Composite cathode materials having improved cycle life
Lithiated composite materials and methods of manufacture are provided that are capable of imparting excellent capacity and greatly improved cycle life in lithium-ion secondary cells. By supplementing a high nickel content lithium storage material with a transition metal oxide lithium storage material or a dopant at relatively low levels, the capacity of the high nickel content lithium storage materials is maintained while cycle life is dramatically improved. These characteristics are promoted by methods of producing the materials that intermix unlithiated precursor materials with a lithium source and sintering the materials together in a single sintering reaction. The resulting lithiated composite materials provide for the first time both high capacity and excellent cycle life to predominantly high nickel content electrodes.
1. A method of making an electrode material for a rechargeable lithium ion electrochemical cell, said method comprising the steps of:
(a) providing a non-lithiated high nickel content lithium storage material comprising Ni a Co b where a is from 81 to 99 and b is from 1 to 19, where a and b are relative atomic amounts of Ni and Co respectively, and a+b=100;
(b) providing a non-lithiated transition metal oxide lithium storage material comprising the formula Ni x Co y Mn z where 0.3≦x≦0.5, 0.2≦y≦0.4, 0.3≦z≦0.4, or combinations thereof, where x, y, and z are relative atomic amounts of Ni Co and Mn respectively, and where x+y+z=1;
(c) mixing by ball milling said non-lithiated high nickel content lithium storage material and said non-lithiated transition metal oxide lithium storage material with a lithium source to form a lithiated composite material, wherein said high nickel content lithium storage material is present as a predominant by weight relative to said transition metal oxide lithium storage material; and
(d) sintering said lithiated composite material, wherein said composite material is characterized by a longer cycle life than that of lithiated high nickel content lithium storage material.
2. The method of claim 1 wherein said composite material following sintering maintains a capacity in excess of 180 milliamphours per gram at 40 cycles.
3. The method of claim 1 wherein said composite material following sintering maintains a capacity in excess of 170 milliamphours per gram at 20 cycles.
4. The method of claim 1 wherein said transition metal oxide lithium storage material is present at from 1 to 20 weight percent relative to said high nickel content lithium storage material.
5. The method of claim 1 wherein said lithium source is present at greater than stoichiometric ratio.
6. An electrode material for a rechargeable lithium ion electrochemical cell, said electrode material comprising:
a non-lithiated high nickel content lithium storage material comprising Ni a Co b where a is 63 or greater and a+b=100;
a non-lithiated transition metal oxide lithium storage material comprising the formula Ni x Co y Mn z wherein 0.3≦x≦0.5, 0.2≦y≦0.4, 0.3≦z≦0.4, or combinations thereof and where x+y+z=1; and
a lithium source;
said non-lithiated high nickel content lithium storage material and said non-lithiated transition metal oxide lithium storage material and said lithium source intermixed by ball milling and sintered to form a lithiated composite material;
wherein said high nickel content lithium storage material is present as a predominant by weight relative to said transition metal oxide lithium storage material; and
wherein said composite material is characterized by a longer cycle life than that of lithiated high nickel content lithium storage material.
7. The electrode material of claim 6 wherein said transition metal oxide lithium storage material is present at from 1 to 20 weight percent relative to said high nickel content lithium storage material.
8. The electrode material of claim 6 wherein said composite material maintains a capacity in excess of 180 milliamphours per gram at 40 cycles.
9. The electrode material of claim 6 wherein said composite material maintains a capacity in excess of 170 milliamphours per gram at 20 cycles.
10. The electrode material of claim 6 wherein a is from 80 to 100 and b is from 0 to 20.
11. The electrode material of claim 6 wherein said high nickel content lithium storage material comprises Ni 92 Co 8 , or combinations thereof.
12. The electrode material of claim 6 wherein said high nickel content lithium storage material further comprises Mn at an atomic percentage of 10% or less.
13. The electrode material of claim 6 wherein said transition metal oxide lithium storage material comprises the formula Ni 0.5 Co 0.2 Mn 0.3 .
14. The electrode material of claim 6 wherein said lithium source is present at greater than stoichiometric ratio.