German researchers propose new high-entropy energy storage materials to promote the development of lithium batteries

According to foreign media reports, researchers at the Karlsruhe Institute of Technology (KIT) in Germany have proposed a new type of high-entropy material suitable for energy storage applications. They reported in the paper that using a recently designed polycationic transition metal-based high-entropy oxide as a precursor and LiF or NaCl as a reactant, a simple mechanochemical method was used to prepare polyanions and polycationic compounds to generate lithiated or sodium化 材料。 Chemical materials.

Lithium-containing entropy-stabilized 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. Unlike traditional (non-entropy stable) oxyfluorides, this new material benefits from entropy stability, exhibits stronger lithium storage performance, changes constituent elements in an unprecedented way, and improves cycle performance. The concept of entropy stability also applies to sodium-containing chlorine oxides with a rock salt structure, thus paving the way for post-development lithium battery technology.

In many different application fields, high-entropy materials (HEM) have received extensive attention because of their novel, unexpected and unprecedented characteristics. HEM is premised on introducing high configuration entropy to stabilize the single-phase structure. A large number of high-entropy compounds that have been synthesized and disclosed, including carbides, diborides, nitrides, chalcogenide compounds and oxides, have a wide range of applications in the fields of thermoelectrics, dielectrics and lithium-ion batteries. The recently appeared high-entropy material, called high-entropy oxide (HEO), was first proposed by Christina M. Rost and others in 2015.

However, to date, there are no literature reports 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 polyanionic and polycationic single-phase structures with obvious signs of entropy stability is of great significance, especially considering that the configurational entropy gain will be greater than that of transition metal-based HEO systems. KIT's paper is the first report of polyanion and polycationic high-entropy oxygen halides and their application in electrochemical energy storage.

The researchers used a HEO based on polycationic transition metals (that is, only oxygen ions occupy the anion site) as a precursor, introducing additional halogen ions (X) and alkali metal ions to generate polyanion, 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 cationic lattice. Because the radii of fluorine and oxygen ions are similar, in a single-phase rock salt structure, this substitution will not cause significant strain.

By adding multiple anions to an entropy-stable polycationic compound, the researchers found for the first time that while maintaining the single-phase rock salt structure, not only the cations but also the anions change. These compounds constitute a new class of entropy-stabilizing materials, and the anionic lattice promotes the formation of configurational entropy, thereby obtaining additional structural stability gains. Through this method, a fluorooxygen positive electrode 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 the entropy stability can significantly improve the cycle performance. In addition, this method can reduce the toxic and expensive elements in the battery positive electrode, while not significantly affecting the energy density. In summary, the concept of multi-anion and multi-cation high-entropy compounds will bring unprecedented new energy storage materials.