Scientists say ‘dangerous’ lithium-ion batteries will be out of use for days after breakthrough in fast-charging sodium-ion replacement

A newly developed sodium-ion (Na-ion) battery has the potential to charge much faster, have higher energy density and be safer than traditional lithium-ion (Li-ion) batteries, scientists say.

Researchers at Tokyo University of Science have used a new carbon-based electrolyte to improve the energy density and charging speed of sodium ions using sodium-ion batteries, an alternative to the lithium-ion batteries used in most of today’s devices.

Scientists have been exploring Na-ion batteries as an alternative to Li-ion batteries because of their improved stability and lower cost, but several bottlenecks and limitations have hindered the technology’s progress.

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All batteries contain an anode and a cathode, and these two electrodes determine how electrical current flows into and out of the device. In lithium-ion batteries, the cathode is primarily made of graphite. This is because it is an excellent material for storing lithium ions that are later released.

However, Na-ion batteries use hard carbon (HC). Hard carbon (HC) is a porous combination of thousands of “turbostratic units”, an inherently complex crystalline structure that is excellent at storing sodium ions. This is a material that theoretically allows for very fast charging.

However, previous studies on HC have found it difficult to prove that this theoretical charging rate is actually possible, as ions entering dense electrolytes at high speeds experience a slowdown similar to congestion. But in a new study published in the journal Chemical Science on December 15, 2025, scientists set out to overcome this hurdle.

Limiting the risks of lithium-ion batteries

The researchers created a composite electrode by combining low concentrations of HC with aluminum oxide, a chemically inert material. This allowed ions to flow freely into the HC particles without any “traffic” problems.

With this problem overcome, the researchers demonstrated that sodium ions can enter the HC at a similar rate to the lithium ions that enter the graphite in lithium-ion batteries.

The researchers also discovered that the bottleneck to the entire process was the rate at which the ions filled the “pores” within the HC. Here, “pore” refers to the process by which ions form pseudometallic clusters within the nanoscale pores on the surface of the HC.

After careful analysis, the researchers discovered that sodium ions require less energy to form these clusters. This finding shows that under the right conditions, Na-ion batteries, also known as SIBs, can achieve faster charging rates than Li-ion batteries.

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“A key focus for developing improved HC materials for fast-chargeable SIBs is to achieve faster kinetics of the pore-filling process so that they can be accessed at high charging rates,” explained study lead author Shinichi Komaba, professor at the Department of Applied Chemistry at Tokyo University of Science, in a statement. “Our results also suggest that sodium insertion is less sensitive to temperature, given its lower activation energy than lithiation.”

In the real world, this result could help Na-ion batteries become more widely adopted in applications that require incredibly fast charge or discharge rates. For example, grid-scale battery energy storage systems will benefit from the ability to quickly discharge energy on demand. Maintaining battery stability is also of paramount importance when batteries are used on a large scale to store energy produced by renewable resources.

Sodium-ion batteries are safer than lithium-ion batteries, as noted in a 2025 study by researchers at the Islamic Institute of Technology, Idaho State University, and the University of Waterloo. This is because the stable sodium ions contained in lithium-ion batteries are less likely to cause chain reactions that can cause lithium-ion batteries to catch fire or explode if damaged.

The UK National Fire Chiefs’ Council said battery energy storage systems using lithium-ion batteries posed a “significant fire risk”, particularly because once a fire ignites, it cannot be easily extinguished.

Thermal runaway is a self-sustaining process that causes lithium-ion batteries to catch fire and can be self-sustaining even in the absence of oxygen. The British Safety Council says some electric car lithium-ion batteries can continue to burn for hours or even days after ignition.

If Na-ion batteries like the one tested in the study were produced on a large scale, these risks could be completely avoided.

“Our results quantitatively demonstrate that the charging speed of SIBs using HC anodes is faster than that of LIBs. [lithium-ion battery]” Komaba said in a statement.