According to foreign media reports, researchers from the Karlsruhe Institute of Technology (KIT) in Germany have proposed a new high-entropy material suitable for energy storage applications. They reported in the paper that they used a recently designed polycationic transition metal-based high-entropy oxide as a precursor and LiF or NaCl as a reactant to prepare polyanionic and polycationic compounds using simple mechanochemical methods to generate lithiation or sodium Chemical materials. Lithium-containing entropy-stable fluorooxy compound (Lix (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)OFx), working potential 3.4Vvs. Li+/Li can be used as cathode active material. Unlike traditional (non-entropically stable) oxyfluoride compounds, this new material benefits from entropic stabilization, exhibits stronger lithium storage properties, changes the constituent elements in an unprecedented way, and improves cycle performance. The concept of entropy stabilization also applies to sodium-containing oxychloride with a rock salt structure, paving the way for the development of post-lithium battery technologies. High-entropy materials (HEMs) have attracted widespread attention due to their novel, unexpected and unprecedented properties in many different application fields. HEM is based on the premise of introducing high configuration entropy to stabilize the single-phase structure. A large number of high-entropy compounds have been synthesized and disclosed so far, including carbides, diborides, nitrides, sulfur compounds and oxides, and have been widely used in fields such as thermoelectricity, dielectrics and lithium-ion batteries. The recently emerged high-entropy material, called high-entropy oxide (HEO), was introduced in 2015 by Christina M. First proposed by Rost et al. However, so far, there are no literature reports on HEM compounds containing multiple anions. Stable high configurational entropy effects, caused only by cations in the crystal structure, since the contribution of anionic sites is zero. Therefore, the preparation of polyanionic and polycationic single-phase structural materials with obvious signs of entropy stabilization is of great significance, especially considering that the configurational entropy gain will be greater than that of transition metal-based HEO systems. The KIT paper is the first report on polyanionic and polycationic high-entropy oxyhalides and their applications in electrochemical energy storage. The researchers used a HEO based on polycationic transition metals (that is, only oxygen ions occupy the anionic sites) as a precursor to introduce additional halide ions (X) and alkali metal ions to generate polyanionic and polycationic rock salt-type compounds. (HEOX). Monovalent fluorine is introduced into the HEO anion lattice occupied by divalent oxygen, and the charge is compensated by adding monovalent lithium (or sodium) to the cation lattice. Since the ion radii of fluorine and oxygen are similar, this substitution does not cause significant strain in the single-phase rock salt structure. By adding multiple anions into an entropy-stable polycationic compound, researchers have discovered for the first time that not only the cations change, but also the anions, while maintaining the single-phase rock salt structure. These compounds constitute a new class of entropy-stable materials in which the anionic lattice promotes configurational entropy formation, thereby obtaining additional structural stabilization gains. Through this method, a fluorine-oxygen-based cathode active material with a rock salt structure was successfully synthesized, which is suitable for next-generation lithium-ion battery applications. It is worth mentioning that entropic stabilization can significantly improve cycle performance. In addition, this approach can reduce toxic and expensive elements in the battery cathode without significantly affecting energy density. In summary, the concept of polyanionic and polycationic high-entropy compounds will bring unprecedented new energy storage materials.

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