Low salt concentration electrolyte reduces the cost of sodium ion batteries
Electrolyte is an indispensable part of energy storage batteries, and regulating the concentration of electrolyte is one of the effective strategies to realize its functional design. In recent years, high-salt concentration electrolytes have been widely used in metal lithium batteries, water-based batteries, etc. due to their special bulk and interface characteristics. But on the contrary, lowering the salt concentration may bring about concentration polarization, so the current actual lithium battery applications are mostly concentrated on the standard 1 M concentration, so that the low salt concentration electrolyte has not been systematically studied. The Stokes radius and desolvation energy of sodium ions are lower than those of lithium ions, so in theory, a lower sodium salt concentration can also achieve sufficient kinetic performance, so that the ultra-low salt concentration electrolyte can be used in sodium ion batteries become possible. Considering that the cost of salt is usually more than ten times that of solvents, reducing the use of sodium salt can effectively reduce the cost of sodium ion batteries, thereby facilitating the large-scale application of sodium ion batteries in the field of energy storage.
Recently, the Institute of Physics of the Chinese Academy of Sciences dissolved sodium hexafluorophosphate (NaPF6) in ethylene carbonate (EC) and propylene carbonate (PC), and designed a low-salt concentration electrolyte that can be applied to sodium ion batteries for the first time ( 0.3 M concentration). Thanks to the low viscosity of the electrolyte, low hydrofluoric acid corrosion and the formation of a solid electrolyte rich in organic components (compared to 1 M concentration), the battery operating temperature window has been significantly widened (-30 to 55°C). The R&D team has further developed Ah-class batteries based on low-salt concentration electrolyte, and the capacity retention rate is over 80% after 3000 weeks. The concept of low salt concentration electrolyte provides a new idea for the stable operation of rechargeable batteries under extreme conditions. In the future, the concept of low salt concentration electrolyte is expected to be extended to other electrolyte systems and other low-cost energy storage batteries.
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