What solutions are there for ATEX and inerting requirements when mixing battery materials?
In the production and processing of battery materials, combustible dusts, conductive powders, moisture-sensitive components and solvent-containing slurries can occur. Typical solids are NMC, NCA, LFP, graphite or silicon composites. Whether they present an explosion hazard, moisture sensitivity or particular reactivity must be assessed individually for each recipe and process stage.
Processes in which combustible dusts and solvent vapours can occur simultaneously are particularly demanding. Such hybrid mixtures can have stricter safety requirements than dust-only or gas-only atmospheres. The protection concept must therefore consider the entire process, including charging, mixer, emptying, conveying technology, filter systems and dry-room environment.
The basis is a substance-specific risk assessment. Relevant characteristic values include, for example, the Kst value, maximum explosion pressure, minimum ignition energy, minimum ignition temperature, electrical resistance and limiting oxygen concentration. For solvent-containing processes, explosion limits, flash point and evaporation behaviour must also be taken into account.
Primary explosion protection through inerting
Inerting is intended to prevent an ignitable atmosphere from forming in the process space. To this end, the oxygen content in the mixer and connected plant components is kept below the limiting oxygen concentration determined for the specific product. Generic oxygen limits are not sufficient, since dust type, solvent, temperature, pressure and particle size all influence the required design.
Nitrogen is usually used as the inert gas. For materials that can react with nitrogen, for example applications involving elemental lithium, argon may be required. Suitable methods include purge inerting, pressure-swing inerting with evacuation followed by refilling, and continuous purging during ongoing processes.
The oxygen content is monitored with suitable measurement and analysis technology. Dew-point or moisture sensors supplement the measurement where the product requires low residual moisture values. The measured values are linked to the control system. Critical process steps may only start once the specified release values have been reached. If limit values are exceeded, the plant must transition to a defined safe state.
Secondary explosion protection through ignition-source avoidance
If an explosive atmosphere cannot be reliably ruled out, effective ignition sources must be avoided. Zone classification depends on the probability, duration and extent of explosive atmospheres. The interior of a mixer can, for example, be classified as Zone 20 for dust-explosible products. Areas at charging, emptying and filter points can be classified as Zone 21 or Zone 22. For combustible solvents, an assessment of possible gas or vapour zones is additionally required.
Mixers, mixing tools, piping, filters, containers and mobile packaging must be integrated into a continuous equipotential bonding and earthing concept. Hoses, seals and linings must be selected so that they do not promote impermissible electrostatic charging. Electrical equipment must be suitable for the respective zone. Mechanical ignition sources such as friction, impact, overheating bearings or defective seals must also be assessed and, where necessary, monitored.
Constructional explosion protection
Constructional explosion protection serves as a further protective layer where an explosion event cannot be ruled out with sufficient certainty despite inerting and ignition-source avoidance. The plant can be designed pressure-shock-resistant or equipped with explosion pressure relief, explosion suppression and decoupling.
Bursting discs or explosion flaps vent the pressure into suitable areas. For indoor installation, flameless venting devices or explosion suppression systems may be required. Quick-closing valves, extinguishing barriers or other suitable systems prevent flame and pressure from being transmitted to upstream or downstream plant components. The suitability of each protective measure must be demonstrated for the specific product and plant configuration.
Hybrid mixtures and dry-room technology
Hybrid mixtures of dust and solvent vapour can exhibit altered ignition behaviour. Even small vapour proportions can lower the minimum ignition energy of a dust mixture. The design of inerting and protective measures must therefore take account of the worst-case realistic scenario.
Closed charging and emptying systems reduce dust release, product loss and the ingress of humid ambient air. Depending on the process, tight container docking systems, airlocks, glove boxes or isolators are used. For very moisture-sensitive materials, the mixer can be integrated into a dry room. The dry room and process inerting must be coordinated with each other in terms of pressure cascades, material transfer and exhaust-air routing.
Safety concept as an overall system
A safe concept for mixing battery materials combines material characterisation, risk assessment, zone concept, inerting, ignition-source avoidance and, where applicable, constructional explosion protection. All safety-relevant components must be testable, maintainable and incorporated into clear operating instructions. What matters is the coordinated interplay of material properties, process control, mixer, peripherals and environment.
How amixon® mixes battery materials: cathode and anode powders with low contamination, gentle handling and minimal segregation
Battery materials place high demands on mixing technology and plant concept. Cathode and anode powders should ideally pick up no metal abrasion, sensitive particle structures should be preserved, and the mix must be capable of complete emptying without appreciable segregation. To achieve this, amixon® combines slow mixing motion, intensive overall flow-through, low-wear materials and a design geared towards residual emptying.
Contamination protection begins with the material
Metallic contamination can impair product quality in battery materials. amixon® therefore matches its material selection to the properties of the respective product. Depending on abrasiveness and purity requirements, wear-resistant materials, hardened or carbide-tipped mixing tools, and ceramic coatings on particularly stressed surfaces can be used.
Slow rotational motion and ideal mixing quality
Slow rotational motion is a central feature of amixon® mixing technology. It combines gentle product handling with intensive circulation of the entire mixing volume. The SinConvex® total flow-through captures the product across the entire mixing chamber and can significantly reduce local shear and impact zones.
This is particularly advantageous for cathode and anode formulations with sensitive components such as conductive carbon blacks, coated particles or spherical granules. Very high mixing quality can be achieved even with differing particle sizes and densities. The aim is a reproducible, statistically uniform distribution of all recipe components with the lowest possible mechanical stress on the product.
Virtually complete, low-segregation emptying
High mixing quality must not be lost during discharge. Emptying is therefore an essential part of the mixing concept at amixon®. ComDisc® elements support the emptying of residual product from the mixing chamber and reduce the risk of segregation during the discharge phase.
The KoneSlid® KS enables very fast emptying of the mixer. The short discharge time can limit heap formation and subsequent separation effects. As a result, the product reaches the downstream process or the intended container as completely, homogeneously and reproducibly as possible. The achievable residual emptying always depends on the product, recipe, moisture, particle structure and plant configuration.
Pressure-resistant or pressure-shock-resistant design
Fine, combustible dusts, solvent atmospheres or oxidation-sensitive active materials can occur with battery materials. The mixer can therefore be designed on a project-specific basis for inerting, vacuum operation, and pressure-resistant or pressure-shock-resistant requirements.
A pressure-resistant design is rated for defined internal pressures and can be required, for example, for vacuum processes, inerting or gas-tight process control. A pressure-shock-resistant design serves as part of an explosion protection concept where the mixer must withstand the mechanical effects of a defined explosion pressure. Which design is required follows from the risk assessment, the safety-relevant characteristic values of the product, and the explosion protection concept of the overall plant.
With appropriate design, the mixing chamber can be suitable for applications in ATEX Zone 20. For oxidation-sensitive or moisture-sensitive materials, the mix can be inerted. Gas-tight units such as the VMT and AMT can additionally enable vacuum processes and vacuum mixer-drying within the same process space. This makes it possible to reduce transfer steps, interfaces and potential sources of contamination.
Sizes up to gigafactory scale
amixon® offers mixing technology from pilot-scale mixers to large-volume production plants. HM twin-shaft mixers are available in standard sizes up to 20 cubic metres and in special sizes up to 50 cubic metres. The Gyraton® GM can be designed for large batches and is also suitable for battery masses in the range of roughly 10 to 100 cubic metres.
The design is trialled with the original product in the amixon® pilot plant before the investment is made. This allows mixing quality, gentle product handling, abrasion, residual emptying, inerting and cleanability to be assessed under realistic conditions. Particle and contamination analyses can be incorporated into the trial concept together with the operator.
Hygienic design as the constructional basis
The amixon® Hygienic Design supports cleanability, product purity and safe batch changeovers. The mixing chamber and mixing tool are seamlessly welded and ground. The mixing tool is supported only at the top. This eliminates the need for a product-contact lower shaft feed-through.
Large Clever-Cut® inspection doors with OmgaSeal® seals provide good access to the product-contact surfaces. Low-dead-space outlet fittings and optional integrated wash lances support dry or wet cleaning. Depending on the product, market and requirements, the plant can be designed to relevant hygiene concepts and standards.
amixon® thus combines slow rotational motion, very high mixing quality, virtually complete emptying and a design that can be rated for pressure resistance or pressure-shock resistance. The result is a mixing plant that processes demanding battery materials gently, safely and reproducibly.