New high-entropy energy storage materials can promote the development of lithium batteries

by:CTECHi     2021-08-04

According to foreign media reports, researchers from the Karlsruhe Institute of Technology (KIT) in Germany have proposed a new type of high-entropy material suitable for energy storage applications. They report in the paper that using the recently designed multi-cation transition metal-based high-entropy oxide as the precursor, LiF or NaCl as the reactant, simple mechanochemical methods are used to prepare polyanionic and polycationic compounds to generate lithiation or sodium化材料。 Material.

Lithium-containing entropy stable fluorooxy compound (Lix(Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)OFx), working potential 3.4 V vs. Li+/Li , Can be used as a positive electrode active material. Different from traditional (non-entropy stable) oxyfluoride compounds, this new material benefits from entropy stability, exhibits stronger lithium storage performance, changes the constituent elements in an unprecedented way, and improves cycle performance. The concept of entropy stability is also applicable to sodium-containing oxychloride with a rock salt structure, paving the way for the development of lithium battery technology.

In many different application fields, high-entropy materials (HEM) have received widespread attention due to their novel, unexpected and unprecedented characteristics. 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 published, including carbides, diborides, nitrides, chalcogenide compounds and oxides, and have a wide range of applications in the fields of thermoelectrics, dielectrics, and lithium-ion batteries. The recently emerged high-entropy material, called high-entropy oxide (HEO), was first proposed by Christina M. Rost and others in the United States in 2015.

However, so far, there is no literature report on HEM compounds containing multiple anions. The stable high configuration entropy effect is only caused by the cations in the crystal structure, because the contribution of the anion sites is zero. Therefore, the preparation of multi-anion and multi-cation single-phase structure materials with obvious signs of entropy stability is of great significance, especially considering that the configurational entropy gain will be greater than that of the transition metal-based HEO system. KIT’s paper is the first report on polyanion and polycation high-entropy oxyhalides and their applications in electrochemical energy storage.

Researchers use a HEO based on multi-cation transition metals (that is, only oxygen ions occupy anion sites), as a precursor, introduce additional halogen ions (X) and Alkali metal ions generate polyanion, polycation rock salt type compound (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 cationic lattice. Since the radii of fluorine and oxygen ions are similar, this substitution does not cause significant strain in the single-phase rock salt structure.

By adding multiple anions to an entropy-stable polycation compound, the researchers discovered for the first time that while maintaining the single-phase rock salt structure, not only the cations change, but the anions also change. Will change. These compounds constitute a new class of entropy stable materials, and the anionic lattice promotes the formation of configurational entropy, thereby obtaining additional structural stability gains. Through this method, a fluoro-oxygen cathode active material with a rock salt structure was successfully synthesized, which is suitable for the next generation of lithium ion battery applications.

It is worth mentioning that entropy stabilization can significantly improve cycle performance. In addition, this method can reduce the toxic and expensive elements in the positive electrode of the battery without significantly affecting the energy density. In summary, the concept of multi-anions and multi-cation high-entropy compounds will bring unprecedented new energy storage materials.

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