Lockheed Martin Energy, LLC

Lockheed Martin Advanced Energy Storage, LLC

Matthew Millard

Scott Thomas Humbarger

Zachariah M Norman

Emily Grace Nelson

Steven Y Reece

John Goeltz

Adam Morris-Cohen

Alexander B Papandrew

Rachel Christine Klet

Roger Frisbee

The present disclosure provides methods and devices for preparing electrolyte solutions containing unwanted impurities at the pg/L levels. The methods generally comprise electrochemically reducing the impurity to a precipitated, plated, or volatilized form, and removing that reduced form from electrolyte solution. This disclosure describes the methods and devices for effecting such methods, and the electrochemical solutions derived or derivable from such methods.

Methods and devices for removing impurities from electrolytes

Electrolyte solutions for flow batteries and other electrochemical systems can contain an active material that is capable of transferring one or more electrons per molecule during an oxidation-reduction cycle. Doubly bridged aromatic groups or their coordination compounds can be particularly suitable active materials. Flow batteries can include a first half-cell containing a first electrolyte solution, and a second half-cell containing a second electrolyte solution, in which at least one of the first electrolyte solution and the second electrolyte solution contains an active material having at least two aromatic groups doubly bridged by a carbonyl moiety and a bridging moiety containing a bridging atom selected from carbon, nitrogen, oxygen, sulfur, selenium and tellurium. Such bridged compounds can directly function as the active material, or coordination compounds containing the bridged compounds as at least one ligand can serve as the active material.

Flow batteries incorporating active materials containing doubly bridged aromatic groups

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.

Titanium catecholate complexes can be desirable active materials for flow batteries and other electrochemical energy storage systems, particularly when incorporated in aqueous electrolyte solutions. It can be desirable to avoid introducing certain organic solvents and/or extraneous salts into aqueous electrolyte solutions. Methods for synthesizing titanium catecholate complexes that can help avoid the unwanted introduction of organic solvents and/or extraneous salts into aqueous electrolyte solutions can include: providing an aqueous solution containing a catechol compound, reacting a titanium reagent with the catechol compound in the aqueous solution to form an intermediate titanium catecholate complex, isolating the intermediate titanium catecholate complex as a solid or slurry, and reacting a ligatable compound with the intermediate titanium catecholate complex in the presence of a base to produce a salt form titanium catecholate complex containing at least one additional ligand.

Aqueous methods for forming titanium catecholate complexes and associated compositions

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

Coordinatively saturated titanium (IV) coordination compounds containing catecholate ligands can be desirable active materials for flow batteries and other electrochemical energy storage systems. Such coordination compounds can be formed advantageously via an intermediate composition containing a coordinatively unsaturated titanium (IV) coordination compound. More specifically, such compositions can include a coordinatively unsaturated titanium (IV) coordination compound having a coordination number of 5 or less and containing two catecholate ligands, wherein the composition is substantially free of non-ligated catechol compound. Methods for forming the coordinatively unsaturated titanium (IV) coordination compounds can include: combining titanium tetrachloride and a catechol compound in an aprotic solvent to form a reaction mixture, and reacting the titanium tetrachloride with the catechol compound in an absence of base to form a coordinatively unsaturated titanium (IV) coordination compound having a coordination number of 5 or less and containing two catecholate ligands and that is insoluble in the reaction mixture.

Coordinatively unsaturated titanium catecholate complexes and processes associated therewith

Titanium complexes containing at least one catecholate ligand can be desirable active materials for flow batteries and other electrochemical energy storage systems. Such complexes can be formed through reacting a catechol compound with a titanium reagent in an organic solvent, removing a byproduct species, and then obtaining an aqueous phase containing a salt form of the titanium catechol complex, particularly an alkali metal salt form. More specifically, the methods can include: forming a catechol solution containing a catechol compound and an organic solvent, contacting a titanium reagent with the catechol solution to form a reaction mixture, reacting the titanium reagent with the catechol compound to form an intermediate titanium catechol complex and a byproduct species, separating the byproduct species, and combining an alkaline aqueous solution containing a base with the intermediate titanium catechol complex to produce a salt form titanium catechol complex at least partially dissolved in an aqueous phase.

Processes for forming titanium catechol complexes

Titanium complexes containing catecholate ligands can be desirable active materials for flow batteries and other electrochemical energy storage systems. Such complexes can be formed, potentially on very large scales, through reacting a catechol compound in an organic solvent with titanium tetrachloride, and then obtaining an aqueous phase containing an alkali metal salt form of the titanium catechol complex. More specifically, the methods can include: forming a catechol solution and heating, adding titanium tetrachloride to the catechol solution, reacting the titanium tetrachloride with a catechol compound to evolve HCl gas and to form an intermediate titanium catechol complex, and adding an alkaline aqueous solution to the intermediate titanium catechol complex to form an alkali metal salt form titanium catechol complex that is at least partially dissolved in an aqueous phase. The aqueous phase can be separated from an organic phase. The resulting complexes can be substantially free of alkali metal halide salts.

Titanium catecholate complexes can be desirable active materials for flow batteries and other electrochemical energy storage systems, particularly when incorporated in aqueous electrolyte solutions. It can be desirable to avoid introducing even traces of certain organic solvents into aqueous electrolyte solutions. Neat methods for synthesizing titanium catecholate complexes can help avoid the unwanted introduction of trace organic solvents into aqueous electrolyte solutions and also provide further advantages. Methods for synthesizing titanium catecholate complexes can include: combining a catechol compound and a titanium reagent in an absence of solvent to produce a reaction mixture, and reacting the titanium reagent with the catechol compound in a neat state to form a titanium catecholate complex containing at least one catecholate ligand. The titanium catecholate complex can be further reacted with a base to produce a salt form titanium catecholate complex, which can be present in an aqueous phase.

Neat methods for forming titanium catecholate complexes and associated compositions

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.

Concerted processes for forming 1,2,4-trihydroxybenzene from hydroquinone

Electrolyte solutions for flow batteries and other electrochemical systems can contain an active material capable of transferring more than one electron per oxidation-reduction cycle. Such active materials can include coordination compounds containing a metal center and at least one redox non-innocent ligand. Accordingly, flow batteries can include a first half-cell having a first electrolyte solution therein, where the first electrolyte solution contains a coordination compound having at least one redox non-innocent ligand coordinated to a metal center. Particular redox non-innocent ligands can include those bearing a quinone functional group, such as substituted catecholates bearing a quinone functional group. Some active materials can include compositions containing a coordination compound having at least one redox non-innocent ligand coordinated to a metal center, where the at least one redox non-innocent ligand is a substituted catecholate or a salt thereof bearing a quinone functional group.

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Cambridge, MA, United States of America

Matthew Millard