Optical thermal-storage battery has gained increasing attention on the world's renewable-energy market, thanks to its capability for long and stable storage of solar energy via chemical bond for release in the form of heat, rather than electricity. Attracted by its potential, a research team at University of Massachusetts, Amherst, has been studying method to enhance its storage efficiency, in order to speed up its commercialization.
The team has managed to boost the average energy density for the battery to 510 joules, more than double 200 joules of existing polymer chain-based optical thermal-storage battery, with the maximum density topping 690 grams x joules, which Prof. Dhandapani Venkataraman, advisor for the project, hopes to raise to 800 grams x joules.
The project derives its idea from a paper on optical thermal-storage battery released by Jeffrey Grossman, professor at Massachusetts Institute of Technology, who suggested employment of recyclable materials and a structure featuring array of Azobenzene molecules along carbon nano-tube, which enables manipulation of interaction of molecules, thereby determining the energy storage and release amount of battery.
Given inability of nano-tube to shorten distance among molecules, the UMass, Amherst team employs flexible polymer instead, which, just like a string linking Christmas bulbs, can gather azine and trigger interaction after collecting energy.
Upon exposure to sunshine, azobenzene's structure will become twisted in shape, from the shape of plane, thereby storing optical energy before release in the form of heat later on. Prof. Venkataraman points out that key for the technology is how to adjust the distance between molecules and flexible polymer, so as to overcome instability deriving from change in the array of the peripheral molecules of polymer triggered by change in the structure of azobenzene.
For that purpose, the research team employs Tetrahydrofuran solvent for arranging array and adjusting structure, on top of achieving most complete packing density, so as to boost the capacity of the battery.