Turning the screw on electrode mixing
Researchers at WMG, University of Warwick, have laid the foundations to boost the sustainability of battery manufacturing with a new method for mixing electrode slurries that uses significantly less toxic solvent than traditional processes.
By using a twin-screw extruder, the team successfully manufactured lithium manganese iron phosphate (LMFP) electrodes from mixes using 45% less solvent than the baseline mixing processes. This innovation could save battery producers significant amounts of time, energy and money by minimising the drying process and its footprint. The researchers are working with industry partners, including Thermo Fisher Scientific, to scale up the process.
Image: Thermo Scientific™ Process 11 Parallel Twin-Screw Extruder equipment optimising and battery slurry mixing processes.
In the mix
Electrodes are typically made by mixing active materials and other powders together with a solvent to create a slurry that is coated onto a metallic foil. The electrode is then dried before the remaining stages of the cell manufacturing process are completed.
The most commonly used solvent in the battery industry for cathodes is N-Methylpyrrolidone (NMP), a substance that is not only toxic to handle, but also adds cost and logistical complexity for manufacturers.
WMG has demonstrated that use of a twin-screw extruder, a machine commonplace in plastics, to mix slurries can significantly reduce the amount of solvent required.
Dr Matthew Capener, Principal Engineer in the Battery Materials and Cells Group at WMG and an investigator on the Faraday Institution’s Nextrode project, explains:
| By the numbers | |
|---|---|
| 0.5-3 kg/hr | of battery slurry processed |
| 6+ | mixing conditions processed per hour |
| ~47% | of total battery manufacturing energy cost attributed to drying/solvent recovery for conventional slurry-coated electrodes |
| 45% | reduction in solvent using optimised process versus baseline |
| ≥20% | increase in the discharge capacity performance at 10C for an optimised LMFP mix. |
The Faraday Institution’s Nextrode project is funded by the Battery Innovation Programme, through the Department for Business and Trade and delivered by Innovate UK.
NMP has a very high boiling point, which means you have to use a lot of energy in the drying stage. Solvent is expensive to buy and needs to be recovered and recycled for future battery manufacturing. Also, drying the solvent from the coated electrodes contributes significantly to the cost, time and factory footprint of the battery manufacturing process. Minimising or eliminating solvents from high-volume battery manufacturing environments is therefore a high-impact target area for innovation.”
Dr Matthew Capener, Investigator on Nextrode in -40˚C dry room at WMG used for processing battery slurries.
Dr Capener continues:
Traditional batch mixing is like making a cheese sauce – you start with the powders, then add solvent to make a thick, viscous dough, and add more liquid over time until you get the final viscosity needed for the coating process. In contrast, the extruder continuously mixes the dry ingredients using two co-rotating screws that push them along the barrel. You then add the solvent at different feed points along the extruder and you can also directly form electrode films that can be laminated onto the foil. With twin screws, you’ve got a lot more flexibility and more parameters to play with than conventional mixers. It is not only more effective at mixing, but its use can accelerate development cycles.”
Video showing co-rotating screws.
Using the twin-screw extruder, the team found it could reduce the amount of NMP required during mixing by up to 45%, making electrode drying faster, cheaper and more sustainable. They are now working to optimise the formulation and processing to reduce solvent use even further.
LMFP – a tricky mix
To date the team has focused their research on lithium manganese iron phosphate (LMFP) – a relatively new cathode material for electric vehicle batteries that is of interest to industry. LMFP offers a higher energy density than lithium iron phosphate (LFP), meaning greater vehicle range, and because LMFP contains no cobalt it is lower cost and benefits from a more secure supply chain than lithium nickel manganese cobalt oxides (NMC).
However, LMFP manufacturing processes are much less mature than those for LFP and NMC, and there is considerable room for optimisation. LMFP’s challenging ionic and electronic conductivity means the cathode must use very small particles of LMFP active material to decrease diffusion distances – but these small particles tend to clump during mixing, limiting the performance of the battery. Achieving a well-mixed slurry using traditional methods can be problematic, especially at scale.
Twin screw extrusion continuous mixing of LMFP cathode battery slurry.
Dr Capener explains:
Getting a good quality mix with a homogeneous distribution of materials that delivers the required electrode morphology — and therefore the required cell performance — is one of the main challenges with LMFP.”
Not only does the technique have the potential to reduce manufacturing costs, but the improved mixing and lower solvent content lead to a more even distribution of the LMFP, conductive carbon and polymer binder, improving electrode electrochemical performance and mechanical properties and allowing the tailoring of electrodes for different applications, for example, very high energy density, power performance or fast charging. Initial results have shown a ≥20% increase in the discharge capacity performance at 10C for an optimised LMFP mix.
Scaling up and next steps
So far, researchers have manufactured batches of up to 100 grams of LMFP material and used them to make single-layer LMFP-graphite pouch cells. The team is now collaborating with several industry partners and hopes to scale up the process with Thermo Fisher Scientific.
Knowledge gained from this research could also inform other parts of the Oxford-led Nextrode project, which is developing the next generation of battery electrodes, including low- and no-solvent electrodes.
Professor Louis Piper, head of the Battery Materials and Cells Group at WMG, and co-principal investigator on the Degradation project comments:
SEM Image showing LMFP cathode electrode microstructure at high solid content, with the slurry mixed via twin screw extrusion.
Elements of this research feed directly into other projects with industry partners including Thermo Fisher Scientific and investigations into anodeless LMFP as part of the Degradation project. While our initial focus has been on LMFP, the mixing process is chemically agnostic and could be used to improve mixing protocols for all major battery chemistries.
The project highlights the role the Faraday Institution can play in helping us translate new trends in battery manufacturing into innovations that industry can adopt.”
Success story published May 2026.