Meltonix 1170 60

Fluorine doped tin oxide (FTO) glass substrates were purchased from Hartford Glass Co., Indiana, USA. Nanocrystalline TiO₂ (Ti-Nanoxide T/SP), scattering TiO₂ (Ti-Nanoxide R/SP), I₃⁻/I⁻ electrolyte (Iodolyte HI-30), activated platinum solution (Platisol T), and thermoplastic sealant (Meltonix 1170-60) were purchased from Solaronix (Aubonne, Switzerland). Organic dyes, L1 (5-[4-(diphenylamino)phenyl]thiophene-2-cyanoacrylic acid) and L2 (3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid), were acquired from Dyenamo, Stockholm, Sweden. All materials were used as received.

Thin MoS₂ flakes (<10 nm) were exfoliated using the Scotch tape method onto 300-nm-thick SiO₂/Si substrate, and electrodes (Ti/Au, 3/50 nm) were designed and patterned on flakes by electron-beam lithography and deposited by e-beam evaporation. A marker array was used for precise alignment of the electrodes to the selected flakes. The MoS₂ sample was then transferred to an Ar-filled glovebox for cell assembly. In the case of Li⁺ and K⁺ intercalation, Li/K metal was cold pressed onto Cu foil as the counter electrode; in the case of Na⁺ intercalation, NaCoO₂ was deposited onto an Al foil as the counter electrode. These electrodes were then sealed between a cover glass and the SiO₂/Si substrate with evaporated Ti/Au electrode, using hot melt sealing film (Meltonix 1170–60, Solaronix), leaving two little openings for liquid electrolyte filling. There is a ~50 μm gap between the glass and the SiO₂/Si substrate, which is then occupied by the corresponding electrolytes. The electrolytes were 1 M LiPF₆, NaPF₆, KPF₆ in EC/DEC for Li⁺, Na⁺, and K⁺ intercalation, respectively. After filling the electrolyte by capillary effect, the two openings were sealed by using epoxy.

The entire cell was assembled inside an Ar-filled glovebox. Patterned gold electrode on the SiO₂/Si substrates was used as the working electrode. Li metal was laminated onto the copper foil and used as the counter electrode. A cover glass slide was placed on top of the electrodes and the cell was then sealed by a thermoplastic ionomer (Meltonix 1170-60, Solaronix), leaving two small openings for filling liquid electrolyte. Here, Li₂S₈ dissolved in DOL/DME (1:1 v/v) with 1 M LiTFSI and 1 wt% LiNO₃ additive was used as the catholyte. 0.2 M Li₂S₈ was used for the sulfur nucleation experiment in Fig. 1 to clearly show the evolution process and 0.5 M Li₂S₈ was used for all other experiments. After filling the electrolyte, epoxy was used to finally seal the remaining two openings.