Berardan et al. showed that 30% Li-doped (CoCuMgNiZn)O demonstrates an ion conductivity of 10−3 S cm−1 (Berardan et al., 2017). Qui et al. prepared a compositionally complex HEAs np-AlNiCoFeX (X = Mo, Nb, Cr) to enhance the oxygen evolution reaction (OER) performance (Qui et al., 2019). They reported that an increased number of elements improves the catalytic activity, kinetics, and overall OER performance. These findings greatly inspired the scientific community on the development of novel high entropy materials composition in electrochemical energy storage and conversion technologies. We design and synthesize novel high entropy spinel oxide for use as a functional interlayer to anchor the polysulfides as well as to facilitate the conversion of soluble LiPS and control the kinetics of electrochemical reactions at the sulfur cathode in a Li-S battery (LSB). We also design and synthesize an advanced high entropy cubic perovskite material using solid-state method for use in PEO-based inorganic solid-state electrolyte in order to improve the ionic conductivity of the electrolyte, stabilize the cubic structure in LSBs. We design a novel high entropy oxide material to verify the suitability for use in Li-air battery system by taking the advantage of the favourable electrocatalytic activity during oxygen redox reactions. We develop high entropy oxysulfides for use as electrocatalysts for overall water-splitting.