“A current collector is more than an electrical contact: in magnesium batteries, its interaction with the anode and electrolyte can influence the stability of the entire cell.”
Battery safety issues and challenges: transfer from lithium to magnesium technology
One of the key challenges for expanding any battery technology and transferring it to the wider market is safety. For batteries used in large-scale applications, particularly electric vehicles, it is essential to ensure safe operation under normal conditions while minimizing the risk of severe failure in the event of an accident. Although Li-ion batteries are currently the dominant technology for electric vehicles, their safety remains a concern, as demonstrated by a number of accidents involving intense fires and explosions.
One of the factors contributing to this issue is the high chemical reactivity of lithium, which is one of the strongest reducing metals. To address this challenge, alternative battery chemistries based on less reactive metals can be considered. Magnesium is a particularly promising candidate, combining high volumetric capacity with greater chemical and electrochemical stability compared with lithium metal and other highly reactive metals.
Safety can be further enhanced through the modification of electrode materials with protective coatings. Such coatings can suppress undesirable reactions between the electrode and electrolyte and protect the electrode material from the surrounding environment under abnormal conditions. At the same time, they can improve the stability of the electrode during normal operation, reducing material degradation and with the potential to enhance cycling stability and battery lifetime
The key parameters of such coatings are their uniformity and thickness. The coating should uniformly cover the entire surface of the active material without leaving uncovered areas, ensuring consistent protection. At the same time, it should be sufficiently thin to allow the transfer of charged ions through the coating during the charge and discharge processes. Therefore, achieving an optimal balance between effective protection and efficient ion transport is essential for the successful application of protective coatings.
Atomic Layer Deposition: A Versatile Tool for Protective Coatings
One of the most powerful techniques for production of conformal, ultrathin thin-film layers is atomic layer deposition (ALD). In its simplest form, ALD is based on the alternating introduction of a volatile metal-containing precursor and an oxygen-containing reactant, such as water or ozone, into the ALD reactor. These precursors react with the substrate or particles surface in a controlled and self-limited process, enabling the growth of a metal-oxide thin films. The thin films thickness is precisely controlled by the ALD parameters, mainly the number of cycles.
Beyond this basic approach, ALD can be adapted to produce a wide range of materials and compositions. For example, molecular layer deposition (MLD) extends the concept of ALD to the deposition of organic materials through the sequential introduction of organic precursors. Combining the two approaches in ALD/MLD enables the deposition of hybrid organic-inorganic materials, providing conformal thin films with tunable chemical composition and improved mechanical flexibility.
The versatility of these techniques also allows multiple metal precursors to be incorporated into a single coating process, enabling the formation of mixed-metal compounds. In addition, by introducing appropriate non-metal-containing precursors, coatings with different chemistries, such as phosphates, sulfates, and other functional materials, can be produced. This broad chemical versatility and controlled process capability make the ALD and MLD highly attractive for tailoring protective coatings to the specific requirements of battery electrodes.
ALD in the HighMag project: Expertise and Capabilities at Bar-Ilan University
As part of the European Union’s Horizon Europe-funded HighMag consortium, Prof. Malachi Noked’s group at Bar-Ilan University (BIU) is responsible for developing ALD-based techniques for applying protective coatings to a wide range of battery components using different ALD thin films chemistries. These include Mg powder anodes, various cathode materials for Mg-ion and Mg-sulphur batteries and separators materials.
Scheme 1 presents schematic illustration of the ALD process for Mg powder surface modification. One ALD cycle consists of sequential metal-precursor exposure, purge, oxidant exposure, and purge, and is repeated to achieve a thin, conformal protective coating with controlled thickness.
Scheme 1: ALD Process for Protective Coatings on Mg powder
Introduction – An essential component that is easy to overlook
When discussing rechargeable batteries, attention usually focuses on the active materials that store energy. Yet electrodes also depend on components that do not directly contribute to energy storage. One of these is the current collector: a conductive substrate that connects an electrode to the external circuit. In commercial lithium-ion cells, copper and aluminium foils are familiar examples. Their selection reflects a balance of electrical conductivity, electrochemical compatibility, cost and processability.
For emerging magnesium-based batteries, this choice cannot simply be transferred from established lithium-ion technology. Different electrode reactions, electrolyte chemistries and operating conditions create a distinct environment at the electrode interface. A current collector that performs well in one cell chemistry may behave very differently in another.
The challenge – Conductivity alone is not enough
The basic task of a current collector is straightforward: it must carry electrons efficiently while supporting the electrode. However, conductivity is only one part of the picture. The collector also needs to remain sufficiently stable in contact with the electrolyte across the relevant electrode potential range. Unwanted surface reactions or corrosion can modify the contact, increase resistance and complicate interpretation of electrochemical measurements.
This is particularly relevant for magnesium metal and magnesium-based powder anodes. Their performance is strongly influenced by the interface between the active material and the surrounding electrolyte. Magnesium electro-plating and -stripping involve the deposition and dissolution of metal, while the formation of resistive surface layers can interfere with these processes. At the same time, the collector may influence local current distribution and the electrical connection to individual particles within a powder-based electrode.
Materials such as copper, aluminium, nickel and stainless steel therefore cannot be treated as interchangeable supports. Each forms different surface oxides and interacts differently with its chemical environment. Even a nominally identical collector may show different behaviour when the electrolyte formulation changes. Surface condition, manufacturing history and electrode preparation may also affect the outcome. This makes it important to evaluate the complete combination of current collector, magnesium electrode and electrolyte rather than ranking substrates solely by their bulk properties.
From material selection to reliable electrode testing
A systematic assessment begins with identifying candidate substrates that offer suitable conductivity, mechanical properties and practical availability. Their compatibility can then be examined under conditions relevant to the intended cell configuration. Electrochemical tests help reveal whether the collector contributes unwanted reactions and whether its behaviour remains stable over time.
For magnesium-based anodes, repeated plating and stripping experiments are especially informative. Changes in potential response, polarisation or cycling stability may signal evolving interfacial processes, although these observations must be interpreted carefully: they are not, by themselves, proof of a particular degradation mechanism. Comparison across current collectors, electrolytes and suitable reference configurations helps distinguish effects associated with the substrate from those arising elsewhere in the cell.
Surface and post-mortem characterisation can provide complementary information about electrode morphology, contact integrity and possible changes at the interface. Beyond conventional metal foils, coated substrates may offer additional routes to tailor surface behaviour. Any potential benefit must, however, be weighed against coating durability, electrical contact, manufacturing complexity and suitability for later scale-up.
The HighMag connection – ZSW’s contribution
Within the European HighMag project, the Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW) contributes its expertise in electrochemical testing and battery materials evaluation to the development of magnesium-based battery concepts. One area of investigation is the compatibility of different current collectors with magnesium powder anodes and the electrolytes used in the project.
This work addresses a practical question: which combinations of electrode support, active material and electrolyte can provide a sufficiently stable basis for reproducible cell operation? By comparing metallic substrates and exploring interface-related effects under controlled electrochemical conditions, ZSW aims to support the selection of suitable components for further electrode and cell development. The objective is not only to identify promising materials but also to understand the constraints that should guide their integration into more practical configurations.
The assessment of current collectors complements other HighMag activities involving electrode materials, protective strategies and advanced characterisation. These connected perspectives are important because improving one component in isolation does not guarantee improved behaviour of the full battery.
Conclusion – Looking beyond the active material
In magnesium battery research, the current collector deserves more attention than its modest role in a cell schematic might suggest. It must provide an effective electrical pathway while remaining compatible with the electrode and electrolyte throughout operation. Selection should therefore be based on the electrochemical system as a whole, not simply on familiar choices from other battery technologies.
Through its work in HighMag, ZSW is helping to clarify these material and interface requirements for magnesium-based powder anodes. Building this understanding is one step towards more reliable experiments, informed component selection and, ultimately, practical magnesium battery cells.
This article was originally created by Mario Marinaro, Team Leader, Electrochemical Energy Technologies / ZSW Baden-Württemberg.
You can read the original piece here
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