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Air Products Awarded Two Key Patents for Lithium-Ion Battery Electrolyte Salts
17 June 2008
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| Poly-flourinated borane clusters are the basis of the Stabilife salt. |
Air Products has received two US patents covering usage of its Stabilife fluorinated electrolyte salts for lithium-ion batteries. These salts have been formulated to stand up to the conditions expected from next-generation portable power applications as well as hybrid electric vehicles (HEVs).
The Stabilife salts are electrolyte salts based on the poly-fluorinated borane cluster anions, [B12FxH12-x]2-. Stabilife salts have exhibited strong thermal and hydrolytic stability that can allow for the use of safer, lower cost electrode materials such as LiMn2O4 and LiFePO4 in large-format lithium-ion batteries, according to the company.
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| Improved cycle life for two different test chemistries with Stabilife salts. Click to enlarge. Source: Air Products |
The salts also expand the operating temperature window of lithium-ion batteries versus currently employed lithium electrolyte salts. In addition, their electrochemistry enables them to provide inherent overcharge protection to lithium-ion batteries through redox shuttle chemistry. They are produced at a pilot plant housed within Air Products’ fluorine-based chemicals plant in Hometown, Pa.
The electrolyte in a lithium-ion battery must have high ionic conductivity to allow the development of a high-power battery; be stable at both the high potential of the battery cathode and the low potential of the battery anode; be compatible with a physical separator (usually a porous polymeric material) that prevents physical or electronic contact between the anode and cathode; adequately wet the anode, cathode, and separator; be environmentally benign; have low vapor pressure; and be low cost, according to a summary provided by the Batteries for Advanced Transportation Technologies (BATT) research program supported by the US Department of Energy.
(The BATT Program is currently running a portfolio of advanced electrolyte research to address these difficult problems. BATT has also issued a new RFP in the area of novel electrolytes and additives, with the expectation that it will make final decisions by early August 2008.)
Electrolyte materials for lithium-ion batteries fall into three basic categories:
Liquid, including organic solvent-based electrolytes; inorganic solvent-based electrolytes; and molten salts (low temperature = ionic liquids).
Solid, including solid polymer electrolytes; ceramic electrolytes; and glassy electrolytes.
Composites, such as gel electrolytes.
Liquid organic electrolytes for lithium-ion batteries are based on solvent mixtures for conductivity reasons. LiPF6 salt in liquid organic electrolytes is the current state of the art, according to Professor Martin Winter of the Institute of Physical Chemistry at the University of Münster (Germany). Given its thermal and chemical instability, however, an alternative or at least a partial replacement is urgently needed, he said during his tutorial on material selection for Li-ion batteries given at the recent Advanced Automotive Batteries Conference (AABC).
Properties of the Stabilife salt includes:
Stable to more than 400°C, enabling higher temperature operation than LiPF6.
Hydrolytically/chemically stable; unlike LiPF6, they do not hydrolyze to generate HF.
Compatible with LiMn2O4 and LiFePO4 electrode materials, with a different SEI from PF6- or BR4-.
Electrochemistry provides inherent overcharge protection and is tunable for a range of cell potentials.
Comparable Li+ Conductivity to LiPF6. Bulk conductivity 5-8 mS/cm in standard carbonate solvents at room temperature at 0.4 to 0.5M concentrations of the salt.
Higher relative Li-ion transference number than LiPF6
In a presentation at this year’s AABC, Bill Casteel, Lead Research Scientist at Air Products, outlined the progress made in optimizing formulations of Stabilife electrolytes for high power and improved thermal stability targeted at automotive applications.
Air Products identified several factors for improved power formulations, including solvent choice (lower viscosity linear carbonates are better) and the optimal salt concentration (~0.3M). The concentration is particularly important when blending with other salt additives for SEI formation.
The improved thermal stability has been shown on high temperature cycling for both hard carbon and graphite-based anodes with LiMn2O4 cathodes.
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Comments
Beside improved operation safety and wider temperature range, does anybody know, what will be the overall battery performance gain or loss with regards to energy density, peak power, recharge time, number of cycles etc when this new electrolyte is used?
Has it been tested with various baterry configurations?
Posted by: HarveyD | Jun 17, 2008 4:59:48 PM
I am wondering if this is another high temp chemistry requiring battery optimization at temps around 300C, like the NaNiCl Zebra.
Posted by: gr | Jun 18, 2008 10:32:57 AM
Fuel hydrogen's lack of compactness is one reason I like boron.
Yes, it's harder to keep boron liquid than to keep hydrogen liquid, but it's compact. Even taking into account the volume of the B2O3 lump bin, it's more compact than any form of fuel hydrogen. Plus, with liquid boron, the marketing problem is pre-solved.
Posted by: G.R.L. Cowan, H2 energy fan 'til ~1996 | Jun 20, 2008 9:37:39 AM
Oops, the above comment was meant for http://www.greencarcongress.com/2008/06/sierra-lobo-to.html
Posted by: G.R.L. Cowan, H2 energy fan 'til ~1996 | Jun 20, 2008 9:39:49 AM
