Key Chemical Juices Up Lithium-Metal Batteries
An electrolyte additive greatly improves charging performance and cycle life.
Lithium metal has long been considered one of the most attractive anodes for high-energy rechargeable batteries, but large-scale application of lithium-metal batteries faces several barriers. Now, researchers have discovered that by adding a small amount of a key chemical to the electrolyte, the performance of lithium-metal batteries can be significantly enhanced.
The addition of an electrolyte additive greatly increased the charging speed, stability, and cycle life of a lithium-metal battery. The study could pave the way for practical application of high energy-density lithium-metal battery systems for powering electric vehicles and storing renewable energy on the grid.
Lithium-ion batteries are common in portable electronics such as cell phones and in today’s plug-in hybrid electric vehicles. Although batteries that use lithium metal in the anode are considered promising energy storage systems, their practical use is hindered by limited cycle life and growth of lithium dendrites. These harmful deposits form on electrode surfaces during the charging process, leading to internal short circuit of the batteries. Researchers from Pacific Northwest National Laboratory’s Environmental Molecular Sciences Laboratory (EMSL), a U.S. Department of Energy (DOE) Office of Science user facility, and Argonne National Laboratory recently discovered that the charging capability and cycling stability of lithium-metal batteries can be greatly improved by adding a key ingredient to the electrolyte — the chemical substance that allows the flow of electrical charge between the cathode and anode. To examine the effects of the additive on lithium-metal anodes, the researchers used the high-resolution microprobe X-ray photoelectron spectrometer (XPS) and Helios focused ion beam/scanning electron microscope (FIB/SEM) at EMSL. Their analysis revealed that adding a small amount of chemical called lithium hexafluorophosphate to the electrolyte created a robust protective layer on the anode, reducing the formation of dendrites. The chemical additive enabled a 4.3-volt battery to retain approximately 97% of initial capacity after 500 repeated charges and discharges, while carrying 1.75 milliamps of electrical current per square centimeter of area. Because the additive is an established component of lithium-ion batteries, it is readily available and relatively inexpensive. The small amounts needed — just 0.6% of the electrolyte by weight — should also keep the electrolyte’s cost low. Ultimately, this finding could pave the way for large-scale implementation of lithium-metal batteries that are highly stable, charge quickly, and require much less frequent recharging.
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, including support of the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science user facility, and by the U.S. DOE Office of Energy Efficiency and Renewable Energy (Office of Vehicle Technologies).
J. Zheng, M.H. Engelhard, D. Mei, S. Jiao, B.J. Polzin, J.-G. Zhang and W. Xu, “Electrolyte additive enabled fast charging and stable cycling lithium metal batteries.” Nature Energy 2, (17012), (2017). doi:10.1038/nenergy.2017.12.