Three-Dimensional Nanoporous Polyethylene-Reinforced PVDF-HFP Separator Enabled by Dual-Solvent Hierarchical Gas Liberation for Ultrahigh-Rate Lithium Ion Batteries

Abstract

High-power lithium ion batteries (LIBs) have extensive applications ranging from electronic devices to electric vehicles. The composition and structure of separators largely impact the rate performances of LIBs. Here, a three-dimensional (3D) nanoporous poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP)-polyethylene (PE) composite separator is obtained through solvent liberation. The composite separator owns a high ionic conductivity of 1.01 mS•cm lithium ion batteries (LIBs) have extensive applications ranging from electronic devices to electric vehicles. The composition and structure of separators largely impact the rate performances of LIBs. Here, a three-dimensional (3D) nanoporous poly( −1 at room temperature due to the high porosity up to 95.6% and the uniform 3D pore distribution. LiFePO 4 /Li half-cells with the composite separator deliver record rate capacities of 97 mAh•g −1 at 10 C and 57 mAh•g −1 at 20 C. PE in the composite separator significantly enhances the mechanical strength and thermal stability of the separator. Theoretical calculations show that the difference in the absorption energy between acetone and NMP solvent on PVDF-HFP is the major driving force for the formation of the inter-island structure, which provides massive Li + transport channels during high-rate battery cycling.

High‐Performance PE‐BN/PVDF‐HFP Bilayer Separator for Lithium‐Ion Batteries

“…The most commonly used separators in LIBs are polyolefin separators predominantly polypropylene (PP), polyethylene (PE), and their multilayer formations like PE/PP or PP/PE/PP owing to their high tensile strength and shutdown ability. Nevertheless, the polyolefin separators suffer from severe dimensional instability at elevated temperatures and poor compatibility with liquid electrolytes due to hydrophobic surface character, and have poor capability to retain electrolyte . Conventionally, polyolefin separators are prepared through dry or wet processes and their tensile strength, porosity, or Gurley number vary with respect to methods of preparation .…”

Recent Development in Separators for High‐Temperature Lithium‐Ion Batteries

“…The interaction between solvent and nonsolvent leads to the formation of pores by creating a thermodynamically stable and/or unstable system. The properties of solvents and nonsolvents have a great impact on the formation of pores during their interaction and phase transformation process, therefore the morphology varies from sponge‐like to finger‐like structure with an asymmetric distribution of pores. The sponge‐like morphology of separator prepared through the phase inversion method is shown in Figure c.…”

“…The blends of polyethylene and polymers have also been reported in order to introduce shutdown effect for avoiding internal short circuits at elevated temperatures (beyond the melting point of PE). Recently, Luo et al reported a PE incorporated PVDF‐HFP separator prepared through the solvent liberation method for ultrahigh C‐rate LIBs. The PVDF‐HFP/PE separator exhibits high thermal stability with 0% shrinkage at 150 °C for 1 h along with robust mechanical strength, as shown in Figure a,b.…”

“…a) Thermal camera images of Celgard 2325, PVDF‐HFP, and PVDF‐HFP/PE‐1.0 separators at different time intervals, b) tensile strength profiles of PVDF‐HFP separators with different weight contents of PE, c) electrolyte uptake graphs of Celgard 2325 and PVDF‐HFP/PE‐1.0 separators (inside SEM image of PVDF‐HFP/PE‐1.0), and d) discharge capacities of Celgard 2325 and PVDF‐HFP/PE‐1.0 separators at high current densities. Reproduced with permission . Copyright 2018, American Chemical Society.…”

“…The conventionally used separators for LIBs on large scale are polyolefin separators polypropylene (PP) and polyethylene (PE) or their multilayer formations due to their high tensile strength, good chemical stability, and thermal shutdown capability. But these separators exhibit high thermal shrinkage and low affinity to liquid electrolyte owing to the electrolyte‐phobic character and poor capability to retain electrolyte during cycle process, which limits their applications in high power, high capacity, and high‐temperature LIBs . Even, other single component separators developed from polymers, copolymers, or their blends are not meeting the requirements of high‐temperature LIBs.…”