Early-stage latent thermal failure of single-crystal Ni-rich layered cathode

High nickel content worsens the thermal stability of layered cathodes for lithium-ion batteries,raising safety concerns for their applications.Thoroughly understanding the thermal failure process can offer valuable guidance for material optimization on thermal stability and new opportunities in monitoring battery thermal runaway(TR).Herein,this work comprehensively investigates the thermal failure process of a single-crystal nickel-rich layered cathode and finds that the latent thermal failure starts at∼120℃far below the TR temperature(225℃).During this stage of heat accumulation,sequential structure transition is revealed by atomic resolution electron microscopy,which follows the layered→cation mixing layered→LiMn_(2)O_(4)-type spinel→disordered spinel→rock salt.This progression occurs as a result of the continuous migration and densification of transition metal cations.Phase transition generates gaseous oxygen,initially confined within the isolated closed pores,thereby not showing any thermal failure phenomena at the macro-level.Increasing temperature leads to pore growth and coalescence,and eventually to the formation of open pores,causing oxygen gas release and weight loss,which are the typical TR features.We highlight that latent thermal instability occurs before the macro-level TR,suggesting that suppressing phase transitions caused by early thermal instability is a crucial direction for material optimization.Our findings can also be used for early warning of battery thermal runaway.

PtNi-W/C with Atomically Dispersed Tungsten Sites Toward Boosted ORR in Proton Exchange Membrane Fuel Cell Devices

The performance of proton exchange membrane fuel cells is heavily dependent on the microstructure of electrode catalyst especially at low catalyst loadings.This work shows a hybrid electrocatalyst consisting of PtNi-W alloy nanocrystals loaded on carbon surface with atomically dispersed W sites by a two-step straightforward method.Single-atomic W can be found on the carbon surface,which can form protonic acid sites and establish an extended proton transport network at the catalyst surface.When implemented in membrane electrode assembly as cathode at ultra-low loading of 0.05 mgPt cm^(−2),the peak power density of the cell is enhanced by 64.4%compared to that with the commercial Pt/C catalyst.The theoretical calculation suggests that the single-atomic W possesses a favorable energetics toward the formation of*OOH whereby the intermediates can be efficiently converted and further reduced to water,revealing a interfacial cascade catalysis facilitated by the single-atomic W.This work highlights a novel functional hybrid electrocatalyst design from the atomic level that enables to solve the bottle-neck issues at device level.

Recent progress on advanced transmission electron microscopy characterization for halide perovskite semiconductors

Halide perovskites are strategically important in the field of energy materials. Along with the rapid development of the materials and related devices, there is an urgent need to understand the structure–property relationship from nanoscale to atomic scale. Much effort has been made in the past few years to overcome the difficulty of imaging limited by electron dose,and to further extend the investigation towards operando conditions. This review is dedicated to recent studies of advanced transmission electron microscopy(TEM) characterizations for halide perovskites. The irradiation damage caused by the interaction of electron beams and perovskites under conventional imaging conditions are first summarized and discussed. Low-dose TEM is then discussed, including electron diffraction and emerging techniques for high-resolution TEM(HRTEM) imaging. Atomic-resolution imaging, defects identification and chemical mapping on halide perovskites are reviewed. Cryo-TEM for halide perovskites is discussed, since it can readily suppress irradiation damage and has been rapidly developed in the past few years. Finally, the applications of in-situ TEM in the degradation study of perovskites under environmental conditions such as heating,biasing, light illumination and humidity are reviewed. More applications of emerging TEM characterizations are foreseen in the coming future, unveiling the structural origin of halide perovskite’s unique properties and degradation mechanism under operando conditions, so to assist the design of a more efficient and robust energy material.

Preface to the Special Topic on In-Situ and in-operando Characterization of Semiconductor Materials and Devices

Characterization of materials and devices is fundamental to the understanding of structure-property relationship and improving device performance. Driven by the rapid progress achieved in semiconductors research, advanced characterization techniques at high spatial resolution are being developed.

Glass crystallization making red phosphor for high-power warm white lighting

Rapid development of solid-state lighting technology requires new materials with highly efficient and stable luminescence,and especially relies on blue light pumped red phosphors for improved light quality.Herein,we discovered an unprecedented red-emitting Mg_(2)AI_(4)Si_(5)0_(18):Eu^(2+)composite phosphor(λex=450 nm,λem=620 nm)via the crystallization of MgO-AI_(2)O_(3)-Sio_(2) aluminosilicate glass.Combined experimental measurement and first-principles calculations verify that Eu^(2+)dopants insert at the vacant channel of Mg_(2)AI_(4)Si_(5)0_(18)crystal with six-fold coordination responsible for the peculiar red emission.Importantly,the resulting phosphor exhibits high internal/external quantum efficiency of 94.5/70.6%,and stable emission against thermal quenching,which reaches industry production.The maximum luminous flux and luminous efficiency of the constructed laser driven red emitting device reaches as high as 274 Im and 54lm W^(-1),respectively.The combinations of extraordinary optical properties coupled with economically favorable and innovative preparation method indicate,that the Mg_(2)AI_(4)Si_(5)0_(18):Eu^(2+)composite phosphor will provide a significant step towards the development of high-power solid-state lighting.

Two-in-one solution using insect wings to produce graphene-graphite films for efficient electrocatalysis

Natural organisms contain rich elements and naturally optimized smart structures,both of which have inspired various innovative concepts and desig ns in human society.In particular,several natural organisms have been used as element sources to synthesize low-cost and environmentally friendly electrocatalysts for the oxygen reduction reaction(ORR)in fuel cells and metal-air batteries,which are clean energy devices.However,to date,no naturally optimized smart structures have been employed in the synthesis of ORR catalysts,including graphene-based materials.Here,we demonstrate a novel strategy to synthesize graphene-graphite films(GGFs)by heating butterfly wings coated with FeCI3 in N2,in which the full power of natural organisms is utilized.The wings work not only as an element source for GGF generation but also as a porous supporting structure for effective nitrogen doping,two-dimensional spreading,and double-face exposure of the GGFs.These GGFs exhibit a half-wave potential of 0.942 V and a H2O2 yield of<0.07%for ORR electrocatalysis;these values are comparable to those for the best commercial Pt/C and all previously reported ORR catalysts in alkaline media.This two-in-one strategy is also successful with cicada and dragonfly wings,indicating that it is a universal,green,and cost-effective method for developing high-performance graphene-based materials.

Solid state reaction for the formation of spinel MgFe_2O_4 across perovskite oxide interface

Solid state reaction is a conventional method to synthesize structurally stable inorganic solids by mixing powdered reactants together at high pressure （over 1 x 105 mbar （1 mbar = 100 Pa）） and high temperature （over 1300 K） [1-4]. This method is effective and sophisticated to prepare solid mate- rials, especially the functional complex oxides such as high temperature superconductors, piezoelectrics, dielectrics, etc. However, the chemical reactions cannot be intrinsically con- trolled and integrated at an atomic level in order to achieve the applications of future thin film devices with reduced dimensions [5]. With the desire of designing high-quality products with the micro/nanoscale integration, many pow- erful physical techniques, such as, pulsed-laser deposition （PLD）, molecular beam epitaxy （MBE）, sputtering deposi- tion, etc., have experienced enormous development due to their ability of lattice and/or interfacial controls. Using these growth techniques, layer-by-layer deposition （multilayer and/or superlattice） can be achieved, providing us a platform to tune the crystal structures at an atomic level by controlling the interfacial terminations and epitaxial strain, which are absent in their bulk counterparts [6-8]. From this point of view, well-controlled interfacial structures may also provide the solid state reaction at an atomic level during the physical depositions, which provides us an effective way to design the desired products from the chemical bonding reconstruction.

Unraveling structure evolution failure mechanism in MoS_(2)anode for improving lithium storage stability

2 H phase molybdenum disulfide(2 H-MoS_(2))possesses the two-dimensional layered structure and high theoretical capacity,presenting excellent lithiation-delithiation property.However,the violent capacity decay within dozens of cycles still remains a great challenge due to lacking of in-depth failure mechanism.Herein,a novel decay-recovery-decay failure phenomenon upon long-term cycles is reported for the first time,which originates from the slow size change of Mo nanoparticles(NPs).Decay stages are triggered by many irregular-shaped Mo NPs with the increasing size up to~15 nm,leading to prominent pseudocapacitance failure and capacity loss.Subsequent recovery stages are attributed to the pulverization of coarse Mo NPs through surface sulfurization and accompanying lithiation.To overcome the instability issue,proper modifiers should be introduced to restrain the spontaneous growth of Mo NPs,such as aluminum oxide(Al_(2)O_(3)).The strong Mo-Al_(2)O_(3)bond gradually"drags"Al_(2)O_(3)fragments into the active material as the cycle continuously proceeds,resulting in the efficient refinement and the reversible conversion between Mo and MoS_(2).Therefore,the enhanced cycling stability and the capacity retention are successfully achieved.It is expected to provide a new insight into the energy storage of transition metal chalcogenide anode materials in rechargeable batteries.