Growing demand for lithium-ion batteries has inspired researchers to develop electrode slurry materials and optimise existing formulations. Electrode slurry consists of electrode particles, small carbon particles to help conduction, and polymers and solvents to hold the structure together. Getting a consistent, even mix and dispersion is highly important for battery efficiency. Here Kevin Brownsill, Head of Technical Learning and Development at adhesives and materials processing instrumentation supplier Intertronics, explains how planetary centrifugal mixers can accelerate the design and development of advanced batteries.
Battery slurry is typically not suitable for traditional mixing (with blades, impellers, paddles, spatulas, etc), for a number of reasons. Contact mixing typically results in operator variance, difficulty validating the process, poor dispersion, introduction of air, or a high defect rate. Due to the high viscosity and heavy filler content of battery slurry, it can be difficult to achieve a homogenous mix, and prolonged manual mixing risks RSI for operators.
Planetary centrifugal mixers
One alternative to contact mixing is using a planetary centrifugal mixer. This non-contact mixing method combines revolution and rotation within a set radius to achieve a fast, homogenous mix for high- and low-viscosity liquid, pastes and powders. Rotation is typically at ~1,000s of RPM, generating mixing forces of about 400 G. Users mix in their own containers, ranging from 12 ml to 20 L, dispersing and degassing materials in seconds to minutes.
THINKY mixers are steadily becoming a standard tool for consistent, repeatable mixing without introducing bubbles, with hundreds installed across the UK in research laboratories, universities, process development teams and production facilities. A search for “THINKY” on Nature.com surfaces more than 340 results, highlighting their prominent role in R&D projects.
While many laboratories opt for a larger mixer for higher-volume applications, others run multiple smaller machines to avoid a large upfront investment, prevent a single point of failure, and increase flexibility.
The benefits of non-contact mixing
Planetary centrifugal mixing takes place in removeable containers, making cleaning straightforward, avoiding cross-contamination, and making the technology easy to repurpose.
A planetary centrifugal mixer can remove steps from a process compared with manual contact mixing, reducing labour costs. Material can be simultaneously mixed, dispersed, and degassed with minimal operator intervention.
The technology can reduce process waste by reducing the risk of contamination, while no decanting means less waste left in containers. Repeatable programmes minimise variation from operator skill and improves product formulation consistency.
Process traceability
Planetary centrifugal mixers enable precise and repeatable control of the mixing process. THINKY mixers can be programmed with different ratios of revolution and rotation, or “recipes”, to add more rotation for the defoaming function or more centrifugal action for mixing. Some difficult-to-mix materials may require a 10- or even 20-step program.
Some models offer data logging and PC connectivity, giving operators information on RPM, mode, and which recipe is in use, along with remote control and traceability functions. Researchers can then validate that the correct programme was used for a particular batch — useful for quality assurance and reporting.
Examples from the field
Due to the increased demand for mobile, rechargeable batteries with ever higher energy and power densities, intensive research is being conducted into modifying electrode structures to increase the active mass loading.
One possible approach is a three-dimensional structuring of electrodes using a metal foam structure, which acts as a current collector. This can increase the electrical conductivity of the electrode, as well as the integrity of the active mass layer. The aim is to improve the electrode thickness while reducing the amount of inactive components.
Characterisation is a very important step in the development process. A small improvement during R&D can lead to a massive improvement in performance and efficiency or a large decrease in costs when produced at a large scale.
In the production of foam electrodes with the highest possible active mass loading, the infiltration of the cellular structure with an electrode slurry is a decisive process step. The degree of infiltration depends to a large extent on the viscosity of the electrode slurry.
To determine the optimum battery slurry composition for a given solids composition (e.g. 84 wt.% NMC, 8 wt.% conductive carbon black + graphite, 8 wt.% binder), different cathode slurries with different solids contents were prepared by a customer using a THINKY ARM-310 planetary mixer, in a very short time to streamline the work and identify the most suitable composition.
Intertronics exclusively supplies the full range of THINKY planetary centrifugal mixers in the UK & Ireland. Click here to learn how the Technical University of Munich used one to manufacture NMC electrodes for lithium-ion batteries.
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