Biomass-derived porous carbon modified glass fiber separator as polysulfide reservoir for Li-S batteries

Insights into the aspect ratio effects of ordered mesoporous carbon on the electrochemical performance of sulfur cathode in lithium-sulfur batteries

Tailoring porous host materials, as an effective strategy for storing sulfur and restraining the shuttling of soluble polysulfides in electrolyte, is crucial in the design of high-performance lithium-sulfur (Li-S) batteries. However, for the widely studied conductive hosts such as mesoporous carbon, how the aspect ratio affects the confining ability to polysulfides, ion diffusion as well as the performances of Li-S batteries has been rarely studied. Herein, ordered mesoporous carbon (OMC) is chosen as a proof-of-concept prototype of sulfur host, and its aspect ratio is tuned from over ∼ 2 down to below ∼ 1.2 by using ordered mesoporous silica hard templates with variable length/width scales. The correlation between the aspect ratio of OMCs and the electrochemical performances of the corresponding sulfur-carbon cathodes are systematically studied with combined electrochemical measurements and microscopic characterizations. Moreover, the evolution of sulfur species in OMCs at different discharge states is scrutinized by small-angle X-ray scattering. This study gives insight into the aspect ratio effects of mesoporous host on battery performances of sulfur cathodes, providing guidelines for designing porous host materials for high-energy sulfur cathodes.

Size Effect for Inhibiting Polysulfides Shuttle in Lithium-Sulfur Batteries

It is undeniable that the dissolution of polysulfides is beneficial in speeding up the conversion rate of sulfur in electrochemical reactions. But it also brings the bothersome "shuttle effect". Therefore, if polysulfides can be retained on the cathode side, the efficient utilization of the polysulfides can be guaranteed to achieve the excellent performance of lithium-sulfur batteries. Based on this idea, considerable methods have been developed to inhibit the shuttling of polysulfides. It is necessary to emphasize that no matter which method is used, the solvation mechanism, and existence forms of polysulfides are essential to analyze. Especially, it is important to clarify the sizes of different forms of polysulfides when using the size effect to inhibit the shuttling of polysulfides. In this review, a comprehensive summary and in-depth discussion of the solvation mechanism, the existing forms of polysulfides, and the influencing factors affecting polysulfides species are presented. Meanwhile, the size of diverse polysulfide species is sorted out for the first time. Depending on the size of polysulfides, tactics of using size effect in cathode, separator, and interlayer parts are elaborated. Finally, a design idea of materials pore size is proposed to satisfy the use of size effect to inhibit polysulfides shuttle.

Natural Products Derived Porous Carbons for CO2 Capture

As it is now established that global warming and climate change are a reality, international investments are pouring in and rightfully so for climate change mitigation. Carbon capture and separation (CCS) is therefore gaining paramount importance as it is considered one of the powerful solutions for global warming. Sorption on porous materials is a promising alternative to traditional carbon dioxide (CO2 ) capture technologies. Owing to their sustainable availability, economic viability, and important recyclability, natural products-derived porous carbons have emerged as favorable and competitive materials for CO2 sorption. Furthermore, the fabrication of high-quality value-added functional porous carbon-based materials using renewable precursors and waste materials is an environmentally friendly approach. This review provides crucial insights and analyses to enhance the understanding of the application of porous carbons in CO2 capture. Various methods for the synthesis of porous carbon, their structural characterization, and parameters that influence their sorption properties are discussed. The review also delves into the utilization of molecular dynamics (MD), Monte Carlo (MC), density functional theory (DFT), and machine learning techniques for simulating adsorption and validating experimental results. Lastly, the review provides future outlook and research directions for progressing the use of natural products-derived porous carbons for CO2 capture.

Biomass Separators as a "Lifesaver" for Safe and Long-Life Lithium Metal Batteries

The growth of lithium dendrites and the shuttle of polysulfides in lithium metal batteries (LMBs) have hindered their development. In LMBs, the cathode and anode are separated by a separator, although this does not solve the battery's issues. The use of biomass materials is widespread for modifying the separator due to their porous structure and abundant functional groups. LMBs perform more electrochemically when lithium ions are deposited uniformly and polysulfide shuttling is reduced using biomass separators. In this review, we analyze the growth of lithium dendrite and the shuttle of polysulfide in LMBs, summarize the types of biomass separator materials and the mechanisms of action (providing mechanical barriers, promoting uniform deposition of metal ions, capturing polysulfides, shielding polysulfide). The prospect of developing new separator materials from the perspective of regulating ion transport and physical sieving efficiency as well as the application of advanced technologies such as synchrotron radiation to characterize the mechanism of action of biomass separators is also proposed.

Improving performances of Lithium-Sulfur cells via regulating of VSe2 functional mediator with Doping-Defect engineering and Electrode-Separator integration strategy

The sluggish redox kinetics and the severe shuttle effect of soluble lithium polysulfides (LiPSs) are the main key issues which would hinder the development of lithium-sulfur (Li-S) batteries. In this work, a nickel-doped vanadium selenide in-situ grows on reduced graphene oxide(rGO) to form a two-dimensional (2D) composite Ni-VSe₂/rGO by a simple solvothermal method. When it is used as a modified separator in Li-S batteries, the Ni-VSe₂/rGO material with the doped defect and super-thin layered structure can greatly adsorb LiPSs and catalyze the conversion reaction of LiPSs, resulting in effectively reducing LiPSs diffusion and suppressing the shuttle effect. More importantly, the cathode-separator bonding body is first developed as a new strategy of electrode-separator integration in Li-S batteries, which not only could decrease the LiPSs dissolution and improve the catalysis performance of the functional separator as the upper current-collector, but also is good for the high sulfur loading and the low electrolyte/sulfur (E/S) ratio for high energy density Li-S batteries. When the Ni-VSe₂/rGO-PP (polypropylene, Celgard 2400) modified separator is applied, the Li-S cell can retain 510.3 mA h g^-1 capacity after 1190 cycles at 0.5C. In the electrode-separator integrated system, the Li-S cell can still maintain 552.9 mA h g^-1 for 190 cycles at a sulfur loading 6.4 mg cm^-2 and 4.9 mA h cm^-2 for 100 cycles at a sulfur loading 7.0 mg cm^-2. The experimental results indicate that both the doped defect engineering and the super-thin layered structure design might optimally be chosen to fabricate a new modified separator material, and especially, the electrode-separator integration strategy would open a practical way to promote the electrochemical behavior of Li-S batteries with high sulfur loading and low E/S ratio.

Research Progress on Multifunctional Modified Separator for Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are recognized as one of the second-generation electrochemical energy storage systems with the most potential due to their high theoretical specific capacity of the sulfur cathode (1675 mAhg^-1), abundant elemental sulfur energy storage, low price, and green friendliness. However, the shuttle effect of polysulfides results in the passivation of the lithium metal anode, resulting in a decrease in battery capacity, Coulombic efficiency, and cycle stability, which seriously restricts the commercialization of LSBs. Starting from the separator layer before the positive sulfur cathode and lithium metal anode, introducing a barrier layer for the shuttle of polysulfides is considered an extremely effective research strategy. These research strategies are effective in alleviating the shuttle of polysulfide ions, improving the utilization of active materials, enhancing the battery cycle stability, and prolonging the cycle life. This paper reviews the research progress of the separator functionalization in LSBs in recent years and the research trend of separator functionalization in the future is predicted.

Mesoporous Ti4O7 nanosheets with high polar surface area for catalyzing separator to reduce the shuttle effect of soluble polysulfides in lithium-sulfur batteries

In the effort to accelerate adsorption and catalytic conversion of lithium polysulfides (Li-PSs) and suppress the shuttle effect of lithium-sulfur batteries (LSBs), the Ti 4 O 7 nanosheets/carbon material-modified separator is successfully fabricated to reducing soluble Li-PSs' crossover from cathode to anode. The catalyst of mesoporous Ti 4 O 7 nanosheets with O-Ti-O units synthesized at low temperature shows both excellent conductivity and high surface area. The modified separator can serve as a diffusion barrier of Li-PSs and catalyst for converting soluble low-chain sulfides into insoluble ones and then remarkably enhance the sulfur utilization and electrochemical performance of the LSB. This work provides a feasible avenue in both design and synthesis of mesoporous catalyst materials for suppressing the shuttle effect of lithium-sulfur batteries.

Revealing the synergistic mechanism of multiply nanostructured V2O3 hollow nanospheres integrated with doped N, Ni heteroatoms, in-situ grown carbon nanotubes and coated carbon nanolayers for the enhancement of lithium-sulfur batteries

Lithium sulfur (Li-S) batteries are regarded as one of the most promising future energy storage candidates on account of high theoretical specific capacity of 1675 mAh g^-1 and energy density of 2600 Wh kg^-1. However, their practical application is seriously hindered due to the poor conductivity and volume expansion of sulfur, the weak redox kinetics of lithium polysulfide (LPS), and the severe shuttle effect of LPS. Herein, V₂O₃@N,Ni-C nanostructures, multiply integrated with zero-dimensional (0D) V₂O₃ nanoparticles, 1D carbon nanotubes, 2D carbon coating layers and graphene, 3D hollow spheres, and doped N and Ni heteroatoms, were synthesized via a solvothermal method followed by chemical vapor deposition. After being used as a modifier for traditional commercial separator of Li-S batteries, the shuttle effect of LPS can be effectively suppressed owing to the abundant active physical and chemical adsorption sites derived from large specific surface area, rich porosity, and tremendous polarity of the V₂O₃ nanoparticles with multiple secondary nanostructure integration. Meanwhile, the transfer of Li⁺ ions and electrons can be effectively enhanced by the highly conductive 2D carbon network, and the kinetics of redox reaction (Li₂S_n ↔ Li₂S) can be accelerated by the doped N and Ni heteroatoms, leading to a synergistic promotion on the reutilization of the adsorbed LPS. Additionally, the unique 3D hollow structure can not only enhance the penetration of electrolyte, but also buffer the volume expansion of sulfur to some extent. Therefore, the rate capacity and cycling performance can be significantly enhanced by the multifunction synergism of adsorption, conductivity, catalysis, and volume buffering. An initial discharge capacity of 1590.4 mAh g^-1can be achieved at 0.1C, and the discharge capacity of 803.5 mAh g^-1can be still exhibited when increasing to 2C. After a long period of 500 cycles, additionally, the discharge specific capacity of 1142.2 mAh g^-1 and capacity attenuation of 0.0617% per cycle can be obtained at 1C.

Chemically Dual-Modified Biochar for the Effective Removal of Cr(VI) in Solution

Here, a dual-modification strategy using KMnO4 (potassium permanganate) and AlCl3·6H2O (aluminum chloride, hexahydrate) as co-modifiers to improve the Cr(VI) removal capacity of K2CO3 activated biochar is introduced. As a result, the dual-modified biochar with KMnO4 and AlCl3·6H2O has the calculated adsorption energy of −0.52 eV and −1.64 eV for HCrO4−, and −0.21 eV and −2.01 eV for Cr2O72−. The Al2O3 (aluminum oxide) and MnO (manganese oxide) embedded on the surface of dual-modified biochar bring more Cr(VI) absorption sites comparing to single-modified biochar, resulting in a maximum Cr(VI) saturated adsorption capacity of 152.86 mg g−1. The excellent removal performance is due to the synthetic effect of electrostatic attraction, reduction reaction, complexation reaction, and physical adsorption. The experimental results also indicated that the spontaneous adsorption process agreed well with the pseudo-second order and Langmuir models. This dual-modification strategy is not limited to the treatment of Cr(VI) with biochar, and may also be incorporated with the treatment of other heavy metals in aqueous environment.

Gifts from Nature: Bio-Inspired Materials for Rechargeable Secondary Batteries

Materials in nature have evolved to the most efficient forms and have adapted to various environmental conditions over tens of thousands of years. Because of their versatile functionalities and environmental friendliness, numerous attempts have been made to use bio-inspired materials for industrial applications, establishing the importance of biomimetics. Biomimetics have become pivotal to the search for technological breakthroughs in the area of rechargeable secondary batteries. Here, the characteristics of bio-inspired materials that are useful for secondary batteries as well as their benefits for application as the main components of batteries (e.g., electrodes, separators, and binders) are discussed. The use of bio-inspired materials for the synthesis of nanomaterials with complex structures, low-cost electrode materials prepared from biomass, and biomolecular organic electrodes for lithium-ion batteries are also introduced. In addition, nature-derived separators and binders are discussed, including their effects on enhancing battery performance and safety. Recent developments toward next-generation secondary batteries including sodium-ion batteries, zinc-ion batteries, and flexible batteries are also mentioned to understand the feasibility of using bio-inspired materials in these new battery systems. Finally, current research trends are covered and future directions are proposed to provide important insights into scientific and practical issues in the development of biomimetics technologies for secondary batteries.

Sustainable Carbon Materials toward Emerging Applications

It is desirable for a sustainable society that the production and utilization of renewable materials are net-zero in terms of carbon emissions. Carbon materials with emerging applications in CO₂ utilization, renewable energy storage and conversion, and biomedicine have attracted much attention both academically and industrially. However, the preparation process of some new carbon materials suffers from energy consumption and environmental pollution issues. Therefore, the development of low-cost, scalable, industrially and economically attractive, sustainable carbon material preparation methods are required. In this regard, the use of biomass and its derivatives as a precursor of carbon materials is a major feature of sustainability. Recent advances in the synthetic strategy of sustainable carbon materials and their emerging applications are summarized in this short review. Emphasis is made on the discussion of the original intentions and various sustainable strategies for producing sustainable carbon materials. This review provides basic insights and significant guidelines for the further design of sustainable carbon materials and their emerging applications in catalysis and the biomedical field.

High-performance nanostructured bio-based carbon electrodes for energy storage applications

Polyacrylonitrile (PAN)-based carbon precursor is a well-established and researched material for electrodes in energy storage applications due to its good physical properties and excellent electrochemical performance. However, in the fight of preserving the environment and pioneering renewable energy sources, environmentally sustainable carbon precursors with superior electrochemical performance are needed. Therefore, bio-based materials are excellent candidates to replace PAN as a carbon precursor. Depending on the design requirement (e.g. carbon morphology, doping level, specific surface area, pore size and volume, and electrochemical performance), the appropriate selection of carbon precursors can be made from a variety of biomass and biowaste materials. This review provides a summary and discussion on the preparation and characterization of the emerging and recent bio-based carbon precursors that can be used as electrodes in energy storage applications. The review is outlined based on the morphology of nanostructures and the precursor's type. Furthermore, the review discusses and summarizes the excellent electrochemical performance of these recent carbon precursors in storage energy applications. Finally, a summary and outlook are also given. All this together portrays the promising role of bio-based carbon electrodes in energy storage applications.

Cationic covalent-organic framework for sulfur storage with high-performance in lithium-sulfur batteries

Covalent organic frameworks (COFs) with pre-designed structure and customized properties have been employed as sulfur storage materials for lithium-sulfur (Li-S) batteries. In this work, a cationic mesoporous COF (COF-NI) was synthesized by grafting a quaternary ammonium salt group onto the pore channel of COFs via a one-pot three components tandem reaction strategy. The post-functionalized COFs were utilized as the matrix framework to successfully construct the Li-S battery with high-speed capacity and long-term stability. The experimental results showed that, after loading active material sulfur, cationic COF-NI effectively suppressed the shuttle effect of the intermediate lithium polysulfide species in Li-S batteries, and exhibited better cycle stability than the as-obtained neutral COF (COF-Bu). For example, compared with COF-Bu based sulfur cathode (521 mA h g^-1), the cationic COF-NI based sulfur cathode maintained a discharge capacity of 758 mA h g^-1 after 100 cycles. These results clearly showed that appropriate pore environment of COFs can be prepared by rational design, which can reduce the shuttle effect of lithium polysulfide species and improve the performance of Li-S battery.

N, O co-doped chlorella-based biomass carbon modified separator for lithium-sulfur battery with high capacity and long cycle performance

As a lithium-ion secondary battery with high energy density, lithium-sulfur batteries have very bright development prospects. But the shuttle effect is still a thorny issue in the development process. The N, O co-doped chlorella-based biomass carbon (CBBC) synthesized by chemical activation method possesses a microporous and mesoporous composite structure, large specific surface area, and good electrical conductivity. The CBBC interlayer can improve the wettability between the separator and the electrolyte, and accelerate the transmission of Li⁺. N, O heteroatoms have a strong chemical adsorption operation for LiPs. The modified separator restrains lithium polysulfide through physical barriers and chemical adsorption, and improves the capacity and cycle performance of lithium-sulfur batteries. The batteries with CBBC exhibit excellent cycling stability (0.067% per cycle at 0.5C) and better rate performance (918 mAh g^-1 at 2C). The first discharge capacity at 0.05C was 1540 mAh g^-1. Even after 600 cycles the discharge capacity retains 656 mAh g^-1 at 0.5C. The low price and simple preparation of CBBC interlayer is an attractive choice for improving lithium-sulfur batteries.

A separator based on natural illite/smectite clay for highly stable lithium-sulfur batteries

In spite of high theoretical specific capacity and specific energy of lithium-sulfur (Li-S) batteries, the poor cycle stability caused by polysulfides shuttle severely hinders their real-world applications. Here, a natural clay mineral (illite/smectite, ISC) and carbon black (C) coated Celgard^@2400 (ISC/C@Celgard) separator is reported. The separator shows super-electrolyte-philicity and good mechanical stability. The low-cost and eco-friendly ISC with abundant -OH groups can quickly trap a lot of polysulfides by Li-O and Li-S bonding with polysulfides. The ISC/C layer with uniform nanopores can also inhibit polysulfides shuttle by physical shield. Moreover, good electrical conductivity of the ISC/C layer can reactivate the adsorbed polysulfides and thus enhance S utilization. So, the separator endows the Li-S battery with very high initial reversible capacity (1322 mA h g^-1) at 0.1 C and excellent cycle stability with low capacity decay rate (0.054% per cycle) during 500 cycles at 1.0 C. Furthermore, a very high areal capacity (5.9 mAh cm^-2) is achieved for the battery composed of the separator and the self-supporting high S loading (8.9 mg cm^-2) CNT/S cathode at 0.32 mA cm^-2. This study opens the possibility of developing advanced separators using natural clay minerals for highly stable Li-S batteries.

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.