Salgenx • Design • Develop • Analysis • Grid Scale Flow Battery
TEL: 1-608-238-6001 (Chicago Time Zone )
Email: greg@infinityturbine.com
The underlying chemistry is sound and the two proposed fixes target real historical failure points — but the headline energy density figures describe a theoretical ceiling, not a deliverable system.
A new pitch is circulating for a zinc-chlorine flow battery that adds a limestone-based electrolyte additive, stores chlorine in an oil-based carrier instead of refrigerated hydrate, and uses dimensionally stable anode (DSA) electrodes. The claim: 600–900 Wh/L and 200–350 Wh/kg on an active-materials basis — roughly on par with lithium chemistries and several times better than existing flow batteries. Here's what holds up, what needs specificity, and what the numbers actually mean.
Dividing that energy by the combined mass of one mole of Zn (65.4 g) and Cl₂ (70.9 g) gives 833 Wh/kg as the absolute reactant-only ceiling — no water, no electrolyte, no cell hardware. The pitch's 200–350 Wh/kg claim is 24–42% of that ceiling, which is thermodynamically plausible and, if anything, conservatively framed — comparable to how 3,860 Wh/kg is quoted as lithium metal's theoretical ceiling that no real cell approaches.
The volumetric claim is more revealing. Using pure liquid Cl₂ (~1.4 g/cm³) and solid Zn (7.14 g/cm³) with zero dilution, theoretical density works out to roughly 1,900 Wh/L — well above the claimed 600–900 Wh/L. Re-running the calculation assuming chlorine is carried as a hydrate (Cl₂·~7H₂O, the storage form used in the historical EDA design) lands at almost exactly 650 Wh/L. That's a strong signal the "oil-stored chlorine" concept is functionally playing the same role hydrate storage did — sequestering Cl₂ in a dense secondary phase — just via a complexing solvent instead of refrigerated ice.
There's real precedent for calcium carbonate in zinc anode chemistry — CaCO₃ combined with acetylene black has been used as an artificial solid-electrolyte-interphase coating that suppresses zinc dendrite growth, and calcium compounds (Ca(OH)₂, CaCO₃, CaCl₂) are known dendrite suppressants in alkaline zinc batteries via CaZn(OH)₄ formation. That mechanism is plausible here.
The complication: ZnCl₂ flow electrolytes typically run mildly acidic (pH 2–4) to keep Zn²⁺ dissolved and prevent hydroxide precipitation. In that environment, CaCO₃ reacts stoichiometrically — CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ — converting to inert CaCl₂ and releasing CO₂ gas that needs venting from a sealed, recirculating loop. That makes it a consumable buffer, not a catalytic or self-regenerating additive, unless it's specifically deployed as a solid coating or fixed bed rather than a dissolved electrolyte component. Worth getting a straight answer on which of those three deployment modes is intended.
| Chemistry | Basis | Wh/L | Wh/kg |
|---|---|---|---|
| Zn-Cl₂ (this pitch) | Theoretical, active materials only | 600–900 | 200–350 |
| Vanadium redox (VRFB) | System level, deployed | 25–35 | 15–25 |
| Zinc-bromine | System level, deployed | 50–70 | 50–70 |
| Zn-Cl₂ (EDA program, 1970s–80s) | System level, actually built | 60–90 | 60–70 |
| Lithium-ion (NMC) | Commercial pack level | ~700–750 | ~250–300 |
The "3x better than other flow batteries" framing compares a theoretical active-materials number for the new chemistry against system-level numbers for VRFB and zinc-bromine. On a like-for-like theoretical basis, the gap is closer to 10–30x, not 3x — which suggests the "3x" figure is actually a realistic system-level projection, quietly paired with a theoretical headline number. That's the same framing gap that made the original EDA program's numbers look better on paper than they performed in the field.
One point worth flagging for competitive context: this approach reintroduces free chlorine gas as a stored reactant in a carrier oil, which brings EPA Risk Management Plan thresholds and siting/insurance costs that a neutral-pH saltwater chemistry avoids by design.