Transcript Theoretical Capacity of the Electrode Material

General introduction on Lithium
Ion Batteries
History of battery….
Pioneering work for the lithium battery began in
1912 by G. N. Lewis but it was not until the early
1970’s when the first non-rechargeable lithium
batteries became commercially available.
Attempts to develop rechargeable lithium
batteries followed in the eighties, but failed due
to safety problems.
the first commercial lithium-ion battery was
released by Sony in 1991. The cells utilised
layered oxide chemistry, specifically lithium
cobalt oxide. These batteries revolutionised
consumer electronics.
Michael Faraday
Charles-Augustin de Coulomb
demonstrated the relation between electricity and chemical bonding,
capacity (mAh/g) =
[F × nLi) / ( M×3600)] × 1000
Where, F = Faraday’s constant( 96,500 coulombs per gm equivalent)
n Li = Number of Li per formula unit of the electrode material
M = Molecular mass of the electrode material.
Cell – Energy storage device that converts chemical energy present in to
electrical energy.
Battery:
Combination of one or more cell;
The cell components: Cathode, Anode and Electrolyte, seperator and
current collector.
Primary Battery
Secondary Battery
Zinc- MnO2: Inexpensive, small in
Rechargeable cell , Ni- Cd, Li size, voltage ~ 1.5V, use in
Ion battery
watches, calculators etc, use and
dispose,
Energy storage of the battery is means that How much charge a battery can deliver to
the external circuit.
coulomb is defined as the quantity of electricity
transported in one second by a current of one ampere.
Named for the 18th–19th-century French physicist
Charles-Augustin de Coulomb
Why Li-based power sources?
• Li is the lightest metal (specific gravity
ρ=0.53 g/cm3)
high energy
density
Theoretical capacity of
Li : 3860 Ah/kg (Li
Li+ + e-)
Extremely high
compared to Zn (820
Ah/kg) and Pb (200
Ah/kg).
Salient Features of LIB
•
High Energy density, Light weight, design
flexibility
•
Preferred choice for portable appliances
•
present world production per year is
~ 300 million cells.
•
Market value ~ US $ 200 Billion
•
expected growth up to 2010 ~ 40%
Courtesy of Panacenia.com.
Specification for the Commercial Battery fabricated by
Panasonic.
Size (DWH)
3.83562 mm
Weight
15g
Nominal capacity
760 mAh
Nominal voltage
3.7 V
Charge voltage
4.2 V
Charge time
150 min.
Energy density (Volumetric)
375 Wh/dm3
Energy density(Gravimetric)
190 Wh/kg
Cycle performance
85% at 1000th cycle
Temperature range
-20C to + 60C
Cathode
LiCoO2
Anode
Graphite
Courtesy of Panasonic website
Principle of Operation
Charging
Co3+
Co4+
Cathode: LiCoO2
Li1-xCoO2 + xLi+ + xeAnode: C + xLi+ + xeLixC
Overall rxn: C + LiCoO2
LixC + Li1-xCoO2; x=0.5
(during charging)
Discharging
Co4+
Co3+
(Oxidation: E° = 0.6V)
(Reduction: E°=-3.0V)
(Ecell=3.6V)
LIB Technology
Different configurations : a) cylindrical b) coin c) prismatic d) thin and
flat (pLiON) [ref. Nature 2001, Tarascon et al .]
Material Considerations
Anodes
• Carbon anodes
Capacity~372 mAh/g
• Graphite – layered, low capacity, high
reversibility
• Hard Carbon- Non-layered, high capacity.
Irreversible capacity loss
Metal coating (Ag,Zn or Sn) of anodes tried
Amorphous Tin Composite Oxides (ATCO)
• SnMxOy (x≥1), M = glass-forming elements
(e.g. a mixture of B and P)
• Gravimetric capacity- high (>600 mAh/g)
• Sn2+,Sn4+/Sn redox couple
SnO + 2 (Li+ + e-) → Sn + Li2O
SnO2 + 4 (Li+ + e-) → Sn + 2Li2O
Sn + 4.4 (Li+ + e-) ↔ Li4.4Sn
Irreversible
loss of Li in Sn
formation
Reversible capacity
 Capacity-fading need to be solved before
these materials can be used commercially
• Other options
• Lithium metal nitrides
 Pros: High capacity(~900 mAh/g), low average voltage
 Cons: High moisture sensitivity, lack of economic manufacturing
processes
• Inter-metallics
 Cu6Sn5 – Capacity fading
 InSb – In (high cost), Sb (toxic)
• Oxides
 Spinel-type oxides- Li4Ti5O12, Li4Mn5O12 and Li2Mn4O12
 Low voltage spinels + high-voltage cathodes= intermediate voltage
Li-ion cells.
 Do not produce metallic Li which is a safety concern in LiC6 or
metallic lithium anodes.
Electrolytes
• Li salt dissolved in a solvent.
• LIB Operation range : 3.0-4.2 V,
Decomposition potential of H2O = 1.23 V
Aqueous electrolyte not used
• 4 types of non-aqueous electrolytes in
use: liquid, gel, polymer and ceramic-solid
electrolytes.
• Liquid electrolytes
 Highly ionizable Li-salts - LiPF6, LiAsF6 etc
dissolved in organic carbonates - ethylene
carbonate (EC), dimethyl carbonate (DMC) etc
 Organic carbonates - aprotic, polar, high K,
solvate Li salts at high concentration (>1M),
good ionic conduction.
 Problems : leakage, sealing, non-flexibility of the
cells, side reactions with charged electrodes
• Solid electrolytes
 Crystalline or glassy matrix - Li ions move
through vacant/interstitial sites - high σionic (~103 - 10-4 S/cm at 25°C)
 Crystalline : Nasicon framework phosphates –
LiM2(PO4)3 and perovskite-based oxides,
(Li,La)MO3 (M = Ge, Zr, Hf)
 Glasses : oxides or sulfides
 Advantages : (i) No leakage, (ii) Wide operating
temperature range (iii) Better charge-discharge
cycling profile (iv) Long life – little self discharge.
•
Polymer electrolyte

A salt dissolved in a high-molecular-weight polar polymer matrix
E.g. PEO (Poly-ethylene oxide)
Chemically stable – contains only C-O, C-C and C-H bonds.




Cation mobility - cation-ether-oxygen co-ordination bonds, regulation local relaxation and segmental motion of the PEO polymer chains -> high
σionic of the electrolyte.
Pros : ease of fabrication, flexibility, lightweight, leak proof
Cons: low conductivities at or below room temperature
Addressed by plasticized or gel electrolytes - polymer electrolytes with a
component (solid or liquid): to enhance the ionic conductivity.
Layered Cathodes
• Layered materials
 Facile Intercalation /
deintercalation – high
reversibility
 α-NaFeO2 structure( sp
grp R3m)
 LiNiO2, LixCoO2 (widely in
use, 140 mAh/g) –
thermally stable : High
cost, toxicity
 LiMnO2 – cheap,
substitution needed to
stabilize the structure
(Li1+x Mn0.5Cr0.5O2, 190
mAh/g )
• NaSICON materials
 Oxyanion scaffolded structures
built from corner-sharing MO6
octahedra (where M is Fe, Ti,
V or Nb) and XO4n tetrahedral
anions (where X is S, P, As,
Mo or W)
 Polyoxyanionic structures
possess M-O-X bonds
 Altering the nature of X ->
change (through an inductive
effect) the iono-covalent
character of the M-O bonding
 Possible to tune M redox
potentials.
 Promising candidate - LiFePO4
Spinels
LiMn2O4 - cubic spinel structure with sp grp Fd3m
Spinels - 3D hosts with Li ions occupying 8a tetrahedral sites.
Capacity fading and poor recyclability
Cost, non-toxicity and availability
Advanced Applications
Mars Exploration rover” spirit”
www.nasa.gov
Koizumi taking a 10 minute spin
Eliica, Japan Speed – 90km/hr
Mechanical grinder
Hydraulic
press
Tubular Furnace
Preparation of Composite Electrodes ( Cathode or Anode).
1. Fine powders of the active materials (LiCoO2, CaSnO3, etc) mixed with
conducting carbon (Super PMMM) and PVDF in N-methyl pyrolidinone
(NMP) solvent.
2. PVDF acts as binder that helps the thick film coating to adhere well to
the metal foil.
3. This mixture of active material : conducting carbon :PVDF in fixed
proportion ( in my case 70:15:15) was stirred to get the homogenous
paste like slurry.
4. The Slurry was coated on to a clean Al or Cu foil. Thick film was dried
at 100oC in an air.
Thick film coater
Furnace
5.
Electrode was then pressed between spherical twin roller at about
1500 KPa pressure. This ensures that the film of the composite
electrode adheres to the Al/Cu foil.
6. Electrode was cut into circular discs (16mm). Thickness ~ 0.05 – 0.12mm
7. Electrode- discs were dried in vacuum oven at 800C for ~ 12 hrs.
8. Electrode disc then transferred to the Glove Box.
O2 and H2O content
< 1ppm
Glove Box
Fabrication of Lithium - Ion Cell
Diameter of coin cell ( 2016) ~ 16mm and height 2.0mm
Parts of Coin cell –
Cup > 16mm diameter and plastic ring,
separators ( polypropylene separators;
Electronically nonconducting but solution/ion
permeable) Steel spring for close packing. Finally
cell was sealed using a press and transferred out
the glove box
Li ion - coin Cell
Micropipette
Punching
Machine
Electrochemical Characterization :
Galvanostatic Cycling and Potentiostatic Cycling:
Galvanostatic Mode: The output voltage of the cell is monitored at constant
current.
Potentiostatic Mode: The current is monitored at a particular voltage
Multi cell analyzer BITRODE
Specific Capacity of the cell :
The capacity of the electrode material in the battery depends
on the amount of Li that can be intercalated / deintercalated into the host structure.
Capacity: Number of Coulombs (Charge) in (amperes-hours) delivered by a
battery.
Specific capacity: Amount of charge delivered per unit weight of electrode
active material (Ah/g or mAh/g ).
Theoretical specific capacity of a Li – containing oxide is calculated by assuming that all
the Li per formula unit of the oxide participate in the electrochemical reaction and is
given by
Specific Theoretical capacity (mAh/g) = [F × nLi) / ( M×3600)] × 1000
Where, F = Faraday’s constant( 96,500 coulombs per gm equivalent)
nLi = Number of Li per formula unit of the electrode material
M = Molecular mass of the electrode material.
Theoretical Capacity of the Electrode Material:
Weight of the active electrode material × its theoretical specific capacity
Experimental Capacity: Our experimental value observed by BITRODE (mAh)
Specific Capacity:
•
Experimental capacity / weight of Electrode Material.
Number of Lithium Ions de – intercalated from the cathode active material during
charging process,
Charging Capacity of Electrode / Theoretical Capacity
Where charging capacity = Charging current × Charging time
In Coin – type cell the weights of electrodes ~ 8-15mg
hence the current will be small.