The polymer flexes with the electrode, preventing cracks under stress.
The promise of solid-state batteries has long been shadowed by a quiet, structural fragility — the tendency of rigid materials to crack under the rhythmic stress of charging and discharging. A team of Korean researchers has addressed this fundamental tension by introducing an elastic, ion-conductive polymer into sulfide-based electrolytes, allowing the battery's interior to flex rather than fracture. Published in May 2026, their work points toward a future where next-generation electric vehicle batteries are not only more durable, but simpler and cheaper to manufacture — a convergence of material science and practical necessity.
- Solid-state batteries, long heralded as the safer successor to lithium-ion technology, have been held back by a deceptively simple flaw: their brittle sulfide electrolytes crack as electrodes expand and contract with each charge cycle.
- Previous buffer-layer solutions either choked ion flow or sparked unwanted chemical reactions, leaving engineers caught between mechanical stability and electrochemical performance.
- Researchers at KRICT, Yonsei University, and Sungkyunkwan University broke the deadlock by infiltrating the electrolyte itself with a crosslinked elastic polymer — a material that simultaneously absorbs stress and opens new pathways for lithium ions.
- The results are striking: batteries with the polymer held 75% capacity after 200 cycles, compared to just 22% for conventional sulfide batteries — more than three times the retention.
- Beyond performance, the polymer reduces the need for high external pressure during operation, a manufacturing burden that adds weight, complexity, and cost to battery pack design.
- The team now moves toward larger-cell testing under real-world EV conditions, with the technology positioned as a credible bridge between laboratory promise and commercial viability.
The central problem with solid-state batteries has always been cracking. Each time a battery charges and discharges, its electrodes swell and shrink, and the rigid sulfide electrolytes surrounding them fracture under that repeated stress. Those fractures sever the ion pathways the battery depends on, and performance collapses. It is a quiet, structural failure that has kept one of the most promising energy technologies from reaching the road.
A team led by Dr. Dong Wook Kim at the Korea Research Institute of Chemical Technology, in collaboration with Yonsei University and Sungkyunkwan University, has developed a way around this. Rather than adding a separate buffer layer between electrode and electrolyte — an approach that historically blocked ion flow or caused unwanted reactions — the researchers infiltrated the sulfide electrolyte itself with an elastic, ion-conductive polymer. A liquid precursor was introduced into the electrolyte's porous structure and hardened into a crosslinked network, producing a composite material that is both flexible and conductive.
The polymer performs two functions simultaneously. It absorbs the mechanical stress of electrode expansion, preventing cracks from forming and strengthening the electrode-electrolyte interface. At the same time, it fills internal voids and creates additional pathways for lithium ions, preserving the battery's conductivity. In testing, batteries with the polymer remained stable for over 2,500 hours under repeated charge-stress conditions. After 200 full cycles, they retained 75% of their original capacity — compared to just 22% for conventional sulfide batteries.
There is also a manufacturing dimension. Standard solid-state batteries require high external pressure to maintain contact between components, adding weight and cost to battery pack design. The new polymer reduces this dependence, allowing batteries to perform reliably under lower-pressure conditions — a potential simplification that matters enormously for commercial production.
Published in Energy Storage Materials in May 2026, the research now moves toward testing in larger cells under conditions that simulate real electric vehicle use. If those results hold, this elastic polymer may prove to be the material bridge that finally brings solid-state batteries from laboratory promise to the road.
The problem with solid-state batteries is that they crack. This seems like a small thing until you realize that those cracks are what stands between electric vehicles and the next generation of safer, longer-lasting power. A team of Korean researchers has now found a way to stop the cracking—by making the battery's interior more like rubber.
Dr. Dong Wook Kim and his colleagues at the Korea Research Institute of Chemical Technology, working with teams at Yonsei University and Sungkyunkwan University, have developed an elastic ion-conductive polymer that can be woven into sulfide-based all-solid-state batteries. The polymer acts as a shock absorber, much like the dampers that keep buildings from swaying in earthquakes. When the battery's electrodes expand and contract during charging and discharging, the polymer flexes with them, preventing the rigid materials from cracking under stress.
Why this matters: all-solid-state batteries are the future of electric vehicles. Unlike the lithium-ion batteries in today's phones and cars, which use flammable liquid electrolytes, solid-state batteries use solid materials instead. They're safer, they can charge faster, and they can deliver more power. Among the solid electrolytes being developed, sulfide-based materials have drawn particular interest from battery makers worldwide because they conduct ions almost as well as liquids do. The catch is that sulfides are brittle. When electrodes swell and shrink with each charge cycle, the rigid electrolyte cracks. Those cracks break the pathways that ions need to travel through the battery, and the battery dies faster.
Previous attempts to solve this problem introduced buffer layers—rubber-like materials sandwiched between the electrode and the electrolyte. But these buffers either blocked ion flow or triggered unwanted chemical reactions, making them impractical. The Korean team took a different approach. Instead of adding a separate layer, they infiltrated the sulfide electrolyte itself with an elastic polymer. A liquid precursor was poured into the porous structure of the electrolyte and then hardened into a crosslinked network, filling the gaps between particles. The result is a composite material that is both flexible and conductive.
The polymer does two jobs at once. It absorbs the mechanical stress from electrode expansion, keeping cracks from forming and strengthening the bond between electrode and electrolyte. At the same time, it fills voids within the electrolyte and creates new pathways for lithium ions to move through, maintaining the battery's ability to conduct charge. In testing, batteries with the new polymer operated stably for more than 2,500 hours during repeated lithium plating and stripping cycles—the kind of stress that mimics real charging and discharging. Conventional sulfide electrolytes degraded progressively over the same period.
The performance difference is stark. After 200 charge-discharge cycles, conventional sulfide batteries retained only 22 percent of their original capacity. Batteries with the elastic polymer maintained 75 percent. That's more than three times better. The improvement holds even under the high-rate charging and discharging conditions that electric vehicles demand.
There's another benefit that matters for manufacturing. Conventional solid-state batteries need to be squeezed under high external pressure to keep the electrode and electrolyte in contact. This pressure requirement adds weight and complexity to the battery pack and drives up costs. The new polymer reduces this dependence on external pressure. Batteries incorporating the elastic material performed relatively stably even under lower-pressure conditions. For companies trying to bring solid-state batteries to market, this could mean simpler designs and lower production costs.
The research, published in May 2026 in Energy Storage Materials, a top-tier materials science journal, represents a step toward making next-generation batteries practical. The team plans to test the technology in larger battery cells and in conditions that mimic real electric vehicle use. If those tests succeed, this polymer could help unlock the potential of solid-state batteries—safer, faster-charging power sources that could reshape the electric vehicle industry.
Notable Quotes
This technology addresses one of the most critical challenges in sulfide-based all-solid-state batteries—the issue of mechanical stability.— Dr. Dong Wook Kim, Korea Research Institute of Chemical Technology
We expect this technology to contribute to the development of highly safe next-generation batteries for electric vehicles and energy storage systems.— Dr. Seokmin Shin, President of KRICT
The Hearth Conversation Another angle on the story
Why does a sulfide-based battery crack in the first place? It seems like a design flaw.
It's not a flaw so much as a fundamental mismatch. The electrodes are made of materials that swell when they absorb lithium ions and shrink when they release them. The sulfide electrolyte is rigid—it doesn't move. So with every charge cycle, you get stress building up at the interface, like two dancers trying to move to different rhythms. Eventually something breaks.
And the polymer fixes this by being flexible?
Exactly. It's like inserting a shock absorber between them. The polymer can stretch and compress along with the electrode, so the stress never accumulates enough to cause cracking. But it's not just mechanical—it also conducts ions, so it doesn't block the battery's ability to work.
The capacity retention numbers are impressive. Seventy-five percent versus twenty-two percent. Why is that difference so important?
Because a battery that loses three-quarters of its capacity after 200 cycles is essentially dead for an electric vehicle. You'd need to replace it constantly. With the new polymer, the battery stays useful much longer. That's the difference between a technology that works in the lab and one that actually works in a car.
The reduced pressure requirement seems like it could be the biggest commercial advantage.
It might be. Right now, manufacturers have to build these batteries under high pressure, which adds weight and cost. If you can get stable performance at lower pressure, you simplify the entire pack. That's not just a technical win—it's an economic one. That's what gets investors interested.
What's the next hurdle?
Scaling. They've proven this works in small cells under controlled conditions. Now they need to show it works in larger batteries and in real-world driving scenarios. That's where many promising battery technologies stumble.