Nanocrystals of polycrystalline layered lithium nickel metal oxides
Provided are electrochemically active secondary particles that provide excellent capacity and improved cycle life. The particles are characterized by a plurality of nanocrystals with small average crystallite size. The reduced crystallite size reduces impedance generation during cycling thereby improving capacity and cycle life. Also provided are methods of forming electrochemically active materials, as well as electrodes and electrochemical cells employing the secondary particles.
1. An electrochemically active polycrystalline particle comprising: a plurality of nanocrystals, the plurality of nanocrystals comprising a first composition defined by Li 1+x MO 2+y , wherein
−0.1≤ x≤ 0.3,
−0.3≤ y≤ 0.3, and
wherein M comprises nickel at greater than or equal to 10 atomic percent; and
said plurality of nanocrystals having an average crystallite size of less than or equal to 85 nanometers as measured by X-ray diffraction.
2. The particle of claim 1 , wherein said size of said plurality of nanocrystals have an average crystallite size of 50 nanometers to less than or equal to 85 nanometers.
3. The particle of claim 1 , wherein said size of said plurality of nanocrystals is less than or equal to 80 nanometers.
4. The particle of claim 1 , wherein said size of said plurality of nanocrystals is less than or equal to 70 nanometers.
5. The particle of claim 1 wherein M further comprises one or more elements selected from the group consisting of Al, Mg, Co, Mn, Ca, Sr, Zn, Ti, Zr, Y, Cr, Mo, Fe, V, Si, Ga and B.
6. The particle of claim 1 , further comprising a grain boundary between adjacent nanocrystals of said plurality of nanocrystals and comprising a second composition optionally having an α-NaFeO 2 -type layered structure, a cubic structure, or a combination thereof, wherein a concentration of cobalt in said grain boundary is greater than a concentration of cobalt in said nanocrystals.
7. The particle of claim 1 , wherein M comprises nickel at an atomic percent greater than or equal to 75%.
8. The particle of claim 1 , further comprising an outer coating on a surface of the particle, the outer coating comprising:
an oxide of one or more elements selected from Al, Zr, Y, Co, Ni, Mg, and Li;
a fluoride comprising one or more elements selected from Al, Zr, and Li;
a carbonate comprising one or more elements selected from Al, Co, Ni, Mn, and Li; or
a phosphate comprising one or more elements selected from Al and Li.
9. A method of manufacturing the electrochemically active particle of claim 1 , said method comprising:
providing a first mixture, said first mixture comprising lithium hydroxide or its hydrate and a precursor hydroxide comprising nickel;
calcining said first mixture to a maximum temperature of less than 700° C. to form a first material comprising a plurality of nanocrystals having a size of less than or equal to 85 nanometers as measured by x-ray diffraction.
10. The method of claim 9 wherein said maximum temperature is 680° C. or less.
11. The method of claim 9 , wherein said step of calcining said first mixture comprises:
increasing a temperature from about 25° C. to about 450° C. at about 5° C./minute;
soaking at said temperature of about 450° C. for about 2 hours,
increasing said temperature from about 450° C. to a maximum temperature of about 650° C. to about 699° C.; and
soaking at said maximum temperature of about 650° C. to about 699° C. for about 6 hours.
12. The method of claim 9 , further comprising:
combining said first material with a second material comprising at least one of cobalt, aluminum, or combinations thereof to form a second mixture; and
heat treating said second mixture to a second maximum temperature of 725° C. or less, to produce a particle further comprising a grain boundary between adjacent nanocrystals, said grain boundary comprising a second composition optionally having an α-NaFeO 2 -type layered structure, a cubic structure, or a combination thereof, wherein a concentration of cobalt in said grain boundary is greater than a concentration of cobalt in said nanocrystals; and wherein the plurality of nanocrystals have a size of less than or equal to 105 nanometers.
13. The method of claim 9 , wherein said particle comprises nickel at an atomic percent greater than or equal to 75%.
14. The method of claim 9 , wherein said average size of said plurality of nanocrystals are greater than or equal to 50 nanometers to less than or equal to 85 nanometers.
15. The method of claim 9 , wherein said size of said plurality of nanocrystals is less than or equal to 80 nanometers.