Electrochemical and Structural Characteristics of Type I and Type II Silicon Clathrate Anodes

Wednesday, 8 October 2014
Expo Center, 1st Floor, Center and Right Foyers (Moon Palace Resort)
Y. Li, R. Raghavan, N. Wagner, and C. K. Chan (Arizona State University)
Lithium-ion batteries are one of the most promising energy storage devices due to their high energy density, long cycle life, high voltage, and excellent rate capability. Si is a promising anode material due to its extremely large theoretical capacity of 3579 mAh/g at room temperature. However, the practical use of Si anodes is hindered by the structural failure upon lithium insertion/extraction processes and the low intrinsic electric conductivity.

In our group, we have investigated several different silicon clathrate materials, which have cage-like structures, as anode materials of Li-ion battery. The work to be presented here will discuss the electrochemical and structure characteristics of both type-I and type-II silicon clathrate anodes.

Type-I clathrates, which are synthesized using thermal annealing and arc-melting methods, are made of two pentagonal dodecahedra (Si20) cages and six tet-rakaidecahedra (Si24 cages) per unit cell and crystallize in the Pm3n space group. Results show that ternary type-I clathrates have the ability to allow lithium insertion and removal without a large volume change or pulverization. Type-II clathrates, which are synthesized by thermal decomposition of the Zintl compound, are made of sixteen pentagonal dodecahedra plus eight hexakaidecahedra (Si28 cages) per unit cell and crystallize in the Fd3m space group. Results show that upon electrochemical lithiation the type-II clathrates become amorphous and transform into c-Li15Si4 at low potentials, then remain an amorphous silicide after delithiation. Ex-situ X-ray diffraction, X-ray photoelectron spectroscopy and nuclear magnetic resonance are also employed to understand the structural changes upon lithiation, delithiation and prolonged cycling.