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MOSCOW, April 13. /TASS/ An international research team, among them scientists from Skoltech, discovered how a crystal structure of a cathode of a lithium-ion rechargeable battery can be changed in order to ramp up its efficiency and longevity, without jeopardizing its safety, Skoltech’s press office said. The researchers’ study has recently been published in the journal Nature Materials, with its results being of crucial significance for modern electronics which makes use of lithium-ion cells.
"In our work, we have shown how one should use lithium-ion batteries’ capacity to the fullest, without fear of explosions, fires or the degradation of the materials," said Professor Artem Abakumov from the Skoltech Center for Electrochemical Energy Storage, a coauthor of the study."
Lithium-ion batteries are the primary energy source in modern portable electronics and can be found in the majority of mobile phones, cameras, and laptops. In such cells, lithium ions serve as charge carriers: when the battery charges, the lithium ions leave a crystal lattice of a cathode, the negative electrode of a battery, and vice versa: when the battery discharges, the lithium ions enter the cathode again. In modern lithium-ion batteries, the cathode’s typical material is a layered mixed oxide of cobalt and lithium.
Lithium-ion batteries are traditionally characterized by two key features: their potential quantity of recharge cycles and their capacity (i.e., a number of lithium ions that leave the battery’s crystal lattice while discharging and return while charging). Typically, no more than 60% of a battery’s lithium ions leave a cathode structure, otherwise, the likelihood of negative consequences such as fires and explosions increases. This can be rationalized by the fact that after lithium ions have left the cathode, oxygen atoms of the mixed oxide could interact with the solvent surrounding the cathode, with the reaction being accompanied by a surge in heat release.
The potential quantity of recharge cycles is also typically limited by the battery’s structure: when a lithium ion leaves its position in the cathode, the vacancy is readily occupied by cobalt atoms which can migrate. As a result, the lithium ion cannot return to its initial position and the battery capacity drops over time.
In their novel approach, researchers have put forward a way of solving these problems. The classical cathode of a lithium-ion battery has a layered structure where the layers of lithium are interleaved with the layers of oxygen and a transition metal (it might be cobalt or any other metal) (Fig.1). Such a structure is favorable for the transition metal ions’ migration. To overcome it, the scientists have come up with a principally new structure of a cathode material.
In this newly suggested structure (Fig.2), layers are shifted relative to each other, causing a framework structure to replace the traditional layered one. This has been shown to boost the stability of cathodes without draining energy upon recharging cycles. Furthermore, using the new structure, nearly all lithium ions can leave the cathode without presenting any increased flammability risk.
As a model device, the framework structure was constructed with a lithium-iridium mixed oxide which is a very expensive material for mass production purposes. Hence, the researchers planned to extend their research, setting their sights on replacing iridium with more abundant and cheaper metals for cathode construction.