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Dpt. of Materials Engineering – Technion Energy Program
There are three major areas where the
chemical energy storage is in high demand:
1. Low power autonomous power storage, such as portable electronics power
supply
2. High power autonomous power storage, such as electric vehicles power
supply
3. Stationary energy power sources for daily consumption power leveling and
for using with alternative power sources.
Chemical
power storage
(batteries)
Autonomous
energy storage
Low power storage
(generally,
electronics)
Stationary
energy storage
High power
storage
(generally, EV)
Power consumption
levelling, alternative
energy production
Low power autonomous power storage – this is indeed a huge market. There
are two major types of cells – primary and secondary (or rechargeable).
1. Primary cells
The most distinct limitation of all primary batteries is their one-time use. Because
of this, the cost of their power is ~30 times higher than that of rechargeable
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Dpt. of Materials Engineering – Technion Energy Program
batteries. The cost becomes even more excessive if the packs are replaced after
each usage (fully discharged or partially used)... It would be much simpler to
issue fresh packs before each activity. Keeping track of these packs in the military
and public sector is time-consuming and awkward. Does it mean that rechargeable
batteries are obsolete relicts of the past? Consider this:
Cheap alkaline cells (these cells are a kind of outgrowth of Leclanché cell, patented
in 1866) are still on demand.
To be sure, households with kids, particularly
younger ones, still use primary batteries, because more-popular gaming devices
chew up disposable batteries. All around the world, people are still buying nearly
equal amount of primary alkaline cells and rechargeable Li-ion cells. No wonder
that currently a lot of attention of scientists and industrialists is focused on the
reduction of Zn corrosion, which enhances Zn utilization and increases battery’s
shelf life.
Our group is on the cutting edge of this
development. Currently we are developing a
new approach to the problem of inhibition of
Zn-corrosion; first results on the matter are –
undeniably! – encouraging.
2. Secondary cells
As it is explained above, overall secondary cells are cheaper and more convenient
than primary cells. Apparently, secondary cells are more “consumer friendly” since
they may be “redeemed” using a common wall power socket. Whereas a piece of a
secondary cell commonly cost more than a piece of an alkaline cell, finally
secondary cells provide cheaper electricity because such cells may be used
repeatedly. Currently, the most advanced and promising cells are Li-ion cells.
Since secondary cells are used in more demanding applications than common
alkaline cells, they are required to be good performers; particularly, a high energy
performance is desirable. The increasing of Li-ion cell voltage is the clear ways to
improve its energy density.
Our group is answering this need and the
research in the field of 5-volt Li-ion cell is
currently standing high on our waiting list.
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Dpt. of Materials Engineering – Technion Energy Program
The other issue is the battery safety; particularly, safety is the first priority if a
product is supposed to be on sale for common public. It could be also easily
comprehended that the higher the energy density of the battery, the bigger hazard
it may potentially pose.
Our group is not standing outside of this research;
we are now involved in the project, which is aimed
at the of Li-ion technology safety enhancement.
High power autonomous power storage – this is the market of the
future! The major potential segment – electric vehicles (EV)
Nowadays, vehicle manufacturers are experiencing challenges of the
environmental regulations and also of skyrocketing gas prises. In response,
serious efforts have been made to develop commercially-viable EV (vehicles with
the battery/[electric motor] propulsion system instead of the common [fossil
fuel]/[internal combustion engine – ICE] propulsion system. It may be argued that
despite of the fact that EV operation is environmentally safe the production of the
needed extra energy would pose a pressure on environment. In depth
consideration reveals, though, that:
(i)
Whereas currently power plants are substantial contributors to
environmental pollution, [fossil fuel]/[power-station]/EV combination is
significantly more energy efficient than [oil well]/refinery/[ICE vehicle]
combination. This fact promises a substantial gas (and money!) saving and a
sizable overall decrease of pollution.
(ii)
If renewable (i.e. wind, solar, etc.) or nuclear energy is used to generate
electricity, the environment impact caused by the energy sector may be
greatly reduced, and the benefits of the electric vehicle are not outweighed.
At this time, the major hurdles, which are preventing the widespread
implementation of electric vehicles, are all related to the fact that battery
technology is not adequately advanced yet. Namely, the major issues are: too low
battery energy performance (i.e. to high battery weight), too high battery price
and insufficient battery safety.
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Dpt. of Materials Engineering – Technion Energy Program
With the most currently advanced Li-ion technology, typical EV battery weights
about 240 kg for 160 km of one-charge-travel; highly performing EV (Tesla
Roadster) has 350 km one-charge-travel but its battery weights about 500 kg,
comprising one third of the car’s curb weight. This vehicle is now priced at
approximately €66,000 whereas ICE vehicle of similar quality (BMW Z4) costs
40% less and runs for 500 km after fuelling.
At approximately €13-15,000 per piece, the battery is an expensive component,
but an EV is expensive not only because of the costly battery but also due to the
high battery weight, so designers have to implement expensive weight-saving
aerospace-grade construction materials to compensate the battery weight.
The above deliberation hints that, first and foremost, the EV-related R&D is to be
focused on the cell chemistries with high energy performance.
In this relation, metal-air batteries appear to have a considerable promise since
these cells demonstrate the highest specific energy compared to all other
batteries. The reason is that the cells are utilising the ambient air, and so there is
no need to store the cathode reactant inside the battery. This feature provides a
substantial weight reduction. Just to give an idea how large the weight reduction
might be, it may be noted that in case of a common Li-MnO2 battery, the cathode
reactant’s weight is 30 times higher than the weight of the metal anode.
Up to now, the development of metal/air batteries is mostly focused on Zn/air
aqueous system, whereas Al-Si-Mg-Li/O2–redox couples have a substantially
higher specific energy than Zn/O2-redox couple. The reason of this is that Al, Si,
Mg and Li being highly reactive suffer a substantial corrosion in aqueous
electrolytes, and so the practically viable design of such Al-Si-Mg-Li/O2 cells should
be based on implementation of non-aqueous electrolytes.
The other important matter lies in the metal-air battery rechargeability. Aqueous
metal/air cells are primary systems par excellence, and up to now attempts to
develop a rechargeable Zn/air cell were unsuccessful; being a one-time use cells,
such systems don’t fit EV application. Contrastingly, non-aqueous metal-air
systems are in essence rechargeable.
Our group is the world leader of non-aqueous metal-air chemistry
R&D. We are currently participating in several projects, which are
related to the research related to Si-Al-Mg-Li/air cells.
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Dpt. of Materials Engineering – Technion Energy Program
• Stationary energy storage
Daily and yearly power consumption is very uneven, so power generation
capacity commonly exceeds the average yearly electric sales twice. The output
of main workhorses of world power production (the thermal coal-firing
powerhouses and nuclear powerhouses) is not malleable, and so certain “pickload power stations” have to be used. The hydraulic power stations are ideal for
this purpose but in most cases these are gas turbine power stations, whose
energy is expensive and which are highly polluting. The other issue is the need
of energy infrastructure, which is adequate for high power pick consumption.
The best solution is to use the “smart distribution greed” (SG); such SG
comprises of combination of energy-transporting means and energy-storing
means. The energy-transporting means are to convey the energy from the
power station to consumers, and energy storage facilities are to be allocated
near consumers being capable storing the energy during low demand hours and
supply the energy to the consumer during pick hours (load leveling facilities).
The introduction of SG would make the existing power production and energy
transporting capabilities to be adequate for several upcoming decades, and also
would avoid the need of pick-load power stations.
The other issue is that the calls on the development of alternative power
production also suggest the introduction of SG. Indeed, the available clean
power sources (wind, solar energy) have the variable nature and thus cannot
be practical without SG introduction.
Currently, the most promising candidate for such energy storage is chemical
power storage, i.e. a battery. The battery-based energy storage facility has
many attractive features. Specifically, it may work without human intervention,
in automatic mode, and needs only minor yearly maintenance, while the stored
energy is available on instant demand; the facility may be easily fortified and
may store energy for many hours in the case of emergency (wars, earthquakes,
hurricanes, etc.). It is possible to start with building a moderately-sized
battery-based electricity facility near particular consumer and extend it on
demand; this eliminates the necessity of investing a vast amount of money at
once and also makes it unnecessary to build new transmitting lines and
distribution facilities with expanding consumer power demands. All these
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Dpt. of Materials Engineering – Technion Energy Program
features make chemical power storage an attractive option for a net-centric
energy infrastructure - SG.
The power rating of such storage could be up to several tens of
megawatts; the energy storage rating may get up to hundreds of
megawatts. The storage is to be reasonably compact but the energy and
power density are not crucial parameters.
Really important features are:




low installment cost
low operational cost
long operational life
high efficiency
Currently redox flow battery technology are considering as holding
promise to suite these requirements; up to now, pilot facilities with flow
batteries have been build having several megawatt-hours energy rating
and several megawatt power rating. At the same time, this technology is
not sufficiently developed yet; the current state-of-art offers too high
installment cost, too low operational life and inadequate efficiency.
Our group is keeping track of this technology,
and is preparing to step up to the plate