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The main application scenarios of sodium-ion batteries include electric two-wheeled vehicles, tricycles, A00-class electric vehicles, heavy trucks, ships, energy storage and other fields. In addition to the above-mentioned fields, with the improvement of energy density brought about by the continuous breakthrough of sodium-ion battery technology, as well as the innovative battery pack method, sodium-ion batteries can also be mixed with other products such as lithium-ion batteries and applied in the field of new energy vehicles. Sodium-ion batteries are currently in the early stage of industrialization.
From the perspective of material systems, some changes have taken place in cathode materials, anode materials, electrolytes, and separators, but the changes are not large, which is very helpful to the development of industrialization. From lead-acid to lithium battery transformation, it is difficult for lead-acid enterprises to truly transform into lithium battery and be very successful. However, it is relatively easy for lithium battery companies to make sodium-ion batteries. In the future, the companies that can rise in the sodium-ion battery industry may still be the current lithium battery companies in the world.
1. Technical route of cathode materials for sodium ion batteries
Lithium batteries face competition from ternary materials and lithium iron phosphate technical routes, and sodium ions also have some technical routes to compete, which is very meaningful. In terms of cathode materials, there are currently three mainstream cathode materials for sodium-ion batteries: transition metal oxides, polyanion compounds, and Prussian blue compounds.
The advantages of layered oxides are high reversible specific capacity, high energy density, high rate performance, and easy technical transformation, but they are easy to absorb moisture and have slightly poor cycle performance. Prussian blue analogs have the advantages of adjustable working voltage, high reversible specific capacity, high energy density, and low synthesis temperature, but they also have disadvantages such as poor conductivity, crystal water, and coulombic efficiency.
The advantages of polyanionic compounds lie in high working voltage, good thermal stability, good cycle, and good air stability, but their reversible specific capacity is low, and some of them contain toxic elements. Professionals said that the representative companies currently deploying cathode materials for sodium-ion batteries include RONBAY, ZEC, Easpring, etc., and some other sodium-ion battery companies in the world, such as HiNa BATTERY, also produce cathode materials for sodium-ion batteries.
2. Technical route of anode materials for sodium ion batteries
In terms of anode materials, the types of anode materials that can be used in sodium-ion batteries include metal compounds, carbon-based materials, alloy materials, and non-metallic elements. The main enterprises of sodium ion battery anode materials include: BTR, Shanshan, HiNa BATTERY, etc. Most of them adopt the hard carbon technology route. The main difference between soft carbon and hard carbon mainly comes from the microstructure of the precursor. If it is a precursor with weak interlayer crosslinking such as coal, petroleum coke, and pitch, the prepared material is soft carbon.
Hard carbon precursors are mainly materials with strong interlayer crosslinking such as biomass, synthetic resins, and carbohydrates. Soft carbon usually refers to carbon materials that are easily graphitized above 2800 °C, with a high degree of order, weak van der Waals forces between soft carbon layers, and greater mobility at high temperatures, so it is easy to form easily crystallized graphite. The hard carbon layers have strong cross-linking interactions, and carbon that is difficult to be completely graphitized even at temperatures above 2800 °C has a low degree of order.
Through research, it is found that the graphitization temperature of the negative electrode material of sodium ion battery is relatively lower than that of natural/artificial graphite of lithium battery, and the artificial graphite needs to be above 3000 ℃. The graphitization cycle takes more than 3 weeks, but the hard carbon and soft carbon drop to more than 1000 ℃, and the carbonization cycle is also reduced, which is the key factor that can reduce the cost.
3. Industrialization development trend of sodium-ion battery
Professionals said that in terms of cost, the actual production cost of sodium batteries in 2021 will be about 0.7 RMB/Wh, even higher than 1 RMB/Wh. The current industry average cost of lithium iron phosphate battery is about 0.51 RMB/Wh, and the cost of ternary battery is about 0.64 RMB/Wh. Compared lithium vs sodium battery, when the price of lithium carbonate rises to 500,000 RMB/ton, the cost of the corresponding lithium iron phosphate battery and ternary battery is close to 1 RMB/Wh. At this stage, sodium-ion batteries do not have a very obvious price advantage over lithium batteries.
From the perspective of industrial chain cultivation, first, the number of upstream raw material manufacturers for sodium-ion batteries is small, and the scale is not high. Second, most companies only have the research and development results of raw materials such as cathode and anode materials and electrolytes for sodium-ion batteries or are in the stage of deployment. Therefore, the current industrial chain layout of sodium-ion batteries is not perfect, and enterprises with technical reserves are still immature in terms of production equipment and preparation processes. Therefore, sodium-ion batteries still have major defects in the cultivation of the industrial chain, which greatly restricts the large-scale production of sodium-ion batteries.
From the perspective of technical defect improvement, the disadvantages of sodium-ion batteries are that the molecular weight of sodium element is higher, the sodium ion potential is higher, and the volume is larger, which is easy to cause a large volume change of the pole piece material when the positive and negative electrodes are embedded. Therefore, sodium-ion batteries have more stringent requirements on the structural stability and dynamic performance of materials. Therefore, sodium-ion batteries have relative disadvantages such as low energy density, poor rate performance, and short cycle life. These technical defects greatly restrict its application market and industrialization progress.
4. Conclusion
From the upstream supply side, due to the immature preparation process, imperfect production equipment, and imperfect industrial chain, the production efficiency of sodium-ion batteries is low and the product consistency is poor. The production yield is not high, the cost advantage has not yet been realized, and the industrialization process of sodium ions is still in the early stage. From the downstream demand side, theoretically, sodium-ion batteries can be widely used in electric two-wheeled vehicles, low-speed electric vehicles, energy storage and other fields.
EVTank predicts that the theoretical sodium-ion market space will reach 369.5GWh by 2026. However, from the current application status, there are only demonstration projects in the field of individual energy storage. Although there are orders in the two-wheeled vehicle field, it is estimated that the complete installation and shipment will be at least in early 2023. It is expected that the industrialization of sodium-ion batteries will also be realized after 2025.
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