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

Table of Contents: Most conventional carbon conductive additives used in Li-ion batteries fail to deliver satisfactory electrochemical performances in sulfide all-solid-state batteries (ASSBs) due to instability with sulfide electrolytes. We demonstrate lithium enhanced functionalized carbon nanofiber (LF-CNF) that was surface-treated at a molecular level to enhance its Li-ion conductivity and chemical stability. As a result, unprecedently high performance was obtained from the cathode composite made of uncoated LiNi0.8Co0.1Mn0.1, argyrodite and LF-CNF. [Display omitted] •Li-enhanced functionalized carbon nanofibers (LF-CNFs) were prepared by simple acid treatment and the subsequent H+ substitution with Li+.•High ionic conductivity of LF-CNF/argyrodite composite (5:95 in wt.%) of 1.51 mS cm−1, which is 3 times larger than that of pure argyrodite.•LF-CNF exhibits exceptionally high stability with argyrodite from long-term storage test.•Comparably the highest discharge capacity compared to the literature review (Table S1), ca. 198 mAh g−1, with an excellent capacity retention of ∼ 79 % over 50 cycles at 0.1C was obtained from the composite of LiNi0.8Co0.1Mn0.1O2, argyrodite, and LF-CNF. Despite the recent advancement of sulfide all-solid-state lithium batteries, the choice of their respective components 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 conductivity. 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 conduc