Stable Anode Material Research Articles

Fabrication of Carbonaceous Nanotubes and Mesoporous Nanofibers as Stable Anode Materials for Lithium-Ion Battery

The morphologies and pore architectures of carbon nanostructures could be precisely controlled via a self-assembly process. This work presented resorcinol-formaldehyde resin-silica composite nanofibers, which were synthesized through a sol–gel method under the help of costructure directing agent (CSDA) (S)-β-citronellol and n-hexanol. The self-assembly process and the nanostructure of obtained composite nanofibers were changed by adding different CSDA. After carbonization and getting rid of silica, carbonaceous nanotubes and mesoporous nanofibers were obtained, respectively. Their electrochemical performance was tested as anode materials for lithium-ion batteries (LIBs). Stable discharge capacities of 574.3 mA h g–1 for carbonaceous nanotubes and 609.9 mA h g–1 for mesoporous carbonaceous nanofibers after 300 cycles were achieved at current density of 0.1 A g–1. Thus, a facile method of designing and fabricating excellent carbon anode candidates for LIBs was provided.

A novel anode for solid oxide fuel cells prepared from phase conversion of La0.3Sr0.7Fe0.7Cr0.3O3-δ perovskite under humid hydrogen

A novel anode for solid oxide fuel cells (SOFCs), consisting of a Ruddlesden-Popper compound, La0.6Sr1.4Fe0.4Cr0.6O3.8, with in situ exsolved α-Fe nanoparticles (RP-LSF + Fe), is prepared from the phase conversion of the La0.3Sr0.7Fe0.7Cr0.3O3-δ (LSFCr-3) perovskite under humid H2 at 800 °C. On the surface of the RP-LSF + Fe anode, Fe cations are presented to be a mixture of Fe2+ and Fe3+, of which the average valence is lower than that in the bulk (Fe3+). The coverage of atomic hydrogen on the RP-LSF + Fe anode is over 0.8 in the pH2 range of 0.017–0.27 atm, implying a significant effect of these small amount (∼8 mol% on the surface) of exsolved Fe nanoparticles (∼200–300 nm) on promoting the dissociative absorption of H2. The charge transfer resistance is found to be closely related to the concentration of surface oxygen vacancies of the oxide matrix. The addition of catalytic amount of Ni (1–3 wt.%) greatly improves the fuel flexibility of the RP-LSF + Fe anode. Furthermore, it contributes to acceleration the phase conversion of the LSFCr-3 perovskite and reduced time for in situ preparation of the RP-LSF + Fe anode. The RP-LSF + Fe anode with 2.7 wt.% Ni exhibits a stable cell performance under 2.7%H2O+1:1-(H2:CO) and 2.7%H2O + CH4 for ∼30 h. It costs shortest time (30 h) to reach a stable cell voltage of 0.76 V at a galvanostatic current density of 0.25 A/cm2 under humid H2, which is clearly an active and stable anode material for SOFCs.

A Reduced Sodium Titanate/Carbon Composite As a Stable, High-Energy Sodium Ion Battery Anode Material

The use of renewable but intermittent energy sources, such as solar and wind energy, means that it is necessary to store this energy for later use. Hence, a shift towards renewable sources of energy requires the development and use of efficient and inexpensive large-scale energy storage devices. Whereas portable electronics conventionally utilize lithium ion batteries (LIBs), this is not an option for large-scale energy storage, since the increased demand for lithium would result in a significant price increase. Therefore, alternative technologies, such as sodium ion batteries (SIBs) should be considered1. Since sodium is widely available across the globe, and is the lightest alkali metal after lithium, SIBs can be a valuable alternative to LIB technologies, despite the lesser reducing nature of sodium. Because of dendrite formation, the use of sodium metal as anode results in a significant safety hazard. Therefore, it is a better option to use a technology where sodium ions are not reduced to their metallic form. Potential alternative SIB anodes are mainly carbonaceous materials, alloys and phosphorus/phosphide, as well as oxides and polyanionic compounds2. However, many reported SIB anode materials suffer from a variety of disadvantages, such as a low electrochemical stability and energy density. Therefore, one of the challenges that the commercialization of SIBs faces is the development of a suitable anode material. Recently, a reduced sodium titanate was reported as SIB anode. However, its low electrochemical stability, together with its cumbersome synthesis method and the lack of understanding of the mechanism of sodium ion intercalation, makes its use in a commercial SIB unlikely. Our density functional theory (DFT) calculations show that the material is an insulator due to its large band gap. Therefore, a new, convenient synthesis method was developed, which results in a composite of reduced sodium titanate with conductive amorphous carbon (NTO/C). This composite material was characterized by powder X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The formation mechanism was studied using thermogravimetric analysis (TGA) and electron paramagnetic resonance (EPR). The electrochemical characteristics were studied using galvanostatic cycling and the galvanostatic intermittent titration technique (GITT). Operando XRD was used to investigate the mechanism of sodium insertion. The NTO/C, with an average operation voltage of ~0.9 V vs. Na/Na+, shows a high electrochemical stability (89% capacity retention after 250 cycles at 1C), and high capacity (135 mAh g-1 at 0.1C, 105 mAh g-1 at 1C and 61 mAh g-1 at 10C). Consequently, this NTO/C is currently the most energy dense material of all stable lithium-free SIB anode materials with an appropriate operation potential, even slightly surpassing O3-NaTiO2 3. As it also requires only abundant and inexpensive elements, we believe that NTO/C is an excellent material for commercial SIB anodes. Slater, M. D., Kim, D., Lee, E. & Johnson, C. S. Sodium-ion batteries. Adv. Funct. Mater. 23, 947–958 (2013).Yabuuchi, N., Kubota, K., Dahbi, M. & Komaba, S. Research Development on Sodium-Ion Batteries. Chem. Rev. 114, 11636–11682 (2014).Wu, D. et al. NaTiO2: a layered anode material for sodium-ion batteries. Energy Environ. Sci. 8, 195–202 (2015).

NiS1.03 Hollow Spheres and Cages as Superhigh Rate Capacity and Stable Anode Materials for Half/Full Sodium-Ion Batteries.

Nickle sulfides as promising anode materials for sodium-ion batteries have attracted tremendous attention owing to their large specific capacity and good electrical conductivity. However, the relative large volume changes during the sodiation/desodiation process usually result in a fast capacity decay, poor cycling stability, and sluggish electrode kinetics which hinder their practical applications. Herein, NiS1.03 porous hollow spheres (NiS1.03 PHSs) and porous NiS1.03 hollow cages (NiS1.03 PHCs) with high yield are designed and selectively fabricated via a simple solvothermal and subsequent annealing approach. The obtained NiS1.03 PHSs display long-term cycling stability (127 mAh g-1 after 6000 cycles at 8 A g-1) and excellent rate performance (605 mAh g-1 at 1 A g-1 and 175 mAh g-1 at 15 A g-1). NiS1.03 PHCs also show high rate capability and outstanding cycling stability. In addition, the analyses results of in situ and ex situ XRD patterns and HRTEM images reveal the reversible Na-ion conversion mechanism of NiS1.03. It is also worth noting that the NiS1.03 PHSs//FeFe(CN)6 full cell is successfully assembled and exhibits an initial reversible capacity of 460 mAh g-1 at 0.5 A g-1, which further evidence that NiS1.03 is a kind of prospective anode material for SIBs.

Porous NaTi2(PO4)3/C Hierarchical Nanofibers for Ultrafast Electrochemical Energy Storage.

NaTi2(PO4)3 (NTP) with a sodium superionic conductor three-dimensional (3D) framework is a promising anode material for sodium-ion batteries (SIBs) because of its suitable potential and stable structure. Although its 3D structure enables high Na-ion diffusivity, low electronic conductivity severely limits NTP's practical application in SIBs. Herein, we report porous NTP/C nanofibers (NTP/C-NFs) obtained via an electrospinning method. The NTP/C-NFs exhibit a high reversible capacity (120 mA h g-1 at 0.2 C) and a long cycling stability (a capacity retention of ∼93% after 700 cycles at 2 C). Furthermore, sodium-ion full cells and hybrid sodium-ion capacitors have also been successfully assembled, both of which exhibit high-rate capabilities and remarkable cycling stabilities because of the high electronic/ionic conductivity and impressive structural stability of NTP/C-NFs. The results show that the nanoscale-tailored NTP/C-NFs could deliver new insights into the design of high-performing and highly stable anode materials for room-temperature SIBs.

High capacity and stable all-solid-state Li ion battery using SnO2-embedded nanoporous carbon

Extensive research efforts are devoted to development of high performance all-solid-state lithium ion batteries owing to their potential in not only improving safety but also achieving high stability and high capacity. However, conventional approaches based on a fabrication of highly dense electrode and solid electrolyte layers and their close contact interface is not always applicable to high capacity alloy- and/or conversion-based active materials such as SnO2 accompanied with large volume change in charging-discharging. The present work demonstrates that SnO2-embedded nanoporous carbons without solid electrolyte inside the nanopores are a promising candidate for high capacity and stable anode material of all-solid-state battery, in which the volume change reactions are restricted in the nanopores to keep the constant electrode volume. A prototype all-solid-state full cell consisting of the SnO2-based anode and a LiNi1/3Co1/3Mn1/3O2-based cathode shows a good performance of 2040 Wh/kg at 268.6 W/kg based on the anode material weight.

Realizing stable lithium and sodium storage with high areal capacity using novel nanosheet-assembled compact CaV4O9 microflowers

Realizing stable cycling performance with high areal capacity is a great challenge for metal-ion battery anodes. Achieveing high areal capacity generally requires the electrode in a high active loading with increased electrode thickness, which is not beneficial to the cycling stability. In this work, novel nanosheet-assembled compact CaV4O9 microflowers are firstly synthesized through a facile method, which exhibit both high areal capacity and stable cycling performance at high mass loadings. The compact microflower structure leads to an increased tap density of the electrode materials, benefiting to reduce the anode thickness at high mass loadings. Meanwhile, the assembled nanosheets maintain the nano-effects of the active materials for favorable electrochemical reactions. These merits together with the intrinsic superior electrochemical properties of CaV4O9, result in the outstanding electrochemical performance. When used as Li-ion battery anodes, a high areal capcity of ~2.5 mAh cm−2 at a high mass loading of 4.4 mg cm−2 is obtained, and a stable cycling over 400 cycles with the areal capacity over 1.5 mAh cm−2 is demonstrated. Besides, the superior electrochemical performance at high mass loadings is also observed for Na storage. These achievements may pave the way for constructing applicable high-capacity and stable anode materials in metal-ion batteries.

β-Sn Nanorods with Active (001) Tip Induced LiF-Rich SEI Layer for Stable Anode Material in Lithium Ion Battery

β-Sn nanorod (NR) with (200) facets and (001) tip is a potential anode material in lithium ion battery (LIB) due to its good cycle stability that can retain ∼600 and 550 mA h g–1 after 100 cycles using 0.2 C for high and low aspect ratios, respectively. The high stability compared to that of spherical nanoparticles can be attributed to the combination of the nanorod morphology that buffers large volumetric change, and the LiF-rich F-containing surface electrolyte interface (SEI) layer that allows for a stable SEI layer and a good ionic and electronic conductivity. The lower SEI resistivity and high Li+ diffusivity of low aspect ratio β-Sn NRs resulted in a better cyclability compared to high aspect ratio β-Sn NRs. These can be attributed to the higher specific surface area of highly reactive (001) surface, i.e., the tip of the rod, that produces a LiF-rich F-containing SEI layer of the lower aspect ratio compared to that of the higher aspect ratio β-Sn NRs.

Silicon Oxycarbide Beads from Continuously Produced Polysilsesquioxane as Stable Anode Material for Lithium-Ion Batteries

Silicon oxycarbides are promising anode materials for lithium-ion batteries. In this study, we used the continuous MicroJet reactor technique to produce organically modified silica (ORMOSIL) spheres which were pyrolyzed to obtain silicon oxycarbides. The continuous technique allows the production of large quantities with a constant quality. Different alkoxysilanes were used to produce the silicon oxycarbides with different compositions. Thereby, the amounts of silicon–carbon bonds, as well as the free carbon content, were modified. Electrochemical testing was carried out in 1 M LiPF6 in ethylene carbonate/dimethyl carbonate. A mixture of vinyl- and phenyltrimethoxysilane was identified as the best anode material with a stable performance due to the increased carbon content. The first-cycle delithiation capacity of the most stable material was 922 mA h/g, and the capacity retention after 100 cycles was 83% (767 mA h/g).

Porous Mn-doped cobalt oxide@C nanocomposite: a stable anode material for Li-ion rechargeable batteries

Cobalt oxide is a transition metal oxide, well studied as an electrode material for energy storage applications, especially in supercapacitors and rechargeable batteries, due to its high charge storage ability. However, it suffers from low conductivity, which effectively hampers its long-term stability. In the present work, a simple strategy to enhance the conductivity of cobalt oxide is adopted to achieve stable electrochemical performance by means of carbon coating and Mn doping, via a simple and controlled, urea-assisted glycine-nitrate combustion process. Structural analysis of carbon coated Mn-doped Co3O4 (Mn-Co3O4@C) confirms the formation of nanoparticles (∼50 nm) with connected morphology, exhibiting spinel structure. The Mn-Co3O4@C electrode displays superior electrochemical performance as a Li-ion battery anode, delivering a specific capacity of 1250 mAh g−1. Mn-Co3O4@C demonstrates excellent performance in terms of long-term stability, keeping charge storage ability intact even at high current rates due to the synergistic effects of fast kinetics—provided by enriched electronic conductivity, which allows ions to move freely to active sites and electrons from reaction sites to substrate during redox reactions—and high surface area combined with mesoporous architecture. The fully assembled battery device using Mn-Co3O4@C and standard LiCoO2 electrode shows 90% capacity retention over 100 cycles.

A Li-dual carbon composite as stable anode material for Li batteries

Tremendous amount of effort has been dedicated to revisit metallic lithium as anode material for high-energy-density lithium batteries in recent years. Although some progresses have been achieved within this field, development of lithium metal anode material with higher specific capacity and better stability is still urgently needed considering the practical application of batteries. Here we report a Li-carbon nanotube-acetylene black (Li-CNT-AB) composite microsphere anode material by a simple and scalable method. The lithiophilic CNTs were used to construct a porous sphere framework, while the lithiophilic AB particles well distributed in the sphere framework were used to utilize the pore space of the sphere thus increasing the lithium content of the composite, and to act as a lithium deposition promoter during battery cycling because AB has lower lithium nucleation barrier. As a result, the Li-CNT-AB composite exhibits a specific capacity as high as 2800 mA h g-1 and a life span of ~ 700 cycles can be achieved when it was cycled with a commercial LiFePO4 (LFP) cathode at 0.5 C (1.25 mA cm-2) in an ether-based electrolyte with the capacity ratio of cathode to anode being 1:8, corresponding to a high Coulombic efficiency (CE) of ~ 98.7%. Furthermore, it was observed that there is no lithium dendrite formation and negligible volume change on the Li-CNT-AB during electrochemical cycling.

SnS2 nanoparticles anchored on three-dimensional reduced graphene oxide as a durable anode for sodium ion batteries

A novel and facile approach is applied to couple SnS2 nanoparticles with three-dimensional reduced graphene oxide (3DRGO), resulting in a SnS2@3DRGO composite which displays remarkable cycling performance and high reversible capacity as anode material for sodium ion batteries. The SnS2@3DRGO composite is equipped with SnS2 nanoparticles with the size of 30 nm robustly anchoring on 3DRGO. Compared with SnS2, SnS2@3DRGO delivers a higher specific capacity of 753.8 mAh g−1 at 0.1 A g−1 and a superior long cycle-life with a capacity retention rate of 75.4% after 700 cycles at 2 A g−1. During the cycling process, the unique porous structure and well confined SnS2 nanoparticles by graphene buffer layer make a critical difference in achieving rapid kinetic of insertion/extraction and suppressing aggregation of SnS2 and the corresponding discharge product, rendering SnS2@3DRGO to be an extraordinary and stable anode material for SIBs.

Conductive Nb25O62 and Nb12O29 anode materials for use in high-performance lithium-ion storage

Conductive M–NbV–O compounds are high-capacity, fast-charging, safe and stable anode materials that have potential use in lithium-ion batteries. However, their studies are very limited. Here, we facilely fabricate Nb25O62 (i.e., NbIVNbV24O62) and Nb12O29 (i.e., NbIV2NbV10O29) from high-temperature reduction of Nb2O5 in a mixed H2/Ar atmosphere. Nb25O62 shows a monoclinic shear ReO3 crystal structure with a C2 space group and a structural unit containing a 3 × 4 octahedron-block and 0.5 tetrahedron, while Nb12O29 shows a similar structure with an A2/m space group and a 3 × 4 octahedron-block. Their resulting open crystal structures lead to their large Li+-ion diffusion coefficients. Due to the unpaired 4d electrons in Nb4+, their electronic conductivities are increased by three orders of magnitude in comparison with Nb2O5. First-principles calculations even demonstrate their conductor characteristics. Hence, Nb25O62/Nb12O29 exhibits comprehensively good electrochemical performance, including a significant pseudocapacitive contribution (72.7/79.0% at 1.1 mV s−1), high specific capacity (289/287 mAh g−1 at 0.1 C), high working potential (∼1.69/∼1.72 V vs. Li/Li+), superior rate capability (133/165 mAh g−1 at 10 C) and prominent cyclic stability (only 0.3/14.5% capacity loss over 1000 cycles at 10 C). These findings demonstrate that Nb25O62 and Nb12O29 are promising anode materials for future use in high-performance lithium-ion storage.

Confining SnS2 Ultrathin Nanosheets in Hollow Carbon Nanostructures for Efficient Capacitive Sodium Storage

Summary Tin disulfide (SnS 2 ) is a promising anode material for sodium-ion batteries because of its high specific capacity. However, the low conductivity and large volume change during reaction with Na + ions greatly limit its practical application. Herein, a multistep templating method has been exploited for the rational design and synthesis of SnS 2 nanosheets confined in carbon nanotubes (SnS 2 @CNTs). To demonstrate the universality of this method, SnS 2 nanosheets confined in carbon nanoboxes (SnS 2 @CNBs) and hollow carbon nanospheres (SnS 2 @CNSs) have also been synthesized by simply changing the template in the reaction system. Due to their unique structural merits, the SnS 2 @CNTs, SnS 2 @CNBs, and SnS 2 @CNSs show improved sodium storage performance in terms of high specific capacity, good cycling stability, and superior rate capability.

Atomic-layer-deposited TiO2-SnZnO/carbon nanofiber composite as a highly stable, flexible and freestanding anode material for lithium-ion batteries

We demonstrate the synthesis of a highly stable, freestanding and flexible anode material for lithium-ion batteries created by depositing a conformal coating of TiO2 on a SnZnO/carbon nanofiber (CNF) composite using atomic layer deposition. The term SnZnO is used here because metallic Sn is observed in the SnZnO/CNF composites after annealing under argon gas. The elemental composition of the material was confirmed by energy-dispersive X-ray spectroscopy, while the oxidation states of the elements were determined by X-ray photoelectron spectroscopy. Cross-sectional transmission electron microscopy showed that the core regions of the composite nanofibers were almost uniformly covered by a TiO2 shell. The specific capacities of the TiO2-coated and uncoated samples at a high current density (5C) were 413 and 159 mAh·g−1, respectively. An analysis of the surface morphology after cycling indicated that the stability of the solid electrolyte interface layer increased after the formation of the protective conformal TiO2 layer. As a result, no signs of anode degradation were observed even after 700 cycles at a current density of 5C. We attribute this exceptional stability to the buffering of the anode material by the protective coating during volumetric expansion.

Graphene-immobilized flower-like Ni3S2 nanoflakes as a stable binder-free anode material for sodium-ion batteries

A binder-free Ni3S2 electrode was prepared directly on a graphene-coated Ni foam (G/Ni) substrate through surface sulfiding of substrate using thiourea as the sulfur source in this work. The Ni3S2 showed a flower-like morphology and was uniformly distributed on the G/Ni surface. The flower-like Ni3S2 was composed of cross-arrayed nanoflakes with a diameter and a thickness of 1-2 μm and ~50 nm, respectively. The free space in the flowers and the thin feature of Ni3S2 buffered the volume changes and relieved mechanical strain during repeated cycling. The intimate contact with the Ni substrate and the fixing effect of graphene maintained the structural stability of the Ni3S2 electrode during cycling. The G/Ni-supported Ni3S2 maintained a reversible capacity of 250 mAh.g−1 after 100 cycles at 50 mA.g−1, demonstrating the good cycling stability as a result of the unique microstructure of this electrode material.

A synergistic “cascade” effect in copper zinc tin sulfide nanowalls for highly stable and efficient lithium ion storage

Applications of lithium ion battery have been hampered by a lack of ideal anode materials in terms of capacity and stability. The emergence of metal chalcogenide as a candidate material has reinvigorated the search of a low cost and high capacity material system. However, debate about the underlying mechanisms and overall appraisal of its usage in lithium ion battery system remains. Here, a comprehensive study on the energy storage mechanism of copper zinc tin sulfide (CZTS) nanowalls possessing ultrahigh rate capability (500mAhg−1 charged within 60s) is reported. Structural evolutions along with the accompanying changes in the oxidation state upon charge/discharge were monitored by ex-situ X-ray diffraction and X-ray photoelectron spectroscopy. During lithiation, lithium ion reacted with CZTS to form lithium sulfides. At the same time, a sequential conversion reactions of copper, zinc and tin sulfides enabled the CZTS nanowalls to achieve excellent electrochemical performance (1400mAhg−1 at a current density of 1000mAg−1 over 400 cycles). Multi-element metal chalcogenides in conjunction with an adhesion-enhancing seed layer and a rational nanostructure design hold the key to such ultrahigh capacity and stable anode materials for next generation energy storage devices.

Electrospun Ti2Nb10O29 hollow nanofibers as high-performance anode materials for lithium-ion batteries

Ti2Nb10O29 is a high-capacity, safe and stable anode material for lithium-ion batteries, but suffers from a poor rate capability. To tackle this issue, nanotechnology is employed, and Ti2Nb10O29 hollow nanofibers with an average fiber diameter of ∼500 nm and shell thickness of ∼90 nm are prepared by a facile co-electrospining technique followed by calcination in air. This material exhibits not only a high reversible capacity (307 mAh g−1 at 0.1 C) and durable cyclic stability (0.06% capacity loss per cycle at 10 C over 500 cycles) but also an outstanding rate capability (136 mAh g−1 at 20 C), thereby becoming a promising anode material for high-performance lithium-ion batteries.

Molecule-confined FeOx nanocrystals mounted on carbon as stable anode material for high energy density nickel-iron batteries

Nickel-iron (Ni-Fe) rechargeable batteries are attractive as sustainable solutions for large-scale electrical energy storage because of their low cost, eco-friendliness and safety, but their iron anodes always suffer from low capacity and poor stability, which greatly limits their wide applications. We present here a molecular confinement strategy to fabricate ultrasmall iron oxide nanocrystals firmly mounted on carbon (mc-FeOx/C) that works as stable anode material for high energy density Ni-Fe batteries. Compared with conventional iron oxide on carbon synthesized without molecular confinement (FeOx/C), the mc-FeOx/C exhibits a much higher capacity (370.2 vs 159.5mAhg−1 at a current density of 2Ag−1) and better stability (capacity retention of 93.5% vs 61.2% after 1000 charge/discharge cycles). When to further combine with a nickel cathode, the mc-FeOx/C based Ni-Fe battery delivers an energy density up to 173.7Whkg−1, among the highest value for Ni-Fe batteries reported so far. The mc-FeOx/C based Ni-Fe battery also offers excellent rate capability (e.g., 112.6Whkg−1 at 28.9kWkg−1) and good stability (capacity retention of 91.6% after 1000 cycles), retaining their applications for large-scale electrical energy storage.

MoS2 Nanosheets with Conformal Carbon Coating as Stable Anode Materials for Sodium-Ion Batteries

MoS2 nanosheets with conformal carbon coating are achieved via a facile, chemical vapor deposition process, employing ethanol vapor as carbon source. The uniform carbon layers are semi-graphitized, which facilitate kinetics for electron and ion transfer, accommodate volume variation of MoS2, and relieve dissolution of polysulfide during repeated discharge/charge cycles. As anode materials for sodium-ion batteries, the optimized carbon coated MoS2 nanosheets show stable reversible capacity of ∼500mAhg−1 for 100 cycles at 0.1Ag−1, and maintain 351.6mAhg−1 after 200 cycles even at 1Ag−1. Furthermore, the enhanced electron transfer, and the stabilized structure are verified through electrochemical impedance spectroscopy, cyclic voltammetry, as well as scanning electron microscopy. Our results show that the carbon coating by chemical vapor deposition is efficient and promising to improve the reversible Na+ storage performance of anode materials.