Transition metal composite hydroxide and lithium composite metal oxide

Abstract

Provided are a transition metal mixed hydroxide comprising an alkali metal other than Li, SO.sub.4 and a transition metal element, wherein the molar ratio of the molar content of the alkali metal to the molar content of the SO.sub.4 is not less than 0.05 and less than 2, and a lithium mixed metal oxide obtained by calcining a mixture of the transition metal mixed hydroxide and a lithium compound by maintaining the mixture at a temperature of 650 to 1000 C.

Claims

1. A method for producing a lithium mixed metal oxide, the method comprising the following steps (1)-(3): (1) a step of bringing an aqueous solution containing a transition metal element and SO.sub.4 into contact with an alkali comprising an alkali metal other than Li to obtain a coprecipitate slurry, (2) a step of obtaining a transition metal mixed hydroxide containing the alkali metal other than Li, SO.sub.4 and the transition metal element from the coprecipitate slurry, and (3) a step of calcining a mixture of the transition metal mixed hydroxide and a lithium compound by maintaining the mixture at a temperature of 650 to 1000 C. to obtain the lithium mixed metal oxide, wherein within the transition metal mixed hydroxide the molar ratio of the molar content of the alkali metal other than Li to the molar content of the SO.sub.4 is not less than 1 and is less than 2 and the molar ratio of the molar content of the alkali metal other than Li to the molar content of the transition metal mixed hydroxide is 0.00001 to 0.003.

2. The method according to claim 1, wherein the transition metal elements composing the transition metal mixed hydroxide are Ni, Mn and Fe.

3. The method according to claim 2, wherein the aqueous solution is an aqueous solution obtained by dissolving a sulfate of Ni, sulfate of Mn and a sulfate of Fe in water.

4. The method according to claim 3, wherein the sulfate of Fe is a sulfate of divalent Fe.

5. The method according to claim 3, wherein the molar ratio of Ni, Mn and Fe is 1xy:x:y (wherein, x is not less than 0.3 and not more than 0.7, y is more than 0 and less than 0.2).

6. The method according to claim 2, wherein the molar ratio of Ni, Mn and Fe is 1xy:x:y (wherein, x is not less than 0.3 and not more than 0.7, y is more than 0 and less than 0.2).

7. The method according to claim 1, wherein the aqueous solution is an aqueous solution obtained by dissolving a sulfate of Ni, sulfate of Mn and a sulfate of Fe in water.

8. The method according to claim 7, wherein the sulfate of Fe is a sulfate of divalent Fe.

9. The method according to claim 8, wherein the molar ratio of Ni, Mn and Fe is 1xy:x:y (wherein, x is not less than 0.3 and not more than 0.7, y is more than 0 and less than 0.2).

10. The method according to claim 7, wherein the molar ratio of Ni, Mn and Fe is 1xy:x:y (wherein, x is not less than 0.3 and not more than 0.7, y is more than 0 and less than 0.2).

11. The method according to claim 1, wherein the molar ratio of the molar content of the alkali metal other than Li to the molar content of the transition metal mixed hydroxide is 0.00001 to 0.002.

12. The method according to claim 1, wherein the molar ratio of the molar content of the alkali metal other than Li to the molar content of the transition metal mixed hydroxide is 0.00001 to 0.001.

Description

EXAMPLES

(1) The present invention is described in more detail below by examples. Evaluations of a lithium mixed metal oxide (positive electrode active material) and a charging/discharging test were carried out as follows.

(2) (1) Preparation of Positive Electrode

(3) A material prepared by mixing acetylene black and graphite in a weight ratio of 9:1 was used as a conductive material. PVdF was used as a binder, and a solution of PVdF in NMP was used as a binder solution. The PVdF was produced by KUREHA Corporation and the NMP was produced by Tokyo Chemical Industry Co., Ltd. A positive electrode active material and the conductive material were mixed and a binder was added thereto and kneaded therewith so as to provide a composition of positive electrode active material:conductive material:binder=86:10:4 (weight ratio), so that a positive electrode mixture paste was obtained. The paste was applied to a 40 m thick Al foil, which was a current collector, and then vacuum dried at 150 C. for 8 hours, so that a positive electrode was obtained.

(4) (2) Preparation of Nonaqueous Electrolyte Secondary Battery (Coin Cell)

(5) A laminated film (thickness: 16 m) produced by laminating a heat resistant porous layer onto a polyethylene porous film described later was used as a separator. A mixed solvent of EC:DMC:EMC=30:35:35 (volume ratio) was used as a solvent for an electrolytic solution. LiPF.sub.6 was used as an electrolyte. An electrolytic solution was prepared by dissolving the electrolyte in the mixed solvent in a concentration of 1 mole/liter. Metal lithium was used as a negative electrode. The positive electrode was placed on the lower lid of a coin cell (manufactured by Hohsen Corporation) with its aluminum foil surface facing down, and the separator was placed thereon, and then the electrolytic solution (300 l) was poured thereto. Next, the negative electrode was put on the upper side of the separator, and the upper lid of the coin cell was placed thereon with a gasket interpolated therebetween, and the lid was caulked using a caulking machine, so that a nonaqueous electrolyte secondary battery (coin-shaped battery R2032) was manufactured. The assembly of the battery was carried out in a glove box filled with an argon atmosphere.

(6) (3) Charging/Discharging Test

(7) By using the above-mentioned coin-shaped battery, a discharging rate test was carried out under the conditions provided below. A 0.2C discharge capacity and a 5C discharge capacity in the discharging rate test were determined, respectively, as follows.

(8) <Discharging Rate Test>

(9) Test temperature: 25 C.

(10) Charging maximum voltage: 4.3 V

(11) Charging time: 8 hours

(12) Charging current: 0.2 mA/cm.sup.2

(13) The discharging minimum voltage was kept constant at 2.5 V during discharge, and discharge was performed while a discharging current was varied as follows. The higher the discharge capacity in 5C (higher current rate), the higher the power is meant to be.

(14) Discharging of first cycle (0.2C): discharging current 0.2 mA/cm.sup.2

(15) Discharging of second cycle (5C): discharging current 5 mA/cm.sup.2

(16) (4) Evaluation of Transition Metal Mixed Hydroxide Composition Analysis of Transition Metal Mixed Hydroxide

(17) For an aqueous solution prepared by dissolving a powder of a transition metal mixed hydroxide in hydrochloric acid, composition analysis was carried out by using inductively coupled plasma spectroscopy (SPS3000 manufactured by SII).

Example 1

(18) 1. Production of Transition Metal Mixed Hydroxide and Lithium Mixed Metal Oxide

(19) In a polypropylene beaker, 30.32 g of potassium hydroxide was added to 200 ml of distilled water and dissolved by stirring. The potassium hydroxide was dissolved completely, so that an aqueous potassium hydroxide solution (aqueous alkali solution) was prepared. In a glass beaker, 18.53 g of nickel (II) sulfate hexahydrate, 12.17 g of manganese (II) sulfate monohydrate, and 2.85 g of iron (II) sulfate heptahydrate (the molar ratio of Ni:Mn:Fe was 0.47:0.48:0.05) were added to 200 ml of distilled water and dissolved by stirring, so that a nickel-manganese-iron mixed aqueous solution was obtained. While the aqueous potassium hydroxide solution was stirred, the nickel-manganese-iron mixed aqueous solution was dropped thereto, so that a coprecipitate as a transition metal mixed hydroxide was generated and a coprecipitate slurry was obtained. The pH at the end of the reaction was 13.

(20) Subsequently, the coprecipitate slurry was filtered, washed using 500 ml of distilled water, and then dried at 100 C., so that a coprecipitate P.sub.1 as a transition metal mixed hydroxide was obtained. The coprecipitate P.sub.1 (4.0 g) and 2.14 g of lithium carbonate as a lithium compound were dry mixed using an agate mortar to obtain a mixture. Subsequently, the mixture was put into a calcination container made of alumina, kept at 850 C. for 6 hours in the atmosphere using an electric furnace to calcine the mixture, and cooled to room temperature, so that a calcined product was obtained. The resultant was pulverized, washed with distilled water by decantation, filtered, and then dried at 300 C. for 6 hours, so that a powder A.sub.1 as a lithium mixed metal oxide was obtained.

(21) The composition analysis of the coprecipitate P.sub.1 found the molar ratio of Li:Ni:Mn to be 0.47:0.48:0.05. The molar ratio of the molar content of K to the molar content of the transition metal mixed hydroxide was 0.000242. The molar ratio of the molar content of SO.sub.4 to the molar content of the transition metal mixed hydroxide was 0.000189, and the molar ratio of the molar content of alkali metals other than Li to the molar content of SO.sub.4 was 1.28.

(22) 2.Discharging Rate Test Of Nonaqueous Electrolyte Secondary Battery

(23) A coin-shaped battery was produced using the powder A.sub.1 and subjected to a discharging rate test. The discharge capacities (mAh/g) at 0.2C and 5C were as high as 140 and 114, respectively.

Comparative Example 1

(24) 1. Production of Transition Metal Mixed Hydroxide and Lithium Mixed Metal Oxide

(25) The same operations as those in Example 1 were performed except that a coprecipitate slurry was filtered and washed with 5000 ml of distilled water, so that a coprecipitate P.sub.2 as a transition metal mixed hydroxide and a powder A.sub.2 as a lithium mixed metal oxide were obtained.

(26) The composition analysis of the coprecipitate P.sub.2 found the molar ratio of Ni:Mn:Fe to be 0.47:0.48:0.05. The molar ratio of the molar content of K to the molar content of the transition metal mixed hydroxide was 0.000002. The molar ratio of the molar content of SO.sub.4 to the molar content of the transition metal mixed hydroxide was 0.000108, and the molar ratio of the molar content of alkali metals other than Li to the molar content of SO.sub.4 was 0.02.

(27) 2.Discharging Rate Test of Nonaqueous Electrolyte Secondary Battery

(28) A coin-shaped battery was produced using the powder A.sub.2 and subjected to a discharging rate test. The discharge capacities (mAh/g) at 0.2C and 5C were as low as 103 and 29, respectively.

Comparative Example 2

(29) 1. Production of Transition Metal Mixed Hydroxide And Lithium Mixed Metal Oxide

(30) The same operations as those in Example 1 were performed except that a coprecipitate slurry was filtered and washing was not performed, so that a coprecipitate P.sub.3 as a transition metal mixed hydroxide and a powder A.sub.3 as a lithium mixed metal oxide were obtained.

(31) The composition analysis of the coprecipitate P.sub.3 found the molar ratio of Ni:Mn:Fe to be 0.47:0.48:0.05. The molar ratio of the molar content of K to the molar content of the transition metal mixed hydroxide was 0.00316. The molar ratio of the molar content of SO.sub.4 to the molar content of the transition metal mixed hydroxide was 0.000586, and the molar ratio of the molar content of alkali metals other than Li to the molar content of SO.sub.4 was 5.39.

(32) 2.Discharging Rate Test of Nonaqueous Electrolyte Secondary Battery

(33) A coin-shaped battery was produced using the powder A.sub.1 and subjected to a discharging rate test. The discharge capacities (mAh/g) at 0.2C and 5C were as low as 130 and 113, respectively.

Production Example 1 (Production of Laminated Film)

(34) (1) Production of Coating Slurry

(35) After 272.7 g of calcium chloride had been dissolved in 4200 g of NMP, 132.9 g of paraphenylenediamine was added thereto and completely dissolved. To the resultant solution was gradually added 243.3 g of terephthaloyl dichloride to be polymerized, so that para-aramid was obtained, and this was further diluted with NMP, so that a para-aramid solution (A) having a concentration of 2.0% by weight was obtained. To the resultant para-aramid solution (100 g) were added 2 g of an alumina powder (a) (alumina C, produced by Nippon Aerosil Co., Ltd., average particle diameter: 0.02 m) and 2 g of an alumina powder (b) (Sumicorundum AA03, produced by Sumitomo Chemical Co., Ltd., average particle diameter: 0.3 m), 4 g in total, and mixed as fillers, and the resultant was processed with a NANOMIZER three times, and further filtered with a wire gauze with 1000 meshes, and then defoamed under reduced pressure, so that a coating slurry (B) was produced. The weight of the alumina powder (filler) relative to the total weight of the para-aramid and the alumina powder was 67% by weight.

(36) (2) Production and Evaluation of Laminated Film

(37) A polyethylene porous film (film thickness: 12 m, air permeability: 140 seconds/100 cc, average pore diameter: 0.1 m, porosity: 50%) was used as a porous film. The polyethylene porous film was secured onto a PET film having a thickness of 100 m, and the coating slurry (B) was applied onto the porous film using a bar coater manufactured by Tester Sangyo Co., Ltd. The PET film and the coated porous film were immersed into water while being integrally kept, so that a para-aramid porous film (heat resistant layer) was deposited thereon, and the solvent was then dried and the PET film was peeled away, so that a laminated film 1 having the heat resistant porous layer and the porous film laminated to each other was obtained. The thickness of the laminated film 1 was 16 m, and the thickness of the para-aramid porous film (heat resistant porous layer) was 4 m. The air permeability of the laminated film 1 was 180 seconds/100 cc, and the porosity thereof was 50%. The observation of the cross section of the heat resistant porous layer in the laminated film 1 by a scanning electron microscope (SEM) found that comparatively small fine pores as small as about 0.03 m to 0.06 m and comparatively large fine pores as large as about 0.1 m to 1 m were present. Laminated films were evaluated by the following methods.

(38) <Evaluation of a Laminated Film>

(39) (A) Measurement of Thickness The thickness of a laminated film and the thickness of a porous film were measured in accordance with JIS (K7130-1992). A value obtained by subtracting the thickness of the porous film from the thickness of the laminated film was used as the thickness of a heat resistant porous layer.
(B) Measurement of Air Permeability by Gurley Method

(40) The air permeability of a laminated film was measured using a Gurley densometer with a digital timer manufactured by Yasuda Seiki Seisakusho Ltd. on the basis of JIS P 8117.

(41) (C) Porosity A sample of a laminated film obtained was cut into a square 10 cm on each side, and the weight W (g) and the thickness D (cm) thereof were measured. The weight of each layer in the sample (Wi (g); i is an integer of 1 to n) was measured and the volume of each layer was calculated from Wi and the true specific gravity (true specific gravity i (g/cm.sup.3)) of the material of each layer. Then, the porosity (volume %) was calculated from the following formula:
Porosity (% by volume)=100{1(W1/(true specific gravity 1)+W2/ (true specific gravity 2)+ . . . +Wn/(true specific gravity n))/(1010D)}

INDUSTRIAL APPLICABILITY

(42) According to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery being superior in capacity and output characteristics to the conventional lithium secondary batteries, and especially, being very useful for a nonaqueous electrolyte secondary battery for applications in which a high capacity and a high output at a high electric current rate are required, that is, for applications in automobiles and in power tools such as electric tools.