battery and energy density Flashcards
Battery
Device which stores chemical energy and converts it into
electrical energy on demand
Components of a battery, Anode
Electroactive material : metals which can undergo oxidation easily
Zn, Pb, Li
Components of a battery,
Cathode
Electroactive material : compounds which can undergo reduction easily
PbO2, MnO2, O2
Components of a battery, Electrolyte
Substance with good ionic conductivity
Acid, alkali or salt solutions; solids- doped oxides, polymers
H2SO4, KOH, Nafion
Components of a battery, seperator
Insulator which separates anode and cathode compartment
To prevent internal short circuit
Transport ions from anode to cathode compartments and vice versa
Polypropylene, Cellophane
Primary battery
Electroactive material cannot be regenerated
electroactive species is consumed
Galvanic cell
* Dry cell, Li-MnO2
Secondary battery
Electroactive material can be regenerated
- Can be used several times
- Galvanic as well as electrolytic cell
- Storage battery
- Li-ion, Pb-acid, Ni-Cd
Voltage and Factors affecting voltage of a battery
Emf of the cell → Δ G → reaction → choice of electrodes
higher the difference
cathode and
anode (Eo), higher
voltage
* Temperature (T) ; increase in temperature voltage decrease
- Reaction quotient (Q) ;a value of Q increases, voltage of changes marginally
Current
Measure of the rate at which battery discharging
- Depends on rapid electron transfer reaction
- Amount of electroactive species
- Conductivity of electrolyte
- Inter-electrode distance
Capacity
Charge or amount of electricity that may be obtained from the battery
and is given in Ah
depends on : Size of the battery
Discharge conditions of the battery
The time period, t, for which the battery will last when a constant current, I, is drawn
* Longer the flat portion of
the curve better is the
capacity
Electricity Storage density
Amount of charge or electricity per unit weight which the battery can hold
*Weight = all the components of the battery
Cycle life
Number of charge/discharge cycles before failure
- Reasons for limited cycle life:
- Corrosion at contact points
- Shedding of active material from the plates
- Shorting between electrodes due to irregular
crystal growth and changes in morphology
shelf life and Tolerance to service conditions
Maximum time for which a battery can be stored without loss of performance
- Low shelf life due to self-discharge
Tolerance to service conditions:
has to be tolerant to different service conditions
such as variation in temperature, vibration and shock
Zinc battery
metal -air
cathode = O2, anode=Zn
Alkaline battery ; electrolyte : alkali
uses O2 from air => electrochemical energy
cathode dont need to be stored in battery
high energy density
construction zinc battery
ANODE
Zn granules (more surface area )with gelling agent ( to immobilize Zn
and small amount of electrolyte
CATHODE
Carbon (graphite) with MnO2(catalyst)
with a wet proofing agent coated on nickel wire mesh support and an outer
layer of air permeable Teflon layer.
Air access holes on the cathode for O2 to enter the battery
Electrolyte : 30% KOH
Separator : Polypropylene membrane soaked in electrolyte
zn battery adv, dis
adv:
High energy density : Air from atmosphere
* Very long shelf life : can be kept sealed
* No ecological problems
* Low cost
dis:
Limited power output
- CO2 may enter the battery. It reacts with
KOH which will reduce the efficiency
CO2 + 2KOH → K2CO3 + H2O
applications zn
As power source in hearing aids
* In various medical devices
* In voice transmitters
* Large zinc-air batteries are used in rail-road signaling
lithium batteries
Light weight metal
high electrochemical equivalence 7g=> 1F
High negative standard reduction potential of -3.05V ;
when coupled with other electrodes = ( about 4V)
Aqueous electrolytes cannot be used as Lithium is very reactive in water
Components of Lithium batteries
Lithium is used as anode;
Cathode: MnO2, SO2Cl2.
Electrolyte can be Li salt in organic
solvents like acetonitrile, propylene carbonate or inorganic solvents like
SOCl2
Types of Lithium batteries
Primary batteries Li-MnO2
Secondary batteries Li-ion battery
ADV and DIS of Li battery
Adv
- High Voltage 4V
- High energy density – Lightest metal
- High tolerance to service conditions (-40 C to 70 C)
- High electricity storage density
- Flat discharge characteristics
DIS - Safety concerns due to high reactivity of Li
- Poor cycle life – due to dendrite formation
- Transportation limit
Li ion principal
Lithium ion moves from anode to cathode (discharge)
cathode to anode (charge)
- Materials used as anode and cathode should lodge
Li ions
Anode material: Lithiated graphite
Cathodic material : LiCoO2
Li ion construction
Anode: Lithiated -Carbon (Graphite) coated on Copper current collector
Cathode: Lithiated transition metal oxide coated on Aluminium
current collector e.g. Lithium cobalt oxide(LiCoO2)
Electrolyte: mixture of organic carbonate solvents such as ethylene carbonate or diethyl carbonate
containing lithium salts like LiPF6, LiClO4
Separator: thin sheet of micro perforated polypropylene
membrane
Li ion Adv and Dis
Adv
Lighter than other rechargeable batteries for a given capacity
* delivers a high open-circuit voltage 3.7 V
* Low self-discharge rate
* Do not suffer from
battery memory effect
(remember” a lower capacity if it is repeatedly only partially discharged before recharging, acts like its full)
- Good cycle life as the problem of dendrite formation is fixed
as in no point Li metal is formed
DIS
Rising internal resistance with cycling and age
* Safety concerns if overheated or overcharged
