Ding-Wen Chung

Nanoscale mapping of ion diffusion in a lithium-ion battery cathode

The movement of lithium ions into and out of electrodes is central to the operation of lithium-ion batteries. Although this process has been extensively studied at the device level, it remains insufficiently characterized at the nanoscale level of grain clusters, single grains and defects. Here, we probe the spatial variation of lithium-ion diffusion times in the battery-cathode material LiCoO(2) at a resolution of ∼100 nm by using an atomic force microscope to both redistribute lithium ions and measure the resulting cathode deformation. The relationship between diffusion and single grains and grain boundaries is observed, revealing that the diffusion coefficient increases for certain grain orientations and single-grain boundaries. This knowledge provides feedback to improve understanding of the nanoscale mechanisms underpinning lithium-ion battery operation.

Validity of the Bruggeman relation for porous electrodes

The ability to engineer electrode microstructures to increase power and energy densities is critical to the development of high-energy density lithium-ion batteries. Because high tortuosities in porous electrodes are linked to lower delivered energy and power densities, in this paper, we experimentally and computationally study tortuosity and consider possible approaches to decrease it. We investigate the effect of electrode processing on the tortuosity of in-house fabricated porous electrodes, using three-dimensionally reconstructed microstructures obtained by synchrotron x-ray tomography. Computer-generated electrodes are used to understand the experimental findings and assess the impact of particle size distribution and particle packing on tortuosity and reactive area density. We highlight the limitations and tradeoffs of reducing tortuosity and develop a practical set of guidelines for active material manufacture and electrode preparation.

Multifunctional calcium carbonate microparticles: Synthesis and biological applications

Multifunctional composites based on calcium carbonate (CaCO3) spherical microparticles stabilized through the embedding of CdSe/ZnS/SiO2 nanoparticles into surface pores were fabricated. The stabilization of the vaterite polymorph of CaCO3 through nanoparticles embedding was necessary to generate a spherical, porous morphology of the microparticles. The CdSe/ZnS quantum dots were obtained and dispersed in aqueous solution after coating them with a silica shell via a reverse microemulsion approach. Green and red-emitting CaCO3-CdSe/ZnS/SiO2 microcomposites were analyzed via confocal laser-scanning fluorescence microscopy were to demonstrate their potential for imaging applications. The acetylcholinesterase (AChE) enzyme was immobilized into the pores of the spherical CaCO3-CdSe/ZnS/SiO2 microcomposites and the resulting hybrid material was used as a platform for the design of a pesticide biosensor. The detection limit for the paraoxon pesticide in aqueous solutions was determined to be of 4.6 nM.