Better Battery Performance

Released: January 13, 2015
Long-term performance possible for rechargeable batteries
Large-scale use of high-energy rechargeable Li metal batteries is limited by harmful deposits called Li dendrites. A recent study evaluated the effect of an electrolyte additive that suppresses Li dendrite formation.

The Science

Lithium (Li) metal has long been considered one of the most attractive anode materials, but large-scale application of high-energy rechargeable Li metal batteries still faces several barriers. One major hurdle is growth of Li dendrites—deposits that form on electrode surfaces during the charging process, causing batteries to short circuit and leading to serious safety hazards such as fires and explosions. This study evaluated the effect of an electrolyte additive that suppresses Li dendrite formation to stabilize Li metal.

The Impact

The findings could help scientists design a safe and stable metallic Li anode: the Holy Grail of Li-based battery research. Ultimately, the study could pave the way for the practical application of several high-energy-density battery systems for powering electric vehicles and storing renewable energy on the grid.

Summary

Researchers from the Department of Energy’s (DOE) Pacific Northwest National Laboratory (PNNL) and Environmental Molecular Sciences Laboratory (EMSL), plus Harbin Institute of Technology, Wuhan University, Tianjin Institute of Power Sources and the US Army Research Laboratory evaluated the effectiveness of an electrolyte additive called cesium hexafluorophosphate (CsPF6) on improving the performance of electrochemical cells and protecting anodes in Li metal batteries, which consisted of Li metal anodes and conventional Li-ion cathode materials. The researchers used high-resolution scanning electron microscopy with energy dispersive x-ray analysis to study microstructure and elemental composition, and high-resolution x-ray photoelectron spectroscopy for more detailed chemical characterization. Both instruments are located at EMSL, a DOE national scientific user facility.

The CsPF6 additive promoted dendrite-free growth of Li films consisting of self-aligned, highly compacted nanorods. The electrolyte additive also promoted the formation of rich lithium fluoride (LiF) in the solid electrolyte interphase (SEI)—a layer on the Li electrode surface that protects against Li dendrite growth. The combined effect of the Cs+ additive and the LiF-rich SEI layer contributed to smooth Li deposition in the electrolyte. Moreover, the Li films remained free of dendrites after repeated stripping/deposition cycles.

Taken together, the findings show CsPF6 promotes ordered and smooth growth of Li metal films, protects the Li anode, and improves battery performance. A better understanding of various factors that affect the formation and evolution of the nanostructure of Li films will lead to new approaches to stabilize long-term cycling performance of Li metal and other metal anodes.

Contacts:

Funding:

Publication:

Zhang Y, J Qian, W Xu, SM Russell, X Chen, E Nasybulin, P Bhattacharya, MH Engelhard, D Mei, R Cao, F Ding, AV Cresce, K Xu, and J-G Zhang. 2014. "Dendrite-Free Lithium Deposition with Self-Aligned Nanorod Structure." Nano Letters.   DOI:10.1021/nl5039117

Program: DOE Office of Basic Energy Sciences

Performers/Facilities:

Additional Information:

In related research published in Nature Communications, a multi-institutional team of scientists using EMSL expertise and resources tested electrolytes to eliminate dendrites in lithium batteries. Read more in the Feb. 24, 2015, PNNL news release – “Dendrite eraser: New electrolyte rids batteries of short-circuiting fibers.”

Publication:

Qian J, W Henderson, W Xu, P Bhattacharya, MH Engelhard, O Borodin and J-G Zhang. 2015. "High Rate and Stable Cycling of Lithium Metal Anode," Nature Communications. DOI:10.1038/ncomms7362.