Research: Extra Capacity of Smart Phones Batteries do not depend on Lithium
The researcher Dr. Laurent Duda and the doctoral student Felix Massel from Uppsala have, together with researchers from the University of Oxford, the University of Kent and the Paul Scherrer Institute, come a long way in finding future lithium free batteries for among other things smart phones and laptops. The new results were published in the journal Nature Chemistry January the 22 2018.
Smart phone and laptop batteries operate by light alkali ions shuttling back and forth between the anode and the cathode. In the rechargeable batteries of today lithium, which is the lightest and smallest of all metal ions, is used for this purpose. The abundance of lithium salts on Earth is probably insufficient for satisfying the future total demand of energy storage in the world. Therefore it is crucial to study and increase the capacity of battery cathodes based on other light ions. Such ions are for example magnesium and also sodium, an alkali ion provided plentifully by the world’s oceans and in table salt.
Modern rechargeable batteries made of metal oxides are limited in their capacity since only the metal ions of the cathode are active. An early breakthrough regarding increased battery capacity was achieved little less than two years ago. At that time part of the research team involved in the new study could show that oxygen ions in lithium rich battery cathodes, lend these cathodes their so called extra capacity. However, lithium rich cathodes lose a part of their extra capacity in repeated charge cycles. This is due to the fact that part of the lithium participating in the battery cycling that resides closely to the oxygen. When the battery is charged and these lithium ions are thereby removed from the cathode, the oxygen becomes instable and the cathode gradually degrades.
- Many researchers thought that this degrading of the cathode was inevitable and related to the extra capacity of the battery, says Laurent Duda, researcher at the department of physics and astronomy.
The new study, where the lithium free material Na2/3[Mg0.28Mn0.72]O2 has been studied, points to the opposite though. It shows that lithium, or any other kind of alkali ion, does not have to be stored close to the oxygen in a battery that has extra capacity. The present material is completely free from lithium and it are the sodium ions that is going back and forth instead. At the same time the magnesium ions close to the oxygen have a stabilizing influence on the material.
The researchers from Oxford have synthesized the studied lithium free material and together with methods of characterization used by the Kent researchers they could confirm that the material had the desired extra capacity and was extremely stable, too.
To confirm that it indeed was the oxygen that was the cause of the extra capacity of the battery and to rule out other explanations the Uppsala researchers used a technique known as resonant inelastic X-ray scattering or RIXS. The Uppsala researchers Laurent Duda and Felix Massel, at the Department of Physics and Astronomy, have contributed a lot to the strong development of this technique during the last decades. The RIXS-experiment was carried out with world leading equipment on the beamline ADRESS at the Swiss synchrotron radiation laboratory Swiss Light Source.
- Discovering that extra capacity also may be found in lithium free batteries is a huge progress, but further optimization of lithium free cathode materials is needed before they become viable for commercial batteries. Further RIXS-experiments will contribute a lot to our work on this in the close future, says Laurent Duda.
Oxygen redox chemistry without excess alkali-metal ions in Na2/3[Mg0.28Mn0.72]O2, Urmimala Maitra, Robert A. House, James W. Somerville et al., Nature Chemistry, DOI: 10.1038/NCHEM.2923.
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