Due to abundant resources and low price, sodium ion battery is considered as a potential large-scale energy storage battery system. Compared with a large number of reported inorganic electrode materials, organic materials have the following advantages. First of all, organic electrode materials are usually prepared by mild methods. The reactions are mostly substitution or polymerization at room temperature or below 200 ℃, which can reduce energy consumption and carbon dioxide emissions during electrode preparation; Secondly, most organic electrode materials can be obtained from natural products or their derivatives to meet the needs of sustainable development; Moreover, the organic electrode materials are based on the charge transfer reaction of redox centers and can withstand a large radius of sodium ions. Most importantly, through reasonable design, the specific capacity of organic cathode materials can be close to 500 ampere hours per kilogram, which is far higher than the inorganic cathode materials reported at present. Despite the above advantages, organic electrode materials also have many problems, such as active materials are easily soluble in organic electrolyte, poor conductivity, low voltage and so on.
At present, the organic electrode materials used in sodium ion battery system are mainly based on carbon oxygen double bond reaction, doping reaction and carbon nitrogen double bond reaction. The electrode materials based on carbon oxygen double bond reaction mainly include quinones, carboxylates, anhydrides and amides. This kind of compound has high capacity and stable cycling performance, and is the most widely studied at present. Electrode materials based on doping reaction mainly include organic radical compounds, conductive polymers, microporous polymers, organometallic compounds, etc. The p-doping reaction is usually participated by the anions in the electrolyte, and the working potential is generally higher than 3V. The n-doping reaction is participated by the cations in the electrolyte, and the working potential is generally below 2V. Compounds based on carbon nitrogen double bond reaction mainly include Schiff bases, pteridine derivatives, etc. At present, there is little research on such electrode materials, and the working principle needs further exploration. In addition, through a series of designs, the voltage, specific capacity, solubility, conductivity and other parameters of organic electrode materials can be reasonably adjusted. For example, the theoretical specific capacity of electrode materials can be improved by increasing the proportion of active functional groups in molecules. By adjusting the energy of the lowest unoccupied orbital level of organic molecules, the voltage of materials can be effectively controlled. The electron withdrawing group can increase the working potential of the material, while the electron donating group can reduce the working potential of the material. By polymerization of organic molecules, the dissolution of electrode materials in electrolyte can be effectively suppressed. Composite with carbon materials can improve the conductivity of the materials and promote the magnification performance of electrode materials.