JP2011086524A - Method of manufacturing positive electrode active material of lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a new positive electrode active material of a lithium ion secondary battery, capable of produce the positive electrode active material of the lithium ion secondary battery for the lithium ion secondary battery having high energy density by shortening a manufacturing time. <P>SOLUTION: In the method of manufacturing the positive electrode active material of the lithium ion secondary battery on the basis of iron phosphate lithium containing carbon, the manufacturing method includes an emulsion production step of producing emulsion including a lithium compound, an iron compound, a phosphorus compound, a carbon compound; a heating step of spraying the emulsion produced in the emulsion production step and heating mist droplet of the sprayed emulsion at first temperature and producing an iron phosphate lithium precursor containing carbon with thermal decomposition; and a calcination step of calcining the iron phosphate lithium precursor produced in the heating step at second temperature and producing iron phosphate lithium containing carbon. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a positive electrode active material for a lithium ion secondary battery using carbon-containing lithium iron phosphate.

  In recent years, non-aqueous secondary batteries with high output density and good cycle characteristics have attracted attention as power sources for electric vehicles, hybrid vehicles, solar power generation, wind power generation and load leveling, power tools, etc. Yes.

The positive electrode active materials for lithium ion secondary batteries include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium, nickel, cobalt (LiNi _0.8 Co _0.2 O ₂ ), lithium manganate (LiMn ₂ O ₄ ) There are composite oxides of lithium and transition metals such as ternary system of lithium, cobalt, nickel and manganese (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ). However, these oxides contain rare metal resources such as cobalt and nickel and are dangerous because the internal temperature of the battery rises due to an exothermic reaction due to the release of oxygen during rapid charge / discharge. In addition, the positive electrode material containing manganese ions has a disadvantage that the charge and discharge life is shortened because the manganese valence is 3.5 or less due to elution of manganese ions at high temperatures.

Therefore, recently, in order to compensate for these drawbacks, the positive electrode activity of olivine-type lithium iron phosphate such as lithium iron phosphate (LiFePO ₄ ) using iron, which is an abundant resource and inexpensive metal. Substances have been proposed. Lithium iron phosphate has a very low electrical conductivity, so that the movement of electrons is not good. Therefore, in order to use it as a positive electrode active material of a lithium ion secondary battery, it is necessary to impart conductivity, and a method of depositing, coating or combining carbon on the surface is known or proposed. (For example, refer to Patent Documents 1 to 5). For example, Patent Document 1 proposes a manufacturing method using a spray pyrolysis method as a method for manufacturing a carbon-containing lithium iron phosphate. The applicant has also proposed a technique relating to a method for producing a lithium iron phosphate powder for electrodes (see, for example, Patent Document 6).

  Further, other proposals have been made regarding the spray pyrolysis method (see, for example, Non-Patent Document 1). For example, in Non-Patent Document 1, lithium iron phosphate is obtained by adding 60 weight percent of white sugar to an aqueous ascorbic acid solution of lithium nitrate, iron nitrate and orthophosphoric acid. Although the discharge capacity of the lithium ion secondary battery shows 150 mAh / g at a discharge rate of 0.1 C, it shows 80 mAh / g at a discharge rate of 1 C, indicating that after 30 cycles it has decreased to 60 mAh / g. Yes.

JP 2007-35295 A JP 2004-303496 A JP 2005-135723 A International Publication No. 2002/027823 Pamphlet US Patent Application Publication No. 2007/0190418 JP 2009-70666 A

Mu-Rong Yang, Tsung-Hsien Teng, She-Hung Wu, “LiFePO4 / carbon cathode materials prepared by ultrasonic spray pyrolysis”, J. Power Sources, 159, 307-311 (2006).

  In the above conventional technique, the method of forming a positive electrode active material by coating carbon on lithium iron phosphate or mixing a large amount can improve the conductivity and can be used as a lithium ion secondary battery. However, since the carbon content in the positive electrode active material is increased, there is a problem that volume energy density and output density cannot be increased.

  The technique of Non-Patent Document 1 is not practically suitable as a power source for electric vehicles and hybrid vehicles because of low discharge capacity and unstable cycle characteristics. In an electric vehicle and a hybrid vehicle, a lithium ion secondary battery with a high output density is required, and therefore, it is necessary to have a high rate charge / discharge performance at 10 C or more of the positive electrode active material.

  The present invention provides a new lithium ion secondary battery positive electrode active material production method capable of producing a lithium ion secondary battery positive electrode active material for a high energy density lithium ion secondary battery with reduced production time. The purpose is to provide.

  One aspect of the present invention is a method for producing a positive electrode active material for a lithium ion secondary battery using lithium iron phosphate containing carbon, the emulsion comprising a lithium compound, an iron compound, a phosphorus compound, a carbon compound, and a hydrocarbon. The emulsion production step to be produced, and the emulsion produced in the emulsion production step are sprayed, and the mist droplets of the sprayed emulsion are heated at a first temperature and thermally decomposed to contain lithium iron phosphate containing carbon Including a heating step of generating a precursor, and a baking step of baking the lithium iron phosphate precursor generated in the heating step at a second temperature to generate carbon-containing lithium iron phosphate. It is the manufacturing method of the lithium ion secondary battery positive electrode active material characterized. According to this, it is possible to generate dense (fine) lithium iron phosphate containing carbon suitably.

  Another aspect of the present invention is characterized in that the spraying of the emulsion in the heating step is performed using a gas containing an inert gas as a carrier gas. According to this, suitable heating can be realized.

  Still another aspect of the present invention is characterized in that the firing step is performed in an atmosphere of a mixed gas in which an inert gas and hydrogen are mixed. According to this, suitable baking can be realized.

  Still another aspect of the present invention is characterized in that the second temperature is equal to or higher than the first temperature. According to this, carbon can be suitably contained.

  According to still another aspect of the present invention, the second temperature is in a range of 400 ° C to 900 ° C. According to this, carbon can be suitably contained. In addition, when it is less than 400 degreeC, while the production | generation of carbon becomes inadequate, when it exceeds 900 degreeC, the produced | generated carbon will volatilize.

  Still another aspect of the present invention is characterized in that the firing of the lithium iron phosphate precursor in the firing step is performed within a range of 1 hour to 24 hours. According to this, suitable baking can be realized.

  Yet another aspect of the present invention is characterized in that an organic acid is used as the carbon compound. According to this, carbon can be suitably contained.

  According to still another aspect of the present invention, in the emulsion generation step, the emulsion in which the amount of carbon contained in the lithium iron phosphate generated in the baking step is in the range of 10 wt% to 50 wt%. It is generated. According to this, a predetermined characteristic can be obtained with the lithium ion secondary battery. When the amount of carbon contained in the lithium iron phosphate is less than 10% by weight, the conductivity of the lithium iron phosphate is decreased. On the other hand, when it exceeds 50% by weight, for example, the volume energy density and the output density are reduced. It cannot be raised.

  Still another aspect of the present invention is characterized in that in the emulsion generation step, the emulsion of micelles or reverse micelles is generated. According to this, a suitable lithium iron phosphate precursor can be produced | generated.

  ADVANTAGE OF THE INVENTION According to this invention, manufacture of the new lithium ion secondary battery positive electrode active material which can produce | generate the lithium ion secondary battery positive electrode active material for lithium ion secondary batteries with high energy density shortening manufacturing time. You can get the method.

(A) shows a spray pyrolysis apparatus, (b) is a figure explaining the manufacturing method of the lithium ion secondary battery positive electrode active material by lithium iron phosphate. FIG. 3 is a powder X-ray diffraction pattern of lithium iron phosphate containing 10 wt%, 30 wt%, and 50 wt% of carbon by weight. It is a scanning electron micrograph of lithium iron phosphate containing 10% by weight of carbon. Lithium ion secondary battery provided with a positive electrode formed of lithium iron phosphate containing 10% by weight of carbon according to the present embodiment, and a positive electrode formed of lithium iron phosphate not containing carbon as a comparative example It is the comparison figure which compared the discharge curve with a lithium ion secondary battery provided with. Lithium ion secondary battery provided with a positive electrode formed of lithium iron phosphate containing 10% by weight of carbon according to the present embodiment, and a positive electrode formed of lithium iron phosphate not containing carbon as a comparative example It is the comparison figure which compared the cycle characteristic with a lithium ion secondary battery provided with. FIG. 3 is a discharge rate characteristic diagram of lithium iron phosphate containing citric acid as a carbon source and containing 10% by weight of carbon by weight. It is a 3C-10C cycle characteristic figure of lithium iron phosphate which contained citric acid as a carbon source and contained carbon 10weight% by weight. It is a discharge rate characteristic view of a lithium ion secondary battery provided with a positive electrode formed of lithium iron phosphate containing citric acid as a carbon source and containing 50% by weight of carbon by weight.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited to the configurations described below, and various configurations can be employed in the same technical idea. For example, in each configuration (process) described below, a predetermined configuration (process) can be omitted.

(Method for producing positive electrode active material for lithium ion secondary battery)
The manufacturing method (spray pyrolysis method) of this embodiment produces | generates lithium iron phosphate as a lithium ion secondary battery positive electrode active material. This manufacturing method includes an emulsion generation step, a heating step, and a baking step. In the emulsion generation process, which is the first process, first, a lithium compound, an iron compound, and a phosphorus compound, which are raw materials for lithium iron phosphate (LiFePO ₄ ), are mixed. Specifically, lithium nitrate (LiNO ₃ ) as a lithium compound, iron nitrate (Fe (NO) ₃ ) as an iron compound, and orthophosphoric acid (H ₃ PO ₄ ) as a phosphorus compound have a molar ratio of 1 : 1: 1. And these are put into a beaker etc., water or alcohol is added, and it melt | dissolves with stirring. In the following description, lithium nitrate (LiNO ₃ ), iron nitrate (Fe (NO) ₃ ), and orthophosphoric acid (H ₃ PO ₄ ) will be described as examples.

  In addition to these substances, at least one of lithium carbonate, lithium acetate and lithium formate, at least one of ferrous chloride and ferric chloride, and at least one of pyrophosphoric acid and metaphosphoric acid May be mixed. Various substances (raw material reagents) can be employed as a method for producing lithium iron phosphate. For example, metal nitrates, acetates, sulfates, ammonium salts, carbonates, and oxides can be employed. When alcohol is used, various alcohols can be used as long as they are primary to tertiary alcohols higher than ethanol. For example, ethanol or methanol (primary), isopropyl alcohol (secondary) or tertiary butyl alcohol (tertiary) can be used.

  Further, a carbon compound, specifically, an organic acid is added in a weight ratio of 10 to 50% by weight with respect to 1 kg of a solution in which lithium nitrate, iron nitrate and orthophosphoric acid are dissolved, and dissolved while stirring. More specifically, disaccharides such as sucrose (sucrose) are added at a weight ratio of 10% to 50% by weight and dissolved while stirring. In addition to these substances, at least one of citric acid, malic acid, lactic acid, malonic acid, tartaric acid, and maleic acid may be added. You may make it add the slurry containing a carbon material, a carbon compound, and an organic acid.

  Furthermore, 10 kg to 80 wt% of a hydrocarbon, specifically, a nonaqueous solvent such as acetonitrile is added to 1 kg of the solution in which the disaccharide is dissolved, and the mixture is emulsified with stirring. In addition to these substances, at least one of propionitrile, butyronitrile, propylene carbonate, acetone, dimethylformamide, and dimethyl sulfoxide may be mixed. Further, as an emulsion stabilizer, a nonionic surfactant such as hydroxypropylcellulose is added in an amount of 5% by weight in 1 kg. In this way, in the emulsion production step, a micelle or reverse micelle emulsion containing the predetermined substance such as lithium nitrate, iron nitrate, orthophosphoric acid, organic acid, hydrocarbon, etc. is produced. In the emulsion generation step, a carbon compound such as an organic acid is added first, and then a hydrocarbon such as acetonitrile is added. By adding and stirring in this order, the time required for the emulsion generation step can be shortened.

  A 2nd heating process is performed using the spray pyrolysis apparatus 100 shown to Fig.1 (a). The spray pyrolysis apparatus 100 includes, for example, a storage tank 110, a two-fluid nozzle 120, a quartz tube 130, an electric furnace 140, and a collection device 150. The storage tank 110 is charged with the emulsion generated in the emulsion generation step, and the storage tank 110 stores the input emulsion. The storage tank 110 is connected to the two-fluid nozzle 120 via a predetermined supply path 160. The two-fluid nozzle 120 is supplied with air measured by a flow meter from a device such as a compressor (not shown in FIG. 1) as a carrier gas, and is a mist of emulsion supplied from the storage tank 110 via a supply path 160. A droplet is sprayed into the quartz tube 130 from the two-fluid nozzle 120. The mist droplet has a diameter of about several μm.

  The quartz tube 130 is installed, for example, in a vertical state in the spray pyrolysis apparatus 100, and the two-fluid nozzle 120 is installed on the upper side of the quartz tube 130 so that the spray direction is on the lower side. Therefore, the mist droplets from the two-fluid nozzle 120 are forcibly sprayed from top to bottom. The nozzle diameter of the two-fluid nozzle 120 is set in the range of 5 μm to 10 μm. As the carrier gas, in addition to the above-described air, for example, any of nitrogen gas, argon gas, argon-hydrogen mixed gas, and nitrogen-hydrogen mixed gas can be used. The flow rate of the carrier gas is set in the range of 2 liters per minute to 30 liters per minute.

  On the outer periphery of the quartz tube 130, an electric furnace 140 is installed as a heat source for heating the mist droplets sprayed in the quartz tube 130. In order to ensure sufficient drying and thermal decomposition of the mist droplets sprayed in the quartz tube 130, the length of the quartz tube 130 is set to 1000 mm to 2000 mm. In order to secure the supply amount of mist droplets, the inner diameter of the quartz tube 130 is set to 30 mm to 300 mm. The quartz tube 130 may be an alumina tube or a stainless tube, for example. In the case of an alumina tube or the like, the configuration is set to the same size as the quartz tube 130. The electric furnace 140 is set to a temperature of 400 ° C to 900 ° C, preferably 400 ° C to 600 ° C. Note that when the temperature of the mist droplet is less than 400 ° C., the generation of carbon becomes insufficient. On the other hand, when the temperature exceeds 900 ° C., the generated carbon volatilizes and the amount of carbon decreases.

In the heating process, as shown on the left side of FIG. 1B, the mist droplets sprayed into the quartz tube 130 are lithium nitrate (LiNO ₃ ) and iron nitrate (Fe (NO) ₃ ) contained in the mist droplets. ) And orthophosphoric acid (H ₃ PO ₄ ) are thermally decomposed to produce lithium iron phosphate (lithium iron phosphate precursor) as primary particles. Here, the mist droplets in the heating step become hollow particles in which the outer peripheral surface is cured and an uncured emulsion is enclosed, as shown in the center portion of FIG. Here, the outer shell formed by curing the outer peripheral surface has a thickness (see the arrow of the double arrow on the outer peripheral portion of the hollow particle shown in the center of FIG. 1B) of about several hundred nm. Thereafter, when the hollow particles are further heated while falling in the quartz tube 130, the hollow particles are rapidly increased in internal pressure due to heat generation of the non-aqueous solvent in the emulsion enclosed therein (FIG. 1 ( It is broken by the arrow from the central part of the hollow particles shown in the center of b) toward the outer periphery). Thereby, the lithium iron phosphate precursor produced | generated at a heating process becomes a particle | grain with a particle diameter of about 100 nm.

  In addition, in the heating step, carbon compounds (such as sucrose in the above example) and hydrocarbons (in the above example such as acetonitrile) added in the emulsion generation step are thermally decomposed and phosphoric acid is used. Carbon is generated inside iron lithium. Therefore, the lithium iron phosphate precursor contains carbon. In addition, the spray pyrolysis apparatus 100 can be configured to include any one of a flame furnace, a plasma furnace, an infrared concentration furnace, and a hot air drying furnace in addition to the electric furnace 140 as a heat source.

  The lithium iron phosphate precursor generated in the heating process is collected by the collection device 150 via a collection path 170 continuous with the quartz tube 130. The suction amount for collecting the lithium iron phosphate precursor by the collection device 150 is set in a range of 15 liters per minute to 30 liters per minute. In addition to this, for example, a cyclone, a glass filter, a bag filter, or electric dust collection can be used as the collection method.

  In the third firing step, the lithium iron phosphate precursor generated in the heating step is fired in the range of 400 ° C. to 900 ° C. and in the range of 1 hour to 24 hours. When the temperature is lower than 400 ° C., carbon is not sufficiently generated. On the other hand, when the temperature is higher than 900 ° C., the carbon volatilizes and the amount of carbon decreases. Here, the temperature range of the baking step can be a range overlapping with the temperature range of the heating step, but the temperature of the baking step is preferably a temperature equal to or higher than the temperature of the heating step. For example, the temperature of the heating process may be 600 ° C., and the temperature of the heating process may be 700 ° C. The firing step is performed in a mixed gas atmosphere of inert gas and hydrogen, for example, an argon-hydrogen mixed gas atmosphere. When the lithium iron phosphate precursor is fired in the firing step, lithium iron phosphate containing carbon and having a particle diameter of about 10 nm to 100 nm is generated as shown on the right side of FIG. The produced lithium iron phosphate is used as a positive electrode active material for a lithium ion secondary battery. The firing process is performed using a predetermined heating furnace, electric furnace, flame furnace, plasma furnace, infrared concentration furnace, hot air drying furnace, or the like.

(Experimental result)
A predetermined experiment was conducted on the lithium iron phosphate containing carbon produced by the manufacturing method of the present embodiment described above. Hereinafter, this result will be described.

  An X-ray diffraction result of lithium iron phosphate containing 10 wt%, 30 wt%, and 50 wt% of carbon by weight will be described with reference to FIG. For the measurement, an X-ray diffractometer (XRD-6100) manufactured by Shimadzu Corporation was used. CuKα ray was used as the X-ray source, the applied voltage and the applied current were 40 kV and 30 mA, respectively, and the range of 2θ from 10 ° to 60 ° was measured with a step width of 0.02 °. As is clear from FIG. 2, regardless of the carbon content, the particles (powder) produced by the production method of this embodiment are crystallized into lithium iron phosphate.

  The observation results of lithium iron phosphate containing 10 wt% carbon by weight with a scanning electron microscope will be described with reference to FIG. 3. The lithium iron phosphate to be observed is obtained by subjecting the lithium iron phosphate precursor produced through the emulsion production step and the heating step to 12 hours at 700 ° C. in a mixed gas atmosphere of argon-hydrogen (5%) in a gas replacement furnace. It is fired. For the observation, a scanning electron microscope (S-2300) manufactured by Hitachi, Ltd. was used. The observation sample was gold coated with an ion coater and then measured at an acceleration voltage of 25 kV. According to FIG. 3, it is recognized that lithium iron phosphate having a refined particle diameter of 10 nm to 100 nm is generated. The produced lithium iron phosphate has a spherical, elliptical, or polyhedral shape in which lithium iron phosphate precursors are assembled.

Further, the carbon-containing lithium iron phosphate produced by firing the carbon-containing lithium iron phosphate precursor produced by the emulsion production step and the heating step of the production method of the present embodiment in the firing step. The positive electrode active material and the conductive binder (carbon / polyvinylidene fluoride) are used as the positive electrode active material of the lithium ion secondary battery, and the positive electrode active material: conductive binder (carbon / polyvinylidene fluoride) = 87: 13 The mixture was mixed at a ratio, and a slurry obtained by adding N-methylpyrrolidone (manufactured by Kureha Co., Ltd.) as a dispersion was applied onto a current collector metal foil, dried and pressed, cut into a predetermined size, and positive electrode Formed. And using this positive electrode, lithium (made by Honjo Chemical Co., Ltd.) as the negative electrode, and 1M (mol) LiPF ₆ EC / DMC (50/50 vol%) solution (made by Toyama Pharmaceutical Co., Ltd.) as the electrolyte. Thus, a lithium ion secondary battery was produced. A charge / discharge test (Hosen Battery Tester BTS2004) was performed using this lithium ion secondary battery. The measurement voltage was in the range of 3.5V to 4.3V.

  A lithium ion secondary battery including a positive electrode formed of lithium iron phosphate containing 10% by weight of carbon according to the present embodiment and a lithium iron phosphate not containing carbon as a comparative example (conventional example) A comparison of discharge curves with a lithium ion secondary battery including a positive electrode formed in step 1 will be described with reference to FIG. In addition, about the lithium ion secondary battery of a comparative example, about another structure, it is the same as the lithium ion secondary battery which concerns on this embodiment.

  The vertical axis of the discharge curve shown in FIG. 4 is the output voltage (Voltage), the horizontal axis is the specific discharge capacity per gram, and its unit is mAh / g. In FIG. 4, “1” indicates a discharge curve of a lithium ion secondary battery as a comparative example including a positive electrode formed of lithium iron phosphate not containing carbon. “2” is a lithium ion secondary battery according to the present embodiment, which is produced by adding sucrose (see emulsion production process) and formed of lithium iron phosphate containing 10% by weight of carbon. The discharge curve of a lithium ion secondary battery provided with is shown. "3" is sucrose, and "4" is citric acid added (see the emulsion production process), each of which is a lithium iron phosphate containing 10% by weight of carbon according to this embodiment. The discharge curve of a lithium ion secondary battery provided with the formed positive electrode is shown. These discharge curves are measured when the discharge rate is 1C.

  As is clear from FIG. 4, the lithium ion secondary battery including the positive electrode formed of lithium iron phosphate containing carbon according to the present embodiment is lithium including the positive electrode formed of lithium iron phosphate not containing carbon. It has a higher capacity than the ion secondary battery. Among lithium ion secondary batteries having a positive electrode formed of lithium iron phosphate containing carbon according to the present embodiment, it can be seen that the one with citric acid has the highest specific discharge capacity.

  A lithium ion secondary battery including a positive electrode formed of lithium iron phosphate containing 10% by weight of carbon according to the present embodiment and a lithium iron phosphate not containing carbon as a comparative example (conventional example) A comparison of cycle characteristics with a lithium ion secondary battery including the positive electrode formed in step 1 will be described with reference to FIG. In addition, about the lithium ion secondary battery of a comparative example, about another structure, it is the same as the lithium ion secondary battery which concerns on this embodiment.

  The vertical axis of the discharge curve shown in FIG. 5 is the specific discharge capacity per gram, and its unit is mAh / g. The horizontal axis is the number of cycles. In FIG. 5, “●” indicates the cycle characteristics of a lithium ion secondary battery as a comparative example provided with a positive electrode formed of lithium iron phosphate not containing carbon. “■” and “▲” indicate cycle characteristics of a lithium ion secondary battery including a positive electrode formed of lithium iron phosphate containing 10 wt% of carbon according to the present embodiment. “■” indicates that citric acid is used as a carbon source, and “▲” indicates that sucrose is used as a carbon source (see emulsion production process). These cycle characteristics are measured when the discharge rate is 1C.

  As is clear from FIG. 5, the lithium ion secondary battery including the positive electrode formed of lithium iron phosphate containing carbon according to the present embodiment is lithium including the positive electrode formed of lithium iron phosphate not containing carbon. Higher capacity and stable cycle characteristics than ion secondary batteries. In the lithium ion secondary battery including the positive electrode formed of lithium iron phosphate containing carbon according to the present embodiment, it can be seen that the specific discharge capacity is higher with the citric acid than with the scroll.

  FIG. 6 shows the discharge rate characteristics of a lithium ion secondary battery including a positive electrode formed of lithium iron phosphate containing citric acid as a carbon source and containing 10% by weight of carbon in a weight ratio according to this embodiment. I will explain. The vertical axis of the discharge curve shown in FIG. 6 is the specific discharge capacity per gram, and its unit is mAh / g. The horizontal axis is the discharge rate, and its unit is C. At 0.1 C, the specific discharge capacity was 160 mAh / g, and at 30 C, the specific discharge capacity was 50 mAh / g.

  Regarding the cycle characteristics of 3C to 10C of a lithium ion secondary battery including a positive electrode formed of lithium iron phosphate containing citric acid as a carbon source and containing 10% by weight of carbon in a weight ratio, FIG. This will be described with reference to FIG. The vertical axis of the discharge curve shown in FIG. 7 is the specific discharge capacity per gram, and its unit is mAh / g. The horizontal axis is the number of cycles. In FIG. 7, “●” indicates the cycle characteristics of the lithium ion secondary battery at 3C rate, “▲” indicates the cycle characteristics of the lithium ion secondary battery at 5C, and “■” indicates the cycle characteristics at 10C. Show. According to FIG. 7, it can be seen that a lithium ion secondary battery including a positive electrode formed of lithium iron phosphate using citric acid as a carbon source has stable cycle characteristics even during rapid charging.

  For discharge rate characteristics of a lithium ion secondary battery including a positive electrode formed of lithium iron phosphate containing citric acid as a carbon source and containing 50% by weight of carbon in a weight ratio, refer to FIG. I will explain. The vertical axis of the discharge curve shown in FIG. 8 is the specific discharge capacity per gram, and its unit is mAh / g. The horizontal axis is the discharge rate, and its unit is C. At 0.1 C, the specific discharge capacity was 160 mAh / g, and at 30 C, the specific discharge capacity was 30 mAh / g.

(Modification)
In the method for producing a positive electrode active material for a lithium ion secondary battery using lithium iron phosphate containing carbon according to the present embodiment, the heating step was performed using the spray pyrolysis apparatus 100 shown in FIG. However, in addition to the spray pyrolysis apparatus 100, for example, a manufacturing method using a spray dryer apparatus may be used. In this case as well, in the emulsion production step, a micelle or reverse micelle emulsion is produced. Moreover, in a spray dryer apparatus, the drying temperature of a mist droplet is set to the range of 100 to 300 degreeC. And the particle | grains produced | generated by this are baked in the range of 400 to 900 degreeC in a baking process. Also by such a method, the same fine lithium iron phosphate containing carbon as the manufacturing method of this embodiment can be produced | generated. A spray drying method, a freeze drying method, an arc plasma method, or a solvent evaporation method can be used.

  Lithium ion secondary battery comprising a positive electrode formed of lithium iron phosphate containing carbon, produced by a method for producing a positive electrode active material of lithium ion secondary battery using lithium iron phosphate containing carbon according to the present invention Compared to conventional lithium ion secondary batteries using lithium iron phosphate, the discharge capacity and output characteristics are improved. And according to the manufacturing method of the lithium ion secondary battery positive electrode active material by the lithium iron phosphate containing carbon which concerns on this invention, each process is simplified and cost reduction can be aimed at.

  For this reason, the present invention can improve the quality of the lithium ion secondary battery and is very useful for reducing the cost by mass production, and if it is used for an electric vehicle / hybrid vehicle, an environment-friendly drive power source can be obtained. . Further, it can be used as a non-load leveling of natural energy such as solar power generation and wind power generation, a power tool, and a power source for driving a robot.

DESCRIPTION OF SYMBOLS 100 Spray pyrolysis apparatus 110 Storage tank 120 Two-fluid nozzle 130 Quartz tube 140 Electric furnace

Claims (9)

A method for producing a positive electrode active material for a lithium ion secondary battery using lithium iron phosphate containing carbon,
An emulsion producing step for producing an emulsion comprising a lithium compound, an iron compound, a phosphorus compound, a carbon compound and a hydrocarbon;
A heating step of spraying the emulsion generated in the emulsion generating step, heating the sprayed mist droplets at a first temperature, and thermally decomposing the precursor to contain lithium iron phosphate containing carbon. When,
A lithium ion secondary battery positive electrode comprising: a calcining step of calcining the lithium iron phosphate precursor produced in the heating step at a second temperature to produce carbon-containing lithium iron phosphate A method for producing an active material.   The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the spraying of the emulsion in the heating step is performed using a gas containing an inert gas as a carrier gas.   The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, wherein the firing step is performed in an atmosphere of a mixed gas in which an inert gas and hydrogen are mixed.   4. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the second temperature is equal to or higher than the first temperature. 5.   The said 2nd temperature exists in the range of 400 to 900 degreeC, The manufacturing method of the lithium ion secondary battery positive electrode active material of any one of Claims 1-4 characterized by the above-mentioned.   The lithium ion secondary according to any one of claims 1 to 5, wherein the firing of the lithium iron phosphate precursor in the firing step is performed within a range of 1 hour to 24 hours. Manufacturing method of battery positive electrode active material.   The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 6, wherein an organic acid is used as the carbon compound.   The said emulsion production | generation process produces | generates the said emulsion in which the quantity of the carbon which the said lithium iron phosphate produced | generated by the said baking process contains is in the range of 10 weight%-50 weight%, It is characterized by the above-mentioned. The manufacturing method of the lithium ion secondary battery positive electrode active material of any one of Claims 1-7.   The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 8, wherein in the emulsion generation step, the emulsion of micelles or reverse micelles is generated.