La tecnología zinc-aire respetuosa con el medio ambiente encuentra su mejor aplicación en prótesis de oído, aparatos electrónicos portátiles y en el sector automotriz. Las baterías de zinc-aire han reemplaza por completo las baterías de mercurio en las prótesis de oído.
La tecnología zinc-aire, una tecnología simple, efectiva y de bajo coste, puede ser utilizada como una solución alternativa en el sector automotriz y en los aparatos electronicos portátiles.
Según la consultora Frost & Sullivan, el mercado mundial de baterías de zinc-aire generó unos ingresos de 251 millones de dólares en 2005, que aumentará rápidamente debido a la mayor utilización de las baterías zinc-aire en aplicaciones emergentes, como los vehículos eléctricos.
Las baterías zinc-aire son del tipo primarias, por lo que una vez agotada la carga no pueden recargarse sino que hay que extraer el zinc y cargarlo fuera de la batería. Sin embargo, la carga del zinc es fácil y rápida.
Uno de los grandes inconvenientes de la tecnología metal-aire es el hecho de que se trata de baterías primarias no recargables. Ello hace que sea necesario comprar pilas nuevas o tratar de sacar el electrolíto y el hidróxido e introducir nuevo metal dentro.
Por esta razón la investigación va encaminada a conseguir una batería recargable basado en los sistemas metal-aire. La empresa ReVolt ya ha desarrollado la primera batería de Zinc-aire recargable.
Este tipo de batería puede proporcionar 3 veces más duración que las de plomo-ácido. Las pilas a base de zinc tienen como principal ventaja la posibilidad de ser recicladas sin límite, sin perder ni sus cualidades químicas, ni sus cualidades físicas.
A pesar de que el zinc representa una fuente de energía limpia y duradera para el futuro, sin embargo, se desconoce el impacto que podría tener su uso masivo sobre el medio ambiente. El zinc se usa en la producción de acero galvanizado, que representa la mitad de su mercado. Un tercio del zinc consumido, se produce a partir del reciclado del zinc usado.
Las baterías Zinc Air Prismatic de Energizer concentran mayor cantidad de energía en un tamaño más reducido, y prometen ser una revolución. Energizer afirma que en el mismo tamaño, su tecnología proporciona el triple de autonomía que una pila de iones de litio actuales. Duracell, una de sus marcas rivales, también está desarrollando pilas Zinc Air.
Este avance ha sido el fruto de varios años de trabajo conjunto de la marca de pilas y baterías con los fabricantes de electrónica de consumo, enfocando el desarrollo hacia equipos más pequeños pero con buena autonomía.
El diseño y principio de las baterías zinc-aire es relativamente simple, pero su construcción no lo es, ya que el electrodo de aire debe ser extremadamente delgado. Se han hecho muchos estudios y grandes avances en el sellado del aire, pero aún queda mucho camino por recorrer.
Pero estamos en los inicios, y sin duda habrá grandes avances. Muchos prefieren, no sin razón, las baterías de zinc-aire a las de iones de litio. Ahora falta que las empresas pongan en el mercado las baterías de zinc-aire, a un precio razonable, y con las prestaciones esperadas.
The Zinc-Air Solution
Why the Automotive Industry Must Adopt Zinc-Air Technology to Overcome Peak Oil and Global Warming
Oil Demand must be reduced greatly over the next 10 years in line with declining oil supplies and to reduce CO2 emissions. The only practicable way to achieve this is to electrify Road Transport and replace petroleum with Electric Propulsion. The Lithium Ion battery has become the prime candidate to power electrified road vehicles in the near future.
Lithium supply and future production will be far from adequate to sustain global electric vehicle production. The current focus on LiIon batteries to the exclusion of all other batteries is a grave error that will lead to EV and PHEV production quickly becoming uneconomic due to insufficient Lithium supply.
Instead, the Automotive Industry should adopt the Zinc Air Battery and Fuel Cell technologies. Zinc Air Batteries have the highest specific energy and lowest cost of any Electric Vehicle rechargeable battery technology and are therefore well suited for mass market introduction in millions of electric automobiles.
The Zinc Air Fuel Cell has even higher specific energy than the ZnAir Battery. The ZnAir Fuel Cell is the only electric propulsion technology that could forseeably permit very quick recharge times comparable to refuelling a conventional vehicle with petrol. Due to its low weight, ZnAir technology is the only viable contender to power large trucks and heavy commercial vehicles which would require batteries 10 times as large as a car.
Zinc production is the third or fourth highest of all metals – it is therefore the cheapest and most abundant battery metal. Indeed, Zinc is the only metal which can sustain large battery production in the volumes required by the Global Automotive Industry.
Zinc Air batteries must be equipped with a filter to absorb CO2 from the entry air. Therefore vehicles equipped with this technology can be designed to permanently reduce atmospheric CO2 levels, contrary to conventional vehicles.
In light of the logistical, temporal, environmental and financial constraints with which the world is faced, National Governments should prioritise the development of Zinc Air Battery powered automobiles and the development of a refuelling infrastructure for Zinc Air Fuel Cell powered commercial and utility vehicles.
A “Zinc Economy” using already available and simple technology presents a viable, practicable and quickly implementable path for society to transition from oil power to renewable electric power, to maintain the essential transport infrastructure on which society depends and lay a foundation for further more advanced developments in Electric Propulsion technology to follow.
ZnAir technology has always been attractive due to its very high specific energy and very low cost. Set against this has been its low specific power, low cycle life and need for carbon dioxide absorption.
Zinc Air chemistry has been studied on and off as an EV power source since at least the 1950s. Leesona Moos developed a rechargeable ZnAir EV battery in the 1960s for city car use. At 140Wh/kg, a 230kg battery provided 31kWh capacity and 160 miles range at moderate acceleration capability. Cycle life was only 100 cycles to 100% DoD.
By the mid 1970s, the French Compagnie Generale d’Electricite had developed a tubular cell ZnAir system that could either be recharged electrically or hydraulically. Practical energy density of 110Wh/kg, at a specific power of 80W/kg and 500 cycles was projected.
By the early 1990s, the leader in ZnAir development was Dreisbach ElectroMotive (DEMI). In 1991, their converted Honda CRX equipped with a nominal 50kWh battery pack demonstrated 150Wh/kg specific energy in an SAE "D" suburban cycle test. The car operated for 215 miles at 45mph, with a 20 mile reserve still available. At 65mph, range was projected to be 150 miles. At 30mph, the car would have a range of over 300 miles. Cycle life did not progress much beyond 100 cycles or a two year life.
Later in the 1990s, Evercel’s Nickel Zinc technology showed very promising improvements in cell cycle life, to 600 cycles 100% DoD at C/2 for both charge and discharge. Lawrence Berkeley’s flowing electrolyte ZnAir system also achieved 600 cycles but only at C/4. Ni-Zn anode technology is directly transferable to ZnAir.
In the late 90s, PSI in Switzerland were also making promising progress in air cathode development and power density improvement, while maintaining cycle life. The German company Zoxy tried to commercialise this without success.
While the leader in ZnAir fuel cell technology is currently Electric Fuel/ Arotech in Israel, the country in which the SOLZINC solar thermal reactor is also being tested, commercialisation of their technology for EV applications has stalled.
A number of smaller US and Taiwanese technology development firms are trying to develop ZnAir fuel cell systems and Teck Cominco have bought the rights to Metallic Power’s technology. However, overall ZnAir technology development is attracting little funding or interest due to the overriding focus on Lithium Ion technology.
Lithium-ion batteries may be impressive, but some people feel they can do better – with zinc. Power Air, a startup from Livermore, CA, is designing zinc oxide fuel cells. In their fuel cells, zinc is dissolved in an electrolyte solution, and exposure to the air causes zinc oxide to form, releasing electrons and generating electricity. In theory, the zinc oxide can be collected, reduced back to zinc metal and fed back into the cycle.
Zinc air batteries are already used in hearing aids, though companies like Power Air hope to build batteries more suited for power and charging mobile electronic devices. Toyota is even researching ways to use zinc-air cells in electric vehicles, though they have put a 2020 timeline on the project, which means we won’t be seeing it any time soon.
As far as the chemistry goes, using zinc is no different than any other fuel cell, or regular battery for that matter (zinc, in fact, is a major component of most alkaline batteries). So what’s so special about it? It has two big advantages over something like lithium. Firstly, it is abundant and cheap, whereas there are fears about the supply of lithium. Secondly, it is safe and recyclable. It also has a relatively high energy density (energy contained per unit of volume).
Of course, it has its drawbacks. How would the zinc actually get recycled? Would battery owners have to recycle it themselves? How much energy would be going into reducing the zinc metal? And how does it make sense to make a car battery out of zinc? Zinc is far heavier than lithium, and delivers far fewer watts per pound… not ideal for a car.
Zinc-air batteries (non-rechargeable), and zinc-air fuel cells, (mechanically-rechargeable) are electro-chemical batteries powered by the oxidation of zinc with oxygen from the air. These batteries have high energy densities and are relatively inexpensive to produce. They are used in hearing aids and in experimental electric vehicles. They may be an important part of a future zinc economy.
Particles of zinc are mixed with an electrolyte (usually potassium hydroxide solution); water and oxygen from the air react at the cathode and form hydroxyls which migrate into the zinc paste and form zincate (Zn(OH)42-), at which point electrons are released and travel to the cathode. The zincate decays into zinc oxide and water is released back into the system.
The water and hydroxyls from the anode are recycled at the cathode, so the water serves only as a catalyst. The reactions produce a maximum voltage level of 1.65 volts, but this is reduced to 1.4–1.35 V by reducing air flow into the cell; this is usually done for hearing aid batteries to reduce the rate of water drying out.
The term zinc-air fuel cell usually refers to a zinc-air battery in which zinc fuel is replenished and zinc oxide waste is removed continuously. This is accomplished by pushing zinc electrolyte paste or pellets into an anode chamber. Waste zinc oxide is pumped into a waste tank or bladder inside the fuel tank, and fresh zinc paste or pellets are taken from the fuel tank.
The zinc oxide waste is pumped out at a refuelling station and sent to a recycling plant. Alternatively, this term may refer to an electro-chemical system in which zinc is used as a co-reactant to assist the reformation of hydrocarbon fuels on an anode of a fuel cell.
Zinc-air batteries have properties of fuel cells as well as batteries: the zinc is the fuel, the rate of the reaction can be controlled by controlling the air flow, and used zinc/electrolyte paste can be removed from the cell and replaced with fresh paste. Research is being conducted in powering electric vehicles with zinc-air batteries.
High specific energy: up to 370 W·h/kg.
Terminal voltage does not drop until 80–85% depletion.
Very long shelf lives when sealed to exclude oxygen.
A very high self-discharge rate when exposed to air due to spontaneous zinc oxidation.
The battery must be resealed when not in use. The electrolyte can be maintained in a humidified environment.
Must not be over saturated or immersed in water.
Zinc is cheap; mass production is inexpensive.
Not electrically rechargeable, but recycling can reduce the zinc oxide back to zinc metal for use in new batteries.