Na-ion Battery Electrolytes

Owing to the low cost and high natural abundance of sodium (Na), Na-ion batteries (NIBs) have been extensively studied very recently. The most common electrolyte formulation for NIBs is NaClO4 or NaPF6 dissolved in carbonate solvents such as ethylene carbonate and propylene carbonate. NaClO4 is potentially explosive, however, and NaPF6 is sensitive to moisture, evolving highly corrosive HF. Since NIBs have been largely considered for stationary energy storage due to its lower power density, and the deployment of NIB stacks would normally require a large quantity of electrolyte, an electrolyte that is both highly safe and efficient is critical. Boron Molecular is teaming up with the University of Wollongong to help the research community to provide alternative candidates by enabling them to readily access alternative high quality electrolyte formulations.

Sodium-difluoro(oxalato)borate (NaDFOB)

Empirical Formula:  C2BF2NaO4

Molecular Weight:  143.77

Description:  White powder. Slowly reacts with water.

Application

Sodium difluoro(oxalate)borate (NaDFOB) is an electrolyte salt for Na-ion batteries. The electrolytes prepared by dissolving this compound in carbonate-based solvents have a wide electrochemical stability window, low viscosity, and good conductivity. It does not yield HF when reacted with water. These could improve the safety of the future Na-ion batteries, which are expected to be used for large-scale electricity storage.

                                   

Fig 1 View along the [100] direction showing bonded chains in the crystal structure of NaDFOB Na, C, O, B and F are represented by the green, black, yellow, red and blue spheres respectively.

                           

Fig 2 Cycling performances at different rates of Na/Na0.44MnO2 half cells using NaX (X = DFOB, CIO4, and PF6) based electrolytes. (NaDFOB: black, NaCIO4: red and NaPF6: blue)

Compared with NaClO4 and NaPF6 which are commonly used in the literature, this compound enables better compatibility with a couple of most studied compounds for Na-ion batteries, such as carbonaceous materials, TiO2, and Prussian blue, and therefore better rate capability and cycling performance. Na-ion batteries are believed to hold promises for large-scale energy storage such as smart-grid where the market has been predicted to be well over billions of dollars per year, NaDFOB could help the development of reliable batteries to meet the great demand for sustainable energy.

Reference:

 1.    J. Chen, Z. Huang, C. Wang, S. Porter, B. Wang, W. Lie, H. K. Liu, “Sodium-difluoro(oxalato)borate (NaDFOB): A new electrolyte salt for Na-ion batteries”, Chemical Communications, 2015, 51, 9809.