Ultraviolet-Cured Al₂O₃-Polyethylene Terephthalate/Polyvinylidene Fluoride Composite Separator with Asymmetric Design and Its Performance in Lithium Batteries

Abstract

An Al 2 O 3 /polyethylene terephthalate (Al 2 O 3 /PET) film can be used as a practical battery separator with superior thermostability, but particle shedding inhibits wide application of this material. We developed a high-security Al 2 O 3 /PET film by incorporating a photoactive oligomer, poly(ethylene glycol)diacrylate (PEGDA), into the Al 2 O 3 coating, followed by ultraviolet (UV) irradiation. One side of the as-prepared film was coated with aqueous polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) to obtain a UV-Al 2 O 3 -PET/PVDF film. Optimizing the added PEGDA content is key to achieving an ideal balance between the strength and ionic conductivity of the UV-cured composite film. A PEGDA content of 18 wt % significantly enhances the adhesion of the inorganic coating after UV irradiation, and the corresponding film remains intact even after 1000 bends. The optimized UV-Al 2 O 3 -PET/PVDF separator has an average pore size of 0.6 μm and a breakdown voltage above 250 V. The separator exhibits good electrochemical performance (δ = 1.03 mS cm −1 , t Li + = 0.71, and electrochemical window = 5.5 V). Using the UV-Al 2 O 3 -PET/PVDF separator in batteries results in good charge retention at room temperature and 55 °C. The discharge capacity of a lithium iron phosphate (LFP)||Li battery is 137.3 mA h g −1 (84.1%) after 300 cycles at 0.2 C. The PVDF-HFP coating enhances the stability of the interface between the separator and the lithium metal anode.

PI-LAGP Separator─Construction, Battery Application Performance, and Chemical Valence Changes of Germanium

“…The ionic conductivity of PI–LAGP was greater than that of PI 5 . The possible reason is that the transmembrane transport of Li ions occurs in two ways: liquid electrolyte transport and LAGP interface transport …”

“…The AC impedance spectra were measured before and after polarization. The film Li-ion transference number was calculated with the BVE equation . The film stability with the Li anode was characterized by constant current cycling experiments at current densities of 0.5 and 5 mA·cm.…”

“…The film Li-ion transference number was calculated with the BVE equation. 42 The film stability with the Li anode was characterized by constant current cycling experiments at current densities of 0.5 and 5 mA•cm. −243 The withstanding voltage was tested according to the reported method.…”

“…−243 The withstanding voltage was tested according to the reported method. 42 The cathode was prepared as follows: LiNi 0.8 Co 0.1 Mn 0.1 O 2 , Super-P, and PVDF were uniformly dispersed in NMP at a mass ratio of 84:10:6 to obtain a mixed solution with a solid content of 20%, which was evenly coated onto 16 μm aluminum foil; then, the electrode sheet was successively dried in a blast oven (7 h@60 °C) and a vacuum oven (−0.1 MPa, 12 h@120 °C), followed by a roll-press at 80 °C to produce a 50 μm thick cathode plate (active material loading 5.5 mg cm −2 ). The 2032 batteries were assembled in a glovebox under argon (both O 2 and H 2 O contents were below 0.1 ppm) using a NCM811 cathode, a Li anode, and a separator film.…”

“…The possible reason is that the transmembrane transport of Li ions occurs in two ways: liquid electrolyte transport and LAGP interface transport. 42 The ability of the electrolyte to transport Li ions is represented by the Li-ion transference number (t Li + ). The separator with a high Li-ion transference number not only suppresses the growth of Li dendrites but also enhances the battery capacity.…”