Metal-air batteries Joan Gómez Chabrera Alejandro Andreu Nácher Pablo Bou Pérez
Index 1. Introduction 2. Principle of operation of metal-air batteries 3. Air cathodes 4. Types 5. General aplications 6. Developed batteries 7. Aplications of the developed batteries 6. Conclusion 2
1. Introduction Problem: CO2 emissions. Industry of main interest: automobile Today: lithium is the king, but for cars there is autonomy of 160 km. Need: more durable and efficient batteries. Create infinite batteries? Aluminum-air, lithium-air, iron-air, sodium-air, magnesium-air or silicon-air. 3
2. Principle of operation of metal-air batteries What is it? It's a cell metal-air electrochemistry, which uses an anode made of pure metal and an external cathode of ambient air. How does it work? The atmospheric oxygen dissociates while the metal of the anode is oxidized, this generates a flow of electrons, among them an electrolyte, therefore, there must be between the air and the electrolyte a permeable but hydrophobic material. 4
3. Air cathodes Air cathodes play an important role in metal air batteries. In general, the air cathode should own three features: 1) 2) 3) Massive and connected channels for the diffusion of gas and deposition of discharge product. Good electrical conductivity to facilitate the electron transportation. Highly catalytic activity for oxygen reduction reaction and oxygen evolution reaction. Carbon based materials are commonly used in metal air batteries due to their excellent electrical conductivity and high porosity. The batteries can offer a high initial discharge capacity. However, the capacity is vanished by the accumulation of insoluble discharge products in the porous network. 5
4. Types Gravimetric and volumetric energy densities of various metal-air battery systems in comparison with Li-ion batteries and conventional gasoline. Credit: Forschungszentrum Jülich / H. Weinrich 6
4.1. Aluminium-air batteries Aluminium air batteries produce current from the reaction of oxygen in the air with aluminium. Advantages: This batteries have one of the highest volumetric energy densities of all metal-air batteries. Problems: Expensive anode preparation. Problems with the product electrolytes. removal when using traditional Aluminium air batteries are non-rechargeable but it is possible to recharge the battery with new aluminium anodes by recycling the hydrated aluminium oxide. 7
4.2. Lithum-air batteries A Li-air battery creates voltage when O2 reacts with the positively charged lithium ions to form lithium peroxide (Li2O2). The main problem of the Li-air batteries is the electrolyte. Lithium reacts violently with water so there is the necessity to find new electrolytes. 1996 - Electrolyte based on a carbonate solvent. Nowadays - Ether and other solvents with lithium salts. The other problem of lithium-air batteries is that Li2O2 is a very bad electron conductor. If deposits of Li2O2 grow on the electrode surface that supplies the electrons for the reaction, it eventually kills off the reaction. 8
4.2. Lithum-air batteries Using a carbon electrode surface made of many thin layers of graphene, a standard electrolyte mixture and adding lithium iodide (LI) and a small amount of water, the reaction as the battery discharges does not form the Li2O2 that would gunge up the electrode s conducting surface. Instead it incorporates hydrogen stripped from the water (H2O) to form lithium hydroxide (LiOH) crystals. These crystals fill the size of the pores in the carbon electrode, but they do not coat and block the vital carbon surface that is generating the supply of voltage. Discharge Charge 9
4.3. Iron-air batteries Iron air rechargeable batteries promise a higher energy density than present-day lithium-ion batteries. The main raw-material of this technology is iron oxide (rust) which is an abundant and cheap material, non-toxic, inexpensive and environmentally friendly. In conjunction with a fuel cell this enables the system to behave as a rechargeable battery creating H2O/H2 via production/consumption of electricity. Furthermore, this technology has minimal environmental impact as it could be used to store energy from intermittent solar and wind power sources, developing an energy system with low carbon dioxide emissions. 10
4.4. Magnesium air batteries A Mg-air battery is composed of an Mg (or Mg alloy) anode, an air cathode and a saline electrolyte. The Mg air battery is a promising electrochemical energy storage and conversion device since Mg is abundant on the earth, has a high reaction activity, is light weight, has low toxicity and has relatively high safety. The Mg air battery can be re-used mechanically by replacing the spent Mg anode and electrolyte with a fresh Mg anode and electrolyte. 11
4.5. Silicon-air batteries Silicon-air batteries are viewed as a promising and cost-effective alternative to current energy storage technology. However, they have thus far only achieved relatively short running times because the consumption of the electrolyte. In order to operate these batteries must be continuously filled with electrolyte. The scientists are now looking for a way to keep the battery running without having to refill the electrolyte. 12
4.6. Zinc-air batteries Zinc air batteries are metal-air batteries powered by oxidizing zinc with oxygen from the air. They are considered non-rechargeable but can be mechanically recharged by changing the zinc anode and the electrolyte. These batteries have high energy densities and are relatively cheap to produce. Sizes range from very small button cells to very large batteries used for electric vehicle propulsion. The operating life of a zinc air cell depends on its interaction with its environment. The electrolyte loses water more rapidly in conditions of high temperature and low humidity. 13
5. General aplications In recent years the need to improve and expand the storage of energy through batteries has increased Integration of renewable energies in traditional electricity networks. Distributed energy sources. Intelligent demand. Self-consumition. 14
6. Developed batteries This type of metal air batteries are of great interest to eliminate the current needs related to the storage of electrical energy. They are devices with a storage capacity superior to those currently known. The use of oxygen as a reagent results in lighter devices. Safer batteries, more respectful with the environment. 15
7. Aplications of the developed batteries (Zn-air) With the development of advanced air electrodes, it was applied in: Small size batteries such as hearing aids Military applications. 16
7. Aplications of the developed batteries (Zn-air) Its main application is electric transport: They are in development phase. It is characterized by mechanical recharging and filling with water. Work is being done to improve the durability of their useful life and the adhesion of anticorrosive materials. 17
7. Aplications of the developed batteries (Al-air) Its main application is electric transport: They are in development phase. Mainly in military aplications. 18
8. Conclusion The following chart summarizes the properties of the metal-air batteries which are more developed nowadays. 19
Thank you for your atention. 20