Posted in Technology - Energy and Cleantech
New Materials for Batteries:
Electrolytes, Conducting Salts, Electrode materials and Additives
Storage of electrical energy will become more and more important in the near future, especially for the use in the automotive sector or for portable electronics. In addition, the extension of the renewable energy sector will require additional buffer capacities of electric energy in order to stabilize the power grit. In this context batteries play an important role today and will become even more important in the future.
In electrical energy storage batteries generally compete with double-layer capacitors (supercaps). Even though batteries have a much lower power density compared to supercaps (battery: 1 kW/kg; supercap: 10 kW/kg) they possess an energy density that is two orders of magnitude higher than that of supercaps (Supercap: 1 Wh/kg; Li-ion battery: 150 Wh/kg). For this reason batteries are the storage device of choice for many applications.
A New Electrolytes
Safety Aspects
Besides energy density and battery life time the aspect of battery safety plays an important role in the development of batteries for applications in mobile electronics or electric mobility. The following movie impressively shows that the hazard potential of lithium ion batteries can not be neglected:
http://www.youtube.com/watch?v=jjAtBiTSsKY
In this context, the thermal and electrochemical stability of the electrolyte and the stability of the separator that separates the two half-cells in the battery play important roles.
Ionic Liquids
New electrolytes for batteries
In recent years ionic liquids have been widely studied as new electrolytes for lithium, lithium-polymer and lithium-ion batteries. A mayor driver of this research was the safety aspect since certain ionic liquids only show a negligible low vapor pressure and very slow decomposition at elevated temperatures[i].
http://www.youtube.com/watch?v=1LNzgC2ufaI
In addition, certain ionic liquids possess wide electrochemical windows, which indicates that they show a good stability against oxidation and reduction, which allows the development of new types of batteries with e.g. highly reactive intermediates. In addition the high electrochemical stability guarantees a high cycle stability of the battery.
At IOLITEC we focus on the challenges of improving the electric conductivity, the viscosity and the wettability of ionic liquids. In our internal research we were able to achieve conductivities of less than 20 mS/cm (25°C). In additiion, mixing of ionic Liquids leads to lower viscosity and enhanced conductivity. Further information can be found here or in Zeitschrift für Physikalische Chemie (Oldenbourg Wissenschaftsverlag, München)
Furthermore, IOLITEC investigates the fundamentals of the use of ionic liquids in lithium ion batteries in cooperation with the Karlsruhe Institute of Technology (KIT) in the joint research project LiB Nano (financed by the Germany Ministry of Education, Research and Science)
Zinc-Air and Lithium-Air Batteries
Ionic Liquids as Electrolytes for New Battery Concepts
Another interesting aspect of ionic liquids is the combination of their low vapor pressure and their ability to dissolve oxygen. This combination makes it possible to use ionic liquids as electrolytes in metal-air batteries.
If you are interested in more information on this topic, please contact us.
Lithium-Metal Batteries:
Avoiding Dendritic Growth
During the charging process in a lithium-metal battery, which is similar to galvanic lithium deposition, lithium metal is deposited on the electrode. In order to prevent dendritic growth of the lithium on the electrode that may lead to short circuits in the battery, ionic liquid electrolytes can be used that allow the nanocrystalline deposition of layered lithium on the electrode. IOLITEC provides a variety of electrolytes that allow the controlled deposition of lithium.
If you are interested in more information on this topic, please contact us.
B Conducting Salts
Lithium bis(trifluoromethylsulfonyl)imid
Today LiPF6 is still the most commonly used conducting salt in lithium-ion batteries. An interesting alternative is Lithium bis(trifluoromethylsulfonyl)amid (Li BTA). The BTA anion shows a much better electrochemical stability compared to the PF6 anion and is much more stable against hydrolysis. The conductivities achieved by using LiBTA as conducting salt are in the range of those achieved with LiClO4 and LiAsF6. A number of applications showed the successful use in lithium-ion batteries, primary and secondary lithium-metal batteries and lithium-polymer batteries.
C Electrode Materials
Carbon-Nanotubes and Graphene
In the past years carbon allotropes such as carbon nanotubes or graphene have inspired a variety of scientific areas, which has led to a number of applications for these materials. In lithium-ion batteries these materials are interesting alternatives to the commonly used graphite electrodes.
IOLITEC supplies a variety of Single and Multi-walled Carbon Nanotubes as well as graphene.
D Fillers
Increasing mechanical and cycling stability
Recently Ahn et al. reported that composites composed of ionic liquids and nanomaterials are useful fillers for increasing the mechanical and cycling stability of batteries. They incorporated a composite material derived from bariumtitanate and 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amid into a poly(vinyliden fluoride co hexafluoropropylen) mebran in a lithium polymer battery and found not only an increased mechanical stability but also an acceptable discharge capacity of 165 mAhg-1 and a good cycling stability.[ii]
Text: Dr. Thomas J. S. Schubert, IOLITEC GmbH, 2011 (German Version; English Translation: Dr. Tom Beyersdorff, IOLITEC Inc.)
[IV B]
[i] P. Raghavan, X. Zhao, J. Manuel, G. S. Chauhan, J.-H. Ahn, H.-S. Ryu, H.-J. Ahn, K.-W. Kim, Changwoon Nah, Electrochimica Acta 2010, 55, 1347.
[ii] K. Hayashi, Y. Nemoto, K. Akuto, Y. Sakurai, J. Power Sources 2005, 146, 689; V. R. Koch, C. Nanjundiah, G. B. Appetecchi, B. Scrosati, J. Electrochem. Soc. 1995, 142, L116–L118; A. B. McEwen, E. L. Ngo, K. LeCompte, J. L. Goldman, J. Electrochem. Soc. 1999, 146, 1687. V. R. Koch, L. A. Dominey, C. Nanjundiah, M. J. Ondrechen, J. Electrochem. Soc. 1996, 143, 798; P. Bonhôte, A.-P. Dias, N. Papageorgiou, K. Kalyanasundaram, M. Grätzel, Inorg. Chem. 1996, 35, 1168; T. E. Sutto, H. C. De Long, P. C. Trulove, Proc. Electrochem. Soc. 2002, 2002-19, 134; F. F. C. Bazito, Y. Kawano, R. M. Torresi, Electrochim. Acta 2007, 52, 6427.
