Page 178 - Battery Reference Book

9/18 Lithium batteries

energy density is up to 100% higher than conven- Several hundred full charge discharge cycles are
tional nickel-cadmium cells and up to 30% higher possible with lithium-molybdenum disulphide cells.
than advanced nickel-cadmium designs. The charge They exhibit good charge retention on storage. No
retention of lithium-molybdenum disulphide cells at voltage delay effects occur upon discharge. Based on
10% per annum at 21°C is at least one order of mag- the change in voltage for cells stored at 1.85 V a
nitude less than is the case with nickel-cadmium cells. self-discharge rate of 5% per annum has been found.
Lithium-molybdenum disulphide cells suffer loss in Stabilization of cells can be achieved by cycling before
performance when cycled continuously at high voltage. storage. Such stabilization exhibits a capacity loss of
The cell should be used with both charge and discharge only 8% per annum and at 2.4V when stored at 21°C.
control circuitry where termination voltages are set and Charging of cells at rates greater than the 1-h rate
should not exceed 2.4 V per cell for charge and 1.1 V leads to cell overheating and eventually combustion.
per cell for discharge. Cell failure which is character- Multicell batteries are not as efficient as individual
ized by the development of gradually worsening short cells due to imbalances between individual cells.
circuits is caused by degradation of active components
in the cell, particularly changes in molybdenum disul-
phide structure and reactions between lithium and the
electrolyte producing ethylene, propylene and lithium 9.13 Lithium (aluminium) iron
carbonate. monosulphide secondary batteries

The system operates with an open circuit voltage
(9.11 of 1.33V. It has a theoretical energy density of
458 W h kg-', the energy density achieved in practical
cells is 105 W h kg-'. Other characteristics of this cell
CH2, are tabulated in Table 9.17. Li(A1)FeS cells can be
co3+
=
I , CHCH3 = CH2 thermally cycled between temperatures of 450/500"C
LiCO3
Li
-k
CHCH3 (9.21 and 20°C without adverse effects.
In addition to the cells, this system requires a ther-
These cells have many safety features and will mal management system to maintain the proper oper-
not explode on being punctured, crushed or inciner- ating temperature for the battery and a specialized
ated. Regulations and exemptions to regulations exist charger in which careful voltage control is maintained
regarding their shipment, particularly on passenger thereby preventing the positive electrode from reach-
aircraft. ing a potential high enough to produce soluble iron
The performance characteristics of lithium molyb- species which deposit in the separator during cycling.
denum sulphide cells are shown in Table 9.16. The battery is contained in a low thermal conductivity
The open circuit voltage varies from 2.4 V at start box with an inner vacuum space lined with aluminium
of discharge to 1 V at 80-100% discharge. foil and glass fibre paper.

Table 9.15 Comparison of sealed rechargeable lithium molybdenum disulphide and sealed cylindrical sintered plate
nickel-cadmium cells
Sealed rechargeable Sealed cylindrical sintered plate
lithium-molybdenum disulphide nickel-cadmium

Open circuit voltage (V) 2.4- 1.1 1.3
Volts under load (V) 1.854 (C10) 1.2 nominal
Discharge voltage profile Sloping Flat
Gravimetric energy density (W h kg-') 61 13-35
Volumetric energy density (W h dn-3) 175 50-120 according to cell size
Gravimetric power density (W kg-') 130 750-1000 according to cell size
Volumetric power density (W dm-') 375 2500-3500 according to cell size
Storage temperatures ("C) -54 to 55 -40 to 70
Operation temperature ("C) -30 to 55 discharge -40 to 70
-10 to 45 charge
Self discharge rate 5% p/a at 21°C 120-300% p/a
Cycle life 200 >500
Calender life 10 y estimated 4-8 y in operation
5-10y in storage
Types available AA (0.6-0.8 Ah) Cylindrical (0.1 - 10 Ah)