Energy is one of the most important factors that determine the level of progress and well-being of human societies. However, the energy sources that we use currently, such as fossil fuels and nuclear, face many challenges and risks, such as depletion, pollution, climate change, and regional and global security. Therefore, the need for alternative and clean and renewable energy sources, such as solar, wind, waves, tides, geothermal, hydrogen, and biomass, is increasing. But these sources are not without drawbacks, as they depend on the weather, geographical, economic, and political conditions of each region, and they require advanced technologies and infrastructure to produce, transport, store, and use them efficiently and safely.
Here comes the role of batteries, which are an important means of storing and providing electrical energy when needed. Batteries are used in various fields, such as electric vehicles, mobile phones, electronic devices, smart grids, homes, factories, hospitals, schools, farms, camps, and remote sites. But the batteries that we use currently, such as alkaline, lead, nickel, cadmium, and lithium, also face many problems and limitations, such as cost, weight, size, capacity, lifespan, safety, and environmental impact.
Therefore, the need for developing a new generation of batteries that have better and more sustainable characteristics, such as efficiency, reliability, durability, rechargeability, dischargeability, and disposability, is increasing. Among the materials that are candidates for this purpose, zinc stands out, which is a common, cheap, non-toxic, biodegradable, and widely available element in nature. But using zinc in batteries is not simple, as it faces technical challenges that require innovative solutions. This is what researchers from the University of California, with Egyptian participation, have achieved, as they have developed a new generation of zinc batteries, opening new horizons for a revolution in the field of renewable energy. In this article, we will learn about the importance, advantages, and mechanism of these batteries, and we will discuss some of the applications and future expectations for them.
Zinc is a chemical element with the symbol Zn and atomic number 30, and it is a shiny, gray-white metal, belonging to the transition group in the periodic table. Zinc is found in nature in raw or compound form with other elements, such as sulfur, oxygen, carbon, phosphorus, chlorine, fluorine, bromine, and iodine. Zinc is extracted from ores by several methods, such as electrolysis, distillation, thermal decomposition, or chemical reactions. Zinc is used in various fields, such as industry, agriculture, medicine, nutrition, cosmetics, art, decoration, coins, and batteries.
Zinc is considered an ideal material for batteries for several reasons, such as:
- Zinc has a high standard potential, which is the amount of electric difference between the negative and positive poles in the battery, which determines the amount of energy that the battery can produce. The potential of zinc is 0.76 volts, compared to 0.3 volts for lithium.
- Zinc has a high theoretical capacity, which is the amount of energy that the battery can store in a unit of weight or volume. The capacity of zinc is 820 milliampere hours per gram, compared to 386 milliampere hours per gram for lithium.
- Zinc has a long cycle life, which is the period of time that the battery maintains its optimal performance. The life of zinc is up to 1000 charge and discharge cycles, compared to 500 cycles for lithium.
- Zinc has a high safety, which is the ability of the battery to withstand harsh conditions such as heat, shocks, penetration, and combustion. Zinc does not cause explosions or fires, compared to lithium, which is a flammable and explosive material.
However, zinc also has some drawbacks, such as:
- Zinc has a low energy density, which is the amount of energy that the battery can deliver in a unit of weight or volume. The energy density of zinc is 130 watt hours per kilogram, compared to 250 watt hours per kilogram for lithium.
- Zinc has a low coulombic efficiency, which is the ratio of the amount of charge that the battery can deliver to the amount of charge that it can accept. The coulombic efficiency of zinc is 70%, compared to 99% for lithium.
- Zinc has a problem of dendrite formation, which is the growth of zinc crystals in the form of branches on the metal surface, which can cause a short circuit between the electrodes and reduce the performance of the battery.
To overcome these drawbacks, researchers have developed various techniques to improve the properties of zinc, such as:
- Using zinc alloys or composites with other metals or materials, such as magnesium, aluminum, bismuth, indium, carbon, or graphene, to increase the stability and conductivity of zinc.
- Coating the zinc surface with protective layers of oxides, hydroxides, sulfides, or polymers, to prevent the corrosion and dissolution of zinc in the electrolyte.
- Changing the shape or structure of the zinc electrode, such as using nanoparticles, nanowires, nanosheets, nanoflowers, or nanosponges, to increase the surface area and porosity of zinc and reduce the dendrite formation.
One of the most recent and promising techniques is the one developed by the Egyptian researcher Maher El-Kady and his colleagues at the University of California, who have created a new generation of zinc batteries that combine the advantages of zinc-air and zinc-ion batteries. Zinc-air batteries use oxygen from the air as the cathode material, which reduces the weight and cost of the battery and increases the energy density. However, zinc-air batteries have low power density and poor rechargeability, as they require mechanical or chemical methods to reverse the discharge reaction. Zinc-ion batteries use metal oxides or sulfides as the cathode material, which allows the intercalation and deintercalation of zinc ions, which means the insertion and extraction of zinc ions between the layers of the cathode material. This increases the power density and rechargeability of the battery, but reduces the energy density and capacity.
The new zinc batteries developed by El-Kady and his team use a bifunctional air electrode, which can act as both a cathode and an anode, depending on the mode of operation. In the discharge mode, the air electrode acts as a cathode, where oxygen is reduced and zinc is oxidized, producing electricity and water. In the charge mode, the air electrode acts as an anode, where water is oxidized and zinc is reduced, consuming electricity and producing oxygen and hydrogen. The hydrogen can be collected and used as a fuel or stored for later use. This way, the new zinc batteries can achieve both high energy density and high power density, as well as high rechargeability and hydrogen production.
El-Kady explained that in the new research, he and his scientific team were able to make modifications that allow controlling the deposition rate of zinc, and distribute its ions evenly on the surface. He added: "We found that adding a substance called polyvinyl alcohol (PVA) to the negative pole of the battery, acts as a stabilizer for zinc ions, and prevents the formation of dendrites, and improves the performance of the battery significantly." He explained that this substance is a non-toxic and biodegradable polymer, and is used in various fields such as medicine, industry, agriculture, and cosmetics.
El-Kady pointed out that the zinc batteries that he developed with his scientific team, have several advantages, such as:
- Zinc is a cheap and abundant material in nature, compared to lithium, which requires costly and complex extraction, purification, and transportation.
- Zinc is a non-toxic and biodegradable material, compared to lithium, which is a toxic and dangerous material for the environment and public health.
- Zinc is a material that can produce hydrogen, which is a clean and renewable energy source, compared to lithium, which does not have this feature.
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