Method for producing lithium ion cell active material particles

Abstract

A method for producing an active material particle for a lithium ion battery, the method including steps of: flowing a plurality of raw material solutions into respective raw material-feeding channels under a pressure of 0.3 to 500 MPa, the solutions being capable of inducing a chemical reaction when mixed, thereby producing an active material particle for a lithium ion battery or an active material precursor particle for a lithium ion battery; and mixing the plurality of raw material solutions at a junction of the raw material-feeding channels to induce the chemical reaction, thereby continuously producing an active material particle for a lithium ion battery or producing an active material precursor particle for a lithium ion battery.

Claims

1. A method for producing an active material particle for a lithium ion battery, the method comprising steps of: flowing a plurality of raw material solutions into respective raw material-feeding channels under a pressure of 0.3 to 500 MPa, the solutions being capable of inducing a chemical reaction when mixed, thereby producing an active material particle of LiMPO.sub.4, wherein M is one or more members selected from Fe, Co, Mn and Ni, for a lithium ion battery; wherein the plurality of raw material solutions is temperature-adjusted before mixing to a temperature from 60 C. to 120 C.; and mixing the plurality of raw material solutions at a junction of the raw material-feeding channels to induce the chemical reaction, thereby continuously producing the active material particle for a lithium ion battery.

2. The method for producing an active material particle for a lithium ion battery according to claim 1, wherein a channel diameter immediately before the junction of the raw material-feeding channels is from 0.05 to 3 mm.

3. The method for producing an active material particle for a lithium ion battery according to claim 1, wherein, near the junction of the raw material-feeding channels, a turbulent flow is imparted to the raw material solutions after joining.

4. The method for producing an active material particle for a lithium ion battery according to claim 1, wherein the chemical reaction includes a neutralization reaction.

5. The method for producing an active material particle for a lithium ion battery according to claim 1, wherein a solvent of the raw material solution is a coordinating solvent.

6. A method for producing a cathode active material particle for a lithium ion battery, wherein, in the method for producing an active material particle for a lithium ion battery according to claim 1, the plurality of raw material solutions includes a first raw material solution containing a lithium compound and a second raw material solution containing a transition metal.

Description

EXAMPLES

(1) The present invention is described specifically below by referring to Examples, but the present invention is not limited only to these Examples.

(2) A. Calculation of Average Particle Diameter of Active Material Particle for Lithium Ion Battery

(3) Particles were observed using a scanning electron microscope (S-5500, manufactured by Hitachi High-Technologies Corporation) at such a magnification that from 30 to 60 particles are included in one visual field, and an average of particle diameters of all particles in the visual field was taken as the average particle diameter. The particle diameter of each particle was an average of the maximum diameter and the minimum diameter of the particle.

(4) B. Identification of Crystal Phase of Active Material Particle for Lithium Ion Battery

(5) The identification was performed by measuring the particle by use of an X-ray diffraction apparatus, D8 ADVANCE, manufactured by Bruker AXS K.K. under the conditions of 2=from 5 to 70, a step angle of 0.040, and a step time of 70.4 seconds. The calculation of the crystallite size was performed using a Rietveld analysis software, TOPAS, attached to D8 ADVANCE.

(6) C. Evaluation of Charge/Discharge Characteristics

(7) 900 Parts by weight of an active material particle, 50 parts by weight of acetylene black (DENKA BLACK (registered trademark) produced by Denki Kagaku Kogyo K.K.) as a conductive assistant, 50 parts by weight of polyvinylidene fluoride (Kynar HSV-900, produced by ARKEMA K.K.) as a binder, and 1,200 parts by weight of N-methylpyrrolidone as a solvent were mixed by a planetary mixer to obtain an electrode paste. The electrode paste was applied onto an aluminum foil (thickness: 18 m) by using a doctor blade (300 m) and dried at 80 C. for 30 minutes to obtain an electrode plate. The electrode plate manufactured was cut into a size of 15.9 mm in diameter and used as a positive electrode, a lithium foil cut out into a size of 16.1 mm in diameter and 0.2 mm in thickness was used as a negative electrode, Celgard (registered trademark) #2400 (produced by Celgard Inc.) cut out into a size of 20 mm in diameter was used as a separator, a solvent composed of 1 M LiPF.sub.6-containing ethylene carbonate:diethylene carbonate=3:7 (by volume) was used as an electrolytic solution, and a 2032 type coin battery constituted from these components was manufactured and subjected to electrochemical evaluations. In the measurement, charge/discharge measurement was performed three times at a rate of 0.1 C and successively performed three times at 3 C, and the third discharge capacity at each rate was taken as the discharge capacity.

Example 1

(8) Production of Li(Ni.sub.1/3Mn.sub.1/3Co.sub.1/3)O.sub.2

(9) A first raw material solution was prepared by dissolving 1.69 g of manganese sulfate monohydrate, 2.81 g of cobalt sulfate heptahydrate and 2.63 g of nickel sulfate hexahydrate in 100 g of pure water. A second raw material solution was prepared by dissolving 3.18 g of sodium carbonate in 100 g of pure water, and 0.8 g of 28% ammonia water was added to the second raw material solution so that when two raw material solutions are mixed, the pH of the mixed solution can become 8. In NanoVater L-ED (manufactured by Yoshida Kikai Co., Ltd.) having a channel diameter of about 200 m and equipped with a microreactor having a turbulent flow mechanism of bending the channel to a right angle at the junction point, the first raw material solution and the second raw material solution were flowed into inner channels of the microreactor and mixed in a ratio of 1:1 under a pressure of 20 MPa at the junction of inner channels of the microreactor to obtain a (Mn.sub.1/3Ni.sub.1/3Co.sub.1/3)CO.sub.3 particle as the solid component. The average particle diameter was calculated and found to be 132.2 nm. The obtained nanoparticle was mixed with 1.28 g of lithium hydroxide monohydrate and fired at 800 C. in an air atmosphere to obtain Li(Ni.sub.1/3Mn.sub.1/3Co.sub.1/3)O.sub.2 having an average particle diameter of 252.3 nm, a crystallite size of 201.2 nm, and a crystallite size of 0.80 relative to the average particle diameter. The charge/discharge characteristics of the obtained Li(Ni.sub.1/3Mn.sub.1/3Co.sub.1/3)O.sub.2 were evaluated according to C described above assuming a theoretical capacity of 160 mAh/g, as a result, the discharge capacity was 145 mAh/g at 0.1 C and 135 mAh/g at 3 C.

Example 2

(10) Production of Lithium Iron Phosphate:

(11) A first raw material solution was prepared by dissolving 2.52 g of lithium hydroxide monohydrate in 15 g of pure water and adding 26.0 g of diethylene glycol. A second raw material solution was prepared by dissolving 5.56 g of iron(II) sulfate heptahydrate and 1 g of ascorbic acid in 12 g of pure water, adding 2.3 g of an aqueous phosphoric acid solution (85%) and then adding 17.3 g of diethylene glycol.

(12) Two raw material solutions were heated up to 80 C. and flowed into channels of NanoVater L-ED in a ratio of first raw material solution:second raw material solution of 1.3:1 under a pressure of 10 MPa, and an active material particle for a lithium ion battery was obtained as the solid component from the solution after joining. Identification of crystal phase was performed according to B described above, and it could be confirmed that the obtained particle was LiFePO.sub.4. In addition, the average particle diameter was calculated and found to be 61.1 nm, the crystallite size was 52.2 nm, and the crystallite size (nm)/average particle diameter (nm) was 0.85. The obtained lithium iron phosphate was mixed with glucose in a weight ratio of 4:1 and fired at 700 C. for 6 hours in an argon atmosphere, thereby applying a carbon coating to the lithium iron phosphate. The charge/discharge characteristics of the carbon-coated lithium iron phosphate obtained were evaluated according to C described above assuming a theoretical capacity of 170 mAh/g, as a result, the discharge capacity was 140 mAh/g at 0.1 C and 115 mAh/g at 3 C.

Example 3

(13) Production of Lithium Manganese Phosphate:

(14) An active material particle for a lithium ion battery was obtained in the same manner as in Example 2 except that 5.56 g of iron(II) sulfate heptahydrate was changed to 3.38 g of manganese sulfate monohydrate. Identification of crystal phase was performed, and it could be confirmed that the obtained particle was LiMnPO.sub.4. In addition, the average particle diameter was calculated according to A. described above and found to be 433 nm, the crystallite size was 39.8 nm, and the crystallite size (nm)/average particle diameter (nm) was 0.92. The obtained lithium manganese phosphate was mixed with glucose in a weight ratio of 4:1 and fired at 700 C. for 6 hours in an argon atmosphere, thereby applying a carbon coating to the lithium manganese phosphate. The charge/discharge characteristics of the carbon-coated lithium manganese phosphate obtained were evaluated according to C described above assuming a theoretical capacity of 171 mAh/g, as a result, the discharge capacity was 136 mAh/g at 0.1 C and 102 mAh/g at 3 C.

Comparative Example 1

(15) Production of Li(Ni.sub.1/3Mn.sub.1/3Co.sub.1/3)O.sub.2:

(16) While stirring the first raw material solution of Example 1 by a magnetic stirrer and keeping the pH at 8 by adding ammonia, the second raw material solution was added dropwise to obtain a (Mn.sub.1/3Ni.sub.1/3Co.sub.1/3)CO.sub.3 particle as the solid component. The average particle diameter was calculated and found to be 384.5 nm and thus, the particle diameter became large. The obtained nanoparticle was mixed with 1.28 g of lithium hydroxide monohydrate and fired at 800 C. in an air atmosphere to obtain, as an active material particle for a lithium ion battery, Li(Ni.sub.1/3Mn.sub.1/3Co.sub.1/3)O.sub.2 in which the particle diameter was enlarged providing an average particle diameter of 789.5 nm, a crystallite size of 531.9 nm, and a crystallite size (nm)/average particle diameter (nm) of 0.67 and the crystallinity was reduced. The charge/discharge characteristics of the obtained Li(Ni.sub.1/3Mn.sub.1/3Co.sub.1/3)O.sub.2 were evaluated according to C described above assuming a theoretical capacity of 160 mAh/g, as a result, the discharge capacity was 133 mAh/g at 0.1 C and 124 mAh/g at 3 C.

Comparative Example 2

(17) The first raw material solution of Example 2 was heated up to 80 C. while stirring at 300 rpm on a hot plate stirrer, and the second raw material solution of Example 2 heated up to 80 C. as well was added dropwise to obtain a solid component. When identification of the crystal phase of the solid obtained was performed, it was found that Li.sub.3PO.sub.4 was present in addition to LiFePO.sub.4. Calculation of the average particle diameter was attempted, but because of a mixture of LiFePO.sub.4 and the impurity, the particle diameter could not be measured.

Comparative Example 3

(18) The first raw material solution of Example 3 was heated up to 80 C. while stirring at 300 rpm on a hot plate stirrer, and the second raw material solution of Example 3 heated up to 80 C. was added dropwise to obtain a solid. When identification of the crystal phase of the solid obtained was performed, it was found that impurities such as Mn.sub.5(HPO.sub.4).sub.2(PO.sub.4).sub.2.4H.sub.2O and Li.sub.3PO.sub.4 were present in addition to LiMnPO.sub.4. Calculation of the average particle diameter was attempted according to A described above, but because of a mixture of LiMnPO.sub.4 and the impurities, the particle diameter could not be measured.