K-ion and Na-ion storage performances of Co3O4-Fe2O3 nanoparticle-decorated super P carbon black prepared by a ball milling process

Micron-Sized Nanoporous Antimony with Tunable Porosity for High-Performance Potassium-Ion Batteries

Potassium-ion batteries (KIBs) are considered favorable candidates for post-lithium-ion batteries, a quality attributed to their low cost, abundance as a resource, and high working potential (-2.93 V for K⁺/K). Owning to its relatively low potassiation potential and high theoretical capacity, antimony (Sb) is one of the most favorable anodes for KIBs. However, the large volume changes during K-Sb alloying and dealloying causes fast capacity degradation. In this report, nanoporous Sb (NP-Sb) is fabricated by an environmentally friendly vacuum-distillation method. The NP-Sb is formed via evaporating low-boiling-point zinc (Zn). The byproduct Zn can be recycled. It is further found that the morphology and porosity can be controlled by adjusting Zn-Sb composition and distillation temperature. The nanoporous structure can accommodate volume expansion and accelerate ion transport. The NP-Sb anode delivers an improved electrochemical performance. These results suggest that the vacuum-distillation method may provide a direction for the green, large-scale, and tunable fabrication of nanoporous materials.

Beyond Graphene Anode Materials for Emerging Metal Ion Batteries and Supercapacitors

Intensive research effort is currently focused on the development of efficient, reliable, and environmentally safe electrochemical energy storage systems due to  the ever-increasing global energy storage demand. Li ion battery systems have been used as the primary energy storage device over the last three decades. However, low abundance and uneven distribution of lithium and cobalt in the earth crust and the associated cost of these materials, have resulted in a concerted effort to develop beyond lithium electrochemical storage systems. In the case of non-Li ion rechargeable systems, the development of electrode materials is a significant challenge, considering the larger ionic size of the metal-ions and slower kinetics. Two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides, MXenes and phosphorene, have garnered significant attention recently due to their multi-faceted advantageous properties: large surface areas, high electrical and thermal conductivity, mechanical strength, etc. Consequently, the study of 2D materials as negative electrodes is of notable importance as emerging non-Li battery systems continue to generate increasing attention. Among these interesting materials, graphene has already been extensively studied and reviewed, hence this report focuses on 2D materials beyond graphene for emerging non-Li systems. We provide a comparative analysis of 2D material chemistry, structure, and performance parameters as anode materials in rechargeable batteries and supercapacitors.

Rechargeable potassium-ion batteries with honeycomb-layered tellurates as high voltage cathodes and fast potassium-ion conductors

Rechargeable potassium-ion batteries have been gaining traction as not only promising low-cost alternatives to lithium-ion technology, but also as high-voltage energy storage systems. However, their development and sustainability are plagued by the lack of suitable electrode materials capable of allowing the reversible insertion of the large potassium ions. Here, exploration of the database for potassium-based materials has led us to discover potassium ion conducting layered honeycomb frameworks. They show the capability of reversible insertion of potassium ions at high voltages (~4 V for K₂Ni₂TeO₆) in stable ionic liquids based on potassium bis(trifluorosulfonyl) imide, and exhibit remarkable ionic conductivities e.g. ~0.01 mS cm⁻¹ at 298 K and ~40 mS cm^–1 at 573 K for K₂Mg₂TeO₆. In addition to enlisting fast potassium ion conductors that can be utilised as solid electrolytes, these layered honeycomb frameworks deliver the highest voltages amongst layered cathodes, becoming prime candidates for the advancement of high-energy density potassium-ion batteries.

The development of potassium-ion batteries requires cathode materials that can maintain the structural stability during cycling. Here the authors have developed honeycomb-layered tellurates K₂M₂TeO₆ that afford high ionic conductivity and reversible intercalation of large K ions at high voltages.

Influence of Nonfused Cores on the Photovoltaic Performance of Linear Triphenylamine-Based Hole-Transporting Materials for Perovskite Solar Cells

The core plays a crucial role in achieving high performance of linear hole transport materials (HTMs) toward the perovskite solar cells (PSCs). Most studies focused on the development of fused heterocycles as cores for HTMs. Nevertheless, nonfused heterocycles deserve to be studied since they can be easily synthesized. In this work, we reported a series of low-cost triphenylamine HTMs (M101-M106) with different nonfused cores. Results concluded that the introduced core has a significant influence on conductivity, hole mobility, energy level, and solubility of linear HTMs. M103 and M104 with nonfused oligothiophene cores are superior to other HTMs in terms of conductivity, hole mobility, and surface morphology. PSCs based on M104 exhibited the highest power conversion efficiency of 16.50% under AM 1.5 sun, which is comparable to that of spiro-OMeTAD (16.67%) under the same conditions. Importantly, the employment of M104 is highly economical in terms of the cost of synthesis as compared to that of spiro-OMeTAD. This work demonstrated that nonfused heterocycles, such as oligothiophene, are promising cores for high performance of linear HTMs toward PSCs.

Novel Potassium-Ion Hybrid Capacitor Based on an Anode of K2Ti6O13 Microscaffolds

To fill the gap between batteries and supercapacitors requires integration of the following features in a single system: energy density well above that of supercapacitors, cycle life much longer than Li-ion batteries, and low cost. Along this line, we report a novel nonaqueous potassium-ion hybrid capacitor (KIC) that employs an anode of K₂Ti₆O₁₃ (KTO) microscaffolds constructed by nanorods and a cathode of N-doped nanoporous graphenic carbon (NGC). K₂Ti₆O₁₃ microscaffolds are studied for potential applications as the anode material in potassium-ion storage for the first time. This material exhibits an excellent capacity retention of 85% after 1000 cycles. In addition, the NGC//KTO KIC delivers a high energy density of 58.2 Wh kg^-1 based on the active mass in both electrodes, high power density of 7200 W kg^-1, and outstanding cycling stability over 5000 cycles. The usage of K ions as the anode charge carrier instead of Li ions and the amenable performance of this device suggest that hybrid capacitor devices may welcome a new era of beyond lithium.

The State and Challenges of Anode Materials Based on Conversion Reactions for Sodium Storage

Sodium-ion batteries (SIBs) have huge potential for applications in large-scale energy storage systems due to their low cost and abundant sources. It is essential to develop new electrode materials for SIBs with high performance in terms of energy density, cycle life, and cost. Metal binary compounds that operate through conversion reactions hold promise as advanced anode materials for sodium storage. This Review highlights the storage mechanisms and advantages of conversion-type anode materials and summarizes their recent development. Although conversion-type anode materials have high theoretical capacities and abundant varieties, they suffer from multiple challenging obstacles to realize commercial applications, such as low reversible capacity, large voltage hysteresis, low initial coulombic efficiency, large volume changes, and low cycling stability. These key challenges are analyzed in this Review, together with emerging strategies to overcome them, including nanostructure and surface engineering, electrolyte optimization, and battery configuration designs. This Review provides pertinent insights into the prospects and challenges for conversion-type anode materials, and will inspire their further study.

Highly nitrogen doped carbon nanofibers with superior rate capability and cyclability for potassium ion batteries

Potassium-ion batteries are a promising alternative to lithium-ion batteries. However, it is challenging to achieve fast charging/discharging and long cycle life with the current electrode materials because of the sluggish potassiation kinetics. Here we report a soft carbon anode, namely highly nitrogen-doped carbon nanofibers, with superior rate capability and cyclability. The anode delivers reversible capacities of 248 mAh g^–1 at 25 mA g^–1 and 101 mAh g^–1 at 20 A g^–1, and retains 146 mAh g^–1 at 2 A g^–1 after 4000 cycles. Surface-dominated K-storage is verified by quantitative kinetics analysis and theoretical investigation. A full cell coupling the anode and Prussian blue cathode delivers a reversible capacity of 195 mAh g^–1 at 0.2 A g^–1. Considering the cost-effectiveness and material sustainability, our work may shed some light on searching for K-storage materials with high performance.

The development of potassium ion batteries calls for cheap, sustainable, and high-performance electrode materials. Here, the authors report a highly nitrogen-doped soft carbon anode that exhibits superior rate capability and cyclability based on a surface dominated charge storage mechanism.

Recent research progress in non-aqueous potassium-ion batteries

The recent research progress in non-aqueous potassium-ion batteries is summarized and the challenges and future research opportunities are briefly discussed.