Potassium Difluorophosphate as an Electrolyte Additive for Potassium-Ion Batteries

Abstract

The limited cyclability and inferior Coulombic efficiency of graphite negative electrodes have been major impediments to their practical utilization in potassium-ion batteries (PIBs). Herein, for the first time, potassium difluorophosphate (KDFP) electrolyte additive is demonstrated as a viable solution to these bottlenecks by facilitating the formation of a stable and K +-conducting solid-electrolyte interphase (SEI) on graphite. The addition of 0.2 wt% KDFP to the electrolyte, results in significant improvements on the (de)potassiation kinetics, capacity retention (76.8% after 400 cycles with KDFP vs. 27.4% after 100 cycles without KDFP) as well as average Coulombic efficiency (~99.9 % during 400 cycles) of graphite electrode. Moreover, the KDFP-containing electrolyte also enables durable cycling of the K/K symmetric cell at higher efficiencies and lower interfacial resistance as opposed to the electrolyte without KDFP. X-ray diffraction and Raman spectroscopy analyses have confirmed the reversible formation of a phase-pure stage-1 potassium-graphite intercalation compound (KC 8) with the aid of KDFP. The enhanced electrochemical performance by the KDFP addition is discussed based on the analysis of the SEI layer on graphite and K metal electrodes by X-ray photoelectron spectroscopy.

Sodium difluorophosphate: facile synthesis, structure, and electrochemical behavior as an additive for sodium-ion batteries

“…This is attributed to the decomposition of the DFP anion, which facilitates the formation of a more conductive SEI layer on the surface of HC electrodes. 38,42 Moreover, XPS peaks after 500 cycles with 1% NaDFP suggested that the contribution of P-O bonds in O 1s and P 2p became larger after 500 cycles compared to those after 20 cycles, indicative of robust SEI formation by NaDFP on HC during cycle.…”

“…In previous studies, electrolytes containing LiDFP and KDFP additives were found to form SEI layers comprising POx species, which improved interfacial properties and reduced the overpotential of graphite electrodes during cycling. [39][40][41][42][43] Despite their efficacy in LIBs and PIBs systems, this class of materials remains underexplored in SIBs.…”

Advances in Carbon Materials for Sodium and Potassium Storage

“…Reproduced with permission. [ 214 ] Copyright 2020, American Chemical Society. f) The molecular structure of TMP and DTD.…”

“…[213] The moderate addition of FEC in ester electrolyte resulted in abundant inorganic KF on the electrode surface, which enabled blocking of the infiltration of the solvent molecules to promise the cycling stability of the batteries (Figure 18a,b). Yang et al further developed a novel electrolyte additive, [214] called potassium difluorophosphate (KDFP). The small addition amount of 0.2%KDFP greatly improved the K storage kinetics, capacity retention (Figure 18c), and average Coulombic efficiency (Figure 18d) of the K/graphite cell, which was due to the formation of stable and K + -conductive SEI (Figure 18e) on the graphite anode in EC/DEC electrolyte by addition of KDFP.…”

Growth Mechanism of Micro/Nano Metal Dendrites and Cumulative Strategies for Countering Its Impacts in Metal Ion Batteries: A Review

“…Fluorine-based additives are employed in commercial LIBs for enhancing the stability of interfacial films. Difluorophosphate salts are used in K-ion batteries for remodeling the electrolyte chemistry to create a stable SEI framework [449]. Polymer additives and binders are utilized in K-ion batteries to significantly advance the molecular adhesion between the electrode-electrolyte interfaces and increase the rated capacity.…”