Entropy‐Mediated Stable Structural Evolution of Prussian White Cathodes for Long‐Life Na‐Ion Batteries

Abstract

The high‐entropy approach is applied to monoclinic Prussian White (PW) Na‐ion cathodes to address the issue of unfavorable multilevel phase transitions upon electrochemical cycling, leading to poor stability and capacity decay. A series of Mn‐based samples with up to six metal species sharing the N‐coordinated positions was synthesized. The material of composition Na1.65Mn0.4Fe0.12Ni0.12Cu0.12Co0.12Cd0.12[Fe(CN)6]0.92□0.08 ⋅ 1.09H2O was found to exhibit superior cyclability over medium/low‐entropy and conventional single‐metal PWs. We also report, to our knowledge for the first time, that a high‐symmetry crystal structure may be advantageous for high‐entropy PWs during battery operation. Computational comparisons of the formation enthalpy demonstrate that the compositionally less complex materials are prone to phase transitions, which negatively affect cycling performance. Based on data from complementary characterization techniques, an intrinsic mechanism for the stability improvement of the disordered PW structure upon Na+ insertion/extraction is proposed, namely the dual effect of suppression of phase transitions and mitigation of gas evolution.

Enhancing the durability of Prussian white based sodium batteries through the lithium salt-mediated electrode interface

“…After literature research, we found that this is one of the characteristic peaks of the tetragonal phase, which indicates that the PW crystals in the 0% electrolyte underwent a monoclinic to tetragonal phase transition. 41,45 When re-discharged to 2 V, this peak persists and the 23.5° monoclinic peak remains unaltered, and we hypothesize that this transition is irreversible.…”

“…During the subsequent charging from 3.8 V to 4.2 V, the peaks in the individual planes continued to move to a lower 2 θ angle, but no new peaks appeared, indicating that the PW crystal had been in the cubic phase during this period. 22,41–43 During discharging, the single peaks change to double peaks at about 23.5°, indicating that the PW re-changed from the cubic phase to the monoclinic phase. 44 In contrast, in the 0% cell, the diffraction peaks change significantly during charging and discharging.…”

Element Screening of High-Entropy Silicon Anodes for Superior Li-Storage Performance of Li-Ion Batteries

“…High-entropy cathodes for rechargeable batteries have considerably been succeeded in enhancing charge and mass transport capabilities, reinforcing structural stability, activating redox couples, and elevating energy and power density. − These advancements are attributed to the high configurational entropy and synergistic benefits arising from the combination of multiple elements. − However, the application of high-entropy principles to anodes is presently limited to oxides and sulfides. − A notable example of the pioneering work by Breitung and colleagues is high-entropy oxide anodes with the improved Li-storage performance . The synergistic effect of multiple cations at both atomic and nanoscale levels on the electrochemical performance, so-called cocktail effect, was confirmed.…”