Anode For Sodium-ion Batteries Research Articles

N, S-Codoped 3D Carbon Protected Nanoporous MnS With Record High Sodium Ion Storage Performance for Potential Industry Applications.

With a high theoretical capacity, the MnS anode, however, exhibits a rather complex sodium diffusion kinetics and poor mechanical stability that hinder its application in sodium-ion batteries (SIBs). In this work, a simple, economical, and scalable strategy is developed to inherently coat nanoporous MnS with a 3D N, S co-doped thin carbon layer by using commercially available MnCO3 as precursors. Specifically, the strategy involves a two-step annealing process, which converts the MnCO3 microparticles into nanoporous Mn2O3 and MnS step by step. The 3D N, S codoped carbon layer is in situ formed during the second annealing process by first coating the nanoporous Mn2O3 with a polyaniline layer. Due to the inherent 3D carbon protection and the strong electronic interaction between N, S dopants and MnS, the N, S codoped carbon protected MnS obtained at 900 °C (NS-C@MnS-900) anode displays a high specific capacity of 845mAhg-1 at 0.1Ag-1, which is higher than all reported MnS-based SIB anodes. It also shows an outstanding cyclability and rate performance, maintaining a stable capacity of ≈493mAhg-1 after 1300 cycles at 10Ag-1, which is also the best according to knowledge. These exceptional electrochemical performances and the scalable/simple/low-cost synthesis make the NS-C@MnS-900 attractive for industry application.

Electrolyte-Salts Regulated Hydrogen-Bonding Configuration and Interphase Formation Achieving Highly Stable Anode for Rechargeable Aqueous Sodium-Ion Batteries.

Hydrogen evolution reactions that cause the alkalization of aqueous electrolytes generally frustrate the structural stability and cycling performance of NaTi2(PO4)3/C anode material for rechargeable aqueous sodium-ion batteries (ASIBs). Herein, a novel highly concentrated electrolyte with a large hydrogen-evolution overpotential and hydroxide-capture ability is rationally established by incorporating a bifunctional Mg(Ac)2 additive into a concentrated NaAc aqueous solution. The highly concentrated electrolyte salts (4m NaAc+3m Mg(Ac)2) favor regulation on hydrogen-bonding configurations and kinetically shift the hydrogen evolution potential to a lower value of -1.37 V (vs Ag/AgCl). The Mg(Ac)2 additive plays particular roles in spontaneously capturing hydroxide ions generated during hydrogen evolution reactions on anode surfaces and simultaneously forming a protective Mg(OH)2-like interphase. As a result, the unique electrolyte significantly improves the structural stability and cycling performance of NaTi2(PO4)3/C anode (94.8% capacity retention after 100 cycles at 100 mA·g-1). The effect of salt concentration on hydrogen bonding configurations of aqueous electrolytes is investigated with Raman spectroscopy and FTIR spectroscopy. The interphase is identified by coupling EDS mapping, X-ray photoelectron spectroscopy, and X-ray diffraction. This work provides a new strategy for improving the cycling stability of aqueous sodium-ion batteries.

Electrolyte Reconfiguration by Cation/Anion Cross-coordination for Highly Reversible and Facile Sodium Storage.

Hard carbon (HC) materials are promising anodes for sodium-ion batteries (SIBs) owing to low cost, high specific capacity and low working potential. However, the poor compatibility of the electrolyte with HC leads to low initial coulombic efficiency (ICE) and sluggish Na+ transport kinetics. Here, we propose an electrolyte reconfiguration strategy based on the hard and soft acid and base (HSAB) theory by introducing methyltriphenylphosphonium bromide (MTPPB). MTPPB can realize a spontaneous cross-coordination solvation structure with NaPF6 by selective affinity, synchronously optimizing the interfacial chemistry and sodium storage process. The advantages of the chemical π-π bridging of MTPP+-HC and interaction of MTPP+-PF6- contribute to preferential and oriented reduction of PF6-, forming a low-resistance supramolecular SEI. Additionally, Na+-Br- coordination weakens the Na+-solvent interactions, facilitating Na+ de-solvation kinetics. Consequently, the HC||Na cell achieves a superior ICE of 96.6%, desirable rate capability under 25 °C and invisible capacity decay after 500 cycles at 1 C under -20 °C. The Na4Fe3(PO4)2P2O7||HC pouch battery displays a high ICE of 90.3% and a 15% increment of energy density under 25 °C. This work provides a guidance through electrolyte reconfiguration engineering for designing practical HC-based SIBs with high energy/power density and long-life span in the extended operating-temperature range.

Biomass derived 3D N, P co-doped porous carbon incorporated with Ni-Cu bimetallic phosphide: Synergistic effect of Ni-Cu boosting Na+ storage performance

Transition metal phosphides (TMPs) as promising anode materials for sodium-ion batteries (SIBs) due to their amazing properties such as high theoretical specific capacity, various bond types and good electrical conductivity. However, TMPs are still facing poor cycling stability and unsatisfactory specific capacity, which restrict their practical application. Herein, NixCu3-xP incorporated in biomass derived 3D N, P co-doped porous carbon (NixCu3-xP-NPC) is constructed as SIB anode and the electrochemical behaviors with various Ni/Cu ratios are explored. The synergistic effect of Ni-Cu in NixCu3-xP is approved by the resulting investigation, and density functional theory (DFT) calculation further confirmed its important influence in enhancing electronic conductivity and boosting Na+ storage. Evidently, the optimum synergistic effect was observed when Ni0.15Cu2.85P/NPC is utilized for SIB anode. It exhibits a reversible specific capacity of 663 mAh g−1 after 200 cycles at 0.2 A g−1, long cycling stability (467 mAh g−1 after 1000 cycles at 1.0 A g−1), and excellent rate capability (432 mAh g−1 at 2.0 A g−1). The ex-situ X-ray diffraction and ex-situ X-ray photoelectron spectroscopy verify the combined conversion mechanism of Ni and Cu during sodiation/desodiation processes, which is greatly favorable for high specific capacity and cycling stability.

Abnormal Gas Generation during First Discharge Process of Sodium Ion Battery.

In recent years, sodium-ion batteries (SIBs) have attracted a lot of attention and are considered an ideal alternative to lithium-ion batteries (LIBs). The hard carbon (HC) anode in SIBs presents a unique challenge for studying the formation process of the solid electrolyte interphase (SEI) during initial cycling, owing to its distinctive porous structure. This study employs a combination of ultrasonic scanning techniques and differential electrochemical mass spectrometry to conduct an in-depth analysis of the two-dimensional distribution and composition of gases during the formation process. The findings reveal distinct gas evolution behaviors in SIBs compared to LIBs during formation. Notably, significant gas evolution is observed during the discharge phase of the formation cycle in SIBs, with higher discharge rates leading to increased gas evolution rates. This phenomenon is likely attributed to the adsorption of CO2 gas by the abundant pores in HC, followed by desorption during discharge. Furthermore, the study demonstrates that the addition of 5A molecular sieves, which competitively adsorb gases, effectively reduces gas adsorption on the anode during formation, thereby significantly enhancing battery performance. This research elucidates the gas adsorption and desorption behavior at the battery interface, providing new insights into the SEI formation process in SIBs.

Abnormal Gas Generation during First Discharge Process of Sodium Ion Battery

AbstractIn recent years, sodium‐ion batteries (SIBs) have attracted a lot of attention and are considered an ideal alternative to lithium‐ion batteries (LIBs). The hard carbon (HC) anode in SIBs presents a unique challenge for studying the formation process of the solid electrolyte interphase (SEI) during initial cycling, owing to its distinctive porous structure. This study employs a combination of ultrasonic scanning techniques and differential electrochemical mass spectrometry to conduct an in‐depth analysis of the two‐dimensional distribution and composition of gases during the formation process. The findings reveal distinct gas evolution behaviors in SIBs compared to LIBs during formation. Notably, significant gas evolution is observed during the discharge phase of the formation cycle in SIBs, with higher discharge rates leading to increased gas evolution rates. This phenomenon is likely attributed to the adsorption of CO2 gas by the abundant pores in HC, followed by desorption during discharge. Furthermore, the study demonstrates that the addition of 5A molecular sieves, which competitively adsorb gases, effectively reduces gas adsorption on the anode during formation, thereby significantly enhancing battery performance. This research elucidates the gas adsorption and desorption behavior at the battery interface, providing new insights into the SEI formation process in SIBs.

CVD-Synthesized Titanium Carbide Nanoflowers as High-Performance Anodes for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have emerged as promising candidates for energy storage applications due to the abundance and low cost of sodium. However, the larger radius of sodium ions limits their diffusion kinetics within electrode materials and contributes to electrode volume expansion. Here, we successfully synthesized porous titanium carbide (TiC) nanoflowers through chemical vapor deposition (CVD). The TiC nanoflowers exhibit exceptional electrochemical performance as SIB anodes, with their porous structure enhancing the conductivity, mechanical stability, and Na-ion diffusion. The TiC nanoflowers demonstrate a high reversible specific capacity of 73.5 mAh g-1 at 1 A g-1 after 2500 cycles, corresponding to an impressive capacity retention of 80.81%. Additionally, we developed a full sodium-ion cell utilizing TiC nanoflowers as the anode and Na3V2(PO4)3 as the cathode, which demonstrates a substantial reversible capacity and outstanding cycling stability. Our work presents a promising strategy for synthesizing nanostructured TiC materials as anode electrodes for SIBs.

Cu2-xSe@MXene (Ti3C2Tx) 2D layered heterostructure as an anode for high-performance sodium-ion batteries

With a notable focus on developing efficient sodium storage electrode materials, sodium-ion batteries (SIBs) have been identified as a promising contender in the pursuit of high-performing substitutes for lithium-ion batteries. Among varying sodium storage anode materials for SIBs, nonstoichiometric Cu2-xSe exhibits significant promise. This material stands out due to its ultrahigh electrical conductivity and theoretical sodium storage capacity. However, the practical implementation of Cu2-xSe-based anodes in SIBs is significantly impeded by their sluggish electrochemical reaction kinetics and severe pulverization during the repeated charge–discharge cycles. In the current research, we introduce a novel and straightforward methodology for the synthesis of a heterostructured SIBs anode material (Cu2-xSe@Ti3C2Tx), by coupling Cu2-xSe nanoparticles with two-dimensional (2D) layered MXene (Ti3C2Tx). The 2D layered Ti3C2Tx can provide abundant fast Na+ transport pathways, which effectively promote the ion transport kinetics in the composite anode. Moreover, the pulverization of Cu2-xSe can be effectively mitigated due to the interlamellar spatial confinement of the 2D layered MXene matrix. Consequently, the electrochemical performances of the Cu2-xSe-based anode are significantly improved. Concretely, the Cu2-xSe@Ti3C2Tx anodes demonstrate remarkable rate performance (248mAh g−1 at 10.0 A/g), along with commendable cycling stability, exhibiting a capacity retention of 92 % at 5.0 A/g after 750 cycles. A comprehensive assessment of the Cu2-xSe@Ti3C2Tx anode has been conducted by assembling a full SIB alongside a Na3V2(PO4)3 cathode. This comprehensive study underscores the significant potential of Cu2-xSe-based composite materials, positioning it as a promising candidate for future advancements in SIB technology.

An Oriented Diffusion Strategy to Configure All-Region Ultrahigh-Density Metal Single Atoms for High-Capacity Sodium Storage.

Single-atom metals (SAMs), despite being promising for high-utilization catalysis, biomedicine, and energy storage, usually suffer from limited catalytic performance caused by low metal loading. Herein, via an oriented diffusion strategy, all-region ultrahigh-loading (18.9wt.%) Sn-SAMs over carbon nanorings matrix (Sn-SAMs@CNR) are initially achieved based on the transformation of a g-C3N4@SnO2@polydopamine ring-like nested structure. The formation process of Sn-SAMs involves a critical conversion from oxygen-coordination (SnO2) to nitrogen-coordination (Sn-N4) and simultaneous anti-Osterwalder ripening promoted under spatial confinement. Notably, the g-C3N4-derived N-containing gaseous intermediates dynamically drive the oriented diffusion (inside-out diffusion) of Sn-SAMs across the carbon nanorings, realizing an all-region ultrahigh loading of SAMs throughout the carbon matrix. This strategy is also applied to other metal materials (Fe, Co, Ni, Cu, and Sb), and features excellent universality. When applied as the anode for sodium-ion batteries, experimental analyses and theoretical calculations demonstrate that high-loading Sn-N4 active sites significantly optimize electron density distribution and improve reaction kinetics. Consequently, Sn-SAMs@CNR exhibits outstanding durability of 364mAhg-1 even after 5000 cycles with an impressively low (0.00068%) capacity decay per cycle. This work opens up a universally new avenue for all-region ultrahigh loading of SAMs to carbon matrix for high-performance energy storage.

Towards More Sustainable Schiff Base Carboxylate Anodes for Sodium-Ion Batteries.

Bismine sodium salt (BSNa), a Schiff base with two sodium carboxylates, has shown promising electrochemical performance as an anode material. However, its synthesis involves toxic reagents and generates impurities, requiring significant solvent use for purification. This study introduces a novel synthetic method using sodium hydroxide as the sole reagent, which acts as both a base and Na source in the ion exchange step. With this procedure, we reduce the amounts of chemicals, diminish toxicity, improve the purity of the target compound, and use less solvent while maintaining comparable electrochemical performance. Additionally, the procedure is carried out under anhydrous conditions that avoid the undesirable hydrolysis of the imine linkages. In a previous report, the processing of the composite electrode was not established. In this article, we address this issue; the electrochemical performance, specifically the rate capability, is enhanced by processing the electrodes in laminate form rather than powder. As alternative to N-methyl-2-pyrrolidone (NMP), a common but disadvantageous solvent in laminate processing, other solvents were explored by testing acetone (DMK), methylisopropylketone (MIPK), and a DMK-NMP mixture. The remarkable electrochemical performance (specific capacity of 260-280 mAh/g, and capacity retentions higher than 84% at 1C (260 mA/g) remained consistent across these solvents. Furthermore, we investigated replacing copper with aluminum as the current collector to reduce costs and increase the energy density of the battery. While aluminum performed comparably to copper at low specific currents C/10 (26 mA/g), it showed a significant shift in the redox process potentials at higher specific currents.

High-Capacity Anode for Sodium-Ion Batteries Using Hard Carbons Derived from Polyurea-Cross-Linked Silica Xerogel Powders

High-Capacity Anode for Sodium-Ion Batteries Using Hard Carbons Derived from Polyurea-Cross-Linked Silica Xerogel Powders

Three-Dimensional Flexible SnO2@Hard Carbon@MoS2@Soft Carbon Fiber Film Anode toward Ultrafast and Stable Sodium Storage.

Developing flexible electrodes for the application in sodium-ion batteries (SIBs) has received great attention and has been still challenging due to their merits of additive-free, lightweight, and high energy density. In this work, a free-standing 3D flexible SIB anode with the composition of SnO2@hard carbon@MoS2@soft carbon is designed and successfully synthesized. This electrode combines the energy storage advantages and hybrid sodium storage mechanisms of each material, manifested in the enhanced flexibility, specific capacity, conductivity, rate, cycling performances, etc. Based on the synergistic effects, it exhibits much higher specific capacity than SnO2 carbon nanofibers, as well as more excellent cycling performance (250 mA h g-1 after 500 cycles at 1 A g-1) than MoS2 nanospheres (32 mA h g-1). In addition, relevant kinetic mechanisms are also expounded with the aid of theoretical calculation. This work provides a feasible and advantageous strategy for constructing high-performance and flexible energy storage electrodes based on hybrid mechanisms and synergistic effects.

Cu3.21Bi4.79S9: Bimetal superionic strategy boosts ultrafast dynamics for Na-ion storage/extraction

Traditional metal sulfides used as anodes for sodium-ion batteries are hindered by sluggish kinetics, which limits their rate performance. Previous attempts to address this issue focused on nanostructured configurations with conductive frameworks. However, these nanomaterials often suffer from low packing density and the tendency for nanoparticles to agglomerate, posing significant challenges for practical applications. To overcome these limitations, this study presents a novel bimetal superionic anode material Cu3.21Bi4.79S9, which effectively resolves the conflict between sluggish kinetics and micrometer-scale particle size. By leveraging the vacancies created by free Cu and Bi atoms, this material forms rapid migration channels during sodium insertion and extraction, significantly reducing the migration barriers for sodium ions. The development of micrometer-scale Cu3.21Bi4.79S9 enables ultrafast charging-discharging capabilities, achieving a reversible capacity of 325.5 mAh g−1 after 4000 cycles at a high rate of 45 C (15 A g−1). This work marks a significant advancement in the field by offering a solution to the inherent trade-off between high capacity and rate performance in coarse-grained materials, reducing the need for reliance on nanostructured configurations for next-generation high-capacity anode materials.

Spatial confinement strategy modulated by kinetic diameters of gaseous molecules for sodium storage

Constructing closed pore structures is essential for improving the plateau capacity of high-capacity hard carbon (HC) anodes for sodium-ion batteries. However, the absence of a straightforward and efficient strategy for constructing closed pores has hindered the advancement of high-capacity HC anodes. Here, we have developed a spatial confinement strategy for constructing closed pore structures using pyrolytic carbon (PC) as substrate and pyrolysis gas as the carbon source for chemical vapor deposition. The deposition of pyrolysis gas effectively tightens the pore entrance, thereby preventing electrolyte infiltration and transforming the open pores in the PC into highly efficient sites for sodium storage. The obtained optimal anodes demonstrate a remarkable specific capacity of 324.6 mAh g-1. More importantly, we calculate the kinetic diameters of the carbon source molecules from their iso-electron density surfaces and correlate them with the mechanism of closed pore formation, which will effectively guide the fabrication of closed pores for sodium storage.

Interface engineering-induced enhancements in sodium-ion batteries: A nexus of ZnS nanoparticles and reduced graphene oxide for augmented storage and conductivity

Due to the inherent sluggish kinetics and the pronounced volumetric expansion of zinc sulfide (ZnS), it has become a prevalent modification strategy to regulate its morphology and composite with graphene for using ZnS as anodes in sodium-ion batteries (SIBs). Nevertheless, the elucidation of mechanisms underpinning the electrochemical performance facilitated by graphene incorporation remains scant. To further describe the synergistic mechanism, the ultrafine ZnS nanoparticles anchored on reduced graphene oxide (rGO) were synthesized through a simple solvothermal method. Research shows that the ZSG (ZnS nanoparticles-reduced graphene oxide composite) electrode suggests superior rate capability, maintaining a reversible specific capacity of 228.6 mAh·g−1 upon returning from a high current density of 5 A·g−1. Furthermore, the nanoscale integration of ZnS particles with rGO synergistically mitigates the structural expansion of the ZSG electrode encountered during cycling, thereby decelerating the degradation of cyclic performance. Insights gleaned from first-principles calculations and comprehensive electrochemical evaluations reveal that the built-in electric field, engendered within the composite architecture, substantially augments charge transfer ability and mitigates the energy barriers impeding sodium ion (Na+) diffusion accordingly. Consequently, the methodology adopted for synthesis and the synergistic modification mechanism can proffer a reference for the design of advanced anode materials in SIBs.

N/P/O co-doped porous carbon derived from agroindustry waste of peanut shell for sodium-ion storage

Porous bio‑carbon from agroindustry waste behaves one of the most promising anode materials for sodium-ion batteries (SIBs) because of its high sodium storage capacity, low cost, sustainability, and low charge/discharge voltage platform. Herein, we have developed a new N/P/O co-doped porous hard carbon derived from peanut shell (PSCNP) synthesized via KOH activation, hydrothermal doping combined with carbonization method, using chitosan as nitrogen source, phytic acid as phosphorus source, and peanut shell as carbon and oxygen source. Through seriously regulating the calcination temperature, the optimal PSCNP-800 carbonization at 800 °C can well combine the advantages of the natural rich porous microstructure of peanut shells, large graphite interlayer spacing (0.379 nm), and short diffusion distance for sodium-ion. As an advanced anode for SIBs, the PSCNP-800 delivered a reversible capacity of 248.8 mAh g−1 after 100 cycles at 25 mA g−1. This work could provide a possible idea for the preparation of N/P/O co-doped porous hard carbon from low-cost agroindustry waste as anodes for SIBs.

Self-Standing vanadium oxide pillared carbon microfiber film as an excellent anode for lithium & sodium ion batteries

Insertion of substances (such as atoms/molecules/ions) into the interlayer spaces of graphite to increase its layer separation is found to be extremely useful for sodium-ion batteries (SIBs). Therefore, expanded graphitic systems are the obvious choice as anode material for both lithium/sodium-ion batteries (LIBs/SIBs). Hard carbon-based materials altogether give a decent electrochemical performance, as well as allow structural integrity for long-term use. Herein, we report a facile route to prepare free-standing vanadium oxide doped carbon microfibers (V@CMFs) films. The V@CMFs show ∼ 200 % expansion in the graphitic interlayer distances while accommodating minute deformations in the final compound which is further theoretically verified as the stage-1 type dilute graphite intercalation compound (GICs) with pillar-like structures. Best battery performance was obtained for the 1 % doped (V1@CMFs) sample, with an initial discharge capacity of 1501.8 and 703.4 mAhg−1, reversible capacities of 1253.8 and 288.7 mAhg−1 at 20 mAg−1, and rate capabilities i.e., 362.4 and 108.1 mAhg−1 at 1600 mAg−1, for LIBs and SIBs, respectively. The results revealed that the rate capability and the reversible specific capacity of the 1 % vanadium oxide doped carbon microfibers (V1@CMFs) are significantly superior compared to the pristine and previous reports. Here, the incorporation of just 1 % vanadium oxide acts as a pillar, enhancing the stability and conductivity of the carbon. Thus, the present work highlights the utility of molecularly doped GICs as potential anode materials for LIBs/SIBs.

Synergistic engineering of heteroatomic N-doping and PPy modification in flower-like vanadium sulfide anode enables stable sodium storage

Vanadium sulfide, an appealing anode candidate for sodium ion batteries (SIBs), still encounters considerable volume fluctuation and sluggish Na+ diffusion kinetics, which inevitably gives rise to unsatisfactory rate capability and severe capacity decay. Herein, we successfully designed and constructed an outstanding sodium-storage feature and exceedingly stable anode for SIBs in the form of three-dimensional flower-like architecture composing of phosphorus doped VS2 wrapped by conductive elastic polypyrrole (PPy) layer (i.e., P-VS2@PPy). Through leveraging the multifunctional synergistic effect of composition and structure, involving enhanced electronic conductivity, reduced volumetric fluctuation, accelerated charge/ion transfer efficiency, and remarkable surface-capacitive behaviors can guarantee significantly enhanced electrochemical sodium-storage ability of P-VS2@PPy composites. As a consequence,such P-VS2@PPy is endowed with desirable rate characteristic accompanied with long-period cyclic lifespan (436.7 mAh/g at 20.0 A/g after 2600 cycles), which far outperform contrastive P-VS2 and pure VS2 samples. Meticulous kinetic analysis combined with theoretical simulations conclude that phosphorus doping and PPy coating have substantial effects on strengthening ionic and electron diffusion kinetics. Thorough examination and analysis of the insertion and conversion mechanisms of P-VS2@PPy was conducted through ex situ tests, revealing superior reversible phase transformation between original VS2, intermediate NaVS2, and final Na2S/V. Additionally, a practical application test demonstrates that sodium ion full-cell and hybrid capacitor based on P-VS2@PPy anode showcase significant capacity contribution and outstanding specific energy output, capable of effortlessly lighting up a LED screen.

Binder-free Cu-Sb-Sn-Zn-P alloys as high-efficiency anodes for sodium-ion batteries via double-pulse electrodeposition

Alloy anodes are widely recognized for their high theoretical specific capacity and have garnered significant attention among the anode materials studied for sodium-ion batteries. In this study, we synthesize Cu68.6Sb23.0Sn3.2Zn0.3P4.9 anodes using a double-pulse electrodeposition method. This binder-free alloy anode, comprising five high-capacity elements, significantly enhances specific capacity and improves cycling stability, while also demonstrating excellent sodium storage capability. Specifically, the Cu68.6Sb23.0Sn3.2Zn0.3P4.9 anode achieves an initial charge capacity of 368.8 mAh∙g−1 and remains highly stable over 100 cycles, with a capacity decay of only 0.1 %. In addition, the anode delivers 290.3 mAh∙g−1 even at a current density of 3200 mA∙g−1. The outstanding electrochemical performance can be attributed to improved electronic transfer efficiency due to the introduction of Cu into Cu68.6Sb23.0Sn3.2Zn0.3P4.9 alloy via reverse potential, as well as the porous structure that facilitates electrolyte penetration and sodium ion transport. The galvanostatic intermittent titration technique reveals a high sodium ion diffusion coefficient, further highlighting the potential of this alloy anode in advancing sodium-ion batteries.

High temperature induced abundant closed nanopores for hard carbon as high-performance sodium-ion batteries anodes

Hard carbon (HC) stands out as the preeminent anode material for sodium-ion batteries (SIBs) which are deployed in expansive energy storage infrastructures. Herein, the large enough graphene nanosheets interlayer and abundant nanopores with a diameter of ∼2.1 nm induced by adjusting the pyrolysis temperature in the thermosetting phenolic resin-derived hard carbon matrix to augment the performance of the sodium ion storage. The presence of sufficiently large carbon interlayers has been proven to provide active sites for reversible adsorption, enabling effective storage of sodium ions in the high-voltage slope region, while also promoting rapid Na+ transport. Meanwhile, forming abundant closed nanopores with larger sizes helps sodium ion storage in the low-voltage plateau region. In the optimized samples, the formation of sufficient long graphene nanosheets with a perfect crystal lattice, which further shrinks to form enclosed nanopores, effectively reduces defective sites and specific surface area. Additionally, the appropriate content of C-O and C=O functional groups contributes to an exceptional initial Coulombic efficiency (ICE) of up to 93%. Simultaneously, the optimized sample HC-1500 contributes to a remarkable plateau capacity of 294 mAh g-1 during the charging process (high reversible capacity of 403 mAh g-1 at 0.1 C). Moreover, based on the microstructure evolution and Na storage behavior of hard carbon, an “adsorption (27%) – filling (73%)” sodium storage mechanism that the sodium storage as a quasi-metallic sodium state is demonstrated. Consequently, this study will offer valuable insights for the development of hard carbon anodes tailored for high-energy practical SIBs, while also advancing the understanding of sodium storage mechanisms.