High-performance Anode For Sodium-ion Batteries Research Articles

Biomass-derived hard carbon material for high-capacity sodium-ion battery anode through structure regulation

Economical and environmentally friendly hard carbon materials are attractive options for high-performance sodium-ion battery anode materials. Biomass-derived hard carbon materials have good economic benefits and environmentally friendliness as anode materials for sodium-ion batteries. In this work, we propose a new hard carbon material prepared from agricultural waste olive shells through a simple and environmentally friendly process. The effects of high-temperature treatments and pre-carbonization strategies on the pore structure and graphitization degree of the hard carbon materials were investigated. Combined with electrochemical performance tests, the influence of structural changes on the sodium storage properties of the olive shell-derived hard carbon was revealed. Under the optimized conditions of carbonization temperature and pre-carbonization strategy, the OSHC-Air electrode exhibits excellent sodium storage capacity with 87 % capacity remaining after 1000 cycles at 1000 mA g−1. The assembled PB//OSHC-Air sodium-ion full cell exhibits a high capacity of 216 mAh g−1. Our research provides a potential candidate for commercial anode materials for high-capacity sodium-ion batteries.

CVD-Synthesized Titanium Carbide Nanoflowers as High-Performance Anodes for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have emerged as promising candidates for energy storage applications due to the abundance and low cost of sodium. However, the larger radius of sodium ions limits their diffusion kinetics within electrode materials and contributes to electrode volume expansion. Here, we successfully synthesized porous titanium carbide (TiC) nanoflowers through chemical vapor deposition (CVD). The TiC nanoflowers exhibit exceptional electrochemical performance as SIB anodes, with their porous structure enhancing the conductivity, mechanical stability, and Na-ion diffusion. The TiC nanoflowers demonstrate a high reversible specific capacity of 73.5 mAh g-1 at 1 A g-1 after 2500 cycles, corresponding to an impressive capacity retention of 80.81%. Additionally, we developed a full sodium-ion cell utilizing TiC nanoflowers as the anode and Na3V2(PO4)3 as the cathode, which demonstrates a substantial reversible capacity and outstanding cycling stability. Our work presents a promising strategy for synthesizing nanostructured TiC materials as anode electrodes for SIBs.

Nanoarchitectured Fe3C@N-Doped C/FeVO4 as High-Performance Anode for Sodium-Ion Batteries.

Ferric vanadate exhibits potential as an attractive anode material for sodium-ion batteries (SIBs) due to the multiple oxidation states of vanadium and natural abundances of iron. However, the design and fabrication of high-performance ferric vanadate-based SIB anode materials with unique composite nanostructures are still challenging. Herein, a facile self-template method is reported to synthesize 1D nanostructured Fe3C@N-doped C/FeVO4 (Fe3C@NC/FeVO4) anode materials by the combination of morphology regulation with hybrid composite construction, for the first time. To this end, a 1D Fe, N-doped carbon nanotube (FeNC) is used as a template, followed by etching and re-growth to obtain the 1D Fe3C@N-doped C/FeVO4 nanostructure. The introduction of Fe3C can improve its electronic conductivity and enhance capacitive behavior. Additionally, the 1D nanostructure can effectively shorten the ions transport path and alleviate volume expansion during the charge-discharge processes. With these advantages, the SIBs using such anodes show a remarkable rate performance with a capacity of 325.4mAhg-1 at 0.1Ag-1, 150.6mAhg-1 at 5Ag-1, and excellent cycling stability with a reversible capacity of 139.6mAhg-1 at 1Ag-1 after 1500 cycles. This work offers a new strategy for the future development of SIBs with ferric vanadate-based anode.

Pomegranate Peel-Derived Hard Carbons as Anode Materials for Sodium-Ion Batteries.

Exploring high-performance carbon anodes that are low-cost and easily accessible is the key to the commercialization of sodium-ion batteries. Producing carbon materials from bio by-products is an intriguing strategy for sodium-ion battery anode manufacture and for high-value utilization of biomass. Herein, a novel hard carbon (PPHC) was prepared via a facile pyrolysis process followed by acid treatment using biowaste pomegranate peel as the precursor. The morphology and structure of the PPHC were influenced by the carbonization temperature, as evidenced by physicochemical characterization. The PPHC pyrolyzed at 1100 °C showed expanded interlayer spacing and appropriate oxygen group content. When used as a sodium ion battery anode, the PPHC-1100 demonstrated a reversible capacity of up to 330 mAh g-1, maintaining 174 mAh g-1 at an increased current rate of 1 C. After 200 cycles at 0.5 C, the capacity delivered by PPHC-1100 was 175 mAh g-1. The electrochemical behavior of PPHC electrodes was investigated, revealing that the PPHC-1100 possessed increased capacitive-controlled energy storage and improved ion transport properties, which explained its excellent electrochemical performance. This work underscores the feasibility of high-performance sodium-ion battery anodes derived from biowaste and provides insights into the sodium storage process in biomass-derived hard carbon.

Steric Hindrance Engineering to Modulate the Closed Pores Formation of Polymer-Derived Hard Carbon for High-Performance Sodium-Ion Batteries.

The closed pores play a critical role in improving the sodium storage capacity of hard carbon (HC) anode, however, their formation mechanism as well as the efficient modulation strategy at molecular level in the polymer-derived HCs is still lacking. In this work, the steric hindrance effect has been proposed to create closed pores in the polymer-derived HCs for the first time through grafting the aromatic rings within and between the main chains in the precursor. The experimental data and theoretical calculation demonstrate that steric-hindrance effect from the aromatic ring side group can increase backbone rigidity and the internal free volumes in the polymer precursor, which can prevent the over graphitization and facilitate the formation of closed pores during the carbonization process. As a result, the as-prepared HC anode exhibits a remarkably enhanced discharge capacity of 340.3 mAh/g at 0.1 C, improved rate performance (210.7 mAh/g at 5 C) as well as boosted cycling stability (86.4 % over 1000 cycles at 2 C). This work provides a new insight into the formation mechanisms of closed pores via steric hindrance engineering, which can shed light on the development of high-performance polymer-derived HC anode for sodium-ion batteries.

Unravelling the anionic stability of an ether-based electrolyte with a hard carbon or metallic sodium anode for high-performance sodium-ion batteries

In hard carbon (HC) anodes, elucidating the relationship between the solid electrolyte interphase formation and the solvated Na+ co-intercalation mechanism is crucial, particularly considering different anionic salts in ether-based electrolytes. Here, we comprehensively explore the impact of different anionic salts on the electrochemical performance of HC/Na half-cell and elucidate the underlying mechanism through experimental studies and theoretical calculations. The surface morphology of the HC anode and its interphasial property are further investigated to evaluate the differences endowed by the presence of various anionic salts in diglyme (2G). The HC/Na half-cells with NaPF6-2G and sodium trifluoromethanesulfonate (NaCF3SO3)-2G display superior electrochemical performance with faster kinetics and lower interfacial resistance than those with NaClO4-2G, sodium bis-(fluorosulfonyl) imide (NaFSI)-2G and sodium bis-(trifluoromethanesulfonyl) imide (NaTFSI)-2G. NaClO4-2G forms a relatively thick interphase layer with high resistance at the electrode/electrolyte interface owing to its insufficient stability. NaFSI-2G and NaTFSI-2G exhibit severe side reactions with Na metal, producing a thick interphase layer on the HC surface with high interfacial resistance from excess electrolyte decomposition, thus deteriorating the electrochemical performance. In summary, the study on the stability of different anionic salts in ether-based electrolyte for the HC anode with the intercalation mechanism provides valuable insights for screening appropriate conductive salts for high-performance sodium-ion batteries, especially when considering Na metal counter/reference electrodes.

Dual carbon confining SnO2 nanocrystals as high-performance anode for sodium-ion batteries

The increasing global demand for sustainable energy sources has driven research into sodium-ion batteries (SIBs) for large-scale energy storage. However, their electrochemical performance is hindered by poor reaction kinetics and significant volume expansion in electrode materials. In this work, we developed a dual-carbon-confined SnO2 nanocrystal anode (CNTs@SnO2@NC) designed for high-performance SIBs. This innovative structure uses carbon nanotubes (CNTs) and a nitrogen-doped carbon (NC) coating to stabilize SnO2, ensuring structural integrity during charge/discharge cycles. The CNTs network in CNTs@SnO2@NC can alleviate the agglomeration of SnO2 nanocrystals to a certain extent; With its superior electronic conductivity, CNTs can enhance the anode's conductivity and function as an electronic highway; The sodiophilic properties and good electrical conductivity of CNTs enable sodium ions to migrate rapidly on the surface of the nanotubes. Moreover, numerous external defects and active sites generated by nitrogen doping enhance the sodium ion absorption capabilities; The existence of nitrogen-doped carbon coating can effectively accommodate the volume changes of SnO2 and enhance the structural stability of CNTs@SnO2@NC composites during the repeated charge and discharge cycles. As a result, the CNTs@SnO2@NC composite demonstrates excellent electrochemical performance, achieving capacity of 235 mAh g−1 at 0.1 A g−1 over 100 cycles and 102 mAh g−1 at 1.0 A g−1 over 300 cycles. In a full-cell configuration with a Na3V2(PO4)3 cathode, it delivers 38 mAh g−1 at 100th cycle at 0.1 A g−1. This study underscores the substantial improvements achieved by dual-carbon confinement for high-performance SIB anodes, offering a promising direction for future anode material design.

Microcrystalline Engineering of Anthracite-Based Carbon Via Salt-Assisted Ball Milling for Enhanced Sodium Storage Performance.

Coal-based carbon material, characterized by abundant resources and low cost, has gained considerable interests as a promising anode candidate for sodium-ion batteries (SIBs). However, the coal-based carbon generally shows inferior Na-storage performance due to its highly-ordered microstructure with narrow interlayer spacing. Herein, a salt-assisted mechanical ball-milling strategy is proposed to disrupt the polycyclic aromatic hydrocarbon structure in anthracite molecules, thereby reducing the microcrystalline regularity of the derived carbon during following pyrolysis process. In addition, the induced C─O─C bonds during ball-milling process can alter the pyrolysis behavior of anthracite and restrain the formation of surface defects. Consequently, in contrast to pristine anthracite-based pyrolytic carbon, which exhibits a Na-storage capacity of 198.4 mAh g-1 with a low initial Coulombic efficiency (ICE) of 65.1%, the ball-milling modified carbon assisted by NaCl salt (NAC), with enhanced structural disordering and reduced surface defects, demonstrate significantly improved Na-storage capacity of 332.1 mAh g-1 and ICE value of 82.0%. The NAC electrode also realizes excellent cycle and rate performance, retaining a capacity of 196.0 mAh g-1 at 1 C after 1000 cycles. Furthermore, when coupled with NaNi1/3Fe1/3Mn1/3O2 cathode, the assembled Na-ion full cell deliveres an exceptional electrochemical performance, highlighting its promising prospect as high-performance anode for SIBs.

Liquid Gallium-Assisted Pyrolysis of MOF Affording CNT Non-Hollow Frameworks in High Yields for High-Performance Sodium-Ion Battery Anode.

Carbon materials have great potential for applications in energy, biology, and environment due to their excellent chemical and physical properties. Their preparation by carbonization methods encounters limitations and the carbon loss during pyrolysis in the form of gaseous molecules results in low yield of carbon materials. Herein a low-energy (600°C) and high-yield (82wt.%) carbonization strategy is developed using liquid gallium-assisted pyrolysis of metal-organic frameworks (MOFs) affording the N-doped carbon nanotube (CNT) non-hollow frameworks encapsulating Co nanoparticles. The liquid gallium layer offers protection against air, promotes heat transfer, and limits the escape of small carbonaceous gaseous molecules, which greatly improve the yields of the pyrolysis reaction. Experimental and theoretical results reveal that the synergistic interaction between CNTs and N/O-containing groups gives a non-hollow framework composed of N/O-enriched and open CNTs (NOCNTF-15, 15 denotes the 15mm thickness of the liquid gallium layer during the pyrolysis) with high specific capacity (185mAhg-1 at 10Ag-1) and ultra-stable cyclability (stable operation at 10Ag-1 and 50°C for 20000 cycles). This study provides a unique approach to carbonization that facilitates the practical application of low-cost CNTs and other MOFs-derived carbon materials in high-performance sodium-ion batteries (SIBs).

CoO nanoparticles anchored on porous pinecone-derived activated carbon as anodes for high-performance lithium and sodium-ion batteries

In this work, a new nanocomposite system based on CoO nanoparticles (NPs) anchored on pinecone-derived activated carbon (PAC), denoted as CoO(x)@PAC, is synthesized by facile ball-milling and sonication processes followed by annealing. H3PO4 is employed as an activation agent to activate the porous carbon derived from pinecone. The loading amount of CoO is varied to obtain the optimum electrochemical performances. Among the nanocomposites, the CoO(20)@PAC delivers a discharge capacity of 886 mA h g−1 after 100 cycles at a current density of 100 mA g−1 when employed as an anode in lithium-ion batteries (LIBs). At higher current rate of 1000 mA g−1, the anode provides an enhanced discharge capacity of 456.6 mA h g−1 after 200 cycles with 99 % capacity retention compared to the 4th cycle capacity. In sodium-ion batteries (SIBs), the CoO(20)@PAC anode delivers a discharge capacity of 290 mA h g−1 at 50 mA g−1. The same nanocomposite anode provides a discharge capacity of 120 mA h g−1 after 900 cycles at a current density of 500 mA g−1. The CoO(20)@PAC nanocomposite shows a great potential as an anode for both LIBs and SIBs, due to its higher capacity, exceptional rate capability, longer cycle life, and a Coulombic efficiency exceeding 99 %.

Synergistic effect of in-situ carbon-coated mixed phase iron oxides and 3d electrode architectures as anodes for high-performance sodium-ion batteries

Due to the high theoretical capacity, iron-oxide-based Fe2O3 (1007 mAh g−1) and Fe3O4 (926 mAh g−1) materials can be a promising conversion-type anode material for Sodium-ion batteries (SIBs). However, the low electronic conductivity (10−14 S cm−1) and 200% volume expansion of iron oxide lead to poor cycle life and capacity retention, limiting its commercial application. In this work, carbon-coated mixed-phase iron oxide C-Fe2O3-Fe3O4 (C-IO) was synthesized by pyrolysis using ferrocene precursor. Subsequently, a 3D carbon fiber (CF) network was introduced to improve the electrochemical performance of the material by resolving the volume expansion and pulverization issues. Both the CF network and Fe3O4 provide an electron transport pathway. The conventional Cu-C-IO electrodes deliver a 2nd cycle capacity of 335 mAh g−1 at 250 mA g−1 and exhibit 61.5% capacity retention after 500 cycles. In contrast, the 3D-CF-based IO electrodes show 2nd cycle capacity of 607 mAh g−1 at 50 mA g−1 with 96.4% capacity retention after 35 cycles and 420 mAh g−1 with ∼85.4% capacity retention after 500 cycles at 250 mA g−1 (w.r.t. CF and C-IO active mass, CF contribute ∼ 27% and C-IO ∼ 73% capacity), making it a potential anode for SIBs.

Rational design of mangosteen-like bismuth nanospheres coated by N-doped carbon shell as superb composite anode for high-performance sodium-ion batteries

Metallic bismuth (Bi) anode materials are promising candidates for alkali-ion batteries due to its high theoretical gravimetric/volumetric capacity. However, the pronounced volume change from Bi to full sodiation phase Na3Bi, inducing the structural collapse, and ionic conduction interruption upon cycling, hinders their implementation in sodium-ion batteries (SIBs). Herein, a mangosteen-like bismuth nanosphere coated by N-doped carbon shell (Bi@NC) was designed and synthesized to address these limitations. Due to the nanosize of Bi core and in situ, generated N-doped carbon shell, this Bi@NC anode can not only effectively accommodate the volume change during the alloying/dealloying process but also provide high-speed channels for electron/ion transport to the highly active bismuth nanospheres. The Bi@NC electrode exhibits outstanding cycling stability (1000 cycles at 5 A g−1 with an impressive capacity retention of 96.5 %) and rapid sodium storage performance (392.8 mAh g−1 at 20 A g−1). Importantly, ex-situ techniques and kinetic analysis have revealed the distinctively sharp multiphase transitions and the “battery-capacitor dual-mode” sodium-storage mechanism. This research introduces a new approach to enhance the performance of bismuth-based anodes in advanced SIBs and demonstrates potential for practical applications.

3D MoS2/graphene oxide integrated composite as anode for high-performance sodium-ion batteries

Sodium-ion batteries (SIBs) are emerging as a promising alternative to conventional lithium-ion technology, due to the abundance of sodium resources. The major drawbacks for the commercial application of SIBs lie in the slow kinetic processes and poor energy density of the devices. Molybdenum sulfide (MoS2), a graphene-like material, is becoming a promising anode material for SIBs, because of its high theoretical capacity (670 mAh g–1) and layered structure that suitable for Na+ intercalation/extraction. However, the intrinsic properties of MoS2, such as low conductivity, slow Na+ diffusion kinetics and large volume change during charging/discharging, restrict its rate capability and cycle stability. Here, molybdenum disulfide and graphene oxide (3D MoS2/GO) with excellent conductivity were fabricated through layer-by-layer method using amino-functionalized SiO2 nanospheres as templates. The 3D MoS2/GO composite demonstrates excellent cycling stability and capacity of 525 mA h g–1 at 500 mA g–1 after 100 cycles, which mainly due to the integrated MoS2/GO components and unique 3D macroporous structure, facilitating the material conductivity and Na+ diffusion rate, while tolerating the volume expansion of MoS2 during the charge/discharge processes.

Triphasic heterostructured Zn–Sn–S hollow nanoboxes encapsulated by N, S-codoped carbon as anodes for high-performance sodium-ion batteries

Metal sulfides have been expected huge practical potential for sodium-ion batteries (SIBs), which are mainly owing to their admirable merits of natural abundance, low price, and high theoretical capacity. However, the inferior electrical conductivity and enormous volume variation originating from sodiation/desodiaziton reactions usually result in unsatisfied rate and cycling properties. In this work, a coprecipitation with a following sulfurization method has been rationally designed to prepare the triphasic heterostructured hollow Zn–Sn–S nanoboxes encapsulated by N, S-codoped carbon (ZSS@NCS) as anodes for SIBs. The coexistence of triphasic ZSS heterostructures that consist of ZnS, SnS2, and Sn2S3 effectively facilitates the fast Na + diffusion. The N, S-codoped carbon (NSC) derived from the polydopamine is coated outside of the ZSS heterostructures, which provides infinite affinity between ZSS and NSC that efficiently accelerates the electron transport and maintains the structural stability via the confinement effect. The synergistic effects of the heterostructured ZSS and NSC endow the ZSS@NSC anode with favorable sodium storage properties including decent discharge capacity (683.8 mAh g−1 at 0.1 A g−1), satisfying rate (232.6 mAh g−1 at 10.0 A g−1) and cycling properties (402.2 mAh g−1 over 150 cycles).

CoSe2-Modified multidimensional porous carbon frameworks as high-Performance anode for fast-Charging sodium-Ion batteries

Transition metal selenides (TMSs) possess relatively high theoretical capacity and unique structures emerge as promising anode materials for sodium-ion batteries (SIBs). However, TMSs anode materials suffer from challenges such as substantial volume expansion, undesired side reactions, and poor active reaction dynamics. Herein, we propose a novel synthesis method that integrates metal salt-assisted polymer-blowing technique with in situ selenization strategy to fabricate multidimensional porous 3D carbon nanosheet frameworks modified by cobalt diselenide nanoparticles (CoSe2-CNF). Such unique architecture bestows intimate structural interconnectivity with high mechanical strength and abundant ion diffusion channels on CoSe2-CNF, exhibiting remarkable reversible capacity and fast-charging capability within diverse electrolyte systems. For instance, the CoSe2-CNF anode in ether electrolyte exhibits prominent rate performance of 349 mAh/g at 15 A/g. Sodium storage mechanism and fast electrochemical kinetics in the discharge/charge processes are investigated by in situ XRD and in situ EIS techniques. Additionally, DFT calculations are utilized to analyze the electrochemical differences observed in various electrolyte systems. When coupled with Na3V2(PO4) (NVP) cathodes, the full batteries also afford enhanced reversible capacity of 105 mAh/g over 100 cycles. The proposed structural engineering for CoSe2-CNF is beneficial for designing fast-charging energy storage devices.

Heterostructured Mn-Sn Bimetallic Sulfide Nanocubes Confined in N, S-co-Doped Carbon Framework as High-Performance Anodes for Sodium-Ion Batteries.

Benefiting from its high theoretical capacity, tin disulfide (SnS2) draws abundant interest and attention for its promising practical prospect for sodium-ion batteries (SIBs). However, the huge volumetric variation in sodiation/desodiation reactions usually results in the fast decay of rate and cycling properties, which seriously obstructs its future applicable foregrounds. Herein, heterostructured Mn-Sn bimetallic sulfide nanocubes confined in N and S-codoped carbon (MSS@NSC) were rationally designed via a facile coprecipitation followed by a sulfurization strategy. When used as anodes for SIBs, the heterojunctions at the interfaces effectively accelerate the Na+ diffusion rate to promote the sodium-storage reaction kinetics. The N and S-codoped carbon provides a rapid conductive framework for the fast charge transport during the sodium-storage process. Moreover, the beneficial confinement effect of the NSC layer effectively guarantees a superb cycle property for the MSS@NSC anode. The favorable synergistic effects between the highly conductive framework of the NSC and MSS heterostructure endow the MSS@NSC anode with satisfactory electrochemical Na-storage properties.

Low cobalt single atoms loading on N-doped carbon for high Na storage performance

Cobalt single atoms on nitrogen-doped carbon (CoSAs/N-C) were successfully synthesized through the pyrolysis of metal-organic supramolecular self-template. Only 0.12 wt% metal-doped CoSAs/N-C anodes bring a rate capacity enhancement of 195 mAh g−1 compared to the blank group of nitrogen-doped carbon electrodes at 0.1 A g−1. In addition, the CoSAs/N-C anodes exhibit remarkable sodium-ion storage capacities of 285 mAh g−1 after 2000 cycles at 1.0 A g−1 and 133 mAh g−1 with an exceptional cycling stability for 10,000 cycles at an ultra-high current density of 20 A g−1, thereby showcasing excellent Na ion storage performance. Ex-situ X-ray photoelectron spectroscopic study demonstrates that some N atoms in CoSAs/N-C can reversibly store and release Na ions during discharge and charge cycles. The full cell assembled with CoSAs/N-C anode and Na3V2(PO4)3 cathode displays Coulombic efficiency of >99.7 % after 200 cycles at 0.5 A g−1. Density functional theory (DFT) calculations further reveal that the presence of single-atom Co results in a decrease in the Na binding energy surrounding pyrrolic-N and pyridinic-N structures. This moderate binding energy may be beneficial for Na ion adsorption and desorption. This study opens up new possibilities of fabricating advanced metal single atom anodes for high-performance sodium-ion batteries.

Rapid synthesis of two-dimensional MoB MBene anodes for high-performance sodium-ion batteries

Two-dimensional (2D) transition metal borides (MBenes) have emerged as a rising star and hold great potential promise for catalysis and metal ion batteries owing to a well-defined layered structure and excellent electrical conductivity. Unlike well-studied graphene, perovskite and MXene materials in various fields, the research about MBene is still in its infancy. The inadequate exploration of efficient etching methods impedes their further study. Herein, we put forward an efficient microwave-assisted hydrothermal alkaline solution etching strategy for exfoliating MoAlB MAB phase into 2D MoB MBenes with a well accordion-like structure, which displays a remarkable electrochemical performance in sodium ion batteries (SIBs) with a reversible specific capacity of 196.5 mAh g–1 at the current density of 50 mA g–1, and 138.6 mAh g–1 after 500 cycles at the current density of 0.5 A g–1. The underlying mechanism toward excellent electrochemical performance are revealed by comprehensive theoretical simulations. This work proves that MBene is a competitive candidate as the next generation anode of sodium ion batteries.

Carbon nanotube reinforced FeMoO4 nanorods as a high-performance anode for sodium-ion batteries

Iron molybdate (FeMoO4) nanostructures show great promise as a superior anode for sodium-ion batteries. However, its use in practical application is hampered by its poor electronic conductivity, large volume changes and sluggish reaction kinetics. Herein, we have developed an interconnected network of multiwall carbon nanotube (CNT) and FeMoO4 (FMO) by a simple one-step hydrothermal method. As well as providing efficient channels for charge transfer and diffusion, highly conductive CNTs also have a degree of volume elasticity and excellent electrical conductivity to ensure migration of sodium ions, enabling both fast kinetics and long-term stability. As a result, the FMO@CNT anode delivers a high reversible capacity of 485 mA h g−1 at 0.05 A/g and very long cycling stability with a capacity of 75 mA h g−1 after 1000 cycles at 1 A/g. Furthermore, by combining the ex-situ X-ray diffraction, ex situ X-ray photoelectron spectroscopy and cyclic voltammetry results, sodium ion storage mechanism of the FMO@CNT electrode obeys a conversion mechanism. The results of this work provide a better understanding on the sodium ion storage mechanism of binary metal oxides.

Vanadium nitride induced method to construct cobalt sulfides homologous heterojunction toward ultrafast and high-capacity sodium-ion storage

In recent years, heterojunction has attracted widespread attention as an anode for sodium-ion batteries since they can effectively optimize the materials’ rate performance and cycling stability. However, the advantage is choked by multi-element composition and stepwise synthesis process. Herein, cobalt sulfide (Co9S8/CoS) homologous heterojunction deposited at vanadium nitride/carbon nanofibers is synthesized as an excellent anode for high-performance sodium-ion batteries in one step by employing the “3d-orbital electron complementary effect” combined with high-temperature heat-treatment technology. The Co9S8/CoS homologous heterojunction successfully overcomes the inherent drawback of Co9S8 and possesses an ultrafast charging/discharging process, outstanding reversible specific capacity, and remarkable rate capability. A systematic study reveals that vanadium nitride is a key trigger for forming Co9S8/CoS heterojunction. When used as anode materials for sodium-ion batteries, it reaches a high specific capacity of 353.0 mAh/g at a current density of 10 A/g (615.8 mAh/g at a current density of 0.05 A/g) due to the presence of heterointerface. Theoretical calculations show that the construction of the heterostructure enhances the sodium-ion storage capacity and storage kinetics compared with pristine Co9S8. This discovery opens an interesting strategy for constructing homogeneous heterojunctions and broadens the horizons for designing energy storage and conversion materials.