Potassium Bis Research Articles

Unraveling the role of ion-solvent chemistry in stabilizing small-molecule organic cathode for potassium-ion batteries

Redox-active organic cathodes are promising high-capacity and low-cost electrode materials for potassium-ion batteries (KIBs), but usually suffer from poor cyclability due to the severe dissolution and notorious K dendrites. Herein, the effects of salt concentrations and solvents on the performance of potassium-organic batteries based on a typical phenothiazine derivative, methylene blue (MB), are explored, and the high-concentration potassium bis(fluorosulfonyl)amide-based ether electrolyte is versatile to achieve long lifespan. The high donor number and strong solvation ability of ether solvent endow MB cathode with high voltage plateaus and reversible capacity as compared to the carbonate counterpart. Moreover, the enhanced interactions of K+-ether and anion-participated ion-ether complexes in concentrated electrolyte not only decrease the amount of free solvent, but also contribute to forming highly ionic-conducting and thin anion-derived interphase layers, which effectively mitigate the shuttle effect and inhibit K dendrite growth. Consequently, MB cathode exhibits a high capacity of 139.5 mAh g−1 after 500 cycles at 0.1 A g−1, and long-term cycling stability for 4500 cycles. The good performance of full cells matched with graphite anode further demonstrates the feasibility of MB as KIB cathode. This work highlights the roles of ion-solvent chemistry in stabilizing small-molecule organic cathodes, which may bring new insights in the electrolyte design for wide organic electrode-based battery systems.

Toward a 1,4-Diphosphinine-Based Molecular CPS-Ternary Compound.

Synthesis of the tricyclic 1,3-dithiole-2-thione-derived 1,4-dihydro-1,4-diphosphinine is presented using a base-induced ring formation protocol and chloro(diethylamino)(1,3-dithiole-2-thion-4-yl)phosphane as the starting point. P-oxidation reactions of dihydrodiphosphinine by chalcogens led to bis(P-oxide), bis(P-sulfide), or bis(P-selenide), respectively; all tricyclic compounds were obtained as cis/trans mixtures. 1,4-Dihydro-1,4-diphosphinine was converted into 1,4-dichloro-1,4-dihydro-1,4-diphosphinine. This compound is almost insoluble in organic solvents, furnished selectively the trans-bis(amino) derivative upon a 2-fold P-substitution reaction with the weak nucleophile potassium bis(trimethylsilyl)amide, and reacted also with alcohols ROH (R = nBu, iPr, tBu) to give cis/trans mixtures of the corresponding bis(alkoxy) derivatives. Furthermore, the dichloro derivative could be reduced to a 1,4-diphosphinine using PnBu3, but, unfortunately, the stubbornly insoluble product could be neither purified nor crystallized. Despite this, we achieved a thermal [4 + 2] cycloaddition reaction of this first CPS-ternary compound with diethylacetylene dicarboxylate to obtain the corresponding diphosphabarrelene, thus providing indirect evidence for the aromatic tricyclic diphosphinine. Detailed density functional theory studies on the formation of 1,4-diphosphinine provided insights into formation pathways as well as NMR, IR, and UV/vis data.

Highly stable potassium metal batteries enabled by regulating surface chemistry in ether electrolyte

Rechargeable potassium (K) metal batteries (PMBs) remain deeply challenged by the lack of suitable electrolytes that are stable against both highly reactive K anodes and 4 V-class cathodes. Despite their good reductive stability with K metal, classic potassium bis(fluorosulfonyl)amide (KFSI)-based ether electrolytes are typically used only in <4.0 V PMBs due to their limited oxidation stability. Herein, a potassium nitrate (KNO3)-containing ether electrolyte, at a moderate KFSI concentration (2.3 M) rather than a high concentration (normally, >3 M), is reported for the first time to be used in 4 V-class PMBs. A stable N/F-rich solid electrolyte interphase (SEI) is formed, enabling dense and uniform K deposition, especially under high current density. Remarkably, the PMBs with Prussian blue cathode exhibits an unprecedented cycle life (1000 cycles, 122 days). This work provides new perspectives of electrolyte design for 4 V-class PMBs.

Hypergolic Hybrid Rocket Engine Ignition and Relights with Mixed Oxides of Nitrogen

Combined with a common fuel binder, solid hypergols can simplify the overall complexity of hybrid rocket engines, as the fuel grain can be ignited and reignited without any external power source or external fluid. Also, with the hypergolic additive embedded in the binder, the flame zone could be placed at the surface of the grain itself, thereby providing heat to the grain to maximize regression rate and promote combustion sustainability. The objective of this study was to demonstrate hypergolic ignition and successive relights of a 2-in motor grain configuration, with a paraffin-based fuel and MON-3 (3 wt % nitric oxide in nitrogen tetroxide) as the oxidizer. With sodium amide and potassium bis(trimethylsilyl)amide as solid hypergolic additives, the study focused on the influence of the additive type, loading, location, and format on the grain ignition delay and combustion sustainability. Hypergolic ignition was achieved with grain configurations composed of a front segment with 90 wt % additive and the main grain with loadings of additive from 40 down to 0 wt %. Two-s single burn tests provided regression rate estimates for the different grain combinations. Grain ignition delays varied between and , depending on the grain configuration, with efficiencies between 64% and 98%.

Mono- and Dinuclear Aluminium Complexes Derived from Biguanide and Carbothiamide Ligands

Dianionic N,N-chelating ligands play a crucial role in coordination chemistry, but reports on related complexes remain limited to certain types of ligands. In here, the reactions of two diprotic ligands, i.e., a biguanide and a carbothiamide, with trimethylaluminium, are reported, which give rise to mono- and dinuclear aluminium(III) complexes. In addition, single deprotonation of the diprotic biguanide using potassium bis(trimethylsilyl)amide gives rise to a one-dimensional coordination polymer. All complexes have been fully characterized, and their solid-state structures were determined by single crystal X-ray diffraction analysis.

A novel dopant for spiro-OMeTAD towards efficient and stable perovskite solar cells

2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD), as the most common used hole transport material (HTM), plays a significant role in the normal structured (n-i-p) high-efficiency perovskite solar cells (PSCs). In general, it is prepared by a halogen solvent (chlorobenzene, CBZ) and needs an ion dopant (lithium bis (trifluoromethanesulfonyl)imide, Li-TFSI) to improve its conductivity and hole mobility. However, such a halogen solvent is not environmentally friendly and the widely used Li-TFSI dopant would affect the stability of PSCs. Herein, we develop a non-halogen solvent—tetrahydrofuran (THF)-prepared spiro-OMeTAD solution with a new p-type dopant, potassium bis(fluorosulfonyl)imide (K-FSI), to apply into PSCs. By this strategy, high-hole-mobility spiro-OMeTAD film is achieved. Meanwhile, the potassium ions introduced by diffusion into perovskite surface passivate the interfacial defects. Therefore, a hysteresis-free champion PSC with an efficiency of 21.02% is obtained, along with significantly improved stability against illumination and ambient conditions. This work provides a new strategy for HTMs toward hysteresis-free high-efficiency and stable PSCs by substituting dopants.

Increasing the Lithium Ion Mobility in Poly(Phosphazene)-Based Solid Polymer Electrolytes through Tailored Cation Doping

Solid polymer electrolytes (SPEs) are promising candidates for usage in rechargeable lithium metal batteries (LMBs) as they possess high mechanical, thermal, and chemical stability. However, the poor ionic conductivity of SPEs in comparison to liquid electrolytes hampers the commercialization of SPE-based LMBs. In the case of poly[bis(methoxy-ethoxy-ethoxy-)phosphazene] (MEEP), one explanation for the low ionic conductivity is the trapping of lithium cations in backbone coordination sites, hindering lithium ion movement through the electrolyte membrane. Herein, modelling the ion coordination in MEEP using DFT calculations reveals that, compared to lithium, heavier alkali cations are more likely to be complexed at the backbone coordination sites. With other alkali cations masking these coordination sites, enhanced lithium ion mobility through the SPE is expected. Experimental data proves these expectations: doping MEEP-based LiBOB-containing SPE membranes with small amounts of in-house synthesized potassium bis(oxalato)borate (KBOB) increases the lithium ion transference number from 0.08 to 0.18. Also, the partial lithium ion conductivity of the salt-in-MEEP electrolyte is boosted to outstanding 0.08 mS cm−1, far exceeding state-of-the-art literature values for this material. A cross-check using SPEs based on the structurally similar poly(ethylene oxide) (PEO) validates the proposed cation displacement model. The obtained insights may aid the development of highly effective poly(phosphazene)-based SPEs.

Novel Quasi-Liquid K-Na Alloy as a Promising Dendrite-Free Anode for Rechargeable Potassium Metal Batteries.

Rechargeable potassium metal batteries are promising energy storage devices with potentially high energy density and markedly low cost. However, eliminating dendrite growth and achieving a stable electrode/electrolyte interface are the key challenges to tackle. Herein, a novel “quasi‐liquid” potassium‐sodium alloy (KNA) anode comprising only 3.5 wt% sodium (KNA‐3.5) is reported, which exhibits outstanding electrochemical performance able to be reversibly cycled at 4 mA cm–2 for 2000 h. Moreover, it is demonstrated that adding a small amount of sodium hexafluorophosphate (NaPF6) into the potassium bis(fluorosulfonyl)imide electrolyte allows for the formation of the “quasi‐liquid” KNA on electrode surface. Comprehensive experimental studies reveal the formation of an unusual metastable KNa2 phase during plating, which is believed to facilitate simultaneous nucleation and suppress the growth of dendrites, thereby improving the electrode's cycle lifetime. The “quasi‐liquid” KNA‐3.5 anode demonstrates markedly enhanced electrochemical performance in a full cell when pairing with Prussian blue analogs or sodium rhodizonate dibasic as the cathode material, compared to the pristine potassium anode. Importantly, unlike the liquid KNA reported before, the “quasi‐liquid” KNA‐3.5 exhibits good processability and can be readily shaped into sheet electrodes, showing substantial promise as a dendrite‐free anode in rechargeable potassium metal batteries.

Electrolyte Salt Chemistry Enables 3D Nitrogen and Phosphorus Dual‐Doped Graphene Aerogels for High‐Performance Potassium‐Ion Batteries

AbstractPotassium‐ion batteries (PIBs) have attracted tremendous attentions for scalable electrical energy storage owing to the abundant K resources. Heteroatom co‐doped hard carbon is considered to be a reliable material to boost ion transport and provide active sites for reversible potassium storage. Herein, N/P dual‐doped 3D graphene aerogels (NPGAs) with hierarchical pores, enlarged interlayer distance, and high doping level are successfully synthesized, which exhibit outstanding electrochemical performance for PIBs. A detailed comparative study found that promoted coulombic efficiency, improved specific capacity (507 mAh g−1 at 100 mA g−1 after 100 cycles) and excellent cycle performance (106 mAh g−1 at 5000 mA g−1 after 3000 cycles) can be reached by replacing KPF6 with potassium bis(fluorosulfonyl)imide (KFSI). Further kinetic analysis reveals that NPGAs present more capacitive behavior of K‐ion, low resistance, and fast K‐ion conductivity by virtue of the advanced solid electrolyte interphase (SEI) film formed in KFSI‐EC/DEC electrolyte. Ex situ XPS, SEM, and TEM all confirm a physical flexible, chemical stable, and inorganic SEI layer formed on the surface of the electrode. In general, this work promotes a deep understanding of the mechanism of potassium storage and provides more opportunities for practical PIBs.

Synthesis, cytotoxicity assessment and antioxidant activity of some new thiazol‐2‐yl carboxamides

AbstractDependence on the biological activity of 2‐aminothiazole, the synthesis and chemical reactions of ethyl 3‐oxo‐3‐(thiazol‐2‐ylamino)propanoate (1) with some different reagents were described for cytotoxic and antioxidant evaluation. The new derivatives 2–19 could be synthesized and characterized by correct analytical and spectral data. In addition to the thiazole ring, these compounds contain 2H‐1,2,3‐triazole (3), 1H‐pyrazole (5, 12), 1,3‐dithiane (7), benzothiazole (10), thiazolidine (13), thiazolidinone (14, 15), 2H‐chromene (17), pyridine (19) moieties. The preparation of compounds 2–19 was performed through the formation of the isolable 2‐(2‐phenylhydrazineylidene) 2, 2‐dimethylaminomethylidene 4, 2‐phenylcarbamothioyl 9, 2‐(methylthio)(phenylamino) methylidene 11 and non‐isolable potassium bis(thiolate) 6, potassium thiolate 8 intermediates from precursor 1. The activity of these derivatives 1–19 against human lung fibroblast (WI38) and human prostate cancer (PC3) were examined in vitro using the MTT assay. The assessment of their antioxidant activities was carried out by following the ABTS method to evaluate their pharmaceutical importance.

A High-Voltage Potassium-Ion Battery with a Potassium Manganese Hexacyanoferrate Cathode

Potassium-ion batteries (KIBs) are a promising complementary technology to lithium-ion batteries that have the potential to be more sustainable and lower in cost. In KIBs lithium is replaced with potassium, the copper current collector is replaced with aluminium, and cathodes can be cobalt and nickel free. KIBs have the crucial advantage over sodium-ion batteries that potassium can reversibly intercalate into graphite whilst sodium cannot. Graphite offers a low operating voltage, high capacity, and good rate performance as a potassium-ion anode material.There remain significant scientific challenges in the development of commercial potassium-ion batteries, notably developing high-capacity high-voltage cathode materials and electrolytes that are compatible with high-voltage cathodes and graphite anodes. In a recent perspective we identified potassium manganese hexacyanoferrate (KMF) as the most promising cathode material as it offers high energy density whilst also being low in cost [1]. However, the cyclability and coulombic efficiency of KMF are typically poor owing to parasitic reactions from water remaining in its structure and aluminium current collector corrosion among other mechanisms.Here we present recent work to improve the performance of the KMF//graphite electrochemical system. Firstly, the citrate-assisted synthesis of KMF is optimised using high throughput synthesis and characterisation techniques to reduce the defect and water content whilst tailoring the particle size [2]. Secondly, an ionic-liquid based electrolyte, 1 M KFSI in Pyr1,3FSI (potassium bis(fluorosulfonyl)imide in N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide)), is employed. This electrolyte successfully forms a passivating layer on the KMF cathode and surpresses aluminium corrosion which enables highly efficient cycling. Additionally, graphite operates exceptionally well with this same ionic-liquid based electrolyte.We will end by offering our perspective on the current state of this research area and promising research directions.

Unraveling the mechanical origin of stable solid electrolyte interphase

Summary The capability of a solid electrolyte interphase (SEI) in accommodating deformation is critical to the electrode integrity. However, the nanoscale thickness and environmental sensitivity of SEI make it challenging to characterize multiple mechanical parameters and identify an appropriate predictor for such capability. Here, we develop a feasible atomic force microscopy (AFM)-based nanoindentation test that circumvents the interference of the anode substrate and allows accurate probing of Young's modulus and elastic strain limit of SEI. The "maximum elastic deformation energy" (U) that an SEI can absorb is proposed to predict the stability of the SEI, as successfully demonstrated in Li/K metal anodes. We show that another asset of U is to provide a rapid and effective means to screen proper electrolytes for the stabilization of Sn and Sb microparticle anodes through building high-U SEIs. Overall, this new indicator, U, offers future directions toward rational design of robust SEIs for advanced anodes.

Covalent sulfur as stable anode for potassium ion battery

The potassium bis(fluoro-sulfonyl)imide(KFSI)-based electrolyte has great application prospects in potassium ion batteries (PIBs). However, their development has been limited by the decomposition of electrolytes and the corrosion of Al foils (current collector) at high potential. Here, a N-doping, sulfur-rich chemically bonded porphyrin organic framework (SPOF) with a high potential plateau were synthesized as an anode to lower the redox potential of full cells and further inhibit the corrosion of Al foils. SPOF as anode delivers high reversible capacity (557 mAh g−1 at 50 mA g−1), excellent cycling performance (94% capacity retention over 1000 cycles at 500 mA g−1), and superior rate performance. Meanwhile, the ex-situ FTIR, Raman, and HRTEM revealed the stability of N-doping and the reversible covalent sulfur and S–S bonds changes during potassiation/depotassiation. In addition, full cells using SPOF anode and PTCDA cathode showed outstanding performance (high capacity of 300 mAh g−1 at 200 mA g−1). And the Al current collector of the full cell was not corroded after 150 cycles. Yet, the Al foils with PTCDA as cathode were seriously corroded. This work provides a new strategy for realizing ultra-high reversible capacity and cyclic stability of PIBs, and also accelerates the process of early commercial application of PIBs.

Spectroscopic and Electrochemical Analyses for Dysprosium Complexes In Potassium Bis(trifluoromethylsulfonyl)amide Melts

The coordination states of multivalent dysprosium complexes of potassium bis(trifluoromethylsulfonyl) amide (K[NTf2]) were investigated by Raman spectroscopy. The concentration dependence of the deconvoluted Raman spectra was investigated for 0.23−0.45 mol kg−1 Dy(III), and a mixed sample of Dy(II)/Dy(III) (molar ratio 1/3), in K[NTf2]. Using conventional analysis, the solvation number, n, of the dysprosium complexes was determined to be 4.12 for Dy(II) and 5.09 for Dy(III). The electrochemical behavior of [DyIII(NTf2)5]2– in K[NTf2] melts was also investigated in this study. It is speculated that the first reduction peak at approximately +2.24 V probably corresponds to the formation of [DyII(NTf2)4]2–. Electrochemical analysis revealed that the reduction peak of [DyIII(NTf2)5]2– at approximately +0.81 V at 483 K is based on an electrodeposition reaction from [DyIII(NTf2)5]2– to Dy(0). The diffusion coefficient and activation energy of [DyIII(NTf2)5]2– in K[NTf2] melts were measured in the range 473–493 K by semi-integral and semi-differential analyses. Furthermore, the nucleation behavior of [DyIII(NTf2)5]2– was evaluated using chronoamperometry. The results indicated that the nucleation mechanism of Dy nuclei changed from instantaneous to progressive nucleation when the overpotential became more negative than the deposition potential of Dy(0). The electrodeposits were identified as mostly the metallic state by X-ray photoelectron spectroscopy.

Sodium and Potassium Complexes of Anionic N‐Heterocyclic Carbenes

AbstractThe reaction of 1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene (IDipp) with n‐BuLi in the presence of sodium and potassium bis(trimethylsilyl)amide was studied, and the resulting polymeric dicarbene species were reacted with the fluoroboranes tris(pentafluorophenyl)borane, B(C6F5)3, and tris[3,5‐bis(trifluoromethyl)phenyl]borane, B(m‐XyF6)3 to produce sodium and potassium salts of an anionic N‐heterocyclic carbene with a weakly coordinating borate moiety (WCA‐NHC).

Reversible potassium-ion intercalation into graphite electrodes in glyoxal-based electrolytes

In this work the use of the solvents 1,1,2,2-tetramethoxyethan (tetramethylglyoxal, TMG) and 1,1,2,2-tetraethoxyethan (tetraethylglyoxal, TEG) in potassium-based systems is reported for the first time. We show that utilizing electrolytes based on these solvents, potassium bis(fluorosulfonyl)imide (KFSI) and the additive vinyl ethylene carbonate (VEC), it is possible to reversibly intercalate and extract potassium-ions into and from graphite electrodes. Graphite electrodes in combination with the electrolyte 1.5 M KFSI in TEG/VEC display an intercalation capacity of 200 mAh g−1, stable for 40 cycles at C/10. This performance is comparable to that achieved with conventional organic electrolytes.

CuP2 as high-capacity and long-cycle-life anode for potassium-ion batteries

Metal phosphides have shown great potential for potassium-ion batteries because of their high theoretical specific capacity. Nevertheless, most of the metal phosphide anodes are plagued by rapid capacity decay (caused by the large volume changes during the discharge/charge process), which would restrict their further practical application. Herein, a chemically bonded CuP2/C composite was prepared by a facile high-energy ball milling method. A potassium bis(trifluoromethanesulfonyl)imide (KFSI)-based electrolyte was adopted instead of a conventional KPF6-based electrolyte for the CuP2/C composite anode. Benefiting from the synergistic effects of the formation of strong P–O–C chemical bonds and the KFSI-based electrolyte, the CuP2/C composite anode exhibited high reversible capacity (451.4 mAh g−1 at 50 mA g−1), excellent rate performance (123.5 mAh g−1 at 1000 mA g−1), and superior cycling stability (300 mAh g−1 after 100 cycles). This work paves the way for the development of high-performance CuP2 anode for potassium-ion batteries.

Asymmetric Total Synthesis of Phomarol

Asymmetric Total Synthesis of Phomarol

Promoting operating voltage to 2.3 V by a superconcentrated aqueous electrolyte in carbon-based supercapacitor

Aqueous supercapacitors (SCs) have attracted more and more attention for their safety, fast charge/discharge capability and ultra-long life. However, the application of aqueous SCs is limited by the low working voltage due to the narrow electrochemical stability window (ESW) of water. Herein, we report a new “water in salt” (WIS) electrolyte by dissolving potassium bis (fluorosulfonyl) amide (KFSI) in water with an ultra-high mass molar concentration of 37 mol/kg. The highly concentrated electrolyte can achieve a wide ESW of 2.8 V. The WIS electrolyte enables a safe carbon-based symmetrical supercapacitor to operate stably at 2.3 V with an ultra-long cycle life and excellent rate performance. The energy density reaches 20.5 Wh/kg at 2300 W/kg, and the capacity retention is 83.5% after 50,000 cycles at a current density of 5 A/g. This new electrolyte will be a promising candidate for future high-voltage aqueous supercapacitors.

Manipulating the Solvation Structure of Nonflammable Electrolyte and Interface to Enable Unprecedented Stability of Graphite Anodes beyond 2 Years for Safe Potassium-Ion Batteries.

Potassium-ion batteries (PIBs) are attractive for low-cost and large-scale energy storage applications, in which graphite is one of the most promising anodes. However, the large size and the high activity of K+ ions and the highly catalytic surface of graphite largely prevent the development of safe and compatible electrolytes. Here, a nonflammable, moderate-concentration electrolyte is reported that is highly compatible with graphite anodes and that consists of fire-retardant trimethyl phosphate (TMP) and potassium bis(fluorosulfonyl)imide (KFSI) in a salt/solvent molar ratio of 3:8. It shows unprecedented stability, as evidenced by its 74% capacity retention over 24 months of cycling (over 2000 cycles) at the 0.2 C current rate. Electrolyte structure and surface analyses show that this excellent cycling stability is due to the nearly 100% solvation of TMP molecules with K+ cations and the formation of FSI- -derived F-rich solid electrolyte interphase (SEI), which effectively suppresses the decomposition of the solvent molecules toward the graphite anode. Furthermore, excellent performance on high-mass loaded graphite electrodes and in a full cell with perylenetetracarboxylic dianhydride cathode is demonstrated. This study highlights the importance of the compatibility of both electrolyte and the interface, and offers new opportunities to design the electrolyte-SEI nexus for safe and practical PIBs.