Positive electrode material
For the two pain points of sodium ion batteries, electrode materials are the key to improving their energy density, voltage and cycle performance. Only by developing the positive and negative electrode materials suitable for the stable removal of sodium ion, can the practical application of sodium ion battery be promoted. The existing cathode materials mainly include layered oxide materials, polyanionic materials, and Prussian blue / white materials. Among them, layered oxide material is the mainstream direction of sodium ion battery. Layer oxide is the fastest cathode material in development and is expected to be the first to achieve mass production.
Negative grade material
At present, the carbon-based materials that can be used as battery cathode materials mainly include graphite carbon materials and amorphous carbon (hard carbon and soft carbon) materials. Graphite materials, commonly used in the anode of lithium-ion batteries, cannot form stable compounds with sodium ions due to thermodynamic reasons, so it is difficult to use graphite as the anode material for sodium-ion batteries. Carbon nanomaterials mainly include graphene, carbon nanotubes, etc. Relying on surface adsorption to achieve sodium storage, it can achieve rapid charging and discharge, but the problems such as low efficiency and poor circulability make it difficult to obtain practical application. Amorphous carbon material with large layer spacing has become the most promising anode material for sodium ion batteries because of its high sodium storage capacity, low sodium storage potential and excellent cycle stability.
In carbon-based materials, compared with soft carbon materials such as graphite, hard carbon materials cannot be graphitized. The carbon layer arrangement of hard carbon material is less orderly than that of soft carbon material, and more micropores can be formed between the layers to facilitate the removal of sodium ions. Hard carbon material has many performance advantages, such as high sodium storage specific capacity, low sodium storage voltage, and good cycle performance. Meanwhile, it has the advantages of rich carbon source, low cost, non-toxic and environmental protection. Compared with graphite electrode, it also has more advantages in cold start and fast charging mode, and is the preferred sodium ion battery cathode material.
Electrolyte
The electrolyte of sodium-ion batteries is similar to the electrolyte of lithium-ion batteries, which can use part of the production equipment and technology of existing lithium-ion batteries. NaPF6 and NaClO4 are the two most frequently studied sodium salts. NaPF6 Until 300℃, with the highest conductivity in the PC based (propylene carbonate) electrolyte. Because its synthesis principle is similar to LiPF6, it can be compatible with the current lithium-ion battery manufacturing process and equipment in terms of manufacturing process, and has become the mainstream direction of sodium-ion battery electrolyte. NaClO4 It has the advantages of fast ion migration speed, strong thermal stability and low cost, but its insufficient high water content, easy explosion and high toxicity affect its practical application. Compared with the traditional sodium salts NaPF6 and NaClO4, sodium containing fluorosulfonyl groups (NaTFSI, NaFTFSI, NaFSI, etc.) has high thermal stability and non-toxicity, but because its anion is corrosive to aluminum foil fluid, it is rarely used as a separate sodium salt.