Kinetically controlled formation of uniform FePO 4 shells and their potential for use in high-performance sodium ion batteries

Using a water-based coating technology, researchers can now turn carbon nanotubes into coaxial cable-like cathodes for sodium batteries. Sodium ion batteries are cheaper alternatives to widely used lithium ion batteries, but they require conductive cathodes capable of storing and releasing sodium ions without changing their shape. An-Min Cao and co-workers from the Chinese Academy of Sciences used nanometer-thin layers of iron phosphate to achieve this goal. By controlling the pH of an aqueous precursor, they developed a way to slowly solidify a non-crystalline shell of iron phosphate — a substance with a high, reversible sodium ion capacity — around polystyrene seed particles. This strategy proved versatile and successfully coated other seed substrates, such as silicon, gold and conductive carbon nanotubes. Sodium battery cathodes made from the iron phosphate-wrapped nanotubes delivered significantly higher discharge capacity than control samples.