Page 436 - Handbook of Battery Materials

408 14 Lithium Alloy Anodes

on the use of these alloys started in 1983 [10], and they became commercially
available somewhat later.
It was also shown in 1983 [11] that lithium can be reversibly inserted into graphite
at room temperatures when a polymeric electrolyte is used. Prior experiments with
liquid electrolytes were unsuccessful due to co-intercalation of species from the
organic electrolytes that were used at that time. This problem has been subsequently
solved by the use of other electrolytes.
There has been a large amount of work on the development of graphites and
related carbon-containing materials for use as negative electrode materials in
lithium batteries in recent years, due in large part to the successful development
by Sony of commercial rechargeable batteries containing negative electrodes based
upon materials of this family.
Lithium–carbon materials are, in principle, no different from other lithium-
containing alloys. However, since this topic is treated in more detail in Part II,
Chapter 13, only a few points will be briefly discussed here.
One is that the behavior of these materials is very dependent upon the details
of both the nanostructure and the microstructure. Therefore, the composition,
as well as thermal and mechanical treatments, play especially important roles
in determining the resulting thermodynamic and kinetic properties. Materials
with a more graphitic structure have more negative potentials, whereas those
with less well-organized structures typically operate over much wider potential
ranges, resulting in a cell voltage that is both lower and more dependent on the
state-of-charge.
Another important consideration in the use of carbonaceous materials as negative
electrodes in lithium cells is the common observation of a considerable loss
of capacity during the first charge–discharge cycle due to irreversible lithium
absorption into the structure. This has the distinct disadvantage that it requires an
additional amount of lithium to be initially present in the cell. If this irreversible
lithium is supplied by the positive electrode, this means that an extra amount
of the positive electrode reactant material must be put into the cell during its
fabrication. As the positive electrode reactant materials often have relatively low
−1
specific capacities, for example, around 140 mAh g , this irreversible capacity in
the negative electrode leads to a requirement for an appreciable amount of extra
material weight and volume in the total cell.
There are some other matters that should be considered when comparing
metallic lithium alloys with the lithium–carbons. The specific volume of some
of the metallic alloys can be considerably lower than that of the carbonaceous
materials. As will be seen later, it is possible by selection among the metallic
materials to find good kinetics and electrode potentials that are sufficiently far
from that of pure lithium for there to be a much lower possibility of the potentially
dangerous formation of dendrites or filamentary deposits under rapid recharge
conditions.
It has been shown that there is a significant advantage in the use of very small
particles in cases in which there is a substantial change in specific volume upon
charging and discharging electrode reactants [12]. Since the absolute magnitude