Bao Yang

Bio: Bao Yang is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Thermal conductivity & Thermoelectric cooling. The author has an hindex of 44, co-authored 141 publications receiving 7219 citations. Previous affiliations of Bao Yang include Massachusetts Institute of Technology & University of California, Los Angeles.

Low Tortuous, Highly Conductive, and High-Areal-Capacity Battery Electrodes Enabled by Through-thickness Aligned Carbon Fiber Framework.

Abstract: Thick electrode with high-areal-capacity is a practical and promising strategy to increase the energy density of batteries, but development toward thick electrode is limited by the electrochemical performance, mechanical properties, and manufacturing approaches In this work, we overcome these limitations and report an ultrathick electrode structure, called fiber-aligned thick or FAT electrode, which offers a novel electrode design and a scalable manufacturing strategy for high-areal-capacity battery electrodes The FAT electrode uses aligned carbon fibers to construct a through-thickness fiber-aligned electrode structure with features of high electrode material loading, low tortuosity, high electrical and thermal conductivity, and good compression property The low tortuosity of FAT electrode enables fast electrolyte infusion and rapid electron/ion transport, exhibiting a higher capacity retention and lower charge transfer resistance than conventional slurry-casted thick electrode design

Mini-Contact Enhanced Thermoelectric Cooling of Hot Spots in High Power Devices

Abstract: Cooling hot-spots with high heat flux (e.g., >1000 W/cm2) is becoming one of the most important technical challenge in today's integrated circuit industry. More aggressive thermal solutions, than would be required for uniform heating, are highly desired. Recently, solid state thermoelectric coolers (TECs) have received more attention for hot-spot thermal management. However, present day TECs typically have cooling flux much lower than heat flux in the hot-spots. In this work, we reported an innovative technique-TE Mini-contact-to significantly increase cooling flux of TECs for the application in hot-spot cooling. A chip package featuring a TE Mini-contact cooler integrated with conventional integrated heat spreader and heat sink is designed. The cooling performance of such chip package has been investigated by using a 3-D numeric model. It is found that the cooling in the hot-spot (1250 W/cm2, 400 mum by 400 mum) can be about 19 degC better in the proposed package than that achieved in the conventional chip package without TEC. The effects of trench, die thickness, and TEC misalignment on the cooling of the hot-spot are also discussed.

High temperature thermal management with boron nitride nanosheets

Abstract: The rapid development of high power density devices requires more efficient heat dissipation. Recently, two-dimensional layered materials have attracted significant interest due to their superior thermal conductivity, ease of production and chemical stability. Among them, hexagonal boron nitride (h-BN) is electrically insulating, making it a promising thermal management material for next-generation electronics. In this work, we demonstrated that an h-BN thin film composed of layer-by-layer laminated h-BN nanosheets can effectively enhance the lateral heat dissipation on the substrate. We found that by using the BN-coated glass instead of bare glass as the substrate, the highest operating temperature of a reduced graphene oxide (RGO) based device could increase from 700 °C to 1000 °C, and at the same input power, the operating temperature of the RGO device is effectively decreased. The remarkable performance improvement using the BN coating originates from its anisotropic thermal conductivity: a high in-plane thermal conductivity of 14 W m−1 K−1 for spreading and a low cross-plane thermal conductivity of 0.4 W m−1 K−1 to avoid a hot spot right underneath the device. Our results provide an effective approach to improve the heat dissipation in integrated circuits and high power devices.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review.

Abstract: The lithium metal battery is strongly considered to be one of the most promising candidates for high-energy-density energy storage devices in our modern and technology-based society. However, uncontrollable lithium dendrite growth induces poor cycling efficiency and severe safety concerns, dragging lithium metal batteries out of practical applications. This review presents a comprehensive overview of the lithium metal anode and its dendritic lithium growth. First, the working principles and technical challenges of a lithium metal anode are underscored. Specific attention is paid to the mechanistic understandings and quantitative models for solid electrolyte interphase (SEI) formation, lithium dendrite nucleation, and growth. On the basis of previous theoretical understanding and analysis, recently proposed strategies to suppress dendrite growth of lithium metal anode and some other metal anodes are reviewed. A section dedicated to the potential of full-cell lithium metal batteries for practical applicatio...

Physics of thin-film ferroelectric oxides

Abstract: This review covers important advances in recent years in the physics of thin-film ferroelectric oxides, the strongest emphasis being on those aspects particular to ferroelectrics in thin-film form. The authors introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices. Following this the review covers the enormous progress that has been made in the first-principles computational approach to understanding ferroelectrics. The authors then discuss in detail the important role that strain plays in determining the properties of epitaxial thin ferroelectric films. Finally, this review ends with a look at the emerging possibilities for nanoscale ferroelectrics, with particular emphasis on ferroelectrics in nonconventional nanoscale geometries.

Bulk nanostructured thermoelectric materials: current research and future prospects

Abstract: Thermoelectrics have long been recognized as a potentially transformative energy conversion technology due to their ability to convert heat directly into electricity. Despite this potential, thermoelectric devices are not in common use because of their low efficiency, and today they are only used in niche markets where reliability and simplicity are more important than performance. However, the ability to create nanostructured thermoelectric materials has led to remarkable progress in enhancing thermoelectric properties, making it plausible that thermoelectrics could start being used in new settings in the near future. Of the various types of nanostructured materials, bulk nanostructured materials have shown the most promise for commercial use because, unlike many other nanostructured materials, they can be fabricated in large quantities and in a form that is compatible with existing thermoelectric device configurations. The first generation of these materials is currently being developed for commercialization, but creating the second generation will require a fundamental understanding of carrier transport in these complex materials which is presently lacking. In this review we introduce the principles and present status of bulk nanostructured materials, then describe some of the unanswered questions about carrier transport and how current research is addressing these questions. Finally, we discuss several research directions which could lead to the next generation of bulk nanostructured materials.

Engineered doping of organic semiconductors for enhanced thermoelectric efficiency

Abstract: The conversion efficiency of heat to electricity in thermoelectric materials depends on both their thermopower and electrical conductivity. It is now reported that, unlike their inorganic counterparts, organic thermoelectric materials show an improvement in both these parameters when the volume of dopant elements is minimized; furthermore, a high conversion efficiency is achieved in PEDOT:PSS blends.