Page 465 - Handbook of Battery Materials

438 15 Lithiated Carbons

for example, carbons with a remarkably high lithium storage capacity (see
Sections 15.2.4 and 15.2.5), and tailored carbons, which were prepared by the use
of inorganic templates [61, 62]. It has to be emphasized that the assumed suitability
of a carbonaceous material for a lithium intercalation host depends strongly on the
method of its evaluation, and quite a few carbons may have been rejected as anode
materials due to an inadequate evaluation method. As a consequence, sometimes
the classification of a carbon as ‘good’ or ‘poor’ anode material can be only prelim-
inary. For instance, though in principle electrochemical intercalation in graphite
was already observed in the mid-1970s [63, 64], it took about 15 years for an appro-
priate electrolyte allowing the highly reversible operation of a graphite anode to be
found [65].

15.2.1
Carbons: Classification, Synthesis, and Structures

Because of the variety of available carbons, classification is inevitable. Most car-
bonaceous materials which are capable of reversible lithium intercalation can be
classified roughly as graphitic and nongraphitic (disordered).
2
Graphitic carbons basically comprise sp -hybridized carbon atoms which are
arranged in a planar hexagonal (‘honeycomb-like’) network such that a so-called
‘graphene layer’ is formed. Van der Waals forces provide a weak cohesion of
the graphene layers, leading to the well-known layered graphite structure. From a
strictly crystallographic point of view the term ‘graphite’ is, however, only applicable
for carbons having a layered lattice structure with a perfect stacking order of
graphene layers, either the prevalent AB (hexagonal graphite, Figure 15.3) or the

graphene layers
arm-chair face
A
prismatic surface B layer plane zig-zag

face

2
A spacing ( C = 0.3354 nm)

0.246 0.142 nm layer A
outline of layer B
unit cell nm

Figure 15.3 (a) Schematic drawing of the crystal structure
of hexagonal graphite showing the AB graphene layer stack-
ing sequence and the unit cell. (b)View perpendicular to the
basal plane of hexagonal graphite. Prismatic surfaces can be
subdivided into armchair and zig-zag faces. Modified and
redrawn from Ref. [2].