Expounding the Initial Alloying Behavior of Na–K Liquid Alloy Electrodes

Abstract

Primary electrodeposition is an accepted strategy to elucidate the nucleation and growth kinetics of metal electrodes. Nevertheless, when confronted with the phase transition process caused by bi-active metals such as NaK liquid alloys, the research process becomes complex and elusive. Herein, we have reduced the intricate issues to relatively simple initial alloying behaviors. Two exchange diffusion mechanisms of the Na atom embedded in K crystals and K atom embedded in Na crystals are investigated by first-principles density functional theory (DFT) calculation and mechanical simulation. As a result, the process of embedding the Na atom in K crystals shows a better thermodynamic stability and lower activation barrier and structural stress than those of the other. The abovementioned conclusions are further proved by stepwise Na and K electrodeposition experiments, and the prepared NaK alloy electrode displays excellent electrochemical performance. Our findings correlate the original alloying mechanism model specification with electrodeposition experimental verification and provide strategies to achieve controllable NaK electrode construction.

Bifunctional Alloy/Solid-Electrolyte Interphase Layer for Enhanced Potassium Metal Batteries Via Prepassivation

“…Pristine Cu@SKS (#0 layer) exhibited C–F at 688.9 eV and K–F at 684.1 eV in F 1s, SO at 533.5 eV and C–O at 532.4 eV in O 1s, and C–O at 286.5 eV and C–C at 284.8 eV in C 1s, which could be partly derived from the residual KFSI during synthesis. C–O & C–C in C 1s and C–F & K–F in F 1s implied an O/F-rich SEI layer on the surface, and K–O and K–F in K 2p 3/2 also proved the prepassivation. Besides, the low content of K–K at 294.8 eV indicated no K atoms in the external area due to the protection of the SEI layer.…”

“…C–O & C–C in C 1s and C–F & K–F in F 1s implied an O/F-rich SEI layer on the surface, and K–O and K–F in K 2p 3/2 also proved the prepassivation. Besides, the low content of K–K at 294.8 eV indicated no K atoms in the external area due to the protection of the SEI layer. After the first sputtering (#1 layer), K–O at 293.4 eV in K 2p 3/2 and K–F at 684.1 eV in F 1s increased significantly, indicating a dense inorganic layer.…”

Cobalt/Nitrogen Co‐Doped Carbon Materials Enhance the Reaction Rate of Sodium–Potassium Alloy Electrodes

“…[31,32] In addition, the K─O 2p 1/2 and K─O 2p 3/2 bonds that appeared after the reaction were attributed to the formation of SEI films at the electrode interface and the reaction of potassium with traces of air in the glove box during the reaction (Figure S6c, Supporting Information). [33,34] And, the XPS spectra of N 1s before the reaction can be clas- sified as four peaks at 399.3, 398.4, 400.6, and 401.3 eV, corresponding to the Co─N x bond, "pyridine" nitrogen, "pyrrole" nitrogen, and "graphite" nitrogen. [35][36][37] This is similar to the N 1s spectrum of N@CNT, except that there are more Co─N x bonds (Figure S7b, Supporting Information).…”

Semi‐Solid CNT@NaK Anode for Potassium Metal Battery

“…[ 17 ] However, the high surface tension of liquid NaK alloy hinders its application to a great extent. Though surface tension can be reduced through special treatment, such as high temperature, vacuum, and electrochemical deposition methods, [ 18–24 ] the reduced surface tension of NaK will return to the original state without bonds when the external force vanishes. [ 25–26 ] Through detailed analysis, NaK can be absorbed into carbon substrates owing to the strong affinity of CK bonds.…”