In Situ Ions Induced Formation of K_xF‐Rich SEI Layers toward Ultrastable Life of Potassium‐Ion Batteries

Abstract

Engineering F‐rich SEI layers is regarded as an effective strategy to enable the long‐term cycling stability of potassium ion batteries (KIBs). However, in the conventional KPF6 carbonate electrolytes, it is challenging to form F‐containing SEI layers due to the inability of KPF6 to decompose into KxF. Herein, AlCl3 is employed as a novel additive to change the chemical environment of the KPF6 carbonate electrolyte. Firstly, due to the large charge‐to‐radius ratio of Al3+, the Al‐containing groups in the electrolyte can easily capture F from PF6− and accelerate the formation of KxF in SEI layer. In addition, AlCl3 also reacts with trace H2O or solvents in the electrolytes to form Al2O3, which can further act as an HF scavenger. The “self‐induced formation” of F‐rich SEI layers (KxF and AlF3) and “self‐elimination” of unexpected species (H2O and HF) guarantee the excellent long‐term cycling stability of KIBs. Upon incorporating AlCl3 into conventional KPF6 carbonate electrolyte, the hard carbon (HC) anode exhibits an ultra‐long lifespan of 10000 cycles with a high coulombic efficiency of ∼100%. When coupled with PTCDA, the full cell exhibits a high capacity retention of 81% after 360 cycles‐significantly outperforming cells using conventional electrolytes. Moreover, PTCDA||HC pouch cell using AlCl3 added KPF6 electrolyte deliver a reversible capacity of 93 mAh g−1 with capacity retention of 86% after 80 cycles. This research paves new avenues for advancing electrolyte engineering towards developing durable batteries tailored for large‐scale energy storage applications.This article is protected by copyright. All rights reserved

KF-Containing Interphase Formation Enables Better Potassium Ion Storage Capability

“…The characteristic peaks in Bi 4f XPS spectra can be clearly observed, which reveal the existence of Bi 0 and Bi 3+ species [23]. Since the main component of the K1 electrolyte is KPF6, the characteristic peaks of KxPFy and KF can be clearly observed in the F 1s XPS spectra [1,29]. These phosphides are also the main constituents of the inorganic SEI layer.…”

“…In the S 2p XPS spectra (Figure 7h), clear characteristic peaks of -SO2-F, -SO2-, and SOx can be observed [30]. In F 1s XPS spectra, characteristic peaks of SO2-F and KF can be clearly observed, and the peak of KF is more obvious [1,29]. This suggests the formation of a KF-containing SEI layer in the K2 electrolyte, which can effectively protect the N-C@Bi anode from degradation during repeated cycling.…”

“…SHE.) [1][2][3][4][5]. In addition, the lower cost of salts for K-ion electrolytes and lower de-solvation kinetic barriers also make KIBs a commercially feasible alternative to conventional lithium ion battery technologies [6][7][8].…”