Tidal Current Energy

Zincate solution
�
�
Figure 15.8 . The zinc flow cell.
Fuel Cells and Batteries
Collector
Anode
Collector
273
3. they are closed systems, and for these applications the power source is very
close to the sensor, so the influence of effluence on measurement is avoided;
4. they can be simply recharged by energy harvesting technologies (photovoltaic,
thermoelectric, piezoelectric) without user intervention.
The pioneering microbatteries created by ORNL [25] show great promise, in
that they:
● use common microfabrication techniques; and
● are completely solid.
Air
These cells are now beginning to be commercialized and are produced
through microfabrication-compatible technologies. Sputtering and chemical
vapor deposition (CVD) produce excellent thin-film microstructures, and the
materials’ performance approaches the theoretical energy densities for lithium
batteries. Unfortunately, these cells are difficult to manufacture in thicknesses
greater than 15 μ m. When the total battery area is constrained to 1 cm 2 , a single
electrode thickness of 15 μ m is simply insufficient to create a useful battery for a
long-term application, even with a nightly recharge. The second major issue is
the processing temperature. The processes that are used to deposit most thinfilm
battery materials require temperatures greater than 300°C, which is greater
than the temperature most CMOS (complementary metal oxide semiconductor)
devices can withstand. While electrical engineers may get around this by
using a separate chip for the battery or by using the battery as the substrate to
build the device, both cases require significant packaging to protect the batteries.
This, to some degree, defeats the purpose of microbatteries. A recent alternative
to thin-film microbatteries involves using traditional slurries of PVDF and
active battery electrode materials such as MCMB (mesocarbon microbeads) and
LiCoO 2 with advances in direct write technologies and solid-polymer electrolytes.
The electrodes for these cells are almost identical to standard lithium-ion
battery electrodes, so their performance is well known. A novel aspect to these
cells is their solid polymer electrolyte. Previous generation solid-polymer electrolytes
were based on PEO structures, where lithium migration occurs through
the complementary mechanisms of chain hopping through viscous drag and
chain motion. This proved problematic below the glass transition temperature
Zinc slurry