nano-structured binary intermetallics as negative ... · pdf file26.04.2007 ·...

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

[email protected]


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


Charge/Discharge Mechanism of LIBCharge/Discharge Mechanism of LIB

http://www.samsungsdi.com/

Graphite powder(MCMB)10-20 µm

LiCoO2 powder

10-20 µm


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


LIB for Note Book PCLIB for Note Book PC

19951995

19941994

19961996

1998199820002000

20012001

Typ.1250mAhTyp.Typ.1250mAh1250mAh

Typ.1370mAhTyp.1370mAh




20022002

4.2V Charging System4.2V Charging System

4.1V Charging System4.1V Charging System

Typ.2000mAhTyp.2000mAhTyp.2100mAhTyp.2100mAh


20032003

Typ.2400mAhTyp.Typ.2400mAh2400mAhCylindrical 18650 LIB:

Capacity doubles

for 10 years

(Improvement in design)

To have 3000 mAh cells:

New electrode materials


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


NanoNano--sized Electrode Materials (LiFePOsized Electrode Materials (LiFePO44))

High power cell using nano phosphate (A 123Systems)

– LiFePO4: poor electronic/ionic conductor


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


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))


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).


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


OutlineOutline

Thin film CuGa2 electrode; active/inactive AB-type intermetallics

Li+ uptake mechanism

Favorable roles of nano-domain structure

CuGa2 + 4Li+ + 4e↔ 2Li2Ga + Cu


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


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


InIn--situ XRD on situ XRD on GaGa electrode at 120electrode at 120ooCC

Ga + 2Li+ + 2e↔ Li2Ga


InIn--situ XRD on CuGasitu XRD on CuGa22 electrode at 120electrode at 120ooCC



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 ?


Ga + 2Li+ + 2e↔ Li2Ga


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


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 !


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


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


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.


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


Performance requirements for applicationsPerformance requirements for applications

nano-structured binary intermetallics as negative ... · pdf file26.04.2007 ·...

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