Chemical & Biomolecular Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/2219
Formerly known as the Department of Chemical Engineering.
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Item INTERFACE DESIGN FOR ALL-SOLID-STATE LITHIUM METAL BATTERIES(2022) He, Xinzi; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lithium-ion batteries (LIBs) have expanded their application from electronics to electric vehicles (EVs). To ease the safety concerns and the “range anxiety”, solid-state lithium batteries (SSLBs) become a more attractive choice. The replacement of flammable and toxic liquid electrolytes with solid-state electrolytes (SSEs) makes it a safer option. The utilization and compatibility of high specific capacity materials such as sulfur cathode and lithium-metal anode increase the cell energy density. However, SSLBs still face challenges towards practical application, which mainly from the solid-solid contact nature on the interfaces. On the anode side, lithium dendrite growth and high interface resistance both hindered the longevity of the cells. On the cathode side, low initial Coulombic efficiency (CE) and low capacity utilization of sulfur obstructed the realization of high loading cathodes.In this dissertation, I addressed both challenges of dendrite and contact on the anode side by adding strontium into lithium anodes. Different from all previous metal/metal oxide coating on garnet or Li alloy anodes that form lithiophilic interlayer, a lithiophilic/lithiophobic bifunctional layer is formed to reduce the interfacial resistance and to suppress the growth of lithium dendrite, which is confirmed by comprehensive material characterizations, electrochemical evaluations, and simulations. The optimum Li-Sr | garnet | Li-Sr symmetric cells achieve a high critical current density (CCD) of 1.3 mA/cm2 and can be cycled for 1,000 cycles under 0.5 mA/cm2 at room temperature, providing a new strategy for high-performance garnet SSLB. Furthermore, I (1) verified the importance of lithiophobic on dendrite suppression by discovering and successfully constructing the highest interface energy (γ, against lithium) material ever reported among all lithium compounds that can be formed on the electrolyte | anode interface; (2) revealed the impact of anode properties on the interface by enhancing the Li self-diffusivity by a co-doping method, achieved an outperformed critical loading of 4.1 mAh/cm2 at 1.0 mA∙cm-2 at room temperature. On the cathode side, I tackled both low CE and low capacity utilization issues by promoting both Li+ and e- transportation across the cathode | SSE interface, resulting in high capacity utilization of 96.5% and high capacity retention of 88.8% after 145 cycles at a high loading of 4.0 mAh cm-2 under room temperature in Li6PS5Cl based SSLB.Item HIGH-SAFETY ELECTROLYTES DESIGN FOR HIGH ENERGY DENSITY BATTERY DEVICES(2021) Zhang, Jiaxun; Wang, Chunsheng CW; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently, the market share of lithium-ion batteries (LIBs) increase rapidly in the global energy market, while accidents related to fires and explosions of LIBs reported worldwide in the past several years, thus battery safety is a vital prerequisite for battery application in our daily life. The flammable organic solvent in the electrolyte of the battery is the main source that leads to fires and explosions of batteries. Designing intrinsically safe electrolytes is the key to enhancing the safety properties of batteries. Fluorinated organic electrolytes, polymer electrolytes, and aqueous electrolytes are attractive due to their inherent non- or less-combustibles. However, the energy density, cycle stability, and battery cycle life of the LIBs using the above electrolyte systems are far from commercial batteries due to poor solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI). In this dissertation, we designed SEI/CEI on anode/cathode surfaces in fluorinated organic electrolytes, polymer electrolytes, and aqueous electrolytes to enhance battery performance. Specifically, 1. By building a highly stable CEI on a high-voltage LiCoO2 cathode, we improved the energy density of fluorinated organic electrolyte batteries. 2. By introducing UV-curable polymer into the organic electrolytes, we lowered the flammability of the sodium batteries and enhanced the energy density of the sodium battery system with stable CEI on sodium cathode. 3. By limiting the water activity in the bulk electrolyte and constructing an effective SEI layer on anode surface, we expanded the electrochemical stability window of the aqueous electrolytes. We seek to understand the working mechanism of SEI/CEI in different high-safety electrolyte systems. The corresponding electrochemistry, thermodynamics, kinetics, and reaction reversibility are studied in this work.Item BEYOND LI ION: INTERFACE ENGINEERING ENABLES HIGH ENERGY DENSITY LI AND NA METAL BATTERIES(2020) DENG, TAO; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ever-increasing demand from electric vehicles and consumer electronics, as well as the expanding market of intermittent renewable energy storage, has sparked extensive research on energy-storage devices with low cost, high energy density, and safety. Although the state-of-the-art Li-ion battery (LIB) based on highly reversible intercalation chemistry has approached its theoretical limit after several decades’ incremental improvement, there is still no great progress in the exploration of alkaline metal chemistry (Li & Na) for next-generation batteries. Compared with Li-ion chemistry, alkaline metal anode is more attractive due to the extremely high capacity (3860/1166 mA g-1 for Li/Na) and low negative electrochemical potential (-3.04/-2.71 V for Li/Na vs. the standard hydrogen electrode), thus enables next-generation batteries with high energy density. To achieve this, significant advances have been made in liquid or solid-state electrolytes that cater to the high capacity Li/Na anodes and high-voltage cathodes, but performance of the battery is still not comparable to that of commercial LIB due to dendrite formation and unstable interphase formation. Such situation requires a deep exploration on the rational design of electrolytes and interfacial stability between the electrolytes and electrodes for realizing next-generation batteries. In this dissertation, I detailed our efforts in exploring new electrolyte systems and proposed some interface engineering strategies or methods to stabilize the electrolyte-electrode interfaces, thus supporting the next-generation battery chemistries beyond LIB technology. They include nonflammable fluorinated electrolytes, polymer composites electrolytes, as well as solid-state garnet-type (Li6.75La3Zr1.75Ta0.25O12) and Na-beta-alumina (β''-Al2O3) electrolytes for Li/Na metal batteries. We studied the dendrite formation and electrode-electrolyte interface stability in the corresponding chemistry, thermodynamics, as well as kinetics. Based on the learned mechanisms, we also proposed our strategies to suppress dendrite formation and realize good performance Li/Na metal batteries by forming stable electrolyte-electrode interphases. Being enabled by the fundamental and scientific breakthroughs in terms of electrochemical mechanisms, interface chemistry, as well as interface modification techniques, this work has provided insights into the development of high-energy Li/Na metal batteries for both academic and industrial communities.Item ACTIVE AND PASSIVE MICROFLUIDICS FOR SAMPLE DISCRETIZATION, MANIPULATION AND MULTIPLEXING(2020) Padmanabhan, Supriya; DeVoe, Don L; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of microfluidic technology to compartmentalize an initial sample into discrete and isolated volumes is an important step for many biological and chemical applications, that allows molecules, cells, particles, reagents, and analytes to be spatially constrained, providing unique benefits for their characterization, sorting, and manipulation with low reagent consumption. Discretization can also increase the overall throughput and enable multiplexing. In this dissertation, two platforms are described to enable microfluidic sample discretization and manipulation. First, (2D) microwell arrays fabricated in thermoplastic cyclic olefin copolymer (COP) are explored as a new approach toward the development of high throughput, low-cost components in disposable diagnostics by utilizing a passive discretization technique. Performance of various 2D array designs is characterized numerically and experimentally to assess the impact of thermoplastic surface energy, fluid flow rate, and device geometry on sample filling and discretization. The design principles are used to successfully scale up the platform without affecting device performance. Loop-mediated isothermal amplification (LAMP) on chip is used to demonstrate the platform’s potential for discretized nucleic acid testing. Next, pin spotting in nanoliter-scale 2D arrays is demonstrated as technique for high resolution reagent integration to enable multiplexed testing in diagnostics. The potential for nucleic-acid diagnostics is evaluated by performing rolling circle amplification (RCA) on chip with integrated reagents. Finally, an innovative platform enabling complex discretization and manipulation of aqueous droplets is presented. The system uses simple membrane displacement trap elements as an active technique to perform multiple functions including droplet discretization, release, metering, capture, and merging. Multi-layer polydimethylsiloxane (PDMS) devices with membrane displacement trap (MDT) arrays are used to discretize sample into nanoliter scale droplet volumes, and reliably manipulate individual droplets within the arrays. Performance is characterized for varying capillary number flows, membrane actuation pressures, trap and membrane geometries, and trapped droplet volumes, with operational domains established for each platform function. The novel approach to sample digitization and droplet manipulation is demonstrated through discretization of a dilute bacteria sample, metering of individual traps to generate droplets containing single bacteria, and merging of the resulting droplets to pair the selected bacteria within a single droplet.Item FUNCTIONAL PARTICLE GENERATION BY AEROSOL-ASSISTED PROCESSES(2018) Liang, Yujia; Ehrman, Sheryl H; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosol-assisted processes are continuous with short residence times, simple operating procedures, and facile equipment requirements. They are scalable and promising for fabrication of functional particles as conductive pastes in solar cell metallization and interference packaging, electrode materials in energy storage devices, and photocatalysts in energy conversion. Although aerosol-assisted processes have long been used in manufacturing and their fundamentals have been intensively explored, further investigation is still required to better understand the particle formation mechanisms of different aerosol-assisted processes. In this dissertation, three different aerosol-assisted processes are investigated, spray pyrolysis, colloidal spray pyrolysis (CSP), and spray drying. These processes can be conducted under mild reaction conditions with simple operation procedures. The product particles are controllable. The effects of process variables on the product particles are studied. Furthermore, the prospects of applying these three aerosol-assisted processes in generating functional particles in applications, including solar cell metallization, battery, and photocatalysis are assessed. Part 1) includes Chapters 3-5. I first present Cu-Sn binary particle generation by spray pyrolysis. Through studying the particle oxidation behaviors under different reaction conditions, the Cu-Sn binary particles exhibit high oxidation-resistance. The one-dimensional and two-dimensional structures fabricated by direct printing inks containing Cu-Sn powders display low resistivity. They all suggest that Cu-Sn binary particles produced by spray pyrolysis are promising materials in the inks in printed electronics and in the conductive pastes in solar cell metallization and interference packaging. In Part 2), Chapters 6, a novel aerosol-assisted process, CSP, is developed. This process addresses one restriction of conventional spray pyrolysis which can only be used to fabricate particles from precursor solutions containing high-solubility salts. By applying CSP, tin@carbon (Sn@C) composite particles are produced with controllable interior structures. These composite particles exhibit high-performance as the anode materials for Li-ion and Na-ion batteries. In Part 3), Chapter 7, spray drying is utilized to fabricate photocatalysts from precursor solutions containing SnO2 colloids and edge-oxidized graphene oxide (eo-GO) sheets. The particle morphology, element distribution, and band structures were investigated by various tools. The photocatalytic activity of the composite particles is five times that of commercialized TiO2 (P25) in reducing CO2 into CH4.