ReVolt Develops Rechargeable High Energy Zinc-Air Battery

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. Further information on ReVolt Technology is available on the Internet at

ReVolt announced it has selected Portland, Oregon as the location for its US headquarters and manufacturing center. By locating in Oregon, the company will be eligible for Business Energy Tax Credits from the Oregon Department of Energy for battery research and production.

Securing government grants and tax credits will allow ReVolt to significantly accelerate its operations in Portland and US expansion. ReVolt’s zinc-air batteries deliver more than twice the energy of conventional rechargeable designs such as lithium-ion. Made using naturally abundant zinc, the batteries have low manufacturing costs and reduce dependence on imported fuels and other energy materials. They degrade into environmentally-safe substances when exhausted, cutting pollution risks and the need for costly battery waste capture programs.

“In applying for government research funding, ReVolt is answering these agencies’ call for innovative technologies driving energy independence and US leadership in advanced battery designs underpinning the next generation of vehicles, networked devices and power grids,” said James P. McDougall, CEO of ReVolt Technology. “There is a tremendous, mutually-beneficial opportunity in Portland’s clean-tech sector and clean energy stimulus programs to fast-track our proven technology and production goals if we are among innovators selected for research funding.”

“For over 100 years zinc has been known as a good and safe source of energy. Zinc’s attributes of high energy and power and easy storage makes it suitable for a variety of battery, fuel and flow cell applications such as the well known button cell battery commonly found in hearing aids. Zinc batteries are now also used in computers and cell phones. Newer and bigger zinc energy storage systems include flow cell applications like the one developed by Revolt Technology,” said, Johan Van Wesemael, Manager of Technology & Market Development for the International Zinc Association (IZA).

“Through the Zinc Energy Storage Technology (ZESTec) consortium, the International Zinc Association promotes the use of zinc in batteries, fuel cells and flow cells,” Van Wesemael added. “Zinc is readily available and fully recyclable without loss of its properties. An increasing number of zinc batteries can be recharged, making it a truly sustainable source of energy.”

ReVolt’s announcements received broad support from state and federal officials intent on fostering both innovative, clean energy technologies and US leadership in this emerging, fast-growing industry.

“Oregon has shown again that supporting efforts to reduce our greenhouse gas emissions is an effective economic development strategy that delivers jobs to Oregonians,” Governor Ted Kulongoski said. “We can attribute today’s good news to our commitment to the next generation of lower and zero-emission vehicles – and the state’s business incentives that foster innovation and grow Oregon’s renewable energy sector.”

“ReVolt’s revolutionary technology is a great addition to Oregon’s clean energy community. With market leaders in solar, wind, bio mass and wave energy located here, Oregon has emerged as a clean energy hub,” U.S. Senator Jeff Merkley (D-OR) said. “It’s thrilling to see innovative companies like ReVolt reshape our technology industry, create jobs and lead Oregon’s economic rebound.”

“ReVolt’s decision to locate its North American headquarters in Portland confirms Oregon’s position as a world leader in the alternative energy industry,” said U.S. Senator Ron Wyden (D-OR). “Once brought to market, ReVolt’s batteries will be a key factor in developing the next generation of clean, green vehicles and in the future of renewable energy storage technology. That’s good for business, good for the environment and good for bringing family-wage corporate and manufacturing jobs to Oregon.”

“I’m very excited that ReVolt Technologies plans to site its U.S. headquarters in Portland, Oregon,” said Congressman David Wu (D-OR), who represents Oregon’s 1st Congressional District. “This decision will generate scores of green, family-wage jobs and further cement our region as the sustainability capital of the world.”

"ReVolt’s entry to the Portland innovation landscape couldn’t be coming at a more critical time," said Portland Mayor Sam Adams. "Not only will ReVolt’s American headquarters and manufacturing operations bring jobs and investment to our region, their presence is further proof of our model — that sustainability and economic prosperity go hand in hand here in Portland."

ReVolt plans to employ up to 75 highly skilled employees at its Portland site during its battery development
phase and up to 250 employees in subsequent pilot and production phases. After months of extensive site reviews and research throughout the US, ReVolt determined Oregon offers the best ecosystem for developing a truly transformational energy storage solution for electric vehicles and renewable energy generation.

“Oregon’s demonstrated commitment to the electrification of transportation, renewable energy generation and storage combined with its strategic plan and commitment to support related economic development made it a clear choice for ReVolt Technology,” McDougall added. “We are impressed with Oregon’s alignment with the current US Administration’s leadership to support the development of transformational energy storage solutions that reduce the dependence on foreign sources of energy and related materials.”

Initially developed in Norway, ReVolt’s patented zinc-air technology is based on research conducted at one of Scandinavia’s top scientific institutes. The company’s US expansion coincides with increasingly sophisticated energy storage demands from consumer electronics makers, vehicle designers and energy utilities. Offering a high-energy storage platform that is both durable and environmentally safe, ReVolt’s battery technology offers these industries a major leap forward.

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.


Air electrode

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.

Zinc electrode

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.

Humidity management

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.


Air electrode

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.

Zinc electrode

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.