Impact Of Anionic Structure Of Lithium Imide Salt On The Performances Of Solid Polymer Electrolytes For Rechargeable Lithium Metal Batteries

Solid polymer electrolyte?SPEs?,which possess great advantages over the liquid or gel polymer electrolytes,including the nonleakage,nonflammability,lighter weight,excellent design flexibility,and somehow inhibit the growth of unwanted Li dendrites,thus,would enhanced the safety and energy density of lithium batteries.The poly?ethylene oxide??PEO?-based SPEs,have been used widely in lithium batteries.SPEs are mainly composed of a polymer matrix and a conductive lithium salt,the performances of the SPEs are dominated by the used conducting salts.The early investigations indicate the FSO₂–group in lithium bis?fluorosulfonyl?imide?Li[?FSO₂?₂N],LiFSI?/PEO SPEs is more compatibility towards Li-metal anode?LMA?in comparison with conventional lithium bis?trifluoromethanesulfonyl?imide?Li[?CF₃SO₂?₂N],LiTFSI?-based one.It is indicated that modification the performance of SPEs can be achieved by rationally changing the anionic structure of the lithium salt?eg.introduce the FSO₂–group into the anionic structure of the lithium salt?.In present work,a spectrum of SPEs,comprising lithium?fluorosulfonyl??perfluoroalkanesulfonyl?imide(Li[?FSO₂?(n-C_mF_2m+1SO₂)N],m=0,1,2,and 4)and Li[?CF₃SO₂?₂N]?LiTFSI?as the conducting salt,and poly?ethylene oxide?as the polymer matrix,are compared for revealing the impact of anionic structure of lithium salt on the electrochemical performances for rechargeable lithium metal batteries.It is found that the Li[?FSO₂?(n-C_m F_2m+1SO₂)N]?m=0,1,2,and 4?/PEO SPEs have decent compatibility towards LMA compared with LiTFSI/PEO-based one,indicate that FSO₂–group exhibits good solid electrolyte interphase?SEI?film formation on LMA.The anodic stabilities of the SPEs and the cycle life of Li/LiFePO₄cells are favorably increased with increasement of n-C_mF_2m+1 group length in Li[?FSO₂?(n-C_mF_2m+1SO₂)N].It can be found that,particularly,for Li[?FSO₂??n-C₄F₉SO₂?N]?LiFNFSI?/PEO,the interfacial stability against both LMA and cathode has been elevated and that,moreover,Li/LiFePO₄ cells can operate stably for 300 cycles with a capacity close to 90% even at 1.0C.