Researchers at Nanjing University and other institutes have developed a new sodium-ion battery cathode that uses iron to make the battery more stable. The new material improved the reversibility of oxygen reactions from 75% to 99%, helping reduce damage during repeated charging and discharging.
The team says the approach could help create high-energy sodium-ion batteries that last longer. The findings were published in Nature Energy.
Lithium-ion batteries are widely used in phones, laptops, electric vehicles and energy storage systems. But researchers are exploring sodium-ion batteries because sodium is much more abundant than lithium and could offer a lower-cost alternative.
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Many sodium-ion batteries use layered oxide materials as their cathodes. These materials can store extra energy when oxygen atoms take part in chemical reactions, but the oxygen does not always return to its original state after the battery is discharged.
The research team, led by Shiyong Chu and Liguang Wang, developed a layered oxide cathode containing sodium, manganese, magnesium, iron and oxygen. Its chemical formula is Na₂/₃Mn₇/₁₂Mg₁/₄Fe₁/₆O₂.
The material was designed to allow oxygen inside the crystal structure to participate in energy storage while also helping it return to its original state after discharge.
The key part of the design is iron. Iron ions help move electrons between the oxygen atoms and the rest of the cathode during charging and discharging.
During charging, Fe⁴⁺ ions take electrons from the oxygen. During discharge, Fe²⁺ ions return electrons to the oxygen. This process helps the oxygen reaction work more reversibly.
Tests showed that adding iron greatly improved the reversibility of the oxygen reactions. According to the researchers, the rate increased from 75% to 99% with the iron-mediated approach.
Better reversibility is important because repeated charging can otherwise change the cathode structure. Over time, this can reduce the battery’s performance and useful life.
The researchers also tested the new material in a sodium-ion pouch cell. The battery reached an energy density of 206 Wh/kg and retained 87.8% of its capacity after 100 charging and discharging cycles at 50 mA/g.
Energy density measures how much energy a battery can store for its weight. A higher value can be useful for applications where keeping battery weight down is important.
The results are promising, but the test lasted for only 100 cycles. Real-world batteries normally need to withstand many more cycles, so longer-term testing will be needed to understand the material’s durability.
The researchers will also need to study how the cathode performs under different operating conditions and how the material could be produced at larger scale.
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The study shows how carefully controlling oxygen reactions could help improve high-energy sodium-ion batteries. Using iron as an electron mediator may offer a practical way to reduce structural damage inside the cathode.
If the approach performs well in longer tests and larger cells, it could support the development of more durable sodium-ion batteries for energy storage and other applications.
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