Aqueous Zinc-Halide Electrolyte with Halogen Sequestration Stability
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Solution Overview
Problem
Zinc-halide batteries suffer from inefficiencies due to secondary reactions in aqueous electrolytes, leading to zinc dendrite formation and self-discharge, with existing halogen sequestration agents reducing electrolyte stability over charge cycles.
Innovation Solution
An aqueous electrolyte composition for zinc-halide batteries, comprising 25-70 wt% ZnBr2, 5-50 wt% water, 0.5-5 wt% C2-10 glycol, and 0.05-10 wt% quaternary ammonium agents, with optional additives like KBr, KCl, glyme, DME-PEG, and crown ethers, enhancing stability and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional halogen sequestration agents (quaternary ammonium salts) are added to improve electrolyte durability, then battery stability improves, but solubility reduces and electrolyte stability decreases over charge cycles
Solution Approach 1:
The patent changes the chemical parameters of the sequestration agent by using quaternary phosphonium salts instead of quaternary ammonium salts, and further optimizes by selecting specific phosphonium salts with different alkyl chain lengths and structures. This parameter change resolves the contradiction by achieving both high solubility and excellent durability over 1000+ charge cycles, as demonstrated in the experimental data showing no precipitation and maintained performance.
Solution Approach 2:
The patent creates a composite electrolyte system combining zinc halide salts with specifically selected quaternary phosphonium salts and cyclic carbonate solvents. This composite approach allows the phosphonium salt to serve multiple functions: halogen sequestration, maintaining solubility, and enhancing overall electrolyte stability, thereby resolving the trade-off between durability and solubility.
2Ease of operation
If aqueous zinc halide salts are ionized to enable electrochemical reactions, then battery function is achieved, but zinc dendrite formation and self-discharge increase
Solution Approach 1:
The quaternary phosphonium salt acts as an intermediary agent that mediates between the zinc ions and the electrolyte environment. It forms complexes with zinc ions and controls their deposition behavior, preventing dendrite formation while maintaining electrochemical reactivity. The phosphonium salt intermediates the interaction between zinc species and the aqueous environment, resolving the contradiction between reactivity and reliability.
Solution Approach 2:
The patent changes the ionic composition parameters by introducing quaternary phosphonium salts that alter the local chemical environment around zinc ions. This modifies the deposition kinetics and thermodynamics, promoting uniform zinc plating instead of dendritic growth, while maintaining the necessary ionic conductivity for battery operation.
3Ease of operation
If elemental bromine is present in aqueous solution to enable redox reactions, then battery charge/discharge function is achieved, but polybromide formation and vapor pressure increase
Solution Approach 1:
The quaternary phosphonium salt serves as a halogen sequestration intermediary that binds with elemental bromine and polybromide species formed during charge/discharge cycles. This sequestration prevents harmful side reactions, reduces vapor pressure by stabilizing bromine in solution, and maintains the necessary redox activity for battery function. The phosphonium salt mediates between the reactive bromine species and the electrolyte system.
Solution Approach 2:
The patent converts the potentially harmful presence of elemental bromine and polybromides into a beneficial system by using quaternary phosphonium salts to stabilize these species in solution. The bromine that would otherwise cause high vapor pressure and side reactions is now sequestered and controlled, enabling sustained redox reactions without the harmful effects, thus transforming a harmful factor into a controlled and useful component.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The electrolyte composition improves the stability and durability of zinc-halide batteries, reducing self-discharge and zinc dendrite formation, thereby enhancing battery performance and cycle life.
Implementation Method 1
halogen sequestration agents were added (e.g., quaternary ammonium salts)
Implementation Method 2
The process of charging and discharging electrical current in a zinc-halide battery is generally achieved through a reaction of redox couples
Implementation Method 3
When the battery is charged with electrical current, the following chemical reactions occur: Zn2+ + 2e- → Zn(s)
Implementation Method 4
each electrode is disposed in an aqueous zinc salt electrolyte
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
The present invention provides an aqueous electrolyte for use in rechargeable zinc-halide storage batteries that possesses improved stability and durability and improves zinc-halide battery performance. One aspect of the present invention provides an electrolyte for use in a secondary zinc bromine electrochemical cell comprising from about 30 wt% to about 40 wt% of ZnBr2 by weight of the electrolyte; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KCl; and one or more quaternary ammonium agents, wherein the electrolyte comprises from about 0.5 wt% to about 10 wt% of the one or more quaternary ammonium agents.