Incorporating the campuses of Kensington; University College; Australian Defence Force Academy; St. George, Oatley; and the College of Fine Arts, Paddington
A new battery technology could hasten the move to electric vehicles, Professor Maria Skyllas-Kazacos said when giving the 1994 ERDIC Annual Lecture on 8 November.
Professor Maria Skyllas-Kazacos of UNSW's School of Chemical Engineering and Industrial Chemistry, was speaking of the vanadium battery that her group has been developing for the past 10 years.
ERDIC is UNSW's Energy Research, Demonstration and information Centre.
In collaboration, Mitsubishi Chemical Corporation and Kashima-Kita Power Co. of Japan, and Professor Skyllas-Kazacos' Battery Research Group at UNSW are continueing parallel research on applications of the vanadium battery.
Through Unisearch Ltd. UNSW's R&D, technology transfer and continueing education company, Professor Skyllas-Kazacos and her group have filed many patents covering the technology the group has developed for the instantly rechargeable battery that has attained efficiencies of 90 per cent.
Soon after the group began its battery research it chose vanadium, a little known but abundant metal, as a candidate for a new battery technology. While the small group's research made steady progress on a miniscule budget, Japan was spending hundreds of millions of dollars examining different energy storage techniques to help overcome its acute shortage of domestic energy supplies.
Mitsubishi has now identified the vanadium redox (reduction-oxidation) battery as technically and economically feasible and has teamed up with Professor Skyllas-Kazacos's group, to benefit from the UNSW findings.
Mitsubishi and Kashima-Kita see the battery as offering the best potential for load-levelling -- needed to accommodate the supply-demand mismatch between coal-fired power stations, which operate most efficiently at their full design capacity, and electricity demand, which fluctuates during the day and during the year.
The Japanese partners are now testing a vanadium battery for island resorts able to deliver 50 kilowatts and plan to have a 200 kW version operating in two years, and a 10 megawatthour grid-connected battery in four years.
By linking megawatt-sized batteries to power grids, electricity suppliers will be able to meet increased demand without increasing generating capacity.
In the meantime, the UNSW group has turned most of its attention to batteries for powering electric vehicles.
Despite 100 years of development of the lead-acid battery, neither it nor any other battery has proved satisfactory for extended use in electric cars. Professor Skyllas-Kazacos outlined these needs and said that she believed that the vanadium battery could meet them.
With the research now in progress, she expects to raise the specific energy (watt-hours per kilogramme) of the batteries from 20 today to 35 within a year, to 70, maybe 80 in two years.
With the great advantage of vanadium batteries -- that they could be recharged at a service station by pumping out spent electrolyte for recharging and pumping in charged electrolyte, or trickle-charged overnight on cheap electricity -- a specific energy of 70 to 80 would make the UNSW battery a prime contender for electric vehicles. The first candidates would be forklift and other heavy-work, short-travel vehicles such as urban busses, with braking energy converted into electrical energy for reuse.
As Professor Peter Rogers, the Chairman or ERDIC, noted at the end of the lecture, the strength and direction of questions from the audience indicated a lot of interest in the battery.
Mr Wal Lamberth, Unisearch's Manager of Vanadium Battery Projetcs, emphasised
the importance of the battery.
"The vanadium battery for vehicular applications offers a great
opportunity for Australian industry to get in at the beginning of a superior new
technology for which there will be a large global market as the need for energy
storage grows with the need to rationalise energy use," he said.
"With UNSW's other energytechnologies, particularly the solar
photovoltaic and high-temperature industrial developments being pioneered by
Professor Martin Green and Professor Graham Morrison, this University has a
comprehensive energy production and storage system it will soon be able to offer
Australia and the world. These are opportunities that we want Australian
industry to take up," he said.
Following Professor Skyllas-Kazacos's mention of the success that the group
had achieved with a relatively small amount of funding, Associate Professor
Geoff Sergeant, ERDIC's Director, said that research in Australia gave a high
return per dollar invested. "in many fields Australian research is at least
as good as any other. The main difference is that our research budgets are often
only 10 percent of overseas budgets, sometimes even less. Coal technology is
just one area where the Americans, for example, came to pick our brains,"
he said.
On July 26, Michael Egan. NSW Minister for Energy, welcomed Asia Pacific
Renewable Energy Symposium delegates. On their visit to the Solarch, solar
architecture facility, of the University of New South Wales.
The symposium was held in Sydney from July 26 to July 28 under the auspices
of the United Nations Economic and Social Commission for Asia and the Pacific.
Michael Egan said high rates to economic growth are forecast for the region:
"More and more power win be needed to run industry, light schools, heat and
cool homes and provide thousands of other economic and social services. It is
estimated that each and every year until 2010, Asia Pacific nations will
increase power generating capacity by more than Australia's present total
capacity of 34 gigawatts. The Asian Development Bank estimates around $US50
billion will be invested in new power projects by Asia Pacific nations between
1991 and 2000.
"The majority will be spent on coal fired power stations, putting
increascd pressure on the regional and global environment.
"I think governments in the region need to take a two pronged approach
that mininises the environmental impact of coal fired generation and encourages
the uptake of renewable energy sources. We should work to ensure that wherever
possible coal fired generators use technology that produces relatively low
levels of carbon dioxide and other greenhouse gases.
"Governments throughout the region should also sponsor programmes to
encourage energy efficiency and reduce demand for energy. We should also try to
direct much of the estimated $US50 billion investment into renewable power
generation."
Michael Egan told the delegates that a Government funded investment pool will
be established in NSW to back the commercialisation of renewable energy
technologies and promote the development and spread of demnd management
techniques and skills.
"It will be known as the Sustainable Energy Fund and established on the
advice of a working group which will include representative of Greenpeace, the
Australian Conservation Foundation, the Sustainable Energy Industries Council
and the energy demand management firm, Energetics.
The fund will go some way towards overcoming barriers to the uptake of energy
efficiency and the problems with any meaningful introduction of renewable energy
technologies.
"The Government will refine its policies towards renewable electricity
generation technology, cogeneration. increased land fill and coal bed methane
generation and greenhouse co-operative agreements with NSW industry,"
Michael Egan said.
Australia was introduced to mileage marathons in 1980. Ralph Sarich's orbital
engine won the first event at Sydney's Warwick Farm with a consumption of 2,948
miles per gallon, 0.096 l/100km.
Ford engineers broke this record in 1985 with a consumption of 5,107 mpg.
When Warwick Farm became unavailable, the event moved to Amaroo Park and an
invitation to participate was extended to schools, universities and TAFE
colleges.
Last year, Shell - event sponsor since its inception - decided not to
continue. Mary Packard and Associates, the organising body, could not gain a
major sponsor, so Mary Packard, Ron Patten and Archie White, financed the event
from their own pocke. With no major sponsor, they decided they could not run the
event this year.
To maintain continuity, a group of Canberra teachers will stage a simlilar
event in the ACT. With the endorsement of Mary Packard and Associates and Shell,
they will run the Australian Fuel Challenge at Canberra International Dragway
from October 26 to 29.
There will be two main divisions, open and schools, and each will have both
single seater and two seater commuter classes. An open class for commuter
vehicles capable, with minor modifications of being road registered, is expected
to be keenly contested.
For further information, phone phone Bob or Helen Alexander (06) 288 6845.
(from "Energy Focus" August 1995, Magazine of the NSW Department of
Energy, 29-57 Christie St. (PO Box 536), St Leonards, NSW 2065, Australia. Phone
+61 2 9901 8223 fax: +61 2 9901 8246 )
1. Introduction Photovoltaic plants (PV) are dependent of the acess to large
scale storage of energy produced during sunny days, PV systems have
traditionally employed lead acid batteries which are relatively cheap and safe.
1.1. The redox flow cell concept The redox flow battery system for energy
storage has a number of advantages over conventional rechargeable batteries.
First, by use of fully soluble redox couples and inert electrodes, undisirable
electrode processes can be eliminated and a large number of cycles can be
reached. Second, the storage capacity is determined by volume and concentraion
of the electorlytes while the size of te battery stack can be built
independently and thus a very flexible design is obtained.
The redox flow cell concept was first proposed by Thaller (1). The name redox
flow cell is derived from the nature of the electrochemical reaction processes
i.e. reduction and oxidation occuring in the cathodic and anodic electrolytes
during discharge and conversely during recharging processes. The redox flow cell
consists of two compartments having each fully soluble electrolytes and inert
electrodes separated by an ion-permeable membrane (Figure 1). The aqueous
solutions are circulated from the storage tanks into the half cell and back to
the tanks. At first the iron chloride - chromium chloride redox system, based on
the Fe(III)/FeII) and Cr(II)Cr(III) couples for the positive and negative sides
of the battery, respectively was selected.
Unfortunately the Cr(II)/Cr(III) couple showed poor electrochemical behaiour
and problem of cross-contamination appeared due to leakage in the ion-exchange
separation. Therefor the use of a System with the same reactive ions in both
halves of the cell has been proposed (2). During the discharge V(II) is oxidised
to V(III) while V(V) is redused to V(IV). The electrochemcial reactions involves
the passage of sulphate ions and hydrogen ions through the membrane. The
transfer of water partly bound to the migrating ions, partly due to the osmotic
pressure is typical for these memebranes. The origin of the electrolytes is
vanadylsulphate, VOSO4, dissolved in diluted suphuric acid. The initial charge
reactions are
2H+ + VO2+ + e- -> VO2+ + H2O eo = 1.00 volt (positive elektrodes)
V2+ -> V3+ + e- eo = -0.255 volt (negativa elektroden)
In the initial charging, twice as many coulombs are required for the negative
electrolyt (anolyte) than for the positive eletrolyte (catholyte). Therefore
when the cell is charged first time, twice the volume of catholyte is employed
in order to prevent overcharging of the positive half-cell and oxygen
generation. At the discharge the reactions are reversed.
The advantages of the vanadium redox flow cell compared with other secondary
systems are:
* the process at the electrodes does not involve any solid phase changing
during battery operation thus a very long life is expected
* the battery can be fully discharged without any damage and also left in a
discharged state for long periods of time
* the energy in the form of electrolytes can be stored at a remote place and
transferrred to battery stack
* the capacity can easily be changed by increasing or decreasing the volume
(or concentraion) of the electrolytes
* since all cells are filled from the same tank with electolyte they are in
every moment at the same state of charge
* cell reversal is not possible since the electrolytes circulates back to the
same tank
* fast recharge by replacing used (discharged) electrolyte with fresh
(charged) electrolyte is possible
The St Jorgen Vandium Redox Battery is designed and built for demonstration
and small scale experiments. It consists of a single cell with only two
compartments for the electrolyte. The cell configuration is shown in figure 2.
Figure 3 is a photography of the assembled cell.
The cell housing is made from plexiglass in two parts and they screw together
by bolts and nuts of stainless steel. It allows for a volume of 60 ml
electrolyte on each side of the membrane. To this volume one shall add the
volume of the two upper tanks, which containes the main part of the electrolyte;
about 2-5 liter each.
The electrodes are made from graphite (Svensk Special grafit AB). A solid
plate of graphite 10 mm thick and having a surface area of 100 cm2 is supporting
a plate of porous graphite 8 mm thick having an area of 90 cm2. The two plates
are heat bonded (National Cement carbon glue type C-34 from Svensk Special
grafit AB) to each other. A graphite rod of same material as the solid plate of
graphite and having a diameter of 8 mm is screwed into the base plate. The
details of the construction is shown in figure 4. 2.1.2. Electrolyte tanks -
"the vanadium wheel"
Four storage tanks with a capacity of 5 litres each were made of plexiglass (Ragnar
Bergstedt AB, G”teborg) The shape of the tanks was made to look like a quarter
of a circle. All four reservoirs were mounted on a 80 cm in diameter wooden disk
connected to stainless steel shaft. This construction allows the whole assembly
to rotate, thats why the name - "the vanadium wheel".
Inside the tanks long pieces of plexiglass are inserted and behind them are
light bulbs arranged. Thus a thin film of the electrolyte is obtained and the
light is transmitted through this film. This was made to be able to see the
colours of the elctrolytes typically for each state of oxidation:
Vanadium(II) sulphate = violet vanadium(III) sulphate = aqua green
vanadium(IV) sulphate = blue vanadium (V) sulphate = yellow
Unfortunately the colours are very dark at concentrations above 1 M and can
not observed without dilution or by transitted light in thin films be used for
indication of the state of charge.
The tanks with the electrolytes were connected with the vanadium cell by
teflon tubes. The eight electronically controlles stop-valves as seen infigure 5
regulate the flow of the electrolytes.
Imagine that the two upper tanks as well as the cell are filled with vanadium
(IV) and vanadium (III). The charging cycle begins and the voltage over the cell
increases. When the voltage reaches a pre-set value, the charging is stopped and
the cell is drained into the lower tanks and then refilled with solutions from
the upper tanks. When all electrolyte have passed the cell to the lower tanks,
the battery is fully charged. The wheel is then automatical rotated 180 degrees
and the discharging can begin. Infrared light detectors sence the flow of
electrolyte i-e- when te cell is empty "no flow is indicated and the valves
are open and shut according to the computer program.
A perflourosulphonic membrane Nafion 117 is used. The resistivity ot this
membrane is 1.5 ohm.cm2 according to the manufactuerr (I.E. Du Pont) It is
important that the membrane is soaked in the electrolyte a couple of hours
before it is inserted in the cell. This is to prevent shrinkage. To protect the
membrane for being scratced by the rather sharp edges of the porous graphite
electrode, a thin (1 mm ) soft, high porous (96%) microfiber glass separator was
placed on each side of the membrane.
where E = the cell voltage ec = the cathodic potential ea = the anode
potential R = the total inner resistance hc = the cathodic polarisation ha = the
anodic polarisation
The inner resistance R can be split into the resistance of the membrane, of
the electrode and the contact resistance. The polarisation has two terms: the
activation polarisation and the concentration polarisation.
The value of R can be minimised by modifying the design of the redox cell
i.e. by reducing the distance between anode and cathode, using thinner
electrodes and a membrane with lower resistnace. The polarisation is decreaed by
increasing temperature, concentration and the flow rate of the electrolyte.
One shall also notice that the discharges and charges as decribed below take
place in stagnant solutions. This is not always the case in other experiments
where the electrolytes are circulated continously trough the cell.
Following experiments were made to characterize the cell i) charging and
discharging at different currents to preset voltage ii) determination of the
inne resistance iii) polarisation measurements
The inner resistance was determined by fast switching the current from one
value to another (pulsed current). The sudden change of the cell voltage or the
electrode potential within 1-2 seconds is divided by the current to give the
appoximate opinion of the resistance.Table 1 shows the experimental values and
the mean value of R and also for 1 cm2 of the cell. All values are referred to
at 50 stae of charge.
The polarisation is measure in the same set of experiments by reading the
value of the cellvoltage after 30 seconds.
Table 1. Polarisation and IR-drop at the demo-cell 60 ml 1 M vaadium, 2 M
H2SO4 Electrode surface area 100 cm2
Current density IR-drop Polarisation (mA/cm2) (mV) (mV) 20 341, 324 109 15
245, 235 128 10 119, 144 54 5 79 31 Mean value of R = 15 ohm.cm2 or 15 ohm per
cell
The voltage versus discharge time for charging at three constant currents and
the discharge with the same currents is shown in igure 1a an d1 . The state of
charge at the beginning of the charging periods is close to zero. A complete
charge of the 60 ml 1 M vanadium (II to IV) sulphate should meed 96.5 Amin. The
charging has beenn only 63, 43.5 and 46 minutes (figure 1a). The Cut off voltage
is 2.0V but probably not high enough due to the high inner resistance to
indicate the fully charged electrolyte. The discharge (figure 1b) is made by 15
A, 0,8 A and 0.48 A to a ut off voltage of about 0.7-0.8 volt. The capacities
are 9, 13.6 nd 23 Amin. respectively and the result seems to follow Peukerts
equation rather well.
which is applicable to lead acid batteries and Ni-Cd batteries and expressing
the log(I) vs log (t) as a straight line.
The polarisation properties of redox cells have been characterised at 50 %
state of charge i.e. when the [VO2+] = [VO2+] and [V2+] =[V3+]. At that SOC the
cell was charged for 1 minute at a constant current varying from 2 to 16 mA/cm2.
After 30 seconds in idle the cell was discharge for 1 minute at the same current
density. The value of cell voltage after 30 seconds has been plotted versus the
current densty in figure 5. Since the inner resistance is known it is possible
to make correction for this and show the true polarisation curves.
The polarisation (overpotential) is the effect of mass transfer and charge
transfer mechanisms. At small deviations of the overpotential from the
equilibrium potential the relation is linear and polarisation can be expressed
Rcf << Rmt when the rate of transfer reaction is greater than the
limiting current (il) The rate constants for the reaction V(V) -> V(IV) and
V(II) -> V(III) are 1.9 and 5.6 .10-3 cm/s respectively which can be
recalculated to io = 0.183 and 0,540 A/cm2 That means that Rct is fairly small
and the polarisation is concentration dependent h = i. Rmt
with Rmt = 30.8 ohm for charging and Rmt = 6.5 ohm for discharging.
The all vanadium redox flow battery is an interesting concept for the future.
The demonstration cell as reported here, is by no means optimized to give best
capacity or power. However, some properties can be judged: the polaristion is
fairly low even tough the discharge has been made in stagnant solution. However
the utilisation of the electolyte seems low but - again - the measurements have
been made in stagnant solution, which certainly reduces the capacity.
The purpose of turning things up side down in the battery worlds seems to
have been fulfilled: the electrolytes flow through the cell, demonstrating the
"no-solid-phase -rection-cell" and one can see that the amount of
elektrolyte i.e. capacity, can be increased.
The technique to build vanadium cells is simple (you need not have them
hanging on the wall). The electrodes are made as bipolar electrodes in plastic
frames which are clamped together with the mebranes.All is assembled in dry
conditions, formation is not necessary, no pasting, no drying. Just fill up with
electrolyte and off you go!
A vanadium opportunity
ENERGY FOCUS
Taking up the Mantle
1.2 The advantages of the All Vanadium Flow Cell
* the vanadium chemicals do not harm the environment
2. The Vandium Redox Demonstraiton Battery
2.1 Battery construction
2.1.1 The electrodes
2.1.3 The membrane
3. Cell perfomance
The cell voltage at discharge is described by the expression
E = (ec-ea) -IR -(hc -ha)
with ec = 1.00 + 0.059.log{VO2+}{H+}2/{VO2+}
ea = - 0.255 + 0,059.log{V3+}/{V2+}
3.1 Experiments
3.1.1 Inner resistanace
3.1.2. Polarisation
Figure 3 The Peukert equation
C = Ikt
here C and k are constants - I and T have their usual meanings
3.1.3 Polarisation
h = i.(Rcf + Rmt)
where Rcf = charge transfer resistance
Rmt = mass transfer resistance
Conclusions
The Swedish Vanadium (Tadde-)
Battery