
Lithium-ion battery electrodes consist of particles that store energy and electrically conductive additives that are held together by a polymeric binder. Although binders critically govern electrode manufacturability, battery lifetime and how quickly the battery can charge and deliver its energy (the charge-rate performance), researchers know surprisingly little about their distribution within electrodes. Previously, understanding was hindered because binders are present only in small amounts (<5 wt%) and have non-specific chemical composition, which makes them hard to see or measure.
As part of the Faraday Institution’s Nextrode project, a team led by Dr Stanislaw Zankowski and Professor Patrick Grant at the University of Oxford has developed a new, easily adopted method for staining modern, watermix-processible binders in graphite or graphite-silicon anodes.
The staining process, now published in Nature Communications, tags commercial cellulose- and latex-derived binders in graphite- and silicon-based anodes with traceable markers of silver and bromine. The silver and bromine make the binders visible in energy-selective X-ray spectroscopy (EDX) and energy-selective backscattered electron (EsB) imaging, allowing previously “invisible” binders to be mapped and quantified.
| By the numbers | |
|---|---|
| 40% and 14% | decrease in ion-transport and electron-transport resistance respectively in lab-scale anodes as a result of using the technique. |
| Up to 97.5% | accuracy in detecting relative difference in binder content between electrode regions with 3.0 wt.% and as little as 0.75 wt.% of binder |
| 15 | hours needed for staining and analysis of through-thickness binder distribution. 1 hr is the desired time for use by industry. |
| 1 | hour already achieved for staining and top-down analysis of conductive binder / carbon black agglomeration. |
The Faraday Institution is primarily funded by the Battery Innovation Programme – a flagship of the UK Industrial Strategy, funded by the Department for Business and Trade and delivered by Innovate UK.
Uses of the staining/imaging technique
Use of the staining and imaging technique could be impactful in a number of ways:
- To accelerate the optimisation of slurry mixing and electrode drying protocols, preventing binder agglomeration and migration when battery manufacturers change formulations or researchers are developing new materials.
- It has already unlocked new insights into how calendering – a stage of the anode manufacturing process – can impact binder coverage on active particle surfaces, which affects battery longevity.
- It will be used across Nextrode to accelerate the development of smart electrodes and novel electrode coating techniques.
- In the long term, it has the potential to be developed for use as an offline quality control tool in a battery manufacturing environment.
As an example of the power of the technique, in small lab-scale tests the method helped researchers refine drying protocols that resulted in a reduction of 40% in the ion-transport resistance in the anode, which would have a significant impact on the speed at which the battery could be charged.
Future outlook
The technique has the potential to provide early adopters with a competitive edge – enabling them to quickly screen out prototype electrodes with sub-optimal binder distributions in the electrode microstructure rather than relying on lengthy, resource-intensive electrochemical testing, which is currently the norm.
A patent covering the staining process was filed in July 2025.
The method has attracted interest from several global automotive OEMs, and from battery and battery materials manufacturers. The team is exploring the adaptation of the technique to meet the needs of industry organisations, and is conducting pilot studies with several parties.
Dr Stanislaw Zankowski outlines how easily the technique could be rolled out to other users:
The staining itself is simple – and doesn’t need specialist equipment – at most, a standard fume hood and a vacuum pump that’s available in most industrial laboratories. The fast backscattered electron imaging technique needs a fairly low-resolution SEM microscope, though the more accurate EDX and EsB analyses require a larger capital outlay and a more specialised operator.”
Dr Stanislaw Zankowski in a lab.
And the challenges ahead? Stan continues:
Work is ongoing in Nextrode to increase the throughput of the analysis. The preparation time is currently about 15 hours per sample as the cross sections through the anodes need a super-smooth surface. To be meaningfully used in industry we’d want to bring that down to 1 hour. We’ve already got some ideas about how to minimise or even avoid the preparation and polishing stage altogether, and we will be testing them in the upcoming months.
We are also turning our focus to analysing thinner (< 80 μm) electrodes that are used in high-power batteries. Additionally, We want to probe larger areas of electrodes in one go, which would significantly increase the analysis throughput compared to measuring a few millimetre-wide cross sections one at the time. And we’d also like to explore applying the technique to a wider range of binders, particularly those used in state-of-the-art dry-processed or silicon-based anodes.
But our priority is to facilitate a successful demonstration of the present technique with industry partners.”
Principal Investigator of the Nextrode project, Professor Patrick Grant, University of Oxford, concludes:
This multidisciplinary effort-spanning chemistry, electron microscopy, electrochemical testing and modelling – has resulted in an innovative imaging approach that will drive forward advancements across a wide range of battery applications.”
Professor Martin Freer, CEO, Faraday Institution comments:
This is a strong example of what the Faraday Institution core projects were set up to deliver – industry-relevant insights and techniques from multidisciplinary research.”
Case study published January 2026.
Want to know more? Example uses of the technique
Preventing binder migration through optimising electrode drying protocols
The team has demonstrated the technique’s potential to optimise electrode drying protocols for improved manufacturing throughput and battery performance. Stan explains:
Drying of electrodes contributes significantly to the cost, time and factory footprint of the battery manufacturing process. Manufacturers want to dry the electrodes as quickly as possible to increase throughput and reduce cost, as each metre of the industrial electrode drying line costs around £90,000 in capital investment.”
But if the electrode dries too quickly the binder particles migrate to the top or bottom of the electrode as the solvent evaporates, resulting in loss of adhesion of particles throughout the electrode. Equally importantly, the accumulation of ionically resistive binder at the top of the electrode leads to a significant decrease (up to 50%) in electrode fast-charging performance.
The staining technique demonstrates any unwanted inhomogeneities in binder distribution, but also shows how changes in drying protocols can lead to unexpected improvements in binder placement that enhance electrode performance. For example, lab-made electrodes rapidly dried at 120 oC (top image) showed binder migration and were easily delaminated from the current collector upon bending.
To prevent the migration, the team then tested briefly dipping freshly manufactured electrodes in isopropanol or acetone prior to rapid drying. The isopropanol dipping led to an even larger accumulation of the binders at the top of the electrode, causing significant cracking in the bulk electrode (middle image).
In contrast, dipping the electrodes in acetone before drying had a markedly opposing effect, concentrating the binders towards the bottom of the electrode coating (bottom image). Electrodes with this beneficial binder distribution had excellent coating adhesion to the current collector and showed a reduction in ionic resistance of more than 40% compared to the reference (not-dipped) electrodes. Upon integrating such optimised electrode in a battery, this would translate to a significant reduction in battery charge time.
EDX cross-sectional image of a reference electrode rapidly dried at 120 oC (top), and dipped for 3 minutes in isopropanol (middle) and acetone (bottom) prior to drying at 120 oC. The bromine-stained styrene-butadiene rubber (SBR) binder is shown as green, graphite electrode particles are shown as brown, and the copper current collector is purple.
Optimising slurry mixing
Battery electrodes are manufactured by spreading a slurry – a semi-liquid mixture of powders and solvent – onto a metallic current collector. The conductive carbon additive and binder need to be well mixed and distributed between the active particles in the slurry and electrode coating, or battery performance is affected. If a manufacturer changes materials supplier or uses materials with slightly different particle sizes or surface chemistry, the slurry mixing protocol may need to be changed to achieve the required homogeneity. There has previously not been any objective and fast method to measure dispersion uniformity of binder and carbon additives in graphite-based anodes.
The team at Oxford has demonstrated that the staining technique has the potential to be used as a fast, offline quality control tool in a battery manufacturing environment and to optimise slurry mixing as formulations change.
In a small lab mix of a graphite anode slurry, the team imaged anodes where there had been agglomeration of binder in the slurry mix. They then demonstrated (i) small improvements in the binder deagglomeration in the anodes after inclusion of mixing balls in the mix vessel, and ii) significant improvements in the binder deagglomeration in the anodes produced from a slurry with initially more concentrated carboxymethyl cellulose (CMC) in the first mixing step. Testing showed that the anodes made from initially concentrated slurry (which had no binder / carbon additive agglomerates larger than 100 μm2) had 14% lower electronic resistivity compared to the anodes made from a standard slurry, which would improve charging time of a battery using such optimised anodes.
Colour-enhanced backscattered electron images of bromine-stained electrodes prepared with different slurry mixing protocols. Binder particles are coloured turquoise. Left: electrodes from a poorly mixed slurry with binder agglomeration (the circled turquoise areas). Right: electrode from a well-mixed slurry.
Insights on processes that affect battery
Staining combined with EsB imaging and modelling have provided the first electrode-scale, high-resolution images of elusive nanoscopic binder layers and agglomerates on active particle surfaces in both research-grade and commercial electrodes. These provided new insights on key processes that affect battery longevity and performance.
For example, the technique was used to image graphite anodes before and after calendering (the step in the electrode manufacturing process that compacts the electrode before it is dried). The binder carboxymethyl cellulose (CMC) is conventionally added to the anode to help prevent agglomeration of particles and increase processibility during electrode mixing. But recent research has shown it also stabilises the solid electrolyte interface (SEI) layer – which protects the active graphite particles from reaction with the electrolyte – and can significantly improve cycling stability of the batteries. However, the mechanism behind these improvements is still unclear.
The staining/EsB technique showed that 90% of the graphite surfaces were coated by the CMC binder before calendering but only 20-30% afterwards. Having a way to visualise the CMC means that researchers could refine manufacturing processes to more uniformly coat the graphite with the protective binder.
Imaging 10 nm-thick CMC binder layers around active particles in a commercial graphite anode. The grey area to the left is the previously available standard view (the secondary electron image from a scanning electron microscope) showing the large graphite particles, but no information about the location of the binder distribution. In the new technique (right), the standard SEM image and EsB electron images are collected at the same time and overlayed. The blue shows areas where CMC binders are present (stained by silver) and the purple shows areas of bare graphite surfaces without the CMC.
Exploring new manufacturing method
Looking beyond traditional, single layer, slurry-coated anodes, the staining and imaging technique will be used throughout Nextrode’s research programme to quantify the potential of smart electrodes, (such as multi-pass coating), and different manufacturing methods (such as spray or electrostatic coating) to improve energy storage devices. These innovative manufacturing techniques are already being commercialised by several international companies, but the effects on binder distribution are still largely unknown.
The Oxford team has verified the new technique on spray-coated bilayered electodes, where the staining reflected what was known to have been produced with up to 97.5% accuracy.
Secondary electron (left) and stained EDX (right) images of a bi-layered electrode (upper image – bromine stained, lower image – silver stained). The graphite anode was made in two stages, with a binder-rich layer deposited first (lower part of the coating), and a layer with only small amounts of binder subsequently deposited (upper part of the coating). The difference in intensity of the green and blue areas in the images accurately reflects the difference in the SBR and CMC binder content between the two layers, respectively