Influencing ionic conductivity and mechanical properties of ionic liquid polymer electrolytes by designing the chemical monomer structure

Figures & data

Figure 1. Chemical structure of the polymer electrolytes examined in this study (m = 0: linear homopolymers; m > 0: polymer networks).

Figure 2. Glass transition temperatures of all investigated PIL networks with varied alkyl spacer X and imidazolium substituent lengths Y as well as crosslinker and conducting salt content (p(AACXImCYCl)/CL (mol%)/conducting salt (mol%)).

Table 1. Glass transition temperatures of the investigated polymer network samples p(AACXImCYCl)/CL (mol%)/conducting salt (mol%).

PIL network	Tg [°C]
p(AAC3ImC4Cl)/2.5/0	−45
p(AAC3ImC4Cl)/5/0	−43
p(AAC3ImC4Cl)/5/5	−54
p(AAC6ImC4Cl)/2.5/0	−53
p(AAC6ImC4Cl)/5/0	−43
p(AAC6ImC4Cl)/5/5	−64
p(AAC6ImC4Cl)/10/0	−50
p(AAC6ImC4Cl)/10/5	−64
p(AAC6ImC6Cl)/5/0	−55
p(AAC6ImC6Cl)/5/5	−51
p(AAC8ImC4Cl)/2.5/0	−53
p(AAC8ImC4Cl)/5/0	−57
p(AAC8ImC4Cl)/5/5	−60

Figure 3. Complex viscosity of the p(AAC6ImC4Cl)/CL (mol%)/conducting salt (mol%) IL networks.

Figure 4. (a) influence of alkyl number N (total number of C atoms) with 2.5 mol% crosslinker and without conducting salt, and (b) influence of conducting salt and crosslinker on the viscosity in dependence of temperature of p(AAC6ImC6Cl)/CL (mol%)/conducting salt (mol%) network samples.

Table 2. Fitting parameters η₀, B, T₀, and the correlation coefficient R² obtained by the VFT equation (1)(1) ${\sigma }_{ion}=\frac{d}{A\ast R_b}$(1) for the p(AACXImCYCl)/CL (mol%)/conducting salt (mol%) network samples.

PIL network	η0 [Pa s]	B [K]	T0 [K]	R^2
p(AAC3ImC4Cl)/2.5/0	1.49	37.97	235.59	0.9935
p(AAC3ImC4Cl)/5/0	1.77	19.50	253.67	0.9859
p(AAC6ImC4Cl)/2.5/0	1.96	8.68	270.50	0.9990
p(AAC6ImC4Cl)/5/0	1.97	7.65	272.30	0.9971
p(AAC6ImC4Cl)/9/0	2.19	2.10	284.12	0.9876
p(AAC6ImC4Cl)/10/0	2.29	1.36	286.13	0.9869
p(AAC6CIm6Cl)/2.5/0	2.38	2.83	277.33	0.9949
p(AAC6ImC6Cl)/2.5/5	2.28	4.88	270.29	0.9962
p(AAC6ImC6Cl)/5/0	2.42	0.83	285.78	0.9942
p(AAC6ImC6Cl)/5/5	2.47	1.16	285.37	0.9928
p(AAC8ImC4Cl)/2.5/0	2.09	5.28	270.16	0.9991

Figure 5. Ionic conductivites of p(AACXImCYCl)/CL (mol%)/conducting salt (mol%) IL networks with different crosslinker content and without conducting salt as a function of temperature.

Figure 6. Ionic conductivites of p(AACXImCYCl)/CL (mol%)/conducting salt (mol%) IL networks with 5 mol% conducting salt TBACl as a function of temperature.

Table 3. Fitting parameters σ_∞, E_A, and the correlation coefficient R² obtained using the Arrhenius equation (8)(8) $\sigma ={\sigma }_{\mathrm{\infty }}\mathrm{e}\mathrm{x}\mathrm{p}\left[\frac{-E_A}{R\ast T}\right]$(8) for the p(AACXImCYCl)/CL (mol%)/conducting salt (mol%) network samples (samples written in italic: one data point was masked for better R² value).

PIL network	σ∞ [S·cm^−1]	EA [J·mol^−1]	R^2
p(AAC3ImC4Cl)/2.5/0	3.50	119.89	0.9931
p(AAC3ImC4Cl)/5/0	3.27	99.43	0.9914
p(AAC3ImC4Cl)/5/5	2.95	79.07	0.9781
p(AAC6ImC4Cl)/5/0	2.92	73.58	0.9857
p(AAC6ImC4Cl)/5/5	2.94	78.90	0.9835
p(AAC6ImC4Cl)/9/0	2.50	56.87	0.9445
p(AAC6ImC4Cl)/10/0	2.92	75.08	0.9818
p(AAC6CIm6Cl)/2.5/0	3.29	99.10	0.9865
p(AAC6ImC6Cl)/2.5/5	3.39	108.91	0.9768
p(AAC6ImC6Cl)/5/0	3.13	88.38	0.9876
p(AAC6ImC6Cl)/5/5	3.18	92.70	0.9867
p(AAC8ImC4Cl)/2.5/0	2.57	60.86	0.9943
p(AAC8ImC4Cl)/5/0	3.22	91.62	0.9887
p(AAC8ImC4Cl)/5/5	2.93	75.41	0.9839

Figure 7. Swelling behavior of p(AAC6ImC6Cl)/CL (mol%)/conducting salt (mol%) IL networks in water (analyzed after one week of swelling).

Table 4. Ionic conductivities (at 20°C) of p(AAC6ImC6Cl)/CL (mol%)/conducting salt (mol%) IL network samples before and after swelling.

PIL network	σion, before [S·cm^−1]	σion, after [S·cm^−1]
p(AAC6CIm6Cl)/2.5/0	9.67·10^−7	7.71·10^−2
p(AAC6ImC6Cl)/2.5/5	2.03·10^−7	2.30·10^−2
p(AAC6ImC6Cl)/5/5	6.64·10^−7	5.10·10^−2

Figure 8. Redox reactions of p(TEMPO-MA)⁺/p(TEMPO-MA) and Zn²⁺/Zn⁰ redox couple.

Figure 9. Nyquist plot of the PEL with crosslinker, conducting salt and ionic liquid.

Figure 10. SEM images taken at a) the cross-section of the cathode p(TEMPO-MA) penetrated with PEL, b) zoom-in.

Figure 11. p(TEMPO-MA)/zinc battery with polymer electrolyte, a) charge/discharge capacities during cycling, b) selected charge/discharge curves.

Data availability statement

The data that support the findings of this study are available in the supplementary material of this article (Supporting Information).