Method for producing cathodes

Abstract

Process for producing cathodes Process for producing cathodes comprising a cathode material comprising (A) at least one lithiated transition metal mixed oxide, (B) carbon in an electrically conductive modification, (C) at least one binder,
and also (D) at least one film,
wherein (a) a mixture comprising lithiated transition metal mixed oxide (A), carbon (B) and binder (C) is applied to film (D), (b) dried, (c) compacted to such an extent that the cathode material has a density of at least 1.8 g/cm.sup.3 to obtain a compacted blank and (d) after compaction as per (c) thermally treated at a temperature in the range from 35 C. below the melting point or the softening point of binder (C) to a maximum of 5 C. below the melting point or the softening point of binder (C).

Claims

1. A process for producing a cathode comprising a cathode material comprising: (A) a lithiated transition metal mixed oxide; (B) carbon in an electrically conductive modification; (C) a binder; and (D) a film, the process comprising: (a) applying a mixture comprising a lithiated transition metal mixed oxide (A), a carbon (B) and a binder (C) to a film (D), to form a coated film; (b) drying the coated film; (c) compacting the coated film to such an extent that a resulting cathode material on the film has a density of at least 1.8 g/cm.sup.3 to obtain a compacted blank; and (d) thermally treating the compacted blank either at a temperature in the range from 35 C. below a melting point of binder (C) to a maximum of 5 C. below the melting point of binder (C) or, if the binder (C) does not have a sharp melting point, at a temperature of 35 C. below a softening point of the binder (C) to a maximum of 5 C. below the softening point of binder (C); wherein the binder (C) is a fluorinated organic (co)polymer.

2. The process according to claim 1, wherein a density of the cathode material is changed by not more than 10% during the thermally treating (d) of the compacted blank.

3. The process according to claim 1, wherein the cathode material has a density of at least 2.0 g/cm.sup.3 after the compacting (c).

4. The process according to claim 1, wherein the cathode material has a density of not more than 3.9 g/cm.sup.3 after compacting (c).

5. The process according to claim 1, wherein no pressure is applied during the thermally treating (d).

6. The process according to claim 1, wherein the mixture is applied to one or both sides of the film (D) during the applying (a).

7. The process according to claim 1, wherein the thermally treating (d) occurs at a temperature which is in a range from 25 C. below to 5 C. below the melting point or the softening point of the binder (C).

8. The process according to claim 1, wherein the lithiated transition metal mixed oxide (A) is a lithiated Mn-comprising spinel.

9. The process according to claim 1, wherein the lithiated transition metal mixed oxide (A) comprises a lithiated sheet oxide comprising manganese and at least one further transition metal selected from the group consisting of cobalt and nickel.

10. The process according to claim 1, wherein the lithiated transition metal mixed oxide (A) is a lithiated sheet oxide comprising at least 35 mol % of manganese, based on a total content of transition metals.

11. The process according to claim 1, wherein the film (D) is a polymer film and the compacted blank is relaminated after the compacting (c) and before the thermally treating (d).

12. The process according to claim 11, wherein the compacted blank is relaminated onto a metal foil.

Description

(1) The invention is illustrated by working examples.

(2) General preliminary remarks:

(3) To determine the cathode density (reported in g/cm.sup.3), round parts, referred to as rounds, having a circle diameter of 19.8 mm (3.079 cm.sup.2 cathode area) were stamped out of the cathode coated on one side and weighed.

(4) The coating was completely removed from one round by means of N-methylpyrrolidone. As reference, film (D.1) was stamped out in the form of rounds having the same diameter and weighed.

(5) The specific cathode loading is given by the average of the masses of the coated rounds corrected by the mass (average) of the rounds, normalized to an area of 1 cm.sup.2.

(6) In addition, the thickness of the coated rounds and the rounds was determined using a micrometer (geometry: flat surface against ball, radius 1.5 mm, measurement force about 0.5 N). The thickness of the cathode material is then given by the difference.

(7) The density of the cathode is then given by the specific cathode loading divided by the thickness of the cathode material.

(8) The density of the cathode can also be determined analogously on cathodes coated on both sides.

(9) I. Production of Cathodes by the Process of the Invention and of Comparative Cathodes

(10) A lithium-nickel-manganese spinel electrode produced as follows was used. The following components: (C.1) 155.4 g of a 10% strength by weight solution of copolymer of vinylidene fluoride and hexafluoropropylene in NMP, commercially available as Kynar Flex 2801 from Arkema Group, melting range: 140-145 C. 163.5 g of NMP, (B.1) 14.0% of carbon black, BET surface area of 62 m.sup.2/g, commercially available as Super P Li from Timcal, and (B.2) 7.0 g of graphite, commercially available as KS6 from Timcal, were intimately mixed with one another (IKA Turrax high-speed stirrer). A suspension was obtained. 55.1 g of the suspension were taken and (A.1) 31.9 g of Li.sub.1.167(Ni.sub.0.21Co.sub.0.12Mn.sub.0.67).sub.0.833O.sub.2 were added thereto. This gave a suspension of cathode material (Susp-K.1).
I.1 Step (a.1)

(11) (Susp-K.1) was applied by means of a doctor blade to one side of an aluminum foil (D.1) having a thickness of 30 m. Doctor blade speed: 5 mm/s, slit width of the doctor blade: 120 m. This gave a film (D.1) coated on one side.

(12) I.2 Step (b.1) or (b.2)

(13) The film (D.1) which had been coated on one side from I.1 was dried for 18 hours in a drying oven, temperature as shown in Table 1. Blanks were obtained.

(14) I.3 Step (c.1)

(15) The blanks from 1.2 were calendered by means of a calender, line pressure of the rollers: 140 N/mm, temperature of the rollers: 23 C. The density of the electrode material was 2.1 g/cm.sup.3.

(16) I.4 Step (d.1) or (C-d.2)

(17) The calendered blanks from I.3 were subjected to thermal treatment in a drying oven for 18 hours at a temperature as shown in Table 1.

(18) TABLE-US-00001 TABLE 1 Temperature conditions for selected steps (b.1) [ C.] (d.1) [ C.] (C-d.2) [ C.] Cat. 1 105 130 Cat. 2 130 130 C-Cat. 3 105 105 C-Cat. 4 130 105

(19) In no case was a density change observed during step (d.1) (measurement limit: 0.1 kg/l; density of the electrode composition was 2.1 kg/l).

(20) II. Testing of Cathodes Produced According to the Invention and of Comparative Cathodes

(21) II.1 Production of Electrochemical Cells

(22) Circular parts of the aluminum foil which had been coated in this way were stamped out (diameter 19.8 mm). The cathodes Cat.1 and Cat.2 or comparative cathodes C-Cat.3 and C-Cat.4 which could be obtained in this way were used to produce electrochemical cells EC.1 and EC.2 produced according to the invention or comparative cells C-EC.3 and C-EC.4.

(23) As electrolyte, use was made of a 1 mol/l solution of LiPF.sub.6 in ethylene carbonate/dimethyl carbonate (1:1 by mass). The anode comprised a lithium foil which was separated from the cathode by a separator made of fiberglass paper.

(24) A set-up as shown in FIG. 1 was used as test cell. In assembling the cell, this was put together from the bottom upward as per the schematic FIG. 1. In FIG. 1, the anode side is at the top and the cathode side is at the bottom.

(25) The reference symbols in FIG. 1 have the following meanings: 1, 1 Punch 2, 2 Nut 3, 3 Sealing ringin each case double; the second, somewhat smaller sealing ring is in each case not shown here 4 Spiral spring 5 Power outlet lead made of steel 6 Housing

(26) The cathode (Cat.1) was applied to the punch of the cathode side 1. A separator made of fiberglass, thickness of the separator: 0.5 mm, was subsequently placed on the cathode (Cat.1). The electrolyte was dribbled onto the separator. The anode was placed on the impregnated separators. A small stainless plate which was placed directly on the anode was used as power outlet lead 5. The seals 3 and 3 were subsequently added and the constituents of the test cell were screwed together. Electrical contact was ensured by means of the steel spring configured as spiral spring 4 and by the pressure generated by screwing on the anode punch 1.

(27) II.2 Test Results

(28) The test cell was cycled according to the following program: 1.sup.st cycle: charging with 0.0667 C to 4.7 V, discharging of 0.0667 C to 2.0 V 2.sup.nd cycle: charging with 0.1 C to 4.6 V, discharging of 0.1 C to 2.0 V 3.sup.rd cycle: charging with 0.1 C to 4.6 V, discharging of 0.1 C to 2.0 V 4.sup.th cycle: charging with 0.333 C to 4.6 V, discharging of 0.333 C to 2.0 V 5.sup.th cycle: charging with 0.333 C to 4.6 V, discharging of 0.333 C to 2.0 V 6.sup.th cycle: charging with 0.333 C to 4.6 V, discharging of 0.333 C to 2.0 V 7.sup.th cycle: charging with 0.8 C to 4.6 V, discharging of 0.8 C to 2.0 V 8.sup.th cycle: charging with 0.8 C to 4.6 V, discharging of 0.8 C to 2.0 V 9.sup.th cycle: charging with 0.8 C to 4.6 V, discharging of 0.8 C to 2.0 V 10.sup.th cycle: charging with 0.8 C to 4.6 V, discharging of 1 C to 2.0 V 11.sup.th cycle: charging with 0.8 C to 4.6 V, discharging of 1 C to 2.0 V 12.sup.th cycle: charging with 0.8 C to 4.6 V, discharging of 1 C to 2.0 V

(29) Each charging step was followed by a constant voltage step at the switch-off voltage (4.7 V for cycle 1, then 4.6 V). Duration: 30 min.

(30) The results of the capacity determinations in the 1.sup.st cycle, the 3.sup.rd cycle, the 6.sup.th cycle, the 9.sup.th cycle and the 12.sup.th cycle are shown in Table 2.

(31) TABLE-US-00002 TABLE 2 Capacity measurements on cathodes according to the invention and comparative cathodes Cycle 1 Cycle 3 Cycle 6 Cycle 9 Cycle 12 Cat. 1 310.5 279.6 265.8 249.7 242.4 Cat. 2 306.1 277.3 264.1 247.9 240.5 C-Cat. 3 299.1 271.5 254.1 230.4 220.9 C-Cat. 4 296.5 270.0 254.0 233.3 225.1

(32) All capacities in A.Math.h/kg.