Anode Material For Sodium-ion Batteries Research Articles

Double-layer carbon coated on the micrometer bismuth by photothermal effect as anode for high-rate sodium-ion batteries

Bismuth (Bi) is considered a promising anode material for high-rate sodium-ion batteries (SIBs) due to its unique layered crystal structure which can easily insert/extract sodium-ion (Na+). However, the cycle stability of micrometer Bi with great commercial potential needs to be improved. Because the large volume change occurs during alloying/dealloying of Bi and sodium (Na) resulting in the crack of Bi, which reduces the stability of the battery. Herein, we design a Bi/Bi2O3@C composite where a double-layer carbon coated commercial micrometer Bi/Bi2O3 particles. The heat generated by Bi/Bi2O3 particles under ultraviolet (UV) exposure (called photothermal effect) accelerates the decomposition rate of photoinitiator, which in turn improves the polymerization rate of the monomer on the surface of Bi/Bi2O3 particles. So that, the surface of Bi/Bi2O3 particles is coated with a dense polymer, while the polymer away from the particle is relatively loose, thus forming a dense-loose double-layer carbon during the annealing process. The dense carbon layer can effectively protect against the volume effect of Bi/Bi2O3, and the loose carbon layer can provide channels for the transport of Na+. As a result, Bi/Bi2O3@C exhibits excellent cycling stability with a capacity retention rate of 94.5 % after 1600 cycles at 10 A g−1.

Constructing Ti-O-C bond in Na0.23TiO2@N-doped carbon sphere using dihydroxybenzene as an anode material for sodium-ion batteries

Na0.23TiO2 particles coated on a nitrogen-doped carbon sphere (NTO@NCS) were synthesized using dihydroxybenzene and hexamethylenetetramine as carbon and nitrogen sources, respectively. In the NTO@NCS-R sample, Na0.23TiO2 particles uniformly cover the surface of electrically conductive NCS by forming the Ti-O-C bonds between Na0·23TiO2 and NCS. The feature is favorable to provide the NTO electrode the structural robustness and sodium ion diffusion during cycling. The NTO@NCS-R electrode exhibits an outstanding discharge capacity of 193.1 mAh g−1 at 0.1 A g−1 after 300 cycles in the voltage range of 0.01–2.5 V, compared to bare Na0·23TiO2, NTO@NCS-C, and NTO@NCS-H. In addition, NTO@NCS-R exhibits a discharge capacity of 114.4 mAh g−1 at 1.0 A g−1 at 2000th cycle and 58.7 mAh g−1 at 2.0 A g−1 at 8000th cycle, respectively, proving fast sodium ion diffusion and excellent cycle stability during long-term cycles.

Effect of polypyrrole-derived N-doped carbon coating on the sodium storage properties of NiCo2S4 synthesized by recycling discarded mobile phone batteries

NiCo2S4 with a spherical spinel structure was innovatively synthesized from discarded mobile phone batteries using a simple hydrothermal method, and the surface was coated with N-doped carbon to form NiCo2S4@NC. The products were used as anode materials of sodium-ion batteries to study the effect of the N-doped carbon layer on the electrochemical properties, structure and morphology. The results of XRD, FESEM and TEM revealed that the N-doped carbon layer derived by carbonizing polypyrrole had a minimal effect on the structure and morphology of NiCo2S4, but was coated on the surface of NiCo2S4 with different thicknesses to adjust the electrochemical performance. The presence of N-doped carbon in NiCo2S4@NC was confirmed by Raman spectroscopy. The mesoporous structure of NiCo2S4 and NiCo2S4@NC was corroborated by N2 adsorption-desorption isotherm analysis, and the optimal specific surface area and pore size were 23.14 cm2/g and 18.0 nm, respectively. X-ray photoelectron spectroscopy indicated that Co2+/Co3+ and Ni2+/Ni3+ coexist in the spinel NiCo2S4@NC50 synthesized upon adding 50 μL of pyrrole monomer. NiCo2S4@NC50 outperformed other products in terms of its electrochemical properties, where its initial discharge specific capacity under the current density of 0.1 A g−1 was 1099.6 mA h g−1 and the specific capacity following 100 cycles reached 327.5 mA h g−1. NiCo2S4@NC50 exhibited an optimal electrochemical performance and demonstrated a competent approach toward recycling discarded mobile phone batteries and building electrodes with high performance for use in energy equipment.

Exploration of electrochemical behavior of Sb-based porous carbon composites anode for sodium-ion batteries

Sb-based materials are considered as promising anode materials for sodium-ion batteries (SIBs) due to their excellent sodium storage capacities and suitable potentials. However, the Sb-based anodes usually suffer from intense volume expansion and severe pulverization during the alloying-dealloying process, resulting in poor cycling performance. Herein, a composite anode with Sb/Sb2O3 nanoparticles embedded in N-doped porous carbon is prepared by the gas–solid dual template method. The volume change of the anode material is mitigated by the carbon layer enwrapping and the confinement of the porous structure. Nitrogen doping provides abundant sodium storage sites, thus enhancing the storage capacity of sodium ion. Furthermore, to gain the accurate kinetic interpretation of the electrochemical process, an ex-situ transmission electron microscope (TEM) characterization combined with distribution of relaxation times (DRT) is conducted. The Sb/Sb2O3@NPC-1.0 demonstrates excellent electrochemical performance, achieving 340.3 mAh g−1 at 1A g−1, and maintains a capacity of 86.7 % after 1000 cycles. This work paves the way for the practical application of SIBs with high-performance and long-life Sb-based anodes.

Preparation of high-performance anode materials for sodium-ion batteries using bamboo waste: Achieving resource recycling

Bamboo exhibits various excellent properties and is widely used in construction. However, appropriate disposal of the bamboo waste generated in a green manner is difficult. To realize resource recycling, we used a simple treatment method to prepare waste bamboo as a negative electrode material exhibiting considerable electrochemical properties for sodium-ion batteries. The electrochemical properties of high-temperature calcination materials considerably improved after impurity removal treatment using an acid solution, which was performed to eliminate the influence of impurities on electrochemical properties. However, the materials still could not meet commercial requirements. A simple pre-oxidation modification treatment enabled the introduction of O atoms into the carbon skeleton to expand the layer spacing, improved the transport kinetics of Na+ in the carbon skeleton, and further increased the platform capacity of the pre-oxidation material. The preoxidative high-temperature co-treated materials exhibited a specific charge capacity close to 280 mAh g−1 at a 0.1 C rate and a capacity attenuation of almost zero after 100 cycles, and showing a specific charge capacity of more than 150 mAh g−1 at a 2 C rate test. In the context of sustainable development, this study makes waste bamboo become a candidate of low-cost negative electrode material for sodium-ion batteries.

Enhancing the sodium-ion storage performance of two-dimensional layered Ti3CN with a molecular riveting strategy

Adjustable 2D layered MXenes hold considerable promising as anode materials for sodium-ion batteries. However, the serious self-stacking and volume variation during sodium-ions insertion/extraction processes inevitably result in inferior rate capability and terrible cycle stability. Herein, we report a novel and effective “molecular riveting” strategy to simultaneously adjust the interlayer spacing and stabilize layered structure of Ti3CN (TCN), which is realized by riveting L-Aspartic acid/L-Glutamic acid/L-2-Aminoadipic acid (LAA/LGA/L2AA, abbreviated as LXA) molecules into interlayers of TCN (named as LAA-TCN/LGA-TCN/L2AA-TCN and abbreviated as LXA-TCN) to form strong amido (HN-C = O) bonds. The riveted LXA molecules between the interlayer of TCN contribute double effects of pillar and strain, achieving the maximum utilization of the 2D layered TCN. As consequences, the interlayer spacing of TCN can be broadened from 1.04 nm to 1.31 nm via altering the carbon chain length of LXA molecules, and the Na+ migration barrier can be reduced from 0.71 eV to 0.08 eV. Meanwhile, the L2AA-TCN with maximum interlayer spacing exhibits a significantly improved reversible capacity of 121.7 mAh/g (45.0 mAh/g for TCN) at 1.0 A/g. The constructed L2AA-TCN//NVP sodium-ion battery (SIB) displays excellent cycle stability with the capacity-retention of 96.6 % after 200 cycles at 10 C. This work opens a new way to broaden interlayer spacing and hinder enormous volume variation of 2D layered MXenes.

Reduced Graphene Oxide-Supported SrV4O9 Microflowers with Enhanced Electrochemical Performance for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have received considerable attention in recent years. Anode material is one of the key factors that determine SIBs' electrochemical performance. Current commercial hard carbon anode shows poor rate performance, which greatly limits applications of SIBs. In this study, a novel vanadium-based material, SrV4O9, was proposed as an anode for SIBs, and its Na+ storage properties were studied for the first time. To enhance the electrical conductivity of SrV4O9 material, a microflower structure was designed and reduced graphene oxide (rGO) was introduced as a host to support SrV4O9 microflowers. The microflower structure effectively reduced electron diffusion distance, thus enhancing the electrical conductivity of the SrV4O9 material. The rGO showed excellent flexibility and electrical conductivity, which effectively improved the cycling life and rate performance of the SrV4O9 composite material. As a result, the SrV4O9@rGO composite showed excellent electrochemical performance (a stable capacity of 273.4 mAh g-1 after 200 cycles at 0.2 A g-1 and a high capacity of 120.4 mAh g-1 at 10.0 A g-1), indicating that SrV4O9@rGO composite can be an ideal anode material for SIBs.

Overview of coals as carbon anode materials for sodium-ion batteries

Abstract Energy storage is an important technology in achieving carbon-neutrality goals. Compared with lithium-ion batteries, the raw materials of sodium-ion batteries are abundant, low-cost, and highly safe. Furthermore, their costs are expected to be further reduced as large-scale applications take off, making them viable for energy storage applications. The primary anode material for sodium-ion batteries is hard carbon, which has a high sodium-ion storage capacity but is relatively expensive, limiting its applications in energy storage. In order to widen the applications of sodium-ion batteries in energy storage and other fields, it is particularly important to develop anode materials that have both high performance and low cost. Coals, with abundant reserves and worldwide availability, can serve as low-cost carbon sources for anode materials. Additionally, coals of different grades of metamorphism have different structural characteristics that can be tailored for the structural characteristics of coal-based anode materials for sodium-ion batteries. Recent research on tailoring coals as the anode materials for sodium-ion batteries is summarized and the recent progress made towards mitigating the existing issues is analysed in this review. Specifically, the impacts of different grades of metamorphism on the sodium-ion storage performance of coal-based anode materials prepared using direct carbonization are discussed in detail. Studies on improving the electrochemical performances of coal-based anode materials through pore and microcrystalline structure controls and surface as well as interface modifications are presented. Finally, the advantages and disadvantages of different preparation methods are identified. To make the industrial applications of coal-based anode materials for sodium-ion batteries more viable, the importance of the de-ashing process is introduced.

Deciphering Sodium-Ion Storage: 2D-Sulfide versus Oxide Through Experimental and Computational Analyses.

Transition metal derivatives exhibit high theoretical capacity, making them promising anode materials for sodium-ion batteries. Sulfides, known for their superior electrical conductivity compared to oxides, enhance charge transfer, leading to improved electrochemical performance. Here, a hierarchical WS2 micro-flower is synthesized by thermal sulfurization of WO3. Comprising interconnected thin nanosheets, this structure offers increased surface area, facilitating extensive internal surfaces for electrochemical redox reactions. The WS2 micro-flower demonstrates a specific capacity of ≈334mAhg-1 at 15mAg-1, nearly three times higher than its oxide counterpart. Further, it shows very stable performance as a high-temperature (65°C) anode with ≈180mAhg-1 reversible capacity at 100mAg-1 current rate. Post-cycling analysis confirms unchanged morphology, highlighting the structural stability and robustness of WS2. DFT calculations show that the electronic bandgap in both WS2 and WO3 increases when going from the bulk to monolayers. Na adsorption calculations show that Na atoms bind strongly in WO3 with a higher energy diffusion barrier when compared to WS2, corroborating the experimental findings. This study presents a significant insight into electrode material selection for sodium-ion storage applications.

Waste tire-derived graphene modified carbon as anodes for sodium-ion batteries

The rational disposal of waste tires poses a ubiquitous challenge globally. Pyrolytic carbon black, a solid by-product produced through pyrolysis, has great application prospects. Carbon-based materials are regard as the most potential commercial anode materials for sodium-ion batteries (SIBs)， which features cheap, environmentally friendly, and low reaction potential. In this study, three-dimensional vertical graphene composite (TCBp@VGSs) was synthesized from waste tires. The graphene with higher defectiveness offers an increased number of active sites for Na+, while the vertically aligned graphene facilitates rapid electron transfer. As a result, the TCBp@VGSs electrode demonstrates the ability to maintain a reversible capacity of 252.7 mAh g−1 after 100 cycles at a current density of 0.2 A g−1. Furthermore, it exhibits a sustained rate performance of 105.4 mAh g−1 at a current density of 5 A g−1. Moreover, even after 1900 cycles at a current density of 1 A g−1, a reversible capacity of 171.5 mAh g−1 is retained, showcasing good stability and a significantly higher capacity compared to TCBp-1100. This study introduces novel approaches for the high-value utilization of solid-phase by-products from waste tires, offering certain economic benefits, and contributes fresh insights into the advancement of SIBs anodes.

Pristine and defective 2D SiCN substrates as anode materials for sodium-ion batteries

Exploring more high-performance anode materials for sodium-ion batteries (SIBs) can smoothly help to build a more sustainable, cleaner, and reliable energy system. This study systematically investigates the potential of 2D pristine SiCN (p-SiCN) and defective (d-SiCN) substrate as candidate materials for SIBs anodes using first-principles computational method. The computational results reveal that the p-SiCN possesses excellent thermal stability and structural cyclical performance, good conductivity, high theoretical specific capacity (1486 mAh·g−1), low diffusion barrier (0.177 eV), and appropriate open-circuit voltage (0.340 V), which allows the p-SiCN substrate more suitable as a potential anode material for SIBs. Furthermore, by investigating the effects of intentionally designed defects on p-SiCN, it is observed that the adsorption energy and diffusion barrier of the Na atom on the d-SiCN substrate increase. Our work demonstrates that investigating the effect of defects on p-SiCN can better explore the properties of anode materials, thus further optimizing the battery performances.

Design of the Particle Size and Morphology of Hard Carbon Anode Materials for Sodium-Ion Batteries Through Hydrothermal Carbonization

With sodium-ion batteries (SIBs) finding widespread application, the demand grows for hard carbon, the most popular anode material for SIBs. Hydrothermal carbonization facilitates the production of hard carbon with desired characteristics from various sources. Despite the considerable volume of literature addressing this subject, there is a notable absence of investigations elucidating the relationship between synthesis conditions and the electrochemical characteristics of the product. Here we study systematically the influence of hydrothermal carbonization parameters on hard carbon characteristics and emphasize the potential of hard carbon as an anode material for SIBs. The initial Coulombic efficiency (ICE) is significantly affected by the particle size of the glucose-derived hard carbon, which, in turn, depends on glucose concentration in the initial solution, pH, and stirring regime. By optimizing the hydrothermal carbonization parameters, the ICE up to 91% and a good reversible capacity of ∼300 mAh g−1 in a half cell are achieved. Full cells with Na3(VO)2(PO4)2F cathode material demonstrate ICE of about 80% and reversible capacity of up to 100 mAh g−1 cath. Considering the effective performance of pouch-cell SIB prototypes based on Na3(VO)2(PO4)2F and hard carbon, hydrothermal carbonization of glucose yields hard carbon with the necessary characteristics required for its successful application in SIBs.

First-principles study on the electrochemical properties of Na-ion-intercalatable heterostructures formed by transitional metal dichalcogenides and blue phosphorus

Extensive first-principles calculations have been performed to examine the electrochemical properties of Na-ion-intercalatable heterostructures formed by transitional metal dichalcogenides (MS2, where M = Ti, V, Nb and Mo) and blue phosphorus (BlueP), which have been reported as potential anode materials for rechargeable sodium-ion batteries. Upon formation of heterostructures, much improved structural stabilities have observed compared with the pristine MS2 and BlueP. Metallic T-TiS2, T-MoS2, H(T)-VS2 and H(T)-NbS2 would retain the conductive character after formation of heterostructures with BlueP, however, H-TiS2/BlueP and H-MoS2/BlueP would undergo a semiconductor to metallic transition accompanied by Na intercalation. Moreover, the presence of relatively low diffusion barriers ranging from 0.04 eV to 0.08 eV, coupled with the suitable average open-circuit voltage spanning from 0.12 eV to 0.89 eV, guarantee exceptional charge-discharge rates and ensure the safety of battery performance. Among these heterostructures, H(T)-NbS2/BlueP and T-TiS2/BlueP exhibit best Na adsorption ability of up to 4 layers, corresponding to theoretical capacities of 570.2 and 746.7 mAh/g, respectively. These encouraging properties indicate that T-TiS2/BlueP and H(T)-NbS2/BlueP could serve as suitable anode materials for high-performance sodium-ion batteries.

Heterostructured MnSe/FeSe nanorods encapsulated by carbon with enhanced Na+ diffusion as anode materials for sodium-ion batteries

The natural abundance of sodium has fostered the development of sodium-ion batteries for large-scale energy storage. However, the low capacity of the anodes hinders their future application. Herein, carbon-encapsulated MnSe-FeSe nanorods (MnSe-FeSe@C) have been fabricated by the in-situ transformation from polydopamine-coated MnO(OH)-Fe2O3. The heterostructure constructed by MnSe and FeSe nanocrystals induces the formation of built-in electric fields, accelerating electron transfer and ion diffusion, thereby improving reaction kinetics. In addition, carbon enclosure can buffer the volumetric stress and enhance the electrical conductivity. These aspects cooperatively endow the anode with superior cycling stability and distinguished rate performance. Specifically, the discharge capacity of MnSe-FeSe@C reaches 414.3 mA h g−1 at 0.1 A g−1 and 388.8 mA h g−1 even at a high current density of 5.0 A g−1. In addition, it still retains a high reversible capacity of 449.2 mA h g−1 after 700 long cycles at 1.0 A g−1. Further, the ab initio calculation has been employed to authenticate the existence of the built-in electric field by Bader charge, indicating that 0.24 electrons in MnSe were transferred to FeSe. The in-situ XRD has been used to evaluate the phase transition during the charging/discharging process, revealing the sodium ion storage mechanism. The construction of heterostructure material paves a new way to design performance-enhanced 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.

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.

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 0.2 A g-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 5 A g-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.

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 10.0 A g-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 112.05 Wh kg-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.

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.

Hydrothermally Assisted Conversion of Switchgrass into Hard Carbon as Anode Materials for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are emerging as a viable alternative to lithium-ion batteries, reducing the reliance on scarce transition metals. Converting agricultural biomass into SIB anodes can remarkably enhance sustainability in both the agriculture and battery industries. However, the complex and costly synthesis and unsatisfactory electrochemical performance of biomass-derived hard carbon have hindered its further development. Herein, we employed a hydrothermally assisted carbonization process that converts switchgrass to battery-grade hard carbon capable of efficient Na-ion storage. The hydrothermal pretreatment effectively removed hemicellulose and impurities (e.g., lipids and ashes), creating thermally stable precursors suitable to produce hard carbon via carbonization. The elimination of hemicellulose and impurities contributes to a reduced surface area and lower oxygen content. With the modifications, the initial Coulombic efficiency (ICE) and cycling stability are improved concurrently. The optimized hard carbon showcased a high reversible specific capacity of 313.4 mAh g-1 at 100 mA g-1, a commendable ICE of 84.8%, and excellent cycling stability with a capacity retention of 308.4 mAh g-1 after 100 cycles. In short, this research introduces a cost-effective method for producing anode materials for SIBs and highlights a sustainable pathway for biomass utilization, underscoring mutual benefits for the energy and agricultural sectors.