A Design for a PVDF-HFP/SN Ionic Conductive Composite Binder for Solid-State Lithium-Air Batteries

Abstract

Solid-state lithium-air batteries (SSLABs) are regarded as an ideal choice for next-generation energy storage technology due to their extremely high theoretical energy density. However, the severe solid-solid interfacial resistance between the air cathode and the solid-state electrolyte, coupled with the significant volume expansion caused by cathode products during charging and discharging, can easily lead to interfacial delamination and battery failure. To address this challenge, this study designed and prepared a multifunctional composite adhesive comprising polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), succinonitrile (SN), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and lithium aluminum titanate phosphate (LATP). By systematically controlling the mass ratio of the polymer backbone (PVDF-HFP) to the highly polar succinonitrile (SN), an optimal balance between mechanical adhesion and ionic conductivity was achieved. At the optimized ratio (PVDF-HFP:SN = 50:20), the composite film not only exhibits excellent room-temperature ionic conductivity (0.45 mS·cm–1), a wide electrochemical stability window exceeding 5 V, and superior mechanical properties but also constructs a continuous three-dimensional ion transport network within the cathode and achieves in-situ flexible wetting. Full-cell testing indicates that SSLABs using this optimized composite adhesive exhibit a significantly reduced first-cycle polarization overpotential of 0.75 V and successfully achieved 210 stable cycles at a current density of 100 mAh·g–1. More importantly, the temperature-dependent full-cell tests in this study demonstrate that, at an ambient temperature of 50 °C, the reaction kinetics and mechanical stability within the full cell achieve optimal synergy, with the battery cycle life increasing to 315 cycles; however, when the temperature rises to 60 °C, the melting phase transition of SN leads to the mechanical collapse of the polymer framework, triggering interfacial delamination and rapid battery failure. This work provides an innovative interfacial engineering strategy for addressing the challenge of interfacial mechanical-electrochemical degradation in SSLABs.