Stable cathode materials
Provided are electrochemically active particles suitable for use as an active material in a cathode of a lithium ion electrochemical cell that include: a plurality of crystallites comprising a first composition comprising lithium, nickel, and oxygen; and a grain boundary between adjacent crystallites of the plurality of crystallites and comprising a second composition comprising lithium, nickel, and oxygen; wherein the grain boundary has a higher electrochemical affinity for lithium than the crystallites. The higher electrochemical affinity for Li leads to increased Li retention in the grain boundaries during or at charge relative to the bulk crystallites and stabilizes the structure of the grain boundaries and crystallites for improved cycling stability with no appreciable loss in capacity.
1. An electrochemically active particle for use in a cathode of an electrochemical cell, the particle comprising:
a plurality of crystallites 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 comprising lithium, nickel, and oxygen;
wherein lithium is present in the grain boundary at a higher concentration than lithium in the crystallites when an electrode incorporating the particle is charged, and wherein the grain boundary has higher electrochemical affinity for Li than the crystallites.
2. The particle of claim 1 wherein lithium is present in the grain boundary at a higher concentration than lithium in the crystallites when the electrode is charged to a potential greater than or equal to 3.5 V versus lithium.
3. The particle of claim 1 wherein lithium is present in the grain boundary at a higher concentration than lithium in the crystallites at a charge capacity of 40 mAh/g or greater.
4. The particle of claim 1 wherein the grain boundary comprises greater than 0.1 moles of lithium per mole of the second composition at said potential or said capacity.
5. The particle of claim 1 wherein the grain boundary comprises greater than 0.15 moles of lithium per mole of the second composition at said potential or said capacity.
6. The particle of claim 1 wherein the plurality of crystallites, the grain boundary or both, has an α-NaFeO 2 -type layered structure, a cubic structure, a spinel structure, a monoclinic structure, or a combination thereof.
7. The particle of claim 1 wherein the second composition is Li 1+x M′O 2+y , wherein M′ comprises Ni, the amount of Ni on the basis of moles Ni per mole of M′ in the second composition is −0≤Ni≤0.99.
8. The particle of claim 7 wherein amount of Ni on the basis of moles Ni per mole of M′ of the second composition is 0.9 or less.
9. The particle of claim 7 , wherein M′ comprises an element having a higher oxidation potential than Ni.
10. The particle of claim 9 wherein the element is capable of substituting for Ni in the 3b site of the Li 1+x M′O 2+y structure.
11. The particle of claim 7 wherein M′ comprises element Mn, Ti, Cr, Fe, Y, Ga, Sb, W, Sc, Zr, Nb, Mo, Zn, Cu, In, Ge, Al, or any combination thereof, where the concentration of the element in the grain boundary is greater than the concentration of the element in the crystallites.
12. The particle of claim 7 wherein M′ comprises two or more elements selected from the group consisting of Mn, Ti, Cr, Fe, Co, Y, Ga, Sb, W, Sc, Zr, Nb, Mo, Zn, Cu, In, Ge, and Al.
13. The particle of claim 7 wherein M′ comprises three or more elements selected from the group consisting of Mn, Ti, Cr, Fe, Co, Y, Ga, Sb, W, Sc, Zr, Nb, Mo, Zn, Cu, In, Ge, and Al.
14. The particle of claim 1 wherein the first composition is defined by Li 1+x MO 2+y , wherein M comprises nickel at greater than or equal to 0.1 moles per mole M.
15. The particle of claim 14 wherein M comprises nickel at greater than or equal to 0.75 moles per mole M, optionally greater than or equal to 0.90 moles per mole M.
16. The particle of claim 15 wherein M further comprises an additional metal, wherein the additional metal is present in an amount of about 0.01 to about 0.90 moles per mole M;
the additional metal optionally selected from the group consisting of Mg, Sr, Co, Al, Ca, Cu, Zn, Mn, V, Ba, Zr, Ti, Cr, Fe, Mo, B, and any combination thereof.
17. 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;
a sulfate 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.
18. An electrochemically active particle for use in a cathode of an electrochemical cell, the particle comprising:
a plurality of crystallites 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 comprising lithium, nickel, and oxygen;
wherein lithium is present in the grain boundary at a higher concentration than lithium inside the crystallites when the particle is at a state of charge greater than or equal to 10 percent; and
wherein the grain boundary has higher electrochemical affinity for Li than the crystallites.
19. The particle of claim 18 wherein the lithium is present in the grain boundary at a higher concentration than lithium inside the crystallites when the particle is at a state of charge greater than or equal to 80 percent.
20. An electrochemical cell comprising a cathode, an anode, and an electrolyte, the cathode comprising a cathode active material comprising the particle of claim 1 .