Manufacturing method of positive active material precursor for sodium rechargeable batteries, positive active material precursor for sodium rechargeable batteries made by the same, and manufacturing method of positive active material for sodium rechargeable batteries, positive active material for sodium rechargeable batteries made by the same

Abstract

Disclosed is a method for producing a cathode active material precursor for a sodium secondary battery by using a coprecipitation technique and a cathode active material precursor for a sodium secondary battery produced thereby, and a cathode active material for a sodium secondary battery using the cathode active material precursor for a sodium secondary battery and a method for producing the same.

What is claimed is: 
     
         1 . A method for producing a cathode active material precursor for a sodium secondary battery by using a coprecipitation technique, the method comprising:
 (a) introducing distilled water and a first pH adjusting agent into a coprecipitation reactor, supplying air or a nitrogen gas to the reactor, and maintaining a pH in the reactor at from 6.5 to 7.5 while stirring;   (b) adjusting the pH in the reactor at from 6.5 to 11 by continuously introducing a second pH adjusting agent into the reactor and mixing the mixture; and   (c) forming particles of a cathode active material precursor for a sodium secondary battery by introducing an aqueous solution of transition metal compounds containing a nickel salt, an iron salt, and a manganese salt in an equivalent ratio and a complexing agent into the reactor.   
     
     
         2 . The method for producing a cathode active material precursor for a sodium secondary battery by using a coprecipitation technique according to  claim 1 , wherein the first pH adjusting agent in (a) above is ammonia or ammonium sulfate. 
     
     
         3 . The method for producing a cathode active material precursor for a sodium secondary battery by using a coprecipitation technique according to  claim 1 , wherein the second pH adjusting agent in (b) above is selected from the group consisting of ammonium oxalate, KOH, and NaOH. 
     
     
         4 . The method for producing a cathode active material precursor for a sodium secondary battery by using a coprecipitation technique according to  claim 3 , wherein the pH in the reactor is adjusted to from 10 to 11 in the case of introducing NaOH or KOH as the second pH adjusting agent in (b) above. 
     
     
         5 . The method for producing a cathode active material precursor for a sodium secondary battery by using a coprecipitation technique according to  claim 3 , wherein the pH in the reactor is adjusted to from 6.5 to 11 in the case of introducing ammonium oxalate as the second pH adjusting agent in (b) above. 
     
     
         6 . The method for producing a cathode active material precursor for a sodium secondary battery by using a coprecipitation technique according to  claim 1 , wherein
 the nickel salt is selected from the group consisting of nickel sulfate, nickel nitrate, nickel chloride, nickel fluoride, nickel acetate, and nickel hydroxide,   the iron salt is selected from the group consisting of iron sulfate, iron nitrate, iron chloride, iron fluoride, iron acetate, and iron hydroxide, and   the manganese salt is selected from the group consisting of manganese sulfate, manganese nitrate, manganese chloride, manganese fluoride, manganese acetate, and manganese hydroxide in (c) above.   
     
     
         7 . The method for producing a cathode active material precursor for a sodium secondary battery by using a coprecipitation technique according to  claim 1 , wherein the complexing agent is selected from the group consisting of an aqueous solution of ammonia (NH 4 OH), ammonium sulfate ((NH 4 ) 2 SO 4 ), ammonium nitrate (NH 4 NO 3 ), and diammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ) in (c) above. 
     
     
         8 . The method for producing a cathode active material precursor for a sodium secondary battery by using a coprecipitation technique according to  claim 1 , wherein a ratio of a concentration of the complexing agent to a concentration of the aqueous solution of transition metal compounds is from 0.8 to 1.2 in (c) above. 
     
     
         9 . A cathode active material precursor for a sodium secondary battery has a spherical shape having a particle size of from 5 to 15 μm, and exhibits a monodisperse type particle size distribution. 
     
     
         10 . The cathode active material precursor for a sodium secondary battery according to  claim 9 , which is represented by any one of the following Chemical Formulas 1 to 3:
   Ni x Fe y Mn 1-x-y (OH) 2  (0.1≦ x≦ 0.3, 0.2≦ y≦ 0.7, 0.1≦1- x - y≦ 0.5);  [Chemical Formula 1]
     Ni x Fe y Mn 1-x-y C 2 O 4  (0.1≦ x≦ 0.3, 0.2≦ y≦ 0.7, 0.1≦1- x - y≦ 0.5);  [Chemical Formula 2]
     and     [Ni x Fe y Mn 1-x-y ] 3 O 4  (0.1≦ x≦ 0.3, 0.2≦ y≦ 0.7, 0.1≦1- x - y≦ 0.5).  [Chemical Formula 3]
   
     
     
         11 . A cathode active material for a sodium secondary battery produced using the cathode active material precursor for a sodium secondary battery according to  claim 9 . 
     
     
         12 . The cathode active material for a sodium secondary battery according to  claim 11 , which is represented by Na x [Ni y Fe z Mn 1-y-z ]O 2  (0.8≦x≦1.2, 0.05≦y≦0.9, 0.05≦z≦0.9, 0.05≦1-y-z≦0.9) and has an O 3 -type crystal structure. 
     
     
         13 . The cathode active material for a sodium secondary battery according to  claim 11 , which has a spherical shape having a particle size of from 5 to 15 μm and exhibits a monodisperse type particle size distribution. 
     
     
         14 . The cathode active material for a sodium secondary battery according to  claim 11 , which has three peaks appearing at 2θ=in a range of from 30° to 40° and the peak (104) of a main peak appearing at 2θ=in a range of from 40° to 45° in XRD pattern. 
     
     
         15 . The cathode active material for a sodium secondary battery according to  claim 11 , which has a tapped density of from 1.0 to 2.4 g/cc. 
     
     
         16 . A method for producing the cathode active material for a sodium secondary battery, the method comprising:
 mixing the cathode active material precursor for a sodium secondary battery according to  claim 9  and a sodium compound; and   subjecting the mixture thus obtained to a heat treatment.   
     
     
         17 . The method for producing a cathode active material for a sodium secondary battery according to  claim 16 , wherein the sodium compound is sodium carbonate, sodium nitrate, sodium acetate, sodium hydroxide, hydrates of sodium hydroxide, sodium oxide, or one of their combinations. 
     
     
         18 . The method for producing a cathode active material for a sodium secondary battery according to  claim 16 , wherein the sodium compound is mixed in a ratio of from 1.0 to 1.5 mole per 1 mole of the cathode active material precursor for a sodium secondary battery. 
     
     
         19 . The method for producing a cathode active material for a sodium secondary battery according to  claim 16 , wherein the heat treatment is conducted at from 800° C. to 1000° C. 
     
     
         20 . A sodium secondary battery comprising the cathode active material for a sodium secondary battery according to  claim 15 .