Highly conductive divalent fluorosulfonyl imide based electrolytes improving Li-ion battery performance: Additive potentiating electrolytes action

Imide-based electrolyte salts are crucial in lithium-ion battery (LIB) research, due to their high oxidative capacity, thermal performance, and cycling stability. LIBs with imide electrolytes exhibit slow charge-discharge (CD) capacity and high efficiency, even though most of these electrolytes show low ionic conductivity (σ). Herein, we have synthesized two highly conductive and pure divalent imide electrolytes, lithium sulfonylbis(fluorosulfonyl)imide (LiSFSI) and lithium (1,3-phenylenedisulfonyl)bis(fluoro sulfonyl)imide (LiPDSFSI), for LIBs application. Compared to LiPDSFSI electrolyte, the LiSFSI imide electrolyte with mixed solvent ethylene carbonate (EC) and dimethyl sulfoxide (DMSO) (75:25 v/v) exhibits better electrochemical stability, σ, transference number (tL+), cycling stability, and high specific capacity of 142 mAhg−1 with the full cell battery configuration of LiFePO4/electrolytes/graphite at 0.1 C. Additionally, lithium bis(fluoro-sulfonyl)imide (LiFSI) (20%), as additive, improve their performance substantially. The results demonstrate that the LiSFSI electrolyte with LiFSI additive shows maximum σ (8.9 mS/cm at 30 °C), tLi+ (0.64), and anodic stability (5.47 V), which concurrently delivers high efficiency and improves specific capacity to 156 mAhg−1 with excellent capacity retention (99.93%) after 500 CD cycles with the full cell LiFePO4/electrolytes/graphite battery system.