Potassium Metal Anodes Research Articles

In situ healing of dendrites in a potassium metal battery

The use of potassium (K) metal anodes could result in high-performance K-ion batteries that offer a sustainable and low-cost alternative to lithium (Li)-ion technology. However, formation of dendrites on such K-metal surfaces is inevitable, which prevents their utilization. Here, we report that K dendrites can be healed in situ in a K-metal battery. The healing is triggered by current-controlled, self-heating at the electrolyte/dendrite interface, which causes migration of surface atoms away from the dendrite tips, thereby smoothening the dendritic surface. We discover that this process is strikingly more efficient for K as compared to Li metal. We show that the reason for this is the far greater mobility of surface atoms in K relative to Li metal, which enables dendrite healing to take place at an order-of-magnitude lower current density. We demonstrate that the K-metal anode can be coupled with a potassium cobalt oxide cathode to achieve dendrite healing in a practical full-cell device.

An amalgam route to stabilize potassium metal anodes over a wide temperature range.

Potassium metal anodes are very appealing due to their high theoretical capacity (687 mA h g-1), but violent reactivity and severe dendrite issues hinder their practical application. Here we report the in situ fabrication of an amalgam layer to stabilize potassium anodes over a wide temperature range of -20-40 °C.

Tutorial review on structure – dendrite growth relations in metal battery anode supports

This tutorial review explains the emerging understanding of the surface and bulk chemistry - electrochemical performance relations in anode supports (aka secondary current collectors, substrates, templates, hosts) for lithium, sodium and potassium metal batteries (LMBs, SMBs or NMBs, and KMBs or PMBs). In relation to each section, the possible future research directions that may yield both new insight and improved cycling behavior are explored. Representative case studies from Li, Na and K metal anode literature are discussed. The tutorial starts with an overview of the solid electrolyte interphase (SEI), covering both the "classic" understanding of the SEI structure and the "modern" insights obtained by site-specific cryogenic stage TEM analysis. Next, the multiple roles of supports in promoting cycling stability are detailed. Without an optimized support architecture, the metal-electrolyte interface becomes geometrically unstable at a lower current density and cycle number. Taking into consideration the available literature on LMBs, SMBs and KMBs, it is concluded that effective architectures are geometrically complex and electrochemically lithiophilic, sodiophilic or potassiophilic, so as to promote conformal electrochemical wetting of the metal during plating/stripping. One way that philicity is achieved is through support oxygen surface chemistry, which yields a reversibly reactive metal-support interface. Examples of this include the well-known oxygen-carbon moieties in reduced graphene oxide (rGO), as well as classic ion battery reversible conversion reaction oxides such as SnO2. Unreactive surfaces lead to dewetted island growth of the metal, which is a precursor to dendrites, and possibly to non-uniform dissolution. Surveying the literature on various Li, Na and K metal supports, it is concluded that the key bulk thermodynamic property that will predict electrochemical wetting behavior is the enthalpy of infinite solution (ΔsolH∞) of the metal (solute) into the support (solvent). Large and negative ΔsolH∞ promotes uniform metal wetting on the support surface, corresponding to relatively low plating overpotential. Positive ΔsolH∞ promotes dewetted islands and a relatively high overpotential. This simple rule explains a broad range of studies on Li, Na and K metal - support interactions, including the previously reported correlation between mutual solubility and wetting.

Enhanced surface binding energy regulates uniform potassium deposition for stable potassium metal anodes

A SnO2-coated carbon fiber mat is fabricated and used to guide uniform K nucleation/deposition for dendrite free K metal anodes.

Three dimensional Ti3C2 MXene nanoribbon frameworks with uniform potassiophilic sites for the dendrite-free potassium metal anodes.

Potassium (K) metal batteries hold great promise as an advanced electrochemical energy storage system because of their high theoretical capacity and cost efficiency. However, the practical application of K metal anodes has been limited by their poor cycling life caused by dendrite growth and large volume changes during the plating/stripping process. Herein, three-dimensional (3D) alkalized Ti3C2 (a-Ti3C2) MXene nanoribbon frameworks were demonstrated as advanced scaffolds for dendrite-free K metal anodes. Benefiting from the 3D interconnected porous structure for sufficient K accommodation, improved surface area for low local current density, preintercalated K in expanded interlayer spacing, and abundant functional groups as potassiophilic nuleation sites for uniform K plating/stripping, the as-formed a-Ti3C2 frameworks successfully suppressed the K dendrites and volume changes at both high capacity and current density. As a result, the a-Ti3C2 based electrodes exhibited an ultrahigh coulombic efficiency of 99.4% at a current density of 3 mA cm−2 with long lifespan up to 300 cycles, and excellent stability for 700 h even at an ultrahigh plating capacity of 10 mA h cm−2. When matched with K2Ti4O9 cathodes, the resulting a-Ti3C2–K//K2Ti4O9 full batteries offered a greatly enhanced rate capacity of 82.9 mA h g−1 at 500 mA g−1 and an excellent cycling stability with high capacity retention (77.7% after 600 cycles) at 200 mA g−1, demonstrative of the great potential of a-Ti3C2 for advanced K-metal batteries.

Dendrite-Free Potassium Metal Anodes in a Carbonate Electrolyte.

Potassium (K) metal anodes suffer from a challenging problem of dendrite growth. Here, it is demonstrated that a tailored current collector will stabilize the metal plating-stripping behavior even with a conventional KPF6 -carbonate electrolyte. A 3D copper current collector is functionalized with partially reduced graphene oxide to create a potassiophilic surface, the electrode being denoted as rGO@3D-Cu. Potassiophilic versus potassiophobic experiments demonstrate that molten K fully wets rGO@3D-Cu after 6 s, but does not wet unfunctionalized 3D-Cu. Electrochemically, a unique synergy is achieved that is driven by interfacial tension and geometry: the adherent rGO underlayer promotes 2D layer-by-layer (Frank-van der Merwe) metal film growth at early stages of plating, while the tortuous 3D-Cu electrode reduces the current density and geometrically frustrates dendrites. The rGO@3D-Cu symmetric cells and half-cells achieve state-of-the-art plating and stripping performance. The symmetric rGO@3D-Cu cells exhibit stable cycling at 0.1-2 mA cm-2 , while baseline Cu prematurely fails when the current reaches 0.5 mA cm-2 . The half-cells cells of rGO@3D-Cu (no K reservoir) are stable at 0.5 mA cm-2 for 10 000 min (100 cycles), and at 1 mA cm-2 for 5000 min. The baseline 3D-Cu, planar rGO@Cu, and planar Cu foil fails after 5110, 3012, and 1410 min, respectively.

MXene-Based Dendrite-Free Potassium Metal Batteries.

Potassium metal batteries are considered as attractive alternatives beyond lithium-ion batteries. However, uncontrollable dendrite growth on the potassium metal anode has restrained their practical applications. A high-performance potassium anode achieved by confining potassium metal into a titanium-deficient nitrogen-containing MXene/carbon nanotube freestanding scaffold is reported. The high electronic transport and fast potassium diffusion in this scaffold enable reduced local current density and homogeneous ionic flux during plating/stripping processes. Furthermore, as verified by theoretical calculations and experimental investigations, such "potassium-philic" MXene sheets can induce the nucleation of potassium, and guide potassium to uniformly distribute in the scaffold upon cycling. Consequently, the as-developed potassium metal anodes exhibit a dendrite-free morphology with high Coulombic efficiency and long cycle life during plating/stripping processes. Such anodes also deliver significantly improved electrochemical performances in potassium-sulfur batteries compared with bare potassium metal anodes. This work can provide a new avenue for developing potassium metal-based batteries.

Capillary Encapsulation of Metallic Potassium in Aligned Carbon Nanotubes for Use as Stable Potassium Metal Anodes

AbstractMetallic potassium (K) is a desirable anode for potassium secondary batteries due to its low electrode potential in nonaqueous electrolytes and high theoretical capacity. Nevertheless, instability caused by dendritic growth, large volume changes, and parasitic side reactions hamper its practical application. Here, an anode containing metallic K is fabricated by infiltrating an aligned carbon nanotube membrane (ACM) with molten K because of its good wettability to molten K due to the strong capillary forces. The K metal is spatially distributed on the 3D ACM framework, which offers sufficient electrode/electrolyte contact for charge transfer. The robust ACM host provides a large number of K nucleation sites and physically confines the K deposited there, thus mitigating dimensional changes during cycling. The pathways for electrons and ions in the anode are associated to form a mixed conducting network, which is beneficial for the electrochemical redox. Consequently, the anode shows stable plating/stripping profiles with low polarization in symmetric cells using conventional carbonate‐based electrolytes. In addition, dendrite growth is suppressed, and the anode demonstrates excellent suitability when paired with a Prussian blue cathode in a full cell. This design strategy is expected to provide a way to address the problems with using metallic K anodes.

Thousands of cycles.

Potassium–air batteries, which suffer from oxygen cathode and potassium metal anode degradation, can be cycled thousands of times when an organic anode replaces the metal.

Simultaneous Stabilization of Potassium Metal and Superoxide in K-O2 Batteries on the Basis of Electrolyte Reactivity.

In superoxide batteries based on O2 /O2- redox chemistry, identifying an electrolyte to stabilize both the alkali metal and its superoxide remains challenging owing to their reactivity towards the electrolyte components. Bis(fluorosulfonyl)imide (FSI- ) has been recognized as a "magic anion" for passivating alkali metals. The KFSI-dimethoxyethane electrolyte passivates the potassium metal anode by cleavage of S-F bonds and the formation of a KF-rich solid-electrolyte interphase (SEI). However, the KFSI salt is chemically unstable owing to nucleophilic attack by superoxide and/or hydroxide species. On the other hand, potassium bis(trifluorosulfonyl)imide (KTFSI) is stable to KO2 , but results in mossy potassium deposits and irreversible plating and stripping. To circumvent this dilemma, we developed an artificial SEI for the metal anode and thus long-cycle-life K-O2 batteries. This study will guide the development of stable electrolytes and artificial SEIs for metal-O2 batteries.

Simultaneous Stabilization of Potassium Metal and Superoxide in K–O2 Batteries on the Basis of Electrolyte Reactivity

AbstractIn superoxide batteries based on O2/O2− redox chemistry, identifying an electrolyte to stabilize both the alkali metal and its superoxide remains challenging owing to their reactivity towards the electrolyte components. Bis(fluorosulfonyl)imide (FSI−) has been recognized as a “magic anion” for passivating alkali metals. The KFSI–dimethoxyethane electrolyte passivates the potassium metal anode by cleavage of S−F bonds and the formation of a KF‐rich solid–electrolyte interphase (SEI). However, the KFSI salt is chemically unstable owing to nucleophilic attack by superoxide and/or hydroxide species. On the other hand, potassium bis(trifluorosulfonyl)imide (KTFSI) is stable to KO2, but results in mossy potassium deposits and irreversible plating and stripping. To circumvent this dilemma, we developed an artificial SEI for the metal anode and thus long‐cycle‐life K–O2 batteries. This study will guide the development of stable electrolytes and artificial SEIs for metal–O2 batteries.

Role of Magnetism and Disorder in Tuning the Electrochemical Properties of the Discharge Product in K-O2 Batteries

The energy density of batteries can be increased by utilizing metal-air batteries, allowing longer driving ranges in electric vehicles. Li-air and Na-air batteries have been investigated, but they come with many issues such as low efficiency, limited capacity, and poor cycle life. Potassium-air batteries have not been investigated nearly as much, but they have a high theoretical energy density of 935 Wh/kg, around three times that of Li-ion batteries. It has been shown that K-air batteries have the lowest reported overpotential of 20-50mV in metal-oxygen batteries, which gives a very high-energy efficiency of 98% [1]. This battery comprises of a potassium metal anode, carbon cathode, and an electrolyte, with potassium superoxide (KO2) as the discharge product growing on the cathode [1]. This discharge product is thermodynamically stable and commercially available, unlike the discharge products of Li-air and Na-air batteries. However, there is very limited knowledge on the discharge product. Given a better understanding on the various phases and properties of the discharge product, we could tune the properties of KO2 to have desirable electrochemical characteristics. For example, we could use a magnetic substrate to alter the properties of the formed discharge product, such as the electronic conductivity of KO2. Electronic conductivity of the discharge product is key to increasing the capacity of the discharge cycle, as seen in Li-air and Na-air batteries [5]. In this work, we will use density functional theory (DFT) to explore the role of magnetism and disorder of the discharge product (KO2) in K-air batteries. We have calculated the formation energy of three different structures of potassium superoxide using the BEEF-vdW functional, in order to determine the most stable phase for both the antiferromagnetic and ferromagnetic configurations. The results of the calculations can be seen in Table I, and agree with previous work that using a metal-chloride reference for calculating the formation energy significantly reduces the mean absolute error (MAE), as well as the variation in calculated energy across various functionals [3]. The BEEF ensemble results as shown in Table II illustrates how the scheme using the metal chloride reference gives the least standard deviation across the various functionals. Table III reveals that the ferromagnetic state is the more stable structure, which disagrees with experimental results that KO2 is paramagnetic at room temperature, and antiferromagnetic at temperatures below 7K [4]. Thus, we will explore the more disordered phases of KO2 under various temperatures, including the tetragonal, monoclinic, and triclinic structures with different orientations of the oxygen dimers [4]. We will report on energetics of these phases within the random phase approximation (RPA). We will discuss the band structures and the band gaps for these various phases and its implications for K-O2 batteries. Lastly, we will explore the possibility of magnetic substrates preferentially nucleating and growing KO2 phases with high electronic conductivity to maximize the battery capacity. [1] X. Ren, Y. Wu, JACS, (2013). [2] X. Ren et al., Adv. Energy Mater., (2016). [3] R. Christensen, J. S. Hummelshoj, H. A. Hansen, T. Vegge, J. Phys. Chem. C, (2015). [4] M. Labhart, D. Raoux, and W. Kanzig, PRB, Volume 20, Number 1, (1979). [5] V. Viswanathan, K. S. Thygesen, J. S. Hummelshoj, J. K., Norskov, G. Girishkumar, B. D. McCloskey, A. C. Luntz, J. Chem. Phys., (2011). Figure 1

Reversible Dendrite-Free Potassium Plating and Stripping Electrochemistry for Potassium Secondary Batteries

Rechargeable potassium metal batteries have recently emerged as alternative energy storage devices beyond lithium-ion batteries. However, potassium metal anodes suffer from poor reversibility during plating and stripping processes due to their high reactivity and unstable solid electrolyte interphase (SEI). Herein, it is reported for the first time that a potassium bis(fluoroslufonyl)imide (KFSI)-dimethoxyethane (DME) electrolyte forms a uniform SEI on the surface of potassium enabling reversible potassium plating/stripping electrochemistry with high efficiency (∼99%) at ambient temperature. Furthermore, the superconcentrated KFSI-DME electrolyte shows excellent electrochemical stability up to 5 V (vs K/K+) which enables good compatibility with high-voltage cathodes. Full cells with potassium Prussian blue cathodes are demonstrated. Our work contributes toward the understanding of potassium plating/stripping electrochemistry and paves the way for the development of potassium metal battery technologies.

Stable Carbon Cathodes for Potassium-Oxygen Batteries

Among energy storage technologies beyond lithium-ion, alkali metal-oxygen batteries stand out for their unparalleled theoretical energy densities. Based on the reaction between dioxygen and alkali metal ions in non-aqueous electrolytes, metal-oxygen batteries could store up to 10 times more energy per unit mass (in the case of Li-O2) when compared to today’s lithium-ion batteries1. Despite extensive efforts elucidating the mechanism of the reaction between alkali cations and dioxygen, this technology is still far from maturing into a commercial device. The main drawbacks of Li-O2 systems are electrolyte and cathode instability, low conductivity of lithium peroxide (Li2O2) leading to poor cycleability. In contrast to Li-O2, potassium-O2 discharge reactions proceeds via a one electron reduction leading to potassium superoxide (KO2) as the sole discharge product2-5. Here, different carbon based cathodes were investigated in K-O2 cells. Furthermore the stability of the K metal anode with different non-aqueous electrolytes was compared. The cell capacity varied depending upon the cathodic carbon structure employed (Figure 1a). KO2 was the only discharge product identified via Raman spectroscopy (Figure 1b) and powder X-ray diffraction. FTIR spectra taken of the cathodes after first discharge, showed no evidence of carbonate species or other parasitic reaction products. These results are encouraging, since the large overpotential observed within Li-O2 cells was found to be related to side reactions on the carbon electrode surface6. The voltage gap in K-O2 cells was lower than 100 mV, and round trip efficiency, as high as 98%. The cycleability of the cells was found to be limited by side reactions between the potassium metal anode and ether-based electrolyte in the presence of dioxygen reduced species, rather than side reactions within the carbon cathode. The main components of this insulating anode surface layer were K2CO3, KOH and KO2. Similar anode surface layer composition was found for different combinations of ether electrolytes and potassium salts. However, while using super-concentrated electrolytes (3M and 5 M KTFSI in dimethoxyethane), O2 crossover was inhibited, and no KO2 was detected on the potassium metal anode surface. As a result, these cells were able to be cycled over 50 times under shallow cycling of 50 mAh/g. The superconcentrated electrolytes had no effect on the cathode reaction product, and the battery cycled through KO2 formation and oxidation. Capacity fade eventually occurred, as repetitive stripping/plating of K metal anode caused the disruption of the protective layer. This work highlights that once a suitable electrolyte has been selected, a metal-O2 cell can indeed be cycled numerous times. The challenge is to increase the cycleable capacity to more appealing values, whilst maintaining cell stability. [1] P.G. Bruce, S.A. Freunberger, L.J. Hardwick, J-M. Tarascon, Nature Mater. 11, 19 (2012). [2] X. Ren, Y. Wu, J. Am. Chem. Soc. 135, 2923 (2013). [3] X. Ren et al. ACS Appl. Mater. Interfaces 6, 19299 (2014). [4] W.D. McCulloch et al. ACS Appl. Mater. Interfaces 7, 26158 (2015). [5] X. Ren et. al. Adv. Energy. Mater. 1601080 (2016). [6] B.D. McCloskey et. al. J. Phys. Chem. Lett. 4, 2989 (2013). Figure 1

A low cost, high energy density, and long cycle life potassium-sulfur battery for grid-scale energy storage.

A potassium-sulfur battery using K(+) -conducting beta-alumina as the electrolyte to separate a molten potassium metal anode and a sulfur cathode is presented. The results indicate that the battery can operate at as low as 150 °C with excellent performance. This study demonstrates a new type of high-performance metal-sulfur battery that is ideal for grid-scale energy-storage applications.

T13.1 Triage® PlGF test: point-of-care assay of plasma placental growth factor to diagnose pre-eclampsia

In this chapter, we start with the lithium metal anode to introduce the basic concepts of solid electrolyte interphase (SEI) and its impacts on the electrode morphology with an emphasis on the SEI heterogeneities in the lateral direction that may explain the initial whisker protrusion behavior. As a complement to many recent review articles on sodium and potassium metal anodes, we then introduce the most promising electrolytes that have successfully enabled stable SEIs, smooth deposits and high Coulombic efficiencies in both half- and full cells. Future research directions for each alkali metal anode are also discussed.