fghjkl;'

1. High-performance lithium battery
anodes using silicon nanowires
EE235 Nanofabrication
John Gerling
4-7-08

2. Lithium Ion Battery Basics
 Electrochemical performance is determined by properties of the anode
and cathode materials.
 Currently, carbon is used as the anode material.
Li Ion Discharge
Electrolyte Cathode
Li Ion
Charge
 Charge battery (lithiation): large volume expansion 200-400% LiM
 Discharge battery (delithiation): volume contraction

3. Silicon NW Anode
 Graphitized carbon (LiC6) – 372
mAh/g
 Silicon (Li22 Si5) – 4200 mAh/g
(10x improvement!)
 Silicon film gets pulverized from
volume changes. Si NW can
accommodate volume change.
 Si NW Anode Advantages:
1) Small NW diameter allows for
better accommodation of large
volume changes.
2) All NW contribute to the capacity.
3) Direct 1D electronic pathways for
efficient charge transport.
4) No need for binders (extra weight
eliminated).

4. Fabrication and Measurement
 Si NWs were synthesized using the VLS process on stainless
steel substrates using Au catalyst.
 The electrochemical properties were evaluated under an argon
atmosphere by both cyclic voltammetry and galvanostatic cycling
in a three electrode configuration, with the Si NWs on the
stainless steel substrate as the working electrode and Li foil as
both reference and counter-electrodes.

5. Silicon NW Anode Results
Peaks related to LiX
formation and
decomposition, the larger
the peak, the larger the
increase in formation and
decomposition.

6. Morphology Changes in Si NW

7. Structural Evolution

8. Comments and Conclusion
 Only 10-20 cycles were performed. Lithium-ion batteries typically
have 1000 cycles. More needed here.
 100% charge capacity achieved. 75% capacity discharge.
Irreversible capacity loss after first cycle. What is the efficiency of
Li-ion batteries now? Wikipedia quotes 99%.