Electrode active material electrode lithium-ion secondary battery method of making electrode active material and method of making lithium-ion secondary battery

Abstract

The positive electrode active material in accordance with the present invention is used for a positive electrode for a lithium-ion secondary battery, includes Li, Mn, Ni, Co, and O atoms, and has a substantially halite type crystal structure. Specifically, it is preferably expressed by Li a Mn b Ni c Co d O e , where a is 0.85 to 1.1, b is 0.2 to 0.6, c is 0.2 to 0.6, d is 0.1 to 0.5, and e is 1 to 2 (the sum of b, c, and d being 1). Because of such composition and crystal structure, the positive electrode active material of the present invention reduces the amount of elution of the battery into the liquid electrolyte and enhances the stability at a high temperature.

1 . An electrode active material used for a positive electrode for a lithium-ion secondary battery; said electrode active material including Li, Mn, Ni, Co, and O atoms, and having a substantially halite type crystal structure.  
     
     
         2 . An electrode active material according to  claim 1 , wherein said electrode active material is an oxide represented by the following expression (1):  
       Li a Mn b Ni c Co d O e   (1)  
       where a, b, c, d, and e satisfy the relationships represented by the following expressions (2) to (7):  
       0 <a≦ 1.1  (2) 0 <b≦ 0.6  (3) 0 <c≦ 1.0  (4) 0 <d≦ 1.0  (5) 1 ≦e≦ 2  (6)  b+c+d= 1  (7)  
     
     
         3 . An electrode active material according to  claim 2 , wherein a, b, c, d, and e in said expression (1) satisfy the relationships represented by the following expressions (6) to (11):  
       1≦ e≦ 2  (6)  b+c+d= 1  (7) 0.85≦ a≦ 1.1  (8) 0.2≦ b≦ 0.6  (9)  0.2≦   c≦ 0.6  (10) 0.1≦ d≦ 0.5  (11)  
     
     
         4 . An electrode active material according to  claim 1 , wherein said electrode active material has an exothermic peak temperature of at least 280° C. in differential scanning calorimetry in a state having a potential of 4.3 V with reference to lithium metal.  
     
     
         5 . An electrode used for a positive electrode of a lithium-ion secondary battery; said electrode comprising an electrode active material containing Li, Mn, Ni, Co, and O atoms, and having a halite type crystal structure.  
     
     
         6 . A lithium-ion secondary battery comprising: 
 a positive electrode including a first electrode active material containing Li, Mn, Ni, Co, and O atoms, and having a substantially halite type crystal structure;    a negative electrode disposed so as to oppose said positive electrode; and    an electrolyte disposed between said positive and negative electrode.    
     
     
         7 . A lithium-ion secondary battery according to  claim 6 , wherein said electrolyte is disposed between said positive and negative electrodes while in a liquid electrolyte state dissolved or dispersed in a solvent including a carbonate compound.  
     
     
         8 . A lithium-ion secondary battery according to  claim 7 , wherein said liquid electrolyte contains a cyclic carbonate compound, a chain carbonate compound, and an alkyl sultone.  
     
     
         9 . A lithium-ion secondary battery according to  claim 7 , wherein said liquid electrolyte satisfies the relationship represented by the following expression (12)  
       10≦ Nk /( Nk+Ns )×100≦50  (12)  
       where 
 Nk is the total content of said cyclic carbonate compound; and  
 Ns is the total content of said chain carbonate compound.  
 
     
     
         10 . A lithium-ion secondary battery according to  claim 7 , wherein said liquid electrolyte contains ethyl methyl carbonate as said chain carbonate and satisfies the relationship represented by the following expression (13):  
         Ne /( Nk+Ns )×100≦50  (13)  
       where 
 Nk is the total volume of said cyclic carbonate compound;  
 Ns is the total volume of said chain carbonate compound; and  
 Ne is the total volume of said ethyl methyl carbonate.  
 
     
     
         11 . A lithium-ion secondary battery according to  claim 7 , wherein said liquid electrolyte contains dimethyl carbonate as said chain carbonate and satisfies the relationship represented by the following expression (14):  
         Ng /( Nk+Ns )×100≦30  (14)  
       where 
 Nk is the total volume of said cyclic carbonate compound;  
 Ns is the total volume of said chain carbonate compound; and  
 Ng is the volume of said dimethyl carbonate.  
 
     
     
         12 . A lithium-ion secondary battery according to  claim 7 , wherein said liquid electrolyte contains 1, 3-propane sultone as said alkyl sultone and satisfies the relationship represented by the following expression (15):  
       1≦Wa≦5  (15)  
       where Wa is the mass ratio (%) of said 1,3-propane sultone in said liquid electrolyte.  
     
     
         13 . A lithium-ion secondary battery according to  claim 7 , wherein said liquid electrolyte contains a lithium salt as an electrolyte salt and satisfies the relationship represented by the following expression (16):  
       0.3≦Ml≦5  (16)  
       where Ml is the mole concentration (mol/L) of said lithium salt in said liquid electrolyte.  
     
     
         14 . A lithium-ion secondary battery according to  claim 7 , wherein said liquid electrolyte includes lithium hexafluorophosphate as an electrolyte salt.  
     
     
         15 . A lithium-ion secondary battery according to  claim 6 , wherein said negative electrode comprises a second electrode active material including a C atom.  
     
     
         16 . A lithium-ion secondary battery according to  claim 15 , wherein said second electrode active material is graphite.  
     
     
         17 . A lithium-ion secondary battery according to  claim 6 , wherein said negative electrode comprises a third electrode active material including Li, Ti, and O atoms.  
     
     
         18 . A lithium-ion secondary battery according to  claim 17 , wherein said third electrode active material is an oxide represented by the following expression (17):  
       Li 1+x Ti 2−x O y   (17)  
       where x and y satisfy the relationships represented by the following expressions (18) and (19):  
       −0.2 ≦x≦ 1.0  (18) 3.0< y≦ 4.0  (19)  
     
     
         19 . A method of making an electrode active material, said method comprising the steps of: 
 preparing a first solution by dissolving an acid salt including an Mn atom, an acid salt including an Ni atom, and an acid salt including a Co atom into water or a solvent mainly composed of water;    preparing a second solution by mixing said first solution with a solution including an NH 4   +  ion;    forming a complex salt including Mn, Ni, and Co atoms by drying said second solution; and    thermally reacting said complex salt with LiOH in an atmospheric air, so as to yield an electrode active material including Li, Mn, Ni, Co, and O atoms and having a substantially halite type crystal structure.    
     
     
         20 . A method of making a lithium-ion secondary battery, said method comprising the steps of: 
 charging an uncharged lithium-ion secondary battery comprising a positive electrode including an electrode active material containing Li, Mn, Ni, Co, and 0 atoms and having a halite type crystal structure and a negative electrode disposed so as to oppose said positive electrode, such that said lithium-ion secondary battery attains a capacity of at least substantially 50% of a full-charge capacity determined beforehand for said lithium-ion secondary battery; and    annealing thus charged lithium-ion secondary battery at a temperature of at least 60° C.    
     
     
         21 . A method of making a lithium-ion secondary battery according to  claim 20 , wherein said charged lithium-ion secondary battery is annealed for at least 4 hours at a temperature of 70° C. to 90° C.