Effect of NASICON-type LiSnZr(PO4)3 ceramic filler on the ionic conductivity and electrochemical behavior of PVDF based composite electrolyte

Abstract

Replacement of liquid electrolytes with polymer-based solid electrolytes is considered as the key to the realization of high-energy lithium metal anode in rechargeable batteries. However, the polymer electrolytes suffer from poor lithium-ion conductivity and low lithium-ion transference number. Poly(vinylidene difluoride) (PVDF) based polymer-ceramic composite electrolytes were fabricated at room temperature via the solution casting method. The effect of NASICON-type lithium tin zirconium phosphate (LiSnZr(PO4)3) particles added as the ceramic filler to the PVDF + LiTFSI polymer-salt matrix on the structure, ionic conductivity, transference number, and electrochemical behaviour was studied. The x-ray diffraction (XRD) and fourier transform infrared (FTIR) absorption studies confirmed the structure of the fabricated polymer as the mixed (α+β) phases of PVDF. The addition of LiSnZr(PO4)3 ceramic filler resulted in the enhancement in Li+ conductivity of the polymer composite and the sample with 15 wt% ceramic filler (CPE-15) showed the highest lithium-ion conductivity of 5.76 × 10−5 Scm−1 at 300 K. The addition of 15 wt% LSZP improved the stability window up to 4.73 V as confirmed by linear sweep voltammetry (LSV). A significant improvement in (tLi+) resulted from the addition of ceramic filler. The reversibility of Li+ transport across the composite ceramic-polymer electrolyte (15 wt% CPE) was confirmed by galvanostatic charging-discharging of symmetric lithium (Li||CPE||Li) cell at various current density for 100 h. Li||CPE||LTO cells with Li4Ti5O15 (LTO) as the working electrode, CPE-15 as the Li+ conducting separator, and Li foil as the counter electrode were fabricated to demonstrate the application of the CPE-15 as the electrolyte in all-solid-state batteries. Li||CPE||LTO cell delivered a specific discharge capacity of 133 mAhg−1 and 88% capacity retention after 20 cycles at 0.1C rate.