A short fuse

By | Science & Technology
Electric car.Credit@abdallahdirie

A new battery technology using lithium air chemistry may be vastly superior to conventional batteries. The technology may have higher energy density, be significantly more efficient and need to be recharged considerably infrequently. The scientists involved in the creation of the battery believe the findings may stimulate the development of these types of batteries.

Lithium air batteries have an energy density similar to gasoline which may allow a car to travel large distances on a single charge. Car technology manufacturers specifically may be influenced by better available energy sources to adopt cleaner energy. Practical matters have meant lithium air batteries might have been a delayed alternative to gasoline.

Scientists from the University of Cambridge may have shown how these challenges might be overcome. The team aims to demonstrate how a battery with higher capacity, efficiency and stability may be possible. This prototype uses a highly porous carbon electrode made from graphene and other chemicals; these change how the battery actually functions leading to improved stability and efficiency. “What chemists may have achieved is a significant advance for this technology and suggests whole new areas for research. Our results do show routes forward towards a practical device,” said senior author Professor Clare Grey of Cambridge’s department of chemistry.

Lithium ion battery.Credit@lithiumbatter.com

Lithium ion battery.Credit@lithiumbatter.com

Conventional batteries work differently to lithium air batteries by converting chemical energy to electrical energy by the use of voltaic cells where each cell has two half cells. One half cell includes an electrolyte and an electrode whereas the other half cell has an electrolyte and a positive electrode. Anions then move towards the electrode and cations move towards the positive electrode. This means cations (electrons) are added at the cathode and anions (electrons) are removed at the anode during charging and when the battery is being used the process is reversed. The electrodes are physically unconnected however, although are connected electrically by the electrolyte, the movement of anions and cations in different directions results in a current. The battery is then a source of electromotive force which converts chemical, mechanical and others into electrical energy. “In their simplest form, batteries are made of three components: a positive electrode, an electrode and an electrolyte” said Dr Tao Liu the paper’s first author.

In lithium-ion (li-on) batteries (used in laptops and smartphones) the electrode is made of graphite, the positive electrode is formed from a metal oxide and the electrolyte is a lithium salt diffused in a solvent. Like other batteries the battery functions by the movement of ions between the electrodes, however the efficiency of these batteries gradually reduces over time and because of a small energy density need to be recharged constantly.

Lithium air battery.Credit@UniversityofCambridge

Lithium air battery.Credit@UniversityofCambridge

Liu and colleagues have developed a lithium air prototype with different chemistry than previous attempts as these batteries use lithium hydroxide instead of lithium peroxide. The team added water and lithium iodide, this aims to result in fewer cells deteriorating due to the chemical reactions and being more stable after charging and recharging. The efficiency of the lithium air battery has been improved by reducing the voltage gap down significantly from previous attempts.

The highly porous graphene electrode increases the capacity of the prototype meaning a higher capacity at particular rates of charge and re-charge. The prototype relies on being encapsulated in a pure oxygen environment whereas general air containing carbon dioxide, nitrogen and moisture may be detrimental to the working of the lithium air battery. Other challenges if overcome may make the battery more stable and efficient in the future with further work and development. “There’s still a lot of work to do,” said Liu. “What may have been seen here suggests that there are ways to solve these issues; maybe we’ve just got to look at things a little differently.” “While there are still plenty of fundamental studies that remain to be done, to iron out some of the mechanistic details, the current results are extremely exciting. We are still very much at the development stage, we may have shown there are solutions to some of the tough challenges associated with this technology,” said Grey.

What audacious advances in energy technologies may be developed subsequently?


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