Outer Carbon Shell Research Articles

Double-Enhanced Core-Shell-Shell Sb2S3/Sb@TiO2@C Nanorod Composites for Lithium- and Sodium-Ion Batteries.

For most alloying- and conversion-type anode materials, a huge volume expansion and structure degradation of the electrodes always hinder their applications. In this work, a novel core-shell-shell Sb2S3/Sb@TiO2@C nanorod composite has been designed layer by layer, which includes an inner Sb2S3/Sb heterostructure core protected by an oxygen-deficient TiO2 shell and a conductive carbon shell. It is interesting to observe that, during the carbothermic reduction process, the previous Sb2S3 nanorod cores are partially reduced into a metallic Sb phase and the reduced TiO2 also creates many oxygen vacancies, which can greatly enhance the conductivity of the semiconductor Sb2S3. Thanks to the double effects of the TiO2 middle shell and carbon outer shell, the unique double-shelled structure design creates an enhanced dual protection, which can better accommodate the volume-expansive deformation and preserve the structural integrity of the active Sb2S3/Sb core. Especially, the TiO2 middle layer is self-assembled by numerous nanoparticles acting as a nanopillar backbone, which supports between the nanorod core and outer carbon shell to better buffer the volume changes. As a result, the core-shell-shell Sb2S3/Sb@TiO2@C anode shows lithium and sodium storage performances superior to those of the pristine Sb2S3 and core-shell Sb2S3@TiO2 electrodes. For lithium-ion batteries, the Sb2S3/Sb@TiO2@C nanorod composite achieves an initial discharge/recharge capacity of 1244.9/1005.1 mAh g-1 with an initial Coulombic efficiency of about 80.7%, an enhanced rate capability with a capacity of 593.2 mA h g-1 at 5.0 A g-1, and prolonged cycling life for 500 cycles with a reversible capacity of 495.8 mAh g-1 at 0.5 A g-1. For sodium-ion batteries, the nanorodalso exhibits an improved performance with an initial discharge/recharge capacity of 781.4/574.0 mAh g-1 (initial Coulombic efficiency of about 73.46%) and cycling for 400 cycles with a reversible capacity of 422.6 mAh g-1 at 0.8 A g-1. This research sheds light upon double-shell structure designs with an effective middle shell to enhance the energy storage performance of electrode materials.

Yolk-double shells hierarchical N-doped carbon nanosphere as an electrochemical nanoreactor for high performance lithium-sulfur batteries

Rechargeable lithium-sulfur (Li–S) batteries are regarded as one of the most promising emerging energy technology due to their high theoretical capacity and energy density. However, the shuttle effect from the weak adsorption, poor diffusion-transfer, and insufficient catalytic site restrains further applications. Herein, the yolk-double shells hierarchical N-doped carbon nanospheres (NCS@C-800) were designed as an electrochemical nanoreactor, the material consists of high-content N-doped core-shell carbon nanospheres and a highly graphitized outer carbon shell, which has a gradient of N content. The unique structure host has many advantages, such as huge internal voids, ordered pore structure, and high electrical conductivity. In addition to the introduction of the N element, which offered a large number of adsorption and catalytic sites. Therefore, the NCS@C-800 effectively addresses the three above primary issues for constructing high performance Li–S. The results show that at 500 cycles at 1 C, the as-prepared material is 649 mAh g−1, while at 1000 cycles at 2 C it is 400 mAh g−1, with ultra-low capacity decays of 0.055% and 0.051% per cycle, respectively. More importantly, with an increase in S loading up to 5.43 mg cm−2, it still maintained excellent cycling stability. This work offered an effective strategy for high-performance Li–S batteries.

Dual-stable engineering enables high-performance Zn2SnO4-based lithium-ion battery anode

The promising high-capacity anode material of Zn2SnO4 suffers from large volume expansion and poor conductivity during cycle, and hence its practical application in lithium-ion batteries is blocked seriously. Herein, to achieve high capacity and improved cyclic stability of Zn2SnO4-based anode, we introduce a dual-stable engineering strategy that the Zn2SnO4 is encapsulated within a porous carbon shell and a void structure is constructed between the inner Zn2SnO4 and outer carbon shell simultaneously. The as-fabricated Zn2SnO4-based composite is therefore referred to as Zn2SnO4 @[email protected] It is demonstrated that the combined action of the porous carbon and the void effectively suppresses the volume effect of the Zn2SnO4 and enhances the electrochemical kinetics of the electrodes and hence the structural stability and electrochemical kinetics of the Zn2SnO4 @[email protected] are improved significantly. As a result, the Zn2SnO4 @[email protected] delivers 961.5 mA h g−1 after 350 cycles at 200 mA g−1 and 438.2 mA h g−1 after 600 cycles at 1000 mA g−1, thereby having potential application in advanced lithium-ion battery anodes.

Template-free synthesis of flower-like hierarchical vanadium nitride/carbon composites for long cycle-life half and full lithium-ion batteries

Vanadium nitride (VN) is a promising energy storage material due to its high theoretical capacity and good electrical conductivity. However, the unbearable volume expansion due to the lithium insertion impedes its application for lithium-ion batteries (LIBs). Herein, a simple, template-free strategy is developed to synthesize a micron-sized flower-like hierarchical structure made of N-doped carbon layers, embedding VN nanoparticles and outer carbon shell (denoted as VN/[email protected]). Profiting from the unique structure, the VN/[email protected] composite delivers an excellent reversible capacity (601 mA h g−1 at 0.1 A g−1) and ultra-long cycle durability with retention of 92.6% after 5000 cycles at 2 A g−1. More remarkably, the LiCoO2 || VN/[email protected] full LIBs also demonstrate extraordinary long-term cycle stability, retaining 94.8% of the initial capacity after 1300 cycles at 1 A g−1. The excellent electrochemical performance of the composite provides inspirations and strategies for developing new unique hierarchical materials with stable, high-performance properties for commercial use in LIBs.

High-performance Fe–N–C electrocatalysts with a “chain mail” protective shield

Nitrogen-coordinated iron atoms on carbon supports (Fe–N–C) are among the most promising noble-metal-free electrocatalysts for oxygen reduction reaction (ORR). However, their unsatisfactory stability limits their practical application. Herein, we demonstrate a dual-shell Fe–N–C electrocatalyst with excellent catalytic activity and long-term stability. Pyrrole and dopamine are sequentially polymerized on a fumed silica nanoparticle template. Metal precursor (FeCl 3 ) and pore formation agent (ZnCl 2 ) were loaded on the inner polypyrrole shell. During carbonization, the Zn evaporation creates abundant mesopores in the polydopamine-derived outer carbon shell, forming a “chain mail” like outer shell that protects Fe–N–C active sites loaded on the inner carbon shell and enables efficient mass transfer. Systematical tuning of the shield thickness and porosity affords the optimal electrocatalyst with a large surface area of 934 ​m 2 ​g −1 and a high Fe loading of 2.04 ​wt%. This electrocatalyst delivers excellent ORR activity and superior stability in both acidic and alkaline electrolytes. Primary Zn-air batteries fabricated from this electrocatalyst delivers a high-power density of 257 ​mW ​cm −2 and impressive durability of continuous discharging over 250 ​h. Creating a graphitic and porous carbon protective shell can be further extended to other electrocatalysts to enable their practical applications in energy conversion and storage.

Core-Shell CoSe2 /WSe2 Heterostructures@Carbon in Porous Carbon Nanosheets as Advanced Anode for Sodium Ion Batteries.

Heterojunction, with the advantage of fast charge transfer dynamics, is considered to be an effective strategy to address the low capacity and poor rate capability of anode materials for sodium-ion batteries (SIBs). As well, carbonaceous materials, as a crucial additive, can effectively ameliorate the ion/electron conductivity of integrated composites, realizing the fast ion transport and charge transfer. Here, motivated by the enhancement effect of carbon and heterojunction on conductivity, it is proposed that the CoSe2 /WSe2 heterojunction as inner core is coated by carbon outer shell and uniformly embedded in porous carbon nanosheets (denoted as CoSe2 /WSe2 @C/CNs), which is used as anode material for SIBs. Combining with density functional theoretical calculations, it is confirmed that the structure of heterojunction can introduce built-in electric-field, which can accelerate the transportation of Na+ and improve the conductivity of electrons. Moreover, the introduction of porous carbon nanosheets (CNs) can provide a channel for the transportation of Na+ and avoid the volume expansion during Na+ insertion and extraction process. As it is expected, CoSe2 /WSe2 @C/CNs anode displays ultrastable specific capacity of 501.9mAhg-1 at 0.1Ag-1 over 200 cycles, and ultrahigh rate capacity of 625mAhg-1 at 0.1Ag-1 after 100cycles.

Mixed transition-metal oxides@carbon core-shell nanostructures derived from heterometallic clusters for enhanced lithium storage

Multicomponent binary metal oxide-involved hybrid structures with unique physicochemical properties have received extensive attention due to their fascinating electrochemical performance. Herein, a flexible strategy, which involves the preparation of dual-functional heterometallic Fe2M clusters and their subsequent sintering treatment, is developed to engineer novel 3D hierarchical porous structures assembled with MFe2O4 (M = Co, Mn, Ni and Zn) nanoparticles confined within carbon outer shell (denoted as MFe2O4@C HPSs). In this intriguing construction, it can be observed that MFe2O4@C HPSs comprised of carbon coated secondary MFe2O4 nanoparticles with an interconnected carbon network. The as-prepared MFe2O4@C HPSs possess combined advantages of high capacity of MFe2O4 and high conductivity of carbon. As expected, the MFe2O4@C HPSs offer a high reversible capacity, high cycling stability and superior rate performance. The interconnected conductive carbon shells facilitates fast ion and electron transport and accommodates the mechanical strain. In addition, nanosized MFe2O4 particles, which shorten the ion-transport path and provide extra electroactive sites, also improve the reaction kinetics. Moreover, these MFe2O4@C HPSs exhibit good structural integrity during repeated charging and discharging. The research perspective and strategy reported here are highly versatile and shed new light on the synthesis of other advanced electrode for various applications.

Metal-organic frameworks-derived CoMOF-D@Si@C core-shell structure for high-performance lithium-ion battery anode

Silicon (Si) is considered as the most promising candidate for anode materials in the next-generation lithium-ion batteries (LIBs). Regulating the morphology and structure of Si plays a vital role in alleviating the volume expansion and improving electronic conductivity. Herein, an ingenious core-shell structure (denoted as CoMOF-D@Si@C) is synthesized by depositing Si uniformly on the pyrolytic metal-organic frameworks (MOFs) via chemical vapor deposition (CVD) method and then encapsulated with a carbon shell. The CoMOF-D@Si@C exhibits excellent rate capability and cycle performance, which delivers a high-rate capability of ~957 mAh g−1 at 10 A g−1 and a reversible capacity of 1493 mAh g−1 after 400 cycles. In particular, the capacity is maintained at 648 mAh g−1 after 1200 cycles at a high current density of 4 A g−1 with a rapid increase of the Coulombic efficiency (CE) to 99.8% after only 5 cycles and the average CE (99.7%) in the whole cycling at 4 A g−1. Profiting from the outer carbon shell, uniform Si deposition and inner porous pyrolytic MOF structure, this architecture can maintain structural stability and provide constructive conductivity during cycling processes. The superior electrochemical performance of the CoMOF-D@Si@C composite makes it a promising anode material for LIBs.

Controllable Preparation of Core-Shell Composites and Their Templated Hollow Carbons Based on a Well-Orchestrated Molecular Bridge-Linked Organic-Inorganic Hybrid Interface.

Controlling the interfacial effect is facing challenges because of the weak interactions between the inorganic and the organic materials. We found that the silane coupling agents with -NH2 groups (e.g., KH550) play a key role as a molecular bridge that links an inorganic silica template with an organic precursor (i.e., pyrrole) in the process of constructing a spherical silica core-polypyrrole shell structure. The molecular bridge is also suitable for inorganic core templates with cube or rod shapes for the construction of different core-shell structures. These template core-polymeric shell structures can be transformed into well-defined hollow carbons after carbonization and template removal. The outer diameter, hollow-core size, and carbon shell thickness of hollow carbon materials (e.g., hollow carbon spheres) could be facilely controlled by changing the template size or the pyrrole amount. We believe that our work will provide a guideline for the preparation of well-orchestrated carbon-based composites and their templated hollow carbons.

Rational design and in-situ formation of nickel–cobalt nitride multi-core/hollow N-doped carbon shell anode for Li-ion batteries

• Nickel–cobalt nitrides with unique multi-core/shell nanostructure are proposed. • Multi-core/shell nanostructures are successfully formed via in-situ thermal annealing process. • Hierarchical composite anodes deliver superior performance for Li-ion batteries. • Structural and morphological evolution at different electrochemical states is elucidated. The construction of a carbon-encapsulated multi-core nanostructure based on transition metal nitride is a preferred approach to efficiently mitigate volume expansion with improved sustainability and to enhance conductivity with more active sites for Li-ion cell reaction. Herein, we report the in-situ formation of carbon-coated nickel–cobalt nitride multi-core nanoparticles encapsulated by hollow N-doped carbon shell via monodispersed Ni 3 [Co(CN) 6 ] 2 Prussian blue analogue/polydopamine precursors using by simultaneous nitridation and calcination process. The (Ni/Co) 3 N multi-core nanoparticles (Ni:Co = 3:2) were highly dispersed in conductive and hollow N-doped carbon shell, thereby (i) mitigating mechanical stress by volume change during the conversion reaction of nitrides, (ii) stabilizing the electrochemical reaction surface with a thin solid electrolyte interphase, and (iii) maintaining the original structure and hierarchical morphologies even after long cycles. The (Ni/Co) 3 N multi-core@hollow N-doped carbon shell demonstrated better electrochemical performance than the (Ni/Co) 3 N@carbon shell without the outer hollow N-doped carbon shell for the Li-ion battery anode, which has an excellent reversible capacity of ~440 mAh g −1 and a stable cycle life of 130 cycles at 200 mA g −1 . The rational synthetic strategy of the unique hybrid nanoarchitecture via in-situ formation of polymer-coated metal–organic frameworks is key in improving the Li-ion storage capacity and cycle stability.

Yolk-shell Si@void@C composite with Chito-oligosaccharide as a C–N precursor for high capacity anode in lithium-ion batteries

The yolk-shell structure of Si@void@C anode for lithium ion batteries with Chito-oligosaccharide (COS) as carbon and nitrogen source was successfully prepared by using a newly designed method. As a low-molecular-weight precursor, COS is completely soluble in an aqueous solution to make the composite more homogeneous. The COS derived carbon has a higher porosity than macromolecules derived carbon, providing reliable channels for ions to shuttle. In addition, amino groups from COS effectually promote the wettability of electrode interface. For the yolk-shell structure of Si@void@C composite, the outer carbon shell is not only conducive to the rapid transmission of electrons and lithium ions, but also to the reduction of charge transfer resistance and effective protection of the silicon core ball from electrolyte corrosion. Furthermore, the void layer between silicon core and carbon shell can adapt to huge volume expansion of Si and stabilize the electrode structure. Therefore, Si@void@C exhibits superior cycle stability and high rate performance. At a current density of 420 mA g−1, after 200 cycles, the Si@void@C maintains a high capacity of 1038.5 mAh g−1. In this experiment, the innovative synthesis of a unique yolk-shell structure of Si@C composites is an effective way to obtain high-performance anode materials.

Zeolitic imidazole framework derived N-doped porous carbon/metal cobalt nanoparticles hybrid for oxygen electrocatalysis and rechargeable Zn-air batteries.

Bifunctional electrocatalysts with high catalytic property for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are vital for high-performance zinc–air batteries (ZnABs). In this study, an efficient bifunctional electrocatalyst with hollow structure (C–N/Co (1/2)) has been successfully prepared through carbonization of ZIF-8@ZIF-67 and evaporation of Zn ions at high temperature. With Co nanoparticles encapsulated by an N-doped porous carbon matrix, the catalyst exhibits excellent stability in aqueous alkaline solution over an extended period and good tolerance to the methanol crossover effect. The integration of an N-doped graphitic carbon outer shell and Co nanoparticles enables high ORR and OER activity, as evidenced by ZnAB using the catalyst C–N/Co (1/2) in an air cathode.

Pomegranate-like silicon-based anodes self-assembled by hollow-structured Si/void@C nanoparticles for Li-ion batteries with high performances

Silicon is considered as one of the most promising alternatives to the graphite anode for lithium-ion batteries due to its high theoretical capacity (4200 mAh g−1). However, its fragile solid electrolyte interphase cannot tolerate the large volume changes of bare silicon induced by the lithium insertion and extraction, resulting in low Coulombic efficiency. In previous reports, a yolk-shell design, such as Si@void@C, in which the well-defined space allows the silicon particles to expand freely without breaking the outer carbon shells, can effectively improve the Columbic efficiency. Here, we design a pomegranate-like silicon-based anodes self-assembled by the hollow-structured Si/void@C nanoparticles, in which silicon and some voids are together sealed in the outer carbon shells, by the magnesiothermic reduction of the colloidal SiO2@PEI nanospheres prepared by the hydrolysis of the tetraethoxysilane under the catalytic effect of polyetherimide (PEI). Due to the tolerance of the presealed void in the carbon shells of the primary hollow-structured Si/void@C nanoparticles, the prepared pomegranate-like silicon-based anodes deliver a high reversible capacity of 1615 mAh g−1 at 0.1 C and long cycle life of 73.5% capacity retention at 2 C after 500 cycles, as well as high Coulombic efficiency of 99%.

A sector deposition mechanism of carbon onions operated in a large discharge furnace

Due to the lack of comprehensive understanding of the formation mechanism, the preparation of carbon onions by arc discharge is still an uncontrollable process, which restrains their massive and stable production. Taking advantage of the transient nature of the arc discharge, we successfully captured the nanoparticle morphology in each growing stage during the carbon onion formation process in a large discharge furnace with chamber radius of 22.5 cm. Scanning electron microscope images of raw soot show that massive spherical aggregations are enriched in nanoparticles, and high-resolution transmission electron microscope images reveal fairly heterogeneous nanoparticles which are corresponding to varying growing stages of carbon onions. It is proposed that the change from the well-ordered graphite to another ordered polyhedral and nickel-encapsulated carbon onions is via a non-crystalline intermediate state, and carbon onions begin to deposit through a novel sector mechanism, i.e. the inner and outer carbon shells are simultaneously precipitated and grow away from or along the catalyst surface to form a polyhedral or metal encapsulated carbon onion, respectively.

Numerical Development of Concentric Cylinder‐Shaped Dual‐Functional Catalyst Structure for Enhanced Charge Transport in Polymer Electrolyte Fuel Cells

AbstractDual‐functional catalyst bilayers of vertical concentric cylinders are proposed and numerically developed using a stochastic modeling approach to improve catalyst utilization for advanced fuel cell applications. A cylindrically bilayered catalyst structure wherein the ion transport materials are confined by concentric outer carbon shells is adopted to increase the number of interconnected electron and ion transport paths. For reliable statistical analysis, each data point is extracted from a set of 25 catalyst layer models to achieve a 95% confidence level. The nanoscale morphologies of the ionomers, including interconnected ion transport networks, surface coverage, and electrochemically active surface areas, are quantitatively evaluated. The statistical investigations reveal that the bilayered cylindrical catalyst structures provide more uniform and improved transport paths for ions and reactants when compared with established catalyst layers. Specifically, the additional ion transport channels in the core of the concentric vertical cylinder enhance catalyst utilization under insufficient ionomer conditions. Furthermore, the bilayered catalyst structures yield remarkably enlarged electrochemically active surface areas, hence facilitating more efficient electron, ion, and reactant transfers to improve catalyst utilization.

Nanocable with thick active intermediate layer for stable and high-areal-capacity sodium storage

Developing electrodes cycling stably at high areal mass loadings is critical for sodium ion batteries (SIB) to reach practical applications, but remains challenging due to the larger ionic radius of Na + and generally sluggish electrochemical kinetics in thick electrodes. Consequently, most of the reported SIB electrodes exhibit low mass loadings (<1 mg cm −2 ) and thereby limited areal capacities. Here, we develop a hybrid network structure with orthorhombic Nb 2 O 5 coatings sandwiched between three-dimensional carbon nanotube (CNT) underlayers and outer carbon shells. By thickening Nb 2 O 5 intermediate layers, we can effectively raise the mass loadings of the sponge anodes with the electron and ion transport kinetics well maintained, owing to the highly conductive CNT substrate, porous network and carbon shell-enabled robust nanocable structures. As a result, the sponge anodes exhibit reversible areal capacities of 2.7 mAh cm −2 after 200 cycles at mass loadings up to 16.6 mg cm −2 , exceeding 9 times those of previous Nb 2 O 5 -based structures, and the achieved cycling stability is also among the best of the high-areal-capacity SIB anodes reported so far. Our work shows that thickening intermediate active coatings in rationally designed nanocable structures represents an effective way to promote their areal sodium storage performance for practical use. • Three-dimensional network structured electrode composed of interconnected nanocables. • Nanocable comprises carbon nanotube core, Nb 2 O 5 intermediate layer and carbon shell. • Thickening intermediate layer to raise electrodes mass loadings and areal capacities. • Robust hierarchical structure enables stable cycling performance for sodium storage.

Building a Cycle-Stable Fe-Si Alloy/Carbon Nanocomposite Anode for Li-Ion Batteries through a Covalent-Bonding Method.

Si is being intensively developed as a safe and high-performance anode for next-generation Li-ion batteries (LIBs); however, its battery application still remains challenging because of its low cycling Coulombic efficiency. To address this issue, we chose a conjugated polymer, polynaphthalene, as a carbon precursor and a low-cost commercial ferrosilicon (Fe-Si) alloy as the active phase to prepare a Fe-Si/C nanocomposite with a core-shell-like architecture through sand milling-assisted covalent-bonding method, followed by a carbonization reaction, thus forming a covalently bonded carbon coating on the surfaces of Fe-Si alloy nanoparticles. Benefitting from the greatly reduced volumetric expansion of Fe-Si alloy cores in the lithiation process and the stable interface provided by the outer carbon shell, the thus-prepared Fe-Si/C nanocomposite exhibits a high structural stability in repeated charge/discharge cycles. The experimental results reveal that the Fe-Si/C composite anode can demonstrate a high reversible capacity of 1316.2 mA h g-1 with an active mass utilization of 82.6%, a long-term cycle stability of more than 1000 cycles even at a considerably high current rate of 2.0 A g-1, and, in particular, a high cycling Coulombic efficiency of 99.7%, showing great prospect for application in practical LIBs.

Yolk-shell structure MnO2@Hollow carbon nanospheres as sulfur host with synergistic encapsulation of polysulfides for improved Li–S batteries

Abstract Increasing the sluggish redox reactions of soluble lithium polysulfides (LiPSs) and suppressing their shuttle effect are the key challenges for lithium-sulfur (Li–S) batteries with long-term cyclic stability. Herein, an integrated design of hollow carbon nanospheres filled by polar manganese oxide (δ-MnO2) nanoflakes (MnO2@HCS) as a sulfur host is proposed, in which the physical confinement and chemical interaction for LiPSs are successfully achieved simultaneously. In this architecture, the outer porous carbon shell can support the fast electron/ion transfer and serve as a physical barrier to confine the soluble LiPSs. Besides, the hollow architecture can accommodate the active sulfur and buffer its volume variation during cycling. Moreover, the inner polar MnO2 nanoflakes can trap and boost the redox reactions of LiPSs through thiosulfate-polythionate conversion leading to inhibited shuttle effect. Due to the unique synergistic encapsulations, the MnO2@HCS-S cathode achieves a high initial specific discharge capacity of 1250 mAh g−1, and exhibits a stable cyclic property maintaining 705 mAh g−1 after 500 cycles at 1.0C corresponding to an ultralow capacity decay of 0.078% per cycle. As a result, this proposed strategy will guide a new direction for the development of polar metal compounds with special architectures for advanced Li–S batteries.

Confining FeS in graphitized carbon with void space for high and stable electrochemical storage performance of Na + and K +

Ferrous sulfides have high theoretical capacity in the electrochemical storage of Na-ion and K-ion, but its obvious volume change during the storage process greatly affects its cycling performance at high current density. In this regard, we construct a unique composites structure of Nitrogen-doped carbon shell coated FeS nanoparticle with inner void spaces. As an anode in Na-ion and K-ion batteries, this structure could provide excellent cycling performance at high rate of charge/discharge process (560 mAh/g at 0.5 A/g for 300 cycles in Na-ion battery and 322 mAh/g at 1 A/g for 300 cycles in K-ion battery). Further research finds the inner void space could not only provide buffer space for the volume change of FeS nanoparticles, but also maintain a stable outer carbon shell during the electrochemical process. These behaviors greatly promote the reversibility of FeS at high rate charge transfer process. Consequently, the construction of inner void space in graphitized carbon shell in this work could be considered as an important reference for the promotion of electrochemical storage in other transitional metal compound system.

Evaporation-induced formation of hollow bismuth@N-doped carbon nanorods for enhanced electrochemical potassium storage

Metal bismuth (Bi) is recognized as an attractive anode material for potassium ion batteries in virtue of its good conductivity and relatively low working potential. However, the large volume expansion during the discharge/charge process leads to poor cycling stability. Herein, Bi nanorods encapsulated in nitrogen-doped carbon nanotubes (hollow Bi@C nanorods) are fabricated via in-situ reduction and carbonization of polydopamine-coated Bi2S3 nanorods and the following partial evaporation of Bi. Benefiting from the robust hollow structure and outer conductive carbon shells, the hollow Bi@C nanorods electrodes achieve a high reversible capacity of about 353 mAh g−1 at 0.05 A g−1 and good cycling stability with a capacity retention of 80.3% over 300 cycles at 0.5 A g−1. Moreover, by pairing the hollow Bi@C anode and potassium Prussian blue cathode, the K-ion full cell exhibits a high capacity retention of 88.6% after 100 cycles.