RESEARCH SUMMARY
This study developed supramolecular polymer binders designed to improve the mechanical integrity and cycling stability of silicon anodes in lithium-ion batteries. Adamantane groups connected through either ethyl- or propyl-based diamide tethers were grafted onto sodium poly(acrylate), producing AEN-PANa and APN-PANa guest polymers that interacted with a crosslinked ฮฒ-cyclodextrin-epichlorohydrin host polymer to form AEN-PANa@ฮฒCDP and APN-PANa@ฮฒCDP networks. Rheological, thermal, nanoindentation, tensile, peel, molecular-dynamics, electrochemical, and microscopy analyses consistently showed that combining host-guest association with hydrogen bonding reinforced the binder network compared with the hydrogen-bond-only PANa-ฮฒCDP control, and that the additional methylene group in the propyl tether substantially strengthened these interactions. In tensile testing, PANa-ฮฒCDP exhibited an elastic modulus of 6.6 ยฑ 1.5 MPa, ultimate tensile strength of 2.4 ยฑ 0.5 MPa, and maximum strain of 109.1 ยฑ 21.9%, while AEN-PANa@ฮฒCDP reached 90.8 ยฑ 6.8 MPa, 9.8 ยฑ 1.1 MPa, and 66.4 ยฑ 7.6%, respectively. APN-PANa@ฮฒCDP was the stiffest and strongest formulation, with an elastic modulus of 183.5 ยฑ 23.6 MPa and ultimate tensile strength of 12.5 ยฑ 1.1 MPa, although its maximum strain decreased to 19.3 ยฑ 1.1%. T-peel testing similarly showed the greatest electrode adhesion for APN-PANa@ฮฒCDP at 0.86 ยฑ 0.09 N, compared with 0.72 ยฑ 0.07 N for AEN-PANa@ฮฒCDP and 0.42 ยฑ 0.06 N for PANa-ฮฒCDP. Molecular-dynamics simulations supported the experimental results, showing substantially stronger association for the propyl-tethered network. These mechanical improvements translated to better electrochemical durability: after 200 galvanostatic cycles, APN-PANa@ฮฒCDP, AEN-PANa@ฮฒCDP, and PANa-ฮฒCDP silicon anodes retained specific capacities of 2575, 1007, and 624 mAh/g, respectively, corresponding to capacity retentions of approximately 69%, 29%, and 18%. Overall, the study demonstrates that a seemingly minor change in tether length can substantially alter supramolecular polymer interactions, electrode adhesion, mechanical robustness, and long-term silicon-anode performance.
A CellScale BioTester biaxial tensile testing machine was used for both T-peel adhesion testing of silicon anodes and uniaxial tensile testing of the polymer binder films. For the T-peel experiments, commercial masking tape was adhered to the silicon-coated side of copper-sheet electrodes containing PANa-ฮฒCDP, AEN-PANa@ฮฒCDP, or APN-PANa@ฮฒCDP binders. Specimens were cut to 16 mm width and 70 mm length, clamped in the CellScale system, and uniaxially peeled at 10 mm/min. Importantly, these tests were conducted according to ISO 11339 for flexible-to-flexible bonded assemblies. The resulting steady-state peel forces were 0.42 ยฑ 0.06 N for PANa-ฮฒCDP, 0.72 ยฑ 0.07 N for AEN-PANa@ฮฒCDP, and 0.86 ยฑ 0.09 N for APN-PANa@ฮฒCDP, demonstrating substantially improved electrode adhesion when host-guest interactions were incorporated and the strongest adhesion with the longer propyl tether. The BioTester was also used for uniaxial tensile testing of freestanding binder films. Rectangular specimens measuring 10 mm ร 30 mm with an average thickness of 0.1 mm were mounted in the system using a 10 N load cell and stretched at a grip speed of 1 mm/min, with at least four specimens tested per formulation. Load and displacement were recorded continuously and converted to engineering stress and strain. These measurements showed progressive increases in elastic modulus and ultimate tensile strength from PANa-ฮฒCDP to AEN-PANa@ฮฒCDP to APN-PANa@ฮฒCDP, confirming that stronger supramolecular association substantially reinforced the polymer network. Together, the CellScale peel and tensile measurements connected molecular-scale host-guest interactions with macroscopic binder strength, electrode adhesion, and ultimately improved silicon-anode cycling stability.
