Effects of N-Doped Graphene and Carbon Black As Conductive Additives on Sulfur Cathodes in Lithium-Sulfur Batteries

Abstract

Lithium-sulfur (Li-S) batteries hold great promise to meet the pursuit on transportation electrification, given their theoretic energy density of 2600 Wh/kg, low cost, and S abundance[1, 2]. However, Li-S batteries are currently being retarded from commercialization due to several severe issues. On the S cathode side, S is highly insulating electrically and ionically. In addition, intermediate products of lithium polysulfides are prone to dissolve in liquid electrolytes and shuttle between the S cathode and Li anode. In this case, conductive materials are essential to maintain S cathodes accessible to electrons and ions. Carbon black is the most widely used conductive materials in various battery systems. In addition, other carbon materials such as carbon nanotubes and graphene have also been used as alternatives in previous studies. However, there lacks a comparative study on identifying their effects. Thus, we recently conducted a systematic study on the effects of a carbon black (Super P) and a nitrogen-doped graphene nanosheets (NGS) on S cathodes. Experimental results showed that the S cathode with Super P (see Figure 1a) achieves higher initial capacity but fade rapidly. In contrast, the S cathode with NGS (see Figure 1b) exhibits more stable cycling performance. In addition, there also are some differences in their discharge/charge profiles of the two S cathodes, indicating different effects of Super P and NGS on S cathodes. Based on the experimental results and other characterizations, fundamental mechanisms as well as the prospects of these two conductive materials are discussed. Manthiram, A., et al., Rechargeable lithium–sulfur batteries. Chemical Reviews, 2014: p. 11751-11787.Sun, Q., et al., Atomic and Molecular Layer Deposition for Superior Lithium-Sulfur Batteries: Strategies, Performance, and Mechanisms. Batteries & Supercaps, 2018. 1(2): p. 41-68. Figure 1