It’s a well-known fact that how far an electric car can travel before it needs recharging is a primary concern among would-be plug-in car drivers. As a consequence, finding ways to increase the energy density — and thus range — of electric car battery packs has become something of a holy grail for the plug-in automotive industry.
To date, the challenge of increasing the energy density of a battery pack has been met by a wide range of solutions, ranging from exotic new battery chemistries to biologically-engineered viruses capable of growing ultra-thin, nano-wires. In every case, laboratory tests have confirmed a massive improvement in energy density in the new cells over the current generations of lithium-ion cells used in production electric cars today, but often at an increased financial cost or more complex manufacturing process.
But the latest contender in the challenge to find a longer-range battery pack boasts not only a massive theoretical improvement in energy density but manages it in a far safer and cheaper way than some of its rivals.
Enter professor Noritaka Mizuno (via GreenCarReports) and his team from the School of Engineering at the University of Tokyo, and a lithium-ion battery pack which makes uses of an oxidation-reduction reaction to improve the energy density of a lithium-ion battery cell by more than seven times current lithium-ion cells.
Designed to make use of the oxidation-reduction reaction between oxide ions and peroxide ions and the positive electrode and the oxidation-reduction reaction of lithium at the negative electrode, the positive electrode is made by adding cobalt to the crystal structure of lithium oxide using a planetary ball mill. The resulting battery chemistry has a theoretical capacity of 897mAh per 1g of electrode active material. That translates to a theoretical energy density of 2,570 Wh per kilogram, although it’s worth noting that current tests have only ventured as far as 200 mAh per gram of mass. Further testing would be required to produce a cell capable of reaching the chemistry’s theoretical limits.
If the researchers, who are backed by Nippon Shokubai Co Ltd., manage to produce cells which match the theoretical 2,570Wh per kilogram energy density their calculations suggest however, the battery chemistry could change the way electric cars are built.
For example, a Nissan LEAF battery pack has an energy density of around 140 Wh per kilogram, while the Tesla Model S — with the most energy-dense battery pack on the market today — is estimated to have an energy density of around 240 Wh per kilogram. If professor Mizumo and his team were to successfully reach the chemistry’s theoretical maximum energy density, they could make a replacement 24 kilowatt-hour Nissan LEAF battery pack it weighing less than ten kilos (20 pounds) excluding any necessary power electronics and monitoring equipment. Currently, the LEAF battery pack weighs more 294 kg (649 pounds).
Professor Mizumo and his team admit that the energy density offered by their new chemistry isn’t quite the level offered by lithium-air battery pack design. However, since it is completely sealed, the engineers say their design is far safer and more reliable than lithium-air technology. Since the positive electrode has a smaller mass ratio of Co to LiCoO2 when compared to existing lithium-ion batteries, it could even reduce the cost of making battery packs as well.
Sadly, like other promising electric car battery technologies however, there’s a big difference between the theoretical maxima and small-scale testing of an academic institution and the real-world application of that same technology on a mass-industrial scale.
For now then, we’ll just have to watch the technology develop with interest, and be content with the far less energy dense packs we have for now.
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