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If electric cars are to be used in large numbers, the batteries presently available will need to be replaced by cheaper, safer ones. Researchers in Uppsala have now produced a promising new electrolyte material from a class of polymers not previously tried.
Lithium-based batteries have the highest energy content of all rechargeable batteries and are therefore very good as energy sources for electric vehicles. If greater numbers of electric vehicles are to be used, however, cheaper batteries are required. There is also a need to rectify some of the safety issues with lithium batteries.
‘As an example, fairly recently safety problems with the batteries in the Boeing Dreamliner passenger jet cost Japanese airlines millions of dollars every day,’ says Daniel Brandell, one of the researchers behind the study.
The liquid electrolyte is the battery component that drives up the cost the most. It is also chemically unstable which makes it a safety risk. It would be better and cheaper to replace it with a solid electrolyte but so far these have only worked well at high temperatures. However, researchers at Uppsala University have now made a breakthrough and produced a new polymer electrolyte material for lithium batteries which also works well at room temperature.
‘By allowing ourselves to be inspired by polymers made of biodegradable organic material, we’ve discovered high levels of conductivity in polymer materials quite unlike the ones normally used in solid electrolytes,’ says Daniel Brandell.
‘These materials are also much easier to work with chemically and may therefore open up a whole new field of materials development leading to better, more sustainable and safer batteries. Our prototype batteries can be charged and discharged in a stable manner for long periods at room temperature. This is unique among solid electrolytes.’
Before the research results can be applied to making commercial batteries, some development work is remains to be done. Among other things, researchers need to ensure that the material is mechanically stable over long periods. It may need some chemical modifications to strengthen it.
‘We’d also very much like to see better movement of ions in order to reach larger segments of the market for lithium batteries. We already know that our electrolytes are not very flammable and therefore safer than the ones currently in use, but more rigorous safety tests still need to be done. The important thing though, is that this category of polymers – polyesters and polycarbonates – has become part of producing battery electrolytes,’ says Daniel Brandell.