Nonaqueous electrolyte secondary cell and method of manufacturing the same
The present invention provides a nonaqueous electrolyte secondary cell having a positive electrode comprising mainly of a positive electrode active material, a negative electrode, and a nonaqueous electrolyte. The positive electrode active material is a lithium-containing transition metal composite oxide of a hexagonal crystal system that includes a compound represented by the general formula LiCo 1-x M x O 2 , where M is at least one species selected from the group consisting of V, Cr, Fe, Mn, Ni, Al, and Ti, and x is a decimal number in a range 0<x<1, magnesium, and halogen. In a nonaqueous electrolyte secondary cell having such a construction, the high-temperature characteristics are improved without reducing the cell capacity.
1. A nonaqueous electrolyte secondary cell comprising:
a positive electrode comprising mainly of a positive electrode active material;
a negative electrode; and
a nonaqueous electrolyte,
wherein the positive electrode active material is a lithium-containing transition metal composite oxide of a hexagonal crystal system, the composite oxide comprising:
a compound represented by a general formula LiCo 1-x M x O 2 , where M is at least one species selected from the group consisting of V, Cr, Fe, Mn, Ni, Al, and Ti, and x is a decimal number in a range 0<x<1;
magnesium; and
halogen;
wherein a halogen content in a total amount of the positive electrode active material is in a range of 0.0007 to 5 mass %; and
wherein the magnesium is in an amount necessary to lower the pH of filtrate to below 9.8, the filtrate collected after dispersing the positive electrode active material in water.
2. The nonaqueous electrolyte secondary cell according to claim 1 , wherein the value x for the general formula LiCo 1-x M x O 2 is in a range of 0.0001 to 0.005.
3. A method of manufacturing a nonaqueous electrolyte secondary cell, comprising the steps of:
preparing a lithium-containing transition metal composite oxide of a hexagonal crystal system containing magnesium and halogen, by mixing a lithium source, a cobalt source, a magnesium source, and a halogen source and calcining the sources, a halogen content in a total amount of the positive electrode active material being in range of 0.0007 to 5 mass %, the magnesium being in an amount necessary to lower the pH of filtrate to below 9.8, the filtrate collected after dispersing the positive electrode active material in water;
preparing a positive electrode using a positive electrode active material containing the composite oxide;
preparing an electrode assembly by arranging the positive electrode and a negative electrode with a separator disposed therebetween; and
sealing, after enclosing the electrode assembly and a nonaqueous electrolyte solution in a cell outer casing, openings of the cell outer casing.
4. The method of manufacturing a nonaqueous electrolyte secondary cell according to claim 3 , wherein MgF 2 is used as the magnesium source and the halogen source.
5. The method of manufacturing a nonaqueous electrolyte secondary cell according to claim 3 , wherein at least one species selected from the group consisting of Mg, MgO, MgCl 2 , and MgCO 3 is used as the magnesium source, and wherein LiF is used as the halogen source.