Surfactant modified CNTs@S as cathode materials for high rate performance lithium sulfur batteries

Abstract

The cathode materials are an important aspect of lithium sulfur battery research. This paper focuses on the electrochemical changes in the interface between cathode and electrolyte, via the surface modification of [email protected] composites by different types of surfactant. And the cause of this phenomenon is speculated through some comparative experiments. We find that the surfactant adsorbed on the surface of the [email protected] produce two effects in opposite directions on the interface between cathode and electrolyte: On the one hand, interaction between the hydrophilic group of surfactant and the electrolyte reducing the charge transfer impedance and improving the electrochemical reaction rate; On the other hand, the contact between the hydrophobic group of surfactant and [email protected] leads a new impedance creating. If these two opposite effects are properly controlled, the battery impedance can be substantially reduced. Finally, with the [email protected] cathode modified by APG, the charge transfer impedance decreased from 127.2 Ω to about 6.3 Ω, even with the newly generated contact impedance, the total impedance is approximately 1/9 of the original. This change increases the maximum charge and discharge current density of the [email protected] battery from 1 C to 7 C. Even both with a high sulfur loading of 5.3 mg cm−2 and a low electrolyte/sulfur ratio of 4.1 mL g−1, the Li-S batteries with [email protected] cathode modified by APG still deliver a high capacity of 2.38 mAh cm−2 (66% of initial capacity) after 50 cycles. Moreover, this simple modification strategy is suitable in different carbon-sulfur composites to improve the high current density charge and the discharge performance of Li-S batteries. It brings a new mentality to the industrial application of Li-S batteries.