Ex-situ Scanning Electron Microscopy Research Articles

Bi Nanospheres Embedded in N-Doped Carbon Nanowires Facilitate Ultrafast and Ultrastable Sodium Storage.

Sodium ion batteries (SIBs) are considered as the ideal candidates for the next generation of electrochemical energy storage devices. The major challenges of anode lie in poor cycling stability and the sluggish kinetics attributed to the inherent large Na+ size. In this work, Bi nanosphere encapsulated in N-doped carbon nanowires (Bi@N-C) is assembled by facile electrospinning and carbonization. N-doped carbon mitigates the structure stress/strain during alloying/dealloying, optimizes the ionic/electronic diffusion, and provides fast electron transfer and structural stability. Due to the excellent structure, Bi@N-C shows excellent Na storage performance in SIBs in terms of good cycling stability and rate capacity in half cells and full cells. The fundamental mechanism of the outstanding electrochemical performance of Bi@N-C has been demonstrated through synchrotron in-situ XRD, atomic force microscopy, ex-situ scanning electron microscopy (SEM) and density functional theory (DFT) calculation. Importantly, a deeper understanding of the underlying reasons of the performance improvement is elucidated, which is vital for providing the theoretical basis for application of SIBs.

Top-down nanostructured multilayer MoS2 with atomically sharp edges for electrochemical hydrogen evolution reaction

Cost-efficient and readily scalable platinum-free electrocatalysts are crucial for a smooth transition to future renewable energy systems. Top-down activation of MoS2 promises the production of sustainable hydrogen evolution electrocatalysts from the Earth-abundant molybdenite ore. Here, the deterministic nanopatterning of multilayer MoS2 with numerous zigzag edges is explored as a pathway to enhance hydrogen evolution reaction (HER). Nanopatterned single-nanosheet MoS2 electrodes are assessed by two highly localized electrochemical techniques: selected area voltammetry (with lithography-defined regions of electrode-electrolyte contact) and Scanning ElectroChemical Microscopy (SECM). The nanopatterning effect is the most pronounced after prolonged electrochemical cycling in an acidic electrolyte. The electrocatalytic hydrogen evolution activity of edge-enriched electrodes is dramatically enhanced: the maximum electrochemical current density (jmax) achieved at -510 mV vs. reversible hydrogen electrode (mVRHE) is increased by two orders of magnitude, reaching >300 mA⋅cm−2. Both the η10 and η100 overpotentials are significantly reduced as well. Meanwhile, pristine MoS2 shows just ≈6 times jmax increase (≈30 mA⋅cm−2) after the very same cycling. The increased electrocatalytic activity comes with electrode morphology degradation, evidenced by ex-situ scanning electron microscopy. SECM directly visualizes stronger HER activity in the regions with densely located zigzag edges. Intense white light illumination significantly boosts HER on MoS2 electrodes due to the photo-enhanced MoS2 conductivity. These results improve the understanding and reveal the limitations of MoS2-based electrocatalytic water splitting.

Ex-situ observation of the short crack initiation and propagation behaviour of nickel-base wrought alloy Inconel 718 for critical rotating components under fatigue conditions at elevated temperatures

In this paper, the initiation and propagation behaviour of short fatigue cracks in nickel-base alloy Inconel 718 is studied extensively in the fatigue loading regime by ex-situ scanning electron microscopy on component-near notched specimens in the temperature range between 400°C and 600°C. To investigate the influence of different surface treatments, both specimens with polished and shot-peened surfaces were tested. For polished specimens, most fatigue cracks initiated at oxidised non-metallic inclusions, whereas for shot-peened specimens, the process-induced surface roughness also served as crack starters. It was found, that the observed scatter in lifetime for repetitive tests is mainly caused within the short crack fatigue regime below 50μm, while cracks larger than 100μm showed similar growth characteristics.

In-situ constructing porous N-doped carbon skeleton with rich defects from modified polyamide acid to boost the high performance of Na3V2(PO4)3 cathode for full sodium-ion batteries

Generally, the transport of electrons and Na+ is seriously constrained in Na3V2(PO4)3 (NVP) due to intense interactions of V-O and PO bonds. Besides, polyamide acid (PAA) is hardly used in the sol–gel route due to insolubility. This work develops a facile liquid synthesis strategy based on modified PAA, achieving in-situ construction of a porous N-doped carbon framework with rich defects to improve the kinetics of NVP. The addition of triethylamine (TEA) reacts with carboxyls in PAA to achieve acid-base neutralization, turning PAA into polyamide salts with good solubility. The special morphology construction mechanism of this unique system was observed by ex-situ scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Specifically, PAA undergoes in-situ conversion into chain-like polyimide (PI) through a thermal polymerization mechanism during the pre-sintering process. Meanwhile, NVP precursors are evenly dispersed in the PI fibers, efficiently reducing the particle size. After the final treatment, the favorable porous carbon skeleton could be generated derived from the partial decomposition of PI, on which small active grains are in situ grown. The resulting N-doped carbon substrate contains rich defects, benefiting from the migration of Na+. Furthermore, the porous construction is conducive to alleviating the stress and strain generated by the high current impact, increasing the contact area between electrodes/electrolytes to improve the utilization efficiency of active substances. Comprehensively, the optimized samples exhibit a capacity of 82.1 mAh g−1 at 15C with a retention rate of 95.45 % after 350 cycles. It submits a capacity of 67.6 mAh g−1 at 90C and remains 52.2 mAh g−1 after 1500 cycles. Even in full cells, it reveals a value of 110.6 mAh g−1. This work guides the application of in-situ multiple modifications of polymers in electrode materials.

Porous lithiophilic Cu-Sn solid solution current collector for dendrite-free lithium metal batteries

Lithium metal batteries (LMBs) have high energy density but suffer from the formation of Li dendrites and unstable solid electrolyte interface. Herein, a three-dimensional porous Cu-Sn solid solution was designed as current collector for LMBs and was fabricated through the combination of vapor phase alloying with subsequent vapor phase dealloying. The effect of the Sn addition on electrochemical performances and Li plating/stripping behaviors was investigated using in-situ X-ray diffraction, ex-situ scanning electron microscopy, as well as density functional theory calculations. As benchmarked with porous Cu (3D-Cu), the addition of lithiophilic Sn can efficiently improve the Li plating/stripping performance, especially for the 1.5 at.% Sn addition (3D-Cu98.5Sn1.5). The 3D-Cu98.5Sn1.5 current collector maintains coulombic efficiency of 95 % up to 200 cycles at 1 mA cm−2. Moreover, the existence of Sn in solid solution exhibits a much lower binding energy (-3.223 eV) and nucleation overpotential (28.9 mV) compared with those of 3D-Cu, indicating that the metallic Li is extremely susceptible to nucleation and growth on the surface. Additionally, the gas evolution scenarios were probed by on-line differential electrochemical mass spectrometry. Our findings show that the 3D-Cu98.5Sn1.5 current collector effectively enhances the uniformity of Li plating and suppresses the generation of dendrites in LMBs.

Co-Fe Prussian blue analogue ultrafine nanocrystal cubes grown in-situ in honeycomb carbon as high-performance anode for lithium-ion batteries

Prussian blue analogues (PBAs) are promising anode materials for lithium-ion batteries due to the unique 3D open frameworks, but inferior cycling performance and poor rate capability restrict their application. Herein, Co-Fe PBA@honeycomb carbon is prepared by means of well-designed solution evaporation assembly and in-situ etching-coordination strategy. K0.90Co[Fe(CN)6]0.97□0.03⋅0·.44H2O (□: vacancy defect) cubes with uniform size of 20 nm are grown within every honeycomb carbon pore with a diameter of ∼ 180 nm. The mass content of Co-Fe PBA reaches 78.61 wt%. The small size, low defects and less interstitial/coordinated water improve kinetics properties and robustness of Co-Fe PBA. Honeycomb carbon further enhances the electronic conductivity and structural stability of Co-Fe PBA. Accordingly, Co-Fe PBA@honeycomb carbon exhibits high reversible capacities of 915 mAh/g at 0.5 A/g after 200 cycles, 658 mAh/g at 1 A/g after 1000 cycles, 496 mAh/g at 2 A/g after 450 cycles. Rate performance and kinetics properties are superior. The reversible capacity at 5 A/g is as high as 328 mAh/g. The diffusion coefficient of Li+ reaches 10−10.0 ∼ 10−11.7 cm2 s−1. Ex-situ scanning electron microscopy and Fourier transform infrared spectrometer demonstrate that the cycled Co-Fe PBA@honeycomb carbon is stable.

Phase-separated bimetal enhanced sodium storage: Dimer-like Sn-Bi@C heterostructures with high capacity and long cycle life

Phase boundaries facilitate the charge transportation and alleviate the intrinsic stress upon cycles. Therefore, how to achieve regular phase boundaries is very attractive. Herein, dimer-like Sn-Bi@C nanostructures, where is a well-defined phase boundary between Sn and Bi, have been prepared by a two-step process for the first time. The phase boundary not only provides additional and fast transportation for Na+, but also mitigates the structure stress/strain upon cycling. Therefore, Sn-Bi@C exhibits a high capacity (472.1 mA h g−1 at 2 A g−1 for 200 cycles), an ultra-long cyclic life (355.6 mA h g−1 at 5 A g−1 for 4500 cycles) and an excellent rate performance (372 mA h g−1 at 10 A g−1) for sodium storage, much higher than those of Sn@C, Bi@C, and Sn@C + Bi@C. Notably, the full cells of Sn-Bi@C//Na3V2(PO4)3/rGO (Sn-Bi@C//NVP/rGO) demonstrate impressive performance (323 mA h g−1 at 2 A g−1 for 300 cycles). The underlying mechanism for such an excellent performance is elucidated by in-situ X-ray diffraction, ex-situ scanning electron microscopy /high-resolution transmission electron microscopy and atomic force microscopy, revealing the good electrode stability and improved mechanical properties of Sn-Bi@C. The synthetic method is extended to dimer-like Sn-Pb@C and Sn-Ag@C heterostructures, which also exhibit the good cycle stability for sodium storage.

Three-dimensional Ag/carbon nanotube-graphene foam for high performance dendrite free lithium/sodium metal anodes

• Porous 3D Ag/CNT-GF structure effectively alleviates the volume expansion of Li/Na. • Lithiophilic/sodiophilic Ag NPs directionally guide Li/Na deposition. • Dendrite free morphology is achieved in Li/Na@3D Ag/CNT-GF anodes. Although lithium metal and sodium metal are promised as ideal anodes for lithium ion batteries (LIBs) and sodium ion batteries (SIBs), they still suffer from inevitable dendrite growth. In light of this, silver nanoparticles (Ag NPs) are sputtered onto three-dimensional carbon nanotube decorated graphene foam (3D CNT-GF) to construct superior 3D Ag/CNT-GF composite matrix for lithium metal anodes (LMAs) and sodium metal anodes (SMAs). With this design, lithiophilic/sodiophilic Ag NPs could provide favorable sites to guide Li/Na metal nucleation and growth, thus leading to low nucleation overpotentials, high Coulombic efficiency and long cycle performance. Accordingly, 3D Ag/CNT-GF electrodes can stably cycle for 1000 and 750 cycles at 3 mA cm −2 with 1 mAh cm −2 for SMAs and LMAs, respectively. More attractively, it can also stably sustain 300 cycles (SMAs) and 500 cycles (LMAs) at a large current density of 5 mA cm −2 with 1 mAh cm −2 . The excellent electrochemical performance can be attributed to the lithiophilic/sodiophilic electrode surface, 3D porous electrode structure and the dendrite-free morphology as demonstrated by ex-situ scanning electron microscopy (SEM) and in-situ optical microscopy analyses. Furthermore, full cells based on Na@3D Ag/CNT-GF||Na 3 V 2 (PO 4 ) 3 @carbon (NVP@C) and Li@3D Ag/CNT-GF||LiFePO 4 (LFP) could deliver highly reversible capacities of 90.1 and 106.4 mAh g −1 respectively at 100 mA g −1 after 200 cycles for SIBs and LIBs, respectively. This work demonstrates a novel 3D Ag/CNT-GF matrix for boosting Li/Na deposition stability for their future applications. Porous 3D Ag/CNT-GF nanostructure was designed and further adopted as the stable host of lithium/sodium metal anodes. Lithiophilic/sodiophilic Ag NPs directionally guide Li/Na deposition with uniform current density distribution over the 3D Ag/CNT-GF current collector surface, enabling a dendrite free deposition morphology and long cycle stability.

Dealloying-induced modulation upon porous layer depth of three-dimensional copper current collector for improving lithium plating/stripping capability

Lithium metal anode has shown great potentials for achieving high energy density due to its high theoretical capacity and low redox potential, but its application is impeded by the dendrite proliferation and unstable solid electrolyte interface. Herein, three-dimensional (3D) porous Cu current collectors were fabricated via the combination of painting-alloying-dealloying with subsequent annealing, where the depth and length scale of the porous layer can be facilely regulated by controlling the alloying and annealing processes. In lithium metal batteries, the relationship between the Li deposition behavior and the porous layer depth was explored in detail via electrochemical measurements and ex-situ scanning electron microscopy. Notably, the A-3D Cu-14 current collector with the porous layer depth of around 34.5 µm exhibits long lifespan over 430 h at 1 mA cm−2 and low voltage hysteresis, in comparison with the pristine Cu foil and the porous Cu with thinner porous layers. The superior electrochemical performance of A-3D Cu-14 can be attributed to the enhanced suppression effect upon the Li dendrite deriving from the more accommodation capability of its thick porous layer, as well as the better homogenization of the Li+ ion flux caused by the porous structure. Furthermore, the Li@A-3D Cu-14 | LiFePO4 full cell shows excellent cycling stability and rate capability in full battery tests.

(Digital Presentation) Influence of Li2s on the Volume Expansion of Sn Particles during Lithiation of Tin Sulfides

In recent years tin sulfides, particularly SnS and SnS2, have attracted significant attention in the energy storage research community. Their high theoretical specific capacities (1111 mAhg-1 for SnS and 1209 mAhg-1 for SnS2) make this group of materials good candidates for anode active materials for Li-ion batteries. Moreover, their low cost and environmental benignity further contribute to the appeal. During lithiation, tin sulfides undergo a conversion reaction with Li in which Li2S and Sn are formed. Further lithiation triggers the alloying reaction between Sn and Li, resulting in the formation of various Sn-Li intermetallic phases. The newly formed Sn-Li phases have a significantly higher unit cell volume than their parent phases, causing cracking of particles on repeated alloying and dealloying. Ultimately, the continuous cracking of particles leads to pulverization of anode material, reduced contact between the particles and capacity fade.In our work, we explored the influence of Li2S formed during the conversion reaction on the stability of the solid electrolyte interphase (SEI) layer and the overall cycling performance of SnS and SnS2 materials. The precipitation reaction was used to synthesised both SnS and SnS2 materials. Furthermore, SnS2 was also synthesised via the widely used hydrothermal method. In all cases, SnClx ·yH2O (x= 2; y= 2 for SnS and x= 4; y= 5 for SnS2) was used as a Sn source and thioacetamide as a S source. The physio-chemical properties of the as-synthesised materials were examined by powder X-ray diffraction (PXRD) and structural parameters were extracted using Rietveld analysis of the measured patterns. Furthermore, the sample morphologies were characterized by scanning electron microscopy (SEM) and the crystallinity of the samples was further investigated by transmission electron microscopy (TEM). The presence of surface impurities which may formed during material synthesis, was examined by X-ray photoemission spectroscopy (XPS).The cycling performance of SnS2 prepared via the precipitation reaction was compared to SnS2 prepared via hydrothermal method as well as to SnS prepared via precipitation reaction. In this way we were able to draw comparisons between materials with the same chemical composition but different particle size and morphology as well as materials with different chemical composition and very similar morphology.The length changes of SnS and SnS2 electrodes during cycling were investigated by the in-situ dilatometry technique, and several ex-situ methods such as ex-situ XRD and ex-situ SEM were utilized to investigate the role of crystal chemistry and particle morphology on electrochemical performance post-mortem. The results showed that on alloying, the electrode comprised of partially amorphous SnS2 synthesised via the precipitation expands the least. Additionally, the cycling data show that partially amorphous SnS2 electrochemically outperformed both SnS and highly crystalline SnS2. This may be attributed to two effects. Firstly, thicker Li2S layers are generally formed on particles with lower surface areas, thereby better restraining the volume changes of Sn during cycling. Secondly, due to the intercalation step prior to the conversion reaction in SnS2, it is postulated that Li2S and Sn are homogeneously distributed on the atomic scale, which further helps to minimize the volume expansion during cycling.

Effect of HF etching on titanium carbide (Ti3C2Tx) microstructure and its capacitive properties

Two-dimensional multi-layered microstructure generated by hydrofluoric acid etching is essential for the high capacitance MXenes. However, the mechanisms dictating the formation, evolution and properties of MXenes during etching remain elusive due to the lack of direct observation. Herein, using ex-situ scanning electron microscopy combined with high resolution transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, we have revealed the fine variation of microstructure and properties of multi-layered titanium carbide Ti3C2Tx etched for different time. The results show that the laminar cracks always formed from the first initial laminar crack at the edge site of the outermost side of the Ti3AlC2 particle, which induces continuous nucleation of other laminar cracks in the nearby area. The early laminar cracks undergo growth accompanying with increased macro-layer density of Ti3C2Tx and the Al(F,O,C)3 precipitation in subsequent etching process. The formation of laminar cracks is revealed to be correlated with the release of local internal stress in Ti3AlC2. In addition, it is found that there are significant changes of Ti valence state, CC and Ti-C bonding as well as Ti-F, CO and Al-O surface groups during etching. Maximum specific capacitance coincides with maximum lattice parameter c of Ti3C2Tx and maximum number of macro-layers, while over-etching produces in-plane microcracks, Ti dissolution, and reduced specific capacitance. The results provide important insight to facilitate optimal synthesis of this material.

Homogeneous electric field and Li+ flux regulation in three-dimensional nanofibrous composite framework for ultra-long-life lithium metal anode

Lithium (Li) metal is considered as the best anode candidate for next-generation high-energy batteries due to its ultralow electrochemical potential and extremely high theoretical capacity. However, issues arising from the undesired growth of lithium dendrites and infinite volumetric change have seriously hindered the practical application of lithium metal batteries (LMBs). Here, we designed a super-lithiophilic amorphous zinc oxide-doped carbon nanofiber framework with uniformly-distributed and parallel multichannels (MCCNF@ZnO) to achieve the homogeneous distribution of electric field and Li+ flux. By the assistances of COMSOL Multiphysics simulations and ex-situ scanning electron microscopy, we reveal that the Li metal preferentially deposits into the porous nanochannels inside the nanofibers, followed by its even distribution on the lithiophilic surface of MCCNF@ZnO. Furthermore, the conductive multichannels of the carbon nanofiber skeleton can effectively minimize the partial current density, thereby effectively avoiding the electrochemical polarization and assisting the uniform metallic deposition. As a result, MCCNF@ZnO exhibits a stable CE over 99.2% as the substrate after 500 cycles at the current density of 1 mA cm−2. The symmetrical cell of lithium-loaded MCCNF@ZnO composite electrodes can stably operate over 3300 h at 0.5 mA cm−2, indicating the great potential of MCCNF@ZnO for stabilizing lithium metal anodes in practical applications of LMBs.

The Effects of the Binder and Buffering Matrix on InSb-Based Anodes for High-Performance Rechargeable Li-Ion Batteries.

C-decorated intermetallic InSb (InSb–C) was developed as a novel high-performance anode material for lithium-ion batteries (LIBs). InSb nanoparticles synthesized via a mechanochemical reaction were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDX). The effects of the binder and buffering matrix on the active InSb were investigated. Poly(acrylic acid) (PAA) was found to significantly improve the cycling stability owing to its strong hydrogen bonding. The addition of amorphous C to InSb further enhanced mechanical stability and electronic conductivity. As a result, InSb–C demonstrated good electrochemical Li-ion storage performance: a high reversible specific capacity (878 mAh·g−1 at 100 mA·g−1 after 140 cycles) and good rate capability (capacity retention of 98% at 10 A·g−1 as compared to 0.1 A·g−1). The effects of PAA and C were comprehensively studied using cyclic voltammetry, differential capacity plots, ex-situ SEM, and electrochemical impedance spectroscopy (EIS). In addition, the electrochemical reaction mechanism of InSb was revealed using ex-situ XRD. InSb–C exhibited a better performance than many recently reported Sb-based electrodes; thus, it can be considered as a potential anode material in LIBs.

Understanding multiscale assembly mechanism in evaporative droplet of gold nanorods

Using in-situ contact angle measurement and ex-situ scanning electron microscopy, we present a direct correlation of the drying profile of CTAB coated AuNRs suspension with observed deposition pattern on hydrophilic silicon substrate. The droplet evaporation reveals the formation of surface pattern that primarily exhibits three different regions of assembly. Region 1, the exterior of droplet's triple phase contact line (TPCL), consists of small arrays of AuNR cluster followed by the much observed multi-layered coffee-ring deposit, comprising of AuNRs assembled in smectic phase. The transient TPCL depinning during the initial stage of evaporation due to autophobic effect results in formation of region 1. The increase in AuNR concentration due to outward capillary flow leads to pinned TPCL and coffee-ring deposit in region 2. The depletion mediated interparticle interaction due to nanoparticle stagnation at TPCL results in surfactant expulsion. The expelled CTAB creates surfactant-induced Marangoni flow and results in the formation of depletion region 3. Further, we will discuss the plasmonic application of the deposit pattern in determination of surface-enhanced Raman scattering signal. The SERS signal enhancement of Rhodamine B analyte, by factor of ~7.6 ∗ 105 and detection limit to concentration as low as ~10−8M has been achieved using the ordered arrays of gold nanorods as substrates. The AuNR assembly can be further explored for fabrication of optical sensors and other application based studies.

Sodiophilic Au/reduced-graphene-oxide for dendrite free sodium metal anode

In this work, a nanocomposite composed of gold nanoparticles (NPs) supported by reduced graphene oxide (Au/rGO) is designed and synthesized via a simple chemical bath reaction method at room temperature followed by post annealing treatment. Au/rGO is further employed as the host of sodium metal anode with a dendrite free morphology, demonstrated by ex-situ scanning electron microscopy (SEM) and in-situ optical microscopy characterization. As a result, Au/rGO electrode exhibits a small overpotential of 3.5 mV at a current density of 2 mA cm−2 with a specific capacity of 2 mAh cm−2. Meanwhile, it can stably cycle for 400 h at a high current density of 5 mA cm−2 with an areal capacity of 1 mAh cm−2. Detailed studies indicate that the excellent electrochemical performance is mainly owing to the sodiophilic surface enabled by Au NPs, guiding the Na metal uniform deposition, thus effectively inhibiting the sodium dendrite formation. Finally, as a proof of concept, a full battery composed of [email protected]/rGO as the anode and Na3V2(PO4)3@C as the cathode is assembled and delivers a capacity of 93.9 mAh g−1 at 100 mA g−1 after 180 cycles. Our work proves that Au/rGO is a promising host for sodium metal anode.

The dynamic evolution of aggregated lithium dendrites in lithium metal batteries

Lithium (Li) metal anodes promise an ultrahigh theoretical energy density and low redox potential, thus being the critical energy material for next-generation batteries. Unfortunately, the formation of Li dendrites in Li metal anodes remarkably hinders the practical applications of Li metal anodes. Herein, the dynamic evolution of discrete Li dendrites and aggregated Li dendrites with increasing current densities is visualized by in-situ optical microscopy in conjunction with ex-situ scanning electron microscopy. As revealed by the phase field simulations, the formation of aggregated Li dendrites under high current density is attributed to the locally concentrated electric field rather than the depletion of Li ions. More specifically, the locally concentrated electric field stems from the spatial inhomogeneity on the Li metal surface and will be further enhanced with increasing current densities. Adjusting the above two factors with the help of the constructed phase field model is able to regulate the electrodeposited morphology from aggregated Li dendrites to discrete Li dendrites, and ultimately columnar Li morphology. The methodology and mechanistic understanding established herein give a significant step toward the practical applications of Li metal anodes.

Combination of in-situ ion beam analysis and thermal desorption spectroscopy for studying deuterium implanted in tungsten

We demonstrate a combinatorial approach integrating ion implantation followed by thermal annealing and simultaneous in situ ion beam analysis with thermal desorption spectroscopy in a single set-up. Atomic and molecular deuterium ions of 3 keV were implanted into bulk tungsten with doses exceeding 1 × 1022 ions m−2. Depth profiling of both, protium and deuterium was performed by elastic recoil detection analysis, while simultaneously the outgassing rates of molecular deuterium by thermal desorption spectroscopy were monitored during temperature ramps from room temperature to ≈1400 K. The combination of the two techniques in situ is shown capable to identify the distinct retention behavior of deuterium at different temperatures and in different reservoirs, e.g. located close to the surface and diffused deep into the material. Ex-situ scanning electron microscopy confirmed blister formation, and recovery of the initial surface morphology after high temperature annealing, in analogy to comprehensive ex-situ studies.

Mechanical behaviour of Li3xLa1/3−xNbO3 with domain structure

This study investigates the mechanical behaviours of A-site deficient perovskite-type Li3xLa1/3−xNbO3 electrolytes (3x = 0.00–0.18) with domain structures. The samples were examined under uniaxial compression in the temperature range of 233–393 K. In the stress vs. strain relationship, the orthorhombic Li3xLa1/3−xNbO3 (3x ≤ 0.06) clearly exhibits non-linear elastic hysteresis, whilst the tetragonal one (3x ≥ 0.12) shows a simple elastic behaviour. Ex-situ scanning electron microscopy observation on a polished surface before and after compression confirmed the martensitic reorientation of the domain structure of the orthorhombic Li3xLa1/3−xNbO3, which explains the observed non-linear hysteresis, whereas the domains of the tetragonal sample remain almost unchanged.

Dealloying-constructed hierarchical nanoporous bismuth-antimony anode for potassium ion batteries

Bi-Sb alloys are appealing anode materials for potassium ion batteries (PIBs) but challenged by their enormous volumetric variation during operation. Herein, a facile one-step dealloying protocol was devised and utilized to prepare the Bi-Sb alloys that manifest an exotic bicontinuous hierarchical nanoporous (np) microstructure ideal for volume-change mitigation and K+ transport percolation. The growth mechanism fostering the peculiar morphology of the np-(Bi,Sb) alloys was investigated and clarified via operando X-ray (XRD) and ex-situ scanning electron microscopy (SEM). In particular, the np-Bi6Sb2 electrode, optimized for comprehensive electrochemical performance, achieves decent reversible capacities and a superior lifespan, as benchmarked with the monometallic references and other Bi-Sb alloy electrodes. The (de)potassiation mechanism of the np-(Bi,Sb) alloys was studied by operando XRD and further rationalized by density functional theory (DFT) calculations, whereby a homogeneous (segregation-free) and robust two-step electrochemically-driven phase transformations’ catenation of (Bi,Sb) ↔ K(Bi,Sb)2 ↔ K3(Bi,Sb) was reliably established to substantiate the outstanding reversibility of the np-(Bi,Sb) anodes in PIBs.

Controlled lithium plating in three-dimensional hosts through nucleation overpotential regulation toward high-areal-capacity lithium metal anode

Three-dimensional (3D) porous hosts with abundant space inside can accommodate volume variation during lithium (Li) plating/stripping and promote reversibility of Li anode; however, the porous structure in 3D hosts usually induces uneven Li-ion/electron migration, giving rise to undesirable surface preferential Li nucleation and growth. A feasible coating strategy is developed herein to create gradient nucleation overpotentials on Cu mesh to realize the ‘bottom-up’ Li plating mode on 3D host. The ex-situ scanning electron microscopy (SEM) characterization confirms that this two-step coating strategy by coating Au and polymer blend (polyacrylonitrile and poly(vinylidene fluoride-co-hexafluoropropylene)) on the bottom and top sides of Cu mesh, respectively, successfully changes the nucleation overpotentials of this 3D host by altering Li affinity. As a result, stable Li plating/stripping and high coulombic efficiency of 97.3% can be achieved under high areal capacity of 5.0 mAh/cm2. The full cell using the modified Cu mesh with predeposited Li as the anode and lithium iron phosphate as the cathode (N/P ratio of ~4) can cycle steadily at 2.0 C with a capacity retention ratio of 96.4% after 150 cycles. The modification strategy proposed in this work is considered as a promising approach for designing a 3D conductive host for long-life and safe Li metal batteries.