A new development from scientists at Northwestern University in the United States could allow for batteries to be built using lithium by itself, rather than distributing lithium atoms into another material – a breakthrough which could greatly increase the storage capacity of li-ion technology.
In most current li-ion batteries, the lithium is distributed into another anode material, such as graphite or silicon. This dilutes the performance of the battery; however, lithium by itself can grow dendrites and filaments as it charges and discharges, which can reduce a battery’s lifetime, and increase the risk of fire.
Creating a scaffold on which lithium can deposit as the battery charges is one potential solution to this, however the volume of lithium changes as the battery charges and discharges, which can easily damage the support structure.
Scientists at Northwestern University found that crumpled graphene balls lend themselves very well to building a scaffold – the ‘balls’ can stack on top of one another, and can survive the stress from the fluctuating lithium, while preventing the growth of dendrites.
“One general philosophy for making something that can maintain high stress is to make it so strong that it’s unbreakable,” said Jiaxing Huang, professor of materials science and engineering in Northwestern’s McCormick School of Engineering. “Our strategy is based on an opposite idea. Instead of trying to make it unbreakable, our scaffold is made of loosely stacked particles that can readily restack.”
The research is described in a paper published in the journal, Joule. The team created the crumpled graphene balls by dispersing graphene-based sheets into tiny water droplets. As the water evaporated, it generated a force which crumpled the graphene into the paper ball-like structure. These balls move apart as the lithium is deposited, and can reassemble themselves as it depletes.
“Closely packed, the crumpled graphene balls operate like a highly uniform, continuous solid,” said Jiayan Luo, the paper’s co-corresponding author and professor of chemical engineering at Tianjin University in China. “We also found that the crumpled graphene balls do not form clusters but instead are quite evenly distributed.”
Using the scaffold makes the battery much lighter than other similar storage technologies, and allows for lithium to be stacked up to 150 microns high. The researchers have filed a provisional patent for their development, through Northwestern’s innovation and new ventures office.