JP2009093858A - Manufacturing method of positive electrode material for lithium secondary battery, and positive electrode material for lithium secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode material, for a lithium secondary battery, capable of restraining generation of stripes on a positive electrode plate and fall of battery voltage. <P>SOLUTION: Powder of the positive electrode material for a lithium secondary battery obtained by mixing, baking and pulverizing raw materials is made to pass a sieving device for detecting that a sieving net is broken, by comparing it with a reference value preset by AE signals obtained from an acoustic emission sensor mounted on a sieving device main body carrying out selection of powder by the particle size with the sieving net. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a positive electrode material for a lithium secondary battery and a positive electrode material for a lithium secondary battery using the same, and more particularly to a sieving apparatus for sorting based on the particle diameter of a powder.

  A positive electrode material for a lithium secondary battery is generally prepared by mixing a lithium compound, which is a raw material, and a compound such as an oxide or hydroxide, such as nickel, manganese, cobalt, and the like, and placing the mixed powder in a container. Bake at 1100 ° C. After firing, the sintered material is pulverized with a pulverizer to form a powder. In the pulverization, particles having a large particle diameter remain in part.

  These large particles cause streaks on the coated surface in the coating process for producing the positive electrode plate. In addition, large particles are often metallic foreign matter mixed from manufacturing equipment and raw materials, and when mixed into the positive electrode plate, it elutes during charge / discharge of the battery, deposits and deposits on the negative electrode plate surface, and finally The positive and negative electrodes are short-circuited, causing a voltage drop.

  For this reason, it is necessary to remove the large particles by passing the pulverized material through a sieving apparatus using a net in order to sort by the particle size.

  However, since the screen of the sieving device may be broken due to wear or the like, and particles having a large particle size may be mixed in, a method for detecting the breakage of the screen is required. Conventionally, various methods as described below have been used as methods for detecting breakage of a network such as a screening device.

  As a first method, there is a method in which a human visually monitors the state of powder flowing on a net while the sieving machine is in operation.

  As a second method, there is a method in which a human visually inspects the net while the sieving device is stopped.

  As a third method, there is a method in which a human passes through a screen based on the powder under the net at regular intervals and determines that the net is broken if there is powder that does not pass through.

  The first method is disadvantageous in that it requires manpower and lack of certainty because it is overlooked by human eyes.

  The second method has a drawback that it cannot be detected during operation.

  The third method is disadvantageous in that it requires manpower and lacks certainty because it is overlooked by human eyes.

  In order to solve these problems, for example, in Patent Document 1, rocks, ores, and other articles that have passed through a net are photographed using a photographing device, and an image signal from the photographing device is sent to the image processing device. Measure the size of individual rocks, ores, and other articles with this image processing device, compare the measured values obtained in this way with preset values using an arithmetic unit, and measure from the set values. When the value is large, an alarm output is issued because the net is broken.

Moreover, in patent document 2, the granular material introduction | transduction process which introduce | transduces a part of granular material which passed the sieve after the sieving apparatus which sifts a granular material with the sieve of the mesh | network of a predetermined | prescribed magnitude | size, and this The sieving step of sieving the introduced granular material by the test sieve having the same size mesh as the sieve used by the sieving device, and the passing particles passed through the test sieve by sieving in this sieving step The first measuring step has a first measuring step for measuring the weight of the body, and a second measuring step for measuring the weight of the residual granular material remaining on the test sieve by inverting the sieve for testing after sieving. The screen breakage of the sieving device is automatically determined from the ratio between the measured value measured in step 2 and the measured value measured in the second measuring step.
JP-A-5-172525 Japanese Patent Laid-Open No. 9-1076

  However, in the conventional method as shown in Patent Document 1, it can be used for rocks and ores with relatively large grains, but due to the resolution of the photographing device and the overlapping of particles, There was a problem that small particles such as the body could not be used.

  Moreover, in the conventional method as shown in Patent Document 2, there is a problem that it is necessary to stop the apparatus in order to confirm the breaking of the screen of the test sieve, and the detection apparatus becomes complicated. It was.

  The present invention eliminates the drawbacks of the above-described methods for detecting breakage of a net, such as a conventional sieving apparatus, and passes through a sieving apparatus that can immediately detect small breakage that is difficult to visually confirm. It is an object of the present invention to provide a method for producing a positive electrode material for a lithium secondary battery that reliably removes particles having a large particle diameter, and a positive electrode material for a lithium secondary battery using the same.

  In order to solve the above-mentioned conventional problems, the sieving apparatus in the method for producing a positive electrode material for a lithium secondary battery according to the present invention is equipped with the following network breakage detection method, and the particles are reliably separated by sorting only when the net is normal. It becomes possible to remove particles having a large diameter.

  An acoustic emission (AE) sensor is attached to the main body of the sieving device that performs selection based on the particle size of the powder using a sieve mesh, and the mesh is broken by comparing the AE signal obtained therefrom with a preset reference value. The AE signal obtained from the AE sensor is monitored at the time of working, and the network breakage is detected by utilizing the difference in level between the normal time and the network breakage.

  In the sieving apparatus used in the present invention, if the net is a metal net, when the net is broken, an AE signal generated by contact between the broken parts of the net increases, and the net breakage is detected. Since it becomes easy, it is preferable.

  In addition, it is preferable that the sieving device main body has a vibration sieving mechanism. That is, it is preferable to perform vibration-type sieving because when the net is broken, the frequency of contact between the broken parts of the net increases, and it becomes easy to detect the breaking of the net.

In this case, it is more preferable that the vibration sieving mechanism is an ultrasonic vibration sieving mechanism, that is, the vibration sieving mechanism is based on ultrasonic waves because the contact frequency is further increased.

  Further, the sieving device used in the present invention includes a sieving device main body that performs screening based on the particle size of the powder using a sieving screen, an acoustic emission sensor attached to the sieving device main body, and a reference value of the AE signal therein. Comprising an arithmetic unit that receives a AE signal transmitted from the acoustic emission sensor and determines that the network is broken by comparing the AE signal with a preset reference value. Is preferred.

  By using the method for producing a positive electrode material for a lithium secondary battery according to the present invention, particles having a large particle diameter can be reliably removed, so that the occurrence of streaks on the positive electrode plate coating surface and voltage drop during battery charge / discharge is reduced. Moreover, since network breakage can be detected immediately, sieving of the positive electrode material becomes possible without reducing the throughput per hour.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  Hereinafter, the present invention will be described based on examples.

  FIG. 1 shows a longitudinal sectional view of a cylindrical battery produced in this example.

  The nonaqueous electrolyte secondary battery in FIG. 1 includes a battery case 1 made of stainless steel and an electrode plate group housed in the battery case 1. The electrode plate group includes a positive electrode 5, a negative electrode 6, and a polyethylene separator 7, and the positive electrode 5 and the negative electrode 6 are wound in a spiral shape via the separator 7. An upper insulating plate 8a and a lower insulating plate 8b are disposed above and below the electrode plate group. The battery case 1 is sealed by caulking the opening plate 2 with a sealing plate 2 through a gasket 3.

  One end of an aluminum positive electrode lead 5a is attached to the positive electrode 5, and the other end of the positive electrode lead 5a is connected to a sealing plate 2 that also serves as a positive electrode terminal. One end of a negative electrode lead 6a made of nickel is attached to the negative electrode 6, and the other end of the negative electrode lead 6a is connected to the battery case 1 that also serves as a negative electrode terminal.

Example 1
(1) Preparation of positive electrode active material After mixing a metal hydroxide containing nickel cobalt manganese at a molar ratio of 1: 1: 1 and lithium carbonate so that the molar ratio of the metal element to the lithium element is 1: 1.01. And calcined in the atmosphere at 950 degrees for 8 hours to obtain lithium nickel cobalt manganate. The positive electrode material for a lithium secondary battery obtained by firing was pulverized with a pulverizer.

  In order to show the effect of the present invention remarkably, about 0.1 part by weight of iron powder having an average particle diameter of 300 μm assuming a metal foreign substance is mixed in 100 parts by weight of the pulverized cathode material for a lithium secondary battery. The sieving was performed through a sieving device.

  FIG. 2 shows a schematic diagram of the sieving apparatus used in this example.

First, a stainless steel net 202 having an opening of 50 μm is attached in the frame of the sieving device main body 201, and powder is supplied onto the net 202 to give vibration. Since the large particles in the powder cannot pass through the mesh 202, the powder particles smaller than the mesh of the mesh 202 pass through the mesh 202 and become the lower material. The upper sieve material is discharged from the sieve material discharge port 203, and the lower sieve material is discharged from the lower sieve material discharge port 204.
The acoustic emission (AE) sensor 205 is attached in close contact with the screening apparatus main body 201. The arithmetic device 206 for analyzing AE is connected to the AE sensor 205 by a cable. The network breakage detection method in the present embodiment will be described in more detail with reference to FIG.

  The powder of the positive electrode material for a lithium secondary battery obtained by pulverization is supplied onto the net 202 of the sieving device main body 201. Particles that are smaller than the meshes of the mesh 202 pass through the meshes of the mesh 202 and become a sieved material, and are discharged from the sieved material discharge port 204. Particles larger than the mesh of the mesh 202 cannot pass through the mesh of the mesh, and are discharged from the sieve upper material discharge port 203. In a normal state in which the mesh 202 is not broken, an AE signal generated by the contact between the powder and the mesh 202 can be detected by the AE sensor 205 through the mesh 202 and the screen frame. In an abnormal state in which the mesh 202 is broken, it is possible to detect an AE signal generated when the broken portions of the mesh 202 contact with each other in addition to the generated AE signal due to the contact between the powder and the mesh 202. The AE signal detected by the AE sensor 205 is transmitted to the arithmetic unit 206 that analyzes the AE through the cable.

  The RMS value data can be obtained by analyzing the AE signal by the arithmetic unit 206. The RMS value is a root mean square, and here shows the square root of the root mean square of the voltage obtained as a result of analysis. The RMS value increases as the vibration obtained from the AE sensor 205 increases.

FIG. 3 shows the RMS value with respect to time obtained as a result of analyzing the AE signal by the arithmetic unit 206 for analyzing AE. It can be seen that in a normal state in which the network 202 is not broken, the RMS value changes at a value close to 0V. After the network breakage occurrence time 301, the RMS value increases to around 5.5V. This is thought to be because the mesh 202 was broken and the RMS value was increased due to the contact between the broken portions of the mesh 202. By setting the reference value 302 between the normal time and the abnormal time in advance, it is possible to detect the network 202 breakage.
After sieving, when the sieve net was confirmed, a hole of about 500 μm, which would be difficult to detect visually, could be confirmed.

  A positive electrode plate was prepared using the positive electrode material for a lithium secondary battery discharged from the discharge port 204 as a lower sieve material before the net break occurrence time 301.

(2) Preparation of positive electrode plate 100 parts by weight of the positive electrode material for a lithium secondary battery, 4 parts by weight of acetylene black as a conductive agent, and 5 parts by weight of a binder of N-methylpyrrolidone (NMP) as a binder. A paste containing a positive electrode mixture was obtained by mixing with a solution in which polyvinylidene fluoride (PVDF) was dissolved. This paste was applied on both sides of a 15 μm thick aluminum foil serving as a current collector, dried, rolled, and cut into a predetermined size to obtain a positive electrode plate.

(3) Production of Negative Electrode Plate 75 parts by weight of artificial graphite powder was mixed with 20 parts by weight of acetylene black as a conductive agent and 5 parts by weight of polyvinylidene fluoride resin as a binder, and these were mixed with dehydrated N-methyl-2 -A slurry-like negative electrode mixture was prepared by dispersing in pyrrolidone. This negative electrode mixture was applied to both surfaces of a negative electrode current collector made of copper foil, dried, rolled, and cut into predetermined dimensions to obtain a negative electrode plate.

(4) Preparation of non-aqueous electrolyte solution 1% by weight of vinylene carbonate was added to a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 3, and LiPF6 was dissolved at a concentration of 1.0 mol / L. A water electrolyte was obtained.

(5) Production of Cylindrical Battery First, the aluminum positive electrode lead 5a and the nickel negative electrode lead 6a were attached to the current collectors of the predetermined positive electrode 5 and negative electrode 6, respectively, and then wound through the separator 7, An electrode plate group was constructed. Insulating plates 8a and 8b are arranged on the upper and lower parts of the electrode plate group, the negative electrode lead 6a is welded to the battery case 1, and the positive electrode lead 5a is welded to the sealing plate 2 having an internal pressure actuated safety valve. 1 was stored inside. Thereafter, a non-aqueous electrolyte was injected into the battery case 1 by a reduced pressure method. Finally, the battery A was completed by caulking the opening end of the battery case 1 to the sealing plate 2 via the gasket 3. The battery capacity of the obtained cylindrical battery was 2400 mAh.

(Comparative Example 1)
A battery produced in the same manner as battery A was designated as battery B, except that the positive electrode material for a lithium secondary battery discharged from the discharge port 204 was used as the sieving material after the net breakage occurrence time 301.

(6) Evaluation About the positive electrode plate and battery obtained as described above, the presence or absence of streaks on the surface of the positive electrode plate was examined, and the voltage drop amount of the battery was investigated.
First, the investigation of streaks on the electrode plate surface will be described. The front and back surfaces of the positive electrode plate were visually observed, and those having even a slight streak were judged to be streaks, and the number of streaked positive electrode plates in 100 positive electrode plates was defined as the number of streaks.

  Next, the investigation of the battery voltage drop will be described. The battery obtained by charging the obtained battery with a constant current (100 mA) up to 4.10 V was subjected to voltage measurement when 24 hours had elapsed after completion of charging. Thereafter, the voltage was measured again after standing at room temperature for 7 days, and the voltage difference was taken as the voltage drop.

  When the iron powder was not mixed in the positive electrode material for the lithium secondary battery, the voltage drop amount was about 0.003V. Therefore, it was determined that a voltage drop amount of 0.01V or more was a voltage abnormality, and 100 batteries were The number of batteries having a voltage drop of 0.01 V or more was defined as the number of voltage abnormalities.

  Table 1 shows the number of streaks and the number of occurrences above the voltage in Example 1 and Comparative Example 1.

From Table 1, it can be seen that the use of the positive electrode material of Example 1 can suppress the generation of streaks and voltage drop. This is because, by using an unbroken sieve mesh, foreign particles larger than 50 μm or metal foreign matter can be removed with a sieve mesh, so that no streaks are generated when applied to the positive electrode plate. The voltage drop due to the elution of metallic foreign matter is less likely to occur in the battery.

  In addition, by using a sieving device using this detection method, it is possible to reliably and instantaneously detect screen breakage during the operation of the screen, so the sieving device is stopped for visual confirmation of sieving screen breakage. This eliminates the need for sieving of the positive electrode material without reducing the throughput per hour.

  In this example, nickel cobalt lithium manganate was used as the positive electrode material for the lithium secondary battery, but it was effective for positive electrode materials including lithium-containing composite oxides such as lithium cobaltate, lithium nickelate, and lithium manganate. Can be obtained.

  In this embodiment, the RMS value obtained by analyzing the AE signal is used for detection of network breakage. However, AMP data indicating the amplitude obtained at the same time can also be used.

  Conventionally known materials such as plastic can be used for the mesh 202 used in the present embodiment, but when the mesh 202 is made of metal, the AE generated by contact between the broken portions of the mesh. Since the signal becomes large, it is preferable in that it is easy to detect a network break.

  By using a vibration screening mechanism for the sieving device main body 201 used in the present embodiment, when the net is broken, the contact frequency between the broken parts of the net is increased, which is preferable in that it is easy to detect the net break. .

  Further, the use of the ultrasonic vibration type as the vibration type is more preferable in that the contact frequency is further increased, so that the detection of network breakage is further facilitated.

  In this embodiment, the AE sensor 205 is in close contact with a sieve frame installed on the net 202, but any portion may be used as long as it is in close contact with a place where an AE signal can be detected.

  Examples of the place where the AE sensor 205 is brought into close contact include the net 202 and a sieve frame installed under the net 202.

  In this embodiment, the AE sensor 205 is vertically attached to the sieve frame installed on the net 202. However, any direction may be used as long as the AE signal can be detected.

  In this embodiment, a cylindrical battery is used, but the same effect can be obtained by using a battery having a different shape such as a square.

  The non-aqueous electrolyte secondary battery of the present invention is excellent in suppressing the generation of streaks on the positive electrode plate coating surface and the battery voltage drop. Therefore, by using the positive electrode material produced by this manufacturing method, there are effects such as improvement of yield and reduction of waste loss, which are useful. Moreover, since it is excellent in safety, it is useful for a portable power source.

1 is a longitudinal sectional view of a cylindrical nonaqueous electrolyte secondary battery according to an embodiment of the present invention. Schematic diagram of the sieving device of one embodiment of the present invention The figure which showed the relationship of the RMS value with respect to time in one embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Gasket 5 Positive electrode 5a Positive electrode lead 6 Negative electrode 6a Negative electrode lead 7 Separator 8a Upper insulating plate 8b Lower insulating plate

Claims (5)

A method for producing a positive electrode material for a lithium secondary battery comprising at least a step of sorting powders obtained by mixing, firing, and pulverizing raw materials according to the particle diameter of the powders using a screen of a sieving device. And
The sieving device is a sieving device having a function of detecting that the net is broken by comparing an acoustic emission signal obtained from an acoustic emission sensor attached to the sieving device body with a preset reference value, A method for producing a positive electrode material for a lithium secondary battery, wherein the screening is performed only when the mesh is normal.   The method for producing a positive electrode material for a lithium secondary battery according to claim 1, wherein the net is a metal net.   The method for producing a positive electrode material for a lithium secondary battery according to claim 1 or 2, wherein the sieving device main body includes a vibrating sieving mechanism.   4. The method for producing a positive electrode material for a lithium secondary battery according to claim 3, wherein the vibration sieving mechanism is an ultrasonic vibration sieving mechanism. The positive electrode material for lithium secondary batteries using the manufacturing method of the positive electrode material for lithium secondary batteries in any one of Claim 1 to 4.

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