CATHODE ACTIVE MATERIAL, METHOD FOR ITS MANUFACTURE, AND USE

Abstract

Process for making a composite oxide according to the formula x.Math.Li.sub.2Ni.sub.1-y1-y2Mn.sub.y1M.sup.1.sub.y2O.sub.3.Math.(1x).Math.LiNi.sub.1-zM.sup.2.sub.zO.sub.2 wherein x is in the range of from 0.01 to 0.5, z is in the range of from zero to 0.5, M.sup.1 is selected from Ti, Zr, Sn, Ge, Ta, Nb, Sb, W, and Mo, and combinations of at least two of the foregoing, M.sup.2 is at least one of Co, Al, Mg, Fe, or Mn, or a combination of at least two of the foregoing,

0.1y10.75, zeroy20.05,

said process comprising the following steps: (a) providing a particulate hydroxide, oxide or oxyhydroxide of TM where TM has the general formula x.Math.Ni.sub.1-y1-y2Mn.sub.y1M.sup.1.sub.y.Math.(1x)Ni.sub.1-zM.sup.2.sub.z, or the respective species without M.sup.1 and/or M.sup.2, (b) adding a source of lithium, (c) treating the mixture obtained from step (b) thermally under an atmosphere comprising oxygen in two steps: (c) heating the mixture obtained from step (b) to 680 to 800 C. in an atmosphere containing in the range of from 10 to 100 vol-% oxygen, and, (e) heating the intermediate from step (c) to 450 to 580 C. in an atmosphere containing at least 90 vol-% oxygen.

Claims

1.-14. (canceled)

15. Process for making a cobalt-free composite oxide according to the formula x.Math.Li.sub.2Ni.sub.1-yMn.sub.yO.sub.3.Math.(1x).Math.LiNiO.sub.2 wherein x is in the range of from 0.1 to 0.5, 0.1y0.75, said process comprising the following steps: (a) providing a particulate hydroxide, oxide or oxyhydroxide of TM where TM has the general formula x.Math.Ni.sub.1-yMn.sub.y.Math.(1x)Ni, (b) adding a source of lithium and, optionally, at least one oxide, hydroxide, or oxyhydroxide of Mn, in a molar ratio of Li:(Ni+Mn) of from 0.9:1 to 1.1:1, (c) heating the mixture obtained from step (b) to 680 to 800 C. in an atmosphere containing oxygen, (d) adding source of lithium, and (e) heating the mixture obtained from step (d) to 450 to 580 C. in an atmosphere containing at least 90 vol % oxygen.

16. Process according to claim 15 wherein 0.15y0.6.

17. Process according to claim 15 wherein steps (c) (and (e) are performed under a forced flow of gas.

18. Process according to claim 15 wherein the source of lithium is selected from lithium hydroxide, lithium carbonate, lithium nitrate, and lithium oxide.

19. Process according to claim 15 wherein x is in the range of from 0.1 to 0.3.

20. Process according to claim 15 wherein said process comprises an additional step (f) subsequent to step (e), and wherein said step (f) is selected from coating steps and wet treatment steps.

21. Particulate cobalt-free composite oxide of the composition x.Math.Li.sub.2Ni.sub.1-yMn.sub.yO3.Math.(1x).Math.LiNiO.sub.2 wherein x is in the range of from 0.01 to 0.5, 0.1y0.75.

22. Particulate composite oxide according to claim 21 wherein 0.15y0.6.

23. Particulate composite oxide according to claim 21 wherein x is in the range of from 0.1 to 0.3.

24. Particulate composite oxide according to claim 21 wherein cations in both the Li.sub.2Ni.sub.1-yMn.sub.yO.sub.3 and the LiNiO.sub.2 domains exhibit a substantially layered ordering, where the Li.sub.2Ni.sub.1-yMn.sub.yO.sub.3 domains display alternating Li and Li.sub.1/3[Ni.sub.1-yMn.sub.y] cation layers, and the LiNiO.sub.2 domains display alternating Ni and Li cation layers, and wherein Li.sub.1/3[Ni.sub.1-yMn.sub.y] cation layers in the Li.sub.2Ni.sub.1-yMn.sub.yO.sub.3 domains exhibit substantially a honeycomb-type cation ordering wherein the Li cations have no other Li cations as their nearest cation neighbors within the same cation layer.

25. Cathode comprising (A) at least one particulate composite oxide according to claim 21, (B) carbon in electrically conductive form, (C) at least one binder.

26. Electrochemical cell comprising a cathode according to claim 25.

Description

EXAMPLE 1: MANUFACTURE OF INVENTIVE CAM.1

[0137] Example 1 describes the synthesis of Li-excess x.Math.Li.sub.2Ni.sub.1-y1-y2Mn.sub.y1M.sup.1.sub.y2O.sub.3.Math.(1x).Math.LiNi.sub.1-zM.sup.2.sub.zO.sub.2 where x=0.22, y1=0.45, and y2=z=0 (equivalently, 0.22.Math.Li.sub.2Ni.sub.0.55Mn.sub.0.45O.sub.3.Math.0.78.Math.LiNiO.sub.2, Li.sub.1.1[Ni.sub.0.9Mn.sub.0.1].sub.0.9O.sub.2, or Li.sub.1.1Ni.sub.0.81Mn.sub.0.09O.sub.2, hereafter CAM.1)

[0138] Step (a.1): A spherical Ni.sub.0.9Mn.sub.0.1(OH).sub.2 precursor was obtained by combining aqueous nickel and manganese sulfate solution (1.65 mol/kg solution) with an aqueous 25 wt. % NaOH solution and using ammonia as complexation agent. The pH value was set at 12.6. The freshly precipitated Ni(OH).sub.2 was washed with water, sieved and dried at 120 C. for 12 hours. P-CAM.1 was obtained. Average particle diameter (D50): 10 m.

[0139] Step (b.1) An amount of 5.0 g P-CAM.1 and 2.383 g LiOH.Math.H.sub.2O (molar ratio of transition metals to lithium 1:1) were mixed and milled without solvent for 1 hour at 300 rpm in a planetary ball mill. A mixture was obtained.

[0140] Step (c.1): The mixture from step (b.1) was heated to 200 C. for 2 hours in a 100% oxygen atmosphere with a temperature ramp rate of 3 C./min in a tube furnace and then cooled to ambient temperature. After re-grounding the mixture was calcined at 700 C. for 24 hours in a 100% O.sub.2 atmosphere and then allowed to cool to room temperature naturally.

[0141] Step (d.1): The material produced in step (c.1) was mixed with Li.sub.2O.sub.2 by mixing with mortar and pestle, 0.25 g of the intermediate from step (c.1) and 0.0145 g Li.sub.2O.sub.2.

[0142] Step (e.1) The resultant mixture was then heated to 550 C. for 20 hours in a 100% O.sub.2 atmosphere with a temperature ramp rate of 3 C./min in a tube furnace, followed by natural cooling to room temperature. CAM.1 was obtained.

COMPARATIVE EXAMPLE 2: MANUFACTURE OF C-CAM.2

[0143] The same procedure as in Example 1 was conducted with the exception that steps (d.1) and (e.1) were omitted, to produce a stoichiometric layered material with Li.sub.1.0Ni.sub.0.9Mn.sub.0.1O.sub.2 composition, C-CAM.2.

EXAMPLE 3: MANUFACTURE OF INVENTIVE CATHODE ACTIVE MATERIAL CAM.3

[0144] Step (b.3) An amount of 3.0 g P-CAM.1 and 1.752 g LiOH.Math.H.sub.2O (molar ratio of transition metals to lithium 1:1) were mixed and milled without solvent for 5 minutes at 8,000 rpm using tube milling. A mixture was obtained.

[0145] Step (c.3): The mixture from step (b.3) was heated to 500 C. for 10 hours in a 100% oxygen atmosphere with a temperature ramp rate of 3 C./min in a tube furnace, and then to 750 C. for 15 hours in a 100% O.sub.2 atmosphere and then allowed to cool to room temperature naturally.

[0146] Step (d.3): The material produced in step (c.3) was mixed with LiOH.Math.H.sub.2O by mixing with mortar and pestle, 0.5 g of the intermediate from step (c.3) and 0.0239 g LiOH.Math.H.sub.2O. The overall molar ratio of Li to transition metal was 1.1:0.9.

[0147] Step (e.3) The resultant mixture was then heated to 570 C. for 15 hours in a 100% O.sub.2 atmosphere with a temperature ramp rate of 3 C./min in a tube furnace, followed by natural cooling to room temperature. CAM.3 was obtained.

Evaluation of the Cathode Active Materials:

[0148] Cathode Active Material Characteristics: XRD patterns of CAM.1 and C-CAM.2 were recorded with Mo K radiation between 5 and 45. [0149] Battery Characteristics: Electrochemical performances were evaluated with CR2032 coin cells between 2.5-4.8 V and 2.5-4.3 V. The cathodes were prepared by mixing 80 wt. % active materials with 10 wt. % carbon black and 10 wt. % PVDF binder, casting the mixture into thin sheets of about 150 m thick on Al foil using a doctor blade. The coin cells were assembled with the thus fabricated cathodes, lithium foil anode, 1 M LiPF.sub.6 in ethylene carbonate/diethyl carbonate (EC/DEC) electrolyte, and Celgard polypropylene separator.

BRIEF EXPLANATION OF THE DRAWINGS

[0150] FIG. 1A is a plot of the XRD patterns of CAM.1 and of C-CAM.2.

[0151] FIG. 1B is an enhanced view of the plot of the XRD patterns of CAM.1 and of C-CAM.2. Both CAM.1 and C-CAM.2 have the typical O3 layered structure (space group: R-3m with Bragg peaks). In FIG. 1B, CAM.1 has superstructure reflections observed around 2=1 0-15 corresponding to the ordering of the transition metal ions and Li ions in the transition metal layer of the layered lattice. The excess Li does not significantly change the main reflections except for the superstructure reflections, indicating that CAM.1 maintains the 03 layered structure with excess Li in transition metal layer in bulk structure. The superstructure reflections indicate the honeycomb ordering of the Li with respect to the Ni/Mn in the Li.sub.2Ni.sub.0.55Mn.sub.0.45O.sub.3 domains.

[0152] FIGS. 2(A)-2(D) are a series of plots showing the first charge-discharge voltage curves and dQ/dV curves at first cycle of the C-CAM.2 (FIGS. 2A and 2B, respectively) and the first charge-discharge voltage curves and dQ/dV curves at first cycle of the CAM.1 (FIGS. 2C and 2D, respectively) at a 10 mA/g rate in the 4.3-2.5V voltage window. In this voltage window sample C-CAM.2 shows a reversible capacity of 215 mAh/g at first cycle, while CAM.1 shows a smaller reversible capacity of 185 mAh/g in the first cycle. sample-CAM.2 exhibits a strong plateau around 4.2V in the charge profile, which has been mainly attributed to H2-H3 phase transition. The H2-H3 phase transition around 4.2V is accompanied by a strong discontinuous shrinkage of the c lattice parameter with volume change, eventually leading to fatigue and mechanical degradation. Compared to sample CAM.2, CAM.1 exhibits a weak plateau this 4.2V plateau.

[0153] FIGS. 3A to 3D are a series of plots showing the first charge-discharge voltage curves and dQ/dV curves of the C-CAM.2 (FIGS. 3A and 3B, respectively) and the first charge-discharge voltage curves and dQ/dV curves of the CAM.1 (FIGS. 3C and 3D, respectively) at 10 mA/g rate in 4.8-2.5V voltage window. sample-CAM.2 shows a reversible capacity of 250 mAh/g in the first cycle, which is similar to the theoretical capacity (275 mAh/g) from Ni redox. Also the voltage profile of C-CAM.2 is almost similar with the voltage profile in 4.3-2.5V without any additional plateau. CAM.1, however, exhibits a plateau around 4.5V in the first charge profile, which has been mainly attributed to a combination of reversible oxygen oxidation and irreversible loss of oxygen from the layered lattice, both of which are enabled byand indicative ofthe presence of the Li.sub.2Ni.sub.0.55Mn.sub.0.45O.sub.3 domains. It also seen FIG. 3C that the Li-excess sample shows higher reversible capacity 230 mAh/g at first cycle than the theoretical capacity from Ni redox reaction (200 mAh/g), which can be attributed to the reversible oxygen redox reaction. Without wishing to be bound by any theory, the difference between the charge and discharge capacity can be attributed to irreversible oxidation reactions, likely involving oxygen gas release from the material. CAM.1 can thus be cycled in a lower voltage window, achieving lower capacity but no oxygen gas release, or to higher voltage (>4.3 V) achieving higher capacity but potentially suffering from oxygen gas release. In both cases, the H2-H3 phase transition and interlayer contraction are mitigated.

[0154] FIGS. 4A and 4B are plots showing the cycling performance (in voltage versus capacity) of CAM.1 and C-CAM.2 between 4.8-2.5V at 10 mA/g for 20 cycles, respectively. C-CAM.2 (FIG. 4B) shows a capacity retention of 88.1% in 20 cycles. In contrast, CAM.1 (FIG. 4A) exhibits the improved capacity retention (93.5%) in the first 20 cycles. Without wishing to be bound by any theory, the better cyclability of CAM.1 can be due to the suppression of the H2-H3 phase transition.