Providing More Active Sites via Reactivation of “Dead Li₂S” to Enhance the Long Cycle Performance of Lithium–Sulfur Batteries

Accelerating Li2S2/Li2S reduction through catalysis to enhance the apparent conversion kinetics has emerged as an innovative paradigm for a highly efficient lithium–sulfur battery. Nonetheless, the sluggish kinetics of the solid–solid conversion from solid-state intermediate product Li2S2 to the final discharge product Li2S (corresponding to the last 50% of the theoretical capacity) leads to the premature end of discharge and low discharge capacity output and sulfur utilization. Here, we add 1-butyl-1-methylpyrrolidine trifluoromethanesulfonate ([P14][OTf]) to a typical ether electrolyte, which in turn promotes the slow Li2S2/Li2S conversion kinetics by increasing the solubility of Li2S/Li2S2. The three-electrode experimental and characterization studies disclose that the exchange current densities of Li2S2 reduction, Li2S oxidation, and Li2S2 oxidation are up to 2.28 times, 4.6 times, and 1.04 times than those of the control electrolyte, respectively. Furthermore, the modified electrolyte could activate “dead Li2S”, thus providing more reactive sites and inducing small particle Li2S/Li2S2 deposition. Accordingly, the LSBs containing the Control/5 wt % [P14][OTf] electrolyte exhibit a significantly improved capacity rate of 40% compared with the traditional electrolyte at 0.5 C for 500 cycles (corresponding to a fading rate 0.1% per cycle). We believe that increasing Li2S2/Li2S solubility via electrolyte modification provides practical opportunities toward long-life batteries

An in Situ Potential-Enhanced Ion Transport System Based on FeHCF–PPy/PSS Membrane for the Removal of Ca²⁺ and Mg²⁺ from Dilute Aqueous Solution

An in situ potential-enhanced ion transport system based on the electrochemically switched ion permselectivity (ESIP) membrane was developed for the effective removal of Ca²⁺ and Mg²⁺ from dilute aqueous solution. In this system, uptake/release of the target ions can be realized by modulating the redox states of the ESIP membrane, and continuously permselective separation of the target ions through the ESIP membrane can be achieved by tactfully applying a pulse potential on the membrane and combining with an external electric field. In this study, iron hexacyanoferrate (FeHCF)–polypyrrole/polystyrenesulfonate (PPy/PSS) ESIP membrane with high conductivity and high flux was prepared by using stainless steel wire mesh (SSWM) as conductive substrate. The driving force for the ion transport was analyzed in detail by the equivalent circuit of the system. It is found that the FeHCF interlayer between the SSWM substrate and the PPy/PSS membrane played an important role in removing Ca²⁺ and Mg²⁺ from aqueous solutions, and markedly enhanced the separation performance of the membrane due to the improvement of the electroactivity as well as the change of the surface morphology. Influences of the applied cell voltage of the external electric field and the pulse (constant) potential across the membrane on the separation of Ca²⁺ and Mg²⁺ were investigated. It is demonstrated that the pulse potential was more beneficial for improving the removal efficiency than the constant potential applied on the membrane. The hardness of the treated water was reduced to 50 ppm (CaCO₃) by applying a pulse potential of ±2.0 V and an cell voltage of 5.0 V when the initial concentration of Ca²⁺ was 10 mM (1000 ppm (CaCO₃)). It is expected that the in situ potential-enhanced ion transport system based on the FeHCF–PPy/PSS membrane could be used as a novel water softening technology