PROCESS FOR MAKING LITHIATED TRANSITION METAL OXIDES

Abstract

The present invention is directed towards a process for making a lithiated transition metal oxide, said process comprising the following steps: (a) providing a precursor selected from mixed oxides, hydroxides, oxyhydroxides, and carbonates of nickel and at least one transition metal selected from manganese and cobalt, wherein at least 45 mole-% of the cations of the precursor are Ni cations, (b) mixing said precursor with at least one lithium salt selected from LiOH, Li.sub.2O, Li.sub.2CO.sub.3, and LiNO.sub.3, thereby obtaining a mixture, (c) adding at least one phosphorus compound of general formula (I) X.sub.yH.sub.3−yPO.sub.4 (I) wherein X is selected from NH.sub.4 and Li, y is 1 or 2, to the mixture obtained in step (b), wherein steps (b) and (c) may be performed consecutively or simultaneously, treating the mixture so obtained at a temperature in the range of from 650 to 950° C.

Claims

1: A process for making a lithiated transition metal oxide, the process comprising: (a) providing a precursor selected from the group consisting of mixed oxides, mixed hydroxides, mixed oxyhydroxides, and mixed carbonates of nickel and at least one transition metal selected from the group consisting of manganese and cobalt, wherein at least 45 mole-% of the cations of the precursor are Ni cations; (b) mixing said precursor with at least one lithium salt selected from the group consisting of LiOH, Li.sub.2O, Li.sub.2CO.sub.3, and LiNO.sub.3, thereby obtaining a mixture; (c) adding at least one phosphorus compound of general formula (I):
X.sub.yH.sub.3−yPO.sub.4  (I) wherein: X is selected from NH.sub.4 and Li, y is 1 or 2, to the mixture obtained in step (b), wherein steps (b) and (c) may be performed consecutively or simultaneously; and (d) treating the mixture so obtained at a temperature in the range of from 650 to 950° C.

2: The process according to claim 1, wherein the precursor contains nickel cations, cobalt cations, and manganese cations.

3: The process according to claim 1, wherein: the precursor has a composition of the transition metals of Ni.sub.aCo.sub.bMn.sub.cM.sub.d; a is in the range of from 0.45 to 0.9; b is in the range of from 0.05 to 0.3; c is in the range of from 0.05 to 0.3; d is in the range of from zero to 0.1; a+b+c+d=1; and M is one or more of Al, Ti, V, Zn, Ca, and Mo.

4: The process according to claim 1, wherein in step (b) the molar ratio of lithium in lithium salt to transition metals in the precursor is in the range of from 1.11:1 to 1:1.03.

5: The process according to claim 1, in step (c) the weight ratio of phosphorus compound and lithium salt of step (b) is in the range of from 1:100 to 1:50.

6: The process according to claim 1, wherein compound (I) is (NH.sub.4).sub.2HPO.sub.4.

7: The process according to claim 1, wherein step (d) is being performed in an atmosphere of oxygen or oxygen-enriched air.

8: A cathode active material having the general formula (II):
Li.sub.1+x(Ni.sub.aCo.sub.bMn.sub.cM.sub.d).sub.1−xO.sub.2.y lithium phosphate  (II), wherein: x is in the range of from zero to 0.1; a is in the range of from 0.45 to 0.9; b is in the range of from 0.05 to 0.3; c is in the range of from 0.05 to 0.3; d is in the range of from zero to 0.1; y is in the range of from 0.005 to 0.03; a+b+c+d=1; M is one or more of Al, Ti, V, Zn, Ca, and Mo; and said lithium phosphate is present in homogeneously dispersed form within the particles of Li.sub.1+x(Ni.sub.aCo.sub.bMn.sub.cM.sub.d).sub.1−xO.sub.2 or in form of separate particles.

9: The cathode active material according to claim 8, wherein the lithium phosphate is selected from Li.sub.3PO.sub.4 and Li.sub.4P.sub.2O.sub.7.

10: The cathode active material according to claim 8, having a residual carbonate content of 0.3% or less.

11: An electrode for a lithium ion battery, the electrode comprising: (A) at least one cathode active material according to claim 8; (B) carbon in an electrically conductive state; and (C) a binder.

12: An electrochemical cell, comprising at least one electrode according to claim 11.

Description

EXAMPLES

[0110] Percentages are percent by weight unless expressly specified otherwise.

I. Manufacture of a Lithiated Transition Metal Oxide

I.1 Manufacture of Inventive Cathode Active Material (CAM.I)

[0111] A precursor was provided, composition Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2. In a ball mill, Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2 was mixed with Li.sub.2CO.sub.3 so that the Li/total transition metal molar ratio was 1.03/1. Then, 1% by 5 weight of LiH.sub.2PO.sub.4 were added, the percentage referring to the sum of Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2 and Li.sub.2CO.sub.3. The mixture so obtained was calcined in a box furnace under air with the following temperature program: raise 3K/min to 350° C., maintain at 350° C. for 4 hours, raise 3K/min to 675° C., maintain at 675° C. for 4 hours, raise 3 K/min to 900° C., maintain at 900° C. for 6 hours. After step (d.1), the material so obtained was cooled to room temperature under air within a period of 12 hours, deagglomerated in a mortar and sifted through a sieve with 32 μm mesh size. Inventive cathode active material (CAM.1) was obtained.

I.2 Manufacture of Inventive Cathode Active Material (CAM.2)

[0112] A precursor was provided, Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2. In a ball mill, Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2 was mixed with Li.sub.2CO.sub.3 so that the Li/total transition metal molar ratio was 1.03/1. Then, 1% by weight of (NH.sub.4).sub.2HPO.sub.4 were added, the percentage referring to the sum of Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2 and Li.sub.2CO.sub.3. The mixture so obtained was calcined in a box furnace under oxygen atmosphere with the following temperature program: raise 3K/min to 350° C., maintain at 350° C. for 4 hours, raise 3K/min to 675° C., maintain at 675° C. for 4 hours, raise 3 K/min to 900° C., maintain at 900° C. for 6 hours. After step (d.2), the material so obtained was cooled to room temperature under the oxygen atmosphere within a period of 12 hours, deagglomerated in a mortar and sifted through a sieve with 32 μm mesh size. Inventive cathode active material (CAM.2) was obtained.

I.3 Comparative Experiment: Manufacture of Comparative Cathode Active Material C-(CAM.3)

[0113] A precursor was provided, Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2. In a ball mill, Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2 was mixed with Li.sub.2CO.sub.3 so that the Li/total transition metal molar ratio was 1.03/1. No phosphate compound was added. The mixture so obtained was calcined in a box furnace under air with the following temperature program: raise 3K/min to 350° C., maintain at 350° C. for 4 hours, raise 3K/min to 675° C., maintain at 675° C. for 4 hours, raise 3 K/min to 900° C., maintain at 900° C. for 6 hours. After step (d.2), the material so obtained was cooled to room temperature under air within a period of 12 hours, deagglomerated in a mortar and sifted through a sieve with 32 μm mesh size. Comparative cathode active material C-(CAM.3) was obtained.

I.4 Comparative Experiment: Manufacture of Comparative Cathode Active Material C-(CAM.4)

[0114] A precursor was provided, Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2. In a ball mill, Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2 was mixed with Li.sub.2CO.sub.3 so that the Li/total transition metal molar ratio was 1.03/1. No phosphate compound was added. The mixture so obtained was calcined in a box furnace under oxygen atmosphere with the following temperature program: raise 3K/min to 350° C., maintain at 350° C. for 4 hours, raise 3K/min to 675° C., maintain at 675° C. for 4 hours, raise 3 K/min to 900° C., maintain at 900° C. for 6 hours. After step (d.2), the material so obtained was cooled to room temperature under the oxygen atmosphere within a period of 12 hours, deagglomerated in a mortar and sifted through a sieve with 32 μm mesh size. Comparative cathode active material C-(CAM.4) was obtained.

TABLE-US-00001 TABLE Li.sub.2CO.sub.3 content of selected cathode active materials Material CAM.1 CAM.2 C-(CAM.3) C-(CAM.4) Content of Li.sub.2CO.sub.3 0.3 ≦0.2 0.8 0.4 [% by weight]

II. Manufacture of Inventive Cathodes and Inventive Electrochemical Cells

II.1 Production of Half Cells

[0115] To produce a cathode (a.1), the following ingredients were blended with one another: 88 g of CAM.1

[0116] 6 g polyvinylidene difluoride, (c.1) (“PVdF”), commercially available as Kynar Flex® 2801 from Arkema Group,

[0117] 3 g carbon black, (b.1), BET surface area of 62 m.sup.2/g, commercially available as “Super C 65L” from Timcal,

[0118] 3 g graphite, (b.2), commercially available as KS6 from Timcal.

[0119] While stirring, a sufficient amount of N-methylpyrrolidone (NMP) was added and the mixture was stirred with an Ultraturrax until a stiff, lump-free paste had been obtained.

[0120] Cathodes were prepared as follows: On a 30 μm thick aluminum foil the paste was applied with a 120 μm doctor blade. The loaded foil was dried for 16 hours in a vacuum oven at 105° C. After cooling to room temperature in a hood, disc-shaped cathodes were punched out of the foil. The cathode discs were then weighed and introduced into an argon glove box where they are again vacuum-dried. Then, cells with the prepared discs were assembled.

[0121] Electrochemical testing was conducted in “TC1” cells. The electrolyte (c.1) used was a 1 M solution of LiPF.sub.6 in ethyl methyl carbonate/ethylene carbonate (volume ratio 1:1).

[0122] Separator (d.1): glass fiber. Anode (b.1): lithium. Potential range of the cell: 3.0 V-4.3 V.

[0123] Inventive electrochemical cell (BAT.1) was obtained.

II.2 Manufacture of Cathodes and Electrochemical Cells According to the Invention, and of Comparative Cathodes and Electrochemical Cells

[0124] The above experiment was repeated but inventive (CAM.1) was replaced by an equal amount of (CAM.2).

[0125] Inventive electrochemical cell (BAT.2) was obtained.

III. Testing of Batteries

[0126] Electrochemical cells according to the invention and comparative electrochemical cells are each subjected to the following cycling program: Potential range of the cell: 3.0 V-4.3 V, 0.1 C (first and second cycles), 2 C in the 3.sup.rd, 4.sup.th, 5.sup.th, 6.sup.th and 7.sup.th cycle, 0.1 C in the 8th cycle, following by the cycles at 0.5C, 1C, 2C, 3C and 5C. 1 C=150 mA/g. Temperature: 25° C.

[0127] Electrochemical cells according to the invention show an overall very good performance compared to comparative electrochemical cells.