Deciphering Structural Origins of Highly Reversible Lithium Storage in High Entropy Oxides with In Situ Transmission Electron Microscopy

Abstract

Configurational entropy‐stabilized single‐phase high‐entropy oxides (HEOs) have been considered revolutionary electrode materials with both reversible lithium storage and high specific capacity that are difficult to fulfill simultaneously by conventional electrodes. However, precise understanding of lithium storage mechanisms in such HEOs remains controversial due to complex multi‐cationic oxide systems. Here, distinct reaction dynamics and structural evolutions in rocksalt‐type HEOs upon cycling are carefully studied by in situ transmission electron microscopy (TEM) including imaging, electron diffraction, and electron energy loss spectroscopy at atomic scale. The mechanisms of composition‐dependent conversion/alloying reaction kinetics along with spatiotemporal variations of valence states upon lithiation are revealed, characterized by disappearance of the original rocksalt phase. Unexpectedly, it is found from the first visualization evidence that the post‐lithiation polyphase state can be recovered to the original rocksalt‐structured HEOs via reversible and symmetrical delithiation reactions, which is unavailable for monometallic oxide systems. Rigorous electrochemical tests coupled with postmortem ex situ TEM and bulk‐level phase analyses further validate the crucial role of structural recovery capability in ensuring the reversible high‐capacity Li‐storage in HEOs. These findings can provide valuable guidelines to design compositionally engineer HEOs for almighty electrodes of next‐generation long‐life energy storage devices.

Nanostructured Porous Polymer with Low Volume Expansion, Structural Distortion, and Gradual Activation for High and Durable Lithium Storage

“…The slight volume expansion favors the structure integrity of NPP-PPT during lithiation and delithiation, ensuring its cycling durability for LIBs. After that, the lithiated NPP-PPT show a rapid delithiation process accompanied by a volume change (10.9%) and finally maintains its initial state without structural degradation (Figure g and h and Movie S1), further indicating its structural stability. − In brief, the resultant NPP-PPT possesses slight volume expansion (≤11.8%) even during repeating lithiation and delithiation (Figure i), which is conducive to obtaining ideal Li-storage performance.…”

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

“…70 On the other hand, following the initial discharge, the high-entropy anodes form certain irreversible alloys, resulting in low initial Coulombic efficiency (ICE). 71,72 However, these alloys offer additional nanoscale electron conductive networks in the electrode, which reduces the electrode impedance.…”

Improved Reversibility of PF6– De/intercalate in Graphite by Building the Artificial PVDF-HFP Polymer Cathode Electrolyte Interphase

“…It is the basis for advanced DIBs. 5,6 The intercalation of PF 6 − anions brings approximately 136% volume change; however, the specific capacity is only 93 mA h g −1 with a charging voltage of 5 V vs Li/Li + . 7 Besides, during the cycle, the cointercalation of solvent and anion is more likely to produce graphite lamellar structure exfoliation, which reduces the cycling stability.…”

“…Li-dual ion batteries (Li-DIBs) are emerging energy storage systems with the merits of high working potential, potentially high energy density, good rate capability, and low cost. – Graphite intercalation compounds (GICs) and (electro)­chemical anions have been inserted into the host material for decades. It is the basis for advanced DIBs. , The intercalation of PF 6 – anions brings approximately 136% volume change; however, the specific capacity is only 93 mA h g –1 with a charging voltage of 5 V vs Li/Li + . Besides, during the cycle, the cointercalation of solvent and anion is more likely to produce graphite lamellar structure exfoliation, which reduces the cycling stability. ,, At the same time, the advantage of the high energy density of store anions is often limited by the decomposition of the traditional carbonate electrolyte at high voltage. , The anion de/intercalation on the graphite cathode usually takes place at a high potential (>4.5 V vs Li + /Li), and the progress will result in cathode electrolyte interphase (CEI) forming on the surface of the graphite electrode by oxidation decomposition of the traditional carbonate electrolyte. , However, the distribution or composition of CEI is often unsatisfactory, the unstable CEI leads to the recontact between electrolyte and electrode interface, and the electrolyte will continue to decompose, resulting in a lower Coulombic efficiency (CE) and solvent cointercalation.…”