Highly Concentrated Salt Electrolyte for a Highly Stable Aqueous Dual-Ion Zinc Battery

Abstract

A zinc metal anode for zinc-ion batteries is a promising alternative to solve safety and cost issues in lithium-ion batteries. The Zn metal is characterized by its high theoretical capacity (820 mAh g −1 ), low redox potential (0.762 V vs SHE), low toxicity, high abundance on Earth, and high stability in water. Taking advantage of the stability of Zn in water, an aqueous Zn ion battery with low cost, high safety, and easy-to-handle features can be developed. To minimize water-related parasitic reactions, this work utilizes a highly concentrated salt electrolyte (HCE) with dual salts�1 m Zn(OTf) 2 + 20 m LiTFSI. MD simulations prove that Zn 2+ is preferentially coordinated with O in the TFSI − anion from HCE instead of O in H 2 O. HCE has a broadened electrochemical stability window due to suppressed H 2 and O 2 evolution. Some advanced ex situ and in situ/in operando analysis techniques have been applied to evaluate the morphological structure and the composition of the in situ formed passivation layer. A dual-ion full Zn||LiMn 2 O 4 cell employing HCE has an excellent capacity retention of 92% after 300 cycles with an average Coulombic efficiency of 99.62%. Meanwhile, the low concentration electrolyte (LCE) cell degrades rapidly and is shortcircuited after 66 cycles with an average Coulombic efficiency of 96.91%. The battery's excellent cycling performance with HCE is attributed to the formation of a stable anion-derived solid-electrolyte interphase (SEI) layer. On the contrary, the high free water activity in LCE leads to a water-derived interfacial layer with unavoidable dendrite growth during cycling.

Fundamental Understanding and Optimization Strategies for Dual-Ion Batteries: A Review

“…In DIBs, the electrolyte system not only serves as the ion transport medium but also acts as the active materials to provide both the cations and anions to be stored in the electrode [ 91 , 92 ]. As a result, the effects of separate electrolyte components (salts, solvents, and additives), their oxidation/reduction at the cathode/anode sides, the “solvation effects” of anions, the formation and instability of SEI layer, the co-intercalation of solvent molecules into cathode materials are key issues to be addressed [ 93 ].…”

. Insights into the design of mildly acidic aqueous electrolytes for improved stability of Zn anode performance in zinc-ion batteries

“…With little solvated water, water activity in such electrolytes is extremely low, which inhibits water-induced side reactions and results in an excellent CE for Zn anodes [115] . Besides, such electrolytes induce the formation of SEI composed of the anion decomposition products at the Zn surface during the initial cycling [116,117] . Sheltered by the SEI layer, the Zn anode is protected from corrosion by electrolytes.…”

Inhibition of side reactions and dendrite growth using a low-cost and non-flammable eutectic electrolyte for high-voltage and super-stable zinc hybrid batteries

“…21 But there still existed plenty of water molecules in the bulk electrolyte, leading to the narrow electrochemical stability window (ESW) due to the decomposition of water molecules. What's more, "water-in-salt" electrolytes (WISEs), 18,22,23 aqueous/organic hybrid electrolytes, 20,24 and nonaqueous electrolytes 25 have been also used to construct the Zn batteries. In a typical WISE, high-concentration LiTFSI/ Zn(TFSI) 2 (TFSI, bis(triuoromethanesulfonyl)imide) can signicantly restrain the water molecules in the metal ion solvated shells, thus weakening their reaction activity and extending the ESW to 3.0 V. 22,23 But the prohibitive cost of TFSIbased electrolytes hinders their practical applications.…”

“…What's more, "water-in-salt" electrolytes (WISEs), 18,22,23 aqueous/organic hybrid electrolytes, 20,24 and nonaqueous electrolytes 25 have been also used to construct the Zn batteries. In a typical WISE, high-concentration LiTFSI/ Zn(TFSI) 2 (TFSI, bis(triuoromethanesulfonyl)imide) can signicantly restrain the water molecules in the metal ion solvated shells, thus weakening their reaction activity and extending the ESW to 3.0 V. 22,23 But the prohibitive cost of TFSIbased electrolytes hinders their practical applications. 26 Lin et al introduced PEG (polyethylene glycol), AN (acetonitrile), and DMA (dimethylacetamide) into the LiTFSI WIS to decrease the content of Li salts and reduce the cost.…”