Toward High-Performance Lithium-Sulfur Batteries: Upcycling of LDPE Plastic into Sulfonated Carbon Scaffold via Microwave-Promoted Sulfonation

Porous carbon materials derived from discarded COVID-19 masks via microwave solvothermal method for lithium‑sulfur batteries

With the spread of COVID-19, disposable medical masks (DMMs) have become a significant source of new hazardous solid waste. Their proper disposal is not only beneficial to the safety of biological systems but also useful to achieve considerable economic value. The first step of this study was to investigate the chemical composition of DMMs. It is primarily composed of polypropylene, polyethylene terephthalate and iron, with fibrous polypropylene accounting for approximately 80% of the total weight. Then, DMMs were sulfonated and oxidised by the microwave-driven concentrated sulfuric acid within 8 min based on the fact that the concentrated sulfuric acid exhibits a good microwave absorption capacity. The co-doping of sulfur and oxygen was achieved while improving the thermal stability of DMMs. Subsequently, the self-activation pyrolysis of sulfonated and oxidised DMMs (P-SO@DMMs) was further realized in low-flow-rate argon. The specific surface area of P-SO@DMMs increased from 2.0 to 830.9 m²·g^-1. P-SO@DMMs sulfur cathodes have promising electrochemical properties because of their porous structures and the synergistic effect of sulfur and oxygen co-doping. The capacity of the samples irradiated by microwave for 10 min at 0.1, 0.2, 0.5, 1, 2 and 5 C were 1313.6, 1010.9, 816.5, 634.4, 513.4 and 453.1 mAh·g^-1, respectively, and after returning to 0.2 C and continuing the cycle for 50 revolutions, maintained 50.5% of the initial capacity. After 400 cycles, its capacity is 38.1% of the initial capacity at 0.5 C. It is slightly higher than the electrochemical performance of the sample treated by microwave for 8 min and significantly higher than the sample treated by 6 min. This work converts structurally complex, biohazardous DMMs into porous carbon with high specific surface area by clean and efficient microwave solvothermal and self-activating pyrolysis, which facilitates the development of carbon based materials at low cost and large scale.

Critical advances and future opportunities in upcycling commodity polymers

The vast majority of commodity plastics do not degrade and therefore they permanently pollute the environment. At present, less than 20% of post-consumer plastic waste in developed countries is recycled, predominately for energy recovery or repurposing as lower-value materials by mechanical recycling. Chemical recycling offers an opportunity to revert plastics back to monomers for repolymerization to virgin materials without altering the properties of the material or the economic value of the polymer. For plastic waste that is either cost prohibitive or infeasible to mechanically or chemically recycle, the nascent field of chemical upcycling promises to use chemical or engineering approaches to place plastic waste at the beginning of a new value chain. Here state-of-the-art methods are highlighted for upcycling plastic waste into value-added performance materials, fine chemicals and specialty polymers. By identifying common conceptual approaches, we critically discuss how the advantages and challenges of each approach contribute to the goal of realizing a sustainable plastics economy.

Upcycling Waste Polyethylene into Carbon Nanomaterial Via A Carbon-Grown-On-Carbon Strategy

Upcycling waste plastics (e.g., polyethylene (PE)) into value-added carbon products is regarded as a promising approach to address the increasingly serious waste plastic pollution and simultaneously achieve carbon neutrality. However, developing new carbonization technology routes to promote the oxidation of PE at low temperature and construct the stable crosslinking network remains challenging. Here, we propose a facile carbon-grown-on-carbon strategy using carbon black (CB) to convert waste PE into core/shell carbon nanoparticles (CN) in high yields at low temperature. The yield of CN remarkably rises when the heating temperature decreases or the dosage of CB grows. The obtained CN displays turbostratic structure and closely aggregated granular morphology with a size of ca. 80 nm. It is found, prior to the oxidation and carbonization of PE, CB forms a 3D network architecture in the PE matrix. More importantly, CB not only catalyzes the partial oxidation of PE to form PE macromolecular radicals and introduce oxygen-containing groups at low temperature in the early stage, but also favors for the construction of a stable crosslinking network in the latter stage. This work offers a facile sustainable strategy for chemical upcycling of PE into value-added carbon products without post-treatments or usage of metallic catalysts. This article is protected by copyright. All rights reserved.

From plastic waste to new materials for energy storage

A perspective on using plastic waste as an alternative feedstock for the energy storage sector through upcycling. Materials for electrodes, electrolytes or binders could be obtained from both advanced combustion and depolymerization methods.

Upcycling Plastic Waste into High Value-Added Carbonaceous Materials

Even though plastic improved the human standard of living, handling the plastic waste represents an enormous challenge. It takes more than 100 years to decompose discarded or buried waste plastics. Microplastics are one of the causes of significantly pervasive environmental pollutants. The incineration of plastic waste generates toxic gases, underscoring the need for new approaches, in contrast to conventional strategies that are required for recycling plastic waste. Therefore, several studies have attempted to upcycle plastic waste into high value-added products. Converting plastic waste into carbonaceous materials is an excellent upcycling technique due to their diverse practical applications. This review summarizes various studies dealing with the upcycling of plastic waste into carbonaceous products. Further, this review discusses the applications of carbonaceous products synthesized from plastic waste including carbon fibers, absorbents for water purification, and electrodes for energy storage. Based on the findings, future directions for effective upcycling of plastic waste into carbonaceous materials are suggested.

Strategic Approach Towards Plastic Waste Valorization: Challenges and Promising Chemical Upcycling Possibilities

Plastic waste, which is one of the major sources of pollution in the landfills and oceans, has raised global concern, primarily due to the huge production rate, high durability, and the lack of utilization of the available waste management techniques. Recycling methods are preferable to reduce the impact of plastic pollution to some extent. However, most of the recycling techniques are associated with different drawbacks, high cost and downgrading of product quality being among the notable ones. The sustainable option here is to upcycle the plastic waste to create high-value materials to compensate for the cost of production. Several upcycling techniques are constantly being investigated and explored, which is currently the only economical option to resolve the plastic waste issue. This Review provides a comprehensive insight on the promising chemical routes available for upcycling of the most widely used plastic and mixed plastic wastes. The challenges inherent to these processes, the recent advances, and the significant role of the science and research community in resolving these issues are further emphasized.

Surface-Functionalized Separator for Stable and Reliable Lithium Metal Batteries: A Review

Metallic Li has caught the attention of researchers studying future anodes for next-generation batteries, owing to its attractive properties: high theoretical capacity, highly negative standard potential, and very low density. However, inevitable issues, such as inhomogeneous Li deposition/dissolution and poor Coulombic efficiency, hinder the pragmatic use of Li anodes for commercial rechargeable batteries. As one of viable strategies, the surface functionalization of polymer separators has recently drawn significant attention from industries and academics to tackle the inherent issues of metallic Li anodes. In this article, separator-coating materials are classified into five or six categories to give a general guideline for fabricating functional separators compatible with post-lithium-ion batteries. The overall research trends and outlook for surface-functionalized separators are reviewed.

Sustainable electrode material for high-energy supercapacitor: biomass-derived graphene-like porous carbon with three-dimensional hierarchically ordered ion highways

Biomass-derived carbonaceous materials have been deemed to be one of the up-and-coming electrode materials for high-performance energy storage systems due to their cost-neutral abundant resources, sustainable nature, easy synthesis methods, and environmentally benign features. In this work, various graphene-like porous carbon networks (GPCs) with three-dimensional (3D) hierarchically ordered "ion highways" have been synthesized by the carbonization/activation of orange-peel wastes for use as an electrode material in high-energy supercapacitors. The porous structures and surface morphologies of the GPCs were rationally fine-tuned as a function of the activation agent ratio. The prepared GPCs offered superior specific surface area in addition to a 3D porous structure with a fine-tuned pore size distribution. The electrochemical behaviors of all the GPCs were evaluated in 6.0 M KOH aqueous electrolyte via a three-electrode electrochemical setup. Owing to their synergistic characteristics, including superior specific surface area (1150 m2 g-1), large pore volume, and fine-tuned 3D porous architecture, GPC-3.0 (synthesized with a KOH : GPC ratio of 3.0, by wt.) exhibited the best capacitive behavior amongst the studied GPCs. The 3D hierarchically ordered architecture acts like well-designed ion highways that boost electron transportation, thereby enhancing electrochemical energy storage. A coin-cell-type symmetrical supercapacitor based on GPC-3.0 was tested in both 1.0 M Na2SO4 (salt-in-water) and 12.0 m NaNO3 (water-in-salt) electrolytes. The supercapacitor cell based on the water-in-salt electrolyte offered a wide operating voltage of 2.3 V. The obtained energy density and power density values were comparable to those of commercial high-performance electrical double-layer capacitors. Such notable findings will shed light on next-generation high-rate electrochemical energy storage systems based on biomass-derived carbonaceous materials.

Beyond Mechanical Recycling: Giving New Life to Plastic Waste

Increasing the stream of recycled plastic necessitates an approach beyond the traditional recycling via melting and re-extrusion. Various chemical recycling processes have great potential to enhance recycling rates. In this Review, a summary of the various chemical recycling routes and assessment via life-cycle analysis is complemented by an extensive list of processes developed by companies active in chemical recycling. We show that each of the currently available processes is applicable for specific plastic waste streams. Thus, only a combination of different technologies can address the plastic waste problem. Research should focus on more realistic, more contaminated and mixed waste streams, while collection and sorting infrastructure will need to be improved, that is, by stricter regulation. This Review aims to inspire both science and innovation for the production of higher value and quality products from plastic recycling suitable for reuse or valorization to create the necessary economic and environmental push for a circular economy.

MXene-Based Co, N-Codoped Porous Carbon Nanosheets Regulating Polysulfides for High-Performance Lithium-Sulfur Batteries

In virtue of their distinctive superiorities, lithium-sulfur (Li-S) batteries were deemed as novel and potential energy storage equipment. However, the low actual energy density and rapid capacity fading are still hindering their practical applications. Herein, MXene-based Co, N-codoped porous carbon nanosheets (MCoNPCNSs) are first developed as sulfur hosts by in situ self-assembly of the bimetallic zeolite imidazole framework on Ti₃C₂T_x MXene nanosheets followed by calcining and etching treatments. Co, N codoping on the one hand highly enhances the adsorptivity to polysulfides and on the other hand significantly promotes the kinetics of sulfur cathodes. Therefore, the MCoNPCNSs/S-M-PP electrode achieves a high capacity of 1340.2 mA h g^-1 in the first-cycle discharge process at 0.2 C and an exceptional capacity retention of 914.7 mA h g^-1 after 1000 cycles at 1 C. Moreover, the integrated structure of the cathode and separator imparts the MCoNPCNSs/S-M-PP electrode a significantly elevated gravimetric energy density of 1211.8 W h kg^-1. Therefore, the integrated MCoNPCNSs/S-M-PP electrode provides a delighted direction for constructing the potentially practical Li-S batteries.

A rational design of the coupling mechanism of physical adsorption and chemical charge effect for high-performance lithium–sulfur batteries

Lithium sulfur batteries are considered as potential energy storage systems for electrical devices owing to their high energy density, low cost, and environmental friendliness. However, the hasty capacity fading originating from the solution and migration of polysulfides is the major obstacle for their industrial application. The polysulfide adsorption and repulsion effect achieved by adding an extra coating layer on the side of the cathode and separator have been separately proved to be effective in mitigating the shuttle effect. Herein, a cooperative coated separator, which employs a hybrid carbon matrix as the coated material, including an appropriate ratio of N-doped activated conductive carbon and commercial acetylene black, and sulfonated polystyrene as the binder, is established to prevent the migration of polysulfides and serves as a secondary current collector to reutilize the active materials for high-performance lithium sulfur batteries. The research results showed that the coated separator with 50 wt% N-doped activated conductive carbon as the coating material and sulfonated polystyrene as the binder showed highlighted cycle performance, and 731 mA h g⁻¹ was maintained after 150 cycles at 800 mA g⁻¹(the capacity retention was 86.0%). The superior performance may be because the coated separator can efficiently restrain the polysulfides by physical and chemical effects and also reject the polysulfides by the anion electrostatic effect. In summary, this study provides a new cooperative way to address the shuttle effect and promotes the development of lithium sulfur batteries.

Trapping LPSs by the anion electrostatic effect of –SO₃H and the chemical adsorption of N-doped carbon for enhanced Li–S batteries.

Surface Functionalization of Carbon Architecture with Nano-MnO2 for Effective Polysulfide Confinement in Lithium-Sulfur Batteries

Li-S batteries have received tremendous attention owing to their high theoretical capacity (1672 mA h g^-1 ), sulfur abundance, and low cost. However, main systemic issues, associated with polysulfide shuttling and low Coulombic efficiency, hinder the practical use of the sulfur electrode in commercial batteries. Herein, we demonstrate an effective strategy of decorating nano-MnO₂ (less than 10 wt %) onto the sulfur reservoir to capture the out-diffused polysulfides through chemical interaction and thereby improve the electrochemical performance of the sulfur electrode without increasing the mass burden of total battery configuration. Pistachio shell-derived sustainable carbon (PC) was employed as effective sulfur containers owing to its structural characteristics (interconnected macro channels and micropores). With the aids of the structural benefits of the PC scaffold and the uniform decoration of nano-MnO₂ , polysulfide shuttling was significantly suppressed and the cycling performance of the sulfur cathode was dramatically improved over 250 cycles.