Sodium-ion Storage Properties Research Articles

Three-dimensional nitrogen-doped dual carbon network anode enabling high-performance sodium-ion hybrid capacitors

It is urgent for sodium-ion hybrid capacitors (SIHCs) to exploit a porous carbon anode that integrates high reversible specific capacity, rapid kinetics and superb cyclability. Herein, a three-dimensional dumpling-like glyururil-derived porous carbon@RGO composite (GLCG) constructed from nitrogen-doped (10.29 at.%) hierarchical porous carbon filling and highly conductive flexible RGO wrapper is synthesized. As for the Na half-cell, GLCG anode delivers high reversible specific capacity (282 mAhg-1 at 0.05 Ag−1) as well as superb rate capability (122.8 mAhg-1 at 10 Ag−1) and lifespan (3000 cycles at 2 Ag−1). Moreover, the origin of the excellent sodium-ion storage properties of GLCG is revealed by in-depth mechanism analysis. Consequently, a SIHCs with GLCG anode is constructed, which displays high energy density of 108 Wh kg−1, high power density of 14.2 kW kg−1 and long lifespan of 66% capacity retention after 5000 cycles at 2 Ag−1. This work provides an alternative avenue for the exploitation of high-performance carbon-based SIHCs anode.

Microwave-assisted synthesis of self-assembled camellia-like CuS superstructure of ultra-thin nanosheets and exploration of its sodium ion storage properties

The major merit of this work is to use a facile microwave-assisted method to synthesize nanosheet-assembled camellia-like CuS material. When investigated as a novel anode for SIBs, the electrode exhibits an outstanding electrochemical performance. • A novel camellia-like CuS superstructure is first prepared by a microwave-assisted heating method. • Structural evolution is explained by the Ostwald ripening and oriented growth mechanism. • The CuS electrode shows excellent cycling stability and rate performance for SIBs. • The obtained nanosheet-assembled CuS anode delivers a large pseudocapacitive behavior. Layered copper sulfide (CuS) has immense commercial application potential in sodium-ion batteries (SIBs) due to its high capacity, diverse structures, and controllable synthetic methods. Despite these advantages, due to the large volume changes and soluble polysulfide intermediates based on the conversion reaction, it is a huge challenge for CuS electrodes to maintain high-rate performance and long-term cycle stability. Herein, a camellia-like CuS superstructure is designed and synthesized to improve cycling stability and rate performance. The cycling stability reflects in a stable capacity of 347.1 mAh g −1 can still be retained at 0.1 A g −1 after 100 cycles, and even after 1000 cycles at 5.0 A g −1 without decay. The excellent rate performance is embodied in the capacity of 352.4 and 255.7 mAh g −1 at 0.05 and 5.0 A g −1 , respectively. This work provides a feasible route to develop CuS anode material of SIBs with remarkable sodium storage performance.

Synergetic Strategy for the Fabrication of Self-Standing Distorted Carbon Nanofibers with Heteroatom Doping for Sodium-Ion Batteries.

Currently, the limited availability of lithium sources is escalating the cost of lithium-ion batteries (LIBs). Considering the fluctuating economics of LIBs, sodium-ion batteries (SIBs) have now drawn attention because sodium is an earth-abundant, low-cost element that exhibits similar chemistry to that of LIBs. Despite developments in different anode materials, there still remain several challenges in SIBs, including lighter cell design for SIBs. The presented work designs a facile strategy to prepare nitrogen-doped free-standing pseudo-graphitic nanofibers via electrospinning. A structural and morphological study implies highly disordered graphitic structured nanofibers having diameters of ∼120–170 nm, with a smooth surface. X-ray photoelectron spectroscopy analysis showed that nitrogen was successfully doped in carbon nanofibers (CNFs). When served as an anode material for SIBs, the resultant material exhibits excellent sodium-ion storage properties in terms of long-term cycling stability and high rate capability. Notably, a binder-free self-standing CNF without a current collector was used as an anode for SIBs that delivered capacities of 210 and 87 mA h g–1 at 20 and 1600 mA g–1, respectively, retaining a capacity of 177 mA h g–1 when retained at 20 mA g–1. The as-synthesized CNFs demonstrate a long cycle life with a relatively high Columbic efficiency of 98.6% for the 900th cycle, with a stable and excellent rate capacity. The sodium storage mechanisms of the CNFs were examined with various nitrogen concentrations and carbonization temperatures. Furthermore, the diffusion coefficients of the sodium ions based on the electrochemical impedance spectra measurement have been calculated in the range of 10–15–10–12 cm2 s–1, revealing excellent diffusion mobility for Na atoms in the CNFs. This study demonstrates that optimum nitrogen doping and carbonization temperature demonstrated a lower Warburg coefficient and a higher Na-ion diffusion coefficient leads to enhanced stable electrochemical performance. Thus, our study shows that the nitrogen-doped CNFs will have potential for SIBs.

Multifunctional flower-like WS2 hybrids with carbon nanotube veins and WS2 petals: Its sodium ion storage and hydrogen evolution properties

Abstract A hierarchical flower-like hybrid with tungsten disulfide (WS2) nano-sheet petals and multi-walled carbon nanotube (MWCNT) veins is prepared via a facile solvothermal method. High concentration functional groups and defects on the acid-treated MWCNTs bundles initiated the growth of WS2 nano-flowers with an average diameter of 500 nm, inducing strong interface interaction between WS2 and MWCNTs. Furthermore, the MWCNTs are adopted as viens to improve the electron transportation and as interconnected 3D network to alleviate the structural change and restacking of WS2 petals. Meanwhile, the WS2 nano-flowers with abundant edge tungsten atoms are beneficial for sodium ion storage and hydrogen evolution reaction. As a result, the hybrid exhibits excellent electrochemical performances: a specific capacity of 250 mAh g−1 at 0.5 A g−1 after 45 cycles is retained as anode for sodium ion battery; an 80 mV dec−1 Tafel slope and an overpotential of −0.25 V (vs. RHE) are delivered with excellent stability in acidic condition.

Sulfur and nitrogen co-doped carbon nanosheets for improved sodium ion storage

Heteroatom doping into specific nanostructure is believed as the leading solution for developing the advanced carbon materials for sodium ion batteries (SIBs), however, the preparation and understanding of heteroatoms co-doped carbon anodes are still challenging. Herein, the sulfur and nitrogen co-doped (weight content of 15.64% for N and 3.1% for S) carbon nanosheets (SNC) are prepared by treating nitrogen-rich carbon nanosheets with sublimation sulfur. The S, N co-doping is responsible for the enlarged interlamellar spacing of 0.38 nm and abundant defect-introduced active sites. These structure features combined with the advantage of nanosheet are significant for activating sodium ion storage properties, endowing SNC with high Na+ storage capacity of 270 mAh g−1 at 0.1 A g−1 and 100 mAh g−1 at 1 A g−1 after 1000 cycles. More importantly, the kinetic analysis is carried out to illustrate that S, N co-doping can improve the Na+ diffusion coefficient in carbon anode and enhance the ion storage. This work deepens the understanding on the boosting effect of heteroatoms dual-doping for the sodium ion storage of carbon materials, which conduces to development of advanced heteroatom doped carbon anodes for SIBs.

Covalently encapsulating sulfur chains into carbon-rich nanomaterials towards high-capacity and high-rate sodium-ion storage

A bottom-up strategy to covalently encapsulate sulfur chains into carbon-rich nanomaterials is reported, and the optimized material with abundant sulfur chains is demonstrated to be capable of synchronously achieving high-capacity and high-rate sodium-ion storage properties.

MoTe2 on Metal-Organic Framework Derived MoO2/N-Doped Carbon Rods for Enhanced Sodium-Ion Storage Properties

MoTe2 on Metal-Organic Framework Derived MoO2/N-Doped Carbon Rods for Enhanced Sodium-Ion Storage Properties

Reduced Graphene Oxide By Modified Hummer’s Method Under Appropriate Drying Temperatures As Anode Material for Rechargeable Li, Na and K Batteries

We have successfully synthesized Reduced graphene oxide (rGO) sheets by modified Hummer’s method without additional reducing procedures, such as chemical and thermal treatment, by using appropriate drying temperatures under ambient atmosphere. The rGO sample dried at the optimum temperature of 250 has the most increased specific surface area and porosity as evidenced by SEM and BET analysis, leading to improved lithium-ion, sodium-ion and potassium-ion storage properties. We confirmed the use of a moderate drying temperature led to electrodes’ enhanced cyclability and good electrochemical performance at high current densities. The dimensions of the sheets ranged from nanometers to micrometres and these were entangled with each other to form aggregates. These morphological features of rGO facilitates the movement of guest ions larger than Li-ions, however there were slight instability during repeated cycling. To improve the electrochemical properties, we adopted simple chemical strategies using surfactant/solvent-assisted ultrasonication or mechanical or thermal methods. Our results will be useful for improving the full cell characteristics, and especially for preventing potential drop in sodium-ion batteries and potassium-ion batteries, which are expected to replace the lithium-ion battery system.

Tuning crystal structure and redox potential of NASICON-type cathodes for sodium-ion batteries

Sodium superionic conductor (NASICON)-type compounds have been regarded as promising cathodes for sodium-ion batteries (SIBs) due to their favorable ionic conductivity and robust structural stability. However, their high cost and relatively low energy density restrict their further practical application, which can be tailored by widening the operating voltages with earth-abundant elements such as Mn. Here, we propose a rational strategy of infusing Mn element in NASICON frameworks with sufficiently mobile sodium ions that enhances the redox voltage and ionic migration activity. The optimized structure of Na3.5Mn0.5V1.5(PO4)3/C is achieved and investigated systematically to be a durable cathode (76.6% capacity retention over 5,000 cycles at 20 C) for SIBs, which exhibits high reversible capacity (113.1 mAh·g−1 at 0.5 C) with relatively low volume change (7.6%). Importantly, its high-areal-loading and temperature-resistant sodium ion storage properties are evaluated, and the full-cell configuration is demonstrated. This work indicates that this Na3.5Mn0.5V1.5(PO4)3/C composite could be a promising cathode candidate for SIBs.

Encapsulating N-Doped Carbon Nanorod Bundles/MoO2 Nanoparticles via Surface Growth of Ultrathin MoS2 Nanosheets for Ultrafast and Ultralong Cycling Sodium Storage.

Conversion-type anode materials possess high theoretical capacity for sodium-ion batteries (SIBs), owing to multi-electron transmission (2-6 electrons). Mo-based chalcogenides are a class of great promise, high-capacity host materials, but their development still undergoes serious volume changes and low transport kinetics during the cycling process. Here, MoO2 nanoparticles anchored on N-doped carbon nanorod bundles (N-CNRBs/MoO2) are synthesized by a facile self-polymerized route and a following annealing. After hydrothermal sulfuration, N-CNRBs/MoO2 composites are encapsulated by surface growth of ultrathin MoS2 nanosheets, acquiring hierarchical N-CNRBs/MoO2@MoS2 composites. Serving as the SIB anode, the N-CNRBs/MoO2@MoS2 electrode exhibits significantly improved sodium-ion storage properties. The reversible capacity is up to 554.4 mA h g-1 at 0.05 A g-1 and maintains 249.3 mA h g-1 even at 10.0 A g-1. During 5000 cycles, no obvious capacity decay is observed and the reversible capacities retain 334.8 mA h g-1 at 3.0 A g-1 and 301.4 mA h g-1 at 5.0 A g-1. These properties could be ascribed to the vertical encapsulation of MoS2 nanosheets on high-crystalline N-CNRBs/MoO2 substrates. The hierarchical architecture and unique heterostructure between MoO2 and MoS2 synergistically facilitate sodium-ion diffusion, relieve volume changes, and boost pseudocapacitive charge storage of N-CNRBs/MoO2@MoS2 electrode. Therefore, the rational growth of nanosheets on complex substrates shows promising potential to construct anode materials for high-performance batteries.

Improved lithium and sodium ion storage properties of WS2 anode with three-layer shell structure

A three-layer shell structured tungsten disulfide-based material for high capacity anode is prepared by a hydrothermal method. The three layers consist of a stable porous carbon shell (PCS), a tungsten disulfide nanosheet (WS2) and a highly conductive nitrogen-doped graphene (NG). While the nanostructured WS2 and NG ensured the fast lithium/sodium ions (Li+/Na+) insertion/extraction, the stable PCS shell provides structural stability during cycling, resulted in the improved rate capability and long cycle life of the PCS/WS2/NG anode material. For lithium-ion batteries (LIBs), the capacity of PCS/WS2/NG anode is 324.7 mAh g−1 after 510 cycles at a high current density of 2 A g−1. The discharge capacities of PCS/WS2/NG, PCS/WS2, WS2 and PCS anodes are 272.9, 105.1, 8.1 and 6.7 mAh g−1, respectively, at a high current density of 4 A g−1. When the current density rebound to 0.1 A g−1, their capacity retentions are 57.8%, 38.3%, 17.6% and 26.4%, respectively. The capacity retention of PCS/WS2/NG anode is 69.6%, higher than that of the pristine WS2 anode. For sodium-ion batteries (SIBs), PCS/WS2/NG anode exhibits a specific capacity of 205.0 mAh g−1 after the 900th cycle at the current density of 0.5 A g−1. The excellent electrochemical performance of the three-layer shell structured PCS/WS2/NG nanomaterial is a promising anode for high performance LIBs and SIBs.

Facile synthesis of heteroatom doped and undoped graphene quantum dots as active materials for reversible lithium and sodium ions storage

Zero-dimensional graphene quantum dots have attractive properties but the synthesis of graphene quantum dots in a simple and scalable technique is tedious, which limits its utilization in different energy storage application. In this study, we present a simple and scalable approach to produce graphene quantum dots and heteroatom doped graphene quantum dots using chemical vapor deposition technique. Graphene quantum dots are prepared using alloy-based catalyst and methane as a carbon source. Boron-doped and nitrogen-doped graphene quantum dots are prepared at low temperature using graphite oxide without the use of dialysis bag. Here, the electrochemical lithium and sodium ion storage properties of doped and undoped graphene quantum dots are studied without being used as a supporting material for the performance enhancement as reported in previous reports. Boron doped GQD (B-GQD) exhibits a high specific capacity of 1097 mAh g−1 and 310 mAh g−1 at a specific current of 50 mA g−1 for lithium and sodium ion batteries respectively. B-GQD exhibits high volumetric energy density of 537 Ah L−1 and 214 Ah L−1 with an average voltage of 0.43 V and 0.57 respectively for lithium ion and sodium ion batteries. Also, the cells observe a satisfactory cyclic performance for 500 cycles with good capacity retention. Detailed investigations show that the edge defects present in GQD and doped GQDs help to enhance the electrochemical storage performance of lithium and sodium ions.

Rational design of Sn-Sb-S composite with yolk-shell hydrangea-like structure as advanced anode material for sodium-ion batteries

To circumvent the poor cycling stability of 2D layered metal sulfide, a novel yolk-shell hydrangea-like Sn-Sb-S microflower composite self-assembled by nanosheets, was successfully designed and fabricated as anode material for sodium-ion batteries. Without any introduction of carbonaceous materials, the Sn-Sb-S microflower composite could possess prominent sodium-ion storage properties through constructing Sb-rich phase with superior cycling stability as the protective shell to envelop the higher-capacity yolk Sn-rich phase. The yolk-shell Sn-Sb-S microflower composite exhibits a first discharge capacity of 1601.1 mAh/g. A highly reversible capacity of >600 mAh/g with a favorable and safe average voltage of ∼0.6 V was achieved, constituting a promising anode material for sodium-ion batteries.

A high-energy sodium-ion capacitor enabled by a nitrogen/sulfur co-doped hollow carbon nanofiber anode and an activated carbon cathode.

Nonaqueous Na-ion capacitors (NICs) have been recently regarded as potential sustainable power devices due to their high specific energy/power and the abundant distribution of sodium resources on the Earth. However, the power performance of current NICs is usually restricted by the kinetics imbalance between sodium deintercalation/intercalation in the anode and surface ion adsorption/desorption in the cathode. Herein, we demonstrate superior sodium-ion storage properties of nitrogen/sulfur co-doped hierarchical hollow carbon nanofibers (N/S-HCNFs) for their application as an ideal anode material for NICs. The N/S-HCNFs are fabricated through in situ gas sulfuration of a hollow polyaniline nanofiber precursor, which is obtained with the aid of citric acid templates. Benefiting from the positive synergistic effects of both N and S co-doping in carbon and the hierarchical hollow one-dimensional structure, the sodium-storage performance of N/S-HCNFs half-cell versus Na/Na+ exhibits a high capacity (∼447 mA h g−1 at 50 mA g−1), excellent rate capability (∼185 mA h g−1 at 10 A g−1), and outstanding cycling stability (no capacity decay after 3000 cycles at 5 A g−1), which is among the best sodium-ion storage performances of carbonaceous Na-storage anodes. Furthermore, a dual-carbon NIC device is constructed with N/S-HCNFs as an anode and activated carbon (AC) as a cathode, and it has a large energy density of 116.4 W h kg−1, a high power density of 20 kW kg−1 (at 48.2 W h kg−1) and a long cycle life of 3000 cycles, which is superior to most reported AC-based NICs.

Size controlling and surface engineering enable NaTi2(PO4)3/C outstanding sodium storage properties

NaTi2(PO4)3 with open and stable frameworks shows great potential for sodium ion batteries (SIBs), while it is suffering from the intrinsic low electronic conductivity, causing poor active material utilization and inferior rate capability. Herein, a facile solvothermal reaction with size controlling and in-situ carbon coating process is developed to synthesize NaTi2(PO4)3/C nanocomposites, in which the well-dispersed NaTi2(PO4)3 nanoparticles with size of 20–40 nm are well coated by carbon shell with uniform thickness of ∼4 nm. The uniform carbon coating layer and small nanoparticles enable the high utilization ratio of carbon and active material, thus nanostructured NaTi2(PO4)3/C with 3.82% carbon content can deliver outstanding sodium ion storage properties in multiple occasions including organic/aqueous electrolyte and half/full cell. In organic electrolyte system, the electrode presents remarkable rate capability with reversible capacity of 92 and 66 mAh g−1 at 20 C and 50C (1C = 150 mA g−1), respectively. Moreover, a NaTi2(PO4)3/C//Na3V2(PO4)2F3 sodium ion full cell with excellent rate capability up to 20C and cycling stability is also demonstrated. In aqueous electrolyte, after the optimization of current collector and electrolyte, the aqueous NaTi2(PO4)3/C//sodium Prussian blue (PB) full cell also demonstrates excellent cycling life up to 500 times with a capacity retention of 86.5% at 1C.

Lithium- and sodium-ion storage properties of modulated titanate morphologies in reduced graphene oxide nanocomposites

Electrochemical energy storage (EES) systems rely on novel materials to meet stringent performance demands in terms of both high energy and high power. Although several new materials have been identified for EES, one method that seeks to amplify material properties has been to modulate morphologies at the nanoscale. This improvement in electrochemical properties is in large part due to the enhancement in surface area and mitigation of solid-state diffusion at the nanoscale domain. By using sodium titanate (Na2Ti3O7) as a model compound, we employ efficient synthetic routes to prepare titanate nanosheets and nanotubes, and assess their charge-storage properties in both Li- and Na-ion non-aqueous electrolytes. Moreover, nanocomposites comprising reduced graphene oxide are constructed to further enhance rate capability. We perform a fundamental electroanalytical treatment of the charge-storage properties for titanate nanosheets and nanotubes and identify the underlying rate-determining mechanisms by kinetic analysis. In both Li- and Na-ion electrolytes, the nanotube–reduced graphene oxide nanocomposite exhibits pseudocapacitive behavior, indicated by broad voltammetric features and sloping charge-discharge voltage profiles under galvanostatic mode. This corresponding charge-storage process supports high capacities of 170 and 80 mAh g−1 in a Li- and Na-ion system, respectively, based on constant current measurements at a C-rate of 5C.

Hierarchical iron sulfide-graphene nanocubes consisting of multiple nanoparticles with superior sodium ion storage properties

Hierarchical iron sulfide nanocubes consisting of multiple iron sulfide-carbon core-shell nanoparticles coated with few-layer graphene (Fe1-xS@C/rGO) were prepared by a two-step in-situ transformation strategy employing Prussian blue (PB) as a starting material. The hierarchical nanocubes delivered an outstanding rate capability of 323 mAh g−1 at the current density of 10 A g−1 when used as the anode of sodium ion half cells. An iron-based sodium-ion full cell composed of a hierarchical Fe1-xS@C/rGO anode and PB cathode had a capacity of 323 mAh g−1 for 150 cycles. We attributed the good sodium ion storage properties of the Fe1-xS@C/rGO nanocubes to the stable hierarchical building structures and the high graphitization degree of carbon obtained during the transformation process. The graphene-coated nanocube structures inhibited the agglomeration of iron sulfide-carbon core-shell nanoparticles and accommodated the huge volume expansion that occurred during cycling. The high graphitization degree of carbon endowed Fe1-xS@C/rGO nanocubes with high electronic conductivity, facilitated sodium ion accessibility, and increased mechanical durability.

MOF-Templated N-Doped Carbon-Coated CoSe2 Nanorods Supported on Porous CNT Microspheres with Excellent Sodium-Ion Storage and Electrocatalytic Properties.

Three-dimensional (3D) porous microspheres composed of CoSe2@N-doped carbon nanorod-deposited carbon nanotube (CNT) building blocks (CoSe2@NC-NR/CNT) can be successfully synthesized using CNT/Co-based metal-organic framework (ZIF-67) porous microspheres as a precursor. This strategy involves the homogeneous coating of ZIF-67 polyhedrons onto porous CNT microspheres prepared by spray pyrolysis and further selenization of the composites under an Ar/H2 atmosphere. During the selenization process, the ZIF-67 polyhedrons on the CNT backbone are transformed into N-doped carbon-coated CoSe2 nanorods by a directional recrystallization process, resulting in a homogeneous deposition of CoSe2@NC nanorods on the porous CNT microspheres. Such a unique structure of CoSe2@NC-NR/CNT microspheres facilitates the transport of ions, electrons, and mass and provides a conductive pathway for electrons during electrochemical reactions. Correspondingly, the composite exhibits a superior dual functionality as both an electrocatalyst for the hydrogen evolution reaction (HER) and an electrode for sodium-ion batteries (SIBs). The CoSe2@NC-NR/CNT microspheres exhibit a small Tafel slope (49.8 mV dec-1) and a superior stability for HER. Furthermore, the composite delivers a high discharge capacity of 555 mA h g-1 after 100 cycles at a current density of 0.2 A g-1 and a good rate capability for SIBs.

Reduced graphene oxide wrapped alluaudite Na2+2xFe2-x(SO4)3 with high rate sodium ion storage properties

Na2+2xFe2-x(SO4)3 (NFS) is recently reported as a promising cathode material for Na-ion batteries with high voltage generation and high energy density, making it competitive to sodium battery cathodes. Nevertheless, owing to its insulating nature, a formidable challenge remains as to realize high rate capability. Herein, Na2+2xFe2-x(SO4)3/reduced graphene oxide (rGO) has been designed and realized by a facile one-stepped synthesis. Its structural, morphological and electrochemical properties have been characterized and compared with those of the bare NFS material. As a result, NFS/rGO cathode demonstrates enhanced electrochemical performance, as reflected by the initial specific capacity of 90 mAh g−1 and a high specific capacity of 80 mAh g−1 over 100 cycles at a current density of 0.1 C (1 C = 120 mA g−1), an excellent rate capability with specific capacity of 60 mAh g−1 at high current density of 20 C (2.4 A g−1) and long-term cycle life with capacity retention of 84% over 500 cycles at 20 C rate (2.4 A g−1). This improvement may be attributed to the high electronic conductivity of rGO, which facilitates the charge transfer reactions between the active materials and electrolyte interface, and promotes the sodium ion diffusion in the electrode. Therefore, Na2+2xFe2-x(SO4)3/rGO is favorable to realizing superior electrochemical performance for the sulfate, which presents a significant step forward in the development of low-cost large-scale batteries.

Self-assembled nickel-cobalt oxide microspheres from rods with enhanced electrochemical performance for sodium ion battery

Exploring new anode materials with promising electrochemical capacity is essential for rechargeable sodium-ion batteries. The selection and structural design of electrode materials play key role in the development of a viable battery with high specific capacity and cycle retention. Herein, self-assembled NiCo2O4 microspheres comprised of numerous sub-micron sized rods are prepared for the first time by a simple co-precipitation method. The synthesized microspheres have homogeneous morphology and a multimodal porosity. The resulting sodium ion storage properties demonstrate that the NiCo2O4 microsphere anode offers excellent electrochemical performance, with a high reversible capacity of 620mAhg−1 at a current density of 0.05Ag−1. It also shows an exceptionally high rate capability up to 10Ag−1 equivalent to 11 C-rate, which can be attributed to the existence of capacitive behavior. Notably, the rate performance and cycling stability are significantly higher than most previously reported results of NiCo2O4 nanostructures for sodium-ion batteries (SIBs).