High nickel cathode material having low soluble base content

1. A positive electrode material for lithium ion batteries, comprising a lithium transition metal oxide powder, wherein the lithium transition metal oxide powder has a general formula Li a ((Ni z (Ni 1/2 Mn 1/2 ) y Co x ) 1−k A k ) 2−a O 2 , wherein x+y+z=1, 0.1≦x≦0.4, 0.36≦z≦0.50, A is a dopant, 0≦k≦0.1, and 0.95≦a≦1.05, wherein the powder is characterized by a soluble base content SBC obtained at room temperature and a soluble base content SBC-heated obtained upon heating the powder for 5 to 10 hours under air at a temperature ranging from 500° C. to a temperature less than the temperature where the morphology of the powder changes by sintering, whereby the ratio SBC-heated/SBC is less than 110%, and wherein the soluble base content SBC is the sum of the soluble base contents of Li2CO3 type base (SBC-Li2CO3) and LiOH type base (SBC-LiOH), both expressed in wt %, whereby (SBC-Li2CO3)≧0.085wt %.

2. The positive electrode material of claim 1 , wherein 0.40≦z≦0.45.

3. A positive electrode material for lithium ion batteries, comprising a lithium transition metal oxide powder, wherein the lithium transition metal oxide powder has a general formula Li a ((Ni z (Ni 1/2 , Mn 1/2 ) y Co x ) 1 − k ) 2−a O 2 , wherein x+y+z=1, 0.1≦x≦0.4, 0.36≦z ≦0.50, A is a dopant, 0≦k≦0.1, and 0.95≦a≦1.05, and has a soluble base content (SBC) that increases by less than 10% when the oxide powder is heated for 10 hours under air at a temperature of 790° C. according to claim 1 .

4. The positive electrode material for lithium ion batteries, according to claim 1 , having a BET surface area between 0.22 and 0.40 m 2 /g, and having a soluble base content (SBC) between 80 and 120 μmol/g.

5. The positive electrode material of claim 1 , wherein (SBC-Li 2 CO 3 )/(SBC-LiOH)>0.2.

6. The positive electrode material of claim 1 , having a surface specific SBC of 80-125μmol/m 2 , wherein the surface specific SBC is the ratio between SBC and BET surface area, wherein the BET surface area is measured after washing and drying.

7. The positive electrode material of claim 1 , wherein A is one or more dopants selected from the group consisting of Al, Ti and Mg, and 0<k<0.1.

8. The positive electrode material of claim 1 , wherein A is one or more dopants selected from the group consisting of B, Ca, Mn, Cr, V, Fe, Zr, S, F, P and Bi, and 0<k≦0.01.

9. A method for preparing the positive electrode material LiMO 2 of claim 1 , comprising the steps of:

providing a transition metal precursor MOOH prepared from the co-precipitation of transition metal sulphates with a base;

mixing the transition metal precursor with Li 2 CO 3 to form a mixture, and

sintering the mixture under a forced flow of air of at least 2 m 3 /kg mixture, at a temperature T between 800° and 1000° C., for a time t between 12 and 40 hrs, until no CO 2 is produced from the reaction MOOH+½Li 2 CO 3 =>LiMO 2 +½CO 2 +½H 2 O.

10. The method according to claim 9 , wherein the sintering step is performed at a temperature between 850 to 960° C.

11. The method according to claim 9 , wherein the transition metal precursor is obtained by co-precipitating transition metal sulphates and NaOH.

12. The method according to claim 9 , wherein the transition metal precursor is a mixed hydroxide or oxyhydroxide containing between 0.1 and 1.0 wt % CO 3 2− .

13. The method according to claim 9 , wherein the sintering step is preceded by heating the mixture for at least 5 hrs at a temperature from 650° C. to 800° C., under a forced flow of air of at least 2 m 3 /kg mixture.

14. A method for preparing the positive electrode material LiMO 2 of claim 1 , comprising the steps of:

providing a transition metal precursor MOOH prepared from the co-precipitation of transition metal sulphates with a base;

mixing the transition metal precursor with Li 2 CO 3 to form a mixture, and

sintering the mixture following the reaction MOOH+½Li 2 CO 3 =>LiMO 2 +½CO 2 +½H 2 O under a forced flow of air of at least 2 m 3 /kg mixture, at a temperature T selected between 800° and 1000° C., for a time t between 12 and 40 hrs, whereby at the completion of the time t no more CO 2 is produced.