A thermoresponsive composite separator loaded with paraffin@SiO_(2) microparticles for safe and stable lithium batteries

Lithium-ion batteries (LIBs)-related accidents have been reported for years and safety issues are stumbling blocks for the practical applications of lithium metal batteries (LMBs) with higher energy density. More effective strategies to shut down the battery at the early stage of thermal runaway with less side effects on the electrochemical performance are greatly desired. In this work, the core–shell structural paraffin@SiO_(2) microparticles were synthesized by in situ emulsion interfacial hydrolysis and polycondensation and the paraffin@SiO_(2)-loaded separator (PSS) was prepared by a facile filtration method. The introduction of hydrophilic silica shells in paraffin@SiO_(2) enhanced the wettability of carbonate electrolyte with the composite separator and improved the processability of soft paraffin. As a result, when used in LMBs at room temperature, the cell with PSS inside had a more uniform deposition of lithium, a much lower overpotential and a more stable electrochemical performance than the cell with the blank separator or the conventional pure paraffin-loaded separator inside. More significantly, when a heating stimulation (i.e. 115 ℃) was subjected to the cell with PSS inside, the paraffin in the core of paraffin@SiO_(2) could be released, blocking the gaps between particles and the pores in the separator and efficiently stopping the transportation of Li+ between two electrodes, resulting in the thermally-induced shutdown of the cell below the melting temperature of PE (~135 ℃) in the Celgard2325 separator. The core–shell structure of paraffin@SiO_(2) enables the maintaining of each component’s benefits while avoiding each one’s drawbacks by elaborating microstructural design. Therefore, the conventional dilemma between the electrochemcial performance and safety of LMBs could be solved in the future.

Regulating the growth of lithium dendrite by coating an ultra-thin layer of gold on separator for improving the fast-charging ability of graphite anode

With the ever-growing application of lithium-ion batteries(LIBs), their fast-charging technology has attracted great interests of scientists. However, growth of lithium dendrites during fast charge of the bat teries with high energy density may pose great threats to the operation and cause serious safety issues Herein, we prepared a functional separator with an ultra-thin(20 nm) layer of Au nanoparticles deposited by evaporation coating method which could regulate growth direction and morphology of the lithium dendrites, owing to nearly zero overpotential of lithium meal nucleation on lithiated Au. Once the Li den drites are about to form on the graphite anode during fast charging(or lithiation), they plate predomi nantly on the Au deposited separator rather than on the graphite. Such selective deposition does no compromise the electrochemical performance of batteries under normal cycling. More importantly, i enables the better cycling stability of batteries at fast charge condition. The Li/Graphite cells with Au nanoparticles coated separator could cycle stably with a high areal capacity retention of 90.5% over 95 cycles at the current density of 0.72 m A cm^(-2). The functional separator provides an effective strategy to adjust lithium plating position at fast charge to ensure high safety of batteries without a compromise on the energy density of LIBs.

Zwitterionic Matrix with Highly Delocalized Anionic Structure as an Efficient Lithium Ion Conductor

The leakage and volatilization of liquid electrolytes raise potential safety risks in the development of electrochemical energy storage devices with high energy density.Herein,novel solid-state zwitterionic materials containing sulfonyl imide as a highly delocalized anionic structure were synthesized for highly targeted lithium ion conducting matrices.The influences of the molecular structure characteristics on thermal behavior and electrochemical property were investigated comprehensively.Due to the weak Coulomb interaction between the sulfonyl imide moiety and cationic species,the rationally designed zwitterionic electrolytes showed a high conductivity of 0.44 mS cm^(-1).And the obtained high lithium ion transference number of 0.43 is four times higher than that of the widely employed sulfonate analogues.Additionally,excellent cycling stability of the lithium plating/stripping process and super resistance to electrochemical oxidation(up to 5.5 V)were observed.This molecular engineering strategy for lithium ion conductor advances new possibilities for developing solvent-free and non-migrating electrolyte matrix materials for lithium metal batteries.