Polycrystalline metal oxides with enriched grain boundaries
Provided are electrochemical cells that include as a cathode active material within the cathode of the cell secondary particles that provide excellent capacity and improved cycle life. The particles are characterized by grain boundaries between adjacent crystallites of the plurality of crystallites and comprising a second composition having a layered α-NaFeO 2 -type structure, a cubic structure, a spinel structure, or a combination thereof, wherein the electrochemically active cathode active material has an initial discharge capacity of 180 mAh/g or greater; and wherein the electrochemical cell has an impedance growth at 4.2V less than 50% for greater than 100 cycles at 45° C.
1. An electrochemical cell, comprising:
an anode,
an electrolyte, and
a cathode, the cathode comprising an electrochemically active cathode active material comprising a plurality of particles, said plurality of particles comprising a plurality of crystallites each comprising a first composition comprising lithium, nickel, and oxygen;
a grain boundary between adjacent crystallites of the plurality of crystallites and comprising a second composition having a layered α-NaFeO 2 -type structure, a cubic structure, a spinel structure, or a combination thereof;
wherein the electrochemically active cathode active material has an initial discharge capacity of 180 mAh/g or greater; and
wherein the electrochemical cell has an impedance growth at 4.2V less than 50% for greater than 100 cycles at 45° C.
2. The cell of claim 1 , wherein the electrochemical cell has an impedance growth at 4.2V less than 120% for greater than 200 cycles at 45° C.
3. The electrochemical cell of claim 1 characterized by an impedance growth at 50% state of charge of less than 50% for greater than 200 cycles at 45° C.
4. The cell of claim 1 , wherein each of the crystallites comprise lithium, nickel, cobalt, and oxygen.
5. The cell of claim 4 , wherein each of the crystallites further comprise Al.
6. The cell of claim 4 , wherein each of the crystallites further comprise Mn.
7. The cell of claim 4 , wherein each of the crystallites further comprise Mg.
8. The cell of claim 1 , wherein the first composition and the second composition have the same elements.
9. The cell of claim 1 , wherein the first composition is defined by Li 1+x MO 2+y , wherein
−0.95≤ x≤ 0.3,
−0.3≤ y≤ 0.3, and
wherein M comprises nickel at greater than or equal to 80 atomic percent.
10. The cell of claim 9 , wherein M further comprises one or more elements selected from the group consisting of Mg, Sr, Co, Al, Ca, Cu, Zn, Mn, V, Ba, Zr, Ti, Nb, Ta, Cr, Fe, Mo, W, Hf, and B, said one or more elements residing in a Li layer, a M layer, or both, of the crystallites.
11. The cell of claim 9 , wherein M comprises an atomic percent of nickel greater than or equal to 90 percent.
12. The cell of claim 1 , wherein the crystallites comprise cobalt, with the cobalt concentration in the range of 1 at % to about 50 at % relative to total transition metal the first composition.
13. The cell of claim 1 , wherein the crystallites comprise cobalt, with the cobalt concentration in the range of 1 at % to about 15 at % relative to total transition metal in the crystallites.
14. The cell of claim 1 , wherein the crystallites comprise Co and Mg.
15. The cell of claim 1 , wherein the second composition comprises Al.
16. The cell of claim 1 , wherein the first composition excludes Al.
17. The cell of claim 1 , wherein the Al in the second composition is substantially uniformly distributed throughout said plurality of particles.
18. The cell of claim 1 , wherein Al is present at less than 4 atomic percent relative to total transition metal in the first composition.