Modification of electrode/electrolyte interface with progressive electrolyte design to ameliorate lithium-sulfur battery performance

Abstract

The necessity of eco-friendly energy generating and storing devices emerges due to the extreme climate changes. In order to replace fossil fuels, energy devices with superior energy density and energy efficiency are required. With the lowest redox potential, light weight, and high specific capacity, lithium has received attention in energy device market as a most valuable material. Various electrochemical reactions, lithium can generate the electric energy and store it by dynamic materials or states. Lithium-ion batteries (LIB) having intercalation chemistry are currently commercialized as first-generation lithium secondary batteries and are widely used. However, LIB needs further developments with respect to the energy density and cost reduction. Basically, it comes from the heavy and expensive transition metal oxide materials. To overcome it, new type of lithium based secondary battery break away from the layered transition metal oxide cathodes. In this respect, researches on lithium-sulfur batteries are active. This thesis begins with the general background and needs of lithium secondary battery systems. It then addresses the requirements of lithium sulfur battery having theoretically high energy density. Specifically, this work deals with the electrolyte designing methods to increase the energy density in terms of electrode/electrolyte interfaces amending in lithium sulfur batteries. Chapter 2 deals with a strategy to enhance the discharge capacity of lithium sulfur battery by addressing the carbon surface passivation by insulating lithium sulfide. By introducing the high AN additive, 3-D growth of Li2S can be achieved due to its high Li2S solubility. Chapter 3 shows the synergetic effect of high DN and AN properties with SCN- anion. Sulfur utilization is raised by increased Li2S and LiPS solubility and Li metal anode is protected by robust Li3N SEI layer. Chapter 4 presents deep analysis to elucidate the challenges for extremely lean electrolyte lithium sulfur batteries and breakthrough of it. It claims that sluggish redox kinetics of lithium polysulfides at the cathode/electrolyte interface and Li metal corrosion by highly active polysulfides are critical for extremely lean electrolyte condition. And it was figured out that RbNO3 additive can modify both cathode/electrolyte and anode/electrolyte interfaces with readily reductive Rb2S material.