Study on the characteristics of advanced alectrolyte and electrode/electrolyte interface

Abstract

The secondary battery of current choice is the lithium ion (polymer) battery, which typically consists of a graphite negative electrode and a $LiCoO_2$ positive electrode. However, it is known that the $graphite/LiCoO_2$ electrode pair has almost reached to their practical limit of energy density under conventional liquid electrolyte. In order to meet the ever-increasing energy demands of mobile devices, researchers are seeking new electrode materials that will lead to smaller, lighter, and longer-lasting batteries. Among various methods, there are two major approaches to increase the energy density of lithium secondary batteries. The best way is to develop new electrode materials with high energy density. However, it is generally accepted that to find a new electrode material with all the required properties is very hard within a limited period. The other efficient way is to get more energy from the conventional electrode materials $(graphite/LiCoO_2)$ by operating the battery under severe condition (high voltage) with help of additives. Therefore, advanced electrolytes containing functional additives such as anion receptor and solid electrolyte interphase (SEI) layer stabilizer must be developed and their effects on electrochemical characteristics must be precisely analyzed. In addition, advanced electrolytes for new electrode materials with large volume change are strongly required. In this work, the interaction behavior of anion receptors with electrolyte components (anion and organic solvent) was investigated. It is found that the dissociation degree of lithium salts, the viscosity of the conducting medium, and the mobility of anions were changed by introducing tris(pentafluorophenyl) borane (TPFPB) as an anion receptor into the liquid electrolyte, EC/DMC (1/2.5, v/v)/1M LiClO4. The transference number of the liquid electrolyte was enhanced with increasing the TPFPB content, but the total ionic conductivity was decreased due to the decreasing anionic ...