Ten-Minute Synthesis of a New Redox-Active Aqueous Binder for Flame-Retardant Li-S Batteries

As a critical role in battery systems,polymer binders have been shown to efficiently suppress the lithium polysulfide shuttling and accommodate volume changes in recent years.However,preparation processes and safety,as the key criterions for Li-S batteries'practical applications,still attract less attention.Herein,an aqueous multifunction binder(named PEI-TIC)is prepared via an easy and fast epoxy-amine ring-opening reaction(10 min),which can not only give the sulfur cathode a stable mechanical property,a strong chemical adsorption and catalytic conversion ability,but also a fire safety improvement.The Li-S batteries based on the PEI-TIC binder display a high discharge capacity(1297.8 mAh g^(-1)),superior rate performance(823.0 mAh g^(-1)at 2 C),and an ultralow capacity decay rate of 0.035%over more than 800 cycles.Even under 7.1 mg cm^(-2)S-loaded,the PEI-TIC electrode can also achieve a high areal capacity of 7.2 mA h g^(-1)and excellent cycling stability,confirming its application potential.Moreover,it is also noted that TG-FTIR test is performed for the first time to explore the flame-retardant mechanism of polymer binders.This work provides an economically and environmentally friendly binder for the practical application and inspires the exploration of the flame-retardant mechanism of all electrode components.

A semi-immobilized sulfur-rich copolymer backbone with conciliatory polymer skeleton and conductive substrates for high-performance Li-S batteries

Sulfur-rich polymers have gained a great deal of attention as the next-generation active materials in lithium-sulfur(Li-S)batteries due to their low cost,environmental compatibility,naturally sulfur uniform dispersion,and distinctive structure covalently bonding with sulfur atoms.However,the poor electrical conductivity and undesirable additional shuttle effect still hinder the commercial application of sulfur-rich polymers.Herein,we report a flexible semi-immobilization strategy to prepare allylterminated hyperbranched poly(ethyleneimine)-functionalized reduced graphene oxide(A-PEI-EGO)as sulfur-rich copolymer backbone.The semi-immobilization strategy can effectively reconcile the demand for polymer skeleton and conductive substrates through forming quaternary ammonium groups and reducing oxygen-containing functional groups,resulting in enhanced skeleton adsorption capacity and substrate electronic conductivity,respectively.Furthermore,the stable covalent bonding connection based on polymer molecules(A-PEI)not only completely prevents the additional shuttle effect of lithiation organic molecules and even sulfur-rich oligomers,but provides more inverse vulcanization active sites.As a result,the as-prepared A-PEI-EGO-S cathodes display an initial discharge capacity of1338 m A h g^(-1)at a rate of 0.1 C and an outstanding cycling stability of 0.046%capacity decay per cycle over 600 cycles.Even under 6.2 mg cm^(-2)S-loaded and sparing electrolyte of 6μL mg^(-1),the A-PEI-EGO-S cathode can also achieve a superior cycling performance of 98%capacity retention after 60 cycles,confirming its application potential.

A flexible design strategy to modify Ti3C2Tx MXene surface terminations via nucleophilic substitution for long-life Li-S batteries

MXene-based materials have gained considerable attention for lithium-sulfur(Li-S)batteries cathode materials due to their superior electric conductivity and high affinitive to polysulfides.However,there are still challenges in modifying the surface functional groups of MXene to further improve the electrochemical performance and increase the structure variety for MXene-based sulfur host.Herein,we report an efficient and flexible nucleophilic substitution(S_(N))strategy to modify the Ti_(3)C_(2)T_(x) surface terminations and purposefully designed Magnolol-modified Ti_(3)C_(2)T_(x)(M-Ti_(3)C_(2)T_(x))as powerful cathode host materials.Benefiting from more C-Ti-O bonds forming and diallyl groups terminations reducing after the dehalogenation and nucleophilic addition reactions,the given M-Ti_(3)C_(2)T_(x) electrode could effectively suppress the lithium polysulfides shuttling via chemisorption and C—S covalent bond formation.Besides,the Magnolol-modified Ti_(3)C_(2)T_(x) significantly accelerates polysulfide redox reaction and reduces the activation energy of Li_(2) S decomposition.As a result,the as-prepared M-Ti_(3)C_(2)T_(x) electrode displays an excellent rate capability and a high reversible capacity of 7.68 mAh cm^(-2)even under 7.2 mg cm^(-2)S-loaded with a low decay rate of 0.07%(from 2 nd cycle).This flexible surface-modified strategy for MXene terminations is expected to be extended to other diverse MXene applications.

MXenes for metal-ion and metal-sulfur batteries:Synthesis,properties,and electrochemistry

In 2011,a new class of 2D materials was discovered;after 2012,they began to be concerned;in 2017,the“gold rush”of the materials was triggered,and they are exactly MXenes.2D MXenes,a new class of transition metal carbides,carbonitrides and nitrides,have become the star and cutting-edge research materials in the field of emerging batteries systems due to their unique 2D structure,abundant surface chemistry,and excellent physical and electrochemical properties.This review focuses on the MXene materials and summarizes the recent advancements in the synthesis techniques and properties,in addition to a detailed discussion on the electrochemical energy storage applications,including alkali-ion(Li^(+),Na^(+),K^(+))storage,lithium-sulfur(Li–S)batteries,sodiumsulfur(Na–S)batteries,and metal anode protection.Special attentions are given to the elaborate design of nano-micro structures of MXenes for the various roles as electrodes,multifunctional components,S hosts,modified separators,and metal anode protective layers.The paper ends with a prospective summary of the promising research directions in terms of synthesis,structure,properties,analysis,and production on MXene materials.

An all-biomaterials-based aqueous binder based on adsorption redox-mediated synergism for advanced lithium–sulfur batteries

The complex multistep electrochemical reactions of lithium polysulfides and the solid–liquid–solid phase transformation involved in the S8 to Li2S reactions lead to slow redox kinetics in lithium–sulfur batteries(Li–S batteries).However,some targeted researches have proposed strategies requiring the introduction of significant additional inactive components,which can seriously affect the energy density.Whereas polymer binders,proven to be effective in suppressing shuttle effects and constraining electrode volume expansion,also have promising potential in enhancing Li–S batteries redox kinetics.Herein,a novel aqueous polymer binder is prepared by convenient amidation reaction of fully biomaterials,utilizing its inherent rich amide groups for chemisorption and redox mediating ability of thiol groups to achieve adsorption redox-mediated synergism for efficient conversion of polysulfides.Li–S batteries based on N-Acetyl-L-Cysteine-Chitosan(NACCTS)binder exhibit high initial discharge specific capacity(1260.1mAhg−1 at 0.2C)and excellent cycling performance over 400 cycles(capacity decay rate of 0.018%per cycle).In addition,the batteries exhibit great areal capacity and stable capacity retention of 83.6%over 80 cycles even under high sulfur loading of 8.4mgcm−2.This work offers a novel perspective on the redox-mediated functional design and provides an environmentally friendly biomaterials-based aqueous binder for practical Li–S battery.

Sulfur polymerization strategy based on the intrinsic properties of polymers for advanced binder-free and high-sulfur-content Li–S batteries

Lithium-sulfur(Li-S)batteries are the promising next-generation secondary energy storage systems,because of their advantages of high energy density and environmental friendliness.Among numerous cathode materials,organosulfur polymer materials have received extensive attentions because of their controllable structure and uniform sulfur distribution.However,the sulfur content of most organosulfur polymer cathodes is limited(S content<60%)due to the addition of large amounts of conductive agents and binders,which adversely affects the energy density of Li-S batteries.Herein,a hyperbranched sulfur-rich polymer based on modified polyethyleneimine(Ath-PEI)named carbon nanotubeentangled poly(allyl-terminated hyperbranched ethyleneimine-random-sulfur)(CNT/Ath-PEI@S)was prepared by sulfur polymerization and used as a Li-S battery cathode.The high intrinsic viscosity of Ath-PEI provided considerable adhesion and avoided the addition of PVDF binder,thereby increasing the sulfur content of cathodes to 75%.Moreover,considering the uniform distribution of elemental sulfur by the polymer,the utilization of sulfur was successfully improved,thus improving the rate capability and discharge capacity of the battery.The binder-free,sulfur-rich polymer cathode exhibited ultra-high initial discharge capacity(1520.7 mAh g^(−1) at 0.1 C),and high rate capability(804 mAh g^(−1) at 2.0 C).And cell-level calculations show that the electrode exhibits an initial capacity of 942.3 mAh g^(−1) electrode,which is much higher than those of conventional sulfur-polymer electrodes reported in the literature.