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The ionic conductivity and activation energy of lithium in the Li3PO4-Li3VO4-Li4GeO4 system was systematically investigated. The sharp decrease in activation energy upon Ge substitution in Li3PO4 and Li3VO4 was attributed to the reduction in the defect formation energy while the variation in activation energy upon increasing Ge content was rationalized in term of the inductive effect. We also found a correlation between the pre-exponential factors and the activation energies in agreement with the well-known Meyer-Neldel rule. The series of compound with and without partial lithium occupancy were shown to fall into two distinct lines. The slope of the line was found to be related to the inverse of the energy scale associated with phonons in the system, which agrees with the multiexcitation entropy theory. The intercept of the line was found to be related to the Gibbs free energy of defect formation. Compiled data of pre-exponential factor and activation energy for commonly studied lithium-ion conductors shows that this correlation is very general, implying an unfavorable trade-off between high pre-exponential factor and low activation energy needed to achieve high ionic conductivity. Understanding the circumstances under which this correlation can be violated might provide a new opportunity to further increase the ionic conductivity in lithium-ion conductors.

Lithium ion conductivity in many structural families can be tuned by many orders of magnitude, with some rivaling that of liquid electrolytes at room temperature. Unfortunately, fast lithium conductors exhibit poor stability against lithium battery electrodes. In this article, we report a fundamentally new approach to alter ion mobility and stability against oxidation of lithium ion conductors using lattice dynamics. By combining inelastic neutron scattering measurements with density functional theory, fast lithium conductors were shown to have low lithium vibration frequency or low center of lithium phonon density of states. On the other hand, lowering anion phonon densities of states reduces the stability against electrochemical oxidation. Olivines with low lithium band centers but high anion band centers are promising lithium ion conductors with high ion conductivity and stability. Such findings highlight new strategies in controlling lattice dynamics to discover new lithium ion conductors with enhanced conductivity and stability.

Li–air (O2) batteries are promising because of their high theoretical energy density. However, these batteries are plagued with numerous challenges, one of which involves modulating the battery discharge process between a solution or surface-driven formation of the desired lithium peroxide (Li2O2) discharge product, and the oxidation of Li2O2 below 4 V (vs Li/Li+). In this work, we show that tetrabutylammonium (TBA) salts dissolved in ether or dimethyl sulfoxide (with no lithium salt present) can be used as a Li–O2 electrolyte with a lithium metal anode to support Li2O2 formation, lead to >500 mV reduction in charging overpotentials at low current rates as compared to that with lithium salt, and support the oxidation of Li2O2 during charge. Furthermore, on the basis of results from several spectroscopic techniques, we propose a mechanism that involves electrochemical-induced transformation of TBA to tributylamine at ∼3.55 V, and the formation of a tributylamine oxide intermediate in the presence of O2 or ...

Development of better energy storage media is vital in the adoption of renewable energy technologies, and lithium–air (O2) batteries have spurred great interest. However, current Li–O2 batteries are plagued by unwanted side reactions, flammable electrolytes, and slow kinetics attributed to the 2 mol e–/mol O2 peroxide chemistry. In this work, we show that a gel polymer electrolyte consisting of a polymer, ionic liquid, and salt can control the oxygen reduction chemistry in a Li–O2 cell (switching from a 2 e– to a 1 e– superoxide chemistry), support the formation of ionic liquid–superoxide complexes, and reduce the number of reactive species present in the cell. A one electron process could allow for newer energy-dense Li–O2 batteries with faster kinetics and higher energy efficiencies typical of superoxide-dominant Na–O2 and K–O2 batteries.

Understanding reactions at the electrode/electrolyte interface (EEI) is essential to developing strategies to enhance cycle life and safety of lithium batteries. Despite research in the past four decades, there is still limited understanding by what means different components are formed at the EEI and how they influence EEI layer properties. We review findings used to establish the well-known mosaic structure model for the EEI (often referred to as solid electrolyte interphase or SEI) on negative electrodes including lithium, graphite, tin, and silicon. Much less understanding exists for EEI layers for positive electrodes. High-capacity Li-rich layered oxides yLi2-xMnO3·(1-y)Li1-xMO2, which can generate highly reactive species toward the electrolyte via oxygen anion redox, highlight the critical need to understand reactions with the electrolyte and EEI layers for advanced positive electrodes. Recent advances in in situ characterization of well-defined electrode surfaces can provide mechanistic insights and strategies to tailor EEI layer composition and properties.

The effectiveness of titanium dioxide (TiO 2 )-loaded high-density polyethylene (HDPE) to reduce light-induced oxidation of extended-shelf-life milk (2% total fat) was studied. The objective was to determine differences over time in sensory quality, vitamin retention, and oxidative chemistry as a function of packaging and retail light exposure duration. Effectiveness of packaging for protecting milk quality was assessed by sensory evaluation (triangle tests, untrained panel), changes in volatile compounds, thiobarbituric reactive substances (TBARS), and riboflavin concentration. Milk (2%) was stored in HDPE packages consisting of TiO 2 at 3 levels (low: 0.6%; medium: 1.3%; high: 4.3%) at 3°C for up to 43 d. Light-protected (translucent, foil-wrapped) and light-exposed (translucent) HDPE packages served as controls. The high TiO 2 -HDPE package provided protection similar to light-protected control package through d 22 of light exposure, with less consistent performance by the medium TiO 2 package. The TBARS increased in all treatments during storage. Under the experimental conditions used, a TBARS value of 1.3mg/L could be considered the limiting sensory threshold for differentiating oxidized milk from light-protected milk. Riboflavin concentration decreased 10.5% in the light-protected control and 28.5% in the high TiO 2 packaged milk past 29 d of light exposure, but losses were greater than 40% for all other packages. The high TiO 2 package protected riboflavin concentration from degradation and controlled aldehyde concentration throughout the test period.

An improved RSA cryptosystem based on chaotic synchronization is newly presented in this paper. First, the design of a discrete sliding mode controller (DSMC) is proposed to make the master and slave chaotic systems synchronized, then a modified RSA encryption algorithm is proposed. In the traditional RSA cryptosystem, the public key needs to be open or transmitted in the public channel which provides an opportunity to attack. In this design, the public key is hidden and does not appear in public channels. Therefore, not only RSA's security features can be retained, but also can significantly promote the security of traditional RSA cryptosystem.

This Review is focused on ion-transport mechanisms and fundamental properties of solid-state electrolytes to be used in electrochemical energy-storage systems. Properties of the migrating species significantly affecting diffusion, including the valency and ionic radius, are discussed. The natures of the ligand and metal composing the skeleton of the host framework are analyzed and shown to have large impacts on the performance of solid-state electrolytes. A comprehensive identification of the candidate migrating species and structures is carried out. Not only the bulk properties of the conductors are explored, but the concept of tuning the conductivity through interfacial effects-specifically controlling grain boundaries and strain at the interfaces-is introduced. High-frequency dielectric constants and frequencies of low-energy optical phonons are shown as examples of properties that correlate with activation energy across many classes of ionic conductors. Experimental studies and theoretical results are discussed in parallel to give a pathway for further improvement of solid-state electrolytes. Through this discussion, the present Review aims to provide insight into the physical parameters affecting the diffusion process, to allow for more efficient and target-oriented research on improving solid-state ion conductors.

LiFePO4/mesocarbon microbead (MCMB) cells of which the carbon electrodes were, respectively, coated with different metal layers were characterized for their charge/discharge cycle performance at 55 °C. The examined metals included Au, Cu, Fe, Ni, Co, and Ti, and the superficial layers were 30–50 nm in thickness and deposited by vacuum sputtering. It was found that the presence of a either Au or Cu layer remarkably reduces capacity fading, while the rest metals only accelerate fading. There was observed a consistent trend between the capacity fading rate and the amount of the soild-electrolyte-interphase (SEI) deposition; the faster the capacity fading, the greater amount of SEI materials appearing on the surface of cycled carbon electrode. Microscopic and composition analyses indicates that the superficial Au and Cu layers act as a sieve to collect the Fe ions that result form erosion of LiFePO4 before they diffuse into the interior of the carbon electrode, and that the so-deposited Fe particles do not show the tendency to catalyze the SEI formation, as in contrast to those directly deposited on the carbon surfaces. Keywords: LiFePO4, MCMB, Cycle performance, Li-ion secondary battery, Fe dissolution

LiFePO4 particles were coated with TiO2 (molar ratio = 3%) via a sol-gel process, and the effects of the coating on cycle performance of LiFePO4 cathode at 55 ◦C against either a Li or a C (mesocarbon microbead) anode were investigated. It was found that, while the coating reduces capacity fading of the LiFePO4/Li cell, it imposes a deteriorating effect on the LiFePO4/C cell. Analyses on cell impedance and electrode surface morphology and composition showed that the oxide coating reduced Fe dissolution from the LiFePO4 cathode and hence alleviated the impedance increase associated with the erosion process. This leads to reduced capacity fading as observed for the LiFePO4/Li cell. However, the oxide coating itself was eroded upon cycling, and the dissolved Ti ions were subsequently reduced at the anode surface. Ti deposit on the C anode was found to be more active than Fe in catalyzing the formation of the solid-electrolyte interphase (SEI) layer, causing accelerated capacity decay for the LiFePO4/C cell. The results point out the importance of evaluating the effect of cathode coating material on the anode side, which has generally been overlooked in the past studies.

Structural transformation taking place during charge/discharge of the LiFePO4 electrode in an organic Li-ion electrolyte has been studied by in situ synchrotron X-ray diffraction (XRD) concurrently with electrochemical analysis. The data reveal complex structural transformation patterns which result from significantly delayed structural transformation, even at low to moderate current rates (C/10 ∼ 1 C). The extent of the deviation is affected by charge/discharge conditions as well as history, and strong deviation appears detrimental to electrode cycle life. Furthermore, the two-phase characteristic of the Li+ insertion/extraction reactions is found to persist even within one metastable crystal structure. The result suggests the presence of domain structures that are probably caused by the strong electron/ion site coulombic interaction as previously suggested. Keywords: LiFePO4, Structural transformation, Synchrotron X-ray diffraction, Li-ion secondary battery, Cathode

Rate equation of LiFePO4 formation via solid-state reaction has been studied by using a model system: Li(CH3COO) + FePO4 in a reducing atmosphere. Kinetic data were acquired by using in-situ synchrotron X-ray diffraction technique, and the analysis was based on a non-isothermal methodology, which shows that the reaction rate is well described by the rate-equation: [F0.7/(1 − F)0.7] = 1.56 × 1011 exp(−24,100/T)t, where F is the fractional conversion to LiFePO4, T, the calcination temperature (K), and t is the calcination time (min). The equation indicates that the formation of LiFePO4 is intrinsically a fast reaction: 95% conversion can be achieved between 550 and 600 °C in a few hours. Nevertheless, the reaction could be significantly hindered if gas-phase diffusion processes of reactant/product species become rate-limiting, and the gas-flow pattern relative to the powder bed during synthesis thus has a decisive effect on the reaction rate in large-scale synthesis. Single-phased, nanocrystalline LiFePO4 powder having an average crystal size of 35 nm can be synthesized by calcination using flow-through configuration at 600 °C in merely 2 h, and the powder exhibits a capacity of ∼140 mAh g−1.

Understanding electrode/electrolyte interface (EEI) is crucial for the development of high-energy batteries for electric vehicle applications. The EEI layer formation of negative electrode (also referred as Solid Electrolyte Interphase) is comprehensively studied [1,2], whereas the electrolyte decomposition and formation of the EEI layer at the positive electrodes are still unknown [3,4]. Especially, at high potentials, the role of oxygen in the transition metal oxide becomes critical, leading to the evolution of oxygen from the oxide lattice or the formation of highly reactive species like surface peroxide and superoxide, which can modify the nature of the EEI layer. Here, we show how EEI layer depends on different positive electrodes (LiCoO2 and NMC electrodes with different Ni content) and different electrolyte additives (diphenyl carbonate and adiponitrile) by using X-ray Photoelectron Spectroscopy (XPS). We also highlight the importance of using carbon-free, binder-free electrodes to unambiguously pinpoint the reactivity of the electrolyte at the positive electrode [5]. The analysis of the XPS results points to a strong dependency of the surface reactivity on different electrode and electrolyte composition. [1] E. Peled, J. Electrochem. Soc. 126, 2047 (1979). [2] D. Aurbach et al., J. Power Sources 81-82, 95 (1999). [3] K. Xu et al., Chem. Rev., 114, 11503 (2014). [4] M. Gauthier, T. Carney, A. Grimaud et al., J. Phys. Chem. Lett. 6, 4653 (2015). [5] M. Gauthier et al., in preparation.

Light energy in the ultraviolet and visible light regions plays a critical role in overall food quality, leading to various degradation and oxidation reactions. Food degradation and oxidation result in the destruction of nutrients and bioactive compounds, the formation of off odors and flavors, the loss of food color, and the formation of toxic substances. Food compounds are sensitive to various light wavelengths. Understanding the effect that specific light wavelengths have on food compounds will allow the development of novel food packaging materials that block the most damaging light wavelengths to photostability of specific food compounds. Future research should focus more specifically on the effect of specific light wavelengths on the quality of specific food products, as there is limited published information on this particular topic. This information also can be directly related to the selection of food packaging materials to retain both high quality and visual clarity of food products exposed to light.

Light energy in the ultraviolet and visible light regions plays a critical role in overall food quality, leading to various degradation and oxidation reactions. Food degradation and oxidation result in the destruction of nutrients and bioactive compounds, the formation of off odors and flavors, the loss of food color, and the formation of toxic substances. Food compounds are sensitive to various light wavelengths. Understanding the effect that specific light wavelengths have on food compounds will allow the development of novel food packaging materials that block the most damaging light wavelengths to photostability of specific food compounds. Future research should focus more specifically on the effect of specific light wavelengths on the quality of specific food products, as there is limited published information on this particular topic. This information also can be directly related to the selection of food packaging materials to retain both high quality and visual clarity of food products exposed to light.

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