Lithium nickel-manganese-cobalt oxide cathode powders for high voltage lithium-ion batteries
A lithium metal oxide powder for a cathode material in a rechargeable battery, consisting of a core and a surface layer, the surface layer being delimited by an outer and an inner interface, the inner interface being in contact with the core, the core having a layered crystal structure comprising the elements Li, M and oxygen, wherein M has the formula M=(Ni z (Ni 1/2 Mn 1/2 ) y Co x ) 1-k A k , with 0.15≤x≤0.30, 0.20≤z≤0.55, x+y+z=1 and 0<k≤0.1, wherein the Li content is stoichiometrically controlled with a molar ratio 0.95≤Li:M≤1.10; wherein A is at least one dopant and comprises Al; wherein the core has an Al content of 0.3-3 mol % and a F content of less than 0.05 mol %; and wherein the surface layer has an Al content that increases continuously from the Al content of the core at the inner interface to at least 10 mol % at the outer interface, and a F content that increases continuously from less than 0.05 mol % at the inner interface to at least 3 mol % at the outer interface, the Al and F contents in the surface layer being determined by XPS. The surface layer may also have a Mn content that decreases continuously from the Mn content of the core at the inner interface, to less than 50% of the Mn content of the core at the outer interface.
1. A lithium metal oxide powder for a cathode material in a rechargeable battery, comprising a core and a surface layer, the surface layer being delimited by an outer and an inner interface, the inner interface being in contact with the core, the cathode material having a layered crystal structure comprising the elements Li, M and oxygen, wherein M has the formula M=(Ni z (Ni 1/2 Mn 1/2 ) y Co x ) 1-k A k , with 0.15≤x≤0.30, 0.10≤z≤0.55, x+y+z=1 and 0<k≤0.1, wherein the Li content is stoichiometrically controlled with a molar ratio 0.95≤Li:M≤1.10; wherein A is at least one dopant and comprises Al, wherein the core has an Al content at the inner interface of 0.3-3 mol % and a F content of less than 0.05 mol %; wherein the surface layer comprises a mixture of Ni, Co, Mn, LiF and Al 2 O 3 determined by XPS; and wherein the surface layer has an Al content that increases on a gradient from the Al content at the inner interface to at least 10 mol % at the outer interface, and a F content that increases on a gradient from less than 0.05 mol % at the inner interface to at least 3 mol % at the outer interface, wherein x, y, z, and k are measured by ICP, and Al and F contents at the inner and outer interfaces are measure by XPS depth profile.
2. The lithium metal oxide powder of claim 1 , wherein the surface layer further comprises one or more compounds from the group consisting of CaO, TiO 2 , MgO, WO 3 , ZrO 2 , Cr 2 O 3 and V 2 O 5 .
3. The lithium metal oxide powder of claim 1 , wherein the surface layer consists of a mixture of Ni, Co and Mn and either LiF and nanometric crystalline Al 2 O 3 or nanometric crystalline Al 2 O 3 and sub-micrometric CaO.
4. The lithium metal oxide powder of claim 1 , wherein either 0.20≤z≤0.55 or 0.15≤x≤0.20, 0.40≤z≤0.55 and 1.00≤Li:M≤1.10.
5. The lithium metal oxide powder of claim 4 , wherein 0.005≤k≤0.02 and either A=Al or A=Al and Ca.
6. The lithium metal oxide powder of claim 1 , wherein k=0.01±0.005, x=0.20±0.02, y=0.40±0.05, z=0.40±0.05, 1.00≤Li:M≤1.10 and either A=Al or A=Al and Ca.
7. The lithium metal oxide powder of claim 1 , wherein the thickness of the surface layer is more than 50 nm and less than 400 nm.
8. The lithium metal oxide powder of claim 1 , wherein the F content of the core=0 mol %.
9. A method for making the lithium metal oxide powder of claim 1 , comprising:
providing a first mixture comprising a lithium M′-oxide powder, with M′=Ni z (Ni 1/2 Mn 1/2 ) y Co x , 0.15≤x≤0.30, 0.10≤z≤0.55 and x+y+z=1, and a first source of A comprising Al,
heating the first mixture to a first sintering temperature of at least 500° C.,
sintering the first mixture at the first sintering temperature for a first period of time,
cooling the first sintered mixture,
adding a fluorine-containing polymer and a second source of A comprising Al to the first sintered mixture, thereby obtaining a second mixture,
heating the second mixture to a second sintering temperature between 250° and 500° C.,
sintering the second mixture at the second sintering temperature for a second period of time, thereby obtaining the lithium metal oxide powder, and cooling the powder.
10. The method according to claim 9 , wherein one or both of the first and the second source of A is Al 2 O 3 .
11. The method according to claim 10 , wherein one or both of the first and the second source of A further comprises one or more compounds selected from the group consisting of CaO, TiO 2 , MgO, WO 3 , ZrO 2 , Cr 2 O 3 and V 2 O 5 .
12. The method according to claim 9 , wherein the source of A comprises a nanometric alumina powder having a D50<100 nm and a BET ≥50 m 2 /g.
13. The method according to claim 9 , wherein the amount of fluorine-containing polymer in the second mixture is between 0.1 and 2 wt %.
14. The method according to claim 9 , wherein the fluorine-containing polymer comprises a PVDF homopolymer, a PVDF copolymer, a PVDF-hexafluoropropylene (HFP) polymer or a PTFE polymer.
15. An electrochemical cell comprising the lithium metal oxide powder of claim 1 .