Surface modification of active material structures in battery electrodes

Abstract

Provided herein are methods of processing electrode active material structures for use in electrochemical cells or, more specifically, methods of forming surface layers on these structures. The structures are combined with a liquid to form a mixture. The mixture includes a surface reagent that chemically reacts and forms a surface layer covalently bound to the structures. The surface reagent may be a part of the initial liquid or added to the mixture after the liquid is combined with the structures. In some embodiments, the mixture may be processed to form a powder containing the structures with the surface layer thereon. Alternatively, the mixture may be deposited onto a current collecting substrate and dried to form an electrode layer. Furthermore, the liquid may be an electrolyte containing the surface reagent and a salt. The liquid soaks the previously arranged electrodes in order to contact the structures with the surface reagent.

1 . A treated electrode active material structure comprising:
 an electrode active material structure comprising a metal selected from the group comprising titanium and nickel; and   a surface layer covalently bound to the electrode active material structure,   the surface layer comprising siloxane,   the surface layer reducing reactivity of the electrode active material structure with respect to electrolyte components.   
     
     
         2 . The treated electrode active material structure of  claim 1 , wherein the electrode active material structure is lithium titanium oxide. 
     
     
         3 . The treated electrode active material structure of  claim 1 , wherein the electrode active material structure is included in a slurry coated onto a current collecting substrate to form an electrode. 
     
     
         4 . The treated electrode active material structure of  claim 1 , wherein the slurry comprises a surface reagent that covalently bonds to the electrode active material structure to form the surface layer. 
     
     
         5 . The treated electrode active material structure of  claim 1 , wherein electrode active material structure is included in a dry cell assembly and wherein the electrode active material structure is combined with an electrolyte or a liquid comprising a surface reagent to form the surface layer. 
     
     
         6 . The treated electrode active material structure of  claim 1 , wherein the electrode active material structure is in a form of a powder, is part of a partially fabricated or a fully fabricated electrode, or is part of a dry cell assembly. 
     
     
         7 . The treated electrode active material structure of  claim 1 , wherein the electrode active material structure chemically reacts with a surface reagent, thereby forming the surface layer covalently bound to the electrode active material structure, 
       or the electrode active material structure catalyzes a chemical reaction involving the surface reagent such that the chemical reaction forms the surface layer covalently bound to the electrode active material structure. 
     
     
         8 . The treated electrode active material structure of  claim 7 , wherein an amount of the surface reagent is between about 0.25% by weight and about 5% by weight relative to the electrode active material structure. 
     
     
         9 . The treated electrode active material structure of  claim 7 , wherein the surface reagent comprises an oxy-silane. 
     
     
         10 . The treated electrode active material structure of  claim 8 , wherein the surface reagent comprises one or more materials selected from the group consisting of methyltrimethoxy-silane, and tridecafluorooctyltriethoxy-silane. 
     
     
         11 . An electrochemical cell, comprising:
 a positive electrode;   a negative electrode, wherein the negative electrode comprises a current collecting substrate and electrode active material structures coated thereon;   a surface layer covalently bound to the electrode active material structures, the surface layer comprising siloxane;   an electrolyte, the electrolyte in contact with the surface layer, wherein the surface layer reduces reactivity of the electrode active material structures with respect to electrolyte components; and   a separator positioned between the positive electrode and the negative electrode.   
     
     
         12 . The electrochemical cell of  claim 11 , wherein the electrolyte comprises a surface reagent that contacts the electrode active material to form the surface layer. 
     
     
         13 . The electrochemical cell of  claim 11 , wherein a slurry is coated on to the current collecting substrate, the slurry comprising the electrode active material and a surface reagent. 
     
     
         14 . The electrochemical cell of  claim 13 , wherein the surface reagent covalently bonds with the electrode active material to form the surface layer. 
     
     
         15 . The electrochemical cell of  claim 13 , wherein the surface reagent comprises an oxy-silane. 
     
     
         16 . The electrochemical cell of  claim 11 , wherein the electrode active material structures comprise lithium titanium oxide. 
     
     
         17 . The electrochemical cell of  claim 16 , wherein the lithium titanium oxide covalently bonds to a surface reagent to form the surface layer. 
     
     
         18 . The electrochemical cell of  claim 11 , wherein the positive electrode comprises electrode active material structures covalently bound to the surface layer. 
     
     
         19 . An electrochemical cell, comprising:
 a positive electrode;   a negative electrode, wherein the negative electrode comprises a current collecting substrate and a slurry dried and coated thereon;   wherein the slurry comprises a surface reagent and electrode active material structures, wherein the electrode active material structures comprise lithium titanium oxide;   wherein the surface reagent comprises methyltrimethoxy-silane and covalently bonds with lithium titanium oxide to form a surface layer;   an electrolyte, wherein the surface layer reduces reactivity of the electrode active material structures with respect to electrolyte components; and   a separator positioned between the positive electrode and the negative electrode.   
     
     
         20 . The electrochemical cell of  claim 19 , wherein the surface layer comprises siloxane.