Magnesium Chloride for Energy & Cement: Magnesium-Ion Batteries and Sorel Cement Explained

Magnesium chloride is best known for melting ice and making tofu. But the same abundant, water-soluble salt is now turning up in two of the most important problems in clean technology: how to store renewable energy without relying on scarce lithium, and how to make cement without its enormous carbon footprint. Here is the chemistry behind those emerging uses — and an honest look at what grade you actually need.

What is magnesium chloride, and where does it come from?

Magnesium chloride is the ionic compound formed between one magnesium cation (Mg²⁺) and two chloride anions (Cl⁻). In its pure anhydrous form it is MgCl₂, but the form you almost always handle — and the form Alliance Chemical stocks — is the hexahydrate, MgCl₂·6H₂O, a white crystalline solid in which six water molecules are bound to each magnesium ion.

Most of the world’s magnesium chloride is not mined as a rock; it is harvested from water. Seawater contains roughly 1,290 mg of magnesium per liter, and the concentrated brine left over after sea-salt or potash production — called bittern or, in its mineral form, bischofite — is especially rich in it. That matters for the energy and cement stories below: unlike lithium, cobalt, or nickel, magnesium is genuinely abundant and can be recovered from brine and even from desalination waste streams, which is why so many researchers see it as a circular-economy raw material.

Industrially, magnesium chloride is produced along a few well-worn routes. The classic seawater process — pioneered by Dow Chemical on the Gulf Coast — precipitates magnesium hydroxide from seawater, then converts it to the chloride. In potash regions it is recovered by dehydrating carnallite (KCl·MgCl₂·6H₂O), and the hexahydrate crystallizes directly out of concentrated bittern. Anhydrous magnesium chloride, which several energy applications demand, is the hard part: you cannot simply bake the water out of the hexahydrate because it hydrolyzes to magnesium hydroxychloride and hydrogen chloride. Producers instead dehydrate carnallite under a dry hydrogen-chloride atmosphere or carbo-chlorinate magnesium oxide — a meaningful reason anhydrous, battery-suitable material costs more than the food-grade crystals.

This article focuses on the emerging energy and construction angles. If you want the full rundown of everyday uses — ice melt, dust control, bath soaks, tofu (nigari), and food applications — see our complete magnesium chloride guide.

What are the key properties of MgCl₂·6H₂O?

Two properties drive nearly every advanced application: magnesium’s divalent (2+) charge, which lets each ion carry twice the charge of a singly-charged ion like lithium or sodium, and magnesium chloride’s extreme solubility in water and many polar solvents, which makes it easy to deliver into a reaction or a cement mix.

Why is magnesium suddenly interesting for energy storage?

Lithium-ion batteries dominate today, but lithium is geographically concentrated and increasingly expensive, and lithium metal anodes form dendrites — needle-like growths that can short a cell. Magnesium offers a tempting set of answers to all three problems.

First, abundance: magnesium is the eighth most abundant element in Earth’s crust — roughly 2.9% of it — and is dissolved in every ocean, so a magnesium-based supply chain is far less constrained than lithium’s. Second, charge density: because Mg²⁺ is divalent, each ion shuttles two electrons’ worth of charge, giving magnesium metal a very high theoretical volumetric capacity (about 3,833 mAh per cubic centimeter, well above lithium’s). Third, and most importantly for safety, magnesium tends to plate smoothly rather than as dendrites, which in principle allows a metal anode without the short-circuit risk that has held back lithium-metal cells.

The supply-chain argument has only grown louder. Lithium, cobalt, and nickel are concentrated in a handful of countries, exposing battery makers to price spikes and trade risk; magnesium is everywhere and can be pulled from the same brines that already produce salt and potash. For stationary storage — the giant battery banks that smooth out solar and wind — weight barely matters, so a heavier but cheaper, safer, more abundant chemistry is exactly the kind of trade the grid would happily make. That is why magnesium keeps reappearing on national long-duration-storage research agendas even though it is years behind lithium commercially.

Can magnesium chloride be used in battery technology?

Yes — but as a building block and electrolyte ingredient in research-stage magnesium batteries, not as a drop-in product you charge today. The central challenge in magnesium batteries has always been the electrolyte: the salt-and-solvent system that lets Mg²⁺ move between electrodes without forming a blocking passivation layer on the metal.

To see why chloride matters, you have to understand the core problem. When magnesium metal meets a conventional electrolyte (the kind that works beautifully for lithium), it instantly grows a thin surface film that magnesium ions cannot pass through — a passivation layer that effectively shuts the battery down. Lithium tolerates such films because lithium ions can migrate through them; the divalent magnesium ion cannot. So the whole game in magnesium electrolytes is finding a chemistry that either prevents that film or keeps the surface clean enough for ions to cross.

Magnesium chloride turns out to be a key piece of the solution. Several of the most-studied reversible magnesium electrolytes are chloride-based complexes built from MgCl₂: the magnesium aluminum chloride complex (MACC), and all-phenyl-complex (APC) electrolytes that combine MgCl₂ with other reagents. In these systems the chloride from MgCl₂ helps strip away passivating films and supports efficient, reversible magnesium plating and stripping. In other words, MgCl₂ is not the battery — it is one of the reagents researchers combine to make a working magnesium electrolyte.

The breakthrough that opened the field came in 2000, when researchers demonstrated the first practical rechargeable magnesium cell using a Chevrel-phase molybdenum-sulfide (Mo₆S₈) cathode paired with a magnesium-organohaloaluminate electrolyte. That cathode is still a benchmark precisely because most other materials trap the slow-moving divalent ion. Chloride-bearing electrolytes derived from MgCl₂ were the key enabler — they keep the magnesium surface active — and almost every high-performance magnesium electrolyte since has kept chloride in the recipe.

There is also a more mature energy role worth mentioning: magnesium-chloride-containing molten salts (for example MgCl₂ blended with KCl and NaCl) are leading heat-transfer and thermal-storage fluids for next-generation concentrated solar power, because they stay liquid across a wide, high-temperature range at low cost. That application uses the anhydrous, technical-grade material in bulk — a different spec from the laboratory hexahydrate, but the same underlying chemistry of abundance and thermal stability.

How do magnesium-ion batteries compare to lithium-ion?

It is tempting to frame this as a contest with a winner. It is not — at least not yet. The honest comparison is a trade between promise and maturity. Magnesium wins on cost, abundance, and inherent safety; lithium wins, decisively for now, on the only thing that ships products — a mature, optimized supply chain and a deep catalog of high-performance cathodes. The table below lays out where each chemistry actually stands today rather than where enthusiasts hope magnesium will be.

The realistic near-term picture: magnesium is a strong candidate for stationary grid storage, where cost-per-kilowatt-hour and safety matter more than the weight and energy density that make lithium ideal for phones and cars. That is exactly the niche where an abundant, dendrite-resistant chemistry could win — if the electrolyte and cathode problems are solved.

There is a circular-economy thread running through both the battery and the cement stories. The magnesium for either can be recovered from waste streams that already exist — the bittern left over from sea-salt production, the brine rejected by desalination plants, and potash tailings — turning a disposal problem into a feedstock. As desalination expands worldwide, the volume of magnesium-rich reject brine grows with it, and several groups are working on pulling magnesium compounds out of that brine specifically to feed cement and energy applications. An abundant element that can be sourced from waste is precisely the profile a durable clean-tech supply chain wants.

What is Sorel cement, and how does magnesium chloride make it?

Sorel cement — more precisely magnesium oxychloride cement (MOC) — is made by mixing reactive magnesium oxide (MgO) powder with a concentrated solution of magnesium chloride. The two react to form interlocking crystalline phases (notably the 5·1·8 and 3·1·8 phases) that set quickly into a hard, dense binder. Patented by Stanislas Sorel in 1867, it is one of the oldest non-Portland cements.

The two binding phases that give MOC its strength are usually written as phase 3 (3Mg(OH)₂·MgCl₂·8H₂O) and phase 5 (5Mg(OH)₂·MgCl₂·8H₂O); phase 5 is the desirable one, and getting the MgO-to-MgCl₂ ratio right is what controls how much of it forms. Get the ratio wrong and you grow weaker phases or leave unreacted magnesia. This is also why the purity and consistency of the magnesium chloride matter to a formulator dialing in a mix — variable chloride content shifts the whole phase balance.

MOC has properties Portland cement cannot match: very high early strength, excellent fire resistance, good abrasion resistance, low thermal conductivity, and the ability to bond with organic fillers like wood flour and sawdust. That is why you find it in industrial flooring, fire-rated boards, decorative and lightweight panels, insulation, and grinding wheels. Its historic weakness is poor water resistance — the phases can leach and lose strength under prolonged moisture — which modern soluble-phosphate admixtures, fly ash, and surface treatments have substantially improved, broadening where MOC can be used.

Is magnesium cement really lower-carbon?

This is where careful language matters. Ordinary Portland cement is responsible for roughly 7–8% of global CO₂ emissions, both from the fuel needed to heat kilns to about 1,450 °C and from the limestone itself, which releases CO₂ as it converts to lime. Magnesium-based cements can improve on both counts — but “carbon negative” is a claim that depends entirely on how the magnesia is sourced.

Reactive magnesia (often called caustic-calcined MgO) can be made at roughly 700–1,000 °C, well below the ~1,450 °C that Portland clinker demands, which cuts fuel emissions. More importantly, some magnesium cements — particularly reactive-magnesia and magnesium-carbonate systems — reabsorb CO₂ from the air as they cure, a process called carbonation, which can offset part or, in favorable cases, all of their production emissions. That is the basis for the “carbon-negative cement” headlines, an idea popularized by reactive-magnesia ‘eco-cement’ research.

The catch lives upstream, in the magnesia. If the MgO is calcined from magnesite (magnesium carbonate), that step releases CO₂ just as limestone does for Portland cement — so the carbonation during curing only claws back what was emitted, at best landing near neutral. The genuinely low-carbon routes make magnesia from sources that do not off-gas carbon: magnesium-rich brines, seawater, or silicate rocks like olivine and serpentine. Magnesium chloride sits right in the middle of those brine routes, which is part of why the salt is interesting to the green-cement community. The honest takeaway: the chloride reactant is constant; the carbon footprint is decided by where the magnesia came from.

What grade of magnesium chloride do these applications need?

Here is the practical part, and we will be direct about what we do and do not sell. Alliance Chemical stocks Magnesium Chloride Hexahydrate, USP Grade (FCC/USP, 99.0–100.5% assay) — a high-purity, food- and pharmaceutical-quality white crystalline powder. That is an excellent material for laboratory and research work, and for pilot-scale formulation, where consistency and low impurity levels matter more than tonnage price.

Why purity is worth paying for in R&D: trace impurities are exactly what muddies early results. In a magnesium electrolyte, stray water or metal-ion contaminants poison the very plating reaction you are trying to characterize; in a Sorel-cement mix, inconsistent chloride content swings the phase balance and your strength data with it. A high, well-documented assay with a certificate of analysis on every shipment lets you change one variable at a time — which is the entire point of bench and pilot work. It is also why food- and pharmaceutical-grade material, made to tight specifications, is often the cleanest, most reproducible starting point even for non-food experiments.

In short: if you are a researcher, formulator, or pilot-line engineer who needs clean, well-characterized magnesium chloride to explore these emerging applications, our USP-grade hexahydrate is a strong fit. If you are scaling to production tonnage of battery molten salts or cement, you will likely specify an anhydrous or technical grade in bulk — tell us the application and target purity and we will help you spec it, including sourcing options beyond the catalog SKU.

Key numbers & authoritative sources