Hard Carbon Research Articles

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.

Reviving Sodium Tunnel Oxide Cathodes Based on Structural Modulation and Sodium Compensation Strategy Toward Practical Sodium-Ion Cylindrical Battery.

As a typical tunnel oxide, Na0.44MnO2 features excellent electrochemical performance and outstanding structural stability, making it a promising cathode for sodium-ion batteries (SIBs). However, it suffers from undesirable challenges such as surface residual alkali, multiple voltage plateaus, and low initial charge specific capacity. Herein, an internal and external synergistic modulation strategy is adopted by replacing part of the Mn with Ti to optimize the bulk phase and construct a Ti-containing epitaxial stabilization layer, resulting in reduced surface residual alkali, excellent Na+ transport kinetics and improved water/air stability. Specifically, the Na0.44Mn0.85Ti0.15O2 using water-soluble carboxymethyl cellulose as a binder can realize a capacity retention rate of 94.30% after 1,000 cycles at 2C, and excellent stability is further verified in kilogram large-up applications. In addition, taking advantage of the rich Na content in Prussian blue analog (PBA), PBA-Na0.44Mn1-xTixO2 composites are designed to compensate for the insufficient Na in the tunnel oxide and are matched with hard carbon to achieve the preparation of coin full cell and 18650 cylindrical battery with satisfactory electrochemical performance. This work enables the application of tunnel oxides cathode for SIBs in 18650 cylindrical batteries for the first time and promotes the commercialization of SIBs.

Sulfur and Nitrogen Codoped Hard Carbon with Expanded Interlayer Distance as an Effective Anode Material for Sodium-Ion Batteries

Sulfur and Nitrogen Codoped Hard Carbon with Expanded Interlayer Distance as an Effective Anode Material for Sodium-Ion Batteries

Effect of introducing oxygen into ethylene tar pitches on their carbonaceous products

Ethylene tar is a prospective precursor for preparing carbonaceous materials, which is regard-ed as a representative soft carbon material after carbonization. However, the introduction of oxygen can influence the morphology of the final carbonaceous materials. For the introduction of oxygen, dealkylation and dehydrogenation will be promoted and the molecules can be linked more effectively. For the subsequent carbonization, the biphenyl structures caused by the deoxygenation via the elimination of CO2, as well as the reserved aromatic ether bonds, can facilitate the strong cross-linking, which will restrain the movement of the carbon layers and the formation of the graphitic structures. After the graphitization treatment at 2800 oC, the oxidized pitch can lead to short-range ordered and long-range unordered structures, while the sample without oxidation can result in long-range ordered graphitic structures. It can be proved that a simple oxidation-carbonization treatment can transform ethylene tar into hard carbon structures.

Inorganic-Enriched Solid Electrolyte Interphases: A Key to Enhance Sodium-Ion Battery Cycle Stability?

The characteristics of solid electrolyte interphase (SEI) at both the cathode and anode interfaces are crucial for the performance of sodium-ion batteries (SIBs). The research demonstrates the merits of a balanced organic component, specifically the organic sodium alkyl sulfonate (ROSO2Na) featured in this work, in conjunction with the inorganic sodium fluoride (NaF), to enhance the interfacial stability. Using a customized electrolyte, it has optimized the interphase, curbing excess NaF production, and created a thin and uniform NaF/ROSO2Na-rich SEI layer. It offers exceptional protection against interface deterioration, transition metal dissolution, and concurrently ensures a consistent reduction in interfacial impedance. This creative approach results in a substantial improvement in the performance of both the Na0.9Ni0.4Fe0.2Mn0.4O2 cathode and the hard carbon anode. The cathode demonstrates remarkable average Coulombic efficiency exceeding 99.9% and a capacity retention of 81% after 500 cycles. Furthermore, the Ah-level pouch cell has shown outstanding performance with an 87% capacity retention after 400 cycles. Moving beyond the prevailing focus on inorganic-rich SEI, these results highlight the effectiveness of the customized organic-inorganic hybrid SEI formulation in improving SIB technology, offering an adaptable solution that ensures superior interfacial stability.

Pomegranate Peel-Derived Hard Carbons as Anode Materials for Sodium-Ion Batteries.

Exploring high-performance carbon anodes that are low-cost and easily accessible is the key to the commercialization of sodium-ion batteries. Producing carbon materials from bio by-products is an intriguing strategy for sodium-ion battery anode manufacture and for high-value utilization of biomass. Herein, a novel hard carbon (PPHC) was prepared via a facile pyrolysis process followed by acid treatment using biowaste pomegranate peel as the precursor. The morphology and structure of the PPHC were influenced by the carbonization temperature, as evidenced by physicochemical characterization. The PPHC pyrolyzed at 1100 °C showed expanded interlayer spacing and appropriate oxygen group content. When used as a sodium ion battery anode, the PPHC-1100 demonstrated a reversible capacity of up to 330 mAh g-1, maintaining 174 mAh g-1 at an increased current rate of 1 C. After 200 cycles at 0.5 C, the capacity delivered by PPHC-1100 was 175 mAh g-1. The electrochemical behavior of PPHC electrodes was investigated, revealing that the PPHC-1100 possessed increased capacitive-controlled energy storage and improved ion transport properties, which explained its excellent electrochemical performance. This work underscores the feasibility of high-performance sodium-ion battery anodes derived from biowaste and provides insights into the sodium storage process in biomass-derived hard carbon.

Identifying the importance of functionalization evolution during pre-oxidation treatment in producing economical asphalt-derived hard carbon for Na-ion batteries

Na-ion batteries (NIBs) are emerging as frontrunners for next-generation energy storage systems, boasting superior safety profiles and promising cost-effectiveness. A crucial hurdle in the commercialization of NIBs lies in developing cost-effective hard carbons (HC) with high carbon yields. This work leverages ultra-affordable asphalt as a precursor, coupled with pre-oxidization to specifically tailor the microstructures of HC, achieving an impressive carbon yield of 63%. Both experimental and theoretical calculation results reveal that the successful introduction of oxidation sites during the pre-oxidation process is a prerequisite for producing non-graphitizable HC with large interlayer spacing. The inclusion of carbonyl groups effectively restricts the movement of carbon atoms during subsequent carbonization, thus hindering the graphitization of carbon layer. Furthermore, abundant ether-oxygen bonds enable the solid-phase carbonization mechanism and prevent the shrinkage of carbon layers, facilitating the crispation of carbon layers. This breakthrough significantly boosts the potential of harnessing low-cost, high-performance HC for NIBs.

Design of cross-linked hard carbon with high initial coulombic efficiency for sodium-ion batteries anode

Cross-linked hard carbon materials (SFCzGLC1) were prepared from Shenfu bituminous coal (SFC) and glucose (GLC) via a one-step carbonization method. The relationship between the microstructure and Na+ storage behavior was explored. The initial coulombic efficiency (ICE) was related to surface defects. Owing to abundant porous structure and low defects, SFC3GLC1 delivered the highest reversible capacity of 413.1 mAh/g at 0.02 A/g with ICE ∼84 % and excellent cycling stability (89.4 % capacity retention over 200 cycles). This work provides a facile route to develop high-performance, low-cost carbon-based anodes for next-generation sodium-ion batteries (SIBs).

Deconstruction Engineering of Lignocellulose Toward High-Plateau-Capacity Hard Carbon Anodes for Sodium-Ion Batteries.

Biomass-derived hard carbon is a promising anode material for commercial sodium-ion batteries due to its low cost, high capacity, and stable cycling performance. However, the intrinsic tight lignocellulosic structure in biomass hinders the formation of sufficient closed pores, limiting the specific capacity of obtained hard carbons. In this contribution, a mild, industrially mature pretreatment method is utilized to selectively regulate biomass components. The hard carbon with a rich closed pore structure is prepared by optimizing the appropriate ratio of biomass composition. Optimized etching conditions enhanced the closed pore volume of hard carbon from 0.15 to 0.26 cm3 g-1. Consequently, the engineered hard carbon exhibited excellent electrochemical performance, including a high reversible capacity of 346 mAh g-1 with a high plateau capacity of 254 mAh g⁻¹ at 50 mA g⁻¹, robust rate capability, and cycling stability. The optimized hard carbon shows an 88 mAh g⁻¹ increase in plateau capacity compared to hard carbon from directly carbonizing bamboo fibers. This mature approach provides an easy-to-operate industrial pathway for designing high-capacity biomass-based hard carbons for sodium-ion batteries.

Structural modulation of Na4Fe3(PO4)2P2O7 via cation engineering towards high-rate and long-cycling sodium-ion batteries

Mixed iron-based phosphate Na4Fe3(PO4)2P2O7/C (NFPP) has gradually emerged as a promising cathode material for sodium-ion batteries (SIBs) owing to its affordability and convenient preparation. However, poor electrical conductivity and inadequate sodium-ion diffusion limit the exertion of its electrochemical properties. Herein, a structural modulation strategy based on Cd doping is applied to NFPP to address the above limitations. In situ X-ray diffraction analysis reveals that Cd-doped NFPP (NFCPP) undergoes an incomplete solid-solution reaction driven by Fe2+/Fe3+ redox. Cd doping effectively stabilises the crystal structure, resulting in a minimal 1 % change in unit cell volume during cycling. Density of state calculations indicate that Cd doping reduces the band gap, increases the local electron density and significantly improves electron conductivity. Benefitting from the enhanced electrochemical kinetics and intercalation pseudocapacitance, the optimised Na4Fe2.91Cd0.09(PO4)2P2O7/C (NFCPP@3%) exhibits exceptional rate performance (capacity of 62 mAh/g at 20 C) and ultra-long cycling life (82.7 % after 6000 cycles at 20 C). A full SIB prepared using NFCPP@3% and hard carbon, display a 91 % capacity retention rate at a current density of 130 mA g−1 over 200 cycles. This work demonstrates that doping can effectively enhance electrochemical performance and offers insights into future development of SIBs.

High‐abundance and low‐cost anodes for sodium‐ion batteries

AbstractNowadays, sodium‐ion batteries are considered the most promising large‐scale energy storage systems (EESs) due to the low cost and wide distribution of sodium sources as well as the similar working principle to lithium‐ion batteries (LIBs). Therefore, screening suitable materials with high abundance, low cost, and excellent reliability and modified with different strategies based on them is the key point for the development of sodium‐ion batteries (SIBs). In addition, the ideal anodes with high abundance, and low cost elements also greatly influence the cost of SIB systems, determining the large‐scale application. Herein, recent advances in carbon, iron, manganese, and phosphorus‐based anodes of various types, such as hard carbon, iron oxides, manganese oxides, and red phosphorus, are highlighted. The various sodium storage mechanisms and structure‐function properties for these four types of materials are summarized and analyzed in detail. Considering the commercial profits that the EESs can bring and their suitability for mass electrode manufacturing, the participation of high‐abundance and low‐cost elements such as Fe, Mn, C, and P is convincing and encouraging.

The induced formation and regulation of closed-pore structure for biomass hard carbon as anode in sodium-ion batteries

Biomass hard carbon is regarded as an advanced anode materials for sodium ion batteries (SIBs) since it possesses balanced performance including satisfactory specific capacity, suitable operating voltage window and low cost. Although numerous instances of utilizing biomass-derived hard carbon in SIBs have been observed, the unregulated pore structure of these hard carbon materials significantly constrains the electrochemical performance of SIBs, leading to diminished initial Columbic efficiency (ICE) and plateau capacity. Herein, taking a biomass hard carbon derived from waste camellia seed shells (CSSHCs) as a template, we display a correlation between synthesis conditions and pore structure of CSSHCs. CSSHCs are synthesized via a facile route including pre‑carbonization, purifying, mechanical ball-milling and high-temperature carbonization, and it is found that adjusting the secondary calcination temperature can induce the formation of closed pore structure, which is of great benefit to increase the ICE and the plateau-capacity. Besides, it is also proved that the obtained CSSHCs anodes obey a sodium storage mechanism that can be classified as “adsorption-intercalation-pore filling”, which endows SIBs with a competitive electrochemical performance. Specifically, the obtained biomass hard carbons at 1300 °C exhibits the best electrochemical performance among these anodes with the reversible capacity of as high as 270.0 mAh g−1 and a high ICE of 80.1 %, together with an excellent cycle stability (91.0 % capacity retention after 200 cycles at 0.1C, 1C = 300 mA g−1). Therefore, this study provides a significant exploration and raw material support for the further utilization of the waste biomass and sustainable development of the anode materials for the large-scale application of SIBs.

Iron-decorated N/S co-doped porous carbon for sodium-ion battery anode to achieve high initial coulombic efficiency

Hard carbon materials are preferred as anode materials for sodium-ion batteries due to their abundance, low price, and environmental friendliness. However, doping-based modification usually induces low initial coulombic efficiency (ICE), which seriously affects the practical application of carbon materials. In this work, Fe-modified N/S co-doped porous carbon is prepared using the salt template method. Fe, N, and S are uniformly distributed on the porous carbon to form an interwoven network structure, providing abundant active sites. Moreover, during the electrochemical reaction, FeNx effectively catalyzes the generation of solid electrolyte interface (SEI) film, which reduces the consumption of Na+ in the side reaction, leading to a high initial coulombic efficiency, and at the same time, the stabilized SEI film accelerates the diffusion of electrons and ions, effectively enhancing the multiplication rate performance. The NFSC exhibits a high specific capacity (371.3 mAh/g) by the co-coordination strategy and a high ICE (85.9 %). This study provides new ideas for research based on the modification of carbon materials.

Defect-rich hard carbon designed by heteroatom escape assists sodium storage performance for sodium-ion batteries

Sodium-ion batteries (SIBs) avoids the use of expensive cobalt element, and the abundance of sodium element is high, so it shows great application potential, and the development of sodium-ion battery materials is of great value. Biomass precursors have the advantages of low cost and widely and sufficiently distributed resources, and embody the environmental concept of waste utilization, however, the poor reversible specific capacity and initial coulombic efficiency (ICE) of pristine corn stover-derived hard carbons (CSHCs) limit their practical application value. In this paper, we propose a method to increase the reversible specific capacity of hard carbon and maintain high ICE, introduce heteroatoms into graphene-like nanosheets at low carbonization temperature, then escape heteroatoms through high pyrolysis temperature, create defects in the graphene-like carbon layer and expand the (002) layer spacing. Density functional theory (DFT) calculations show that defects are beneficial to the adsorption of Na+ on graphene-like nanosheets, and Na+ have a lower diffusion barrier between layers rich in defects and extended (002) layer spacing. Compared with the conventional low pyrolysis temperature heteroatom doping process, the present method exhibits superior ICE. In the ester-based electrolyte, the modified hard carbon (D-CSHC) exhibits a superior specific capacity of 284.5 mAh/g and an ICE of 85.9 % as compared to the pristine corn stover-derived hard carbon (233.5 mAh/g, 72.7 %). In addition, the capacity retention rate was 92.6 % after 500 turns of constant current cycles at 0.15 A/g.

Tailoring closed pore structure in phenolic resin derived hard carbon enables excellent sodium ion storage

The existed plenty of oxygen-containing species in phenolic resin easily inhibit the migration and rearrangement of carbon atoms during pyrolysis, which disfavors the formation of pseudo-graphite structure with larger lateral length (La) and hence leads to poor closed pores, accounting for a low capacity and initial Coulombic efficiency (ICE). Herein, hard carbon with rich closed pores and the most suitable pore size and volume is constructed via a two-step carbonization strategy. It is found that the pre-annealing step can effectively decrease oxygen content by changing the interconnection form of molecule chains, which promotes the growth of La during post-carbonization process, accelerating the formation of closed pores. Besides, with decreasing oxygen content, closed pore size gradually increases, while closed pore number and volume both first increase and then decrease, unveiling that an excessive high and too low oxygen content are unfavorable for the formation of ideal closed pores, resulting from an unsuitable La size. Therefore, the resulting sample, featured by the optimal balance between closed pore number, size (2.52 nm), and volume (0.215 cm3 g−1), delivers a high capacity of 351 mAh g−1 along with an excellent ICE of 83 %.

Growth performance, antioxidant capacity, intestinal microbiota, and metabolomics analysis of Nile tilapia (Oreochromis niloticus) under carbonate alkalinity stress

To explore the effect of carbonate alkalinity stress on Nile tilapia (Oreochromis niloticus), fish were cultured at 3 alkalinity levels (0, 2 and 3 g/L NaHCO3) for six weeks. Survival, weight gain, and specific growth rate were measured. Liver samples were collected for measuring superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), and malondialdehyde (MDA) content. Intestinal microbiota was analyzed using 16S rRNA gene sequencing, and metabolomic profiling identified differentially abundant metabolites. The results showed that the survival rate decreased in the fish exposed to 3 g/L NaHCO3, while weight gain and specific growth rate were not affected by the increased carbonate alkalinity. In the group exposed to 3 g/L NaHCO₃, activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), and malondialdehyde (MDA) content in liver increased, while in 2 g/L NaHCO₃, only SOD and T-AOC activities rose compared to the control. Long-term carbonate alkalinity stress increased the abundance of Luteolibacter in intestine but decreased the abundance of Cetobacterium, Bacteroides, and Lactiplantibacillus. Metabolomics results showed that differentially abundant metabolites were highly enriched in pathways such as purine metabolism, vitamin B6 metabolism, lysine degradation, glycerophospholipid metabolism, and biosynthesis of cofactors in fish cultured at 3 g/L NaHCO3. These results suggested that carbonate alkalinity stress affects intestinal health by increasing the proportion of pathogenic bacteria and reducing beneficial bacteria. The correlation between N6,N6,N6-trimethyllysine, Ne,Ne-dimethyllysine, and Luteolibacter may represent an effective physiological adaptation and tissue repair pathway for Nile tilapia under carbonate alkalinity stress.

Nitrogen and phosphorus co-doped hard carbon materials as high-performance anode for sodium ion batteries

Abstract The negative electrode of sodium ion batteries has always faced severe challenges in the commercialization process. To improve capacity, increase the first Coulomb efficiency, and enhance performance under high current density, we have prepared a nitrogen phosphorus co-doped hard carbon material. Phosphorus groups are doped in the material to achieve sodium storage, at the same time, coating phenolic resin for material modification. At the same time, nitrogen and carbon nanotube structures are added during the preparation process to make it have good conductivity. In order to solve the problem of low first Coulomb efficiency, adopted CMC binder and ether based electrolyte to solve the problem of excessive reaction between the negative electrode and the electrolyte during the first discharge process. In actual testing, this material has a capacity of 365 mAh g−1 and a capacity retention rate of 112% under long cycles.

Steric Hindrance Engineering to Modulate the Closed Pores Formation of Polymer-Derived Hard Carbon for High-Performance Sodium-Ion Batteries.

The closed pores play a critical role in improving the sodium storage capacity of hard carbon (HC) anode, however, their formation mechanism as well as the efficient modulation strategy at molecular level in the polymer-derived HCs is still lacking. In this work, the steric hindrance effect has been proposed to create closed pores in the polymer-derived HCs for the first time through grafting the aromatic rings within and between the main chains in the precursor. The experimental data and theoretical calculation demonstrate that steric-hindrance effect from the aromatic ring side group can increase backbone rigidity and the internal free volumes in the polymer precursor, which can prevent the over graphitization and facilitate the formation of closed pores during the carbonization process. As a result, the as-prepared HC anode exhibits a remarkably enhanced discharge capacity of 340.3 mAh/g at 0.1 C, improved rate performance (210.7 mAh/g at 5 C) as well as boosted cycling stability (86.4 % over 1000 cycles at 2 C). This work provides a new insight into the formation mechanisms of closed pores via steric hindrance engineering, which can shed light on the development of high-performance polymer-derived HC anode for sodium-ion batteries.

Deposition of Wear-Resistant Nanocomposite Coatings from Accelerated С<sub>60</sub> Ions

Hard wear-resistant carbon coatings were deposited from accelerated C60 ions at temperatures of 200 and 300°C. It has been established that the mechanical properties of the coatings are determined by the substrate temperature (Ts) and the energy composition of the beam. The hardness of coatings deposited from C+60 ions with an energy of 7 keV exceeds 50 GPa and is virtually independent of Ts. The presence of C602+ and C603+ with an energy of ~14 and 21 keV, respectively, in the beam leads to a result that is not typical for carbon coatings – the hardness increases by more than 1.3 times with an increase in Ts from 200 to 300°C (from 31.6 GPa to 41.6 GPa). In this case, according to Raman spectroscopy data, the size of graphite nanocrystals in the coating increases with temperature up to almost 2 nm. Coatings obtained under conditions of irradiation with C602+ and C603+ ions are characterized by minimal wear (1.5×10–8 mm3/N∙m, Ts = 200°C) and minimal friction coefficient (µ = 0.05 for Ts = 300°C). We attribute the unusual dependence of hardness on Ts and the improvement in the tribological properties of coatings to the formation of a composite structure based on a diamond-like matrix and graphite nanocrystals in this range of Ts.

Enhancing the stability of sodium-ion capacitors by introducing glyoxylic-acetal based electrolyte

Sodium-ion Capacitors (SICs) are becoming increasingly important energy storage devices. This study presents an in-depth comparison of a largely used electrolyte for said application, sodium hexafluorophosphate in ethylene carbonate:propylene carbonate (NaPF6 in EC:PC), with the novel electrolyte sodium bis(trifluoromethanesulfonyl)imide in 1,1,2,2-tetraethoxyethane:propylene carbonate (NaTFSI in TEG:PC). Firstly, half-cells of the SIC standard electrode materials, hard carbon (HC) and activated carbon (AC), are shown to perform comparably well with the two electrolytes. However, the use of the novel electrolyte in SICs allows for an improved stability during float tests. All in all, the novel electrolyte NaTFSI in TEG:PC appears to be a very promising alternative electrolyte for SIC application.