Which mixers are suitable for battery materials (cathode/anode powders) to preserve particle structure and conductivity?
For battery materials, mixers must distribute active materials, conductive additives and binders homogeneously without uncontrollably altering sensitive particles, coatings or agglomerate structures. No single mixer type is suitable for all applications. What matters are the process step, the recipe and the required balance between product protection and dispersion energy.
For free-flowing cathode and anode powders, vertical conical mixers, vertical precision mixers and gently operated paddle or ploughshare mixers are particularly suitable. They generate a three-dimensional product movement at comparatively low mechanical stress. This allows active materials such as NMC, LFP, graphite or silicon composites to be homogenised without causing unnecessary abrasion or pronounced size reduction.
Tumble, container and V-mixers are likewise very gentle. They are suitable above all for free-flowing powders with similar physical properties. For incorporating and dispersing very fine conductive additives such as carbon black, CNTs or graphene, they are often not sufficient. In this case, a separate, precisely dosed dispersing step may be required.
For dry-coating and dry-electrode processes, intensive mixers are used in which product transport and local dispersion can be controlled separately. The active material is circulated gently. Fine conductive additives and powdered binders can be incorporated in a targeted manner. The shear energy must be set so that conductive-additive agglomerates are sufficiently distributed without unnecessarily stressing the active material or surface coatings.
For anode and cathode slurries, vacuum planetary mixers, dual planetary mixers and intensive batch mixers with an adjustable dispersing unit are proven solutions. They combine the slow circulation of highly viscous masses with targeted dispersion of conductive carbon black, binder and other fine fractions. Vacuum supports degassing of the slurry and reduces air entrapment. Coolable mixing vessels limit heat input and improve the reproducibility of the coating process.
For large continuous processes, continuous dispersing and mixing systems or twin-screw extruders can be useful. Prerequisites are precise gravimetric dosing, a defined residence time and robust process monitoring. The final selection must be made through trials with the original recipe. Only in this way can it be demonstrated that particle structure, dispersion, rheology, coating quality and electrical cell performance are all compatible.
How amixon® solves this task
This is how amixon® mixes battery materials: cathode and anode powders without contamination and without segregation. amixon® is only partially active in the field of slurry production and micro-de-agglomeration for dry battery active materials. amixon®'s far greater activity extends to raw material homogenisation – in particular where batches of up to 100 m³ need to be mixed to a technically ideal standard. Gyraton® mixing silos are used for this purpose. They produce ideal mixing qualities with minimally small drives. The homogenisation process extends over several hours. The combination of two movements is the secret to ideal mixing qualities: the rotation of a SinConcave®/SinConvex® helical mixing tool and the precession of the mixing-shaft axis. Only when the input materials are homogeneous can the subsequent process route be operated economically – without quality fluctuation and at the best possible efficiency.
Contamination protection begins with the material
With battery materials, metal abrasion is a knock-out criterion for quality. amixon® addresses this in several stages: wear-resistant materials (Hardox, duplex stainless steels), hardened or carbide-tipped mixing tools, and ceramic plasma coatings on heavily stressed surfaces. The low-speed operating mode (from approximately 0.8 m/s circumferential speed) reduces abrasion generation at the source – friction and impact energy remain minimal.
Preserving structure and additives
Cathode and anode formulations contain sensitive constituents – conductive carbon blacks, coatings, spherical particles. SinConvex® total flow-through homogenises without shear or impact zones; the mixing quality is the technically ideal random mixture, even with extreme differences in density and grain size (reference environment: powder metallurgy, density ratios above 1:20, particles 2–70 µm). ComDisc® elements, or the second-scale discharge of the KoneSlid® KS, prevent segregation during discharge.
Safety: Zone 20 and inerting
The mixing chamber is designed for ATEX Zone 20; on request, the process can be run under vacuum with the mix inerted – relevant equally to ignitable fine dusts and to oxidation-sensitive active materials. Gas-tight apparatus (VMT, AMT down to 5 mbar abs.) keeps solvent atmospheres safely contained within the system and enables vacuum mixer-drying in the same apparatus.
Unit sizes up to gigafactory scale
From pilot-plant mixers through HM twin-shaft mixers (standard grid up to 20 m³, special sizes up to 50 m³) to the Gyraton® GM, which is explicitly designed to mix battery masses precisely and gently in batches from 10 to approximately 100 m³. amixon® provides evidence of abrasion, mixing quality and inerting in advance, in the pilot plant with the original product – documented, including the operator's particle and contamination analysis.
Verification in the amixon® pilot plant
Before the investment comes the proof: at the amixon® pilot plant at the Paderborn headquarters, more than 30 test units in different sizes stand ready – supplemented by pilot plants in Japan, India, Thailand, China, South Korea and the USA. The trials are run with the original product, with real fill levels and batch sizes, in the intended temperature and pressure range. Mixing quality, product protection, energy input, cleanability and reproducibility in later series operation are assessed; the results are evaluated and documented together with amixon® experts – as a robust basis for the decision that clears away technical and economic risks before the purchase.
Hygienic design as the constructional basis
All the properties described rest on amixon® hygienic design: the mixing chamber and mixing tool are welded free of joints and ground smooth, and the mixing tool is mounted at the top only – the contamination-critical lower shaft passage is eliminated. Large Clever-Cut® inspection doors with permanently dead-space-free OmgaSeal® sealing make all product-contact surfaces ergonomically accessible; dead-space-free discharge devices and integrated washing lances (fully automatic wet cleaning on request) make both dry and wet cleaning validatable – in accordance with the EHEDG guidelines, FDA hygiene guidelines and 3-A Sanitary Standards.