Hard Carbon Spheres Research Articles

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.

KOH-activated hard carbon spheres with enhanced pseudo-capacitance for superior low-temperature electrochemical performance of Li-ion batteries

KOH-activated hard carbon spheres with enhanced pseudo-capacitance for superior low-temperature electrochemical performance of Li-ion batteries

Enhancing the Tribological Properties of Low-Density Polyethylene Using Hard Carbon Microfillers.

The application of low-density polyethylene (LDPE) has been confined to packaging applications due to its inadequate mechanical and tribological characteristics. We propose enhancing LDPE by integrating hard carbon spheres (CSs) to improve its strength, frictional characteristics, and wear resistance. LDPE/CS composites were created by blending LDPE with varying CS amounts (0.5-8 wt.%). Analysis using scanning electron microscopy and Raman spectroscopy confirmed CS presence in the LDPE matrix, with X-ray diffraction showing no microstructural changes post-blending. Thermal characterization exhibited notable improvements in thermal stability (~4%) and crystallinity (~7%). Mechanical properties such as hardness and Young's modulus were improved by up to 4% and 24%, respectively. Tribological studies on different composite samples with varying surface roughness under various load and speed conditions revealed the critical role of surface roughness in reducing friction by decreasing real contact area and adhesive interactions between asperities. Increased load and speed amplified shear stress on asperities, possibly leading to deformation and failure. Notably, integrating CSs into LDPE, starting at 1 wt.%, effectively reduced friction and wear. The composite with the highest loading (8 wt.%) displayed the most significant tribological enhancement, achieving a remarkable 75% friction reduction and a substantial 78% wear reduction.

Nitrogen/phosphorus co-doped ultramicropores hard carbon spheres for rapid sodium storage

Hard carbon (HC) is a prospective energy storage anode material in sodium-ion batteries (SIBs). However, their unimpressive rate capability and poor initial Coulombic efficiency (ICE) have driven the requirements for superior capability HC anode materials. In our work, nitrogen (N)/phosphorus (P) co-doped ultramicropores (≈0.5 nm) hard carbon spheres (NPUCS) with the boosted pyridinic-N content are successfully prepared. The ultramicropores structure (<0.7 nm) effectively prevents the electrolyte from contacting the carbon surface but allows the rapid diffusion of Na+ in the carbon layer, leading to high-efficiency sodium storage. Pyridinic-N has the highest reactivity, and could significantly promote the Na+ adsorption in HC. The NPUCS exhibits an excellent rate capability, providing capacities of 257.7 and 157.0 mA h g−1 at 0.1 and 5.0 A g−1 along with a high ICE to 75 %. Furthermore, when integrated into a full battery configuration, the prepared full battery displays a high energy density to 135.9 Wh kg−1 at 0.1 A g−1 with long-time stability (350 cycles at 0.2 A g−1). These excellent electrochemical behaviors highlight the potential of our approach for the synthesis of advanced HC anode for SIBs.

Impact of Hard Carbon Properties on Their Performance in Potassium-Ion Batteries

This work reports on the synthesis of hard carbon spheres (HCS) and the impact of the pyrolysis temperature (1500 to 1900 °C) on the properties of HC and its relationship with the electrochemical performance in potassium-ion batteries (KIBs). Comparison with commercial graphite performance is provided as well. Spherical morphology, disordered structure, and low surface area were obtained for the HCSs. Most properties (interlayer space, active surface area, and oxygen-based functional groups) were found to decrease with increasing pyrolysis temperature, except for the helium density and closed porosity, which increase. However, graphite presents a flake-like morphology with a larger particle size, a higher helium density, an ordered structure with a smaller interlayer distance, and no closed pores. Electrochemical tests in a half-cell vs K+/K showed that HCSs perform better than graphite with higher initial Coulombic efficiency (ICE) and better specific capacities. The HCSs pyrolyzed at 1500 and 1700 °C exhibit the best initial Coulombic efficiency, ICEs of 54 and 62%, and specific capacities of 254 and 247 mAh g–1 (C/20, 11.5 mA g–1), respectively. The ICE is affected by multiple surface and bulk parameters but also by electrolyte formulation (67% for 0.8 M KFSI vs 62% for 0.8 M KPF6). The capacity is governed by diffusive phenomena, and a larger interlayer graphitic spacing and defects favor a better insertion of K ions. Closed pores did not lead to an improvement in capacity. Furthermore, HCSs exhibit significantly better capacity retention (97%) than graphite (84%), especially when cycled at high current rates (up to 10C depotassiation rate).

Back Cover Image, Volume 5, Number 2, February 2023

Back cover image: Hard carbons are promising anode materials for sodium-ion batteries. Developing appropriate strategies to expand the area of pseudographite carbon are urgently needed for increasing the low-potential platform capacity. In article number 10.1002/cey2.191, Fuping Chen et al. prepared a series of vanadium-modified hard carbon with sufficient pseudographitic domains and stable interface. The optimized hard carbon spheres modified by vanadium carbide exhibited high low-potential plateau capacity and cycling stability.

Optimization of tannin-derived hard carbon spheres for high-performance sodium-ion batteries

Eco-friendly and low-cost polyphenol precursors were used to obtain hard carbon spheres with tuned properties (particle size, structure, and porosity). Optimized materials exhibit high Coulombic efficiency and specific capacity in Na-ion batteries.

Mechanochemistry assisted surface chemical modification on hard carbon for sodium storage: Size effect

Mechanochemical modification has been proved to be an effective and green method for carbon materials in the field of electrochemical energy storage. However, the research on the size effect during mechanochemical process seems still in blank for carbon materials. In this work, the size effect on the variations of the structural and electrochemical properties after mechanochemical treatments is studied through hard carbon spheres (CSs) with sizes of 170 nm, 492 nm and 0.9 μm. The size effect during the treatments affects the specific surface areas, pore structures, defects, functional groups, and the sodium storage properties. It comes as a surprise to find that parts of CO groups are converted to CO groups directionally. Significantly, the content variation of oxygen functional groups of large-sized CSs is more drastic, causing larger fluctuation in electrochemical performance. Interestingly, the performance improvement of the large-sized CSs is 18.4 % which is higher than that of medium-sized CSs (10.7 %) and small-sized CSs (9.3 %). The present work has provided a new scientific significance for carbon materials from lab-scale to industrial-scale in the field of battery electrode.

Coaxial Hard Carbon‐coated Carbon Nanotubes as Anodes for Sodium‐ion Batteries

AbstractAlthough being advantageous, the sodium‐ion storage capability of hard carbon would be better if its electrical conductivity could be improved. Herein, 3D hard carbon‐coated carbon nanotubes (CNTs@C) with interconnected conductive networks are fabricated by inducing hard carbon uniformly growth on CNTs. Compared with the isolated hard carbon spheres, the interconnected wire shape of CNTs@C reduces the ion transfer distance and increases the conductivity of hard carbon. By optimizing the thickness of the hard carbon layer and annealing temperature, the optimized CNTs@C displays a reversible specific capacity of 275.9 mAh g−1 at 0.1 A g−1 as anode material for SIBs. Furthermore, the material shows remarkable rate capability (102.8 mAh g−1 at 5 A g−1) and long‐life cycling performance (∼100% capacity retention after 1000 cycles at 5 A g−1). The results of this study provide an effective route for designing novel carbon‐based composite materials as anodes for SIBs.

Boosting ultrafast and durable sodium storage of hard carbon electrode with graphite nanoribbons

Hard carbons are emerged as one of the most promising candidates for sodium storage, but suffer from poor rate performance and inferior cycling stability. Herein, we design novel hierarchically hollow hard carbon spheres by combining hydrothermal growth and catalytic graphitization. The carbon spheres have a unique tremella-like morphology assembled from ultrathin heterostructured nanosheets with interwoven graphitic ribbons/amorphous carbon textures. When employed as anode in sodium-ion batteries, the 3D hierarchical structure is able to minimize the reaction length and accelerate the ion transfer; meanwhile, the graphite nanoribbons can offer electron immigration pathways and serve as supporting framework to protect the electrode off crack. As such, the carbon electrode delivers a high capacity of 278 mAh g−1 at 0.1 A g−1, and presents no dramatic capacity loss during a long-term charge/discharge test for 1000 cycles. More importantly, the hard carbon electrode has unexpectedly ultrafast sodium storage capability. Even under a very high current density of 10 A g−1, it retains a large capacity of 146 mAh g−1, giving a retention rate of 68% against the capacity at 0.05 A g−1, which is rarely achieved for state-of-the-art hard carbon anodes.

Optimizing ultramicroporous hard carbon spheres in carbonate ester‐based electrolytes for enhanced sodium storage in half‐/full‐cell sodium‐ion batteries

AbstractSodium‐ion batteries (SIBs) have received considerable attention as promising next‐generation energy storage systems due to a large abundance of sodium and ion storage chemistry similar to that of lithium‐ion batteries (LIBs). We report ultramicroporous hard carbon microspheres (HCMSs) derived from sucrose via a microwave‐assisted solvothermal reaction as anode for SIBs. Because of the HCMSs with a larger interlayer spacing in graphitic domains and ultramicropores, it delivers excellent 3‐RC features (reversible capacity, rate capability, and retention of capacity) reported to date for hard carbons derived from sugar‐based carbon precursors through electrolyte optimization of carbonate esters (EC:PC, EC:DEC, EC:DMC). The HCMS‐PC delivered the best reversible capacity of 265 mAh g−1 at a current density of 300 mA g−1, showing 85.8% capacity retention after 100 cycles and 66.3% capacity retention after 500 cycles in a half‐cell. A full‐cell fabricated with an HCMS‐PC anode and a Na3V2(PO4)3 cathode delivered reversible capacities of 81 and 48 mAh g−1 at current densities of 30 and 300 mA g−1, respectively.

Vanadium‐modified hard carbon spheres with sufficient pseudographitic domains as high‐performance anode for sodium‐ion batteries

AbstractHard carbons are promising anode materials for sodium‐ion batteries. To meet practical requirements, searching for durable and conductive carbon with a stable interface is of great importance. Here, we prepare a series of vanadium‐modified hard carbon submicrospheres by using hydrothermal carbonization followed by high‐temperature pyrolysis. Significantly, the introduction of vanadium can facilitate the nucleation and uniform growth of carbon spheres and generate abundant V–O–C interface bonds, thus optimizing the reaction kinetic. Meanwhile, the optimized hard carbon spheres modified by vanadium carbide, with sufficient pseudographitic domains, provide more active sites for Na ion migration and storage. As a result, the HC/VC‐1300 electrode exhibits excellent Na storage performance, including a high capacity of 420 mAh g−1 at 50 mA g−1 and good rate capability at 1 A g−1. This study proposes a new strategy for the synthesis of hard carbon spheres with high tap density and emphasizes the key role of pseudographitic structure for Na storage and interface stabilization.

A General Multi-Interface Strategy toward Densified Carbon Materials with Enhanced Comprehensive Electrochemical Performance for Li/Na-Ion Batteries.

Fast charging rate and large energy storage are key requirements for lithium-ion batteries (LIBs) in electric vehicles. Developing electrode materials with high volumetric and gravimetric capacity that could be operated at a high rate is the most challenging problem. In this work, a general multi-interface strategy toward densified carbon materials with enhanced comprehensive electrochemical performance for Li/Na-ion batteries is proposed. The mixture of graphene oxide and sucrose solution is sprayed into a water/oil system and furtherly carbonized to get graphene/hard carbon spheres (GHSs). In this material, abundant ingenious internal interfaces between the crystalline graphene and the carbon matrix are created inside the hard carbon spheres. The constructed interfaces can not only work as a pathway for the escape of volatile gas generated during sucrose pyrolysis to prevent the formation of abundant pores, which leads high packing density of 0.910gcm-3 and low surface area of 13.3m2 g-1 , but can also provide a conductive "highway" for ions and electrons. When used as the anode material for both LIBs and sodium-ion batteries (SIBs), the GHS shows the high gravimetric/volumetric reversible capacities, high-rate performance, and low temperature properties simultaneously, implying the great potential application in practical LIBs and SIBs.

Unraveling the Intercorrelation Between Micro/Mesopores and K Migration Behavior in Hard Carbon.

Pore-structure design with increased ion-diffusion ability is usually regarded as an effective strategy to improve K-storage performance in hard carbon (HC). However, the relationship between porous structure and K+ migration behavior remains unclear and requires further exploration. Herein, a series of chemically activated hard carbon spheres (denoted as AHCSs) with controllable micro/mesopores structure are successfully synthesized to explore intercorrelation between micro/mesopores and K migration behavior. The experimental results indicate AHCSs have two different K+ storage ways, that is, adsorption behavior at high potential region and intercalation process at low potential region. These behaviors are closely related to the pores structure evolution: the micropores afford extra active sites for efficient K-ions adsorption, and therefore positive correlation between micropores and adsorption-contributed capacity is confirmed; the mesopores permit more K-ions intercalation/deintercalation by offering adequate pathways, and as a result positive correlations between mesopores and intercalation-contributed capacity as well as initial Coulombic efficiency are revealed. All these together contribute to achieving excellent reversible capacity, and exceptional rate capability with an ultra-long cycle lifespan in PIBs, and simultaneously exhibit a high energy density as well as considerable cycling stability for potassium-ion full cells. These results promote a fundamental understanding of K+ migration behaviors in hard carbon.

Porous hard carbon spheres derived from biomass for high-performance sodium/potassium-ion batteries

Hard carbon is the most attractive anode material for electrochemical sodium/potassium-ion storage. The preparation of hard carbon spheres directly from the broad sources of biomass is of great interest but barely reported. Herein, we developed a simple two-step hydrothermal method to construct porous carbon microspheres directly from the original waste biomass of camellia shells. The porous carbon microspheres have high specific capacities of 250 mAh g−1 and 264.5 mAh g−1 at a current density of 100 mA g−1 for sodium-ion batteries and potassium-ion batteries, respectively. And it has excellent cycle stability for sodium ions and potassium ions outperforming most reported hard carbons, which is mainly attributed to the microporous structure and spherical morphology. The work paves a way to prepare porous hard carbon spheres directly from biomass for alkali metal-ion batteries.

Tuning the microstructures of uniform carbon spheres by controlling the annealing conditions for high-performance lithium-ion full batteries and lithium-ion capacitors

Microstructures include graphited microcrystal structures, micro-pores, specific areas, and pore volume of hard carbon spheres (CSs), have been tuned to optimize their Li+ storage performance by annealing at different temperature. The sample annealed at 650 °C (CS-650) exhibits the best performance for Li+ storage with high specific capacity, stable cycling stability, and superior rate performance. The CS-650 displays an initial capacity of 284 mAh g–1 at a specific current of 0.3 A g–1 with 277 mAh g–1 can be retained after 400 cycles, and a specific capacity of 180 mAh g–1 can be achieved at a high specific current of 2.0 A g–1. More significantly, the CS-650 exhibits a high capacitive contribution ratio from 62.2% to 76.0% as the scan rate increases from 0.3 to 1.0 mV s−1 due to its high specific area and large pore volume. The capacitive behaviour of CS-650 enhances the reaction kinetics for high energy and high-power applications in both full battery and Li-ion capacitor (LIC), which are assembled with LiNi0.5Co0.2Mn0.3O2 cathode and activated carbon positive electrode, respectively. The CS-650-based full battery shows a specific capacity of 66.1 mAh g−1 at 0.1 A g−1 combined with high cycling stability. The LIC displays a specific energy of 115 Wh kg−1 at 242 W kg−1 with a specific energy of 48 Wh kg−1 at 2364 W kg−1. Our work indicates that the Li+ storage performance of hard carbon can be tuned by the microstructure and both high energy and high power performances can be achieved.

Engineering hard carbon with high initial coulomb efficiency for practical sodium-ion batteries

Although hard carbons holds the most promise as anodes for practical sodium-ion batteries, high cost and low initial coulomb efficiency (ICE) limit their commercial application. In the present work, we develop an efficient solvothermal stabilization method to fabricate hard carbon spheres with high carbon yield from the wheat starch precursor. As anode for sodium-ion batteries, the obtained samples deliver not only a high capacity above 300 mAh g−1, but also an enhanced initial coulombic efficiency up to 90% and long cycle stability. Furthermore, when coupled with Na0.9[Cu0.22Fe0.30Mn0.48]O2 as cathode electrode, the full cell exhibited a high ICE of 85%, an average voltage of 3.2V and excellent stability during 300 cycles charging and discharging. These desirable electrochemical performances, combined with the renewable precursor and efficient synthesis route, make the obtained hard carbon sphere a promising anode for practical material for sodium-ion batteries.

Hard carbon spheres prepared by a modified Stöber method as anode material for high-performance potassium-ion batteries.

The Stöber method is a highly efficient synthesis strategy for homogeneous monodisperse polymer colloidal spheres and carbon spheres. This work delivers an extended Stöber method and investigates the synthesis process. By calcining the precursor under appropriate conditions, solid secondary particles of amorphous carbon (SSAC) and hollow secondary particles of graphitized carbon (HSGC) can be directly synthesized. The two materials have a nano-primary particle structure and a closely-packed sub-micron secondary particle structure, which can be used in energy storage. We find that SSAC and HSGC have high potassium-ion storage capacity with reversible capacities of 274 mA h g−1 and 283 mA h g−1 at 20 mA g−1 respectively. Significantly, SSAC has better rate performance with a specific capacity of 107 mA h g−1 at 1 A g−1.

Extended low-voltage plateau capacity of hard carbon spheres anode for sodium ion batteries

Hard carbon is now one of the most promising anode materials for sodium-ion batteries, but achieving high reversible capacity at low voltage plateau (0–0.1 V) is still a major challenge, which can actually enhances the operating voltage as well as the energy density when coupled with cathodes. In this work, a series of hard carbon spheres (HCS) with controlled architectures for sodium ion batteries (SIBs) are prepared by carbonizing synthetic phenolic resin over a wide temperature range from 900 to 2800 °C. HCS treated at 1900 °C (HCS-1900) has a pure hard carbon structure with appropriate graphitic interlayer distance (0.358 nm) and microcrystal size (La ~ 1.61 nm, Lc ≈ 3.07 nm). It delivers a reversible capacity of 295 mAh g−1 and an ultra-large capacity of 248.2 mAh g−1 (84% of the reversible capacity) at low-voltage plateau, in which an intercalation mechanism is proposed for Na ion storage. Exquisite differential scanning calorimetry (DSC) analysis suggests that soliated hard carbon has better thermal stability than that of metallic Na.

Effects of ester-based electrolyte composition and salt concentration on the Na-storage stability of hard carbon anodes

Hard carbon (HC) is the most feasible anode for Na-ion batteries (NIBs). However, HC electrodes suffer from low initial coulombic efficiency (ICE), poor rate capability and cyclic instability. Here, a systematic investigation was carried out to understand the effect of Na salt, esters-based solvent and concentration on the electrochemical performance of hard carbon spheres (HCSs) electrodes. Based on the experimental results, 2 M NaTFSI/DC:DMC electrolyte delivers the best initial reversible capacities of 332 mAh·g−1, high ICE of 83.5% and excellent electrochemical stability of 90% after 100 cycles at 0.1C and 80% after 300 cycles at 1C. In addition, the drastic capacity fading phenomenon of HCSs electrode occurs in ultrahigh concentration electrolyte (5 M NaTFSI/EC:DMC) after cycles, and this drastic capacity fading mechanism is revealed by the ex-situ strategies of the Raman, SEM and capacity-recovery experiment. The proposed moderate concentrated electrolyte and failure mechanism of ultrahigh concentration electrolyte for HC electrode provide further insights in developing preferable electrolyte for NIBs.