Browsing by Author "Pang, WK"
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- ItemCapacity enhancement of the quenched Li-Ni-Mn-Co oxide high-voltage Li-ion battery positive electrode(Elsevier, 2017-03-23) Jena, A; Lee, CH; Pang, WK; Peterson, VK; Sharma, N; Wang, CC; Song, YF; Lin, CC; Chang, H; Liu, RSLi-rich metal oxides, regarded as a high-voltage composite cathode, is currently one of the hottest positive electrode material for lithium-ion batteries, due to its high-capacity and high-energy performance. The crystallography, phase composition and morphology can be altered by synthesis parameters, which can influence drastically the capacity and cycling performance. In this work, we demonstrate Li1.207Ni0.127Mn0.54Co0.127O2, obtained by a co-precipitation method, exhibits super-high specific capacity up to 298 mAh g−1 and excellent capacity retention of ∼100% up to 50 cycles. Using neutron powder diffraction and transmission X-ray microscopy, we have found that the cooling-treatments applied after sintering during synthesis are crucially important in controlling the phase composition and morphology of the cathodes, thereby influencing the electrochemical performance. Unique spherical microstructure, larger lattice, and higher content of Li-rich monoclinic component can be achieved in the rapid quenching process, whereas severe particle cracking along with the smaller lattice and lower monoclinic component content is obtained when natural cooling of the furnace is applied. Combined with electrochemical impedance spectra, a plausible mechanism is described for the poorer specific capacity and cycling stability of the composite cathodes. © 2017 Elsevier Ltd.
- ItemChromium ion pair luminescence: a strategy in broadband near- infrared light-emitting diode design(American Chemical Society, 2021-11-04) Rajendran, V; Fang, MH; Huang, WT; Majewska, N; Lesniewski, T; Mahlik, S; Leniec, G; Kazmarek, SM; Pang, WK; Peterson, VK; Lu, KM; Chang, H; Liu, RSPortable near-infrared (NIR) light sources are in high demand for applications in spectroscopy, night vision, bioimaging, and many others. Typical phosphor designs feature isolated Cr3+ ion centers, and it is challenging to design broadband NIR phosphors based on Cr3+–Cr3+ pairs. Here, we explore the solid-solution series SrAl11.88–xGaxO19:0.12Cr3+ (x = 0, 2, 4, 6, 8, 10, and 12) as phosphors featuring Cr3+–Cr3+ pairs and evaluate structure–property relations within the series. We establish the incorporation of Ga within the magentoplumbite-type structure at five distinct crystallographic sites and evaluate the effect of this incorporation on the Cr3+–Cr3+ ion pair proximity. Electron paramagnetic measurements reveal the presence of both isolated Cr3+ and Cr3+–Cr3+ pairs, resulting in NIR luminescence at approximately 650–1050 nm. Unexpectedly, the origin of broadband NIR luminescence with a peak within the range 740–820 nm is related to the Cr3+–Cr3+ ion pair. We demonstrate the application of the SrAl5.88Ga6O19:0.12Cr3+ phosphor, which possesses an internal quantum efficiency of ∼85%, a radiant flux of ∼95 mW, and zero thermal quenching up to 500 K. This work provides a further understanding of spectral shifts in phosphor solid solutions and in particular the application of the magentoplumbites as promising next-generation NIR phosphor host systems. © 2021 American Chemical Society
- ItemComparison of the so-called CGR and NCR cathodes in commercial lithium-ion batteries using in situ neutron powder diffraction(Cambridge University Press, 2014-12-18) Alam, M; Hanley, TL; Pang, WK; Peterson, VK; Sharma, NThe evolution of the 003 reflection of the layered Li(Ni,Co,Mn)O2 (CGR) and Li(Ni,Co,Al)O2 (NCR) cathodes in commercial 18650 lithium-ion batteries during charge/discharge were determined using in situ neutron powder diffraction. The 003 reflection is chosen as it is the stacking axis of the layered structure and shows the largest change during charge/discharge. The comparison between these two cathodes shows that the NCR cathode exhibits an unusual contraction near the charged state and during the potentiostatic step, where the potentiostatic step is recommended by the manufacturer. This feature is not shown to the same degree by the CGR cathode. The behavior is likely related to the compositions of these cathodes, the amount of Li/Ni site mixing and the presence of Al or Mn. © 2014 International Centre for Diffraction Data. Published by Cambridge University Press
- ItemComparison of thermal stability in MAX 211 and 312 phases(Insitute of Physics, 2010-05-03) Pang, WK; Low, IM; O'Connor, BH; Studer, AJ; Peterson, VK; Sun, ZM; Palmquist, JPThe susceptibility of four MAX phases (Ti 2 AlC, Cr 2 AlC, Ti 3 AlC 2 , and Ti 3 SiC 2 ) to high-temperature thermal dissociation in vacuum has been investigated using in-situ neutron diffraction. In high vacuum, these phases decomposed above 1400°C through the sublimation of M and A elements, forming a surface coating of MC. The apparent activation energies for the decomposition of sintered Ti 3 SiC 2 , Ti 3 AlC 2 , and Ti 2 AlC were determined to be 179.3, -71.9, and 85.7 kJ mol −1 , respectively. The spontaneous release of Ti 2 AlC and TiC from de-intercalation during decomposition of Ti 3 AlC 2 resulted in a negative activation energy.© 2010, Insitute of Physics
- ItemCorrelating cycling history with structural evolution in commercial 26650 batteries using in operando neutron powder diffraction(Elsevier, 2017-03-01) Goonetilleke, D; Pramudita, JC; Hagan, M; Al Bahri, OK; Pang, WK; Peterson, VK; Groot, J; Berg, H; Sharma, NEx situ and time-resolved in operando neutron powder diffraction (NPD) has been used to study the structural evolution of the graphite negative electrode and LiFePO4 positive electrode within ANR26650M1A commercial batteries from A123 Systems, in what to our knowledge is the first reported NPD study investigating a 26650-type battery. Batteries with different and accurately-known electrochemical and storage histories were studied, enabling the tell-tale signs of battery degradation to be elucidated using NPD. The ex-situ NPD data revealed that the intensity of the graphite/lithiated graphite (LixC6 or LiyC) reflections was affected by battery history, with lower lithiated graphite (LiC12) reflection intensities typically corresponding to more abused batteries. This indicates that the lithiation of graphite is less progressed in more abused batteries, and hence these batteries have lower capacities. In operando NPD allows the rate of structural evolution in the battery electrode materials to be correlated to the applied current. Interestingly, the electrodes exhibit different responses to the applied current that depend on the battery cycling history, with this particularly evident for the negative electrode. Therefore, this work illustrates how NPD can be used to correlate a battery history with electrode structure. Crown Copyright ©2016 Published by Elsevier B.V.
- ItemDeveloping high-voltage spinel LiNi0.5Mn1.5O4 cathodes for high-energy-density lithium-ion batteries: current achievements and future prospects(Royal Society of Chemistry, 2020-05-22) Liang, GM; Peterson, VK; See, KW; Guo, ZP; Pang, WKHigh-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode for the next-generation high-performance lithium-ion batteries (LIBs) due to its high energy density (650 W h kg−1), high operating voltage (∼4.7 V vs. Li), low fabrication cost, and low environmental impact. However, the short cycle life of LNMO caused by rapid capacity decay during cycling limits its wide application and commercialization. Intense research effort to improve the electrochemical performance of LNMO has been moderately successful. Accordingly, it is absolutely necessary to revisit and summarize the up-to-date findings and deeper understanding of how to modify LNMO. In this review, the crystallographic structure and electrochemical properties of LNMO spinel, as well as its existing issues and corresponding solutions, are discussed in detail. In addition, the current accomplishments relating to LNMO application in full-cell configurations are also discussed. Finally, some insight into the future prospects for LNMO cathode developments is provided. © The Royal Society of Chemistry 2020
- ItemDiffraction study on the thermal stability of Ti3SiC2/TiC/TiSi2 composites in vacuum(American Institute of Physics, 2009-06-29) Pang, WK; Low, IM; O’Connor, BH; Studer, AJ; Peterson, VK; Palmquist, JPTitanium silicon carbide (Ti3SiC2) possesses a unique combination of properties of both metals and ceramics, for it is thermally shock resistant, thermally and electrically conductive, damage tolerant, lightweight, highly oxidation resistant, elastically stiff, and mechanically machinable. In this paper, the effect of high vacuum annealing on the phase stability and phase transitions of Ti3SiC2/TiC/TiSi2 composites at up to 1550° C was studied using in‐situ neutron diffraction. The role of TiC and TiSi2 on the thermal stability of Ti3SiC2 during vacuum annealing is discussed. TiC reacts with TiSi2 between 1400–1450°C to form Ti3SiC2. Above 1400° C, decomposition of Ti3SiC2 into TiC commenced and the rate increased with increased temperature and dwell time. Furthermore, the activation energy for the formation and decomposition of Ti3SiC2 was determined. © 2009 American Institute of Physics
- ItemDomination of second-sphere shrinkage effect to improve photoluminescence of red nitride phosphors(ACS Publications, 2014-11-14) Huang, WY; Yoshimura, F; Ueda, K; Pang, WK; Su, BJ; Jang, LJ; Chiang, CY; Zhou, WZ; Duy, NH; Liu, RSRed Ca0.99Al1–4δ/3–xSi1+δ+xN3–xCx:Eu2+0.01 (δ = 0.345; x = 0–0.2) nitride phosphors exhibit a blue-shifted emission with increased eye sensitivity function and excellent thermal stability. The variations in the photoluminescence in the Ca0.99Al1–4δ/3–xSi1+δ+xN3–xCx:Eu2+0.01 (δ = 0.345; x = 0–0.2) system are thoroughly investigated. The enhanced emission energy and the improved thermal stability with increasing x are dominated by the second-sphere shrinkage effect via the substitution of small Si4+ for large Al3+ with simultaneous charge compensation. Related proofs of the second-sphere shrinkage effect control for photoluminescence are confirmed via high-resolution neutron powder diffraction, EXAFS, and 29Si solid-state NMR techniques. © 2014, American Chemical Society.
- ItemEffect of AlF3-coated Li4Ti5O12 on the performance and function of the LiNi0.5Mn1.5O4||Li4Ti5O12 full battery—an in-operando neutron powder diffraction study(Frontiers Media S.A., 2018-09-10) Liang, GM; Pillai, AS; Peterson, VK; Ko, KY; Chang, CM; Lu, CZ; Liu, CE; Liao, SC; Chen, JM; Guo, ZP; Pang, WKThe LiNi0.5Mn1.5O4 ||Li4Ti5O12 (LMNO||LTO) battery possesses a relatively-high energy density and cycle performance, with further enhancement possible by application of an AlF3 coating on the LTO electrode particles. We measure the performance enhancement to the LMNO||LTO battery achieved by a AlF3 coating on the LTO particles through electrochemical testing and use in-operando neutron powder diffraction to study the changes to the evolution of the bulk crystal structure during battery cycling. We find that the AlF3 coating along with parasitic Al doping slightly increases capacity and greatly increases rate capability of the LTO electrode, as well as significantly reducing capacity loss on cycling, facilitating a gradual increase in capacity during the first 50 cycles. Neutron powder diffraction reveals a structural response of the LTO and LNMO electrodes consistent with a greater availability of lithium in the battery containing AlF3-coated LTO. Further, the coating increases the rate of structural response of the LNMO electrode during charge, suggesting faster delithiation, and enhanced Li diffusion. This work demonstrates the importance of studying such battery performance effects within full configuration batteries. Copyright © 2018 Liang, Pillai, Peterson, Ko, Chang, Lu, Liu, Liao, Chen, Guo and Pang.
- ItemEffect of vacuum annealing on the thermal stability of Ti3SiC2/TiC/TiSi2 composites(The Australian Ceramic Society, 2009-01-01) Pang, WK; Low, IM; O’Connor, BH; Studer, AJ; Peterson, VK; Palmquist, JPTitanium silicon carbide (Ti3SiC2) possesses a unique combination of properties of both metals and ceramics, for it is thermally shock resistant, thermally and electrically conductive, damage tolerant, lightweight, highly oxidation resistant, elastically stiff, and mechanically machinable. In this research, the effect of high vacuum annealing on the phase stability and phase transitions of Ti3SiC2/TiC/TiSi2 composites up to 1550°C was studied using in-situ neutron diffraction. The role of TiC and TiSi2 on the thermal stability of Ti3SiC2 during vacuum annealing is discussed. TiC reacts with TiSi2 between 1400-1450°C to form Ti3SiC2. Above 1400°C, decomposition of Ti3SiC2 into TiC commenced and the rate increased with increased temperature and dwell time. Furthermore, the activation energy for the formatiTitanium silicon carbide (Ti3SiC2) possesses a unique combination of properties of both metals and ceramics, for it is thermally shock resistant, thermally and electrically conductive, damage tolerant, lightweight, highly oxidation resistant, elastically stiff, and mechanically machinable. In this research, the effect of high vacuum annealing on the phase stability and phase transitions of Ti3SiC2/TiC/TiSi2 composites up to 1550°C was studied using in-situ neutron diffraction. The role of TiC and TiSi2 on the thermal stability of Ti3SiC2 during vacuum annealing is discussed. TiC reacts with TiSi2 between 1400-1450°C to form Ti3SiC2. Above 1400°C, decomposition of Ti3SiC2 into TiC commenced and the rate increased with increased temperature and dwell time. Furthermore, the activation energy for the formation and decomposition of Ti3SiC2 was determined. on and decomposition of Ti3SiC2 was determined. © 2009, The Australian Ceramic Society
- ItemEffects of fluorine and chromium doping on the performance of lithium-rich Li1+xMO2 (M = Ni, Mn, Co) positive electrodes(American Chemical Society, 2017-12-26) Pang, WK; Lin, HF; Lu, CZ; Liu, CE; Liao, SC; Chen, JM; Peterson, VKLithium-rich metal oxides Li1+zMO2 (M = Ni, Co Mn, etc.) are promising positive electrode materials for high-energy lithium-ion batteries, with capacities of 250-300 mAh·g-1 that closely approach theoretical intercalation limits. Unfortunately, these materials suffer severe capacity fade on cycling, among other performance issues. While ion substitution can improve the performance of many of these materials, the underlying mechanisms of property modification are not completely understood. In this work we show enhanced performance of the Li1+zMO2 electrode, consisting of Li2MnO3 (with C2/m space group) and LiMO2 (with R3m space group) phases, and establish the effects of cationic and anionic substitution on the phase and structure evolution underpinning performance changes. While the undoped material has a high capacity of ∼270 mAh·g-1, only 79% of this remains after 200 cycles. Including ∼2% Cr in the material, likely at the R3m metal (3a) site, improved cycle performance by ∼13%, and including ∼5% F in the material, likely at the R3m oxygen (6c) site, enhanced capacity by ∼4-5% at the expense of a ∼12% decline in cycle performance. Moreover, Cr doping enhances energy density retention by ∼13%, and F doping suppresses this by 17%. We find that these changes arise by different mechanisms. Both anionic and cationic substitution promote faster Li diffusion, by 48% and 20%, respectively, as determined using cyclic voltammetry and leading to better rate performance. Unlike anionic substitution, cationic substitution enhances structural stability at the expense of some capacity, by suppressing lattice distortion during Li insertion and extraction. This work implicates strategic cationic-anionic codoping for enhanced electrochemical performance in lithium-rich layered metal-oxide phases. © 2017 American Chemical Society.
- ItemElectrochemistry and structure of the cobalt-free Li1+xMO2 (M = Li, Ni, Mn, Fe) composite cathode(Royal Society of Chemistry, 2014-07-01) Pang, WK; Kalluri, S; Peterson, VK; Dou, SX; Guo, ZPThe development of cathode materials with high capacity and cycle stability is essential to emerging electric-vehicle technologies, however, of serious environmental concern is that materials with these properties developed so far contain the toxic and expensive Co. We report here the Li-rich, Co-free Li1+xMO2 (M = Li, Ni, Mn, Fe) composite cathode material, prepared via a template-free, one-step wet-chemical method followed by conventional annealing in an oxygen atmosphere. The cathode has an unprecedented level of cation mixing, where the electrochemically-active component contains four elements at the transition-metal (3a) site and 20% Ni at the active Li site (3b). We find Ni2+/Ni3+/Ni4+ to be the active redox-center of the cathode with lithiation/delithiation occurring via a solid-solution reaction where the lattice responds approximately linearly with cycling, differing to that observed for iso-structural commercial cathodes with a lower level of cation mixing. The composite cathode has ∼75% active material and delivers an initial discharge-capacity of ∼103 mA h g−1 with a reasonable capacity retention of ∼84.4% after 100 cycles. Notably, the electrochemically-active component possesses a capacity of ∼139 mA h g−1, approaching that of the commercialized LiCoO2 and Li(Ni1/3Mn1/3Co1/3)O2 materials. Importantly, our operando neutron powder-diffraction results suggest excellent structural stability of this active component, which exhibits ∼80% less change in its stacking-axis than for LiCoO2 with approximately the same capacity, a characteristic that may be exploited to enhance significantly the capacity retention of this and similar materials.
- ItemEnhanced high voltage stability of spinel‐type structured LiNi0.5Mn1.5O4 electrodes: targeted octahedral crystal site modification(Wiley, 2024-05-01) Zou, JS; Liang, G; Zhang, SH; Thomsen, L; Fan, Y; Pang, WK; Guo, ZP; Peterson, VKHigh‐voltage spinel‐type structured LiNi0.5Mn1.5O4 (LNMO) shows promise as a next‐generation high‐energy‐density lithium‐ion battery cathode material, however, capacity decay on extended cycling hinders its widespread adoption, underscoring an urgent need for further development. In this work, we introduce Zn at octahedral 16c crystal sites in LNMO with Fdm space group to improve rate capability and reduce the rapid capacity decay otherwise experienced during extended cycling. The current work resolves the detailed influence of isolated modification at octahedral 16c crystal sites, unveiling the mechanism for these performance improvements. We show that occupation of Zn at previously empty 16c sites prevents the migration of Ni/Mn to adjacent 16c sites, eliminating transformation to a rock‐salt type structured Ni0.25Mn0.75O2 phase above 4.8 V, preventing structure degradation and suppressing voltage polarization. This study provides insights into the fundamental structure‐function relationship of the LNMO battery cathode, pointing to pathways for the crystal structure engineering of materials with superior performance. © 2024 The Authors. Batteries & Supercaps published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
- ItemEnhanced rate-capability and cycling-stability of 5 V SiO2- and polyimide-coated cation ordered LiNi0.5Mn1.5O4 lithium-ion battery positive electrodes(American Chemical Society, 2017-01-23) Pang, WK; Lin, HF; Peterson, VK; Lu, CZ; Liu, CE; Liao, SC; Chen, JMThe ordered LiNi0.5Mn1.5O4 spinel exhibits great promise as a potential high-energy positive electrode for lithium-ion batteries due to its exceptionally high working potential of 4.7 V (vs. Li) and energy density of 640 Wh kg–1. The commercial application of this material at such voltages is unfortunately prevented by reaction phenomena including hydrofluoric acid attack and manganese dissolution, as well as the two-phase mechanism of Li insertion and extraction, with these limiting Li diffusivity and cycling stability. In this work, we demonstrate the improved performance of LiNi0.5Mn1.5O4 achieved by encapsulating the material in a thin layer of silica (SiO2) or polyimide using a simple wet-chemical method and organic solvents. The pristine and coated ordered LiNi0.5Mn1.5O4 spinel are both confirmed to have P4332 symmetry, with only a minor difference in their lattice parameter. The SiO2 coating is found to reduce capacity fade of ordered LiNi0.5Mn1.5O4 by 45 and 65% at 25 and 55 °C, respectively, with the improvement attributed to enhanced Li diffusivity alongside the suppression of the hydrofluoric acid attack. The polyimide coating is found to have a marginally negative effect on both capacity and rate performance of ordered LiNi0.5Mn1.5O4, with this being greatly offset by excellent thermal stability leading to high-temperature protection, with the material having the low capacity fade of 0.0585 mAh g–1 cycle–1 at 55 °C, which is comparable to that at 25 °C. While similar effects of these coatings are found for disordered LiNi0.5Mn1.5O4, the magnitude of enhancement to properties offered by these coatings is significantly lesser than those found here for the ordered LiNi0.5Mn1.5O4. A stabilizing effect of the coatings that mitigates against phase segregation occurring during the additional two-phase reaction in the ordered but not the disordered phase of the material may explain the greater benefit of the coatings to the ordered phase. © 2017 American Chemical Society
- ItemEvidence of solid-solution reaction upon lithium insertion into cryptomelane K0.25Mn2O4 material(ACS Publications, 2014-02-05) Pang, WK; Peterson, VK; Sharma, N; Zhang, CF; Guo, ZPCryptomelane-type K0.25Mn2O4 material is prepared via a template-free, one-step hydrothermal method. Cryptomelane K0.25Mn2O4 adopts an I4/m tetragonal structure with a distinct tunnel feature built from MnO6 units. Its structural stability arises from the inherent stability of the MnO6 framework which hosts potassium ions, which in turn permits faster ionic diffusion, making the material attractive for application as a cathode in lithium-ion batteries. Despite this potential use, the phase transitions and structural evolution of cryptomelane during lithiation and delithiation remain unclear. The coexistence of Mn3+ and Mn4+ in the compound during lithiation and delithiation processes induces different levels of Jahn–Teller distortion, further complicating the lattice evolution. In this work, the lattice evolution of the cryptomelane K0.25Mn2O4 during its function as a cathode within a lithium-ion battery is measured in a customized coin cell using in situ synchrotron X-ray diffraction. We find that the lithiation–delithiation of cryptomelane cathode proceeds through a solid-solution reaction, associated with variations of the a and c lattice parameters and a reversible strain effect induced by Jahn–Teller distortion of Mn3+. The lattice parameter changes and the strain are quantified in this work, with the results demonstrating that cryptomelane is a relatively good candidate cathode material for lithium-ion battery use. © 2014, American Chemical Society.
- ItemGallium-doped Li7La3Zr2O12 garnet-type electrolytes with high lithium-ion conductivity(American Chemical Society, 2016-12-22) Wu, JF; Chen, EY; Yu, Y; Liu, L; Pang, WK; Peterson, VK; Guo, XOwing to their high conductivity, crystalline Li7–3xGaxLa3Zr2O12 garnets are promising electrolytes for all-solid-state lithium-ion batteries. Herein, the influence of Ga doping on the phase, lithium-ion distribution, and conductivity of Li7–3xGaxLa3Zr2O12 garnets is investigated, with the determined concentration and mobility of lithium ions shedding light on the origin of the high conductivity of Li7–3xGaxLa3Zr2O12. When the Ga concentration exceeds 0.20 Ga per formula unit, the garnet-type material is found to assume a cubic structure, but lower Ga concentrations result in the coexistence of cubic and tetragonal phases. Most lithium within Li7–3xGaxLa3Zr2O12 is found to reside at the octahedral 96h site, away from the central octahedral 48g site, while the remaining lithium resides at the tetrahedral 24d site. Such kind of lithium distribution leads to high lithium-ion mobility, which is the origin of the high conductivity; the highest lithium-ion conductivity of 1.46 mS/cm at 25 °C is found to be achieved for Li7–3xGaxLa3Zr2O12 at x = 0.25. Additionally, there are two lithium-ion migration pathways in the Li7–3xGaxLa3Zr2O12 garnets: 96h-96h and 24d-96h-24d, but the lithium ions transporting through the 96h-96h pathway determine the overall conductivity. © 2016 American Chemical Society
- ItemGarnet-type fast Li-ion conductors with high ionic conductivities for all-solid-state batteries(American Chemical Society, 2017-07-23) Wu, JF; Pang, WK; Peterson, VK; Wei, L; Guo, XAll-solid-state Li-ion batteries with metallic Li anodes and solid electrolytes could offer superior energy density and safety over conventional Li-ion batteries. However, compared with organic liquid electrolytes, the low conductivity of solid electrolytes and large electrolyte/electrode interfacial resistance impede their practical application. Garnet-type Li-ion conducting oxides are among the most promising electrolytes for all-solid-state Li-ion batteries. In this work, the large-radius Rb is doped at the La site of cubic Li6.10Ga0.30La3Zr2O12 to enhance the Li-ion conductivity for the first time. The Li6.20Ga0.30La2.95Rb0.05Zr2O12 electrolyte exhibits a Li-ion conductivity of 1.62 mS cm–1 at room temperature, which is the highest conductivity reported until now. All-solid-state Li-ion batteries are constructed from the electrolyte, metallic Li anode, and LiFePO4 active cathode. The addition of Li(CF3SO2)2N electrolytic salt in the cathode effectively reduces the interfacial resistance, allowing for a high initial discharge capacity of 152 mAh g–1 and good cycling stability with 110 mAh g–1 retained after 20 cycles at a charge/discharge rate of 0.05 C at 60 °C. © 2017 American Chemical Society
- ItemHigh rate capability core–shell lithium titanate@ceria nanosphere anode material synthesized by one-pot co-precipitation for lithium-ion batteries(Elsevier, 2014-07-01) Yang, XJ; Huang, YD; Wang, XC; Jia, DZ; Pang, WK; Guo, ZP; Tang, XCCore–shell Li4Ti5O12@CeO2 nanosphere has been synthesized by a one-pot co-precipitation method. The structure and morphology of the as-prepared materials have been analyzed by X-ray diffraction and transmission electron microscopy. The results show that CeO2 is successfully coated on the surface of the Li4Ti5O12 besides partial doping of Ce4+ into the Li4Ti5O12 structure. The Li4Ti5O12@CeO2 nanosphere exhibits excellent capacity of 152 mAh g−1 even after 180 cycles at 10 C, with no noticeable capacity fading. Furthermore, the sample shows much improved rate capability at 40 C compared with pure Li4Ti5O12 when used as anode material for lithium-ion batteries. The introduction of CeO2 enhances not only the electric conductivity of Li4Ti5O12, but also the lithium ion diffusivity in Li4Ti5O12, resulting in significantly improved electrochemical performance of the Li4Ti5O12. © 2014, Elsevier B.V.
- ItemHigh temperature diffraction studies of in-situ crystallization of nanostructured TiO2 photocatalysts(The Ameican Ceramic Society, 2012-01-01) Low, IM; Pang, WK; Prida, VDL; Vega, V; Kimpton, JA; Ionescu, MThe in-situ crystallization of anatase and rutile on chemically-treated Ti-foils in the temperature range 20-900 degrees C has been investigated using synchrotron radiation diffraction and x-ray diffraction. The processing methodology has a profound influence on the morphology, crystallite size and growth rate of nanostructured TiO2. The anatase formed was metastable and transformed to rutile at similar to 800 degrees C. Increasing the temperature from 400 to 900 degrees C caused the sharpening of anatase (101) peaks and resulted in a concomitant coarsening in crystallite size. The surface of annealed samples exhibited TiO2 nanorods, nanowires or nanotubes depending on the processing method. Ion-beam analysis has indicated the existence of composition gradation within the annealed TiO2 samples at the near-surface. © 2012, The American Ceramic Society.
- ItemA high-performance and long-cycle-life spinel lithium-ion battery cathode achieved by site-selective doping(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Liang, GM; Dider, C; Gou, ZP; Peterson, VK; Pang, WKLithium-ion batteries (LIBs) form an important part of our daily life, powering portable electronic devices, as well as electric and hybrid electric vehicles. However, the limited energy density of current LIBs results in their failure to meet the increasing requirements of rapidly developing technologies. Since the performance limitation in existing LIB technology is the cathode, exploring high-energy-density cathode candidates becomes extremely important. Spinel LiNi0.5Mn1.5O4 (LNMO) is considered one of the most promising cathode materials for next-generation high energy-density LIBs, owing to its high operating voltage of 4.7 V vs. Li, low fabrication cost, and high energy density approaching 650 Wh kg-1, which is beyond that of most other LIB cathode materials, such as LiFePO4 at ∼560 Wh kg-1, LiMn2O4 at ∼480 Wh kg-1, and LiMn1/3Ni1/3Co1/3O2 at ∼510 Wh kg-1. Unfortunately, LNMO suffers from rapid capacity decay and unsatisfactory cycle stability, limiting its practical application and commercialization. Various doping strategies have been widely adopted to enhance the electrochemical stability of LNMO. Although the electrochemical performance of LNMO is enhanced through doping, the mechanism by which the performance is improved remains unclear, with the chemistry- and structure-function relationships for chemically modified LNMOs relatively unknown. In this work, we not only demonstrate a site-selective doping strategy for an easily-prepared high-performance LNMO cathode through Mg doping, but also comprehensively reveal the underlying enhancement mechanisms using a series of in operando and ex situ characterization techniques. Mg dopants, selectively residing at 8a and 16c sites of the Fd-3m structure, change the way how LNMO responses to the lithium intercalation and de-intercalation during charge-discharge processes. Meanwhile, the addition of Mg ions at such sites significantly prohibits the partially-irreversible two-phase behavior of LNMO, mitigates against the dissolution of transition metals, thus preventing the formation of the undesirable rock-salt phase and reducing the Jahn-Teller distortion and voltage polarization, consequently offering the extraordinary structure stability to LNMO. Consequently, the modified LNMO exhibits excellent extended-long-term electrochemical performance, retaining ~ 86 % and ~ 87 % of initial capacity after 1500 cycles at 1 C and 2200 cycles at 10 C, respectively in half cell configuration, which is reported for the first time and demonstrates their great commercial potential. Such excellent cycle and rate performance are also reflected in a prototype full-battery with a novel TiNb2O7 counter electrode. This work provides a new strategy for the chemical modification of electrode materials that may be applied more generally in battery researches, whereby dopants may be used strategically to address specific electrode issues.