Correlation between the Coherence Length and Ionic Conductivity in LiNbOCl4LiNbOCl_4 via the Anion Stoichiometry

$LiNbOCl_4$ is a recently reported material with high $Li^+$ conductivities of ∼10 $mS·cm^{–1}$ at room temperature. Here, we explore how changing the anion ratio and the $Li^+$ content in the $Li_{1–x}NbO_{1–x}Cl_{4+x}$ series (−0.4 ≤ x ≤ 0.2) affects the ionic conductivity of the material. In doing so, we find that the maximum coherence length and ionic conductivity of $LiNbOCl_4$ are highly dependent on the $O^{2–}$/$Cl^–$ anion ratio in the material. Specifically, we show that, while an amorphous phase fraction of $LiNbOCl_4$ remains constant throughout the substitution series, any excess of $O^{2–}$ results in a rapid decrease in the maximum coherence length of the crystaline fraction in each sample. Through a combination of diffraction and spectroscopic techniques, we show that this occurs because the $O^{2–}$ anions cannot exist on the terminal sites of the $[NbOCl_4]_∞^{–}$ chains in the material, even when it is made with an excess of $O^{2–}$ resulting in a shortening of those chains. In contrast, it was observed that $Cl^–$ can occupy the bridging sites resulting in a dependence of the coherence length to the anion ratio. As such, the ionic conductivity of $LiNbOCl_4$ can be maximized by controlling the maximum coherence length in the material through the anion ratio. Notably, we achieved high ionic conductivities for $LiNbOCl_4$ consistent with literature reports only when the material was slightly $Li^+$ and $O^{2–}$ deficient, suggesting that the literature samples may also have been off-stoichiometry. In addition, we highlight the features missing from the current structural models of $LiNbOCl_4$ including the presence of mixed $Cl^–$/$O^{2–}$ sites, even in the stoichiometric material, which were previously thought to not exist. Finally, we show that slightly reducing the $Li^+$ and $O^{2–}$ contents in $LiNbOCl_4$ also translates to higher capacities when it is used as a catholyte in solid-state batteries. These findings show the importance of careful control of the stoichiometry in $LiNbOCl_4$ to optimize its properties and highlights the potential of $LiNbOCl_4$ for use as a catholyte in solid-state batteries

Graded Cathode Design for Enhanced Performance of Sulfide-Based Solid-State Batteries

Solid-state batteries present a promising technology to overcome the energy density limitations of lithium-ion batteries. However, achieving a high areal loading in cathodes without introducing significant transport limitations remains a key challenge, particularly in thick electrodes. In this work, we study the impact of a three-layer graded cathode design on the performance of a $LiNi_{0.83}Co_{0.11}Mn_{0.06}O_2$ (NCM83)$/ Li_6PS_5Cl$ (LPSCl) composite cathode using a combination of experiments and microstructure-resolved simulations. An increased LPSCl content at the separator and higher NCM83 content toward the current collector improve effective charge transport, resulting in better rate performance and reduced overpotentials at high current densities. This comprehensive experimental and theoretical study demonstrates that the optimization of cathode design has the potential to significantly enhance the performance of solid-state batteries