Newly developed sodium-ion (Na-ion) batteries could offer much faster charging speeds, higher energy density and improvements in safety compared with conventional lithium-ion (Li-ion) batteries, scientists say.
Using Na-ion batteries, an alternative to the 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 Na-ion energy density and charge speeds.
Scientists have been investigating Na-ion batteries as an alternative to Li-ion batteries because of their improved stability and low cost, but several bottlenecks and limitations have blocked the technology's advancement.
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 made primarily of graphite, as it's 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. This is, in theory, a very fast-charging material.
Previous research into HC found it difficult to prove that this theoretical charging rate is practically possible, however, because ions entering the dense electrolyte at high speed experience a slowdown similar to a traffic jam. But in a new study published Dec. 15, 2025, in the journal Chemical Science , the scientists set out to overcome this hurdle.
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 ions to flow freely into the HC particles with no "traffic'" issues.
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With the problem overcome, the researchers then proved that sodium ions could enter HC at similar rates to lithium ions entering graphite in a Li-ion battery.
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