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Fe(II)-catalyzed ferrihydrite (Fh) transformation to more crystalline iron (oxyhydr)oxide phases is a widely occurring geochemical process which has been extensively studied as a function of Fe(II)/Fh ratios at fixed Fh loadings. However, recent isolation of an intermediate Fe(III) species resulting from Fe(II)-Fh contact that facilitates transformation by dissolution/reprecipitation suggests that the kinetics and properties of product phases will instead depend mostly on its rate of accumulation to a critical concentration, consistent with principles in the classical nucleation theory (CNT). This suggests a dependence both on the loading of Fe(II) on the surface, which controls the rate of labile Fe(III) formation, as well as the available volume of solution, which also impacts how fast it can achieve its critical concentration to nucleate product phases. To specifically examine the latter effect, here we studied transformation of 15 mg Fh in 1 mM FeSO4 solutions at pH 7.2 in batch suspensions of 30 mL, 150 mL, and 450 mL volumes. Time-dependent concentrations of aqueous Fe(II), surface-associated Fe(II), and resulting labile Fe(III) were monitored along with bulk solids characterization as a function of time. Transmission electron microscopy (TEM) was used to visualize the evolution of phases at identical locations on TEM grids. The collective results show that the rates of Fh loss and emergence of product lepidocrocite (Lp) and goethite (Gt) as well as their phase proportions, nucleation mode and morphological properties depend directly on the rate of accumulation of the labile Fe(III) precursor to its critical concentration, which in our experiments was controlled simply by varying the available volume of solution into which it enters. Statistical analyses of TEM image data suggest that while both heterogeneous and homogeneous nucleation occurred in all experiments, the former was increasingly favored at lower Fh/solution ratio due to its lower nucleation barrier being more favorable at attendant lower supersaturations of Fe(III). Analysis of the collective results in the framework of CNT shows that the transformation process is fully consistent with dissolution/reprecipitation and that transformation kinetics, phase outcomes and their properties accordingly are directly related to effective supersaturation of the intermediate labile Fe(III) species.

Practically adapted physical integration of silicon and carbon predominates as a viable solution to realize high energy density batteries, however, the composite structure is vulnerable to fracture. Here we report a molecular-level mixed silicon-carbon composite anode through thermal pyrolysis of silane and subsequent mechanical mill, entailed by electrochemical dissociation and reclustering of such disordered silicon-carbon bonds during the cycles. Lithium insertion induces heterolytic fission of the bonds into sub-nanometre silicon particles segregated by redox-active carbon framework validated by microscopy analysis and reactive molecular dynamics simulation. The embedded structure with a high packing density of silicon prevents detrimental electrochemical coalescence and direct contact to a liquid electrolyte to stabilize the interfaces, while three-dimensional (3D) carbon framework buffers large volume expansion of silicon to enable an extended full battery cycling.

Rechargeable lithium (Li) metal batteries (LMBs) with ultrahigh-nickel (Ni) layered oxide cathodes offer a great opportunity for applications in electrical vehicles. However, increasing Ni content inherently arouses a tradeoff between specific capacity and electrochemical cyclability due to the aggressive side reactions with electrolyte contributed by the highly reactive Ni species. Here, a protective and stable cathode/electrolyte interphase featuring enriched and evenly-distributed LiF is in situ formed on ultrahigh-Ni cathode LiNi0.94Co0.06O2 (NC) with an advanced ether-based localized high-concentration electrolyte (LHCE), which concurrently shows good compatibility with Li metal anode. Subsequently, the NC cathode can deliver high capacity retentions of 81.4% after 500 cycles at 25 °C and 91.6% after 100 cycles at 60 °C in the voltage range of 2.8–4.4 V in Li||NC cells at 1C cycling rate (1.5 mA cm−2). Meanwhile, the conductive electrode/electrolyte interphases formed in LHCE enable a high reversible capacity of about 209 mAh g−1 at 3C charging rate. This work provides an effective approach and important insight from the perspective of in situ ultrahigh-Ni cathode/electrolyte interphase protection for high energy–density, long-lasting LMBs.

Single-atom catalysts show a promising future in many reactions even though great challenges still remain such as facile synthesis and long stability. In this work, a single-atom Pd catalyst attached to a designed N8 Lewis base species (Pd1-N8/CNT) is synthesized with cyclic voltammetry (CV) method. The catalyst demonstrates long stability and enhanced C2H4 selectivity in selective hydrogenation of acetylene at 40 °C. CV is carried out in a three-electrode setup with PdO/CNT as the working electrode in NaN3 solution. HAADF-STEM confirms single-atom Pd sites are successfully isolated. XPS measurements and Bader charge calculations indicate N8 is effectively synthesized on CNT substrate after CV treatment while single-atom Pd is stabilized by attaching to the end N of N8. Acetylene-temperature programed desorption (C2H2-TPD) and density functional theory (DFT) calculations suggest C2H2 favors the π bonding on single Pd atom, while H2 dissociates on the N atom (next to Pd) instead of conventionally on Pd. The synergistic effect favors C2H4 formation but prevents full hydrogenation of acetylene to C2H6. This work opens up a new perspective to design and synthesize more selective catalysts with isolated single-atom sites.

Ferrihydrite (Fh) is a major Fe(III)-(oxyhydr)oxide nanomineral distinguished by its poor crystallinity and thermodynamic metastability. While it is well known that in suboxic conditions aqueous Fe(II) rapidly catalyzes Fh transformation to more stable crystalline Fe(III) phases such as lepidocrocite (Lp) and goethite (Gt), because of the low solubility of Fe(III) the mass transfer pathways enabling these rapid transformations have remained unclear for decades. Here, using a selective extractant, we isolated and quantified a critical labile Fe(III) species, one that is more reactive than Fe(III) in Fh, formed by the oxidation of aqueous Fe(II) on the Fh surface. Experiments that compared time-dependent concentrations of solid-associated Fe(II) and this labile Fe(III) against the kinetics of phase transformation showed that its accumulation is directly related to Lp/Gt formation in a manner consistent with the classical nucleation theory. 57Fe isotope tracer experiments confirm the oxidized Fe(II) origin of labile Fe(III). The transformation pathway as well as the accelerating effect of Fe(II) can now all be explained on a unified basis of the kinetics of Fe(III) olation and oxolation reactions necessary to nucleate and sustain growth of Lp/Gt products, rates of which are greatly accelerated by labile Fe(III).

Volumetric performance of lithium ion batteries becomes increasingly significant in applications of miniaturized consumer electronics, such as cellphones. Herein, we report a successful design of compact Sn/SnO2 microspheres with a concentration gradient assembled by nanoparticles to realize high volumetric performance. In the structure, the secondary microsphere is able to offer more compact space in realizing higher volumetric capacity. The primary nanoparticles condense together, leading to a dense and porous structure, which can provide more efficient utilization of volume as well as effectively minimize volume variation. Due to the utilization of microstructure as well as the concentration gradient structure, the concentration gradient Sn/SnO2 microspheres deliver a high volumetric capacity (1593 mAh cm−3 at 200 mA g−1 after 200 cycles), outstanding rate capability (retaining a capacity of 1230 mAh cm−3), and stable cycling performance (a capacity retention of 97% after 900 cycles at 5 A g−1). This concentration gradient microsphere structure not only provide a high performance conversion-type composite anode, but also a strategy to engineer the energy density of anode materials in compact space towards high energy density.

Summary Rechargeable lithium (Li)-metal batteries (LMBs) offer a great opportunity for applications needing high-energy-density battery systems. However, rare progress has been demonstrated so far under practical conditions, including high voltage, high-loading cathode, thin Li anode, and lean electrolyte. Here, in opposition to common wisdom, we report an ether-based localized high-concentration electrolyte that can greatly enhance the stability of a Ni-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode under 4.4 and 4.5 V with an effective protection interphase enriched in LiF. This effect, in combination with the superior Li stability in this electrolyte, enables dramatically improved cycling performances of Li||NMC811 batteries under highly challenging conditions. The LMBs can retain over 80% capacity in 150 stable cycles with extremely limited amounts of the Li anode and electrolyte. The findings in this work point out a very promising strategy to develop practical high-energy LMBs.

Sulfide-based solid electrolytes have attracted much attention for their potential application in high energy and power bulk-type all-solid-state lithium batteries, due to their excellent transport properties and favorable mechanical properties. The Li10GeP2S12-type materials with extremely high ionic conductivity have been demonstrated in all-solid-state cathodes, however they cannot be deployed directly in common anodes due to the interfacial instability. An electrolyte stable with anodes is urgently needed for construction of all-solid-state batteries. In this work, we explore the phase and transport properties of mechanically-milled Li7P2S8Br0.5I0.5, with emphasis on the favorable kinetics at Li metal anode. The low temperature crystalline phase Li7P2S8Br0.5I0.5 (LT-LPSBI) has exceptionally high ionic conductivity of 4.7 mS/cm at room temperature. Moreover, the LT-LPSBI supports long-term Li cycling at 0.5 mA cm−2 with low and stable interfacial resistance (5 Ω cm2). Transport phenomenon of Li/LT-LPSBI interface and cycling behavior of Li symmetric cells are studied and discussed in detail.

Lithium (Li) is one of the critical industrial materials and an indispensable component in manufacturing Li-ion/Li batteries. However, Li resource is very limited and geographically uneven in earth’s crust and its mining is not sustainable due to the low efficiency and complicated separation and refining processes. Hence, direct Li recovery (from brines, seawater or used cells) and utilization are desired. Here, we report a novel technology to recover Li from low concentration solutions into a form of Li resource, which can be directly used for commercial battery materials production by fully eliminating the costly Li separation steps. By using both Li-ion selective membrane and low-cost Li host structural material, highly selective Li extraction was realized. Li-ion cathodes (e.g., spinel LiMn2O 4 and layered LiNix MnyCozO2) were synthesized with the extracted Li and have high phase purities and economic superiorities (e.g., $12.8 kg-1 for LiMn2O4) over other Li extraction methods and even commercial cathodes ($15 kg-1 for LiMn2O4). This contribution provides a potential technical pathway to overcome the challenges of both Li supply and battery cost for future electrification and decarbonization of socioeconomic system.

Thio-Lithium Superionic Conductor (Thio-LISICON) Li10GeP2S12 equivalent Li10SnP2S12 (LSPS) is comparable in ionic conductivity yet with a lower cost as an electrolyte for all solid-state batteries (ASSBs). ASSBs with LSPS solid electrolyte (SE), lithium-indium alloy anode, and LiCoO2 (LCO) cathode were successfully fabricated and their electrochemical performance at 60 °C was examined. Atomic layer deposition of Li3NbO4 on LCO was conducted to improve the interfacial stability. The Li3NbO4 coating effectively improves the cycle stability of the ASSB. Electrochemical impedance spectroscopy tests indicate a rapid growth of charge transfer resistance upon cycling for the cell with the uncoated LCO, primarily due to the surface instability and build-up of a space charge layer. However, the ASSBs with Li3NbO4 coated LCO show a more stable interface with a negligible impedance increase upon cycling, attributable to the buffering and passivating roles of the Li3NbO4 coating. The interfacial microstructure was analyzed to elucidate at the underlying reasons for the impedance increase and the pivotal role of the Li3NbO4 coating.

Nickel(Ni)-rich lithium transition metal oxides (e.g. LiNi0.8Co0.15Al0.05O2 (NCA), LiNi1−x−yMnxCoyO2 (x + y

High energy density, nickel (Ni)-rich, layered LiNixMnyCozO2 (NMC, x ≥ 0.6) materials are promising cathodes for lithium-ion batteries. However, several technical challenges, such as fast capacity fading and high voltage instability, hinder their large-scale application. Herein, we identified an optimum calcining temperature range for the Ni-rich cathode LiNi0.76Mn0.14Co0.10O2 (NMC76). NMC76 calcined at 750–775 °C exhibits a high discharge capacity (~215 mAh g−1 when charged to 4.5 V) and retains ca. 79% of its initial capacity after 200 cycles. It also exhibits an excellent high-rate capability, delivering a capacity of more than 160 mAh g−1 even at a 10 C rate. The high performance of NMC76 is directly related to the optimized size of its primary particles (100–300 nm) (which constitute the spherical secondary particles of >10 µm) and cation mixing. Higher calcination temperature (≥800 °C) leads to rapid increase of primary particle size, poor cycling stability, and inferior rate capability of NMC76 due to severe micro-strain and -crack formation upon repeated lithium-ion de/intercalations. Therefore, NMC76 calcined at 750–775 °C is a very good candidate for the next generation of Li ion batteries.

Phase boundaries in multiphase alloys govern defect interaction and chemical intermixing across different phases during plastic deformation. Dynamic interaction of defects with phase boundaries in multiphase alloys, especially for immiscible alloys, has generated more research interest in recent years. Here, we describe a novel approach for carrying out in-situ TEM shear deformation to directly observe interfacial microstructural evolution of a Cu-Nb alloy. A unique double shear specimen geometry is microfabricated by a focused ion beam technique to apply shear deformation upon push loading inside the TEM. From the real-time observation, we discover that the phase boundary with a zigzag morphology effectively blocks stacking faults nucleated in a Cu grain from slipping into a Nb grain. Meanwhile, the Cu phase bears the most plastic deformation through slip or twinning mechanisms. This work sheds light on understanding the shear deformation and the behavior of phase boundaries in multiphase alloys during shear deformation.

Despite great advances in sodium-ion battery developments, the search for high energy and stable anode materials remains a challenge. Alloy or conversion-typed anode materials are attractive candidates of high specific capacity and low voltage potential, yet their applications are hampered by the large volume expansion and hence poor electrochemical reversibility and fast capacity fade. Here, we use antimony (Sb) as an example to demonstrate the use of yolk-shell structured anodes for high energy Na-ion batteries. The Sb@C yolk-shell structure prepared by controlled reduction and selective removal of Sb 2 O 3 from carbon coated Sb 2 O 3 nanoparticles can accommodate the Sb swelling upon sodiation and improve the structural/electrical integrity against pulverization. It delivers a high specific capacity of ~ 554 mAh g −1 , good rate capability (315 mhA g −1 at 10 C rate) and long cyclability (92% capacity retention over 200 cycles). Full-cells of O3-Na 0.9 [Cu 0.22 Fe 0.30 Mn 0.48 ]O 2 cathodes and Sb@C-hard carbon composite anodes demonstrate a high specific energy of ~ 130 Wh kg −1 (based on the total mass of cathode and anode) in the voltage range of 2.0–4.0 V, ~ 1.5 times energy of full-cells with similar design using hard carbon anodes.

Oxygen evolution reaction (OER) plays a crucial role in various energy conversion devices such as water electrolyzers and metal–air batteries. Precious metal catalysts such as Ir, Ru and their oxides are usually used for enhancing reaction kinetics but are limited by their scarcity. The challenges associated with alternative non–precious metal catalysts such as transition metal oxides and (oxy)hydroxides are their low electronic conductivity and durability. The carbon encapsulating transition metal nanoparticles are expected to address these challenges. However, the relationship between precursor compositions and catalyst properties, and the intrinsic functions of each component has been rarely studied. Herein, we report a highly durable (no degradation after 20,000 cycles) and highly active (360 mV overpotential at 10 mA cm–2GEO) OER catalyst derived from bimetallic metal–organic frameworks (MOFs) precursors. This catalyst consists of NiFe nanoparticles encapsulated by nitrogen–doped graphitized carbon shells. The electron–donation/deviation from Fe and tuned lattice and electronic structures of metal cores by Ni are revealed to be primary contributors to the enhanced OER activity, whereas N concentration contributes negligibly. We further demonstrated that the structure and morphology of encapsulating carbon shells, which are the key factors influencing the durability, are facilely controlled by the chemical state of precursors.

In this study, the numerical simulations with graded p-Al x Ga 1−x N/In y Ga 1−y N shortperiod superlattice (SPS) electron blocking layer (EBL) of blue InGaN/GaN light-emitting diodes (LEDs) have been investigated by the Advance Physical Model of Semiconductor Devices (APSYS) program. The simulation results show that the LEDs with graded p-Al x Ga 1−x N/In y Ga 1−y N SPS EBL exhibit better performances of internal quantum efficiency (IQE) and efficiency droop than those of conventional p-AlGaN/GaN SPS EBL. This is attributed to higher and lower effective potential barrier heights created in the conduction and valence band for electron and hole, respectively. The electron overflow effect can be effectively suppressed and the hole injection ability can also be remarkably enhanced. Therefore, the simulation results exhibit a significant increment in the IQE and the ratio of efficiency droop of the LEDs can be obviously reduced from 17.2% to 4.7%.

In this study, the properties of 370-nm InGaN/AlGaN ultraviolet light emitting diodes (UV LEDs) with different thicknesses of un-doped Al 0.3 Ga 0.7 N insertion layer (IL) between the last quantum barrier and electron blocking layer (EBL) have been numerically simulated by Advance Physical Model of Semiconductor Devices (APSYS). The results show that the LEDs using the high Al composition IL can effectively improve the efficiency droop, light output power, and internal quantum efficiency (IQE) compared to the original structure. The improvements of the optical properties are mainly attributed to the energy band discontinuity and offset created by IL, which increase the potential barrier height of conduction band to suppress the electron overflow from the active region to the p-side layer.

Pyrochlore-structure oxides, A2B2O7, may exhibit remarkable radiation tolerance due to the ease with which they can accommodate disorder by transitioning to a defected fluorite structure. The mechanism of defect formation was explored by evaluating the radiation damage behavior of high quality epitaxial La2Zr2O7 thin films with the defected fluorite structure, irradiated with 1 MeV Zr+ at doses up to 10 displacements per atom (dpa). The level of film damage was evaluated as a function of dose by Rutherford backscattering spectrometry in the channeling geometry (RBS/c) and scanning transmission electron microscopy (STEM). At lower doses, the surface of the La2Zr2O7 film amorphized, and the amorphous fraction as a function of dose fit well to a stimulated amorphization model. As the dose increased, the surface amorphization slowed, and amorphization appeared at the interface. Even at a dose of 10 dpa, the core of the film remained crystalline, despite the prediction of amorphization from the model. To inform future ab initio simulations of La2Zr2O7, the bandgap of a thick La2Zr2O7 film was measured to be indirect at 4.96 eV, with a direct transition at 5.60 eV.

Graphene cellular monolith (GCM) can be used as an excellent support for nanoparticles in widespread applications. However, it's still a great challenge to deposit the desirable nanoparticles in GCM that have small size, controllable structure, composition, and high dispersion using the current methods. Here we demonstrate a green, efficient and large-scale method to address this challenge using supercritical fluid (SCF). By this superior method, graphene hydrogel can be transferred into GCM while being deposited with ultrafine and highly dispersive nanoparticles. Specifically, the bimetallic PtFe/GCM and the trimetallic PtFeCo/GCM catalysts are successfully synthesized, and their electrocatalytic performances toward oxygen reduction reaction (ORR) are also studied. The resultant PtFe/GCM shows the significant enhancement in ORR activity, including a factor of 8.47 enhancement in mass activity (0.72 A mgPt−1), and a factor of 7.67 enhancement in specific activity (0.92 mA cm−2), comparing with those of the commercial Pt/C catalyst (0.085 A mgPt−1, 0.12 mA cm−2). Importantly, by introducing the Co, the trimetallic PtFeCo/GCM exhibits the further improved ORR activities (1.28 A mgPt−1, 1.80 mA cm−2). The high ORR activity is probably attributed to the alloying structure, ultrafine size, highly dispersive, well-defined, and a better interface with 3D porous graphene support.

Lithium-oxygen (Li-O2) batteries have extremely high theoretical specific capacities and energy densities when compared with Li-ion batteries. However, the instability of both electrolyte and carbon-based oxygen electrode related to the nucleophilic attack of reduced oxygen species during oxygen reduction reaction and the electrochemical oxidation during oxygen evolution reaction are recognized as the major challenges in this field. Here we report the application of boron carbide (B4C) as the non-carbon based oxygen electrode material for aprotic Li-O2 batteries. B4C has high resistance to chemical attack, good conductivity, excellent catalytic activity and low density that are suitable for battery applications. The electrochemical activity and chemical stability of B4C are systematically investigated in an aprotic electrolyte. Li-O2 cells using B4C-based air electrodes exhibit better cycling stability than those using carbon nanotube- and titanium carbide-based air electrodes in the electrolyte of 1 M lithium trifluoromethanesulfonate in tetraglyme. The performance degradation of B4C-based electrode is mainly due to the loss of active sites on B4C electrode during cycles as identified by the structure and composition characterizations. These results clearly demonstrate that B4C is a very promising alternative oxygen electrode material for aprotic Li-O2 batteries. It can also be used as a standard electrode to investigate the stability of electrolytes.

Perovskite Li3x La2/3−x TiO3 (LLTO) nanofibers have been heat-treated in the hydrogen-containing atmosphere and then incorporated with the poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) polymer to form a composite electrolyte. Hydrogen treatment has created oxygen vacancies in the LLTO nanofibers, which has reduced the activation energy of Li ion transport along intra-grains and inter-grains, leading to an improvement in the ion conductivity of LLTO nanofibers. Hydrogen treatment of the LLTO nanofibers has also enhanced the chemical interaction between the LLTO nanofibers and the polymer matrix in the composite electrolyte, and favored the Li ion transport at the nanofiber/polymer interface, improving the ion conductivity of the composite electrolyte to 3.4 × 10−4 S/cm at room temperature. As a result, the Li|composite-electrolyte|Li half-cell exhibits good stability during lithium plating/stripping cycling at room temperature, showing an overpotential of ~91 mV at a constant current density of 0.5 mA/cm2. The full-cell battery with the composite electrolyte, lithium metal anode and lithium iron phosphate cathode shows excellent rate capacity and cycling performance.

With the ever-increasing demands for higher energy densities in Li-ion batteries, alternative anodes with higher reversible capacity are required to replace the conventional graphite anode. Here, we demonstrate a cost-effective hydrothermal carbonization approach to prepare a hard carbon coated nano-Si/graphite (HC-nSi/G) composite as a high performance anode for Li-ion batteries. In this hierarchical structured composite, the hard carbon coating not only provides an efficient pathway for electron transfer, but also alleviates the volume variation of Si during charge/discharge processes. The HC-nSi/G composite electrode shows excellent performance, including a high specific capacity of 878.6 mAh g−1 based on the total weight of composite, good rate performance, and a decent cycling stability, which is promising for practical applications.

Na-ion battery, as an alternative high-efficiency and low-cost energy storage device to Li-ion battery, has attracted wide interest for electrical grid and vehicle applications. However, demonstration of a full-cell battery with high energy and long cycle life remains a significant challenge. Here, we investigated the role of solid electrolyte interphase (SEI) formation on both cathodes and anodes and revealed a potential way to achieve long-term stability for Na-ion battery full-cells. Pre-cycling of cathodes and anodes leads to preformation of SEI, and hence mitigates the consumption of Na ions in full-cells. The example full-cell of Na0.44MnO2-hard carbon with pre-cycled and capacity-matched electrodes can deliver a specific capacity of ~116 mAh/g based on Na0.44MnO2 at 1 C rate (1 C=120 mA/g). The corresponding specific energy is ~313 Wh/kg based on the cathode. Excellent cycling stability with ~77% capacity retention over 2000 cycles was demonstrated at 2 C rate. Our work represents a leap forward in Na-ion battery development.

The early-stage oxidation of Ni (001) thin films alloyed with 10 or 20 at.% Cr at 700 °C has been directly visualized using in-situ TEM. Independent of Cr concentration, the oxidation initiates via nucleation of surface NiO islands and subsurface Cr2O3. The NiO grows and transitions into a continuous film, followed by the nucleation and growth of NiCr2O4 islands. For Ni–20 at.% Cr, a continuous Cr2O3 was developed, but not for Ni–10 at.% Cr. NiO whiskers are observed to preferentially nucleate/grow from the NiCr2O4 islands through a short-circuit diffusion of Ni along the NiCr2O4 interfaces in Ni–10 at.% Cr.

Porous silicon prepared by low-cost and scalable magnesiothermic reactions is a promising anode material for Li-ion batteries; yet, retaining good cycling stability for such materials in electrodes of practical loading remains a challenge. Here, we engineered the nanoporous silicon from a modified magnesiothermic reaction by controlled surface oxidization forming a

Electrochemical reduction of CO2 is still far away from the practical application because of the stability of CO2 and the diversity of reduction products. It is thus of great importance to further explore catalysts with high efficiency for CO2 reduction to targeting products. Herein, for the first time, a hybrid of BiOx decorated with carbon thin layer is developed as high active electrocatalyst for CO2 conversion, which is synthesized by pyrolysis using Bi MOF as precursor and sacrificial template. It is found that the as-prepared BiOx catalyst is enriched with oxygen vacancies stabilized by the decorated carbon thin layer. The oxygen vacancies enriched BiOx catalyst exhibits superior performance for CO2 reduction to formate, achieving a maximum Faradaic efficiency of 89.3% and a maximum current density of 37.8 mA cm−2. The thin carbon layer and oxygen vacancies improve the charge transfer of the catalyst and hence in favor of the high formate current density. The defects of oxygen vacancies play a vital role in CO2 adsorption and activation and thereby further enhancing the electrocatalytic ability for formate production.

The cracking phenomenon of Ni-rich NMC (LiNixMnyCo1−x−yO2, x ≥ 0.6) secondary particles is frequently discovered and believed to be one of critical reasons deteriorating the long-term cycling stability of NMC cathode in lithium ion batteries (LIBs). However, the initiation and evolution of those cracks is still controversial due to the limited quantification especially by in situ monitoring, leading to the challenge of identifying an efficient approach to inhibit the formation of the fractures during repeated cycling. Herein, the irreversible, anisotropic cycling lattice and mesoscale expansion/shrinkage of nano-grains during the first cycle, as revealed by in situ X-ray diffraction (XRD) and in situ atomic force microscopy (AFM), have been quantified and confirmed to be the dominant driving forces of microcracks initiation at the grain boundaries. These microcracks preferentially nucleate at the core region with random oriented nano-grains in early stage. The further growth and aggregation of microcracks into macrocrack eventually results in microfracture propagation radially outward to the periphery region with more uniform nano-grain orientation. This mesoscale nano-grain architecture controlled cracking process highlights the importance of predictive synthesis of cathode materials with controllable multiscale crystalline architecture for high-performance LIBs.

In this work, we report solution-based doping and coating strategies to improve the electrochemical performance of the Co-free layered oxide cathode LiNi0.5Mn0.5O2 (NM-50/50). Small amounts of d0 dopants (e.g., Mo6+and Ti4+, 0.5–1 at. %) increase the cathode's specific capacity, cycling stability, and rate capability. For example, a Mo-doped cathode with the nominal composition LiNi0.495Mn0.495Mo0.01O2 exhibits a high reversible capacity of 180 mA h/g at 20 mA/g compared to only 156 mA h/g for undoped NM-50/50. Effects of 1 at.% Mo dopant on the cathode structure were studied using a suite of characterization tools including X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy. These measurements demonstrate that Mo6+ dopant is enriched near the particle surface and improves the electrochemical performance of LiNi0.5Mn0.5O2 by: (i) reducing Li+/Ni2+ cation mixing which facilitates Li+ transport, (ii) mitigating undesirable phase transformations near the cathode surface, and (iii) altering the cathode/electrolyte interfacial chemistry. This work also reports the use of an inorganic Mn2P2O7 coating which enhances the cycling stability of Mo-doped NM-50/50, presumably through formation of a stable cathode electrolyte interphase (CEI) layer. Overall, the synthesis approaches reported herein are quite general and can potentially be expanded to other high voltage Li-ion battery cathodes.

Lithium (Li)-rich manganese (Mn)-rich oxide (LMR) cathode materials, despite of the high specific capacity up to 250 mAh g−1 suffer from instability of cathode/electrolyte interfacial layer at high working voltages, causing continuous voltage decay and capacity fading, especially at elevated temperatures. In various battery systems, localized high-concentration electrolytes (LHCEs) have been widely reported as a promising candidate to form effective electrode/electrolyte interphases. Here, an optimized LHCE is studied in graphite (Gr)-based full cells containing LMR cathode, being cycled at 25, 45 and 60 °C with the reference of a conventional LiPF6-based electrolyte. It is revealed that the LHCE can effectively suppress continuous electrolyte decompositions and mitigate the dissolution of Mn ions due to the formation of more protective electrode/electrolyte interphases on both anode and cathode, which, in turn, lead to significantly improved cycling stability and enhanced rate capability under the selected temperatures. The mechanistic understanding on the failure of the conventional LiPF6-containing electrolyte and the function of the LHCE in Gr||LMR cells under high temperatures provides valuable perspectives of electrolyte development for practical applications of LMR cathodes in high energy density batteries over a wide temperature range.

The rechargeable aqueous zinc-ion batteries (ZIBs) based on the Zn/MnO2 couple and mildly acidic electrolyte have emerged as promising large-scale energy storage systems. This work reports an in situ electrochemical activation approach to oxidizing MnS into an electrochemically derived oxide (MnS-EDO), which unlocks its potential as high-performance cathodes for ZIBs. MnS-EDO contains fragmented layers with abundant defects and thus demonstrates large electrochemically active surface areas, high electrochemical reactivity, fast ion diffusion kinetics, accelerated charge transfer and exceptional structural robustness during cycling compared to α-MnO2. MnS-EDO exhibits a specific capacity of 335.7 mAh g−1 with ~100% capacity retention after 100 cycles at 0.3 A g−1, outstanding rate capability and long-term stability retaining 104 mAh g−1 after 4000 cycles at 3 A g−1. This work elucidates the underlying electrochemical insights and a hybrid discharge mechanism involving homogeneous Zn2+ intercalation at ~1.4 V and subsequent heterogeneous reactions of insertion of both H+ and Zn2+ at ~1.25 V. The ambiguities among Zn buserite, birnessite and zinc hydroxide sulfate are clarified. This work provides a simple and low-cost approach to unlocking the potential of MnS-EDO cathode for promising aqueous rechargeable ZIBs and sheds light on a mechanistic understanding of manganese oxide-based cathodes.

β-NiAl is widely used as a protective coating for high-temperature corrosion, where the selective oxidation of Al leads to the formation of a thin alumina scale to prevent further oxidation. However, understanding how the selective oxidation couples to the structural and chemical evolution of the base alloy remains largely unexplored. Here, by using in-situ environmental transmission electron microscopy and density functional theory calculations, we reveal at the atomic scale that the selective oxidation of Al is accompanied by injection of vacancies into the bulk lattice. In particular, we discovered that during the layer-by-layer oxidation process, the injected vacancies preferentially cluster along directions on the (0 0 1) planes of β-NiAl, leading to the formation of band-like structural features. This finding sheds lights on the atomic mechanism of oxidation in β-NiAl, which may also extend to the selective oxidation of other ordered intermetallic alloys.

Rechargeable Lithium (Li) metal batteries (LMBs) offer great opportunity for high-energy-density energy storage applications. However, rarely any progress has been demonstrated so far under practical conditions including high voltage, high loading cathode, thin Li anode, and lean electrolyte. Here, in opposite to the common wisdom, we report an ether-based localized high concentration electrolyte that can greatly enhance the stability of Ni-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode under 4.4 V and 4.5 V with an effective protection interphase enriched in LiF. This effect, in combination with the superior Li stability in this electrolyte, enables dramatically improved cycling performances of Li||NMC811 batteries under highly challenging conditions. The LMB can retain over 80% capacity retention in 150 stable cycles with only 1.1 times excess Li anode and an extremely limited electrolyte amount. The findings in this work point out to a very promising strategy to develop practical high-energy Li metal batteries.

Silicon (Si), associated with its natural abundance, low discharge voltage vs. Li/Li+, and extremely high theoretical capacity (~4200 mAh g−1,), has been extensively explored as anode for lithium ion battery. One of the key challenges for using Si as anode is the large volume change upon lithiation and delithiation, which causes a fast capacity fading. Over the last few years, dramatic progress has been made for addressing this issue. In this paper, we review the progress towards tailoring of Si as anode for lithium ion battery. The paper is organized such that it covers the fundamentals, the promises offered by nanoscale designs, and the challenges that remained to be addressed to allow the application of Si based materials as high capacity anode for lithium ion batteries.

Structural defects, e.g. Mn3+/oxygen non-stoichiometry, largely affect the electrochemical performance of both Li2MnO3 and lithium-rich manganese-rich (LMR) layered oxides with Li2MnO3 as one of the key components. Herein, Li2MnO3 samples with different amount of structural defects of Mn3+/oxygen non-stoichiometry are prepared. The results clearly demonstrate that the annealed Li2MnO3 (ALMO), quenched Li2MnO3 (QLMO), and quenched Li2MnO3 milled with Super P (MLMO) all show pure C2/m monoclinic phase with stacking faults. MLMO shows the largest amount of Mn3+, followed by the QLMO and then the ALMO. The increased amount of Mn3+ in Li2MnO3 (such as sample MLMO) facilitates the activation of Li2MnO3 and leads to the highest initial discharge specific capacity of 167.7 mA h g−1 among the samples investigated in this work. However, accelerated activation of Li2MnO3 also results in faster structural transformation to spinel-like phase, leading to rapid capacity degradation. Therefore, the amount of Mn3+ needs to be well controlled during synthesis of LMR cathode in order to reach a reasonable compromise between the initial activity and long-term cycling stability. The findings of this work could be widely applied to explain the effects of Mn3+ on different kinds of LMR cathodes.

Composite Li-ion anode can be fabricated using silicon nanopowders synthesized by induced plasma atomization. Properties of such nanopowder were characterized by physical and electrochemical methods. Primary particles were crystalline with spherical shape and the typical diameter ranging from 50 to 200 nm. The Si nanopowder showed a high gravimetric capacity (4900 mAh/g) at first discharge and around 12% irreversible loss of lithium. In addition, observations of a single silicon particle made by in situ TEM permitted to compare the volume change during lithiation with other silicon anode nanomaterials.

Coupling between transport kinetics of chemical participants and mechanical stress is a universal phenomenon in numerous chemo-physical processes. In this Letter, we present a set of in-situ transmission electron microscopy studies along with atomistically informed continuum mechanics modeling to evidence the strong coupling between lithiation kinetics and stress generation and failure of silicon (Si) and germanium (Ge) electrodes. On the one hand, we show that anisotropic lithiation in crystalline Si (c-Si) leads to anisotropic swelling and surface fracture, in contrast to isotropic lithiation, isotropic swelling, and tough behavior in c-Ge and amorphous Si (a-Si). On the other, we demonstrate that lithiation self-generated stress leads to lithiation retardation and externally applied bending breaking the lithiation symmetry in c-Ge nanowires. Our studies shed lights on the design of durable high-performance lithium ion batteries.

Lithium titanate (Li4Ti5O12) is well known as a zero strain material inherently, which provides excellent long cycle stability as a negative electrode for lithium ion batteries. However, the low specific capacity (175 mA h g−1) limits it to power batteries although the low electrical conductivity is another intrinsic issue need to be solved. In this work, we developed a facile hydrothermal and ion-exchange route to synthesize the self-supported dual-phase Li4Ti5O12–TiO2 nanowire arrays to further improve its capacity as well as rate capability. The ratio of Li4Ti5O12 to TiO2 in the dual phase Li4Ti5O12–TiO2 nanowire is around 2:1. The introduction of TiO2 into Li4Ti5O12 increases the specific capacity. More importantly, by interface design, it creates a dual-phase nanostructure with high grain boundary density that facilitates both electron and Li ion transport. Compared with phase-pure nanowire Li4Ti5O12 and TiO2 nanaowire arrays, the dual-phase nanowire electrode yielded superior rate capability (135.5 at 5 C, 129.4 at 10 C, 120.2 at 20 C and 115.5 mA h g−1 at 30 C). In-situ transmission electron microscope clearly shows the near zero deformation of the dual phase structure, which explains its excellent cycle stability.

In this study, the effect of quantum barrier thickness in the multi-quantum wells active region on electrical and optical properties of nitride-based light emitting diodes (LEDs) were investigated and demonstrated. The forward voltage decreased as the thickness of quantum barrier decreased owing to the reduction of series resistance. The external quantum efficiency (EQE) and droop effect can be effectively improved by decreasing the barrier thickness which was attributed to the enhancement of the holes injection and uniform distribution in the active region. However, if barrier was too thin, it would get the opposite effect due to the influence of electron overflow. Regarding the hot/cold factor, the thinner quantum barrier of LEDs achieved a better performance. The reason is that the thicker quantum barrier with poor holes distribution resulted in the holes accumulation of a few MQWs near the p-side layer was more easily influenced by thermal effect and escaped from the QWs.

In this article, two-dimensional, Co 3 O 4 hexagonal nanodiscs are prepared using a hydrothermal method without surfactants. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been employed to characterize the structural properties. As revealed by the SEM and TEM experiments, the thickness of our as-fabricated Co 3 O 4 hexagonal nanodiscs is about 20 nm, and the pore diameters range from several nanometers to 30 nm. As an anode for lithium-ion batteries, porous Co 3 O 4 nanodiscs exhibit an average discharge voltage of ∼1 V (vs. Li/Li + ) and a high specific charge capacity of 1161 mAh g −1 after 100 cycles. They also demonstrate excellent rate performance and high Columbic efficiency at various rates. These results indicate that porous Co 3 O 4 nanodiscs are good candidates as anode materials for lithium-ion batteries.

Nanocrystals play a key role in modern science and technology, and there has been much effort in recent years in tailoring the size, shape, and properties of nanocrystals. The capability to monitor the colloidal nanocrystal growth in liquid is essential for fully understanding the growth and shape control mechanisms. In current study, we imaged nanocrystals in a eutectic-based ionic liquid and studied the growth of five-fold twined gold nanocrystal with in situ transmission electron microscopy (TEM). Our studies suggest that the coalescence-based growth may be also an important mechanism for the formation of twinned nanocrystals in solution in addition to nucleation-based layer-by-layer growth and successive growth twinning mechanisms. This observation reveals much important information about colloidal nanocrystal growth, and is very beneficial in a detailed understanding of growth mechanisms and precise shape controlling synthesis of nanoparticles.

Epitaxial thin films of Cr x V 1 − x over the entire composition range were deposited on MgO(001) by molecular beam epitaxy. The films exhibited the expected 45° in-plane rotation with no evidence of phase segregation or spinodal decomposition. Pure Cr, with the largest lattice mismatch to MgO, exhibited full relaxation and cubic lattice parameters. As the lattice mismatch decreased with alloy composition, residual epitaxial strain was observed. For 0.2 ≤ x ≤ 0.4 the films were coherently strained to the substrate with associated tetragonal distortion; near the lattice-matched composition of x = 0.33, the films exhibited strain-free pseudomorphic matching to MgO. Unusually, films on the Cr-rich side of the lattice-matched composition exhibited more in-plane compression than expected from the bulk lattice parameters; this result was confirmed with both x-ray diffraction and Rutherford backscattering spectrometry channeling measurements. The effect of thermal expansion mismatch on strain in the heterostructure was estimated. High resolution transmission electron microscopy was utilized to characterize the misfit dislocation network present at the film/MgO interface. Dislocations were found to be present with a non-uniform distribution, which is attributed to the Volmer–Weber growth mode of the films. The Cr x V 1 − x /MgO(001) system can serve as a model system to study the fundamentals of defect formation in bcc films.

Phenomena related to the interaction of point defects and dopants with grain boundaries and interfaces have been very well documented. However, a quantitative understanding of such an interaction is still missing. In this paper we explore the correlation between radiation damage and interface structure. In doing so, Cr x Mo 1− x (0 0 1) films of thickness ∼100 nm were epitaxially grown on MgO (0 0 1) using molecular beam epitaxy. The interface dislocation density can be systematically varied by controlling the composition of the film. This system allows us to probe the response of the defects generated during the irradiation to the interface dislocation density. The microstructural features of these films before and after irradiation are carefully studied using high resolution scanning/transmission electron microscopy and electron diffraction. It has been found that the film/substrate system is very resistant to ion-induced irradiation damage. No visible point defect clusters, dislocation network or amorphization has been identified, which is contrasted with other materials of either metallic or ionic bonding. In combination with RBS analysis, we conclude that the defects in the present system appear to be very mobile and were annihilated during the irradiation process.