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Materials utilised in lithium batteries.

James RohanElectrochemical Materials & Energy

Tyndall National InstituteUCC

Inaugural IEEE VTS UKRI chapter meeting

ITRN 2011

30th August

1

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Why Lithium?

Li lightest Metal6.9g – 1 mole of electrons

Pb – 103.5g – 1 M

Volts

0

H+

/H2

-3 -2 -1 +1 +2

Li+

/Li Li+

/C Li+

/LiCoO2

Li+

/LiMn2O4

MnO2/Mn2O3

Li+

/LiMnxNiyCozO4

Li large Voltage gain

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Batteries for EV’s

Developments in battery materials processing can be scaled

Car makers have been signing agreements with electronics companies that have 15 years experience of Li ion technology to bring the batteries to the automotive market.

Nissan/Renault NEC

Mitsubishi GS Yuasa

Tesla Panasonic

FORD LG Chem

GM LG Chem

Toyota Matsushita (Panasonic)

BMW Samsung/Bosch

VW Sanyo

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Rate of discharge• C rate

– is the current used to fully discharge the battery in 1 hour

• 5 C rate

– is at five times that rate and therefore the capacity achievable when discharged in 12 mins

• At higher rates generally utilise less of the capacity

• Power vs. Energy

Increased Powerby

increased area

Increased Energy

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Lithium metal

• Thermodynamically unstable to aqueous systems

– Li + H2O LiOH + 1/2H2

• Also thermodynamically unstable in non-aqueous systems but passivates

• Must be handled in low humidity dry room

– Cost

– Most research performed in argon recirculating glovebox with O2 and H2O < 1 ppm

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Non-aqueous solvent systems

Polar solvents

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Li salts

• Polar solvents enable dissolution of Li salts with complex monovalent anions, e.g. LiCl low solubility– LiClO4

– LiBF4

– LiAsF6

– LiPF6

– LiCF3SO3

– LiN(CF3SO2)2

• Conductivities of these salts in organic solvents ~ 10-2 S cm-1

For higher temperature cells such as polymer based

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Polymer Li ion batteries

• Polyethylene oxide electrolytes

– Poor ionic conductivity at rt (10-8 S cm-1)

– But at 60 – 100 oC conduction in amorphous PEO orders of magnitude higher e.g. 2.5 x 10-4 S cm-1 at 90oC

– Higher T operation requires higher T compatible lithium salts

• LiCF3SO3

• LiN(CF3SO2)2

– Thin film versions

• 25 to 50 m

• Low current

– iR drop across electrolyte maintained low

• Possible to laminate

– Both electrodes and polymer electrolyte

– Various sizes

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Polymer gel electrolytes

• Using the typical carbonate electrolytes

• Add a plasticiser polymer ((20%)– Polyvinylidene fluoride (PVDF)

– Polyacrylonitrile (PAN)

– Polymeylmethacrylate (PMMA)

• Forms a gel– Like solid polymer electrolyte in terms of

mechanical stability

– But rt operation possible

– Conductivities similar to solvent only

• ~ 0.01 S cm-1

– Functions as separator and electrolyte

• This gel can also be incorporated into electrodes as binder

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Insertion Cathodes

• Electronically conducting framework

• Transition metal ions in mixed valence state

• Insertion of alkali metal ion reduces the framework– TiIVS2 + Li+ + e- LiTiIIIS2

• Extraction reoxidises the framework

Volts 0

H+/H2

-3 -2 -1 +1 +2

Li+/Li Li+/LiCoO2

Li+/LiMn2O4

MnO2/Mn2O3

If the reaction does not change the cathode structure over a useful compositional range it can be used as

an insertion electrode

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Cathodes

• LiFePO4– Inexpensive, abundant,

environmentally friendly, thermally stable

– Theoretical capacity 170 mAh/g– Li diffusion coeff. = 10-14 cm2 s-1

– Electronic conductivity = 10-11 S cm-1

• Carbon coated = 10-5 S cm-1

As more cathodes investigated found that transition metal oxides intercalate Li at higher potentials

More ionic character in M-O rather than M-S bonds

• LiCoO2

– Expensive, environmental concerns,

– Theoretical capacity 273 mAh/g• Practical capacity 140 mAh/g but

excellent cyclability in limited range

– Li diffusion coeff = 10-10 cm2 s-1

– Electronic conductivity = 10-3 S cm-1

• Cu = 5 x 105 S cm-1

• Graphite = 400 S cm-1

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Insertion anodes

• Carbon investigated

– Cheap, Abundant

– Li++ e- + 6C LiC6

• Capacity (mAh/g) = (96,485/3,600)/72 = 372 mAh/g

• 10X less capacity than Li metal (but no dendrites – safer)

• Sony cell 1991

Volts 0

H+/H2

-3 -2 -1 +1 +2

Li+/Li Li+/LiCoO2

Li+/LiMn2O4

MnO2/Mn2O3

As oxide cathodes introduced

Possibility to use other than Li metal anode and still have a useable cell voltage

Li+

/C

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Planar Li batteries

Li ion batteries

• Since the introduction to mass production in 1991

• Gradual increase in energy density achieved through improvements in electrode materials.

150

250

350

450

550

650

1991 1994 1997 2000 2003 2006 2008 2011Year

W h

/li

tre

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

mW

h /

cm

2 (

10

m t

hic

k)

Projected

2X in 14

years

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Main challenges

Energy Storage

Cycle life

CostSafety

Power output

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Solutions

• New materials

– Cathodes• Advanced oxides

• Air

• Sulphur

– Electrolytes• Polymer gel

combinations

• Solid state

• Ionic liquids

• Structuring

– 2D to 3D to 1D

– Core – shell• Nanoscale active

region

• New materials

– Anodes– Metals

– Alloys

– Semiconductors

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Solid state electrolytes

• LiCoO2 cathode• LiPON solid state electrolyte

– 10-6 S cm-1

• Li anode

J.B. Bates , N.J. Dudney, B. Neudecker,

A. Ueda and C.D. Evans, Solid State Ionics,

135, (2000) 33.

• Typical thin film Li microbatterycapacity – 100 Ah/cm2

• And volumetric energy density– 300 Wh/cm2

• But mW/cm2 and mAh/cm2

desirable• Footprint on Si is a big factor

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FP7 Nanofunction & Guardian Angel

• NANOFUNCTION : Beyond CMOS Nano-devices for Adding Functionalities to CMOS– ‘More than Moore’ devices (Analogue-RF-sensors-actuators-biochips-

energy harvesters, etc.) for adding functionalities to ICs and Beyond-CMOS nanostructures (nano-wires, nano-structured materials, etc.) which could be integrated on CMOS platforms.

– In particular, the interest of these nano-devices for the development of innovative applications with increased performance in the field of nano-sensing, energy harvesting & storage, nano-cooling and RF being investigated

• Micro/nanobattery materials and integration schemes

• Guardian Angels : – Zero Power devices harvest and store energy from their immediate

surroundings, including light, vibrations and temperature. By combining these new sources of energy with low-power electronics, to develop completely autonomous systems at an affordable price

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Charge and discharge rate

• Li diffuses in & out of the active material on cycling– Diffusion times limit the rate capability of the battery

• Time for diffusion in a spherical particle estimated using

– = r2 / D

• Diffusion length example using 10-14 cm2 s-1

– 1 nm = 0.3 s

– 10 nm = 32 s

– 1 m = 316,000 s (88 hrs)

• Small particles desirable and access to good electrical conductor – LiCoO2= 10-3 S cm-1 to 1 S cm-1

– Graphite = 400 S cm-1

• Cu = 5 x 105 S cm-1

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2D to 3D

• Advantage of smaller length scales is the distance the ions travel in the solid state electrodes

– where the lithium diffusion is orders of magnitude lower than that in non-aqueous solvent or polymer gel electrolytes.

- J.W. Long, B. Dunn, D.R. Rolison and H.S. White, Chem. Rev., 104, (2004) 4463.

Increased Powerby

increased area

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Micro to Nano

• If 5 m radius wires separated from each other by 10 m– 222,222 wires / cm2

• Active surface area per unit footprint– For 500 m long wires

– 35 cm2 surface area

• If the wires were 50 nm diameter separated by approx 50 nm – 10 m long

– to get 35 cm2/cm

Increased Powerby

increased area

- J.W. Long, B. Dunn, D.R. Rolison and H.S. White, Chem. Rev., 104, (2004) 4463.

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Capacity

• Need to increase the electrode length to increase storage capacity – without decreasing the benefits

of the 3D design

• To do this need good electronic conductivity in high aspect ratio structures

Increased Energy

- J.W. Long, B. Dunn, D.R. Rolison and H.S. White, Chem. Rev., 104, (2004) 4463.

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Conductor materials

• Micro/nanoelectronics– Since 1998 – Cu used as

electrical interconnect • lowest resistivity of practical

metals

• Resistivities– Cu = 1.7 cm

– Graphite = 2,500 cm

Sub 100 nmEven for Cu there are issues due to

sidewall and grain boundary scattering

ITRS Roadmap

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Alternative anodes

• Metals

– Sn (990 mAh/g)

• Semiconductors

– Si (4,200 mAh/g)

– Ge (1,600 mAh/g)

• Metal alloys

• CuSn (400 to 600 mAh/g depending on alloy)

• Metal oxides

• SnO (500 mAh/g)

• Cu2O (374 mAh/g)

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New high capacity anode issues

• Large volume changes on Li+

insertion

• Isotropic contraction on Li+ removal

• Leads to cracking– Loss of electrical

contact

– Loss of useful battery capacity

– Very poor cycling capability

J.P. Maranchi, A.F. Hepp, A.G. Evans, N.T. Nuhfer, P.N. Kumta, J. Electrochem.. Soc. 153 (2006) A1246.

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Si nanowires

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Nanotube growth

• + typical Cu bath additives PEG and Cl-

• No additives

T. Chowdhury, D.P. Casey and J.F. Rohan, Electrochemistry Communications, 11(2009) 1203-1206, Additive influence on Cu nanotube electrodeposition in anodisedaluminium oxide templates.

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If overoxidised

• If essentially all converted to Cu2O

• Very poor initial capacity & retention

Cu2O

Cu

Cu core

Cu2O shell

Cu2O + 2Li+ + 2e- 2Cu + Li2O

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After cycling

• Structural integrity retained

• Changed morphology

M. Hasan, T. Chowdhury and J.F. Rohan, Journal of theElectrochemical Society. 157, 6 (2010), Nanotubes of core/shellCu/Cu2O as anode materials for Li-ion rechargeable batteries.

Cu core

Cu2O shell

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New materials

M. Hasan, Ph.D Thesis, UCC, 2010

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Ionic liquid electrolytes

• New materials

– Electrolytes• Polymer gel

combinations

• Solid state

• Ionic liquids

The archetype of ionic liquids

1-ethyl-3-methylimidazolium (EMI) cation&

N,N- bis(trifluoromethane)sulphonamide (TFSI) anion

Armand et al, Nature Materials, 8 (2009) 621

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Li-Air

Cho. Adv. Energy Mater. 2011, 1, 34–50

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Acknowledgements

Enterprise Ireland for Funding Microbattery research

CFTD/05/IT/317

Nanofunction

Beyond CMOS Nanodevices for Adding Functionalities to CMOS (10/2010 –9/2013)

EU ICT Network of Excellence, Grant No.257375

Guardian Angels

Guardian Angels for a Smarter Life. (5/2011 – 4/2012)

EU Future and Emerging Technologies (FET) flagship pre-proposal phase, FP7-ICT-2011-FET-F, Grant No. 285406

Energy storage - Scoping study

Strategic research challenges and opportunities

International Energy Research Centre (IERC), EI & IDA, Grant No. SCR2-019

Funded through the European Commission

National Development Plan

European Regional Development Fund.