Lithium-Sulfur Battery Patents — Why Hasn’t It Been Commercialized Yet?

① What’s the Story

The core reason lithium-sulfur (Li-S) batteries have long failed to cross the commercialization threshold is the “polysulfide shuttle,” and the patent literature has developed along several routes that “suppress” this problem rather than eliminate it. This article compares a material-based barrier membrane (KR101725650B1, filed by LG Chem) with an electrode-operation design (KR20090080996A, filed by Oxis Energy) and sets out what the difference means for scope of rights and FTO (freedom-to-operate) judgments.

Starting with the industry situation, lithium-sulfur batteries are reported to have a theoretical sulfur specific capacity of 1,675mAh/g and a calculated theoretical specific energy of about 2,600Wh/kg. Add the fact that sulfur is a cheap and abundant element, and they have long been named a “dream battery” candidate. This is where the tension arises. They have been studied long enough that a patent with a 2006 priority date already exists, yet widespread commercialization has still not happened.

This article answers two questions. First, why is the polysulfide shuttle so hard to solve? Second, with what rights structure did the representative published patents claim solutions to this problem, and where can later entrants look for design-around options?

② Basic Principle

During discharge, the sulfur in a lithium-sulfur cell reacts with lithium to form an intermediate compound called lithium polysulfide. The problem is that this polysulfide dissolves readily in the electrolyte. The dissolved polysulfide diffuses across the separator toward the anode and is then re-oxidized, repeating the cycle — a process called the “shuttle phenomenon.”

By analogy, the cathode is a warehouse and sulfur is the cargo stacked inside. But at an intermediate stage the cargo turns into something like sugar dissolving in water, leaks out through the warehouse door (the separator), and sticks to the wall of the building next door (the anode). The cargo keeps shrinking and the neighboring wall gets fouled. This is the process by which repeated shuttling causes cathode active material to be lost and the anode surface to become unstable, making capacity fade quickly.

A review published in Communications Materials in 2025 likewise states that lithium polysulfides dissolved in liquid electrolytes cause irreversible loss of active material, aggravated self-discharge, and reduced Coulombic efficiency. The same review names volume expansion and non-uniform lithium metal deposition as further cycle-life challenges, and states that EV use requires a minimum cycle life of 1,500 cycles.

• Shuttle phenomenon: dissolved polysulfides travel back and forth → active-material loss and self-discharge
• Lithium dendrites: branch-like deposition of lithium metal at the anode → reduced safety
• Volume change: expansion and contraction during cycling → damage to electrode structure

③ Comparison

The table below sets out the character of lithium-sulfur and conventional lithium-ion batteries side by side, using figures from published sources and the general industry assessment. Because theoretical and actual cell values differ greatly, it is safest to read it for direction.

Category	Lithium-sulfur (Li-S)	Lithium-ion (conventional)
Cathode active material theoretical capacity (mAh/g)	Sulfur 1,675	(comparison figure not verified in this article)
Anode theoretical capacity (mAh/g)	Lithium metal 3,860	Graphite-based (figure not verified)
Specific energy (Wh/kg)	Theoretical ~2,600	~250 (review’s comparison figure)
Volumetric energy density and cycle life	Falls short of commercial Li-ion	Relatively superior
Key weaknesses	Polysulfide shuttle, volume expansion, lithium dendrites	Cost and resource burden (cobalt, nickel, etc.)

What this table says: Li-S’s theoretical specific energy (~2,600Wh/kg) is about ten times the lithium-ion comparison figure given in the review (~250Wh/kg), but this gap compares a theoretical value with a practical one. In real cells, the shuttle, volume change, and dendrites act at the same time and cut deeply into that difference.

④ Patent Perspective

First, the bibliographic data of the two patents, checked against Google Patents, are as follows.

Item	KR101725650B1	KR20090080996A
Title	Lithium sulfur battery	Lithium-sulfur battery with high specific energy and method of operation
Applicant (current owner)	LG Chem (assigned to LG Energy Solution on 2021-11-05)	Oxis Energy Limited
Priority date / filing date	2014-10-29 / 2015-08-14	2006-10-25 (GB0621197A) / 2007-10-11
Publication / grant	Granted 2017-04-12	Published 2009-07-27; granted 2015-01-30 as KR101487862B1
Legal status	Active, anticipated expiration 2035-08-14	Expired – Fee Related
Approach	Material-based: protective film blocks diffusion	Operation-based: separate charging and discharging cathode groups

What this table says: The material-based patent (KR101725650B1) may remain in force until 2035, whereas the Korean grant (KR101487862B1) of the earlier operation-based patent has already lapsed for non-payment of annuity fees, so the possibility of enforcing it in Korea is gone.

Claim gist (KR101725650B1): This patent is easily read as a “dual defense structure that blocks the problem from both sides at once,” but paraphrasing claim 1 shows a slightly different structure. Claim 1 claims a lithium-sulfur battery with a cathode, anode, separator, and electrolyte in which at least one of the following is provided as a protective film: a lithium-ion-conductive polymer membrane containing sulfonic acid groups (-SO₃H) between the cathode and the separator, or a metal oxide film between the anode and the separator. Using both films as a dual defense reads as one of the embodiments covered, not a mandatory requirement of claim 1. The polymer membrane is described as improving cycle life by blocking polysulfide diffusion toward the anode, and the metal oxide film as improving safety by suppressing dendrite growth.

This difference matters for judging the scope of rights. With an “at least one” structure, a design that uses only a sulfonated polymer interlayer, or only a metal oxide protective film, could fall within the literal scope. In other words, infringement risk for this patent should be judged not by whether a dual structure is adopted, but by whether even one of the two films exists in the claimed position and material. Family members US10468650B2, EP3203567B1, JP6917888B2, CN107078343B, and WO2016068534A1 are listed, so the same review is needed for overseas markets.

Claim gist (KR20090080996A / KR101487862B1): This patent is often summarized as a design dividing the electrodes into a “polarized electrode group and a non-polarized electrode group.” Paraphrasing claim 1, it is a multi-electrode lithium-sulfur cell with an anode of lithium metal or similar and two or more distinct cathode groups, configured so that the first cathode group is used for charging and the second for discharging. The concept of polarization is used in the specification to explain the operating principle, and the aim is to raise specific energy by preventing highly concentrated polysulfide solutions from forming. It approaches the shuttle problem through electrode arrangement and operation rather than materials.

Design-around scenario (counterargument): A later entrant seeking to avoid KR101725650B1 could consider coating the protective layer onto the separator itself or mixing an adsorbent into the cathode, so as to omit the positional requirement of a “separate film between the cathode and the separator” as limited in the claim. There is a counterargument, however. If a separator surface coating performs substantially the same function in substantially the same position, it could become subject to a doctrine-of-equivalents assessment. As an alternative, the technical idea of the operation-based patent that has already lapsed in Korea may be relatively free to practice in Korea, but the status of its overseas family (US8188716B2, EP2076936B1, etc.) must be checked separately.

⑤ Limitations and Outlook

As the use of terms like “suppress” and “block” in patent documents shows, no technology has yet emerged that completely eliminates the shuttle phenomenon. Lithium-sulfur batteries have a clear strength in energy density by weight, but still fall short of commercial lithium-ion in volumetric energy density and cycle life. The general industry view is that they are more likely to find a foothold first in niche applications where weight is absolutely critical, such as drones or UAM (Urban Air Mobility), than in EVs.

To add one observation here: the fact that one of the early lithium-sulfur patents lapsed for non-payment of fees before its term expiry (anticipated in 2027) indirectly shows the rights holder’s judgment about technological maturity. When commercialization expectations fall below the cost of maintaining rights, even foundational patents can be abandoned early. Conversely, the material-based patent held by LG Energy Solution remains in force, which can be read as the rights competition in Li-S shifting from electrode operation toward materials and interface design.

There is also a counter-scenario. If approaches that remove the liquid in which polysulfides dissolve, such as solid-state electrolytes, mature, barrier-membrane patents premised on liquid electrolytes could lose technical importance. The strategic alternative is to avoid treating shuttle suppression as a single path and to take a portfolio view that tracks material-based, operation-based, and electrolyte-based approaches in parallel.

Practical action: Planning and IP personnel evaluating lithium-sulfur cells should check whether their design contains even one polymer interlayer between the cathode and separator or a metal oxide layer protecting the anode, and if so, first draw up an FTO comparison chart against the claims of KR101725650B1 and its overseas family.

Items requiring verification

• Current legal status of each overseas family member of the Oxis Energy patent (US8188716B2, EP2076936B1, JP5297383B2)
• Whether the claim scope of the overseas family of KR101725650B1 (US10468650B2, etc.) matches the Korean claims
• Representative actual cell-level specific energy (Wh/kg) and volumetric energy density (Wh/L) of current commercial lithium-sulfur cells
• The earliest filing date of lithium-sulfur-related patents and the yearly filing trend

Sources

1. Google Patents, KR101725650B1 – Lithium sulfur battery (LG Chem, now LG Energy Solution)
2. Google Patents, KR20090080996A – Lithium-sulfur battery with high specific energy and method of operation (Oxis Energy)
3. Google Patents, KR101487862B1 – granted patent of the above application
4. Wang, G. et al., “Assessing the practical feasibility of solid-state lithium–sulfur batteries,” Communications Materials (2025)