Metal-Embedded Porous Graphitic Carbon Fibers Fabricated from Bamboo Sticks as a Novel Cathode for Lithium-Sulfur Batteries

Spatially Confined Fe7S8 Nanoparticles Anchored on a Porous Nitrogen-Doped Carbon Nanosheet Skeleton for High-Rate and Durable Sodium Storage

Iron sulfides are widely explored as anodes of sodium-ion batteries (SIBs) owing to high theoretical capacities and low cost, but their practical application is still impeded by poor rate capability and fast capacity decay. Herein, for the first time, we construct highly dispersed Fe₇S₈ nanoparticles anchored on a porous N-doped carbon nanosheet (CN) skeleton (denoted as Fe₇S₈/NC) with high conductivity and numerous active sites via facile ion adsorption and thermal evaporation combined procedures coupled with a gas sulfurization treatment. Nanoscale design coupled with a conductive carbon skeleton can simultaneously mitigate the above obstacles to obtain enhanced structural stability and faster electrode reaction kinetics. With the aid of density functional theory (DFT) calculations, the synergistic interaction between CNs and Fe₇S₈ can not only ensure enhanced Na⁺ adsorption ability but also promote the charge transfer kinetics of the Fe₇S₈/NC electrode. Accordingly, the designed Fe₇S₈/NC electrode exhibits remarkable electrochemical performance with superior high-rate capability (451.4 mAh g^-1 at 6 A g^-1) and excellent long-term cycling stability (508.5 mAh g^-1 over 1000 cycles at 4 A g^-1) due to effectively alleviated volumetric variation, accelerated charge transfer kinetics, and strengthened structural integrity. Our work provides a feasible and effective design strategy toward the low-cost and scalable production of high-performance metal sulfide anode materials for SIBs.

Employing Ni-Embedded Porous Graphitic Carbon Fibers for High-Efficiency Lithium-Sulfur Batteries

The rational electrode design is one of the most important ways to enhance the electrochemical properties of lithium-sulfur batteries (LSBs). In this contribution, we use Ni-embedded porous graphitic carbon fiber (PGCF@Ni) as the scaffold to construct a novel cathode and anode for LSBs. With the help of elaborate surface engineering, the constructed solid electrolyte interface (SEI)@Li/PGCF@Ni anodes can effectively restrain the growth of lithium dendrites during the cycle, exhibiting an ultralow overpotential of ∼10 mV for 2000 h at 1 mA cm^-2/1 mA h cm^-2. The underlying mechanism is further investigated by COMSOL Multiphysics simulations. Additionally, the PGCF@Ni/S cathode fabricated by the molten sulfurizing method manifests superior rate performance and stability. Ultimately, the assembled SEI@Li/PGCF@Ni||PGCF@Ni/S full battery exhibits prominent electrochemical property with a high capacity retention of about 77.9% after 600 cycles at 1 C. Such success at the performance improvement in LSBs may open up avenues toward other rational designs of high-quality electrodes in electrochemical energy storage.

Organic/Inorganic Hybrid Fibers: Controllable Architectures for Electrochemical Energy Applications

Organic/inorganic hybrid fibers (OIHFs) are intriguing materials, possessing an intrinsic high specific surface area and flexibility coupled to unique anisotropic properties, diverse chemical compositions, and controllable hybrid architectures. During the last decade, advanced OIHFs with exceptional properties for electrochemical energy applications, including possessing interconnected networks, abundant active sites, and short ion diffusion length have emerged. Here, a comprehensive overview of the controllable architectures and electrochemical energy applications of OIHFs is presented. After a brief introduction, the controllable construction of OIHFs is described in detail through precise tailoring of the overall, interior, and interface structures. Additionally, several important electrochemical energy applications including rechargeable batteries (lithium-ion batteries, sodium-ion batteries, and lithium-sulfur batteries), supercapacitors (sandwich-shaped supercapacitors and fiber-shaped supercapacitors), and electrocatalysts (oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction) are presented. The current state of the field and challenges are discussed, and a vision of the future directions to exploit OIHFs for electrochemical energy devices is provided.

Potassium Hexafluorophosphate Additive Enables Stable Lithium-Sulfur Batteries

Uncontrollable dendrite growth and low Coulombic efficiency are the two main obstacles that hinder the application of rechargeable Li metal batteries. Here, an optimized amount of potassium hexafluorophosphate (KPF₆, 0.01 M) has been added into the 2 M LiTFSI/ether-based electrolyte to improve the cycling stability of lithium-sulfur (Li-S) batteries. Due to the synergistic effect of self-healing electrostatic shield effect from K⁺ cations and the LiF-rich solid electrolyte interphases derived from PF₆^- anions, the KPF₆ additive enables a high Li Coulombic efficiency of 98.8% (1 mA cm^-2 of 1 mAh cm^-2). The symmetrical Li cell can achieve a stable cycling performance for over 200 cycles under a high Li utilization up to 33.3%. Meanwhile, the polysulfide shuttle has been restrained due to the higher concentration of the LiTFSI in the electrolyte. As a result, the assembled Li-S full cell displays excellent capacity retention with only 0.25% decay per cycle in the final electrolyte. Our work offers a smart approach to improve both the anode and cathode performance by the electrolyte modification of rechargeable Li-S batteries.

Superhierarchical Conductive Framework Implanted with Nickel/Graphitic Carbon Nanocages as Sulfur/Lithium Metal Dual-Role Hosts for Li-S Batteries

High-energy-density Li-S batteries (LSBs) are considered as a promising next-generation energy-storage system. However, the sluggish redox kinetics and severe polysulfide shuttle effect in elemental sulfur cathodes, along with uncontrollable dendrite propagation in lithium metal anodes, inevitably depress the electrochemical performance of LSBs and impede their practical implementation. Motivated by a unique hierarchical geometry, specific chemical affinity, and nitrogen-enriched collagen component of natural skin fibers (SFs), here we proposed an effective structural engineering strategy for crafting an SF-derived superhierarchical N-doped porous carbon framework in situ implanted with nickel/graphitic carbon nanocages as a dual-role host to simultaneously address the challenges faced on the sulfur cathode and lithium anode in LSBs. The experimental results and theoretical calculation disclose that the implanted Ni nanoparticles and highly graphitic sp² carbon nanocages together with doped N heteroatoms not only provide a synergetic trapping-catalytic-conversion effect for regulating soluble polysulfides with promoted redox kinetics in the cathode at both room and elevated (55 °C) temperatures but also yield Ni-enhanced lithiophilic N-heteroatom active sites in the host framework to control Li deposition and suppress Li dendrite growth in anodes. Combining the cathodic and anodic improvements further achieves a superb rate and cycling performance in full LSB cells with stable Coulombic efficiency, showing great potential in developing reliable LSBs.

Highly Graphitized Porous Carbon-FeNi3 Fabricated from Oleic Acid for Advanced Lithium-Sulfur Batteries

Improving the electrical conductivity of sulfur, suppressing shuttle/dissolution of polysulfide, and enhancing reaction kinetics in Li-S batteries are essential for practical applications. Here, for the first time, we have used inexpensive oleic acid as a single carbon source, and have added commercial SiO₂ as a template to form a porous structure, whereas introducing Fe(NO₃ )₃ and Ni(NO₃ )₂ as catalysts to increase the degree of graphitization. Moreover, the dual metal salts Fe(NO₃ )₃ and Ni(NO₃ )₂ can also form FeNi₃ alloy, and our results show that FeNi₃ nanoparticles accelerate the kinetic conversion reactions of polysulfide. By virtue of the well-developed porous structure and high degree of graphitization, the highly graphitized porous carbon-FeNi₃ (GPC-FeNi₃ ) has high conductivity to ensure fast charge transfer, and the hierarchically porous structure facilitates ion diffusion and traps polysulfide. Thus, a GPC-FeNi₃ /S cathode displays excellent electrochemical performance. At current rates of 0.2 and 1 C, a cathode of the GPC-FeNi₃ /S composite with a sulfur content of 70 % delivers high initial discharge capacities of 1108 and 880 mA h g^-1 , respectively, and retains reversible specific capacities of 850 mA h g^-1 after 200 cycles at 0.2 C and 625 mA h g^-1 after 400 cycles at 1 C.

Ultrafine nanosulfur particles sandwiched in little oxygen-functionalized graphene layers as cathodes for high rate and long-life lithium-sulfur batteries

Although lithium-sulfur batteries are one of the promising candidates for next-generation energy storage systems, the practical applications are still hampered by the poor cycle life, which can be attributed to the insulating properties of sulfur and the shuttle effect of electrochemical intermediate polysulfides. To address these problems, we synthesize sandwich-like composites which consist of ultrafine nanosulfur particles enveloped by little oxygen-functionalized graphene layers (F-GS@S). In this structure, the little oxygen-functionalized graphene backbone can not only accelerate the redox kinetics of sulfur species, but also eliminate the shuttle effect of polysulfides by strong chemical interaction. Moreover, the sandwich confinement structures can further inhibit the dissolution of polysulfides by physical restraint and accommodate the volume contraction/expansion of sulfur during cycling. As a result, the F-GS@S composites used as cathodes for lithium-sulfur batteries display a superior rate capability with the high capacities of 1208 mAh g^-1 at 0.1 C and 601.7 mAh g^-1 at 2 C and high cycling stability with a capacity retention of 70.5% after 500 cycles at 2 C. In situ characterizations and real-time monitoring experiments during the charge-discharge process are carried out to elucidate the reaction mechanism of the F-GS@S composites as cathodes for high rate and long-life lithium-sulfur batteries.

Multi-scale characterization of bamboo bonding interfaces with phenol-formaldehyde resin of different molecular weight to study the bonding mechanism

Understanding the bonding mechanism of the interfacial region between bamboo and adhesives is essential for accelerating the development of improved adhesives for advanced bamboo-based materials. In this study, Br-labelled phenol-formaldehyde (PF) resins with four different molecular weights (MWs) were used to make bamboo-adhesive interfaces for tracing the adhesives in bamboo. Ultra-depth-of-field microscopy and scanning electron microscopy in conjunction with energy dispersion spectrometry were used to access the distribution and penetration of resin in the bamboo polymer. Fourier transform infrared images and solid-state cross-polarization/magic angle spinning nuclear magnetic resonance spectra were used to access the molecular-scale interactions between PF resins and bamboo cell walls. The results showed that the PF resins with high MW infiltrated into the lumina of damaged bamboo cells near the bondline to form glue nails, while those with low MW penetrated into the bamboo cell wall to form nanomechanical interlocking. Chemical bonds and secondary forces such as polar forces and hydrogen bonds were generated between bamboo and PF resin. Finally, the twice-adhesive dispensing method combining low-MW resins with high-MW resins was used to improve the bonding strength of the interface.

A review of biomass materials for advanced lithium-sulfur batteries

High energy density and low cost make lithium-sulfur (Li-S) batteries famous in the field of energy storage systems. However, the advancement of Li-S batteries is evidently hindered by the notorious shuttle effect and other issues that occur in sulfur cathodes during cycles. Among various strategies applied in Li-S batteries, using biomass-derived materials is more promising due to their outstanding advantages including strong physical and chemical adsorptions as well as abundant sources, low cost, and environmental friendliness. This review summarizes the recent progress of biomass-derived materials in Li-S batteries. By focusing on the aspects of carbon hosts, separator materials, bio-polymer binders, and all-solid-state electrolytes, the authors aim to shed light on the rational design and utilization of biomass-derived materials in Li-S batteries with high energy density and long cycle lifespan. Perspectives regarding future research opportunities in biomass-derived materials for Li-S batteries are also discussed.

Atomic Layer Deposition-Assisted Construction of Binder-Free Ni@N-Doped Carbon Nanospheres Films as Advanced Host for Sulfur Cathode

Rational design of hybrid carbon host with high electrical conductivity and strong adsorption toward soluble lithium polysulfides is the main challenge for achieving high-performance lithium-sulfur batteries (LSBs). Herein, novel binder-free Ni@N-doped carbon nanospheres (N-CNSs) films as sulfur host are firstly synthesized via a facile combined hydrothermal-atomic layer deposition method. The cross-linked multilayer N-CNSs films can effectively enhance the electrical conductivity of electrode and provide physical blocking "dams" toward the soluble long-chain polysulfides. Moreover, the doped N heteroatoms and superficial NiO layer on Ni layer can work synergistically to suppress the shuttle of lithium polysulfides by effective chemical interaction/adsorption. In virtue of the unique composite architecture and reinforced dual physical and chemical adsorption to the soluble polysulfides, the obtained Ni@N-CNSs/S electrode is demonstrated with enhanced rate performance (816 mAh g-1 at 2 C) and excellent long cycling life (87% after 200 cycles at 0.1 C), much better than N-CNSs/S electrode and other carbon/S counterparts. Our proposed design strategy offers a promising prospect for construction of advanced sulfur cathodes for applications in LSBs and other energy storage systems.

Cobalt disulfide-modified cellular hierarchical porous carbon derived from bovine bone for application in high-performance lithium-sulfur batteries

Improving the insulating nature of sulfur and retaining the soluble polysulfides in sulfur cathodes are crucial for realizing the practical application of lithium-sulfur batteries (LSBs). Biomass-based carbon is becoming increasingly popular for fabricating economical and efficient cathodes for LSBs owing to its unique structure. Herein, we report a facile strategy to transform bovine bone with an organic-inorganic structure into cellular hierarchical porous carbon via carbonization and KOH activation, followed by CoS₂ modification through hydrothermal treatment. The synthesized composite can load abundant sulfur and produce a dual effect of "physical confinement and chemical entrapment" on polysulfides. The conductive carbon frame with the developed porous structure provides adequate space to accommodate sulfur and physically suppress the shuttle effect of polysulfides. The embedded half-metallic CoS₂ sites can chemically anchor the polysulfides and enhance the electrochemical reaction activity as well. Owing to the multifunctional structure and dual restraint effect, the designed electrode exhibits enhanced electrochemical properties including high initial capacity (1230.9 mAh g^-1 at 0.2 C), improved cycling stability and enhanced rate capability.

Porous nitrogen-doped carbon nanofibers assembled with nickel nanoparticles for lithium-sulfur batteries

High-efficiency cathodes in lithium-sulfur (Li-S) batteries play an important role in the pursuit of high electrochemical performance. However, a number of Li-S batteries currently reported suffer from severe drawbacks such as the insulating nature of sulfur, sluggish redox kinetics, and the shuttle effect of intermediate polysulfides. To overcome these challenges, herein, carbonyl group functionalized porous carbon nanofibers assembled with nickel (Ni/PCNFO) are proposed to serve as an efficient sulfur host in Li-S batteries. Such a Ni/PCNFO-S composite cathode exhibits outstanding electrochemical performances, which are attributed to three factors: (1) the large inner space of the PCNF can afford a high S content and accommodate the volume expansion; (2) high electrical conductivity is provided by the carbon nanofiber skeleton and the electrocatalytically active Ni species embedded in the PCNF significantly facilitate the redox kinetics of the S species; and (3) the carbonyl group anchored on the Ni/PCNF can effectively suppress the polysulfide effect via strong chemical affinity/adsorption with polysulfides. With these advantageous features, the Li-S batteries based on Ni/PCNFO-S cathodes exhibit a high specific capacity (1320 mA h g-1), excellent rate capability (780 mA h g-1), and long cycling stability (910 mA h g-1 after 500 cycles at 0.2C).

Spore Carbon from Aspergillus Oryzae for Advanced Electrochemical Energy Storage

Development of novel advanced carbon materials is playing a critical role in the innovation of electrochemical energy storage technology. Hierarchical porous spore carbon produced by Aspergillus oryzae is reported, which acts as a biofactory. Interestingly, the spore carbon not only shows a porous maze structure consisting of crosslinked nanofolds, but also is intrinsically N and P dual doped. Impressively, the spore carbon can be further embedded with Ni₂ P nanoparticles, which serve as porogen to form a highly porous spore carbon/Ni₂ P composite with increased surface area and enhanced electrical conductivity. To explore the potential application in lithium-sulfur batteries (LSBs), the spore carbon/Ni₂ P composite is combined with sulfur, forming a composite cathode, which exhibits a high initial capacity of 1347.5 mAh g^-1 at 0.1 C, enhanced cycling stability (73.5% after 500 cycles), and better rate performance than the spore carbon/S and artificial hollow carbon sphere/S counterparts. The synergistic effect on suppressing the shuttle effect of intermediate polysulfides is responsible for the excellent LSBs performance with the aid of a physical blocking effect arising from the electrical maze porous structure and the chemical adsorption effect originating from N, P dual doping and polarized compound Ni₂ P.

An in situ chemically and physically confined sulfur–polymer composite for lithium–sulfur batteries with carbonate-based electrolytes

A sulfur–polymer composite synthesized by one-step thermal sulfurization of PANI is proposed to show excellent long-term cycling stability in carbonate-based electrolytes.