Lignin organic molecule aggregate derived turbine-like nanocarbon with high nitrogen doping for potassium ion hybrid capacitors

Potassium-ion hybrid capacitors (PIHCs) represent a burgeoning class of electrochemical energy storage devices characterized by their remarkable energy and power densities. Utilizing amorphous carbon derived from sustainable biomass presents an economical and environmentally friendly option for anode material in high-rate potassium-ion storage applications. Nevertheless, the potassium-ion storage capacity of most biomass-derived carbon materials remains modest. Addressing this challenge, nitrogen doping engineering and the design of distinctive nanostructures emerge as effective strategies for enhancing the electrochemical performance of amorphous carbon anodes. Developing highly nitrogen-doped nanocarbon materials is a challenging task because most lignocellulosic biomasses lack nitrogen functional groups. In this work, we propose a general strategy for directly carbonizing supermolecule-mediated lignin organic molecular aggregate (OMA) to prepare highly nitrogen-doped biomass-derived nanocarbon. We obtained lignin-derived, highly nitrogen-doped turbine-like carbon (LNTC). Featuring a three-dimensional turbine-like structure composed of amorphous, thin carbon nanosheets, LNTC demonstrated a capacity of 377 mAh g-1 when used as the anode for PIHCs. This work also provides a new synthesis method for preparing highly nitrogen-doped nanocarbon materials derived from biomass.

Versatile potassium vanadium fluorophosphate (KVPO4F) composites as Dual-Function cathode and anode materials for Potassium-Ion hybrid capacitors

Potassium-based energy storage has emerged as a promising alternative for advanced energy storage systems, driven by the abundance of potassium, fast ion migration, and low standard electrode potential. Hybrid capacitors, which combine the desirable characteristics of batteries and supercapacitors, offer a compelling solution for efficient energy storage. In this study, we present the development of versatile composite materials, specifically potassium vanadium fluorophosphate (KVPO4F) composites, utilizing a sol-gel method. These composites enable tunable potassium storage and charge transport kinetics within regulated voltage windows, serving as both cathode and anode materials. The anode composite, composed of KVPO4F and hierarchical porous carbon (HPC), exhibited exceptional stability over 400 cycles within a low-voltage window. On the other hand, the cathode composite, consisting of battery-like KVPO4F and physisorption activated carbon (AC), demonstrated great potential as a cathode material, striking a balance between specific energy and cycle life within a regulated high-voltage window. By integrating KVPO4F/C as the anode and KVPO4F/AC as the cathode, we successfully created potassium-ion hybrid capacitors (PIHCs) that showcased an impressive capacity retention of 83% after 10,000 cycles within a high voltage window of 0.5-4.3 V. Furthermore, to explore the application of these materials in miniaturized energy storage, we fabricated potassium-ion micro hybrid capacitors (PIMHCs) with interdigitated electrodes. These devices exhibited a high areal energy density of 18.8 μWh cm-2 at a power density of 111.6 μW cm-2, indicating their potential for compact energy storage systems. The results of this study demonstrate the versatility and efficacy of the developed KVPO4F composite materials, highlighting their potential for future advancements in potassium-based energy storage technologies.

3D ordered amorphous and porous TiO(2) framework anode with low insertion barrier and fast kinetics for K-ion hybrid capacitors

TiO₂ is considered as a low cost, long-term stable, and safe anode for high power K-ion hybrid capacitors (KICs) due to its abundant reserve, small volume expansion rate, and sloping voltage plateau that avoids K-ion plating at high voltage polarization. However, the enhancement of its low capacity and sluggish kinetics caused by poor electroconductivity and high insertion barrier is still challenging to further develop high-performance KICs. Herein, the reduced graphene oxide (rGO) is embedded in the walls of 3D ordered macro-/mesoporous TiO₂ (termed as TiO₂@rGO framework) to create intimate TiO₂/rGO interfaces, ensuring the effectively electron transportation during potassiation/depotassiation of TiO₂ while maintaining rapid ions/electrolyte diffusion. Furthermore, the controlled amorphous TiO₂ framework can further lower the lattice insertion energies, contributing to a fast accommodation of K-ion. As expected, the amorphous TiO₂@rGO framework (TiO₂@rGO-1) exhibits a superior rate capability (148.8 mAh g^-1 at 5 A g^-1) and cycling stability (171.2 mAh g^-1 at 1 A g^-1 after 800 cycles). The assembled KICs can reach a high energy/power density of 125.2 Wh kg^-1/4267.4 W kg^-1 as well as a long-term lifespan. This tactic provides a reliable and general way to design a TiO₂-based anode with fast kinetics toward high-performance KICs.

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

Amorphous carbons are promising anodes for high-rate potassium-ion batteries. Most low-temperature annealed amorphous carbons display unsatisfactory capacities. Heteroatom-induced defect engineering of amorphous carbons could enhance their reversible capacities. Nevertheless, most lignocellulose biomasses lack heteroatoms, making it a challenge to design highly heteroatom-doped carbons (> 10 at%). Herein, we report a new preparation strategy for amorphous carbon anodes. Nitrogen/sulfur co-doped lignin-derived porous carbons (NSLPC) with ultra-high nitrogen doping levels (21.6 at% of N and 0.8 at% of S) from renewable lignin biomacromolecule precursors were prepared through a supramolecule-mediated pyrolysis strategy. This supermolecule/lignin composite decomposes forming a covalently bonded graphitic carbon/amorphous carbon intermediate product, which induces the formation of high heteroatom doping in the obtained NSLPC. This unique pyrolysis chemistry and high heteroatom doping of NSLPC enable abundant defective active sites for the adsorption of K+ and improved kinetics. The NSLPC anode delivered a high reversible capacity of 419 mAh g‒1 and superior cycling stability (capacity retention of 96.6% at 1 A g‒1 for 1000 cycles). Potassium-ion hybrid capacitors assembled by NSLPC anode exhibited excellent cycling stability (91% capacity retention for 2000 cycles) and a high energy density of 71 Wh kg-1 at a power density of 92 W kg-1.

A General Self-Sacrifice Template Strategy to 3D Heteroatom-Doped Macroporous Carbon for High-Performance Potassium-Ion Hybrid Capacitors

Potassium-ion hybrid capacitors (PIHCs) tactfully combining capacitor-type cathode with battery-type anode have recently attracted increasing attentions due to their advantages of decent energy density, high power density, and low cost; the mismatches of capacity and kinetics between capacitor-type cathode and battery-type anode in PIHCs yet hinder their overall performance output. Herein, based on prediction of density functional theory calculations, we find Se/N co-doped porous carbon is a promising candidate for K⁺ storage and thus develop a simple and universal self-sacrifice template method to fabricate Se and N co-doped three-dimensional (3D) macroporous carbon (Se/N-3DMpC), which features favorable properties of connective hierarchical pores, expanded interlayer structure, and rich activity site for boosting pseudocapacitive activity and kinetics toward K⁺ storage anode and enhancing capacitance performance for the reversible anion adsorption/desorption cathode. As expected, the as-assembled PIHCs full cell with a working voltage as high as 4.0 V delivers a high energy density of 186 Wh kg^-1 and a power output of 8100 W kg^-1 as well as excellent long service life. The proof-of-concept PIHCs with excellent performance open a new avenue for the development and application of high-performance hybrid capacitors.

Cocoon Silk-Derived, Hierarchically Porous Carbon as Anode for Highly Robust Potassium-Ion Hybrid Capacitors

Potassium-ion hybrid capacitors (KIHCs) have attracted increasing research interest because of the virtues of potassium-ion batteries and supercapacitors. The development of KIHCs is subject to the investigation of applicable K+ storage materials which are able to accommodate the relatively large size and high activity of potassium. Here, we report a cocoon silk chemistry strategy to synthesize a hierarchically porous nitrogen-doped carbon (SHPNC). The as-prepared SHPNC with high surface area and rich N-doping not only offers highly efficient channels for the fast transport of electrons and K ions during cycling, but also provides sufficient void space to relieve volume expansion of electrode and improves its stability. Therefore, KIHCs with SHPNC anode and activated carbon cathode afford high energy of 135 Wh kg-1 (calculated based on the total mass of anode and cathode), long lifespan, and ultrafast charge/slow discharge performance. This study defines that the KIHCs show great application prospect in the field of high-performance energy storage devices.