Lockheed Martin Energy, LLC

Lockheed Martin Advanced Energy Storage, LLC

Scott Thomas Humbarger

Matthew Millard

Zachariah M Norman

Emily Grace Nelson

Flow batteries can include a first half-cell containing a first aqueous electrolyte solution. a second half-cell containing a second aqueous electrolyte solution, and a separator disposed between the first half-cell and the second half-cell. The first aqueous electrolyte solution contains a first redox-active material, and the second aqueous electrolyte solution contains a second redox-active material. At least one of the first redox-active material and the second redox-active material is a nitroxide compound or a salt thereof. Particular nitroxide compounds can include a doubly bonded oxygen contained in a ring bearing the nitroxide group, a doubly bonded oxygen appended to a ring bearing the nitroxide group, sulfate or phosphate groups appended to a ring bearing the nitroxide group, various heterocyclic rings bearing the nitroxide group, or acyclic nitroxide compounds.

Flow batteries incorporating a nitroxide compound within an aqueous electrolyte solution

Flow batteries can include a first half-cell containing a first aqueous electrolyte solution, a second half-cell containing a second aqueous electrolyte solution, and a separator disposed between the first half-cell and the second half-cell. The first aqueous electrolyte solution contains a first redox-active material, and the second aqueous electrolyte solution contains a second redox-active material. At least one of the first redox-active material and the second redox-active material is a nitroxide compound or a salt thereof. Particular nitroxide compounds can include a doubly bonded oxygen contained in a ring bearing the nitroxide group, a doubly bonded oxygen appended to a ring bearing the nitroxide group, sulfate or phosphate groups appended to a ring bearing the nitroxide group, various heterocyclic rings bearing the nitroxide group, or acyclic nitroxide compounds.

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 More particularly, the coordination complex can be a titanium coordination complex with a formula of DTi(L)(L)(L), in which D is a counterion selected from H, NH, Li, Na, K, or any combination thereof g ranges between 3 and 6; and L, Land Lare ligands, where at least one of L, Land Lis 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&#xb0; C. or above to form 3,4-dihydroxybenzenesulfonic acid or a salt thereof.

Coordination complexes containing monosulfonated catecholate ligands and methods for producing the same

Coordination complexes can have a metal center with at least one unsubstituted catecholate ligand and at least one monosulfonated catecholate ligand or a salt thereof bound thereto. Some coordination complexes can have a formula of DTi(L)(L), in which D is a counterion selected from NH, Li, Na, K, or any combination thereof; g ranges between 2 and 6; Lis an unsubstituted catecholate ligand; Lis a monosulfonated catecholate ligand; and x and y are non-zero numbers such that x+y=3. Methods for synthesizing such coordination complexes can include providing a neat mixture of catechol and a sub-stoichiometric amount of sulfuric acid, heating the neat mixture to form a reaction product containing catechol and a monosulfonated catechol or a salt thereof, and forming a coordination complex from the reaction product without separating the catechol and the monosulfonated catechol or the salt thereof from one another.

Processes for forming coordination complexes containing monosulfonated catecholate ligands

Flow batteries incorporating an active material with one or more catecholate ligands can have a number of desirable operating features. Commercial syntheses of catechol produce significant quantities of hydroquinone as a byproduct, which presently has limited value in the battery industry and can represent a significant waste disposal issue at industrial production scales. Using a concerted, high-yield process, low-value hydroquinone can be transformed into high-value 1,2,4-trihydroxybenzene, which can be a desirable ligand for active materials of relevance in the flow battery industry. Methods for forming 1,2,4-trihydroxybenzene can include: oxidizing hydroquinone in a first reaction to form p-benzoquinone, converting the p-benzoquinone in a second reaction to form 1,2,4-triacetoxybenzene, deacetylating the 1,2,4-triacetoxybenzene in a third reaction to form 1,2,4-trihydroxybenzene, and isolating the 1,2,4-trihydroxybenzene after performing the first reaction, the second reaction and the third reaction consecutively.

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Scott Thomas Humbarger