Unraveling the degradation mechanism of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) at the high cut-off voltage for lithium ion batteries

LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)layered oxides have been regarded as promising alternative cathodes for the next generation of high-energy lithium ion batteries(LIBs)due to high discharge capacities and energy densities at high operation voltage.However,the capacity fading under high operation voltage still restricts the practical application.Herein,the capacity degradation mechanism of NCM811 at atomic-scale is studied in detail under various cut-off voltages using aberration-corrected scanning transmission electron microscopy(STEM).It is observed that the crystal structure of NCM811 evolution from a layered structure to a rock-salt phase is directly accompanied by serious intergranular cracks under 4.9 V,which is distinguished from the generally accepted structure evolution of layered,disordered layered,defect rock salt and rock salt phases,also observed under 4.3 and 4.7 V.The electron energy loss spectroscopy analysis also confirms the reduction of Ni and Co from the surface to the bulk,not the previously reported only Li/Ni interlayer mixing.The degradation mechanism of NCM811 at a high cut-off voltage of4.9 V is attributed to the formation of intergranular cracks induced by defects,the direct formation of the rock salt phase,and the accompanied reduction of Ni^(2+)and Co^(2+)phases from the surface to the bulk.

Degradation mechanism of 2,4,6-trinitrotoluene in supercritical water oxidation

The 2,4,6-trinitrotoluene （TNT） is a potential carcinogens and TNT contaminated wastewater, which could not be effectively disposed with conventional treatments. The supercritical water oxidation （SCWO） to treat TNT contaminated wastewater was studied in this article, The TNT concentration in wastewater was measured by high-performance liquid chromatograph （HPLC） and the degraded intermediates were analyzed using GC-MS. The results showed that SCWO could degrade TNT efficiently in the presence of oxygen. The reaction temperature, pressure, residence time and oxygen excess were the main contributing factors in the process. The decomposition of TNT was accelerated as the temperature or residence time increased. At 550℃, 24 MPa, 120 s and oxygen excess 300%, TNT removal rate could exceed 99.9%. Partial oxidation occured in SCWO without oxygen. It was concluded that supercritical water was a good solvent and had excellent oxidation capability in the existence of oxygen. The main intermediates of TNT during SCWO included toluene, 1,3,5-trinitrobenzene, nitrophenol, naphthalene, fluorenone, dibutyl phthalate, alkanes and several dimers based on the intermediate analysis. Some side reactions, such as coupled reaction, hydrolysis reaction and isomerization reaction may take place simultaneously when TNT was oxidized by SCWO.

The degradation mechanism of an AlGaN/GaN high electron mobility transistor under step-stress

Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AIGaN/GaN high electron mobility transistor （HEMT）. It is found that the stress current shows a recoverable decrease during each voltage step and there is a critical voltage beyond which the stress current starts to increase sharply in our experiments. We postulate that defects may be randomly induced within the A1GaN barrier by the high electric field during each voltage step. But once the critical voltage is reached, the trap concentration will increase sharply due to the inverse piezoelectric effect. A leakage path may be introduced by excessive defect, and this may result in the permanent degradation of the A1GaN/GaN HEMT.

STUDY OF DEGRADATION MECHANISM AND PACKAGING OF ORGANIC LIGHT EMITTING DEVICES

Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to theircommercialization. Here we present a brief summary of our studies on both extrinsic and intrinsic causes for the fastdegradation of OLEDs. In particular, we focus on the origin of the dark spots by 'rebuilding' cathodes, which confirms thatthe growth of dark spots occurs primarily due to cathode delamination. In the meantime, we recapture the findings from thesearch for suitable OLED packaging materials, in particular polymer composites, which provide both heat dissipation andmoisture resistance, in addition to electrical insulation.

STUDIES ON FLUORESCENCE ENHANCING EFFECT AND ALKALINE DEGRADATION MECHANISM OF DOXYCYCLINE AND METHACYCLINE

Degradation reaction of doxycycline or methacycline was carried out in KOH solution and intense fluorescence was obtained.A degradation mechanism of doxycycline or methacycline was suggested.

Degradation mechanism of two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures

This paper finds that the two-dimensional electron gas density in high Al-content A1GaN/GaN heterostructures exhibits an obvious time-dependent degradation after the epitaxial growth. The degradation mechanism was investigated in depth using Hall effect measurements,high resolution x-ray diffraction,scanning electron microscopy,x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy.The results reveal that the formation of surface oxide is the main reason for the degradation,and the surface oxidation always occurs within the surface hexagonal defects for high Al-content AlGaN/GaN heterostructures.

Degradation Mechanism of the Superconducting Transition Temperature in Nb Thin Films

Systemic measurements show that there is no 3D to 2D crossover in the reduction of the superconducting transition temperature Tc in Nb thin films. This result is consistent with all previous measurements while it is contrary to the prevailing understanding based on the interplay between proximity, localization, and lifetime broadening. Our study indicates that the decrease of Tc can be interpreted by the combined effects of electron-phonon coupling parameter λ and the defect scattering rate pw, being uniquely determined by their ratio λ/ρw. Other factors such as film thickness and irradiation do not produce additional effects beyond these two parameters.

Preparation of Perovskite Solar Cells in the Air:Degradation Mechanism and Prospects on Large-Area Fabrication

The preparation of perovskite solar cells(PsCs)in the air environment has attracted the attention of numerous experimenters due to its low preparation cost and the possibility of commercialization.Although the power conversion efficiency(PCE)of PSCs has increased rapidly and exceeded 25%,which is comparable to commercial polysilicon solar cells,most certified or reported high-efficiency perovskite solar cells are still confined to glove boxes or relatively small active areas in the air environment due to moisture,oxygen,high temperature,and ultraviolet(UV)factors.In this review.

Structural evolution of layered oxide cathodes for spent Li-ion batteries:Degradation mechanism and repair strategy

Sustainable development has long been recognized as one of the most critical issues in today’s energy and environment-conscious society.It has never been more urgent to recycle and reuse the end-of-life cathode materials.Here,this work systematically investigates the structure-critical degradation mechanism of polycrystalline LiNi_(x)Co_(y)Mn_(1−x−y)O_(2)(NCM),combining experimental characterization and DFT simulations.Targeting the key degradation factors,a synergistic repair strategy based on deep mechanochemical activation and heat treatment was successfully proposed to direct regenerate the degradedNCMmaterial.Studies indicate the induction and promotion of synergistic repair technique on the reconstruction of particlemorphology,the recovery of the chemical composition and crystal structure,and the favorable transformation of the impurities phase in the failed materials.In particular,the synergistic repair process induces a gradient distribution of LiF and further enables partial fluorine doping into the NCM surface,forming abundant oxygen vacancies and increasing the content of highly reactive Ni2+.Benefiting from the comprehensive treatment for the multi-scale and multi-form degradation behaviors,the repaired material exhibits a capacity of 176.8 mA h g^(-1)at 0.1 C,which is comparable to the corresponding commercial material(172.8 mA h g^(-1)).The satisfactory capacity of the recovered cathode proves that it is an effective direct renovating strategy.

Theoretical insights into the degradation mechanisms, kinetics and eco-toxicity of oxcarbazepine initiated by OH radicals in aqueous environments

As an anticonvulsant,oxcarbazepine(OXC)has attracted considerable attention for its potential threat to aquatic organisms.Density functional theory has been used to study the mechanisms and kinetics of OXC degradation initiated by OH radicals in aqueous environment.A total of fourteen OH-addition pathways were investigated,and the addition to the C8 position of the right benzene ringwas themost vulnerable pathway,resulting in the intermediate IM8.The H-abstraction reactions initiated by OH radicalswere also explored,where the extraction site of the methylene group(C14)on the seven-member carbon heterocyclic ring was found to be the optimal path.The calculations show that the total rate constant of OXC with OH radicals is 9.47×10^(9)(mol/L)^(−1)sec^(−1),and the half-life time is 7.32 s at 298 K with the[·OH]of 10^(−11) mol/L.Moreover,the branch ratio values revealed that OH-addition(89.58%)shows more advantageous than H-abstraction(10.42%).To further understand the potential eco-toxicity of OXC and its transformation products to aquatic organisms,acute toxicity and chronic toxicity were evaluated using ECOSAR software.The toxicity assessment revealed that most degradation products such as OXC-2OH,OXC-4OH,OXC-1O-1OOH,and OXC-1OH’are innoxious to fish and daphnia.Conversely,green algae are more sensitive to these compounds.This study can provide an extensive investigation into the degradation of OXC by OH radicals and enrich the understanding of the aquatic oxidation processes of pharmaceuticals and personal care products(PPCPs).

Performance degradation mechanism of lithium compounds ceramic fuel cell with GDC as electrolyte

The performance degradation mechanism of ceramic fuel cell with NCAL(Ni_(0.8)Co_(0.15)Al_(0.05)LiO_(2))as symmetrical electrode and GDC as electrolyte in H2 is investigated.It is found that under the condition of 550◦C and constant current density of 0.2 A⋅cm^(-2),the output voltage of the cell is about 1.005 V in the initial 10 h and remains relatively stable.After 10 h,the voltage of the cell began to decrease gradually,and by 50 h,the voltage had decreased to 0.522 V.The results testing electrochemical performance of the cell and characterizing the cell materials before and after test using SEM,TOF-SIMS and FTIR indicate that the distribution of Li_(2)O/LiOH/Li_(2)CO_(3)compounds generated from NCAL anode in the cell plays a vital role in significantly improving the ionic conductivity of electrolyte and gas tightness of the cell.The dynamic migration of molten salt destroyed the continuity of molten salt in the cell,which in turn adversely impacted the ionic conductivity of electrolyte,gas tightness of the cell,and electrochemical reactions on both sides of the cathode and anode.These finally lead to the degradation of the cell performance.

Microwave photocatalytic degradation of Rhodamine B using TiO_2 supported on activated carbon:Mechanism implication

The photocatalytic degradation of Rhodamine B （RhB） was carried out using TiO2 supported on activated carbon （TiO2-AC） under microwave irradiation. Composite catalyst TiO2-AC was prepared and characterized using X-ray diffraction （XRD）, transmission electron microscopy （TEM） and Brunauer-Emmett-Teller （BET）. In the process of microwave-enhanced photocatalysis （MPC）, RhB （30 mg/L） was almost completely decoloured in 10 min, and the mineralization efficiency was 96.0% in 20 min. The reaction rate constant of RhB in MPC using TiO2-AC by pseudo first-order reaction kinetics was 4.16 times of that using Degussa P25. Additionally, according to gas chromatography/mass spectrometry （GC/MS） and liquid chromatography/mass spectrometry （LC/MS） identification, the major intermediates of RhB in MPC included two kinds of N-de-ethylation intermediates （N,N-diethyl-N＇-ethyl-rhodamine （DER））, oxalic acid, malonic acid, snccinic acid, and phthalic acid, maleic acid, 3-nitrobenzoic acid, and so on. The degradation of RhB in MPC was mainly attributed to the destruction of the conjugated structure, and then the intermediates transformed to acid molecules which were mineralized to water and carbon dioxide.

Cathodic Zn underpotential deposition:an evitable degradation mechanism in aqueous zinc-ion batteries

Aqueous zinc-ion batteries(AZIBs)are promising for large-scale energy storage,but their development is plagued by inadequate cycle life.Here,for the first time,we reveal an unusual phenomenon of cathodic underpotential deposition(UPD)of Zn,which is highly irreversible and considered the origin of the inferior cycling stability of AZIBs.Combining experimental and theoretical simulation approaches,we propose that the UPD process agrees with a two-dimensional nucleation and growth model,following a thermodynamically feasible mechanism.Furthermore,the universality of Zn UPD is identified in systems,including VO_(2)//Zn,TiO_(2)//Zn,and SnO_(2)//Zn.In practice,we propose and successfully implement removing cathodic Zn UPD and substantially mitigate the degradation of the battery by controlling the end-ofdischarge voltage.This work provides new insights into AZIBs degradation and brings the cathodic UPD behavior of rechargeable batteries into the limelight.

Influence of laser surface remelting on microstructure and degradation mechanism in simulated body fluid of Zn-0.5Zr alloy

In this study,the Zn-0.5 wt%Zr(Zn-Zr)alloy was treated by laser surface remelting(LSR),and then the microstructure and degradation mechanism of the remelting layer were investigated and compared with the original as-cast alloy.The results reveal that after LSR,the bulky Zn(22)Zr phase in the original Zn-Zr alloy is dissolved and the coarse equiaxed grains transform into fine dendrites with a secondary dendrite arm space of about 100 nm.During the degradation process in simulated body fluid(SBF),the corrosion products usually concentrate at some certain areas in the original alloy,while the corrosion products distribute uniformly and loosely in the LSR-treated surface.After removing the corrosion products,it was found that the former suffers obvious pitting corrosion and then localized corrosion.The proposed mechanism is that corrosion initiates at grain boundaries and develops into the depth at some locations,and then leads to localized corrosion.For the LSR-treated sample,corrosion initiates at some active sites and propagates in all directions,corrosion takes place in the whole surface with distinctly uniform thickness reduction,while the localized corrosion and peeling of bulky Zn(22)Zr particles were eliminated.The electrochemical results also suggest the uniform corrosion of LSR-treated sample and localized corrosion of original sample.Based on the results,a new approach to regulate the corrosion mode of the biodegradable Zn alloy is proposed.

Refined model analysis of basement rock degradation mechanism of heavy-haul railway tunnel

This study investigated the degradation mechanism of the surrounding rock of a heavy-haul railway under a water-rich condition,based on the construction of the Taihangshan tunnel for the Wari Railway,a heavy-haul railway that used standard construction practices for axle loads of 30 t.Remote monitoring demonstrated that the coupling effect between the dynamic load of a heavy-haul train and the groundwater leads to the deterioration and hollowing of the surrounding rock.This study clarified the void evolution process and deterioration mechanism of the basement rock under the comprehensive influence of the groundwater–train dynamic load using a refined discrete element numerical simulation.The results revealed that the groundwater was the primary influencing factor in the deterioration of the lower part of the heavy-haul railway tunnel.Rock particles were gradually lost under the effects of long-term erosion due to groundwater and heavy-haul trains,which inevitably damaged the basement rock after the construction was completed.Based on this observation,the critical conditions for the deterioration and attenuation law of the physical parameters of the basement rock were obtained.The results of this study can provide ideas and serve as a reference for the forecasting and disaster treatment of basement rock damage in heavy-haul railway tunnels.

Degradation of Alkaline Lignin in the Lactic Acid-Choline Chloride System under Mild Conditions

Lignin is a natural polymer,second only to cellulose in natural reserves.Degradation is one of the ways to achieve the high-value transformation of lignin.Deep eutectic solvent(DES)thermal degradation of lignin can be used as an excellent green degradation method.This paper introduces the degradation mechanism and effect of the lactic acid-choline chloride DES system in dissolving and degrading alkaline lignin,and the final solvent recovery.It can also be found from the scanning electron microscope(SEM)images that the surface of the degraded solid product is transformed from smooth to disordered.Fourier transform infrared(FTIR)spectroscopy and 1H-NMR spectroscopy were used to characterize the changes in lignin functional groups during DES treatment.The results showed that the content of phenolic hydroxyl groups increased after degradation,indicating that theβ-O-4 ether bond was broken.The molecular weight of the degraded lignin was observed by gel permeation chromatography(GPC),and the lignin residue with low molecular weight and narrow polydispersity index was obtained.The lowest average molecular weight(Mw)reached 2512 g/mol.The ratio of oxygen to carbon atoms in lignin increased substantially during degradation as measured by X-ray photoelectron spectroscopy(XPS),probably because DES treatment was accompanied by many oxidation reactions,which led to significant structural changes in lignin and a large number of ether bond breakage reactions during the reaction.The main final degradation products are aromatic monomers,vanillin,butyrovanillone,etc.

Mechanisms of Accelerated Degradation in the Front Cells of PEMFC Stacks and Some Mitigation Strategies

The accelerated degradation in the front ceils of a polymer electrolyte membrane fuel cell（PEMFC） stack seriously reduces the reliability and durability of the whole stack. Most researches only focus on the size and configuration of the gas intake manifold, which may lead to the maldistribution of flow and pressure. In order to find out the mechanisms of the accelerated degradation in the front cells, an extensive program of experimental and simulation work is initiated and the results are reported. It is found that after long-term lifetime tests the accelerated degradation in the front cells occurs in all three fuel cell stacks with different flow-fields under the U-type feed configuration. Compared with the rear cells of the stack, the voltage of the front cells is much lower at the same current densities and the membrane electrode assembly（MEA） has smaller active area, more catalyst particle agglomeration and higher ohmic impedance. For further investigation, a series of three dimensional isothermal numerical models are built to investigate the degradation mechanisms based on the experimental data. The simulation results reveal that the dry working condition of the membrane and the effect of high-speed gas scouting the MEA are the main causes of the accelerated degradation in the front cells of a PEM fuel cell stack under the U-type feed configuration. Several mitigation strategies that would mitigate these phenomena are presented： removing cells that have failed and replacing them with those of the same aging condition as the average of the stack; choosing a Z-type feed pattern instead of a U-type one; putting several air flow-field plates without MEA in the front of the stack; or exchanging the gas inlet and outlet alternately at a certain interval. This paper specifies the causes of the accelerated degradation in the front cells and provides the mitigation strategies.

The thermal and irradiation degradation mechanisms of Eu^(2+),Mn^(2+) co-doped BaMgAl_(10)O_(17) phosphor

The mechanisms of thermal,ultraviolet and vacuum ultraviolet radiation degradation behaviors of the Eu2+,Mn2+ co-doped BaMgAl10O17 phosphors were investigated comparatively.The result indicated that the Mn2+ ions which replaced the Mg2+ sites in the sample were stable and negligibly influenced by treatments.The oxidation and migration of Eu2+ ions primarily caused the thermal degradation of the sample.The vacuum ultraviolet radiation degradation was primarily because of the migration of Eu2+.The ultraviolet radiation increased traps which trended the Eu2+r to be in a metastable state,leading to the ultraviolet radiation degradation of the sample.The vacuum ultraviolet excited luminous loss of samples after ultraviolet radiation partly originated from the interruption of energy transfer from the host to activators by traps.

Interpretable hybrid machine learning demystifies the degradation of practical lithium-sulfur batteries

The ever-increasing future demands of electrification and grid storage have spurred continued research to develop rechargeable battery chemistries for reliable energy storage[1].Beyond current lithium-ion batteries,lithium–sulfur battery represents a promising system due to its high energy density(2600 Wh kg^(-1))and low material cost[2].

The Mechanism of Carotenoid Degradation in Flue-Cured Tobacco and Changes in the Related Enzyme Activities at the Leaf-Drying Stage During the Bulk Curing Process

The mechanism of carotenoid degradation and the changes in the activities of related enzymes in flue-cured tobacco at the leaf-drying stage during the bulk-curing process were studied in order to provide theoretical basis for optimization of curing technology. The effect of different rising speeds of temperature on the carotenoid degradation and the related enzymes activities at the color-fixing stage during the bulk curing process was studied by using the electric-heated fluecuring barn designed by Henan Agricultural University, China, based on curing technology with yellowing at low temperature and moderate humidity and leaf drying at moderate humidity. The results showed that the carotenoid degradation components （β-carotene, lutein, neoxanthin, and violaxthin） decreased gradually at the color-fixing stage during the bulk curing process. The carotenoid degradation components viz.,β-carotene, lutein, neoxanthin, and violaxthin at the slow heating curing （T1） were relatively higher than the rapid heating curing （T2） accounting for 10, 2, 32 and 32% respectively, but there were no differences among treatments （P〉 0.05）. The effect of different conditions of curing on the activities of enzymes related to carotenoids degradation were significant. The lipoxygenase, phenylalanine ammonialyase, peroxidase, and polyphenol oxidase enzymes had a bidirectional effect on the quality of tobacco leaves and it was beneficial to form more premise matter of aroma based on the higher enzyme activities at the early leaf-drying stage. The slow heating could regulate the change in various enzymes＇ activities reasonably, making cell redox reaction to reach the dynamic balance and make the degradation of carotenoids adequately. Meanwhile, it could avoid the occurrence of browning reaction and provide foundation for improving the quality of tobacco and optimization of technology for bulk curing and further enhancing aroma.