Primary cells
Primary cells
HISTORY
Luigi Galvani (1737 1798)
Alessandro Volta (1745 1827)
galvanic cells with liquid electrolyte
G. Leclanche (1839 1882)
1866 dry cell
zinc alloy anode-manganese dioxide cathode with an electrolyte
mix of 80 percent ammonium chloride and 20 percent zinc
chloride surrounding a carbon rod electrode
Ideal cell
Internal voltage is during whole usage constant
Internal resistance of the cell is zero, so terminal
voltage is independent on the load current and
discharge time
Real cell
Internal voltage is during whole usage not
constant
Internal resistance of the cell is not zero, so
terminal voltage is dependent on the load current
and discharge time
Electrochemical processes are carried out at a
reduced extent even when the cell is not loaded,
so the cell discharges itself
Basic types of primary galvanic
cells
With acid electrolyte
Zinc-carbon surrounded by a mixture of manganese
dioxide and carbon powder; electrolyte zinc chloride
and ammonium chloride dissolved in water
With alkaline electrolyte
Zinc-manganese dioxide; electrolyte potassium
hydroxide
Special
Zn-HgO, Zn-Ag2O, electrolyte NaOH ; zinc-air,
Zinc-carbon cells
Cathode graphite (C) rod + Manganese dioxide
(MnO2)
Anode zinc alloy can (Zn) contains Hg, Cd
Electrolyte ammonium + 20 % of zinc chloride
Reactions:
Zn(s) Zn2+(aq) + 2 e [E = -0.7626 volts]
2MnO2(s) + 2 e + 2NH4Cl(aq) Mn2O3(s) + 2NH3(aq) +
H2O(l) + 2 Cl [E +0.5 V]
Zn(s) + 2MnO2(s) + 2NH4Cl(aq) Mn2O3(s) + Zn(NH3)2Cl2
(aq) + H2O(l)
Zinc-carbon cells
Cathode and Anode are separated by the
separator
Storage time max. 2 years
Carbon is not a part of reaction!
From the energy
balance implies
that for achieving 1
Ah is consumed
1.22 g of Zn.
Zinc-carbon - Zinc-chloride cells
Also called heavy-duty
Improved basic zinc-carbon concept
using of plastic seals possibility of using only zincchloride electrolyte
pure materials
pure zinc without Hg or Cd
Suitable for higher load currents htan basic
concept like motorized toys, flashlights,
Usually 2-3 times longer life than basic concept
Zinc-carbon cells
Alkaline cells
Cathode
manganese-dioxide (MnO2)graphit mixture cathode
silver oxide (Ag2O) button batteries
oxygen (O2) button batteries, coin jackets
Anode powdered zinc alloy
Electrolyte potassium hydroxide (KOH)
Anode collector steel
Steel can no electrolyte leakage!
Alkaline cells
Reactions:
The half-reactions are:
Zn(s) + 2OH(aq) ZnO(s) + H2O(l) + 2e [e = 1.28 V]
2MnO2(s) + H2O(l) + 2e Mn2O3(s) + 2OH(aq) [e = +0.15 V]
Overall reaction:
Zn(s) + 2MnO2(s) ZnO(s) + Mn2O3(s) [e = 1.43 V]
Electrolyte is not a part of the reaction!
Usually about 3-5 times more lifetime than Zn-C
Alkaline cells
Alkaline cells
Discharge characteristics
Continual discharging
Discharge characteristics
Periodical discharging
Lithium primary cells
Many different Li cells construction differed in
properties, dimensions, jackets and mainly
applications. Capacity range starts at Li-MnO2 with 20
mAh (1.5 g) and for example Li-SOCl2 (lithium-thionyl
chloride) with 30 Ah and 250 g mass.
Basic types of Li primary cells
Li-MnO2
Un = 3.0 V, CA = 0.16 1.8 (AA) 11 (D) Ah
Operation temperature -40 to +70 C
Max. load 50 1000 mA (AA, C, D)
Li-SOCL2
Un = 3.6 V, CA = 0.36 2.4 (AA) 38 (D) Ah
Operation temperature -60 to +85 C
Max. load 10 200 mA (C, D)
Li-FeS3
Lithium primary cells
Some reactions:
Li + MnO2 = LiMnO2
Li + FeS2 = Li2S + Fe, where FeS2 is pyrite
Li + (CF)n = LiF + C, where (CF)n is the layer material
produced by fluorization of graphite in high
temperatures
Lithium primary cells
Discharge characteristics of Li
primary cells
Li primary cells jackets
Lithium primary cells lifetime
Advantage very low self-discharging
even only 1 % of Ah capacity drop for one year! very
high storage times
But! Lithium is degraded by corrosion, real lifetime
between 5 and 10 years.
High discharge rates
Disadvantage
Li very reactive
Expensive
Mercury and Silver-Zinc cells
Mercury cell
positive electrode HgO, negative electrode Zn
operational voltage about 1.35 V, low dependence on
discharging
Silver-Zinc cell
positive electrode Ag2O, negative electrode Zn
operational voltage about 1.55 V, low dependence on
discharging
Using low loads (A, mA) watches, hearing
aids, usually button jackets
Jackets and design of cells
Terminals
Thank you for your attention!
