Liquid-feed flame spray pyrolysis enabled synthesis of Co- and Cr-free, high-entropy spinel oxides as Li-ion anodes

Typically, high-entropy oxide (HEO) and medium-entropy oxide (MEO) electrochemical studies rely on Co and/or Cr for high capacity; however, safety and cost issues can be prohibitive for large scale application. To this end, we report the synthesis and characterization of two Co-free, novel HEO compositions, replacing Co [(CoNiMnFeTi)(3)O-4] with Zn [(ZnNiMnFeTi)(3)O-4] and Cu [(CuNiMnFeTi)(3)O-4], for use as next generation anode active materials. The distinction between HEO and MEO is calculated based on the entropy metric via the sublattice model due to the two cationic sublattices in the spinel structure. XRD results indicate a single phase was maintained for all synthesized samples, and SEM/EDX showed uniform elemental distributions for each synthesized nanomaterial. While the best performing nanomaterial (ZnNMFT) showed some gravimetric capacity improvement over the industry standard graphite "Gr" (480 mAh g(HEO)(-1) vs. 372 mAh g(Gr)(-1)), there is a clear gain in volumetric capacity (2460 mAh cm(HEO)(-3) vs. 820 mAh cm(Gr)(-3)). A decrease in performance was expected by replacing Co in favor of Zn/Cu; however, galvanostatic cycling results show improved performance for ZnNMFT compared to both CoNMFT and CuNMFT when using high loading electrodes (>1 mAh cm(-2)). While performance alone is critical for industrial applications, cost can also act as an enabling or limiting factor. To this end, a brief economic analysis was undertaken showcasing the effect of high- vs. low-cost raw materials on both overall material cost and cost effiveness by factoring in electrochemical performance. By including observed discharge capacity, ZnNMFT showed improvements in capacity per cost 2x CoNMFT.