Electrolytes for
Sodium-Ion
Batteries
Sodium-ion batteries (SIBs) are considered an attractive alternative to lithium-ion batteries (LIBs) due to the better global availability of sodium and its compounds compared to the lithium analogs, representing a potential cost advantage. Furthermore, SIBs often contain less critical transition metals, such as cobalt or nickel, than high-energy LIBs.
Challenges
The operating principle of a SIB is very similar to that of LIBs and is based on the shuttling of ions between a positive and a negative electrode enabled by a suitable sodium ion-conducting electrolyte. The most widely used negative electrode material for SIBs are hard carbons. Sodium-containing compounds serve as positive electrode materials. Three types of material are currently being considered for commercial applications: Prussian blue or Prussian white (PBA analogues) type materials, polyanionic compounds or layered oxides. Regarding the electrolyte, established concepts from LIB technology have been adapted for SIBs, with the lithium salt being exchanged with its sodium analogs. However, a simple transfer of the concepts from LIBs to SIBs is not possible due to the more complex formation of stable interphases (SEI and CEI) in SIBs. This complexity results from the higher solubility of sodium-derived interphases, which is due to the size difference between lithium and sodium ions. In addition, the higher coordination number of sodium has a negative effect on the diffusion of the solvated ion, which poses a further challenge. Both electrodes (anode and cathode) usually contain an aluminum current collector, so electrolyte compatibility is of great importance.
Regarding the electrolyte, established concepts from LIB technology have been adapted for SIBs, with the lithium salt being exchanged with its sodium analogs. However, a simple transfer of the concepts from LIBs to SIBs is not possible due to the more complex formation of stable interphases (SEI and CEI) in SIBs. This complexity results from the higher solubility of sodium-derived interphases, which is due to the size difference between lithium and sodium ions. In addition, the higher coordination number of sodium has a negative effect on the diffusion of the solvated ion, which poses a further challenge. Both electrodes (anode and cathode) usually contain an aluminum current collector, so electrolyte compatibility is of great importance.
The Solution
Formation: 3 cycles 0.1C CCCV charge / 0.1C CC discharge
Cycling rate: 1C CCCV charge / 1C CC discharge
Temperature: 40 °C
Voltage range: 4.0 – 1.5 V
