The basic architecture of a liquid metal battery is deceptively simple. Two liquid metal electrodes of different densities sit in a container, one above the other, with a molten salt electrolyte sandwiched between them because it is denser than the light negative electrode but less dense than the heavy positive electrode. Because everything is liquid, there are no fragile solid microstructures to crack or degrade, which is why these cells can tolerate tens of thousands of charge and discharge cycles. The concept traces back to fused-salt galvanic cells studied at Argonne National Laboratory in the 1960s, but it was the 2013 landmark review by Donald Sadoway’s group at MIT and the 2014 demonstration of a lithium-antimony-lead cell in Nature that transformed the idea into a serious contender for stationary storage. Sodium, with its abundance, low cost, and favorable electrochemistry, has emerged as the most attractive negative electrode metal for grid applications.

Yet sodium brings a fundamental problem that has dogged the technology for years. Molten sodium dissolves appreciably in conventional single-cation halide molten salts, such as the sodium chloride-based systems long used as electrolytes. Dissolved sodium, along with solvated electrons in the melt, can shuttle across the electrolyte to the positive electrode without passing through the external circuit, causing severe self-discharge and dragging Coulombic efficiency down to levels that would be unacceptable in a commercial product. The review highlights how researchers have attacked this problem by reformulating the electrolyte itself. Instead of relying on a single cation, teams have developed multi-cation molten salts that blend sodium with lithium, calcium, potassium, or other ions, fundamentally changing the chemistry of the melt and suppressing the dissolution of sodium metal.

The mechanism behind this improvement is one of the most technically interesting threads in the review. In a multi-cation electrolyte, the additional cations compete for space in the salt structure and alter the activity of sodium in the melt, lowering its solubility and thereby choking off the parasitic dissolution pathway that causes self-discharge. Multi-cation salts also tend to have lower melting points than their single-cation counterparts, which allows the entire battery to operate at reduced temperatures. That matters enormously for engineering: lower operating temperatures mean less thermal stress on seals and containers, slower corrosion of structural materials, and reduced parasitic energy consumption to keep the cell molten. Studies from groups in China and Germany, including work on multi-cationic electrolytes published in Energy Storage Materials and the Journal of Power Sources, have demonstrated sodium-based cells with markedly improved cycling stability and efficiency when these mixed-salt electrolytes are employed.

The positive electrode presents a different set of challenges. In a sodium-based liquid metal battery, the positive electrode is typically a molten alloy of antimony, bismuth, tin, or combinations of these metals, and during discharge, sodium ions arriving from the electrolyte alloy into this pool. The trouble is that sodium diffuses sluggishly through many of these alloy electrodes, which limits how much of the active material can actually be used and therefore caps the energy density of the cell. The review describes design principles for overcoming this bottleneck, including engineering liquid-phase diffusion pathways within the electrode and tuning the alloy composition to accelerate interfacial reaction kinetics. Ternary systems such as bismuth-antimony-tin have shown synergistic stabilization mechanisms, with bismuth contributing a self-healing action that helps the electrode recover its structure over repeated cycles, an approach the review’s lead author has explored in earlier work on lithium-based systems.

Interfacial behavior between the liquid electrodes, the molten salt, and the solid current collectors emerges as another decisive factor. Wetting, the tendency of a liquid to spread across a solid surface, governs how well the molten positive electrode makes electrical contact with its current collector, and poor wetting can raise internal resistance and destabilize cycling. Researchers have found that improving wettability at the positive electrode enhances the cycling stability of bismuth-based cells, and the review emphasizes that controlling these interfacial phenomena is as important as bulk chemistry. The review also covers the charge and discharge mechanisms themselves, noting that mass transport in the liquid phases creates asymmetries between charging and discharging behavior, since convection patterns driven by thermal gradients and electrical currents redistribute species differently depending on the direction of operation.

That last point opens onto one of the most fascinating aspects of liquid metal battery physics: the multiphysics coupling inside the cell. Because the electrodes and electrolyte are all molten, the battery is a fluid-dynamical system as much as an electrochemical one. Thermal convection of the Rayleigh-Bénard type, driven by temperature differences between the bottom and top of the cell, interacts with electro-vortex flows generated by the current entering and leaving the electrodes, and with solutal convection caused by composition gradients during alloying and dealloying. A comprehensive review of the fluid mechanics of sodium-zinc liquid metal batteries published in Applied Physics Reviews catalogued these coupled phenomena, and the new Ionics review integrates them into a thermal-flow-electrical-corrosion framework. How these flows behave determines whether the salt layer stays cleanly between the electrodes or whether metal droplets could short the cell, so understanding and regulating them is essential for scaling up.

Scaling up is precisely where the engineering challenges become daunting. A grid-storage module must be sealed reliably against oxygen and moisture ingress for decades while operating at several hundred degrees Celsius, and the review identifies sealing, thermal management, and corrosion as the central integration problems. Molten salts and molten metals are aggressive corrosive media, and current collectors in particular must survive prolonged contact with them; research on stainless steel and coated collectors for lithium-antimony-tin cells illustrates the materials science effort underway. Thermal management systems, studied numerically for liquid metal battery modules, must keep the entire cell within its operating window without wasting energy. Cost, the ultimate arbiter for grid storage, depends on cheap raw materials but also on manufacturing reliability and the ability to build large-capacity cells without defects.

Looking forward, the review maps out four directions that its authors believe will determine whether sodium-based liquid metal batteries make the leap from laboratory to substation. Computation-driven materials screening promises to accelerate the discovery of optimal electrolyte and electrode combinations by simulating thermodynamics and kinetics before any crucible is filled. Multiphysics collaborative regulation aims to exploit, rather than merely tolerate, the fluid dynamics of the cell to enhance mass transport and performance. Highly reliable packaging must deliver the hermetic, corrosion-resistant enclosures that decades of service demand. And full-lifecycle recycling, already demonstrated for key materials of low-cost liquid metal batteries in work published in ACS Sustainable Chemistry and Engineering, could give the technology a decisive sustainability advantage, since the constituent metals and salts can in principle be recovered and reutilized with relative ease compared with the complex chemistries of conventional lithium-ion cells.

The stakes for getting this right are considerable. Recent analyses of long-duration storage, including studies of the value of storage in zero-emissions grids and of Europe’s vulnerability to prolonged wind droughts known as Dunkelflaute events, all point to the same conclusion: decarbonized electricity systems will need vast quantities of affordable storage capable of discharging for many hours or days. Sodium-based liquid metal batteries, with their abundant raw materials, tolerance of deep cycling, and potential for decades-long lifetimes, fit that requirement profile unusually well. The review by Cui, Du, and Wang makes clear that the remaining hurdles are real, spanning electrolyte chemistry, electrode kinetics, fluid mechanics, and heavy engineering, but it also shows a field that has moved from proving the concept to systematically dismantling each obstacle. If the multi-cation electrolyte strategy and the accompanying electrode and packaging advances continue on their current trajectory, the strange and elegant idea of storing electricity in pools of molten metal may soon be humming quietly beside the power plants it helps to tame.

Subject of Research: Sodium-based liquid metal batteries for grid-scale energy storage

Article Title: Research progress in Na-based liquid metal batteries: multi-cation systems, interfacial mechanisms, and engineering challenges

Article References: Cui, K., Du, Y., & Wang, L. (2026). Research progress in Na-based liquid metal batteries: multi-cation systems, interfacial mechanisms, and engineering challenges. Ionics. https://doi.org/10.1007/s11581-026-07567-z

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07567-z

Keywords: sodium liquid metal batteries, molten salt electrolytes, multi-cation systems, grid energy storage, self-discharge, alloy electrodes, interfacial wetting, electro-vortex flow, thermal management, corrosion, recycling, long-duration storage

The approach belongs to a family of technologies known as electrochemically mediated carbon capture, or EMCC. Rather than relying on heat to strip carbon dioxide from a solvent, as conventional amine scrubbing plants do, EMCC uses molecular sorbents whose affinity for CO2 can be switched on and off simply by adding or removing electrons. In the capturing state, the sorbent molecule is reduced at an electrode and becomes a strong Lewis base that eagerly binds carbon dioxide. When the bound gas needs to be released, a small reverse voltage oxidizes the adduct, liberating a concentrated stream of CO2 and regenerating the sorbent for another round. Because the process is driven by electricity, it pairs naturally with renewable power and avoids the enormous thermal energy penalty that has historically made post-combustion capture so expensive.

In most demonstrations of this concept, however, the electrochemical cell has contained a critical complication: an ion-exchange membrane that physically separates the sorbent compartment from the counter-electrode compartment. The membrane’s job is to shuttle charge-balancing ions between the two sides while keeping the redox-active sorbent molecules away from the counter-electrode, where they would otherwise react indiscriminately. But membranes bring a long list of problems. They add resistance, which raises the voltage and therefore the energy cost of every cycle. They degrade in the organic solvents often used in these systems. They are expensive to manufacture in large areas, and their permselectivity is rarely perfect, allowing some sorbent to leak across and undermining efficiency over time. For a technology that aspires to gigatonne-scale deployment, the membrane has become a liability.

The Johns Hopkins team, led by corresponding author Yayuan Liu, set out to eliminate the membrane entirely by substituting a solid-state counter-electrode that can host the charge-balancing ions within its own crystal lattice. The idea sounds simple, but it collides with a fundamental obstacle that has deterred researchers for years: self-discharge. In a membraneless cell, the reduced sorbent molecules inevitably encounter the counter-electrode surface. If the counter-electrode is thermodynamically poised to accept their electrons, the sorbent will be re-oxidized there unintentionally, quietly undoing the capture chemistry and wasting the electrical energy that was invested in the first place. It is analogous to a battery that drains itself even when nothing is connected.

The pivotal insight of the new study is that this self-discharge is not governed by the thermodynamic driving force, as conventional wisdom assumed, but rather by kinetics, and specifically by the rate at which ions diffuse within the solid counter-electrode material. The team demonstrated that even when the thermodynamic potential difference between the sorbent and the counter-electrode would predict rapid parasitic reaction, a counter-electrode with sluggish solid-state ion transport can suppress the process to negligible levels. The practical consequence is profound: the design criterion for a membraneless capture cell shifts from hunting for counter-electrode materials with precisely matched redox potentials, a nearly impossible constraint, to selecting materials whose ionic diffusion is kinetically slow on the timescale of a capture cycle. That reframing opens a vastly larger palette of candidate materials.

Guided by this kinetic design rule, the researchers screened sodium intercalation compounds and identified sodium iron phosphate, NaFePO4, as an ideal partner for an azopyridine molecular sorbent dissolved in a DMSO electrolyte. Azopyridine is a nitrogen-rich organic molecule that reversibly binds CO2 in its reduced state, and sodium iron phosphate provides a lattice that accommodates sodium ions during charging but conducts them so sluggishly that self-discharge is effectively throttled. The system captures CO2 when the azopyridine is reduced at the working electrode while sodium ions insert into the phosphate counter-electrode, and releases the gas when the current is reversed and the sodium ions return to solution. The electrochemistry is elegant in its symmetry: the same ion traffic that stores charge in a sodium-ion battery underpins the capture and release of a greenhouse gas.

The experimental results are striking for their durability. The membraneless cell operated through 75 consecutive capture and release cycles spanning 350 hours, maintaining consistent CO2 capacity utilization and high Coulombic efficiency throughout. Equally important, the performance held up under conditions that matter in the real world rather than only in idealized laboratory settings. The system continued to function at high current densities, which determines how compact and productive a commercial module could be. It captured CO2 efficiently from dilute feed gases, the regime relevant to direct air capture, where the target gas is present at roughly 420 parts per million. And it tolerated aerobic environments, a notorious Achilles heel for redox-active capture chemistries, since oxygen competes for the electrons intended for the sorbent and can degrade it irreversibly.

To assess what these performance figures would mean commercially, the team built a techno-economic model comparing the membraneless architecture with its membrane-based counterpart. The analysis indicated a potential 28.9 percent reduction in the cost per tonne of captured CO2, driven by the elimination of membrane capital costs, reduced ohmic losses and the simplified engineering of a single-compartment cell. While the authors are careful to frame this as a projected figure rather than a demonstrated one, the magnitude of the savings is significant in a field where every dollar per tonne matters for adoption, particularly for direct air capture, where costs remain the central barrier to scale.

Beyond the specific materials pairing, the study establishes what the authors describe as a scalable and generalizable framework for next-generation electrochemical carbon capture. Because the key design principle is kinetic rather than thermodynamic, other sorbent chemistries, including quinones, alkoxides and redox-tunable Lewis bases explored by this and other groups, could in principle be matched with kinetically suppressive solid counter-electrodes without membranes. The conceptual bridge to battery science is also notable: the same intercalation compounds engineered for sodium-ion energy storage become enabling components of climate infrastructure, and the self-discharge problem they were designed to mitigate turns out to be the very lever that makes membraneless operation viable.

The work arrives at a moment when the urgency of carbon removal has never been clearer. Direct air capture and point-source capture both need processes that run on clean electricity, tolerate real-world gas mixtures and cost little enough to deploy by the thousands of tonnes. By eliminating the membrane and rewriting the design logic that had constrained the field, the Johns Hopkins team has taken a concrete step toward electrochemical capture systems that could eventually be manufactured as simply as batteries. Much work remains, from long-term degradation studies to fully continuous flow operation and pilot-scale demonstrations, but the 350 hours of stable membraneless cycling and the projected cost reduction suggest that the field’s most persistent architectural assumption was one it could finally afford to abandon.

Subject of Research: A membraneless electrochemically mediated carbon capture architecture using solid-state counter-electrodes to suppress self-discharge and reduce capture costs

Article Title: Electrochemically mediated carbon capture using a membraneless architecture

Article References: Liu, A., Mathur, A., Jayarapu, K. N., Li, Z., Li, T., McDaniel, G., & Liu, Y. (2026). Electrochemically mediated carbon capture using a membraneless architecture. Nature Chemical Engineering. https://doi.org/10.1038/s44286-026-00438-4

Image Credits: AI Generated

DOI: 10.1038/s44286-026-00438-4

Keywords: carbon capture, electrochemistry, membraneless architecture, sodium iron phosphate, azopyridine sorbent, self-discharge, direct air capture, CO2 removal, redox-active sorbents, techno-economic analysis, chemical engineering, climate technology

The commentary accompanies two independent studies that, taken together, reveal a previously underappreciated failure mode: self-discharge driven by residual electronic conductivity in solid electrolytes. Self-discharge is familiar to anyone who has picked up a gadget after months of storage only to find the battery partially drained. In conventional liquid-electrolyte cells, self-discharge arises from parasitic side reactions and impurity-driven shuttles. In solid-state cells, the story turns out to be more subtle. Because the electrolyte is a solid, the cell can be fully assembled and sealed, and yet an internal electronic pathway can still allow charge to bleed from one electrode to the other without any external connection at all.

Physically, the mechanism can be understood as an internal short circuit of very high resistance. A solid electrolyte is never a perfect electronic insulator; its electronic conductivity, while many orders of magnitude lower than its ionic conductivity, is finite. When a cell is charged, the two electrodes sit at different electrochemical potentials, separated by the full cell voltage. That potential difference drives a minute electronic current through the electrolyte even at open circuit, slowly transferring electrons and, through coupled chemical processes, neutralizing the stored lithium gradient between the cathode and the anode. Individually the leakage currents are vanishingly small, but battery storage is a marathon measured in months and years, and even minuscule currents accumulate into meaningful capacity loss over a product’s shelf life.

The two studies highlighted in the commentary converge on this conclusion from complementary directions, and both emphasize that the problem becomes more severe as cells become thinner and more practical. Laboratory demonstration cells often use thick, mechanically robust solid electrolyte layers, which present a long, high-resistance path to stray electrons. Real commercial designs, however, demand thin electrolyte membranes to maximize volumetric and gravimetric energy density. Halving the electrolyte thickness doubles the electronic leak for a given cell voltage, meaning that the very design changes needed to make solid-state batteries commercially competitive also amplify the hidden leak. The studies identify the conductivity limits that solid electrolytes must satisfy to guarantee long shelf life, effectively setting an engineering specification that materials designers can now target explicitly.

This framing represents a shift in how the field thinks about solid electrolyte characterization. Historically, researchers have compared candidate materials almost exclusively by their ionic conductivities, chasing sulfides, oxides and halides that transport lithium ions as fast as possible. Values exceeding ten millisiemens per centimeter, rivaling or exceeding liquid electrolytes, are now routinely reported. Electronic conductivity, by contrast, has often been measured only sporadically, and sometimes under conditions that do not reflect the electrochemical potentials a real cell experiences. The new work makes clear that the ratio of electronic to ionic transport is not a curiosity but a first-order design parameter, and that a material with spectacular ionic conductivity can still fail the shelf-life test if its electronic leakage is too high.

The commentary’s authors situate these findings within a broader body of literature on electronic transport in solid electrolytes. Prior theoretical and computational studies had already established that many widely used solid electrolytes, including thiophosphate-based materials, possess non-negligible electronic conductivity, and that redox-active elements within their crystal structures can mediate electronic conduction. Experimental reports had also documented oxidative decomposition at cathode interfaces and the formation of electronically conductive interphases. What the two new studies add is the direct connection between this background knowledge and a measurable, practically consequential phenomenon: capacity loss at open circuit in assembled cells, quantified against electrolyte thickness, voltage and storage time.

The practical implications reach into nearly every corner of the solid-state battery program. For cell engineers, the results suggest that shelf-life specifications cannot be met by sealing and thermal management alone; the intrinsic electronic conductivity of the electrolyte layer must be engineered below a critical threshold that scales with allowable storage duration. For materials scientists, the findings add an optimization target that may sometimes conflict with existing goals, since processing routes that densify electrolyte membranes or improve interfacial contact could also alter their defect chemistry and electronic transport. For theorists, the work underscores the value of first-principles predictions of electronic band structure, defect ionization and polaron hopping in complex solid electrolytes, which can guide screening before samples are ever synthesized.

There is also a diagnostic dimension. Because self-discharge through electronic leakage leaves distinctive signatures, such as voltage decay profiles at open circuit that depend systematically on electrolyte thickness and temperature, the phenomenon offers an accessible experimental probe. Testing protocols that deliberately vary membrane thickness can separate electronic leakage from other degradation pathways, such as interfacial decomposition or dendrite formation, giving the community a cleaner way to attribute capacity loss to its root cause. In an industry where a single misdiagnosed failure mode can misdirect years of development, such discriminating tests carry real value.

None of this diminishes the fundamental appeal of solid-state batteries, and the commentary is careful to frame the new results as a design constraint rather than a fatal flaw. The ionic conductivities of the best solid electrolytes are extraordinary, the interface chemistry is increasingly well controlled, and manufacturing routes for thin membranes are maturing rapidly. What the findings change is the checklist. A viable solid electrolyte must now demonstrate not only fast lithium transport and electrochemical stability but also electronic insulation sufficient to keep a charged cell from slowly draining itself while it sits in a warehouse waiting to be installed in a vehicle.

The image of a solid that leaks like a sieve, only for electrons rather than for ions, is likely to resonate well beyond the battery community, because it illustrates a recurring theme in materials science: properties that are negligible at one scale or one timescale can dominate at another. As solid-state cells move from laboratory prototypes toward commercial products with multi-year warranties and grid-scale storage duties, the hidden leak identified in these studies will need to be plugged, measured and monitored with the same rigor that the field has long applied to ionic conduction. The two studies and the accompanying commentary give researchers the conceptual tools and the quantitative limits to do exactly that, turning a subtle electrochemical surprise into an actionable engineering target.

Subject of Research: Self-discharge in solid-state batteries caused by residual electronic conductivity of solid electrolytes

Article Title: A hidden leak in solids

Article References: Noh, J., & Kang, K. (2026). A hidden leak in solids. Nature Energy. https://doi.org/10.1038/s41560-026-02133-3

Image Credits: AI Generated

DOI: 10.1038/s41560-026-02133-3

Keywords: solid-state batteries, solid electrolytes, self-discharge, electronic conductivity, ionic conductivity, shelf life, lithium-ion transport, energy storage, battery degradation, Nature Energy, hidden, leak