UNIKEN The University of New South Wales

Incorporating the campuses of Kensington; University College; Australian Defence Force Academy; St. George, Oatley; and the College of Fine Arts, Paddington

 

--- No.379 (No 19 of 1994) fortnightly 18.November 1994 ---

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.

 

By comparision, the lead-acid battery has a rating of about 35.

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.

 

(In the same publication:)

A vanadium opportunity

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.

ENERGY FOCUS

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.

Taking up the Mantle

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 )

A Vanadium Battery for Demonstration at St Jorgen Park (The PROPHECY - project)

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.

 

1.2 The advantages of the All Vanadium Flow Cell

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 vanadium chemicals do not harm the environment

 

2. The Vandium Redox Demonstraiton Battery

 

2.1 Battery construction

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.

 

2.1.1 The electrodes

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.

 

2.1.3 The membrane

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.

 

3. Cell perfomance

 

The cell voltage at discharge is described by the expression

 

E = (ec-ea) -IR -(hc -ha)

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

 

with ec = 1.00 + 0.059.log{VO2+}{H+}2/{VO2+}

 

ea = - 0.255 + 0,059.log{V3+}/{V2+}

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.

 

3.1 Experiments

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

 

3.1.1 Inner resistanace

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

 

3.1.2. Polarisation

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.

 

Figure 3 The Peukert equation

 

C = Ikt

 

here C and k are constants - I and T have their usual meanings

which is applicable to lead acid batteries and Ni-Cd batteries and expressing the log(I) vs log (t) as a straight line.

 

3.1.3 Polarisation

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

 

h = i.(Rcf + Rmt)

 

where Rcf = charge transfer resistance

 

Rmt = mass transfer resistance

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.

Conclusions

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!

For further information see also The Swedish project (bad pages!)
The Swedish Vanadium (Tadde-) Battery

--------------------here the usenet-text----------------

 

sci.chem.electrochem

A G wrote: > In article Norbert writes: > >I heard something on Vanadium Batteries on Radio Australia > >"science file" (ABC) they raved about their future use in homes > >and EVs. > >is there a web-site concerned with Vanadium Batteries...?

> Various vanadium oxides (V2O5, V6O13, etc.) differing in their > crystallographic structure and initial composition have for years > been > used as the positive (cathode) intercalation > materials in rechargeable > Li batteries. Valence Technology, Hydroquebec, > Dowty and many others > have described their properties and performance in considerable > detail. These are all intermediate-voltage systems > (2-3.4 V per cell).

> Tony > --------------------- > Antoni PWr '72 'Atoms are not things' > W. Heisenberg

 

This is true but not what he wanted to know.

The radio report would probably be about Vanadium Flow Batteries, which the University of NSW (I think) have been working on for several years.

They use two half cell based on Va oxides in different oxidation states.

They could be recharged by replacing the Va solns for each cell, (ie external recharge). And also have uses in Solar houses.

 

A nice concept, with some promising results.

Try a web search, or check back issues of Nature, who have had stories on it.

Paul Connor Dunedin New Zealand.