The Utilization of Ionic Liquid in Aqueous Electrolyte with Nitrogen and Sulfur Co-Doped Reduced Graphene Oxide Combination with Carbon Nanotubes for Improving Charge Storage and Long-Life Zinc Ion Batteries

Rechargeable aqueous Zn||MnO2 batteries are promising alternatives to lithium-ion batteries because of their safety, environmental friendliness, recyclable, and low cost. However, unstable pure α-MnO2 causes poor practical performance and a short life cycle. In this work, firstly, we design and synthesize α-MnO2 nanofibers and nitrogen and sulfur co-doped reduced graphene oxide (N&S-rGO) using a simple hydrothermal process. Then, α-MnO2 /N&S-rGO/CNT composite was fabricated using a ball milling process as a cathode material for zinc ion batteries (ZIBs). Secondly, we modified the water-based electrolyte by adding 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][SO4]) to improve the cycle stability by suppressing zinc dendrite of ZIBs. As a result, the electrochemical performances of ZIBs using α-MnO2 /N&S-rGO/CNT with 5% (w/v) [EMIM][SO4] containing aqueous electrolyte possessed a high specific capacity, reaching 110 mAh g-1 at 25 mAg-1. In addition, the excellent cycle life at 150 mA g-1 exhibited by the utilization of 5–15% [EMIM][SO4] in aqueous electrolyte could be extended to 1000 cycles. The cylindrical cell ZIB achieved a discharge capacity of 80.2 mAh at 100 mA and maintained a capacitive retention of 70% over 150 cycles at 300 mA. The findings open the way to ZIBs' practical application.