Sodium-ion battery is a low cost energy storage device, which are similar in some ways to lithium-ion batteries. In both systems, Na/Li ions are shuttled between the battery’s positive and negative electrodes during charging and discharging. Taking into account recent concerns about a possible lithium shortage with the spread of electric vehicles, it is urgent to search for alternative energy storage systems that could complement the existing Li-ion technology. For this purpose, Na-ion technology can be a suitable choice in terms of battery cost, safety, and raw material abundance. Due to the increased size and heavier weight of the Na atom compared to the Li atom, the volumetric energy density and specific energy density obtainable for the sodium-ion battery would be significantly less than those obtainable with the lithium-ion battery. However, Na-ion batteries would be interesting for very low cost systems for grid storage, which could make renewable energy a primary source of energy rather than just a supplemental one.
There are mainly three types of anode materials for sodium-ion batteries including carbon materials, alloy-based materials such as Sn, Sb, and P and insertion type sodium metal oxide materials. Alloy-based anode materials such as Sn, Sb, and P show high theoretical capacity of 847 (Na15Sn4), 660 (Na3Sb), 2,596 (Na3P) mAh g-1towards sodium, but with more than 300% volume expansion. The theoretical capacity and the volume expansion ratio were shown in Figure 1. It can be found that the expansion ratio for Sodium based anode materials is more serious than Lithium based anode materials due to the bigger size of Na+ ions leading to poor cycle life. Several studies have shown that this massive volume expansion can lead to poor cycle life. Capacity fade can be caused by pulverization of the active particles or degradation of the electrode coating. Based on previous experience , the capacity fade of alloy-based negative electrodes is very sensitive to the choice of binder [2-4]. A good binder must ideally maintain adhesion of the electrode to the current collector, maintain ionic contact, and facilitate the formation of a stable interface with the electrolyte . However, great efforts have to be made to find appropriate active materials for anodes of SIBs with cheaper price and environmental friendliness.
Here, we will present our work on anode materials for sodium ion battery. The materials include carbon based materials, Sn-based materials and red phosphorous based composites with high specific capacity and excellent capacity retention [6-12].