Compositionally gradient nickel-rich cathode materials and methods for the manufacture thereof
The present invention relates to lithium rechargeable battery cathode materials. More specifically, the cathode materials are compositionally gradient nickel-rich cathode materials produced using single-source composite precursor materials containing inorganic and/or metalorganic salts of lithium, nickel, manganese, and cobalt. Methods and systems for manufacturing the cathode materials by a combined spray pyrolysis/fluidized bed process are also disclosed.
1. A method for synthesizing a lithium-nickel-manganese-cobalt oxide (NMC) powder having a layered structure, comprising:
(a) spray-pyrolyzing a liquid mixture comprising at least one lithium salt, at least one nickel salt, at least one manganese salt, and at least one cobalt salt at a temperature of less than about 750° C. to form an amorphous NMC powder comprising oxides of lithium, nickel, manganese, and cobalt, wherein a ratio of a molar concentration of lithium in the mixture to a combined molar concentration of nickel, manganese, and cobalt in the mixture is between about 0.9 and about 1.1; and
(b) reacting the amorphous NMC powder in a fluidized bed reactor at a temperature of less than about 1,000° C. to crystallize the NMC powder.
2. The method of claim 1 , wherein a concentration of nickel in a primary particle of the NMC powder decreases with increasing distance from a center of the primary particle and a concentration of manganese in the primary particle increases with increasing distance from the center of the primary particle.
3. The method of claim 2 , wherein the NMC powder comprises a substantially spherical secondary particle having a surface texture composed of primary particles.
4. The method of claim 1 , wherein the liquid mixture comprises at least one inorganic salt and at least one metalorganic salt.
5. The method of claim 1 , wherein a molar concentration of manganese in the mixture and a molar concentration of cobalt in the mixture are approximately equal, and wherein a ratio of a molar concentration of nickel in the mixture to the sum of the molar concentrations of manganese and cobalt in the mixture is between about 0.5 and about 4.
6. The method of claim 1 , wherein the mixture of salts is defined by at least one condition selected from the group consisting of:
(i) the at least one lithium salt comprises at least one selected from the group consisting of lithium carboxylate, fluorinated lithium carboxylate, lithium nitrate, and another water-soluble lithium salt;
(ii) the at least one nickel salt comprises at least one selected from the group consisting of nickel carboxylate, fluorinated nickel carboxylate, nickel nitrate, and another water-soluble nickel salt;
(iii) the at least one manganese salt comprises at least one selected from the group consisting of manganese carboxylate, fluorinated manganese carboxylate, manganese nitrate, manganese propionate, manganese trifluoroacetate, and another water-soluble manganese salt; and
(iv) the at least one cobalt salt comprises at least one selected from the group consisting of cobalt carboxylate, fluorinated cobalt carboxylate, cobalt nitrate, and another water-soluble cobalt salt.
7. The method of claim 6 , wherein the at least one lithium salt comprises at least one of lithium acetate and lithium nitrate, the at least one nickel salt comprises nickel nitrate, the at least one manganese salt comprises at least one of manganese acetate and manganese trifluoroacetate, and the at least one cobalt salt comprises cobalt nitrate.
8. The method of claim 1 , wherein the temperature in step (a) is at least about 500° C.
9. The method of claim 1 , wherein the temperature in step (b) is about 875° C.
10. The method of claim 1 , wherein step (b) is conducted for no more than about five hours.
11. The method of claim 1 , wherein at least one of steps (a) and (b) is carried out under an atmosphere comprising at least one gas selected from the group consisting of air, oxygen gas (O 2 ), and combinations and mixtures thereof.