High capacity positive electrodes for use in lithium-ion electrochemical cells and methods of making same
Positive electrode for lithium-ion electrochemical cells are provided that have capacity retentions of greater than about 95% after 50 charge-discharge cycles when comparing the capacity after cycle 52 with the capacity after cycle 2 when cycled between 2.5 V and 4.7 V vs. Li/Li + at 30° C. Compositions useful in the provided positive electrodes can have the formula, Li 1+x (Ni a Mn b Co c ) 1−x O 2 , wherein 0.05≦x≦0.10, a+b+c=1, 0.6≦b/a≦1.1, c/(a+b)<0.25, and a, b, and c are all greater than zero. The process of making these positive electrodes includes firing the compositions at 850° C. to 925° C.
1. A positive electrode for a lithium-ion electrochemical cell comprising a composition that comprises a plurality of particles comprising:
a core having the formula,
Li 1+x (Ni a Mn b Co c ) 1−x O 2 ,
wherein 0.05≦x≦0.10, a+b+c=1, 0.6≦b/a≦1.1, c/(a+b)<0.25, a, b, and c are all greater than zero; and
a shell substantially surrounding the core comprising a lithium mixed transition metal oxide comprising manganese and nickel wherein the molar ratio of manganese to nickel is greater than b/a and b/a>1,
wherein said composition has a capacity retention of greater than about 95% after 50 cycles when comparing the capacity after cycle 52 with the capacity after cycle 2 when cycled between 2.5 V and 4.7 V vs. Li/Li + at 30° C.
2. A positive electrode for a lithium-ion electrochemical cell according to claim 1 , wherein the core has a formula wherein 0.10≦c≦0.20.
3. A positive electrode for a lithium-ion electrochemical cell according to claim 1 , wherein the core has a formula wherein 0.05≦x≦0.07.
4. A positive electrode for a lithium-ion electrochemical cell according to claim 1 , wherein the composition has been prepared by heating to a temperature ranging from 850° C. to 925° C.
5. A positive electrode for a lithium-ion electrochemical cell according to claim 1 , wherein said composition has a capacity retention of greater than about 90% after 50 cycles when comparing the capacity after cycle 52 with the capacity after cycle 2 when cycled between 2.5 V and 4.7 V vs. Li/Li + at 50° C.
6. A positive electrode for a lithium-ion electrochemical cell according to claim 1 , wherein the core has a formula, Li 1.06 [Ni 0.42 Mn 0.42 Co 0.16 ]O 2 and the shell has a ratio of b/a of 1.27.
7. A lithium-ion electrochemical cell comprising:
an anode;
an electrolyte; and
a positive electrode according to claim 1 .
8. A method of making a positive electrode comprising: first forming a mixed transition metal hydroxide or carbonate by precipitating an aqueous mixture of Ni:Mn:Co salts with a hydroxide or carbonate source, where the molar ratio a:b:c is with respect to the formula
Li 1+x (Ni a Mn b Co c ) 1−x O 2 ,
wherein 0.05≦x≦0.10, a+b+c=1, 0.6≦b/a≦1.1, c/(a+b)<0.25 and a, b, and c are all
greater than zero to form a transition metal hydroxide or carbonate mixture;
dispersing the transition metal hydroxide or carbonate mixture in ammoniated water;
heating the transition metal hydroxide or carbonate mixture to greater than about 60° C.;
adding an aqueous solution of soluble mixed transition metal salts comprising manganese and nickel wherein the molar ratio of manganese to nickel is greater >1 and precipitating to form a core-shell hydroxide or carbonate;
drying the core-shell hydroxide or carbonate;
mixing the core-shell hydroxide or carbonate with a lithium salt;
sintering the core-shell hydroxide or carbonate mixture at about 500° C. for at least about 4 hours; and
firing the core-shell hydroxide or carbonate mixture from about 850° C. to about 925° C. for least 12 hours after sintering.