Outer Carbon Shell Research Articles

Yolk-shell structured FeS0.5Se0.5@N-doped mesoporous carbon composite as high-performance lithium-ion battery anodes

Transition metal selenides/sulfides are drawing growing attention as promising electrode material for lithium-ion batteries owing to their larger layer spacing and weaker ionic bond compared to transition metal oxides, which are conducive to the intercalation/de-intercalation of Li ions. However, the intrinsic low conductivity and large volume expansion remain a major obstacle for their practical applications. In this work, with the prediction help of the theory model, we design a yolk-shell structure of single-phase ternary FeS0.5Se0.5 and nitrogen-doped mesopore carbon (YS-FeS0.5Se0.5@NMC) via an interfacial co-assembly, followed by one-step selenization and vulcanization. In the composite, single-phase ternary FeS0.5Se0.5 yolk provides more active sites and faster ion/electron transport dynamics than binary Fe2O3, while N-doped mesoporous carbon shell effectively alleviates the large volume expansion of FeS0.5Se0.5, as revealed by in-situ Raman analysis and TEM observation. Meanwhile, the spatial confinement of outer carbon shell also ensures the mechanical stability of the electrode during cycles. These merits endow the YS-FeS0.5Se0.5@NMC anode with a high reversible capacity of 1417mA h/g at 200mA h/g after 120 cycles, and an exceptional rate capability. This work offers an inspired approach for achieving high-performance energy storage electrode materials

Internal Space Modulation of Yolk-Shell FeSe2@Carbon Anode with Peanut-Shaped Morphology Enabling Ultra-Stable and Fast Potassium-Ion Storage.

The poor cycling stability and rate performance of transition metal selenides (TMSs) are caused by their intrinsic low conductivity and poor structural stability, which hinders their application in potassium-ion batteries (PIBs). To address this issue, encapsulating TMSs within carbon nanoshells is considered a viable strategy. However, due to the lack and uncontrollability of internal void space, this structure cannot effectively mitigate the volume expansion induced by large K+, resulting in unsatisfactory electrochemical performance. Herein, peanut-shaped FeSe2@carbon yolk-shell capsules are prepared by modulation of the internal space. The active FeSe2 is encapsulated within a robust carbon shell and an optimal void space is retained between them. The outer carbon shell promotes electronic conductivity and avoids FeSe2 aggregation, while the internal void mitigates volume expansion and effectively ensures the structural integrity of the electrode. Consequently, the FeSe2@carbon anode demonstrates exceptional rate performance (242 mAh g-1 at 10 A g-1) and long cycling stability (350 mAh g-1 after 500 cycles at 1 A g-1). Furthermore, the effect of internal space modulation on electrochemical properties is elucidated. Meanwhile, ex situ characterizations elucidate the K+ storage mechanism. This work provides effective guidance for the design and the internal space modulation of advanced TMSs yolk-shell structures.

A novel approach to synthesize micrometer-sized porous Si/SiOx@C with internally and externally interweaved CNTs as a high performance anode for lithium-ion batteries

Silicon-based materials are prospective anodes because of the high capability of lithium (Li) storage, but the large volumetric expansion seriously destroys the integrity of the electrodes and further results in unsatisfactory cycling performance. Reasonable structure design based on low-cost nano silicon (Si) prepared by an feasible method is still an enormous challenge. Herein, the carbon-coated and cross-linked carbon nanotube/porous-Si/SiOx microspheres (CNT/SFDP-Si/SiOx@C) are firstly synthesized by combining an inverse water-in-oil microemulsion approach with magnesiothermic reduction. One high value-added route for utilizing silica fume as the precursor to form nano silicon is provided. The collaborative strategy via wired CNTs network, porous-Si/SiOx flexible matrix, and carbon coating is employed to keep the integrity and stability of electrode structure. Benefiting from the synergistic effect of the flexibility of CNTs network, protection of outer carbon shell, doping of diverse nitrogen (N) species, and accommodation of porous-Si/SiOx, CNT/SFDP-Si/SiOx@C exhibits excellent electrochemical performance. The long cycling lifespan with a reversible capacity of 675.8 mAh g−1 after 1000 cycles at 2 A g−1, a slight decay rate per cycle of 0.018 %, and a high-rate performance are simultaneously obtained. The prelithiated LiFePO4||CNT/SFDP-Si/SiOx@C full cell is also assembled, showing the reversible capacity of 129.4 mAh g−1 at 0.2C.

Confining WS2 hierarchical structures into carbon core-shells for enhanced sodium storage

The growing demand for clean energy has heightened interest in sodium-ion batteries (SIBs) as promising candidates for large-scale energy storage. However, the sluggish reaction kinetics and significant volumetric changes in anode materials present challenges to the electrochemical performance of SIBs. This work introduces a hierarchical structure where WS2 is confined between an inner hard carbon core and an outer nitrogen-doped carbon shell, forming HC@WS2@NCs core–shell structures as anodes for SIBs. The inner hard carbon core and outer nitrogen-doped carbon shell anchor WS2, enhancing its structural integrity. The highly conductive carbon materials accelerate electron transport during charge/discharge, while the rationally constructed interfaces between carbon and WS2 regulate the interfacial energy barrier and electric field distribution, improving ion transport. This synergistic interaction results in superior electrochemical performance: the HC@WS2@NCs anode delivers a high capacity of 370 mAh g−1 at 0.2 A/g after 200 cycles and retains261 mAh g−1 at 2 A/g after 2000 cycles. In a full battery with a Na3V2(PO4)3 cathode, the Na3V2(PO4)3//HC@WS2@NC full-cell achieves an impressive initial capacity of 220 mAh g−1 at 1 A/g. This work provides a strategic approach for the systematic development of WS2-based anode materials for SIBs.

Adjustable nanoarchitectonics of N-doping Yolk-Shell carbon spheres via “Pyrolysis-Capture” method for High-Performance supercapacitor

The energy storage capacity of porous carbon materials is closely tied to their surface structure and chemical properties. However, developing an innovative and straightforward approach to synthesize yolk-shell carbon spheres (YCs) remains a great challenge till date. Herein, we prepared a series of porous nitrogen-doped yolk-shell carbon spheres (NYCs) via a “pyrolysis-capture” method. This method involves coating the resorcinol–formaldehyde (RF) resin sphere with a layer of compact silica shell induced by 2-methylimidazole (ME) catalysis to produce a confined nano-space. Based on the confined effect of compact silica shell, volatile gases emitted from the RF resin and ME during pyrolysis can not only diffuse into the pores of the RF resin but can also be captured to form an outer carbon shell. This results in the tunable structures of NYCs materials. As the pyrolysis temperature rises, the shell thickness of NYCs reduces, the pore size expands, the roughness increases, and the N/O content of surface elements is enhanced. Notably, as an electrode material used forsupercapacitors,the optimized NYCs-800 exhibits excellent performance with a capacitance of 301.2F g−1 at the current density of 1 A/g and outstanding cycling life stability of 96.1% after 10,000 cycles. These results signify that controlling the surface structure and chemical properties of NYCs materials is an effective approach for constructing advanced energy storage materials.

Rapid Release of Silicon by Ultrafast Joule Heating Generates Mechanically Stable Shell-Shell Si/C Anodes with Dominant Inward Deformation.

As a promising anode material, silicon-carbon composites encounter great challenges related to internal stress release and contact between the composites during lithiation. These issues lead to material degradation and concomitantly rapid capacity decline. Here, we report a type of shell-shell silicon-carbon (SS-Si/C) composite, which consists of a carbon shell tightly coated with a silicon shell. The mechanical analysis unveils that the dominant inward expansion of the Si shell is achieved through the synergistic effect of the outer carbon shell and the inner hollow structure. Benefiting from the well-tailored shell-shell structure, the SS-Si/C anode exhibits exceptional performance, boasting a high specific capacity (1690.3 mA h g-1 after 550 cycles at 0.5 A g-1), a high areal capacity (2.05 mA h cm-2 after more than 400 cycles at 0.5 mA cm-2), and an extended cycling life (1055.6 mA h g-1 after 1000 cycles at 8 A g-1), far exceeding commercially available Si/C anodes. Using the well-designed SS-Si/C anode, full cells assembled with LiCoO2 (LCO) or LiFePO4 (LFP) cathodes achieve favorable rate capability and cyclic stability. Notably, at a high rate of 6 C (1 C = 170 and 270 mA g-1 for LFP and LCO, respectively), these full cells deliver high specific capacities of 79.5 mA h g-1 and 64.9 mA h g-1 when using LCO and LFP, respectively, demonstrating the potential of SS-Si/C anodes for practical applications. The straightforward and safe synthesis method in this work enables the rational design of hollow structures with distinct properties.

Vacancy-Defect Ternary Topological Insulators Bi2Se2Te Encapsulated in Mesoporous Carbon Spheres for High Performance Sodium Ion Batteries and Hybrid Capacitors.

Ternary topological insulators have attracted worldwide attention because of their broad application prospects in fields such as magnetism, optics, electronics, and quantum computing. However, their potential and electrochemical mechanisms in sodium ion batteries (SIBs) and hybrid capacitors (SIHCs) have not been fully studied. Herein, a composite material comprising vacancy-defects ternary topological insulator Bi2Se2Te encapsulated in mesoporous carbon spheres (Bi2Se2Te@C) is designed. Bi2Se2Te with ample vacancy-defects has a wide interlayer spacing to enable frequent insertion/extraction of Na+ and boost reaction kinetics within the electrode. Meanwhile, the Bi2Se2Te@C with optimized yolk-shell structure can buffer the volume variation without breaking the outer protective carbon shell, ensuring structural stability and integrity. As expected, the Bi2Se2Te@C electrode delivers high reversible capacity and excellent rate capability in half SIB cells. Various electrochemical analyses and theoretical calculations manifest that Bi2Se2Te@C anode confirms the synergistic effect of ternary chalcogenide systems and suitable void space yolk-shell structure. Consequently, the full cells of SIB and SIHC coupled with Bi2Se2Te@C anode exhibit good performance and high energy/power density, indicating its widespread practical applications. This design is expected to offer a reliable strategy for further exploring advanced topological insulators in Na+-based storage systems.

Constructing hierarchical MoS2/WS2 heterostructures in dual carbon layer for enhanced sodium ions batteries performance

The escalating global demand for clean energy has spurred substantial interest in sodium-ion batteries (SIBs) as a promising solution for large-scale energy storage systems. However, the insufficient reaction kinetics and considerable volume changes inherent to anode materials present significant hurdles to enhancing the electrochemical performance of SIBs. In this study, hierarchical MoS2/WS2 heterostructures were constructed into dual carbon layers (HC@MoS2/WS2@NC) and assessed their suitability as anodes for SIBs. The internal hard carbon core (HC) and outer nitrogen-doped carbon shell (NC) effectively anchor MoS2/WS2, thereby significantly improving its structural stability. Moreover, the conductive carbon components expedite electron transport during charge–discharge processes. Critically, the intelligently engineered interface between MoS2 and WS2 modulates the interfacial energy barrier and electric field distribution, promoting faster ion transport rates. Capitalizing on these advantageous features, the HC@MoS2/WS2@NC nanocomposite exhibits outstanding electrochemical performance when utilized as an anode in SIBs. Specifically, it delivers a high capacity of 415 mAh/g at a current density of 0.2 A/g after 100 cycles. At a larger current density of 2 A/g, it maintains a commendable capacity of 333 mAh/g even after 1000 cycles. Additionally, when integrated into a full battery configuration with a Na3V2(PO4)3 cathode, the Na3V2(PO4)3//HC@MoS2/WS2@NC full cell delivers a high capacity of 120 mAh/g after 300 cycles at 1 A/g. This work emphasizes the substantial improvement in battery performance that can be attained through the implementation of dual carbon confinement, offering a constructive approach to guide the design and development of next-generation anode materials for SIBs.

Innovative design of silicon-core mesoporous carbon composite for high performance anode material in advanced lithium-ion batteries

Silicon is widely recognized as an exceptionally auspicious anode material for lithium−ion batteries due to its remarkable specific capacity, suitable operational potential, and ecologically innocuous characteristics. This study presents a novel silicon@void@FC (fibrous carbon) composite anode material for lithium-ion batteries. Utilizing a one-step synthesis approach, the resulting hollow core–shell structure, combined with a mesoporous carbon shell, demonstrates exceptional electrochemical performance. The Si@Void@FC electrode exhibits remarkable cycle stability and rate performance, maintaining structural integrity over 500 cycles without observable degradation. The outer carbon shell acts as a protective layer and accommodates silicon volume expansion during cycling, preventing excessive contact with the electrolyte. The rich mesoporous structure facilitates efficient lithium-ion diffusion, enhancing lithiation and delithiation processes. The simplified one-step synthesis method further streamlines the preparation process, eliminating the need for complete silica template formation. This innovative Si@Void@FC composite material holds promise for advancing lithium-ion battery technology, addressing challenges associated with silicon-based anode materials, and offering insights into the design and synthesis of high-performance energy storage materials.

Electronic structure modulation of metallic Co via N-doped carbon shell and Cu-doping for enhanced semi-hydrogenation of phenylacetylene to styrene

Styrene, an important monomer in the production of polystyrene, is usually mixed with a small number of phenylacetylene which readily causes the poisoning of catalyst during styrene polymerization. To address this issue, we reported a nitrogen-doped carbon encapsulated CuCo bimetallic catalyst (CuxCo@NC) for styrene production from phenylacetylene semi-hydrogenation. The CuxCo@NC catalyst obtained a 100% conversion of phenylacetylene along with a high 94.6% selectivity of styrene, far higher than those of single metal Co@C and Co@NC catalysts. Detailed characterizations unveiled that the CuxCo@NC catalyst fabricated by a dual-regulation strategy showed Mott-Schottky effect, in which the electrons transferred from metallic Cu to Co and then to outer N-doped carbon shells. Moreover, the electron transfers of metallic Co could be regulated by Mott-Schottky effect with which to improve the semi-hydrogenation of phenylacetylene to styrene. This work provides an feasible pathway to effectively design the supported metal catalysts for highly selective semi-hydrogenation of alkynes to alkenes.

Advanced core-shell hollow carbon nanofibers for ion and electron accessibility in sodium ion batteries.

One-dimensional core-shell hollow carbon nanofibers (HCNFs) have been synthesized by coaxial electrospinning, deacetylation and carbonization, which exhibit multi-surface properties that enhance electrolyte infiltration and facilitate ion/electron transport. The nitrogen-doped hard carbon outer shell compensates for the low conductivity of amorphous carbon, and the inner core carbon supports the stability of core-shell hollow structures. This unique structure ensures the accessibility of electrons/ions during electrochemical reactions and contributes to the superior rate performance of HCNFs. Ultimately, a high retention rate of 77% of the initial capacity value (0.1 A g-1) was demonstrated at a current density of 2 A g-1. The core-shell hollow structure designed in this work greatly optimizes the sodium transport dynamics.

Dual immobilization of porous Si by graphene supported anatase TiO2/carbon for high-performance and safe lithium storage

Smart surface coatings have been proven to be an effective strategy to significantly enhance the electronic conductivity and cycling stability of silicon-based anode materials. However, the single/conventional coatings face critical challenges, including low initial Coulomb efficiency (ICE), poor cyclability, and kinetics failure, etc. Hence, we proposed a dual immobilization strategy to synthesize graphene supported anatase TiO2/carbon-coated porous silicon composite (denoted as PSi@TiO2@C/Graphene) using industrial-grade ferrosilicon as lithium storage raw materials through the simple etching, combined with sol–gel and hydrothermal coating processes. In this work, the dual immobilization from the “confinement effect” of the inner TiO2 shell and the “synergistic effect” of the outer carbon shell, improves the kinetics of the electrochemical reaction and ensures the integrity of the electrode material structure during lithiation. Furthermore, the introduction of the graphene substrate offers ample space for dispersing and anchoring the Si-based granules, which in turn provides a stable 3D conductive network between the particles. As a result, the PSi@TiO2@C/Graphene electrode delivers high reversible capacity of 1605.4 mAh g−1 with 93.65% retention at 0.5 A g−1 after 100 cycles (vs. 4th discharge), high initial Coulomb efficiency (82.30%), and superior cyclability of 1159.9 mAh g−1 after 250 cycles. The above results suggest that the particle structure has great potential for applications in Si-based anode and may provide some inspiration for the design of other energy storage materials.

Design of SiO x /TiO2@C hierarchical structure for efficient lithium storage

The large volume expansion effect and unstable solid electrolyte interface films of SiO x -based anode materials have hindered their commercial development. It has been shown that composite doping is a general strategy to solve critical problems. In this study, TiO2-doped core–shell SiO x /TiO2@C composites were created using the sol–gel method. On the one hand, the uniformly dispersed TiO2 nanoparticles can alleviate the volume expansion of the SiO x active material during the lithiation process. On the other hand, they can react with Li+ to form Li x TiO2, thereby increasing the ion diffusion rate in the composite material. The outer carbon shell acts as a protective layer that not only alleviates the volume expansion of the composite, but also improve the electron migration rate of the composite. The prepared SiO x /TiO2@C composite has a reversible capacity of 828.2 mA h g−1 (0.2 A g−1 100 cycles). After 500 cycles, it still maintains a reversible capacity of 500 mA h g−1 even at a high current density of 2 A g−1. These findings suggest that SiO x /TiO2@C composites have a bright future in applications.

Internal interface engineering of yolk-shell structure toward fast and robust potassium storage

Advanced anode materials with stable and fast K-ion storage behavior are of great significance for potassium-ion batteries (PIBs) toward large-scale applications, while it still remains a big challenging due to their intrinsic poor conductivity and large volume variation during cycles. Herein, we develop an internal interfacial engineering by encapsulating core-shell NiS2@C nanoparticles within MOF-derived hollow carbon shell for superior PIB anodes. As-prepared yolk-shell NiS2@C@C composite integrates the structure superiority of abundant interior void space, outer protective carbon shell and internal conductive carbon layer. Comprehensive experimental and theoretical methods illuminate that internal NiS2/C interface is conductive to boost charge transport kinetics, enhance pseudocapacitive behavior, and mitigate mechanical stress in outer carbon shell. As a result, it manifests an ultrahigh capacity of 481 mA h g−1 at 0.2 A g−1, and guarantees the rate capability of 306 mA h g−1 at 20 A g−1. Moreover, it presents excellent cycle stability (358 mA h g−1 after 1600 cycles at 1 A g−1), which is extremely competitive among the best reported conversion anodes for PIBs.

Constructing novel SiOx hybridization materials by a double-layer interface engineering for high-performance lithium-ion batteries

SiOx-based anode materials (0 < x < 2) have been regarded as an appealing candidate for anode material of commercial Lithium-ion batteries accounting for their ultrahigh theoretical capacity and low cost. However, its large-scale applications have been hampered by the serious volume expansion during repeated cycles, low intrinsic conductivity and unsatisfactory initial Coulombic efficiencies. Herein, to address these inherent deficiencies, a hierarchical SiOx-based anode with double-layer coatings of Sn inner layer and N-doped carbon outer shell is elaborately designed by a facile two-step hydrolysis process and polymer coating technology. Benefiting from the “synergistic effect” between Sn and SiOx at different working potentials and a well-designed double-layer coating structure, the resultant SiOx/C@Sn@NC anode displays excellent electrochemical properties, including an enhanced initial Coulomb efficiency (73.3%) efficiency, higher reversible capacity (991 mAh g−1) and superior long lifespan. Moreover, comprehensive characterization based on the reaction kinetics and structural stability proved that such enhanced ICE and cycling stability of anode material stem from its unique double-layer coating structure and multiple active components, which can significantly improve the diffusion of ion and charge transport, stabilize solid-electrolyte interphase (SEI) layer and absorb the expansion stress of electrode. Therefore, this study provides an efficient and feasible strategy to overcome the limitations of high-capacity SiOx-based anode materials via hybridization design with various active components and a double-layer coating strategy.

Biogenic carbon encapsulated iron oxides mediated oxalic acid for Cr(VI) reduction in aqueous: Efficient performance, electron transfer and radical mechanisms

Carbonaceous materials have a potential to mediated oxalic acid (OA) for Cr(VI) reduction, but the rational modification is needed for boosting the mediation of electron transfer. Herein, we utilized polyvinyl alcohol to envelop schwertmannite synthesized by Acidithiobacillus ferrooxidans biomineralization, and pyrolyzed them to obtain the carbon encapsulated iron oxides (C-2.0-Sch-PVA). SEM and TEM results demonstrated that a moderate calcination temperature would yield a neural network-like carbon encapsulated structure. C-2.0-Sch-PVA efficiently mediated OA to reduce Cr(VI), 98.4% of Cr(VI) (40 mg L−1) was reduced with 0.75 g L−1 C-2.0-Sch-PVA and 4 mM OA in 60 min. It still performed excellent results in a wide pH range, multiple anions and different water matrixes. The carbon encapsulated structure as electron shuttle mediated the electron transfer, and the O-moieties on its surface were a premise for initiating the Cr(VI) reduction process. The electron transfer from the inner iron oxides to the conjugated structure of the outer carbon shells facilitated Cr(VI) reduction as well. Moreover, OA raised the persistent free radicals' level in C-2.0-Sch-PVA as another important pathway for Cr(VI) reduction. Overall, C-2.0-Sch-PVA provides an excellent demonstration in the carbonaceous materials modification for mediating OA to reduce Cr(VI) in aqueous.

Carbon coated bimetallic sulfides Co9S8/ZnS heterostructures microrods as advanced anode materials for lithium ion batteries

Lithium ion batteries (LIBs) are widely used in portable electronic devices and hybrid vehicles because of their high energy density, long cycle life and environmental friendliness. Constructing bimetallic sulfide have been demonstrated as most promising strategy for prepare high performance anode materials for LIBs. However, the huge volume change resulting in poor cycle life during the change and discharge process was the key issue of transition metal sulfides. Here, bimetallic sulfide carbon micro-rods consist of Co9S8/ZnS core and outer carbon shell (Co9S8/ZnS@C MRs) is synthesized as anode materials for LIBs. Such a well-designed architecture have various advantages including the bimetallic sulfide Co9S8/ZnS heterostructures can generate built-in electric field, which boosting the ion and electron transfer at the interfaces between Co9S8 and ZnS. Moreover, the outer carbon layer can enhance the conductivity, and buffer the volume expansion of Co9S8/ZnS during the lithiation/delithiation process. As a result, combined with the merits of heterostructures and core-shell structure, the Co9S8/ZnS@C MRs exhibits outstanding electrochemical performance. Specifically, it can deliver a high capacity of 591.1 mAh g−1 after 1000 cycles at 1.0 A g−1, and maintain a capacity of 367 mAh g−1 even at 5.0 A g−1.

Regulation of the Co–Nx Active Sites of MOF-Templated Co@NC Catalysts via Au Doping for Boosting Oxidative Esterification of Alcohols

The Co–Nx active sites play a critical role over the Co@NC catalyst in the heterogeneous catalysis. However, the effective methods for the regulation of the content and electronic structure of Co–Nx active sites to enhance the catalytic efficiency of heterogeneous catalysts are still insufficient. Herein, a nitrogen-doped porous carbon-encapsulated Au-doped Co nanoparticle catalysts with abundant and electron-rich Co–Nx sites in the outer carbon layer was designed by a Au doping strategy through pyrolysis of the HAuCl4-modified ZIF-67 metal organic framework precursor. The optimal catalyst exhibits improved catalytic performance in alcohol selective oxidative esterification. The linear relationship between the ester yield and Co–Nx species content, combined with a series of control experiments, indicated that the Co–Nx active sites are crucial for achieving the excellent catalytic activity (yield: 99.9%). In situ diffuse reflectance infrared Fourier transform spectroscopy, O2-temperature-programed desorption characterizations, active oxygen species quenching experiments together with density functional theory calculations results indicate that Au doping in the Co nanoparticle core increases the content and the electron density of Co–Nx species on the outer carbon shell, which enhanced the chemical adsorption and activation of molecular O2 for producing reactive O2•– species. This study demonstrated a novel Co–Nx active site regulation strategy for the efficient selective oxidative esterification of alcohols under mild reaction conditions.

Dual carbon enables highly reversible alloying/dealloying behavior of ultra-small Bi nanoparticles for ultra-stable Li storage

Bismuth (Bi) have attracted attentions as promising anode material for lithium-ion batteries (LIBs) due to its high capacity and suitable working potential. Nevertheless, poor ion diffusion kinetics and huge volume expansion, lead to irreparable particle pulverization and re-agglomeration in the discharge/charge process, which is not conducive to the rapid and ultra-long-period storage of Li+. Herein, ultra-small Bi nanoparticles encapsulated in double carbon microrods (Bi/C@C MRs) are synthesized via using Bi-based MOFs precursor coupled with polymerization coating process and followed calcination. The MOF-derived inner cross-linked carbon encapsulated ultra-small Bi nanoparticles, and the polymeric layer of resorcinol- formaldehyde transformed into outer carbon shell was coated on the outer surface of Bi/C microrods. The inner cross-linked carbon can suppress the severe volume change and re-agglomeration of Bi nanoparticles during the repeated alloying/de-alloying process, as well as accelerate the Li+ and electron transition. Furthermore, outer carbon layer can not only further buffer the volume change, but also avoid directly contact between Bi nanoparticles and electrolyte during the cycling process. As a result, the Bi/C@C MRs exhibits excellent structural stability and highly reversible alloying/dealloying behavior during the long-term cycling process. Bi/C@C MRs sustain a ultra-long cycle life of ∼ 506 mA h g−1 at 1000 mA g−1 up to 3000 loops, and an excellent rate performance of 279 mA h g−1 at an ultrahigh rate of 10000 mA g−1. Above results provided new insight to achieve ultra-long cycle life and excellent rate performance anodes for practical LIBs.

ZIF-8-derived N-doped porous carbon wrapped in porous carbon films as an air cathode for flexible solid-state Zn-air batteries

Metal-organic frameworks are a new type of catalyst precursor with high specific surface area and controllable composition, which can be modified by post-treatment and are suitable for use as cathode catalysts for Zn-air batteries (ZABs). Here, a self-doped nitrogen nanocatalyst (N-PC@CF) with a double-layered porous structure is rationally designed for flexible solid-state ZABs. The outer porous carbon shell of the N-PC@CF is highly hydrophilic and O2 permeable, while the layered porous structure exposes sufficient active sites to shorten the mass transfer distance, which would promote electrocatalytic performance and increase flexibility efficiently. The obtained N-PC@CF has an onset potential of 0.926 V and a half-wave potential of 0.843 V in the oxygen reduction reaction test, which is equivalent to commercial Pt/C. Most importantly, the maximum power density of the assembled ZAB is 134.7 mW cm−2 and it exhibits a specific capacity of 776.8 mA h g−1 at 10 mA cm−2, which is better than the 99.9 mW cm−2 of the Pt/C-based battery. An obvious improvement in the constant current discharge–charge cycle durability of the ZAB is found when compared with Pt/C. The specific capacities of ZAB with N-PC@CF as the air cathode at 5, 10 and 15 mA cm−2 are 842.7, 776.8 and 715.0 mAh g−1 (calculated by the mass of zinc consumed), respectively, corresponding to high energy densities of 1089.7, 977.3 and 842.2 Wh kg−1. A flexible solid-state battery is assembled with excellent flexibility and stability, even if the battery is folded into a large angle (160°). This work provides a new strategy for the design and synthesis of metal-free air cathodes.