Days numbered for ‘risky’ lithium-ion batteries, scientists say, after fast-charging breakthrough in sodium-ion alternative
Newly developed sodium-ion (Na-ion) batteries could offer much faster charging speeds, higher energy density and safety improvements compared to conventional lithium-ion (Li-ion) batteries, scientists say.
Using Na-ion batteries, an alternative to Li-ion batteries found in the majority of today’s devices, researchers at the Tokyo University of Science used a new carbon-based electrolyte to improve the energy density and charging rates of Na ions.
All batteries contain an anode and a cathode, the two electrodes that determine how current flows into and out of the device. In Li-ion batteries, the cathode is mainly made of graphite, as it is an excellent material for storing lithium ions to be discharged later.
But Na-ion batteries use hard carbon (HC) – a porous combination of thousands of “turbostratic basic structural units,” essentially a complex crystalline structure, that excels at storing sodium ions. In theory it is a very fast charging material.
Previous research on HCs, however, has struggled to prove that this theoretical charging rate is practically possible, because ions entering the dense electrolyte at high speed experience a slowdown similar to a traffic jam. But in a new study published on December 15, 2025 in the journal Chemical sciencescientists decided to overcome this obstacle.
Limit the risks of Li-ion batteries
The researchers combined small concentrations of HC with aluminum oxide, a chemically inactive material, in a combination electrode. This allowed the ions to flow freely within the HC particles without “traffic” issues.
Once the problem was overcome, the researchers then proved that sodium ions could penetrate HCs at rates similar to lithium ions penetrating graphite in a Li-ion battery.
The researchers also discovered that the bottleneck of the entire process is the rate at which ions fill the “pores” of the HC, where “pores” describes the process in which ions form pseudo-metallic clusters inside the nanoscopic pores on the surface of the HC.
Through careful analysis, the researchers discovered that sodium ions require less energy to form these clusters. The results indicate that, under the right conditions, Na-ion batteries – also called SIBs – can achieve faster charging rates than Li-ion batteries.
“A key point in developing improved HC materials for fast-charging SIBs is to achieve faster kinetics of the pore-filling process so that they are accessible at high charging rates,” said the study’s lead author. Shinichi Komabaprofessor at the Department of Applied Chemistry at Tokyo University of Science, explained in a statement. “Furthermore, our results suggest that sodium insertion is less sensitive to temperature, based on accounting for a lower activation energy than lithiation.”
In the real world, the results could help Na-ion batteries be more widely adopted for uses requiring incredibly fast charge or discharge rates. For example, grid-scale battery energy storage systems would benefit from the ability to rapidly discharge energy on demand. It is also essential that batteries remain stable when used on a large scale to store energy produced by renewable sources.
Na-ion batteries are safer than Li-ion batteries, as stated in a Study 2025 by researchers from the Islamic University of Technology, Idaho State University and the University of Waterloo. Indeed, the stable sodium ions they contain are less subject to the chain reaction that causes Li-ion batteries to burn or even explode when damaged.
The National Council of Fire Chiefs of the United Kingdom declared that battery energy storage systems using Li-ion batteries pose a “significant fire risk”, particularly because once on fire, these batteries cannot be easily extinguished.
Thermal runaway, the self-sustaining process that causes Li-ion batteries to ignite, can even persist without oxygen. THE British Safety Council noted that after ignition, Li-ion batteries in some electric vehicles can burn for hours or even days.
If produced at scale, Na-ion batteries like those tested in the study could avoid these risks altogether.
“Our results quantitatively demonstrate that the charging speed of a SIB using an HC anode can achieve faster rates than that of a LIB. [lithium-ion battery]” Komaba said in the statement.
Y. Fujii, ZT Gossage, R. Tatara and S. Komaba, Chemical. Sci.2026, advanced article, DOÏ: 10.1039/D5SC07762A
