Understanding the Carbon Additive/Sulfide Solid Electrolyte Interface in Nickel-Rich Cathode Composites and Prioritizing the Corresponding Interplay between the Electrical and Ionic Conductive Networks to Enhance All-Solid-State-Battery Rate Capability.

All-solid-state lithium batteries, including sulfide electrolytes and nickel-rich layered oxide cathode materials, promise safer electrochemical energy storage with high gravimetric and volumetric densities. However, the poor electrical conductivity of the active material results in the requirement for additional conducive additives, which tend to react negatively with the sulfide electrolyte. The fundamental scientific principle uncovered through this work is simple and suggests that the electrical network benefits associated with the introduction of short-length carbons will eventually be overpowered by the increase in bulk resistance associated with their instability in the sulfide electrolyte. However, applying just the right amount of short carbon fibres minimizes degradation of the sulfide solid electrolyte and maximizes the electron movement. Therefore, we propose the application of a low-weight-percent carbon nanotubes (CNTs) coating on the nickel-rich cathode LiNi0.8Co0.1Mn0.1O2 (NCM811) along with large-aspect-ratio carbon nanofibers (CNFs) as the primary conductive additive. When only 0.3 wt % CNTs was utilized with 4.7 wt % CNFs, an initial Coulombic efficiency of 83.55% at 0.05C and a notably excellent capacity retention of 90.1% over 50 cycles at 0.5C were achieved along with a low ionic resistance. This work helps to confirm the validity of applying short carbon pathways in sulfide-electrolyte-based cathode composites and proposes their combination with a larger primary carbon additive as a solution to the ongoing all-solid-state battery rate and instability issues.

Distinctive optical transitions of tunable multicolor carbon dots.

Three types of carbon dots (CDs) are synthesized from isomers of phenylenediamine to develop multicolor nanomaterials with low toxicity, high stability, and high quantum yield. The distinctive electronic structures of CDs lead to the characteristic optical transitions, such as three colors of blue, green, and red, which are primarily attributed to the difference in configurations, despite the similar basic structures of conjugated systems. The excitation-independent emission and the single exponential decay of CDs indicate the single chromophore-like nature in each type of CD. In addition, the two-photon luminescence of CDs exhibits a comparable shape and time profile to the typical photoluminescence with high photostability. Although the surface-related defect states are observed by intragap excitation, the contribution of defect states is barely observed in the emission profile upon band gap excitation. Consequently, the controllability of optical transitions in CDs enhances the potential of tunable multicolor nanomaterials for various applications as alternatives to quantum dots containing toxic elements.