A promising novel phase for silicon anode lithium-ion battery - Dr. Zhidan Zeng

APRIL 14, 2015

A team led by Dr. Zhidan Zeng at the Center for High Pressure Science & Technology Advanced Research (HPSTAR) synthesizes a new phase of Li15Si4 (beta-Li15Si4) under pressure. This beta-Li15Si4 phase shows higher packing density and superior mechanical properties than alpha-Li15Si4. This provides a new perspective on how to overcome the long-standing challenge in the application of silicon anodes for lithium-ion batteries.

Silicon is widely regarded as one of the most promising anode materials for next-generation lithium-ion batteries. However, the lithiation of silicon will induce large volume changes and ultra-high stress, which eventually causes mechanical failure of the material. This hinders the application of silicon anodes.  Pressure was found to be a unique method which could change the properties and structure of the Li–Si system.

Combining in-situ synchrotron x-ray diffraction, and Raman spectroscopy measurements at high pressure conditions together with ab initio evolutionary metadynamics calculations, Zeng and co-workers investigated the structure and properties change of Li15Si4, which is the only crystalline phase from silicon anode lithium-ion batteries. They discovered a novel phase (beta-Li15Si4, space group: Fdd2) when Li15Si4 (alpha-Li15Si4, space group: I43d) was compressed to above 7 GPa. Moreover, this beta-Li15Si4 phase could be quenched to ambient pressure. Theoretical modeling shows beta-Li15Si4 has higher elastic modulus, packing density while lower volume expansion (~25%) compared with alpha-Li15Si4 during lithiation. These show that beta-Li15Si4 have superior resistance to deformation and fracture under stress. This means that the mechanical weakness of the anode material could be effectively improved.

The results in this work not only bring a new member to the important Li-Si system, but also provide a new perspective on how to overcome the long-standing challenge of the mechanical failure in silicon anode lithium-ion batteries by the atomic level structure design for the first time.

The paper’s other co-authors are Q. S. Zeng of HPSTAR, W. L. Mao, Y. Cui and N. Liu of Stanford University, A. R. Oganov of State University of New York Stony Brook., and Q. F. Zeng of Northwestern Polytechnical University.

This work is recently published by Advanced Energy Materials.

Caption: The atomic structure of alpha-Li15Si4 (lower left) and beta-Li15Si4 (upper right). Each silicon atom is surrounded by lithium atoms (green spheres) with the coordination number of 12 (shown in blue polyhedra) or 13 (shown in pink polyhedra).