What are the best materials for sodium-ion batteries?

Recent advancements in sodium-ion battery materials have highlighted anatase titanium dioxide (TiO?) as a promising anode material, due to its low cost, non-toxicity, and abundance. Enhanced with a carbon shell through a sol-gel synthesis approach, this material has shown significant improvements in performance and stability. Batteries using anatase TiO? anodes exhibit high capacity and energy density, maintaining robust capacity retention even after numerous cycles, positioning it as a key material in the development of efficient sodium-ion batteries

Anodic materials serve as negative electrodes that store sodium ions during charging and release them during discharging. The most common anodic material for LIBs is graphite, which can intercalate lithium ions between its layers. However, graphite is unsuitable for SIBs as sodium ions are too large to fit into the interlayer spaces. Hence, researchers have explored alternative anodic materials for SIBs, such as metal oxides, metal sulfides, metal phosphides, and hard carbon. Hard carbon is an amorphous form of carbon with a disordered structure featuring large pores and defects, enabling the accommodation of sodium ions.

Apart from Prussian blue analogues here are few more suggestions : Layered Metal Oxides: Materials like NaMO2 (M = transition metal) have shown promise due to their high energy density Eg P2-Na2/3Fe1/2Mn1/2O2,O3-Na0.9Cu0.22Fe0.3Mn0.48O2 Sulfur Compounds: Sodium sulfur batteries have shown potential with materials like Na2S, offering high theoretical energy density. Polyanions :Na4Fe7(PO4)6,Na3V(PO3)3N/NGO

Cathodic materials act as positive electrodes that accept sodium ions during charging and release them during discharging. The most common cathodic material for LIBs is lithium cobalt oxide (LCO), featuring a layered structure and high voltage. However, LCO is unsuitable for SIBs as sodium ions cannot intercalate within its layers. Hence, researchers have explored alternative cathodic materials for SIBs, such as polyanionic compounds, layered oxides, and Prussian blue analogs. Polyanionic compounds contain anions like phosphate, sulfate, or silicate, providing structural stability and preventing volume changes. Layered oxides have a structure similar to LCO but with different transition metals, such as manganese, nickel, or iron.

Electrolytic materials serve as the medium transporting sodium ions between the anode and cathode. The most common electrolytic material for LIBs is a liquid organic solvent with dissolved lithium salts, such as lithium hexafluorophosphate (LiPF6). However, liquid electrolytes have drawbacks like flammability, leakage, corrosion, and degradation. Therefore, researchers have explored alternative electrolytic materials for SIBs, including solid-state electrolytes, ionic liquids, and aqueous electrolytes. Solid-state electrolytes are materials with a solid structure that can conduct sodium ions, such as sodium superionic conductors (NASICONs), sodium borohydrides (NaBH4), and sodium sulfides (Na2S).

Interestingly, in the quest for more sustainable energy storage solutions, researchers are also exploring the potential of sodium-ion batteries in large-scale applications, such as grid storage. The abundance of sodium compared to lithium and the similarities in the fundamental electrochemical principles make sodium-ion batteries an attractive option for storing renewable energy on a larger scale. This could play a significant role in enhancing the efficiency and reliability of renewable energy sources, contributing to a greener and more sustainable future.