Succulent-Inspired Implicit Structural Change for Smart "ON/OFF" Switchable and Flexible EMI Shielding Coating

Modern miniaturized intelligent electronics call for smart switchable and flexible electromagnetic interference (EMI) shielding material for highly precise applications. However, most switchable EMI shielding materials are based on an explicit structural change. Herein, we report a succulent-inspired smart switchable MXene (WR-MXene) coating film realized by inner implicit structural change, which benefits from the insertion of our reversible large-cavity yolk-shell biomicrospheres. The novel switchable yolk-shell biomicrospheres contain a soft N-isopropylacrylamide (PNIPAM) hydrogel core, an "ON/OFF" switchable cavity (over 30% volume fraction), and a porous polydopamine (p-PDA) shell. The yolk-shell biomicrospheres can be obtained by a facile two-step polymerization and a simple drying-dehydration treatment. Because of the "ON/OFF" switchable void space brought by the smart biomicrospheres and conductive framework of MXene, an optimized ultralight and flexible WR-MXene coating film (vWR-coating film) showed both large switchable change (over 60 dB) and extraordinary EMI shielding effectiveness, reaching 95 and over 50 dB in the whole X band (8.2-12.4 GHz). These novel reversible yolk-shell biomicrospheres and the succulent-inspired switchable coating films are promising for smart flexible wearable devices and many advanced multifunctional systems needing dynamic real-time response.

Upconversion Nanoparticle-Based Cell Membrane-Coated cRGD Peptide Bioorthogonally Labeled Nanoplatform for Glioblastoma Treatment

Glioblastoma is hard to be eradicated partly because of the obstructive blood-brain barrier (BBB) and the dynamic autophagy activities of glioblastoma. Here, hydroxychloroquine (HDX)-loaded yolk-shell upconversion nanoparticle (UCNP)@Zn0.5Cd0.5S nanoparticle coating with the cyclic Arg-Gly-Asp (cRGD)-grafted glioblastoma cell membrane for near-infrared (NIR)-triggered treatment of glioblastoma is prepared for the first time. UCNPs@Zn0.5Cd0.5S (abbreviated as YSN, yolk-shell nanoparticle) under NIR radiation will generate reactive oxygen species for imposing cytotoxicity. HDX, the only available autophagy inhibitor in clinical studies, can enhance cytotoxicity by preventing damaged organelles from being recycled. The cRGD-decorated cell membrane allowed the HDX-loaded nanoparticles to efficiently bypass the BBB and specifically target glioblastoma cells. Exceptional treatment efficacy of the NIR-triggered chemotherapy and photodynamic therapy was achieved in U87 cells and in the mouse glioblastoma model as well. Our results provided proof-of-concept evidence that HDX@YSN@CCM@cRGD could overcome the delivery barriers and achieve targeted treatment of glioblastoma.

Yolk-Shell-Type Gold Nanoaggregates for Chemo- and Photothermal Combination Therapy for Drug-Resistant Cancers

Epithelial ovarian cancer is a gynecological cancer with the highest mortality rate, and it exhibits resistance to conventional drugs. Gold nanospheres have gained increasing attention over the years as photothermal therapeutic nanoparticles, owing to their excellent biocompatibility, chemical stability, and ease of synthesis; however, their practical application has been hampered by their low colloidal stability and photothermal effects. In the present study, we developed a yolk-shell-structured silica nanocapsule encapsulating aggregated gold nanospheres (aAuYSs) and examined the photothermal effects of aAuYSs on cell death in drug-resistant ovarian cancers both in vitro and in vivo. The aAuYSs were synthesized using stepwise silica seed synthesis, surface amino functionalization, gold nanosphere decoration, mesoporous organosilica coating, and selective etching of the silica template. Gold nanospheres were agglomerated in the confined silica interior of aAuYSs, resulting in the red-shifting of absorbance and enhancement of the photothermal effect under 808 nm laser irradiation. The efficiency of photothermal therapy was first evaluated by inducing aAuYS-mediated cell death in A2780 ovarian cancer cells, which were cultured in a two-dimensional culture and a three-dimensional spheroid culture. We observed that photothermal therapy using aAuYSs together with doxorubicin treatment synergistically induced the cell death of doxorubicin-resistant A2780 cancer cells in vitro. Furthermore, this type of combinatorial treatment with photothermal therapy and doxorubicin synergistically inhibited the in vivo tumor growth of doxorubicin-resistant A2780 cancer cells in a xenograft transplantation model. These results suggest that photothermal therapy using aAuYSs is highly effective in the treatment of drug-resistant cancers.

Ingeniously Designed Yolk-Shell-Structured FeSe2@NDC Nanoboxes as an Excellent Long-Life and High-Rate Anode for Half/Full Na-Ion Batteries

Thanks to their high conductivity and theoretical capacity, transition metal selenides have demanded significant research attention as prospective anodes for sodium-ion batteries. Nevertheless, their practical applications are hindered by finite cycle life and inferior rate performance because of large volume expansion, polyselenide dissolution, and sluggish dynamics. Herein, the nitrogen-doped carbon (NC)-coated FeSe₂ nanoparticles encapsulated in NC nanoboxes (termed FeSe₂@NDC NBs) are fabricated through the facile thermal selenization of polydopamine-wrapped Prussian blue precursors. In this composite, the existing nitrogen-doped dual carbon layer improves the intrinsic conductivity and structural integrity, while the unique porous yolk-shell architecture significantly mitigates the volume swelling during the sodium/desodium process. Moreover, the derived Fe-N-C bonds can effectively capture polyselenide, as well as promote Na⁺ transportation and good reversible conversion reaction. As expected, the FeSe₂@NDC NBs deliver remarkable rate performance (374.9 mA h g^-1 at 10.0 A g^-1) and long-cycling stability (403.3 mA h g^-1 over 2000 loops at 5.0 A g^-1). When further coupled with a self-made Na₃V₂(PO₄)₃@C cathode in sodium-ion full cells, FeSe₂@NDC NBs also exhibit considerably high and stable sodium-storage performance.

C/MnO@void@C with Triple Balances for Superior Microwave Absorption Performance

It is very promising and challenging to construct a yolk-shell structure with highly efficient microwave absorption (MA) performance through a simple fabrication process. Here, a novel C/MnO@void@C (MCC) yolk-shell structure has been successfully synthesized by one-step calcination without additional processing. The as-obtained MCC composites with tunable crystallinity degrees and hollowness can be obtained by treatment at various temperatures. The MCC composites treated at 700 °C (MCC-700) show an impressive MA performance, and the optimal reflection loss of -53.2 dB and an effective absorption bandwidth of 5.4 GHz can be obtained. This excellent performance results from multiple balance mechanisms. First, the regulated permittivity of MCC-700 due to proper crystallinity and hollowness is beneficial for the balance between dielectric loss (tan δ_ε) and impedance match (Z_im). Second, the optimal balance between the increasing polarization range and decreasing polarization intensity can be achieved, which is favorable for the improvement of the MA performance. Third, the multicore yolk-shell structure of MCC-700 is conducive to multiple scattering and continuous energy dissipation. Thus, our new findings provide a rational way for the utilization of yolk-shell structural manganese-based materials.

Nitrogen-Coordinated CoS2@NC Yolk-Shell Polyhedrons Catalysts Derived from a Metal-Organic Framework for a Highly Reversible Li-O2 Battery

Transition-metal sulfides (TMS) are one of the most promising cathode catalysts for Li-O₂ batteries (LOBs) owing to their excellent stabilities and inherent metallicity. In this work, a highly efficient mode has been used to synthesize Co@CNTs [pyrolysis products of metal-organic frameworks (MOFs)]-derived CoS₂(CoS)@NC. Benefiting from the special yolk-shell hierarchical porous morphology, the existence of Co-N bonds, and dual-function catalytic activity (ORR/OER) of the open metal sites contributed by MOFs, the CoS₂@NC-400/AB electrode illustrated excellent charge-discharge cycling for up to nearly 100 times at a current density of 0.1 mA cm^-2 under a limited capacity of 500 mA h g^-1 (based on the total weight of CoS₂@NC and AB) with a high discharge voltage plateau and a low charge cut-off voltage. Meanwhile, the average transferred electron number (n) is around 3.7 per O₂ molecule for CoS₂@NC-400, which is the chief approach for a four-electron pathway of the ORR under alkaline media. Therefore, we believe that the novel CoS₂@NC-400/AB electrode could serve as an excellent catalyst in the LOBs.

Flexible Carbon Nanotubes Confined Yolk-Shelled Silicon-Based Anode with Superior Conductivity for Lithium Storage

The further deployment of silicon-based anode materials is hindered by their poor rate and cycling abilities due to the inferior electrical conductivity and large volumetric changes. Herein, we report a silicon/carbon nanotube (Si/CNT) composite made of an externally grown flexible carbon nanotube (CNT) network to confine inner multiple Silicon (Si) nanoparticles (Si NPs). The in situ generated outer CNTs networks, not only accommodate the large volume changes of inside Si NPs but also to provide fast electronic/ionic diffusion pathways, resulting in a significantly improved cycling stability and rate performance. This Si/CNT composite demonstrated outstanding cycling performance, with 912.8 mAh g-1 maintained after 100 cycles at 100 mA g-1, and excellent rate ability of 650 mAh g-1 at 1 A g-1 after 1000 cycles. Furthermore, the facial and scalable preparation method created in this work will make this new Si-based anode material promising for practical application in the next generation Li-ion batteries.

Surface Modification of the LiNi0.8Co0.1Mn0.1O2 Cathode Material by Coating with FePO4 with a Yolk-Shell Structure for Improved Electrochemical Performance

Coating with FePO₄ with the size of 20-30 nm on the surface of a LiNi_0.8Co_0.10Mn_0.1O₂ (NCM811) cathode produces an LFP3@NCM811 cathode via a sol-gel method, which markedly reduces secondary crystal cracking. A stable particle structure greatly improves the cycling stability of the LFP3@NCM811cathode, which retains 97% of its initial discharge capacity compared to NCM811 (78%) after 100 cycles at 2.7-4.5 V. Furthermore, it retains 86 and 63% of its initial discharge capacity after 400 cycles for LFP3@NCM811 and NCM811, respectively. The initial discharge capacity of the LFP3@NCM811 cathode is 218.8 mAh g^-1 at 0.1 C, and the discharge capacity of the LFP3@NCM811 cathode is achieved to be 151.4 mAh g^-1 at 5 C, which is 15 mAh g^-1 higher than that of the NCM811 cathode. These are due to the reduction of cation mixing for a certain amount of Fe²⁺/Fe³⁺ or PO₄^3- doped into the NCM811 surface, and the yolk-shell structure formed by coating with FePO₄ helps improve the electronic conductivity and accelerate the Li⁺ transport. The cycling stability is mainly due to the secondary cleavage inhibition, which maintains the structural integrity of the cathode particles during the long cycle process and protects the inside of the particle from harmful electrolytes.

Enhancing the Charge Transportation Ability of Yolk-Shell Structure for High-Rate Sodium and Potassium Storage

The microstructure of large-capacity anodes is of great importance in determining the performance of sodium- and potassium-ion batteries. Yolk-shell nanostructures promise excellent structural stability but suffer from insufficient charge transfer rate during cycles. Herein, we tackle this challenge by constructing a single-walled carbon nanotube (SWNT) internally bridged yolk-shell structure, inside which SWNTs cover the surface of the yolk and connect the yolk and shell, for better electron/ion transportation. Combining the merits of both yolk-shell structure and conductive SWNT channels, the as-prepared Fe_1-xS/SWNT@C composite manifests high reversible capacity and ultralong cycling stability up to 8700 cycles. Moreover, it displays the best rate capability (317 mA h g^-1 at 20 A g^-1 for Na⁺ and 236 mA h g^-1 at 10 A g^-1 for K⁺) among the reported yolk-shell structures and iron-sulfide-based anodes thus far. The kinetic analysis and density functional theory calculations further reveal that the Fe_1-xS/SWNT heterointerface can effectively enhance the reversibility of K⁺ storage and decrease the K⁺ diffusion energy barrier, leading to excellent pseudocapacitive behavior and fast ion transportation for outstanding rate capability.

Cancer-Cell-Membrane-Coated Nanoparticles with a Yolk-Shell Structure Augment Cancer Chemotherapy

Despite rapid advancements in antitumor drug delivery, insufficient intracellular transport and subcellular drug accumulation are still issues to be addressed. Cancer cell membrane (CCM)-camouflaged nanoparticles (NPs) have shown promising potential in tumor therapy due to their immune escape and homotypic binding capacities. However, their efficacy is still limited due to inefficient tumor penetration and compromised intracellular transportation. Herein, a yolk-shell NP with a mesoporous silica nanoparticle (MSN)-supported PEGylated liposome yolk and CCM coating, CCM@LM, was developed for chemotherapy and exhibited a homologous tumor-targeting effect. The yolk-shell structure endowed CCM@LM with moderate rigidity, which might contribute to the frequent transformation into an ellipsoidal shape during infiltration, leading to facilitated penetration throughout multicellular spheroids in vitro (up to a 23.3-fold increase compared to the penetration of membrane vesicles). CCM@LM also exhibited a cellular invasion profile mimicking an enveloped virus invasion profile. CCM@LM was directly internalized by membrane fusion, and the PEGylated yolk (LM) was subsequently released into the cytosol, indicating the execution of an internalization pathway similar to that of an enveloped virus. The incoming PEGylated LM further underwent efficient trafficking throughout the cytoskeletal filament network, leading to enhanced perinuclear aggregation. Ultimately, CCM@LM, which co-encapsulated low-dose doxorubicin and the poly(ADP-ribose) polymerase inhibitor, mefuparib hydrochloride, exhibited a significantly stronger antitumor effect than the first-line chemotherapeutic drug Doxil. Our findings highlight that NPs that can undergo facilitated tumor penetration and robust intracellular trafficking have a promising future in cancer chemotherapy.

Engineering Hollow Porous Carbon-Sphere-Confined MoS2 with Expanded (002) Planes for Boosting Potassium-Ion Storage

Potassium-ion batteries (PIBs) are emerging as promising next-generation electrochemical storage systems for their abundant and low-cost potassium resource. The key point of applying PIBs is to exploit stable K-host materials to accommodate the large-sized potassium ion. In this work, a yolk-shell structured MoS₂@hollow porous carbon-sphere composite (MoS₂@HPCS) assembled by engineering HPCS-confined MoS₂ with expanded (002) planes is proposed for boosting potassium-ion storage. When used as a PIB anode, the as-synthesized MoS₂@HPCS composite shows superior potassium storage performance. It delivers a reversible capacity of 254.9 mAh g^-1 at 0.5 A g^-1 after 100 discharge/charge cycles and maintains 126.2 mAh g^-1 at 1 A g^-1 over 500 cycles. The superior potassium-ion storage performance is ascribed to the elaborate yolk-shell nanoarchitecture and the expanded interlayer of the MoS₂ nanosheet, which could shorten the transport distance, enhance the electronic conductivity, relieve the volume variation, prevent the self-aggregation of MoS₂, facilitate the electrolyte penetration, and boost the intercalation/deintercalation of K⁺. Moreover, the potential application of the MoS₂@HPCS composite is also evaluated by assembled K-ion full cells with a perylenetetracarboxylic dianhydride cathode. Accordingly, the as-developed synthetic strategy can be extended to manufacture other host materials for PIBs and beyond.

Extraction-Induced Fabrication of Yolk-Shell-Structured Nanoparticles with Deformable Micellar Cores and Mesoporous Silica Shells for Multidrug Delivery

Yolk-shell-structured nanoparticles (YSNs) provide useful carriers for applications in biomedicine and catalysis due to the excellent loading capability and versatile functionality of the flexible core and porous shell. Unfortunately, the reported YSNs always require complex multistep synthesis processes and a harsh hard-template etching strategy. Herein, a facile "selective extraction" strategy is developed to synthesize yolk-shell-structured polymer@void@mSiO₂ nanoparticles (designated as YSPNs) comprising deformable and soft polystyrene-b-poly(acrylic acid) (PS-b-PAA) micellar cores and mesoporous silica shells. The YSPNs are formed by a morphological change and volume shrinkage of the PS-b-PAA aggregates from large compound vesicles to large compound micelles during the extraction process. As a multidrug vehicle, both hydrophobic curcumin (Cur, 6.4 wt %) and hydrophilic doxorubicin hydrochloride (Dox, 19.4 wt %) can be coloaded onto YSPNs through a successive impregnation method. Moreover, the resulting Cur/Dox@YSPNs possess intelligent pH-responsive capability, time-sequenced release behavior, and high in vivo antitumor efficiency, demonstrating excellent potential as safe and efficient multidrug nanocarriers for tumor chemotherapy. We envision that such a facile "selective extraction" strategy will enable pathways to construct organic-inorganic hybrid nanoparticles with yolk-shell structures for various applications.

Yolk-Shell-Structured Bismuth@N-Doped Carbon Anode for Lithium-Ion Battery with High Volumetric Capacity

As an anode for lithium-ion batteries, metallic bismuth (Bi) can provide a superb volumetric capacity of 3800 mA h cm^-3, showing perspective value for application. It is a pity that the severe volume swelling during the lithiation process leads to the dramatic deterioration of the cycling performances. To overcome this issue, Bi nanorods encapsulated in N-doped carbon nanotubes (yolk-shell Bi@C-N) are elaborately designed through in situ thermal reduction of Bi₂S₃@polypyrrole nanorods. In comparison with the commercial Bi, the lithium storage capacities of Bi@C-N are significantly enhanced, and it presents a stable volumetric capacity of 1700 mA h cm^-3 over 500 cycles at a high current density of 1.0 A g^-1, nearly 2.2 times that of graphite. The N-doped carbon nanotube and the cavity between the carbon wall and Bi jointly contribute to this superior performance. Especially, the failure mechanism of Bi nanorods and the protective effect of the carbon shell are revealed by ex situ TEM, which illuminates the decreasing tendency in the initial 10-20 cycles and the subsequent stable trend of cyclic performance.

Optimizing the Electromagnetic Wave Absorption Performances of Designed Co3Fe7@C Yolk-Shell Structures

Due to the increasing demand for military and commercial applications, magnetic metal-based core@shell nanostructures have attracted extensive attention in the field of electromagnetic wave (EMW) absorption materials. To further improve the overall performance, herein, an effective strategy is designed to fabricate Co₃Fe₇@C yolk-shell structures by using (Co_0.9Fe_0.1)Fe₂O₄@phenolic resin core@shell structures as precursors. The structure parameters, including the size of the CoFe alloy cores, the thickness of the carbon shell, and the void between the core and the shell, can be tailored by controlling the reaction conditions. It is demonstrated that the EMW absorption properties of the as-prepared Co₃Fe₇@C yolk-shell structures are closely related to their structure parameters. The optimized Co₃Fe₇@C yolk-shell structure shows excellent EMW absorption performance, the strongest reflection loss (RL) is up to -35.3 dB at 9.1 GHz with the matching thickness of 2.0 mm, and the effective bandwidth (RL < -10 dB) can reach 8.4 GHz (9.6-18 GHz) with a thickness of only 1.5 mm. It is revealed that the excellent performances stem from the unique yolk-shell structure as well as the complementarities and synergies between the dielectric loss and the magnetic loss. By rational designing, the magnetic metal alloy@carbon yolk-shell structures will be convinced to have the potential as novel high-efficiency EMW absorption materials with lightweight, low thickness, wide absorption frequency, high stability, and strong absorption characteristics.

Tumor Catalytic-Photothermal Therapy with Yolk-Shell Gold@Carbon Nanozymes

Nanozymes, as a new generation of artificial enzymes, offer great opportunities in biomedical engineering and disease treatment. Synergizing the multiple intrinsic functions of nanozymes can improve their performance in biological systems. Here, we report a novel nanozyme with yolk-shell structure fabricated by combining a single gold nanoparticle core with a porous hollow carbon shell nanospheres (Au@HCNs). Au@HCNs exhibited enzyme-like activities similar to horseradish peroxidase and oxidase under an acidic environment, showing the ability of ROS generation. More importantly, the ROS production of Au@HCNs was significantly improved upon 808 nm light irradiation by the photothermal effect, which is often used for tumor therapy. Cellular and animal studies further demonstrated that the efficient tumor destruction was achieved through the combination of light-enhanced ROS and photothermal therapy. These results implied that the intrinsic enzyme-like activity and photothermal conversion of nanozymes can be synergized for efficient tumor treatment, providing a proof-of-concept of tumor catalytic-photothermal therapy based on nanozymes.

808 nm Light-Triggered Thermometer-Heater Upconverting Platform Based on Nd3+-Sensitized Yolk-Shell GdOF@SiO2

The realization of real-time and accurate temperature reading at subcutaneous level during the photothermal therapy (PTT) could maximally avoid the collateral damages induced by overheating effects, which remains a formidable challenge for biomedical applications. Herein, 808 nm light-driven yolk-shell GdOF:Nd³⁺/Yb³⁺/Er³⁺@SiO₂ microcapsules were developed with thermal-sensing and heating bifunctions. Under 808 nm excitation, sensitive thermometry was implemented by monitoring thermoresponsive emission from ²H_11/2/⁴S_3/2 levels of Er³⁺; meanwhile, the addition of Nd³⁺ with rich metastable intermediate levels and the yolk-shell configuration with large specific surface area triggered efficient light-to-heat conversion via enhanced nonradiative channels. The potentiality of dual-functional samples for controlled subcutaneous photothermal treatment was validated through ex vivo experiments, and the antibacterial activity against Escherichia coli was also elaborately evaluated. Results open a general avenue for designing and developing upconverting platforms with sensitive thermal-sensing and efficient heating bifunctions, which makes a significant step toward the achievement of real-time controlled PTT.

Nonsacrificial Template Synthesis of Magnetic-Based Yolk-Shell Nanostructures for the Removal of Acetaminophen in Fenton-like Systems

Recently, yolk-shell structured materials with active metal cores have received considerable attention in heterogeneous Fenton-like systems, which have excellent catalytic performance. In this study, we initially attempted the nonsacrificial template synthesis of yolk-shell structured nanoparticles with magnetite cores encapsulated in a mesoporous silica shell (Fe₃O₄@SiO₂) via a modified sol-gel process and then evaluated their catalytic activity for acetaminophen degradation in Fenton-like systems. Second, copper nanoparticles were decorated on the surface of the Fe₃O₄@SiO₂ microspheres (Fe₃O₄@SiO₂@Cu) to enhance the catalytic activity. The morphological, structural, and physicochemical properties of the prepared materials were characterized via X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, field emission transmission electron microscopy, nitrogen adsorption-desorption isotherms, specific surface area, ζ-potential, magnetic properties, and Fourier transform infrared spectroscopy. The results demonstrated a successful fabrication of the targeted materials. The yolk-shell structured materials possess a spherical morphology with an active core, protective shell, and hollow void. The Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂@Cu variants showed acetaminophen removal rates significantly higher compared to those of their counterparts, i.e., the Fe₃O₄ and Fe₃O₄@Cu core-shell structures. Fe₃O₄@SiO₂@Cu showed that the copper nanoparticles were firmly immobilized on the mesoporous silica shell, dramatically improving the catalytic performance. Both the yolk-shell structured Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂@Cu exhibited good separation and satisfactory regeneration properties, which could be recycled six times without any obvious decline in catalytic activity. Overall, the results of this study suggested that Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂@Cu yolk-shell nanostructures could be promising catalysts for a heterogeneous Fenton-like system by which the removal of emerging contaminants can be greatly improved.

Heterogeneous Double-Shelled Constructed Fe3O4 Yolk-Shell Magnetite Nanoboxes with Superior Lithium Storage Performances

Among the numerous candidate materials for lithium ion batteries, ferroferric oxide (Fe₃O₄) has been extensively concerned as a prospective anode material because of its high theoretical specific capacity, abundant resources, low cost, and nontoxicity. Here, we designed and fabricated a unique yolk-shell construction by generating heterogeneous double-shelled SnO₂ and nitrogen-doped carbon on Fe₃O₄ yolk (denoted as Fe₃O₄@SnO₂@C-N nanoboxes). The yolk-shell structured Fe₃O₄@SnO₂@C-N nanoboxes have the adjustable void space, which permits the free expansion of Fe₃O₄ yolks without breaking the double shells during the lithiation/delithiation processes, avoiding the structural pulverization. Moreover, the heterogeneous double-shelled SnO₂@C-N can meaningfully improve the electronic conductivity and enhance the lithium storage performance. Two metal oxides also show the specific synergistic effect, promoting the electrochemistry reaction. As a result, this yolk-shell structured Fe₃O₄@SnO₂@C-N exhibits high specific capacity (870 mA h g^-1 at 0.5 A g^-1 after 200 cycles), superior rate capability, and long cycle life (670 mA h g^-1 at 3 A g^-1 after 600 cycles). This design and construction method can be extended to synthesize other yolk-shell nanostructured anode materials with improved electrochemistry performance.

New Nanoconfined Galvanic Replacement Synthesis of Hollow Sb@C Yolk-Shell Spheres Constituting a Stable Anode for High-Rate Li/Na-Ion Batteries

In the current research project, we have prepared a novel Sb@C nanosphere anode with biomimetic yolk-shell structure for Li/Na-ion batteries via a nanoconfined galvanic replacement route. The yolk-shell microstructure consists of Sb hollow yolk completely protected by a well-conductive carbon thin shell. The substantial void space in the these hollow Sb@C yolk-shell particles allows for the full volume expansion of inner Sb while maintaining the framework of the Sb@C anode and developing a stable SEI film on the outside carbon shell. As for Li-ion battery anode, they displayed a large specific capacity (634 mAh g^-1), high rate capability (specific capabilities of 622, 557, 496, 439, and 384 mAh g^-1 at 100, 200, 500, 1000, and 2000 mA g^-1, respectively) and stable cycling performance (a specific capacity of 405 mAh g^-1 after long 300 cycles at 1000 mA g^-1). As for Na-ion storage, these yolk-shell Sb@C particles also maintained a reversible capacity of approximate 280 mAh g^-1 at 1000 mA g^-1 after 200 cycles.

Yolk-Shell Ni@SnO2 Composites with a Designable Interspace To Improve the Electromagnetic Wave Absorption Properties

In this study, yolk-shell Ni@SnO₂ composites with a designable interspace were successfully prepared by the simple acid etching hydrothermal method. The Ni@void@SnO₂ composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results indicate that interspaces exist between the Ni cores and SnO₂ shells. Moreover, the void can be adjusted by controlling the hydrothermal reaction time. The unique yolk-shell Ni@void@SnO₂ composites show outstanding electromagnetic wave absorption properties. A minimum reflection loss (RL_min) of -50.2 dB was obtained at 17.4 GHz with absorber thickness of 1.5 mm. In addition, considering the absorber thickness, minimal reflection loss, and effective bandwidth, a novel method to judge the effective microwave absorption properties is proposed. On the basis of this method, the best microwave absorption properties were obtained with a 1.7 mm thick absorber layer (RL_min= -29.7 dB, bandwidth of 4.8 GHz). The outstanding electromagnetic wave absorption properties stem from the unique yolk-shell structure. These yolk-shell structures can tune the dielectric properties of the Ni@air@SnO₂ composite to achieve good impedance matching. Moreover, the designable interspace can induce interfacial polarization, multiple reflections, and microwave plasma.

Yolk-Shell Sn@C Eggette-like Nanostructure: Application in Lithium-Ion and Sodium-Ion Batteries

Yolk-shell carbon encapsulated tin (Sn@C) eggette-like compounds (SCE) have been synthesized by a facile method. The SCE structures consist of tin cores covered by carbon membrane networks with extra voids between the carbon shell and tin cores. The novel nanoarchitectures exhibit high electrochemical performance in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). As anodes for LIBs, the SCE electrodes exhibit a specific capacity of ∼850 mA h g(-1) at 0.1 C (100 mA g(-1)) and high rate capability (∼450 mA h g(-1) remains) at high current densities up to 5 C (5000 mA g(-1)). For SIBs, the SCE electrodes show a specific capacity of ∼400 mA h g(-1) at 0.1 C and high rate capacity (∼150 mA h g(-1) remains) at high current densities up to 5 C (5000 mA g(-1)).

MOF-Derived ZnO/Ni3ZnC0.7/C Hybrids Yolk-Shell Microspheres with Excellent Electrochemical Performances for Lithium Ion Batteries

In this study, ZnO/Ni3ZnC0.7/C spheres were synthesized successfully via a simple method based on metal-organic frameworks (MOFs). The experimental results show that the reaction time has a great influence on the structure of the material. ZnO/Ni3ZnC0.7/C spheres with controlled solid and yolk-shell structures have been obtained by altering the reaction time. When applied as anode materials, both the solid and the yolk-shell ZnO/Ni3ZnC0.7/C composites present excellent electrochemical performance. In addition, it is worth mentioning that the yolk-shell structure composite's property is superior to that of the solid one's in terms of lithium storage. The stable reversible capacity of yolk-shell ZnO/Ni3ZnC0.7/C can be retained at 1002 mA h g(-1) at 500 mA g(-1) after completion of 750 cycles, and it also exhibits superior rate performance. In contrast, the solid ZnO/Ni3ZnC0.7/C under the same conditions of testing shows a reversible capacity of 824 mA h g(-1).

Controlled Formation of Metal@Al₂O₃ Yolk-Shell Nanostructures with Improved Thermal Stability

Yolk-shell structured nanomaterials have shown interesting potential in different areas due to their unique structural configurations. A successful construction of such a hybrid structure relies not only on the preparation of the core materials, but also on the capability to manipulate the outside wall. Typically, for Al2O3, it has been a tough issue in preparing it into a uniform nanoshell, making the use of Al2O3-based yolk-shell structures a challenging but long-awaited task. Here, in benefit of our success in the controlled formation of Al2O3 nanoshell, we demonstrated that yolk-shell structures with metal confined inside a hollow Al2O3 nanosphere could be successfully achieved. Different metals including Au, Pt, Pd have been demonstrated, forming a typical core@void@shell structure. We showed that the key parameters of the yolk-shell structure such as the shell thickness and the cavity size could be readily tuned. Due to the protection of a surrounding Al2O3 shell, the thermal stability of the interior metal nanoparticles could be substantially improved, resulting in promising performance for the catalytic CO oxidation as revealed by our preliminary test on Au@Al2O3.

Beyond yolk-shell nanoparticles: Fe3O4@Fe3C core@shell nanoparticles as yolks and carbon nanospindles as shells for efficient lithium ion storage

To well address the problems of large volume change and dissolution of Fe3O4 nanomaterials during Li(+) intercalation/extraction, herein we demonstrate a one-step in situ nanospace-confined pyrolysis strategy for robust yolk-shell nanospindles with very sufficient internal void space (VSIVS) for high-rate and long-term lithium ion batteries (LIBs), in which an Fe3O4@Fe3C core@shell nanoparticle is well confined in the compartment of a hollow carbon nanospindle. This particular structure can not only introduce VSIVS to accommodate volume change of Fe3O4 but also afford a dual shell of Fe3C and carbon to restrict Fe3O4 dissolution, thus providing dual roles for greatly improving the capacity retention. As a consequence, Fe3O4@Fe3C-C yolk-shell nanospindles deliver a high reversible capacity of 1128.3 mAh g(-1) at even 500 mA g(-1), excellent high rate capacity (604.8 mAh g(-1) at 2000 mA g(-1)), and prolonged cycling life (maintaining 1120.2 mAh g(-1) at 500 mA g(-1) for 100 cycles) for LIBs, which are much better than those of Fe3O4@C core@shell nanospindles and Fe3O4 nanoparticles. The present Fe3O4@Fe3C-C yolk-shell nanospindles are the most efficient Fe3O4-based anode materials ever reported for LIBs.