Salt Phase Research Articles

Uncovering Unique Interfacial Properties in Different Lithium Fluoride Phases: A First-Principles Prediction

Electrolytes are susceptible to reductive decomposition on the surface of negative electrodes leading to the formation and growth of solid-electrolyte interphase (SEI) layer [1]. Stable SEI can be beneficial as a protective layer, given that it can provide insulation to electron transport from the anode to electrolyte, prevent solvent molecules from reaching the anode, and at the same time allow transport of Li+ [2]. Thus, the SEI can contribute critically to the safety and operability of lithium-ion batteries (LIBs), but its functionality heavily depends on the conditions under which it gets synthesized [3]. This can have a significant effect on battery performance. For instance, nucleation and growth of lithium dendrites during cycling is known to result in continuous electrolyte degradation, destruction of the SEI, agglomeration of so-called “dead lithium”, and short-circuiting of the battery [4]. This greatly affects next-generation electric vehicles (EVs), for which all-solid-state lithium-metal batteries (ASSLMBs) have garnered significant attention due to their superior energy storage capacity and safety over LIBs [5]. However, the considerable interfacial impedance originating from poor physical contact and/or parasitic reactions at the Li/SSE interface hinders the development of ASSLMBs. Alternative approaches towards achieving a stable protective interface have been pursued: like use of electrolyte additives to manipulate the constituents and compositions of SEI or designing artificial protective layers to improve performance. For instance, admixture of optimum amounts of fluorine-rich additives like fluoroethylene carbonate (FEC) to traditional carbonate electrolytes (like EC/DMC) has been seen to generate a robust LiF-rich SEI. However, the intrinsic role of LiF remains a topic of uncertainty. Conventional understanding would posit that dominance of LiF leaves the SEI susceptible to poor lithium-ion transport properties. Previously, theoretical works reported significantly lower ionic conductivities in crystalline LiF when compared to other common inorganic SEI materials like Li2O and Li2CO3. Underwhelming transport properties pose serious rate limitations in its effectiveness as a serious candidate for interfacial protection in ASSLMBs. To potentially overcome such bottleneck, this study systematically investigates different phases of LiF: their structures, stabilities and interfacial properties are described using first principles calculations. Careful analysis of the structural models reveals that unlike the widely studied rock salt ordered counterpart, certain phases of LiF exhibit excellent Li+ transport properties with a high predicted diffusivity at room temperature. Mechanically too, improved interfacial qualities are demonstrated with increased flexibility and fracture resistance, opening up important avenues for structural and compositional stability over cell cycling while maintaining its desirable electron-blocking characteristics. However, it is also important to take a step back and note that the rock salt phase is the most energetically stable among LiF phases, which thereby exhibit a propensity for phase transformation under ambient conditions. To overcome this, a strategy of incorporating hetero dopants as impurities to stabilize the host matrix is discussed. By increasing the dopant concentration up to an optimum amount, relative thermodynamic stability of the interface-friendly phases of LiF is achieved. Our examination of the structure reveals unique lithium-dopant interactions which help sustain such LiF phases in the host matrix. The combination of excellent Li-ion transport properties and electron blocking ability makes such LiF-rich composites an excellent candidate for use as an interfacial protective layer that can effectively suppress electrolyte decomposition and Li dendrite propagation, while simultaneously improving the contact and compatibility of the electrode/electrolyte interface. These unique and exceptional traits make them materials of great promise for protecting critical interfaces in ASSLMBs and LIBs.[1] M. Gauthier, T.J. Carney, A. Grimaud, L. Giordano, N. Pour, H.-H. Chang, D.P. Fenning, S.F. Lux, O. Paschos, C. Bauer, F. Maglia, S. Lupart, P. Lamp, Y. Shao-Horn, Electrode−Electrolyte Interface in Li-Ion Batteries: Current Understanding and New Insights, J. Phys. Chem. Lett. 6 (2015) 4653−4672. https://doi.org/10.1021/acs.jpclett.5b01727[2] D. Bedrov, O. Borodin, J.B. Hooper, Li+ Transport and Mechanical Properties of Model Solid Electrolyte Interphases (SEI): Insight from Atomistic Molecular Dynamics Simulations, J. Phys. Chem. C 121 (2017) 16098–16109. https://doi.org/10.1021/acs.jpcc.7b04247[3] D. Aurbach, B. Markovsky, I. Weissman, E. Levi, Y. Ein-Eli, On the Correlation Between Surface Chemistry and Performance of Graphite Negative Electrodes for Li Ion Batteries, Electrochim. Acta 45 (1999) 67−86. https://doi.org/10.1016/S0013-4686(99)00194-2[4] W. Xu, J. Wang, F. Ding, X. Chen, E. Nasybulin, Y. Zhang, J.G. Zhang, Lithium Metal Anodes for Rechargeable Batteries, Energy Environ. Sci. 7 (2014) 513−537. https://doi.org/10.1039/C3EE40795K[5] J. G. Kim, B. Son, S. Mukherjee, N. Schuppert, A. Bates, O. Kwon, M. J. Choi, H. Y. Chung, S. Park, A review of lithium and non-lithium based solid state batteries, J. Power Sources 282 (2015) 299−322. https://doi.org/10.1016/j.jpowsour.2015.02.054

A thermodynamic model for high temperature corrosion applications: The (Na2SO4 + K2SO4 + ZnSO4 + PbSO4) system

The (Na2SO4 + K2SO4 + ZnSO4 + PbSO4) salt system is important for deposit buildup, fouling and associated corrosion of metallic structural and heat exchanger materials of municipal solid waste incinerators, low-grade fuel firing boilers, as well as metallurgical heat recovery boilers. In this study, a complete critical evaluation of all available phase diagram and thermodynamic data has been performed for all condensed phases of the (Na2SO4 + K2SO4 + ZnSO4 + PbSO4) system, and optimized model parameters have been found. The Modified Quasichemical Model for short-range ordering was used for the molten salt phase while most of the relevant solid solutions were modeled using the Compound Energy Formalism. The (Na2SO4 + K2SO4) sub-system has been critically evaluated in a previous article. A (60 mol% PbSO4 + 40 mol% ZnSO4) binary mixture was investigated by DTA-TGA since no thermodynamic data were available in the literature for this particular sub-system. The model parameters obtained for the binary and ternary sub-systems of the (Na2SO4 + K2SO4 + ZnSO4 + PbSO4) system can be used to predict thermodynamic properties and phase equilibria for the multicomponent system. In particular, ternary and quaternary eutectics (corresponding to the formation of a liquid phase at low temperatures) may be predicted, thus permitting to avoid “catastrophic” corrosion. This work is part of a large thermodynamic model for the Na+, K+, Zn2+, Pb2+ // Cl−, SO42− system.

Synthesis and Characterization of PANi/PVA Nanofibers with Variation of Nozzle to Collector Distance Using Electrospinning Method

Fumaric acid doped polyaniline was confirmed by FTIR as a sample of polyaniline emeraldine salt phase. This study aims to determine the value of the electrical conductivity of PANi/PVA with variations in distance. The electrospinning method was carried out on a PANi/PVA solution to form polyaniline nanofibers. The electrospinning solution used a percent ratio of 1:1 PANi/PVA (10%) with variations in the distance of the nozzle to the collector, namely 13 cm, 15 cm, and 17 cm. The morphological characterization and fiber properties obtained from electrospinning were characterized using FTIR, optical microscopy, and SEM-EDX. The number of fibers decreases and becomes finer as the distance increases. Fiber decreased in number due to evaporation of PVA. The diameter comparisons obtained from PANi/PVA fiber and pure PVA fiber are 263 nm and 240 nm. So the PANi/PVA fiber diameter is slightly larger than that of the PVA fiber. Electrical conductivity was carried out using the four-point probe method. The electrical conductivity value from the measurement of the best PANi/PVA sample is 1.39 × 10-6 S/cm at a distance of 15 cm with the best fiber shape.

Interfacial and cycle stability of sulfide all-solid-state batteries with Ni-rich layered oxide cathodes

The interfacial compatibility between sulfide solid electrolyte (SSE) and Ni-rich layered oxide (NRLO) cathode is critical for high-performance sulfide all-solid-state Li-ion batteries (SASSLIBs). However, the reasons for interfacial/capacity degradation of SASSLIBs are not yet clearly resolved. Herein, the impacts of surface structures and chemical environments of LiNi0.83Co0.11Mn0.06O2 (NCM83) on SASSLIB performances are systematically investigated. Surface lithium vacancies of NCM83 facilitate Li ion migration from SSE to NCM83 side, suppressing the H1 phase transformation of NCM83 and expanding the space charge layer. Surface LixNi1−xO type rock salt phases inhibit oxygen-participating interfacial reactions at high voltages due to their low susceptibility to oxygen evolutions, enhancing the H2/H3 phase transformation of NCM83. Surface Li2O and Li2CO3 mitigate the space charge layer effect and interfacial reactions at high voltages, activating H1 and H2/H3 phase transformations of NCM83. On the other hand, the combination of LiOH and Li2CO3 causes severe side reactions with SSE, resulting in escalated interfacial resistance and drastic capacity fading over cycling. Importantly, while the suppression of H1 and H2/H3 transformations reduces the reversible capacity, it mitigates the internal stress and micro-cracks in NCM83 particles, contributing to superior cycling stability of NCM83-sulfide ASSLIBs (94.1 % capacity retention over 500 cycles).

Thermal behaviors of energy storage process of eutectic hydrated salt phase change materials modified by Nano-TiO2

This paper investigated the thermal behaviors of energy storage process of eutectic hydrated salt phase change materials (EHS PCMs) modified by Nano-TiO2, including energy storage efficiency and energy storage density of the sample. The energy storage process of EHS PCMs with different mass fraction of Nano-TiO2 was divided into three stages – solid-solid stage, solid-liquid stage and liquid-liquid stage. The factors affecting energy storage efficiency and energy storage density at each stage were analysed, and the whole energy storage process was comprehensively evaluated. Before that, the study about SrCl2·6H2O as an auxiliary nucleator was carried out to ensure the stability of EHS PCMs. Results show that the synergistic effect of Nano-TiO2 and SrCl2·6H2O could optimize the crystallization of EHS PCMs and reduce the supercooling degree to 1.7 °C. The EHS PCMs with 0.5 wt% Nano-TiO2 has the highest energy storage efficiency, the energy storage density of EHS PCMs with 0.3 wt% Nano-TiO2 increased about 10.4% compared to that without Nano-TiO2. This attributes to the Nano-TiO2 in EHS PCMs changes the crystallinity and crystallization morphology of PCMs affecting the latent heat, and the different changes of thermal conductivity and specific heat capacity of the sample occurring in solid and liquid energy storage stages. This experiment provides a macro comprehensive evaluation of energy storage process of EHS PCMs with nanoparticles and explains the change regularity of thermal properties in different energy storage stages, giving a reference for EHS PCMs using nanoparticles.

Composition Dependence of Structural, Optical, Magnetic and Photodegradation Properties of Nanocrystalline NiO/CuO Heterostructured Powders

Nanocrystalline NiO/CuO solid solutions and heterostructured powders are prepared by a sol–gel auto combustion method. Herein, the NiO/CuO compounds at various molar ratio, including 100/0, 97.5/2.5, 95/5, 92.5/7.5, 90/10, 80/20, 50/50, 20/80, 10/90, 5/95 and 0/100, are investigated. The structures, morphologies, optical, and magnetic properties of all samples are explored. The detailed structures of the NiO/CuO system are deduced from Rietveld refinements of X‐ray diffraction (XRD) data and the combination of experimental and simulation studies of X‐ray absorption spectroscopy (XAS) spectra. It is found that a small addition of CuO in NiO enhances the formation of rock salt CuxNi1–xO solid solutions with 0 ≤ x ≤ 0.1. The NiO/CuO composites with CuO mole fractions (m) of 20% ≤ m ≤ 95% are affirmed by the coexistence of NiO rock salt and CuO tenorite phases. The composites rich in CuO exhibit strong adsorption in the visible and ultraviolet spectral regions, while the absorption of composites rich in NiO is absent in certain regions of visible and infrared light. In addition, the superparamagnetism of NiO can be tuned to ferromagnetism by a small addition of CuO. The photocatalytic degradation efficiencies of rhodamine B, methylene blue, methyl orange, and methyl red over NiO/CuO reach 92%–97% within a period of 150 min under sunlight irradiation.

Storage degradation mechanism of layered Ni-rich oxide cathode material LiNi0.8Co0.1Mn0.1O2

With advantages such as high specific capacity and low cost, Ni-rich layered oxides are considered to be ideal cathode materials for power batteries. However, due to the high sensitivity of materials to air, structural degradation occurs during transportation and storage, resulting in the formation of an impurity layer. The degradation of the structure will weaken the comprehensive properties of Ni-rich cathode materials. The impurity layer will bring difficulties to the subsequent electrode manufacturing process, which seriously limits the practical application of Ni-rich materials. Therefore, it is particularly important to explore the storage decline mechanism of Ni-rich materials. Herein, the decay mechanism of structure and electrochemical properties of LiNi0.8Co0.1Mn0.1O2 materials after storage at room temperature and high humidity and high-temperature and humidity were studied. It is found that the instability of Ni3+ leads to the appearance of NiO rock salt phase on the surface of the material, accompanied by the formation of reactive oxygen species. Lithium and reactive oxygen species in the material react with H2O and CO2 in the air to form surface residual lithium compounds. The formation of the inert NiO layer and residual lithium compounds hinders the diffusion kinetics of Li+, resulting in serious capacity loss. During the high-temperature storage process, the material forms thicker residual lithium compounds, which aggravates the decay process. After 28 days of high-temperature storage, a residual lithium compound layer of about 7 nm thickness was formed, which seriously hindered the transmission of Li+. This study is helpful to deeply understand the storage failure behavior of Ni-rich cathode materials and promote the large-scale industrial production and application of Ni-rich cathode materials.

The in-depth description of phonon transport mechanisms for XC (X=Si, Ge) under hydrostatic pressure: Considering pressure-induced phase transitions

In this paper, the effect of hydrostatic pressure on the thermal transport properties of silicon carbide (SiC) and germanium carbide (GeC) with zinc blende (ZB) and rock salt (RS) phases at room temperature is investigated by solving the phonon Boltzmann heat transport equation. Studies show that the thermal conductivities of the two materials increase with the raising pressure before the phase transition, however, the enhancement of GeC (40%) is much smaller than that of SiC (100%). Combined with phonon analysis, it is found that this phenomenon originates from the abnormal enhanced phonon scattering rate under high pressure, which partly offsets the increase of phonon group velocity and further suppresses the increase of thermal conductivity. Next, when the phase transition occurs, the thermal conductivities of SiC and GeC decrease sharply by 76% and 86%, respectively, which is mainly caused by the increase of the anharmonic characteristic related to phonon scattering. Finally, after the phase transition, the thermal conductivities of the two materials still show increasing trends with the raising pressure, however, the phonon group velocity of GeC does not change significantly and the variation of its thermal conductivity is mainly determined by the phonon lifetime, which is opposite to the case before phase transition, whose enhancement of thermal conductivity is mainly caused by the increase of phonon group velocity. The results indicate that GeC has a more complex phonon transport mechanism compared with SiC, i.e., its thermal conductivity before phase transition is determined by harmonic characteristic and that after phase transition shows a closer relationship with the anharmonic characteristic. This study provides data and mechanism support for the regulation of thermal conductivity from the perspective of pressure-induced phase transition, and as well as supplies some guiding suggestions for engineering applications in the field of thermal transport regulation.

Highly stable surface and structural origin for lithium-rich layered oxide cathode materials

Surface/interfacial engineering is critical for preventing particle degradation of Li-rich layered oxides (LLOs), particularly facet degradation, thereby optimizing their electrochemical performance. Thus, the current study details the investigative analysis of the surface structure of an LLO, followed by its surface engineering. The surface structure was analyzed using scanning transmission electron microscopy (STEM) and soft X-ray absorption spectroscopy (sXAS), and the electrochemical performance was evaluated. The results indicate that an integrated spinel/rock salt (ISR) surface structure formed on the surface in situ. More precisely, the spinel phase originated from the C2/m surface, whereas the rock salt phase originated from the R3m surface, which significantly increased the cycle stability and suppressed voltage decay. After 2000 cycles, the surface-modified LLO cathode retained an extremely high capacity of 69.6% and a low discharge medium voltage with a decay rate of 0.44 mV cycle−1. Additionally, the structural and morphological changes observed after prolonged cycling confirmed the stability of the surface layer. The outstanding performance was attributed to the ultra-stable ISR surface layer, the presence of multiple ion conductivities (LiPO3 and Li2SO4), and the substantial prevention of electrochemical facet degradation. The findings, therefore, highly suggest that the ISR surface concept and the method for surface modification is highly likely to aid in the rapid commercialization of LLOs for battery applications.

Investigation of the corrosion of electro-less nickel-plated alloys in molten salt and its effect on phase change properties for energy storage applications

Interactions between electroless nickel plated Inconel 601, Monel 400, and stainless steel 316L alloys with two eutectic salts used as phase change materials, K2CO3 + Na2CO3 and NaCl + Na2CO3, were investigated at 720 °C (isothermal). The results of this study show that at these high temperatures, which is the target temperatures of the next generation of concentrated solar thermal power plants, these salt phase change materials are highly corrosive to stainless steel, whereas the Inconel 601, a high temperature nickel alloy, was resistant. Monel 400 experienced the most corrosion damage (500 µm thick corrosion layer) and resulted in the salts experiencing the greatest latent heat decrease by 18.1%, as confirmed by Differential Scanning Calorimetry (DSC). IN601 performed the best with an observed corrosion layer thickness of 107 µm, and resulted in one of the salts only decreasing in latent heat by 5.9%. IN601 with the nickel plating has shown improved corrosion resistance over uncoated samples. The thermophysical properties of the salt was measured before and after the exposure tests to demonstrate the significant effect corrosion has on the performance of the salts as a phase change material. Scanning Electron Microscopy (SEM) analysis showed that constituent elements have diffused from the alloy specimens, through the nickel plated layer and leached into the molten sat, which was characterized by Inductively Coupled Plasma- Optical Emission Spectroscopy (ICP-OES). A correlation was found between the corrosion of the specimens, the solubility of the alloying elements and a large decrease in the salt’s latent heat properties.

Entropy Stabilized Oxide Nanocrystals as Reaction Promoters in Lithium‐O2 Batteries

AbstractCharge transport limitations at the Li2O2 discharge product‐electrode interfaces hinder the rechargeability of Li−O2 batteries. Herein, we introduce entropy stabilized oxides (ESO) as reaction ′promoters′ in positive electrodes that can facilitate charge transport by reducing the binding energy of the intermediates. In this work, we developed a rock‐salt type entropy stabilized oxide. We show that the rock salt phase transforms into a pure, equimolar, quinary spinel on heat treatment. A Li−O2 battery with the developed ESOs at the positive electrode is cycled with an areal capacity of 1 mAh cm−2 at a current rate of 0.25 mA cm−2 to study its role as a reaction promoter. The surface, bulk, and morphological characterization are carried out for both materials. The presence of multiple cations and defects on the surface of the ESO is found to benefit the discharge product oxidation and improve the cyclic stability.

RT-XAMF and TR-XRD studies of solid-state synthesis and thermal stability of NaNiO2 as cathode material for sodium-ion batteries

Room-temperature sodium storage technology has been attracting considerable attention, and its potential as a alternative technology to lithium-ion batteries for electrical energy storage has been studied owing to the abundance of sodium resources and its inexpensiveness. In situ X-ray diffraction (XRD) techniques, such as real-time X-ray analytical micro-furnace (RT-XAMF) and time-resolved X-ray diffraction (TR-XRD), are utilized to identify the synthesis process and thermal stability of the NaNiO2 cathode material for Na-ion batteries. Using the RT-XAMF technique, the solid-state reaction of Na2O2 and NiO was investigated in real-time to verify the phase transition from rhombohedral NaNiO2 at temperatures above 243 °C to monoclinic NaNiO2 at temperatures below 243 °C during heat treatment. In addition, the structural instability of the monoclinic NaNiO2 phase changes to the Na-deficient Na0.91NiO2 phase. The TR-XRD technique was used to investigate the thermal stability of the desodiated Na1−xNiO2 (x = 0.09, 0.5) cathodes in the presence of an electrolyte. It was confirmed that the structural changes of desodiated Na1−xNiO2 were relatively simple compared to those of the Ni-based cathode material in Li-ion batteries. First, the layered structure of Na1−xNiO2 at room temperature turns into an MO-type rock salt phase (NiO) and subsequently into a metallic phase (Ni) without the appearance of spinel-type (Li1−xM2O4 and M3O4) intermediates, which are typically observed in lithium nickel-based oxides. In addition, it was concluded that desodiated Na1−xNiO2 materials have higher thermal stability than delithiated Li1−xNiO2 (x = 0.5, below ∼200 °C) based on its high decomposition temperature (∼300 °C for Na0.91NiO2 and ∼280 °C for Na0.5NiO2). From these results, we believe that our in-situ XRD findings on the real-time solid-state synthesis process and thermal stability can be used as a fundamental guide for the development of Ni-based NaMO2 (M = Ni, Co, Mn, etc.) oxides for next-generation advanced Na-ion batteries.

Mixed B-site ruddlesden-popper phase Sr2(RuxIr1-x)O4 enables enhanced activity for oxygen evolution reaction

Development of high performance electrocatalysts for oxygen evolution reaction (OER) in acidic media remains a challenge for direct water splitting using an electrolyzer. Recently, Ruddlesden-Popper phase Sr2IrO4 was discovered to be an efficient OER catalyst because of its unique structure, which consists of layers of both rock salt and perovskite phases simultaneously. In this study, we prepared a series of B-site mixed, Ruddlesden-Popper phase of Sr2(RuxIr1−x)O4 and examined their electrocatalytic properties for OER in acidic media. Through partial substitution of Ru in the B-site of Ruddlesden-Popper phase materials, we achieved much enhanced OER performance for this series of Sr2(RuxIr1−x)O4 electrocatalysts, among which Sr2(Ru0.5Ir0.5)O4 exhibited the best catalytic activity with a current density of 8.06 mA/cm2 at 1.55 V and a Tafel slope of 47 mV/dec. This current density is three times higher than that of Sr2IrO4. The B-site mixed Sr2(Ru0.5Ir0.5)O4 retained good stability in acidic conditions for > 24 h at 10 mA/cm2. A range of techniques were used to characterize the crystal and electronic structures of the Sr2(RuxIr1−x)O4 samples. Our data indicate that the improved OER performance can be correlated to the formation of high level of hydroxyl groups and the enhanced overlap between Ir/Ru 4d and O 2p orbitals, revealing a new way for the design of efficient OER electrocatalysts by regulating their composition and electronic structures.

Superhydrophilic Modified Elastomeric RGO Aerogel Based Hydrated Salt Phase Change Materials for Effective Solar Thermal Conversion and Storage

As a typical phase-change material (PCM) with high heat storage capacity and wide distribution, hydrated salts play broad and critical roles in solar energy utilization in recent years. However, the leakage and supercooling problems of hydrated salts have been a constraint to their further practical applications. In the current work, the super-hydrophilic reduced graphene oxide (RGO) aerogels modified by konjac glucomannan (KGM) as supporting structural materials are prepared by the hydrothermal reaction-freeze-drying, which can effectively absorb and convert visible sunlight energy into thermal energy. In addition, the super-hydrophilic aerogels compounded with PCMs can ameliorate the shortcoming of leakage and suppress the supercooling temperature as low about 0.2-1.5 °C in the freezing process. Under 1 sun irradiation, the prepared sodium acetate trihydrate/KGM-modified graphene oxide aerogel (SAT/KRGO) composite PCM achieves a high photothermal conversion efficiency (86.3%) due to its good light absorption property. The number of cycles has no apparent effect on the supercooling of the composite materials, suggesting their stable thermal cycles and thermal storage.

Interfacial Reviving of the Degraded LiNi0.8 Co0.1 Mn0.1 O2 Cathode by LiPO3 Repair Strategy.

Nickel-rich cathode materials, owing to their high energy density and low cost, are considered to be one of the cathodes with the most potential in next-generation lithium-ion batteries. Unfortunately, this kind of cathode with highly active surface is easy to react with H2 O and CO2 when exposed to ambient air, resulting in the formation of lithium impurities and interfacial phase transition as well as deterioration of the electrochemical properties. In this work, the evolution mechanism of the structure and interface of LiNi0.8 Co0.1 Mn0.1 O2 during air-exposure is systematically investigated. Furthermore, a facile reviving strategy is proposed to restore the degraded LiNi0.8 Co0.1 Mn0.1 O2 by using LiPO3 as the repair agent. The lithium impurities on the surface of the degraded sample can transform into the repair/coating layer, and part of the rock salt phase on the subsurface can revive to layered phase after repair heat treatment. As a result, the optimized cathode delivers an initial discharge capacity of 198.3 mAh g-1 at 0.1C and a capacity retention of 85.5% after 50 cycles. Although slightly lower than the bare sample (201 mAh g-1 and 88%), they are obviously higher than the exposed samples (166.5 mAh g-1 and 40.4%). The regenerated electrochemical properties should be attributed to the multifunctional repair layer that can efficiently reduce the surface lithium impurities, prevent the corrosion of electrolyte, and improve the interfacial Li+ diffusion kinetics. This work can effectively reduce the waste of the degraded Ni-rich ternary materials and realize the transformation of "waste" into wealth.

Thermal, structural and transport properties of composite solid electrolytes (1-x)(C4H9)4NBF4–xAl2O3

Thermal, structural and electrical properties of composite solid electrolytes (1-x)(C4H9)4NBF4–xAl2O3 with nanocrystalline γ-alumina were investigated by DSC, X-ray diffraction, IR spectroscopy, impedance and electrochemical measurements. It was found that the melting enthalpy of (C4H9)4NBF4 in the composites strongly decreases and its value approaches to zero in the composites with x ≥ 0.9, where x is the molar fraction of alumina, indicating the transformation of (C4H9)4NBF4 to an interface-stabilized amorphous state. This effect was quantitatively interpreted in terms of the brick-wall model assuming that a layer of amorphous phase of the ionic salt is formed at salt/oxide interfaces. At the alumina concentration of x = 0.9, corresponding to a volume fraction of alumina f = 0.53, almost all the ionic salt gets into the interface layer the thickness of the amorphous layer is nearly 3 nm. These results agree with the results of X-ray diffraction studies and IR spectroscopy. Introduction of nanocrystalline γ-alumina into the (C4H9)4NBF4 matrix leads to a relative increase in conductivity by more than 2 orders of magnitude, conductivity goes through a maximum of 0.21 mS/cm at 130 °C for the composite with x = 0.9. This composite is characterized by a non-Arrhenius temperature dependence, typical for glassy electrolytes. It was shown that the electrochemical voltage for the composite 0.1(C4H9)4NBF4–0.9Al2O3 is nearly 4 V.

High entropy oxide nanofiber by electrospun method and its application for lithium battery anode material

AbstractMg0.2Co0.2Ni0.2Cu0.2Zn0.2O high entropy oxide (HEO) with outstanding cycling stability and high capacity retention indicates it is a promising anode material for rechargeable lithium‐ion batteries. Rock salt HEO nanofiber has been prepared by electrospinning method. Polyacrylonitrile polymer facilitates the formation of nanowire morphology. The effect of calcination temperature on the phase composition and microstructure evolutions has been investigated. Pure rock salt phase can be obtained after firing at 850°C for 2 min. Calcination at higher temperature than 850°C will break the fiber into short segments and lead to the growth of grain. A reversible capacity of 365 mAh g−1 was achieved after 300 cycles at .2 A·g−1.

Exploration of lower critical solution temperature DES in a thermoreversible aqueous two-phase system for integrating glucose conversion and 5-HMF separation

With the deepening of the research on the conversion of cellulose biomass to furfural, there is no green and efficient method to separate sugars and 5-HMF. This study utilized a thermoreversible aqueous two-phase system (ATPS) coupled with tetrabutylammonium bromide ([N4444]Br)- based deep eutectic solvents (DES) and inorganic salts for separating glucose and 5-HMF. The thermal characteristics of DESs were analyzed by thermogravimetry (TGA) and differential scanning calorimetry (DSC). The thermoreversible phase behavior of ATPS was determined by phase diagram. Furthermore, the process factors were optimized, such as the type and concentration of DES and phosphate, the temperature, and the time of ATPS were investigated, to maximize the separation of glucose and 5-HMF. Finally, the ATPS was a successful integrated catalytic reaction of glucose involving CrCl3 and 5-HMF separation. The results showed that the ATPS consist of 30 wt% [N4444]Br-EG and 25 wt% K2HPO4 had the most efficient extraction rate, 5-HMF reached 96.0 ± 0.6%, and mainly existed in the DES phase, while glucose was enriched in salt phase, and the extraction rate reached 99.9 ± 0.03%. And the 5-HMF yield reached 25.6 ± 1.1% in the production separation integrated platform. This thermoreversible ATPS may provide a guide for the effective extraction of furfural from biomass-derived glucose.

Aluminum doping of mesoporous silica as a promising strategy for increasing the energy storage of shape stabilized phase change materials containing molten NaNO3: KNO3 eutectic mixture

Efficient thermal energy storage at high temperature is necessary for both industrial waste heat utilization and continuous solar power generation. Shape-stabilized phase change materials containing mesoporous aluminosilicates and eutectic NaNO3: KNO3 (1:1 mol) molten salt mixture were obtained at 90% wt. salt. The influence of aluminum doping was studied for the first time. All samples show thermal stability up to 550 °C and two distinct phase transitions corresponding to the melting/freezing of nanoconfined and interparticle salt phases. The radius and spherical shape of the nanoconfined phase were determined from the melting and freezing point depressions with respect to bulk. The enthalpy decrease was quantified in terms of surface tension and the contributions of a non-melting fraction of surface adsorbed ions. SBA-15 type aluminosilicates matrices yield composites with high latent heat storage of 76–77 Jg−1, of which 8 Jg−1 for the nanoconfined phase and good thermal reliability. Aluminum doping is a simple and promising strategy for obtaining high temperature, efficient thermal energy storage materials due to a lack of non-melting salt fraction. The resulting shape-stabilized PCMs have a higher operating temperature range and latent heat storage, offering a 36% increase in total heat capacity over the pristine salt.

Improvement of safe bromine electrolytes and their cell performance in H2/Br2 flow batteries caused by tuning the bromine complexation equilibrium

Hydrogen bromine redox flow batteries utilize bromine electrolytes in their positive half cell, offering capacities larger than 100 Ah L −1 . Addition of quaternary ammonium compounds, so-called bromine complexing agents (BCA), may increase safety as they reduce the vapour pressure of bromine in the posolyte. However, they have not been applied so far. They (a) interact with perfluorosulfonic acid membranes leading to significant reduction of membrane conductivity and (b) they form a low conductive ionic liquid with polybromides, leading to high overvoltage if the formation happens at the electrode. In this work a solution to this problem is proposed by an excess addition of Br 2 to these electrolytes. The excess bromine leads to a permanent bromine fused salt phase in the tank. Bromine formed in the cell stays in the aqueous phase and bromine transfer between the two phases happens in the tank. Transfer of Br 2 without the transfer of [BCA] + cations exists between the phases, while [C2Py] + cations remain in the fused salt and do not influence cell performance. For the first time a posolyte capacity of 179.6 Ah L −1 based on 7.7 M hydrobromic acid with BCA is achieved compared to previous investigations with e.g. 53.9 Ah L −1 . • Evaluation of bromine posolytes with complexing agents (BCA) for energy storage. • Investigation of Br 2 transfer mechanism between aqueous electrolyte and fused salt. • Successful development of electrolyte by intervention in complexation reaction. • Reduced influence of BCA cation on PFSA membrane performance and cell performance. • Increase of the useable electrolyte capacity from 53.9 Ah L −1 to 179.6 Ah L −1 .