Nano structured electrodes for lithium ion batteries

1
Nano structured electrodes for lithium ion
batteries

• Vivek Krishnan
• Materials Research and Education Center
• Auburn University, AL

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Presentation Outline

• Introduction to Batteries History and
  Principles
• Solid State Batteries
• Lithium Battery Technology
• Nano-technology in lithium batteries
• Conclusions and future trends

3
Introduction to BatteriesHistory

• Voltaic Cell- In the last years of the 18th
  century Alessandro Volta (1745-1827) built the
  first electrochemical cell to generate power.
• Leclanche Cell- The Leclanche Cell was described
  by Georges Leclanche (1839-1882) in 1867.

http//www2.kenyon.edu/depts/physics/EarlyApparatu
s/Electricity/ Electrochemical_Cell/Electrochemica
l_Cell.html
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General Principle and Classification

• Principle
• Electrons released at the negative electrode.
• These flow through the load and are accepted by
  the positive electrode.
• A voltage is measured due to the potential
  difference between the two electrodes of the
  cell.

http//spacepwr.jpl.nasa.gov/battery.htmLithium
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Solid State Batteries

• Classification
• Primary and Secondary Batteries.
• Solid State Batteries.
• Properties of solid state devices
• natural seal.
• resistance to shock and vibrations.
• broad stability of electrolyte.
• high selectivity of charge carriers.
• temperature and pressure resistance.
• simpler designs
• POTENTIAL TO BE MINIATURIZED.

http//www.itnes.com/pages/batteries.html
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Advantages of Thin Film Processing

• Devices manufactured using the same techniques as
  the microelectronics industry. Use of silicon.
• Deposition in a vacuum chamber avoids moisture
  problems.
• Very good adhesion between layers and large
  contact areas.
• electrode/electrolyte resistance.
• battery encapsulation is simple - insulating
  layer.
• microbatteries can be constructed in almost any
  two dimensional shape.

Lithium batteries New Materials, Developments
and Perspectives, G. Pistoia, Elsevier 1994
7
Lithium Batteries

• Introduced by Sony in 1991.
• Have been widely used to provide power for
  consumer products.
• Offer low safety risks, greater flexibility in
  battery configuration and energy densities
  exceeding 120 Wh/kg.
• Excellent pressure tolerance and neutral
  buoyancy.
• Make use of intercalant solids as electrodes.
• Host atoms or molecules within its lattice with
  very few structural changes.

Lithium batteries New Materials, Developments
and Perspectives, G. Pistoia, Elsevier 1994
8
Intercalation
http//spacepwr.jpl.nasa.gov/lithumbgr.htm
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Working Principles

• Electrochemical chain characterized by continued
  transport of lithium ions from a higher potential
  ( anode) to a lower potential (cathode).
• Electrical energy liberated while discharging is
  equal to the change in lithium free energy due to
  the transfer.
• Cell reactions in a Li/ Lix(cathode) system
• dx Li dx Li dx e-
  (Li anode)
• dx Li dx e- Lix(host) Lix dx
  (host cathode)
• Overall reaction
• dx Li Lix(host) Lix dx (host)

Lithium batteries New Materials, Developments
and Perspectives, G. Pistoia, Elsevier 1994
10
Lithium MicroBattery

• Miniaturized power supply needed for
  micro-mechanical devices.
• Lithium microbatteries built using thin film
  technologies.

1 Lithium metal complex
2 Electrolyte
3 Intercalating electrode
Substrate
Hundreds of microcells on a four-inch diameter
silicon wafer.
Typical lithium microgenerator
http//www.afrlhorizons.com/Briefs/Dec01/PR0104.ht
ml
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Intercalation Electrodes

• Lithiated metal oxides-
• VOx, LiCoO2, LixMn2O4, LixNiO2, LixSn
• Thin film deposition- CVD, RF Sputtering, Pulsed
  Laser Deposition.

Lithium batteries New Materials, Developments
and Perspectives, G. Pistoia, Elsevier 1994
12
Advantages of Lithium Ion Batteries

• Store 2-3 times more energy per unit weight and
  volume than lead-acid or Ni-Cd batteries.
• Long cycle lives (gt1000 cycles)
• Low self-discharge and long shelf life.
• Widespread use in electronic devices.
• Potential applications promise in the areas of
  communications and remote sensing devices too!!!

Sides, C.R. Li, N. Patrissi, C.J. Scrosati,
B. Martin, C.R. Nanoscale Materials for Li-ion
Batteries, MRS Bulletin, 2002, 27, 604-607.
13
Limitations

• Critical area for improvement rate capability
• Rate capability- ability to deliver large
  capacity when discharged at high C rates. ( rate
  of C/1 corresponds to the current required to
  completely discharge an electrode in 1 hour)
• Future applications require high-discharge-rate
  periods.

Sides, C.R. Li, N. Patrissi, C.J. Scrosati,
B. Martin, C.R. Nanoscale Materials for Li-ion
Batteries, MRS Bulletin, 2002, 27, 604-607.
14
Motivation for use of Nano technology

• Limitations in rate capabilities slow diffusion
  process
• Shorter diffusion distance for Li ion
• Increased surface area
• Promise better rate capabilities.
• Smaller effective current density during
  discharge.
• Better cyclability due to smaller particles.
• Need for energy sources to power nano devices

Martin, C.R. Li, N. Scrosati, B.
Nanomaterial-Based Li-Ion Battery Electrodes,
J. Power Sources, 2001, 97-98, 240-243.
15
Fabrication Technique

• Template method-
• General method to synthesize nanomaterials.
• Synthesis entails deposition of material of
  interest/ precursor, within cylindrical and
  monodisperse pores of a microporous template
  membrane.
• Cylindrical nanostructures with monodisperse
  diameters and lengths obtained.
• May be solid nanofibers or hollow nanotubes
  depending on membrane used.

C.R.Martin, Science, 266, 1961 (1994)
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Electrode Fabrication

• 50 nm pores filled with triisopropoxyvanadium
  oxide.
• Gel formation after 12 hrs.
• Template removed with oxygen plasma(100mTorr O2,
  2hrs)
• Processed at 400C for 10hrs in 150psi O2

Patrissi, C.J. Martin, C.R. J. Electrochem. Soc.
1999, 146, 3176-3180.      
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SEM micrographs
SEM images of the componenents of a
nanostructured electrode (A) low-magnification
image of the V2O5 nanofibrils, (B)
high-magnification image of the nanofibrils, and
(C) the underlying V2O5 surface layer.
Patrissi, C.J. Martin, C.R. J. Electrochem.
Soc., 2001, 148, A1247-A1253.
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Sn-based anodes

• Can store twice as much lithium compared to
  carbon anodes.
• 4Li 4e- SnO2 2Li2O Sn
• xLi xe - Sn LixSn
• Can store upto 4.4 Li atoms per atom of Sn.
• Volume changes during alloying/dealloying cause
  internal damage to electrode lower cyclability.
• Nanostructure based designs can better
  accommodate for volume changes

Li, Naichao Martin, C.R. J. Electrochem. Soc.
2001, 148, A164-A170.
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Sn- based anodes

• Fabricated using template synthesis with a SnCl2
  based precursor.
• Nanofibers heated at 440C to convert them to
  crystalline SnO2.
• Fiber dia. 110nm
• Thin film electrode fabricated without template
  membrane.(550nm)

Li, Naichao Martin, C.R. J. Electrochem. Soc.
2001, 148, A164-A170.
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Template based electrodes

• Observed improved rate capabilities
• Loss of volumetric energy density due to
  extremely low porosity of polycarbonate
  membranes(1.2)
• Low number density of nanofibers protruding from
  current collector surface.
• Problem addressed by using alumina membranes
  (highly porous)
• Dissolution of membrane in aqueous acid or base
  but this also dissolves the electrode materials.
• Chemical etching used to increase porosity of
  polycarbonate membranes.

Sides, C.R. Li, N. Patrissi, C.J. Scrosati,
B. Martin, C.R. MRS Bulletin, 2002, 27, 604-607.
21
Conclusions and Future Trends

• Nano materials are useful to fabricate
  lithium-ion batteries with improved performances.
• Current research is on to develop improved
  anodes, cathodes and electrolytes.
• Work is needed to integrate these components and
  build devices.
• Prototype device predicted within 3 years.
• (An AAAAAAAAA battery???!!!)

http//www.napa.ufl.edu/2002news/nanobattery.htm
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Questions

• 1. Why is intercalation important in secondary
  lithium batteries?
• 2. What is the template method for fabricating
  nanomaterials?

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Glossary

• Cycle Life How many charge/discharge cycles the
  battery can endure before it loses its ability to
  hold a useful charge.
• Current density Electric flux per unit area. It
  is generally defined in terms of the geometric or
  projected electrode area and is measured in Am-2
  or ma cm-2 cut-off voltage Final voltage of a
  discharge or charge operation.
• Capacity, rated The value of the output
  capability of a battery, expressed in Ah, at a
  given discharge rate before the voltage falls
  below a given cut-off value
• Depth of Discharge The amount of energy that has
  been removed from a battery (or battery pack).
• Electrode A conductor by which electrical current
  enters or leaves a non-metallic medium, such as
  the electrolyte in a battery (as well as vacuum
  tubes and lots of other devices).
• Electrolyte An elctrically conductive medium, in
  which current flow is due to the movement of
  ions. In a lead-acid battery, the electrolyte is
  a solution of sulfuric acid. In other batteries,
  the electrolyte may be very different.
• Energy Density The amount of energy that can be
  contained in a specific quantity of the fuel
  source. Typically quoted in watt-hours per pound,
  wh/lb, or watt-hours per kilogram, wh/kg.

http//www.rtpnet.org/teaa/battery.html
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Glossary contd.

• Inhibitor - A substance added to the electrolyte
  which prevents an electrochemical process,
  generally by modifying the surface state of an
  electrode.
• Load - Electrical power being consumed at any
  given moment.
• Open circuit voltage (OCV) The voltage of a cell
  or battery under no-load condition, measured with
  a high impedance voltmeter or potentiometer.
• Overpotential, overvoltage Difference between
  the actual electrode voltage when a current is
  passing and the equilibrium (zero current)
  potential.
• Polarization Deviation from equilibrium
  conditions in an electrode or galvanic cell
  caused by the passage of current. It is related
  to the irreversible phenomena at the electrodes
  (electrode polarization) or in the electrolytic
  phase (concentration polarization).
• Power density The power output of a battery per
  unit volume, usually expressed in W dm-3 and
  quoted at 80 per cent depth of discharge.
• Shelf-life Period of time a cell can be kept
  idle after manufacture without significant
  deterioration.
• Working electrode the test or specimen electrode
  in an electrochemical cell

http//voltaicpower.com/Principles/Glossary.htm
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Feedback sheet

• Information given by the presenter
• Date 06/23/03
•     Presenters name Vivek Krishnan
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