Secondary‐Phase‐Induced Charge–Discharge Performance Enhancement of Co‐Free High Entropy Spinel Oxide Electrodes for Li‐Ion Batteries

Abstract

High entropy oxide (HEO) has emerged as a new class of anode material for Li‐ion batteries (LIBs) by offering infinite possibilities to tailor the charge–discharge properties. While the advantages of single‐phase HEO anodes are realized, the effects of a secondary phase are overlooked. In this study, two kinds of Co‐free HEOs are prepared, containing Cr, Mn, Fe, Ni, and Zn, for use as LIB anodes. One is a plain cubic‐structure high entropy spinel oxide HESO (C) prepared using a solvothermal method. The other HESO (C+T) contains an extra secondary phase of tetragonal spinel oxide and is prepared using a hydrothermal method. It is demonstrated that the secondary tetragonal spinel phase introduces phase boundaries and defects/oxygen vacancies within HESO (C+T), which improve the redox kinetics and reversibility during electrode lithiation/delithiation. Density functional theory calculation is performed to assess the phase stability of cubic spinel, tetragonal spinel, and rock‐salt structures, and validate the cycling stability of the electrodes upon charging–discharging. The secondary‐phase‐induced rate capability and cyclability enhancement of HEO electrodes are for the first time demonstrated. A HESO (C+T)||LiNi0.8Co0.1Mn0.1O2 full cell is assembled and evaluated, showing a promising gravimetric energy density of ≈610 Wh kg−1 based on electrode‐active materials.

Constructing Heterointerfaces in Dual-Phase High-Entropy Oxides to Boost O2 Activation and SO2 Resistance for Mercury Removal in Flue Gas

“…The interplanar distances determined from the IFFT images are 0.243, 0.195, and 0.281 nm, which correspond to the (311) plane of the spinel phase and the (110) and (100) planes of fluorite CeO 2 , respectively. The results of IFFT images further confirmed the coexistence of the dual-phase high-entropy structure and the lattice distortion in Co-HEO . Schematic (Figure E) corresponding to heterointerfaces indicates the existence of structural defects (point defects and lattice distortion) in the spinel/fluorite HEO.…”

“…The results of IFFT images further confirmed the coexistence of the dual-phase high-entropy structure and the lattice distortion in Co-HEO. 24 Schematic (Figure 2E) corresponding to heterointerfaces indicates the existence of structural defects (point defects and lattice distortion) in the spinel/fluorite HEO. The presence of heterointerfaces can lead to the exposure of additional reactive sites and is proposed to modulate the local electronic structure of the active centers, hence promoting the charge transfer to enhance the catalytic effect.…”

“…Studies have shown that HEOs containing transition metals and rare-earth elements exhibit excellent resistance to SO 2 owing to their unique high-entropy effects and high stability. , Moreover, the atomic size mismatch between metal cations in HEOs produces significant lattice distortions, resulting in various structural defects. , Nevertheless, developing nanostructured HEOs with abundant structural defects remains a challenge for catalytic applications of HEOs. To address this issue, introducing a second phase has been considered a valid way to tune the properties of HEOs because it would create rich heterointerfaces to increase the defect concentration and guarantee electron transfer. , Therefore, the dual-phase HEOs with abundant structural defects should adsorb O 2 effectively and supply robust active sites with good electron mobility to activate O 2 at low temperatures . As reported, the chemisorbed oxygen can be generated by activating gas-phase O 2 and serve as the primary active site in catalytic oxidation. , In light of these findings, it is anticipated that dual-phase HEOs have the potential to become SO 2 -tolerant catalysts for Hg 0 removal.…”

“…To address this issue, introducing a second phase has been considered a valid way to tune the properties of HEOs because it would create rich heterointerfaces to increase the defect concentration and guarantee electron transfer. 23,24 Therefore, the dual-phase HEOs with abundant structural defects should adsorb O 2 effectively and supply robust active sites with good electron mobility to activate O 2 at low temperatures. 25 As reported, the chemisorbed oxygen can be generated by activating gas-phase O 2 and serve as the primary active site in catalytic oxidation.…”

High-entropy oxides: an emerging anode material for lithium-ion batteries

“…These oxygen vacancies enhance electronic conductivity and promote migration of Li + , resulting in a specific capacity of 428 mA h g −1 at a high current density of 10 A g −1 , coupled with exceptional high-rate performance. Ting et al 82 obtained a two-phase oxide Cr–Mn–Fe–Ni–Zn–O (denoted as HESO (C + T)) with major cubic spinel Fd 3̄ m and minor tetragonal spinel structure I 41 /amd . The phase boundary and defects/oxygen vacancies are introduced through the secondary tetragonal spinel phase in HESO (C + T), further improving the redox kinetics and reversibility in the lithiation/delithiation process.…”