In-Situ construction of Lithium-Ion channel within PVDF/VNs@PDA composite separators for remarkable enhanced cycle stability and safety for lithium batteries (LIBs)

In this work, a non-solvent induced phase separation (NIPS) technique was used to prepare polyvinylidene difluoride (PVDF) lithium battery (LIB) separators. Firstly, vermiculite nanosheets (VNs) coated by polydopamine (PDA), i.e., VNs@PDA, was ultrasonically dispersed in DMAc and PVDF was solution-blended with VNs@PDA with final porous composite films obtained after the extraction of DMAc. Effects of the presence of VNs@PDA on both structure and properties of PVDF films were intensively studied, and the SEM observations further suggested that the addition of VNs@PDA heavily affected the thermodynamic parameters between the polymer and solvent, causing a remarkable enhancement on the thermodynamic instability of the PVDF solution system. The polymer-solvent phase separation by the addition of less nonsolvent tended to induce the formation of long finger-like pores. An incorporation of 7.0 wt% VNs@PDA resulted in an increase in ionic conductivity of the composite membrane from 0.320 mS·cm-1 to 1.515 mS·cm-1 via AC impedance tests. The incorporation of VNs@PDA not only enhanced the hydrophilicity of the composite films (as judged by water contact angle dropping from 112.7° to 74.2°), but also significantly improved both battery performance and mechanical properties. The present study provides a facile way of fabricating LIB separators with sufficiently high safety and superior performance.