METHOD FOR PREPARING A POSITIVE ELECTRODE MATERIAL FOR RECHARGEABLE LITHIUM ION BATTERIES

Abstract

This invention relates to a process for manufacturing lithium nickel cobalt oxide-based cathode compounds for lithium ion secondary batteries. As part of this process, nickel, cobalt, and optionally manganese-bearing precursor compounds are lithiated and sintered at a high temperature. When cooled down, a high cooling rate will benefit the throughput of the process and the economics. It has however been found that the cooling rate should not exceed 10° C./min in what has been determined to be a critical temperature domain, ranging from 700° C. to 550° C.

Claims

1-15. (canceled)

16. A process for preparing a positive electrode material for lithium-ion batteries comprising the steps of: subjecting a mixed metal compound pM comprising nickel and at least one metal selected from cobalt, manganese and aluminium to a heat treatment at a temperature Ts of at least 650° C., thereby obtaining a heat-treated mixed metal compound M; in a first cooling stage, cooling said heat-treated mixed metal compound M to an intermediate temperature T.sub.1 being the lower of 700° C. and the sintering temperature T.sub.s; in a second cooling stage, cooling said heat-treated mixed metal compound M from said intermediate temperature T.sub.1 to 550° C. at a mean cooling rate of more than 2° C./min and of less than 10° C./min; and in a final cooling stage, cooling said heat-treated mixed metal compound M to ambient temperature, thereby obtaining a positive electrode material for lithium-ion batteries.

17. The process according to claim 16, whereby said mixed metal compound pM is sintered by heating to a sintering temperature Ts between 750° C. and 1050° C.

18. The process according to claim 16, wherein the second cooling stage is performed at a cooling rate of less than 10° C./min as measured during any 1-minute interval.

19. The process according to claim 16, wherein the second cooling stage is performed at an instantaneous cooling rate of less than 10° C./min.

20. The process according to claim 16, whereby said heat treatment further comprises a third cooling stage, whereby said heat-treated mixed metal compound M is cooled from a temperature between 550° C. and 400° C. to a temperature between 250° C. and 100° C. at a mean cooling rate of at least 5° C./min.

21. The process according to claim 20, whereby said heat-treated mixed metal compound M is cooled in said third cooling stage at a mean cooling rate of at least 10° C./min.

22. The process according to claim 16, whereby in said second cooling stage, said heat-treated mixed metal compound M is cooled from said intermediate temperature T.sub.1 to 550° C. at a mean cooling rate of 2.5° C./min or more.

23. The process according to claim 16, whereby said mixed metal compound M is a lithiated precursor having a general formula of Li.sub.1+aM′.sub.1−aO.sub.2, wherein −0.03≤a≤0.10, and M′=Ni.sub.xM″.sub.yCo.sub.zE.sub.d, wherein 0.30=x≤0.92, 0.00≤y≤0.40, 0.05≤z≤0.40, and 0≤d≤0.05, with M″ being either one or both of Mn or Al, and with E being a dopant different from M″, comprising the steps of: sintering the precursor by heating it above a sintering temperature of at least 650° C.; during a first cooling stage, cooling the sintered precursor to an intermediate temperature being the lower of 700° C. and the sintering temperature; during a second cooling stage, cooling the sintered precursor from the intermediate temperature to 550° C. at a mean cooling rate of more than 2° C./min and of less than 10° C./min; during a third cooling stage, cooling the precursor from 550° C. to 200° C. at a mean cooling rate of more than 10° C./min; and, during a fourth cooling stage, cooling the precursor from 200° C. to ambient temperature.

24. The process according to claim 23, wherein the second cooling stage is performed at a cooling rate of less than 10° C./min as measured during any 1-minute interval.

25. The process according to claim 23, wherein the second cooling stage is performed at an instantaneous cooling rate of less than 10° C./min.

26. The process according to claim 23, wherein the first cooling stage is performed at a mean cooling rate of more than 10° C./min.

27. The process according to claim 23, whereby 0.60≤x≤0.95.

28. The process according to claim 16, whereby the cooling rate at any time during said second cooling stage is ±10% of said mean cooling rate during said second cooling stage.

29. A secondary lithium-ion battery comprising a positive electrode active material obtained by a process according to claim 16.

Description

EXAMPLES

[0086] The invention is further exemplified in the examples provided hereunder.

[0087] Example EX1-01

[0088] The positive electrode material, EX1-01, is prepared by a double firing method as described in WO 18/158078 A, Manufacturing Example 3. The process comprises the following steps:

[0089] 1) Preparation of metal bearing precursor: a metal bearing precursor (named MBP) having a general formula of Ni.sub.0.60Mn.sub.0.20Co.sub.0.20O.sub.0.17(OH).sub.1.83 is prepared by a co-precipitation process in a large scale continuous stirred tank reactor (CSTR) with mixed nickel-manganese-cobalt sulfates, sodium hydroxide, and ammonia.

[0090] 2) First blending: to obtain a lithium deficient sintered precursor, Li.sub.2CO.sub.3 and the MBP are homogenously blended with a Li/M′ molar ratio of 0.85, wherein M′ is Ni, Mn, and Co.

[0091] 3) First sintering: the mixture from the 1.sup.st blending step is sintered in a furnace at 800° C. for 2 hours of residence time.

[0092] 4) Second blending: the lithium deficient sintered precursor from the first sintering is blended with LiOH.Math.H.sub.2O in order to correct the Li stoichiometry in the intermediate product to the final target composition of Li.sub.1.017(Ni.sub.0.60Mn.sub.0.20Co.sub.0.20).sub.0.983O.sub.2.

[0093] 5) Second sintering: the mixture from the second blending step is sintered at 855° C. for 10 hours under dry air atmosphere in a furnace. The mean heating rate from 25° C. to 855° C. is 2.5° C./min.

[0094] 6) Cooling: the sintered compound is naturally cooled down to 200° C. with a mean cooling rate of 2.5° C./min.

[0095] 7) Post treatment: after the cooling step, the cooled sintered compound is crushed, classified, and sieved so as to obtain a non-agglomerated NMC powder.

[0096] Example EX1-02

[0097] The positive electrode material, EX1-02, is prepared by a double firing method as described in WO 18/158078 A, Manufacturing Example 3. The process comprises the following steps:

[0098] 1) First blending: to obtain a lithium deficient sintered precursor, Li.sub.2CO.sub.3 and the MBP are homogenously blended with a Li/M′ molar ratio of 0.725, wherein M′ is Ni, Mn, and Co.

[0099] 2) First sintering: the mixture from the first blending step is sintered in a furnace at 700° C. for 2 hours of residence time.

[0100] 3) Second blending: the lithium deficient sintered precursor from first sintering is blended with LiOH.Math.H.sub.2O in order to correct the Li stoichiometry in the intermediate product to the final target composition of Li.sub.1.017(Ni.sub.0.60Mn.sub.0.20Co.sub.0.20)0.983O.sub.2.

[0101] 4) Second sintering: the mixture from the second blending step in an alumina crucible is sintered at 910° C. for 1 hours under dry air atmosphere in a chamber furnace. The mean heating rate from 25° C. to 910° C. is 2.5° C./min.

[0102] 5) Cooling: the sintered compound is cooled down fast from 910° C. to 700° C. by a transportation of the alumina crucible into a second chamber furnace where the temperature is 700° C. The compound is then naturally cooled down from 700° C. to 550° C. in the second chamber furnace with a mean cooling rate of 4.4° C./min. When the temperature of the second chamber furnace reaches 550° C., the compound in the alumina crucible is poured on a copper metal block and it is pressed against another copper metal block as a quenching step. The mean cooling rate from 550° C. to room temperature is around 70° C./min.

[0103] 6) Post treatment: the cooled sintered compound is crushed, classified, and sieved, so as to obtain a non-agglomerated NMC powder.

Example 2 and Comparative Example 2

[0104] The positive electrode materials having a formula of Li.sub.1.005(Ni.sub.0.60Mn.sub.0.20Co.sub.0.20).sub.0.995O.sub.2, EX2-01, EX2-02, CEX2-01, CEX2-02 and CEX2-03 are prepared by a single firing method. The process comprises the following steps:

[0105] 1) Blending: Li.sub.2CO3 and the MBP are homogenously blended with a Li/M′ molar ratio of 1.01, wherein M′ is Ni, Mn, and Co.

[0106] 2) Sintering: the mixture from the blending step in an alumina crucible is sintered at 860° C. for 10 hours under dry air atmosphere in a furnace. The mean heating rate from 25° C. to 860° C. is 2.5° C./min.

[0107] 3) Cooling: The sintered agglomerated compound is naturally cooled down from 860° C. to a temperature X.sub.c according to Table 2. The mean cooling rate from 860° C. to X.sub.c is 4.4° C./min. When the temperature reaches X.sub.c, the compound in the alumina crucible is poured on a copper metal block and it is pressed against another copper metal block as a quenching step.

[0108] 4) Post treatment: the cooled sintered compound is crushed, classified, and sieved, so as to obtain a non-agglomerated NMC powder.

TABLE-US-00001 TABLE 1 Cooling condition and assessment of samples in Example 1-01 and Example 1-02. Cooling conditions XRD CR2 CR3 Total Crystallite Ni on Coin cell Sample ° C./ ° C./ cooling size Li DQ1 ID min min min nm % mAh/g EX1-01 2.5 2.5 262 48 2.7 176.0 EX1-02 4.4 70 44 46 3.2 176.4

[0109] Table 1 shows the cooling conditions and assessment of the samples prepared according to Example 1-01 and Example 1-02. CR2 is the mean cooling rate from 700° C. to 550° C., and CR3 is the mean cooling rate from 550° C. to 200° C. Due to relatively faster CR2 and very fast CR3 of the process for EX1-02, the total cooling time is significantly reduced. In spite of relatively high Ni on Li of EX1-02, the discharge capacity of EX1-02 is comparable to EX1-01. Therefore, it is proven that the cooling time can be reduced without scarifying the electrochemical performance.

TABLE-US-00002 TABLE 2 Cooling condition and assessment of samples in Comparative Example 2 and Example 2. Cooling conditions XRD Total Crys- Ni Coin CR2 CR3 cool- tallite on cell Sample X.sub.C C./ ° C./ ing size Li DQ1 ID ° C. °min min min nm % mAh/g CEX2-01 850 130 130 16 44 3.6 170.9 CEX2-02 750 110 110 39 45 3.7 172.3 CEX2-03 650 12 90 62 44 3.7 175.2 EX2-01 550 4.4 70 85 44 2.9 177.8 EX2-02 100 4.4 1.7 285 44 2.6 177.6

[0110] Table 2 show the cooling conditions and assessment of the samples prepared according to Comparative Example 2 and Example 2. CR2 is the mean cooling rate from 700° C. to 550° C., and CR3 is the mean cooling rate from 550° C. to 200° C.

[0111] According to Example EX-01 and EX2-02 good products are obtained. However, the total cooling times amount to respectively 262 and 285 minutes, which is less preferred. This is due to the too low cooling rates applied.

[0112] CEX2-01 and CEX2-02, and CEX2-03 are cooled too rapidly in the critical region between 700 and 550° C., and consequently deliver poor products. More particularly, CEX2-01 and CEX2-02 are cooled from respectively 850° C. and 750° C. to 200° C. at a rate of respectively 130 and 110° C./min; and CEX2-03 is cooled from 650° C. to 200° C. at a rate of 90° C./min.

[0113] Examples EX1-02 and EX2-01 are also according to the invention. More particularly, EX1-02 is cooled rapidly from 900° C., i.e. the sintering temperature, to 700° C., and then at a suitable rate of 4.4° C./min in the critical region between 700 and 550° C.; and EX2-01 is cooled from 860° C., i.e. the sintering temperature, to 550° C., at a rate of 4.4° C./min, thus also ensuring a suitable rate in the critical region between 700 and 550° C.