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www.tyndall.ie1
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.
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