Greatly Improved Conductivity of Double‐Chain Polymer Network Binder for High Sulfur Loading Lithium–Sulfur Batteries with a Low Electrolyte/Sulfur Ratio

Abstract

Binders have been considered to play a key role in realizing high-energy-density lithium-sulfur batteries. However, the accompanying problems of limited conductivity and inferior affinity of soluble polysulfide intermediates bring down their comprehensive performance for practical applications. Herein, the synthesis of a novel double-chain polymer network (DCP) binder by polymerizing 4,4'-biphenyldisulfonic acid connected pyrrole monomer onto viscous sodium carboxymethyl cellulose matrix, yielding a primary crystal structure is reported. Consequently, the resulted binder enables superior rate performance from 0.2 C (1326.9 mAh g ) to 4 C (701.4 mAh g ). Moreover, a high sulfur loading of 9.8 mg cm and a low electrolyte/sulfur ratio (5:1, µL mg ) are achieved, exhibiting a high area capacity of 9.2 mAh cm . In situ X-ray diffraction analysis is conducted to monitor the structural modifications of the cathode, confirming the occurrence of sulfur reduction/recrystallization during charge-discharge process. In addition, in situ UV-vis measurements demonstrate that DCP binder impedes the polysulfide migration, thereby giving rise to high capacity retention for 400 cycles.

Rational Design of Binders for Stable Li‐S and Na‐S Batteries

“…It was reported that some common conductive polymers such as polyaniline (PANI), [102] polypyrrole (Ppy), [103,104] PEDOT:PSS [105] are too rigid to sever as good binder. [39] It is noted that the introduction of soft segments or soft polymers inevitably reduces the electric conductivity of the binder. For example, poly(9,9dioctylfluorene-co-fluorenone-co-methylbenzoic ester) (PFM) was designed, in which the methylbenzoic ester segment was responsible for enhancing the elasticity, while the octyl side chains and fluorenone functional groups provided high conductivity.…”

“…The binder in Li-S batteries has experienced a remarkable evolution in terms of functions, from fundamental structural and mechanical stabilizer (linear, hybrid, [30] dendrimer, [31] and crossedlinked binder [32,33] ) to versatile functions of polysulfide immobilization (polymer with functional groups [34][35][36] or cation groups [37] ) and facilitation of electron transport on the basis of conductive polymer. [38,39] It opens up the research of multifunctional binder. The analogous development route in the binder is found in Na-S batteries.…”

“…[38] Royal Society of Chemistry Reproduced with permission. [39] Copyright 2018, Wiley-VCH. Reproduced with permission.…”

“…Over the past decade, the design of binder molecules has gone through tremendous evolution from primarily maintaining the structural integrity of the electrode against volume change to rationally immobilizing polysulfide intermediate and facilitating electron/ion transport in the charge and discharge process. [38,39] It opens up the research of multifunctional binder. It also points out the future challenge and the potential solutions to address them.…”

One‐Pot Synthesis of a Copolymer Micelle Crosslinked Binder with Multiple Lithium‐Ion Diffusion Pathways for Lithium–Sulfur Batteries

“…Binders, as one of the most important electrode components, play a crucial role in resolving these issues. However, the traditional binder, polyvinylidene fluoride (PVDF), offers weak adhesion strength, requires the hazardous and volatile solvent N ‐methyl pyrrolidinone (NMP), and provides poor adsorption for LiPS and low Li‐ion conductivity . In contrast, water‐soluble binders have the advantages of environmental benignity and fewer safety concerns.…”