Investigating the Interface of Li{N(SO2F)2}(NCCH2CH2CN)2 Molecular Crystal Electrolytes for 5 V Class Solid-State Batteries

Molecular crystals composed of lithium bis(fluorosulfonyl)amide (LiFSA) and succinonitrile (SN), hereafter referred to as Li(FSA)(SN)2, are a promising solid electrolyte. To realize a wider application of molecular crystal solid electrolytes, it is critical to investigate the interface of Li(FSA)(SN)2 and 5 V-class positive electrodes. Here, we studied the interface of Li(FSA)(SN)2 with 5 V-class LiNi0.5Mn1.5O4 (LNMO) positive electrodes utilizing modeled thin-film batteries. The Li(FSA)(SN)2|LNMO interfaces degrade, leading to an increase in interface resistance and capacity loss. By inserting an amorphous Li3PO4 layer into the Li(FSA)(SN)2|LNMO interface, the low interface resistance remains, and no interphase layer is observed. The discharge capacity remains at 96% after 100 charge and discharge cycles. This study demonstrated the feasibility of operating Li(FSA)(SN)2 in a 5 V-class solid-state battery revealing the potential of molecular crystal solid electrolytes in high-energy-density batteries.