Browsing by Author "Fu, Yongzhu"
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Item Advanced Materials for Rechargeable Lithium-Sulfur Batteries(Office of the Vice Chancellor for Research, 2014-04-11) Fu, YongzhuRechargeable batteries are essential power supplies for our daily life, and they are widely used in portable electronics, hybrid electric vehicles, and grid energy storage. Lithium-ion (Li-ion) batteries, which have the highest energy density among rechargeable batteries, have reached the capacity limits of current electrode materials, such as transition metal oxides (e.g., LiCoO2, LiMn2O4, and LiFePO4). To meet the increasing demand of high energy density batteries, rechargeable lithium-sulfur (Li-S) batteries are considered as one of the most promising systems with significant potential for many practical applications. Sulfur has a theoretical capacity of 1,672 mAh/g by taking two electrons per atom, which is an order of magnitude higher than those of transition metal oxides. However, several challenges impede practical application of Li-S batteries, such as high resistivity of sulfur, dissolution of intermediate polysulfides, and shuttle of these polysulfides from cathode to anode in Li-S batteries. Significant improvements have been achieved over the past years, but further improvements and better understanding of Li-S batteries are still needed. This poster will present several strategies that have been developed including sulfur-conductive polymer nanocomposites, lithium/dissolved polysulfide cells, sandwiched Li2S electrodes, and in situ formed Li2S cathodes. A nanolayer of conductive polypyrrole was fabricated on sulfur particles, which can enhance electrical conductivity and reduce dissolution of polysulfides. Binder-free carbon nanotube current collector was used in lithium/dissolved polysulfide cells, which exhibit unprecedented capaciteis of 1,600 mAh/g in the first cycle and over 1,400 mAh/g after 50 cycles. Lithium metal anode is used in current Li-S batteries since the sulfur cathodes do not have any lithium in the initial stage, which is a safety hazard. Lithium-rich sulfur cathode materials such as Li2S can allow a variety of non-lithium metal anodes to be used, which can advance the Li-S battery technology to an unprecedented level. However, the high reactivity of Li2S results in limited approaches that have been explored. A sandwiched Li2S electrode consisting of two layers of carbon nanotube paper has been developed which shows high capacities and high rate capabilities. In addition, a novel in situ formed Li2S cathode is developed, which utilizes lithiated graphite as a lithium donor to convert lithium polysulfide Li2S6 to the end discharge product Li2S. These materials and strategies are promising for practical applications.Item Bis(aryl) Tetrasulfides as Cathode Materials for Rechargeable Lithium Batteries(Wiley, 2017) Guo, Wei; Wawrzyniakowski, Zachary D.; Cerda, Matthew M.; Bhargav, Amruth; Pluth, Michael D.; Ma, Ying; Fu, Yongzhu; Department of Mechanical Engineering, School of Engineering and TechnologyAn organotetrasulfide consists of a linear chain of four sulfur atoms that could accept up to 6 e− in reduction reactions, thus providing a promising high-capacity electrode material. Herein, we study three bis(aryl) tetrasulfides as cathode materials in lithium batteries. Each tetrasulfide exhibits two major voltage regions in the discharge. The high voltage slope region is governed by the formation of persulfides and thiolates, and the low voltage plateau region is due to the formation of Li2S2/Li2S. Based on theoretical calculations and spectroscopic analysis, three reduction reaction processes are revealed, and the discharge products are identified. Lithium half cells with tetrasulfide catholytes deliver high specific capacities over 200 cycles. The effects of the functional groups on the electrochemical characteristics of tetrasulfides are investigated, which provides guidance for developing optimum aryl polysulfides as cathode materials for high energy lithium batteries.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 A Class of Organopolysulfides As Liquid Cathode Materials for High-Energy-Density Lithium Batteries(ACS, 2018) Bhargav, Amruth; Bell, Michaela Elaine; Karty, Jonathan; Cui, Yi; Fu, Yongzhu; Mechanical Engineering, School of Engineering and TechnologySulfur-based cathodes are promising to enable high-energy-density lithium–sulfur batteries; however, elemental sulfur as active material faces several challenges, including undesirable volume change (∼80%) when completely reduced and high dependence on liquid electrolyte wherein an electrolyte/sulfur ratio >10 μL mg–1 is required for high material utilization. These limit the attainable energy densities of these batteries. Herein, we introduce a new class of phenyl polysulfides C6H5SxC6H5 (4 ≤ x ≤ 6) as liquid cathode materials synthesized in a facile and scalable route to mitigate these setbacks. These polysulfides possess sufficiently high theoretical specific capacities, specific energies, and energy densities. Spectroscopic techniques verify their chemical composition and computation shows that the volume change when reduced is about 37%. Lithium half-cell testing shows that phenyl hexasulfide (C6H5S6C6H5) can provide a specific capacity of 650 mAh g–1 and capacity retention of 80% through 500 cycles at 1C rate along with superlative performance up to 10C. Furthermore, 1302 Wh kg–1 and 1720 Wh L–1 are achievable at a low electrolyte/active material ratio, i.e., 3 μL mg–1. This work adds new members to the cathode family for Li–S batteries, reduces the gap between the theoretical and practical energy densities of batteries, and provides a new direction for the development of alternative high-capacity cathode materials.Item Development of Novel Cathodes for High Energy Density Lithium Batteries(2016-04) Bhargav, Amruth; Fu, Yongzhu; Zhu, Likun; Zhang, Jing; Anwar, SohelLithium based batteries have become ubiquitous with our everyday life. They have propelled a generation of smart personal electronics and electric transport. Their use is now percolating to various fields as a source of energy to facilitate the operation of devices from nanoscale to mega scale. This need for a portable energy source has led to tremendous scientific interest in this field to develop electrochemical devices like batteries with higher capacities, longer cycle life and increased safety at a low cost. To this end, the research presented in this thesis focuses on two emerging and promising technologies called lithium-oxygen (Li-O₂) and lithium-sulfur (Li-S) batteries. These batteries can offer an order of magnitude higher capacities through cheap, environmentally safe and abundant elements, namely oxygen and sulfur. The first work introduces the concept of closed system lithium-oxygen batteries wherein the cell contains the discharge product of Li-O₂ batteries namely, lithium peroxide (Li₂O₂) as the starting active material. The reversibility of this system is analyzed along with its rate performance. The possible use of such a cathode in a full cell is explored. Also, this concept is used to verify if all the lithium can be extracted from the cathode in the first charge. In the following work, lithium peroxide is chemically synthesized and deposited in a carbon nanofiber matrix. This forms a free-standing cathode that shows high reversibility. It can be cycled up to 20 times, and while using capacity control protocol, a cycle life of 50 is obtained. The cause of cell degradation and failure is also analyzed. In the work on full cell lithium-sulfur system, a novel electrolyte is developed that can support reversible lithium insertion and extraction from a graphite anode. A method to deposit solid lithium polysulde is developed for the cathode. Coupling a lithiated graphite anode with the cathode using the new electrolyte yields a full cell whose performance is characterized and its post-mortem analysis yields information on the cell failure mechanism. Although still in their developmental stages, Li-O₂ and Li-S batteries hold great promise to be the next generation of lithium batteries, and these studies make a fundamental contribution towards novel cathode and cell architecture for these batteries.Item Electrochemical behavior of tin foil anode in half cell and full cell with sulfur cathode(Elsevier, 2019-01) Cui, Yi; Li, Tianyi; Zhou, Xinwei; Mosey, Aaron; Guo, Wei; Cheng, Ruihua; Fu, Yongzhu; Zhu, Likun; Mechanical Engineering, School of Engineering and TechnologyTin-based (Sn) metal anode has been considered an attractive candidate for rechargeable lithium batteries due to its high specific capacity, safety and low cost. However, the large volume change of Sn during cycling leads to rapid capacity decay. To address this issue, Sn foil was used as a high capacity anode by controlling the degree of lithium uptake. We studied the electrochemical behavior of Sn foil anode in half cell and full cell with sulfur cathode, including phase transform, morphological change, discharge/charge profiles and cycling performance. Enhanced cycling performance has been achieved by limiting the lithiation capacity of the Sn foil electrode. A full cell consisting of a pre-lithiated Sn foil anode and a sulfur cathode was constructed and tested. The full cell exhibits an initial capacity of 1142 mAh g−1 (based on the sulfur mass in the cathode), followed by stable cycling performance with a capacity retention of 550 mAh g−1 after 100 cycles at C/2 rate. This study reports a potential prospect to utilize Sn and S as a combination in rechargeable lithium batteries.Item Electrochemical model based fault diagnosis of lithium ion battery(2015-08) Rahman, Md Ashiqur; Anwar, Sohel; Izadian, Afshin; Fu, YongzhuA gradient free function optimization technique, namely particle swarm optimization (PSO) algorithm, is utilized in parameter identification of the electrochemical model of a Lithium-Ion battery having a LiCoO2 chemistry. Battery electrochemical model parameters are subject to change under severe or abusive operating conditions resulting in, for example, Navy over-discharged battery, 24-hr over-discharged battery, and over-charged battery. It is important for a battery management system to have these parameters changes fully captured in a bank of battery models that can be used to monitor battery conditions in real time. In this work, PSO methodology has been used to identify four electrochemical model parameters that exhibit significant variations under severe operating conditions. The identified battery models were validated by comparing the model output voltage with the experimental output voltage for the stated operating conditions. These identified conditions of the battery were then used to monitor condition of the battery that can aid the battery management system (BMS) in improving overall performance. An adaptive estimation technique, namely multiple model adaptive estimation (MMAE) method, was implemented for this purpose. In this estimation algorithm, all the identified models were simulated for a battery current input profile extracted from the hybrid pulse power characterization (HPPC) cycle simulation of a hybrid electric vehicle (HEV). A partial differential algebraic equation (PDAE) observer was utilized to obtain the estimated voltage, which was used to generate the residuals. Analysis of these residuals through MMAE provided the probability of matching the current battery operating condition to that of one of the identified models. Simulation results show that the proposed model based method offered an accurate and effective fault diagnosis of the battery conditions. This type of fault diagnosis, which is based on the models capturing true physics of the battery electrochemistry, can lead to a more accurate and robust battery fault diagnosis and help BMS take appropriate steps to prevent battery operation in any of the stated severe or abusive conditions.Item Geometric and Electrochemical Characteristics of LiNi1/3Mn1/3Co1/3O2 Electrode with Different Calendering Conditions(Elsevier, 2017-04) Kang, Huixiao; Lim, Cheolwoong; Li, Tianyi; Fu, Yongzhu; Yan, Bo; Houston, Nicole; De Andrade, Vincent; De Carlo, Francesco; Zhu, Likun; Department of Mechanical Engineering, School of Engineering and TechnologyThe impact of calendering process on the geometric characteristics and electrochemical performance of LiNi1/3Mn1/3Co1/3O2 (NMC) electrode was investigated in this study. The geometric properties of NMC electrodes with different calendering conditions, such as porosity, pore size distribution, particle size distribution, specific surface area and tortuosity were calculated from the computed tomography data of the electrodes. A synchrotron transmission X-ray microscopy tomography system at the Advanced Photon Source of the Argonne National Laboratory was employed to obtain the tomography data. The geometric and electrochemical analysis show that calendering can increase the electrochemically active area, which improves rate capability. However, more calendering will result in crushing of NMC particles, which can reduce the electrode capacity at relatively high C rates. This study shows that the optimum electrochemical performance of NMC electrode at 94:3:3 weight ratio of NMC:binder:carbon black can be achieved by calendering to 3.0 g/cm3 NMC density.Item Geometric and Electrochemical Characteristics of NMC Electrodes with Different Calendering Conditions(Office of the Vice Chancellor for Research, 2016-04-08) Kang, Huixiao; Lim, Cheolwoong; Fu, Yongzhu; Zhu, LikunThe energy and power capabilities of Li ion batteries (LIBs) have been considered critical factors to determine the commercial values of the LIB powered applications. Many efforts have been done to improve the energy density and rate capability of LIBs. In addition to intrinsic material properties of anode and cathode active materials, the structure of electrode at micro and nano scales also plays a critical role in determining the energy density and rate capability of a LIB [1-3]. Calendering is a process in battery manufacturing to lower the porosity of the electrode and increase electrical contact. Increased calendering can increase the packing density of active materials in LIB electrodes, thereby increasing the volumetric energy density. The specific energy density is also increased by calendering via decreasing the percentage of inactive materials, such as current collector and separator. However, higher fraction of active materials in LIB electrodes can change electrodes’ structural properties significantly, such as porosity, specific surface area, pore size distribution and tortuosity [4]. To this end, there are few reports on the geometric characteristics and their impact on the electrochemical performance of LIB electrodes with different calendering conditions due to the inhomogeneity, complexity, and three-dimensional (3D) nature of the electrode’s microstructure [5-6]. Recently, porous electrode microstructures have been reconstructed by advanced tomography techniques such as X-ray nano-computed tomography (nano-CT) and focused ion beam scanning electron microscope (FIB-SEM)[7-8]. The reconstructed microstructures have been employed to investigate the geometric characteristics and spatial inhomogeneity of porous electrodes. In this study, we investigated real 3D Li[Ni1/3Mn1/3Co1/3]O2 (NMC) electrode microstructures under different calendering conditions and the effect of calendering on the performance of LIBs[4]. To investigate geometric characteristics of porous microstructures, cathode electrodes were fabricated from a 94:3:3 (weight %) mixture of NMC, PVDF, and super-P carbon black. To change the calendering condition, initial thickness of the electrodes was set 50μm, 80um, 90um, 100um. Then all electrodes were pressed down to 50 μm by using a rolling press machine. A synchrotron X-ray nano-CT at the Advanced Photon Source of Argonne National Lab was employed to obtain morphological data of the electrodes, with voxel size of 58.2 × 58.2 × 58.2 nm3. The morphology data sets were quantitatively analyzed to characterize their geometric properties. The geometric analysis showed that high packing density can result in smaller pore size and more uniform pore size distribution. The specific surface area and tortuosity of different electrodes will be reported. The charge/discharge experiments were also conducted for these electrodes. The geometric properties and cell testing results will be analyzed and reported.Item A Graphite-Polysulfide Full Cell with DME-Based Electrolyte(ECS, 2016) Bhargav, Amruth; Wu, Min; Fu, Yongzhu; Department of Mechanical Engineering, School of Engineering and TechnologyOver the last decade, vast improvements have been made in the field of lithium-sulfur batteries bringing it a step closer to reality. In this field of research, deep understanding of the polysulfide shuttle phenomenon and their affinity with carbons, polymers and other hosts have enabled the design of superior cathodes with prolonged life. However, the anode side has undergone comparatively less transformation. In this work, we have developed a new electrolyte based on 1,2-dimethoxyethane (DME) solvent that enables reversible intercalation of lithium ions in graphite. A novel method to introduce solid lithium polysulfide into a carbon current collector as the cathode has been demonstrated and the electrode shows stable cycling with the new electrolyte. A full cell consisting of a lithiated graphitic anode and lithium polysulfide cathode is constructed, which exhibits an initial capacity as high as 1,500 mAh g−1 (based on the sulfur in the cathode) and a reversible capacity of 700 mAh g−1 for 100 cycles. This full cell is capable of delivering over 460 mAh g−1 at rates as high as 2C. The cell degradation over prolonged cycles could be due to the polysulfide shuttle which results in instability of the SEI layer on the graphitic anode.