Improving Silicon Anode Durability through Uniform Dispersion and Binding Enhancement with Polyacrylamide-Grafted CNTs

Silicon (Si) is a promising anode material for high-energy-density anodes in rechargeable lithium-ion batteries (LIBs), given its high specific capacity (>3500 mA h g⁻ 1 ) and low lithiation potential (~0.4 V vs. Li/Li⁺).However, its commercial application is hindered by a substantial volume expansion of up to 300% during cyclingand intrinsically low electronic conductivity. Although polymer-based binders have been extensively explored to alleviate Si particle expansion, their non-conductive properties restrict efficient electron transfer throughout the Si anodes. Consequently, Si anodes necessitate large amounts of conductive additives, reducing the proportion of active material within the electrode and consequently resulting in energy density losses.Thus, overcoming these limitations is crucial for enabling the practical application of Si anodes in high-energy-density LIBs. Super P (SP) carbon black, a widely used commercial conductive agent, consists of small spherical particles that form conductive networks within the electrode based on a point-to-point conduction model.In this model, electrons must traverse numerous contact points, with each point introducing resistance and thereby diminishing the overall conduction efficiency. Consequently, SP alone is insufficient for achieving optimal conductivity in Si anodes. On the other hand, carbon nanotubes (CNTs) feature an elongated strand-like structure that provides continuous electron transport paths, promoting uninterrupted and efficient electron flow across the electrode. The large surface area of CNTs further increases contact with active materials, boosting conductivity even with minimal CNT content. However, incorporating CNTs in Si electrodes faces challenges due to the hydrophobicity of CNT surfaces and pronounced van der Waals interactions arising from their large surface area, which result in aggregation in polar solvent-based Si electrode slurries. As the non-uniform dispersion of CNTs can disrupt ion and electron flow, ensuring the homogeneous distribution of CNTs is imperative to enhance the electrochemical performance of electrodes. Several methods have been reported to improve the dispersibility of CNTs. Avilés et al . introduced oxygen-containing functional groups onto CNT surfaces through acid treatment, increasing the hydrophilicity of CNTs and promoting stronger interactions with polar solvents, thereby reducing aggregation.However, the use of strong acids can damage the sp² hybridization of CNTs, adversely affecting electron transport. Zhou et al . synthesized Si-CNT composites by growing CNTs on the Si surface via chemical vapor deposition at 850 °C, achieving stable cycling performance for up to 1200 cycles.Nevertheless, the high operational temperatures (700–1000 °C) required for synthesis limit its commercial feasibility. Alternatively, polymer grafting has emerged as an effective strategy, enabling surface functionalization at moderate temperatures (60–100 °C) with minimal impact on CNT structural stability. Herein, we synthesized polyacrylamide-grafted CNTs (PAM-g-CNTs) by grafting acrylamide (AAm) onto the CNT surface. The introduction of amide groups offers a strong affinity for water molecules, and hydrogen bonding interactions between aqueous solvent and PAM-g-CNT promote uniform dispersion in water-based slurries. This homogeneous arrangement of CNT ultimately facilitates an efficient network to transport lithium ions (Li + ) and electrons.Also, PAM-g-CNT establishes a robust binding system through a hydrogen bond between polar functional groups and slurry components. Consequently, the PAM-g-CNT electrode could maintain a stable electrode structure beyond consecutive volume change based on stronger mechanical strength and adhesion of the electrode compared to CNT. The high diffusivity of ions and electrons and structural integrity made a synergetic effect on the electrochemical performance of the battery utilizing PAM-g-CNT. Notably, in electrodes with an elevated active material content of 80% and reduced binder and conductive agent ratios, PAM-g-CNT demonstrated stable cycling (72.1%) after 100 cycles. In contrast, commercial conductive agents exhibited substantial capacity fading (20.1%). PAM-g-CNT can efficiently interact with solvent and slurry components through hydrogen bonds, enhancing water affinity and improving the resistance of Si electrodes against swelling. These characteristics of conductive agents realized advanced electrochemical properties, rate performance, long-term cell performance, and electrodes with high energy density. Figure 1