Calculations of the amount of energy involved in the chemical reactions involved suggest it could produce batteries that last three to five times as long as existing lithium-ion ones – hinting at a day when your smartphone could once again hold a working week’s worth of charge. However, Prof Bruce says much work is still needed, particularly in identifying stable electrolytes that only allow useful electrochemical reactions without wasteful additional reactions.
Meanwhile other groups in the US, Europe and Asia have joined the race. "It's an exciting time, but there are still considerable challenges remaining," says Prof Bruce. “The science is promising but we can't yet guarantee it will end in a workable technology."
But it is not the only lithium-based battery looking to sneak into your next phone. Researchers are also investigating light weight lithium-sulfur packs, which are likely to have a life span of three times that of current lithium-ion batteries. These were first touted in the 1940s and use one electrode made from sulfur and another from lithium. They are already used in specialist communications and military applications but, despite high hopes and high-profile displays of the technology, they have never managed to hit the mainstream. In part, this is because they have had inherent problems such as losing their ability to recharge efficiently after a relatively short space of time and safety issues which mean the metal can melt and potentially catch fire if it comes into contact with water.
However, Sion Power, of Tucson, Arizona, says it has overcome these problems. It has a prototype with around 50% more energy capacity by weight than existing lithium-ion batteries, and says it plans to target markets including mobile phones and notebooks. In 2010 it was awarded a grant worth up to $5 million from the US government to develop safe, practical and economically viable rechargeable lithium-sulfur batteries in three years.
The firm refuses to give specific details about the technology it uses but says it has dealt with the safety issues. These are known to be caused when branch-like growths grow on the lithium metal electrode, causing it to heat up and potentially short-circuit. Prototypes seen elsewhere suggest that they may have accomplished this by treating the electrodes to stop the growths and adding plastic or ceramic membranes to separate the electrodes and prevent short circuits. The company says it has also made progress with the recharging problem. It has prototypes that keep their capacity over 50 cycles but has claimed it is hopeful of reaching 1,000 cycles soon – the equivalent of today’s lithium-ion batteries.
But some firms and researchers argue that despite intense research and millions of dollars of investment, both of these lithium based technologies are far from delivering on their promise. As a result, MIT’s Professor Ceder is taking a more radical approach. He has used high-performance computers to create a public database of around 20,000 chemical compounds. A series of algorithms predict the properties of these materials, allowing researchers to quickly model how two compounds would react with each other in a battery.
“The kind of properties we're talking about are the kind of battery voltages possible with compounds, the mobility of ions and electrons in materials, chemical stability, safety, also indications about how the materials might be made,” he says. The Materials Project, as it is known, has already been used to identify three new materials with the potential to be used in batteries. A lot more work needs to be done on these, he said, but his computational approach is already paying off in work on another technology known as magnesium-ion batteries.