The heart of the advance is a battery built around disulfur dichloride, S2Cl2, a sulfur-containing compound in which sulfur sits at a higher oxidation state than the elemental sulfur used in traditional lithium–sulfur cells. Rather than cycling sulfur between its elemental form and lithium sulfide through the conventional two-electron pathway, the new chemistry reversibly converts lithium sulfide, Li2S, back into disulfur dichloride through a three-electron sulfur redox process. That extra electron transfer per sulfur atom is the key to unlocking both a higher cell voltage and a greater storage capacity, since the total energy a battery delivers is the product of its voltage and the charge it can move.

The numbers reported by the team are striking. At room temperature, 25 degrees Celsius, and a moderate discharge rate of 0.2C, the average operating voltage of the cell rises from approximately 2.05 volts in a conventional lithium–sulfur configuration to 2.54 volts. The sulfur-specific capacity increases by 58 percent relative to standard sulfur chemistry. Taken together, these gains translate into an electrode-level specific energy exceeding 1,700 watt-hours per kilogram, a figure far beyond what today’s commercial cathodes can achieve, and the cells sustain this performance over more than 100 charge–discharge cycles.

Achieving reversible high-valence sulfur chemistry has proven notoriously difficult in the past, and the reasons illuminate why this result matters. When chemists have attempted to push sulfur into higher oxidation states using halogens such as chlorine, two obstacles have consistently emerged. First, chloride species in typical electrolytes bind strongly to lithium ions, tying up the charge carriers needed for the battery to function. Second, halogen-mediated reactions tend to consume the electrolyte itself, degrading the cell from the inside out and destroying reversibility over repeated cycles. The new work demonstrates that both problems can be overcome with a carefully designed liquid medium.

The enabling technology is a free-chloride-rich ionic liquid electrolyte, a class of molten salts that remain liquid at or near room temperature and consist entirely of ions. Unlike conventional solvent-based electrolytes, this ionic liquid keeps chloride anions in an unbound, or free, state rather than locking them to lithium cations. In this configuration, the electrolyte does far more than simply conduct ions between the electrodes. It functions as an ionic mediator, actively participating in the redox chemistry that shuttles sulfur between its low-valence and high-valence states, while contributing only a minor share of the measured capacity itself.

The researchers support their electrochemical measurements with an extensive suite of characterization techniques, including synchrotron X-ray absorption spectroscopy performed at beamline 8-BM of the National Synchrotron Light Source II at Brookhaven National Laboratory, X-ray photoelectron spectroscopy, in situ Raman spectroscopy and galvanostatic intermittent titration. Molecular dynamics simulations, conducted with custom force field parameters and code that the team has released openly on Zenodo, provide atomistic insight into how the phase-separated ionic-liquid structure stabilizes the chloride-mediated reaction pathway. Together, these tools confirm that the conversion between lithium sulfide and disulfur dichloride is genuinely reversible across repeated cycles.

The implications for energy storage are considerable. Lithium–sulfur batteries are attractive not only for their theoretical energy density but also for their supply chain: sulfur is a byproduct of petroleum refining and is available in quantities that dwarf the demand of any conceivable battery market. Raising the operating voltage by nearly half a volt may seem like a modest increment, but because energy scales directly with voltage, this single improvement multiplies the practical energy output of every gram of active material in the cell. Combined with the capacity boost from three-electron redox, the approach could move lithium–sulfur technology from a laboratory curiosity toward a genuine competitor for electric vehicles, grid storage and aerospace applications.

The research also reframes how battery scientists think about electrolytes. For most of the history of electrochemistry, the electrolyte has been treated as a passive component, chosen primarily for its stability and ionic conductivity. Here, the electrolyte is an active chemical participant, engineered with precision so that its chloride content mediates sulfur oxidation without parasitic consumption. This concept of an electrolyte that serves as a reaction mediator while remaining substantially intact echoes strategies explored in other emerging chemistries, including lithium–chlorine, lithium–sulfur dioxide and lithium–sulfur hexafluoride systems, but the authors show that their formulation achieves a rare combination of high voltage, high capacity and sustained reversibility.

Significant engineering challenges remain before cells of this type could leave the laboratory. The performance was demonstrated at the electrode level rather than in fully optimized pouch or cylindrical formats, and scaling ionic-liquid electrolytes to mass production will require attention to cost, viscosity and low-temperature behavior. Nevertheless, the demonstration of more than 100 stable cycles at an electrode-level specific energy above 1,700 watt-hours per kilogram establishes a new benchmark for sulfur-based batteries and offers the field a compelling proof of concept: that pushing sulfur to higher oxidation states, long considered a dead end because of irreversible halogen side reactions, can be made practical when the electrolyte is designed as an ally rather than a bystander.

As the global demand for high-energy, low-cost batteries intensifies, breakthroughs of this kind underscore how much untapped potential remains in some of chemistry’s most abundant elements. By coaxing a single sulfur atom to give up or take on three electrons instead of two, and by recruiting chloride ions as willing chemical partners rather than destructive interlopers, the University of Maryland-led team has shown that even the oldest rival to lithium-ion technology still holds surprises. The work was funded in part by the US Department of Energy’s Basic Energy Sciences program and its Vehicle Technologies Office, and the authors report no competing financial interests.

Subject of Research: Chloride-mediated three-electron sulfur redox chemistry in rechargeable lithium–disulfur dichloride batteries using a free-chloride-rich ionic liquid electrolyte

Article Title: Lithium–disulfur dichloride batteries

Article References: Zhang, N., Zhang, J., Zhang, W., Wang, Z., Zhao, C.-X., Li, A.-M., Liu, Y., Xia, K., Mesirow, C., Yang, Y., Lucht, B. L., Hu, E., Ji, X., Jiang, D.-E., Xu, J., & Wang, C. (2026). Lithium–disulfur dichloride batteries. Nature Energy. https://doi.org/10.1038/s41560-026-02120-8

Image Credits: AI Generated

DOI: 10.1038/s41560-026-02120-8

Keywords: lithium-sulfur batteries, disulfur dichloride, ionic liquid electrolyte, sulfur redox chemistry, energy density, chloride mediator, lithium sulfide, high-voltage batteries, electrolyte design, polysulfide shuttling, rechargeable batteries, Nature Energy