The development of new organic batteries — lightweight energy storage devices that work without the need for toxic heavy metals — has a brighter future now that chemists have discovered a new way to pass electrons back and forth between two molecules.
Bielawski and Sessler credit graduate student Jung Su Park for his detailed work growing crystals of the two molecules. Other collaborators include graduate student Elizabeth Karnas from The University of Texas at Austin, Professor Shunichi Fukuzumi at Osaka University and Professor Karl Kadish at the University of Houston.
Transparent devices have recently attracted substantial attention. Various applications have been demonstrated, including displays, touch screens, and solar cells; however, transparent batteries, a key component in fully integrated transparent devices, have not yet been reported. As battery electrode materials are not transparent and have to be thick enough to store energy, the traditional approach of using thin films for transparent devices is not suitable. Here we demonstrate a grid-structured electrode to solve this dilemma, which is fabricated by a microfluidics-assisted method. The feature dimension in the electrode is below the resolution limit of human eyes, and, thus, the electrode appears transparent. Moreover, by aligning multiple electrodes together, the amount of energy stored increases readily without sacrificing the transparency. This results in a battery with energy density of 10 Wh/L at a transparency of 60%. The device is also flexible, further broadening their potential applications. The transparent device configuration also allows in situ Raman study of fundamental electrochemical reactions in batteries.
High rate capabilities Fe3O4-based Cu nano-architectured electrodes for lithium-ion battery applications
All battery technologies are known to suffer from kinetic problems linked to the solid-state diffusion of Li in intercalation electrodes, the conductivity of the electrolyte in some cases and the quality of interfaces. For Li-ion technology the latter effect is especially acute when conversion rather than intercalation electrodes are used. Nano-architectured electrodes are usually suggested to enhance kinetics, although their realization is cumbersome. To tackle this issue for the conversion electrode material Fe3O4, we have used a two-step electrode design consisting of the electrochemically assisted template growth of Cu nanorods onto a current collector followed by electrochemical plating of Fe3O4. Using such electrodes, we demonstrate a factor of six improvement in power density over planar electrodes while maintaining the same total discharge time. The capacity at the 8C rate was 80% of the total capacity and was sustained over 100 cycles. The origin of the large hysteresis between charge and discharge, intrinsic to conversion reactions, is discussed and approaches to reduce it are proposed. We hope that such findings will help pave the way for the use of conversion reaction electrodes in future-generation Li-ion batteries.
- Cobalt oxides;
- Inorganic nanostructures;
- Lithium-ion batteries;
A one-step, self-supported topotactic transformation approach for synthesizing electrochemically active Co3O4 needlelike nanotubes is reported. Used as the active material in the negative electrode of a rechargeable lithium ion battery, the Co3O4 nanotubes manifest ultrahigh Li storage capacity with improved cycle life and rate capability. These features are discussed in terms of the unique structure of the materials.