Atomic structure of sensitive battery materials and interfaces revealed by cryo–electron microscopy

storage. [3] Recently, as a result of the abundance of K, potassium-ion batteries (PIBs) provide a cheaper alternative to LIBs and thus attract more attention. [4] The standard electrode potential of K/K + (−2.93 V vs E 0 ) is close to Li/Li + (−3.04 V vs E 0 ) in aqueous system, even lower than Li/Li + in nonaqueous electrolytes, [5] indicating that PIBs would potentially perform at a higher voltage/power operation. Additionally, recent studies have shown that high-energy metal-O 2 batteries based on K metal have higher round-trip efficiency than their Li and Na counterparts because potassium superoxide, the species generated in the O 2 cathode, is both thermodynamically and kinetically stable. [6] Using K metal anodes poses a particular challenge because K is highly reactive and reacts spontaneously with solvents and salt anions, forming a solid-electrolyte interphase (SEI) layer on the K surface. [7] However, the SEI layer is not optimized to accommodate large volume change during K plating/stripping, resulting in the unrecoverable cracking of the SEI layer. These phenomena will become serious especially at high deposition capacity. Furthermore, the resultant inhomogeneities in resistance and ion flux on SEI layer drive the morphologically nonuniform K growth (dendrite, granule, etc.) that could induce internal short-circuit and other serious safety hazards. [8] This highlights a compelling issue regarding safe cyclability of metal anode, that is, how to regulate the surface reactivity of metal toward organic electrolytes. However, the Secondary batteries based on earth-abundant potassium metal anodes are attractive for stationary energy storage. However, suppressing the formation of potassium metal dendrites during cycling is pivotal in the development of future potassium metal-based battery technology. Herein, a promising artificial solid-electrolyte interphase (ASEI) design, simply covering a carbon nanotube (CNT) film on the surface of a potassium metal anode, is demonstrated. The results show that the spontaneously potassiated CNT framework with a stable self-formed solid-electrolyte interphase layer integrates a quasi-hosting feature with fast interfacial ion transport, which enables dendrite-free deposition of potassium at an ultrahigh capacity (20 mAh cm −2 ). Remarkably, the potassium metal anode exhibits an unprecedented cycle life (over 1000 cycles, over 2000 h) at a high current density of 5 mA cm −2 and a desirable areal capacity of 4 mAh cm −2 . Dendrite-free morphology in carbon-fiber and carbon-black-based ASEI for potassium metal anodes, which indicates a broader promise of this approach, is also observed.

Section: Formation and Characterization Of A Stable Asei Layer On K Msupporting

confidence: 62%

Artificial Solid‐Electrolyte Interphase Enabled High‐Capacity and Stable Cycling Potassium Metal Batteries

Wang

Dong

et al. 2019

“…[67] Although the above advanced characterization techniques are helping to understand the lithium dendrite growth behavior in a given condition such as gel electrolyte or glass capillary cell, [68] they can only qualitatively or semiquantitatively analyze the formation of lithium dendrites and partially understand the failure mechanisms of lithium anodes. Owing to the high sensitivity of in situ NMR, it could be employed to simply and accurately monitor the early formation stages of lithium dendrites in lithium metal batteries.…”

Section: Discussionmentioning

confidence: 99%

A Material Perspective of Rechargeable Metallic Lithium Anodes

Wang

Yang

2018

111

Rechargeable lithium‐based batteries are long considered as the most promising candidates for application in various electronic devices, electric vehicles, and even electrical grids owing to their ultrahigh energy densities. However, to date, metallic lithium‐based batteries are still far from practical applications due to the low Coulombic efficiency and fast capacity decay of lithium anodes. The poor electrochemical performances of metallic lithium anodes are inherently related to random growth of lithium dendrites and infinite volume charge of lithium anodes. In this review, the failure mechanisms of metallic lithium anodes are summarized and ascribed to the unstable and inhomogeneous solid electrolyte interphase, uneven distributions of electric field, and lithium‐ion flux during the lithium plating processes. Correspondingly, efficient strategies for mitigating these problems, including surficial engineering, electric field, and lithium‐ion flux regulation are discussed from the perspective of anode materials. Finally, an outlook is proposed for the design and fabrication of next‐generation rechargeable metallic lithium anodes that aims to address the intrinsic problems of metallic lithium anodes.

“…While compared with the pristine sample, the thickness decreases to ≈7 µm in the s-KBir sample after ion exchange, which decreases the K + ion diffusion pathway. This phenomenon is probably ascribed to the loss of lattice water upon the acquirement of TEM image, [31] which is actually sensitive to the interlayer H 2 O content. This phenomenon is probably ascribed to the loss of lattice water upon the acquirement of TEM image, [31] which is actually sensitive to the interlayer H 2 O content.…”

Section: Structure Of K-birnessitementioning

confidence: 99%

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

Gao

Guo

et al. 2018

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...