High Rate Capability Research Articles

Incorporation of Graphene Quantum Dots into Magnesium Copper Phosphate (GQDs-MgCuPO4) for Supercapattery and Electrocatalysis Applications

Abstract We efficiently synthesize magnesium copper phosphate nanoparticles (MgCuPO4) doped with graphene quantum dots (GQDs) using a hydrothermal method for supercapattery and oxygen evolution reactions in KOH electrolyte. The GQDs-MgCuPO4 electrode has a high specific capacity (1188 Cg-1 at 1.0 Ag-1) and a high-rate capability (67%). The symmetric supercapattery (GQDs-MgCuPO4/GQDs-MgCuPO4) provides a staggering energy density of 46 Wh-kg-1, as well as a high-power density of 1300 W-kg-1 and a high cyclic stability of 93% after 10,000 cycles. Furthermore, it demonstrates high efficiency in the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), with corresponding low overpotentials of 181 mV and 119 mV. The GQDs-MgCuPO4 stands out as a capable solution for various energy storage and conversion difficulties.

Magnesium Fluoride Interlayers Enabled by Wet‐Chemical Process for High‐Performance Solid‐State Batteries

AbstractGarnet‐type solid‐state electrolytes (SSEs) exemplified by Li6.5La3Zr1.5Ta0.5O12 (LLZT) are chemically unstable when exposed to air, leading to the formation of impurities and poor wettability with Li metal. Herein, a protocol to address this Li/LLZT interface challenge is demonstrated by constructing a lithiophilic MgF2 nanofilm on the LLZT pellet. Specifically, a solution‐based process is developed for the surface engineering of LLZT, utilizing magnesium trifluoroacetate (MTF) as the molecular precursor while poly(acrylic acid) (PAA) as the coordinating agent in a sol‐gel process. It is demonstrated that a facile spin‐coating treatment followed by high‐temperature annealing reliably forms crack‐free MgF2 nanofilms with precise thickness control. Introduction an MgF2 interlayer transforms the LLZT pellet into a highly lithophilic, facilitating close contact with the lithium anode, thereby leading to a significantly reduced interfacial resistance from 1190 Ω cm2 to 6 Ω cm2. Such an interfacial engineering enables stable cycling of full batteries with high reversibility and rate capability using commercial LiFePO4 and LiNi0.83Co0.07Mn0.1O2 as cathodes. This study unfolds the possibility of a solution‐based method as a facile and scalable process for the construction of fluoride nanofilms, which is promising to address the critical interfacial challenges of solid‐state batteries (SSBs) to facilitate its practical applications.

Ferroelectric Dipoles Tailoring Solid‐Electrolyte‐Interphase Chemistry to Enable Reversible Lithium Metal Batteries

AbstractSolid‐electrolyte interphase (SEI) plays a decisive role in building reliable Li metal batteries. However, the scarcity of anions in Helmholtz layer (HL) caused by electrostatic repulsion usually leads to the inferior SEI derived from solvents, resulting in dendrites and ‘dead’ Li. Therefore, regulating the distribution of anions in electric double layer (EDL) and continuously introducing more anions into HL to tailor anions‐derived SEI is crucial for achieving stable Li plating/stripping. Herein, by jointly utilizing the controlled defects of reduced graphene oxide (rGO) and the oriented dipoles of ferroelectric BaTiO3 (BTO), the rGO‐BTO composite layer sustainedly brings more TFSI− and NO3− into anion‐defecient HL, promoting favorable decomposition of anions and guiding the generation of robust and fast‐Li+‐transport SEI containing more inorganics LiF and Li3N species. Thus, the resulting Li deposit shows smooth and dense morphologies without dendrites, leading to high average Coulombic efficiency. The Li//Cu@rGO‐BTO (10 mAh cm−2 plated Li) cell exhibits an enhanced Li plating/stripping stability (2700 h) and a higher rate capability. The LiFePO4 full cell (N/P≈6.3) using rGO‐BTO displays an enhanced capacity retention (82.0 % @ 430 cycles). This work provides a new insight on the construction of robust SEI by regulating the distribution of anions within EDL.

Central metal coordination environment optimization enhances Na diffusion and structural stability in Prussian blue analogues

Prussian blue analogues, particularly metal hexacyanoferrates with double octahedral coordination (DOC) structures, hold great promise as cathode materials for sodium-ion batteries. However, their practical application is hindered by limited structural stability and restricted ionic diffusion channels inherent to the DOC structure. In this study, we have successfully integrated a mixed tetrahedral and octahedral coordination (TOC) structure with the DOC structure by a dual polymerization and high-entropy strategy, thereby optimizing the central metal coordination environment in hexacyanoferrate cathodes. It leverages the TOC structure's superiorities in structural stability and ionic diffusion, resulting in a hexacyanoferrate-based cathode that exhibits exceptional performance, with a capacity retention of 81.6% after 1000 cycles at 0.5 A g-1 and high rate capabilities of 96.7 and 89.1 mAh g-1 at 0.5 and 1 A g-1, respectively. These findings not only underscore the potential of the TOC design for prussian blue cathodes but also pave the way for the development of high-performance, durable sodium-ion battery systems.

How Do the Four Core Factors of High Entropy Affect the Electrochemical Properties of Energy-Storage Materials?

High-entropy materials (HEMs) are extremely popular for electrochemical energy storage nowadays. However, the detailed effects of four core factors of high entropy on the electrochemical properties of HEMs are still unclear. Here, a high-entropy La1/4Ce1/4Pr1/4Nd1/4Nb3O9 (HE-LaNb3O9) oxide is prepared through multiple rare-metal-ion substitution in LaNb3O9, and uses HE-LaNb3O9 as a model material to systematically study the effects of the four core factors of high entropy on electrochemical energy-storage materials. The high-entropy effect lowers the calcination temperature for obtaining pure HE-LaNb3O9. The lattice distortion in HE-LaNb3O9 leads to its decreased unit-cell-volume variations, which benefits its cyclability. Based on the restrained diffusion arising from the lattice distortion, the Li+ diffusivity of HE-LaNb3O9 at room temperature (25°C) is limited, which causes its lowered rate capability. However, the Li+ diffusivity of HE-LaNb3O9 at high temperature (60°C) becomes faster than that of LaNb3O9, which is attributed to the alleviated lattice distortion at the high-temperature, resulting in higher rate capability. The cocktail effects in HE-LaNb3O9 enable its larger electronic conductivity, better electrochemical activity, more intensive Nb5+ ↔ Nb3+ redox reaction, and larger reversible capacity. The insight gained here can provide a guide for the rational design of new HEMs with good energy-storage properties.

Overcoming volumetric capacitance-rate performance tradeoff with 0D/2D conductive carbon nitride/phosphorene heterostructure for flexible supercapacitor

Few-layer black phosphorus (FL-BP) is considered a rising star 2D material for flexible supercapacitors (FSCs) due to its exceptional properties, including mechanical flexibility and high active surface area. However, the disordered deposition of FL-BP nanoflakes often leads to face-to-face restacking, which diminishes the effective active area and ion transport channels. This poses a huge challenge in simultaneously achieving high volumetric capacitance and rate capability. To address this, a 3D porous 0D/2D FL-BP/conductive carbon nitride (FL-BP/c-CN) film has been developed. The introduction of 0D c-CN nanoparticles effectively prevents the restacking of FL-BP nanoflakes and expands the nanofluidic channels, thus facilitating charge transport and ions diffusion. Additionally, the highly conductive c-CN nanoparticles embedded into the FL-BP layers significantly improve overall conductivity. As a result, the FL-BP/c-CN film-based FSC demonstrates a remarkable rate performance, retaining 70% capacitance as the scan rate increases from 10 to 100 mV/s. Moreover, the incorporation of 0D c-CN nanoparticles increases the available space for charge accumulation, yielding a volumetric capacitance of 28.5 F/cm3 at a scan rate of 10 mV/s, which is three times higher than that of a pure FL-BP film electrode (9.2 F/cm3). This work presents an innovative approach for developing high-performance FL-BP-based FSCs.

In situ growth of MnO2 on graphitized cellulose nanocrystal: A novel coaxial heterostructures with unblocked conductive networks as advanced electrode materials for supercapacitor

Manganese dioxide (MnO2) with high theoretical capacitance and natural abundance has attracted great attention but is still challenging for use in supercapacitors, due to the limited conductivity and lower electron and ion migration. Here, a facile in situ growth strategy is developed to prepare heterostructural graphitized cellulose nanocrystal (GCNC)/MnO2 with unblocked conductive networks through a hydrothermal reaction. The GCNC with highly ordered graphitic carbon layers as conductive support framework solves the agglomeration problem of MnO2 and increases effective specific surface areas in contact with electrolyte ions. Meanwhile, the stable connection of MnOC covalent bonds enhances the interface bonding, which effectively reduces the contact resistance at the interface of heterostructural GCNC/MnO2 and enhances the interface firmness. The resulting GCNC/MnO2 electrode shows a remarkable specific capacitance of 528.2 F g−1 at 0.5 A g−1. Furthermore, the symmetric supercapacitor based on GCNC/MnO2-15 mM exhibits high rate capability and excellent cycle stability of 100 % capacitance retention after 3000 cycles. This work provides a new path to designing high performance electrode material for sustainable energy technologies.

Resource-efficient electrodes with metallized woven-glass-grid current collectors for lithium-ion batteries.

A novel class of resource-efficient, woven-glass-grid current collectors (CCs) for Li-ion batteries is introduced. These CCs are based on ultra-light multifilament glass threads, woven to a grid and surrounded with a thin metal layer (equivalent to a 1 µm-thick metal foil) in a roll-to-roll physical vapor deposition process. This saves > 90% of the required Cu and Al metals and reduces the mass of the CCs by > 80%. At the same time, the gravimetric capacity of anodes with graphite and cathodes with LiCoO2 active material increases by 48% and 14%, respectively, while full cells are characterized by an increase of 26%. Thus, the specific energy can be improved by 25%. A complete anode and cathode fabrication process from preparing the CCs and electrodes to cells is described and demonstrated in coin cell format. Coin cells with woven-glass-grid CCs achieved 300 cycles with a capacity retention of 93%, a Coulombic efficiency of > 99.9%, and a higher rate capability until a C-rate of 3C. This technology opens up new possibilities for designing ultralight CCs with dedicated surface properties for Li and beyond Li batteries.

Design and Synthesis of Sb-Doped CuS@C Hollow Nanocubes as Efficient Anode Materials for Sodium-Ion Battery.

Copper sulfide has received widespread attention for application as anode materials in sodium-ion batteries due to their potent capabilitiess and eco-friendly properties. However, it is a challenge to achieve a high rate capability and long cycle stability owing to the heterogeneous transfer of sodium ions during charge-discharge, the interior poor electron conductivity and repeated volumetric expansion of copper sulfide. In this study, Sb-doped copper sulfide hollow nanocubes coated with carbon shells (Sb-CuS@C) was designed and constructed as anode nanomaterials in sodium-ion batteries. Thanks to the intrinsic good electron conductivity and chemical stability of carbon shells, Sb-CuS@C possesses a higher overall electron transfer as anode material, avoids agglomeration and structural destruction during the cycling. As a result, the synthesized Sb-CuS@C achieved an excellent reversible capacity of 595 mA h g-1 after 100 cycles at 0.5 A g-1 and a good rate capability of 340 mA h g-1 at a higher 10 A g-1. DFT calculations clarify that the uniformly doped Sb would act as active sodiophilic nucleation sites to help adsorbing sodium-ion during discharging and leading uniform sodium deposition. This work provides a new insight into the structural and componential modification for common transition-metal sulfides towards application as anode materials in sodium-ion battery.

MnO2 nanowires modified reduced graphene oxide thick film cathode for aqueous zinc-ion prismatic battery

Aqueous zinc-ion batteries are an excellent alternative to lithium-ion batteries that can meet the energy requirements while also being safe and eco-friendly. However, developing a suitable cathode material with good energy density and high-rate capability is challenging. In this study, we developed an aqueous zinc-ion battery with a high surface area MnO2 nanowires modified reduced graphene oxide nanocomposite screen printed interdigitated array electrodes and a distinctive aqueous electrolyte comprising 1 M each of ZnSO4 and Na2SO4, 0.1 M MnSO4, and 0.8 mM sodium dodecyl sulfate. The charge-discharge curves reveal that the cathode material exhibits a high reversible storage capacity of 164 mAh g−1 at a current density of 50 mA g−1. The battery retained 99.59% of its Coulombic efficiency after 300 cycles when cycled at a high current rate of 300 mA g−1. The prismatic battery realized exhibited a calculated energy density of 505.5 Wh kg−1 which is higher than previously reported works. On account of the large energy density and high rate capability coupled with non-toxic components, low cost and facile fabrication method, the Zn||MnO2/rGO battery shows good promise for energy storage application.

High rate capability performance of cobalt-free lithium-rich Li1.2Ni0.18Mn0.57Al0.05O2 cathode material synthesized via co-precipitation method

High rate capability performance of cobalt-free lithium-rich Li1.2Ni0.18Mn0.57Al0.05O2 cathode material synthesized via co-precipitation method

Effect of Various Carbon Coating Techniques on the Electrochemical Performance of Li4Ti5O12 Synthesized by Sol-Gel Method

This study aimed to prepare spinel carbon-coated Li4Ti5O12 (LTO/C) via sol-gel reaction and applied as a high-performance lithium-ion battery anode. The LTO powder was coated using various carbon sources, super P (SP), sugar and PVDF-assisted SP. The crystal structure, morphology, conductivity and electrochemical performance of the samples were examined using X-ray diffraction (XRD), Field Emission scanning electron microscopy (FESEM), Fourier Transform Infrared (FTIR) spectroscopy, Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry/Charge-discharge (CV/CD), respectively. The XRD analysis results showed that the samples contain highly crystalline spinel LTO as the main phase and rutile as impurity. The FESEM image showed that SP covers the entire LTO surface more homogenous than sugar. However, sugar carbon makes roughness on the LTO surface. FTIR spectra showed that the coating using sugar and PVDF still contain hydrocarbon element. Electrochemical performance evaluations showed that SP carbon-coated-LTO possesses higher lithium diffusion and specific capacity than pure LTO, while sugar-coated-LTO shows the lowest specific capacity. Moreover, the SP carbon-coated-LTO sample high-rate capability has improved during full cell evaluation, delivering a discharge capacity of 249, 231, 211, 194, 58, and 23 mAhg-1 at the charge or discharge current density of 0.05, 0.1, 0.5, 1, 5, and 10 C, respectively.

Free-standing medium-entropy porous needle-like FeCoCuNi phosphide nanowires-formed flower clusters/carbon fiber anode with high capacity and long durability for sodium-ion batteries

The drastic volume expansion and slow sodium-ion kinetics hinder the practical application of phosphides with high specific capacity and low discharge voltage in sodium-ion batteries (SIBs). Herein, we introduced entropy configuration into nanostructures and prepared a novel free-standing, three-dimensional, porous needle-like medium-entropy Fe, Co, Cu, Ni phosphide (ME-FCCNP) nanowires-formed flower clusters/carbon fiber cloth (CFC) anode (ME-FCCNP@CFC) for SIBs. The distorted lattices caused by medium-entropy configuration provide abundant sites for sodium-ion reactions and improve the electron transfer rate. The medium-entropy effects improve the mechanical stability, while the three-dimensional networks and porous needle-like nanowires provide sufficient space for the volume expansion. These combined properties enable the ME-FCCNP@CFC electrode to exhibit a high-rate capability of 170.8 mAh g−1 at 5.0 A g−1 and deliver a specific capacity of 325.8 mAh g−1 after 2000 cycles at 2.0 A g−1, far surpassing most of reported transition-metal phosphides. Moreover, the Na3V2(PO4)3 || ME-FCCNP@CFC full cell showcases a high-energy density of 256.8 Wh kg−1 and a long cycling life (267.8 mAh g−1 at 2.0 A g−1 with a capacity retention of 83.2 % after 1000 cycles). These results provide significantly promising implications for the anode design of SIBs by employing self-supporting and medium-entropy structures.

Atomic-scale probing of ion migration dynamics in Na3Ni2SbO6 cathode for sodium ion batteries

Honeycomb-layered phases like Na3Ni2SbO6 have been extensively researched as high-voltage and high-rate capability cathode materials for sodium-ion batteries. However, our understanding of the structural stability and dynamic reaction mechanisms of Na3Ni2SbO6 cathode during cycling, especially at atomic-scale, remains limited. Here, we track the microstructure evolution during extraction of Na+ ions in Na3Ni2SbO6 cathode at atomic scale in an aberration-corrected transmission electron microscope. The electron beam irradiation that can provide a driving force for the Na+ ion migration, allows us to mimic the battery charge process. By controlling the electron beam dose, we study the structure evolution behavior to obtain insights into understanding the work principle and failure mechanism of Na3Ni2SbO6 cathode under different charge rate conditions. We find that the real-time structural evolution and ion migration pathways of Na3Ni2SbO6 cathode are distinct under different electron beam doses. High-dose irradiation reveals Na ion depletion, surface cracks, and phase transformations, mimicking rapid capacity decay. In contrast, low-dose irradiation shows slower ion migration, ordered Na vacancy formation, and maintaining structural integrity, which more closely resembles the electrochemical process of actual battery. This study provides an atomistic understanding of the structural stability and Na ions deintercalation mechanism in Na3Ni2SbO6 cathodes, offering new insights into optimizing electrode materials.

Understanding ultrafast rechargeable Al/graphite battery by visualizing phase separation

Al/graphite batteries (ABs) using ionic liquid electrolytes exhibit exceptionally fast charging and cycling stability. However, the mechanisms underlying their high rate capabilities remains elusive. In this study, in situ optical microscopy is employed to investigate the intercalation dynamics of single-flake graphite in ABs. Observations reveal that surface reaction limitations, rather than AlCl4− mass transfer, primarily govern performance in the graphite cathode. During charging under varying current densities, the ABs display distinct phase separation behaviour with an intercalation wave morphology, indicating that surface reactions restrict the intercalation process. This finding explains the ultrafast recharge capability of ABs, where active sites in graphite become nearly fully intercalated with AlCl4− at high current densities. Additionally, slight rate performance loss occurs due to increasing ohmic and charge transfer polarisation (ηohm and ηct) at higher current densities. To address this limitation, we propose increasing the cut-off voltage as a straightforward and effective method to mitigate these polarization effects. This study offers valuable insights into the electrochemical behaviour of rechargeable secondary ion batteries by visualising their phase separation.

Optimization of FeMn-MOF doped with silver nanoparticles for high-performance supercapattery devices

Supercapacitors are demanded by energy storage devices for both fast charging and discharging performance as well as extended life cycles. The design and manufacture of higher supercapacitor electrodes help a device to function much better. Ag nanoparticles were produced on Fe-MOF and Mn-MOF using the hydrothermal synthesis technique to synthesize unique composite material called FeMn-MOF/Ag (NPs). These refined composites find use in supercapacitors, hydrogen evolution reactions (HER), and electrochemical sensors. Highly conductive silver nanoparticles were added to FeMn-MOF with high rate capability. Apart from their inherent benefits of metal–organic frameworks, the as-made FeMn-MOF/Ag nanoparticles also improved electrical conductivity. When the scan rate was 3 mV s−1, the FeMn-MOF/Ag (NPs) showed a specific capacity (CV) of 1417 C g−1. Similarly, when the applied current density was 2 A g−1, it displayed a specific capacity (GCD) of 2346 C g−1. The FeMn-MOF/Ag (NPs)//AC asymmetric supercapacitor exhibited an energy density of 13 (Wh/kg) and a power density of 1685 (W/kg). For the hydrogen evolution process, the material exhibited an overpotential of 90.22 mV and a Tafel slope of 58.4 mV dec−1. Furthermore, it exhibited exceptional durability in cycling, maintaining 93.3% of its capacitance after undergoing 12,000 cycles. Therefore, these results offer crucial insights into the progress of different electrode materials. The results suggest that FeMn-MOF/Ag nanoparticles possess advantageous characteristics suitable for utilization as electrodes in supercapattery and HER (hydrogen evolution reaction) applications.

A highly capacitive Graphene/Multiholed N‐CNTs hybrid evolved from black humate‐Co‐melamine precursor

Black humic acid (BA) is a black mixture of organic macromolecules isolated from humic acid, which has a greater potential for graphene transformation than fulvic acid and ulmic acid because of more and larger aromatic units and higher molecular weights exceeding 5000 Dalton. Here, chemically bonded BA‐Co‐Melamine precursors are initially constructed using different BA fractions as substrate, Co2+ as bridge bond and melamine as ligand. A series of Graphene/N‐CNTs hybrids (GNCs) is eventually synthesized after the precursor pyrolysis. Resultantly, Fraction Ⅰ, separated at a pH value of 4.16, plays a significant role on constructing the BA‐Co‐Melamine precursor and further producing multiholed GNCs. Due to abundant CNTs, rich mesopores, moderate nitrogen incorporation and a certain graphitized assembly structure, the prepared GNC‐Ⅰ‐b has high capacitance performances. The assembled AC//GNC‐Ⅰ‐b supercapacitor has high specific capacitance (147 F g‐1 at 0.5 A g‐1), rate capability, cycling stability and energy density (16.8 Wh kg‐1 at 14.4 KW kg‐1). The 2032 coin‐type Li//GNC‐Ⅰ‐b half‐cell has high initial discharge capacity (759 mAh g‐1 at 0.03 A g‐1), initial Coulombic efficiency (81.8%), rate performance and cycling stability. Hence, the GNC is a favorable high‐performance carbon material hopefully applied as electrode materials of supercapacitors and LIBs.

Unraveling the Anionic Redox Chemistry in Aqueous Zinc‐MnO2 Batteries

AbstractActivating anionic redox reaction (ARR) has attracted a great interest in Li/Na‐ion batteries owing to the fascinating extra‐capacity at high operating voltages. However, ARR has rarely been reported in aqueous zinc‐ion batteries (AZIBs) and its possibility in the popular MnO2‐based cathodes has not been explored. Herein, the novel manganese deficient MnO2 micro‐nano spheres with interlayer “Ca2+‐pillars” (CaMnO‐140) are prepared via a low‐temperature (140 °C) hydrothermal method, where the Mn vacancies can trigger ARR by creating non‐bonding O 2p states, the pre‐intercalated Ca2+ can reinforce the layered structure and suppress the lattice oxygen release by forming Ca−O configurations. The tailored CaMnO‐140 cathode demonstrates an unprecedentedly high rate capability (485.4 mAh g−1 at 0.1 A g−1 with 154.5 mAh g−1 at 10 A g−1) and a marvelous long‐term cycling durability (90.6 % capacity retention over 5000 cycles) in AZIBs. The reversible oxygen redox chemistry accompanied by CF3SO3− (from the electrolyte) uptake/release, and the manganese redox accompanied by H+/Zn2+ co‐insertion/extraction, are elucidated by advanced synchrotron characterizations and theoretical computations. Finally, pouch‐type CaMnO‐140//Zn batteries manifest bright application prospects with high energy, long life, wide‐temperature adaptability, and high operating safety. This study provides new perspectives for developing high‐energy cathodes for AZIBs by initiating anionic redox chemistry.

Unraveling the Anionic Redox Chemistry in Aqueous Zinc-MnO2 Batteries.

Activating anionic redox reaction (ARR) has attracted a great interest in Li/Na-ion batteries owing to the fascinating extra-capacity at high operating voltages. However, ARR has rarely been reported in aqueous zinc-ion batteries (AZIBs) and its possibility in the popular MnO2-based cathodes has not been explored. Herein, the novel manganese deficient MnO2 micro-nano spheres with interlayer "Ca2+-pillars" (CaMnO-140) are prepared via a low-temperature (140 °C) hydrothermal method, where the Mn vacancies can trigger ARR by creating non-bonding O 2p states, the pre-intercalated Ca2+ can reinforce the layered structure and suppress the lattice oxygen release by forming Ca-O configurations. The tailored CaMnO-140 cathode demonstrates an unprecedentedly high rate capability (485.4 mAh g-1 at 0.1 A g-1 with 154.5 mAh g-1 at 10 A g-1) and a marvelous long-term cycling durability (90.6 % capacity retention over 5000 cycles) in AZIBs. The reversible oxygen redox chemistry accompanied by CF3SO3 - (from the electrolyte) uptake/release, and the manganese redox accompanied by H+/Zn2+ co-insertion/extraction, are elucidated by advanced synchrotron characterizations and theoretical computations. Finally, pouch-type CaMnO-140//Zn batteries manifest bright application prospects with high energy, long life, wide-temperature adaptability, and high operating safety. This study provides new perspectives for developing high-energy cathodes for AZIBs by initiating anionic redox chemistry.

Sustainable Sulfur-Carbon Hybrids for Efficient Sulfur Redox Conversions in Nanoconfined Spaces.

Nanoconfinement is a promising strategy in chemistry enabling increased reaction rates, enhanced selectivity, and stabilized reactive species. Sulfur's abundance and highly reversible two-electron transfer mechanism have fueled research on sulfur-based electrochemical energy storage. However, the formation of soluble polysulfides, poor reaction kinetics, and low sulfur utilization are current bottlenecks for broader practical application. Herein, a novel strategy is proposed to confine sulfur species in a nanostructured hybrid sulfur-carbon material. A microporous sulfur-rich carbon is produced from sustainable natural precursors via inverse vulcanization and condensation. The material exhibits a unique structure with sulfur anchored to the conductive carbon matrix and physically confined in ultra-micropores. The structure promotes Na+ ion transport through micropores and electron transport through the carbon matrix, while effectively immobilizing sulfur species in the nanoconfined environment, fostering a quasi-solid-state redox reaction with sodium. This translates to ≈99% utilization of the 2e- reduction of sulfur and the highest reported capacity for a room temperature Na-S electrochemical system, with high rate capability, coulombic efficiency, and long-term stability. This study offers an innovative approach toward understanding the key physicochemical properties of sulfurcarbon nanohybrid materials, enabling the development of high-performance cathode materials for room-temperature Na-S batteries with efficient sulfur utilization.