Ethylene carbonate and sulfolane, mixed 3 to 7, stretch a lithium metal cell to 150 cycles
KAIST and UNIST researchers kept a lithium metal cell at about 80% capacity for 150 cycles, triple a conventional carbonate electrolyte. The recipe avoids fluorinated solvents and concentrated salts. Its savings depend on prices not yet published.
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Four figures: the EC-sulfolane electrolyte lasted 150 cycles to about 80% capacity versus roughly 50 for a conventional carbonate electrolyte; its average Coulombic efficiency was 99.35% (initial 98.24%); it lost roughly 0.13% of initial capacity per cycle.
- 150 cycles to ~80% New EC-sulfolane electrolyte, claim 6 NCM811 cathode at 4.5 volts
- 50 cycles to ~80% Conventional carbonate electrolyte, claim 11 roughly
- 99.35% Average Coulombic efficiency, claim 5 initial: 98.24%
- 0.13% of initial Avg capacity loss per cycle, claim 14 derived from about 80% over 150 cycles
| Figure | Value | Note | Claim |
|---|---|---|---|
| New EC-sulfolane electrolyte | 150 cycles to ~80% | NCM811 cathode at 4.5 volts | 6 |
| Conventional carbonate electrolyte | 50 cycles to ~80% | roughly | 11 |
| Average Coulombic efficiency | 99.35% | initial: 98.24% | 5 |
| Avg capacity loss per cycle | 0.13% of initial | derived from about 80% over 150 cycles | 14 |
What happened
- Lithium metal cells can hold far more capacity than graphite-anode lithium-ion cells, but side reactions with the electrolyte cut their cycle life, and high-voltage charging makes the loss worse.
- The team mixed ethylene carbonate and sulfolane at a weight ratio of 3 to 7 and added a small amount of an additive that stabilizes the protective film.
- Hydrogen bonding between the hydrogen in ethylene carbonate and the oxygen in sulfolane weakens the pair's grip on lithium ions, an effect the team calls cooperative solvation.
- KEIT, under the trade ministry, and the National Research Council of Science and Technology funded the work, which was published in ACS Nano.
Why it matters
- cost The cost case is a list of ingredients avoided. Until the blend, the additive and a cell format are priced, cost per cycle cannot be computed from the 150-cycle result.
- constraint The retention evidence is one cathode, NCM811, at one voltage, 4.5 volts, over 150 cycles, so the energy-storage and electric-vehicle claims for the electrolyte are extrapolations.
- capability Both solvents were previously left out of lithium metal design for binding lithium ions too strongly. If cooperative solvation holds, solvents screened out on that ground become candidates again.
Song put the cost case in one sentence. "We improved electrolyte performance using only commercial solvents, without depending on expensive fluorinated solvents or high-concentration salts," he said [8]. Cost per cycle is a price divided by a cycle count, and the report supplies the count: about 80% retention at 150 cycles, against a conventional carbonate electrolyte that fell below 80% after about 50, a ratio of three [6][11]. The report does not include a price for the blend, a name or cost for the stabilizing additive [2], the cell format, or a comparison with the fluorinated and high-concentration electrolytes the team set aside.
An average Coulombic efficiency of 99.35% [5] means 0.65% of the charge is lost each cycle on average [12]. Compounded over 150 cycles in a cell with no spare lithium, that leaves about 38% [13]. The NCM811 cell kept about 80% [6], a loss of roughly 0.13% a cycle [14]. Two explanations fit: the efficiency came from a different test cell than the cathode run, or the cell carried more lithium than cycling consumed. In the second case, part of the 150 cycles was bought with extra metal that would also have to be paid for.
In our view the chemistry holds up on the evidence given. Gas generation from electrolyte decomposition and nickel leaching from the cathode were also suppressed [7], so other evidence supports the cycle count, while nothing in the report yet supports the cost claim the same way.
Three results would sink the cost thesis: an additive expensive enough to cancel the solvent saving, a cell with limited lithium that falls short of 150 cycles, or a fluorinated electrolyte that matches 150 cycles at 4.5 volts for similar money. Hong Jin-ki, the paper's first author, said the approach "can be extended not only to lithium metal batteries but also to commercial lithium-ion batteries and next-generation battery systems" [15].
What to watch
- A disclosed identity and cost for the stabilizing additive, plus the cell format and any excess-lithium ratio behind the 150-cycle run.
- Cycle counts beyond 150 at 4.5 volts, and a head-to-head test against a fluorinated or high-concentration electrolyte in the same cell.
- A test of Hong's claim that the solvent-mixing principle carries over to commercial lithium-ion cells.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence45
- Adoption
- Insufficient
- Hype gap+30
- Incentives40
- Confidence45
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
A joint team led by Song Hyun-kon of UNIST and Seo Dong-hwa of KAIST said on the 12th that it had developed an electrolyte that extends lithium metal battery life by exploiting the attraction between two commercial solvents.
- [2]
The team mixed ethylene carbonate (EC) and sulfolane (SL) at a weight ratio of 3 to 7 and added a small amount of an additive that stabilizes the protective film.
- [3]
Both EC and SL had previously been excluded from lithium metal battery design because they bind lithium ions too strongly, hindering deposition on the electrode surface.
- [4]
When combined, hydrogen bonding formed between the hydrogen in EC and the oxygen in SL, which weakened the solvents' grip on lithium ions; the team calls this phenomenon 'cooperative solvation'.
- [5]
The new electrolyte recorded an initial Coulombic efficiency of 98.24% and an average Coulombic efficiency of 99.35%.
- [6]
A battery with a high-nickel (NCM811) cathode retained about 80% of its initial capacity after 150 charge-discharge cycles at 4.5 volts, three times the cycle life of conventional carbonate-based electrolytes, which fell below 80% after about 50 cycles.
- [7]
Gas generation from electrolyte decomposition and nickel leaching from the cathode material were also suppressed.
- [8]
"We improved electrolyte performance using only commercial solvents, without depending on expensive fluorinated solvents or high-concentration salts," Song said.
- [9]
The research was supported by the Korea Evaluation Institute of Industrial Technology (KEIT) under the Ministry of Trade, Industry and Energy and by the National Research Council of Science and Technology (NST), and was published in ACS Nano.
- [10]
Lithium metal batteries can deliver far greater capacity than commercial lithium-ion batteries with graphite anodes, but their cycle life falls sharply because lithium metal triggers side reactions with the electrolyte, and capacity loss is worse under high-voltage charging.
- [11]
The new electrolyte's 150 cycles to about 80% retention is three times the baseline's roughly 50 cycles.
- [12]
An average Coulombic efficiency of 99.35% implies about 0.65% of charge lost per cycle on average.
- [13]
If 0.65% were lost every cycle with no spare lithium, about 38% of capacity would remain after 150 cycles.
- [14]
Retaining about 80% over 150 cycles is an average loss of roughly 0.13% of initial capacity per cycle.
- [15]
Hong Jin-ki, first author of the paper, said the approach "can be extended not only to lithium metal batteries but also to commercial lithium-ion batteries and next-generation battery systems."
Sources
1 independent publisher whose own reporting we read for this story.
- en.sedaily.comKorean Researchers Triple Lithium Metal Battery Life With New Electrolyte
1 article · October 11, 2026
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