Synthesis and application of bifunctional flame retardants and TFSI resembled salt additives for Li battery

Abstract

Overall, many researchers insisted that common lithium ion battery could not satisfy a battery candidate for electric vehicle due to its low energy density. To overcome this problem, lithium metal anode came up as a great candidate because of the highest charge capacity. However, lithium metal was too reactive, so lithium dendrite formation was problematic. To solve this problem, we designed and synthesized novel electrolyte additives using various synthetic method. Chapter I introduces the synthesis and application of bifunctional flame retardants for Li battery. We embodied common flame retardant such as phosphate and SEI forming agent like vinyl or vinyl carbonate in one molecule using simple synthesis and purification. We expanded our work into diversification of linker (carbon, oxygen, nitrogen, etc.) and SEI forming agent. Also, we tested our additives by co-working with prof. Nam-soon Choi’s group. Unfortunately, two candidates NKCP-1 and NKOP-1 were not that effective in case of cell performance, but we got that NKOP series had much higher flame retardancy. |Chapter II presents the synthesis and application of TFSI resembled salt additives for Li battery. We utilized TFSI main anion due to its structural stability and compatibility with common electrolyte. We synthesized LiMTFSI composed by lithium cation and methane(trifluoromethane)sulfonimide anion. It 8 was synthesized by common acid-base SN reaction, and purified by simple filter using solubility difference. Also, we moved on to synthesize silver salt AgFSI·2MeCN. It was easily and perfectly synthesized with KFSI (potassium bis(flourosulfonyl)imide salt) and AgNO3. By nmr spectra, we checked 100% conversion in a very short reaction time. These two additives was tested as electrolyte additives by prof. Nam-soon Choi’s group too, and fortunately silver salt showed a possibility as a candidate to stabilize the electrode surface and electrolyte system.