A new approach developed by researchers at the University of Waterloo could hold the key to greatly improving the performance of commercial lithium-ion batteries. The scientists have developed a new type of silicon anode that would be used in place of a conventional graphite anode, which they claim will lead to smaller, lighter and longer-lasting batteries for everything from personal devices to electric vehicles.
Graphite has served the lithium-ion battery world as material for negative electrodes well so far, but also presents something of a roadblock for improved capacity. This is due to the relatively small amount of energy it can store, which comes in at around 370 mAh/g (milliamp hours per gram). Silicon has become an increasingly popular substitute for battery researchers looking to up the ante, with a specific capacity of 4,200 mAh/g. However, it isn't without its limitations either.
As silicon interacts with lithium inside the cell during each charge cycle, it expands and contracts by as much as as 300 percent. This immense swelling brings about cracks that diminish the battery's performance over time, leading to short circuits and ultimately cell failure. Other recent attempts to overcome this problem have turned up battery designs that use sponge-like silicon anodes developed at the nanoscale, silicon nanowires measuring only a few microns long and ones that bring graphene and carbon nanotubes into the mix.
The University of Waterloo scientists' approach involved developing yet another way to modify the structure of the silicon anode. It takes advantage of a chemical reaction between sulfur-doped graphene, silicon nanoparticles and cyclized polyacrylonitrile, a material often used to make surgical gloves, to result in what they describe as a robust nanoarchitecture.
In testing this new nanoarchitecture, the researchers report that the anode design resulted in less contact between the lithium and the electrode, which in turn averted much of the expansion and contraction and resulted in higher stability.
They also claim the design led to a capacity of more than 1,000 mAh/g over 2,275 cycles (a marked improvement on graphite's average of 500) and a Coulombic efficiency of 99.9 percent, which pertains to the charge transferred to and from the electrode and has been seen as another weakness of silicon anodes.
The researchers say the new anode can bring about a 40 to 60 percent increase in energy density of lithium ion batteries and could see electric cars driven up to 500 km (310 mi) per charge. They plan on commercializing the technology and, quite promisingly, expect to see it incorporated into new batteries within the next year.
The research was published in the journal Nature Communications.
Source: University of Waterloo
