Design of multifunctional polymeric binders in silicon anodes for lithium‐ion batteries

Silicon(Si)is a promising anode material for lithium‐ion batteries(LIBs)owing to its tremendously high theoretical storage capacity(4200 mAh g−1),which has the potential to elevate the energy of LIBs.However,Si anodes exhibit severe volume change during lithiation/delithiation processes,resulting in anode pulverization and delamination with detrimental growth of solid electrolyte interface layers.As a result,the cycling stability of Si anodes is insufficient for commercialization in LIBs.Polymeric binders can play critical roles in Si anodes by affecting their cycling stability,although they occupy a small portion of the electrodes.This review introduces crucial factors influencing polymeric binders'properties and the electrochemical performance of Si anodes.In particular,we emphasize the structure–property relationships of binders in the context of molecular design strategy,functional groups,types of interactions,and functionalities of binders.Furthermore,binders with additional functionalities,such as electrical conductivity and self‐healability,are extensively discussed,with an emphasis on the binder design principle.

Design and Synthesis of Multi-Functional Polymeric Binders for High-Performance Lithium-Sulfur Batteries Based on Ring Opening Polymerization of Thiolactone

The application of high-performance lithium-sulfur(Li-S)batteries is severely influenced by the“shuttle effect”of polysulfides and the volume change of sulfur cathode.Herein,two different polymeric binders SOT-A and SOT-C with three-dimensional network structure containing polar groups(sulfhydryl groups,amide groups and amino groups)are synthesized by the nucleophilic ring-opening polymerization(ROP)of thiolactone with amino groups.The network structure formed by hydrogen bonds and functional groups can resist the volume change of the cathode.The sulfhydryl groups and the S-S bond formed by oxidative dehydrogenation of sulfhydryl group participate in the charge and discharge process of the battery as active materials,which improves the discharge specific capacity of the battery.Polar functional groups have strong chemisorption on polysulfides and effectively inhibit the“shuttle effect”.The electrochemical performances of Li-S batteries containing SOT-A and SOT-C binders are significantly enhanced.At 1 C rate,the batteries achieve initial discharge specific capacity of 871 and 837 mAh·g^(-1),respectively,and have 83.9%and 62.5%capacity retention after 500 cycles.

Multifunctional binder designs for lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries are promising next-generation high energy density batteries but their practical application is hindered by several key problems,such as the intermediate polysulfide shuttling and the electrode degradation caused by the sulfur volume changes.Binder acts as one of the most essential components to build the electrodes of Li-S batteries,playing vital roles in improving the performance and maintaining the integrity of the cathode structure during cycling,especially those with high sulfur loadings.To date,tremendous efforts have been devoted to improving the properties of binders,in terms of the viscosity,elasticity,stability,toughness and conductivity,by optimizing the composition and structure of polymer binders.Moreover,the binder modification endows them strong polysulfide trapping ability to suppress the shuttling and decreases the swelling to maintain the porous structure of cathode.In this review,we summarize the recent progress on the binders for Li-S batteries and discuss the various routes,including the binder combination use,functionalization,in-situ polymerization and ion cross-linking,etc.,to enhance their performance in stabilizing the cathode,building the high sulfur loading electrode and improving the cyclic stability.At last,the design principles and the problems in further applications are also highlighted.

Compound Rejuvenation of Polymer Modified Asphalt Binder

The objective of this research was to show a way to conduct rejuvenation of aged polymer modified asphalt binder（PMB） successfully.To fully evaluate and understand the rejuvenation of aged PMB,the Penetration grade tests including penetration,soften point,ductility and elastic recovery and SuperpaveTM PG grade tests including DSR,BBR and DDT were conducted.The rejuvenation effect of aged PMB by utilizing a fluid recycling agent in common use for binder rejuvenation was evaluated.And then the compound rejuvenation effect of aged PMB by utilizing the recycling agent with a new modifying additive for binder modification was evaluated.The experimental results indicated that the recycling agent in common use currently does not apply to polymer modified asphalt binder rejuvenation.But the recycling agent together with the modifying additive can restore the characteristics of aged polymer modified binder very well.Therefore,compound rejuvenation of polymer modified asphalt binder is recommended.

Functional copolymer binder for nickel-rich cathode with exceptional cycling stability at high temperature through coordination interaction

Nickel-rich layered oxide LiNi_(1-x-y)Co_(x)Al_yO_(2)(NCA) with high theoretical capacity is a promising cathode material for the next-generation high-energy batteries.However,it undergoes a rapid capacity fading when operating at high temperature due to the accelerated cathode/electrolyte interfacial reactions and adhesive efficacy loss of conventional polyvinylideneffuoride(PVdF) binder.Herein,poly(acrylonitrile-co-methyl acrylate) copolymer is designed with electron-rich-C≡N groups as a novel binder for LiNi_(0.8)Co_(0.1)Al_(0.1)O_(2) cathode at high temperature.The electron-rich-C≡N groups are able to coordinate with the active Ni^(3+) on the surface of NCA,alleviating electrolyte decomposition and cathode structure degradation.Moreover,the strong adhesive ability is conducive to maintain integrity of electrodes upon cycling at 55℃.In consequence,the NCA electrodes with this functional binder display improved cycling stability(81.5% capacity retention after 100 cycles) and rate performance at 55℃.

Revealing the working mechanism of a multi-functional block copolymer binder for lithium-sulfur batteries

The lithium-sulfur(Li-S)battery is one of the most promising substitutes for current energy storage systems because of its low cost,high theoretical capacity,and high energy density.However,the high solubility of intermediate products(i.e.,lithium polysulfides)and the resultant shuttle effect lead to rapidly fading capacity and a low coulombic efficiency,which hinder the practical application of Li-S batteries.In this study,block copolymers are constructed with both an ethylene oxide unit and a styrene unit and then used as binders for Li-S batteries.Electrochemical performance improvements are attributed to the synergistic effects contributed by the different units of the block copolymer.The ethylene oxide unit traps polysulfide,which bonds strongly with the intermediate lithium polysulfide,and enhances the transport of lithium ions to reach high capacity.Meanwhile,the styrene unit maintains cathode integrity by improving the mechanical properties and elasticity of the constructed block copolymer to accommodate the large volume changes.By enabling multiple functions via different units in the polymer chain,high sulfur utilization is achieved,polysulfide diffusion is confined,and the shuttle effect is suppressed during the cycle life of Li-S batteries,as revealed by operando ultraviolet-visible spectroscopy and S Kedge X-ray absorption spectroscopy.

Poly(thiourea triethylene glycol) as a multifunctional binder for enhanced performance in lithium-sulfur batteries

A mechanically strong binder with polar functional groups could overcome the dilemma of the large volume change during charge/discharge processes and poor cyclability of lithium-sulfur batteries(LSBs).In this work,for the first time,we report the use of poly(thiourea triethylene glycol)(PTTG)as a multifunctional binder for sulfur cathodes to enhance the performance of LSBs.As expected,the PTTG binder facilitates the high performance and stability delivered by the Sulfur-PTTG cathode,including a higher reversible capacity of 825 mAh g^(-1) at 0.2 C after 80 cycles,a lower capacity fading(0.123%per cycle)over 350 cycles at 0.5 C,a higher areal capacity of 2.5 mAh cm^(-2) at 0.25 mA cm^(-2),and better rate capability of 587 mAh g^(-1) at 2 C.Such superior electrochemical performances could be attributed to PTTG's strong chemical adsorption towards polysulfides which may avoid the lithium polysulfide shuttle effect and excellent mechanical characteristics which prevents electrode collapse during cycling and allows the Sulfur-PTTG electrode to maintain robust electron and ion migration pathways for accelerated redox reaction kinetics.

Enhancement of Toxic Gas Detecting Ability of Film Type Colorimetric Sensor

In this study, we tried to develop the in situ coating methods of hydrophilic polymer solution containing water soluble dye on nonwoven sheet for the colorimetric film sensor. And color change of coated dye according to contact various gas samples (as strong acid and base, chloroform, ammonia and HF) of this dye-coated nonwoven film was examined for the application of chemically toxic materials detecting tools in the actual site of working place without aid of any kinds of detecting devices. By the addition of electron transfer agent (quinone derivatives), quick color change behaviors were observed within 10 seconds under the contact of various toxic gases in general condition(room temperature, 50% humidity).

A flame-retardant binder with high polysulfide affinity for safe and stable lithium–sulfur batteries

Lithium-sulfur(Li-S) batteries have shown promises for the next-generation, high-energy electrochemical storage, yet are hindered by rapid performance decay due to the polysulfide shuttle in the cathode and safety concerns about potential thermal runaway. To address the above challenges, herein, we show a flame-retardant cathode binder that simultaneously improves the electrochemical stability and safety of batteries. The combination of soft and hard segments in the polymer framework of binders allows high flexibility and mechanical strength for adapting to the drastic volume change during the Li(de)intercalation of the S cathode. The binder contains a large number of polar groups, which show the high affinity to polysulfides so that they help to anchor active S species at the cathode. These polar groups also help to regulate and facilitate the Li-ion transport, promoting the kinetics of polysulfide conversion reaction. The binder contains abundant phosphine oxide groups, which, in the case of battery's thermal runaway, decompose and release PO· radicals to quench the combustion reactions and stop the fire. Consequently, Li-S batteries using the new cathode binder show the improved electrochemical performance, including a low-capacity decay of 0.046% per cycle for 800 cycles at 1 C and favorable rate capabilities of up to 3 C. This work offers new insights on the practical realization of high-energy rechargeable batteries with stable storage electrochemistry and high safety.

Advances of polymer binders for silicon-based anodes in high energy density lithium-ion batteries

Conventional lithium-ion batteries(LIBs)with graphite anodes are approaching their theoretical limitations in energy density.Replacing the conventional graphite anodes with high-capacity Si-based anodes represents one of the most promising strategies to greatly boost the energy density of LIBs.However,the inherent huge volume expansion of Si-based materials after lithiation and the resulting series of intractable problems,such as unstable solid electrolyte interphase layer,cracking of electrode,and especially the rapid capacity degradation of cells,severely restrict the practical application of Sibased anodes.Over the past decade,numerous reports have demonstrated that polymer binders play a critical role in alleviating the volume expansion and maintaining the integrity and stable cycling of Si-based anodes.In this review,the state-of-the-art designing of polymer binders for Si-based anodes have been systematically summarized based on their structures,including the linear,branched,crosslinked,and conjugated conductive polymer binders.Especially,the comprehensive designing of multifunctional polymer binders,by a combination of multiple structures,interactions,crosslinking chemistries,ionic or electronic conductivities,soft and hard segments,and so forth,would be promising to promote the practical application of Si-based anodes.Finally,a perspective on the rational design of practical polymer binders for the large-scale application of Si-based anodes is presented.

How Do Polymer Binders Assist Transition Metal Oxide Cathodes to Address the Challenge of High‑Voltage Lithium Battery Applications?

Research on the chemistry of high-energy-density transition metal oxide cathodes(TMOCs)is at the forefront in the pursuit of lithium-ion batteries with increased energy density.As a critical component of these cathodes,binders not only glue cathode active material particles and conducting carbons together and to current collectors but also play pivotal roles in building multiscale compatible interphases between electrolytes and cathodes.In this review,we outline several vital design considerations of high-voltage binders,several of which are already present in traditional binder design that need to be highlighted,and systematically reveal the chemistry and mechanisms underpinning such binders for in-depth understanding.Further optimization of the design of polymer binders to improve battery performance is also discussed.Finally,perspec-tives regarding the future rational design and promising research opportunities of state-of-the-art binders for high-voltage TMOCs are presented.

Imparting Pulley Effect and Self-healability to Cathode Binder of Li-S Battery for Improvement of the Cycling Stability

To construct structurally stable sulfur cathode of Li-S battery with improved cycling performance,poly(acrylic acid)(PAA)crosslinked by cationic hydroxypropyl polyrotaxane(HPRN+)via dynamically reversible boronic ester bonds is synthesized and serves as the cathode binder.The smart polymer networks offer multifunction including buffering the volume change of the cathode during charge/discharge through the pulley effect of polyrotaxanes(PR),suppressing the shuttle effect by adsorption of polysulfide using the plentiful carboxyl,hydroxyl and quaternary ammonium cationic groups,and self-healing the micro-damages to ensure stable conduction pathways of the electrode.As a result,the Li-S batteries based on this novel multifunctional binder and simple commercial sulfur/carbon composites cathode exhibit excellent specific capacity and cycling stability.In particular,the specific capacity decay per cycle of the cell is only 0.064%along with high Coulombic efficiency after 550 cycles at 1.0 C,which is superior to most of the reported binders.Even under high sulfur loading,moreover,the cathode can deliver superior areal capacity and cycling stability.This proposed binder provides a new way for the design of high-stability sulfur cathodes.

Impact of fabrication methods on binder distribution and charge transport in composite cathodes of all-solid-state batteries

The manufacturing process of all-solid-state batteries necessitates the use of polymer binders.However,these binders,being ionic insulators by nature,can adversely affect charge transport within composite cathodes,thereby impacting the rate performance of the batteries.In this work,we aim to investigate the impact of fabrication methods,specifically the solvent-free dry process versus the slurry-cast wet process,on binder distribution and charge transport in composite cathodes of solid-state batteries.In the dry process,the binder forms a fibrous network,while the wet process results in binder coverage on the surface of cathode active materials.The difference in microstructure leads to a notable 20-fold increase in ionic conductivity in the dry-processed cathode.Consequently,the cells processed via the dry method exhibit higher capacity retention of 89%and 83%at C/3 and C/2 rates,respectively,in comparison to 68%and 58%for the wet-processed cells at the same rate.These findings provide valuable insights into the influence of fabrication methods on binder distribution and charge transport,contributing to a better understanding of the binder’s role in manufacturing of all-solid-state batteries.

Phase segregation mechanisms of small molecule-polymer blends unraveled by varying polymer chain architecture

As phase separation between the small-molecule semiconductor and the polymer binder is the key enabler of blend-based organic field-effect transistors(OFETs)fabricated by low-cost solution processing,it is crucial to understand the underlying phase separation mechanisms that determine the phase morphology,which significantly impacts device performance.Beyond the parameter space investigated in previous work,here we investigate the formation of blends by varying the branch architecture of the polymer binder and by shortening the solvent dry time using ultrasonic spray casting.The phase morphologies of the resulting blend films have been thoroughly characterized with a variety of techniques in three dimensions over multiple length scales,including AFM,energy-filtered transmission electron microscope,and neutron reflectivity,and have been correlated with electrical transport performance.From the results,we have inferred that the phase morphology is kinetically determined,limited by the inherent slow movement of polymer macromolecules.The kinetic picture,supported by molecular dynamics modeling,not only consistently explains our observations but also resolves inconsistencies in previous works.The achieved mechanistic understanding will guide further optimization of blend-based organic electronics,such as OFETs and organic photovoltaics.