Page 288 - Battery Reference Book

Lithium solid electrolyte primary batteries 2416 1

Cover These batteries currently under development hold
EB Weld assembly the promise of spill-proof, rugged batteries with long
shelf lives, with high energy density and virtually
unlimited geometrical possibilities. They are based on
a range of materials known as fast ion conductors
such as beta alumina which are capable of conducting
Insulator (cover)
alkali metal ions such as lithium to levels greater than
s
RS Weld 10-~ cm-'.
In solid polymer electrolyte-composite cathode
Top spacer types, solid polymer electrolytes, a more recently
developed material, have this required conductivity
and are seen as ideal electrolytes for solid state
Spacer batteries.
A recent solid state battery design, lithium compos-
ite cathode batteries, developed at Harwell, features
Anode a lithium ion conducting polymer electrolyte (e.g.,
SeDarator ~ assembly
assembly polyethylene oxide) and a solid intercalation cathode.
The battery is made up of a sandwich of lithiurn foil
(50 pm), polymer-electrolyte (50 pm)3 composite cath-
ode (various types have been studied including 'V6Q13,
Cathodeand --i
case assembly Tis2, MoO2, etc., plus 5% carbon black) (56pm) and
a nickel foil current collector (10 pm). Thus total cell
thickness is 150-200pm and areas can range from
cm2 to m2.
In a typical V601s-based cell design a cell area is
40cm2 and this gives a capacity of 80m Ah. The
(a) G2679 energy density is about 200W h/kg-'. This cell, when
discharged at 120°C from 2.8V to 1.7V at the C/1@
rate yielded 100% of its theoretical capacity. More than
TlG Weld 50% of theoretical cell capacity was available when
Ball seal Anode discharge was carried out at the C rate, 80% at the C/2
assem bl y rate and 100% at the C/4 rate or less. A disadvantage
! I of this type of cell is capacity decline during cycling.
14, Thus after 300 cycles capacity had decreased to about
60% of theoretical capacity. Attention to charging
Electrolyte
detail may overcome this limitation.
Current work is concerned with the development
of cells which operate at room temperature as these
are seen to have applications in the small. portable
equipment market.

(b) G3025
The Hawell development lithium-V205 solid state
Figure 24.12 Honeywell lithium-vanadium pentoxide cells: battery
typical construction of active non-reserve cells (Courtesy of
Honeywell) The development of these solid state batteries hinged
on the discovery of the fast ion conductions or solid
electrolytes, e.g. /3 alumina and lithium nitride (Li3N)
Lithium iodidle is virtually a pure ionic conductor. which are capable of conducting alkali metals.
The ionic con(ductivity is l@-'/(Qcm) at room Modern solid state batteries ose poiymeric elec-
temperature. Thle conductivity can be enhanced by trolytes. Heteroatom containing high molecular weight
incorporating high-surface-area alumina in the solid polymers can conduct alkali metals.
lithium iodide. The solid electrolyte used in these cells Hanvell UK are developing a solid state cell based
has an ionic conductivity of about 10-5/(Q~m) at room on four very thin layers (50-60pm each) comprising
temperature, which enables the cell to deliver currents a lithium foil-polymer electrolyte-composite cath-
of 10 pA/sm2 at XYC with high utilization of the active ode-nickel foil current sollector (10 pm).
materials. The polymer electrolyte comprises polyethylene
These batteries are available in button and circular oxide containing lithium triflate or polyethylene oxide
disc designs. containing lithium perchlorate. The composite czhode