Dynamic Reversible Evolution of Solid Electrolyte Interface in Nonflammable Triethyl Phosphate Electrolyte Enabling Safe and Stable Potassium‐Ion Batteries

Abstract

Potassium-ion batteries (PIBs) are a favorable alternative to lithium-ion batteries (LIBs) for the large-scale electrochemical storage devices because of the high natural abundance of potassium resources. However, conventional PIB electrodes usually exhibit low actual capacities and poor cyclic stability due to the large radius of potassium ions (1.39 Å). In addition, the high reactivity of potassium metal raises serious safety concerns. These characteristics seriously inhibit the practical use of PIB electrodes. Here, zinc phosphide composites are rationally designed as PIB anodes for operation in a nonflammable triethyl phosphate (TEP) electrolyte to solve the above-mentioned issues. The optimized zinc phosphide composite with 20 wt% zinc phosphate presents a high specific capacity (571.1 mA h g −1 at 0.1 A g −1 ) and excellent cycling performance (484.9 mA h g −1 with the capacity retention of 94.5% after 1000 cycles at 0.5 A g −1 ) in the KFSI-TEP electrolyte. XPS depth profile analysis shows that the improved cycling stability of the composite is closely related to the reversible dynamic evolutions and conversions of the sulfurcontaining species in the solid electrolyte interphase (SEI) during the charge/ discharge process. This dynamic reversible SEI concept may provide a new strategy for the design of superior electrodes for PIBs.

Integrating Chemical Pre‐Potassiation with Pre‐Modulated KF‐Rich Electrolyte Interfaces for Dual‐Carbon Potassium Ion Hybrid Capacitor

“…The sputtering XPS results for the GDC-CP and CAC-CP electrodes exhibit the electrolyte interface films are both rich in KF with the thickness of about 10 nm (Figure 2d-f). [24] The scanning electron microscope (SEM) and transmission electron microscope (TEM) present the uniform and dense electrolyte interface films with the thickness of about 3.0 nm for the GDC-CP and about 5.0 nm for the CAC-CP, respectively (Figure S38, Supporting Information). [4a, 25] The atomic force microscope (AFM) suggests that Young's modulus of the GDC and CAC electrode surfaces decreases significantly and becomes more uniform after pre-potassiation (Figure 2g-j The functions of the pre-formed electrolyte interface films on the electrodes by pre-potassiation treatment are further investigated during the discharge/charge process.…”

Integrating Chemical Pre‐Potassiation with Pre‐Modulated KF‐Rich Electrolyte Interfaces for Dual‐Carbon Potassium Ion Hybrid Capacitor

“…The sputtering XPS results for the GDC‐CP and CAC‐CP electrodes exhibit the electrolyte interface films are both rich in KF with the thickness of about 10 nm (Figure 2d–f). [24] The scanning electron microscope (SEM) and transmission electron microscope (TEM) present the uniform and dense electrolyte interface films with the thickness of about 3.0 nm for the GDC‐CP and about 5.0 nm for the CAC‐CP, respectively (Figure S38, Supporting Information) [4a, 25] . The atomic force microscope (AFM) suggests that Young's modulus of the GDC and CAC electrode surfaces decreases significantly and becomes more uniform after pre‐potassiation (Figure 2g–j and Figure S39, Supporting Information).…”

Recent Advances in Electrolytes for Potassium‐Ion Batteries

“…[60][61][62] Furthermore, the formation of a thin and uniform SEI improves the cycling stability and rate performance of the battery. [31,[63][64][65][66] Both solvents and salts play important roles in the formation of SEI. The generation of the SEI layer proceeds through three major steps: first, the salt anions and the solvent molecules in the electrolyte are reduced.…”

“…More recently, Chen et al explored the electrochemical performance of ZnP 2 as the anode materials in the TEP‐based electrolyte (2.0 m KFSI in TEP). [ 65 ] In addition to the inherent non‐flammable advantage of TEP‐based electrolytes, the authors found that the sulfur‐containing species formed by the decomposition of KFSI in SEI can reversibly evolve and transform through charge/discharge processes in TEP‐based electrolytes, instead of repeated formation and degradation in EC/DEC‐based electrolytes. This interesting reversible SEI helps improve the cycling stability of the electrode (Figure 7 h,i).…”

“…High-resolution S 2p XPS spectra at different etching times after discharging and charging to different states in h) TEP-based electrolyte and i) In EC/DEC-based electrolyte. Reproduced with permission [65]. Copyright 2022, Wiley-VCH GmbH.…”