How Do the Four Core Factors of High Entropy Affect the Electrochemical Properties of Energy-Storage Materials?

Abstract

High-entropy materials (HEMs) are extremely popular for electrochemical energy storage nowadays. However, the detailed effects of four core factors of high entropy on the electrochemical properties of HEMs are still unclear. Here, a high-entropy La_1/4Ce_1/4Pr_1/4Nd_1/4Nb₃O₉ (HE-LaNb₃O₉) oxide is prepared through multiple rare-metal-ion substitution in LaNb₃O₉, and uses HE-LaNb₃O₉ as a model material to systematically study the effects of the four core factors of high entropy on electrochemical energy-storage materials. The high-entropy effect lowers the calcination temperature for obtaining pure HE-LaNb₃O₉. The lattice distortion in HE-LaNb₃O₉ leads to its decreased unit-cell-volume variations, which benefits its cyclability. Based on the restrained diffusion arising from the lattice distortion, the Li⁺ diffusivity of HE-LaNb₃O₉ at room temperature (25 °C) is limited, which causes its lowered rate capability. However, the Li⁺ diffusivity of HE-LaNb₃O₉ at high temperature (60 °C) becomes faster than that of LaNb₃O₉, which is attributed to the alleviated lattice distortion at the high-temperature, resulting in higher rate capability. The cocktail effects in HE-LaNb₃O₉ enable its larger electronic conductivity, better electrochemical activity, more intensive Nb⁵⁺ ↔ Nb³⁺ redox reaction, and larger reversible capacity. The insight gained here can provide a guide for the rational design of new HEMs with good energy-storage properties.

Keywords: electrochemical property; four core factors of high entropy; high‐entropy material; high‐temperature operation; in situ characterization.