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

V.C.13 Wiring Up Silicon Nanoparticles for High-Performance Lithium-Ion
Battery Anodes (Stanford U)
Yi Cui (PI)
Stanford University
476 Lomita Mall, McCullough 343
Stanford, CA 94305
Phone: (650) 723-4613
E-mail: yicui@stanford.edu
Start Date: January 2011
Projected End Date: December 2015
Objectives
· Go beyond the charge capacity limitation of
conventional carbon anodes by designing nanoarchitectured
silicon electrodes.
· Design, synthesize and characterize Si nanostructurebased
anodes to overcome the volume change-induced
materials challenges and to realize high performance.
· Understand the fundamendal structure-property
relationship on electrode materials with large structure
and volume change.
· Develop low-cost materials processing methods.
Technical Barriers
The large structure and volume changes of Si during
battery cycling cause multiple materials challenges: 1)
Mechanical breaking 2) Unstable solid electrolyte
interface. 3) Challenge to maintain good electrical
connection. These fundamental challenges result in
technical barriers in battery performance:
· Large first cycle irreversible loss
· Poor cycle life
· Inadequate coulombic efficiencies
Technical Targets
· Develop fundamental materials guideline through
structure and property correlation and design
nanostructured Si anodes with the features to address
the three material challenges outlined above.
· Develop synthesis techniques to produce the designed
nanostructured Si anodes.
· Develop techniques for structure-property correlation
at the single nanostructure level.
· Demonstrate high performance Si anodes with cycle
life above 3000 at 1000mA/g and 5C rate, and first
cycle irreversible loss less than ~15%.
Accomplishments
· Developd synthesis strategy to connect Si particles
electrically.
· Developed ex situ TEM to study Si volume changes
and discovered the dependence of volume change on
surface oxide layer and on size.
· Developed synthesis methods to produce Si electrodes
with engineered pore sizes.
· Obtain detailed information on the volume expansion
and contraction of Si.
· Determining size effects on fracture upon
electrochemical lithiation/delithiation of silicon
nanopillars.
· Developed conductive, mechanically robust,
electrochemically inactive nanoscale scaffolding for
supporting Si active material.
· Develop a prelithiation method to load lithium into Si
anodes.
Introduction
Next generation high capacity electrode materials are
needed in order to generate high energy battery technology
to meet the demands of transportation. Silicon is an
exciting and promising anode material to replace carbon in
Li-ion batteries due to: 1) a high gravimetric capacity of
~4200 mAh/g, ten times higher than graphite (~370
mAh/g); 2) a high volume capacity of 9786 mAh/cm 3 ; 3)
its relatively low working potential suitable as an anode (~
0.5 V Vs Li/Li + ); 4) abundance of Si element, safe and
environmentally benign; 5) The fundamental and
manufacturing knowledge established in Si semiconductor
industry and solar industry can be leveraged. However,
there exist several scientific and technical challenges for
silicon anodes: 1) Mechanical breaking caused by large
volume change. The electrochemical alloying reaction of
Li with Si involves volume expansion of up to 400% and
significant contraction during lithium extraction. The stress
induced by the large volume changes causes cracking and
pulverization of silicon, which leads to loss of electrical
FY 2011 Annual Progress Report 585 Energy Storage R&D