Ionic liquids (ILs) have been extensively studied as promising electrolytes for lithium batteries owing to their highly conductive and thermally stable characteristics. Although their low t Li + and fluid nature can lead to weakened rate capability and higher leakage risks, these challenges can be tackled by incorporating ILs into solid hosts with controlled properties. Herein, we designed a heterogeneous metal organic framework (MOF)/polymerized ionic network (PIN) core-shell composite as a porous host for IL, DEME-TFSI. The PIN shell with abundant ionic structures not only exhibit nice compatibility with ILs to achieve high loading, but also provide transfer pathways through its charged backbone to fasten Li + transference; while the MOF core has narrow nanopores to confine large ions in ILs and enhance Li + selectivity. The as-synthesized conductive solid electrolyte (HKUST@PIN-IL-Li) showed intergrated merits of both MOF and PIN, including high IL loading, high ionic conductivity over 4×10 -4 S cm -1 at 25 o C and increased Li + transfer number (0.367) in comparison to hollow H-PIN-IL-Li bare IL-Li electrolyte. The assembled LiFePO 4 /Li solid batteries delivered a stable capacity of over 150 mAh g −1 for 100 cycles at 0.1 C and 130 mAh g −1 for 300 cycles at 0.5 C. Overall, our research demonstrates for the first time a novel MOF@PIN core-shell structure as a solid framework for IL with high battery performance.

Ionic liquids (ILs) are promising candidates as fast Li+ conductors owing to their high ionic conductivity and admirable stability. However, the mobile ions in ILs will contribute to the overall ion conductivity which decreases Li ions transfer efficiency and rate capability of batteries. The improvemnt of Li ions transfer efficiency in ILs electrolyte materials is a great challenge. Covalent organic frameworks (COFs) with high porosity and aligned nanosize channels can offer free flowing pathways for Li+ migration as well as abundant active sites to anchor anions and liberate free Li+, which can maximize Li+ transfer efficiency. Herein we design a cationic COF and a neutral COF as porous hosts for immobilizing the anions of IL N,N-diethyl-N-(2-methoxyethyl)-N-methylammoniumbis(trifluoromethylsulphonyl)imide (DEME-TFSI) to enhance Li+ transference efficiency. The obtained quasi-solid COFs-IL electrolytes exhibit high IL loading amount owing to strong interactions between COFs and the IL. Moreover, COFs-IL electrolytes show good electrochemical stability and high ionic conductivity over 1x10(-3) S cm(-1), along with a 90% increase of Li+ transfer number in comparison to the bare IL electrolyte (IL/LiTFSI). Our research provides a general strategy for immobilizing mobile anions to liberate Li+ and improve Li+ transfer efficiency in IL-based electrolytes. (C) 2021 Elsevier Ltd. All rights reserved.

锂离子电池因其清洁、充放电快、高能量密度等优点广泛应用于电动汽车.最近,电动汽车起火、爆炸事故引起人们对锂离子电池安全性的担忧.针对锂离子电池电解液易燃、易爆、易泄漏等安全问题,本文综述了电解液中加入阻燃剂磷酸酯、离子液体、氢氟醚的最新研究进展及其优缺点.电池如果在过充危险状况下会造成热积累,进而引发电池内部一系列危险副反应.本文还总结了氧化还原保护和电聚合保护两种措施来避免电池过度充电的研究进展.由于锂电池发生危险事故前内部会有一个热积累过程以及随着电池内部温度上升隔膜难以保持其力学性能,本文分别从热响应开关正极材料和安全隔膜两部分阐述了近年来锂离子电池内部热积累的应对策略,以期为最终解决锂离子电池的安全问题指明方向.

As a unique branch of Li-S batteries, solid-phase sulfur conversion polymer cathodes have shown superior stability with fast ion-transfer kinetics and high discharge capacities owing to the mere existence of short-chain sulfur species during charging/discharging. However, representative compounds such as sulfurized polyacrylonitrile (SPAN) and polyaniline (SPANI) suffer from low sulfur contents and poor cycling performances under large current densities due to the sulfurization occurring only on polymers' surface. Here, a graphdiyne-like porous organic framework, denoted as GPOF, is synthesized and used as a host for enabling solid-phase sulfur conversion. Plenty of unsaturated bonds in GPOF provide sufficient reaction sites to bind sulfur chains, resulting in a high active sulfur content in the cathode. Moreover, the microporous GPOF possesses suitable cavities to accommodate the volume expansion, leading to favorable long-term cycling stability. As a result, the sulfurized GPOF cathode (SGPOF-320) displays outstanding electrochemical stability with negligible capacity decline after 250 cycles at 0.2 C with an average discharge capacity of 925 mA h g-1. Our work applies a facile procedure to produce sulfur conversion porous polymer cathodes, which could provide a proper way for exploring more suitable cathode materials for high-performance Li-S batteries.

A pomegranate-like cathode, VN/S@G, is synthesized according to a simple principle of electrostatic attraction through a controllable Zeta potential method, establishing a hierarchical-structured VN/S nanoclusters encapsuled with graphene nanosheets. Internal VN nanoparticles trap lithium polysulphides (LiPSs) and catalyse them transforming from long-chain to short-chain species; whereas the external cladding layers of graphene nanosheets confine the transformations in a nanoscale-catalysis reactors. VN/S@G cathode exhibits excellent long-cycling life at 2 C rate during the 2000 cycles, corresponding to 0.038 percent of capacity fade per cycle. According to in-situ Raman and electrochemical impedance spectroscopies, VN catalyst accelerates chemical transformations of liquid-state LiPSs to solid-state Li2S2/Li2S and graphene intensifies Li+ diffusion behaviour. Improvement of electrochemical performance of the VN/S@G cathode depends on a coefficient of physical and chemical interactions between VN catalyst and LiPSs species.

Lithium-sulfur batteries are considered as the most promising candidate for next-generation energy storage devices. However, they are subjected to the "shuttle effect" of soluble lithium polysulfides (LiPSs). Herein, a free-standing membrane composed of two-dimensional MXene material (Ti3C2Tx) and graphene oxide (GO) is synthesized by a simple vacuum-filtration method. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy are carried out to determine structure, morphology, and composition of the Ti3C2Tx/GO composite membrane, respectively. As a functional layer of trapping LiPS species, the Ti3C2Tx/GO composite membrane and commercial polypropylene (PP) are successfully assembled to be a hybrid separator, Ti3C2Tx/GO@PP, to suppress the shuttle effect of LiPSs. The porous and rough surface of the Ti3C2Tx/GO composite membrane is beneficial to improve the wettability of the commercial separator in an ether-based electrolyte. The cells with the Ti3C2Tx/GO@PP hybrid separator exhibit a low polarization potential of 0.26 V in the conversion from Li2S4 to Li2S2/Li2S and deliver a discharge capacity of 640.0 mA h g(-1) for 5 C rate, indicating that the hybrid separator benefits the rate performance. According to the results of electrochemical impedance spectroscopy, increased discharge capacity is attributed to the reduced internal resistance and intensified Li+ diffusion. The results of X-ray photoelectron spectroscopy focusing on the surfaces of both sides of the hybrid separator indicate that the shuttle effect of LiPSs is suppressed through a coefficient of the terminated groups' catalytic conversion on long-chain LiPSs and the titanium-reactive centers' Lewis acid-base pairs on short-chain LiPSs. Combining with digital photographs of the H-type electrolytic cell, the results of UV-visible absorption spectroscopy suggest that the concentration of long-chain polysulfides declines instantly under the redox effect of the terminated groups on Ti3C2Tx surfaces and then infiltrate through the hybrid separator by virtue of concentration difference impetus. Generally, a Ti3C2Tx/GO@PP hybrid separator restrains LiPS diffusion and improves the rate performance of Li-S batteries.

Lithium-sulfur (Li-S) batteries with ultrahigh theoretical specific capacity (1675 mAh g(-1)) have become a research hotpot, which focuses on the solution of shuttle effect of soluble lithium polysulfides (LIPS). Chemical immobilization of LIPS and encapsulation structure of the sulfur cathode are effective strategies to suppress the shuttle effect. Herein, high entropy metal nitride (HEMN) was prepared by mechanochemical-assisted synthesis as an innovative anchor to restrain LIPS via the chemical bonding interaction between HEMN and LIPS. Furthermore, the composite of HEMN and S was encased by graphene (GR) through electrostatic attraction caused by opposite zeta potential, thus as the effective cathode (HEMN/S@GR) of Li-S batteries. HEMN has plentiful active metal sites which can chemically adsorb LIPS, enhancing the cycle life of Li-S batteries. Graphene can accelerate surface charge transfer of sulfur cathode to reduce the interface resistance because of its high conductivity. The initial specific capacity of HEMN/S@GR cathode is 1193 mAh g(-1) and still maintains 695 mAh g(-1) after 100 cycles at 0.1 C. When increased to 1.0 C, the initial specific capacity is 556 mAh g(-1) and exhibits remarkable stability in long cycles. This study presents the synergetic effect of HEMN and graphene on LIPS in Li-S batteries, which introduces a new application way of high entropy materials in the field of energy storage devices.

The safety problems of lithium ion batteries (LIBs) have been the main obstacles that hinder their broad applications in portable electronic devices, electric vehicles, and energy storage. Such problems originate from flammable solvent-containing liquid electrolytes that could be easily oxidized upon excessive heat, leading to further heat accumulation and, subsequently, thermal runaway. The design strategies of a safe electrolyte could control the flammability and volatility of the liquid electrolyte, might prevent the thermal runaway, and ultimately ensure the risk-free and fire-free operation of LIBs. This work is to explore the mechanism of thermal runaway and review the state-of-the-art of the designs of a safe electrolyte for LIBs, including the additions of flame retardant additives, overcharge additives, and stable lithium salts and the adoption of solid-state electrolytes, ionic liquid electrolytes, and thermosensitive electrolytes. The features, advantages, and drawbacks of these strategies are systematically summarized, compared, and discussed, while the development direction of a safer electrolyte for future LIBs is proposed in the end.

作为最丰富的可再生有机芳香族聚合物之一,木质素的生物降解和利用具有较好的环境、经济和社会效益,但繁多的木质素降解酶活测试方法为生物降解木质素的相关研究带来一定困难.本文围绕已发现的5种重要木质素降解酶(漆酶、锰过氧化物酶、木质素过氧化物酶、多功能过氧化物酶和染料脱色过氧化物酶),针对其来源、特性和酶与底物的作用机理,深入地比较和分析了多种木质素降解酶酶活测试方法.通过对ABTS法、2,6-DMP法、藜芦醇法、天青B法和其他特色方法从原理到应用的综合讨论,全面评估了上述方法的底物多样性、测试条件及适用范围.此外,本文还针对木质素降解酶酶活测试研究中所存在的主要挑战提出了解决思路,旨在为生物法降解木质素及其高值化利用的研究提供有效参考和策略.