Cathode material for rechargeable solid state lithium ion battery

1. A lithium transition metal oxide powder for a positive electrode material in a solid-state lithium ion battery, the powder comprising particles, the particles comprising

a core having the general formula Li x CoO 2 with 0.99<x<1.04; and

a surface layer, the surface layer having an inner layer and an outer layer, wherein the inner surface layer comprises Li y Ni 1-a-b Mn a Co b O 2 , with 0<y<1, 0.3<a<0.8 and 0<b<0.3, and the outer surface layer comprises discrete, monolithic, sub-micron sized particles having the general formula

Li 1+z (Ni 1-m-n Mn m Co n ) 1-z O 2 ,

with 0≤z≤0.05, 0<m≤0.50 and 0<n≤0.70;

wherein the powder has a D50 between 35 and 60 μm.

2. The lithium transition metal oxide powder of claim 1 , wherein 0.20<y<0.60, 0.45<a<0.60 and 0.05≤b≤0.15.

3. The lithium transition metal oxide powder of claim 1 , wherein 0<z<0.03, 0.25≤m≤0.35 and 0.15≤n≤0.25.

4. The lithium transition metal oxide powder of claim 1 , wherein the particles have a BET value that is at least twice the BET value of the core material before the application of the surface layer.

5. The lithium transition metal oxide powder of claim 4 , wherein the particles have a BET value of at least 0.20 m 2 /g.

6. The lithium transition metal oxide powder of claim 1 , wherein the core further comprises up to 5 mole % of a dopant A, with A being one or more elements selected from the group consisting of Al, Mg, Ti, Cr, V, Fe and Ga.

7. The lithium transition metal oxide powder of claim 1 , wherein the surface layer further comprises up to 5 mole % of a dopant A′, with A′ being one or more elements selected from the group consisting of A, F, S, N, Ca, Sr, Y, La, Ce and Zr.

8. The lithium transition metal oxide powder of claim 1 , wherein the inner surface layer comprises a multitude of islands densely sintered to the core material, the islands being Mn and Ni rich islands have a thickness of at least 100 nm and covering less than 70% of the surface of the core.

9. A method for preparing the lithium transition metal oxide powder of claim 1 , comprising:

providing a first mixture of lithium carbonate and Co 3 O 4 , with a molar ratio of Li:Co between 1.07:1 and 1.12:1,

firing the first mixture at a temperature between 950 and 1050° C., for 8 to 24 hours under air atmosphere, thereby obtaining a core material having a D50 value between 35 and 60 μm,

providing a second mixture of the core material and either a first Li—Ni—Mn—Co-oxide, or a set of a Ni—Mn—Co precursor powder and a Li-precursor compound,

sintering the second mixture at a temperature of at least 900° C. for 1 to 48 hrs,

providing a second lithium nickel-manganese-cobalt oxide powder having the general formula Li 1+z (Ni 1-m-n Mn m Co n ) 1-z O 2 , with 0≤z≤0.05, 0<m≤0.40 and 0<n≤0.30,

reducing the D50 value of the second lithium nickel-manganese-cobalt oxide powder below 1 μm, and

mixing the second lithium nickel-manganese-cobalt oxide powder with the sintered second mixture, and heating the obtained mixture at a temperature between 750 and 850° C. for 3 to 10 hours.

10. The method according to claim 9 , wherein the sintered first mixture consists of Mn and Ni bearing LiCoO 2 particles, said particles having Mn and Ni enriched islands on their surface, said islands comprising at least 5 mole % of Mn.

11. The method according to claim 9 , wherein the D50 value of the second lithium nickel-manganese-cobalt oxide powder is reduced to a value between 100 and 200 nm.

12. The method according to claim 9 , wherein the quantity of second lithium nickel-manganese-cobalt oxide powder is between 3 and 10 wt % of the sintered second mixture.

13. A rechargeable solid-state lithium ion battery comprising the lithium transition metal oxide powder of claim 1 .