Nikhil Koratkar 110 8 Street, Troy,
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Silicon based Nano-Scoops for High-Power Lithium-Ion Battery Anodes Nikhil Koratkar Professor Editor CARBON (Elsevier) Department of Mechanical, Aerospace, and Nuclear Engineering Rensselaer Polytechnic Institute 110 8 th Street, Troy, New York, USA.
Transcript of Nikhil Koratkar 110 8 Street, Troy,
Silicon based Nano-Scoops for
High-Power Lithium-Ion Battery Anodes
Nikhil Koratkar
ProfessorEditor CARBON (Elsevier)
Department of Mechanical, Aerospace, and Nuclear Engineering
Rensselaer Polytechnic Institute
110 8th Street, Troy,
New York, USA.
Research Objective
• Need for a power source that can provide high power density and high energy density
• Research aim: To design electrode nano-architectures that can retain mechanical integrity over hunderds of cycles while providing a high capacity even when cycled at very high C-rates (> 20C)
Source: M. Winter, R. J. Brodd, Chem. Rev. 2004, 104, 4245.
Why is power output low for Li-ion Cells ?
Cathode: It is the source of Lithium. Ex: LiCoO2, LiFePO4
Anode: It is a host material for insertion of Li+. Ex: Graphite, porous carbon
Electrolyte: It offers a medium for the transport of Li+. Ex: solution of lithium-salt electrolytes, such as LiPF6, LiBF4, or LiClO4, in an organic solvent such as alkene carbonates
Source: R. Teki, M. K. Datta, R. Krishnan, T. C. Parker, T. –M. Lu, P. N. Kumta, N. Koratkar, Small, 2009, 5, 2236.
Need for improvement ?
• Charge / discharge capacity: It is a measure of the total charge per unit weight stored or recovered from the electrode material. The standard units for specific capacity are (mAh/g). The specific capacity is also a measure of the “Energy Density” of the battery.
• C-rate: A rate of nC corresponds to a full discharge in 1/n hours. This parameter monitors rate of charge/discharge as well as magnitude of current. It captures the “Power Density” of the battery.
Alternative Anode Materials: Quest for Higher Energy Density !
Alloy Capacity (mAh/g) Volumetric change (%)
Li22Si5 4200 400
Li3As 840 201
Li3Sb 564 147
LiAl 993 94
LiC6 372 10
Silicon has been proposed as the anode instead of carbon. Higher the Li capacity, larger the accompanying volumetric change
Source: A. Patil, V. Patil, D. Shin, J. Choi, D. Paik, S-J. Yoon, Mater. Res. Bull. 2008, 43, 1913.
Prior Art: Silicon Films as Anode
Advantage: High theoretical charge capacity of 4200 mAh/g (10 times larger than carbon) Disadvantage: 400 % volume expansion leading to pulverization and delamination of the electrode films.
(a) Specific capacity plotted as a function of cycle number. (b) Stress-induced cracking of the film after a few cycles. (c) Delamination and peeling of the film from the collector electrode after extended cycling [2]
Source: J. P. Maranchi, A. F. Hepps, A. G. Evans, N. T. Nuhfer, P. N. Kumta, J. Electrochem. Soc. 2006, 153, A1246.
Nano-Silicon Reports
(a) Scanning electron micrographs of the porous Si particles indicating a pore wall size of ~40 nm. (b) Capacity vs. cycle number.
Source: H. Kim, B. Han, J. Choo, J. Cho, Angew. Chem. 2008, 47, 10151.
(a) Concept schematic of Si nanowire electrode (b) Scanning electron micrograph of Si nanowires that comprise the device anode. (c) Capacity vs. cycle number.
Source: C. K. Chan, H. Peng, G. Lin, K. McIlwrath, X. F. Zhang, R. A. Huggins, Y. Cui, Nat. Nanotechnol. 2008, 3, 31.
0.05C
Our Concept: Strain graded carbon-aluminum-silicon nano-scoop anode architecture
• C nanorods – oblique angle flux (85° from normal)
• Al and Si scoops – normal flux incidence
• Tested at 40C (51.2 A/g), 60C (76.8 A/g), 100C (128 A/g)
10%
94%280%
C
AlSi
Before
Lithiation
After
Lithiation
10%
94%280%
C
AlSi
10%
94%280%
10%
94%280%
C
AlSi
Before
Lithiation
After
Lithiation
200 nm
Si
Al
C
100 nm
Si wafer 200 nm
Si
Al
C
100 nm
Si wafer 200 nm
Si
Al
C
100 nm
200 nm200 nm
Si
Al
C
100 nm
Si wafer
Coin cell testing
C-Al-Si Nanorods: Oblique Angle Deposition (OAD)
Sputter Target (C, Al, Si)
Results: Specific Capacity vs. Cycle Index
C-rate: 40C
Evidence of Li Insertion into Si scoops at 40C
Unlithiated
Lithiated: 40C
Direct Physical
Evidence of
Li+ insertion into
The Si Scoops
Effect of Strain Gradation
C
Al
Si Si
Cr Vs.
(0%)
(280%)
(10%)
(94%)
(280%)
C
Al
Si Si
C Vs.
(280%)
(10%)
(10%)
(94%)
(280%)
Results: Ragone Plot
Advantages: Energy density of 100 Wh/kg at C-rate of 40C Power density as high as 250 kW/kg Stability in performance
Journal Publication: Nano Letters
5th Highest Downloaded Paper
on Nano Letters Web-site in
Jan/Feb 2011
Limitation of Nanoscoops • Poor Mass Scalability !
Area Mass Density Target: ~5 mg/cm2
(need 100-fold increase as compared to nano-scoops to build a compact cell)
Exploring silicon spirals with gradation in strain
Questions ?
