Days numbered for 'risky' lithium-ion batteries, researchers say after fast-charging breakthrough in sodium-ion alternatives

Newly developed sodium-ion (Na-ion) batteries could offer much faster charging speeds, higher energy density and improved safety compared to conventional lithium-ion (Li-ion) batteries, researchers say.

Using Na-ion batteries, an alternative to the Li-ion batteries found in most devices today, researchers at Tokyo University of Science have used a new carbon-based electrolyte to improve Na-ion energy density and charging speed.

All batteries contain an anode and a cathode, two electrodes that determine how current flows to and from the device. In Li-ion batteries, the cathode is made primarily of graphite because it is an excellent material for storing lithium ions that are later discharged.

However, Na-ion batteries use hard carbon (HC) – a porous combination of thousands of “turbostratic building blocks”, essentially a complex crystalline structure that excels at storing sodium ions. It is theoretically a very fast charging material.

Previous HC research has found it difficult to demonstrate that this theoretical charging rate is practically possible because ions entering the dense electrolyte at high speed experience a traffic jam-like deceleration. But in a new study published on December 15, 2025 in the journal Chemical sciencescientists decided to overcome this obstacle.

Limiting the risks of Li-ion batteries

The researchers combined small concentrations of HC with aluminum oxide, a chemically inactive material, into a combined electrode. This allowed the ions to flow freely into the HC particles without “transportation” problems.

After overcoming the problem, the researchers proved that sodium ions can enter HC at a similar rate to lithium ions entering graphite in a Li-ion battery.

The researchers also found that the bottleneck of the entire process is the rate at which the ions fill the “pores” in the HC, where “pores” describe the process by which the ions form pseudo-metallic clusters inside the nanoscopic pores on the surface of the HC.

Through careful analysis, the researchers found that sodium ions need less energy to form these clusters. The finding suggests that under the right conditions, Na-ion batteries – also called SIBs – can achieve faster charging than Li-ion batteries.

Shinichi Komabaprofessor at the department of applied chemistry at Tokyo University of Science, explained va declaration. “Our results also suggest that sodium insertion is less sensitive to temperature, based on the consideration of a smaller activation energy than lithiation.”

In the real world, the results could help na-ion batteries become more widespread for applications that require incredibly fast charging or discharging. For example, battery systems for grid energy storage would benefit from the ability to quickly discharge energy on demand. It is also of utmost importance that the batteries remain stable when they are used on a large scale to store energy produced from renewable sources.

Na-ion batteries are safer than Li-ion batteries as stated in point a study 2025 researchers from the Islamic University of Technology, Idaho State University and the University of Waterloo. The stable sodium ions they contain are less prone to the chain reaction that causes Li-ion batteries to burn or even explode when damaged.

British National Council of Firefighters stated that battery energy storage systems that use Li-ion batteries pose a “significant fire risk”, particularly because once they catch fire, the batteries cannot be easily extinguished.

Thermal runaway, the self-sustaining process that causes Li-ion batteries to ignite, can be sustained even without oxygen. The British Security Council noted that once ignited, Li-ion batteries in some electric vehicles can burn for hours or even days.

If na-ion batteries like those tested in the study were produced on a large scale, they could avoid these risks entirely.

“Our results quantitatively show that the charging rate of SIBs using an HC anode can reach higher rates than LIBs. [lithium-ion battery]Komaba said in a statement.