Anode Material For Sodium-ion Batteries Research Articles

Facile Fabrication of Large-Area CuO Flakes for Sodium-Ion Energy Storage Applications

CuO is recognized as a promising anode material for sodium-ion batteries because of its impressive theoretical capacity of 674 mAh g−1, derived from its multiple electron transfer capabilities. However, its practical application is hindered by slow reaction kinetics and rapid capacity loss caused by side reactions during discharge/charge cycles. In this work, we introduce an innovative approach to fabricating large-area CuO and CuO@Al2O3 flakes through a combination of magnetron sputtering, thermal oxidation, and atomic layer deposition techniques. The resultant 2D CuO flakes demonstrate excellent electrochemical properties with a high initial reversible specific capacity of 487 mAh g−1 and good cycling stability, which are attributable to their unique architectures and superior structural durability. Furthermore, when these CuO flakes are coated with an ultrathin Al2O3 layer, the integration of the 2D structures with outer nanocoating leads to significantly enhanced electrochemical properties. Notably, even after 70 rate testing cycles, the CuO@Al2O3 materials maintain a high capacity of 525 mAh g−1 at a current density of 50 mA g−1. Remarkably, at a higher current density of 2000 mA g−1, these materials still achieve a capacity of 220 mAh g−1. Moreover, after 200 cycles at a current density of 200 mA g−1, a high charge capacity of 319 mAh g−1 is sustained. In addition, a full cell consisting of a CuO@Al2O3 anode and a NaNi1/3Fe1/3Mn1/3O2 cathode is investigated, showcasing remarkable cycling performance. Our findings underscore the potential of these innovative flake-like architectures as electrode materials in high-performance sodium-ion batteries, paving the way for advancements in energy storage technologies.

Industrial-scale Hard Carbon Designed to Regulate Electrochemical Polarization for Fast Sodium Storage.

Given the merits of abundant resource, low cost and high electrochemical activity, hard carbons have been regarded as one of the most commercializable anode material for sodium-ion batteries (SIBs). However, poor rate capability is one of the main obstacles that severely hinder its further development. In addition, the relationships between preparation method, material structure and electrochemical performance have not been clearly elaborated. Herein, a simple but effective strategy is proposed to accurately construct the multiple structural features in hard carbon via adjusting the components of precursors. Through detailed physical characterization of the hard carbons derived from different regulation steps, and further combined with in-situ Raman and galvanostatic intermittent titration technique (GITT) analysis, the network of multiple relationships between preparation method, microstructure, sodium storage behavior and electrochemical performance have been successfully established. Simultaneously, exceptional rate capability about 108.8 mAh g-1 at 8 A g-1 have been achieved from RHC sample with high reversible capacity and desirable initial Coulombic efficiency (ICE). Additionally, the practical applications can be extended to cylindrical batterywith excellent cycle behaviors. Such facile approach can provide guidance for large-scale production of high-performance hard carbons and provides the possibility of building practical SIBs with high energy density and durability.

Tetrathiafulvalene carboxylate-based anode material for high-performance sodium-ion batteries.

Organic electrode materials are promising to be applied in sodium ion batteries (SIBs) due to their low cost and easily modified molecular structures. Nevertheless, low conductivity and high solubility in electrolytes still limit the development of organic electrodes. In this work, a carboxylate small molecule (BDTTS) based on tetrathiafulvalene is developed as anode material for SIBs. BDTTS has a large rigid π-conjugated planar structure, which may reduce solubility in the electrolyte, meanwhile facilitating charge transporting. Experimental results and theoretical calculations both support that apart from the four carbonyl groups, the sulfur atoms on tetrathiafulvalene also provide additional active sites during the discharge/charge process. Therefore, the additional active sites can well compensate for the capacity loss caused by the large molecular weight. The as-synthesized BDTTS electrode renders an excellent capacity of 230 mAh g-1 at a current density of 50 mA g-1 and an excellent long-life performance of 128 mAh g-1 at 2C after 500 cycles. This work enriches the study on organic electrodes for high-performance SIBs and paves the way for further development and utilization of organic electrodes.

Controllable Preparation and Sodium Storage Properties of Sb2Te3–Te Heterojunction

Antimony-based materials possess high theoretical capacities and suitable potential, which could be promising anode materials for sodium-ion batteries (SIB). However, poor stabilities and sluggish kinetics are drawbacks. Building heterojunction is an ideal method to solve these issues. Its unique structure develops internal electric fields spontaneously to boost the charge transport and relieve stress. Nevertheless, the controllable preparation of face-to-face (2D) heterojunctions is still hard-pressed. Herein, Sb2Te3–Te nanoheterojunctions, which consist of two-dimensional Sb2Te3 nanoblades attached to a one-dimensional Te nanorod, are fabricated through a two-step solvothermal method. Among that, the density of nanoblades is adjustable through the engineering feed ratio. When employed as anodes for SIBs, Sb2Te3–Te nanoheterojunctions display a reversible capacity of 463.2[Formula: see text]mAh[Formula: see text]g[Formula: see text] at 100[Formula: see text]mA[Formula: see text]g[Formula: see text]. Even a capacity of 305.5[Formula: see text]mAh[Formula: see text]g[Formula: see text] remains after 1000 cycles under a high current of 1.5[Formula: see text]A[Formula: see text]g[Formula: see text]. Moreover, the density functional theory (DFT) calculations also identify the high conductivity of heterojunction. This work offers an effective way to design the structures and properties of heterojunctions, further expanding their application range.

Novel paddy-like Bi-Sb-Cu alloy fabricated via pulse reverse potential electrodeposition enabling high-performance sodium-ion batteries

Sodium-ion batteries (SIBs) have gained remarkable interest as cost-effective and scalable energy storage devices. Nevertheless, their further application has been significantly hindered due to the limited selection of desirable anode materials that can provide both high capacity and excellent cycling stability. Herein, we developed a hierarchical paddy-like Bi42.3Sb35.2Cu22.5 alloy anode on Cu foil via template-free pulse reverse potential electrodeposition. The Bi42.3Sb35.2Cu22.5 anode obtains a considerable specific capacity of 529.5 mAh·g−1 after 120 cycles with a remarkable capacity retention of 95.5 %, signifying a capacity loss of only 0.0375 % per cycle. However, Bi44.9Sb55.1 anodes obtained by the pulse potential electrodeposition strategy reveal a conventional irregular cluster structure, delivering only 64.5 mAh·g−1 after 100 cycles and also demonstrating inferior rate performance compared to Bi42.3Sb35.2Cu22.5 anodes. The enhanced cycling performance of the paddy-like Bi42.3Sb35.2Cu22.5 anode is primarily attributed to the introduced Cu-doped network facilitating the rapid diffusion of Na+ and also ensuring the stability of the electrode structure. Moreover, the unique paddy-like structure of Bi42.3Sb35.2Cu22.5 mitigates volume expansion-related stress and facilitates efficient charge transport through open channels. This is further corroborated by conducting CV measurements, indicating a greater capacitive contribution in the case of the Bi42.3Sb35.2Cu22.5 electrode compared to the Bi44.9Sb55.1 electrode. Additionally, SEM images show a stabilized surface morphology for the Bi42.3Sb35.2Cu22.5 electrode after cycling, demonstrating improved electrochemical performance. This work offers new insights into the development of high-performance anode materials for SIBs.

Yolk-shell FeS@N-doped carbon nanosphere as superior anode materials for sodium-ion batteries

Iron sulfides have shown great potential as anode materials for sodium-ion batteries (SIBs) because of their high sodium storage capacity and low cost. Nevertheless, iron sulfides generally exhibit unsatisfied electrochemical performance induced by sluggish electron/ion transfer and severe pulverization upon the sodiation/desodiation process. Herein, we constructed a yolk-shell FeS@NC nanosphere with an N-doped carbon shell and FeS particle core via a simple hydrothermal method, followed by in-situ polymerization and vulcanization. The FeS particles intimately coupled with N-doped carbon can accelerate the electron transfer, avoid severe volume expansion, and maintain structural stability upon repeated sodiation/desodiation process. Furthermore, the small particle size of FeS can shorten ion-diffusion distance and facilitate ion transportation. Therefore, the FeS@NC nanosphere shows excellent cycling performance and superior rate capability that it can deliver a high capacity of 520.1 mAh g−1 over 800 cycles at 2.0 A g−1 and a remarkable capacity of 625.9 mAh g−1 at 10.0 A g−1.

Self-assembled nano-MnS@N,P dual-doped lignite based carbon as high-performance sodium-ion batteries anode

Manganese sulfide (MnS) is a suitable electrode material for use in sodium-ion batteries (SIBs) due to its high theoretical capacity and low cost. However, its practical application is still hampered by disadvantages such as large volume expansion during charging/discharging and limited cycle life. Therefore, reasonable structural design is of great importance in order to achieve an excellent sodium storage performance of the electrode materials for SIBs. Herein, nano-MnS@N,P dual-doped lignite based porous carbon (MnS@N,P-LPC) composite with a single MnS cube encapsulated in an N,P dual-doped lignite derived porous C is successfully prepared as superior anode material for SIBs. The multilayer pore structure and the combined effect of N and P dual-doping can enhance electrochemical performance by supplying more sodium storage sites. After 200 cycles at 0.1 A g−1, the composite complex produced a maximum capacity of 519 mA h g−1 and demonstrated a capacity of 392.5 mA h g−1 even at 1.6 A g−1. It exhibits outstanding cycling stability and superior rate performance. This excellent electrochemical performance is ascribed to the presence of the multilayer pore N,P dual-doped C skeleton, which effectively addresses the volume expansion of MnS particles during charging/discharging and facilitates efficient transport of ions and electrons through an effective conductive network.

Coupling the fast electron transportation of cobalt diselenide-based anode via cationic modulation for high rate Na+ storage

The sodium-ion batteries (SIBs), as compelling candidate for partially replacing lithium-ion batteries (LIBs) in relevant application scenarios, is gaining increasing attention. The development of high-rate performance anode materials for sodium-ion batteries is exceptionally crucial. Here, a ZIF (zeolitic imidazolate framework) compound targeting bimetallic cations has applied through a pyrolysis-induced in-situ selenization strategy. This resulted in a nitrogen-doped porous carbon-encapsulated Fe-ion-modified CoSe2 material with a rhombic dodecahedron morphology (Fe-CoSe2@NC). The architecture not only effectively alleviates the bulk stress induced by the insertion/extraction of sodium ions, but also enhances the migration and transport of electrons/ions. Additionally, Fe doping enhances the material's conductivity and expedites reaction kinetics. Consequently, the Fe-CoSe2@NC exhibits outstanding rate performance and cycling stability (362.54 mAh g-1 after 1000 cycles at a current density of 10.0Ag-1) when utilized as an anode for SIBs in a coin-type half-cell. The Fe-CoSe2@NC also delivers a high initial coulombic efficiency (ICE) of 70.14%. This is substantiated by diffusion analysis and in-situ electrochemical impedance spectroscopy (EIS) characterization. The charging and discharging mechanisms of Fe-CoSe2@NC were verified through XRD and TEM characterizations during the electrochemical processes. When coupled with Na3V2(PO4)3 as the cathode material to form a full cell, the Fe-CoSe2@NC// Na3V2(PO4)3 battery system achieves a high energy density of 112.05Whkg-1. In this study, the successful construction of a transition metal selenide anode material for SIBs characterized by a stable structure and facilitation of rapid ion migration was demonstrated.

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.

Liquid metal in prohibiting polysulfides shuttling in metal sulfides anode for sodium-ion batteries

Metal sulfides are a class of promising anode materials for sodium-ion batteries (SIBs) owing to their high theoretical specific capacity. Nevertheless, the reactant products (polysulfides) could dissolve into electrolyte, shuttle across separator, and react with sodium anode, leading to severe capacity loss and safety concerns. Herein, for the first time, gallium (Ga)-based liquid metal (LM) alloy is incorporated with MoS2 nanosheets to work as an anode in SIBs. The electron-rich, ultrahigh electrical conductivity, and self-healing properties of LM endow the heterostructured MoS2-LM with highly improved conductivity and electrode integrity. Moreover, LM is demonstrated to have excellent capability for the adsorption of polysulfides (e.g., Na2S, Na2S6, and S8) and subsequent catalytic conversion of Na2S. Consequently, the MoS2-LM electrode exhibits superior ion diffusion kinetics and long cycling performance in SIBs and even in lithium/potassium-ion battery (LIB/PIB) systems, far better than those electrodes with conventional binders (polyvinylidene difluoride (PVDF) and sodium carboxymethyl cellulose (CMC). This work provides a unique material design concept based on Ga-based liquid metal alloy for metal sulfide anodes in rechargeable battery systems and beyond.

Oxygen-driven closing pore formation in coal-based hard carbon for low-voltage rapid sodium storage

The coal-derived hard carbon is considered a promising anode material for sodium-ion batteries (SIBs) due to its ample resources, low cost, and unique pore structure. However, the ordered carbon microstructure of this material leads to inferior sodium storage capacity and low initial Coulombic efficiency (ICE). Herein, we propose a strategy to inhibit over-graphitization and promote the formation of closed pores during subsequent carbonation processes through oxygen-driven carbon sheets development. The formation mechanism of closed pores in coal-based hard carbon has been systematically established, and its contribution to the capacity of the low-voltage plateau in hard carbon anode for SIBs has been explained. In-situ characterizations demonstrate that the presence of abundant closed pores and moderate graphitization provides sufficient active sites for Na+ ion pore-filling. The closed pore structure ensured the realization of a high plateau capacity, resulting in a high reversible capacity of 303.1 mA h g−1, which was significantly higher than that of the open-pore dominant carbon (161.1 mA h g−1). This study offers innovative perspectives on designing high-performance carbon anodes with closed porosity, utilizing cost-effective and highly aromatic precursors.

Reasonable regulation of carbon layers and micropores to promote the extreme capacity of hard carbons for sodium-ion batteries

Hard carbons are classic anode materials for sodium-ion batteries (SIBs) with huge development potential. They have the advantages of high capacity and great stability. However, the complex and diverse structure poses a formidable challenge for the development of hard carbons. Carbon layers and pores are important components of hard carbons, they play important roles in sodium storage. Structural regulation is often used to improve the properties of hard carbons in order to enhance the sodium storage capacity. Hence, a series of hard carbons were prepared in this work. Zinc acetate was used to construct micropore structure, and the amount and morphology of micropores can be regulated by controlling the dosage of zinc acetate. The sodium storage capacity of hard carbons was maximized by adjusting the ratio of carbon layers to micropores reasonably. The optimized electrode can provide an ultra-high reversible capacity of 415.3 mAh/g. The amazing capacity can still maintain 292.2 mAh/g even at the high current of 2 A/g over 1000 cycles. This study regulates the proper control between carbon layers and micropores, which provides suitable insights for the research and development of hard carbons.

Heterostructure CoSe2/Sb2Se3 Nanocrystals Embedded into Nanocage-in-Nanofiber Carbon Framework for Ultralong-Life Sodium-Ion Batteries

Transition metal selenides are considered as one of the most promising anode materials for sodium-ion batteries (SIBs) on account of their high theoretical specific capacity. However, the poor conductivity, sluggish kinetics and volume expansion during the (de)sodiation process hinder its application. Herein, a novel heterostructure of CoSe2/Sb2Se3 nanocrystals embedded into nanocage-in-nanofiber carbon framework is designed and constructed via electrospinning, carbonization, ion exchange and selenization processes. In this structure, bimetallic selenide heterostructure accelerates electron/ion transfer kinetics and Na+ adsorption capacity, carbon nanocages structure alleviates the volume expansion and maintains structural integrity during the (de)sodiation process, and carbon nanofibers connect the nanocages in series to shorten the electron transmission path and enhance electrical conductivity. As a self-supporting anode for SIBs, as-synthesized CoSe2/Sb2Se3@C@CNF shows a high reversible capacity of 406 mAh g-1 at 0.2Ag-1 after 200 cycles and displays excellent rate capability. More remarkably, the CoSe2/Sb2Se3@C@CNF anode manifests an outstanding cycling stability for over 2000 and 12,000 cycles at 1 and 5Ag-1, with the capacity retention being 97% and 103% respectively. Meanwhile, the excellent sodium storage performance is revealed by kinetic analysis, energy level analysis and density functional theory calculations.

Zn0.76Co0.24S Embedded in Multiwalled Carbon Nanotubes as Anode Material for Sodium-Ion Batteries

Zn0.76Co0.24S Embedded in Multiwalled Carbon Nanotubes as Anode Material for Sodium-Ion Batteries

Double-enhanced core-shell Sb@Sb2O3 heterostructure encapsulated in porous carbon for long life sodium storage

Antimony (Sb) based materials have been regarded as highly competitive anodes sodium ion batteries (SIBs) due to their high theoretical capacity. However, it suffers from poor electrochemical performance because of the large volume expansion and the sluggish kinetics of the Na+ ions. To address the above problem, we prepare the core-shell Sb@Sb2O3 heterostructure encapsulated in a porous carbon (Sb@Sb2O3@C) as high performance anode material for SIBs. A facile NaCl template-assisted freeze-drying strategy could easily to acquire the porous carbon structure and the slow oxidation treatment process could realize the component from Sb to Sb@Sb2O3, finally Sb2O3. The perfect combination of core-shell Sb@Sb2O3 heterostructure with robust porous carbon can further accelerate the electron diffusion, promote the Na+ transfer, and enhance the structural stability of the electrode. Benefit from the advantages of structure and composition, the Sb@Sb2O3@C exhibits a long life and high rate capability for SIBs, with an initial discharge/recharge capacity of 530.2/446.7 mAh g−1 and an initial Coulombic efficiency of 84.3%. In addition, it displays a high rate capacity with 450 mA h g−1 at 1 A g−1 and excellent long-term cycling stability with 440.6 mAh g−1 after 5000 cycles even at a high current density of 5 A g−1.

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

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

Electrospun Core–Shell Carbon Nanofibers as Free-Standing Anode Materials for Sodium-Ion Batteries

Electrospun Core–Shell Carbon Nanofibers as Free-Standing Anode Materials for Sodium-Ion Batteries

Revealing Na+-coordination induced Failure Mechanism of Metal Sulfide Anode for Sodium Ion Batteries.

Metal sulfide (MS) is regarded as a promising candidate of the anode materials for sodium-ion battery (SIB) with ideal capacity and low cost, yet still suffers from the inferior cycling stability and voltage degradation. Herein, the coordination relationship between the discharge product Na2S with the Na+ (NaPF6) in the electrolyte, is revealed as the root cause for the cycling failure of MS. Na+-coordination effect assistants the dissolution of Na2S, further delocalizing Na2S from the reaction interface under the function of electric field, which leads to the solo oxidation of the discharge product element metal without the participation of Na2S. Besides, the higher highest occupied molecular orbital of Na2S suggest the facilitated Na2S solo oxidation to produce sodium polysulfides (NaPSs). Based on these, lowering the Na+ concentration of the electrolyte is proposed as a potential improvement strategy to change the coordination environment of Na2S, suppressing the side reactions of the solo-oxidation of element metal and Na2S. Consequently, the enhanced conversion reaction reversibility and prolonged cycle life are achieved. This work renders in-depth perception of failure mechanism and inspiration for realizing advanced conversion-type anode.

Cobalt-catalyzed soft-hard carbon composite anodes for enhanced sodium-ion storage

Hard carbon is expected to be a high-capacity anode material for sodium-ion batteries (SIBs). However, its Na+ storage performance, especially the low discharge capacity, remains a great challenge. Herein, the soft-hard carbon composite anodes with high degree of graphitization were synthesized via low-temperature pyrolysis (at only 900 °C) of Cobalt-catalyzed perylene tetracarboxylic dianhydride (PTCDA-Co) and cotton, with subsequent removal of cobalt. The composite resulting from a 2:3 mass ratio of soft to hard carbon exhibits a good discharge capacity of 355.81 mAh g−1 at a current density of 50 mA g−1 and an enhanced initial Coulombic efficiency (ICE) of 81.41%. The enhanced electrochemical storage performance of cotton is attributed to the introduction of PTCDA-Co, which creates low-defect graphitic layer, hierarchical porous channels, and carbon shielding coating on hard carbon.

Sulfur vacancies and heterogeneous interfaces promote high performance sodium storage of bimetallic chalcogenide hollow nanospheres

Transition metal sulfides have high theoretical capacities and are considered as potential anode materials for sodium-ion batteries. However, due to low inherent conductivity and significant volume expansion, the electrochemical performance is greatly limited. In this study, a nickel/manganese sulfide material (Ni0.96Sx/MnSy-NC) with adjustable sulfur vacancies and heterogeneous hollow spheres was prepared using a simple method. The introduction of a concentration-adjustable sulfur vacancy enables the generation of a heterogeneous interface between bimetallic sulfide and sulfur vacancies. This interface collectively creates an internal electric field, improving the mobility of electrons and ions, increasing the number of electrochemically active sites, and further optimizing the performance of Na+ storage. The direction of electron flow is confirmed by Density functional theory (DFT) calculations. The hollow nano-spherical material provides a buffer for expansion, facilitating rapid transfer kinetics. Our innovative discovery involves the interaction between the ether-based electrolyte and copper foil, leading to the formation of Cu9S5, which grafts the active material and copper current collector, reinforcing mechanical supporting. This results in a new heterostructure of Cu9S5 with Ni0.96Sx/MnSy, contributing to the stabilization of structural integrity for long-cycle performance. Therefore, Ni0.96Sx/MnSy-NC exhibits excellent electrochemical properties following our modification route. Regarding stability performance, Ni0.96Sx/MnSy-NC demonstrates an average decay rate of 0.00944% after 10,000 cycles at an extremely high current density of 10000 mA g−1. A full cell with a high capacity of 304.2 mA h g−1 was also successfully assembled by using Na3V2(PO4)3/C as the cathode. This study explores a novel strategy for interface/vacancy co-modification in the fabrication of high-performance sodium-ion batteries electrode.