JP2007230784A - Manufacturing process of lithium-iron complex oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new manufacturing process of an olivine-type lithium-iron complex oxide exhibiting an excellent battery performance using an inexpensive iron compound as a raw material and an electrode active material for non-aqueous electrolyte secondary cells having a high discharge capacity and excellent charge/discharge characteristics using the lithium-iron complex oxide manufactured. <P>SOLUTION: The manufacturing process of the lithium-iron complex oxide comprises pulverizing raw material components including an iron compound containing a trivalent iron, a lithium compound, a phosphate compound and a carbon-containing compound to the extent that the 50% volume-accumulative size (D50) of the finely pulverized particle is ≤2 μm and the 90% volume-accumulative size (D90) is ≤10 μm, coagulating the finely pulverized particle to the extent that the 50% volume-accumulative size (D50) of the finely pulverized particle is ≤30 μm and the 90% volume-accumulative size (D90) is ≤100 μm and heat-treating the particle at 300-1,150°C to obtain LiFePO<SB>4</SB>having an olivine structure. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a lithium iron composite oxide having an olivine structure and a non-aqueous electrolyte electrode active material containing the produced lithium iron composite oxide.

  A lithium ion secondary battery having a high output and a high energy density has been recognized as an energy source for mobile devices, and has been rapidly replaced with conventional alkaline secondary batteries and nickel metal hydride batteries. On the other hand, lithium-ion secondary batteries of medium- and large-sized batteries are expected as one solution that can alleviate the seriousness of environmental problems and energy problems, but the safety concerns have not been resolved and are not progressing.

As a safe and inexpensive positive electrode active material, investigations centering on Mn-based and Fe-based materials have been made so far. In particular, spinel type LiMn ₂ O ₄ was a material that has been energetically studied, but it has not been able to overcome the shortcomings of poor stability during high-temperature storage, and has not yet been put into practical use. Although the layered rock salt structure LiFeO ₂ has been studied for many years, it is still in a situation where satisfactory electrochemical properties cannot be expressed.

On the other hand, LiFePO ₄ proposed by Patent Document 1 is extremely safe and excellent in stability because all oxygen in the positive electrode active material related to safety is covalently bonded to phosphorus and firmly fixed. It was expected to be a positive electrode active material. However, the electrochemical characteristics have a problem that only 70% of the theoretical amount can be expressed (Non-patent Document 1).

The problem with conventional LiFePO ₄ is that LiFePO ₄ crystals have poor electronic conductivity. For this reason, lithium insertion into the crystal and desorption from the crystal are difficult to proceed, and diffusion within the crystal is slow, so that charging and discharging cannot be smoothly repeated. Further, since LiFePO ₄ is a divalent iron compound, the divalent iron compound was easily used as the iron source. The divalent iron compounds that are easy to handle are limited and are not versatile and expensive.

One countermeasure for overcoming the above problem is atomization of the active material (Non-patent Document 2). Thereby, the surface which can contribute to a charge transfer reaction can be increased, and the electron transfer distance in a crystal | crystallization can be shortened. Non-Patent Document 2 reports that LiFePO ₄ containing particles having a particle size of 10 μm or less was prepared to achieve a discharge capacity of 160 mAh / g. However, this is an iron compound having a valence of 2, which uses iron acetate as an extremely expensive iron source, and hardly exhibits load characteristics in which sintered particles are frequently generated.

It has been reported that the electrochemical properties can also be improved by applying a conductive coating to the surface of the active material particles to increase the conductivity of the particle surface and the electrode composite. It is also effective to use a carbonaceous material used as a conductive aid for the composite for the conductive coating of the particles. Non-Patent Document 3 reports that LiFePO ₄ obtained by baking a mixture of a phenol resin-derived carbon and a raw material can exhibit a high discharge capacity even under a high load. However, also in this case, expensive iron acetate is used as the iron source.

Patent Document 2 proposes a method in which carbon substance fine particles are combined with LiFePO ₄ particles having an average particle diameter of 0.2 to 5 μm. However, the initial discharge capacity of the battery assembled using the active material thus prepared can only exhibit a low characteristic of 88 mAh / g, although iron oxalate, which is a divalent iron compound, is used as the iron source. This is considered to be because the battery performance of the fine particles difficult to handle could not be drawn out well.

Attempts to improve the electrochemical properties of the active material by increasing the conductivity of the crystal itself are also being considered. Non-Patent Document 4 reports that by doping 1 mol% of Nb, Zr, or the like, the electronic conductivity of LiFePO ₄ was increased by 8 orders of magnitude, and battery performance excellent in high load characteristics could be expressed. However, these are also studied using iron oxalate, which is a divalent iron compound, as an iron source, and economically impractical.

Attempts to synthesize LiFePO ₄ using an iron compound that is highly versatile and inexpensive are also being studied. Non-Patent Document 5 uses Fe ₂ O ₃ , which is a readily available and inexpensive trivalent iron compound, as an iron source, and a carbonaceous material as a reducing agent for reducing trivalent iron to divalent iron. Thus, it has been reported that LiFe _0.9 Mg _0.1 PO ₄ can be synthesized to exhibit good battery performance. However, the XRD profile of LiFePO _{4 in} the report leaves a diffraction peak of unreacted iron oxide, indicating that the reaction is not complete.

Although it has been possible to synthesize LiFePO ₄ that can express good battery performance as described above, they are based on a synthesis method using a divalent iron compound as a raw material, and abundantly stable inexpensive LiFePO ₄ From the point of trying to supply, it is not practical.

On the other hand, iron oxide is advantageous as an iron compound that is inexpensive, easy to handle and easily available. Although a method for synthesizing LiFePO ₄ using iron oxide as an iron source has been conventionally known, it has not been put to practical use because the reaction cannot be completed and the high load characteristics are greatly reduced.
Japanese Patent No. 3319258 JP 2003-36889 A J. Electrochem. Soc. 144,1188 (1997) J. Electrochem. Soc. 148, A224 (2001) Electrochem. Solid-State Lett. 4, A170 (2001) Nature Mater. 2, 123 (2002) Electrochem. Solid-State Lett. 6, A53 (2003)

  The present invention overcomes the above-mentioned problems of the prior art and uses a general-purpose and inexpensive iron compound containing trivalent iron as a raw material, and can carry out a synthesis reaction while maintaining the optimal particle shape for battery characteristics expression. It is an object of the present invention to provide a novel method for producing a lithium iron composite oxide and an olivine type lithium iron composite oxide produced by such a method and having a high discharge capacity and excellent charge / discharge characteristics.

The present inventor has intensively studied to achieve the above-mentioned problems. As a result, the raw material components including iron compound, lithium compound, phosphate compound, and carbon-containing compound containing iron having a valence of 3 are refined. After the 50% volume cumulative diameter (D50) of the fine particles is 2 μm or less and the 90% volume cumulative diameter (D90) is 10 μm or less, the fine particles are agglomerated to give 50% of the aggregate particles. % Volume cumulative diameter (D50) of 30 μm or less and 90% volume cumulative diameter (D90) of 100 μm or less, followed by heat treatment at 300 to 1150 ° C. to give olivine type structure LiFePO ₄ A method for producing a composite oxide has been reached.

According to the production method of the present invention, the fine iron compound and the fine carbon-containing compound are homogeneously distributed in the raw material components, and the carbon reduces the adjacent trivalent iron almost quantitatively by 2 It acts to maintain the valence, performs the synthesis reaction of LiFePO ₄ , and functions to prevent undesirable side reactions such as reoxidation. In addition, the agglomerated particles of the raw material component having a pre-controlled particle size distribution act so as to maintain many characteristics of the distribution before the heat treatment even after being heat-treated to become LiFePO ₄ , so that primary particles, secondary particles It functions to prevent excessive sintering.

  Thus, the lithium iron composite oxide of the present invention comprises aggregated particles having a controlled particle size in which fine primary particles are gathered, and a carbonaceous particle layer derived from a carbon-containing compound is provided on the surface of the primary particles. ing. Reflecting such a form, the non-aqueous electrolyte secondary battery using the lithium iron composite oxide of the present invention as the positive electrode active material allows the interface charge transfer reaction to proceed smoothly and exhibits excellent battery characteristics. That is, a large current can be flowed to obtain power, and a highly reliable safety and long life can be achieved.

  On the other hand, the conventional lithium iron composite oxides have left unreacted parts and reoxidized parts because micro-mixing of raw material components having greatly different specific gravities was insufficient. In addition, independent primary particles and fine secondary particles became a binder during heat treatment, and large primary particles and agglomerated particles were frequently generated. It is inferred that such a defect caused deterioration of cycle characteristics and load characteristics when a conventional lithium iron composite oxide was used as an electrode active material for a non-aqueous electrolyte secondary battery.

The present invention is characterized in that the synthesis of LiFePO ₄ , which is a divalent iron compound, can be achieved even from a raw material containing trivalent iron, and is compatible with the development of high-performance battery characteristics. Therefore, the iron raw material that can be used in the present invention is not limited at all and can be selected from a wide range of iron compounds. However, since it is easy to obtain and handle and is inexpensive, iron oxide is preferably used as an iron raw material component in the present invention. As the iron oxide, not only Fe ₂ O ₃ but also Fe ₃ O ₄ or FeOOH is preferably used. Acicular iron oxide having strong anisotropy is also preferably used.

  Any lithium compound may be used as long as it contains lithium. However, from the viewpoint of easy handling, lithium oxides, hydroxides, salts, or a mixture of two or more of these compounds are preferred.

  The phosphoric acid compound used in the present invention is not limited at all. However, since it is easy to obtain and easy to handle, phosphoric acid esters such as phosphoric acid, iron phosphate, lithium phosphate and ammonium phosphate, triethyl phosphate and 2-ethylhexyldiphenyl phosphate can be exemplified, and all are preferable. Can be used.

  The carbon-containing compound that can be used in the present invention can also be selected from a wide range of compounds containing carbon. However, it is preferable that the compound has a carbon content of at least 35% by weight and exhibits a liquid state or a solid state at normal temperature because the reduction reaction from trivalent iron to divalent iron can proceed efficiently. Specifically, reducing sugars such as glucose, sucrose and lactose; organic compounds such as ethylene oxide, glycerin, ascorbic acid, lauric acid and stearic acid; water-soluble polymers such as polyvinyl alcohol and polyethylene glycol; polypropylene, polystyrene and polyacrylonitrile Examples thereof include resins and plastics such as cellulose, epoxy resin and phenol resin, and carbonaceous materials such as acetylene black, carbon black and graphite. The carbon-containing compound can be used as it is, but it can also be used in the form of a solution, emulsion, suspension or the like.

  The raw material component containing the iron compound, lithium compound, phosphate compound, and carbon-containing compound containing iron having a valence of 3 is subjected to a fine treatment. The refinement process is performed through a process of crushing and crushing raw material components. Each raw material component can be refined separately or two or more raw material components can be simultaneously refined. The respective raw material components subjected to the fine treatment are preferably mixed uniformly. In the present invention, the miniaturization process and the mixing process can be performed independently, but two processes can be performed almost simultaneously.

  It is preferable to carry out the above-mentioned raw material component refinement treatment with a slurry formed from the raw material component and the dispersion medium because sufficient refinement is possible while preventing dissipation. The dispersion medium of the slurry may be a raw material component solvent. As the dispersion medium, any of an aqueous system, a hydrocarbon system, and a halogenated carbon system can be used. Among these, an aqueous dispersion medium is particularly preferable because it is easy to handle and inexpensive.

  In the present invention, any method such as applying a shearing force to the slurry can be used as the method for refining the raw material components in the form of the slurry. In particular, the slurry consisting of the raw material and the dispersion medium can be passed between two rotors, two disks, or between a rotor and a stator, which have greatly different rotational speeds, because it can be efficiently miniaturized and the contamination can be controlled low. , Method of pulverizing by cavitation in the slurry, bead mill, planetary ball mill, or ball mill Such a method is preferably used.

  In this way, in the miniaturization treatment, it is preferable that D50 of the fine particles of the raw material component is 2 μm or less, preferably 1 μm or less, and D90 is 10 μm or less, preferably 5 μm or less. If D90 is larger than 10 μm, the synthesis reaction cannot be achieved, and the battery characteristics are greatly impaired. Further, if D50 is larger than 2 μm, cycle characteristics and load characteristics are impaired, which is not preferable.

  The above-mentioned refinement of the raw material component slurry can be performed individually for each raw material component, or two or more raw material components can be simultaneously processed. In the latter case, the homogenous mixing of the raw materials can be completed simultaneously with the refinement of the raw material components.

  The present invention then agglomerates the raw material component particles that have been refined. The method of aggregating the raw material component particles can be carried out by various means, and the agglomerated particles are preferably obtained in a dry state. Thus, for example, it is preferable to use a method in which the slurry obtained by the refining treatment is preferably stirred and placed under heating and / or reduced pressure while applying a shearing force to aggregate the raw material components, remove the solvent, and dry. Thereby, almost all of the raw material components can be recovered, and the particle size control of the obtained aggregated particles can be easily performed.

  In addition, a means for simultaneously aggregating and drying the raw material component particles by supplying a finely-treated slurry in a dry air stream is also preferably used. Furthermore, the raw material components can be coagulated and dried simultaneously by spray drying the refined slurry, which is suitable for the present invention.

  The raw material component particles thus agglomerated are preferably such that the D50 of the raw material component aggregated particles is 30 μm or less, preferably 20 μm or less, and D90 is 100 μm or less, preferably 60 μm or less. If D50 is larger than 30 μm, cycle characteristics and load characteristics are impaired. On the other hand, if D90 is larger than 100 μm, the synthesis reaction cannot be achieved, and the battery characteristics are greatly impaired.

  Further, if the aggregated particles of the raw material component are excessively small, excessive sintering of the primary particles and the secondary particles proceeds, so that it is preferable that D50 is 2 μm or more and D90 is 10 μm or more.

In the present invention, the aggregated particles of the raw material components are then heat-treated at 300 to 1150 ° C., preferably 350 to 1100 ° C., thereby synthesizing LiFePO ₄ . If the heat treatment temperature is lower than 300 ° C., it is difficult to achieve the synthesis reaction.

The processing time in the heat treatment varies greatly depending on the degree of refinement of each raw material component, the uniformity of mixing, the heating system, the processing temperature, and the like. In the present invention, the heat treatment is preferably performed in the range of several seconds to 48 hours. The synthesis reaction of LiFePO ₄ can also be achieved on the order of seconds. Further, the processing time can be shortened, but this does not improve the characteristics, and it is difficult to improve the characteristics even if the heat treatment is continued for more than 48 hours.

The above heat treatment of the present invention are those which proceed essentially trivalent synthesis reaction of LiFePO ₄ of reduced to olivine structure iron compound bivalent, the treatment atmosphere oxygen concentration control also of LiFePO ₄ Affects the synthesis reaction. In the present invention, since the carbon-containing compound in the raw material component functions as a reducing agent in the vicinity of the raw material iron compound, it is possible to complete the heat treatment even in an air atmosphere. In particular, when using a method capable of achieving the reaction with a short heat treatment, or when the ratio of the atmosphere gas in the heat treatment atmosphere is small relative to the raw material, there is no problem even if the atmosphere is left as it is.

  The heat treatment can also be performed in an inert atmosphere or in an inert air stream. By inactivating the heat treatment atmosphere, there are less restrictions on facilities and processing conditions, and various heat treatment methods can be employed. Further, in the present invention, it is possible to perform heat treatment in a reducing gas atmosphere such as hydrogen or carbon monoxide. In order to prevent excessive reduction of the raw material, it is effective to dilute the reducing gas with an inert gas such as nitrogen.

In the present invention, LiFePO ₄ can also be synthesized directly from a slurry of raw material components using a spray pyrolysis technique. By supplying the refined slurry while spraying it into the furnace adjusted to the heat treatment temperature of the present invention, the aggregation, drying, and heat treatment of the raw material components proceed almost simultaneously, and LiFePO ₄ is made in one step. It is preferable because it can be synthesized. The atmosphere control during spray pyrolysis can be adjusted by using compressed air, inert gas or reducing gas for spraying. Furthermore, it is also possible to use a technique of using a combustion furnace and spraying slurry in a reducing flame to advance the reduction reaction.

  The olivine-type lithium iron composite oxide produced in the present invention can be blended with other substances for the purpose of improving powder characteristics and electrochemical characteristics. For example, zinc, aluminum, sulfur, indium, cadmium, gallium, calcium, chromium, cobalt, zirconium, tin, strontium, cerium, tungsten, tantalum, titanium, copper, thorium, lead, niobium, nickel, vanadium, barium, bismuth, Fluorine, beryllium, boron, magnesium, manganese, molybdenum and the like are preferably used. These are used alone or in the form of various compounds, and are used alone or in combination of two or more thereof, and are blended in and / or on the surface of the lithium iron composite oxide of the present invention.

  These auxiliary substances can be used alone or in the form of oxides, hydroxides, peroxides, salts, alkoxides, acylates, chelates, etc., powders, liquids, solutions, and dispersions. . These substances may be added to the raw material components in the production process of the above-described lithium iron composite oxide, or may be added to the lithium iron composite oxide after the lithium iron composite oxide is synthesized. it can.

  The lithium iron composite oxide having an olivine structure produced by the method of the present invention is effectively used as a positive electrode active material for battery electrodes and secondary battery electrodes. In particular, it is extremely effective as a positive electrode active material for non-aqueous electrolyte secondary batteries such as lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries, including lithium primary batteries. The non-aqueous electrolyte secondary battery using the electrode active material of the present invention has a large charge / discharge capacity and high energy density, and exhibits excellent cycle characteristics, high load characteristics, low temperature characteristics, high temperature characteristics, and safety. In particular, the lithium iron composite oxide of the present invention, which has both high energy density and high load characteristics that can be powered, and reliable safety, is effective as a positive electrode active material for medium- and large-sized secondary batteries and in-vehicle secondary batteries. Applicable.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. In the examples, the capacity retention rate was determined by the following formula.
Capacity retention rate (%) = 100th cycle discharge capacity / initial discharge capacity
× 100

Example 1
Iron oxide having an iron content of 69.4% by weight obtained by agglomerating needle-like crystals having an average particle length in the major axis direction of 1.0 μm was obtained. 79.8 g of this iron oxide, 115.0 g of ammonium dihydrogen phosphate, 36.9 g of lithium carbonate, and 6.1 g of carbon black were weighed in a stainless steel vat, and pure water was added to make 3 kg. While stirring this, a raw material component slurry having a D50 of 0.64 μm and a D90 of 0.99 μm was obtained through a homogenizer comprising a stator and a rotor rotating at high speed. As a result of supplying and drying this slurry together with a large amount of hot air into a cutter rotating at high speed, a raw material component powder having D50 of 4.37 μm and D90 of 10.1 μm was obtained.

This raw material component powder was heat-treated at 600 ° C. in a nitrogen gas stream at 0.8 liter / min for 24 hours to obtain 138.1 g of LiFePO ₄ (A) having a D50 of 5.10 μm and a D90 of 11.1 μm. . 1, 2, and 3 are an X-ray diffraction pattern, a particle size distribution, and an SEM observation photograph, respectively. From the figure, it can be seen that it is LiFePO ₄ with fine crystal grains and good crystallinity.

  20 parts by weight of N-methylpyrrolidone was added to 90 parts by weight of (A), 5 parts by weight of carbon, and 5 parts by weight of polyvinylidene fluoride and kneaded to obtain a paste. This paste was applied to an aluminum foil, dried, rolled and punched to a predetermined size to obtain a positive electrode plate. Next, 95 parts by weight of carbon and 5 parts by weight of polyvinylidene fluoride were mixed with 20 parts by weight of N-methylpyrrolidone to obtain a paste. This paste was applied to a copper foil, dried, rolled and punched to a predetermined size to obtain a negative electrode plate.

Lead wires were attached to the positive electrode plate and the negative electrode plate obtained in this way, respectively, and stored in a stainless steel cell case via a polyolefin-based separator. Subsequently, an electrolyte solution in which 1 mol / liter of lithium hexafluorophosphate was dissolved in a mixed solution of ethylene carbonate and diethylene carbonate was injected to form a model cell. Battery characteristics were measured using a charge / discharge measuring device at a charge current of 0.6 mA / cm ² at 25 ° C. until the battery voltage reached 4.3 V, and then a discharge current of 2.0 mA / cm ² (corresponding to a 1.25 C rate). Charging / discharging was repeated until the voltage reached 2.0 V, and the initial discharge capacity and the discharge capacity after 100 cycles were determined and evaluated. The results are shown in Table 1.

Example 2
A homogenizer treatment was carried out in the same manner as in Example 1 except that 50 g of a polystyrene resin emulsion having a resin content of 17.3% by weight was used instead of 6.1 g of carbon black. As a result, D50 was 0.68 μm and D90 was 0.98 μm. The raw material component slurry was obtained. When this slurry was dried under reduced pressure at 92 ° C. with high-speed stirring, raw material component powders having D50 of 5.41 μm and D90 of 15.5 μm were obtained. This raw material component powder was heat-treated at 500 ° C. in a nitrogen gas stream at 0.8 liter / min for 24 hours to obtain 152.8 g of LiFePO ₄ (B) having a D50 of 5.56 μm and a D90 of 19.2 μm.
Table 1 shows the results of creating a model cell in the same manner as in Example 1 and examining the charge / discharge characteristics except that (B) was used instead of (A).

Example 3
Iron oxide having an iron content of 69.5% by weight and an average aggregated particle diameter of 2.1 μm in which sub-micron-order pseudospherical particles are aggregated was obtained. 79.8 g of this iron oxide, 115.0 g of ammonium dihydrogen phosphate, and 36.9 g of lithium carbonate were weighed in a stainless steel vat, and pure water was added to make 3 kg. This was bead milled for 1 hour using 0.5 mm zirconia balls, then 90 g of a 13.3% by weight aqueous polyvinyl alcohol solution was added and stirred and mixed to obtain a raw material having a D50 of 0.72 μm and a D90 of 1.29 μm. A component slurry was obtained. As a result of sending this slurry into a large amount of hot air flowing at high speed and drying, a raw material component powder having D50 of 5.17 μm and D90 of 12.2 μm was obtained. This raw material component powder was heat-treated in a nitrogen gas stream at 0.8 liter / min for 5 hours at 700 ° C. to obtain 134.6 g of LiFePO ₄ (C) having a D50 of 6.21 μm and a D90 of 20.8 μm.
Table 1 shows the results of creating a model cell in the same manner as in Example 1 and examining the charge / discharge characteristics except that (C) was used instead of (A).

Example 4
79.8 g of iron oxide of Example 1, 115.0 g of ammonium dihydrogen phosphate, 36.9 g of lithium carbonate, and 6.1 g of carbon black were weighed in a stainless steel vat, and pure water was added to make 3 kg. When this was subjected to bead mill treatment in the same manner as in Example 3, a raw material component slurry having D50 of 0.49 μm and D90 of 0.83 μm was obtained. When this slurry was spray-dried, raw material component powders having D50 of 4.59 μm and D90 of 9.86 μm were obtained. This raw material component powder was heat-treated at 650 ° C. for 12 hours in a nitrogen gas stream of 0.8 liter / min to obtain 129.8 g of LiFePO ₄ (D) having a D50 of 5.27 μm and a D90 of 10.4 μm.
Table 1 shows the results of creating a model cell and examining the charge / discharge characteristics in the same manner as in Example 1 except that (D) was used instead of (A).

Example 5
Raw material component slurry having a D50 of 0.64 μm and a D90 of 1.00 μm, as in Example 4, except that instead of the bead mill treatment, the slurry was discharged from two opposing nozzles at high pressure and collided with each other. Got. This slurry was heat-treated in a furnace set at 875 ° C. while spraying with nitrogen gas to obtain 115.2 g of LiFePO ₄ (E) having D50 of 10.6 μm and D90 of 23.2 μm.
Table 1 shows the results of preparing a model cell in the same manner as in Example 1 and examining the charge / discharge characteristics except that (E) was used instead of (A).

Example 6
When the raw material component slurry similar to that in Example 5 was spray-dried, raw material component powders having D50 of 8.03 μm and D90 of 13.5 μm were obtained. This raw material component powder was spread on an alumina tray, and then covered with an alumina plate, and heat treated at 600 ° C. for 2 minutes in an air atmosphere using a microwave furnace. LiFePO ₄ (D50: 8.15 μm, D90: 12.7 μm) F) 130.2 g was obtained.
Table 1 shows the results of creating a model cell in the same manner as in Example 1 and examining the charge / discharge characteristics except that (F) was used instead of (A).

Example 7
Raw material component slurry having a D50 of 0.68 μm and a D90 of 1.05 μm, as in Example 4, except that the slurry was passed through the gap between the disk rotating at high speed and the fixed disk instead of the bead mill process. Got. As a result of drying this slurry in the same manner as in Example 1, a raw material component powder having D50 of 5.44 μm and D90 of 10.8 μm was obtained. This raw material component powder was heat-treated using a rotary kiln while flowing nitrogen gas of 1.5 liters / minute to obtain 140.5 g of LiFePO ₄ (G) having a D50 of 5.58 μm and a D90 of 10.8 μm. At this time, the heat treatment applied to the raw material component powder was 10 minutes at 1085 ° C.
Table 1 shows the results of creating a model cell in the same manner as in Example 1 and examining the charge / discharge characteristics except that (G) was used instead of (A).

Example 8
Fe3O4 formed by agglomeration of pseudospherical primary particles having an average particle diameter of 0.6 μm was mixed with the iron oxide of Example 3 to prepare an iron oxide mixture having an iron content of 70.4% by weight.

In place of 79.8 g of the iron oxide of Example 1, 79.3 g of this iron oxide mixture was used in the same manner as in Example 4 except that 14.3 g of sucrose was used instead of 6.1 g of carbon black. A raw material component slurry having 0.57 μm and D90 of 1.01 μm was obtained, and further, raw material component powder having D50 of 4.96 μm and D90 of 11.3 μm was obtained. This raw material component powder was heat-treated at 450 ° C. for 30 hours in a nitrogen gas stream of 0.8 liter / min to obtain 130.3 g of LiFePO ₄ (H) having a D50 of 5.04 μm and a D90 of 11.0 μm.
Table 1 shows the result of examining the charge / discharge characteristics by creating a model cell in the same manner as in Example 1 except that (H) was used instead of (A).

Example 9
Agglomerated FeOOH having an average particle length in the long axis direction of 0.8 μm was obtained. This FeOOH and the iron oxide of Example 1 were mixed to prepare an iron oxide mixture having an Fe content of 63.9% by weight.

A raw material component slurry having a D50 of 0.45 μm and a D90 of 0.75 μm was obtained in the same manner as in Example 4 except that 87.4 g of this iron oxide mixture was used instead of 79.8 g of the iron oxide of Example 1. Furthermore, raw material component powders having D50 of 4.63 μm and D90 of 9.57 μm were obtained. This raw material component powder was heat-treated in a nitrogen gas stream at 0.8 liter / min for 24 hours at 550 ° C. to obtain 127.4 g of LiFePO ₄ (J) having a D50 of 4.85 μm and a D90 of 9.88 μm.
Table 1 shows the results of creating a model cell and examining the charge / discharge characteristics in the same manner as in Example 1 except that (J) was used instead of (A).

Example 10
79.8 g of ultrafine particle iron oxide having an average particle size of 0.03 μm, 115.0 g of ammonium dihydrogen phosphate, 36.9 g of lithium carbonate, and 6.1 g of carbon black were mixed in a mortar and then heat treated in the same manner as in Example 4. , 154.0 g of LiFePO ₄ (K) having a D50 of 29.8 μm and a D90 of 97.4 μm was obtained.
Table 1 shows the results of creating a model cell and examining the charge / discharge characteristics in the same manner as in Example 1 except that (K) was used instead of (A).

Example 11
200 g of the iron oxide of Example 1 was weighed into a stainless steel vat, and pure water was added to make 3 kg. This was subjected to bead mill treatment in the same manner as in Example 4 to obtain an iron oxide slurry having D50 of 0.40 μm and D90 of 0.66 μm. When this slurry was spray-dried, an iron oxide powder having a D50 of 5.43 μm and a D90 of 10.7 μm was obtained.

79.8 g of this iron oxide powder, 115.0 g of ammonium dihydrogen phosphate, 36.9 g of lithium carbonate, and 6.1 g of carbon black were mixed in a mortar to obtain a raw material component powder. This was heat-treated in the same manner as in Example 4 to obtain 152.8 g of LiFePO ₄ (L) having a D50 of 30.7 μm and a D90 of 107.5 μm.
Table 1 shows the results of creating a model cell and examining the charge / discharge characteristics in the same manner as in Example 1 except that (L) was used instead of (A).

Example 12
50 g of (L) was ball milled with an ethanol medium to obtain 48.3 g of LiFePO ₄ (M) having a D50 of 6.72 μm and a D90 of 31.1 μm.
Table 1 shows the results of creating a model cell in the same manner as in Example 1 and examining the charge / discharge characteristics except that (M) was used instead of (A).

Example 13
In the same manner as in Example 4, a raw material component slurry was obtained. This slurry was dried under reduced pressure with an evaporator and pulverized with a cutter mill to obtain a raw material component powder having a D50 of 12.5 μm and a D90 of 40.9 μm. This was heat-treated in the same manner as in Example 4 to obtain 121.5 g of LiFePO ₄ (N) having a D50 of 25.9 μm and a D90 of 50.6 μm.
Table 1 shows the results of creating a model cell in the same manner as in Example 1 and examining the charge / discharge characteristics except that (N) was used instead of (A).

Example 14
130.5 g of LiFePO ₄ (P) having a D50 of 4.47 μm and a D90 of 9.81 μm was obtained in the same manner as in Example 4 except that the heat treatment which was 12 hours at 650 ° C. was replaced with 48 hours at 250 ° C. It was.
Except for using (P) instead of (A), a model cell was prepared in the same manner as in Example 1 and the charge / discharge characteristics were examined, but charge / discharge could not be performed.

Example 15
Except that the heat treatment, which was 12 hours at 650 ° C., was replaced with 12 hours at 1250 ° C., LiFePO ₄ (Q) 123.6 g having a D50 of 59.2 μm and a D90 of 257 μm was obtained in the same manner as in Example 4.
Table 1 shows the results of creating a model cell in the same manner as in Example 1 and examining the charge / discharge characteristics except that (Q) was used instead of (A).

X-ray diffraction pattern diagram of LiFePO ₄ (A) prepared in Example 1. 2 is a particle size distribution diagram of LiFePO ₄ (A) prepared in Example 1, its raw material component slurry, and raw material component powder. FIG. A scanning electron microscope (SEM) observation photograph of LiFePO ₄ (A) prepared in Example 1.

Claims (7)

A raw material component containing an iron compound, a lithium compound, a phosphate compound, and a carbon-containing compound containing iron having a valence of 3 is refined, and the 50% volume cumulative diameter (D50) of the refined particles is 2 μm or less. And the 90% volume cumulative diameter (D90) is reduced to 10 μm or less, and then the fine particles are agglomerated, and the 50% volume cumulative diameter (D50) of the aggregated particles is 30 μm or less and 90% volume cumulative. A method for producing a lithium iron composite oxide, wherein the diameter (D90) is set to 100 μm or less and heat treatment is performed at 300 to 1150 ° C. to obtain LiFePO ₄ having an olivine structure.   The manufacturing method according to claim 1, wherein the carbon-containing compound exhibits a liquid state or a solid state at a normal temperature with a carbon content of 35 wt% or more.   The manufacturing method of Claim 1 or 2 with which the refinement | miniaturization process of the said raw material component is given to the slurry formed from the said raw material component and a dispersion medium.   The production method according to claim 1, wherein the aggregation process of the fine particles is performed by separating and collecting the raw material components from the slurry after the refinement process.   The manufacturing method according to any one of claims 1 to 4, wherein the heat treatment is performed in air, in an inert atmosphere, or in a reducing atmosphere.   The manufacturing method according to any one of claims 1 to 3, wherein the agglomeration treatment and heat treatment of the fine particles are performed by a spray pyrolysis method in which the slurry after the refinement treatment is sprayed into a heating furnace.   The electrode active material for nonaqueous electrolyte secondary batteries containing the lithium iron complex oxide obtained by the manufacturing method in any one of Claims 1-6.

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