Core-shell Architecture Research Articles

Constructing a core-shell structure in Ti-based alloys with exceptional mechanical properties through semi-solid sintering

In this work, we developed a semi-solid sintering method for constructing a core-shell architecture in Ti68.8Nb13.6Co6.8Cr5.1Al6.5 alloy and revealed the underlying mechanism of microstructure evolution and deformation behavior. Fundamentally, the semi-solid state was achieved by sintering amorphous powders at temperatures between the melting point of the CoTi2 phase and the β-Ti matrix. During the process, the liquid CoTi2 phase was squeezed towards the β-Ti boundaries due to the sintering pressure and the growth of β-Ti grains. Subsequently, it transformed into a hard ultrafine CoTi2 phase distributed along the β-Ti boundaries, constructing a core-shell structure. The resulting core-shell structure exhibited a high compressive yield strength of 1560 MPa, an ultimate strength of 3006 MPa, and a remarkable compressive strain of 40.1%, surpassing typical Ti-based alloys under compressive loading. The high strength was attributed to dislocation-impeding effect of the CoTi2 phase, while the activation of multiple slip systems triggered by the CoTi2 shell contributed to plasticity. The results provide fundamental insights into the fabrication of Ti-based alloys with exceptional mechanical properties for structural materials applications.

Hollow dodecahedron K3PW12O40/CdS core-shell S-scheme heterojunction for photocatalytic synergistic H2 evolution and benzyl alcohol oxidation

Simultaneous generation of clean energy, H2, and organic products holds immense potential in the realm of photocatalysis. The S-scheme heterojunction stands out for these dual-function applications due to its robust redox capacity, facilitating both the water reduction reaction and organic oxidation reactions. In this study a Keggin-type polymetallic oxide, H3PW12O40 hollow dodecahedron (KPW), was synthesized using a hydrothermal approach. Subsequently, cadmium sulfide (CdS) nanoparticles averaging 15 nm in size were integrated in situ onto the KPW shell, resulting in the creation of a core-shell KPW@CdS S-scheme heterojunction. This optimized composite showcased a hydrogen evolution rate of 18.7 mmol g−1 h−1, alongside a value-added product, benzaldehyde, with a yield of 17.5 mmol g−1 h−1 substantially surpassing the performance of standalone CdS. This S-scheme junction, featuring a pronounced internal electronic field, emerges between the KPW and CdS. It significantly enhances the segregation of photogenerated carriers while preserving formidable redox capability. Furthermore, the hollow structure augments light absorption and utility, and the core-shell architecture delivers dual reduction and oxidation sites. As a result, the interplay between the hollow core-shell configuration and the S-scheme mode intensifies the photocatalytic activity. This research provides an innovative approach to crafting hollow S-scheme heterojunctions, aiming to optimize photocatalytic redox reactions for effective solar energy utilization.

One-Dimensional, First-Row Transition Metal, Core-Shell Architectures as Multifunctional Electrocatalysts in Alkaline and Acidic Conditions

The development of practical electrocatalysts for fuel cells, electrochemical sensors, and batteries requires nanostructured architectures with high catalytic activity and good long-term durability. It is also essential that they have very low or even no platinum content. There has also been a recent emphasis on the importance of designing multifunctional catalysts with the ability to efficiently catalyze a wide-range of electrochemical reactions in both acidic and alkaline media. In light of these requirements, we have developed a solution-based synthetic method to prepare core-shell nanowires consisting of inexpensive and abundant first-row transition metals coated with precious metal shells. The core-shell motif enables a substantial quantity of platinum to be removed from the catalytically inactive core of the material, while also resulting in the ability to tune the activity of platinum through electronic and structural interactions between the two metals. The as-synthesized core-shell nanowires have a complex surface structure that brings together metal oxide and precious metal active sites that are active toward OER and result in a significant reduction in the overpotential for OER when compared with pure Pt and Co nanowires. In addition, we have developed an electrochemical process that selectively removes the metal oxide from the surface of the nanowires enabling the catalysts to be activated toward SOM oxidation in acidic media and ORR in alkaline media. For example, the activated core-shell nanowires display a 1.5-fold and a 4-fold increase in the specific activity and mass activity of methanol oxidation, respectively, relative to a pure platinum nanowire.

Rational design of hierarchical zeolitic imidazolate framework-67@Cu2CoO3 core–shell architectures for hybrid supercapacitor applications

Hierarchical core–shell architectures constructed with zeolitic imidazolate frameworks (ZIFs) and binary metal oxides are attracting much attention as an efficient electrode material for supercapacitors (SCs). In this regard, we reported the ZIF-67 amorphous nanoparticles (NPs)@Cu2CoO3 (ZIF-67@CCO) via a two-step synthesis process. Initially, the CCO electrode material with soap nuts-like core–shell hollow sphere (SNHS) morphology was synthesized by a facile solvothermal method and post-annealing treatment. The optimized CCO SNHS (CCO-9 h (9 h growth time)) electrode demonstrated higher areal capacity (CA)/specific capacity (CS) values than the CCO-6 h and CCO-12 h electrodes. Next, ZIF-67 NPs were deposited on the CCO-9 h material using the solvothermal method. The resulting ZIF-67@CCO-9 h electrode exhibited improved electrochemical properties of CA = 176.3 μAh cm−2 (CS = 117.5 mAh g−1) at 1 mA cm−2 and superb cycling stability after 25,000 cycles (83.4% retention). The ZIF-67 layer on the CCO-9 h with SNHS structure may provide faster electron transfer as well as more active sites, benefiting the electrochemical characteristics. Furthermore, the hybrid supercapacitor (HSC) cell was assembled using ZIF-67@CCO-9 h and activated carbon/Ni foam as positive (+) and negative (−) electrodes, respectively. The as-constructed HSC cell revealed high energy density value of 25.2 Wh kg−1. Also, the commercial application of the fabricated HSC cell was verified by driving different electronic components.

Near-Unity Emitting, Widely Tailorable, and Stable Exciton Concentrators Built from Doubly Gradient 2D Semiconductor Nanoplatelets.

The strength of electrostatic interactions (EIs) between electrons and holes within semiconductor nanocrystals profoundly affects the performance of their optoelectronic systems, and different optoelectronic devices demand distinct EI strength of the active medium. However, achieving a broad range and fine-tuning of the EI strength for specific optoelectronic applications is a daunting challenge, especially in quasi two-dimensional core-shell semiconductor nanoplatelets (NPLs), as the epitaxial growth of the inorganic shell along the direction of the thickness that solely contributes to the quantum confined effect significantly undermines the strength of the EI. Herein we propose and demonstrate a doubly gradient (DG) core-shell architecture of semiconductor NPLs for on-demand tailoring of the EI strength by controlling the localized exciton concentration via in-plane architectural modulation, demonstrated by a wide tuning of radiative recombination rate and exciton binding energy. Moreover, these exciton-concentration-engineered DG NPLs also exhibit a near-unity quantum yield, high photo- and thermal stability, and considerably suppressed self-absorption. As proof-of-concept demonstrations, highly efficient color converters and high-performance light-emitting diodes (external quantum efficiency: 16.9%, maximum luminance: 43,000 cd/m2) have been achieved based on the DG NPLs. This work thus provides insights into the development of high-performance colloidal optoelectronic device applications.

Synergistic effect of Z-scheme junction and core–shell architecture over NH2-MIL-125@Ag@AgCl ternary heterojunction for cooperative CO and H2O2 production

Herein, a NH2-MIL-125(Ti)@Ag@AgCl (NM@Ag@AgCl) stacked core–shell heterojunction with Z-scheme carrier transfer mechanism was developed to fulfil the goal of synchronous reactions of CO2 reduction and H2O oxidation. In detail, the NM@Ag@AgCl was obtained by in-situ loading the AgCl as the shell-inorganic semiconductor on the octahedral NM as the core-organic semiconductor, followed by in-situ transforming part of the AgCl shell into the plasmonic Ag nanoparticles using a photo-reduction method. As a result, the interface effects of core–shell architecture majorized by the Ag electronic mediator can favor the transmission of photogenerated carriers and reduce electron transport resistance; while the plasmonic Ag mediated Z-scheme mode with a giant internal electronic field provided a strong driving force to recombine the carriers with weak redox ability, reserving the carrier with strong redox ability on the NH2-MIL-125-core and AgCl-shell for the simultaneous reactions. The CO and H2O2 yields of the optimal NM@Ag@AgCl were 6.02 and 5.43 μmol⋅g−1⋅h−1, which were 3.31 and 4.02 times that of the NM, respectively. This study furnishes a novel thread for the design of core–shell organic–inorganic heterojunction with high interfacial charge transfer for realizing the simultaneous reactions.

Epitaxial growth of Cu2-xSe on Cu (220) crystal plane as high property anode for sodium storage

Three-dimentional (3D) transition metal selenides with sufficient channels could produce significant superiority on enhancing reaction kinetics for sodium-ion batteries. However, the thorough exploration of 3D architecture with a facile strategy is still challenging. Here we report that a polycrystalline Cu2-xSe film was epitaxial grown on (220) facets-exposed Cu by direct selenization of a nanoporous Cu skeleton, which is obtained by dealloying rolled CuMn@Cu alloy foil. Density functional theory calculation result shows strong adsorption energy for Se atoms on Cu (220) planes during selenization reaction, rendering a low energy consumption. By virtue of this core-shell 3D nanoporous architecture to offer abundant active sites and endow fast electron/ion transportation, the nanoporous Cu2-xSe@Cu-0.15 composite electrode exhibits remarkable sodium-ion storage properties with high reversible capacity of 950.6 µAh/cm2 at 50 µA/cm2, suprior rate capability of 457.6 µAh/cm2 at 500 µA/cm2, as well as an ultra-long stability at a high current density. Mechanism investigation reveals that the electrochemical reaction is a typical conversion-type reaction with different intermediates. This novel electrode synthetic strategy provides useful instructions to design the high-performance anode material for sodium-ion batteries.

Preparation of hollow core-shelled MnCoSex/MnO@nitrogen-doped carbon composite by multiple interfaces coupling and its electrochemical properties

Hollow MnCoSex/MnO nanospheres wrapped with nitrogen-doped carbon shell (MnCoSex/MnO@N-C) were prepared via a simple solvothermal and selenization strategy followed by the carbon coating procedure. Benefitting from the multiple interfaces coupling between MnCoSex and MnO and unique hollow core-shell architecture, MnCoSex/MnO@N-C composites possess high specific capacitance and superior rate capability, even at a high current density of 5 A/g, the MnCoSex/MnO@N-C can operate steadily for 20000 cycles with 84.6% of initial specific capacitance maintained. An asymmetric supercapacitor device assembled by MnCoSex/MnO@N-C and active carbon depicts a high energy density of 11.2 W·h/kg at a power density of 810 W/kg and a long cycle life with 84.0% of the initial specific capacitance retained after 20000 cycles.

Poly (3, 4-ethylenedioxythiophene) engineered hollow Bi2O3 core-shell architectures for long cycle performance of flexible supercapacitors

The booming development of electronic devices has promoted the in-depth research on flexible supercapacitors. The structural design of core@shell can be regarded as an effective method of achieving excellent electrochemical performance and outstanding flexibility of electrode materials. Herein, a special structure of core@shell hybrid Bi2O3-x@carbon fiber@poly (3, 4-ethylenedioxythiophene) (Bi2O3-x@CF@PEDOT) electrode derived from a Bi-metal-organic framework (Bi-MOF) is fabricated by using the electrospinning technique, and using the stabilization, pyrolyzation and polymerization procedures. The amount of Bi-MOF is regulated to obtain an optimized flexible substrate (Bi2O3-x@CF). The free space of the hollow Bi2O3 microrod can effectively alleviate the volume expansion during long cycling processes and further promote ion diffusion. The effective optimizations for the structure and content could significantly improve the conductivity and electrochemical performance of the constructed electrode. The prepared Bi2O3–0.5@CF@PEDOT electrode exhibits a satisfied specific capacitance of 460 F g−1 (1 A g−1) and great cycling stability. The assembled symmetric supercapacitor yields a desired energy density (i.e., 16.4 Wh kg−1) and power density (i.e., 500.34 W kg−1), and remarkable cycling performance (i.e., 99 % capacitance retention after 8500 cycles). Moreover, the excellent flexibility of the device is demonstrated by folding the supercapacitor into different angles and without obvious capacitance loss. This work provides a special structural design method of constructing high-performance flexible electrodes.

Anammox-Mediated Hydroxyapatite Granules: Physicochemical Properties, 3D Hierarchy, and Biofilm Thickness.

Biomineralization inspired the development of simultaneous biological transformations and chemical precipitation for simultaneous nitrogen removal and phosphorus recovery from wastewater, which could compensate for the incapacity of phosphorus management in the new biological route of anaerobic ammonium oxidation (anammox). In this study, we strengthened anammox-mediated biomineralization by long-term feeding of concentrated N, P, and Ca substrates, and a self-assembled matrix of anammox bacteria and hydroxyapatite (HAP) was fabricated in a granular shape, defined as HAP-anammox granules. HAP was identified as the dominant mineral using elemental analysis, X-ray diffraction, and Raman spectroscopy. The intensive precipitation of HAP resulted in a higher inorganic fraction and substantially improved settleability of anammox biomass, which facilitated HAP precipitation by acting as nucleation and metabolically elevated pH. By using X-ray microcomputed tomography, we visually represented the hybrid texture of interwoven HAP pellets and biomass, the core-shell layered architecture of different-sized HAP-anammox granules, and their homogeneously regulated thickness of the outer biofilm (from 118 to 635 μm). This unique architecture endows HAP-anammox granules with outstanding settleability, active biofilm, and tightly bonded biofilm with the carrier, which may explain the excellent performance of these HAP-anammox granules under various challenging operational conditions in previous studies.

Fine-tuning of plasmonics by Au@AuY/Au core–shell nanoparticle monolayer for enhancement of third-order nonlinearity

The manipulation of plasmonics on noble metal nanoparticles (NPs) is of great interest in developing nonlinear photonic devices, such as all-optical switches and frequency combs. An Au@AuY-core/Au-shell nanoparticle (Au@AuY/Au NP) monolayer is proposed for the fine-tuning of plasmonics and enhanced third-order nonlinearity. Based on the different thermodynamic mechanisms of Au and Y ions, the compact Au@AuY/Au core–shell architectures are designed and surface-modified in fused silica (SiO2) with enhanced free electron density, mobility, and quantum size effect. The flexible modulation of plasmonics is realized, resulting in significant absorption enhancement (165% for interband absorption and 38% for free electron absorption, respectively) and fine-tuning of the localized surface plasma resonance (LSPR) band. In addition, the physical mechanism is investigated by density functional theory (DFT) and Mie theory, which reveals a transition from size-independence to size-dependence of LSPR owing to the synergistic effect of multiple physical factors such as free electron density and mobility. With the above advantages, the third-order nonlinearity is enhanced by 4.4 times compared with traditional Au NPs. It indicates the significant potential of Au@AuY/Au core–shell NP monolayer in the performance improvement of nonlinear photonic devices.

Hard-Soft Core-Shell Architecture Formation from Cubic Cobalt Ferrite Nanoparticles.

Cubic bi-magnetic hard-soft core-shell nanoarchitectures were prepared starting from cobalt ferrite nanoparticles, prevalently with cubic shape, as seeds to grow a manganese ferrite shell. The combined use of direct (nanoscale chemical mapping via STEM-EDX) and indirect (DC magnetometry) tools was adopted to verify the formation of the heterostructures at the nanoscale and bulk level, respectively. The results showed the obtainment of core-shell NPs (CoFe2O4@MnFe2O4) with a thin shell (heterogenous nucleation). In addition, manganese ferrite was found to homogeneously nucleate to form a secondary nanoparticle population (homogenous nucleation). This study shed light on the competitive formation mechanism of homogenous and heterogenous nucleation, suggesting the existence of a critical size, beyond which, phase separation occurs and seeds are no longer available in the reaction medium for heterogenous nucleation. These findings may allow one to tailor the synthesis process in order to achieve better control of the materials' features affecting the magnetic behaviour, and consequently, the performances as heat mediators or components for data storage devices.

Core‐Shell‐Type All‐Inorganic Heterometallic Nanoclusters: Record High‐Nuclearity Cobalt Polyoxoniobates for Visible‐Light‐Driven Photocatalytic CO2 Reduction

AbstractOnly rarely have polyoxometalates been found to form core–shell nanoclusters. Here, we succeeded in isolating a series of rare giant and all‐inorganic core–shell cobalt polyoxoniobates (Co−PONbs) with diverse shapes, nuclearities and original topologies, including 50‐nuclearity {Co12Nb38O132}, 54‐nuclearity {Co20Nb34O128}, 62‐nuclearity {Co26Nb36O140} and 87‐nuclearity {Co33Nb54O188}. They are the largest Co−PONbs and also the polyoxometalates containing the greatest number of Co ions and the largest cobalt clusters known thus far. These molecular Co−PONbs have intriguing and atomically precise core–shell architectures comprising unique cobalt oxide cores and niobate oxide shells. In particular, the encapsulated cobalt oxide cores with different nuclearities have identical compositions, structures and mixed‐valence Co3+/Co2+ states as the different sized Co−O moieties of the bulk cubic‐spinel Co3O4, suggesting that they can serve as various molecular models of the cubic‐spinel Co3O4. The successful construction of the series of the Co−PONbs reveals a feasible and versatile synthetic method for making rare core–shell heterometallic PONbs. Further, these new‐type core–shell bimetal species are promising cluster molecular catalysts for visible‐light‐driven CO2 reduction.

Core-Shell-Type All-Inorganic Heterometallic Nanoclusters: Record High-Nuclearity Cobalt Polyoxoniobates for Visible-Light-Driven Photocatalytic CO2 Reduction.

Only rarely have polyoxometalates been found to form core-shell nanoclusters. Here, we succeeded in isolating a series of rare giant and all-inorganic core-shell cobalt polyoxoniobates (Co-PONbs) with diverse shapes, nuclearities and original topologies, including 50-nuclearity {Co12 Nb38 O132 }, 54-nuclearity {Co20 Nb34 O128 }, 62-nuclearity {Co26 Nb36 O140 } and 87-nuclearity {Co33 Nb54 O188 }. They are the largest Co-PONbs and also the polyoxometalates containing the greatest number of Co ions and the largest cobalt clusters known thus far. These molecular Co-PONbs have intriguing and atomically precise core-shell architectures comprising unique cobalt oxide cores and niobate oxide shells. In particular, the encapsulated cobalt oxide cores with different nuclearities have identical compositions, structures and mixed-valence Co3+ /Co2+ states as the different sized Co-O moieties of the bulk cubic-spinel Co3 O4 , suggesting that they can serve as various molecular models of the cubic-spinel Co3 O4 . The successful construction of the series of the Co-PONbs reveals a feasible and versatile synthetic method for making rare core-shell heterometallic PONbs. Further, these new-type core-shell bimetal species are promising cluster molecular catalysts for visible-light-driven CO2 reduction.

Implementation of a Core-Shell Design Approach for Constructing MOFs for CO2 Capture.

Adsorption-based capture of CO2 from flue gas and from air requires materials that have a high affinity for CO2 and can resist water molecules that competitively bind to adsorption sites. Here, we present a core-shell metal-organic framework (MOF) design strategy where the core MOF is designed to selectively adsorb CO2, and the shell MOF is designed to block H2O diffusion into the core. To implement and test this strategy, we used the zirconium (Zr)-based UiO MOF platform because of its relative structural rigidity and chemical stability. Previously reported computational screening results were used to select optimal core and shell MOF compositions from a basis set of possible building blocks, and the target core-shell MOFs were prepared. Their compositions and structures were characterized using scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction. Multigas (CO2, N2, and H2O) sorption data were collected both for the core-shell MOFs and for the core and shell MOFs individually. These data were compared to determine whether the core-shell MOF architecture improved the CO2 capture performance under humid conditions. The combination of experimental and computational results demonstrated that adding a shell layer with high CO2/H2O diffusion selectivity can significantly reduce the effect of water on CO2 uptake.

Region-Controlled Framework Interface Mediated Anion Exchange Chemical Transformation to Designed Metal Phosphosulfide Heteronanostructures.

Postsynthetic chemical transformation provides a powerful platform for creating heteronanostructures (HNs) with well-defined materials and interfaces that generate synergy or enhancement. However, it remains a synthetic bottleneck for the precise construction of HNs with increased degrees of complexity and more elaborate functions in a predictable manner. Herein, we define a general transformative protocol for metal phosphosulfide HNs based on tunable hexagonal Cu1.81S frameworks with corner-, edge- and face-controlled growth of Co2P domains. The region-controlled Cu1.81S-Co2P framework interfaces can serve as "kinetic barriers" in mediating the direction and rate between P and S anion exchange reactions, thus leading to a family of morphology and phase designed Cu3P1-xSx-Co2P HNs with hollow (branched, dotted and crown), porous and core-shell architectures. This study reveals the internal transformation mechanism between metal sulfide and phosphide nanocrystals, and opens up a new way for the rational synthesis of metastable HNs that are otherwise inaccessible.

In situ investigations of failure mechanisms of silica fibers from the venus flower basket (Euplectella Aspergillum).

The fibers of the deep-sea sponge Euplectella aspergillum exhibit exceptional mechanical properties due to their unique layered structure at a micrometer length scale. In the present study, we utilize a correlative approach comprising of in situ tensile testing inside a scanning electron microscope (SEM) and post-failure fractography to precisely understand mechanisms through which layered architecture of fibers fracture and improves damage tolerance in tensile loading condition. The real-time observation of fibers in the present study confirms for the first time that the failure starts from the surface of fibers and proceeds to the center through successive layers. The concentric layers surrounding the central core sacrifice themselves and protect the central core through various toughening mechanisms like crack deflection, crack arrest, interface debonding, and fiber pullout. STATEMENT OF SIGNIFICANCE: Biological materials often exhibit multiscale hierarchical structures that can be incorporated into the design of next generation of engineering materials. The fibers of deep-sea sponge E. aspergillum possess core-shell like layered architecture. Our in situ study reveals astounding strategies by which this architecture delays the fracture of the fiber. The core-shell architecture of these fibers behaves like fiber-reinforced ceramic matrix composite, where the outer shells act as a matrix and the central core acts as a fiber. The outer shells take the environmental brunt and scarify themselves to protect the central core. The precise understanding of damage evolution presented here will help to design architected materials for load-bearing applications.

Hybrid Nanostructured Materials as Electrodes in Energy Storage Devices

The global demand for energy is constantly rising, and thus far, remarkable efforts have been put into developing high-performance energy storage devices using nanoscale designs and hybrid approaches. Hybrid nanostructured materials composed of transition metal oxides/hydroxides, metal chalcogenides, metal carbides, metal–organic frameworks, carbonaceous compounds and polymer-based porous materials have been used as electrodes for designing energy storage systems such as batteries, supercapacitors (SCs), and so on. Different kinds of hybrid materials have been shown to be ideal electrode materials for the development of efficient energy storage devices, due to their porous structures, high surface area, high electrical conductivity, charge accommodation capacity, and tunable electronic structures. These hybrid materials can be synthesized following various synthetic strategies, including intercalative hybridization, core–shell architecture, surface anchoring, and defect control, among others. In this study, we discuss applications of the various advanced hybrid nanostructured materials to design efficient batteries and SC-based energy storage systems. Moreover, we focus on their features, limitations, and real-time resolutions.

A benign strategy toward mesoporous carbon coated Sb nanoparticles: A high-performance Li-ion/Na-ion batteries anode

Antimony (Sb)-based anodes can offer excellent gravimetric capacity (∼660 mAhg−1) in lithium-ion/sodium-ion batteries (LIBs/SIBs) fabricated using carbonate-based electrolytes complexed with lithium/sodium salt. However, high first-cycle irreversible loss (35–40%) and gradual capacity fade (25–30%/cycle) originate from solid electrolyte interphase (SEI), and severe volumetric stress (∼300%) associated with alloyed phase(s) impede real-life applications. Herein, we devise a benign strategy to develop mesoporous carbon coating onto antimony nanoparticles (Sb@C) based core-shell architecture for LIBs/SIBs anode. In particular, ∼30–50 nm thick mesoporous carbon spheres (∼1 ± 0.5 μm) were obtained from resorcinol-formaldehyde (RF)-based polycondensation reaction by sol-gel chemistry engulfing Sb nanoparticles by suitably controlling Cetyltrimethylammonium bromide (CTAB)-induced steric stabilization and pH modulation during synthesis. The core-shell Sb@C helps faster Li+/Na+-ion migration preventing the structural collapse of Sb during electrochemical cycling and thereby improving the capacity fade. Electrochemical results demonstrate Sb@C can deliver a specific capacity of ∼536 mAhg−1 and ∼ 291 mAhg−1 at 0.1C current rate in LIBs and SIBs, respectively, up to 200 cycles. Electrochemical impedance spectroscopy (EIS) indicates lower charge transfer (Rct) and SEI resistance (RSEI) of Sb@C cycled electrode than the bare Sb-NPs was the probable reason for improved Li/Na-ion storage in Sb@C anode. A detailed galvanostatic intermittent titration technique (GITT) and internal resistance measurements during 1st and 2nd cycles shed light on distinguishably different Li-ion/Na-ion storage behavior. The bulk Li+/Na+-ion diffusion coefficients found diminishes at reaction voltages (0.9 V/0.6 V for lithiation and 0.6 V/0.4 V for sodiation) corresponding with alloyed phase(s) concurrent with a drop in internal resistance at the quasi-open-circuit voltage (QOCV) during 1st and 2nd discharge cycle. On the contrary, de-alloying phenomena from the fully lithiated/sodiated phase(s) display an entirely opposite trend. The Li+ diffusion coefficient reaches minima at ∼1.1 V with a sudden jump in the internal resistance at QOCV during 1st and 2nd charge cycle. However, Na+ diffusion coefficient gradually drops along with a steep increase in the internal resistance, indicating partial Na-ion trapping and irreversible capacity loss.

Architecting “Li-rich Ni-rich” core-shell layered cathodes for high-energy Li-ion batteries

Li-rich or Ni-rich layered oxides are considered ideal cathode materials for high-energy Li-ion batteries (LIBs) owing to their high capacity (> 200 mAh g–1) and low cost. However, both are suffering from severe structural instability upon high-voltage cycling (> 4.5 V). Here, “Li-rich Ni-rich” Li1.08Ni0.9Mn0.1O2 oxides with core-shell architecture are designed and synthesized to improve their high-voltage cyclability. These oxides are determined to be composed of a less reactive “Li-rich Mn-rich” shell and a high-capacity “Li-rich Ni-rich” core. As Li-ions gradually enter into the core-shell precursor during high-temperature lithiation reaction, the interdiffusion of elements across the interphase between the Mn-rich shell and the Ni-rich core successively occurs. Such thermally-driven atomic interdiffusion could lead to a thickness-controllable “Li-rich Mn-rich” shell, which can guarantee an exceptional structural reversibility for the layered “Li-rich Ni-rich” core upon long-term cycling. As a consequence, the optimized core-shell Li1.08Ni0.9Mn0.1O2 achieves a capacity retention of 96% at 0.1 C after 100 cycles in the voltage range of 2.7–4.6 V. These findings might open up a new avenue for rational design of advanced cathode materials for LIBs and beyond.