Page 291 - Battery Reference Book

24/14 Lithium batteries
The separator is non-woven polypropylene cloth.
The electrolyte is lithium perchlorate dissolved in 1:2
dimethoxypropane. The cell is housed in a stainless
steel container. gasket)
Flat-type cells are available for low drain rates,
and cylindrical cells with spiral wound and inside-
out structures are available for high drain rates in
applications such as strobes and cameras. Capacities
in the range 35-5000mAh are available.
The Cell reactions:
Anode: Li + Li+ + e- (24.14)
Cathode: Mn"02 + Li' + e- + Mn"'Oz(Li') (24.15)
Overall: Mn"02 + Li + Mn"'Oz(Li+) (24.16)
(Li ion in MnOz lattice) tnsulator
Figure 24.17 Cross sectional views of commercial Li-CFx bat-
24.7 Lithium-copper oxide primary tery, cylindrical type
batteries
The separator is made from non-woven cloth made
Lithium-copper oxide primary cells have been estab- from polyethylene or microporous polypropylene.
lished since 1969 as a versatile and reliable power Lithium-carbon monofluoride cells are available in
source in a range of applications. capacities below 1 Ah although attempts are now in
Cell reaction: progress to produce larger cells.
Overall: 2Li i CuO -+ Liz0 -t CuO, E" = 2.24V (24.17)
Each cell comprises a pure lithium anode, a solid 24.9 Lithium - molybdenum disulphide
cupric oxidelgraphite cathode and a porous non-woven secondary batteries
glass separator. The electrolyte is lithium perchlorate The development of this rechargeable lithium battery
dissolved in 1,3 dioxolane. Cells are available in a bob- owes much to the discovery of a new crystalline
bin cylindrical cell format in which an electrolyte filled
central tube (lithium anode) is wrapped in the separator phase of molybdenum disulphide in which a small
and surrounded by an annular cathode (cupric oxide). quantity of lithium introduced into the crystal lattice
stabilizes the crystalline phase (Lix MoS2). This shifts
The cell is sealed with a crimp-sealed polypropylene
joint or glass to metal seals. the equilibrium so the potential of the material is
considerably more electropositive than occurs with
molybdenum disulphide.
24.8 Lithium-carbon monofluoride The main reaction is the electrochemical oxidation
primary batteries of lithium metal and the reduction of molybdenum
disulphide via the intercalation reaction:
The basic chemistry is:
xLi + MoSz + LiwMoSz (24.19)
xLi + CF, + XLIF + C , E" = 3.2V (24.18)
(X = 0.5-1.0) Lithium ions are generated at the anode during dis-
charge and then transported through the liquid elec-
Cylindrical, pin and coin cell designs are available. trolyte and inserted into the molybdenum disulphide
A typical design for a cylindrical cell is shown in crystals without substantially changing the structure
Figure 24.17. of the latter. Electrons are transported through the
The cathode is a mixture of CF, with acetylene external circuit and recombined with lithium ions in
black and binder such as PTFE. The electrolyte is a 1 : 1 the molybdenum disulphide host.
mixture of dimethoxyethane and propylene carbonate In these cells a lithium foil anode strip is placed
containing 1M lithium borotetrafluoride. Alternatively, between two molybdenum disulphide cathode strips.
lithium arsenic hexafluoride in y-butyrolactone has The latter electrode consisting of aluminium foil coated
been used. with the metal sulphide and organic binder with a final
The cylindrical cell construction in Figure 24.17 thin coating of molybdenum dioxide to ensure good
employs a spiral winding of lithium, separator and conductivity.
cathode. The cathode is bound to an expanded tita- The electrode stack is spirally wound around a
nium metal grid. Sealing is achieved by means of a mandrel and inserted in a nickel plated steel can. The
polypropylene disc which incorporates a safety vent. anode is connected to a centre pin which is insulated