hence is the key to the extremely good power performance, the
microscopic network guarantees high absolute capacities, easy
of fabrication and quick infiltration.[19] The hierarchical 3D
mixed conducting networks put new insight for large-sized
lithium-ion batteries to be used for EVs, HEVs, and SSBs.
The power of this concept is demonstrated by the synthesis
of mesoporous TiO2:RuO2 nanocomposite which shows superior
high rate capability when used as anode materials for
lithium-ion batteries.[19] It is noteworthy that in addition to the
electronic function, RuO2 or LixRuO2 formed during Li
insertion also allows for quick Li permeation. It was found that,
at the very high rate of 30C (Discharge/charge of all the TiO2
within 2 min!), the specific charge capacity of the mesoporous
TiO2:RuO2 nanocomposite is still 91mAh g1, which is about
two times larger than that of 5 nm anatase (48mAh g1) and
nine times larger than that of mesoporous anatase spheres
without interior electronic wiring (10mAh g1).[19]
The concept is simple, yet very effective, and owing to its
versatility, is also successfully extended to other cathode
materials such as LiFePO4.[23] A key to its success is, besides
the preparation of mesopores, the use of a suitable electronic
conductor – here the oxide RuO2 – that enables favorable
surface-surface interactions. RuO2 is most beneficial as it is,
owing to similar bonding properties, expected to spread much
better on TiO2 and LiFePO4 than carbon would, and thus can
efficiently coating the tiny channels in porous TiO2 and even
‘repairing’ incomplete carbon networks in porous LiFePO4
due to the ionic characteristic of both oxides (RuO2 and TiO2;
RuO2 and LiFePO4). However, the challenge is how to further
make the ‘ionic’ and ‘electronic’ wiring down to 10nm scale
especially for cathode materials, and the finding of low cost
ionic coating materials to replace RuO2.
Recently reported optimization procedure of Fe3O4-based
Cu nano-architectured electrodes intend for high power
performance may be mentioned in the context of conducting
networks.[24] The use of a 3D current collector network of Cu
nanorods is the key to the high rate capabilities, but is naturally
not meant for achieving high energy demands due to the
limitation of electrode thickness, which is limited by the
thickness of the porous alumina template used.
It should be noted that, in addition to electrochemical
properties, packing density of anode and cathode is also
important for higher volumetric energy density. An electrode
consisting of homogeneous particle is expected to have a regular
network which canmaintain a uniformintercalation reversibility
of each particle through repeated cycles. So, the morphology
uniformity of assembled nanoparticles in terms of shape and size
should be paid more attention for the practical application.
2.3.2. Surface Coatings
The surface structures of electrode materials are of great
importance to their electrochemical performance. In the case
of nanostructured electrode materials, the effect becomes
more remarkable due to the high surface area as discussed
above. Though it has been demonstrated in many cases that by
using proper surface coatings remarkable improvements in the