Spinel to Rock-Salt Transformation in High Entropy Oxides with Li Incorporation

Abstract

High entropy oxides (HEOs) constitute a promising class of materials with possibly new and largely unexplored properties. The virtually infinite variety of compositions (multi-element approach) for a single-phase structure allows the tailoring of their physical properties and enables unprecedented materials design. Nevertheless, this level of versatility renders their characterization as well as the study of specific processes or reaction mechanisms challenging. In the present work, we report the structural and electrochemical behavior of different multi-cationic HEOs. Phase transformation from spinel to rock-salt was observed upon incorporation of monovalent Li+ ions, accompanied by partial oxidation of certain elements in the lattice. This transition was studied by X-ray diffraction, inductively coupled plasma-optical emission spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and attenuated total reflection infrared spectroscopy. In addition, the redox behavior was probed using cyclic voltammetry. Especially, the lithiated rock-salt structure HEOs were found to exhibit potential for usage as negative and positive electrode materials in rechargeable lithium-ion batteries.

High-entropy energy materials: challenges and new opportunities

“…18,67 The perovskite structure comprises at least two cation sublattices, both of which can be substituted and shared by multiple metals to form a variety of HECs. 43,[68][69][70][71][72] Other lattice structures, such as fluorite, 73-75 spinel 16,76,77 and layered oxides 13,55 were also identified and demonstrated their potential in various energy storage and conversion technologies (Fig. 2b).…”

“…Entropy stabilization and the occurring interactions between the different incorporated elements endow unique properties of HEMs. In this review, we will focus particularly on the effect that entropy stabilization (and the cocktail effect) has on the applications in electrochemical energy storage, for example, in batteries 12,13,17,18,53,55,69,[76][77][78][79] and supercapacitors. 23,[80][81][82]…”

“…Chen et al 76 reported a spinel-type (Ti 0.2 Mg 0.2 Zn 0.2 Fe 0.2 Cu 0.2 ) 3 O 4 with fast reaction kinetics and good stability as anode material for LIBs, delivering a specific capacity of 504 mA h g À1 at 100 mA g À1 after 300 cycles. Wang et al 77 examined the influence of lithium introduction into the lattice structure of a series of spinel materials, (FeNiMnCoCr) x O y , (FeNiMnMgCr) x O y and (FeNiMnMgZn) x O y . They found when lithium ions were incorporated, a phase transformation occurred from spinel to rock-salt accompanied by partial oxidation of certain elements in the lattice.…”

Sustainable high‐entropy ceramics for reversible energy storage: A short review

“…Mg was present as Mg 2+ in lithiated and nonlithiated materials, so, not actively participating to the electrode reaction. Similarly, the valence of Ni did not change 28 . During the lithiation process, the chemical valences of Co and Cr were changed.…”

Mechanochemical synthesis of novel rutile-type high entropy fluorides for electrocatalysis

“…However with this method the existence of a minor contribution of Ni 3+ ions cannot be fully excluded, since the binding energies of Ni 2+ and Ni 3+ ions are very close to each other, at least in oxide samples. [45][46][47][48][49] In the peak fitting of the Ni spectrum, overlapping F KLL, Mn LMM, and Fe 2s peaks are taken into consideration. The majority of F ions (Figure 6g) at 685.4 eV with a FWHM of 2 eV are attributed to the F ions in the crystal structure and have a binding energy similar to the binary fluorides (shown in Figures S5-S12).…”