ACTIVE CATHODE MATERIAL AND ITS USE IN RECHARGEABLE ELECTROCHEMICAL CELLS

Abstract

The present invention relates to an active cathode material of the general formula (I): M.sub.xNi.sub.a-yM.sup.1.sub.bM.sup.2.sub.cM.sup.3.sub.yO.sub.2, in which the variables are each defined as follows: M is an alkali metal, M.sup.1 is V, Cr, Mn, Fe, Co or a mixture thereof, M.sup.2 is Ge, Sn, Ti, Zr or a mixture thereof, M.sup.3 is Mg, Zn, Cu or a mixture thereof, x is in the range from 0.5 to 0.8, a is in the range from 0.1 to 0.4, b is in the range from 0.05 to 0.7, c is in the range from 0.02 to 0.6, y is in the range from 0.05 to 0.2 wherein a+b+c=1. The present invention further relates to an electrode material comprising said active cathode material, to electrodes produced from or using said electrode material and to a rechargeable electrochemical cell comprising at least one electrode. The present invention further relates to a process for preparing said active cathode material of the general formula (I).

Claims

1. An active cathode material of formula (I):
M.sub.xNi.sub.a-yM.sup.1.sub.bM.sup.2.sub.cM.sup.3.sub.yO.sub.2 (I) M is Na, M.sup.1 V, Cr, Mn, Fe, Co or a mixture thereof, M.sup.2 is Ge, Sn, Ti, Zr or a mixture thereof, M.sup.3 is Zn, x is in the range from 0.5 to 0.8. a is in the range from 0.25 to 0.35. b is in the range from 0.05 to 0.7, c is in the range from 0.02 to 0.6, y is in the range from 0.05 to 0.2, and wherein a+b+c=1.

2. (canceled)

3. The active cathode material according to claim 1, wherein M.sup.1 is Mn.

4. The active cathode material according to claim 1, wherein M.sup.2 is Ti.

5-7. (canceled)

8. The active cathode material according to claim 1, wherein M is Na, M.sup.1 is Mn M.sup.2 is Ti, M.sup.3 is Zn, x is in the range from 0.6 to 0.7, a is in the range from 0.33 to 0.34, b is in the range from 0.45 to 0.55, c is in the range from 0.16 to 0.17 and y is in the range from 0.075 to 0.09.

9. The active cathode material according to to claim 1, wherein the material has a P2-type layered structure identified in X-ray diffraction.

10. An electrode material, comprising: (A) an active cathode material according to claim 1; (B) carbon in a polymorph comprising at least 60% sp.sup.2-hybridized carbon atoms; and (C) optionally at least one polymer as a binder.

11. An electrode, comprising an electrode material according to claim 10.

12. A rechargeable electrochemical cell, comprising at least one electrode according to claim 11.

13. The rechargeable electrochemical cell according to claim 12, wherein the rechargeable electrochemical cell is suitable in motor vehicles, bicycles operated by electric motor, aircraft, ships or stationary energy stores.

14. A device, comprising at least one rechargeable electrochemical cell according to claim 12.

15. A process for preparing an active cathode material of the general formula (I):
M.sub.xNi.sub.a-yM.sup.1.sub.bM.sup.2.sub.cM.sup.3.sub.yO.sub.2 (I) according to claim 1, the method comprising: (a) preparing a mixture of oxides of M, Ni, M.sup.1, M.sup.2 and M.sup.3 or compounds of said metals forming oxides during calcination ierein in said mixture the metals are available in the following molar ratio: 0.5 to 0.8 molar equivalents of M, 0.05 to 0.35 molar equivalents of Ni, 0.05 to 0.7 molar equivalents of M.sup.1, 0.02 to 0.6 molar equivalents of M.sup.2, and 0.05 to 0.2. molar equivalents of M.sup.3; (b) optionally pelletizing the mixture formed in (a); and (c) calcinating the mixture formed in (a) or (b) in a temperature range of from 300 C. to 1200 C.

16. The active cathode material according to claim 1, wherein x is in the range from 0.6 to 0.7, b is in the range from 0.4 to 0.6, and c is in the range from 0.1 to 0.24.

Description

[0126] The invention is illustrated by the examples which follow but do not restrict the invention.

[0127] Figures in percent are each based on % by weight, unless explicitly stated otherwise.

[0128] Active cathode materials were characterized by X-ray diffraction and scanning electron microscopy. The structural refinement of active cathode materials was carried out using the diffraction patterns obtained by using an X-ray diffractometer (MultiFlex, Rigaku Co.) with Cu K radiation without air exposure by using a laboratory made attachment. The morphological features of samples of active cathode material were observed by using a scanning electron microscope (Carl Zeiss Inc., SUPRA40, Germany).

[0129] I. Preparation of Active Cathode Materials

[0130] I.1 Synthesis of Na.sub.2/3Ni.sub.1/4Mn.sub.1/2Ti.sub.1/6Zn.sub.1/12O.sub.2 (ACM-1)

[0131] The single phase and well crystallized P.sub.2-type Na.sub.2/3Ni.sub.1/4Mn.sub.1/2Ti.sub.1/6Zn.sub.1/12O.sub.2 was prepared by solid state reaction. Na.sub.2/3Ni.sub.1/4Mn.sub.1/2Ti.sub.1/6Zn.sub.1/12O.sub.2 samples were prepared from Na.sub.2CO.sub.3 (purity 99.0%), Mn.sub.2O.sub.3 (purity not determined), NiO (purity 99.0%), TiO.sub.2 (purity 99.0%) and zinc citrate. The precursors were mixed using a ballmill (600 rpm, 12 h). The resulting mixture was pelletized. Thus obtained pellet was then heated at 900 C. for 12 h under an air atmosphere. The used Mn.sub.2O.sub.3 was prepared by calcination of MnCO.sub.3.nH.sub.2O with a Mn-content of 43-46% by weight. Therefore the purity of the prepared Mn.sub.2O.sub.3 was not determined.

[0132] I.2 Synthesis of Na.sub.2/3Ni.sub.1/4Mn.sub.1/2Ti.sub.1/6Mg.sub.1/12O.sub.2 (ACM-2)

[0133] The single phase and well crystallized P.sub.2-type Na.sub.2/3Ni.sub.1/4Mn.sub.1/2Ti.sub.1/6Mg.sub.1/12O.sub.2 was prepared by solid state reaction. Na.sub.2/3Ni.sub.1/4Mn.sub.1/12Ti.sub.1/6Mg.sub.1/12O.sub.2 was prepared from the stoichiometric amount of Na.sub.2CO.sub.3 (purity 99.0%), Mn.sub.2O.sub.3 (purity not determined), Ni(OH).sub.2 (purity 95%), TiO.sub.2 (purity 99.0%) and MgO (purity 98.0%). The precursors were mixed using a ballmill (600 rpm, 12 h). The resulting mixture was pelletized. Thus obtained pellet was then heated at 900 C. for 12 h under an air atmosphere.

[0134] The used Mn.sub.2O.sub.3 was prepared by calcination of MnCO.sub.3.nH.sub.2O with a Mn-content of 43-46% by weight. Therefore the purity of the prepared Mn.sub.2O.sub.3 was not determined.

[0135] I.3 Synthesis of Na.sub.2/3Ni.sub.1/4Mn.sub.1/6Ti.sub.1/6Cu.sub.1/12O.sub.2 (ACM-3)

[0136] The single phase and well crystallized P2-type Na.sub.2/3Ni.sub.1/4Mn.sub.1/2Ti.sub.1/6Cu.sub.1/12O.sub.2 was prepared by solid state reaction. Na.sub.2/3Ni.sub.1/4Mn.sub.1/2Ti.sub.1/6Cu.sub.1/12 O.sub.2 was prepared from the stoichiometric amount of Na.sub.2CO.sub.3 (purity 99.0%), Mn.sub.2O.sub.3 (purity not determined), Ni(OH).sub.2 (purity 95%), TiO.sub.2 (purity 99.0%) and Cu.sub.2O (purity 90.0%). The precursors were mixed using a ballmill (600 rpm, 12 h). The resulting mixture was pelletized. Thus obtained pellet was then heated at 900 C. for 12 h under an air atmosphere.

[0137] The used Mn.sub.2O.sub.3 was prepared by calcination of MnCO.sub.3.nH2O with a Mn-content of 43-46% by weight. Therefore the purity of the prepared Mn.sub.2O.sub.3 was not determined.

[0138] C-I.4 Synthesis of Comparative Sample Na.sub.2/3Ni.sub.1/3Mn.sub.1/2Ti.sub.1/6O.sub.2 (C-ACM-4)

[0139] The single phase and well crystallized P2-type Na.sub.2/3Ni.sub.1/3Mn.sub.1/2Ti.sub.1/6O.sub.2 was prepared by solid state reaction. Na.sub.2/3Ni.sub.1/3Mn.sub.1/2Ti.sub.1/6O.sub.2 was prepared from the stoichiometric amount of Na.sub.2CO.sub.3 (purity 99.0%), Mn.sub.2O.sub.3 (purity not determined), NiO (purity 99%) and TiO.sub.2 (purity 99.0%). The precursors were mixed using a ballmill (600 rpm, 12 h). The resulting mixture was pelletized. Thus obtained pellet was then heated at 900 C. for 12 h under an air atmosphere. The used Mn.sub.2O.sub.3 was prepared by calcination of MnCO.sub.3.nH.sub.2O with a Mn-content of 43-46% by weight. Therefore the purity of the prepared Mn.sub.2O.sub.3 was not determined.

[0140] C-I.5 Synthesis of Comparative Sample Na.sub.2/3Ni.sub.1/4Mn.sub.2/3Zn.sub.1/12O.sub.2 (C-ACM-5)

[0141] The single phase and well crystallized P2-type Na.sub.2/3Ni.sub.1/4Mn.sub.2/3Zn.sub.1/12O.sub.2was prepared by solid state reaction. Na.sub.2/3Ni.sub.1/4Mn.sub.2/3Zn.sub.1/12O.sub.2 was prepared from the stoichiometric amount of Na.sub.2CO.sub.3 (purity 99.0%), Mn.sub.2O.sub.3 (purity not determined), NiO (purity 99%) and zinc citrate (purity 99%). The precursors were mixed using a ballmill (600 rpm, 12 h). The resulting mixture was pelletized. Thus obtained pellet was then heated at 900 C. for 12 h under an air atmosphere.

[0142] The used Mn.sub.2O.sub.3 was prepared by calcination of MnCO.sub.3.nH.sub.2O with a Mn-content of 43-46% by weight. Therefore the purity of the prepared Mn.sub.2O.sub.3 was not determined.

[0143] II. Characterization of Active Cathode Materials

[0144] Active cathode materials were characterized by X-ray diffraction All of Bragg diffraction lines of ACM-1, ACM-2, ACM-3, C-ACM-4, and C-ACM-S were assigned into P2 type layered structure (space group: P6.sub.3/mmc)

[0145] Note: Impurity of ZnO was observed in ACM-1, C-ACM-S.

[0146] III. Electrochemical Testing of Active Cathode Materials

[0147] Assembly and operation of an electrochemical cell comprising an electrode comprising an active cathode material ACM

[0148] Coin-type cells (2032 type) were assembled to evaluate the electrode performance of an ACM. Positive electrodes consisted of 80 wt % ACM 10 wt % acetylene black, and 10 wt % poly(vinylidene fluoride), which were mixed with NMP and pasted on Al foil, and then dried at 80 C. in vacuum. Metallic sodium was used as a negative electrode. Electrolyte solution used was 1.0 mol/I NaPF.sub.6 dissolved in propylene carbonate (Kishida Chemical Co. Ltd., Japan). A glass fiber filter (GB-100R, ADVANTEC Co. Ltd., Japan) was used as a separator. The cells were electrochemically cycled at a current density of 13 mA/g in a voltage range between 2.5 and 4.5 V at 25 C. r).

[0149] Table 1 shows the comparison of inventive and non-inventive active cathode materials

TABLE-US-00001 TABLE 1 Comparison of active cathode materials 1.sup.st discharge Energy Capacity/ Capacity density/ V.sub.ave mAh g.sup.1 retention (40.sup.th)/% Wh g.sup.1 at 1st dis./V ACM-1 113.8 99.46 410 3.60 ACM-2 121.1 91.25 437 3.61 ACM-3 122.8 95.39 446 3.63 C-ACM-4 119.6 85.07 441 3.68 C-ACM-5 111.0 97.31 397 3.58