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Search for High Energy Density Cathode MaterialsEvaluation of Li2MSiO4 (M = Mn, Fe, Co) System

ILias Belharouak (PI)R. Amine, A. Abouimrane, D. Dambournet, K. Amine.Argonne National Laboratory

DOE Merit Review9 June, 2010

This presentation does not contain any proprietary, confidential, or otherwise restricted information

Project ID # ES018

Argonne National Laboratory, Chemical Siences and Engineering Division

2

Overview

Start – October 2008 Finish – September 2014 15% complete

Energy density of available Li-ion battery technologies

– Weight, volume, and affordability Abuse tolerance

– Energy storage systems that must be intrinsically tolerant of abusive conditions

Timeline

Budget

Barriers

Partners Collaboration:

– Center for Nanoscale Materials (ANL)– Electron Microscopy Center (ANL)– Advanced Photon Source (ANL)

Support: R. Amine, D. Dambournet,A. Abouimrane, K. Amine.

Project lead: ILias Belharouak

Total project funding in FY09 + FY10: $600K

Funding received in FY09: $300K Funding in FY10: $300K


3

General Objectives of this StudySearch for High Energy Density Cathode Materials

0

25

50

75

100

125

150

175

200

225

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300

Negative Electrode Capacity, mAh/g

Cel

l Spe

cific

Ene

rgy

( Wh/

kg)

Ele

ctro

de T

hick

ness

(mic

rons

)

1

1.5

2

2.5

3

3.5

Cel

l Cap

acity

(Ah)

Cell Specific EnergyNegative Electrode ThicknessCell Capacity

When an NCA cathode electrode (100 µm-thick) combined with higher capacity anodes,only about third of energy density increase is expected in 18650 cell. There are technological hurdles (electrode design) to what higher-capacity anode canadd to the value of energy density in a Li-ion cell based on available cathode materials. Search for high-energy density (gravimetric and volumetric) cathode materials is equivalent to the search for high-capacity (per Kg), high-potential, high packing bulk density cathode materials.


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Develop new preparation methods to synthesize high purity Li2MSiO4

(M = Mn, Fe, Co) materials.

Understand the structure of these materials at the local and bulklevels.

Check whether these materials pertain to the concept of 2-lithium ionsextraction and insertion cathode materials.

Develop ways to overcome the barrier of the insulating properties ofthese materials.

Achieve an overall evaluation of these materials from structural andelectrochemical standpoints with regard to their possible applicabilityin high-energy density Li-ion batteries.

Term Objectives of this StudyEvaluation of Li2MSiO4 (M = Mn, Fe, Co) System


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Materials preparation and characterization Introduction of new preparation methods including solid state, Pechini, and sol-gelreactions to synthesize pure Li2MnSiO4 phase. (Completed) Initiation of physical and structural characterizations in order to elucidate the impact ofthe morphological and atomic arrangement on the electrochemical properties ofLi2MnSiO4. (Completed) Understand the capacity fade observed for Li2MnSiO4. (Ongoing) Investigation of Li2(Mn1-xFex)SiO4 stabilized phases. (Ongoing)

Electrochemical performances Positive electrodes made of the as-prepared Li2MnSiO4 material have been assembledwith lithium negative anode and conventional electrolytes to check the capacity of thematerial. (Completed)

Materials optimization To achieve better electrochemical performances, ways such as carbon coating, carbonnanotube integration, and ball milling have been adopted to improve the electronicconductivity of Li2MnSiO4. (Completed)

Milestones for FY09 and FY10

Check the applicability of Li2MnSiO4 in Li-ion cells. (Completed)


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General Approach Search for high-capacity cathode (per Kg) requires:

- Materials that can vehicle more than one lithium per their unit formulas.

- Materials whose active cations has a lower valence.

- Reduction of matter in the materials (simply Li2O).

Enabling of high-potential cathodes above 4V but not exceeding 5V.

- Advanced environmentally friendly and economically sound synthetic methods,

- LiNi0.5Mn1.5O4 (~4.7V,148mAh/g), Li(Mn-or-Co)PO4 (~4.1V-or-4.8V, 170mAh/g), ANL-composite materials (~4.0V, 250mAh/g).

Optimize packing density of the materials for practical use (morphology and

particle size).


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Term Approach

Li2MnSiO4 can be iso-structural to certain forms of Li3PO4.

The extraction/insertion of 2-Li ions can lead to the delivery of 333mAh/g capacity according to the following scheme:

Li2Mn2+SiO4 Mn4+SiO4 + 2Li+ + 2ē

Strong covalent Si-O bonds can be good for safety.

Li+ ions

Structure Model of Li3PO4

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.000.00

0.25

0.50

0.75

1.00

SiO2

MnO

Li2O0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.000.00

0.25

0.50

0.75

1.00

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.000.00

0.25

0.50

0.75

1.00

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.000.00

0.25

0.50

0.75

1.00

Li2MnSiO4

MnSi2 O

5

Mn2 SiO

4MnSiO3

Li 8SiO 6

Li 6Si 2

O 7

Li 4SiO 4

Li 2Si 3

O 7

Li 2SiO 5

Li 2SiO 3

Phase Diagram and Structure


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Materials Synthesis

Sol/gel process has been found to yield the purest phases Batch 1: gelation occurred in acetic acid medium containing lithium, manganese, and siliconacetates followed by subsequent heat treatments up to 700 oC.

Batch 2: during gelation, high surface area carbon was added to be part a compositematerial.

Batch 3: during gelation, cellulose, ethylene glycol, etc. were incorporated to yield a carbon coated material.

10 20 30 40 50 60 70

*

*

*

Li2MnSiO4

3rd Batch

2nd Batch

2 θ, ο

1st Batch

* MnO

MnO impurity level increases with C


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0 50 100 150 200 250 3000

20

40

60

80

χ-1 m, m

ol/e

mu

T, K

χ-1 = 6.44 + 0.22 T

2400 2800 3200 3600 4000 4400

dB/d

P, a

.u.B, G

Validation of the Structural Model of Li2MnSiO4

EPR Analysis Magnetic Measurements

µeff(cal) = 5.92 µB

TN = 12 K

Curie-Weiss Law

g-factor (exp) = 2.003

g-factor(cal) = 2.0

X-ray diffraction confirmed the structural model of Li3PO4 for Li2MnSiO4.

Magnetic measurements confirmed the valence state of manganese that is Mn2+.

EPR measurements confirmed the occurrence of magnetic interactions at low

temperature.

15 20 25 30 35 40 45 50 55 60

Simulated Li2MnSiO4

2 θ, ο

800oC

700oC

600oC

XRD Analysis


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Agglomeration of Li2MnSiO4

0 2 4 6 8 10 12

2

3

4

5

Vol

tage

, V

Capacity, mAh/g

Li2MnSiO4 Pristine is Barely Active

As-prepared Li2MnSiO4 is “almost” electrochemically inactive because of its large

aggregates and low electronic conductivity.

Therefore, particle size reduction and coating have been applied as ways to

activate Li2MnSiO4.

Capacity of Li2MnSiO4

Carbon added duringelectrode preparation


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Particles Size Reduction: Silica Template200 nm spherical SiO2

Develop a simple synthesis method to prepare spherical nano-silica.

Use the silica template to prepare nano-Li2MnSiO4 material.

On the addition of manganese and lithium sources in solid state reactions, re-agglomeration has been observed.


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Particles Size Reduction: Ball MillingLi2MnSiO4, As-prepared Li2MnSiO4, after ball milling

0 50 100 150 200

2

3

4

5

Discharge

Vol

tage

, V

Capacity, mAh/g

Charge

High-energy ball milling was found to be an effective way to breakdown the largeagglomerates of Li2MnSiO4 to smaller particles.

The method has been found to be none destructive because the structure ofLi2MnSiO4 was preserved after the completion of ball milling.

Significant improvement of the initial capacity of the material has been observed.

Voltage profile


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Carbon Integration: Implantation of CNTsCarbon nanotubes CNTs were injected during the gel maturation process

CNTs were well dispersed within the agglomerates of Li2MnSiO4.

CNTs became parts of the aggregates.

CNTs formed a conductive network in Li2MnSiO4/CNT.


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Carbon Integration: Carbon coatingLi2MnSiO4, As-prepared Li2MnSiO4, after carbon coating

0 50 100 150 200

2

3

4

5

Discharge

Charge

Vol

tage

, V

Capacity, mAh/g

Voltage profile

Cellulose as a carbon source was added during the preparation of the material.

Significant improvement of capacity has been observed for carbon-coatedLi2MnSiO4.


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0 50 100 150 2000

1

2

3

4

5

Discharge

Charge

Volta

ge, V

Capacity, mAh/g

Li2MnSiO4 Capacity Fade Issue

0 2 4 6 8 10 12 14 160

50

100

150

200 ChargeDischarge

Capa

city,

mAh

/g

Cycle number

Typical charge/discharge of Li2MnSiO4 Typical cycling of Li2MnSiO4

X-ray analysis

Evidence of Li2MnSiO4 amorphization. Amorphoziation is responsible for the quick capacity fade. Questions:

- How can an amorphous phase cycle lithium?- Is it possible to impeach the amorphization?

Answers:- PDF analysis: very powerful tool to look at the local structure of amorphous materials. - Crystal chemistry and Materials approach.


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2 4 6 8 10 12 14 16 18 20-3

-2

-1

0

1

2

3

G(r)

r (interatomic distances, Å)

Laminate Charge 4.15 V Charge 4.5V Charge 4.6V Charge 4.8V Discharge 3.6V Discharge 2.6V Discharge 1.5V

Pair Distribution Analysis Upon Lithium Removal and Uptake

1.5 2.0 2.5 3.0 3.5 4.0-3

-2

-1

0

1

2

3

Li-O

Li-Si

Mn-O

Li-LiC-C

G(r)

r (interatomic distances, Å)

Laminate Charge 4.8V Discharge 1.5V

Si-O

Local range order

Long-range order

Radial distribution function Radial pair distribution function G(r) gives direct information on interatomic distances.

G(r) is independent of orientation, it thus provides valuable structural information on glasses and polymers.

The radial PDF can be calculated directly from x-ray powder diffraction through the use of Fourier Transform.

The structure of crystalline Li2MnSiO4 is kept when the latter is fully charged or discharged.

Evidence of lithium removal and uptake through the Mn-O shortening and enlargement.

Full analysis and structural fitting is underway.


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Structural Stabilization Through Fe2+ Ions Incorporation

10 15 20 25 30 35 40 45 50 55 60

Structure model

Li2FeSiO4

Li2(Mn0.25Fe0.75)SiO4

Li2(Mn0.5Fe0.5)SiO4

Li2(Mn0.75Fe0.25)SiO4

2 θ

Li2MnSiO4

0 25 50 75 100 125 150 175 2000

1

2

3

4

5

Vo

ltage

, V

Capacity, mAh/g

0 50 100 150 2000

1

2

3

4

5

Volta

ge, V

Capacity, mAh/g

0 50 100 150 2000

1

2

3

4

5

Volta

ge, V

Capacity, mAh/g

Investigation of Li2(Mn1-xFex)SiO4 (0≤x≤1)

Li2MnSiO4

Li2FeSiO4

Li2Mn0.5Fe0.5SiO4


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Collaborations Center for Nano-scale Materials (ANL)

Magnetic and EPR measurements

Electron Microscopy Center (ANL)Scanning Electron Microscopy SEM of Li2MnSiO4 cathode

Advanced Photon Source (ANL)Pair Distribution Function (PDF) analysis of Li2MnSiO4 cathode

Brookhaven National Laboratory (Future)

X-ray absorption spectroscopy (XANES, EXAFS) and x-ray diffraction

California Institute of Technology Institute (future)Mossbauer spectroscopy on Li2Mn1-xFexSiO4


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Future Work Achieve a full understanding on the mechanistic reasons behind the

amorphization of Li2MnSiO4 upon lithium removal. Stabilization of Li2MnSiO4 through iron incorporation has shown promise.

A full structural and electrochemical investigation of Li2Mn1-xFexSiO4 isongoing.

Achieve an overall evaluation of these materials from the structural andelectrochemical with regard to their possible applicability in Li-ionsbatteries.

Continue the effort of achieving full capacity of these materials using:- Carbon coating and integration using carbonaceous additives and gas phase reaction.- Particle size reduction through templating in silica matrix.

- High-energy ball milling. . The information learned from the study of Li2MnSiO4 will be used to

investigate the compositions with iron as the electrochemically active ion. Li2Mn1-xFexSiO4 Materials will be sent to BNL and Caltech for X-ray

absorption spectroscopy and Mossbuaer studies, respectively. Explore new multi-electron cathodes.


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Summary Amorphization is responsible for the capacity fade of Li2MnSiO4 upon

lithium removal. Pair distribution function analysis confirmed that this is nota structural disintegration of Li2MnSiO4. It will be quite challenging toimpeach this phenomenon from happening.

We successfully integrated carbon nanotube as conductive matrix duringthe synthesis of Li2MnSiO4. The materials are on schedule forelectrochemical tests. The method can extended to other materials aswell.

Stabilization of Li2MnSiO4 through iron incorporation has led to structurestabilization. Li2Mn1-xFexSiO4 materials have shown promise in terms ofcapacity retention.

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