Interweaving Elastic and Hydrogen Bond‐Forming Polymers into Highly Tough and Stress‐Relaxable Binders for High‐Performance Silicon Anode in Lithium‐Ion Batteries

Abstract

A central challenge in practically using high‐capacity silicon (Si) as anode materials for lithium‐ion batteries is alleviating significant volume change of Si during cycling. One key to resolving the failure issues of Si is exploiting carefully designed polymer binders exhibiting mechanical robustness to retain the structural integrity of Si electrodes, while concurrently displaying elasticity and toughness to effectively dissipate external stresses exerted by the volume changes of Si. Herein, a highly elastic and tough polymer binder is proposed by interweaving polyacrylic acid (PAA) with poly(urea‐urethane) (PUU) elastomer for Si anodes. By systematically tuning molecular parameters, including molecular weights of hard/soft segments and structures of hard segment components, it is demonstrated that the mechanical properties of polymer binders, such as elasticity, toughness, and stress relaxation ability, strongly affect the cycling performance of Si electrodes. This study provides new insight into the rational design of polymer binders capable of accommodating the volume changes of Si, primarily by judicious modulation of the mechanical properties of polymer binders.

Assembling a dense grid structure with green polyhydroxyurethane and a high-capacity Si-based anode for lithium ion batteries

“…19 Moreover, the flexible and resilient three-dimensional (3D) network combining soft polymers with PAA suppresses the pulverization of Si particles and facilitates sustained contact even after pulverization occurs. 20 This further stabilizes the SEI layer and extends the life span of batteries using Si-based anodes. Nevertheless, these soft polymers with limited crosslinkable sites are prone to lose their bond durability once the PAA significantly ruptures.…”

“…Recently, Jeong et al synthesized polyurea-urethane (PUU) by introducing an epoxy cross-linker at the terminal. 20 PAA-PUU demonstrated a decent conformation of rigid–soft combination while the terminal-oriented crosslinking limits the connection of multiple PAA chains. More critically, all the PU utilized for the anode binders are derived from non-eco-friendly isocyanate, which contradicts the increasing demand for environmentally friendly materials in LIBs.…”

Research progress of robust binders with superior mechanical properties for high-performance silicon-based lithium-ion batteries

“…Increasing the strength of peel force could be achieved by increasing the interaction between binders and the current collectors by postprocessing treatment or increasing the interaction between binders with other components of electrodes, which includes introducing elastomers in polymer binders to make elastic polymers and increase bonding intensity of binders with Si-based materials. Later methods of forming elastic binders could be achieved by block polymerization, random polymerization, or in situ synthesis of elastic monomers or chain segments, 112–114 grating other molecules with interaction function groups 57,115 or other small molecules or chain segments as crosslinking agents. 116–118…”

How to Make the Stress Relaxation Experiment for Polymers More Informative

“…However, in the ongoing debate on the application of the KWW function to relaxation phenomena in different polymers [48,49], in particular to liquids and glasses, this model is widely used. Examples of research published this year alone include modeling of the mechanical properties of highly elastic and tough polymer binders with interweaving polyacrylic acid (PAA) with a poly(urea-urethane) (PUU) elastomer [50]; modeling of the relaxation curve describing the local dynamics of ions and hydration water near the RNA interface [51]; studying the relaxation processes for bulk antipsychotic API aripiprazole (APZ) and the active pharmaceutical ingredients (API) incorporating anodic aluminum oxide (AAO) or silica (SiO 2 ) systems that are collected during the "slow-heating" procedure [52]; description of the rheological properties of the cross-linked blends of Xanthan gum and polyvinylpyrrolidone-based solid polymer electrolyte [53]; studies concerning the stress relaxation process in annealed metallic and polymer glasses [54]; and the stress relaxation behavior of glass-fiber-reinforced thermoplastic composites [55].…”