“We have successfully fabricated and tested the first totally solid-state lithium-air battery, which represents a major advancement in the quest for a commercially viable, safe rechargeable battery with high energy and power densities and long cycle life,” said Binod Kumar, a distinguished research engineer and leader of UDRI’s electrochemical power group.
Kumar, who has been involved in the work for 20 years, and his team have developed and tested the batteries in quarter-size forms suitable for experimentation. Commercializing the technology would allow manufacturing of larger batteries that could make them available in as little as two years for powering electronic devices and eight years for powering automobiles, he said.
The batteries also could generate electricity to support utility power grids, or supplement the intermittent generation of solar or wind power systems, said Dan Rastler, manager of the energy storage program at Electric Power Research Institute, an independent, nonprofit research organization funded by the electric utility industry.
Kumar said there is enormous demand in defense and industry for safer, lighter lithium rechargeable batteries for applications ranging from electric vehicles to unmanned aerial vehicles, adding that billions of federal stimulus dollars have already been directed for research, development and manufacturing of lithium batteries. “We believe this breakthrough represents a great opportunity to companies who are eager to incorporate significantly higher energy, longer-life and safer batteries into their products,” he said.
Rechargeables commonly found in today’s portable consumer electronic devices are lithium-ion batteries. They are considered superior to other types of rechargeables, such as nickel cadmium, because of their high energy-to-weight ratios, slow discharge when not in use, and absence of “lazy battery effect,” a phenomenon which causes a battery to lose maximum energy capacity when it is repeatedly charged after only partial discharge.
Because of their lighter weight and high energy capacity, lithium-ion batteries are increasingly used in aerospace and automotive applications, but their full potential for larger applications remains untapped because of technological challenges – primarily related to safety.
“There have been a number of accidents and a large number of recalls involving lithium batteries,” Kumar said. “Most batteries use a liquid electrolyte, which creates a number of problems. They are corrosive and can leak. A short circuit or excessive heat from exposure to direct sunlight or use in a poorly vented laptop, for example, not only shortens battery life, but can cause the battery to rupture, ignite or explode.” Because of their volatility, restrictions exist for ground and air transport of lithium batteries.
Kumar and his colleagues addressed the safety issues by developing an entirely solid-state lithium battery – no liquid is present in the cell. “We’ve replaced the liquid electrolyte with a solid electrolyte that works just as well, but is far safer,” Kumar said. The primary component of the new electrolyte is a glass-ceramic material which is very stable, even when in contact with water.
The researchers applied innovations on solid electrolytes to develop the new technology in the form of a lithium-air battery, rather than a lithium-ion, because they are much lighter and have the potential to be the most energy-dense and most environmentally friendly rechargeables.
In traditional lithium batteries, all the chemicals that power the battery are stored inside, Kumar said. In a lithium-air battery, one of the chemicals – oxygen – is left out. Instead, the battery is specially designed to draw oxygen from the air around it. By extracting oxygen, rather than storing it, and by using lithium metal as an anode, lithium-air batteries are 10 to 15 times more energy dense than other lithium rechargeables.