South Korean researchers develop an anode-free solid-state battery just 2.77 micrometres thick

The battery forms its anode during charging

The study, published in the scientific journal Advanced Energy Materials under the title “Pushing Energy Density Limits: Anode-Less Solid-State Battery Integrated With Amorphous Lithium Vanadium Oxide Thin-Film Cathode”, focuses on controlling lithium deposition in solid-state batteries. In a conventional lithium-ion battery, the anode and cathode are separate, and lithium ions move between them during charging. The new design has no conventional anode layer when manufactured. During the first charge, lithium moves from the cathode to the current collector, forming a layer of metallic lithium on it.

This approach makes it possible to reduce battery size and increase the energy stored per unit of volume. The problem, however, lies in uneven lithium deposition, which can cause capacity loss and internal short circuits.

Tin and carbon improve battery stability

The researchers' solution uses a copper current collector to which they added an ultrathin tin-and-carbon interlayer.

Tin helps initiate lithium deposition, while carbon helps distribute the lithium more evenly. This reduces the risk of irregular lithium structures forming during charging, or of lithium becoming electrically isolated and no longer contributing to energy storage. The researchers also used prelithiation, adding a small lithium reserve to the system to compensate for irreversible losses during the initial operating cycles.

The prototype combines a lithium vanadium oxide cathode with a LiPON-type solid electrolyte. The cathode is approximately 2 micrometres thick, while the entire battery cell measures 2.77 micrometres in thickness.

After 100 charge-discharge cycles, the cell achieved a volumetric energy density of 235.13 Wh/l. Testing was conducted at a very low current, with a charging rate of 0.01 C.

Energy density is not yet sufficient for electric vehicles

Although the result demonstrates a new approach to developing solid-state batteries, 235 Wh/l is not an exceptional figure by the standards of today's electric vehicles.

Modern lithium-ion batteries can achieve energy densities of several hundred Wh/l at cell level. The Dongguk prototype therefore cannot be considered a direct competitor to the electric vehicle batteries being developed by Toyota, CATL or other major battery manufacturers.

The underlying design principle is more important. An anode-free architecture could reduce material use and enable more compact battery cells in the future.

For the current prototype, however, questions remain over long-term durability, high-current charging, production costs and adapting the technology for large-scale battery production.

The new approach could be particularly suitable for wearable electronics, medical devices and small sensors, where battery dimensions are often more important than energy density.

An important research direction for Europe's battery industry

European battery manufacturers and automotive groups are investing in solid-state batteries in the hope of increasing driving range, improving safety and reducing dependence on conventional lithium-ion batteries.

Dongguk University's work nevertheless shows that the success of solid-state batteries does not depend solely on new electrolytes. Controlling processes at electrode interfaces is at least as important.

The study's real value lies not in its energy density of 235 Wh/l, but in the possibility of making an anode-free battery more stable. If researchers can apply the same principle to larger cells and at higher charging currents, it could contribute to the development of next-generation batteries.

For now, the technology remains in the laboratory. It would need significant further development before it could be used in electric vehicles.