Browsing by Author "Zhu, Likun"
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Item A 3D microfluidic device fabrication method using thermopress bonding with multiple layers of polystyrene film(IOP, 2015-05) Cao, Yuanzhi; Bontrager-Singer, Jacob; Zhu, Likun; Department of Mechanical Engineering, School of EngineeringIn this article, we present a fabrication method that is capable of making (3D) microfluidic devices with multiple layers of homogeneous polystyrene (PS) film. PS film was chosen as the primary device material because of its advantageous features for microfluidics applications. Thermopress is used as a bonding method because it provides sufficient bonding strength while requiring no heterogeneous bonding materials. By aligning and sequentially stacking multiple layers (3 to 20) of patterned PS film that were achieved by a craft cutter, complicated 3D structured microfluidic devices can be fabricated by multiple steps of thermopress bonding. The smallest feature that can be achieved with this method is approximately 100 μm, which is limited by the resolution of the cutter (25 μm) as well as the thickness of the PS films. Bonding characteristics of PS films are provided in this article, including a PS film bonding strength test, bonding precision assessment, and PS surface wettability manipulation. To demonstrate the capability of this method, the design, fabrication, and testing results of a 3D interacting L-shaped passive mixer are presented.Item Atomistic Study of the Effect of Magnesium Dopants on Nancrystalline Aluminium(2019-08) Kazemi, Amirreza; Yang, Shengfeng; Zhang, Jing; Zhu, LikunAtomistic simulations are used in this project to study the deformation mechanism of polycrystalline and bicrystal of pure Al and Al-Mg alloys. Voronoi Tessellation was used to create three-dimensional polycrystalline models. Monte Carlo and Molecular Dynamics simulations were used to achieve both mechanical and chemical equilibrium in all models. The first part of the results showed improved strength, which is included the yield strength and ultimate strength in the applied tensile loading through the addition of 5 at% Mg to nanocrystalline aluminum. By viewing atomic structures, it clearly shows the multiple strengthening mechanisms related to doping in Al-Mg alloys. The strength mechanism of dopants exhibits as dopant pinning grain boundary (GB) migration at the early deformation stage. At the late stage where it is close to the failure of nanocrystalline materials, Mg dopants can stop the initiation of intergranular cracks and also do not let propagation of existing cracks along the GBs. Therefore, the flow stress will improve in Al-Mg alloy compared to pure Al. In the second part of our results, in different bicrystal Al model, ∑ 3 model has higher strength than other models. This result indicates that GB structure can affect the strength of the material. When the Mg dopants were added to the Al material, the strength of ∑5 bicrystal models was improved in the applied shear loading. However, it did not happen for ∑ 3 model, which shows Mg dopants cannot affect the behavior of this GB significantly. Analysis of GB movements shows that Mg dopants stopped GBs from moving in the ∑ 5 models. However, in the ∑ 3 GB, displacement of grain boundary planes was not affected by Mg dopants. Therefore, the strength and flow stress are improved by Mg dopants in ∑ 5 Al GBs, not in the ∑ 3 GBs.Item Bayesian Optimization of Active Materials for Lithium-Ion Batteries(SAE, 2021-04) Valladares, Homero; Li, Tianyi; Zhu, Likun; El-Mounayri, Hazim; Tovar, Andres; Hashem, Ahmed; Abdel-Ghany, Ashraf E.; Mechanical Engineering, School of Engineering and TechnologyThe design of better active materials for lithium-ion batteries (LIBs) is crucial to satisfy the increasing demand of high performance batteries for portable electronics and electric vehicles. Currently, the development of new active materials is driven by physical experimentation and the designer’s intuition and expertise. During the development process, the designer interprets the experimental data to decide the next composition of the active material to be tested. After several trial-and-error iterations of data analysis and testing, promising active materials are discovered but after long development times (months or even years) and the evaluation of a large number of experiments. Bayesian global optimization (BGO) is an appealing alternative for the design of active materials for LIBs. BGO is a gradient-free optimization methodology to solve design problems that involve expensive black-box functions. An example of a black-box function is the prediction of the cycle life of LIBs. The cycle life cannot be predicted using a simple closed-form expression but only through the cycling performance test or a numerical simulation. BGO has two main components: a surrogate probabilistic model of the black-box function and an acquisition function that guides the optimization. This research employs BGO in the design of cathode active materials for LIB cells. The training data corresponds to the initial capacity and cycle life of five coin cells with different compositions of LiNixMn2 − xO4 in their cathode, where x is the content of Ni. BGO utilizes the experimental data to identify five new compositions that can produce cells with high initial capacity and\or large cycle life. The surrogate models of the initial capacity and cycle life are Gaussian Processes. The acquisition function is the constrained multi-objective expected improvement. The results show that BGO can identify high-performance active materials for LIBs. Designers can use the data generated during the optimization to decide the composition of the next batch of active materials to be tested, i.e., guide the physical experimentation.Item Blade-Type Reaction Front in Micrometer-Sized Germanium Particles during Lithiation(ACS, 2020-09) Zhou, Xinwei; Li, Tianyi; Cui, Yi; Meyerson, Melissa L.; Weeks, Jason A.; Mullins, C. Buddie; Jin, Yang; Shin, Hosop; Liu, Yuzi; Zhu, Likun; Mechanical and Energy Engineering, School of Engineering and TechnologyTo investigate the lithium transport mechanism in micrometer-sized germanium (Ge) particles, in situ focused ion beam–scanning electron microscopy was used to monitor the structural evolution of individual Ge particles during lithiation. Our results show that there are two types of reaction fronts during lithiation, representing the differences of reactions on the surface and in bulk. The cross-sectional SEM images and transmission electron microscopy characterizations show that the interface between amorphous LixGe and Ge has a wedge shape because of the higher Li transport rate on the surface of the particle. The blade-type reaction front is formed at the interface of the amorphous LixGe and crystalline Ge and is attributed to the large strain at the interface.Item Boosting Superior Lithium Storage Performance of Alloy‐Based Anode Materials via Ultraconformal Sb Coating–Derived Favorable Solid‐Electrolyte Interphase(Wiley, 2020-01) Xiong, Bing-Qing; Zhou, Xinwei; Xu, Gui-Liang; Liu, Yuzi; Zhu, Likun; Hu, Youcheng; Shen, Shou-Yu; Hong, Yu-Hao; Wan, Si-Cheng; Liu, Xiao-Chen; Liu, Xiang; Chen, Shengli; Huang, Ling; Sun, Shi-Gang; Amine, Khalil; Ke, Fu-Sheng; Mechanical and Energy Engineering, School of Engineering and TechnologyAlloy materials such as Si and Ge are attractive as high‐capacity anodes for rechargeable batteries, but such anodes undergo severe capacity degradation during discharge–charge processes. Compared to the over‐emphasized efforts on the electrode structure design to mitigate the volume changes, understanding and engineering of the solid‐electrolyte interphase (SEI) are significantly lacking. This work demonstrates that modifying the surface of alloy‐based anode materials by building an ultraconformal layer of Sb can significantly enhance their structural and interfacial stability during cycling. Combined experimental and theoretical studies consistently reveal that the ultraconformal Sb layer is dynamically converted to Li3Sb during cycling, which can selectively adsorb and catalytically decompose electrolyte additives to form a robust, thin, and dense LiF‐dominated SEI, and simultaneously restrain the decomposition of electrolyte solvents. Hence, the Sb‐coated porous Ge electrode delivers much higher initial Coulombic efficiency of 85% and higher reversible capacity of 1046 mAh g−1 after 200 cycles at 500 mA g−1, compared to only 72% and 170 mAh g−1 for bare porous Ge. The present finding has indicated that tailoring surface structures of electrode materials is an appealing approach to construct a robust SEI and achieve long‐term cycling stability for alloy‐based anode materials.Item Characterization of dynamic morphological changes of tin anode electrode during (de)lithiation processes using in operando synchrotron transmission X-ray microscopy(Elsevier, 2019) Li, Tianyi; Zhou, Xinwei; Cui, Yi; Lim, Cheolwoong; Kang, Huixiao; Yan, Bo; Wang, Jiajun; Wang, Jun; Fu, Yongzhu; Zhu, Likun; Mechanical and Energy Engineering, School of Engineering and TechnologyThe morphological evolution of tin particles with different sizes during the first lithiation and delithiation processes has been visualized by an in operando synchrotron transmission X-ray microscope (TXM). The in operando lithium ion battery cell was operated at constant current condition during TXM imaging. Two-dimensional projection images with 40 nm resolution showing morphological evolution were obtained and analyzed. The analysis of relative area change shows that the morphology of tin particles with different sizes changed simultaneously. This phenomenon is mainly due to a negative feedback mechanism among tin particles in the battery electrode at a constant current operating condition. For irregular-shaped tin particles, the contour analysis shows that the regions with higher curvature started volume expansion first, and then the entire particle expanded almost homogeneously. This study provides insights for understanding the dynamic morphological change and the particle-particle interactions in high capacity lithium ion battery electrodes.Item CHEMICAL AND PHASE TRANSFORMATION FROM VANADIUM SULFIDE TO OXIDE VIA A NEW CHEMICAL ROUTE FOR THE SYNTHESIS OF Βʹ-LIXV2O5 AS A HIGH PERFORMANCE CATHODE(Office of the Vice Chancellor for Research, 2014-04-11) Lee, Wen Chao; Mahootcheian Asl, Nina; Kim, Youngsik; Zhu, LikunThe used of rechargeable lithium ion batteries are so widely nowadays on consumer electronics especially portable devices such as cellphones, laptops and etc. The advancement of technology has created batteries with providing high energy density without memory effect and minimum the self-discharge on standby mode. Even with these features, researchers are still trying to improve the batteries with more energy density, low cost, better safety and high durability. The energy density improves with high operation voltage and high capacity. All these features came from one source, material. The resources for current commercial cathode material are decreasing and so new alternative cathode with high performance is needed to replace the commercial cathode in the future. The high temperature vanadium pentoxide phase, βʹ-LixV2O5, was synthesized via a new chemical synthesis involving the evolution of vanadium oxides from the 600°C heat treatment of the pure LiVS2 in air. By employing this method of synthesis, well-crystalized, rod-shaped βʹ-LixV2O5 particles 20 – 30 μm in length and 3 – 6 μm in width were obtained. Moreover, the surface of βʹ-LixV2O5 particles was found to be coated by an amorphous vanadium oxysulfide film (~20 nm in thickness). In contrast to a low temperature vanadium pentoxide phase (LixV2O5), the electrochemical intercalation of lithium into the βʹ-LixV2O5 was fully reversible where 0.0 < x < 2.0, and it delivered a capacity of 310 mAh/g at a current rate of 0.07 C between 1.5 V and 4 V. Good capacity retention of more than 88% was also observed after 50 cycles even at a higher current rate of 2 C.Item Chemo-Mechanical Modeling of Stress Evolution in All-Solid-State Lithium- Ion Batteries Using Synchrotron Transmission X-ray Microscopy Tomography(Elsevier, 2021-01) Fathiannasab, Hamed; Zhu, Likun; Chen, Zhongwei; Mechanical and Energy Engineering, School of Engineering and TechnologyIn this study, a chemo-mechanical modeling framework was developed by adopting a reconstructed three-dimensional morphology of all-solid-state lithium-ion battery (ASSB) composite electrodes, using a synchrotron transmission X-ray microscopy tomography system. The developed model aimed to elucidate the effects of the electrode microstructure, specifically solid electrolyte/active material (SE/AM) interface and void space, toward the lithiation-induced stress evolution. The results show that the peak stress points happen at the SE/AM interface, while void space can partially accommodate the AM swelling and alleviate the stress formation. Although applying higher pressing pressure during the electrode fabrication can improve the ion pathways, it adversely affects the stress formation and may cause crack propagation. The results reveal that SE stiffness has a key impact on stress formation and AM displacement. Although employing SE with a lower stiffness can attenuate the stress within the microstructure, it can exacerbate the anisotropic displacement of AM particles. In contrast, applying external pressing pressure can prevent anisotropic displacement of AM particles. The developed framework highlights the significance of microstructural design of ASSBs and provides invaluable insights.Item Coupled Dynamic Analysis of Flow in the Inlet Section of a Wave Rotor Constant Volume Combustor(2011-12) Smith, Keith Cameron; Nalim, M. Razi; Zhu, Likun; Xie, JianA wave rotor constant volume combustor (WRCVC) was designed and built as a collaborative work of Rolls Royce LibertyWorks, Indiana University-Purdue University at Indianapolis (IUPUI), and Purdue University, and ran experimental tests at Purdue's Zucrow Laboratories in 2009. Instrumentation of the WRCVC rig inlet flow included temperature and pressure transducers upstream of the venturi and at the fuel delivery plane. Other instrumentation included exhaust pressures and temperatures. In addition, ion sensors, dynamic pressure sensors, and accelerometers were used to instrument the rotating hardware. The rig hardware included inlet guide vanes directly in front of the rotating hardware, which together with concern for damage potential, prevented use of any pressure transducers at the entrance to the rotor. For this reason, a complete understanding of the conditions at the WRCVC inlet is unavailable, requiring simulations of the WRCVC to estimate the inlet pressure at a specific operating condition based on airflow. The operation of a WRCVC rig test is a sequence of events over a short time span. These events include introduction of the main air flow followed by time-sequenced delivery of fuel, lighting of the ignition source, and the combustion sequence. The fast changing conditions in the rig inlet hardware make necessary a time-dependent computation of the rig inlet section in order to simulate the overall rig operation. The chosen method for computing inlet section temperature and pressure was a time-dependent lumped volume model of the inlet section hardware, using a finite difference modified Euler predictor-corrector method for computing the continuity and energy equations. This is coupled with perfect gas prediction of venturi air and fuel flow rates, pressure drag losses at the fuel nozzles, pressure losses by mass addition of the fuel or nitrogen purge, friction losses at the inlet guide vanes, and a correlation of the non-dimensional flow characteristics of the WRCVC. The flow characteristics of the WRCVC are computed by varying the non-dimensional inlet stagnation pressure and the WRCVC's operational conditions, assuming constant rotational speed and inlet stagnation temperature. This thesis documents the creation of a computer simulation of the entire WRCVC rig, to understand the pressure losses in the inlet system and the dynamic coupling of the inlet section and the WRCVC, so that an accurate prediction of the WRCVC rotor inlet conditions can be computed. This includes the computational development of the WRCVC upstream rig dynamic model, the background behind supporting computations, and results for one test sequence. The computations provide a clear explanation of why the pressures at the rotor inlet differ so much from the upstream measured values. The pressure losses correlate very well with the computer predictions and the dynamic response tracks well with the estimation of measured airflow. A simple Fortran language computer program listing is included, which students can use to simulate charging or discharging of a container.Item Crack-Free Silicon Monoxide as Anodes for Lithium-Ion Batteries(ACS, 2020-12) Lu, Wenquan; Zhou, Xinwei; Liu, Yuzi; Zhu, Likun; Mechanical and Energy Engineering, School of Engineering and TechnologyThe volume expansion of Si and SiO particles was investigated using a single-particle battery assembled with a focused ion beam and scanning electron microscopy (FIB-SEM) system. Single Si and SiO particles were galvanostatically charged and discharged as in real batteries. Microstructural changes of the particles were monitored in situ using FIB-SEM from two different angles. The results revealed that the volume expansion of micrometer size particle SiO was not only much smaller than that of Si, but it also kept its original shape with no sign of cracks. This isotropic mechanical property of a SiO particle can be attributed to its microstructure: nanosized Si domains mixed with SiO2 domains. The nanosized Si domains can mitigate the anisotropic swelling caused by the orientation-dependent lithium-ion insertion; the surrounding SiO2 domains can act as a buffer to further constrain the localized anisotropic swelling.