K‐Birnessite Electrode Obtained by Ion Exchange for Potassium‐Ion Batteries: Insight into the Concerted Ionic Diffusion and K Storage Mechanism

Abstract

kind of secondary batteries will find promising applications in large-scale energy storage. [3] Owing to the low-cost [4] and low standard potential [5] of potassium (K), KIBs could in principle offer cost-effectiveness and higher energy density, which would lead to a substantial advance in energy storage technology. The fast K + ion diffusion property provides the possibility of saving the charging time of KIBs as the next generation energy storage and transport devices. [6] Then compared with Na-ion battery (NIB), a huge advantage lies in the application of graphite anode for KIB, [7] which is not feasible for Na + insertion into the graphite. [8] And also, the weaker Lewis acidity of K + ions ensures smaller solvated ions, leading to the higher mobility and larger transference number in electrolytes and lower desolvation energy, which offers faster K + ion diffusion kinetics with regard to that of Li + or Na + ions. [4,9] Based on these advantages, many investigations on the available anode materials for KIBs, such as carbonaceous materials, [8a,10] oxides, [11] sulfides, [12] organic materials, [13] alloy, [5] prussian blue analogues, [14] etc., have been reported continuously in the past few decades, [2a,15] however, fewer studies are devoted to the development of cathode. Present cathodes could be summarized as the layered transition metal oxides, [16] polyanions and pyrophosphates, [17] prussian blue analogs, [18] nanostructured iron composite, [19] organic materials, [20] and other potential materials. Up to now, most of the available studies are working on screening for new electrode materials with enhanced electrochemical performance, while the underlying K storage and transport mechanism in the electrode materials is lack of exploration and comprehension. [2a,21] Therefore, studying the electrochemical behavior of potassium ions is very important for building a better KIBs system.In specific, alkali transition metal oxides (AMO 2 : A = Li, Na, K; M = Ni, Co, Mn, Fe, etc.) with layered structure have been widely studied as promising cathodes for rechargeable batteries, [22] because of the topotactic de/intercalation feature. However, the accommodation of the bulky K + ion is less favorable than that of Li + and Na + ion in such compact structures, [2a] which will plausibly hinder the K + ion diffusion kinetics. [23] Previous reports [16e,24] have shown the sluggish diffusion performance of K + ions in KIBs with alkali transition Novel and low-cost rechargeable batteries are of considerable interest for application in large-scale energy storage systems. In this context, K-Birnessite is synthesized using a facile solid-state reaction as a promising cathode for potassium-ion batteries. During synthesis, an ion exchange protocol is applied to increase K content in the K-Birnessite electrode, which results in a reversible capacity as high as 125 mAh g −1 at 0.2 C. Upon K + exchange the reversible phase transitions are verified by in situ X-ray diffraction (XRD) characterization. The underlying mechani...

Birnessite Nanosheet Arrays with High K Content as a High‐Capacity and Ultrastable Cathode for K‐Ion Batteries

“…As demonstrated by the FESEM images in Figure S13 (Supporting Information), the nanosheet morphology of S2 is well retained even after the long‐term cycling, demonstrating superior structural stability of the high K content birnessite. A comparison of PIB electrochemical performance between the as‐presented S2 electrode and other reported cathodes is shown in Figure f and Table S4 (Supporting Information),3a–e,8,16,17 indicating that the electrochemical performance reported in this work, in terms of specific capacity, cycling stability, and rate capability, has surpassed the records of previously reported PIB cathodes, and “hydrothermal potassiation” is an effective strategy to develop high‐performance cathode materials for advanced PIBs.…”

Review on Recent Advances of Cathode Materials for Potassium‐ion Batteries

“…Due to the low cost and their relatively high redox potentials, Birnessite has attracted much attention among layered metal oxide materials, but the low K content in Birnessite limits its reversible capacity and leads to poor structural stability. Recently, a K‐Birnessite was synthesized by a solid‐state reaction, and this high K content K‐Birnessite electrode exhibited a reversible capacity as high as 125 mAh g −1 at 0.2 C . Latterly, Birnessite nanosheet arrays (K 0.77 MnO 2 ·0.23H 2 O) were prepared by “hydrothermal potassiation,” and demonstrated a high reversible specific capacity of about 134 mAh g −1 at 100 mA g −1 …”

Kinetics Enhanced Nitrogen‐Doped Hierarchical Porous Hollow Carbon Spheres Boosting Advanced Potassium‐Ion Hybrid Capacitors

“…Potassium‐based electrochemical energy storage devices (PEES) have been exhibiting a promising application prospect due to its much higher natural abundance than lithium, and lower redox potential and solvated ionic radius than sodium . So far, potassium‐ion batteries (PIBs) are the most attracting PEES, and extensive research efforts have been carried out on the exploitation of a new generation of PIBs recently . However, similar to other alkali metal ion batteries, PIBs suffer from inferior cycling lifespan (typically less than 500 cycles) and insufficient power density .…”