Methods Of Making Transition Metal Compounds Useful As Cathode Active Materials

Abstract

A method for carrying out solid state reactions under reducing conditions is provided. Solid state reactants include at least one inorganic metal compound and a source of reducing carbon. The reaction may be carried out in a reducing atmosphere in the presence of reducing carbon. Reducing carbon may be supplied by elemental carbon, by an organic material, or by mixtures. The organic material is one that can form decomposition products containing carbon in a form capable of acting as a reductant. The reaction proceeds without significant covalent incorporation of organic material into the reaction product. In a preferred embodiment, the solid state reactants also include an alkali metal compound. The products of the method find use in lithium ion batteries as cathode active materials. Preferred active materials include lithium-transition metal phosphates and lithium-transition metal oxides. In a preferred embodiment, the reaction product contains carbon particles intimately mixed among crystals of the active materials.

1 . A composition comprising an active material of general formula  
         A a M b (XY 4 ) c Z d    
       wherein 
 (a) A is selected from the group consisting of Li, Na, K, and mixtures thereof, and 0<a≦8;  
 (b) M comprises one or more metals, comprising at least one metal which is capable of undergoing oxidation to a higher valence state, and 1≦b≦3;  
 (c) XY 4  is selected from the group consisting of X′O 4-x Y′ x , X′O 4-y Y′ 2y , X″S 4 , and mixtures thereof, where X′is selected from the group consisting of P, As, Sb, Si, Ge, V, S, and mixtures thereof; X″ is selected from the group consisting of P, As, Sb, Si, V, Ge and mixtures thereof; Y′ is selected from the group consisting of halogen, S, or N; 0≦x<3; and 0<y≦2; and 0<c≦3; and  
 (d) Z is OH, halogen, or mixtures thereof, and 0≦d≦6; and  
 wherein M, X, Y, Z, a, b, c, d, x and y are selected so as to maintain electroneutrality of the compound, prepared by a process comprising the steps of:  
 combining starting materials comprising at least one particulate metal compound and at least one organic material to form a mixture; and  
 heating the mixture at a temperature and for a time sufficient to form a reaction product,  
 wherein at least one metal of the starting material is reduced in oxidation state during heating to form the inorganic metal compound.  
 
     
     
         2 . A composition according to  claim 1 , wherein the organic material is provided in stoichiometric excess.  
     
     
         3 . A composition according to  claim 1 , wherein the stating materials further comprise an alkali metal compound.  
     
     
         4 . A composition according to  claim 1 , wherein the process further comprises the step of reacting an alkali metal compound with the reaction product.  
     
     
         5 . A composition according to  claim 1 , wherein d>0.  
     
     
         6 . A composition according to  claim 1 , wherein A comprises lithium.  
     
     
         7 . A composition according to  claim 1 , wherein the organic material comprises a carbohydrate.  
     
     
         8 . A composition according to  claim 7 , wherein the organic material comprises sucrose.  
     
     
         9 . A composition according to  claim 1 , wherein XY 4  comprises phosphate.  
     
     
         10 . An active material according to  claim 1 , wherein A comprises lithium, XY 4  comprises phosphate, and Z comprises fluorine.  
     
     
         11 . An active material according to  claim 1 , wherein XY 4  comprises phosphate, A comprises Li, and M comprises M′ e M″ f , wherein e+f=b, wherein M′ comprises one or more transition metals from Groups 4 to 11 of the Periodic Table, and M″ comprises one or more elements from Groups 2, 3, 12, 13, or 14 of the Periodic Table.  
     
     
         12 . An active material according to  claim 11 , wherein 0.8≦a≦1.2 and 0.8≦b≦1.2.  
     
     
         13 . An active material according to  claim 12 , wherein M′ comprises one or more elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu, and M″ comprises one or more elements selected from the group consisting of non-transition elements with a +2 oxidation state and non-transition elements with a +3 oxidation state.  
     
     
         14 . An active material according to  claim 13 , wherein M′ comprises Fe and Co.  
     
     
         15 . An active material according to  claim 12 , wherein M′ comprises Fe and Co, and M″ comprises one or more elements selected from the group consisting of Mg, Al, Ca, Zn, and Ba.  
     
     
         16 . A composition according to  claim 1 , further comprising particles of carbon intimately mixed with the active material.  
     
     
         17 . A composition according to  claim 1 , comprising crystals of the active material nucleated onto carbon particles.  
     
     
         18 . A battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the electrodes comprises an active material according to  claim 1 .  
     
     
         19 . A battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the electrodes comprises an active material according to  claim 10 .  
     
     
         20 . A battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the electrodes comprises an active material according to  claim 11.