Aggregation‐Resistant 3D Ti₃C₂T_x MXene with Enhanced Kinetics for Potassium Ion Hybrid Capacitors

Abstract

Potassium-ion hybrid capacitors have attracted increasing attention due to good energy density, high power density, and low cost. Ti 3 C 2 T x-MXene is considered as a promising anode material for K ion storage. However, undesirable stacking issues decrease its exposed area and breeds sluggish K ion transport. Herein, a facile spray-lyophilization strategy is proposed to construct stacking-resistant Ti 3 C 2 T x with 3D structures. As-prepared Ti 3 C 2 T x hollow spheres/tubes present stack resistance, a large specific surface area, and a short ion diffusion pathway. When serving as an anode material, it shows enhanced capacity and thickness-independent rate performance compared to 2D Ti 3 C 2 T x. After 10 000 cycles, a specific capacity of 122 mAh g −1 is obtained at 1 A g −1. Systematic kinetics analyses demonstrate the significance of concentration polarization on the electrode's rate ability. Furthermore, a 3D Ti 3 C 2 T x ‖hierarchical porous activated carbon (HPAC) K-ion hybrid capacitor is assembled and displays remarkable energy and power densities with energy retention of 100% after 10 000 cycles at 1 A g −1. Following this strategy, other 3D structures from nanosheets can also be obtained, such as 3D Ti 3 C 2 T x microtubes and graphene oxide nanoscrolls. This study provides a viable approach to solve the stacking issues of 2D nanosheets to promote the application of 2D materials.

Phosphorus and Oxygen Dual‐Doped Porous Carbon Spheres with Enhanced Reaction Kinetics as Anode Materials for High‐Performance Potassium‐Ion Hybrid Capacitors

“…Such excellent rate capability and energy output are superior to many reported state‐of‐the‐art hybrid capacitors, as summarized in Figure 6d. [ 52–60 ] In addition, the constructed device also shows an exceedingly high‐capacity retention of 94.5% after 30 000 cycles at 5 A g −1 with a Coulombic efficiency above 99% (Figure 6e). Meanwhile, light‐emitting diode (LED) arrays can be successfully illuminated by two lab‐assembled PIHCs connected in series (see the inset in Figure 6e).…”

“…d) Ragone plots of different hybrid capacitors according to previous works. [ 52–60 ] e) Long‐term cycle performance of the P/O‐PCS//AC device at 5 A g −1 up to 30 000 cycles. The inset displays the illuminated LED arrays powered by our fabricated P/O‐PCS//AC device.…”

Two-dimensional MXenes for electrochemical capacitor applications: Progress, challenges and perspectives

“…A K ion capacitor combining K V 2 C anode and K x MnFe(CN) 6 cathode can operate at an average volt age of 3.3 V in KPF 6 EC/DEC electrolyte and achieve an energy density of 145 Wh kg −1 at a power density of 112.6 W kg − 1 (based on the total mass of active materials). Another advanced structure designed for fast K + transport is 3D Ti 3 C 2 T x hollow spheres/tubes, which was prepared by a spray lyophilization method [272]. A K ion capacitor combining such 3D Ti 3 C 2 T x anode together with a hierarchical porous activated carbon cathode displays an energy density of 98.4 Wh kg − 1 and a power density of 7 kW kg − 1 (based on the total mass of the anode and cathode) along with cycling stability of 100% after 10,000 cycles in KPF 6 EC/DEC electrolyte.…”

Achieving High‐Performance 3D K+‐Pre‐intercalated Ti3C2Tx MXene for Potassium‐Ion Hybrid Capacitors via Regulating Electrolyte Solvation Structure

“…Among them, transition metal carbides and/or nitrides, known as MXenes, are emerging as competitive candidates owing to their high metallic conductivity and abundant surface‐active sites for efficient pseudocapacitance. The high flexibility and large interlayer distance of MXenes are especially well adapted for potassium storage [20–24] . However, MXene‐based 2D materials have a strong tendency to aggregate or restack, which blocks ionic diffusion pathways and lowers the reaction kinetics upon electrochemical cycling [25] .…”

“…Through tailoring nanostructure with different dimensions and enlarging the interlayer distance, the potassium‐ion storage capability of MXenes can be significantly improved [25, 27] . Recent reports suggest that the transformation of MXenes from multilayered 2D nanosheets to three‐dimensional (3D) architectures can effectively solve the self‐stacking issue and creates additional active sites for K + adsorption [21, 28] . The open framework is beneficial to the impregnation of electrolyte and shortens the K + transport pathway.…”