Soft Carbon Research Articles

Pore-size control of soft mesoporous carbon by hot pressing

Pore-size control of soft mesoporous carbon by hot pressing

Depth distribution of alkali metal ions on supported graphene in the presence of water

The interaction of alkali ions with multilayer graphene is critical in many applications, for example in energy storage devices. This requires a detailed understanding of ion interactions with carbonaceous layers. The mechanism of ion intercalation into graphene can be different from that observed for hard graphite. In this paper, we present an investigation of the vertical alkali ion (Na, K, Cs) distribution on multilayer graphene deposited onto SiO2 in vacuum and in the presence of water vapor using Standing Wave Ambient Pressure Photoemission Spectroscopy. It was found that Cs, K, and Na ions do not intercalate into multilayer graphene under vacuum conditions. The most likely reasons for this behavior are the reversibility of the process due to large inter-sheet spacing or lack of time for intercalation. When exposed to water vapor, Na ions intercalate soft carbon whereas Cs ions do not. This is a clear indication for the difference in the intercalation mechanisms on hard graphite and soft graphene.

Engineering a wirelessly self-powered and electroconductive scaffold to promote peripheral nerve regeneration

Electroactive biomaterials have been shown useful for the repair of injured peripheral nerve. While for conventional conductive conduits, outer electrical stimulation device is unavoidably employed to exert electrical signals, and their rigid microstructures are usually incompatible with neural cells. Herein, a soft carbon nanotubes@gelatin methacryloyl/poly(L-lactic acid) (CNTs@GelMA/PLLA) nerve tissue-engineering scaffold was fabricated, which provided an endogenous piezoelectric stimulation and conductive microenvironment. Based on amounts of in-vitro experiment data, such composite scaffold significantly improved adhesion and elongation of Schwann cells, and meanwhile promoted axonal outgrowth and neurites number of dorsal root ganglions. More interestingly, the scaffold was applied to a 10-mm sciatic nerve defect in rats and harvested at 12 weeks post-implantation. Immunohistochemical staining results indicated that our proposed graft significantly facilitated peripheral nerve regeneration by promoting myelination and axon outgrowth, meanwhile an enhanced motor functional recovery caused by the scaffold was also revealed due to the obviously-improved sciatic functional index and muscle weights. Overall, the soft, self-powered, and electroconductive CNTs@GelMA/PLLA scaffold is a promising candidate for the treatment of peripheral nerve injuries.

Unveil Overcharge Performances of Activated Carbon Cathode in Various Li-Ion Electrolytes

Typically, the practical lithium-ion capacitor (LIC) is composed of a capacitive cathode (activated carbon, AC) and a battery-type anode (graphite, soft carbon, hard carbon). There is a risk of the LIC cell overcharging to an unsafe voltage under electrical abuse conditions. Since the anode potential is usually quite low during the charging process and can be controlled by adjusting the amount of anode materials, the overcharge performances of LIC full-cell mainly depend on the AC cathode. Thus, it is necessary to independently investigate the overcharge behaviors of the AC cathode in nonaqueous Li-ion electrolytes without the interference of the anode electrode. In this work, the stable upper potential limits of the AC electrode in three types of lithium-ion electrolytes were determined to be 4.0−4.1 V via the energy efficiency method. Then, the AC//Li half-cells were charged to 5.0 V and 10.0 V, respectively, to investigate the overcharge behaviors. For the half-cells with propylene carbonate (PC)-based electrolytes, the voltage increased sharply to 10.0 V with a vertical straight line at the end of the overcharging process, indicating that the deposits of electrolyte decomposition had separated the AC electrode surface from the electrolytes, forming a self-protective passivation film with a dielectric capacitor behavior. The dense and compact passivation film is significant in separating the AC electrode surface from the electrolytes and preventing LIC cells from volume expansion and explosion risks under electrical abuse and overcharging conditions.

Reasonable intrinsic microstructure of microcrystalline graphite for high-rate and long-life potassium-ion batteries

Carbon materials, including non-graphite carbon and graphite have been extensively studied as anode materials for Potassium-ion batteries (PIBs). However, due to the slow kinetics of potassiation, it is still challenging to obtain anode materials with rate capability, good stability and low price. Microcrystalline graphite (MG) possesses ordered graphene layers and abundant interparticle voids and correspondingly undergoes a surface adsorption behavior at first and then the intercalation of K+ at low potential, which is conductive to high energy density. In addition, the larger interplanar spacing of MG with suitable crystalline size can stand for the fluctuation of interlaminar spacing caused by repeated K+ bombardment because strain in such structure can be relaxed due to sufficiently available free space. When used as anode material of PIBs, microcrystalline graphite can deliver a high reversible capacity of 249 mAh g−1 at 100 mA g−1 after 100 cycles in a readily-available electrolyte of 0.8 M KPF6 in EC/DEC (1:1 vol%), which offer a significant cost-saving opportunity. Furthermore, compared to flake graphite and soft carbon, MG exhibits the highest capacity of 139 mAh g−1 at 500 mA g−1 after 500 cycles. Our investigations will greatly promote the MG's industrial development in China.

Manipulating K-Storage Mechanism of Soft Carbon via Molecular Design-Driven Structure Transformation.

The emerging potassium-ion batteries (PIBs) have been placing stratospheric expectations for realizing grid-scale electrochemical storage of renewable energy. However, the unsatisfactory K-storage of PIB anode materials, especially promising carbonaceous materials, significantly limited the development of PIBs. Here, a molecular design strategy was proposed to realize controllable structure transformation of soft carbon (SC) materials for enhanced K-storage performance. The optimized SC-PCN material delivered a high reversible K-storage capacity of 838 mAh/g at 50 mA/g, outstanding rate capability (213 mAh/g at 1000 mA/g), and excellent long-term cycling performance (301 mAh/g maintained after 300 cycles at 500 mA/g), superior to most previously reported carbon-based PIB anodes materials. Reaction kinetic analysis revealed that the proposed molecular design strategy can achieve the transformation from a surface capacitive-dominated mechanism to a capacitive-diffusion hybrid mechanism for SC-PCN, benefiting from its unique microstructures with highly defective surface generated via the synergistic effect from template removal, N doping, and surface reconstruction. The optimal hybrid K-storage mechanism should be responsible for the excellent K-storage properties of the prepared SC-PCN.

Pore-size control of soft mesoporous carbon by hot pressing

Pore-size control of soft mesoporous carbon by hot pressing

Concurrent function of high-strength dry carbon fiber as resistive heating element and thermistor in ambient air

Measuring temperature through carbon fiber reinforced plastics requires an implanted contact-based temperature sensor during resistive heating. Implanting the sensor brings about considerable complications in the heat-joining of soft biocompatible Carbon Fiber Reinforced Plastics (CFRPs). In this paper, the concurrent temperature-dependent Electrical Resistance (ER) behavior of Carbon Fiber (CF) tow along with resistive heating is introduced. The temperature feedback from CF tow was investigated in the range of 60–200 °C in the room condition. The process is characterized by high nonlinearity due to complex mode of heat loss, orthotropic and semi-conductive nature of CF, resistivity of contacts, gas-moisture adsorption and ambient changes. In such conditions, experiments were conducted to study the Current-Voltage (I–V), ER-time and ER-temperature in steady-state and transient modes. I–V relationship was non-ohmic and ER-temperature relationship showed negative temperature coefficient at temperatures above 60 °C. Exponential behavior similar to that of thermistors was identified in ER-temperature relationship. The relationship is expressed by Hoge-quartic model, 1T=a+b(lnR(T))+c(lnR(T))2+d(lnR(T))3+e(lnR(T))4, showing the best fit among the conventional calibration equations of thermistor. The reversibility of ER-temperature relationship with maximum error of 16.4 °C was observed. The repeatability of the relationship shows the CF viability of providing concurrent temperature feedback during high-current Joule heating in the room condition.

High-rate soft carbon anode in potassium ion batteries: The role of chemical structures of pitches

Soft carbons (SCs) have become a promising anode for potassium ion batteries (PIBs). However, it is challenging to maintain high capacity and long cycle life at rapid charge/discharge rate due to the sluggish insertion/deinsertion of K+. To solve this problem, the morphology of the SCs was regulated by using pitches with different chemical structures. The results showed that the chemical structure of the pitch characterized by less long aliphatic chains led to the largest average distance between polycyclic aromatic nuclei, which caused mild condensation of polycyclic aromatic nuclei and thus the formation of lamellar structures. Abundant short chains of the pitch ignited violent cyclization and aromatization and the shortened average distance, inducing violent condensation to generate the bulk structures. The cyclopenta-fused rings and aromatic methyl groups of the pitch minimized the average distance, which also built the bulk structures. More exposed defect-edge sites and larger active surface of the lamellar SC contributed to the adsorption of K+ and improved reaction kinetics. When the current density increased to 3C,bulk structures did not work while the lamellar still remained high reversible capacity of 160.9 mAh g−1 after 1000 cycles. These findings paved a new way for the design of SCs at the molecular level to satisfy high electrochemical performance at high charge/discharge rate.

CNT-Reinforced Self-Healable Epoxy Dynamic Networks Based on Disulfide Bond Exchange.

The design and utilization of polymers with healing capability have drawn increasing attention owing to their enhanced chain mobility and opportunity to heal minor cracks in composites. Rehealable thermoset polymers promise reduction in the maintenance cost and thus prolonged lifetime, reshaping, and recyclability. Introducing reversible covalent bonds is the mainstay strategy to achieve such plasticity in crosslinked polymers. Herein, we report a dynamic epoxy, which includes associative covalent adaptive networks (CANs) based on disulfide exchange bonds. Epoxy resin is chosen to study rehealing, as it is one of the most critical thermosetting polymers for various industries from aerospace to soft robotics. This study enlightens us about not only the consequences of CANs in the epoxy but also various factors such as soft segments and carbon nanotubes (CNTs). Epoxy dynamic networks are investigated in an attempt to explore the synergistic effect of the soft-segmented resins and CNTs on the healing and reshaping characteristics of epoxy networks along with varying stiffness. This research discusses epoxy dynamic networks in three main aspects: crosslink density, CAN density, and CNTs. Introducing soft segments into the epoxy network enhances the healing efficiency due to the increased chain mobility. A higher CAN density accelerates network rearrangement, improving the healing efficiency. It should also be noted that even with a low weight fraction of nanotubes, CNT-reinforced samples restored their initial strength more than neat samples after healing. The tensile strength of dynamic networks is at least 50 MPa, which is significant for their utility in primary or secondary structural components.

Open pollution routing problem of logistics distribution in medical union based on differential search algorithm

Medical care is a guarantee of people's daily life. Improving healthcare contributes to people's well-being. However, healthcare resources are characterized by uneven distribution. Financially well-off areas will have higher quality health care resources. Most of the medical resources are concentrated in public general hospitals, however, primary care institutions can hardly meet the growing needs of people. To solve this problem, Medical Union achieves efficient deployment of resources by integrating various medical institutions in the same area. In the process of logistics integration of the medical union, the scale of logistics distribution expands accordingly. Transportation vehicles have high operating costs and produce greenhouse gases in the process of distribution. The optimization of the driving path of logistics distribution vehicles can reduce the operating cost, fuel consumption and carbon emission. To solve this kind of decentralized and complex vehicle routing problem, this paper proposes a pollution routing problem model considering electrical vehicle usage, customer's soft time window expectation, open path and carbon cost. A modified Differential Search Algorithm with the comprehensive learning strategy and dynamic Cauchy variation strategy is advanced to solve the problem. Results show that the improved algorithm has good solving performance, and verifies the rationality of the proposed model, which will help to reduce carbon emissions and save the logistics and operating costs of medical devices.

Design Strategies toward High‐Performance Hybrid Carbon Bilayer Anode for Improved Ion Transport and Reaction Stability

AbstractCompositing carbon‐based materials with different properties can significantly improve the energy density of lithium‐ion batteries for applications that require high power, such as electric vehicles, owing to their effective current distribution. Nevertheless, the chemical reaction is not uniform throughout the entire depth of conventionally blended electrodes. This study proposes a hybrid patterned bilayer anode that comprises a blended layer of spherical crystalline graphite (SCG) and soft carbon and a single layer of SCG alone, which maintains a stable ionic reaction at the electrode surface and improves ion transport. This bilayer anode has a smaller, more uniform solid electrolyte interphase layer that is more evenly distributed throughout the electrode compared with the blended electrode. The electrode pattern interfaces, which are optimized by controlling the pattern size, ensure excellent mechanical adhesion and low internal resistance. Consequently, the patterned bilayer half‐cell achieves a high‐capacity retention of 85.9% after 500 charge–discharge cycles at 1 C. The full cell also attains an energy density of 178.7 Wh kg−1 with fast discharging at 10 C, which is 2.3 times higher than that of the single‐layer SCG electrode.

Molecularly chemical prelithiation of soft carbon towards high-performance lithium-ion capacitors

The crucial role of prelithiation in lithium-ion capacitor arises from the lithium-deficiency hurdle intrinsic to cathode. Although a multitude of efforts have been dedicated to investigating electrochemical compensation of lithium ions, the homogeneity and safety hazards limit the development of prelithiation. Herein, a molecularly chemical prelithiation of amorphous soft carbon is reported for the first time. Using 2-methyltetrahydrofuran (MTHF) as prelithiation solvent and a suitable prelithiation time of 5 min, prelithiated soft carbon (SC-5-MTHF) has a low potential of 0.21 V vs. Li/Li+. The structure of SC-5-MTHF is chemically stable, and the preformed solid electrolyte interface layer on the surface of soft carbon can ensure a high reversibility of lithium-ion during charge-discharge process. Lithium-ion capacitor constructed with SC-5-MTHF as anode and activated carbon as cathode exihibits a high capacitance retention of 96.7 % after 5000 cycles.

Recovery of carbon fiber-reinforced polymer waste using dimethylacetamide base on the resin swelling principle.

The mechanical recycling method of the carbon fiber-reinforced polymer (CFRP) has the advantages of simple process, less pollution and low cost, but only low utilization value of carbon fibers in powder or short fibers form can be obtained. To reduce the length and strength loss of the recycled carbon fibers, a novel and cost-effective dimethylacetamide (DMAC) swelling technique was developed to achieve rapid delamination of the CFRP laminates under mild conditions (120°C-160°C, 1h). The corresponding swelling ratios and mass-loss rates of cured epoxy resin (CEP) were about 121.39%-157.39% and 0-0.69%, respectively. Excessive swelling of CEP in DMAC resulted in the cracking of the resin matrix between the adjacent carbon fiber layers. Thus the CFRP laminates were delaminated into soft single carbon fiber layers, which showed excellent cutting performance and reinforcing properties. The delamination products were cut into thin strips of different sizes and vacuum bag molded into new CFRP laminates. The flexural strength and tensile strength of the newly produced CFRP laminates were about 76.38%-90.98% and 94.61%-98.54% of the original CFRP laminates, respectively. More importantly, the chemical compositions of DMAC and CEP were unchanged during the physical swelling process. No organic pollutants (caused by resin degradation) were generated. And the used DMAC can be easily recycled by filtration. Therefore, this study provides a strategy for low-cost and high-valued recycling of CFRP waste.

Fluorinated soft carbon as an ultra-high energy density potassium-ion battery cathode enabled by a ternary phase KxFC

Fluorinated carbons (CFx) have been widely applied as lithium primary batteries due to their ultra-high energy density. It will be a great promise if CFx can be rechargeable. In this study, we rationally tune the C-F bond strength for the alkaline intercalated CFx via importing an electronegative weaker element K instead of Li. It forms a ternary phase KxFC instead of two phases (LiF + C) in lithium-ion batteries. Meanwhile, we choose a large layer distance and more defects CFx, namely fluorinated soft carbon, to accommodate K. Thus, we enable CFx rechargeable as a potassium-ion battery cathode. In detail, fluorinated soft carbon CF1.01 presents a reversible specific capacity of 339 mA h g−1 (797 Wh kg−1) in the 2nd cycle and maintains 330 mA h g−1 (726 Wh kg−1) in the 15th cycle. This study reveals the importance of tuning chemical bond stability using different alkaline ions to endow batteries with rechargeability. This work provides good references for focusing on developing reversible electrode materials from popular primary cell configurations.

Microwave Preparation of Porous Graphene from Wasted Tires and Its Pyrolysis Behavior

Nowadays, most waste tires are disposed of by direct combustion or via landfill, which inevitably creates a large volume of waste. However, the soft carbon found in tires can be an excellent precursor in the preparation of graphene. In this study, waste tires were mixed with potassium hydroxide and heated in a microwave environment to be converted rapidly into porous graphene, a process having no complicated pre-processing. Moreover, the processes, tools, and chemical reagents are distinct and inexpensive. This research innovatively uses the characteristics of microwave rapid and selective heating to study the pyrolysis behavior of waste tires after adding alkali, and realizes the conversion of soft carbon in tires to graphene. At the same time, the time required for the preparation process is greatly reduced which compared with conventional heating methods. Thermogravimetric analysis and dielectric property testing of the tires and mixtures were conducted to study their pyrolysis behavior and catalytic reactions. It was found that when the temperature reached more than 750 °C, potassium ions and carbon underwent a reduction reaction to generate potassium vapor, which catalyzed the carbon in the tires into porous graphene, and that microwave heating could shorten the heating time. Simultaneously, the carbon in the tire could be sheared smaller and thinner during the rapid pyrolysis and volatilization of the gas, benefitting the graphene production. The products of the mixed materials were then characterized and analyzed at different holding temperatures and times. As the holding time increased, the degree of graphitization of the products increased, the number of layers increased slightly, and the impurity elements were completely removed from the products.Graphical Abstract

Cocoon-shaped P3-type K0.5Mn0.7Ni0.3O2 as an advanced cathode material for potassium-ion batteries

Potassium ion batteries (PIBs) are emerging as potential next-generation energy storage systems on account of their low cost and high theoretical energy density. Nevertheless, they also face challenges of low specific capacity and suboptimal cycling stability. Herein, we synthesize a cocoon-like P3-type K0.5Mn0.7Ni0.3O2 (KMNO) cathode material by a self-template method. The KMNO cocoons possess a hierarchical layered architecture composed of nanoparticle stacking, which can accelerate the transport kinetics of potassium ions, mitigate the stress caused by K+ intercalation and deintercalation, and improve structural stability. In addition, Ni can not only alleviate the Jahn-Teller distortion and suppress the phase transition to stabilize the structure, but also act as an electrochemically active element, providing the capacity of two electrons from Ni2+ to Ni4+. Combining the advantages of structure and nickel substitution, the P3-type KMNO cocoons are used for electrochemical performance testing of PIB cathodes, delivering an excellent rate capability of 57.1 mA h g−1 at 500 mA g−1 and a remarkable cycling stability of 77.0% over 300 cycles at 100 mA g−1. Impressively, the KMNO cocoons//pitch-derived soft carbon assembled full battery exhibits superior electrochemical performance with a reversible capacity of 79.7 mA h g−1 at 50 mA g−1. Moreover, ex-situ XRD also further reveals a solid solution phase reaction with a volume change of only 1.46%. This work furnishes a suitable approach to fabricating high-performance layered oxide cathodes for PIBs with outstanding cycling stability and rate capability.

Designing carbon anodes for advanced potassium-ion batteries: Materials, modifications, and mechanisms

Recently, the limited abundance and uneven geographical distribution of Li resources seriously hamper the growing demand for lithium-based energy storage devices. In this regard, potassium-ion batteries (KIBs) sharing similar “rocking chair” working principles with lithium-ion batteries have started to attract increasing attention due to their high energy density and abundant potassium resources. Carbon material is considered to show great potential for using as high-performance anode in KIBs. However, it is still a challenge to simultaneously achieve satisfactory specific gravimetric and volumetric capacities, high initial Coulombic efficiency, superior rate performance, and excellent cycle stability due to the sluggish reaction kinetics of the large-sized K-ions. Herein, we summarize the latest research achievements of different types of carbon anodes for KIBs, including graphite, graphene, hard carbon, soft carbon, and carbon nanotubes, in which the key factors affecting the electrochemical performance are explored. Importantly, the alternative strategies for addressing the low gravimetric/volumetric capacity and low initial Coulombic efficiency of carbons are thoroughly emphasized. Finally, the critical issues, challenges, and perspectives are proposed to show the development direction of KIBs. We hope this review can provide researchers with new ideas to design high-performance carbon materials and give insightful perspectives to accelerate the application of carbon electrodes for KIBs. The latest research achievements of different types of carbon anodes for KIBs are summarized, including graphite, graphene, hard carbon, soft carbon, and carbon nanotubes, in which the key factors affecting the electrochemical performance are demonstrated. Importantly, the alternative strategies for addressing the low gravimetric/volumetric capacity and low initial Coulombic efficiency of carbons are thoroughly emphasized. Finally, the critical issues, challenges, and perspectives are proposed to show the development direction of KIBs. • The latest progress of carbon materials in potassium ion batteries are presented. • Promising strategies to improve the potassium storage performances are emphasized. • Challenges and prospects for the future development of carbon materials are highlighted.

N, P co-doped pitch derived soft carbon nanoboxes as high-performance anodes for sodium-ion batteries

Carbonaceous materials have been regarded as promising materials for sodium-ion batteries (SIBs), owing to their high electrical conductivity and stable chemical properties. High-performance sodium-ion batteries need high quality carbon materials as anodes with low cost. Herein, we report a facile method of preparing N/P co-doped soft carbon nanoboxes (NPSC) using petroleum pitch as raw material. Benefitting from the nanobox-like morphology, expanded graphitic layer spacing and excellent electrical conductivity, the NPSC anodes show fast sodium-ion diffusion and high pseudo capacitance ratio, as a result, excellent rate capability and cycling performance can be achieved. The NPSC can deliver a high reversible capacity of 162 mAh g −1 over 3000 cycles at high current density of 1 A g −1 . DFT calculations reveal that N, P co-doping carbon has more electrons near fermi level, thus facilitating electron transport. This work puts forward a convenient method to prepare carbon based anode for high performance SIBs with low cost petroleum pitch. • Petroleum pitch derived carbon was applied as high performance anode for sodium-ion batteries. • The special nanobox-like structures were constructed by a recrystallized NaCl template. • A high reversible capacity of 162 mAh g −1 was achieved at high current density of 1 A g −1 for over 3000 cycles.

CO2 Etching Modulates Lithium and Sodium Storage Performance of Hard-Soft Carbon Composite-Based Freestanding Thick Electrodes.

Carbon-based materials are the most prospective anodes. Typically, a single carbon-based material is applied to different energy storage systems (EESs) without modification. However, the microcrystal structure of carbon plays a decisive role in the energy storage performance, and therefore, it should be adjusted when applied to different EESs. Here, a hierarchical porous carbon monomer monolith (HPCM) embedded with carbon nanotubes blooming on ZIF-67 was designed as a soft-hard carbon-based freestanding thick electrode for achieving high-energy lithium-ion and sodium-ion batteries. HPCM is resorcinol-formaldehyde (RF) resin-derived carbon, mainly composed of hard carbon, which has outstanding mechanical properties, a high surface area, and high porosity. Carbon nanotubes (CNTs) derived from ZIF-67 have extraordinary electronic conductivity, which provides soft carbon. High-temperature CO2 etching was performed to adjust the microcrystal structure, and the lithium/sodium storage performance of the electrode was evaluated. After CO2 etching, the materials lose almost half their weight (mainly hard carbon), and pseudocapacitive contribution decreases for both lithium-ion and sodium-ion batteries, whereas the specific capacity increases for lithium-ion batteries and decreases for sodium-ion batteries. Capacities of 5.96 mAh cm-2 (areal) and 132.48 mAh cm-3 (volumetric) were achieved for lithium storage, and those for sodium storage were 2.31 and 51.24 mAh cm-3, respectively. In summary, it is significant to adjust the microcrystal structure of carbon-based electrodes, and this study provides related experience for lithium and sodium storage.