Apr 19 2011

Is Lithium-Ion the ideal battery?

Published by genportadministrator under Batteries

Today, the major battery systems are the rechargeable lead acid and the primary manganese dioxide-zinc: both have a long history and are at an advanced state of technical maturity.

The Lithium-Ion Battery (LIB), conceived and developed in Japan by Asahi Kasei Co. and first commercialized by Sony Co. in 1991, is poised to challenge these established systems as the demand for higher-performance battery systems continues.

Lithium has a low atomic number and a high electrode potential that results in significantly high energy density for the LIB compared to lead and zinc in the traditional batteries. However, the development of new high energy lithium systems has been neither simple nor easy. It has required a total system approach and the development of breakthrough technologies based on new anodes, cathodes and non-aqueous electrolytes to continue the steady improvement of high energy lithium battery systems.

The early rechargeable lithium cells were plagued with safety problems caused by the tendency of lithium metal anodes to form dendrites and powder deposits on recharging. The lithium metal rechargeable cells now are restricted mainly to small capacity coin cells.

Since lithium metal constituted a safety problem, attention shifted to the use of a lithium-intercalation material as an anode. H. Ikeda of Sanyo was the first to patent an intercalation material in an organic solvent such as graphite in his June 1981 Japanese Patent No. 1769661. Later, I. Kuribayashi and A. Yoshino developed a new cell design using an intercalation carbon anode and a LiCoO2 cathode and filed patents worldwide. Using a pilot plant developed for rechargeable Li-MnO2 cells, Sony Energytec Inc. began to produce commercial cells (called the Li-Ion Battery) based on the Asahi patents in 1991. They also introduced electronic circuitry to control the charge-discharge, the use of a current interrupt device to interrupt current flow on build-up of excessive internal cell pressure and the use of a “shut-down” polymer separator.

The name “Lithium-Ion” now is accepted by the battery community worldwide, although there is no lithium metal in the cell. However, very often lithium metal deposition occurs during charging with the graphite anode and it may cause the many troubles on the LIB. Both electrodes operated by intercalation of lithium ions into the structure of the active materials. AT Battery Co., a joint venture of Toshiba Battery Co. and Asahi Chemical Co., was the second to commercialize the technology using Asahi patent portfolio.

The early cylindrical 18650 cell LIBs (18 mm in diameter and 65.0 mm long) had a capacity of 800 mAh and an end-of-charge voltage of 4.1 V. The initial cells used hard-carbon anode materials, which had a capacity of about 200 mAh/g, and the LiCoO2 had a capacity of nearly 130 mAh/g due to 4.1 V charging voltage. The early lithium-ion cells used a propylene carbonate-based electrolyte. However, energy density of LIB improved rapidly and increased on average by 10% per year and has approached 3.1 Ah in 2010. Responding to pressure from device manufactures, the cell capacity improved through engineering and the introduction of graphite anodes, improved LiCoO2-based cathode materials and the introduction of electrolyte additives.

Other recent developments include the incorporation of a fire retardant, which retards the combustion of the solvent, and a new additive to improve the wetting of the separator. New electrolytes and/or additives also are under development.

Today, LIBs are used in very high volumes in low power applications, such as mobile phones, laptops, cameras and other consumer electronic products. They have many attractive performance advantages, which make them also ideal for higher power applications, such as automotive and standby power:

  • High energy/power density (about 4 times better than lead acid) and potential for yet higher capacities (high cell voltage of 3.6 Volts means fewer cells and associated connections and electronics are needed for high voltage batteries, so that, for instance, one lithium cell can replace three NiCad or NiMH cells which have a cell voltage of only 1.2 Volts).
  • Does not need prolonged priming when new; one regular charge is all that’s needed.
  • Relatively low self-discharge (self-discharge is less than half that of nickel-based batteries and they can retain charge for up to ten years).
  • Low Maintenance (no periodic discharge is needed and there is no memory).
  • Specialty cells can provide very high current to applications such as power tools.
  • No liquid electrolyte means they are immune from leaking.
  • Very small batteries also available. Solid state chemistry can be printed on to ceramic or flexible substrates to form thin film batteries with unique properties.
  • Low weight.
  • Can be optimised for capacity or rate.
  • Can be discharged at the 40C rate or more: the high discharge rate means that for automotive use the required cold cranking power or boost power for hybrid vehicles can be provided by a lower capacity battery.
  • Fast charge possible.
  • Can be deep cycled: the cell maintains a constant voltage for over 80% of its discharge curve. It thus delivers full power down to 80% DOD versus 50% for Lead acid. This means that in practice, for a given capacity, more of the stored energy is usable or that the battery will accept more starting attempts or boost power requests before becoming effectively discharged.
  • Very high Coulombic efficiency (Capacity discharged over Capacity charged) of almost 100%: thus very little power is lost during the charge/discharge cycles.
  • No memory effect and no reconditioning needed (as for nickel based batteries).
  • Tolerates microcycles.
  • Long cycle life: 1000 to 3000 deep cycles. Cycle life can be extended significantly by using protective circuits to limit the permissible DOD of the battery. This mitigates against the high initial costs of the battery.
  • Variants of the basic cell chemistry allow the performance to be tuned for specific applications.
  • Available in a wide range of cell constructions with capacities from less than 500 mAh to 1000 Ah from a large number (over 100) of suppliers world-wide.
  • Flexible form factor (manufacturers are not bound by standard cell formats): with high volume, any reasonable size can be produced economically.

For high power applications, which require large high cost batteries, the price premium of lithium batteries over the older lead acid batteries becomes a significant factor, impeding widespread acceptance of the technology. This in turn has discouraged investment in high volume production facilities keeping prices high and has for some time discouraged take up of the new technology. This is gradually changing and lithium is also becoming cost competitive for high power applications.

Among the limitations of LIBs, we can cite:

  • Requires protection circuit to maintain voltage and current within safe limits.
  • Subject to aging, even if not in use (but storage in a cool place at 40% charge reduces the aging effect).
  • Transportation restrictions (shipment of larger quantities may be subject to regulatory control); this restriction does not apply to personal carry-on batteries.
  • Internal impedance higher than equivalent NiCads.
  • Expensive to manufacture (about 40 percent higher in cost than nickel-cadmium).
  • Not fully mature (metals and chemicals are changing on a continuing basis).
  • Degrades at high temperatures and when discharged below 2 Volts.
  • Capacity loss or thermal runaway when overcharged.
  • Venting and possible thermal runaway when crushed.

Measurement of the state of charge of the cell is more complex than for most common cell chemistries: the state of charge is normally extrapolated from a simple measurement of the cell voltage, but the flat discharge characteristic of lithium cells, so desirable for applications, renders it unsuitable as a measure of the state of charge and other more costly techniques such as coulomb counting have to be employed.

Although lithium cell technology has been used in low power applications for some time now, there is still not a lot of field data available about long term performance in high power applications. Reliability predictions based on accelerated life testing however shows that the cycle life matches or exceeds that of the most common technologies currently in use.

These drawbacks are far out weighed by the advantages of lithium cells and are now being used in an ever widening range of applications.

In order to control battery performance and safety it is necessary to understand what needs to be controlled and why it needs controlling. This requires an in depth understanding of the fundamental cell chemistries, performance characteristics and battery failure modes, particularly lithium battery failures. The battery can not simply be treated as a black box.

The Battery Management Systems (BMSs) encompass not only the monitoring and protection of the battery, but also methods for keeping it ready to deliver full power when called upon and methods for prolonging its life. This includes everything from controlling the charging regime to planned maintenance. There are many varieties of BMS.

There are three main objectives common to all Battery Management Systems:

  1. protect the cells or the battery from damage;
  2. prolong the life of the battery;
  3. maintain the battery in a state in which it can fulfil the functional requirements of the application for which it was specified.

To achieve these objectives, the BMS may incorporate one or more of the following functions: cell protection, charge control, demand management, SOC (State of Charge) determination, SOH (State of Health) determination, cell balancing, battery’s history, authentication and identification, communications between the battery and the charger or test equipment and many others.

The cell voltage used for charging LIB is typically 4.2 Volts (charging to 4.1 Volts will increase the cycle life but reduces the effective cell capacity by about 10%). Battery lasts longer with partial charges rather than full charges. They can not tolerate overcharging and hence should not be trickle charged. Fast chargers typically operate during the constant current charging phase only when the charging current is at a maximum. They switch off at the point when the constant voltage, reducing current phase, starts. At this point the battery will only be charged to about 70% of its capacity.

Rechargeable lithium cells are used in a wide range of consumer products, including cameras, camcorders, electric razors, toothbrushes, calculators, medical equipment, communications equipment, instruments, portable radios and TVs, pagers and PDA’s.

They are fast replacing Nickel Metal Hydride cells as the preferred power in mobile phones. Laptop computers almost exclusively use lithium batteries.

Now high power versions of up to 1000Ah capacity and more are becoming available for use in traction applications in electric and hybrid vehicles as well as for standby power.

The price of Lithium cells continues to fall as the technology gains more acceptance: the target price for high power cells is around 300 $/kWh, but cell makers are still quite some way from achieving that.

Although lithium secondary batteries may cost two or three times more than the cost of equivalent lead acid batteries and even more when the necessary battery management electronics are taken into account, this is more than compensated for by their longer cycle life, which may be five to ten times the life of lead acid batteries. Valid cost comparisons should therefore take into account the lifetime costs as well as the initial capital costs.

As society advances, a variety of new technologies, machines and systems have been developed and more efficient industrial operations have been adopted. The concern for global warming and a clean environment along with the development of advanced electric and hybrid vehicles may be served well by advanced LIB. This situation has resulted in increased demand for high-performance batteries and power generation and storage. At the same time, demand has increased for a cleaner environment and a more efficient energy production, coupled with low power consumption systems. In this context, the LIB has made and will continue to make significant contributions and advances.

In the pictures below, you can see, respectively, the charging characteristics and the CC/CV 3 cycles charge/discharge and temperature monitoring (at 1C and 23°C) of 18650 LIB packs.





GENPORT‘s activity in designing Li-Ion battery pack BMSs involves, among others, the acquisition of cell’s electrochemical data using an Arbin battery tester, the configuration and parametrization of the fuel gauge and protection the integrated circuit and the BMS PCB (Printed Circuit Board) final design.

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Apr 19 2011

History of battery invention and development

Published by genportadministrator under Batteries

In June 1936, workers constructing a new railway near the city of Baghdad uncovered an ancient tomb. Relics in the tomb allowed archeologists to identify it as belonging to the Parthian Empire. The Parthians, although illiterate and nomadic, were the dominating force in the Fertile Crescent area between 190 BC to 224 AD. It is known that in 129 BC they had acquired lands up to the banks of the Tigris River, near Baghdad.

Among the relics found in the tomb was a clay jar or vase, sealed with pitch at its top opening. An iron rod protruded from the centre, surrounded by a cylindrical tube made of wrapped copper sheet. The height of the jar was about 15 cm, and the copper tube was about 4 cm diameter by 12 cm in length. Tests of replicas, when filled with an acidic liquid such as vinegar, showed it could have produced between 1.5 and 2 Volts between the iron and copper. It is suspected that this early battery, or more than one in series, may have been used to electroplate gold onto silver artifacts. A German archeologist, Dr. Wilhelm Konig, identified the clay pot as a possible battery in 1938.

In 1747 Sir William Watson demonstrated in England that a current could be sent through a long wire, using the conduction through the earth as the other conductor of the circuit.
In 1786, Luigi Galvani was remarkably close to discovering the principle of the battery, but missed it. In 1800, Alessandro Volta published details of a battery: that battery was made by piling up layers of silver, paper or cloth soaked in salt, and zinc. Many triple layers were assembled into a tall pile, without paper or cloth between zinc and silver, until the desired voltage was reached. Even today the French word for battery is ‘pile’ (English pronunciation “peel”.) Volta also developed the concept of the electrochemical series, which ranks the potential produced when various metals are in contact with an electrolyte. How handy for us that he was well known for his publications and received recognition for this through the naming of the standard unit of electric potential as the Volt.
The Voltaic Pile was not good for delivering currents for long periods of time. This restriction was overcome in the Daniell Cell. British researcher John Frederich Daniell developed an arrangement where a copper plate was located at the bottom of a wide-mouthed jar. A cast zinc piece commonly referred to as a crowfoot, because of its shape, was located at the top of the plate, hanging on the rim of the jar. Two electrolytes, or conducting liquids, were employed. A saturated copper sulphate solution covered the copper plate and extended halfway up the remaining distance toward the zinc piece. Then a zinc sulphate solution, a less dense liquid, was carefully poured in to float above the copper sulphate and immerse the zinc. As an alternative to zinc sulphate, magnesium sulphate or dilute sulphuric acid was sometimes used. The Daniell Cell was one of the first to incorporate mercury, by amalgamating it with the zinc anode to reduce corrosion when the batteries were not in use. This battery, which produced about 1.1 Volts, was used to power telegraphs, telephones, and even to ring doorbells in homes for over 100 years. The applications were all stationary ones, because motion would mix the two electrolyte liquids.

In 1859, Raymond Gaston Planté made a cell by rolling up two strips of lead sheet separated by pieces of flannel, and the whole assembly was immersed in dilute sulphuric acid. By alternately charging and discharging this cell, its ability to supply current was increased. An improved separator was obviously needed to resist the sulphuric acid.

1866 was the year of the Leclanchè carbon-zinc battery: it could be used in various positions and moved about without spilling. Carbon-zinc dry cells are sold to this day in blister packages labeled “heavy duty” and “transistor power”. The anode of the cell was zinc, which was made into a cup or can which contained the other parts of the battery. The cathode was a mixture of eight parts manganese dioxide with one part of carbon black, connected to the positive post or button at the top of the battery by a carbon collector rod. The electrolyte paste may also contain some zinc chloride. Around 1960, sales of Leclanché cells were surpassed by the newer alkaline-manganese batteries.

In 1881, Camille Faure‘s acid battery used a grid of cast lead packed with lead oxide paste, instead of lead sheets. This improved its ability to supply current. It formed the basis of the modern lead acid battery used in autos, particularly when new separator materials were developed to hold the positive plates in place, and prevent particles falling from these plates from shorting out the positive and negative plates from the conductive sediment.

Between 1898 and 1908, Thomas Edison, the most prolific of all American inventors, developed an alkaline cell with iron as the anode material and nickelic oxide as the cathode material. The electrolyte used was potassium hydroxide, the same as in modern nickel-cadmium and alkaline batteries. The cells were well suited to industrial and railroad use. They survived being overcharged or remaining uncharged for long periods of time. Their voltage (1 to 1.35 Volts) was an indication of their state of charge.

In parallel with the work of Edison, but independently, Jungner and Berg in Sweden developed the nickel-cadmium cell. In place of the iron used in the Edison cell, they used cadmium, with the result that it operated better at low temperatures, self-discharged itself to a lesser degree than the Edison cell and could be trickle-charged, that is, charged at a much-reduced rate. In a different format and using the same chemistry, nickel-cadmium cells are still made and sold.

The alkaline-manganese battery, or as we know it today, the alkaline battery, was developed in 1949 by Lew Urry at the Eveready Battery Company Laboratory in Parma, Ohio. Alkaline batteries could supply more total energy at higher currents than the Leclanché batteries. Further improvements since then have increased the energy storage within a given size package.

In 1950, Samuel Ruben (an independent inventor) developed the zinc-mercuric oxide alkaline battery, which was licensed to the P.R. Mallory Co., which later became Duracell, International. Mercury compounds have since been eliminated from batteries to protect the environment.

For many years, nickel-cadmium had been the only suitable battery for portable equipment from wireless communications to mobile computing. Nickel-metal-hydride and lithium-ion emerged in the early 1990s, fighting nose-to-nose to gain customer’s acceptance.

Pioneer work with the lithium battery began in 1912 under G.N. Lewis, but it was not until the early 1970s when the first non-rechargeable lithium batteries became commercially available. Lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest energy density for weight.

Attempts to develop rechargeable lithium batteries failed due to safety problems. Because of the inherent instability of lithium metal, especially during charging, research shifted to a non-metallic lithium battery using lithium ions. Although slightly lower in energy density than lithium metal, lithium-ion is safe, provided certain precautions are met when charging and discharging. In 1991, the Sony Corporation commercialized the first lithium-ion battery. Other manufacturers (e.g. A&T Battery Co.) followed suit.

Today, lithium-ion is the fastest growing and most promising battery chemistry.

In the figure below, a comparison of energy densities of various small, sealed common battery systems can be observed.

Below you will see a battery pack under construction by Genport designed for Small Vehicles.

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Apr 04 2011

Hydrogen Fuel Cells – Hannover Messe 2011

Published by genportadministrator under Events

April, 4th 2011

Definitely excellent the report of this first day of the fair. Our portable generation systems had a great success and they aroused the interest of everybody.

Especially, GENPORT 300 Hybrid Fuel Cell, still in the CE certificating phase, attracted for its design (the carbon fyber cover version is really noteworthy), its wearability and its strength. It is one of the principal news of this year of the hall 27.

GENPORT 300 Hybrid PEM Solar, instead, is unique in its field: with its walkable, light and flexible panels, it produces electrical energy, without any external fuel. Fantastic!

For the first time, as last, has been presented a little jar containing our solid hydrogen, GENFUEL; we opened it and showed it to the people.  It doesn’t produce heat, it is not explosive and it’s safe. In few grams of powder, you have got 400 Wh of energy. What an extraordinary thing!

From Hannover is all for today… tomorrow with the next updates!


April, 5th 2011

Also today, there has been a large flow of visitors at our stand from all over the world (Japan, United States, China, Turkey, India, Nigeria, United Kingdom, Denmark, Chile, Russia and many others), so confirming the big interest in our technologies and how international this fair is.

A lot of people have been attracted by our products for varies applications, in the nautical, militar, electromedical, camper van sectors and so on.

In most of all Fuel Cells field, we are the only ones to produce portable hybrid generators, even wearable!

Our GENFUEL got so much success, that has been called the “handy energy“!

From Hannover also for today is all… I will be in touch even tomorrow folks!


April, 6th 2011

This morning a big wave of Chineses and Koreans has crowded our hall 27, obviously also stopping over in our stand, in order to take pictures of our unequalled products. I have never seen such a crowd!

We also did a small experimental demo of hydrogen generation, putting our GENFUEL in a glass of water: everybody gaped, enchanted by this extraordinary fuel, so much safe and handy. Resounding!

Very interesting the request of a Danish sailor, who would like to cross the ocean in a green and ecological way; nowadays, batteries cannot provide such this shipping range, but our GENPORT 300 Hybrid PEM Solar system can allow him to undertake this venture!

Well then, you can notice that our portable generator systems are suitable for the most various applications.

And also for today from Hannover Fair is all… obviously tomorrow with the next news!


April, 7th 2011

The present day has been studded by the arrival of a lot of visitors from all over the world and many international delegations from all continents. Anyone was struck by our products, which have been defined “indispensable” in many emergency operations and in case of disasters, where electricity network is not available.

In fact, our portable power generators are primary utility devices for the first aid teams, who are faced emergencies and operate in the middle of unexpected catastrophes (the past few weeks case of Japan is a striking example).

There also have been many multinational distributors, with which we have had the opportunity to discuss several collaborations, in order to put our products on the market.

Through GENFUEL, we were the only ones to bring in fair the hydrogen safe storage for portable systems and mobile devices!

And also for today is all… Tomorrow the next updates!


April, 8th 2011

The last day of the exhibition today, with a very positive report for us! So, a good reason to come back next year, with other new products and, especially, with our unique hydrogen generator, fed with handy and safe GENFUEL cartridges.

Many others international distributors have proposed us today some collaborations, to market our products and use them in the most disparate applications and fields (military, portable electromedical devices, remote telecommunications, sailing, camping, off-grid residential and so on).

For example, a foreign company has proposed us to work together, to perform a super 5 kW generator powered by GENFUEL cartridges, because of the exceptional features of this solid fuel, its intrinsic safety, its high energy density and its no environmental impact.

There also have been a lot of overseas visitors, even two from Australia; they were fascinated by our technologies: GENPORT 300 Hybrid Fuel Cell’s wearability, GENPORT 300 Hybrid PEM Solar’s portability (without any external fuel!) and, obviously, our innovation, GENFUEL.

In short, Hannover fair is an absolutely international one and it has been a clear success for us!

Thank all those who came to visit us in fair and also all those who have daily followed us, instead, through this our blog!

And it’s all from Hannover… Now we’ll get set for go back home!  ;-)

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Mar 25 2011

Fuel cell vs battery: what is better?

There is a recent growing interest in the replacement of batteries by fuel cells for portable consumer electronics, such as cellular phones, laptop computers, digital cameras and so on. This is perhaps partly due to the success of lithium-based batteries in powering laptop computers, cellular phones and the like. The requirement for higher energy density or longer operational time between recharges was generally well served by the Li-ion battery and high-energy density nickel-based batteries, especially those based on metal hydrides. Safety and environmental factors were key considerations in addition to the high energy density of these batteries.

There is now growing pressure on battery manufacturers to further increase energy density for the next generation of portable electronic equipment, which will require much higher energy densities, if the equipment is to be conveniently portable. This is not just because of marketing and product differentiation – it is a technological requirement for high-bandwidth and advanced microprocessing applications, which demand much more power. The situation becomes critical as cellphones and laptop computers merge to provide users with broadband wireless and multifunctional portable computing capability. Unfortunately, battery technology is unlikely to keep pace with these growing power demands and laptop equipment manufacturers are already being faced with introducing various power down options and low-power components to save battery energy. In the future, this may severely limit the practical capability of the planned broadband computing devices.

Projections for the size and growth rate of these new product markets are impressive are beginning to inspire researchers and developers of fuel cell to address the issues of scale-down of their technology, which has generally and for some time now been targeting automotive and distributed power applications.

Because we are approaching the energy density limits of rechargeable commercial battery technology, small fuel cells are being considered as possible solutions to the problems of providing portable power, at least at a theoretical level. Although the primary interest is the advantageous energy content of electrochemical fuels, such as hydrogen or methanol, in terms of weight and volume, there are many factors that will influence and possibly hinder the changeover to a radically different powering technology. Customer considerations – especially cost, safety and convenience – will inevitably become the primary commercial factors in the success or failure of any new power source. These considerations will be especially critical for the successful introduction of fuel cells as replacements for batteries.

From the point of view of cost, fuel cells for the new applications look very promising. Their competition – batteries – becomes relatively expensive as the required energy storage rises for the new broadband computing applications. For example, the cost of adding 100 Wh of energy storage using methanol can be less than 1% of the cost of adding this energy in the form of battery materials. In addition, the carrying weight and volume of the stored energy is advantageously reduced by a factor of ten (in theory at least). The practical problem, of course, is the energy converter for the energy-dense fuel, i.e. the fuel cell itself. Scale-down of what is after all an energy-converting system consisting of a fuel cell plus a fuel supply, rather than a “simple” energy storing electrode couple, presents a technological challenge.

Unlike the relatively simple battery, subsystems for fuel cells are involved in the supply of both fuel and air and the removal of product water, and carbon dioxide in the case of hydrocarbon fuels. Miniature electromechanical delivery and control systems will add complexity which may affect the reliability and operational lifetime of the entire fuel cell system. These concerns will be in addition to the usual list of electrochemical and materials degradation factors which reduce the longevity of batteries, but which are less troublesome in fuel cells. Fortunately, since the main competition is a battery power source, with comparatively low energy content, the commercially acceptable or “allowable” cost of a small fuel cell may exceed US$ 5 per watt, even in mass consumer applications. This may allow for the introduction of more sophisticated and reliable miniaturized engineering solutions.

Safety concerns impeded the early introduction of the now successful Li-ion battery and must again be a primary consideration in the introduction of fuel cells. The safety consequences of the requirement for pure hydrogen in hydrogen-based fuel cells (e.g. PEMFC) must be addressed at the most fundamental design level for consumer applications. For instance, limiting the amount of free hydrogen in any part of such a fuel cell system would be important in satisfying safety regulations.

Another class of ambient temperature and pressure fuel cell being considered for portable equipment, is the liquid-fed direct methanol fuel cell (DMFC). From the safety point of view, this system suffers from the perception of toxicity of the methanol, which will have to be addressed.

The third customer consideration -convenience – is a demonstrable advantage of using fuel cells, in that recharging is eliminated, saving time and additional carrying weight for the consumer.

Reasonable comparisons between batteries and fuel cells can be made if, and only if, the total energy content, including converter, fuel and fuel tank, of the energy conversion device is compared with an energy storage device, such as a battery pack, have an equal amount of stored energy.

In other words, the total energy produced by each system must be measured under the identical load conditions (i.e. power profile) to obtain an accurate comparison between the two.

Fueled systems, which are in various stage of development, can be used to replace batteries or supplement them as part of a hybrid system.

Batteries have shown a continuous, steady increase in energy density for the last 50 years, from about 30 to 350 Wh/kg. The possibilities for further improvement are good and need to be pursued aggressively, but the pace of improvements is likely to continue to be slow compared with other areas of technology development. The most attractive candidates that have been demonstrated at high readiness levels are PEM/H2 systems. With the advent of small, lightweight stacks (e.g. Protonex), the performance could improve even further. A PEM/H2 system can include a Li-Ion battery, which could be used for brief peak loads. This system has the highest specific energy for long duration missions (24 hours or more) when one considers the total energy delivered. If hydrogen is unaccettable, DMFC could be developed further and could outperform primary or rechargeable batteries. There are opportunities for significant mass reduction in both of these systems, which will make these comparisons even better.

Energy conversion systems based on fuel cells become more attractive at the 72-hr mission length, where there is a potential for reducing the total mass by a factor of 4 or 5. They are all significantly better than rechargeable lithium ion and, with development, will be much better than primary Li/MnO2.

It should be noted that these systems are more complex than batteries alone and require that attention be paid to such things as start-up, fuel and oxidant control, water management, shutdown and storage below freezing.

Let’s give an example, comparing the two above mentioned energy storage systems for an application in which a constant power of 300W is required for a 200-hr mission (e.g. portable electro-medical devices, remote telecommunications displaced in off-grid locations, electronics-based equipment of soldiers, nautical setup and so on).

Using a Li-Ion 18650 rechargeable battery system, many pieces of battery would be required, with a total cost and a total weight of 55200 € and 332 kg, respectively. Power density would be of 180 Wh/kg and unit price of about 0.92 €/Wh.

Instead, if we use a PEMFC-based system with pre-packaged hydrogen (e.g. GENPORT300 Hybrid Fuel Cell with GENFUEL cartridges), the overall cost would be of only 7240 € (with a consumption of 150 “solid hydrogen” cartridges) and the total weight of around 124 kg. Therefore, the power density of such energy conversion system would be of more than 500 Wh/kg, with a unit cost of 0.12 €/Wh.

In essence, energy conversion systems based on fuel cells are somewhat better than batteries for long missions, but are more complex to operate. However, mission length is easily extended by fuel addition and the longer the mission, the more competitive energy conversion systems based on fuel cells become (see the under graphs). An added benefit is the ability to continue a mission (provided enough fuel is left) even if resupply is not forthcoming in 24 hours.

Fuel cell systems are currently one fourth as massive as rechargeable batteries for longer missions ( 72 hours). From a logistic perspective, pre-packaged fuels can be treated as battery packs as long as appropriate safety and handling procedures are developed. Such pre-packaged fuels (for instance in the form of appropriate cartridges) will enhance the attractiveness of fueled energy conversion alternatives. For the 72-hr missions, energy conversion systems are an attractive alternative to batteries and could offer fivefold to tenfold mass reductions. Finally, fueled systems become more attractive as power demand increase.

The various challenges in developing small portable fuel cells – including their cost, safety and technological feasibility – are being carefully examined as a solution to the growing portable power needs of the mobile workforce, and the major industries that support them.


An Ion Lithium Battery Pack includes Cells and a Battery Management System (BMS)

Genfuel reacts with water and generates pure Hydrogen.

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Mar 07 2011

Effects of temporary reverse voltage on proton exchange membrane fuel cell performance

Polymer electrolyte membrane fuel cells are gaining great attention as a source of power generation for automotive applications. One key requirement for automotive applications is that the fuel cell must be tolerant of frequent start-stop cycling. A new decay mechanism related to local hydrogen starvation, which may be present during start-stop procedures, has been discovered.

Before the start up of the power plant, air is present on both the anode and cathode due to leakage from outside air and/or crossover through the membrane. When hydrogen is introduced into the anode during start up, a condition is created where hydrogen occupies only part of the anode. This creates a high interfacial potential difference in the region where hydrogen is absent, causing carbon corrosion and oxygen evolution at the cathode electrode. A similar transition can occur during the shut down procedure, when the air, introduced to the anode from the outside or through the membrane, replaces the hydrogen. This mechanism, hereafter referred to as reverse-current, is also possible during operation when localized hydrogen starvation occurs, even for a short time. The performance of PEMFC was also decreased by uneven gas distribution in flow channel.

Potential inversion of one or more cells in a PEMFC stack could drastically reduce its performance or, in the worst case, seriously damage the entire stack, owing to thermal deterioration and perforation of the membrane electrode assembly (MEA). The causes of potential inversion are numerous, including inhomogeneous gas distribution, drying of membranes and flooding of electrodes. However, the symptoms are always the same: the polarization curve of such a malfunctioning cell is very steep and rapidly reaches the short-circuit voltage before the other cells of the stack.

Water condensation in the flow field, which can increase the input/output pressure difference, can prevent homogeneous hydrogen distribution in one or more cells (homogeneous gas supply in a fuel cell stack is very important in keeping the voltage of all cells at a similar value, particularly when the stack is operating at high current). These cells can reach negative voltage, long before other correctly supplied cells. Depending on the duration and degree of negative voltage, the fuel cells can recover or be rendered completely ineffective. The surface area loss of the cathode platinum particle by cell reversal was also detected.

One possible mitigation strategy is to employ system changes and stack design practices that can effectively mitigate this decay, without necessarily making any changes to the electrodes structures (e.g. the development of non-carbon-based catalyst supports, that are more corrosion resistant). These strategies include: (1) minimizing the time that the adverse conditions exist, and/or (2) controlling the potentials during start up and/or shut down using external loads, and/or (3) minimizing the number of adverse cycles that occur in a given application. These solutions are relatively simple to implement and are not overly expensive. Furthermore, they can enable one to meet the performance and durability requirements of almost any application, including those with a relatively large number of idle time and start-stop cycles (e.g. automotive), using existing materials.

Do you think these systems strategies are enough to mitigate the electrocatalyst degradation in PEMFC caused by cell reversal?

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Mar 07 2011

Electrocatalytic corrosion of carbon support in PEMFC and durability enhancement strategies

Polymer electrolyte membrane fuel cell is the most appropriate power source candidate for the next-generation electric vehicle and small-scale stationary power. In recent years, durability has been one of the most important issues to be solved before the commercialization of PEMFCs.

PEMFC performance loss under steady-state and cycling conditions has been attributed to the significant loss of electrochemical active surface area (EAS) of Pt catalyst, especially in the cathode, where it is subjected to low pH (< 1), high potential (0.6-1.2 V), high oxygen concentration and high temperature (50-90 °C). It was found that the Pt particle agglomeration could be accelerated by both potential cycling and steady-state processes. It has also been observed that the Pt electrode could dissolve to some extent in PEMFC operation process. Pt dissolution-deposition and agglomeration lead to the increase of Pt particle size (sintering), which results in the decrease of the Pt EAS. Thus, the fuel cell performance is decreased.

A variety of carbon materials with high surface areas are widely used as the supports for Pt catalyst. As the catalyst support, besides the enhanced catalytic activity, the support should show good corrosion resistance because the corrosion behavior might affect the performance and stability of the Pt catalyst, especially in the cathode of PEMFC. This is because that oxygen reduction reaction occurs at potentials closer to those where oxidation of carbon can also happen. When carbon is oxidized, some Pt particles may detach from the carbon support, resulting in a decrease of catalytic activity of the catalyst. And the interaction of Pt-support may be weakened. Thus, carbon material corrosion plays a negative effect on the stability of the Pt/C catalyst. Furthermore, the corrosion rate of carbon catalyst support is accelerated in the presence of Pt-containing catalysts.

The degradation of carbon on PEMFC electrodes has been reported as carbon corrosion recently. These carbon corrosion phenomena are fatal problems for the PEMFC commercialization because of the short life time. The developments of catalyst materials, cell designs and the management of operation condition are important to solve these problems.

Generally speaking, the carbon corrosion requires high overpotential in PEMFC because of slow kinetic properties, though the carbon might start to be oxidized even at 0.2 V (vs. RHE) based on thermodynamics. In steady PEMFC operations, the carbon materials on both electrodes are rarely exposed to such high potential. But, in transient conditions, the carbon materials on electrodes are often exposed to such conditions. Some cases are predicted: start up, after shut down, load change, partially hydrogen starvation and so on. In every case, it is predicted that the hydrogen deficiency or hydrogen and oxygen co-existence on anode electrode will cause a large enough overpotential between the solution and the cathode metal to oxidize the carbon supports on the cathode electrode. Fuel starvation on the anode side (i.e. low anode stoichiometry) is one of the most damaging operational modes of fuel cells and fuel cell stacks. In particular, high current densities are leading to critical conditions, especially during dynamic operation. Fuel starvation caused severe and permanent damage to the electrocatalyst of the PEMFC and it must be absolutely avoided even if the operation under fuel starvation is momentary.

Catalyst durability study in PEMFC is a difficult topic because of the lengthy duration of the test time required and the complexity of failure analysis. One strategy to reduce Pt/C catalyst performance degradation due to carbon corrosion is to use alternative more stable carbon support (for example carbon nanotube). Another approach for increasing Pt/C catalyst durability is alloying other transition non-precious metals with platinum.

Interaction between the carbon support and the Pt plays an important role in the properties of the Pt/C catalyst. It has been demonstrated that this interaction is attribute to the electron transferring from platinum to carbon support. Electronic structure change of platinum catalytic layer by the presence interaction leads to the change of the catalyst properties. Generally, this electronic interaction has the positive effect towards the enhancement of catalytic properties and the improvement of the catalysts’ stability in PEMFC operation. Oxygen surface groups are of greatest interest in the preparation of carbon-supported catalysts and can be obtained through surface treatment of carbon by chemical methods with different oxidants. Proper heat treatment of carbon support can increase the stability of Pt/C catalyst.

The promising strategies for the durability improvement of Pt/C catalysts are: (a) building proper surface functional groups (including surface oxygen functional groups) or increasing the basic sites on carbon supports to enhance the Pt-C interaction; (b) increasing surface stability of carbon support, e.g. increasing the hydrophobicity of carbon support through proper surface treatment; (c) preparing catalysts with high platinum uniformity and low platinum load.

In your opinion, what of these budding strategies plays the leading role in durability improvement of carbon supported platinum catalyst?

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Mar 03 2011

Sodium borohydride vs ammonia borane, in hydrogen storage and fuel cell applications

Boron- and nitrogen-based chemical hydrides are expected to be potential hydrogen carriers for PEM fuel cells, because of their high hydrogen contents. Among them, sodium borohydride (NaBH4, denoted SB) and ammonia borane (NH3BH3, denoted AB) have attracted much attention as promising hydrogen storage materials.

There are many similarities between SB and AB in their features and applications. Nevertheless, SB and AB as hydrogen storage materials do not compete. Rather, SB is intended more to portable technologies, while AB to vehicular applications.

Due to the fact that the US DOE has in a way compared SB and AB, it may be beneficial and interesting to compare these hydrides in terms of their basic and their state-of-the-art for either application.

SB is a versatile boron hydride. It is widely utilized in industrial processes (e.g. pharmaceutical, paper blenching and wastewater treatment). Accordingly it is produced in large amounts. Ever since the late 1990s it has also been suggested as a promising source of hydrogen because it contains 10.8 wt% of hydrogen. Stored hydrogen can be released by thermolysis or hydrolysis. Otherwise, SB can be oxidized to liberate eight electrons and thus it can power the direct borohydride fuel cell (denoted DBFC).

Unlike SB, the utilization of AB is not widespread. For example, it finds a use in organic chemistry as an air-stable derivative of diborane. This is especially detrimental for its production cost. Actually AB is a promising material by virtue of its gravimetric hydrogen storage capacity of 19.5 wt%. Besides this, it is the fuel of the direct ammonia borane fuel cell (denoted DABFC).

For both boron hydrides, finding cost-effective production routes with the prospect of application is one of the main objectives. Investigations are in progress but none of the proposed routes has reached sufficient efficiency. One way to reduce the cost is to recycle the spent fuel (i.e. the reaction by-products) back to the hydrides. Both hydrides suffer from their high cost and AB is even more expensive than SB.

Safety is important for chemicals intended for large-scale utilization. Information on safety is generally available in the chemicals’ material safety data sheet. The few about AB are incomplete. The ones on SB are much more complete. SB and AB are white solids. They are recognized as being safe and stable at room temperature if stored in a closed vessel and anhydrous medium. Both are moisture sensitive, hydrolyzing and generating hydrogen; to be stable and safe, AB must be of high purity. The main difference between SB and AB is the thermal stability. AB decomposes at very low temperatures in relation to SB.

Neither boron hydride is mature enough to envisage applications, especially automotive applications. Both suffer from low (not-optimized) hydrogen storage capacities, inefficiency in spent fuel recycling and catalyst inefficiency in terms of durability. With respect to SB, the most efficient process is hydrolysis; with respect to AB, the most efficient hydrogen release reaction is thermolysis. This has consequences with regard to their potential applications. It appears that SB is more suitable for portable applications (commercially available) if it is hydrolyzed, while AB is suitable for automotive applications if it is thermally decomposed. In other words, SB is not really competing with AB because they are intended for different, specific applications.

The question that arise is: what are the effective capacities of SB and AB for such application?

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Feb 03 2011

Cold start-up of PEMFCs

The polymer electrolyte membrane fuel cell (PEMFC) is widely regarded as a potential power source for portable and mobile applications, due to its noteworthy features of high efficiency and zero emission.

Successful start-up from subzero temperatures is of paramount importance for the commercialization of PEMFCs for practical applications, such as backup power and automotive applications.

Under freezing environmental conditions, water produced at the cathode has a tendency to freeze in open pores in the catalyst layer and GDL, rather than be removed from the fuel cell, thus creating mass transport limitations which, eventually, end the ability for operation.

Even though various external heating methods can be used to ensure the cold start capability, the volume and weight of the system, as well as the operation complexity and installation costs, all increase with the increment of the external heating power requirement.

Analysis of the various cold start processes to achieving optimal design and operating strategy is therefore critical to simplify or cast off the external heating system.

While the characteristics of PEMFC dynamics have been studied by several groups, research on PEMFC cold start-up is relatively new and some aspects of degradation caused by freeze/thaw cycling are discussed controversially in literature.

Water is produced during the operation of a fuel cell; in PEMFCs, water within the cell is necessary to ensure high protonic conductivity of the polymer electrolyte membrane. During normal operation, the generated waste heat is sufficient to keep the water within the cell above the freezing point, even at ambient temperatures significantly belov 0°C. Howevwr, when fuel cells are switched off under sub-zero conditions, the volume expansion by ice formation within the cell can lead to structural damage.

In order to ensure good gas diffusivity and to extend the electrochemically active surface area, the materials of the gas diffusion layers, micro-porous layer and electrodes are highly porous. If water freezes within these media, volume expansion can lead to cracks in their structure and a change in the pore size distribution of the electrodes.

The physical state of water within the membrane seems to be a key issue in membrane degradation under freezing conditions. Due to the high capillary pressure in small pores, the freezing point of water within the membrane can fall below 0°C. In a Nafion membrane, besides free and loosely bound freezable water, non-freezing water can be present, which is still moveable even at –20°C.

For the membrane/electrode interface, some authors reported delamination of the electrodes from the membrane due to freeze/thaw cycling, while some others didn’t find any indication for delamination of catalyst layers. Performance degradation in PEMFCs is highly dependent on the cell components.

Purging with reactant gases (dried or humidified) seems to be a promising approach to prevent degradation of PEMFCs caused by freeze/thaw cycling. Such purging procedures are applied before switching off the cell, in order to remove residual water from the porous media.

In summary, to avoid degradation at low temperatures, water has to be removed before freezing from the cell or the PEMFC components have to be redesigned with greater material flexibility to allow volume expansion at the phase transition of liquid water to ice.

What do you think is the best mitigation strategy in order to allow a cold start-up, preventing a cell degradation at sub-zero temperatures?

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Feb 03 2011

Hydrogen generation through hydrolysis of sodium borohydride

The increasing energy demand and the contemporary concern about urban environment raised the necessity to develop a hydrogen-based economy; it requires the development of hydrogen storage technologies.

Hydrogen can be stored and transported in different ways, each one showing advantages and disadvantages: as compressed gas, in liquid form, as metal hydride. In carbon nanotubes, in metal-organic frameworks. In each system, hydrogen is reversibly loaded and released; the temperature and pressure of the tank control the kinetic of the absorption/desorption process..

The chemical hydrogen storage represents an alternative approach: the highly efficient production of pure hydrogen by hydrolysis of chemical hydrides, such as sodium borohydride (NaBH4), could make the transition to a “hydrogen economy” a reality.

Hydrogen from borohydride hydrolysis can be supplied to a PEMFC on demand to power mobile electronic devices, such as mobile phones, laptop computers and so on.

Among the different chemical hydrides, sodium borohydride is very stable and easy to handle and it has been selected for its high hydrogen content. Moreover, it can be obtained from borax, which is a globally abundant natural substance.

Solid state sodium borohydride belongs to a group of chemical hydrides based on metal-hydrogen complex, that can react spontaneously and exothermically with water, in the presence of catalysts or acids, and release pure hydrogen via hydrolysis reaction.

A sodium metaborate (analogous to borax) could be formed as a by-product during the reaction, but it is water-soluble and environmentally benign.

Hence, sodium borohydride is regarded as a promising hydrogen source with the prediction that the water vapor presented in the hydrogen gas stream can be used to humidify the PEMFC membranes.

However, sodium borohydride hydrolysis reaction is very fast in acidic media, while slows down with increasing pH, so that aqueous sodium borohydride solutions may be considered stable at pH > ca. 13.

In fact, the most favoured technology for hydrogen generation from sodium borohydride is, to date, contacting an alkaline solution of sodium borohydryde (eg, NaOH + NaBH4) with suitable catalysts that accelerate the reaction to practically acceptable rates. This technology has some drawbacks: handling of caustic solutions; using transition metal catalysts, which may be expensive and make the disposal of by-products difficult; catalyst deactivation due to agglomeration and borate film deposition on its surface.

A different approach is based on hydrolysis of NaBH4 in acidic medium: the acids varied greatly in effectiveness but, in general, the stronger acids produced the greater acceleration. The reaction with some organic acids doesn’t involve any harsh solution and results in environmentally benign by-products.

What do you think is the best way to generate hydrogen from hydrolysis of sodium borohydride? In the presence of catalysts or acids? And why?

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Jan 23 2011

Energy Storage

GENPORT systems are based on  polymeric membrane fuel cell.

Hydrogen operates as a fuel and it supplies the anode, whereas air enters the fuel cell from the cathode side.

If the fuel cell is used instead of a secondary battery, the recharging time will be related to the time necessary for replacing the cartridge, instead of several hours which would be necessary for recharging an accumulator pack.

Moreover, transforming chemical energy into electric energy, without combustion, it provides an absolutely clean and non-polluting process, since the single residue will consists of water steam.

An hybrid system combines quick and easy start of batteries and fuel cell, utilizing hydrogen as fuel.  This type of system technology coniugates both energy density  and safety requirements, extending  runtime as well as providing pick power when requested for limited time.

This emerging technology has a potential to benefit of the expected future improvements in the field of hydrogen and ion lithium storage technologies .

Where do you see the  portable fuel cell technology is moving in the next 10 years?

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