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(Ni_1/3 Mn_1/3 Co_1/3 )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 (T_Li⁺), 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 T_Li⁺ 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°∥Li° and Li°∥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(Ni_1/3Mn_1/3Co_1/3)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.