Anion Solvation Reconfiguration Enables High‐Voltage Carbonate Electrolytes for Stable Zn/Graphite Cells

Solvent-derived Fluorinated Secondary Interphase for Reversible Zn-graphite Dual-ion Batteries

The irreversibility of anion intercalation-deintercalation is a fundamental issue in determining the cycling stability of a dual-ion battery (DIB). In this work, we demonstrate that using a partially fluorinated carbonate solvent can drive a beneficial fluorinated secondary interphase layer formation. Such layer facilitates reversible anion (de-)intercalation processes by impeding solvent molecule co-intercalation and the associated graphite exfoliation. The enhanced reversibility of anion transport contributes to the overall cycling stability for a Zn-graphite DIB-a high Coulombic efficiency of 98.5 % after 800 cycles, with an attractive discharge capacity of 156 mAh g-1 and a mid-point discharge voltage of ≈1.7 V (at 0.1 A g-1 ). In addition, the formed fluorinated secondary interphase suppresses the self-discharge behavior, preserving 29 times of the capacity retention rate compared to the battery with a commonly used carbonate solvent, after standing for 24 hours. This work provides a simple and effective strategy for addressing the critical challenges in graphite-based DIBs and contributes to fundamental understanding to help accelerate their practical application.

Electrochemistry-Driven Interphase Doubly Protects Graphite Cathodes for Ultralong Life and Fast Charge of Dual-Ion Batteries

Dual-ion batteries (DIBs) with graphite as cathode material, show superiority in terms of sustainability, affordability, and environmental impact over Li-ion batteries that rely on transition-metal based cathodes. However, graphite cathodes severely suffer from poor structural stability during anion storage at high potentials because of the co-intercalation and oxidative decomposition of electrolytes. This work presents an in situ electrochemistry-driven route to create a bifunctional interphase through implantation of diethylenetriaminepenta(methylene-phosphonic acid) (DTPMP) on the surface of graphite particles. The reaction mechanisms and functions of DTPMP are investigated both experimentally and theoretically. The DTPMP-derived interphase not only improves the antioxidative stability of electrolytes but also benefits the desolvation of PF₆ ^- anions, which doubly protect the graphitic structure and give rise to fast-charge and ultralong cycling performance of graphite cathodes in DIBs.

Rational Design of Functional Electrolytes Towards Commercial Dual-Ion Batteries

Dual-ion batteries (DIBs) based on anion (de)intercalation into low-cost graphitic carbon cathodes hold great promise in grid-scale energy storage. Different from the electrolyte in rocking-chair batteries, which only serves as a charge transporter, both cations and anions in the electrolyte for DIBs participate in battery reactions. Hence, the impact of the electrolyte formulation on cycle life, energy density, as well as cost has become a subject of vital importance. This review discussed the challenges and recent progress of electrolytes for DIBs, with a particular focus on the exploration of electrolytes with high oxidation stability, high salt concentration, high ionic conductivity, and low cost. Moreover, the influence of varied ion concentrations at different state-of-charge levels on the electrolyte properties such as ionic conductivity and electrochemical stability is analyzed. Finally, perspectives on the current limitations and future research directions of electrolytes for DIBs are provided.

A High-Voltage Zn-Organic Battery Using a Nonflammable Organic Electrolyte

Owing to undesired Zn corrosion and the formation of Zn dendrites in aqueous electrolytes, most of the examples of aqueous Zn batteries with reported excellent performance are achieved with low Zn-utilization (<0.6 %) in the anode and low mass-loading (<3 mg cm^-2 ) in the cathode. Herein, we propose a new organic electrolyte for Zn batteries, which contains a zinc trifluoromethanesulfonate (Zn-TFMS) salt and a mixed solvent consisting of propylene carbonate (PC) and triethyl phosphate (TEP). We demonstrate that this electrolyte with an optimized PC/TEP ratio not only exhibits high ionic conductivity and a wide stable potential window, but also facilitates dendrite-free Zn plating/stripping. In particular, the TEP solvent makes the electrolyte nonflammable. Finally, a 2 V Zn//polytriphenylamine composite (PTPAn) battery is fabricated with the optimized electrolyte; it shows a high rate and a long lifetime (2400 cycles) even with a high mass-loading (16 mg cm^-2 ) of PTPAn in the cathode and with a high Zn-utilization (3.5 %).