YU Research Group – Nano Energy Lab

Explore advanced energy technology and science, nano/micro-systems, thermal engineering and science


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● Next Generation Lithium-Sulfur Batteries with High Energy Density and Low Cost

This project is to overcome the key hurdle in deploying electric vehicles and renewable energy conversion systems such as solar panels by lowering the cost of rechargeable batteries as well as increasing their energy density. Our battery technology can potentially achieve an energy density five times higher than that of the current Li-ion batteries as well as a manufacturing cost as low as 1/300 of the cost of Li-ion batteries, based on the testing results with lab-scale batteries. 


High energy density Li-S batteries have been enabled by carbon nanotube sponges, serving as cathode. Porous and self-standing carbon nanotube sponges were used as catholyte (dissolved active material in electrolyte) reservoirs. The carbon nanotube sponges are composed of highly conductive carbon nanotubes enabling a 3D conductive framework. Li-S pouch cells fabricated in lab with size similar to small commercial Li-ion pouch cells also shows higher energy densities (cell level).

- X. Pu, G. Yang, C. Yu, “Trapping polysulfides in free-standing carbon nanofiber sponges for improving the performances of sulfur batteries,” J. Electrochem. Soc., 162, A1396-A1400 (2015).

- X. Pu, G. Yang, C. Yu, “Liquid-type cathode enabled by 3D sponge-like carbon nanotubes for high energy density and long cycling life of Li-S batteries,” Adv. Mater., 26, 7456-7461 (2014).

- X. Pu, G. Yang, C. Yu, “Safe and reliable operation of sulfur batteries with lithiated silicon,” Nano Energy, 9, 318-324 (2014).



● Lithium-Air Batteries with Extremely High Energy Density and Improved Cycling Performance


Large capacity and long cycling performance nonaqueous Li-O2 batteries have been made with carbon nanotube (CNT) arrays containing in-situ decorated 𝛼-Fe2O3 nanoparticles as both a binder-free catalyst and a cathode. Fe2O3-decorated CNTs greatly helped to form Li2O involving the four-electron reduction pathway in addition to Li2O2 commonly formed via the one/two-electron reduction pathway, and thereby delivered a very large capacity of 26.5 Ah/g at the 1st discharge and a relatively long cycling performance (48 cycles with a capacity limit of 1.5 Ah/g).

- S. Jee, W. Choi, C. H. Ahn, G. Yang, H. K. Cho, J.-H. Lee, C. Yu, “Enhanced oxygen reduction and evolution by in-situ decoration of hematite nanoparticles on carbon nanotube cathode for high-capacity nonaqueous lithium-oxygen batteries,” J. Mater. Chem. A, 3, 13767-13775 (2015).



● Thermally Chargeable Solid-State Supercapacitor for Wearable Electronics & Internet of Things (IoT)

Figure 1.

Energy conversion and storage are becoming the two most important technologies for the rapid development of portable and wearable electronic devices. Typically, energy harvesting and storage devices are two different physical units, which should be connected together by a power management circuit to enable a sustainable power supply. For wearable applications, it is highly desirable to improve the integration level so that we can simplify the structure and minimize the energy loss between each unit. The goal of this research is to develop new self-charging flexible energy devices by integrating a thermal energy harvester into an electrochemical supercapacitor, which can simultaneously convert thermal energy into electricity and store electrical energy into chemical energy. Solid-state polymeric ion conductors have been utilized as thermal energy harvesters, which can produce high voltage by using thermally-driven ion diffusions (Soret effect) at a temperature gradient. Such an integrated device can be simply charged up by any temperature gradients (e.g., human body heat for wearable electronics).

- S. L. Kim, H. T. Lin, C. Yu, “Thermally chargeable solid-state supercapacitor,” Adv. Energy Mater., Accepted.



Flexible Thermoelectric Polymer Nanocomposites for Energy Harvesting and Cooling  


Typical organic materials have low thermal conductivities that are best suited to thermoelectrics, but their poor electrical properties with strong adverse correlations have prevented them from being feasible candidates. Our composites, containing partially percolated single-wall carbon nanotubes and poly(3,4 ethylenedioxythiophene) (PEDOT) with tetrakis(dimethylamino) ethylene treatment show rarely reported n-type behavior and a high thermoelectric figure-of-merit up to ~0.5 at 300 K. A high power factor up to ~1050 µW/m-K2 was achieved owing to relatively low carrier concentrations (resulting in high thermopower) and high mobility from carbon nanotubes (resulting in high electricl conductivity).    

- H. Wang, J.-H. Hsu, S.-I. Yi, S. L. Kim, K. Choi, G. Yang, C. Yu, “Thermally driven large n-type voltage responses from hybrids of carbon nanotubes and poly(3,4-ethylenedioxythiophene) with tetrakis(dimethylamino)ethylene,” Adv. Mater., 27, 6855-6861 (2015).

- J.-H. Hsu, G. Yang, H. Wang, C. Yu, “Unusual thermoelectric transport behaviors in carbon nanotube filled polymer composites after solvent/acid treatments,” under review.



● Non-toxic Low-cost Mg2Si-Mg2Sn Thermoelectric Materials with High Thermal Stability and Performance 

Abstract Image

Bulk Mg2(Si,Sn) solid solutions are good candidates for waste heat recovery at intermediate temperature ranges (500-800 K) due to the their good thermoelectric properties beside abundance of their constituents and non-toxicity. Their thermoelectric figure-of-merit is relatively high, but the thermoelectric performance degrades due to nanostructure coarsening and phase segregation over time under thermal cycling. The main objective is to improve their thermal stability and figure-of-merit using extraneous nanoparticles.


- A. S. Tazebay, S.-I. Yi, J. K. Lee, H. Kim, J.-H. Bahk, S. L. Kim, S.-D. Park, H. S. Lee, A. Shakouri, C. Yu, “Dissimilar thermal transport driven by extraneous nanoparticles and phase segregation in nanostructured Mg2(Si,Sn) and estimation of optimum thermoelectric performance,” ACS Appl. Mater. Inter., 8, 7003-7012 (2016).



● Self-powered Health Monitoring Systems with Wearable Thermoelectrics 


Wearable power generation system based on body heat is being constructed using thermoelectric modules, and power management systems and wireless data communication systems are being integrated to build a comprehensive electronic system free of battery charging (or intermittent charging). Considering the small power consumption of recent personal electronic devices (2 mW for Fitbit and 20 mW for Apple watch), energy harvesting utilizing thermoelectric conversion to operate electronic systems could be viable. The objective is to properly configure thermoelectric devices for maximum power output via effective heat transfer as well as integrate multiple components to have a fully functional prototype.  


● Power Generation and Wastewater Treatment with Microbial Fuel Cells

Carbon nanotube (CNT) sponges are used as key materials for both cathode and anode of microbial fuel cells in order to replace precious metal based catalysts used in typical microbial fuel cells. For the cathode, the CNT sponge incorporated with nitrogen on the surface shows higher voltage output and power density. For the anode, CNT sponge showed excellent charge transfer (13 times lower charge transfer resistance compared to that of carbon felt) between its surface and microbes. Both cathode and anode demonstrate excellent long-term stability and substantially reduced cost compared to commercial Pt-based catalysts.

- G. Yang, C. Erbay, S.-I. Yi, P. de Figueiredo, R. Sadr, A. Han, C. Yu, “Bifunctional nano-sponges serving as non-precious metal catalysts and self-standing cathodes for high performance fuel cell applications,” Nano Energy, 22, 609-614 (2016). 

- C. Erbay, G. Yang, P. de Figueiredo, R. Sadr, C. Yu, A. Han, “Three-dimensional porous carbon nanotube sponges for high-performance anodes of microbial fuel cells,” J. Power Sources, 298, 177-183 (2015).

- C. Erbay, X. Pu, W. Choi, M.-J. Choi, Y. Ryu, H. Hou, F. Lin, P. de Figueiredo, C. Yu, A. Han, “Control of geometrical properties of carbon nanotube electrodes towards high-performance microbial fuel cells,” J. Power Sources, 280, 347-354 (2015).



Non-Precious Metal Catalysts for Proton Exchange Membrane Fuel Cells

One of the common major roadblocks in commercializing electrochemical cells including proton exchange membrane fuel cells is the high cost of Pt-based electrocatalysts. We are developing low-cost and high-performance bifunctional catalysts/electrodes made of three-dimensional sponge-like carbon nanotubes with Fe-C-N complexes on their surfaces. They are self-standing and highly porous, and their high electrical conductivity and high corrosion resistance (high stability) show great potential in lowering the cost of various types of electrochemical cells.

- G. Yang, W. Choi, X. Pu, C. Yu, “Scalable synthesis of bi-functional high-performance carbon nanotube sponge catalysts and electrodes with optimum C-N-Fe coordination for oxygen reduction reaction,” Energy Environ. Sci., 8, 1799-1807 (2015).

- W. Choi, G. Yang, S. L. Kim, P. Liu, H.-J. Sue, C. Yu, “One-step synthesis of nitrogen-iron coordinated carbon nanotube catalysts for oxygen reduction reaction,” J. Power Sources, 313, 128-133 (2016).



Flexible and Lead-Free Piezoelectric Nanocomposites for Energy Harvesting and Noise Reduction

Piezoelectric composites made of piezoelectric ceramic fillers and polymer matrices offer a high dielectric constant and breakdown strength with mechanical flexibility and formability. The flexible and lead-free piezoelectric nanocomposites are composed of BaTiO3 nanowires (filler) and polyvinylidene fluoride (PVDF) (matrix). BaTiO3 nanowires with high aspect ratios were synthesized and incorporated into PVDF matrix. Lead-free piezoelectric nanocomposites are eco-friendly, which are promising substitutes with the added benefit of mechanical flexibility suitable for wearable electronics.

- W. Choi, K. Choi, J. Kim, C. Yu, “Improving piezoelectric performance of lead-free polymer composites with high aspect ratio BaTiO3 nanowires,” Polymer Testing, 53, 143-148 (2016).




Last updated: June-2016