Luminescent properties of hydrothermally prepared zinc silicate phosphors

Li, Qinghua The Pennsylvania State University 2004 해외박사(DDOD)

Mn substituted willemite Zn2SiO4:Mn2+ phosphor is traditionally used in low refresh rate display technology. This phosphor shows high quantum efficiency, high luminance and purer green color than other green phosphors such as Tb3+-activated phosphates and aluminates. The long lifetime of the phosphor limits its use in the display that needs a rapid change in its image. In this research, the decay properties of Zn silicate phosphor were investigated by a new experimental technique. Hydrothermal reactions were carried out at high temperatures to synthesize pure and dopant-containing Zn2SiO 4:Mn2+ phosphors. The dopants include the ion pairs of Ga3+ + Li+ and Al3+ + Li +. High emission intensity was obtained at 700°C under hydrothermal conditions for the pure and dopant-containing phosphors. For the pure Zn2SiO4:Mn2+ phosphor, the decay properties at low Mn contents were investigated. The intrinsic decay time t1/e (the decay time to the 1/e emission point) is about 13 ms at room temperature. The influence of the Mn content on the decay time t10 was studied. The Mn distribution in each single particle and among particles was adjusted by the solid/water ratio and the reactivity of ZnO. Mode emission wavelength was measured to determine the Mn concentration in the emission layer of phosphor particles. The results show that the decay time t10 of an isolated Mn2+ ion pair is not less than 15 ms. Fast decay rate is attributed to the formation of Mn clusters in willemite structure. For the phosphors with dopants, the dopants (Ga + Li; Al + Li) do not influence the decay time t10 at 11 ms or below. The solubility of (Ga + Li) in Zn silicate willemite phase at 700°C is estimated to be 1.5--2atm% of the Zn couples, or 3--4atm% of the Zn sites can be occupied by the Ga + Li ion couples. About 4--5atm% of Zn sites can be occupied by Al + Li ion couples at 700°C. The addition of the Al + Li ion couples promotes the quantum efficiency in the VUV range, that is, from 120 to 200 nm.

Synthesis and physical properties of impurity doped ZnO materials

Li Guojie 부경대학교 대학원 2014 국내박사

ZnO is becoming more and more popular as third-generation semiconductor for its wide band gap (~3.4 eV) and large exciton binding energy (60meV) at room temperature, which permits efficient excitonic emission processes, therefore ZnO has gereat development potential in the field of optoelectronic devices. In addition, ZnO has a high melting point, high thermal and chemical stability. ZnO single crystal thin film can be obtained at the high temperature at certain condition, so it can greatly reduce the defects formed in ZnO. Furthermore, ZnO is abundant, cheap, innoxious, easy to be prepared and with potential commercial value. To realize the ZnO-based device applications, an imperative issue is to fabricate the high quality n- and p-type ZnO. While ZnO is naturally n-type conductivity due to the various native defects, which is the difficulty in achieving high-quality stable p-type ZnO. Powder, ceramic and thin film n- and p-type ZnO-based samples are made by various methods including sol-gel, solid phase and pulsed laser deposition (PLD) methods. The physical properties of the samples are characterized by X-ray diffraction (XRD), Field-Emission Scanning Electron Microscope (FE-SEM), Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Hall test instruments. A special phenomenon is observed during the investigation that the Li-doped thin films show ferromagnetism at room temperature. The detailed contents and innovations would be introduced next. For n-type ZnO, Al is chosen as the dopant element in research. Ceramics and thin films are prepared to do the investigation with various doping compositions (Zn1−xAlxO, x = 0.02-0.2). The XRD patterns show the Al is well doped into the host material and higher reaction temperature may improve the composition. The good target ceramics also affect the quality of the thin films. Except the substrate peak, there is only the (002) c-axis direction peaks are observed from the XRD patterns of thin films. The flat surface and low roughness thin films are observed from FE-SEM and AFM images. The optical transmittance of the thin film is good, and the carrier concentration of electrons of Zn1-xAlxO film is as high as 4×1021 cm-3. Both the powder and ceramic Li-doped ZnO show no impurity peak from the XRD patterns. The reaction temperature and time would affect the morphology of the powder which is made by sol-gel method. pH value should be another considerable condition during the experiment. All of the samples show the signature dielectric property follow the changeable test conditions. For p-type Li doped ZnO thin film, conditions has been changed including different substrates, temperatures and various dopant concentration. Thin films are grown on the Al2O3(0001) substrate at 600 ℃ with the Li concentration from 2% to 18%. SEM and AFM images show the surface conditions of the thin films while the optical absorption studies in the wavelength range 200-900 nm revealed an increase in the band gap of the Li-doped ZnO films from 3.19 to 3.41 eV. And during the Zn1−xLixO thin films for x=0.01, 0.05 and 0.10 on Pt (111) /Ti/SiO2/Si substrate under 500 ℃, 5 at% and 10 at% Li doped ZnO thin films show p-type behavior by Hall effect testing results. The existence of defects such as Lii (interstitial Li) and LiZn (substitutional Li on the Zn site) should be considered in the host materials. The stabilization of p-type thin films is also discussed in defects theoretically. In further research, the structural, electric and magnetic properties of ZnO:Li thin films for 2%, 5%, 8% and 10% Li-doped thin films which are prepared on Pt(111)/TiO2/Si/SiO2 substrates by pulsed laser deposition are reported. Lattice parameters and Zn-O bond lengths are calculated from X-ray diffraction (XRD) results. The 8% ZnO:Li thin film show room temperature ferromagnetism and the hysteresis loop is observed. In particular, the native point defects in ZnO (such as Zni, Vo, Vzn) and Li-related defects (Lii and Lizn) are analyzed by X-ray photoelectron spectroscopy (XPS). Zni and Vo defects give indirect evidences, while the photoluminescence results show circumstantial proof of the existence of VZn, LiZn and VZn defects play a vital role in p-type films and ferromagnetism, respectively. Moreover, the Hall effect results also corroborate the formation and stabilization of efficiency factors and thus stabilizing the p-type ferromagnetism predicted for cation vacancy in ZnO thin film.

Applying nanoscale science to lithium-ion battery and membrane transport

Li, Naichao University of Florida 2003 해외박사(DDOD)

This dissertation provides background information on nanoscale science, the template synthesis of nanomaterials, and its application to Li-ion battery and membrane transport. My work has shown that compared with conventional thin-film electrodes with the same mass, the template-synthesized SnO 2 nanofibers and the nanoporous carbon-honeycomb have much higher rate capability and cycling performance as Li-ion battery anodes. This is because the high-rate capacity of Li-ion battery is limited by slow solid-state Li + diffusion in electrode materials, and the nanostructured electrodes decrease the distance that Li+ must diffuse in the solid state. Furthermore, the surface area of the nanostructured electrode was larger, making the effective current-density during discharge smaller than that for a conventional electrode. Better cycling performance was achieved because the spaces between the nanostructures of electrode materials could accommodate the volume changes due to Li+ insertion and extraction through the electrode materials. In an effort to combine the advantages of both nanostructured electrodes and all-solid-state Li-ion batteries, a nanostructured all-solid-state Li-ion battery was investigated. This battery was designed to use the carbon honeycomb as the anode and the substrate; the surface and the inner walls of the carbon honeycomb were then covered with an ultrathin electrochemically polymerized poly(phenylene oxide) (PPO) film, which was used as the solid electrolyte. The PPO film was very thin (0.5--1.9 nm) and could be easily deposited into the inner walls of the carbon honeycomb. PPO film was only conductive to cations (e.g., Li+) after sulfonation. My research also showed that O2 plasma etching could be used to prepare not only the carbon honeycomb anode but also nanostructured conical pores in polymeric membranes. Conical pore embedded membranes can be used for enhanced membrane transport and resistive-pulse sensing of particles such as molecules and ions. The plasma etch method provides a simple and convenient route for preparing conical-nanopore membranes.

Dielectric properties of Li-doped ZnO thin films prepared by pulsed laser deposition

Li Guojie 부경대학교 2010 국내석사

ZnO is becoming more and more popular third-generation semiconductor for its wide band gap and large exciton binding energy. But the pure ZnO gradually can?ft meet the people?fs demands in nowadays, then impurity doping and the using of the defects which can improve and enlarge the properties are hot spot in nowadays. This article introduces the way of Li doped into ZnO. Thin films of Li-doped ZnO with different compositions (Zn1−xLixO, x = 0.02-0.2) have been prepared on heavily doped Si substrates by a pulsed laser deposition technique, and we get the good quality transparent conducting oxides thin film with a ferroelectric nature. Through many substantial tests, theoretical studies and comparisons to the conclusions in hand, our mainly contents as following: 1. We choose the Li element doped into the ZnO and the impurities are well doped into the ZnO; the impurities affect little to the structure of the ZnO. 2. The thin films are made by the PLD method, and the structure of the crystal in the thin film grows well follow the c-axis. The ferroelectricity of the thin film Zn0.88Li0.12O is observed in the P-E hysteresis loop test ,and Ec is 5.53 KV/cm and Pr is 0.186 ??c/cm2 3. The permittivity of the Zn1-xLixO is involved with the temperature and the frequencies. And we also find a crest in the test around certain temperature, so we can call the change temperature Tc for short , for example, the Tc of the Zn0.85Li0.15O is about 95?? 4. The optical transmission of the .Zn1-xLixO thin films are good, most are over 75%; through the calculation with the test dates, we can roughly get the academic thickness of the thin film, which is coincide with the actual result.

(A) study on CuO conversion cathode based on LiAlCl4·3SO2 electrolyte system for lithium rechargeable batteries

Li, Siying Sungkyunkwan university 2021 국내박사

Due to the high energy density, long cycle life, and environmental friendliness features, lithium-ion batteries (LIBs) have been widely applied in portable electronic devices and have become a promising power source for electric vehicles. However, numerous safety accidents related to thermal runaways due to battery failures have occurred over the past decade, indicating that the fire hazard of LIBs can no longer be ignored. Among the strategies to improve the thermal stability of the battery system, the use of non-flammable electrolytes is an effective way to prevent battery ignition and explosion. SO2-in-salt electrolyte composed of LiAlCl4·3SO2, as one of the non-flammable inorganic ionic liquids with high conductivity and Li-ion transference number, has attracted increasing attention. This dissertation mainly focuses on a high-energy-density LiAlCl4·3SO2 electrolyte lithium rechargeable battery system based on CuO cathode. Chapter 2 presents a natural-activable CuO hollow nanocube (HNC) cathode material for dual-ion Li metal batteries using SO2-in-salt electrolyte. Natural activation is achieved via spontaneous chlorination of CuO HNCs into an electrochemically active CuCl2 phase upon immersed in the SO2-in-salt electrolyte. The on-site conversion reactions are proposed with the support of thermodynamic calculations; the phase transformations of active materials are confirmed through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (SEM). As a solution to alleviate the volume expansion after chlorination, the HNC structure of CuO allows the resulting CuCl2 cathode material to deliver a reversible capacity up to 262.2 mAh g-1 (894.2 Wh kgCuO-1) with stable cycle performance over 150 cycles. The Li-CuO battery system presented here demonstrates the feasibility of non-flammable, high-energy-density Li/Cl dual-ion Li metal batteries as a potential alternative to currently used lithium-ion batteries. Chapter 3 introduces the optimization of CuO cathode for the Li/Cl dual-ion Li metal batteries system with polyacrylonitrile (PAN). The multi-yolk-shell (MYS) CuO has been fabricated and used as the active material for the CuO cathode. The oxidative cyclization of PAN at different temperatures has been investigated through Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), and XPS. The effect of cyclized PAN on electrode performance has been studied by experiments on Cu ion adsorption and active material loss as well as electrochemical tests. The extent of cyclization increases with temperature leading to an increase in electrical conductivity owing to the formation of N-doped delocalized C-ring in cyclized-PAN. This oxidative process also leads to the formation of O-containing functional groups, which facilitates the transfer of Li ions and adsorbs Cu ions to slow the capacity decay. The MYS-CuO electrode with 280℃ cyclized-PAN achieves a significantly enhanced initial energy density of 1074.0 Wh kg-1 and maintains 866.2 Wh kg-1 at the 250th cycle with a retention rate of 80.7%. A unique flower-like morphology with a blooming-fading evolution during discharge and charge has been observed in the electrode with 280 ℃ cyclized-PAN, which is also related to the effect of cyclized PAN.

Taxonomic Study of Genus Bryoria(Lichenized Ascomycota, Parmeliaceae) from the Sino-Himalays : Sino-Himalaya 지역에서의 Bryoria 속 지의류의 분류학적 연구

Wang, Li-Song The Graduate School Sunchon Nation Universty 2006 국내박사

Sino-Himalaya 지역에서 Bryoria 속에 속하는 20종을 기록하여 보고하였다. 그 중에서 Bryoria fastigiata Li S. Wang과 B. flocculosa Li S. Wang를 신종으로 보고하며, B. himalayana var. sorediata Li S. Wang은 새로운 변종으로 보고하며, B. nadvornikiana, B. trichodes subsp. trichodes와 B. tenuis종은 중국에서 최초로 보고하며, B. trichodes subsp. americana와 B. furcellata는 Sino-Himalaya 지역에서 최초로 보고하며, B. asiatica, B. himalayana와 B. poeltii는 신장자치구 지역에서 B. divergescens, B. lactinea, B. nitidula와 B. variabilis는 사천성 지역에서, B. bicolor는 신장과 사천성 지역, B. furcellata는 사천성과 운남성 지역에서 최초로 보고한다. 각 종에 대한 이차대사산물을 분석한 결과, usnic acid와 lobaric acid를 본 속에서 최초로 보고 하였다. 각 종에 대한 분류키와 형태, 서식처 및 분포에 대하여 기술하였다. Twenty taxa of the genus Bryoria were recognized and recorded in the Sino-Himalayas. Among them, Bryoria fastigiata Li S. Wang and B. flocculosa Li S. Wang are new species, B. himalayana var. sorediata Li S. Wang is a new variety; Bryoria nadvornikiana, B. trichodes subsp. trichodes and B. tenuis are new to China; B. trichodes subsp. americana and B. furcellata are new to the Sino-Himalayas; B. asiatica, B. himalayana and B. poeltii are new to Xizang; B. divergescens, B. lactinea, B. nitidula and B. variabilis are new to Sichuan; B. bicolor is new to Sichuan and Xizang; B. furcellata is new to Sichuan and Yunnan. Secondary chemical products were studied for each taxon. Among them, usnic and lobaric acids were first reported in the genus. A key to the species and notes on morphology, habitat and distribution are given. One of specimen was collected from the type locality of B. divergescens (Li-S. Wang 04-23413, in KUN-L), which was selected as an epitype of this species, because of the fragmental nature of the holotype (H-Nyl. 35972).

Design and Performance Evaluation of DNA @ Metal-Organic Framework (MOF) composites for next-generation electrochemical energy storage devices

LI MAN 가천대학교 일반대학원 2023 국내박사

Based on the main problems existing in the current development of lithium-sulfur batteries (Li-S batteries), including low areal sulfur-loading (˂ 2.0 mg cm −2), poor polysulfides conversion kinetic, the "shuttle effect" of soluble intermediate polysulfides (Li2Sx, 4 ≤ x ≤ 8), growth of lithium dendrites and safety problems of liquid electrolytes, this thesis is mainly focusing on the modification of cathode/separator materials and designing solid-state electrolyte to enhance the performances of Li-S batteries. Deoxyribonucleic acid (DNA) decorated metal-organic framework (MOF)-derived cathode composites, and double-layer structured MOF/carbon nanotube (CNT)@DNA interlayer have been rationally designed and fabricated to enhance the performance of Li-S batteries. The morphology, microstructure, electrochemical storage mechanism, and theoretical computation were studied to investigate the roles of as-fabricated materials in enhancing the performance of L-S batteries.

HEAT TRANSFER AND THERMAL MANAGEMENT STUDIES OF LITHIUM POLYMER BATTERIES FOR ELECTRIC VEHICLE APPLICATIONS

SONG, LI UNIVERSITY OF CALIFORNIA, BERKELEY 1999 해외박사(DDOD)

The thermal conductivities of the polymer electrolyte and composite cathode are important parameters characterizing heat transport in lithium polymer batteries. The thermal conductivities of lithium polymer electrolytes, including poly-ethylene oxide (PEO), PEO-LiClO₄, PEO-LiCF₃SO₃, PEO-LiN(CF₃SO₂)₂, PEO-LiC(CF₃SO₂)₃, and the thermal conductivities of TiS₂ and V₆O₁₃ composite cathodes, were measured over the temperature range from 25°C to 150°C by a guarded heat flow meter. The thermal conductivities of the electrolytes were found to be relatively constant for the temperature and for electrolytes with various concentrations of the lithium salt. The thermal conductivities of the composite cathodes were found to increase with the temperature below the melting temperature of the polymer electrolyte and only slightly increase above the melting temperature. Three different lithium polymer cells, including Li/PEO-LiCF₃<math> <f> <?Eqn TeX input=" break"></f> </math>S<math> <f> <?Eqn TeX input=" -"></f> </math>O₃/TiS₂, Li/PEO-LiC(CF₃<math> <f> <?Eqn TeX input=" -"></f> </math>S<math> <f> <?Eqn TeX input=" -"></f> </math>O₂)₃/V₆<math> <f> <?Eqn TeX input=" -"></f> </math>O₁₃, and Li/PEO-LiN(CF₃<math> <f> <?Eqn TeX input=" break"></f> </math>S<math> <f> <?Eqn TeX input=" -"></f> </math>O₂)₂/<math> <f> <?Eqn TeX input=" -"></f> </math>Li_1+x<math> <f> <?Eqn TeX input=" -"></f> </math>Mn₂<math> <f> <?Eqn TeX input=" -"></f> </math>O₄ were prepared and their discharge curves, along with heat generation rates, were measured at various galvanostatic discharge current densities, and at different temperature (70°C, 80°C and 90°C), by a potentiostat/galvanostat and an isothermal microcalorimeter. The thermal stability of a lithium polymer battery was examined by a linear perturbation analysis. In contrast to the thermal conductivity, the ionic conductivity of polymer electrolytes for lithium-polymer cell increases greatly with increasing temperature, an instability could arise from this temperature dependence. The numerical calculations, using a two dimensional thermal model, were carried out for constant potential drop across the electrolyte, for constant mean current density and for constant mean cell output power. The numerical calculations were approximately in agreement with the linear perturbation analysis. A coupled mathematical model, including electrochemical and thermal components, was developed to study the heat transfer and thermal management of lithium polymer batteries. The results calculated from the model, including temperature distributions, and temperatures at different stages of discharge are significantly different from those calculated from the thermal model. The discharge curves and heat generation rates calculated by the electrochemical-thermal model were in agreement with the experimental results. Different thermal management approaches, including a variable conductance insulation enclosure were studied.

Structure and Properties Study on Energy Materials: Thermoelectric Material Tetrahedrite and Lithium Ion Conductor LiPON

Li, Junchao Michigan State University ProQuest Dissertations & 2020 해외박사(DDOD)

Development of efficient energy materials is critical in order to ease the energy demand and reduce our dependence of fossil fuel. Thermoelectric materials are promising due to their capability of generating electrical power by recovering waste heat. The performance of thermoelectric materials is quantified by a dimensionless figure of merit zT, which depends on their properties such as electrical conductivity, Seebeck coefficient and thermal conductivity. Tetrahedrites, a copper antimony sulfosalt mineral, typified by Cu12-xMxSb4S13, where M is a transition metal element such as Ni, Zn, Fe or Mn, have great potential for thermoelectric application due to their relatively high zT (close to 1 at 700 K), earth-abundance, environmental friendliness, favorable electrical properties, and most importantly intrinsic low lattice thermal conductivity (less than 1 W m-1 K-1) in wide temperature. In addition to energy recovery, reliable energy storage devices are also emerging to relieve the energy demand and improve the efficiency of consuming energy resources. Lithium-ion batteries are known to be reliable and successful electrochemical energy storage devices and appliable in various aspects, including laptops, smartphones and electrical vehicles. Lithium phosphorous oxynitride (LiPON) are widely used as thin-film solid-state electrolytes in Li-ion battery, which is the only demonstrated solid-state electrolyte that is quite stable in direct contact with Li metal at potentials from 0-5 V. However, the structure of LiPON, the effects of N doping, and the origin of its good electrochemical stability remains inconclusive.In this thesis, reliable modeling techniques accompanied with experimental tools, are applied to study the thermoelectric material tetrahedrite and the ionic conductor LiPON, in order to study their structural and dynamical properties. Accurate and efficient density-functional theory (DFT) and density-functional tight-binding (DFTB) methods, combined with molecular dynamics (MD) simulations are utilized in order to investigate the structures and properties of these energy materials. The incoherent and coherent atomic dynamics study of tetrahedrite Cu10.5NiZn0.5Sb4S13 provides the origin of softening upon cooling by investigate the motion of Cu12e at different temperatures. The dynamic structure factors in the longitudinal and transverse direction will also be discussed. The Cu movement of Cu-rich tetrahedrite Cu14Sb4S13 is revealed by Cu self-diffusivity, nuclear density map and “nudged elastic band” (NEB). Moreover, we investigate the effect of simulation cell size and basis sets on the DFT-based MD simulation results using tetrahedrite Cu10Zn2Sb4S13 thermoelectric as a model material, showing the advantage of larger cell by accessing smaller Q range. In addition, the low-temperature structural properties of Cu12Sb4S13 is measured by neutron diffraction, which indicates that no cubic to tetragonal transition occurs at metal-semiconductor transition (MST) temperature. Thermoelectric properties such as Seebeck coefficient, electrical resistivity and electrical thermal conductivity will also be investigated. DFTB method is implemented to study the structure and transport properties of Li3PO4 and LiPON, while the exploration of N doping effect is included. Lastly, the LiPON/Li interphase will be revealed in order to study the origin of electrochemical stability.

Diagnosis and Optimization of High Voltage Cathode Materials and Electrolyte for Next Generation Li-ion Batteries

Li, Yixuan ProQuest Dissertations & Theses University of Cali 2022 해외박사(DDOD)

The rapid growth of the electric vehicle market requires the development of Li-ion batteries (LIBs) with higher energy density and longer cycle life. The classical layered nickel, manganese, and cobalt oxides (NMC) and lithium-rich layered oxides (LRLO) have attracted great interest as high-energy LIB cathode materials due to their high theoretical capacity. However, their inherent structure instability at the highly-delithiated state and the electrolyte degradation induced at high voltage cause cell degradation as cycling proceeds. In this thesis, different degradation mechanisms and the corresponding mitigating strategies are studied for both NMC and LRLO materials. Firstly, twin boundary defect engineering was adopted in a series of NMC cathodes to improve the structure and cycling stability. The radially aligned twin boundaries with the formation of rocksalt-like phase along the boundaries are observed through STEM, acting as a rigid framework that mitigates the anisotropic changes during charge and discharge, as confirmed by operando XRD. The reduced microcrack formation is also confirmed by FIB and SEM. Secondly, an in-depth understanding of the heat treatment induced structure and voltage recovery in cycled LRLO is provided. The transition metal layer reordering is identified as the key factor under the structure recovery of degraded LRLO. The reappearance of the honeycomb superlattice during heat treatment is captured through NPD, PDF, and EXAFS. In addition, an ambient-air relithiation combined with heat treatment is proved to effectively recover both the voltage and capacity of cycled LRLO. Lastly, lithium bis-(oxalate)borate (LiBOB) is studied as an electrolyte additive in protecting cathode-electrolyte interphase (CEI) from hydrofluoric acid (HF) corrosion induced by electrolyte decomposition at high voltage. Analytical EM under cryo-condition confirms the formation of a uniform CEI and less phase transformation on the LRLO particle surface. The formation of B-F species is identified in the cycled electrolyte with NMR, elucidating the HF scavenger effect of LiBOB. Due to less HF corrosion on both CEI and SEI, a reduced amount of transition metal dissolution and redeposition has been proved by EDX and XPS. The prevention of cell crosstalk thereby mitigates the capacity decay in LRLO/graphite full cells.