In recent years, battery projects based on new chemical systems such as lithium (sodium/aluminum)-air, lithium-sulfur, magnesium (calcium) ions, sodium (potassium) ions, and zinc-manganese dioxide aqueous solutions have been launched at the national level, and new startups relying on private funding have also begun to emerge. However, for young scientists and industrial entities seeking to enter the market, distinguishing between hype and reality amidst the rising research topics related to social and commercial drivers is becoming a real burden.
Sodium-ion batteries are the closest to replacing lithium-ion batteries, giving rise to companies such as Faradion (UK), Novasis (USA), HiNa (my country), and Tiamat (France). The sustainability of sodium-ion batteries has attracted the attention of industry because Na2CO3 is cheaper and less volatile than lithium-based materials like Li2CO3. Research on sodium-ion batteries, like that of lithium-ion batteries, focuses on positive and negative electrode materials and electrolytes.
Anode: Because many sodium-based intercalation compounds have similar structural types to lithium-based materials, inspired by the research on lithium-ion materials, all-sodium-ion batteries were rapidly assembled. The absorption of sodium ions in hard carbon, which consists of disordered graphene layers and nanopores, occurs first in the tilted region and then in the low-pressure steady section. This corresponds to inserting Na+ into the disordered layers and filling the nanopores. Compared with embedding Li+ into graphite, sodium batteries can achieve a higher rate.
For the cathode: Sodium-based layered oxides exhibit richer crystal chemistry than lithium-ion layered oxides. This structural difference not only explains the variations in sodium stoichiometry and capacity, but also indicates that layered oxides are more prone to sodium-driven structural phase transitions, thus reducing lifetime and power density. Furthermore, Na-based polyanionic phases have been extensively studied, such as phosphate (NaFePO4), sulfate Na2Fe2(SO4)3, and fluorophosphate (NaVPO4F). The Na3V2(PO4)2F3 (NVPF) compound possesses a specific crystal structure composed of open channels for rapid ion diffusion. At an average potential of 3.9V, each unit of the compound (i.e., 128 mAh/g) can reversibly release 2 Na+ ions, thus supplying a material-level specific energy of approximately 507 Wh/kg, equivalent to 580 Wh/kg for the lithium-ion cathode material LiFePO4 (LFP).
advantage
1. Sodium salt raw materials are abundant and inexpensive, resulting in lower raw material costs compared to lithium-ion battery ternary cathode materials;
2. Sodium-ion batteries relying on an open 3D structure perform quite well in terms of power capabilities for fast charging, regenerative braking and start-stop functions, as well as frequency regulation functions for power grids;
3. Sodium ions do not form alloys with aluminum, so aluminum foil can be used as the current collector in the negative electrode, which can further reduce costs;
4. Sodium batteries can be released or maintained at 0V without altering their subsequent performance.
5. Because sodium has a milder chemical composition, it is less likely to develop dendrites and explode at high charging rates compared to lithium batteries.
Preliminary performance comparison of 18650 sodium-ion batteries and lithium batteries
shortcoming
1. Sodium is three times heavier than lithium and has a redox potential 300mV lower. This inherently makes the energy density of sodium batteries at least 30% lower than that of lithium batteries. Therefore, sodium-ion batteries are not suitable for applications requiring high energy density.
2. Due to their large radius, sodium ions experience significant resistance to insertion/extraction in both positive and negative electrodes, resulting in poor reversibility and substantial irreversible capacity loss.
Sodium-ion battery technology is becoming a reality, but it shouldn't be seen as a revolutionary new idea. By highlighting the advantages and disadvantages of various sodium-ion and lithium-ion batteries, the author hopes that users will now have a clear understanding of sodium-ion batteries: not as a replacement for lithium-ion batteries, but as a supplement to lithium batteries for large-scale storage applications with low energy density requirements, thereby minimizing concerns about lithium battery shortages.
