Hard Carbon Research Articles

Entropy-Assisted Anion-Reinforced Solvation Structure for Fast-Charging Sodium-Ion Full Batteries.

Anion-reinforced solvation structure favors the formation of inorganic-rich robust electrode-electrolyte interface, which endows fast ion transport and high strength modulus to enable improved electrochemical performance. However, such a unique solvation structure inevitably injures the ionic conductivity of electrolytes and limits the fast-charging performance. Herein, a trade-off in tuning anion-reinforced solvation structure and high ionic conductivity is realized by the entropy-assisted hybrid ester-ether electrolyte. Anion-reinforced solvation sheath with more anions occupying the inner Na+ shell is constructed by introducing the weakly coordinated ether tetrahydrofuran into the commonly used ester-based electrolyte, which merits the accelerated desolvation energy and gradient inorganic-rich electrode-electrolyte interface. The improved ionic conductivity is attributed to the weakly diverse solvation structures induced by entropy effect. These enable the enhanced rate performance and cycling stability of Prussian blue||hard carbon full cells with high electrode mass loading. More importantly, the practical application of the designed electrolyte was further demonstrated by industry-level 18650 cylindrical cells.

Defect engineering of sulfur vacancies in vanadium disulfide integrated with graphene as advanced potassium-ion battery cathode

Potassium-ion batteries (PIBs) have economic and environmental potential, but slow potassium ion diffusion and electrode material degradation hinder the development of effective cathode materials. This research designs a composite cathode material that vanadium disulfide with sulfur vacancies integrated with reduced graphene oxide (VS2-x@rGO). The introduction of sulfur vacancies increases active sites for ion storage, while rGO ensures a stable electronic conductivity and structural integrity. VS2-x@rGO shows a great rate performance of 116.2 mAh g−1 at 20 mA g−1, 77.5 mAh g−1 at 500 mA g−1, and high cycling stability with 94.5 % retention of capacity after 100 cycles at 100 mA g−1. Moreover, the full cell assembled with hard carbon achieves a specific capacity close to 120 mAh g−1. Energy density up to 220 Wh kg−1 in 38.4 W kg−1 and 72 Wh kg−1 in 960 W kg−1. Through in-situ XRD and other ex-situ analyses, the crystal structure rapidly transformed into K0.6VS2 and slight displacement of the crystal plane occurred during K+ insertion until KxVS2 formed in the discharge process. The charging process is reversible and forms VS2. This study provides a novel approach for advancing PIBs cathode materials, contributing valuable insights into the optimization of energy storage solutions.

Innovative Tin and hard carbon architecture for enhanced stability in lithium-ion battery anodes

Tin (Sn), with a theoretical capacity of 994 mAh g-1, is a promising anode material for lithium-ion batteries (LIBs). However, fundamental limitations like large volume expansion during charge-discharge cycle and confined electronic conductivity limit its practical utility. Here, we report a new material design and manufacturing method of LIB anodes using Sn and Hard Carbon (HC) architecture, which is produced by Physical Vapor Deposition (PVD). A bilayer HC/Sn anode structure is deposited on a carbon/copper sheet as a function of deposition time, temperature, and substrate heat treatment. The developed anodes are used to make cells with a lithium-ion electrolyte using a specific fabrication process. The morphology, atomic structure, conductivity, and electrochemical performance of the developed HC/Sn anodes are studied with SEM, TEM, XPS, and electrochemical techniques. At a discharge rate of 0.1C, the Snheated + HC anode performs exceptionally well, offering a capacity of 763 mAh g-1. It is noteworthy that it achieves a capacity of 342 mAh g-1 when fast charging at 5C, demonstrating exceptional rate capability. The Snheated + HC anode maintains >97 % Coulombic efficiency of its capacity after 3000 cycles at a rate of 0.1C after 3000 cycles 730.5 mAh g-1 recorded, demonstrating an impressive cycle life. The novel material design approach of the Snheated + HC anode, which has a multi-layered structure and HC acting as a barrier against volumetric expansion and improving electronic conductivity during battery cycling, is perceived as influential in uplifting anode's performance.

An Engineering Porous Spherical Carbon Cathode for High-Energy Sodium-Ion Capacitor.

Sodium-ion hybrid capacitors (SICs) are emerging as promising devices that can balance energy and power output. However, the lack of a high-capacity cathode that can match the anode has limited its further application. In this work, we develop an efficient method to prepare spherical porous carbons (SPCs) with great specific surface area and narrow pore size distribution from coal-based humic acid via spray drying and a subsequent chemical activation process. Thanks to this unique porous structure, the SPC cathode has a superb capacity of 223 F g-1 at 0.05 A g-1, as well as splendid rate performance and cycling stability. SICs constructed by an SPC cathode and hard carbon anode can exhibit a high energy density of 179.8 Wh kg-1 at 155 W kg-1 and achieved 89.4% capacity retention after 10 000 cycles at 0.5 A g-1. This outcome presents a viable approach to attaining high-capacity cathodes for constructing outstanding performance hybrid capacitors.

Manipulating micropore structure of hard carbon as high‐performance anode for Sodium-Ion Batteries

Hard carbon (HC) is the most promising anode material for sodium-ion batteries (SIBs), but its low initial coulombic efficiency (ICE) and specific capacity limit its practical application. Herein, a chemical vapor deposition (CVD) strategy is used to address these challenges via filling the micropores of sucrose-based HC with pyrolysis by-products from acetonitrile, thereby reducing the specific surface area of HC microspheres. This approach mitigates the formation of solid electrolyte interphase (SEI) film leading to an enhancement in ICE. Moreover, the conversion of open micropores into closed pores creates additional storage space for sodium ions, effectively extending the specific capacity within the plateau region. Specifically, the HC prepared with a deposition duration of 1 h demonstrates the most favorable electrochemical performance. The optimal HC anode manifests an enhanced specific capacity of 307.6 mAh g−1 with an ICE of 66.01 % and exhibits excellent cycle stability (84.9 % capacity retention after 200 cycles at 100 mAh g−1). This study provides a feasible approach to optimize hard carbon anode materials for SIBs.

Extremely Durable K-Ion Batteries Enabled by Heteroatom Co-Doped Highly-Ordered Porous Carbon Spheres with Nearly 100% Capacity Retention up to 11,000 Cycles.

Currently, one major target for exploring K-ion batteries (KIBs) is enhancing their cycle stability due to the intrinsically sluggish kinetics of large-radius K+ ions. Herein, we report a rationally designed electrode, the S/O co-doped hard carbon spheres with highly ordered porous characteristics (SPC), for extremely durable KIBs. Experimental results and theory calculations confirm that this structure offers exceptional advantages for high-performance KIBs, facilitating rapid K+ diffusion and (de)-intercalation, efficient electrolyte penetration and transport, improved K+ storage sites, and enhanced redox reaction kinetics, thus ensuring the long-term cycle stability. As a result, the as-constructed SPC anode delivers a high reversible capacity of ca. 200 mAh g-1 at a high current density of 2.0 A g-1 and robust stability with ∼100% capacity retention up to 11,000 cycles, outperforming most carbon-based KIB anodes. This work offers insight into developing advanced KIBs with durable stability toward practical applications.

Measuring enhanced weathering: inorganic carbon-based approaches may be required to complement cation-based approaches

The removal of atmospheric carbon dioxide (CO2) is now essential to meet net zero goals and limit the impacts of climate change. Enhanced weathering is a method of sequestering CO2 that involves the distribution of finely ground silicate rocks over agricultural land. The weathering of these silicate rocks releases cations into solution which can balance dissolved inorganic carbon, effectively removing CO2 from the atmosphere. Despite being a promising method of carbon dioxide removal (CDR), enhanced weathering has been limited by uncertainty surrounding the measurement of CO2 sequestration. This study compares current measurement approaches that focus on quantifying inorganic carbon and cations within the soil and leachate. Cation-based calculations of CDR were compared to inorganic carbon-based calculations of CDR and soil results were compared to leachate results. The recovery rate of cations in the soil fraction was also tested. Three different ground silicate minerals/rocks – basalt, olivine and wollastonite, were mixed with two different soils and were allowed to weather over 16 weeks in 320 pots with and without plants under different watering regimes and the application of an acidifying fertiliser. Soil and leachate samples were analysed for cations by ICP-OES and inorganic carbon by direct CO2 analysis after acidification and total alkalinity titration (in leachate only). The results indicate that the soil retains most enhanced weathering products through the cation exchange reactions. CDR estimated by cations is often greater than CDR estimated by inorganic carbon. Measurement approaches to estimate cations are susceptible to incomplete or improper accounting through the under-extraction of cations stored within the soil-exchangeable pool, the activity of non-carbonic acids and CO2 outgassing. Inorganic carbon-based measurements, including direct inorganic carbon and total alkalinity analysis, are also complicated by the potential for CO2 loss through carbonate precipitation and re-equilibration. Therefore, inorganic carbon-based approaches and cation-based approaches should be reconciled to validate the estimation of CDR. The inorganic carbon-based estimation of CDR in leachate should equal the cation-based estimation of CDR in leachate—which will be achieved after quantification or estimation of the natural mechanisms that affect each approach. These findings will support the development of accurate measurement processes for enhanced weathering.

Precisely Tunable Instantaneous Carbon Rearrangement Enables Low-Working-Potential Hard Carbon Toward Sodium-Ion Batteries with Enhanced Energy Density.

As the preferred anode material for sodium-ion batteries, hard carbon (HC) confronts significant obstacles in providing a long and dominant low-voltage plateau to boost the output energy density of full batteries. The critical challenge lies in precisely enhancing the local graphitization degree to minimize Na+ ad-/chemisorption, while effectively controlling the growth of internal closed nanopores to maximize Na+ filling. Unfortunately, traditional high-temperature preparation methods struggle to achieve both objectives simultaneously. Herein, a transient sintering-involved kinetically-controlled synthesis strategy is proposed that enables the creation of metastable HCs with precisely tunable carbon phases and low discharge/charge voltage plateaus. By optimizing the temperature and width of thermal pulses, the high-throughput screened HCs are characterized by short-range ordered graphitic micro-domains that possess accurate crystallite width and height, as well as appropriately-sized closed nanopores. This advancement realizes HC anodes with significantly prolonged low-voltage plateaus below 0.1V, with the best sample exhibiting a high plateau capacity of up to 325mAhg-1. The energy density of the HC||Na3V2(PO4)3 full battery can therefore be increased by 20.7%. Machine learning study explicitly unveils the "carbon phase evolution-electrochemistry" relationship. This work promises disruptive changes to the synthesis, optimization, and commercialization of HC anodes for high-energy-density sodium-ion batteries.

Implementing the iCORAL (version 1.0) coral reef CaCO3 production module in the iLOVECLIM climate model

Abstract. Coral reef development is intricately linked to both climate and the concentration of atmospheric CO2, specifically through temperature and carbonate chemistry in the upper ocean. In turn, the calcification of corals modifies the concentration of dissolved inorganic carbon (DIC) and total alkalinity in the ocean, impacting air–sea gas exchange, atmospheric CO2 concentration, and ultimately the climate. This feedback between atmospheric conditions and coral biogeochemistry can only be accounted for with a coupled coral–carbon–climate model. Here we present the implementation of a coral reef calcification module into an Earth system model. Simulated coral reef production of the calcium carbonate mineral aragonite depends on photosynthetically active radiation, nutrient concentrations, salinity, temperature, and the aragonite saturation state. An ensemble of 210 parameter perturbation simulations was performed to identify carbonate production parameter values that optimize the simulated distribution of coral reefs and associated carbonate production. The tuned model simulates the presence of coral reefs and regional-to-global carbonate production values in good agreement with data-based estimates, despite some limitations due to the imperfect simulation of climatic and biogeochemical fields driving the simulation of coral reef development. When used in association with methods accounting for bathymetry changes resulting from different sea levels, the model enables assessment of past and future coral–climate coupling on seasonal to millennial timescales, highlighting how climatic trends and variability may affect reef development and the resulting climate–carbon feedback.

Multi boron-doping effects in hard carbon toward enhanced sodium ion storage

Hard carbon (HC) has been considered as promising anode material for sodium-ion batteries (SIBs). The optimization of hard carbon’s microstructure and solid electrolyte interface (SEI) property are demonstrated effective in enhancing the Na+ storage capability, however, a one-step regulation strategy to achieve simultaneous multi-scale structures optimization is highly desirable. Herein, we have systematically investigated the effects of boron doping on hard carbon’s microstructure and interface chemistry. A variety of structure characterizations show that appropriate amount of boron doping can increase the size of closed pores via rearrangement of carbon layers with improved graphitization degree, which provides more Na+ storage sites. In-situ Fourier transform infrared spectroscopy/electrochemical impedance spectroscopy (FTIR/EIS) and X-ray photoelectron spectroscopy (XPS) analysis demonstrate the presence of more BC3 and less B–C–O structures that result in enhanced ion diffusion kinetics and the formation of inorganic rich and robust SEI, which leads to facilitated charge transfer and excellent rate performance. As a result, the hard carbon anode with optimized boron doping content exhibits enhanced rate and cycling performance. In general, this work unravels the critical role of boron doping in optimizing the pore structure, interface chemistry and diffusion kinetics of hard carbon, which enables rational design of sodium-ion battery anode with enhanced Na+ storage performance.

Olivine-Type Fe2GeX4 (X = S, Se, and Te): A Novel Class of Anode Materials for Exceptional Sodium Storage Performance.

The introduction of abundant metals to form ternary germanium-based chalcogenides can dilute the high price and effectively buffer the volume variation of germanium. Herein, olivine-structured Fe2GeX4 (X = S, Se, and Te) are synthesized by a chemical vapor transport method to compare their sodium storage properties. A series of in situ and ex situ measurements validate a combined intercalation-conversion-alloying reaction mechanism of Fe2GeX4. Fe2GeS4 exhibits a high capacity of 477.9mA h g-1 after 2660 cycles at 8 A g-1, and excellent rate capability. Furthermore, the Na3V2(PO4)3//Fe2GeS4 full cell delivers a capacity of 375.5mA h g-1 at 0.5 A g-1, which is more than three times that of commercial hard carbon, with a high initial Coulombic efficiency of 93.23%. Capacity-contribution and kinetic analyses reveal that the alloying reaction significantly contributes to the overall capacity and serves as the rate-determining step within the reaction for both Fe2GeS4 and Fe2GeSe4. Upon reaching a specific cycle threshold, the assessment of the kinetic properties of Fe2GeX4 primarily relies on the ion diffusion process that occurs during charging. This work demonstrates that Fe2GeX4 possesses promising practical potential to outperform hard carbon, offering valuable insights and impetus for the advancement of ternary germanium-based anodes.

Designing high-performance phosphate cathode toward Ah-level Na-ion batteries

The phosphate material Na3V2(PO4)3 is one of promising cathodes for Na-ion batteries owing to its superior electrochemical reversibility. However, the high-potential V4+/V5+ redox couple (4.0 V vs. Na+/Na) in pure Na3V2(PO4)3 cathode is not activated, resulting in a limited energy density. Although conventional single-metallic substitutions can activate V4+/V5+ redox plateau, the energy density has no significant improvement due to the limited capacity of V4+/V5+ redox plateau. Here, we propose a bi-metallic (Al3+ and Fe3+) substitution strategy, which can increase the reversible capacity of V4+/V5+ couple via lowering the energy needed during desodiation process, thus realizing a remarkable improvement of energy density. Moreover, we reveal that Fe3+substitution can improve the rate performance of cathode by reducing band gap and Na-ion diffusion activation energy. As a result, the designed Na3V1.5Al0.3Fe0.2(PO4)3 cathode delivers a high energy density of 399.7 Wh kg-1 (capacity 116.2 mAh g−1, average voltage 3.44 V) and a high rate capability (91.2% capacity retention from 0.1 C to 20 C), as well as superior cycling stability (89.5% capacity retention after 8000 cycles at 10 C). In addition, we demonstrate a 0.8 Ah 18,650-type Na3V1.5Al0.3Fe0.2(PO4)3//hard carbon full cell with 92.4% capacity retention over 400 cycles at 0.5 C. This work presents the design of high-performance phosphate cathode via bi-metallic substitution, boosting the development of practical Na-ion batteries.

Achieving High-Capacity Cathode Presodiation Agent Via Triggering Anionic Oxidation Activity in Sodium Oxide.

Compensating for the irreversible loss of limited active sodium (Na) is crucial for enhancing the energy density of practical sodium-ion batteries (SIBs) full-cell, especially when employing hard carbon anode with initially lower coulombic efficiency. Introducing sacrificial cathode presodiation agents, particularly those that own potential anionic oxidation activity with a high theoretical capacity, can provide additional sodium sources for compensating Na loss. Herein, Ni atoms are precisely implanted at the Na sites within Na2O framework, obtaining a (Na0.89Ni0.05□0.06)2O (Ni-Na2O) presodiation agent. The synergistic interaction between Na vacancies and Ni catalyst effectively tunes the band structure, forming moderate Ni-O covalent bonds, activating the oxidation activity of oxygen anion, reducing the decomposition overpotential to 2.8V (vs Na/Na+), and achieving a high presodiation capacity of 710 mAh/g≈Na2O (Na2O decomposition rate >80%). Incorporating currently-modified presodiation agent with Na3V2(PO4)3 and Na2/3Ni2/3Mn1/3O2 cathodes, the energy density of corresponding Na-ion full-cells presents an essential improvement of 23.9% and 19.3%, respectively. Further, not limited to Ni-Na2O, the structure-function relationship between the anionic oxidation mechanism and electrode-electrolyte interface fabrication is revealed as a paradigm for the development of sacrificial cathode presodiation agent.

Cation-inspired polyhedral distortion boosting moisture/electrolyte stability of iron sulfate cathode for durable high-temperature sodium-ion storage

Alluaudite-type iron-based sulfates are prospective positive-electrode active materials for sodium-ion batteries given their low-cost and high operation voltage, yet suffer from poor intrinsic ionic conductivity and (electro)chemical instability at high temperatures. Herein, a cation-modified Na2.466Fe1.724Mg0.043(SO4)3 with micron-sized spherical structure was reported. The substitutive MgO6 octahedron featured stronger covalent bonding interactions and enriched the ion transfer pathways within the crystals, facilitating the ionic kinetics in bulk. Using in situ mass spectrometry and quartz crystal microbalance techniques, Mg cations were demonstrated to lower the electron density around O atoms and surficial nucleophilicity of materials, which effectively suppressed their side reactions with H2O in air and active ester molecule in electrolyte. This interaction enables an inorganic-rich and uniform interphase to stabilize the cathode/electrolyte interface at high voltage (4.5 V vs. Na+/Na). The as-prepared cathode exhibits a high discharge capacity of 102.2 mAh g−1 (voltage platform at 3.74 V), remarkable reaction reversibility (average Coulomb efficiency of 99.3% over 300 cycles) at high loading (9.0 − 9.6 mg cm−2) and temperature (60 °C), as well as long-lasting cyclability (70.8%, 5000 cycles). Its application was verified in assembled sodium-ion full cells with a hard carbon negative electrode, showing a long cycling lifetime over 190 cycles.

Mechanistic insight into assimilation capture: Implication for high-efficiency nitrogen removal from mature landfill leachate

The AO (Anoxic/oxic) process for treating high-strength ammonia in landfill leachate requires external carbon source and alkalinity. Alternatively, the processes of partial nitrification-Anammox (PNA) and partial denitrification-Anammox (PDA) with less or no carbon source have been developed, but enabled modulation difficulty due to nitrogen valence transformation. Ammonia assimilation for nitrogen removal immobilize ammonia (NH4+-N) as organic nitrogen, without nitrogen valence conversion and reducing greenhouse gases emission. This study offers a novel approach for nitrogen removal from low chemical oxygen demand (COD) to nitrogen (C/N) ratio leachate. The nitrogen removal response of biomass to ammonia assimilation in landfill leachate was established. Results demonstrated that the nitrogen removal contribution of ammonia assimilation and organics utilization by microorganisms significantly increased with biomass. When the initial mixed liquor suspended solid (MLSS) was 11200 mg/L, the removal efficiency of total nitrogen (TN) and COD in the landfill leachate achieved 98.42 ± 0.12 % and 80.60 ± 0.35 % after 30 days of operation, respectively. The corresponding assimilation contributions for TN and COD removals were 82.00 ± 0.96 % and 52.24 ± 0.82 %, respectively. Cell protein analysis showed that higher biomass significantly increased the production of intracellular and extracellular proteins or amino acids. The enrichment of bacterial genera such as Defluviicoccus, Aequorivita, Truepera, and Proteiniphilum played a crucial role in organics removal and NH4+-N assimilation. Functional gene analysis further demonstrated that most NH4+-N and organics were removed through bacterial assimilation. This research offered a green, efficient, and economical solution for the treatment of low C/N ratio landfill leachate.

Linking the size of hard carbon particles with electrochemical response in sodium ion storage

Hard carbon is considered to be one of the most promising anodes for sodium-ion batteries (SIBs) owing to its high capacity and abundant resources. However, the role of particle size on sodium ion storage is unclear, which leads to low capacity and initial coulombic efficiency (ICE) in practical application. In this work, a series of hard carbons with different particle sizes were prepared by an “up to down” strategy using simple grinding and ball-milling method to investigate the effect of particle size on electrochemical response of sodium ion storage. The particle size of hard carbon has negligible effect on initial specific capacity. However, it has a strong effect on the ICE and rate capability. The ICE reduces as the particle size decreases, but the rate performance in reverse. Moreover, impedance analysis and electrochemical kinetics show huge differences for different particle sizes. In-situ Raman technique was also adopted to further illustrate the sodium ion storage mechanism of hard carbon, and an “adsorption-intercalation-pore filling” mechanism is proposed. This work could provide a new perspective for the design of hard carbon materials with suitable structure for efficient sodium ion storage, helping to develop high performance SIBs.

Alkaline range pH sensor based on chitosan hydrogel: A novel approach to pH sensing

Monitoring of pH under extreme alkaline range is still a challenge due to the lack of accuracy and validity. This research developed a novel pH sensor (hydrogel/BTB) based on the transition of bromothymol blue from the hydrogel matrix into the pH-examining sample solution. The hydrogel/BTB sensor was synthesized through the solvent casting of chitosan, citric acid as the crosslinker, and bromothymol blue as a pH-sensitive dye. The structure of hydrogel/BTB was characterized using Fourier-transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDS), Field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) analysis, and thermogravimetric analysis (TGA). The effect of various parameters on pH determination was investigated. The developed pH sensor demonstrated a linear detection range validated from pH 10 to 14 using the gravimetric method, and from pH 11 to 14 using the colorimetric method. The sensor successfully detected pH in alkaline tap water, carbonate buffer, and ethanol amine buffer. The transition of bromothymol blue is described by the Peppas-Korsmeyer kinetic model. The activation and Gibbs free energy were obtained as 357.1 J/mol and 260 J/mol, respectively. This work furnished a new mechanism for pH detection, and it has excellent potential for developing novel sensors in this field.

Mercerization-enhanced cellulose-II cotton fiber-based low-temperature hard carbon for sodium-ion batteries

Hard carbons from cellulose are highly regarded as promising anode options for sodium-ion batteries (SIBs). However, a high carbonization temperature (>1300 °C) is usually required to obtain high-performance hard carbons, which leads to high-energy consumption and high cost. Moreover, hard carbons generally have poor rate capability and unsatisfactory cyclability which restrict their commercial applications. Herein, a low-temperature (900 °C) approach for the preparation of high-quality hard carbons for SIBs from waste cotton fibers is reported. It involves a mercerization pretreatment to convert cellulose-I cotton fibers into cellulose-II structure and dissolve the amorphous cellulose to form highly crystalline cellulose. This pretreatment process benefits forming abundant pseudo-graphitic structures at a low carbonization temperature of 900 °C. Consequently, the mercerized cotton fibers-based carbons (MCFC) exhibit excellent sodium storage properties, possessing a high capacity (316 mAh g−1 at 0.1 A g−1), high-rate capability (210 mAh g−1 at 10 A g−1), and long-term cyclability (83.2 % retention after 3000 cycles). This mercerization approach coupled with waste cotton fibers provides a sustainable pathway for the preparation of high-quality hard carbons for SIBs.

Hard carbon/graphene microfibers as a superior anode material for sodium-ion batteries

Hard carbon is one of the most promising anode materials for sodium-ion batteries (SIBs). However, it still suffers from low specific capacity and poor rate capability, which impede its practical application. Herein, one-dimensional hard carbon/graphene microfibers are synthesized by encapsulating hard carbon particles in graphene nanosheet using a wet-spinning technique followed by pyrolysis treatment. Benefiting from the unique structure, when used as the anode material for SIBs, the as-obtained hard carbon/graphene microfibers not only exhibit a high reversible capacity of 321 mAh g−1 at 0.1 C but also deliver long cycling stability and excellent rate capability, maintaining its capacity as 203 mAh g−1 even after 350 cycles at 1 C. In addition, the sodium storage mechanism of the as-prepared hard carbon/graphene microfibers is investigated by in-situ Raman technique. Moreover, a full cell adopting the hybrid microfiber as the anode and Na3V2(PO4)3 as the cathode exhibits high specific capacities of 291 mAh g−1 and 204 mAh g−1 at 0.2 C and 4 C (vs. anode), respectively. This work provides a sustainable and cost-effective strategy for the synthesis of high-capacity and stable hard carbon anode materials.

Coupling Liquid Electrochemical TEM and Mass-Spectrometry to Investigate Electrochemical Reactions Occurring in a Na-Ion Battery Anode.

A novel approach for investigating the formation of solid electrolyte interphase (SEI) in Na-ion batteries (NIB) through the coupling of in situ liquid electrochemical transmission electron microscopy (ec-TEM) and gas-chromatography mass-spectrometry (GC/MS) is proposed. To optimize this coupling, experiments are conducted on the sodiation of hard carbon materials (HC) using two setups: in situ ec-TEM holder and ex situ setup. Electrolyte (NP30) is intentionally degraded using cyclic voltammetry (CV), and the recovered liquid product is analyzed using GC/MS. Solid product (µ-chip) is analyzed using TEM techniques in a post-mortem analysis. The ex situ experiments served as a reference to for insertion of Na+ ions in the HC, SEI size (389 nm), SEI composition (P, Na, F, and O), and Na plating. The in situ TEM analysis reveals a cyclability limitation, this issue appears to be caused by the plating of Na in the form of a "foam" structure, resulting from the gas release during the reaction of Na with DMC/EC electrolyte. The foam structure, subsequently transformes into a second SEI, is electrochemically inactive and reduces the cyclability of the battery. Overall, the results demonstrate the powerful synergy achieved by coupling in situ ec-TEM and GC/MS techniques.