SEM, AFM, and AC Impedance Studies of Lithium Battery Cathode Materials

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SEM, AFM, and AC Impedance Studies of Lithium
Battery Cathode Materials

• Anjuli Appapillai
• Research Update
• February 9, 2005

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Lithium Cobalt Oxide Cathode

• LixCoO2
• Theoretical capacity 274 mAh/g
• Cutoff voltage 4.2V
• x 0.5

LiCoO2
Linden et al. Handbook of Batteries. 3rd ed. 2002.
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Barriers to Accessing Higher Capacity

• Very poor capacity retention
• Mechanical stress due to repeated expansion and
  contraction of lattice structure
• Dissolution of cobalt into electrolyte

• Thermal instability at high voltages
• Decomposition of electrolyte, causing heat
  generation
• Side reactions at electrolyte-cathode interface

Biensan et al. J. Power Sources. 1999, 81-82,
906-912. Maleki et al. J.
Electrochem. Soc. 1999, 146, 3224-3229.
Kim et al. J. Power Sources. 2004, 126, 190-192.
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AlPO4 coating on LiCoO2

• Decreases maximum temperature on charging to 12V
• Improves capacity retention
• Various studies disagree on reasons for these
  positive effects

Kim et al. J. Power Sources. 2004, 126,
190-192. Chen et al. Electrochimica Acta. 2004,
49(7), 1079-1090. Liu et al. Solid State Ionics.
2004, 132, 195-200.
Cho et al. Chem Mat. 2003. 15, 3190-3193. Cho et
al. Ang. Chem. Int. Ed. 2001, 40(8)
3367-3369. Fey et al. J. Power Sources. 2004,
132, 172-180.
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AFM and AC Impedance Studies

• Purpose
• Examine the microstructure and topography of bare
  and coated LiCoO2 particles while
  electrochemically cycling
• Investigate transport properties of bulk and
  individual particles

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Bare vs. Coated LiCoO2
1 mm
1 mm
Bare
AlPO4-Coated
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Particles Pressed into Gold Foil
5000 psi
particles
gold
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SEM of Pressed Coated Particles
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AFM of bare LiCoO2
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AFM of AlPO4-coated LiCoO2
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Bare LiCoO2 in Gold Foil Coin Cell
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AlPO4-Coated LiCoO2 in Gold Foil Coin Cell
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Future Work

• Impedance spectroscopy on coin cells with gold to
  get transport properties bulk particles
• Impedance spectroscopy with microprobe to test
  individual particles
• In-situ AFM of bare and coated particles while
  charging to see changes in surface morphology
• Further SEM imaging of fractured particles to
  look at coating cross-section