Rechargeable Zn2+/Al3+ dual-ion electrochromic device with long life time utilizing dimethyl sulfoxide (DMSO)-nanocluster modified hydrogel electrolytes

Despite recent advances in hydrogel electrolytes for flexible electrochemical energy storage, ion conductors still exhibit some major shortcomings including low ionic conductivity and short lifetimes. As such, for applications in electrochromic batteries, a transparent, highly conductive electrolyte based on a dimethyl-sulfoxide (DMSO) modified polyacrylamide (PAM) hydrogel is being developed and implemented in a dual-ion Zn2+/Al3+ electrochromic device consisting of a Zn anode and WO3 cathode. Gelation in a DMSO : H2O mixed solvent leads to highly increased electrolyte retention in the hydrogel and prolonged life time for ionic conduction. The hydrogel-based electrochromic device offers a specific charge capacity of 16.9 μAh cm−2 at a high current density of 200 μA cm−2 while retaining 100% coulombic efficiency over 200 charge–discharge cycles. While the DMSO-modified electrolyte shows ionic conductivities up to 27 mS cm−1 at room temperature, the formation of DMSO : H2O nanoclusters enables ionic conduction even at temperatures as low as −15 °C and retention of ionic conduction over more than 4 weeks. Furthermore, the electrochromic WO3 cathode gives the device a controllable absorption with up to 80% change in transparency. Based on low-cost, earth abundant materials like W (tungsten), Zn (zinc) and Al (aluminum) and a scalable fabrication process, the introduced hydrogel-based electrochromic device shows great potential for next-generation flexible and wearable energy storage systems.

In Fig. S3(a), an assembled single layer dual-ion device on ITO/glass was tested towards its ionic conductivity in operation.The fresh device shows a resistance of 17 Ohm as the x-intercept, which is reduced to 16 Ohm when colored and 16.5 Ohm for the bleached device, indicating the insulator/metal transition of the device 2 .Resistance values were determined as the high frequency intercept with the x-axis following a Randles Cell model for an equivalent circuit with mixed kinetic and charge-transfer control (Fig. S14).  the unmodified sample dries out after approximately 8 days and does not show any conductivity after 4 days.The modified sample retains 5% of its conductivity after 10 days.With increasing humidity, the unmodified samples retain their conductivity longer, but not as long as the modified samples.The DMSO modified hydrogel retains nearly 75% ionic conductivity after 10 days of storage at 50% RH.
The RH was held constant by nitrogen and air flow into a closed of box.Optical transmission spectra of ITO/PET, the polyacrylamide hydrogel and the combination of both.
The optical transmission of the single substrate is around 82% throughout the visible spectrum.PAM shows slightly increased transmission around 90%, while the combination of PAM and ITO shows nearly perfect transmission around 95%.The increase in transmission can be attributed to the change at the ITO interface.When in contact with PAM, the scattering from the ITO surface roughness is decreased.The WO 3 electrodes were bleached/colored in aqueous mixed electrolytes before investigation and repeatedly rinsed in DI water to remove traces of the electrolyte.For the colored device, there is a slight increase in aluminum signal, which is a signature of aluminum intercalation.Fig. S10 shows the faradaic capacity over the square root of the scan rate.By interpolating the experimental values (black), the surface capacitive contribution towards the overall capacity can be determined. 3The intercept is 96.7 mF/cm², and the slope is 167 mF/cm².

Figure S1 :
Figure S1: EDX spectra of dried hydrogels with and without DMSO modification.

Fig
Fig.S1shows the EDX spectra of dried hydrogel samples.Both samples were soaked in ZnSO 4 for 72h to create a reference background of Zn.Freeze drying was conducted for over 24h to ensure full

Figure S2 :
Figure S2: Possible mechanisms of DMSO incorporation into PAM-hydrogel.(a) Water molecule

Fig
Fig. S2 shows the proposed mechanisms for DMSO incorporation upon gelation of acrylamide.The

Figure S3 :
Figure S3: Electrochemical properties of the electrolyte, electrodes and device.(a) EIS analysis of the

Fig. S3(
Fig. S3(b) shows CV cycling of a first and a 100 times cycled device with a sweep rate of 100 mV/s

Figure S4 :
Figure S4: (a) Relative Weight and (b) ionic conductivity over time for samples with and without

Figure S5 :
Figure S5: Optical transparency of ITO/PET substrate, DMSO-modified hydrogel and a combined

Figure S6 :
Figure S6: Photographs of hydrogel samples after 28 days of drying with (left) and without (right)

Fig
Fig. S6 depicts a photograph of two hydrogel samples with and without DMSO modification, which

Figure S7 :
Figure S7: CV measurement of WO3-zinc electrochromic device at 0.5 mV/s sweep rate.Sample was

Fig. S7 illustrates
Fig. S7 illustrates the cyclic voltammetry of the electrochromic device at 0.5 mV/s.Indicated in red

Figure S8 :
Figure S8: Retention of device capacity over 30 cycles of repeated pressure (a) and bending (b).(c)

Figure S9 :
Figure S9: (a) XPS spectra of Al2p-region with early onset of Al2p X-ray emission.XPS spectra of oxygen 1s region corresponding to lattice oxygen O 2-(530 eV) and OH -as defect oxygen (531.9 eV) in

Fig. S9(
Fig. S9(b-d) illustrates the XPS signal of O1s in a pristine, single cycled and 100 times cycled WO 3 electrode.The figures indicate that lattice oxygen gets replaced when Al 3+ intercalation occurs, while

Figure S10 :
Figure S10: Capacity extracted from the CV-measurements in Fig. 4(a) over one over the square root

Fig. S11(
Fig. S11(a) and (b) show charge discharge profiles for electrochromic double layer dual-ion batteries

Fig. S12 :
Fig. S12: Comparison of charge-discharge capacity for dual-ion electrochromic devices in different

Fig. S12 depicts
Fig.S12depicts the dependence of charge capacity on the electrolyte concentration.The best charge capacity is achieved for a balanced electrolyte, while high relative concentrations of Al 3+ lead to high

Fig. S13 :
Fig. S13: Modified schematic for wearable prototype device.The zinc strip is attached to the side of

Fig
Fig.S14illustrates the equivalent circuit used to determine the ionic conductivity of devices.Here, R s is the series resistance of the cables and the electrolyte, R ct is the Faradaic charge-transfer resistance at the electrolyte/electrode interface, C dl is the double-layer capacitance at the interface, and Z w is the Warburg impedance which models ion diffusion into electrodes.

Table S1 :
Elemental composition of hydrogel samples with and without DMSO modification as

Table S2 :
EDX analysis of a pristine, one time cycled and post mortem (1000 cycles) WO 3 electrode of an electrochromic device in ZnAl electrolyte.EDX analysis was conducted at 20 kV at 2000 times magnification.

Table
S2 compares the elemental composition of electrochromic devices during their life cycle.The pristine sample shows elements W from the tungsten oxide and In, Sn from the ITO layer.Si arises from the glass substrate.Trace amounts of C are atmospheric impurities.Chlorine and Sulphur species are part of the electrolyte.The first cycle shows an atomic relation of 4.6:1 Al to Zn, while the post mortem electrode shows a relation of 5.4:1 of the two species.

Table S3 :
EDX analysis of hydrogel samples.Weight percentage of elements in a pristine hydrogel and the one used in cycling an electrochromic device.Both samples were initially soaked in 1M ZnAl electrolyte.