Functionally graded materials (FGMs) and functionally graded structures (FGSs) are special types of advanced composites with peculiar features and advantages. This article reviews the design criteria of functionally graded additive manufacturing (FGAM), which is capable of fabricating gradient components with versatile functional properties. Conventional geometrical‐based design concepts have limited potential for FGAM and multi‐scale design concepts (from geometrical patterning to microstructural design) are needed to develop gradient components with specific graded properties at different locations. FGMs and FGSs are of great interest to a larger range of industrial sectors and applications including aerospace, automotive, biomedical implants, optoelectronic devices, energy absorbing structures, geological models, and heat exchangers. This review presents an overview of various fabrication ideas and suggestions for future research in terms of design and creation of FGMs and FGSs, benefiting a wide variety of scientific fields.

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A hybrid inorganic-organic ionic liquid based on sodium bis(fluorosulfonyl)amide (Na[FSA]) and [N-ethyl-N-methylpyrrolidinium][FSA] ([C2C1pyrr][FSA]) is investigated as an electrolyte for sodium secondary battery operation over an extended temperature and Na + ion fraction ranges. The phase diagram of the system reveals a wide liquid-phase temperature range at Na[FSA] mole fractions ranging from 0.3 to 0.7 near room temperature, where the 0.7 mole fraction equates to a molar concentration of 5.42 mol L −1. The viscosity and molar ionic conductivity are consistent with the fractional Walden rule, and the temperature dependence of these quantities obeys the Vogel−Tammann−Fulcher equation. The optimal Na[FSA] content of the ionic liquid occurs at mole fractions between 0.3 and 0.7 based on the sodium metal deposition/dissolution behavior and the rate and cycle properties of a NASICON-type cathode, Na3V2(PO4)3/C (NVPC). The greatest cycle efficiency, εcycle, of Na metal deposition/dissolution is observed at x(Na[FSA]) = 0.6 (εcycle = 93.3%). Although Na/NVPC half-cell tests indicate a maximum rate and cycle performance at x(Na[FSA]) = 0.6 (83.5% retention at 100 C (11700 mA g −1) and 80% retention after 4000 cycles at 2 C (234 mA g −1), NVPC/NVPC symmetric cell tests indicate that the greater Na[FSA] fraction provides better rate performance and that half-cell tests with a Na metal electrode do not provide reliable data for the target electrode/electrolyte system.

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The phase behavior of [N][BF] and [N][PF] (N = tetraethylammonium cation) binary systems has been investigated in the present study. Differential scanning calorimetry revealed that the crystal-to-plastic-crystal transition temperature decreases upon mixing the two salts, with a minimum at x([N][PF]) = 0.4, where x([N][PF]) denotes the molar fraction of [N][PF]. Powder X-ray diffraction analysis indicated the formation of a solid solution with a rock-salt type structure in the plastic crystal phase at all ratios and the lattice parameter a changes according to Vegard's law. In the crystal phase, two solid solution phases based on the structures of the single salts are observed. Raman spectroscopy confirmed the changes in the solid-solid transition temperature as observed by differential scanning calorimetry. Consequently, in the resulting phase diagram, the solid solution is formed in a wide x([N][PF]) range for both the crystal and plastic crystal phases.