TMS 2014 - San Diego, California, USA.

2D Materials for Energy Storage

The Vivek B. Shenoy Research GroupDepartment of Materials Science and

EngineeringThe University of Pennsylvania

Philadelphia, PA 19104 United States

Dibakar Datta

Solid Mechanics GroupSchool of Engineering

Brown UniversityProvidence, RI 02912

United States1

Organization of the Talk1.Why 2D Materials for Energy Storage ?

2.Defective Graphene as a promising anode materials for

(a) Li-Ion Battery (b) Na- and Ca-Ion Batteries

3. MXene based Li-, Na-, K- and Ca-Ion battery

4. Conclusions

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Why 2D Materials for Energy Storage ? 0D : Nanosphere

3D : Nanocube

1D : Nanowire2D : Nanosheet

Why2D ?

Inspired by Nature !Leaves : The Natural 2D

Structure Billion Years of Evolution !

Liu et al. Adv. Mater. 2012, 24, 4097–4111

• More active sites than 0D and 1D and exhibit more effective surface than other structures

• Superior properties including small weight, large surface area and a sensible distribution

• Ideal frameworks for fast energy storage, which requires stability, high active surface area and open shortened path for adatom insertion/deinsertion 3

Why 2D Materials ? ( Geim et al. Nature 2013 )

Family of 2D Materials

Stable under ambient condition (room temperature in air)Probably stable under ambient conditionUnstable in air but may be stable in inert atmosphere3D compounds that have been successfully exfoliated down to monolayer, as is clear from AFM.Many other 2D crystals—including borides, carbides, nitrides and so on - have probably been or can be isolated

MXene : New 2D Material recently synthesized (Adv. Mater. 2011, 23, 4248–4253)

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Graphene for Li-Ion Batteries (LIBs) For Graphite, we have capacity C =

372 mAh/g

Li on Top on two sides of graphene plane

Li on Hexagon on two sides of graphene plane

Li adsorption is not possible in pristine graphene. WHAT ABOUT DEFECT?

What about pristine graphene ?Lithiation Potential

-ve Potential Adsorption not possible

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DFT using

VASP

Defects in Graphene : Two types of defects - Vacancy & Stone-Wales Defect

Single Vacancies (SV)

( Meyer et al. Nano Lett. 2008 ) ( Gass et al. Nature Nanotech. 2008 )

Formation energy of such a defect is high because of the presence of an under-coordinated carbon atom

( Brunetto et al. JPCC. 2012 ) Double Vacancies (DV)(Most common type of defect)

( Lahiri et al Nature Nanotech. 2008 )

Stone-Wales Defect (SW)

( Meyer et al. Nano Lett. 2008 )

Defective Graphene for Energy Storage ?

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Defects in Graphene : Divacancy Defect

Divacancy (DV)(b) 6.25%(c) 12.50% (d) 16.00 %(e) 18.75%(f) 25.00%

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Defects in Graphene : Stone-Wales Defect

Stone-Wales (SW) Defect(a) 25%(b) 50%(c) 75%(d) 100%

8Haeckelite Structure

Enhanced Li Adsorption in Graphene with Vacancy Defect

V = 0.7415 eV

V = 0.6350 eV V = 0.3658 eV

A

B

CA

B

C

Defect in graphene enhances adsorption and hence increases capacity.

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Recent experiment observed Li3C8 i.e. 800 mAh/g capacity (submitted)

Enhanced Li Adsorption in Graphene with SW Defect

R. Mukherjee, A. V. Thomas, D.Datta, J.Li, E. Singh, V.B.Shenoy, N. Koratker Defect Induced Storage of Lithium Metal within a Porous Graphene Network , Submitted

75% SW Defect

100% SW Defect

50% SW Defect

50% SW Defect

75% SW Defect

100% SW Defect

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Graphene Allotropes for LIBs Octagonal Graphene E0 /atom = -8.6189 eV

Cyclic Graphene E0 /atom = -8.0226 eV

Graphene Allotropes might be potential candidate for anode materials for LIBs

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Na- and Ca-Ion Battery : Motivation Trouble with LIBs • Among light metals, Li is a very rare (concentration 35ppm) (Teng. et al, Geochimica et Cosmochimica Acta 2004 ) • Li resources buried in the earth would not be sufficient to meet the ever increasing demands for LIBs. ( Palomares. et al, Energy & Environmental Science 2012 )

Suitable Alternatives : Na- and Ca-Ion Batteries

• The abundance and low cost of Na & Ca in the earth (e.g. for Na ,10,320 ppm in seawater and 28,300 ppm in the lithosphere) (Lin. et al, ACS Appl Mater Interfaces 2013 ; Seyfried et al, Geochimica et Cosmochimica Acta 1984)

• Low reduction potential (Na : -2.71V vs. Standard Hydrogen Electrode (SHE) , Ca : -2.87 V vs. SHE ) ( Zhu. et al, Nano Lett 2013 ; Sadoway et al. PRiME 2012)

NIB & CIB for Large Scale Storage ? Energy density of a NIB/CIB is generally lower than that of a LIB, high energy density becomes less critical for battery applications in large-scale storage.

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NIB & CIB for large-scale storage

NIB from Wood ( Zhu. et al, Nano Lett 2013 ) lucrative low-

cost, safe, and environmentally benign alternative to LIBs

Better Electrode Materials for NIBs and CIBs

The best starting point is the investigation of the structure and chemistries of electrode materials that function well for Li intercalation.

Moreover, nature stores energy with Na and Ca ions, not Li ions. (Xu. et al, Nature Nanotech 2008)

( Image : Report by Jun Liu, PNNL )

Can we develop high capacity NIBs & CIBs like LIBs ?

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Na- and Ca-Ion Battery : Defect Induced Enhanced Adsorption

V En

For both DV & SW, two sites are considered :

1. Top (on top of carbon in graphene)

2. Hex (on hexagonal site of graphene)

For each site, following three positions are considered :

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Charge Transfer Mechanism for Adsorption Bader Charge

Analysis

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• Charge-density difference between the valence charge density before and after the bonding

• Potential increases with the increase in charge transfer

• Any amount of charge transfer does not imply adsorption.

• There is a threshold of charge transfer beyond which adsorption is possible.

Na-Ion Battery : Defect Induced Enhanced Capacity

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Ca-Ion Battery : Defect Induced Enhanced Capacity

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Na- and Ca-Ion Battery : Defect Induced Enhanced Adsorption

D.Datta, J.Li, V.B.Shenoy Defective Graphene as a Promising Anode Materials for Na- and Ca-Ion Batteries , ACS Applied Materials and Interfaces , 10.1021/am404788e

Capacity C (mAh/g) can be computed from percentage of adsorption p as :

p : Percentage of adsorption of adatoms on graphene (in %)

v : Valence (Na= 1; Ca = 2)

F : Faraday Constant (26.801 Ah/Mole)

Ac : Atomic mass of Carbon (12.011)

Capacity for Maximum Possible DV defect (25%) :NIB : 1450 mAh/g ; CIB : 2900 mAh/g

& Stone-Wales defects (100%),NIB : 1071 mAh/g ; CIB : 2142 mAh/g

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MXene based Li-, Na-, K- and Ca-Ion battery Mn+1AXn M : early transition metal (such as: Ti, V, Cr, Nb, etc.), A : stands for a group A element (such as: Al, Si, Sn, In, etc.), X : stands for carbon and/or nitrogen, and n=1, 2, or 3. Binary MXene Ti3C2 : (Adv. Mater. 2011, 23, 4248–4253 ; Nano

Today, Volume 7, Issue 1)

• Ti3C2 MXene systems have been successfully synthesized recently.

• Exfoliated graphene, graphene oxide and TMDs have no capacity for Li, Na, K, and Ca.

• Theoretical and experimental works have predicted and confirmed the capacity for Li on Ti3C2 systems.

• Ti3C2 is only one member of the MXene family, indicating the potential applications for more than 60 other MXenes.

Ti-terminated Mxene-Ti3C2 Structure

Top view

Side view

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(Y. Gogotsi Group @ Drexel)

Adatom potential expressed in OCV vs adatom content

Atomic Radius(Å)

+1 Ionic Radius(Å)

Effective electrons

Effective Radius(Å)

Li

1.55 0.68 0.21 (+0.79)

0.86

Na

1.90 0.97 0.40 (+0.60)

1.34

K 2.35 1.33 0.47 (+0.53)

1.81

Ca

1.97 0.99 1.31 (+0.69)

1.63

dAA=1.55Å

D.Er, J.Li, M. Naguib, Y. Gogotsi, V.B.Shenoy Mxenes as High Capacity Electrode Materials for Metal (Li,Na,K,Ca)-ion batteries , Submitted

MXene can be a new promising anode material

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Conclusions

• Graphene with DV and SW defects can be a potential candidate as anode material for ion-batteries.

• Enhanced adsorption is observed on defective graphene because of increased charge transfer between the adatoms and defects

• MXene can be an alternate promising anode materials for energy storage

Our work will help to create better anode materials that can replace graphite for higher capacity and better cycling performance for ion-batteries.

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Thank You

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