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First Look at Gradient Crystals Print
Friday, 16 March 2012 15:14

Professor Nitash Balsara and his team at the University of California, Berkeley have developed nanostructured electrolytes for use in lithium batteries that will make them safer and also have the potential to increase the energy density of batteries. The electrolyte is a block copolymer consisting of two covalently bound polymers that are immiscible, like oil and water. They have studied the structure of the block copolymer using x-ray scattering at Advanced Light Source Beamline 7.3.3. When current is applied to the block copolymer, as in charging a battery, a new structure emerges.

 

balsara-gradient cystals

 

(a) “Sundial” x-ray scattering pattern of block copolymer developed by passing current. The impinging beam is located at the center of the pattern. The bright continuous ring is caused by randomly oriented structures. Bright streaks emanating from the ring are due to gradient crystals. (b) Gradient crystal of gyroid morphology.

 

The new structure is called a “gradient crystal.”  In ordinary crystals, the size of the lattice is fixed by thermodynamics, but in gradient crystals, the size of the lattice varies continuously within the crystal, leading to radial streaks in the x-ray scattering pattern. This structure allows the material to adapt to gradients caused by the current without breaking down. Not only is this study the first instance of examining block copolymer structure with x-ray scattering while applying current, but it is also the first time that a structure of this type has been seen. In addition to improving battery performance, this new structure may find other applications related to selective transport such as water filtration.

 


 

Work performed on ALS Beamline 7.3.3.

Citation: S.A. Mullin, G.M. Stone, A.A. Teran, D.T. Hallinan, A. Hexemer, and N.P. Balsara,  "Current-Induced Formation of Gradient Crystals in Block Copolymer Electrolytes," Nano Letters 12, 464 (2012).