The following guest post was written by Wei-Qiang Han, a materials scientist working at Brookhaven Lab’s Center for Functional Nanomaterials.
With gasoline prices still hovering near $4 per gallon, scientists at Brookhaven Lab’s Center for Functional Nanomaterials (CFN) are helping to develop electric vehicles capable of driving hundreds of miles on a single charge. A new compound of five tin atoms and one iron atom (FeSn5) created at the CFN is another development along the road to higher capacity lithium-ion batteries for those vehicles of the future.
Compared to other types of rechargeable batteries, lithium-ion batteries weigh less, can store more electricity for longer periods of time, and can handle more cycles of use and recharging. They are used in some electric cars today, but are not yet powerful enough to compete with cars that can travel 300-400 miles on a single tank of gasoline.
Lithium-ion batteries provide energy as electricity flows from an anode to the device being powered and then back to the battery’s cathode. One way researchers compare batteries with different components is by examining theoretical capacities — how much charge a battery can store theoretically in ideal conditions, and practical capacities — how much charge a battery can store in real-world conditions that are more similar to everyday use.
Our team found that the practical capacity for anodes of FeSn5 was 100 percent higher than the ideal capacity for anodes used in conventional lithium-ion batteries.
This performance surpasses the highest-performance lithium-ion batteries on the market today. The iron used in the new compound is also non-toxic and less expensive than the cobalt currently used in high-performance lithium-ion batteries. The main issue we encounter, however, is the small number of charge-recharge cycles that FeSn5 can sustain before its capacity drastically degrades.
Researchers (standing, from left) Jianming Bai, Wei-Qiang Han, Xiao-Liang Wang, and (seated) Haiyan Chen with empty coin-cell cases that will be filled and assembled to test materials such as the new iron-tin compound.
Xiao-Liang Wang and I fabricated the new iron-tin compound at the CFN’s material synthesis facility using preformed, nano-sized, spherical templates of tin and a conversion chemistry process. Then, we inserted the sample anode into a lithium-ion battery and tested the cell by running it through a series of cycles.
When our tests showed that the FeSn5 anodes could lead to a lithium-ion battery with a significantly higher practical capacity, scientists Jianming Bai, Haiyan Chen, and Trevor Tyson used x-ray diffraction at the National Synchrotron Light Source to document the new material’s crystal structure. Then, scientists Meigan Aronson, Mikhail Feygenson, Wei Ku, and Chia-Hui Lin used a magnetometer and other tools to measure the material’s magnetic properties. The findings from those tests showed that the compound might also be useful in magnetic storage devices such as hard drives for computers.
This is very exciting work, but FeSn5 is not ready for commercial use. Our next steps are to study other aspects including its charge-recharge cycle limitations, because FeSn5 is one of a number of reported materials with high capacity. Real solutions will combine high capacity with high cycle life.
The work at Brookhaven was supported by the DOE’s Office of Science (Basic Energy Sciences) as well as its Office of Energy Efficiency and Renewable Energy, and Vehicle Technologies programs. Funding was also provided through Brookhaven’s Laboratory Directed Research and Development program, which promotes highly innovative and exploratory research. Scientists who collaborated on this research represent several other institutions, including the New Jersey Institute of Technology, Stony Brook University, the University of Tennessee, and DOE’s Oak Ridge National Laboratory.