Anode For Sodium-ion Batteries Research Articles

Nitrogen-Doped Bioderived Mesoporous Hard Carbon as a Promising Anode for Long-Life Sodium-Ion Battery

Nitrogen-Doped Bioderived Mesoporous Hard Carbon as a Promising Anode for Long-Life Sodium-Ion Battery

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.

The C-BixSnSb composite toward fast-charging and long-life sodium-ion batteries

Sodium ion batteries (SIBs) fitted with high-rate and high-capacity anodes are attractive for their higher energy density and faster charging capability. However, it is still a challenge to develop high-energy SIBs with high power and long life, due to the sluggish kinetic and limited Na+ insertion in electrode materials. The inherent crystal structure and constituent element are two important factors to resolve the critical issues faced above. Taking the merits of layer-structure and middle-entropy, herein, we proposed and designed a high ion-conductive composite combing with ternary alloy and layered BixSnSb@C nanofibers, which eliminate ion migration barriers while maintaining the structural framework for superior rate property and cycle stability. Used as anode for SIBs, the multiphase BixSnSb@C with adjustable Bi content exhibits excellent Na storage capability as compared to their single phase counterpart. Specially, up to a rate of 132C (50 A g−1), the capacity is still as high as 400 mAh g−1, meanwhile, after 5000 charge and discharge cycles at a current density of 12C, the capacity still maintains 85 % of its initial capacity, which outperform the individual Bi- or SnSb-based materials. The superior electrochemical performances originate from the middle-entropy nature and layer structure of BiSnSb alloy, which can provide more channels for fast Na+ transport, and accommodate large volume changes. Besides, the activity energy and ions transport resistance of Na+ in different composites were evaluated. Furthermore, the full-cell coupled with NaNi1/3Fe1/3Mn1/3O2 as cathode was formed and a capacity retention of ∼80 % is realized in 100 cycles. The results show that the BixSnSb@C is a potential anode for fast-charging Na-ion batteries and could be used to guide the design of multi-component alloy-base anodes.

Engineering fast diffusion channels in metal Sulfide/Selenide heterostructures via confinement effect for high-performance sodium storage

Structural modulation plays a pivotal role in enhancing the energy storage properties of electrochemical hybrids by adjusting their interfacial and electronic characteristics. Nevertheless, facile and effective strategies for tuning the structural properties of these hybrids at the nanoscale remain scarce. In this study, we propose a novel in-situ electrochemically self-driven strategy for embedding FeSe/FeS heterostructures with rich phase boundaries concurrently encapsulated into one-dimensional porous N, S-doped carbon tubes with inner void (FeSe/FeS@SNC). This approach facilitates the creation of heterogeneous interface phases via a simple electrochemical conversion from FeS0.75Se0.25. Notably, the resultant unique one-dimensional porous structure with inner void, along with a highly conductive N/S-co-doped carbon matrix, promotes charge transfer and reinforces structural stability. in-situ/ex-situ microscopic and spectroscopic characterizations, supported by theoretical simulations, validate that FeSe/FeS heterostructures offer rapid electron transport pathways, while the abundant heterojunctions with strong electric fields facilitate ion migration and Na adsorption. As an anode in sodium-ion batteries, the FeSe/FeS@SNC electrdoe exhibits exceptional rate capability (347 mAh/g at 10 A/g) and stable cycling performance (91% capacity retention after 12000 cycles).

Review and Recent Advances in Metal Compounds as Potential High-Performance Anodes for Sodium Ion Batteries

Review and Recent Advances in Metal Compounds as Potential High-Performance Anodes for Sodium Ion Batteries

Mo4/3B2Tx induced hierarchical structure and rapid reaction dynamics in MoS2 anode for superior sodium storage

Molybdenum sulfide (MoS2) with large layer distance and high theoretical capacity has been identified as one of the most promising anodes for sodium ion batteries, but the poor intrinsic conductivity and severe structural agglomeration restricted its diffusion kinetic and specific capacity. In this work, the synergistic effect of heterogeneous interface and Na2S adsorption/conversion active sites was employed to construct Mo4/3B2Tx-MoS2@C composites using a self-assembly and calcination strategy. Theoretical calculation and experimental results demonstrated that the charge transfer and interface between Mo4/3B2Tx and MoS2 along with the 3D hydrangea-like structure improved the intrinsic conductivity and provided fast ion diffusion channels, boosting the electrochemical kinetics; while the favorable adsorption of Na2S and weakened Na-S bond at Mo4/3B2Tx-Mo interface optimized the recombination energies of Mo-S bond, accelerating the ion diffusion and enhancing the electrochemical reversibility. In addition, the copious sulfur vacancies provided additional active sites for ion storage, ameliorating the electrochemical capacity. As expected, the novel Mo4/3B2Tx-MoS2@C electrode delivered a satisfactory rate capacity (340.6 mAh g−1 at 1 A g−1) and durable cyclic performance (267.2 mAh g−1 after 600 cycles at 2 A g−1). When paring with Na3V2(PO4)3, the Mo4/3B2Tx-MoS2@C||Na3V2(PO4)3 full cell exhibited high energy densities of 234.0 and 131.7 Wh kg−1 at 215.7 W kg−1 and 4.4 kW kg−1, respectively. The proposed synergistic strategy of heterogeneous interface and Na2S adsorption/conversion active sites provided a new guidance for the rational design of transitional metal sulfide anodes for sodium ion batteries.

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

AbstractMetal 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.

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.

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.

Tailoring of High-Valent Sn-Doped Porous Na3V2(PO4)3/C Nanoarchitechtonics: An Ultra High-Rate Cathode for Sodium-Ion Batteries.

NASICON structured Na3V2(PO4)3 (NVP) has captured enormous attention as a potential cathode for next-generation sodium-ion batteries (SIBs), owing to its sturdy crystal structure and high theoretical capacity. Nonetheless, its poor intrinsic electronic conductivity has led to inferior electrochemical performance in terms of rate capability and long cycling performance. To address this problem, a combined strategy is adopted, such as (1) carbon coating and (2) high valent Sn4+ ion doping in the lattice site of vanadium in the NVP cathode. Carbon coating can effectively enhance the surface electronic conductivity, wherein high-valent Sn4+ improves the bulk intrinsic electronic conductivity of the materials. Moreover, Sn is a well-known alloying/dealloying type anode for SIBs; thus, doping of such metal in cathode materials will assume the role of structure stabilizing pillars and establishing high-performing cathode materials. Herein, Na3V2-xSnx(PO4)3/C (denoted as Sn(x)-NVP/C, where x = 0.00, 0.03, 0.05, 0.07, 0.1) were synthesized via sol-gel route, followed by calcination at 800 °C. XRD, Raman, XPS, and electron microscopy data confirmed the high purity of the synthesized cathode. The optimized Sn(0.07)-NVP/C exhibited excellent electrochemical performance in terms of high rate capability and long cycling performance, a high appreciable capacity of 98 mAh g-1 with capacity retention of 85% after 500 cycles. Similarly, at a high current of 20C, it is still able to deliver a stable capacity of 76 mAh g-1 with 85% capacity retention after 3000 cycles. The rate capability study indicates the high current tolerance of Sn(0.07)-NVP/C up to 70 C with a capacity delivery of 55 mAh g-1. It is worth mentioning that CV and EIS analysis for Sn(0.07)-NVP/C cathode displayed minimum voltage polarization and enhanced diffusion coefficient. Moreover, DFT calculation also proved that the electronic and ionic conductivity of NVP is promoted by Sn doping. Hence, the present results demonstrated that Sn(0.07)-NVP/C is considered a promising cathode for sodium-ion battery application.

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

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

Amorphous Fe2O3 Anchored on N-Doped Graphene with Internal Micro-Channels as an Active and Durable Anode for Sodium-Ion Batteries.

The reduced graphene oxide (rGO) exhibits outstanding electrical conductivity and a high specific surface area, making it a promising material for various applications. Fe2O3 is highly desirable due to its significant theoretical capacity and cost-effectiveness, high abundance, and environmental friendliness. However, the performance of these r-GO/Fe2O3 composite electrodes still needs to be further improved, especially in terms of cycle stability. The composite of Fe2O3 anchored on N-doped graphene with inside micro-channels (Fe2O3@N-GIMC) was used to be efficiently prepared. Because the inside channels can furnish extra transmission pathways and absorption websites and the interconnected structure can efficaciously forestall pulverization and aggregation of electrode materials. In addition, N doping is also beneficial to improve its electrochemical performance. Thus, it demonstrates exceptional sodium storage characteristics, including notable electrochemical activity, impressive initial Coulombic efficiency, and favorable rate performance. The optimized Fe2O3@N-GIMC indicates outstanding discharge capacity (573.5 mAh g-1 at 1 A g-1), significant rate performance (333.6 mAh g-1 at 8 A g-1), and stable long-term cycle durability (308.9 mAh g-1 after 1000 cycles at 1 A g-1, 200.8 mAh g-1 after 4000 cycles at 1 A g-1) as a sodium-ion battery anode. This presents a new approach for preparing graphene-based high-functional composites and lays a stable basis for further expanding its application field.

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.

Pseudocapacitive contribution in sulfur-doped porous carbon nanosheets enables high-performance sodium-ion storage

Sulfur-doped carbon materials have sparked considerable attention as the anodes for sodium-ion batteries (SIBs) due to their relatively high reversible specific capacity and excellent pseudocapacitive effect. However, the content of sulfur dopants in carbon materials is usually limited and an efficient doping strategy is urgently imperative to date. Herein, a space-confined doping strategy is proposed to fabricate porous carbon nanosheets with high sulfur dopant content by using low-cost pitch as a precursor with the help of sodium thiosulfate (Na2S2O3). The thermostable nano-MgO used in this system can occupy the specific space during pitch decomposition to induce the formation of hierarchical carbon nanosheets. Interestingly, such a space-confinement effect of nano-MgO is able to enlarge the accessible contact area of reactants and inhibit the loss of sulfur from Na2S2O3, thus significantly increasing sulfur dopant content within carbon frameworks. The optimized sulfur-doped carbon nanosheets (S-PCNs-2) with a high sulfur content of about 20.56 wt% as anode for SIBs delivers an ultrahigh pseudocapacitive contribution of 92.55 % at 5 mV s−1 and thus enable a desirable specific capacity of 428.6 mAh g−1 at 0.1 A g−1 with a high initial Coulombic efficiency of 84.9 % and superior rate performance of 380.6 mAh g−1 at 5 A g−1. Furthermore, a long cycling lifespan with a capacity retention of 88 % after 1000 charge/discharge cycles can be achieved for the S-PCNs-2 anode. This work provides a simple yet efficient doping approach to fabricate carbon anodes with high heteroatom contents for SIBs.

Hybrid catalyst‐assisted synthesis of multifunctional carbon derived from Camellia shell for high‐performance sodium‐ion batteries and sodium‐ion hybrid capacitors

AbstractBiomass‐derived carbon as energy storage materials have gradually attracted widespread attention due to their low cost, sustainability, and inherent structural advantages. Herein, hard carbon (H‐1200) and porous carbon (PC‐800) for sodium‐ion batteries (SIBs), sodium‐ion capacitors (SICs) half cells and sodium‐ion hybrid capacitors (SIHCs) have been synthesized from the same biomass precursor of Camellia shells through different treatments. H‐1200 synthesized by directly high‐temperature carbonization possesses a rational graphitic layer structure and plentiful heteroatoms. When applied as anode for SIBs, it exhibits a reversible capacity of 365.5 mAh g–1 at 25 mA g–1 and capacity retention 89.0% after 400 cycles at 200 mA g–1. Additionally, PC‐800 prepared by catalytic carbonization of K2C2O4/CaC2O4 hybrid catalyst has a sophisticated porous structure and a high surface area of 2186.9 m2 g–1. When employed as a cathode for SICs, it delivers a maximum capacity 104.2 mAh g–1 at 100 mA g–1 and 35.0 mAh g–1 at 5 A g–1. Furthermore, the all carbon assembled SIHC (H‐1200||PC‐800) using H‐1200 as anode and PC‐800 as cathode, features a broad output voltage range (0.01 ~ 4.1 V), high energy density of 161.5 Wh kg–1, power density of 12896.1 W kg–1, and superior capacity retention of 90.32% after 10000 cycles at 10 A g–1. This research result provide a new horizon for constructing low‐cost and large‐scale production of biomass derived carbon for energy storage materials.

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.

Low-Surface-Area Nitrogen-Doped Carbon Submicrospheres as High-Coulombic-Efficiency and High-Capacity Anodes for Practical Sodium-Ion Batteries.

Nitrogen-doped carbon submicrospheres (NCSMs) are synthesized via an efficient and environmentally friendly one-pot polymerization reaction at room temperature, in which dopamine hydrochloride serves as the source for both carbon and nitrogen. Through leverage of its distinctive structure characterized by minimal surface area, fewer oxygen-containing functional groups, and a heightened presence of active nitrogen-doping sites, the synthesized NCSM showcases a noteworthy initial Coulombic efficiency (ICE) of 84.8%, a remarkable sodium storage capacity of 384 mAh g-1, an impressive rate capability of 215 mAh g-1 at 10 A g-1, and a superior cyclic performance, maintaining 83.0% of its capacity after 2000 cycles. The submicron spherical structure, with its limited surface area and scarce oxygen-containing moieties, effectively curtails the irreversible sodium-ion loss in solid-electrolyte interphase film formation, resulting in heightened ICE. The abundant nitrogen doping can expand carbon-layer spacing as well as improve the electron/ion-transport dynamics, guaranteeing a high sodium storage capacity and a strong rate capability. Crucially, the synthesis method presented here is straightforward, effective, and amenable to scaling, offering a novel avenue for the commercialization of sodium-ion batteries.

Binary Co3S4/SnS chalcogenide composites anchored on graphene oxide and carbon nanotubes as anodes for Na-ion batteries

Hetero-architectures are smart for modern energy storage appliances owing to fast charge transportation. However, the smooth and rational assembly with adequate Na+ storage kinetics so far is a significant challenge. Herein, transition-bimetallic sulfides hetero-structured Co3S4/SnS (CTS) and its composites implanted in reduced graphene oxide (CTS.rGO) and carbon nanotubes (CTS.CNTs) have been synthesized and employed as anodes for sodium-ion batteries. The use of highly conductive nature of carbon frames benefits the stability and conductivity of the bimetallic sulfides CTS composites. As a result, the CTS.CNTs delivered a charge capacity 298 mAh/g, whereas CTS.rGO and bare CTS exhibited 229 and 76 mAh/g after 200cycles at 0.05C. In addition, the CTS.CNTs and CTS.rGO displayed excellent rate performance at different rates (0.05C – 10.0C) and upon reversing the C-rate to 0.05C, CTS.CNTs fully restored the charge capacity 329 mAh/g while CTS.rGO restored to 293 mAh/g. The ultra-cyclic stability and improved rate performance enlightening the synergistic effect between CTS and carbon conducting agents. Moreover, the CTS.CNTs displayed the lowest charge transfer resistance (Rct = 604 Ω) as compared to CTS.rGO and bare CTS (Rct = 618 Ω, Rct = 642 Ω), indicating the rapid charge transport.

Regulating the “core-shell” microstructure of hard carbon through sodium hydroxide activation for achieving high-capacity SIBs anode

Pore structure engineering has been acknowledged as suitable approach to creating active sites and enhancing ion transport capabilities of hard carbon anodes. However, conventional porous carbon materials exhibit high BET and surface defects. Additionally, the sodium storage mechanism predominantly occurs in the slope region. This contradicts practical application requirements because the capacity of the plateau region is crucial for determining the actual capacity of batteries. In our work, we prepared a novel “core-shell” carbon framework (CNA1200). Introducing closed pores and carboxyl groups into coal-based carbon materials to enhance its sodium storage performance. The closed pore structure dominates in the “core” structure, which is attributed to the timely removal of sodium hydroxide (NaOH) to prevent further formation of active carbon structure. The presence of closed pores is beneficial for increasing sodium ion storage in the low-voltage plateau region. And the “shell” structure originates from coal tar pitch, it not only uniformly connects hard carbon particles together to improve cycling stability, but is also rich in carboxyl groups to enhance the reversible sodium storage performance in slope region. CNA1200 has excellent electrochemical performance, it exhibits a specific capacity of 335.2 mAh g−1 at a current density of 20 mA g−1 with ICE = 51.53 %. In addition, CNA1200 has outstanding cycling stability with a capacity retention of 91.8 % even when cycling over 200 times. When CNA1200 is used as anode paired with Na3V2(PO4)3 cathode, it demonstrates a capacity of 109.54 mAh g−1 at 0.1 C and capacity retention of 94.64 % at 0.5 C. This work provides valuable methods for regulating the structure of sodium-ion battery (SIBs) anode and enhances the potential for commercialization.