Sulfones with additives as electrolytes for rechargeable lithium ion batteries

So far the commercial lithium ion batteries and the three baseline chemistries identified by the BATT Program as reference, i.e. (a): High-voltage, high-energy Gr/LiPF6+EC:DEC/ LiNi1/3Mn1/3Co1/3O2; (b): Low-voltage, high-stability Gr/LiPF6+EC:DEC/LiFePO4; (c): Highvoltage, high-power Gr/LiPF6+EC:DEC/LiMn2O4, are all based on the use of mixed carbonate solvents (EC-DMC, etc). However, for applications in electric vehicles (EVs), hybrid-electric vehicles (HEVs), and plug-in hybrid-electric vehicles (PHEVs), the carbonate systems face two major challenges, or reasons for concern. The first relates to the presence of low boiling point linear carbonates (DMC DEC etc) which make thermal stability a major (safety) concern with these cells, especially under abuse or accident conditions. The second major concern arises from the fact that the carbonate systems are not compatible with high voltage cathodes (especially those above 5.0V) [1-4], which have been actively developed to increase the energy density of the battery and while bringing the battery cost down. Thus new electrolyte solvents with good thermal stability and wider electrochemical window are urgently needed. Here we propose to design, synthesize and characterize sulfone solvents that will permit the use of > 4.3V cathodes while maintaining both electrochemical and thermal stability. Sulfones, in which sulfur occurs in its highest oxidation state, are remarkably resistant to oxidation, and equally stable against reduction, with electrochemical windows as wide at 5.7 V by a conservative criterion [5]. Our work will build upon previous studies [5-7] which made sulfone solvents accessible by designing low symmetry and partially derivatized molecular variants with low melting points and lithium/graphite anode compatibility while maintaining the >5.0 window. We will synthesize new partially fluorinated and per-fluorinated sulfones and/or ethersulfones, as described below. The materials will be fully characterized for chemical, thermal and electrochemical properties to address their fitness for applications to high voltage, high energy density rechargeable lithium ion batteries. The proposed work will involve a staged three year effort that will address the synthetic and evaluation issues in a progressive fashion and will ensure that each years work provides a usable deliverable. Three stages will be executed sequentially since the results of prior phases will determine the course of subsequent phases.