Sodium‐Ion Batteries

Sodium (Na) belongs to the same family as lithium and has similar physical and chemical properties. Therefore, the principles of operation for Na-ion batteries are similar to the well-known Li-ion. Na-ion batteries have a high energy storage conversion efficiency and long cycle life, which provide an opportunity to gradually replace the use of lead–acid batteries. The cathode material is a key factor affecting the voltage, energy density, power density, safety, and cycle life of Na-ion batteries. According to the characteristic structure of the material, the cathode material is divided into three types: Na-ion transition-metal oxides, polyanionic compounds, and Prussian blue compounds. A promising anode material should have a lower oxidation–reduction potential than the cathode, small volume expansions upon Na-ion insertion, high electronic conductivity and ion mobility, and good compatibility with the electrolyte. Na-ion anode materials involve three types of storage mechanisms: insertion/extraction reaction mechanism, alloying/dealloying reaction mechanism, and conversion reaction mechanism.