High potassium ion storage capacity with long cycling stability of sustainable oxygen-rich carbon nanosheets

Self-hybridization structures of BiOBr0.5Cl0.5: An ultra-high capacity anode material for half/full potassium-ion batteries

Potassium-ion batteries (PIBs) are gaining attention among emerging technologies for their cost-effectiveness and the abundance of resources they utilize. Within this context, bismuth oxyhalides (BiOX) have emerged as exceptional candidates for anode materials in PIBs due to their unique structural and superior electrochemical properties. However, challenges such as structural instability and low electronic conductivity remain to be addressed. In this study, a flower-like BiOBr0.5Cl0.5/rGO composite anode material was synthesized, demonstrating outstanding K+ storage performance. The self-hybridized structure enhances ion adsorption and diffusion, which in turn improves charge and discharge efficiency as well as long-term stability. In situ X-ray diffraction (XRD) tests confirmed the gradual release and alloying potassium storage mechanism of Bi metal, which occurs through the intermediate KxBiOBr0.5Cl0.5 phase within the BiOBr0.5Cl0.5 anode. This composite exhibited a high specific capacity of 246.4 mAh/g at 50 A/g and maintained excellent capacity retention after 2400 cycles at 5 A/g. Additionally, in full battery tests, it showed good rate performance and long cycle life, maintaining a discharge specific capacity of 119.6 mAh/g at a high current density of 10 A/g. Comprehensive characterizations revealed insights into the structural, electrochemical, and kinetic properties, advancing high-performance PIBs.

Dual Activation for Tuning N, S Co-Doping in Porous Carbon Sheets Toward Superior Sodium Ion Storage

Porous carbon has been widely focused to solve the problems of low coulombic efficiency (ICE) and low multiplication capacity of Sodium-ion batteries (SIBs) anodes. The superior energy storage properties of two-dimensional(2D) carbon nanosheets can be realized by modulating the structure, but be limited by the carbon sources, making it challenging to obtain 2D structures with large surface area. In this work, a new method for forming carbon materials with high N/S doping content based on combustion activation using the dual activation effect of K2SO4/KNO3 is proposed. The synthesized carbon material as an anode for SIBs has a high reversible capacity of 344.44 mAh g-1 at 0.05 A g-1. Even at the current density of 5 Ag-1, the capacity remained at 143.08 mAh g-1. And the ICE of sodium-ion in ether electrolytes is ≈2.5 times higher than that in ester electrolytes. The sodium storage mechanism of ether/ester-based electrolytes is further explored through ex-situ characterizations. The disparity in electrochemical performance can be ascribed to the discrepancy in kinetics, wherein ether-based electrolytes exhibit a higher rate of Na+ storage and shedding compared to ester-based electrolytes. This work suggests an effective way to develop doubly doped carbon anode materials for SIBs.

Enhancing potassium ions adsorption on mesoporous carbon spheres with abundant internal surface via engineering sulfur doping sites towards superior rate capability

Mesoporous carbon spheres (MCSs) show great potential for using as high-performance anodes in potassium-ion batteries (PIBs). Design and synthesis of MCSs with suitable multiscale structures and heteroatom doping or co-doping in MCSs are successfully employed to optimize the ion and electron transportation, however, it is still a challenge to explore MCS-based anodes with satisfactory potassium storage performance. In this work, we report novel S-doped MCS samples with abundant internal surfaces for potassium storage. The S doping sites are controlled during the synthesis, and the effect of different doping sites on the potassium storage is systematically studied. It is found that S doping between the carbon layers enlarges interlayer spacing and facilitates potassium ion adsorption. Consequently, the optimized sample shows an excellent rate capability of 144 mAh/g at 5.0 A/g, and a high reversible specific capacity of 325 mAh/g after 100 cycles at 0.1 A/g with a capacity retention of 91.2%. The important role of element doping sites on ion adsorption and ion storage performance is confirmed by theoretical investigations. Controlling the doping sites in MCSs provides a new approach to designing high-performance electrodes for energy storage and conversion applications.

Densified graphene-like carbon nanosheets with enriched heteroatoms enabling superior gravimetric and volumetric potassium storage capacities

Constructing carbon electrodes with abundant heteroatoms and appropriate graphitic interlayer spacing remains a major challenge for achieving high gravimetric and volumetric potassium storage capacities with fast kinetics. Herein, we constructed 3D graphene-like N, F dual-doped carbon sheets induced by Ni template (N, F-CNS-Ni) with dense structure and rich active sites, providing a promising approach to address the facing obstacles. Highly reversible K-ion insertion/extraction is realized in the graphitic carbon structure, and K-adsorption capability is enhanced by introducing N/F heteroatoms. As a result, the N, F-CNS-Ni electrode exhibits ultrahigh gravimetric and volumetric capacities of 404.5 mA h g^-1 and 281.3 mA h cm^-3 at 0.05 A/g, respectively, and a superb capacity of 259.3 mA h g^-1 with a capacity retention ratio of 90 % even after 600 cycles at 5 A/g. This work presents a simple Ni-based template method to prepare graphene-like carbon nanosheets with high packing density and rich heteroatoms, and offers mechanism insight for achieving superior K-ion storage.

Exploring 2D Energy Storage Materials: Advances in Structure, Synthesis, Optimization Strategies, and Applications for Monovalent and Multivalent Metal-Ion Hybrid Capacitors

The design and development of advanced energy storage devices with good energy/power densities and remarkable cycle life has long been a research hotspot. Metal-ion hybrid capacitors (MHCs) are considered as emerging and highly prospective candidates deriving from the integrated merits of metal-ion batteries with high energy density and supercapacitors with excellent power output and cycling stability. The realization of high-performance MHCs needs to conquer the inevitable imbalance in reaction kinetics between anode and cathode with different energy storage mechanisms. Featured by large specific surface area, short ion diffusion distance, ameliorated in-plane charge transport kinetics, and tunable surface and/or interlayer structures, 2D nanomaterials provide a promising platform for manufacturing battery-type electrodes with improved rate capability and capacitor-type electrodes with high capacity. In this article, the fundamental science of 2D nanomaterials and MHCs is first presented in detail, and then the performance optimization strategies from electrodes and electrolytes of MHCs are summarized. Next, the most recent progress in the application of 2D nanomaterials in monovalent and multivalent MHCs is dealt with. Furthermore, the energy storage mechanism of 2D electrode materials is deeply explored by advanced characterization techniques. Finally, the opportunities and challenges of 2D nanomaterials-based MHCs are prospected.

O-Doping Configurations Reduce the Adsorption Energy Barrier of K-Ions to Improve the Electrochemical Performance of Biomass-Derived Carbon

In recent years, atomic-doping has been proven to significantly improve the electrochemical performance of biomass-derived carbon materials, which is a promising modification strategy. Among them, there are relatively few reports about O-doping. Here, porous carbon derived from orange peel was prepared by simple carbonization and airflow-annealing processes. Under the coordination of microstructure and surface groups, the derived carbon had excellent electrochemical performance for the K-ion batteries’ anode, including a high reversible specific capacity of 320.8 mAh/g, high rate performance of 134.6 mAh/g at a current density of 2000 mA/g, and a retention rate of 79.5% even after 2000 long-term cycles, which shows great application potential. The K-ion storage mechanisms in different voltage ranges were discussed by using various characterization techniques, that is, the surface adsorbed of K-ionswas in the high-potential slope area, and the intercalation behavior corresponded to the low-potential quasi-plateau area. In addition, the density functional theory calculations further confirmed that O-doping can reduce the adsorption energy barrier of K-ions, change the charge density distribution, and promote the K-ion storage. In particular, the surface Faraday reaction between the C=O group and K-ions plays an important role in improving the electrochemical properties.

Exploring the physicochemical role of Pd dopant in promoting Li-ion diffusion dynamics and storage performance of NbS2 at the atomic scale

The two-dimensional layered niobium disulfide (NbS2), as a kind of anode material for Li-ion batteries, has received great attention because of its excellent electronic conductivity and structural stability.

N, O and S co-doped hierarchical porous carbon derived from a series of samara for lithium and sodium storage: Insights into surface capacitance and inner diffusion

Efficiently selecting biomass precursors to prepare porous carbon with rich pore structure and heteroatom doping, and clearly distinguishing the storage behavior of Li⁺ and Na⁺ in porous carbon are still the key issues for the development and utilization of biomass-based carbon materials. In this work, four kinds of samara with a hollow structure are used as carbon sources to prepare an N, O and S co-doped hierarchical porous carbon. As the anode for Li/Na-ion batteries, the reversible specific capacity of N, O and S co-doped hierarchical porous carbon (HPC-UP-6) is 1072.3 mAh·g^-1 (0.0744 A·g^-1) and 333.2 mAh·g^-1 (0.1 A·g^-1), respectively. The ultra-high specific capacity reveals the rationality of preferentially selecting plant fruits with hollow structures as precursors. In addition, further comparative studies show that the contribution rate of surface-induced capacitance in sodium-ion batteries is more than 10% higher than that in lithium-ion batteries, indicating that Na⁺ tends to be stored on the surface of porous carbon. This principle of selecting biomass precursors and the new understanding of the storage mechanism of Li⁺/Na⁺ in biomass-based porous carbon can guide the design and preparation of new carbon materials with high capacity and high-rate performance.

Application of 2D Materials to Potassium-Ion Hybrid Capacitors

Metal-ion hybrid supercapacitors (MICs) are a new type of electrochemical energy storage (EES) device, consisting of a battery-type electrode and a supercapacitor (SC)-type electrode. Exhibiting the advantages of both batteries and SCs (e. g., good energy density, excellent power density and long cycle life), these advanced energy storage devices have considerable commercial application prospects. Among MICs, potassium-ion hybrid supercapacitors (PICs) have several further advantages, including abundancy of resources, low standard electrode potential, and low cost. PICs are regarded as potential substitutes for lithium- or sodium-ion hybrid supercapacitors. However, the practical applications of PICs remain limited, owing to the imbalance of kinetics and capacity between the electrodes, the slow ion/electron diffusion rate, and the poor electrode structural stability. Recently, 2D materials with distinct structures and fascinating features have elicited widespread attention for application in PICs, thus achieving significant enhancements, ranging from charge storage capacity to reaction kinetics. This Review discusses research progress in 2D materials for PICs. Firstly, the energy storage principle and development requirements of MICs are introduced. The pivotal advantages and significant roles of 2D materials in the fabrication of PICs are then discussed in detail. Lastly, the challenges and prospects of the application of 2D materials to high-performance PICs are presented.