A state-of-the-art review on biomass-derived carbon materials for supercapacitor applications: From precursor selection to design optimization

Biomass-derived carbon materials have the characteristics of a wide range of precursor sources, controllable carbon nano-dimension, large specific surface area and abundant heteroatoms doping. At present, biomass-derived carbon materials have been widely used in electrochemical energy storage devices, especially the research and development of biomass-derived carbon materials for supercapacitors has become mature and in-depth. Therefore, it is of importance to summarize the advanced technologies and strategies for optimizing biomass-derived carbon materials for supercapacitors, which will effectively promote the further development of high-performance supercapacitors. In this review, the recent research progress of biomass-derived carbon materials is provided in detail, including the selection of biomass precursors, the design of carbon nano-dimension and the theory of heteroatom doping. Besides, the preparation methods of biomass-derived carbon materials and the related processes of optimizing the electrochemical performance are also summarized. This review ends with the perspectives for future research directions and challenges in the field of biomass-derived carbon materials for electrochemical applications. This review aims to provide helpful reference information for the nano-dimensional design and electrochemical performance optimization of biomass-derived carbon materials for the practical application of supercapacitors.

Rational design of nitrogen (N), boron (B), and phosphorous (P) tri-doped carbon nano-spheres as advanced anode materials for sodium-ion batteries with an ultra-long lifespan

Developing improved anode materials is critical to the performance enhancement and the lifespan prolonging of sodium-ion batteries (SIBs). In this context, carbon-based nanostructures have emerged as a promising candidate. In this work, we have synthesized N, B, and P tri-doped carbon (NBPC) spheres using a one-step carbonization method. The as-prepared NBPC exhibits exceptional properties, including an expanded layer space, sufficient structural defects, and enhanced electrical conductivity. These characteristics synergistically contribute to the remarkable rate capability and ultra-long lifespan when NBPC is employed as an anode material for SIBs. The as-prepared NBPC demonstrates a reversible capacity of 290.6 mAh/g at 0.05 A/g, with a capacity retention of 98.4% after 800 cycles. Furthermore, NBPC exhibits an impressively ultra-long cycle life of 2400 cycles at 1.0 A/g with a reversible capacity of 140.2 mAh/g. First principle calculations confirm that the introduction of N, B, and P heteroatoms in carbon enhances the binding strength of sodium ions within NBPC. This work presents a novel approach for fabricating advanced anode materials, enabling the development of long-life SIBs for practical applications.

Na Storage in Sb2S3@C Composite: A Synergistic Capacity Contribution Mechanism with Wider Temperature Adaptability

The practical applications of metallic anodes are limited due to dendritic growth, propagation in an infinite volume during the plating process, and parasitic interfacial reactions between sodium (Na) and the electrolyte. Herein, we developed Sb₂S₃ microrods as a template to regulate the nucleation of metallic Na. Additionally, the propagation of the deposited metal could be spatially regulated via a "nanoconfinement effect", that is, within the conformal hard carbon (C) layer of nanothickness. Moreover, we carefully studied the seed effect of the in situ-formed Na-Sb and Na-S alloys within the hard C sheath during the Na plating process. The symmetrical cells of the Sb₂S₃@C composite anode achieved dendrite-free cycling at 1 mA cm^-2 for 1100 h at a high capacity loading of 1 mA h cm^-2 and considerably mitigated a nucleation overpotential of 20 mV. Pairing a NaVPO₄F (NVPF) cathode (4.6 mg cm^-2) with an in situ presodiation Sb₂S₃@C composite (2*Na excess) prototype delivered a high energy density and a high power density of 173.75 W h kg^-1 and 868.57 W kg^-1, respectively. Therefore, this study provides tremendous possibilities for employing the proposed hybrid storage mechanism in low-cost and practical applications of high-energy-density Na metal batteries.

Centrifugally Spun PVA/PVP Based B, N, F Doped Carbon Nanofiber Electrodes for Sodium Ion Batteries

Owing to their high electrical conductivity, high surface area, low density, high thermal stability, and chemical stability, carbon nanofibers have been used in many fields, including energy storage, electromagnetic shielding, filtering, composites, sensors, and tissue engineering. Considering the environmental impact of petroleum-based polymers, it is vital to fabricate carbon nanofibers from environmentally-friendly materials using fast and safe techniques. PVA/PVP nanofibers were fabricated via centrifugal spinning and the effects of variations in the PVP content on the morphology and thermal properties of PVA/PVP-blend nanofibers were studied using SEM and DSC analyses. Moreover, the effects of carbonization conditions, including stabilization time, stabilization temperature, carbonization time, and carbonization temperature on the morphology and carbon yield, were investigated. Centrifugally spun PVA/PVP-based carbon nanofiber electrodes with an average fiber diameter around 300 nm are reported here for the first time. Furthermore, centrifugally spun PVA/PVP-based B, N, F-doped carbon nanofibers were fabricated by combining centrifugal spinning and heat treatment. Through B, N, F doping, CNFs demonstrated a high reversible capacity of more than 150 mAh/g in 200 cycles with stable cycling performance.

Progress and Perspectives on Covalent-organic Frameworks (COFs) and Composites for Various Energy Applications

Covalent-organic frameworks (COFs), being a new member of the crystalline porous materials family, have emerged as important materials for energy storage/conversion/generation devices. They possess high surface areas, ordered micro/mesopores, designable structures and an ability to precisely control electro-active groups in their pores, which broaden their application window. Thanks to their low weight density, long range crystallinity, reticular nature and tunable synthesis approach towards two and three dimensional (2D and 3D) networks, they have been found suitable for a range of challenging electrochemical applications. Our review focuses on the progress made on the design, synthesis and structure of COFs and their composites for various energy applications, such as metal-ion batteries, supercapacitors, water-splitting and solar cells. Additionally, attempts have been made to correlate the structural and mechanistic characteristics of COFs with their applications.