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The past decades have witnessed the rapid development of lithium-ion batteries (LIBs), which are applied in nearly every aspect of our daily life. However, the increasing number of spent LIBs (S-LIBs) poses a great threat to the environment. Thus, to protect the environment and preserve limited lithium resources, it is necessary to recycle S-LIBs. In this review, we initially provide a brief introduction on the structure and degradation mechanism of LIBs and pretreatment of S-LIBs. Subsequently, we highlight the recent advancements in the development of recycling the cathode of S-LIBs, including its direct, hydrometallurgical, and pyrometallurgical recovery. The advantages and disadvantages of each recycling process are also discussed from the viewpoint of the environment and economy. In addition, we also introduce the recycling of S-LIBs through a green and environmentally friendly process of treating waste with waste. Finally, the overall perspective of this technology and areas requiring particular attention in the future are discussed. [ABSTRACT FROM AUTHOR]

Over a century ago, phenolic formaldehyde (PF) resin was developed and continues to increase in yield due to its diverse applications. However, PF resin is a thermosetting plastic lacking fluidity and moldability, which are nondegradable in natural environments, leading to severe threats to fossil resources as well as global environmental crises. As a result, recycling PF resin is extremely important. In this review, we provide the recent advances in the recycling of PF resin, which includes mechanical recycling, chemical recycling, and utilization of carbon-based materials. The advantages and disadvantages of each strategy are evaluated from a green chemistry perspective. This article aims to attract interest in PF resin design, synthesizing, application and recycling, offering useful suggestions. [ABSTRACT FROM AUTHOR]

Transition metal sulfides with designed nanostructures are expected to provide superior electrochemical performance when used as electrode materials for pseudocapacitors compared to their oxide counterparts. In this paper, hollow Co3S4 dodecahedra were successfully prepared using cobalt‐based zeolite imidazolium skeleton (ZIF‐67) as the precursor and thioacetamide (TAA) as the sulfur source combined with a facile one‐step vulcanization process. The hollow cavity structure not only shortens the carrier transport distance but also provides a higher specific surface area and abundant active sites, which promotes an efficient mass transfer process. In addition, the one‐step synthesis of hollow Co3S4 has greater advantages than the one‐step synthesis in terms of cost control and process simplification. The specific capacitance of the produced hollow Co3S4 nanopolyhedra was 668 F/g at 1 A/g and remained at 353 F/g at 10 A/g when used as a pseudocapacitor electrode, demonstrating its superior multiplication capability. In addition, the capacitance retention is 86.4% after 5000 cycles at 4 A/g, indicating its long cycle stability. Notably, employing commercial activated carbon as negative electrode and the as‐prepared hollow Co3S4 polyhedrons as positive electrode, the assembled asymmetry supercapacitor device delivers a high energy density of 20.7 Wh/kg at a power density of 716 kW/kg. The capacitance value of the device remains up to 81.4% after 2000 charging/discharging cycles. The simple synthesis process opens new opportunities to develop advanced hollow nanostructures exhibiting potential for various applications. [ABSTRACT FROM AUTHOR]

Zn-BTC (H3BTC refers to 1, 3, 5-benzoic acid) MOF was used as a self-template and a zinc source to prepare ZnS/NiS2 with a layered heterogeneous structure as a promising electrode material using cation exchange and solid-phase vulcanization processes. The synergistic effect of the two metal sulfides enhances the application of ZnS/NiS2. And the high specific surface area and abundant active sites further promote the mass/charge transfer and redox reaction kinetics. In the three-electrode system, the specific capacitance was as high as 1547 F/g at a current density of 1 A/g, along with satisfactory rate capability (1214 F/g at 6 A/g) and cycling performance. Coupled with activated carbon (AC), the prepared hybrid device (ZnS/NiS2 as the positive electrode and AC as the negative electrode) (ZnS/NiS2/AC) can be operated under a potential window of 1.6 V and provides a high energy density of 26.3 Wh/kg at a power density of 794 W/kg. Notably, the assembled ZnS/NiS2//AC showed little capacity degradation after 5000 charge/discharge cycles. [ABSTRACT FROM AUTHOR]

Carbon-based materials have demonstrated excellent thermal, electric, optical, magnetic, and mechanical properties, offering promising application potential in many fields. Corresponding synthetic approaches meeting the requirements of sustainable development goals are always desired. Compared with chemical vapor deposition, solvothermal, conventional pyrolysis, and salt-assisted methods are emerging as advanced synthetic technologies for the fabrication of carbon-based materials since these processes are expected to be more sustainable. Herein, we provide a comprehensive review on the salt-assisted synthesis of carbon-based materials and their typical energy-related applications. First, the properties of carbon and a comparison of various synthetic techniques are briefly introduced. In particular, we highlight the advantages of salt-assisted synthesis in view of sustainable development goals. For convenience, we divide the roles of salt in assisting the synthesis of carbon-based materials into four subclasses: reaction medium, pore-forming agent, morphology control, and precursors. Simultaneously, the applications of these carbon-based materials in energy-related fields are discussed. Lastly, the major challenges in this field are outlined, and future research avenues in salt-assisted synthesis of carbon-based materials for energy-related applications are also highlighted. It is expected that this tutorial review will supply necessary background information to further advance salt-assisted synthesis of carbon-based materials for energy-related applications. [ABSTRACT FROM AUTHOR]

Carbon materials play an important role in supercapacitors due to their structural diversity, rich surface morphology, excellent chemical stability and highly active surfaces. Currently, there are many reports on the synthesis methods for carbon-based materials. The molten salt method stands out among the many methods for its advantages of economy, environmental protection, high efficiency, and maneuverability. Here, we focus on the different roles played by molten salts as templates, sealants, reaction media, and catalysts from the point of view of their functions. The properties and selection principles of the molten salts are discussed in depth, focusing on the morphology, structure, and capacitive properties of the carbon materials prepared using the molten salt strategy. Finally, the current research status of the preparation of carbon-based materials by the molten salt method is summarized, the shortcomings of existing technology are pointed out, and the prospects for its development are envisioned. It is hoped that this review can provide some basic knowledge for the preparation of carbon-based materials by the molten salt method and promote further research on molten salt technology. [ABSTRACT FROM AUTHOR]

The construction of electrode materials with high rate and excellent cycling stability is the key to supercapacitors. Due to their remarkable high conductivity and great electrochemical activity, transition bimetallic sulfides are extremely appealing electrode materials for supercapacitors, but their synthesis is still challenging. In this study, a NiCo bimetallic sulfide (NiCo2S4) microspheres with porous structure were prepared via direct vulcanization of NiCo‐EG complexes followed by a thermal treatment, which were pre‐synthesized via coordination of ethylene glycol (EG) with transition metal ions (Ni2+, Co2+) under hydrothermal condition. Some experimental parameters were investigated, including the control of NiCo2S4 microspheres produced by the ratio of precursor NiCo‐EG to different masses of sulfur sources, which in turn affects the electrochemical properties. When applied as electrode for supercapacitor, the NiCo2S4 microspheres obtained under optimal condition delivered a high capacitance (1386 F g−1 at 1 A g−1), excellent rate capability (845 F g−1 at 10 A g−1) and stable cycling performance (80.05% after 5000 cycles at 10 A/g). Furthermore, for checking the practicality of the produced NiCo2S4 microspheres, an asymmetric supercapacitor device was built using activated carbon (AC) as the negative electrode and NiCo2S4 microspheres as the positive electrode. The assembled NiCo2S4//AC cell had a power density of 799.9 W kg−1 and an energy density of 30.5 Wh kg−1, confirming that the structurally optimized NiCo2S4 porous nanomicrospheres have excellent electrochemical properties and have a wide range of application prospects. [ABSTRACT FROM AUTHOR]

Polyvinyl chloride (PVC) is one of the most important plastics derived from petroleum, which has been extensively used in everyday life for the last few decades due to its superior properties. Without reasonable manageability, the volume of PVC is increasing steadily in the natural world. Owing to its features of non-biodegradability, the traditional disposal of PVC waste by either pouring it into the oceans or landfilling causes serious environmental issues. Due to sustainable development, PVC solid waste can be recycled to obtain products with the same quality as the starting material, reused in other fields, or converted into other high-value chemicals. Over the past decades, great progress has been made in the recycling of PVC. In this review, we initially provide a brief introduction to PVC, including its chemical structure, annual production and application fields, followed by an overview of mechanical approaches, including separation techniques, inclusion in other materials, and non-conventional mechanical recycling. The advantages and disadvantages of these techniques are also considered. Various chemical approaches to converting PVC waste into new products or chemicals to enhance the sustainability of the environment, such as gasification, pyrolysis, and de-chlorination are discussed in detail. Finally, the challenges and future perspectives of recycling PVC solid waste are discussed. [ABSTRACT FROM AUTHOR]

Utilizing the synergistic effect of binary/ternary transitional metal oxides to boost the electrochemical performance of supercapacitors is demonstrated to be an efficient strategy to construct advanced high-performance supercapacitors. In this work, a ternary Fe2O3@N-C@MnO2 (N-C refers to N-doped carbon) composite with a Chinese-chestnut structure was prepared and used as the electrode of a supercapacitor. It was demonstrated that both the high electrical conductivity of N-C and the synergistic effect between Fe2O3 and MnO2 help to improve the electrochemical performance of the material. At current density of 1 A g−1, the results show that the specific capacitance of Fe2O3@N-C@MnO2 is as high as 1712.5 F g−1 in 1.0 M KOH solution. When the voltage window is 0–1.7 V, the energy density is 17.6 Wh kg−1 and the power density is 424.9 W kg−1. This work may provide an approach for the design and fabrication of transition metal oxide-based binary/ternary composite electrodes with high electrochemical performance for energy storage devices. [ABSTRACT FROM AUTHOR]

Considering their high abundance in the earth, iron-based materials have occasionally been regarded as promising electrode materials for supercapacitors. However, monometallic iron-based electrodes still demonstrate an insufficient specific capacitance value in comparison to monometallic Mn-, Ni-, and Co-based compounds and their combined materials. Herein, an enhanced iron-based heterostructure of Fe3O4@Fe2P was prepared via the in situ phosphorization of Fe3O4. Compared to pristine Fe3O4, the Fe3O4@Fe2P heterostructure showed a capacity enhancement in KOH aqueous solution. The improved electrochemical performance can be attributed to both the core shell structure, which favors buffering the collapse of the electrode, and the synergistic effect between the two iron compounds, which may provide abundant interfaces and additional electrochemically active sites. Moreover, the assembled asymmetric supercapacitor device using the Fe3O4@Fe2P heterostructure as the positive electrode and activated carbon as the negative electrode delivers a high energy density of 13.47 Wh kg−1, a high power density of 424.98 W kg−1, and an acceptable capacitance retention of 78.5% after 5000 cycles. These results clarify that monometallic Fe based materials can deliver a potential practical application. In addition, the construction method for the heterostructure developed here, in which different anion species are combined, may represent a promising strategy for designing high-performance electrodes. [ABSTRACT FROM AUTHOR]

Supercapacitors which have been widely used in portable electronics and hybrid electric vehicles are considered to be fascinating energy storage devices owing to their higher energy density than traditional capacitors and higher power density than batteries. The performance of supercapacitors is much dependent on the properties of the used electrode materials, and much effort has been devoted to exploring high‐performance electrodes. During the past decade, cobalt‐based materials, especially Co3O4 and its composites, have been regarded as prominent electrode materials for supercapacitors in view of their relatively low cost, high theoretical specific capacitance, non‐toxicity, and excellent electrochemical activity. In this review, we attempt to provide some basic insights into the rational design of Co3O4 based materials/composites and their capacitive properties for supercapacitors. The electrochemical advantages of Co3O4 as a supercapacitor material are summarized, and many examples are illustrated. The remaining challenges in exploration of Co3O4‐based materials as efficient electrodes for supercapacitors are also discussed and the future research directions are offered. [ABSTRACT FROM AUTHOR]