Soft Carbon Research Articles

Sustainable Polyvinyl Chloride-Derived Soft Carbon Anodes for Potassium-Ion Storage: Electrochemical Behaviors and Mechanism.

Soft carbon is a promising anode material for potassium-ion batteries due to its favorable properties such as low cost, high conductivity, stable capacity, and low potential platform. Polyvinyl chloride, as a white pollutant, is a soft carbon precursor that can be carbonized at varying temperatures to produce soft carbons with controllable defect and crystal structures. This work investigates the effect of carbonization temperature on the crystalline structures of the obtained soft carbons. In situ Raman spectroscopy was used to elucidate the adsorption-intercalation charge storage mechanism of potassium ions in soft carbons. Soft carbons prepared at the temperature of 800 °C have a defect-rich, short-range ordered structure, which provides optimal intercalation and adsorption sites for potassium ions, resulting in a satisfactory capacity of 302 mAh g-1 . This work presents new possibilities for designing soft carbon materials from recycling plastics for potassium-ion batteries.

Improved electrochemical performance of soft carbon derived from coal liquefaction residue coated with expanded graphite for Lithium/Potassium batteries

This study investigated the use of asphaltene from coal liquefaction residue (CLRA) as a precursor for creating carbon nanosheets, which were then used to create a unique sandwich structure of soft carbon (SC) coated with expanded graphite (EG) composite (SC@EG) anodes for both lithium-ion and potassium-ion batteries. The SC@EG was formed through a covalent bond between EG and SC, resulting in a porous structure with favorable porosity and copious defects that expedited the migration of both Li+ and K+ ions. The SC@EG showed good electrochemical properties including high reversible capacity (510 mAh/g at 0.5 A/g in LIBs and 268 mAh/g at 0.1 A/g in KIBs), good rate performance (172 mAh/g at 4 A/g in LIBs and 154 mAh/g at 1 A/g in KIBs) and cyclic stability, attributed to the exceptional electronic conductivity and profound porosity of the structure.

Realization of high-pressure dry methane reforming by suppressing coke deposition with Co-Rh intermetallic clusters

It is economical to perform methane and carbon dioxide reforming under high-pressure and temperature conditions, but the harsh operation condition poses a grand challenge for coke-resistant catalyst design. We report herein that surface-segregation-free Co1Rh3 clusters are stable catalysts under 20 bars at 850 oC. Microkinetic analysis discloses that balanced and lowered surface coverages of C* and O* constitute the most abundant reaction intermediates on Co1Rh3 clusters at elevated pressures, with respect to that of the monometallic ones, thus avoiding surface carbon accumulation or surface oxidative deactivation. Moreover, density functional theory calculations of carbon atom nucleation discloses that adsorbed carbon transformation to refractory, graphene-like carbon is suppressed on Co1Rh3 cluster surface, owing to increased energetic barrier and ensemble size, hence, only CO2 gasifiable soft carbon could form. The revelation of the electronic/geometric features of Co1Rh3 is regarded to provide a guidance for future coke-resistant catalyst design.

Strengthening synergistic effects between hard carbon and soft carbon enabled by connecting precursors at molecular level towards high-performance potassium ion batteries

Strengthening synergistic effects between hard carbon and soft carbon enabled by connecting precursors at molecular level towards high-performance potassium ion batteries

Soft Carbon as Cathode with High Rate Performance for Dual-Ion Batteries via Fast PF6 - Intercalation Improved by Surface Effect.

Dual-ion battery is a new type of battery in which both anions and cations participate in the energy storage process. However, this unique battery configuration imposes high requirements on the cathode, which typically presents a poor rate performance due to the sluggish diffusion dynamics and intercalation reaction kinetics of anions. Herein, we report petroleum coke-based soft carbon as the cathode for dual-ion batteries, exhibiting a superior rate performance with a specific capacity of 96 mAh g-1 at a rate of 2 C and 72 mAh g-1 remained even at 50 C. In situ XRD and Raman demonstrate that the anions can directly form lower-stage graphite intercalation compounds during the charge process owing to the surface effect, skipping the long evolutionary process from higher to lower stage, thus significantly improving the rate performance. This study highlights the impact of the surface effect and provides a promising perspective for dual-ion batteries.

Pseudocapacitive Potassium-Ion Intercalation Enabled by Topologically Defective Soft Carbon toward High-Rate, Large-Areal-Capacity, and Low-Temperature Potassium-Ion Batteries.

Carbonaceous materials are widely investigated as anodes for potassium-ion batteries (PIBs). However, the inferior rate capability, low areal capacity, and limited working temperature caused by sluggish K-ions diffusion kinetics are still primary challenges for carbon-based anodes. Herein, a simple temperature-programmed co-pyrolysis strategy is proposed for the efficient synthesis of topologically defective soft carbon (TDSC) based on inexpensive pitch and melamine. The skeletons of TDSC are optimized with shortened graphite-like microcrystals, enlarged interlayer spacing, and abundant topological defects (e.g., pentagons, heptagons, and octagons), which endow TDSC with fast pseudocapacitive K-ion intercalation behavior. Meanwhile, micrometer-sized structure can reduce the electrolyte degradation over particle surface and avoid unnecessary voids, ensuring a high initial Coulombic efficiency as well as high energy density. These synergistic structural advantages contribute to excellent rate capability (116mAhg-1 at 20 C), impressive areal capacity (1.83mAhcm-2 with a mass loading of 8.32mg cm-2 ), long-term cycling stability (capacity retention of 91.8% after 1200h cycling), and low working temperature (-10°C) of TDSC anodes, demonstrating great potential for the practical application of PIBs.

Hierarchical porous soft carbon host for the cathode of an aqueous zinc-iodine battery with ultra-long cycle life

Aqueous zinc−iodine battery (AZIB) is a promising energy-storage system due to its high operational safety and the suitable theoretical capacity of 211 mAh g−1 of I2. However, it suffers from poor rate performance and low capacity retention due to the easy loss of active substance and the shuttle effect caused by polyiodide species. Herein, we rationally designed a perylene−3, 4, 9, 10−tetracarboxylic anhydride (PTCDA)−based carbon host at the annealing temperature of 900°C (PTCC900) to alleviate the problems mentioned above. PTCC900 embraces a hierarchical porous structure with the pore width ranging from 1.8 nm to 13 nm, which is beneficial for the confinement of I2 and polyiodide. In addition, the turbostratic graphitic microstructures spread inside PTCC900 also provide fast electronic transmission path to increase the electrical conductivity. Benefitting from the above features, the produced PTCC900@I2 cathode delivers an initial capacity of 240 mAh g−1 and remains a high capacity of 187 mAh g−1 after 600 cycles at the current density of 0.5 A g−1. More importantly, an ultra−long cycle life of over 50000 cycles is also obtained for PTCC900@I2 cathode when the current density increases to 5 A g−1. The improved electrochemical performances corroborate that PTCC900 is expected to be a potentially promising cathode host for zinc-iodine batteries.

Highly Stretchable and Sensitive Strain Sensor Based on Porous Materials and Rhombic‐Mesh Structures for Robot Teleoperation

AbstractWearable sensors for human motion capture offer a promising human–robot interface to control robots in the teleoperation scenario, where robots could function as the second body of human operators to fulfill tasks remotely and accurately. In this paper, a novel strain sensor based on a soft polyurethane (PU) sponge and carbon nanotubes (CNT) is designed for motion capture of human joints. The unique 3D porous microstructure of the PU‐CNT sponge provides the sensor with high sensitivity. To bridge the gap between the high sensitivity and high stretchability of the strain sensor, a rhombic‐mesh structure with optimized geometric parameters, in conjunction with a pre‐compression design, is proposed for strain sensor prototyping, which endows the sensor with an extra elongation rate during the stretching process. The proposed PU‐CNT strain sensor manifests promising sensing performance with a stretchability of up to 300% and a maximum gauge factor of 3893, together with long‐term durability, low detection limit, and fast response capacity. Finally, the validation of the strain sensor is carried out by deploying the sensor on a human elbow to realize the teleoperation of a robot arm, which could be monitored through the digital twin model of the robot in a real‐time manner.

Nickel-templated carbon foam anodes for sodium-ion batteries

Sodium-ion batteries, which are abundant in resources and cost-effective, are widely considered to be suitable for large-scale energy storage. However, unstable intercalation compounds and large sodium ion radius cause carbonaceous anodes to perform poorly. Herein, a soft-and-hard composite hollow carbon foam (HCF) was one-step prepared by nickel-templated blowing strategy. The sodium-ion storage performances were enhanced by soft carbon skeleton with high conductivity, hard carbon with abundant pores, and nitrogen doping. When applied as anodes for sodium-ion storage, HCF demonstrates remarkable capacity, rate, and cycling performances. It delivers 256mAhg−1 at 0.05Ag−1 and can be cycled for 2000 times at 1Ag−1 with remaining a capacity of 139mAhg−1. Kinetic studies reveal that soft-and-hard carbon structure, nitrogen doping, and porous structure can effectively promote sodium-ion absorption, as well as the transport of electrons and ions. Therefore, sodium-ion batteries based on the carbon could facilitate the development of renewable energy sources.

Is Soft Carbon a More Suitable Match for SiOx in Li-Ion Battery Anodes?

Silicon oxide (SiOx ), inheriting the high-capacity characteristic of silicon-based materials but possessing superior cycling stability, is a promising anode material for next-generation Li-ion batteries. SiOx is typically applied in combination with graphite (Gr), but the limited cycling durability of the SiOx /Gr composites curtails large-scale applications. In this work, this limited durability is demonstrated in part related to the presence of a bidirectional diffusion at the SiOx /Gr interface, which is driven by their intrinsic working potential differences and the concentration gradients. When Li on the Li-rich surface of SiOx is captured by Gr, the SiOx surface shrinks, hindering further lithiation. The use of soft carbon (SC) instead of Gr can prevent such instability is further demonstrated. The higher working potential of SC avoids bidirectional diffusion and surface compression thus allowing further lithiation. In this scenario, the evolution of the Li concentration gradient in SiOx conforms to its spontaneous lithiation process, benefiting the electrochemical performance. These results highlight the focus on the working potential of carbon as a strategy for rational optimization of SiOx /C composites toward improved battery performance.

Dual‐Interfering Chemistry for Soft‐Hard Carbon Translation toward Fast and Durable Sodium Storage

AbstractDirect pyrolysis of low‐cost and resource‐abundant pitch generally produces highly graphitized soft carbon, showing low reversible capacity and a negligible charge‐discharge plateau owing to its unsuitable microstructure for sodium storage. Herein, for the first time, an innovative dual‐interfering chemistry strategy is proposed to solve the soft‐hard carbon translation challenge. Multifunctional zinc gluconate generates dual‐mechanism interference upon decomposition and successfully regulates pitch pyrolysis: 1) the gas decomposition products (carbon oxides) may consume excess hydrogen to realize fusion‐to‐solid‐state pyrolysis of pitch, hindering microcrystalline ordering; 2) the solid compounds (i.e., organic zinc salt and ZnO nanoparticles) not only weakens strong π–π interactions between the aromatic chains of pitch but also introduces abundant closed pores into the carbon matrix. The optimized pitch‐derived hard carbon (PZHC 450–1200) shows an absorption‐insertion‐pore filling sodium storage mechanism after microstructure conversion from graphitic structure to a pore‐rich and turbostratic structure. As a result, the PZHC 450–1200 exhibits a high reversible capacity of 320 mAh g−1 at 30 mA g−1 with a more than twofold‐enhanced low‐voltage plateau capacity ratio, and outstanding rate capability that outperforms almost all previously reported pitch‐derived carbons. The concept of dual‐interfering chemistry contributes to achieving low‐cost and high‐performance hard carbon for fast and durable sodium storage.

Polyaniline coated sugar derived soft carbon sphere as electrode material in all-solid state symmetric supercapacitor with enhanced cyclic stability

Design and bulk synthesis of low cost electrode materials with high energy density and improved cyclic stability is extremely important. We have synthesized sugar derived soft carbon spheres by simple one step hydrothermal method. To increase the energy density, we coated the carbon spheres with polyaniline via vapour phase and colloidal chemical polymerization methods. By colloidal synthesis method, two composites CS-PANI-11 and CS-PANI-31 were prepared by using CS: aniline (w/w) ratios 1:1 and 3:1 respectively whereas the sample prepared by vapor phase polymerization is denoted as CS-PANI-VP. The performance of these four electrode materials depending on specific capacitance and specific energy is in the order CS< CS-PANI-VP< CS-PANI-31 < CS-PANI-11. The best performing material CS-PANI-11 showed specific capacitance, specific energy and specific power of 84.3 F g−1, 11.7 W h kg−1 and 500 W kg−1 respectively at current density 1 A g−1. Moreover the symmetric cell constructed by using CS-PANI-11 as electrode material gave areal capacitance, energy density and power density values 42 mF cm−2, 5.8 μW h cm−2 and 50 μW cm−2 respectively at current density 0.1 mA cm−2. This symmetric SC showed capacitance retention of 80.33 % after 5000 galvanostatic charge discharge cycles demonstrating excellent cyclic stability.

Explosive effect-assisted synthesis of hierarchical porous carbon for high-performance aqueous Zn-ion hybrid supercapacitors with commercial level mass loading

Aqueous Zn-ion hybrid supercapacitors (AZHCs) are potential types of energy storage applications that combine the advantages of supercapacitors and batteries. The low mass loading and poor rate performance of cathodes, however, severely limits their practical application. Herein, an explosive effect assisted strategy is reported for the efficient synthesis of N, O co-doped porous carbon nanosheets (NPCNs) by synergistic activation of high-quality soft carbon precursor perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) with KOH and Zn(NO3)2. Benefiting from the comprehensive modulation of the morphology, pore structure, and surface chemistry, the obtained NPCNs show the significant enhancement in diffusion kinetics. Consequently, the as-fabricated AZHCs exhibited remarkably improved Zn-ion storage capability (189.3 mAh g−1 at 0.1 A g−1, 96.7 mAh g−1 at 20 A g−1) and long-term cycling stability at 20 A g−1 (∼ 92.5 % retention upon 6000 cycles). Moreover, NPCNs also deliver a superb areal capacity of 1.6 mAh cm−2 with a mass loading of 15.4 mg cm−2. Most importantly, we demonstrate that such porous carbon framework with competent electrochemical properties can be easily produced from diverse soft carbon precursor. This work thus introduces a universal and efficient strategy to produce high-performance porous carbon electrode materials for AZHCs.

Lightweight Bioinspired Exoskeleton for Wrist Rehabilitation Powered by Twisted and Coiled Artificial Muscles

Stroke, cerebral palsy, and spinal cord injuries represent the most common leading causes of upper limb impairment. In recent years, rehabilitation robotics has progressed toward developing wearable technologies to promote the portability of assistive devices and to enable home rehabilitation of the upper extremities. However, current wearable technologies mainly rely on electric motors and rigid links or soft pneumatic actuators and are usually bulky and cumbersome. To overcome the limitations of existing technologies, in this paper, a first prototype of a lightweight, ungrounded, soft exoskeleton for wrist rehabilitation powered by soft and flexible carbon fibers-based twisted and coiled artificial muscles (TCAMs) is proposed. The device, which weighs only 0.135 kg, emulates the arrangement and working mechanism of skeletal muscles in the upper extremities and is able to perform wrist flexion/extension and ulnar/radial deviation. The range of motion and the force provided by the exoskeleton is designed through simple kinematic and dynamic theoretical models, while a thermal model is used to design a thermal insulation system for TCAMs during actuation. The device’s ability to perform passive and active-resisted wrist rehabilitation exercises and EMG-based actuation is also demonstrated.

Soft diamond-like carbon coatings with superior biocompatibility for medical applications

Biomedical applications of diamond-like carbon (DLC) coatings are continuously increasing due to their superior mechanical properties, low friction coefficient, antiwear characteristics, and biocompatibility. The mechanical and tribological characteristics of DLC coatings have been comprehensively investigated on various substrate systems as a function of their deposition parameter dependant features for various biomaterial applications. However, the relationship between biocompatibility and resulting hardness of DLC coatings as a function of their bias voltage driven intrinsic features like sp2 and sp3 bonds remains largely unexplored. In this work, a series of DLC coatings are prepared as a function of varying bias voltage from 0 to −120 V, and characterised for their atomic structure, physical, and mechanical properties, and biocompatibility. The contact angle and surface roughness of the DLC coatings reduce while hardness increases from 7.8 to 20.3 GPa with increasing bias voltage from 0 to −120 V. A relatively soft DLC coating is shown to retain excellent biocompatibility which is approximately 38% higher than the harder DLC coatings following exposure of their leached extracts to L929 mouse fibroblast cells. This work demonstrates the complex interdependence of biocompatibility and hardness of DLC coatings and the outcomes will support correct material selection with an appropriate balance of these key properties for specific biomedical applications such as load-carrying and non-load carrying devices.

Pore-size control of soft mesoporous carbon by hot pressing

Pore-size control of soft mesoporous carbon by hot pressing

One stone two birds: Pitch assisted microcrystalline regulation and defect engineering in coal-based carbon anodes for sodium-ion batteries

Coal-based carbons with abundant resources and low cost are regarded as promising anode materials for sodium‐ion batteries (SIBs). However, their ordered carbon microstructure and abundant surface defects often result in low Na-storage capacity and poor initial coulombic efficiency (ICE). Herein, we propose a simple vapor deposition strategy to synthesize coal-based carbons coated with pitch-based soft carbon layer (PCLC) for potential use as anodes for SIBs. The deposition of pitch-based volatile species allows for an efficient cross-linking reaction between hydroxyl‑containing volatile species and oxygen-rich functional groups of coal, thus generating a disordered inner-phase microcrystalline structure with dominant pseudo-graphitic phase in coal-derived carbon. Meanwhile, the exterior soft carbon coating layer substantially reduces surface defects and increases the electrical conductivity of coal-based carbon. Unlike the pristine lignite coal pyrolytic carbon which exhibited a Na-storage capacity of 290.2 mAh g−1 and ICE of 59.9%, the optimal PCLC (PCLC-1) delivered a higher reversible capacity of 312.2 mAh g−1 and a much-improved ICE of 85.3%. In addition, the PCLC-1 electrode also demonstrated excellent cycle stability with 93.4% retention after 1,000 cycles. When coupled with O3-NaNi1/3Fe1/3Mn1/3O2 cathode, PCLC-1 as an anode in a full cell configuration achieved a high energy density of 220.9 Wh kg−1 with excellent cycling and rate performance. The proposed work offers a unique insight into modulating the microcrystalline structure and surface chemistry of high-performance coal-based carbon anode materials for commercial SIBs.

Flexible hard−soft carbon heterostructure based on mesopore confined carbonization for ultrafast and highly durable sodium storage

Despite great progress in sodium-ion battery, exploiting carbonaceous anodes incorporating large capacity, high rate performance and long-term cycling stability is still a big challenge. In this work, novel heterostructured, hollow hard−soft carbon spheres are designed by mesopore confined carbonization. The results show that the confined carbonization makes the carbon layers spontaneously arrange in different levels, resulting in the formation of nanometer-scale, interwoven hard and soft carbon domains. Moreover, the unique composite carbon layers provide a flexible and breathable shell capable of maintaining nanostructure during long-term repeated charge/discharge processes. As such, the hard−soft carbon heterostructure is able to deliver a capacity >240 mA h g−1 under a current density of 1 A g−1. Even with an ultralarge current density of 30 A g−1, the capacity remains 104 mA h g−1, demonstrating a very short Na output time of 12.5 s. Moreover, the hard−soft carbon heterostructure shows no dramatic capacity loss during a long-term repeated charge/discharge tests over 10,000 cycles, showing a very low capacity loss rate of 0.0026% per cycle. As far as is known, such high-rate capability and outstanding cycling durability has been rarely achieved before.

Fast-Charging Sodium-Ion Batteries Enabled by Molecular-Level Designed Nitrogen and Phosphorus Codoped Mesoporous Soft Carbon.

Soft carbons have attracted extensive interests as competitive anodes for fast-charging sodium-ion batteries (SIBs); however, the high-rate performance is still restricted by their large ion migration barriers and sluggish reaction kinetics. Herein, we show a molecular design approach toward the fabrication of nitrogen and phosphorus codoped mesoporous soft carbon (NPSC). The key to this strategy lies in the chemical cross-linking reaction between polyphosphoric acid and p-phenylenediamine, associated with pyrolysis induced in-situ self-activation that creates mesoporous structures and rich heteroatoms within the carbon matrix. Thanks to the enlarged interlayer spacing, reduced ion diffusion length, and plentiful active sites, the obtained NPSC delivers a superb rate capacity of 215 mAh g-1 at 10 A g-1 and an ultralong cycle life of 4,700 cycles at 5 A g-1. Remarkably, the full cell shows 99% capacity retention during 100 continuous cycles, and maximum energy and power densities of 191 Wh kg-1 and 9.2 kW kg-1, respectively. We believe that such a synthetic protocol could pave a novel venue to develop soft carbons with unique properties for advanced SIBs.

Electrochemical intercalation of rubidium into graphite, hard carbon, and soft carbon.

The electrochemical insertion of Rb into carbonaceous materials, including graphite, was achieved herein. Rubidium ions were reversibly inserted into and extracted from graphite via electrochemical processes using different non-aqueous electrolytes containing rubidium bis(trifluoromethanesulfonyl)amide (RbTFSA) salts in carbonate esters, glymes, and ionic liquids, similar to the process used for other lighter alkali metal ions such as Li+ and K+. The chemical compositions of the rubidiated graphite were determined to be RbC8, RbC24, and RbC36 at each step of the electrochemical reduction process. Graphite underwent a phase transition to RbC8 exhibiting a stage-1 structure, with stage-3 RbC36 and stage-2 RbC24 as intermediates, as confirmed by ex situ and in situ X-ray diffraction and ex situ Raman spectroscopy, similar to the electrochemical phase evolution of staged potassium graphite intercalation compounds (K-GICs). Furthermore, Rb was reversibly inserted into and extracted from graphitizable and non-graphitizable carbons such as pitch-derived soft carbon and commercial hard carbon, along with other alkali metals such as Li, Na, and K.