Scientists at the university have been developing lithium-air batteries, also referred to as lithium-oxygen, that seek to exploit a much higher theoretical energy density than lithium-ion batteries, the current and clear leader in next gen battery tech. If perfected, the battery could enable an electric car to travel around 400 miles on one charge, while it could also withstand more cycling than its lithium-ion counterparts.
However, lithium-air is also the far more volatile chemistry of the two. The Cambridge team claims that by using electrodes made with a highly porous form of graphene and adding lithium iodide as a “mediator”, many of the instabilities associated with lithium batteries, which cause cells to deteriorate in capacity with time, can be mitigated.
Chris Robinson, an analyst with Lux Research, said the work of the lithium-air battery team from Cambridge appeared to have demonstrated a “big jump” in efficiency over previous lithium-air devices. Robinson also said that the improved cycle life of the batteries the Cambridge scientists achieved was a “major step” to making the new technology a commercial competitor to Li-Ion.
However, Robinson pointed out – as did the University of Cambridge team report’s lead author, Dr Clare Grey – there are still significant “technical hurdles” before the product is ready for mass market use and the technology could be “years away from commercialisation”. Robinson even said that the technology was taking on an almost mythical status among scientists and industry.
“Li-air batteries have been a bit of a white whale in energy storage: although Li-air has a theoretical energy density upwards of 10,000 Wh/kg (for a reference, Li-ion is closer to 200 Wh/kg), but numerous technical hurdles have prevented this number from being realised,” Robinson told PV Tech Storage.
“Cycle life has been a major issue for the batteries, historically struggling to get past the 100 cycle mark, so achieving 2,000 cycles is a major step [towards] making it competitive with many Li-ion batteries today.
Grey and her team have reduced the “voltage gap” between charge and discharge in the lab-created batteries to around 0.2 Volts. This equates to an energy efficiency of 93%, comparable to lithium-ion devices.
“Li-air batteries have struggled with energy efficiency, and by that less energy comes out of the battery during discharge than is put in during charging. For Li-air batteries this has historically been in the 70% to 80% range at best, so an improvement to 93% is a big jump.”
Into the Valley of Death
The gap between prototype tech in the R&D lab and commercialisation has often been referred to in tech circles, especially around Silicon Valley start-ups, as the “Valley of Death”. Products that cannot be mass produced easily, for example, will flounder and probably never get off the ground.
The gap between academia and the market is often even further apart. Another of the Cambridge scientists, Dr Tao Liu, admitted that there was “still a lot of work to do”, although the team’s work suggested the problems inherent in the technology could be solved, Liu said.
Lux Research’s Chris Robinson said that one of the problems that might hamper Li-Air’s progress was, like the earlier years of lithium-ion, concern over safety. The Cambridge team, like all others before them, was not able to overcome the formation of dendrites in the cell – where lithium metal fibres start to grow into string-like forms that can cause explosions in the battery. Another big challenge in battery’s development was the fact that it cannot yet be used in real-world conditions, the chemistry requires that the battery is only cycled in pure oxygen, as common elements in air can affect its performance.
Finally, Robinson said, the tech race that had seen competing battery chemistries fall by the wayside to lithium-ion a few years ago was far from over. Some analysts have said that lithium-ion is expected to hold its dominant position in the space, but that a limit to improvements could be reached in the medium to long term.
While Cambridge’s Clare Grey said her team’s work had made “significant advances” in developing lithium-air (LO2) batteries and showed the “routes forward towards a practical device”, the time this new path might take could still be too long, according to Robinson.
Part of the problem was that while lithium-air might race to succeed or overtake lithium-ion, other chemistries and sub-chemistries were not standing still either, with companies such as the UK’s Oxis Energy looking to commercialise lithium sulfur. Robinson also said it was impossible to discount the possibility there may be overlooked, long-term potential for lithium-ion.
“…Ten years from now there will have been major advances in Li-ion technology, as there are major efforts and a lot of competition in the space. It is likely that other chemistries, such as solid-state batteries and possibly Li-S batteries, will achieve commercialisation prior to Li-air batteries.”
The Cambridge team claims that by using electrodes made with a highly porous form of graphene and adding lithium iodide as a “mediator”, many of the instabilities associated with lithium batteries, which cause cells to deteriorate in capacity with time, can be mitigated.
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