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Understanding a flower-like arrangement of atoms may lead to lithium batteries with double the capacity

Flower-like arrangement of atoms that currently limits the lifetime of promising lithium battery materials

Widely used in laptop computers, digital cameras, and many other devices, lithium ion batteries store more energy for their weight, operate at a higher voltage, and hold a charge much longer than other rechargeable batteries. They are currently even being considered for hybrid vehicles. The obstacle to even lighter and longer-life batteries is the development of better cathode electrodes. The limitation of current materials arises from the fact that only one electron can be stored in the transition metals used in the oxide electrodes. Recently, the discovery that Ni can exchange two electrons at high potential has opened up the exciting possibility for batteries with higher energy density and therefore longer run-time. One of the earliest materials in which this double electron exchange has been realized experimentally is Li(Ni 0.5 Mn 0.5 )O 2.   Though this material performs well, it has not yet been possible to obtain the full theoretically realizable capacity from this compound. By calculating the structure of this material, Professor Ceder's group of the MIT MRSEC was able to trace the origin of this limitation to the unusual flower-like cation arrangement in the structure (see figure below; Van der Ven et al., Electrochemistry Communications 6 , 1045-1050, 2004). Now that the capacity limitation of this material is understood, approaches to circumvent it have been proposed. It is expected that these will result in batteries with significantly longer lifetimes.

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