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- 2019
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- DIT University
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Probing Electrolyte Solvents at Solid/Liquid Interface Using Gap-Mode Surface-Enhanced Raman Spectroscopy
摘要： Understanding the aprotic solution structures at the immediate vicinity of solid/liquid interface (SLI) is critically important for next generation lithium ion battery development. Yet, it is still challenging to investigate the carbonate chemical profiles close to the diffuse layer (about 10 nm) of the electrical double layer at SLI due to the lack of a ultrahigh surface sensitive tool. In this work, we demonstrate the structures of commonly used carbonate solvents (ethylene carbonate (EC) and diethyl carbonate (DEC)) and a carbonate additive (fluoroethylene carbonate (FEC)) in a commercial Li-ion battery electrolyte can be determined at ～17 nm above the electrode surface. This is only enabled by a nanogap surface-enhanced Raman spectroscopy (SERS) technique based on a monolayer gold nanoparticle (Au NP) ensemble. The SERS enhancement factor (EF) of those carbonates was found to depend on the molecular polarizability, with the maximum EF at ～105 found for EC and FEC. Despite their alike chemical structures, this monolayer Au NP SERS substrate is fully capable of discrimiating the different Raman finger prints of EC and FEC. Compared to EC, several vibration modes in FEC, such as C-C skeletal deformation, ring breathing band and C=O stretching band, shift to higher frequencies because of the displacement of a hydrogen atom by a much heavier fluorine atom in a methylene bridge. This counterintuitive observation against the commonly used “ball and spring” model in vibrational spectroscopy is mostly due to the increased bond strength in the FEC ring versus that of EC. A second order empirical polynomial best describes the correlation between the SERS band integration of EC or DEC molar concentration. Our findings open up new opportunities for in-depth understanding of the electrolyte molecular vibrational behaviors at direct solid/liquid interface and developing advanced electrolytes for next generation lithium-ion batteries.
关键词： carbonate solvents,electrolyte,solid/liquid interface,lithium-ion battery,surface-enhanced Raman spectroscopy
更新于2025-09-23 15:22:29
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Thermal Mapping of a Lithium Polymer Batteries Pack with FBGs Network
摘要： In this paper, a network of 37 fiber Bragg grating (FBG) sensors is proposed for real-time, in situ, and operando multipoint monitoring of the surface temperature distribution on a pack of three prismatic lithium polymer batteries (LiPBs). Using the network, a spatial and temporal thermal mapping of all pack interfaces was performed. In each interface, nine strategic locations were monitored by considering a three-by-three matrix, corresponding to the LiPBs top, middle and bottom zones. The batteries were subjected to charge and discharge cycles, where the charge was carried out at 1.0 C, whereas the discharge rates were 0.7 C and 1.4 C. The results show that in general, a thermal gradient is recognized from the top to the bottom, but is less prominent in the end-of-charge steps. The results also indicate the presence of hot spots between two of the three batteries, which were located near the positive tab collector. This occurs due to the higher current density of the lithium ions in this area. The presented FBG sensing network can be used to improve the thermal management of batteries by performing a spatiotemporal thermal mapping, as well as by identifying the zones which are more conducive to the possibility of the existence of hot spots, thereby preventing severe consequences such as thermal runaway and promoting their safety. To our knowledge, this is the first time that a spatial and temporal thermal mapping is reported for this specific application using a network of FBG sensors.
关键词： in situ monitoring,lithium polymer batteries pack,FBGs network,safety,thermal mapping
更新于2025-09-23 15:22:29
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Effect of Defects on Spontaneous Polarization in Pure and Doped LiNbO3: First-Principles Calculations
摘要： Numerous studies have indicated that intrinsic defects in lithium niobate (LN) dominate its physical properties. In an Nb-rich environment, the structure that consists of a niobium anti-site with four lithium vacancies is considered the most stable structure. Based on the density functional theory (DFT), the specific configuration of the four lithium vacancies of LN were explored. The results indicated the most stable structure consisted of two lithium vacancies as the first neighbors and the other two as the second nearest neighbors of Nb anti-site in pure LN, and a similar stable structure was found in the doped LN. We found that the defects dipole moment has no direct contribution to the crystal polarization. Spontaneous polarization is more likely due to the lattice distortion of the crystal. This was verified in the defects structure of Mg2+, Sc3+, and Zr4+ doped LN. The conclusion provides a new understanding about the relationship between defect clusters and crystal polarization.
关键词： defects,lithium niobate,dipole moment,spontaneous polarization
更新于2025-09-23 15:22:29
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Metaheuristic <i>Ab Initio</i> Optimum Search for Doping Effects in Nanocarbons
摘要： We have developed a combined approach of metaheuristic optimization algorithms (MOA), such as the genetic algorithm, with an ab-initio materials simulation engine. Concurrent run of the ab-initio calculations with each different parameter set selected by the MOA searches the optimum condition within a given input-parameter space. Using this methodology, the optimum dopant and its position/structure at a graphene edge are found to be a multiple N-atoms doping at graphitic sites, which predicts to lead to better charging/discharging performance when it is used as an anode material of Li-ion battery.
关键词： genetic algorithm,lithium-ion battery,nano-carbon,ab-initio simulation,doping effect
更新于2025-09-23 15:22:29
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Electrochemical and Structural Investigation on Ultrathin ALD ZnO and TiO <sub/>2</sub> Coated Lithium-Rich Layered Oxide Cathodes
摘要： Ultrathin coatings (1.5 ± 0.3 nm) of titanium dioxide and zinc oxide were deposited on lithium-rich layered oxide cathodes (Li1.2Mn0.6Ni0.2O2, LLO) by atomic layer deposition (ALD). The structures, electrochemical performances, and thermal stabilities of these coatings were investigated. An ultrathin uniform coating was obtained for TiO2 but not for ZnO because of di?erences in the layer growth mechanism. Regarding the initial charge?discharge curves under a current density of 0.04 C rate, the TiO2 coated samples exhibited a higher discharge capacity, 242 mAhg?1, compared with the ZnO coated samples, 220 mAhg?1, or the pristine samples, 228 mAhg?1. Both coated samples exhibited more stable cycling performance and thermal stability than the pristine samples. After 80 cycles under 0.5 C rate, the TiO2 and ZnO coated samples were found to have higher capacity retention (～94% and 78%, respectively) than the pristine samples (68%). The reaction temperature of the exothermic peak of the TiO2 and ZnO coated samples at 4.8 V shifted to 280 °C with heat release of 88.7 J/g for TiO2 and 270 °C with heat release of 154.6 J/g for ZnO. This is compared with an exothermic peak at 258 °C with heat release of 253.5 J/g for the pristine sample. In particular, an enhanced rate capability was only observed for the TiO2 coated samples. When the current densities were higher than 2 C rate, the TiO2 coated samples exhibited superior capacities than the pristine and ZnO coated samples. At a current density of 5 and 10 C rate, the capacities were found to be 120 and 95 mAhg?1. The improved electrochemical performances were mainly attributed to lower resistance ?lm. This feature lead to more preactivation of the charge transfer, which resulted from the layer morphology of the TiO2 LLO, smoother electron transport, and suppression of more side reactions, when compared with the island structure of the ZnO ?lm.
关键词： ZnO,Cathode,Atomic layer deposition,Lithium-rich layered oxides,TiO2,Lithium ion battery
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Investigations on electrical properties and correlations to electron and X-ray energies of pyroelectric LiTaO<inf>3</inf> and LiNbO<inf>3</inf>
摘要： The electrical properties of pyroelectric Lithium Tantalate (LiTaO3) and Lithium Niobate (LiNbO3) were investigated and compared to accessible X-ray energies by using the pyroelectric effect to generate X-rays. The capacitances of different crystals of varying sizes were measured and the resulting permittivities were calculated. A vacuum setup enabled a correlation to the maximum X-ray energies at a variable pressure. The presented results provide an overview of fundamental material properties and the effect on the generated difference of potential.
关键词： Lithium Niobate,pyroelectric crystal,vacuum electron source,X-ray spectrum,permittivity,X-ray energy,electron acceleration,electron emission,capacitance,Lithium Tantalate
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Self-focusing of electrons emitted by rectangular pyroelectric crystals: A study on geometrical conditions for optimized X-ray intensities
摘要： Pyroelectric crystals such as LiTaO3 or LiNbO3 offer the opportunity to produce X-rays with high energy and intensity. These pyroelectric X-ray sources may be used in XRF applications due to particular advantages. This report deals with systematic studies on the behavior of these crystals enabling an optimization of X-ray intensity. Furthermore, the focusing of electrons emitted by rectangular pyroelectric crystals has been studied.
关键词： Lithium Niobate,pyroelectric crystal,vacuum electron source,X-ray intensity,X-ray spectrum,focusing,electron acceleration,electron emission,Lithium Tantalate
更新于2025-09-23 15:21:21
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Optimization of synthesis condition of water-resistant and thin titanium oxide layer-coated Ni-rich layered cathode materials and their cathode performance
摘要： In this study, in order to develop water-resistant LiNiaCobAl1?a?bO2 (a > 0.85, NCA) cathode materials which exhibit high-rate performance, the surface coating of NCA with titanium oxide (TiOx) was examined. The synthesis conditions for the TiOx-coated NCA cathode materials were investigated, by taking into account some essential factors in the surface coating of NCA by TiOx, with a view to improving the rate performance. We successfully prepared the TiOx-coated NCA cathode material, the rate performance of which is superior to that of the conventionally prepared NCA cathode materials, typically using a polyvinylidene difluoride (PVdF) binder and N-methyl-2-pyrrolidone (NMP) solvent. Their surface analysis suggested that the specific surface structure of TiOx layer coated on the NCA particle leads to both a water-resistant property and a high permeability of Li+ ions through it in the charging/discharging process.
关键词： Lithium ion secondary battery,Water-based hybrid polymer binder,TiOx coating layer,Water resistance,Ni-rich lithium transition metal oxide
更新于2025-09-23 15:21:21
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General synthesis of uniform three-dimensional metal oxides/reduced graphene oxide aerogels by a nucleation-inducing growth strategy for high-performance lithium storage
摘要： Three-dimensional (3D) transition metal oxides/reduced graphene oxide aerogels (TMOs/rGO-G) have received great attention for boosting the performance of alkali-ion batteries owing to abundant active sites and short lithium ion diffusion path. In this paper, we design a general self-assembly strategy for preparing uniform 3D porous TMOs/rGO-G (TMOs = CoO, MnO, Fe2O3) hybrids even with very high TMOs content (especially > 80% for CoO/rGO-G and Fe2O3/rGO-G). This strategy contains successive self-assembly processes: self-assembly nucleation of TMOs on GO nanosheets in N,N-Dimethylformamide (DMF)/H2O mixed solvent, and 3D reduction-assembly of the obtained precursor for hybrid hydrogels along with nucleation-inducing growth of TMOs. Benefitting from the 3D porous network for fast ion/electron transport, and uniform hybrid between TMOs and rGO with high TMO content, the 3D TMOs/rGO-G demonstrates an impressive lithium storage performance with both outstanding rate capability and excellent cycling stability. Specifically, the 3D CoO/rGO-G delivers a reversible capacity of 1142.8 mAh g-1 after 100 cycles at 0.5 A g-1, and high pseudocapacitive lithium storage behavior with 93.1% at 2 mV s-1 leading to outstanding rate capability with 624.7 mAh g-1 at 8 A g-1, as well as excellent stability with 493.3 mAh g-1 over 800 cycles at 4 A g-1. This general strategy demonstrates a general method in design and synthesis of uniform 3D porous TMOs/rGO-G for the energy storage.
关键词： nucleation-inducing growth,aerogels,3D transport channels,uniform hybrids,lithium storages
更新于2025-09-23 15:21:21
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[IEEE 2018 International Power Electronics Conference (IPEC-Niigata 2018 –ECCE Asia) - Niigata, Japan (2018.5.20-2018.5.24)] 2018 International Power Electronics Conference (IPEC-Niigata 2018 -ECCE Asia) - Green Base Station Using Robust Solar System and High Performance Lithium ion battery for Next Generation Wireless Network (5G) and against Mega Disaster
摘要： To secure wireless communication services, we are researching and developing disaster-resistant and environmentally friendly green base stations. One effective disaster countermeasure in carriers is to make backup time long for base stations during a power outage. Therefore, we have developed a photovoltaics (PV) system for green base stations to prolong the backup. In this paper, we propose a power control method that realizes long-term autonomous operation by PV and lithium-ion batteries (LiB) and regeneration operation by only PV for when commercial power is lost during a power outage and describe the results obtained at field test station.
关键词： Lithium- ion battery,Green Base Station
更新于2025-09-23 15:21:21