A Binder Free and High Sulfur Loaded Three-Dimensional Carbon Nanotubes Electrode for High Performance Li-S Batteries

Abstract

Rechargeable Li-S batteries represent advanced battery system offering high energy density with low cost and environmentally benign electrochemical energy storage compared to currently available Li-ion batteries. The critical limitations are mainly associated with the insulating nature of sulfur (5 x 10-30 S/m), and formation and dissolution of intermediate polysulfides (Li2Sx; 2<x<8) into the electrolyte during charge/discharge processes resulting in capacity fading and low cycling stability. Most of the previous strategies reported in literature suggested for entrapment of polysulfides considered the areal density of the sulfur in the cathode to be less than 2mg/cm2. However, in order to obtain superior electrochemical performance (high volumetric and gravimetric energy density) compared to currently available state-of-the art Li-ion batteries, the sulfur loading amount has to be incremented substantially, increasing the sulfur weight percentage in the cathode electrode, and optimize with the electrolyte (µL)/sulfur (mg) ratio for maximum electrochemical performance. Here in, we develop a simple and facile binder free approach without the use of any complex chemical routes (use of carbon black, PVDF, and NMP) to impregnate different S loading amount into micro-channeled conducting framework of three dimensional carbon nanotubes (3D CNTs). It also provides effective utilization of sulfur particles, high electrolyte absorbability facilitating well-localized polysulfides within the electrode structure, and maintaining good structural integrity during volume expansion. The proposed strategy delivered a specific capacity of ~1285mAh/g at 0.5C rate (1.55mA/cm2) and excellent rate capability for all different loading amounts. Furthermore, in this presentation the detailed synthesis for higher loading amount of sulfur and their superior electrochemical performance with unique physical and electrochemical properties will be discussed in detail.