Electrode active composite materials and methods of making thereof

Abstract

A method of synthesizing a lithium metal phosphate composite usable for a lithium secondary battery includes the steps of forming a nanometer-size precursor comprising lithium source and metal phosphate nanoparticles having each nanoparticle at least partially coated a layer of carbon precursor, spray drying the nanometer-size precursor at a first desired temperature to form micron-size particles packed with the lithium metal phosphate precursor nanoparticles, and sintering the micron-size particles at a second desired temperature under an inert and/or reduction atmosphere to form a micron-size lithium metal phosphate composite.

What is claimed is: 
     
         1 . A method of synthesizing a lithium iron phosphate composite usable for a lithium secondary battery, comprising the steps of:
 providing a first solution and a second solution, wherein the first solution comprises ferric chloride hexahydrate dissolved in water, and wherein the second solution comprises diammonium hydrogen phosphate and pyrrole dissolved in water;   drop-wisely adding the first solution into the second solution with stirring to form a first mixture;   stirring the first mixture for a first period of time;   filtering and rinsing the stirred mixture with water to obtain solid substances;   forming a composite of FePO 4  and carbon precursor from the solid substances;   mixing an equivalent mole of a lithium compound and a sucrose with the FePO 4  composite to form a second mixture;   ball-milling the second mixture for a second period of time to form a lithium iron phosphate precursor comprising nanometer-sized particles; and   sintering the lithium iron phosphate precursor under an argon and hydrogen gas mixture at a first temperature for a third period of time to form a lithium iron phosphate composite.   
     
     
         2 . The method of  claim 1 , wherein the lithium compound comprises Li 2 CO 3 . 
     
     
         3 . The method of  claim 1 , wherein the lithium iron phosphate precursor is formed with Li:Fe:P=1:1:1 by mole ratio. 
     
     
         4 . The method of  claim 1 , wherein the argon and hydrogen gas mixture comprises about 95% argon and about 5% hydrogen by volume. 
     
     
         5 . The method of  claim 1 , wherein the first temperature is in a range of about 500-1200° C. 
     
     
         6 . The method of  claim 1 , wherein the first period of time, the second period of time and the third period of time are respectively in ranges of about 1-10 hours, about 18-30 hours and about 5-24 hours. 
     
     
         7 . The method of  claim 1 , wherein the forming step comprises the steps of:
 drying the solid substances at a second temperature for a fourth period of time;   heating the dried solid substances to a third temperature under argon for a fifth period of time, and cooling it to the room temperature to form the composite of FePO 4  and carbon precursor.   
     
     
         8 . The method of  claim 7 , wherein the second temperature and the third temperature are respectively in ranges of about 20-150° C. and about 20-500° C. 
     
     
         9 . The method of  claim 7 , wherein the fourth period of time and the fifth period of time are respectively in ranges of about 6-18 hours and about 1-3 hours. 
     
     
         10 . The method of  claim 1 , wherein the lithium iron phosphate composite comprises a micron-size composite that is packed with a plurality of nanometer-sized LiFePO 4  particles. 
     
     
         11 . The method of  claim 1 , wherein the lithium iron phosphate composite has a tap density that is in a range of about 0.5 to 3 g/cm 3 . 
     
     
         12 . A lithium iron phosphate composite synthesized according to the method of  claim 1 . 
     
     
         13 . A method of synthesizing a lithium metal phosphate composite usable for a lithium secondary battery, comprising the steps of:
 forming a nanometer-size precursor comprising lithium source and metal phosphate nanoparticles having each nanoparticle at least partially coated a layer of carbon precursor;   spray drying the nanometer-size precursor at a first desired temperature to form micron-size particles packed with the lithium metal phosphate precursor nanoparticles; and   sintering the micron-size particles at a second desired temperature under an inert and/or reduction atmosphere to form a micron-size lithium metal phosphate composite.   
     
     
         14 . The method of  claim 13 , wherein the first desired temperature and the second temperature are respectively in ranges of about 20-500° C. and about 500-1200° C. 
     
     
         15 . The method of  claim 13 , wherein the inert and/or reduction atmosphere comprises an argon and hydrogen gas mixture. 
     
     
         16 . The method of  claim 13 , wherein the layer of carbon precursor comprises at least one of carbonaceous materials, and is coated through in situ oxidation polymerization during the formation of the nanometer-size metal phosphate nanoparticles. 
     
     
         17 . The method of  claim 13 , wherein the metal comprises a transitional metal or a mixture of transition metals. 
     
     
         18 . The method of  claim 17 , wherein the transitional metal comprises Fe, Mn, V, Co, Ni, or a combination of them, and preferably comprises Fe. 
     
     
         19 . The method of  claim 17 , wherein the metal comprises optionally at least one non-transition metal. 
     
     
         20 . A lithium metal phosphate composite synthesized according to the method of  claim 13 .