Lithiation-induced stress in Li-ion batteries from micro-Raman Spectroscopy - Dr. Zhidan Zeng

FEBRUARY 25, 2016

Stress is along standing challenge for the applications of silicon(Si) anodes in lithium(Li)ion batteries. Using in situ micro Raman spectroscopy, a team of scientists led by Dr. Zhidan Zeng at the Center for High Pressure Science & Technology Advanced Research (HPSTAR) measured the stress in silicon nanoparticles in a working Li-ion battery for the first time. This new study would be helpful in understanding how the nanostructured silicon anodes fracture during battery operation, and therefore provide guidance for their future design.

Silicon as a promising anode material for next generation high capacity Li-ion batteries faces a major challenge in enormous stress that develops during battery operation, which results in electrode fracture, capacity decay and poor cycle life. Nanostructured silicon anodes have shown significantly improved performance compared with their bulk counterpart. Knowledge of the stress evolution in nanostructured silicon anodes is important for understanding this improvement and guiding the future design.

Recently, using in situ Raman measurements on a specially designed optically transparent lithium-ion battery, Zeng and her colleagues were able to monitor the stress evolution in Si nanoparticles anodes in a working battery for the first time. They observed a transition in stress from tension to compression during lithiation of silicon nanoparticles. When the outlayer silicon starts lithiating, an increasing compressive stress (up to ~300 MPa) developes in silicon core of nanoparticles. This observation explains why the cracks are formed in the lithiated layer (LixSi) of nanoparticles during lithiation. It also offers valuable information for the theoretical study and improvement of silicon anodes design.

“Nanoparticles are too small for conventional techniques on stress measurement such as multi-laser beam or x-ray diffraction.” said Dr. Zeng. “Fortunately, we found that micro-Raman spectroscopy is a sensitive technique to probe the stress in silicon, and we could use in situ high pressure Raman to calibrate the effect of hydrostatic stress on the Raman spectrum of silicon. Of course, the optically transparent design of the battery is important, as it allows us to get Raman signal from the silicon anode inside a battery. We are expecting more exciting studies by using this technique in other systems.”

Other co-authors in this team include HPSTAR’s Qiaoshi Zeng and Wendy Mao.

This new work is  published in recent Nano Energy (doi:10.1016/j.nanoen.2016.02.005).

Caption: A schematic diagram of the stress evolution in a Si nanoparticle during lithiation. The Si core experiences no stress before lithiation (left), tensile stress when oxide layer starts lithiating (middle) and compressive stress after Si starts lithiating (right). The thickness of the oxide layer is exaggerated for a better view.