CH5715
Energy Conversion and Storage
Part 2: Ionic Conduction, Electrochemistry, Batteries and
Other Applications
John T.S. Irvine
Room 216
jtsi@st-and.ac.uk
Aims:
To introduce students to the principals and applications of ionic
conductors, electrochemistry and batteries
For lecture notes: http://koruk.wp.st-andrews.ac.uk
Summary
Conductivity in ionic solids, Crystalline Conductors,
Polymer Electrolytes
Lithium Ion Batteries, Electrodes Intercalation
Electrochemical Reactions and Impedance Spectroscopy
Other Applications High Temperature Batteries, Oxygen Transport
Membranes
John B. Goodenough and Youngsik Kim
Challenges for Rechargeable Li Batteries DOI:10.1021/cm901452z
Chemistry of Materials
The Li-Ion Rechargeable Battery: A Perspective - JACS.
pubs.acs.org/doi/abs/10.1021/ja309143
Issues and challenges facing rechargeable lithium batteries
J.-M. Tarascon1 & M. Armand Nature 2001,414, 359-367 |
doi:10.1038/35104644
Electrochemical Cells
Electrolyte
Oxidation
electrode
Reduction
electrode
cathode
Ions only
mobile species
anode
ee-
Cathode - reduction
X + ne- -> XnFuel Cell O2 + 4e- -> 2 O2Anode - oxidation
M -> Mn+ + neFuel Cell H2 -> 2H+ + 2e-
• Fuel cells and batteries are electrochemical
devices used to provide dc electrical energy
• Fuel Cells similar to battery under discharge
• Fuel cells energy source is external
• Batteries energy source is internal
BATTERIES
Discharge
Electrolyte
Oxidation
electrode
Reduction
electrode
cathode
Ions only
mobile species
anode
eei
BATTERIES
Charge
Electrolyte
Reduction
electrode
Oxidation
electrode
Ions only
mobile species
anode
cathode
eei
Batteries
• Comparison
• Conventional batteries, in brief
Advanced Rechargeable batteries
• Nickel metal hydride
• Lithium ion batteries
• Sodium sulphur batteries, high temperature
2
( aq )
Cu
Daniel Cell
2
( aq )
 Zn( s )  Cu( s )  Zn
E = 0.337-(-0.763) = 1.10 V
2
( aq )
Cu
Daniel Cell
2
( aq )
 Zn( s )  Cu( s )  Zn
E = 0.337-(-0.763) = 1.10 V
Advanced Batteries
Batteries have been developed for utilisation in modern batteries for
electric vehicles and consumer products
Primary or secondary - In primary, electrodes are consumed as a
fuel, secondary are rechargeable
- High energy/power density required
Na, Li (-3.0, -2.7VH) - large, negative redox potentials
Use Na or Li electrode as negative electrode
Need electrolyte that conducts Na or Li-ions
Counter electrode redox process must be compatible with Na or Li
and ideally at as positive a potential as possible.
Comparison
of battery
technologies
Nickel-metal hydride batteries
Positive electrode
Discharge

NiOOH  H 2 O  e  Ni (OH ) 2  OH
charge
Negative electrode
Discharge

MH x  OH  MH x 1  H 2 O  e
charge
MHx = LaNi5H6 or TiH2
Electric vehicle application possible
1.3V per cell


Lithium batteries
low mass, often rechargable.
e-
Li/C
LiClO4 solution
on polyethylene
mesh/
-
Li/CoO2
+
Li+
Discharge/ charging involves reverse processes
e-
Electrolytes
Polymer electrolytes are particularly promising-safety
However, liquids now widely commercialised in solid state
batteries.
Organic electrolyte encapsulated in polymer mesh
Solution Electrolytes
salt + solvent  solution
-ve DG
DG = DH − TDS
DS of salt increases DS of solvent decreases
Overall DS positive but still small
Dissolution depends on enthalpy changes
NaCl does not dissolve in hexane
Aprotic
Anions less strongly solvated; barely solvated in non-aqueous solvents.
First: ions interact with the solvent molecules immediately surrounding them
ion-solvent interactions
Second: ions interact with each other. Around any ion there will be an atmosphere of
oppositely charged ions. Net negative charge around each cation will interact
electrostatically with it
 lower energy.
Debye-Hückel ion atmosphere ion-ion interactions
Electrolyte characteristics for Batteries
1) Large electrolyte potential window Eg so does not decompose
across potential range:
2) Retention of the electrode/electrolyte interface during cycling when
the electrode particles are changing their volume.
3) A Li -ion conductivity sLi>10-4 S/cm over the temperature range of
battery operation.
4) An electronic conductivity se<10-10 S/cm.
5) A transference number se/stotal ~1
6) Chemical stability over ambient temperature ranges and
temperatures in the battery under high power.
7) Chemical stability with respect to the electrodes, including the
ability to form rapidly a passivating solid/electrolyte-interface (SEI)
layer.
8) Safe materials, i.e., preferably nonflammable and nonexplosive if
short-circuited.
9) Low toxicity and low cost.
Polymer Electrolytes
Schematic representations of polymer electrolyte networks.
a, Pure (dry) polymer consisting of entangled chains, through which the
Li ions (red points) move assisted by the motion of polymer chains.
b, A hybrid (gel) network consisting of a semicrystalline polymer,
whose amorphous regions are swollen in a liquid electrolyte, while the
crystalline regions enhance the mechanical stability.
c, A poly-olefin membrane (Celgard for instance) in which the liquid
electrolyte is held by capillaries.
1, PEO-LiCF3SO3;
2, new solutes with high-dissociation PEO-Li [(CF3SO2)2N] bis(trifluoromethanesulfone)imide (TFSI)
3, low-Tg combination polymer;
4 plasticized polymer electrolyte PEO-Li[(CF3SO2)2N] +25% w/w PEG-dimethylether (mol wt, 250)
5,6 liquid crystalline polymer electrolytes;;
7, gel-type polymer (X-linked PEO-dimethacrylate- Li [(CF3SO2)2N]-PC 70%);
8, liquid electrolyte PC/DME LiCF3SO3; trifluoromethanesulfonate
9, liquid electrolyte EC/DMC-LiPF6 at low temperature ;
10, gel electrolyte P(VDF-HFP)/EC/DMC-LiPF6.
Putting together a lithium battery