nano-structured binary intermetallics as negative ... · pdf file26.04.2007 ·...
TRANSCRIPT
1/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
NANONANO--STRUCTURED BINARY INTERMETALLICS STRUCTURED BINARY INTERMETALLICS
AS NEGATIVE ELECTRODE AS NEGATIVE ELECTRODE
FOR LITHIUM ION BATTERIESFOR LITHIUM ION BATTERIES
April 26, 2007
Seung M. Oh*, Kyu T. Lee, Yoon Seok Jung, Ji Y. Kwon, Jun H. Kim
School of Chemical and Biological Engineering, and Research Center for Energy
Conversion and Storage, Seoul National University, Seoul 151-742, Korea
2/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
Lithium Ion Battery (LIB)Lithium Ion Battery (LIB)
High energy density
High voltage
High rate discharge/Fast charge
No memory effect
Long cycle life
High storage characteristics
Minimal self-discharge
Reliability
J. M. Tarascon et al., Nature 414, 359 (2001).
At present: Mobile phones, Note book PCs, Power tools
Future: HEV, Robotics, Electricity Storage
3/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
Charge/Discharge Mechanism of LIBCharge/Discharge Mechanism of LIB
http://www.samsungsdi.com/
Graphite powder(MCMB)10-20 µm
LiCoO2 powder
10-20 µm
4/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
Electrode materials for each applicationElectrode materials for each application
High loading,
thicker plate
100 1000 100000
50
100
150
200
EN
ER
GY
DEN
SIT
Y (
Wh
/kg
)
POWER DENSITY (W/kg)
Mobile IT
HEV
EV
Robot
Large area,
thinner plate
Electrode materials, design: specified for each application
5/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
LIB for Note Book PCLIB for Note Book PC
19951995
19941994
19961996
1998199820002000
20012001
Typ.1250mAhTyp.Typ.1250mAh1250mAh
Typ.1370mAhTyp.1370mAh
Typ.1420mAhTyp.1420mAh
Typ.1700mAhTyp.1700mAh
Typ.1900mAhTyp.1900mAh
20022002
4.2V Charging System4.2V Charging System
4.1V Charging System4.1V Charging System
Typ.2000mAhTyp.2000mAhTyp.2100mAhTyp.2100mAh
Typ.2200mAhTyp.2200mAh
20032003
Typ.2400mAhTyp.Typ.2400mAh2400mAhCylindrical 18650 LIB:
Capacity doubles
for 10 years
(Improvement in design)
To have 3000 mAh cells:
New electrode materials
6/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
Nanotechnology for Advanced Electrode Materials ?Nanotechnology for Advanced Electrode Materials ?
Nano-sized electrode materials (vs. nano-structured materials)
– Advantage
• Larger electrode/electrolyte contact area ; higher charge/discharge rates
• Short path length for Li+ transport; higher charge/discharge rates
• Better accommodation of strain induced by lithium insertion/removal,
improving cycle life
– Disadvantage
• Undesirable electrode/electrolyte reactions due to higher surface area,
leading to self-discharge, poor cycling and calendar life
• Hard to handle unstable ultra-fine powders; in mixing and slurry making
processes
• Potentially more complex synthesis
• Environmental, health and safety issues
7/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
NanoNano--sized Electrode Materials (LiFePOsized Electrode Materials (LiFePO44))
High power cell using nano phosphate (A 123Systems)
– LiFePO4: poor electronic/ionic conductor
8/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
NanoNano--sized sized rutilerutile TiOTiO22
High lithium electroactivity of nano-sized rutile TiO2 (Y. Hu et al., Adv. Mater. 18, 1421 (2006))
– Rutile TiO2 (known to be inactive) becomes active by using nano-sized particles!
– Nano-sized rutile TiO2 exhibits excellent rate performance.
20 µm 0.5-5 µm
500 nm 10-40 nm
9/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
NanoNano--structured Materials (Unexpected Reaction)structured Materials (Unexpected Reaction)
Unexpected reaction: Reverse reaction
– Nano-sized Co ; enhances the
electrochemical activity towards the
decomposition of Li2O.
Lithiated De-lithiatedAs-prepared
nano-sized
(P. Poizot et al., Nature 407, 496 (2000))
10/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
NanoNano--structured Materialsstructured Materials
Nano-domain structure of LixMn2-yO4 derived from layered LixMn1-yO2
– Spinel LiMn2O4
Cubic to tetragonal phase transition leads to capacity fading
– Layered LiMnO2
– Nanodomain structure formed during the layered-to-spinel transformation enables the system to accommodate the strain induced by cubic to tetragonal transition
Regular LixMn2-yO4spinel
LixMn2-yO4 spinelobtained on cycling layered LixMn1-yO2
A. Arico et al., Nat.. Mater. 4, 366 (2005).
11/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
Introduction: Binary Introduction: Binary IntermetallicsIntermetallics
Intermetallic compounds; Active/inactive A-B type – One approach to enhance the poor cyclability of alloying anode materials
(Sn, Si, Ga)– Inactive B; buffering role against volume change of active A.
Reaction mechanism of binary intermetallics
– Li + AyB ↔ LiAyB : Addition reaction
• Cu6Sn5, Cu2Sb, etc
– Li + AyB ↔ LiAy + B : Conversion reaction
• SnSb, CoSb, InSb, Sn2Fe, Mg2Si, etc• Bond cleavage between A-B • Inactive B is extracted and active A is lithiated
12/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
OutlineOutline
Thin film CuGa2 electrode; active/inactive AB-type intermetallics
Li+ uptake mechanism
Favorable roles of nano-domain structure
CuGa2 + 4Li+ + 4e↔ 2Li2Ga + Cu
13/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
ExperimentalExperimental
Electrode preparation– Ga electrode
• Spreading liquid Ga on Cu foil
- CuGa2 electrode
• Spreading liquid Ga on Cu foil and annealing at 120oC for 1 day
– Thin film electrodes ( > a few micron thick).
Cell tests at 25, 120oC– Electrolyte: LiBOB/EC+DEC or LiBeti/PC
In-situ XRD at 120oC
14/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
LiLi--uptake Mechanism; CuGauptake Mechanism; CuGa22
Similar lithiation profile but larger polarization for CuGa2 electrode
– CuGa2 + 4Li+ + 4e↔ 2Li2Ga + Cu : Conversion reaction (Cu extraction)
– Larger polarization for bond cleavage; Cu-Ga
15/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
InIn--situ XRD on situ XRD on GaGa electrode at 120electrode at 120ooCC
Ga + 2Li+ + 2e↔ Li2Ga
16/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
InIn--situ XRD on CuGasitu XRD on CuGa22 electrode at 120electrode at 120ooCC
CuGa2 + 4Li+ + 4e↔ 2Li2Ga + Cu
17/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
Reaction Mechanism in Reaction Mechanism in GaGa and CuGaand CuGa22 at 120at 120ooCC
Similar lithiation mechanism
Noticeable difference in de-lithiation mechanism
Any interaction between Li2Ga and metallic Cu ?
CuGa2 + 4Li+ + 4e↔ 2Li2Ga + Cu
Ga + 2Li+ + 2e↔ Li2Ga
18/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
HRHR--TEM Image; TEM Image; NanoNano--domain of domain of LiLixxGaGa and Cuand Cu
Lithiated to LiGa with 100 mA gGa-1 at 55oC
EDS Results Cu Kα Ga Kα
Nano-domains of LixGa and extracted Cu are formed after Li uptake
Large contact area between two domains; any favorable behaviors ?
Schematic diagram representing the nano-structured domain
19/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
Cycle Performance of Cycle Performance of GaGa and CuGaand CuGa2 2 electrodeelectrode
Cycle number0 5 10 15 20 25 30
Spe
cific
cap
acity
/ mA
h g
Ga-1
0
200
400
600
8000.1~2V ,Ga, discharge0.1~2V, Ga, charge0~2V, Ga, discharge0~2V, Ga, charge0~2V, CuGa2, discharge0~2V, CuGa2, charge
CuGa2 electrode:
- Negligible 1st irreversible capacity !
- Excellent cyclablity !
20/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
High Discharge (DeHigh Discharge (De--lithiationlithiation) Rate; CuGa) Rate; CuGa22
A very high discharge rate !
A good candidate as the negative electrode for high-power LIB
21/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
High DeHigh De--lithiationlithiation Rate: partial bonding Rate: partial bonding
Analogous to SN2 reaction in organic chemistry
– Partial bond between Ga in LixGa and extracted Cu weakens Li-Ga bond.
Thereby, delithiation rate is dramatically increased.
Cu Ga Li
Cu + 2Li2Ga ↔ CuGa2 + 4Li+ + 4e
22/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
Evidences for Partial BondingEvidences for Partial Bonding
Raman shift / cm-1
150 200 250 300
Inte
nsity
/ A
.U.
LiGa (CuGa2)LiGa (Ga)
2θ/ degree
25 30 35 40 45 50
Inte
nsity
/ A.U
.
LiGa (CuGa2)LiGa (Ga)
(111)(220)
(311)
Be
Raman shift to lower frequency; stretching of Li-Ga bond
Cu-Ga-LiWeaker Li-Ga bond strength due to partial bonding between Cu-Ga.
Raman spectra XRD patterns
(220) peak shift in XRD pattern; Distortion of LiGa structure; may be induced by the partial bonding.
23/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
ConclusionConclusion
1) CuGa2 electrode; lithiated by conversion reaction : Nano-structured LixGa and Cu domains are formed: Slower lithiation than pure Ga electrode
2) Large contact area between two domains; Partial bonding between Cu-Ga → weakens the Li-Ga bond → enhances the de-lithiation rate
Similar results with Cu3Si, Cu3Sn
Electrochemically driven nano-structured materials: interesting for fundamental research and practical application
24/244th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007
Performance requirements for applicationsPerformance requirements for applications