The sodium-ion battery's working principles [3]. In terms of operating temperature range and safety, sodium-ion battery operating temperature range is large compared to lithium battery, usually at -40 ℃-80 ℃. The ternary lithium-ion battery usually works at -20-60℃. The performance of lithium-ion batteries will go down below 0 ℃. In contrast, when sodium-ion batteries can work at -20 ℃, the state of charge (SOC) retention rate is above 80% [7]. In terms of thermal runaway, sodium-ion batteries have higher internal resistance than Li-ion batteries, hence, the temperature of the battery will not rise easily during short circuit, guaranteeing the safety of the battery [7]. The resources of sodium are widely distributed and rank fourth on earth, while the majority of lithium deposits are concentrated in South America. Na is abundant in the crust at around 2%, while Li is only present in the crust in amounts of about 20 ppm [4]. In addition, the ocean's sodium resources are unlimited. As a result, the cost of lithium sources was between $5,000 per ton, while the cost of sodium sources was only about $135-165 per ton [4]. Hence, compared with the lithium-ion battery, for the sake of the low cost of Na element, the sodium-ion battery is substantially less expensive. However, sodium-ion batteries also have more prominent shortcomings that need to be solved, such as the sodium ions' large radius, which may result in the crack of the material when it is removed from the electrode material, thus affecting the battery's overall dynamic performance and the integrity of the electrode [8]. Compared to lithium, sodium has a higher standard electrode potential, resulting in sodium-ion batteries' lower energy density [8]. In order to solve the above problems, researchers conducted research deeply and made great progress. If the electrode material is narrowed to the nanoscale and utilized synergistic effects of composite materials and other modification methods, it can greatly improve sodium-ion batteries' capacity for energy. Researches about nanotechnology in Na-ion batteries are introduced in the next chapter.

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... Li-ion battery and the Na-ion battery both operate on the same principles [3][4][5]. Figure 1 depicts the process that Na ions insert/extract from the battery's negative electrode to the battery's positive electrode to realize the charge and discharge of the battery. In order to maintain charge balance, electrons are transferred to the negative electrode during charging while Na + is withdrawn from the battery's positive electrode material and incorporated into the battery's negative electrode material via the electrolyte. ...