A University of Maryland-led team pushed sulfur to the +1 oxidation state, lifting average voltage from 2.05 V to 2.54 V and sulfur-specific capacity by 58%. The pouch cell they actually built ran at roughly 1 mAh/cm² — and that gap is the story.
Why a Lithium-Sulfur Battery Never Delivers Its Own Numbers
Sulfur is the cheapest high-capacity cathode material on the periodic table. It stores 1,675 mAh per gram — close to ten times what a nickel-cobalt-manganese oxide holds — and it is abundant enough that supply has never been the constraint. That combination has kept a durable roster of companies funded and busy for two decades: Lyten, Zeta Energy, Sion Power, Solidion, Gelion.
Not one of them has put a lithium-sulfur pack in a passenger car.
The obstacle is not capacity. It is voltage. Lithium-sulfur runs on the S²⁻/S⁰ couple, a two-electron reaction with an average discharge voltage of about 2.05 V. A 3.7 V NCM cathode does not hold more lithium per gram, but every electron it moves carries nearly twice the energy. To match the energy of a conventional cell, a lithium-sulfur electrode needs roughly twice the areal capacity — thicker electrodes, more electrolyte per unit of energy, slower kinetics, and the polysulfide dissolution that has defined the chemistry’s public reputation.
The industry’s answer has been to grind at the edges: redox catalysts, protective separators, sulfurised carbon composites, quasi-solid electrolytes. All of it makes lithium-sulfur better inside the same box.
The Maryland team argued the box was the problem. Their paper, published in Nature Energy on September 10, reports a lithium–disulfur dichloride chemistry that pushes sulfur past zero to the +1 oxidation state and lifts average voltage to 2.54 V at 25 °C.
What This Lithium-Sulfur Chemistry Does Differently
The mechanism turns on free chloride — and in a normal ether electrolyte there is almost none of it.
Chloride binds tightly to Li⁺, which strips it of reactivity. That is precisely why every commercial ether-based lithium-sulfur cell is stuck on the two-electron reaction. The Maryland team, working with Vanderbilt University, Brookhaven National Laboratory, the University of Rhode Island and Oregon State University, added an imidazolium chloride (EMIMCl) to flood the electrolyte, then tuned the Li⁺/Cl⁻ ratio until roughly 80% of the chloride sat free rather than coordinated to lithium. That free chloride is what allows sulfur to be oxidised past zero.
Charging drives the electrode from Li₂S through S₈ to S₂Cl₂ — three electrons per sulfur atom instead of two, spread across two plateaus at 2.0–2.5 V and 3.3–3.4 V.
That created a second problem. S₂Cl₂ dissolves readily in most solvents, turning the cathode into a shuttling mess and draining capacity within cycles. The fix was a fluorinated ether (TTE) immiscible with S₂Cl₂: the reaction product stays trapped inside the porous carbon host, and the shuttling stops.
The Control Experiment Behind This Lithium-Sulfur Result
Reviewers pushed on an obvious suspicion, and the supplementary information answers it head-on: was the energy actually coming from the electrode, or was the chloride-rich electrolyte quietly doing the work and inflating every number?
The authors ran three controls.
They built cells with a chloride-free G3 electrolyte and showed sulfur oxidation still occurred at 3.7–3.8 V, meaning the LiCl already inside the electrode was sufficient on its own. They then ran sulfur cathodes containing no LiCl and found the electrolyte’s own chloride contributed just 30–50 mAh per gram of sulfur in high-voltage capacity — noise next to the electrode’s total. And they tracked the electrode with SEM and EDS at 2.6 V, 3.2 V and 3.6 V, watching needle-like LiCl crystals dissolve and recrystallise before vanishing completely at full charge.
Their conclusion: the electrolyte contributes 2–3% of cell energy. That matters, because it means energy density can legitimately be calculated from electrode materials alone — a claim halogen-mediated chemistries have not always been able to make.
The Numbers, and the Gap Between Them
At 0.2C, the cell delivers 1,838 mAh per gram of sulfur — 58% above the 1,165 mAh/g of a conventional two-electron sulfur cathode — at the higher voltage. Combined, that puts electrode-level specific energy above 1,700 Wh/kg. Rate performance runs 722, 617, 530 and 445 mAh/g at 0.2C, 0.3C, 0.5C and 1C.
At stack level, counting the lithium anode, separator, electrolyte and current collectors, the figure falls to 477 Wh/kg and 1,102 Wh/L.
| Stack-level — Li metal anode, 4.00 mAh/cm² | Specific energy | Energy density |
|---|---|---|
| S–LiCl (this paper) | 477 Wh/kg | 1,102 Wh/L |
| Conventional Li–S (S–C) | 346 Wh/kg | 1,023 Wh/L |
| LFP | 312 Wh/kg | 815 Wh/L |
| NCM811 | 443 Wh/kg | 1,150 Wh/L |
The gap between the abstract’s headline and the stack figure is not the interesting part. The gap between the stack figure and the hardware is.
Those 477 Wh/kg assume an areal capacity of 4.00 mAh/cm². The single-layer pouch cell the team actually assembled ran at roughly 1 mAh/cm², holding 78% of its capacity after 100 cycles with coulombic efficiency above 97%. Scaling areal capacity is the step that has broken nearly every lithium-sulfur promise so far: thick sulfur electrodes crack and delaminate, and they demand electrolyte volumes that eat the energy gain.
Why the Rest of the Industry Is Still Working Inside the Box
Lyten, the most visible lithium-sulfur player, has spent 2026 consolidating manufacturing rather than chemistry. In February it completed a nearly $5 billion acquisition of Northvolt’s Swedish assets — the Skellefteå plant and the Västerås research centre — taking on 16 GWh of existing capacity. The Skellefteå lines will build NMC cells first; lithium-sulfur sits at the R&D centre, being industrialised for later.
That is the shape of the industry today. Lithium-sulfur cells are shipping, but into drones, defence platforms and stationary storage where weight matters more than cost per kilowatt-hour — and almost every one of them runs the same two-electron reaction at roughly 2.05 V. The engineering has improved. The electrochemistry has not moved.
The Maryland result is an argument that the electrochemistry was the thing to move.
Accuracy note: The 1,700 Wh/kg figure is electrode-level, calculated from the sulfur–lithium chloride composite rather than a finished cell. The stack-level equivalent in the paper’s supplementary Table 2 is 477 Wh/kg and 1,102 Wh/L, and that table is a modelled projection at 4.00 mAh/cm² areal capacity — not a measurement of the pouch cell, which ran at roughly 1 mAh/cm². Cycle-life values (713 mAh/g at cycle 5, 432 mAh/g at cycle 100, 1.035 and 0.8065 mAh/cm² for the pouch) were read from the paper’s published Source Data files; EVsays has not seen the plotted figures in the paywalled article, and retention percentages depend on which cycle is used as the baseline. The 2–3% electrolyte energy contribution is the authors’ own estimate, derived from sulfur-only control cells. The paper gives no commercialisation timeline and none should be inferred. Lyten acquisition details are from the company’s own press release of February 27, 2026. Analysis and interpretation are original to EVsays.
The Bottom Line: Climbing sulfur’s oxidation state is the most credible route anyone has shown to a lithium-sulfur cell that beats lithium-ion on voltage rather than on paper capacity alone — and the three-control experiment that rules out the electrolyte is what makes the claim stand up. But 477 Wh/kg at 4 mAh/cm² is a projection, and the pouch cell behind it is thin. Watch for follow-up work on areal loading. That, not the voltage record, decides whether this chemistry ever leaves the lab.
Sources & Further Reading
- Zhang, N., Zhang, J., Zhang, W. et al. — “Lithium–disulfur dichloride batteries,” Nature Energy (2026) — the primary paper.
- Nature Energy — article page — abstract, author list, and the free Source Data files behind Figures 1–5.
- Shen, Y. et al. — “Unlocking high-valence chalcogen redox with halide-rich electrolytes,” Nature Communications (2026) — the open-access companion paper from the same group, extending the approach to selenium.
- University of Maryland Energy Innovation Institute — news release (2026-09-10) — comment from first author Nan Zhang.
- Lyten — “Lyten Completes Acquisition of Northvolt Sweden” (2026-02-27) — 16 GWh of Swedish capacity, and where lithium-sulfur sits in the company’s plans.
