Does Salt Concentration Matter? New Insights on the Intercalation Behavior of PF6−${\rm{PF}}_6^ - $ into Graphite Cathode for the Dual‐Ion Battery

Abstract

A high-concentration electrolyte is favored in dual-ion batteries (DIBs) due to the lower onset potential for anion intercalation, higher specific discharge capacity, and better oxidation stability. Inspired by the correlation between the high-concentration electrolytes and localized high-concentration electrolytes, it is suspected that it is not the salt concentration but the solution structure of the electrolyte that determines the intercalation behavior of anion into graphite cathode. To prove the viewpoint, a series of electrolytes are prepared by controlling the salt concentration or solution structure and the intercalation behavior of PF 6 − within the graphite cathode is investigated in Li||graphite and graphite||graphite cells. It is found that PF 6 − anions exhibit similar onset potentials and specific discharge capacities in the electrolytes with different salt concentrations but similar solution structures. This study provides a new perspective on designing promising electrolytes for DIBs, which can accelerate the further exploitation of high-performance DIBs.

Insight into Multiphase Interlayer Molecular Packing and Stepwise Phase Transition in 4-(Phenylazo)benzoate Anion-Intercalated Layered Zinc Hydroxide

“…The new comprehensive insight reported herein may attract new interest in more anion-intercalated hybrids. New and rich intercalation chemistry might be discovered in more functional intercalation hybrids beyond the layered zinc hydroxide intercalation hybrid, such as anion-intercalated graphite , and layered perovskite . To explore the correlation of the interlayer molecular packing with the molecular structure of anions, we are currently studying the intercalation of more anionic azo derivatives with tailorable structural flexibility and molecular length.…”

Producing Bilayer Graphene Oxide via Wedge Ion-Assisted Anodic Exfoliation: Implications for Energy and Electronics

“…It is noticed that the anion intercalation voltage for PF 6 – is ca. 4.5 V vs Li/Li + . , Theoretically, we can convert Li/Li + into the Ag/AgCl scale according to the difference of their standard electrode potential difference (−3.04 V for Li/Li + and +0.23 V for Ag/AgCl). However, the Li/Li + potential in nonaqueous solvents could be significantly affected by the solvent–electrolyte interaction, electrolyte salt, and lithium concentration .…”

“…During this process, guest molecules or ions can be intercalated into the graphite layers under the electric potential, weakening the van der Waals interactions between the interlayers, and facilitating further steps of graphene exfoliation. ,− Depending on the electrochemical conditions, anodic and cathodic exfoliation has been successfully implemented. For anodic intercalation, some commonly used intercalant anions include sulfate (SO 4 2– ), bisulfate (HSO 4 – ), perchlorate (ClO 4 – ), and tetrafluoroborate (BF 4 – ), in either acid or salt form. − Sulfate and bisulfate anions are the most widely used intercalants for scalable graphene exfoliation, particularly in aqueous solution of acidic (H 2 SO 4 ) or neutral inorganic salts (i.e., (NH 4 ) 2 SO 4 ). − Meanwhile, cationic intercalants such as alkylammonium (i.e., tetrabutylammonium, TBA + ) and large metal ions (i.e., Cs + ) in salt form are commonly employed ones for cathodic exfoliation in organic solvents. , More recently, dual-electrode exfoliation via alternating applied potential or simultaneous anodic and cathodic intercalation on both graphite electrodes has been developed to improve the production efficiency. , Besides, the co-intercalation of anionic complexes combining metal cations and chelating anions (i.e., [Mg­(TFSI) 3 ] − ) also has shown their potential in anodic intercalation of graphite electrodes . The above molecules or metal ions act like “wedges” driven by the electric field and insert into the graphite layers through edges, causing an increased interlayer spacing.…”

Sustainable Dual‐Ion Batteries beyond Li

“…For example, it has been elucidated that the electrolyte architecture, as opposed to the salt concentration of the EMCbased electrolyte, predominantly governs the initiation potential of PF 6 − integration into the graphite cathode. [38] Interestingly, expedited intercalation was distinctly observed in electrolytes of high concentration and those manifesting localized high-concentration regions. Recent empirical evidence has revealed the distinct roles of EMC and EC in anion intercalation processes.…”