LithiumIon Batteries

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Lithium-Ion Batteries

• Introduction what is a battery
• Applications
• Aims of research
• Advanced research on materials for cathodes
• Advanced research on materials for anodes and
  electrolytes

R. Armstrong and A. Robertson, Chemistry in
Britain, 2002, 38(2), 38
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Batteries
Definition devices that transform chemical
energy into electricity
Every battery has two terminals the positive
cathode () and the negative anode (-)
Functioning
Device switched on
chemical reaction started
electrons travel from (-) to ()
electrons produced
electrical work is produced
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Electrochemical Cell
Batteries consist of electrochemical cells that
are electrically connected
An electrochemical cell comprises
1. a positive electrode that receives electrons
from the external circuit when the cell is
discharged 2. a negative electrode that donates
electrons to the external circuit as the cell
discharges 3. electrolyte which provides a
mechanism for charge to flow between positive and
negative electrodes 4. a separator which
electrically isolates the positive and negative
electrodes
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Re-chargeable Batteries
Also known as secondary batteries, storage
batteries or accumulators
Batteries capable of repeated use
The chemical reaction is reverted by applying
electrical current to recharge the battery
Ideally

• High operating cell voltage (2.4 - 4V)
• Rechargeable many hundreds of times
• Operating over a wide range of temperatures
• High energy density (volumetric and gravimetric)

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Applications
Portable battery powdered electronic
devices Mobile phones Laptop computers Palmtop
computers Digital cameras
Over 50 of manufacturing output in the
electronic industry
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Aims of Research
Devices as small as possible
Impediment re-chargeable batteries
Improve volumetric energy density
gravimetric energy density
Ni-Cd batteries may be totally banned by 2008 due
to environmental concerns
Replacements Li-ion batteries Ni-metal hydride
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Li-ion Batteries
Li are the carriers
LiCoO2
cathode
Graphite (C)
anode
SONY battery (1990)
Organic liquid
electrolyte
Li ions are shuttled between electrodes during
charge and discharge
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LiCoO2
Li cations
layers of Co-O edge-sharing octahedra
LiCoO2 Li CoO2 CoO2 shows the CdI2 structure
O2- form a HCP lattice, Co2 occupy half
octahedral holes
only alternate sheets of octahedral holes fully
occupied
Li can insert and de-insert in unoccupied holes
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Disadvantages of the Sony Battery
Cathode Co is expensive and a possible biohazard
Li1-xCoO2 unstable and reactive
Liquid electrolytes moisture sensitive
toxic
Li
LixC unstable and reactive
Anode C is passivated by the electrolyte
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New materials for cathodes
Focus materials which can replace LiCoO2 (cheap,
non-toxic)
Requisites layered structure or 3D structures
containing pathways for Li

• LiNiO2
• LiNi1-yCoyO2
• LiMnO2
• LiMn2O4 (spinel structure)
• LiFePO4 (olivine structure)

Layered structures
3D structures
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LiNiO2
Li
Same structure as LiCoO2
layers of Ni-O edge-sharing octahedra
Advantage higher capacity than LiCoO2
Disadvantages Li/Ni crystallographic disorder
decline in battery reversibililty
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LiNi1-yCoyO2
Used commercially in second generation Li cells
in electric vehicles, laptop computers and
mobile phones
Advantage 30/40 Co for Ni prevents Li/Ni
disorder
Batteries with longer lifetimes
Disadvantage Ni4 is unstable and oxidises the
electrolyte (Ni3 or Ni2)
Safety concerns due to the heat generated by this
redox reaction
Solution partial substitution of Ni3 with
electrochemically inactive Ti4 or Mg2
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LiMn2O4
Li-O tetrahedra
Mn-O octahedra
Spinel structure (MgAl2O4), cubic
Advantages
Mn is cheaper than Co relatively non-toxic stable
as Mn3 and Mn4
Disadvantages
Li insertion reduces 50 Mn4 to Mn3
cubic
tetragonal transition (unfavourable)
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The Spinel Structure (LiMn2O4)
Mg-O tetrahedra
Al-O octahedra
MgAl2O4
General formula AB2O4, where A2, B3 CCP array
of O2-, with A occupying 1/8 of the tetrahedral
holes and B occupying 1/2 of the octahedral holes.
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LiMnO2
Li
Analogous to LiCoO2
layers of Mn-O edge-sharing octahedra
Synthesis is not direct but achieved through ion
exchange. Li substitutes for Na in NaMnO2
(University of St Andrews)
Disadvantage after several charge-discharge
cycles LiMnO2 transforms into a spinel-like
structure
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LiFePO4
Ideally, LiFeO2 for low cost and toxicity
LiFeO2 does not offer satisfactory performance
LiFePO4 offers better performance
Olivine LiFePO4
Layered LiFeO2
(PO4)3- substitutes for O2-
Disadvantage low conductivity
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The Olivine Structure (LiFePO4)
Mg2SiO4 MgFeSiO4 Fe2SiO4
Isolated tetrahedra (PO4) and chains of octahedra
((Fe,Li)O6)
Two octahedral cation sites (O1 and O2)
Fe2 and Li occupy either O1 or O2
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ANODES
Research on materials for anodes alternative to
graphite
Materials metals and oxides
Advantages
Higher capacity Better safety
than graphite
Disadvantages
Irreversible chemical reaction with lithium
Changes in structure
Shorter life
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Materials for Anodes
Sn oxides (Fujifilm Celltec, Japan)
Co3O4, NiO, Cu2O, CuO, FeO (JM Tarascon
coworkers, France)
No capacity fade over 100 cycles
Reaction with Li is not an insertion-de-insertion
process
The mechanism for this reaction is not fully
understood
It may involve the formation and decomposition of
Li2O
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ELECTROLYTES
Solid electrolytes
Higher performance Leakproof Safer
than liquid electrolytes
Ionically conducting ceramics, glasses, polymers
Materials
Disadvantage low conductivity at room temperature
Gel Electrolytes
Combine the advantage of solid and liquid
electrolytes
Disadvantage potential loss of volatile
components
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THE FUTURE
Microscopic batteries on silicon wafers (US
Nanocorp)
Paper-thin batteries (Power Paper, Israel)
THE FUTURE OF RECHARGEABLE BATTERIES IS BRIGHT