Lithium ion remains the technology of choice, says battery pioneer

2 min read

For much of the last Century, battery technology didn't really need to progress. But the transistor radio changed all that; suddenly, people needed small batteries with a reasonable operating life at reasonable cost. That need was met at first by dry cells. But as electronic products became more complex and power hungry, it became obvious something better was required and lithium technology met the requirements; at least in part.

Dr Yoshio Nishi, previously director of materials research for Sony, knows a few things about battery technology. He told a recent seminar at the Japanese Embassy in London – sponsored jointly by Johnson Matthey Battery Systems and silicon anode pioneer Nexeon – there are 110million possible combinations of materials that could be used to create a battery, but only 30 of these have been put to practical use. "Even an amateur can make a battery," he said, "using zinc, copper and fruit juice. But it's better to eat the fruit, rather than use it in a battery." And he was critical of the work undertaken by Sony. "Mistakes were made when choosing the anode material [for lithium batteries]. We took the wrong route," he admitted. Of the 110m combinations, lithium and hydrogen are the best, in Dr Nishi's opinion. "In a metal hydride, 10litre of hydrogen gas are contained in 7.5ml of metal hydride. Lithium, meanwhile, was promising, but there were issues with dendrite formation, poor cycle performance and safety. However, a lithium containing cathode seemed feasible." Sony applied for patents covering its approach on 4 July 1980, but found that another application had been made in April 1980 by US Professor John Goodenough. His work focused on LiNiO2 and LiCoO2 cathodes. "Sony decided to license the patent exclusively," Dr Nishi said. Sony pursued the development of lithium carbon anodes and decided that, of three options, hard carbon lithium anodes would be best. "But it didn't satisfy our customers and they shifted to graphite based anodes," he said. Where Sony went wrong in its development of lithium ion batteries, he admitted, was not taking a range of important parameters into consideration; its work was focused entirely on the battery's specific energy capacity, expressed in mAhr/g. "We should have taken into consideration such variables as volumetric energy, average discharge voltage, the initial charge/discharge efficiency and the cut off voltage. We realised that Whr was more important than Ahr." But how does Dr Nishi see battery technology developing? He pointed to a number of possible future battery technologies, but didn't see any of them being in a position to displace lithium ion cells. "Rubeanic acid is one possible approach," he said. Rubeanic acid, also known as dithiooxamide, is a sulphur containing compound. "It has a capacity of around 600mAhr/g and doesn't use rare metals. But 60% of the lithium in the anode is lost in the first charge/discharge cycle and the average discharge voltage is 2.5V." Another possible approach, he continued, is based on trioxotriangulene. "This has a capacity of 225mAhr/g," he said, "and has been the subject of a recent claim that such a battery used in a mobile phone could be recharged in 1s." But he pointed out that, if the discharge capacity of such a battery is 1000mAhr, it would need 3600C in order to recharge it in 1s, which equates to a charger supplying 14.4kW. "Sulphur cathodes also show potential," he continued. "But, on a volumetric basis, this technology has a lower energy than lithium cobalt oxide." His conclusion? "Lithium ion battery development continues, with new anode and cathode materials being investigated. I think the capacity of lithium ion cells will increase and I believe polymer gels will help to increase this capacity and to reduce the size of a battery cell."