However, a variation of the battery chemistry, developed by a team at MIT, could be used in a conventional sealed battery. The new approach relies on the creation of nanoscale particles – nanolithia – containing lithium and oxygen, confined tightly within a matrix of cobalt oxide, which stabilises the particles and acts as a catalyst.
Professor Ju Li says there is a mismatch between the charging and discharging voltages, with the output voltage more than 1.2V less than charging voltage. “You waste 30% of the electrical energy as heat in charging. It can actually burn if you charge it too quickly,” he says.
Conventional lithium-air batteries draw in oxygen from the air to drive a chemical reaction with lithium during the discharging cycle. Oxygen is then released to the atmosphere during the reverse reaction.
In the new variant, called a nanolithia cathode battery, the same kind of electrochemical reactions take place, but without the oxygen reverting to a gaseous form. Instead, says the team, the oxygen transforms directly between its three redox states, while bound in the form of three different solid chemical compounds – Li2O, Li2O2, and LiO2 – which are mixed together in the form of a glass. This reduces the voltage loss to 0.24V, so only 8% of the electrical energy is turned to heat. “This means faster charging for cars, as heat removal from the battery pack is less of a safety concern, as well as energy efficiency benefits,” Prof Li adds.
Because the ‘solid oxygen’ cathodes are lighter than conventional lithium-ion battery cathodes, the new design could store up to twice the amount of energy for a given cathode weight, the team says. With further refinement of the design, says Prof Li, the new batteries could double that capacity again.
The team expects to move from a lab scale proof of concept to a practical prototype within a year.
