Crystal structure and cation-anion interactions of potassium (Difluoromethanesulfonyl) (trifluorome thanesulfonyl)imide.

Sulfonimide salts are of great interest for battery use thanks to their special properties including sufficient superior chemical/thermal stabilities, structural flexibility, etc. In particular, the hydrogen-containing sulfonimide (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide anion {[N(SO2CF2H) (SO2CF3)]-, DFTFSI-}, stands out owing to its suppressed anion mobility and superior electrochemical properties. We herein report the structural analyses of potassium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide {K [N(SO2CF2H) (SO2CF3)], KDFTFSI} by virtue of single crystal X-ray diffraction and computational approaches. Our results reveal that KDFTFSI crystallizes in a orthorhombic cell (space group: Pbcn) comprising of cationic and anionic layers, which is similar to the conventional sulfonimide salt, potassium bis(trifluoromethanesulfonyl)imide {K [N(SO2CF3)2], KTFSI}. Gas-phase density functional theory calculations show that the conversion from trans to cis DFTFSI- anions is hindered due to the presence of stabilizing intramolecular H-bonding interactions in the trans conformer; yet interaction with K+ substantially minimizes the energy difference between the two conformers due to the formation of strong tridentate K+ coordination with oxygen atoms in the cis KDFTFSI. This work is anticipated to provide further understanding on the structure-property relations of hydrogenated sulfonimide anions, and thus inspire the structural design of new anions for battery research.

Organocatalytic Enantioselective Vinylcyclopropane-Cyclopentene (VCP-CP) Rearrangement.

We have demonstrated that the catalytic and enantioselective vinylcyclopropane-cyclopentene rearrangement can be carried out on (vinylcyclopropyl)acetaldehydes through activation via enamine intermediates. The reaction makes use of racemic starting materials that, upon ring opening facilitated by the catalytic generation of a donor-acceptor cyclopropane, deliver an acyclic iminium ion/dienolate intermediate in which all stereochemical information has been deleted. The final cyclization step forms the rearrangement product, showing that chirality transfer from the catalyst to the final compound is highly effective and leads to the stereocontrolled formation of a variety of structurally different cyclopentenes.

Single Lithium Ion Conducting "Binderlyte" for High-Performing Lithium Metal Batteries.

Rechargeable lithium metal batteries (LMBs) are deemed as a viable solution to improve the power and/or energy density of the contemporary lithium-ion batteries (LIBs). However, poor Li-ion diffusivity within high-energy cathodes causes sluggish kinetics of the corresponding redox reactions particularly at high C-rates, thereby largely impeding the performance of rechargeable LMBs. In this work, a dual-functional single Li-ion conducting polysalt is proposed as both catholyte and binding agent (coined "Binderlyte") for rechargeable LMBs. The designed Binderlyte is thermally and electrochemically stable, allowing its use for high-energy cathodes like Li(Ni1/3 Mn1/3 Co1/3 )O2 (NMC111). The implementation of designer Binderlyte endows the Li° || NMC111 cell with superior cycling stability and capacity retention even at an extremely high C-rate of 10C. In particular, the soft and flexible nature of the Binderlyte allows the thick NMC cathode to operate at extremely low porosity (20 vol%) with almost no capacity decay. This work may provide a paradigm shift on the design of innovative polymeric materials, which are essential for developing high-performing rechargeable LMBs.

Anion π-π Stacking for Improved Lithium Transport in Polymer Electrolytes.

Polymer electrolytes (PEs) with excellent flexibility, processability, and good contact with lithium metal (Li°) anodes have attracted substantial attention in both academic and industrial settings. However, conventional poly(ethylene oxide) (PEO)-based PEs suffer from a low lithium-ion transference number (TLi+), leading to a notorious concentration gradient and internal cell polarization. Here, we report two kinds of highly lithium-ion conductive and solvent-free PEs using the benzene-based lithium salts, lithium (benzenesulfonyl)(trifluoromethanesulfonyl)imide (LiBTFSI) and lithium (2,4,6-triisopropylbenzenesulfonyl)(trifluoromethanesulfonyl)imide (LiTPBTFSI), which show significantly improved TLi+ and selective lithium-ion conductivity. Using molecular dynamics simulations, we pinpoint the strong π-π stacking interaction between pairs of benzene-based anions as the cause of this improvement. In addition, we show that Li°âˆ¥Li° and Li°âˆ¥LiFePO4 cells with the LiBTFSI/PEO electrolytes present enhanced cycling performance. By considering π-π stacking interactions as a new molecular-level design route of salts for electrolyte, this work provides an efficient and facile novel strategy for attaining highly selective lithium-ion conductive PEs.

Stable non-corrosive sulfonimide salt for 4-V-class lithium metal batteries.

Rechargeable lithium metal (Li0) batteries (RLMBs) are considered attractive for improving Li-ion batteries. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) has been extensively used as a conducting salt for RLMBs due to its advantageous stability and innocuity. However, LiTFSI-based electrolytes are corrosive towards aluminium (Al0) current collectors at low potentials (>3.8 V versus Li/Li+), thereby excluding their application in 4-V-class RLMBs. Herein, we report on a non-corrosive sulfonimide salt, lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide (LiDFTFSI), that remarkably suppresses the anodic dissolution of the Al0 current collector at high potentials (>4.2 V versus Li/Li+) and significantly improves the cycling performance of Li(Ni1/3Mn1/3Co1/3)O2 (NMC111) cells. In addition, this sulfonimide salt results in the growth of an advantageous solid electrolyte interphase on the Li0 electrode. The replacement of either LiTFSI or LiPF6 with LiDFTFSI endows a Li0||NMC111 cell with superior cycling stability and capacity retention (87% at cycle 200), demonstrating the decisive role of the salt anion in dictating the electrochemical performance of RLMBs.

Enhanced Lithium-Ion Conductivity of Polymer Electrolytes by Selective Introduction of Hydrogen into the Anion.

The anion chemistry of lithium salts plays a pivotal role in dictating the physicochemical and electrochemical performance of solid polymer electrolytes (SPEs), thus affecting the cyclability of all-solid-state lithium metal batteries (ASSLMBs). The bis(trifluoromethanesulfonyl)imide anion (TFSI- ) has long been studied as the most promising candidate for SPEs; however, the Li-ion conductivities of the TFSI-based SPEs still remain low (Li-ion transference number: ca. 0.2). In this work, we report new hydrogen-containing anions, conceived based on theoretical considerations, as an electrolyte salt for SPEs. SPEs comprising hydrogen-containing anions achieve higher Li-ion conductivities than TFSI-based ones, and those anions are electrochemically stable for various kinds of ASSLMBs (Li-LiFePO4 , Li-S, and Li-O2 batteries). This opens up a new avenue for designing safe and high-performance ASSLMBs in the future.

Electrolyte Additives for Room-Temperature, Sodium-Based, Rechargeable Batteries.

Owing to resource abundance, and hence, a reduction in cost, wider global distribution, environmental benignity, and sustainability, sodium-based, rechargeable batteries are believed to be the most feasible and enthralling energy-storage devices. Accordingly, they have recently attracted attention from both the scientific and industrial communities. However, to compete with and exceed dominating lithium-ion technologies, breakthrough research is urgently needed. Among all non-electrode components of the sodium-based battery system, the electrolyte is considered to be the most critical element, and its tailored design and formulation is of top priority. The incorporation of a small dose of foreign molecules, called additives, brings vast, salient benefits to the electrolytes. Thus, this review presents progress in electrolyte additives for room-temperature, sodium-based, rechargeable batteries, by enlisting sodium-ion, Na-O2 /air, Na-S, and sodium-intercalated cathode type-based batteries.

Organocatalytically Generated Donor-Acceptor Cyclopropanes in Domino Reactions. One-Step Enantioselective Synthesis of Pyrrolo[1,2-a]quinolines.

An easy and straightforward procedure has been developed for the synthesis of highly enantioenriched pyrrolo[1,2-a]quinolines through a one-pot process that comprises a domino cyclopropane ring opening/aza-Michael/aldol reaction followed by acid-promoted lactamization. The key feature of the synthetic approach relies on the ability of conveniently functionalized cyclopropaneacetaldehydes to undergo organocatalytic activation by a chiral secondary amine that enables the catalytic generation of a donor-acceptor cyclopropane. This intermediate has the potential to undergo a ring opening that generates an electrophilic α,ß-unsaturated iminium ion that subsequently reacts through the already mentioned domino sequence and in which stereochemical information is very efficiently transferred from the amine catalyst to the final products. Moreover, one of the alkoxycarbonyl moieties can be easily removed by standard hydrolysis/decarboxylation, providing access to the target adducts as single stereoisomers.

Enantioselective Synthesis of Tertiary Propargylic Alcohols under N-Heterocyclic Carbene Catalysis.

A straightforward procedure to carry out the enantioselective benzoin reaction between aldehydes and ynones by employing a chiral N-heterocyclic carbene (NHC) as catalyst was developed. Under the optimized reaction conditions, these ynones undergo a clean and selective 1,2-addition with the catalytically generated Breslow intermediate, not observing any byproduct arising from competitive Stetter-type reactivity. This procedure allows the preparation of tertiary alkynyl carbinols as highly enantioenriched materials, which have the remarkable potential to be used as chiral building blocks in organic synthesis.