Vanadium pentoxide materials prepared through sol‐gel processes act as excellent intercalation hosts for lithium as well as for polyvalent cations. Previous ex situ X‐ray absorption spectroscopy and X‐ray diffraction characterizations have shown that the electrochemical performance of vanadium pentoxide xerogels depends inversely on the long‐range order of the structure. Recently, new ways to prevent the self‐organization of the dry materials, which takes place upon water removal from the starting hydrogel, have been introduced. In the present paper we report on the in situ X‐ray absorption spectroscopy characterization of a spray‐coated (freeze‐dried) xerogel cathode upon lithium intercalation. © 1999 The Electrochemical Society. All rights reserved.

High‐entropy oxides (HEOs) have emerged as promising anode materials for next‐generation lithium‐ion batteries (LIBs). Among them, spinel HEOs with vacant lattice sites allowing for lithium insertion and diffusion seem particularly attractive. In this work, electrospun oxygen‐deficient (Mn,Fe,Co,Ni,Zn) HEO nanofibers are produced under environmentally friendly calcination conditions and evaluated as anode active material in LIBs. A thorough investigation of the material properties and Li⁺ storage mechanism is carried out by several analytical techniques, including ex situ synchrotron X‐ray absorption spectroscopy. The lithiation process is elucidated in terms of lithium insertion, cation migration, and metal‐forming conversion reaction. The process is not fully reversible and the reduction of cations to the metallic form is not complete. In particular, iron, cobalt, and nickel, initially present mainly as Fe³⁺, Co³⁺/Co²⁺, and Ni²⁺, undergo reduction to Fe⁰, Co⁰, and Ni⁰ to different extent (Fe < Co < Ni). Manganese undergoes partial reduction to Mn³⁺/Mn²⁺ and, upon re‐oxidation, does not revert to the pristine oxidation state (+4). Zn²⁺ cations do not electrochemically participate in the conversion reaction, but migrating from tetrahedral to octahedral positions, they facilitate Li‐ion transport within lattice channels opened by their migration. Partially reversible crystal phase transitions are observed.