Design, Synthesis, and Characterization of a Novel Tetra-Block Copolymer for High-Performance Self-Healing Batteries

Abstract

Lithium-ion batteries (LIBs) have become the dominant energy storage technology due to their versatility and superior performance across diverse applications. Silicon (Si) stands out as a particularly promising high-capacity anode material for next-generation LIBs, offering a theoretical capacity nearly ten times greater than conventional graphite anodes. However, its practical implementation faces a critical challenge: the material undergoes a ~300% volume expansion during lithiation/delithiation, which causes severe mechanical stress, electrode pulverization, and rapid capacity decay. In addressing these limitations, advanced polymer binders serve as essential components for preserving the structural integrity of Si-based anodes. Notably, self-healing polymeric binders have emerged as a groundbreaking solution, capable of autonomously repairing cycle-induced damage and significantly enhancing electrode durability. The evaluation of self-healing performance is generally based on mechanical characterization methods while morphological observations by scanning electron microscopy provide direct evidence of crack closure; for electrochemically active materials, electrochemical techniques including GCD, EIS, and CV are employed to monitor recovery of functionality. In this study, a novel self-healing copolymer (PHX-23) was synthesized for Si anodes using a combination of octadecyl acrylate (ODA), methacrylic acid (MA), 2-hydroxyethyl methacrylate (HEMA), and polyethylene glycol methyl ether methacrylate (PEGMA). The copolymer was thoroughly characterized using NMR, FTIR, TGA, SEM, and EDX to confirm its chemical structure, thermal stability, and morphology. Electrochemical evaluation revealed that the PHX-23 binder markedly improves cycling stability, sustaining a reversible capacity of 427 mAh g^-1 after 1000 cycles at 1C. During long-term cycling, the Coulombic efficiency of the PHX-23 polymer is 99.7%, and similar functional binders in the literature have shown similar results at lower C-rates. Comparative analysis with conventional binders (e.g., PVDF and CMC/SBR) demonstrated PHX-23's exceptional performance, exhibiting higher capacity retention and improved rate capability. These results position PHX-23 as a transformative binder for silicon anodes in next-generation lithium-ion batteries.

Keywords: self-healing polymer; silicon anode; tetra-block copolymer.

Scheme 1

Synthesis of PHX via free-radical polymerization.

Figure 1

Self-healing test for PHX-23 polymer.

Figure 2

(a) ¹H, (b) ¹³C NMR, (c) FTIR, and (d) TGA-DSC results of PHX-23.

Figure 3

(a) 5.0k and (b) 15.0k SEM images, (c) all elements, (d) C, (e) O, and (f) N elements EDX of PHX-23.

Figure 4

(a) CV curves obtained at a scan rate of 0.05 mV/s within a voltage range of 0.01 to 1.2 V, (b) Nyquist plots (before and after CV), and (c) equivalent circuit form Nyquist plot of Si/PHX-23 electrode.

Figure 5

(a) GCD and coulombic efficiency at 1C, (b) C-rate test, and (c) voltage profile at 1C of Si/PHX-23 electrode.

Figure 6

SEM images of pre-CV and post-CV form of PHX-Si electrode.

Figure 7

EDX images of Si/PHX-23 electrode.