High electrochemical and mechanical performance of zinc conducting-based gel polymer electrolytes

Abstract

Zinc ionic conducting-based gel polymer electrolytes (GPEs) were fabricated from carboxymethyl cellulose (CMC) and three different zinc salts in a mass ratio ranging within 0-30 wt%. The effects of zinc salt and loading level on the structure, thermal, mechanical, mechanical stability, and morphological properties, as well as electrochemical properties of the GPEs films, were symmetrically investigated. The mechanical properties and mechanical stability of CMC were improved with the addition of zinc acetate, zinc sulphate, and zinc triflate, approaching the minimum requirement of a solid state membrane for battery. The maximum ionic conductivity of 2.10 mS cm^-1 was achieved with the addition of 15 wt% zinc acetate (ZnA), GPE_A15. The supported parameters, indicating the presence of the amorphous region that likely supported Zn²⁺ movement in the CMC chains, were clearly revealed with the increase in the number of mobile Zn²⁺ carriers in FT-IR spectra and the magnitude of ionic transference number, the decrease of the enthalpy of fusion in DSC thermogram, and the shifting to lower intensity of 2θ in XRD pattern. The developed CMC/ZnA complex-based GPEs are very promising for their high ionic conductivity as well as good mechanical properties and the ability for long-term utilization in a zinc ion battery.

Figure 1

Representative FT-IR spectra of CMC/zinc salt complex: (a) pure CMC, (b) GPE_A15, (c) GPE_S15, and (d) GPE_T15.

Figure 2

Tensile strength (a) and tensile modulus (b) of CMC with different zinc salts and concentration. (Blue) GPE_Ax system, (red) GPE_Sx system, and (green) GPE_Tx system. Data derived from 5 independent repeats. The curves are drawn as guides to the eyes.

Figure 3

Rheology characterization (a): (solid symbols) shear modulus, G′, and (hollow symbols) loss modulus, G″ of CMC host polymer in black colour and GPE_A15 sample in blue colour. The shear modulus at 1 Hz (b) of (blue) GPE_Ax, (red) GPE_Sx, and (green) GPE_Tx systems. The curves in (b) are drawn as guides to the eyes.

Figure 4

Representative DSC thermograms (A) of samples: (a) CMC, (b) GPE_A5, (c) GPE_S5, (d) GPE_T5, (e) GPE_A25, (f) GPE_S25 and (g) GPE_T25. Enthalpy of fusion of samples (B) in different zinc salts and concentration: (a) GPE_Ax, (b) GPE_Sx, and (c) GPE_Tx systems.

Figure 5

Tensile modulus as a function of temperature of CMC and GPEs composed of 15 wt% different zinc salts; inset: the physical appearance of (a) CMC and (b) GPEs.

Figure 6

Representative XRD patterns (A) of (a) CMC, (b) GPE_A15, (c) GPE_S15, and (d) GPE_T15; inset: deconvolution of CMC peak. Representative SEM micrographs (B) (×1000 magnification) of (a) CMC, (b) GPE_A15, (c) GPE_S15, and (d) GPE_T15.

Figure 7

Representative Nyquist plots of the symmetrical cell with separators (a) of swollen CMC in (blue) ZnA, (red) ZnSO₄, and (green) Zn(Tr)₂ solutions and without separators (b) of CMC, fitting with blue line and GPE_A15, fitting with red line. The fitting curves was performed with the equivalent circuit models using Z-view software. Ionic conductivity (c) with different salt content of GPE_Ax system: (black) the assembly cells with separators and (blue) without separators. Representative chronoamperometry profiles (d): (black) CMC and (blue) GPE_A15. Inset: the t_ion, of GPE_Ax system with different ZnA contents.

Scheme 1

The equivalent circuit models, fitting for the assembly cells including separator of (a) GPE_Ax, (b) GPE_Sx and GPE_Tx systems and (c) the assembly cells without the separator of GPE_Ax system.

Figure 8

Half Zn battery cell testing for charge/discharge cycle of (a) CMC, (b) GPE_A15, (c) charging process of CMC, and (d) charging process of GPE_A15.