Monosulfonated Catecholate Coordination Complexes for Flow Battery Electrolytes
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Solution Overview
Problem
Flow batteries face sub-optimal energy storage performance and limited cycle life due to the poor solubility and conductivity of coordination complexes, particularly those containing organic ligands, which leads to precipitation issues and reduced charge storage capacity.
Innovation Solution
Development of coordination complexes with monosulfonated catecholate ligands bound to a metal center, such as titanium, which enhances solubility and stability, allowing for higher concentrations of active material in electrolyte solutions without the need for additional electrolytes, thereby improving ionic conductivity and reducing precipitation risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coordination complexes containing organic ligands are used as active materials, then electrochemical energy storage is enabled, but solubility is poor leading to precipitation
Solution Approach 1:
The patent applies parameter changes by modifying the ligand structure through monosulfonation of the catecholate ligand. This chemical modification changes the solubility parameters of the coordination complex, enabling it to maintain high solubility in aqueous electrolyte solutions without precipitation, thus resolving the contradiction between enabling electrochemical energy storage and preventing precipitation.
2Quantity of substance
If coordination complexes with poor solubility are used, then active material concentration must be kept low, but this reduces energy density
Solution Approach 1:
By changing the solubility parameter through monosulfonation of the catecholate ligand, the patent enables much higher active material concentrations (up to 2.5 M or higher) in the electrolyte solution. This directly increases the energy density of the flow battery system, resolving the contradiction between maintaining low concentration for solubility and achieving high energy density.
3Reliability
If extraneous electrolyte is added to enhance conductivity, then ionic conductivity improves, but active material solubility decreases due to common-ion effect
Solution Approach 1:
The monosulfonated catecholate ligand makes the coordination complex itself ionic and highly soluble in aqueous media. The complex serves its own electrolyte function through the sulfonate group, eliminating the need for additional extraneous electrolytes. This self-service approach resolves the contradiction between enhancing conductivity and maintaining solubility, as adding extraneous electrolyte is no longer necessary.
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 use of monosulfonated catecholate ligands in coordination complexes increases solubility and maintains desirable electrochemical properties, enhancing the energy density and cycle life of flow batteries while minimizing the risk of precipitation and improving ionic conductivity, thus addressing the limitations of existing coordination complexes.
Implementation Method 1
coordination complexes having at least one monosulfonated catecholate ligand or a salt thereof bound to a metal center
Implementation Method 2
The metal center can cycle between an oxidized form and a reduced form in an electrolyte solution, where the oxidized and reduced forms of the metal center represent states of full charge or full discharge
Data Source
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AI summary
Flow batteries and other electrochemical systems can contain an active material that is a coordination complex having at least one monosulfonated catecholate ligand or a salt thereof bound to a metal center. The monosulfonated catecholate ligand has a structure of : formula (1) More particularly, the coordination complex can be a titanium coordination complex with a formula of DgTi(L1)(L2)(L3), in which D is a counterion selected from H, NH4 +, Li+, Na+, K+, or any combination thereof; g ranges between 3 and 6; and L1, L2 and L3 are ligands, where at least one of L1, L2 and L3 is a monosulfonated catecholate ligand. Methods for synthesizing such monosulfonated catecholate ligands can include providing a neat mixture of catechol and up to about 1.3 stoichiometric equivalents of sulfuric acid, and heating the neat mixture at a temperature of about 80°C or above to form 3,4-dihydroxybenzenesulfonic acid or a salt thereof.