Defect Engineering of Disordered Carbon Anodes with Ultra-High Heteroatom Doping Through a Supermolecule-Mediated Strategy for Potassium-Ion Hybrid Capacitors

Enhanced sodium-storage performances of crumpled MXene nanosheets via alkali treatment-induced active ammonium ions

Ti3C2Tx MXene demonstrates excellent potential as an anode material for sodium-ion capacitors. However, the narrow interlayer spacing and self-stacking phenomenon limit its applicability. In this study, we demonstrate an easy two-step method involving freezing and crumpling of MXene nanosheets to improve their Na-ion storage via the addition of ammonium ions (referred to as FCM nanosheets). Flat MXene particles aggregate and undergo folding in an alkaline solution. Ammonium ions can penetrate the gaps between MXene nanosheets, expanding interlayer spaces and inducing the formation of folds. Compared to MXene nanosheets, FCM nanosheets exhibit improved ion transfer kinetics and additional high capacity owing to the intercalated ammonium ions. The manufactured FCM anode exhibits remarkable electrochemical properties, including a high specific capacity of 313 mAhg-1 and stability over 15,000 cycles.

Recent advances in rational design for high-performance potassium-ion batteries

The growing global energy demand necessitates the development of renewable energy solutions to mitigate greenhouse gas emissions and air pollution. To efficiently utilize renewable yet intermittent energy sources such as solar and wind power, there is a critical need for large-scale energy storage systems (EES) with high electrochemical performance. While lithium-ion batteries (LIBs) have been successfully used for EES, the surging demand and price, coupled with limited supply of crucial metals like lithium and cobalt, raised concerns about future sustainability. In this context, potassium-ion batteries (PIBs) have emerged as promising alternatives to commercial LIBs. Leveraging the low cost of potassium resources, abundant natural reserves, and the similar chemical properties of lithium and potassium, PIBs exhibit excellent potassium ion transport kinetics in electrolytes. This review starts from the fundamental principles and structural regulation of PIBs, offering a comprehensive overview of their current research status. It covers cathode materials, anode materials, electrolytes, binders, and separators, combining insights from full battery performance, degradation mechanisms, in situ/ex situ characterization, and theoretical calculations. We anticipate that this review will inspire greater interest in the development of high-efficiency PIBs and pave the way for their future commercial applications.

Molecular structure regulation of FCCs enabling N/S co-doped hollow amorphous carbon with enlarged interlayer spacing and rich defects for superior potassium storage

Constructing high-performance and low-cost carbon anodes for potassium-ion batteries (PIBs) is highly desirable but faces great challenges. In this study, we present a novel approach to fabricating N/S co-doped hollow amorphous carbon (LNSHAC) for superior potassium storage through a template-assisted molecular structure regulation strategy. By tailoring a 3D crosslinked aromatics precursor from fluid catalytic cracking slurry (FCCs), the LNSHAC features a N/S co-doped hollow structure with enlarged interlayer spacing of up to 0.405 nm and rich defects. Such unique microstructure offers fast transport channels for K-ion intercalation/deintercalation and provides more active sites, leading to boosted reaction kinetics and potassium storage capacity. Consequently, the LNSHAC electrode delivers an impressive reversible capacity (466.2 mAh g-1 at 0.1 A/g), excellent rate capability (336.3 mAh g-1 at 2 A/g), and superior cyclic performance (256.9 mAh g-1 after 5000 cycles at 5 A/g with admirable retention of 76.9 %), standing out among the reported carbon-based anodes. When KFeHCF is employed as the cathode, the LNSHAC-based K-ion full cell exhibits a high reversible capacity of 176.6 mAh g-1 at 0.1 A/g and excellent cyclic stability over 200 cycles. This work will inspire the development and application of advanced carbon-based materials for potassium electrochemical energy storage.

Constructing Carbon Nanotube-Enhanced Ultra-Thin Organic Compounds with Multi-Redox Sites for "All-Temperature" Potassium-Ion Battery Anode and its Step-Wise K-Storage Mechanism

Organic compounds are regarded as important candidates for potassium-ion batteries (KIBs) due to their light elements, controllable polymerization, and tunable functional groups. However, intrinsic drawbacks largely restrict their application, including possible solubility in electrolytes, poor conductivity, and low diffusion coefficients. To address these issues, an ultrathin layered pyrazine/carbonyl-rich material (CT) is synthesized via an acid-catalyzed solvothermal reaction and homogeneously grown on carbon nanotubes (CNTs), marked as CT@CNT. Such materials have shown good features of exposing functional groups to guest ions and good electron transport paths, exhibiting high reversible capacity and remarkable rate capability over a wide temperature range. Two typical electrolytes are compared, demonstrating that the electrolyte of LX-146 is more suitable to maximize the electrochemical performances of electrodes at different temperatures. A stepwise reaction mechanism of K-chelating with C═O and C═N functional groups is proposed, verified by in/ex situ spectroscopic techniques and theoretical calculations, illustrating that pyrazines and carbonyls play the main roles in reacting with K+ cations, and CNTs promote conductivity and restrain electrode dissolution. This study provides new insights to understand the K-storage behaviors of organic compounds and their "all-temperature" application.

Nitrogen-doped lignin-derived electrode materials for supercapacitors were prepared using the domain-limited effect

Supercapacitors, pivotal in mitigating the energy crisis stemming from dwindling fossil fuel reservoirs, necessitate meticulous consideration of electrode material preparation. While lignin-derived carbon materials sourced sustainably exhibit commendable potential as electrode materials, their intrinsic low capacitance limits widespread utilization. Herein, nitrogen atom doping of lignin (CNL) was accomplished employing a chemical modification technique employing cyanuric chloride as a dopant. The resultant nitrogen content measured at 2.85 %. Subsequent to CNL carbonation, the generated C3N4 was selectively confined to the internal surface of the CNLMS-800 through a domain-limited activation method, thereby rendering it suitable for deployment as a supercapacitor electrode material. CNLMS-800 manifests a substantial specific surface area of 1778.0 m2 g-1 and a concomitantly diminutive pore size of 2.6 nm. Noteworthy, the specific capacitance of CNLMS-800 attains 473.0 F g-1 at a current density of 0.5 A g-1 in a 6 M KOH electrolyte. The resultant energy density reaches 39.0 Wh kg-1 at a power density of 338.0 W kg-1. Crucially, even after 20,000 charge/discharge cycles at a current density of 10 A g-1, the capacitance retention attains an impressive 87.5 % in the KOH electrolyte. This innovative utilization of sustainable resources for electrode fabrication epitomizes a seminal advancement in the field of energy technology.

Controllable synthesis of electric double-layer capacitance and pseudocapacitance coupled porous carbon cathode material for zinc-ion hybrid capacitors

The designability of the porous structure of carbon material makes it a popular material for zinc-ion hybrid capacitors (ZIHCs). However, the micropore confinement effect leads to sluggish kinetics and is not well resolved yet. In this work, a pore-size controllable carbon material was designed to enhance ion accessibility. The experimental and calculated results revealed that suitable pore sizes and defects were beneficial to ion transfer/adsorption. Meanwhile, oxygen-containing functional groups could introduce a pseudocapacitance reaction. Its large specific surface area and interconnecting network structure could shorten the ion/electron transfer length to reach high ion adsorption capacity and fast kinetic behavior. When used as a zinc-ion hybrid capacitor cathode material, it showed 9.9 kW kg-1 power density and 100 W h kg-1 energy density. Even at 5 A g-1, after 50 000 cycles, there was still 93% capacity retention. Systemic ex situ characterization and first-principles calculations indicated that the excellent electrochemical performance is attributed to the electric double layer capacitance (EDLC) - pseudocapacitance coupled mechanism via the introduction of an appropriate amount of oxygen-containing functional groups. This work provides a robust design for pore engineering and mechanistic insights into rapid zinc-ion storage in carbon materials.

Highly Stable ZnS Anodes for Sodium-Ion Batteries Enabled by Structure and Electrolyte Engineering

Zinc sulfide is a promising high-capacity anode for practical sodium-ion batteries, considering its high capacity and the low cost of zinc and sulfur sources. However, the pulverization of particulate zinc sulfide causes active mass collapse and penetration-induced short circuits of batteries. Herein, a zinc sulfide encapsulated in a nitrogen-doped carbon shell (ZnS@NC) was developed for high-performance anodes. The confinement effect of nitrogen-doped carbon stabilizes the active mass structure during cycling thanks to the robust chemically and electronically bonded connections between nitrogen-doped carbon and zinc sulfide nanoparticles. Furthermore, the cycling stability of the ZnS@NC anode is boosted by the robust inorganic-rich solid electrolyte interphase (SEI) formed in cyclic and linear ether-based electrolytes. The ZnS@NC anode displayed a reversible specific capacity of 584 mAh g-1, an excellent rate capability of 327 mAh g-1 at 70 A g-1, and a highly stable cycling performance over 10000 cycles. This work provides a practical and promising approach to designing stable conversion anodes for high-performance sodium-ion batteries.

Sustainable Polyvinyl Chloride-Derived Soft Carbon Anodes for Potassium-Ion Storage: Electrochemical Behaviors and Mechanism

Soft carbon is a promising anode material for potassium-ion batteries due to its favorable properties such as low cost, high conductivity, stable capacity, and low potential platform. Polyvinyl chloride, as a white pollutant, is a soft carbon precursor that can be carbonized at varying temperatures to produce soft carbons with controllable defect and crystal structures. This work investigates the effect of carbonization temperature on the crystalline structures of the obtained soft carbons. In situ Raman spectroscopy was used to elucidate the adsorption-intercalation charge storage mechanism of potassium ions in soft carbons. Soft carbons prepared at the temperature of 800 °C have a defect-rich, short-range ordered structure, which provides optimal intercalation and adsorption sites for potassium ions, resulting in a satisfactory capacity of 302 mAh g-1 . This work presents new possibilities for designing soft carbon materials from recycling plastics for potassium-ion batteries.

Design and Synthesis Strategy of MXenes-Based Anode Materials for Sodium-Ion Batteries and Progress of First-Principles Research

MXenes-based materials are considered to be one of the most promising electrode materials in the field of sodium-ion batteries due to their excellent flexibility, high conductivity and tuneable surface functional groups. However, MXenes often have severe self-agglomeration, low capacity and unsatisfactory durability, which affects their practical value. The design and synthesis of advanced heterostructures with advanced chemical structures and excellent electrochemical performance for sodium-ion batteries have been widely studied and developed in the field of energy storage devices. In this review, the design and synthesis strategies of MXenes-based sodium-ion battery anode materials and the influence of various synthesis strategies on the structure and properties of MXenes-based materials are comprehensively summarized. Then, the first-principles research progress of MXenes-based sodium-ion battery anode materials is summarized, and the relationship between the storage mechanism and structure of sodium-ion batteries and the electrochemical performance is revealed. Finally, the key challenges and future research directions of the current design and synthesis strategies and first principles of these MXenes-based sodium-ion battery anode materials are introduced.

Novel Bilayer-Shelled N, O-Doped Hollow Porous Carbon Microspheres as High Performance Anode for Potassium-Ion Hybrid Capacitors

With the advantages of high energy/power density, long cycling life and low cost, dual-carbon potassium ion hybrid capacitors (PIHCs) have great potential in the field of energy storage. Here, a novel bilayer-shelled N, O-doped hollow porous carbon microspheres (NOHPC) anode has been prepared by a self-template method, which is consisted of a dense thin shell and a hollow porous spherical core. Excitingly, the NOHPC anode possesses a high K-storage capacity of 325.9 mA h g-1 at 0.1 A g-1 and a capacity of 201.1 mAh g-1 at 5 A g-1 after 6000 cycles. In combination with ex situ characterizations and density functional theory calculations, the high reversible capacity has been demonstrated to be attributed to the co-doping of N/O heteroatoms and porous structure improved K+ adsorption and intercalation capabilities, and the stable long-cycling performance originating from the bilayer-shelled hollow porous carbon sphere structure. Meanwhile, the hollow porous activated carbon microspheres (HPAC) cathode with a high specific surface area (1472.65 m2 g-1) deriving from etching NOHPC with KOH, contributing to a high electrochemical adsorption capacity of 71.2 mAh g-1 at 1 A g-1. Notably, the NOHPC//HPAC PIHC delivers a high energy density of 90.1 Wh kg-1 at a power density of 939.6 W kg-1 after 6000 consecutive charge-discharge cycles.

Status and Opportunities of Zinc Ion Hybrid Capacitors: Focus on Carbon Materials, Current Collectors, and Separators

Zinc ion hybrid capacitors (ZIHCs), which integrate the features of the high power of supercapacitors and the high energy of zinc ion batteries, are promising competitors in future electrochemical energy storage applications. Carbon-based materials are deemed the competitive candidates for cathodes of ZIHC due to their cost-effectiveness, high electronic conductivity, chemical inertness, controllable surface states, and tunable pore architectures. In recent years, great research efforts have been devoted to further improving the energy density and cycling stability of ZIHCs. Reasonable modification and optimization of carbon-based materials offer a remedy for these challenges. In this review, the structural design, and electrochemical properties of carbon-based cathode materials with different dimensions, as well as the selection of compatible, robust current collectors and separators for ZIHCs are discussed. The challenges and prospects of ZIHCs are showcased to guide the innovative development of carbon-based cathode materials and the development of novel ZIHCs.