Improvement Of Li-S Battery By The Application Of Conductive Polymer

As a multi-electrons reaction cathode active material, the elemental sulfur has a theoretical capacity of 1675 m Ah/g. When matched with metallic lithium, the theoretical energy density of lithium-sulfur battery can reach up to 2600 Wh/kg. Besides, the elemental sulfur has advantages of natural abundance, low cost, safety and environmentally friendliness. Therefore, lithium-sulfur battery is considered as a promising high specific energy secondary battery system for the next generation.However, lithium-sulfur battery has problems of poor cycling stability and low coulombic efficiency. The main reason for those problem lie in:(1) Poor conductivity of elemental sulfur;(2) intermediate product during charge-discharge process are easy to dissolve into the electrolyte, generating “shuttle” effect;(3)density difference between elemental sulfur and the final discharge product Li2 S, resulting in 80% volume expansion, which will cause chalking and structure collapse of cathode. To solve these problems, we can start from the following aspects:(1) adding one or more electron conductor with sulfur to improve conductivity;(2) improving electrolyte system;(3) protection of lithium anode. In this paper, we applied conductive polymers to cathode of lithium-sulfur battery cathode to improve battery performance based on characteristics of conductive polymers. The main contents and results are as follows:1. Commercial conductive polymer-poly-3,4-ethylene dioxythiophene: polystyrene sulfonate(PEDOT: PSS) was used to paste on the surface of the pristine S electrode of lithium-sulfur battery. Because of its conductivity, hydrophily, flexibility and other characteristics suitable for lithium-sulfur battery, PEDOT:PSS-coated S cathode helps to improve the specific capacity, limit polysulfide migration and relieve volume expansion. The first discharge capacity is 1061 m Ah/g at 0.2 C, and it still retain 650.6 m Ah/g after 100 cycles, the capacity retention is 61.3%. In addition, the battery energy density outstrips that of traditional Li Co O2/graphite battery, which is a breakthrough. It is noteworthy that the method is simple and suitable for large-scale industrial production.2. Hollow tubular conductive polymer-polyaniline(PANI) was synthesized, then PANI/S composite cathode material was obtained through a two-step thermal treatment. High-temperature treatment helps that a small amount of elemental sulfur reacts with polyaniline to form a cross-linked stereo SPANI network, and the rest of the melted elemental sulfur concurrently diffuses into the newly formed polymer networks or infuses into the hollow voids. Based on the high conductivity three-dimensional hollow tubular structure of PANI, the initial discharge capacity of PANI/S composite can reach 1303.5 m Ah/g at 0.2 C.