A gel helps silicon store more energy
Researchers at South Korea's Pohang University of Science and Technology (POSTECH) have developed a silicon and gel battery system that the university says delivers approximately 40% higher energy density while maintaining stable performance. Announced on February 2, 2024, the research uses silicon particles measuring 5 micrometres and an electron beam to help the battery withstand the material's repeated swelling and shrinking.
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The work aims to bring electric vehicles closer to travelling 1,000 kilometres on one charge. POSTECH presents that distance as a research goal. Its announcement describes results from a battery system, with a vehicle demonstration, a commercial launch date and a price still unspecified.
Professor Soojin Park, PhD candidate Minjun Je and Dr. Hye Bin Son, from POSTECH's Department of Chemistry, developed the approach. Their study appeared online in Advanced Science on January 17, 2024, before the university published its research announcement.
The central idea is to make a material with a large storage capacity easier to use. Silicon can hold much more lithium than the graphite commonly used in battery anodes, but it changes size dramatically during charging. POSTECH's team joined silicon particles to an elastic gel through chemical bonds, helping the structure cope with that movement.
For drivers, the attraction is straightforward: storing more energy in a battery could support longer journeys between charging stops. For battery makers, the research addresses another concern, how to use relatively inexpensive silicon particles without sacrificing stable operation.
Why silicon is difficult to use
Silicon's storage advantage comes with a mechanical problem. POSTECH says the material expands to more than three times its original size during charging, then contracts as the battery discharges. Repeating that movement puts stress on the electrode and the materials around it.
An anode is one of a battery's two electrodes. During charging, lithium ions move through the electrolyte and enter the anode, where energy is stored. During use, the process reverses. An electrolyte must let those ions travel while the electrode structure keeps working through repeated charging cycles.
Researchers have often used extremely small silicon particles to help manage the strain. POSTECH describes the production of silicon at the nanoscale as complex and expensive. Larger particles at the microscale offer advantages in production cost and energy density, but their expansion is harder to accommodate.
The particles in POSTECH's experiment measured 5 micrometres, or five millionths of a metre. The university says they were about 100 times larger than those used in traditional silicon anodes at the nanoscale. That is the specific particle comparison given in the official announcement, rather than the factor of 1,000 stated in the initial description of the research. A micrometre itself is 1,000 times the length of a nanometre.
How the gel and electron beam work
POSTECH's team paired the larger silicon particles with a gel polymer electrolyte. A polymer is a material made from long molecular chains. In this battery, its elastic structure helps the electrolyte accommodate changes in the silicon's size while allowing lithium ions to move.
The researchers then used an electron beam to create covalent bonds between the silicon particles and the gel. Covalent bonds are chemical connections in which atoms share electrons. Here, those connections help spread the internal stress produced as silicon expands and contracts.
The approach treats the silicon and its surrounding electrolyte as an integrated structure. Rather than relying only on smaller particles, the researchers changed how the particles connect to the material around them. POSTECH attributes the resulting structural stability to those connections and the gel's ability to accommodate movement.
Park, the POSTECH chemistry professor leading the team, described the result as progress toward putting silicon's storage capacity to practical use:
We used a micro-silicon anode, yet, we have a stable battery. This research brings us closer to a real high-energy-density lithium-ion battery system.
The university also reports that the gel system had ion conductivity similar to conventional batteries using liquid electrolytes. Ion conductivity describes how easily charged particles move through a material. Keeping that movement effective matters because the electrolyte must support the flow of ions as the battery charges and supplies power.
What the 40% gain means for range
POSTECH reports an approximate 40% improvement in energy density for its silicon and gel electrolyte system. Energy density describes how much energy a battery stores relative to its mass or volume. Increasing it is one route toward carrying more energy without making a battery proportionately heavier or larger.
The university's announcement uses around 700 kilometres as a reference for the range of electric vehicles and 1,000 kilometres as the distance researchers are pursuing. Moving from 700 to 1,000 kilometres would add 300 kilometres, an increase of about 43%.
Those figures explain the appeal of a 40% energy density gain. As a simple illustration, increasing 700 kilometres by 40% gives 980 kilometres, close to the stated goal. That calculation assumes the vehicle uses energy at the same rate and the battery's usable energy rises by the same proportion.
A vehicle's actual range also depends on its weight, efficiency, speed, temperature and battery pack design. The practical task is to carry the material's storage advantage into a complete battery and then into a vehicle. POSTECH's reported combination of stable operation, larger silicon particles and comparable ion conductivity addresses several parts of that task together.
Another study tackles silicon's protective layer
A different research team, whose authors include Ai-Min Li and Chunsheng Wang, published a Nature Communications study on February 8, 2024. It also used silicon particles measuring 5 micrometres, but pursued a different solution: a liquid electrolyte designed to form a protective surface layer that tolerates silicon's movement.
The paper explains that a major source of capacity loss is damage to the solid electrolyte interphase, usually shortened to SEI. This is a thin protective layer that forms on the anode. When it cracks, liquid electrolyte can enter damaged silicon particles and react again, creating fresh layers and disrupting electrical contact.
Li and colleagues designed an electrolyte containing fluoroethylene carbonate, sulfolane and TTE, a fluorinated ether. Their formulation supports cells operating at 4.3 volts and creates a protective layer rich in lithium fluoride and lithium oxide.
The authors describe this layer as silicon-phobic, meaning it binds weakly to the lithium and silicon material beneath it. That weak attachment lets the silicon expand and contract inside the protective shell with less stress on the shell itself. POSTECH's approach instead uses strong chemical connections between silicon and an elastic gel to distribute stress.
The two studies therefore address the same movement problem at different boundaries. One connects silicon to a flexible surrounding structure; the other allows silicon to move within a protective layer that attaches less strongly.
What the second team's tests measured
The Nature Communications study reports that its silicon anodes delivered a capacity of 2,175 milliampere hours per gram for more than 250 cycles, with Coulombic efficiency of 99.8%. Capacity per gram describes how much electrical charge a given mass of material can store. A cycle is a round of charging and discharging.
Coulombic efficiency compares the charge taken out during discharge with the charge put in during charging. At 99.8%, the difference is about 0.2% per measured cycle. Keeping this difference small matters because repeated unwanted reactions consume charge and materials over time.
The team also tested a pouch cell with a nominal capacity of 100 milliampere hours. It delivered 172 milliampere hours per gram of cathode material for 120 cycles, with Coulombic efficiency above 99.9%. A pouch cell contains its battery components inside a flexible enclosure.
Those measurements describe electrode capacity, efficiency and cycling performance for the liquid electrolyte design. POSTECH's headline result concerns an approximately 40% energy density improvement from its gel system. Each study contributes a different set of measurements toward making larger silicon particles useful in lithium-ion batteries.
From publication to production
POSTECH describes its manufacturing process as straightforward and ready for application. Using larger silicon particles addresses the cost and complexity associated with producing particles at the nanoscale, while the electron beam creates the bonds needed for the integrated structure.
The university's announcement identifies support from the Independent Researcher Program of the National Research Foundation of Korea. The sequence of publications places the result alongside another effort to solve silicon's expansion problem during the same period:
- January 17, 2024: The POSTECH team's study appeared online in Advanced Science.
- February 2, 2024: POSTECH announced its silicon and gel electrolyte results and the ambition of reaching 1,000 kilometres of vehicle range.
- February 8, 2024: Nature Communications published the separate study of a liquid electrolyte for silicon particles measuring 5 micrometres.
The practical attraction running through both projects is the same: silicon is abundant and offers high storage capacity, while larger particles can reduce production difficulties. Making the surrounding materials tolerate silicon's movement is central to turning those advantages into batteries that retain useful capacity through repeated use.
Key Points
- POSTECH reports approximately 40% higher energy density from an integrated silicon and gel electrolyte battery system.
- The researchers used an electron beam to form chemical bonds that help distribute stress as silicon expands and contracts.
- The stable system used particles measuring 5 micrometres, described by POSTECH as 100 times larger than traditional silicon nanoparticles.
- A vehicle range of 1,000 kilometres is the research ambition; the announcement focuses on battery development.
- A separate Nature Communications study used a liquid electrolyte and a protective surface layer, reporting silicon anode performance over more than 250 cycles.
