El Ministerio de Industria y el CSIC ya tendría que haber destinado varias decenas de millones de euros a investigar y promover las baterías de zinc-aire, una de las tecnologías más prometederas para un país como España, que ni tiene petróleo ni litio, pero sí abundantes recursos de viento y sol, y está esperando como agua de mayo una tecnología como las baterías recargables de zinc-aire, que tiene una densidad energética que triplica a las de las mejores baterías de litio.
El zinc puede competir en un futuro próximo con las baterías de litio, en todas sus variedades. Algunos expertos lo califican como el combustible eléctrico del futuro. Entre sus principales ventajas destaca su facilidad de carga y su alto potencial energético. A diferencia de otros tipo de baterías estas necesitan que el vehículo vaya equipado con un sistema de filtrado e inyección de aire y de un sistema de monitoreo a bordo.
Las baterías zinc-aire son del tipo primarias, osea que una vez agotada la carga no pueden recargarse sino que hay que extraer el zinc y cargarlo fuera de la batería, pero ahí es donde entra ReVolt con sus baterías recargables.
Las baterías de zinc-aire almacenan tres veces más electricidad que las de litio. Un tercio del zinc consumido, se produce a partir del reciclado del zinc usado. La industria está muy familiarizada con el zinc y los recursos son abundantes.
Las baterías de zinc-aire son una clara alternativa a las de iones de litio. Tienen una densidad energética de 370 Wh/kilogramo.
ReVolt Technology Selected as a Top-24 European Cleantech Leader
Recognized as One of the Most Promising Cleantech Companies in Europe
ReVolt Technology, Ltd, a technology company, which has developed a rechargeable zinc-air battery, today announced that it has been chosen as a one of the Top-24 leading European start-up and early stage cleantech companies from a pool of over 300 applicants. The Top-24 winning companies were selected by a committee composed of experienced cleantech investors and professionals across Europe to present at the Cleantech Summit 2009. The Cleantech Summit was held in Geneva, on June 17 and 18, where an international delegation of more than 140 influential investors, technology industry leaders, service providers and academics participated in the event. The selected companies span cleantech segments such as: solar, wind, wave and bio energy; energy efficiency and storage; clean transport; biomaterials and waste management.
“This summit is about what our society needs to address the climate change issue: collaboration. We are facilitating the collaboration between entrepreneurs and investors, start-ups and established companies, energy generators and energy users; and between business and politics,” said Bernard Vogel, President Cleantech Summit 2009. “Some very exciting start-ups took part in the Cleantech Summit 2009, many with the potential to impacts consumers’ lives for the better in the long term.”
ReVolt’s zinc-air, rechargeable battery technology provides a high energy solution for consumer and industrial market applications that is environmentally safe, reusable and recyclable. Revolt’s zinc-air technology offers up to three times the energy density of lithium-ion in an inherently safe package representing a major leap forward and compelling value proposition for energy-hungry devices.
“The ReVolt Technology team is indeed honored to receive recognition as one of Europe’s Top-24 cleantech companies,” stated James P. McDougall, CEO of ReVolt Technology, Ltd. “We are grateful for the selection committee’s decision to include ReVolt Technology as a member of this esteemed group of industry leaders. The summit provided a very useful platform for ReVolt Technology to present to a very dynamic delegation and facilitated collaboration with several of its members on some exciting and important opportunities.”
About ReVolt Technology
ReVolt Technology Ltd. is a technology company, which has developed a rechargeable zinc-air battery. ReVolt’s batteries may enable more high-power consumer devices and increase the lifetime of existing consumer devices significantly. The technology is a result of six years of intense research and development at SINTEF (the largest independent research institute in Scandinavia). Research on material combinations has solved issues historically related to the metal-air technology; power, lifetime and rechargeability. Details are available at www.revolttechnology.com
The European Tech Tour Association (ETT) was founded in Geneva in 1998 in response to the growing interest in emerging technology companies in various European regions. ETT is an independent, not-for-profit organization composed of key contributors to the high-technology industry. The association recognizes that continued prosperity in Europe lies in its ability to transform today’s innovative projects into tomorrow’s global technology leaders. In keeping with the theme, the Cleantech Tech Tour will compensate the carbon footprint for all participants. Details are available at www.techtour.com
RWE Innogy Invests €5.5M in ReVolt; Rechargeable Zinc-air Storage Systems
RWE Innogy, the renewable power generation arm of Germany-based RWE Group, is investing €5.5 million (US$7.3M) in ReVolt Technology AS, a technology company developing of rechargeable zinc-air storage systems. The RWE investment was part of a €10 million Series B round that included current investors NorthZone Ventures (Sweden), SINTEF (Norway), Sofinnova Partners (France), TVM Capital (Germany), Verdane Capital (Norway) and Viking Venture (Norway).
The new €10 investment combined with an earlier €5.5 million investment in 2007 by current investors brings the total B round commitment to €15.5 million and total amount invested in ReVolt technology since inception to €24 million (US$31.8 million).
High energy density zinc-air technology, although offering high energy density—about twice the gravimetric density (Wh/kg) and three times the volumetric density (Wh/L) of Li-ion technology—has been generally limited to low-power, non-rechargeable (primary batteries) applications up to now.
Barriers to successful commercialization have included low-power, rapid loss of power, and a lack of a satisfactory mechanism for recharging them. Secondary batteries that have used zinc as an anode active material can suffer from short cycle life due to dendrite formation during the charging of the battery, resulting in short circuits; and shape changes of the electrode, resulting in a loss of active surface area.
Revolt’s rechargeable zinc-air technology, in an inherently safe and cost-effective package, is working to address those issues and open up a variety of future markets, such as consumer electronics, specialty markets, and transportation.
Revolt had been focusing its development efforts initially on consumer electronics; RWE is interested in the larger-scale applications such as grid storage and electric vehicles.
Due to their high energy density, zinc-air batteries could be used not only for electricity storage from wind and solar power, but also for electric vehicles. In contrast to lithium-ion rechargeable batteries commonly used today, zinc-air batteries are more powerful, cheaper to produce, safer and more benign to the environment.
——Crispin Leick, RWE Innogy Ventures
ReVolt was spun-off from SINTEF in Norway to commercialize six years of R&D on a rechargeable Zn-air system.
Metal-air electrochemical cells use an anode made from metals such as zinc (Zn), aluminium (Al), magnesium (Mg), iron (Fe), lithium (Li) or vanadium (V) (earlier post) and a cathode made from a porous structure with catalytic properties for the oxygen reaction. An alkaline electrolyte maintains high ionic conductivity between the two electrodes. A separator between the anode and cathode prevents short circuits.
Discharging the metal-air cells entails the conversion of oxygen from the atmosphere to hydroxyl ions in the air electrode. The hydroxyl ions then migrate to the metal electrode, where they cause the metal contained in the electrode to oxidize.
Charging of metal-air cells converts hydroxyl ions to oxygen in the air electrode, releasing electrons. On the metal electrode the metal oxides or ions are reduced to form the metal while electrons are consumed.
ReVolt is focusing on the areas of power, battery life, rechargeability and compact size. Some issues remain to be addressed prior to successful market introduction, the company says.
ReVolt’s technology developments include placement of the zinc (microscopic localization) on the anode; humidity management in the cell; and a bi-functional air-electrode. In a bi-functional air electrode, both the oxygen reduction and oxygen evolution reactions occur.
RWE is among Europe’s five largest utilities and is active in the generation and transmission as well as the sale and trading of electricity and gas. RWE is also active in the water business in Continental Europe.
The investment in Revolt Technology AS is RWE Innogy’s third venture capital deal. Last year, the company bought shares in a UK developer of micro-wind turbines as well as in a Dutch company developing a process for the production of biocoal pellets.
ReVolt’ s rechargeable Zinc-air battery is the technology breakthrough that will breathe new life into consumer electronics – mobile phones, laptop computers, digital cameras, etc. – and give users the freedom to go further and the power to more than ever before.
Rechargeable Zinc-air batteries have more than twice as much energy than conventional Li-ion batteries, they cost less to manufacture, they are safer to use, and they are environmentally friendly. The net result is a new battery, developed by ReVolt, that will transform the way we use mobile electronic devices, multiply our lifestyle choices, and reenergize the business and pleasure of day-to-day life.
Reenergizing battery technology
The metal-air battery, which boasts high energy density and low production cost, is not a new concept in the portable power market, but today’s metal-air batteries are primary (non-rechargeable) and used almost exclusively for low power applications, e.g hearing aids.
The barriers to successful commercialization of metal-air batteries can be summed up as follows:
-They can’t deliver sufficient power
-They lose a lot of power very quickly
-The cell dry out, becoming useless after only a few months
-There is no satisfactory way to recharge them
Alternative solutions, like non-electrical refill batteries, are not at all suited to portable devices and/or their space- and power-hungry peripherals.
It would be difficult to overestimate the impact of ReVolt Technology’s breakthrough achievement in developing a metal-air battery that overcomes all of the above barriers to deliver:
POWER: ReVolt’s new technology has a theoretical potential of up to 4 times the energy density of Lithium-Ion batteries at a comparable or lower production cost.
LIFETIME: Extended battery life due to stable reaction zone, low rates of dry-out and flooding, and no pressure build-up problems.
RECHARGEABILITY: Controlled deposition with no short-circuit, high mechanical stability.
COMPACT SIZE: No need for bulky peripherals such as cooling fans or temperature control systems.
ReVolt Technology description
Metal-air batteries consist of a negative electrode made from metals such as zinc (Zn), aluminium (Al), magnesium (Mg), iron (Fe), lithium (Li) and a positive electrode made from a porous structure with catalytic properties for the oxygen reaction. An alkaline electrolyte is used to maintain high ionic conductivity between the two electrodes.
In order to prevent short circuit of the battery, a separator is placed between the anode and the cathode. On discharging metal-air cells, oxygen from the atmosphere is converted to hydroxyl ions in the air electrode. The hydroxyl ions then migrate to the metal electrode, where they cause the metal contained in the electrode to oxidize. In particular, the desired reaction in the air electrode of a metal-air cell involves the reduction of oxygen, the consumption of electrons and the production of hydroxyl ions. The hydroxyl ions can migrate through the electrolyte towards the metal electrode, where oxidation of the metal may occur, forming oxides and liberating electrons.
Charging of metal-air cells converts hydroxyl ions to oxygen in the air electrode, releasing electrons. On the metal electrode the metal oxides or ions are reduced to form the metal while electrons are consumed. Development of the air electrode in general has been focused on the use in fuel cell applications. Therefore, studies of the oxygen reduction reaction dominate. The alkaline fuel cell (AFC) system shows high reaction rates and stability for oxygen reduction with the use of non-noble materials.
The reaction takes place on finely dispersed catalysts with a high surface area for reaction. By careful control of the hydrophobicity and the pore size distribution, a stable three phase zone is established inside the electrode.
Typically, air electrodes in AFC applications show stable behaviour. Such systems are operated at temperatures of 60-90ºC. At lower temperatures increased lifetime has been shown. Before such electrodes can be used in secondary battery applications (rechargeable batteries) the electrodes have to be modified. Charging the battery requires air electrodes with additional high oxygen evolution rates.
Bifunctional air electrodes showing high rate capability and stability for oxygen evolution must be developed. Stable reactions for oxygen reduction and oxygen evolution over several hundred charge/discharge cycles are required for secondary metal-air batteries. Zinc (Zn) has been used in many batteries as the anode material. This is due to the high energy density of zinc and its chemical stability in the electrolyte. Zinc electrodes enable high current densities and a flat discharge curve. Battery systems such as the Nickel- Zinc battery, the Silver-Zinc battery, Zinc-Chloride battery, Zinc-Bromide battery the Zinc-Manganese battery etc. are well known.
A zinc electrode can be made from a solid plate, pellets or powder zinc materials. If powder material is used, an organic gelling agent is often added to allow sufficient electrolyte penetration and to maintain particle to particle contact. For secondary batteries with zinc as the anode active material, low cost and relatively high energy density can be obtained. This is offset by the short cycle life of the battery. The short cycle life is mainly due to the following:
· Dendrite formation during charging of the battery. Such dendrites penetrate the separator and cause a short circuit of the battery system.
· Shape changes of the electrode. This results in a loss of active surface area, contact inside the electrode or a local densification of the electrode.
Development of ReVolt’s portable battery has been achieved by focusing on the areas of power, battery life, rechargeability and compact size. Some issues remain to be addressed prior to successful market introduction.
One consideration for development of a metal-air battery for portable electronics is ensuring that it can provide sufficient power. The power capacity of a system is limited by the reaction rates of the electrodes and the conductivity of the electrolyte. ReVolt has developed high power electrodes. In combination with an electrolyte of high conductivity the ohmic voltage drop is minimized.
The air electrode
The oxygen reaction takes place within a thin flexible layer. Air diffuses into this layer through a network of hydrophobic channels. By capillary forces the electrolyte penetrates the structure. The liquid- gas interface established within the electrode creates a three phase reaction zone. High power is enabled by a stable high surface area reaction zone within the air electrode.
High current at a low voltage drop is shown. It should be noticed that currents as high as 200 mA/cm2 are obtained before diffusion starts limiting the reaction rate at a temperature of 20ºC. The result is obtained by choosing the correct materials and production methods. The use of a low-cost catalyst is of particular importance.
The zinc electrode
Zinc used as a battery anode is recognized as a good choice for high power battery applications. This is due to the flat discharge curve for zinc. ReVolt’s zinc electrode is made from carefully selected powder materials. The objective of the electrode is to maintain this flat discharge curve for electrodes that are stable over several hundred charge/discharge cycles.
High stability of the air electrode is crucial for use in rechargeable metal-air batteries. In order to make a stable air electrode the three-phase reaction zone should be stable for several thousand hours at high current densities. The degradation of the air electrode is related to the current density. At low currents and at open circuit potential, the electrode is stable. At high current s, radicals formed in the air electrode can alter the properties of the electrode, resulting in a loss of reaction rate and increase of cell resistance. The degradation mechanism is thus closely related to the current density and operating temperature.
Lifetime cycling tests at high current densities were performed to investigate any degradation. The high stability of the air electrode is a result of the careful choice of materials. The catalyst is provided on a stable carrier and a pore former is added to give a porous structure with a high surface area for reaction.
The total lifetime of the zinc electrode is given by the number of charge/discharge cycles available. The lifetime between charges is given by the energy density available from the zinc electrode. To reduce the loss of capacity at open circuit (self discharge) requires the prevention of unwanted dissolution of metal. A method for accomplishing this has been developed. Alloying the metal with elements that give high overpotential for the hydrogen reaction and a careful selection of materials are implemented.
The air electrode in a metal-air battery interacts with the environment by gas transport in and out of the air electrode. The hydrophobic backing layer prevents any liquid penetration. At low relative humidity and high temperature, water will evaporate resulting in a slow drying out of the battery.
ReVolt’s approach to this challenge is modification of the electrolyte and the electrodes. A stable water balance is obtained even at high temperatures and dry ambient conditions. After several thousand hours in test no weight loss is observed due to water evaporation in ReVolt’s modified system.
The use of bifunctional air electrodes gives many advantages to establish a compact rechargeable metal-air battery. In a bifunctional air electrode, both the oxygen reduction and oxygen evolution reactions occur. Previously, it has been show that high reaction rates of the oxygen reduction reaction are obtained with ReVolt’s electrodes. High power and lifetime for the oxygen evolution reaction is also obtained. High rates of oxygen evolution are obtained at low overpotent ial. Oxygen evolution at a potential of less than 2 V is important in order to preserve the catalysts and porosity of the electrode. Oxygen evolution rates of 200mA/cm2 are obtained at potentials less that 2 V. This allows rapid charging of the metal-air battery without degradation of the air electrode.
High stability of the oxygen evolution reaction is maintained after repeated charging (more than 100 cycles) at an oxygen evolution current density of 100-200 mA/cm2.
One critical part for enabling rechargeable metal-air batteries is the development of a rechargeable metal electrode. The electrode should not give unwanted dendrite growth, leading to short circuits in the battery or shape changes causing loss of capacity. The charge/discharge process is remarkably stable with high rates for both charge and discharge. After 200 cycles with 5 percent of total capacity, no dendrites or loss of capacity were observed.
The charge/discharge reaction proceeded up to about 50 percent of total capacity. A slight increase in capacity was observed with cycling. This is due to an increase in the available surface area during cycling. After 100 cycles the experiment was terminated. No dendrite formation was observed.
Introducing portable metal-air batteries in the consumer electronics market requires a compact battery configuration without peripherals such as cooling fans, temperature control systems or electrolyte circulation. ReVolt’s metal-air battery provides a compact battery without any such peripherals. The high mobility and activity of oxygen in the battery enables air diffusion to give sufficient power.