Aluminum-air batteries: A promising future for energy storage

Lithium-ion batteries are used in a wide range of applications, from mobile devices to electric vehicles. Meanwhile, "aluminum-air" batteries, currently under development, are generating excitement with promises of fast charging and high capacity. Experts say, "They have the potential to meet consumer needs in the future."

The world is shifting away from fossil fuels toward more environmentally friendly energy sources. One of the most important developments in this area is the batteries used in everything from mobile devices to electric vehicles.

Historically, lead-acid batteries gave way to nickel-cadmium, then to nickel-metal hydride batteries. Afterward, lithium-ion and lithium-sulfur batteries became available to consumers.

Today, lithium-ion batteries are the most widely used due to their advantages, such as fast charging, higher efficiency, and the ability to recharge before completely depleting. Mobile devices like phones and tablets, electric vehicles, buses, marine vessels, and even airplanes use lithium-ion batteries.

ALUMINUM-AIR BATTERIES: A NEW ALTERNATIVE

However, recent research into "aluminum-air batteries" has created a buzz across various industries. Unlike lithium, which is a limited resource, aluminum is abundant in many countries, including Turkey. Aluminum-air batteries are touted to have advantages like "40 times more energy storage than lithium-ion batteries" and "up to 100 times faster charging."

This means that a battery of the same size could offer much longer range, and a phone could be used for days on a single fast charge. The drawbacks, however, include "high recycling requirements" and the fact that "the technology is not yet suitable for end-users."

WHAT EXPERTS SAY

Sabancı University is the only institution in Türkiye with a minor program in Battery Science and Engineering. Faculty members from the university's Faculty of Engineering and Natural Sciences, Dr. Selmiye Alkan Gürsel, Dr. Alp Yürüm, and Associate Dean Burç Mısırlıoğlu, answered questions for TRT Haber about aluminum-air batteries. According to the experts, while aluminum-air batteries hold significant potential, there is still a long way to go.

WHAT ARE ALUMINUM-AIR BATTERIES?

Academics summarize the characteristics of aluminum-air batteries as follows:

"They are a type of metal-air (or oxygen) battery. Metal-air batteries generally have higher energy density than conventional batteries. A typical example of a metal-air battery is the zinc-air battery, which has been used for many years in specialized applications like hearing aids. Zinc-air batteries are usually non-rechargeable. Their energy density is about five times higher than lead-acid batteries and comparable to lithium-ion batteries. The practical energy density of aluminum-air batteries is about twice that of zinc-air (and lithium-ion) batteries. However, these batteries' charge/discharge cycles are limited due to corrosion. The negative terminal (anode) is made of aluminum metal, while the positive terminal (cathode) is a porous material that reacts with ambient oxygen. The charging reaction is not very efficient. For every 100 units of energy used to charge the battery, about 75 units are used to actually charge it, while the remaining energy is lost due to resistance and other factors."

"While there is an electron-donating reaction at the anode, there is an electron-accepting reaction at the cathode. During these reactions, free electrons and ions are produced, and the flow of electrons from the anode to the cathode provides the necessary electrical power for a device. In conventional batteries, these reactions occur in a closed system. However, in aluminum-air batteries, there is an 'open' system because continuous oxygen intake from the outside is required for energy production. In this way, aluminum-air batteries are similar to fuel cells. The lightness of aluminum and the oxygen reaction providing many electrons result in a high energy density, but unwanted reactions also occur, which reduces the efficiency and lifespan of the aluminum-air batteries."

ONGOING RESEARCH

"Research on this technology is being conducted in three main areas: anode, cathode, and electrolyte. For the anode, reducing unwanted side reactions using different alloys is a primary focus. For the cathode, catalysts are being developed to enhance oxygen reactions. Additionally, porous and conductive structures for oxygen gas flow are being investigated. Instead of water-based electrolytes, organic solvents or solid-state electrolytes are also being explored. At Sabancı University, research is being conducted on oxygen catalysts, porous cathode structures, and solid-state polymer electrolytes for metal-air batteries."

A PROMISING TECHNOLOGY

"Aluminum-air batteries have the potential to meet future consumer needs. Their wide application range, from electric vehicles to military systems, environmentally friendly reactions, and the abundant and inexpensive availability of aluminum, make them a promising battery technology for the future. However, the current aluminum-air battery technology still requires improvements to enable industrial-scale production of electrodes and electrolytes."

FOCUS ON OPTIMIZATION

"Research on aluminum-air batteries should focus on optimizing the production of the anode, cathode, electrolyte, and other battery components to ensure they are easily produced at an industrial scale, perform well, and remain economically viable."