V. Focused Fundamental Research - EERE - U.S. Department of ...

V.C.12 Synthesis and Characterization of Silicon Clathrates for Anode
Applications in Lithium-Ion Batteries (SwRI)
Kwai S. Chan and Michael A. Miller
Southwest Research Institute
Department of Materials Engineering
Mechanical Engineering Division
6220 Culebra Road
San Antonio, TX 78238
Phone: (210) 522-2053; Fax: (210) 522-6965
E-mail: kchan@swri.org; mmiller@swri.org
Start Date: January 1, 2011
Projected End Date: December 31, 2014
Objectives
· Develop scalable synthesis methods for producing
empty and substituted silicon clathrates
· Design, synthesize, and characterize silicon
clathrate compounds for anode applications in Liion
batteries
· Fabricate and characterize prototype silicon
clathrate anodes designed to exhibit small volume
expansion during lithiation, high specific energy
density, while avoiding capacity fading and
improving battery life and abuse tolerance
Technical Barriers
This project addresses the following technical
barriers of the lithium-ion battery technology, especially
focusing on the silicon clathrate anode materials:
· Low-energy density
· Low-power density
· Short calendar and cycle lives
Technical Targets
· Develop silicon clathrate anodes to meet PHEV and
EV goals by exceeding current benchmarks
(Conoco Phillips CPG-8 Graphite/1 M
LiPF 6 +EC:DEC (1:2)/ Toda High-energy layered
(NMC) in the following metrics:
· Energy density
· Power density
· Calendar and cycle lives
Accomplishments
· Prepared 12 gram quantities of Type I barium
aluminum-substituted silicon clathrates
(Ba 8 Al 8 Si 38 ) by an arc-melting technique
· Synthesized 100 milligram quantities of Ba 8 Si 46
by a high-pressure, high-temperature multi-anvil
technique
· Synthesized 10 milligram quantities of empty
Si 46 by a plasma magnetron sputtering technique
· Performed first-principles computations to
identify possible reaction pathways for the
formation of empty clathrates Si 46 , Li x Si 46 ,
Ba x Li y Al z Si 46-z and Li 15 Si 4
· Constructed and evaluated electrochemical halfcells
using silicon clathrate materials synthesized
in this program
Introduction
To achieve the DOE’s performance targets for
PHEV and EV applications, low-cost advanced anode
materials with high-energy density, high-power density,
and longer calendar and cycle lives are needed. To
address this need, this project focuses on the
development of synthesis methods, characterization of
electrochemical performance, and the design and
fabrication of prototype silicon clathrate anodes for
potential applications in Li-ion batteries for PHEV and
EV.
Silicon clathrate, a polymorph of silicon, is an
emerging anode material that is composed of sp 3 bonded
silicon atoms arranged in cage-structures. The silicon
clathrate, Si 46 , consists of crystalline Si with a regular
arrangement of 20-atom and 24-atom cages fused
together through 5 atom pentagonal rings (Type I
clathrate). It has a simple cubic structure with a lattice
parameter of 10.335 Å and 46 Si atoms per unit cell.
The crystal structure (Space Group Pm3n ) of the Si 46
clathrate is different from the common form of
crystalline Si (c-Si), which is diamond cubic (Space
Group Fd 3m ) with a lattice parameter of about 5.456
Å.
First-principles computations performed at SwRI
have revealed that significant amounts of Li ions can be
Energy Storage R&D 580 FY 2011 Annual Progress Report