Lithium-enhanced functionalized carbon nanofibers as a mixed electronic/ionic conductor for sulfide all solid-state batteries

Despite the recent advancement of sulfide all-solid-state lithium batteries, the choice of their respective com-ponents yet requires further comprehensive investigations into their functionality and compatibility. While the development of cathode materials and sulfide electrolytes appears to be greatly advanced, there seems a lack of attention on carbon conductive additives. As sulfide electrolytes are unstable with conventional carbon conductive additives, it is necessary to develop conductive additives with a satisfactory electronic conductivity and good chemical/electrochemical stability with sulfide electrolytes. This study proposes a new mixed conductor based on carbon nanofiber (CNF), namely lithium-enhanced functionalized carbon nanofiber (LF-CNF), exhibiting a greatly enhanced Li-ion conductivity with a little compensation of their electronic conduc-tivity. By utilizing LF-CNF, a discharge capacity of ca. 198 mAh g-1 at 0.05C and ca. 148mAh g-1 after 50 cycles at 0.1C were achieved from the cathode composite of LiNi0.8Co0.1Mn0.1O2, argyrodite solid electrolyte and LF-CNF (70:30:5 in mass). Furthermore, LF-CNF appears to reduce detrimental cation mixing after storage in Ar-atmosphere over one month and at high voltage cycling of 4.5 V. Our work highlights that the conductivity tuning of conductive additives offers a great performance enhancement for high-energy sulfide electrolyte based solid-state batteries.