AG13 battery

German researchers propose new high-entropy energy storage materials to promote the development of AG13 battery

According to foreign media reports, researchers at the Karlsruhe Institute of Technology (KIT) in Germany have proposed a new high-entropy material suitable for energy storage applications. In their paper, they reported that recently designed multi-cation transition metal-based high-entropy oxides were used as precursors, LiF or NaCl was used as reactants, and polyanion and polycation compounds were prepared using a simple mechanochemical method to generate lithium or sodium materials.

Lithium-containing entropy-stabilized fluorine-oxygen compounds (Lix(Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)OFx), with a working potential of 3.4Vvs.Li+/Li, can be used as positive electrode active materials. Unlike traditional (non-entropy-stabilized) fluorine-oxygen compounds, this new material benefits from entropy stabilization and exhibits stronger lithium storage performance, changing the constituent elements in an unprecedented way to improve cycle performance. The concept of entropy stabilization is also applicable to sodium-containing chloride oxides with rock salt structures, paving the way for the development of post-lithium battery technology.

High entropy materials (HEMs) have attracted wide attention for their novel, unexpected and unprecedented properties in many different application areas. HEMs are based on the introduction of high configurational entropy to stabilize a single-phase structure. A large number of high entropy compounds, including carbides, diborides, nitrides, chalcogenides and oxides, have been synthesized and published, and have a wide range of applications in the fields of thermoelectrics, dielectrics and lithium-ion batteries. A recently emerged high entropy material, called high entropy oxides (HEOs), was first proposed by Christina M. Rost et al. in 2015.

However, there are no literature reports on HEM compounds containing multiple anions so far. The stable high configurational entropy effect is caused only by the cations in the crystal structure, because the contribution of the anionic sites is zero. Therefore, the preparation of polyanionic and polycationic single-phase structured materials with clear signs of entropy stabilization is of great significance, especially considering that the configurational entropy gain will be larger than that of transition metal-based HEO systems. The KIT paper is the first report of polyanionic and polycationic high entropy oxyhalides and their application in electrochemical energy storage.

The researchers used a polycationic transition metal-based HEO (i.e., only oxygen ions occupy anionic sites) as a precursor to introduce additional halogen ions (X) and alkali metal ions to generate polyanionic, polycationic rock salt-type compounds (HEOX). Monovalent fluorine was introduced into the HEO anion lattice occupied by divalent oxygen, and the charge was compensated by adding monovalent lithium (or sodium) to the cation lattice. Since the fluorine and oxygen ion radii are similar, this substitution does not cause significant strain in the single-phase rock salt structure.

By adding multiple anions to an entropy-stabilized polycationic compound, the researchers found for the first time that not only the cations but also the anions change while maintaining the single-phase rock salt structure. These compounds constitute a new class of entropy-stabilized materials, in which the anion lattice promotes the formation of configurational entropy, thereby obtaining additional structural stability gains. In this way, a fluorine-oxygen cathode active material with a rock salt structure was successfully synthesized for next-generation lithium-ion battery applications.

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

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