ABSTRACT

Currently， rechargeable lithium batteries are widely used in our consumer electronic products， including cell phones， laptop computers， and cameras and so on． They have extraordinary potential for application in electric and hybrid electric vehicles due to their high energy and power density ［1］； however， the major challenges including the higher cost， safety issues related to the solvents and conductibility at lower temperatures are still waiting to be fixed．

In this Ph． D． thesis， two types of rechargeable lithium batteries： lithium-ion batteries and lithium-sulfur batteries are discussed． Two different approaches are presented， in the direction of achieving an enhanced electrolyte system for rechargeable lithium batteries．

One approach is based on the conventional poly （ ethylene oxide ）（PEO） -based solid polymer electrolyte （ SPE） system． The key feature of this approach is the preparation of nanoparticle lithium salts （NPLS） and low lattice energy fluorinated di-lithium salts． The ionic conductivities of these PEO-based SPEs were markedly improved， due to a decrease in the glass transition temperature （T _g ） of the polymer．

For lithium-sulfur （ Li-S ） batteries， the polysulfide shuttle （ PSS ），caused by the dissolution of cathode polysulfide intermediates into the electrolyte， has delivered a mortal blow to nearly every attempt at obtaining a viable Li-S battery． So， another approach involves the strategic design and synthesis of a series of room temperature ionic liquids （RTILs） to prevent PSS： i） Three series of di-cationic ionic liquids （DILs） were synthesiyed and characterized． DILs-based electrolytes display excellent properties， such as nonflammability， high electrochemical stability and thermal stability． ii） Twelve new asymmetric fluorinated RTILs （FRTILs） were also introduced． The FRTILs based electrolytes show even better properties than DILs-based electrolytes．