The Charge for the Future

Man’s eternal struggle to harness energy could take a step forward in the next decade through the use of tiny charged particles of matter: ions. Ions, which are composed of atoms or molecules that have lost or gained electrons, prove to be a promising source of energy in multiple fields of chemical engineering and material science. The secret to harnessing the power stored in ionic charges is to separate ions so electrons can flow freely, usually through melting or dissolving. Delocalized ions can almost act as superconductors for charges and can be controlled to generate power. However, ionic liquids (ILs) melt at extremely high temperatures (NaCl has a boiling point of 801ºC), which is why a new class of ionic liquids that are liquid at room temperature (“cold” ILs) are promising in our hunt for clean energy.

Ionic liquids thermodynamically compatible with Lithium metal are particularly promising for applications in the real world ((© 2007 Electrochemical Society. All rights reserved.)).  Out of the thousands of possible ILs involving Lithium, 1-methyl-3-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P13TFSI) proves to be the most favorable because it is dimensionally stable, flexible, nonvolatile, and has high electrochemical stability. This compound has been successfully synthesized by dissolving Li in the P13TFSI liquid, mixing it with the copolymer poly(vinylidene-co-hexafluoropropylene) (PVDF-HFP). The mass synthesis of this Lithium polymer on an industrial level could one day power cars, planes, households, and industries with high demands for electricity.

Nonetheless, rechargeable Lithium batteries with higher capacities and higher specific energies (up to 13,000W/g) are still unavailable on the market because of aqueous Lithium’s susceptibility to corrosion ((Ye H, Huang K, Xu J, Greenbaum S. (007) J. Chem Phys)). Breakthrough methods of using organic copolymers with ILs could replace aqueous solutions in modern batteries permanently. If these electrolytes could be made resistant to corrosion, IL batteries would not produce toxic waste and would outlast conventional Lithium batteries.

Like any other speculative scientific breakthrough, there are problems that must be addressed as theories become reality. The Li-IL primarily consists of three ions: Li+, the cation of the IL, and the anion from the Lithium salt and the IL. Out of the three, the Li+ is the main contributor to the charge/discharge of batteries ((Ono S, Seki, S, Hirahara, R, Tominari Y, Takeya J. (2008) Appl Phys 92)).  Unfortunately, Japanese nuclear magnetic resonance studies have discovered that the diffusion coefficients of the cation is higher than the anion of the IL. This could lead to cell polarization and reduce the rate of performance. The research of Ye and his colleagues proposes using ethylene carbonate to improve dissociation and transport. This would form a “protective film on the carbon black of the cathode,” allowing Li+ to pass but protecting the electrode side from the IL cation ((Ye H, Huang K, Xu J, Greenbaum S. (007) J. Chem Phys)).

Though the process is still being tested in laboratories, ionic liquids have the potential to revolutionize energy use. Short of nuclear fusion, ionic liquids are the most auspicious and practical resource for increasing energy efficiency. Harnessing energy from ions will power the world in a very different way – charge up, because the future has already begun.

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