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Seeing is believing when it comes to understanding battery instability

3-D electrochemical atomic force microscopy image showing surface particles of Li 2 CO 3 impurities on an LiCoO2 crystal and the large facets that undergo dimensional changes during battery operation.

Lithium rechargeable batteries not only dominate the portable electronic industry, but also have great promise to power plug-in hybrid and electric vehicles. However, high lithium battery energy cost and poor service life prevent their market introduction and penetration in this area. These two shortcomings primarily arise from energy and stability constraints of the positive electrode materials used in these batteries. The key to solving stability problems that arise during lithium battery operation requires a better understanding of the surface and dimensional instabilites of the individual oxide crystals in the positive electrode material. Using in-situ electrochemical atomic force microscopy, Shao-Horn 's group of the MIT MRSEC has discovered that the dissolution of Li 2 CO 3 impurities (the small surface particles on the flat facets in the Figure below) on LiCoO2 crystals - the most commonly used positive electrode material - can promote surface instability. Moreover, the technique allowed the researchers to in-situ monitor and quantify dynamic changes in the crystal dimensions, which had been proposed as one of leading causes of oxide instability during battery cycling. In particular, dimensional changes in the direction perpendicular to the large flat facets of Lix CoO2 single crystals were revealed. This approach enables in-depth understanding of the surface and structural instability of oxide electrode materials, and facilitates the development of concepts and technologies to produce lithium batteries with significantly longer service life.

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