JP4804045B2 - Method for producing lithium iron composite oxide - Google Patents

Description

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

  High power and high energy density lithium ion secondary batteries have been recognized as energy sources for mobile devices and have been rapidly replaced by conventional alkaline secondary batteries and nickel metal hydride batteries. On the other hand, medium- and large-sized lithium-ion secondary batteries are expected to be one solution that can mitigate the seriousness of environmental and energy problems. However, safety concerns have not been resolved, and they are still in practical use. It has not reached.

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 state 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. Therefore, lithium insertion and desorption from the crystal is difficult to proceed, and diffusion in the crystal is slow, so that charging and discharging cannot be smoothly repeated. Further, since LiFePO ₄ is a divalent iron compound having an iron valence of 2, the divalent iron compound is easily used as an iron source. The divalent iron compounds that are easy to handle are limited and are not versatile and expensive.

As one countermeasure for overcoming the above problems, it has been proposed to atomize 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 on 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 has only a low characteristic of 88 mAh / g even though iron oxalate, a divalent iron compound, is used as the iron source. . This is considered to be because the battery performance could not be sufficiently obtained due to the fine particles which are difficult to handle.

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 describes a reducing agent for reducing easily a readily available and inexpensive trivalent iron compound Fe ₂ O ₃ as an iron source and a carbonaceous material from trivalent iron to divalent iron. 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, these are based on a synthesis method using a divalent iron compound as a raw material, and LiFePO ₄ can be stably abundantly cheaply. From the point of trying to supply, it is not practical.

On the other hand, iron oxide (such as Fe ₂ O ₃ ) is advantageous as an iron source that is easy to handle, inexpensive, 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 problems of the prior art, and uses a general-purpose and inexpensive trivalent iron compound as a raw material to carry out a synthesis reaction while maintaining the optimal particle shape for battery characteristics expression. Novel production method of iron composite oxide, and electrode for nonaqueous electrolyte secondary battery having high discharge capacity and excellent charge / discharge characteristics, comprising lithium iron composite oxide having olivine structure produced by such method The purpose is to provide active materials.

As a result of diligent research, the present inventor has reached the present invention characterized by the following.
1. A method for producing a lithium iron composite oxide represented by LiFePO ₄ having an olivine structure, wherein at least a valence of 3 among an iron compound, a carbon-containing compound, a lithium compound, and a phosphorus compound containing trivalent iron the average of the raw material component containing iron compounds and carbon-containing compounds of iron, a slurry containing a dispersion medium, under SL (1), the condition for satisfying the (2) and (3) (where, x is an iron compound The primary particle size (μm), y is the particle size (mm) of the beads used in the bead mill) is refined by a bead mill, and the resulting refined particles are agglomerated and the above slurry is LiFePO _4. In the case where the stoichiometric amount of the lithium compound and / or phosphorus compound necessary for the synthesis is not included, a mixture obtained by adding the lithium compound and / or phosphorus compound to the aggregated particles is 300 to Method for producing a lithium-iron composite oxide, characterized by a heat treatment at 0.99 ° C..
(1) When x ≦ 0.6, y ≦ 10.0
(2) When 0.6 <x ≦ 2.0,
y ≦ −0.342x ³ + 1.768x ² −3.158x + 2.322
(3) When 2.0 <x ≦ 10.0, y ≦ 0.35
2. 2. The method for producing a lithium iron composite oxide according to 1 above, wherein the raw material component in the slurry contains a stoichiometric amount of a lithium compound and / or a phosphorus compound necessary for the synthesis of LiFePO ₄ .
3. 3. The production method according to 1 or 2 above, wherein the dispersion medium is water or a medium containing water.
4). 4. The production method according to any one of 1 to 3 above, wherein the carbon-containing compound has a carbon content of 35% by weight or more and is in a liquid state or a solid state at normal temperature.
5. 5. The production method according to any one of 1 to 4 above, wherein the agglomeration treatment is performed by separating and collecting the refined raw material components from the slurry after the refinement treatment in the bead mill.
6). 6. The production method according to any one of 1 to 5, wherein the heat treatment is performed in the air, in an inert atmosphere, or in a reducing atmosphere.
7). The manufacturing method according to any one of 1 to 6 above, wherein the aggregation treatment and the heat treatment are performed by spraying the slurry after the refinement treatment in the bead mill into a heating furnace.
8). The electrode active material for nonaqueous electrolyte secondary batteries containing the lithium iron complex oxide obtained by the manufacturing method of any one of said 1-7.

According to the production method of the present invention, a slurry composed of a raw material component containing a trivalent iron compound and a carbon-containing compound and a dispersion medium is subjected to a refinement treatment with a bead mill to uniformly disperse both originally lacking affinity. Can be contacted. As a result, the carbon in the carbon compound functions to efficiently and quantitatively reduce the trivalent iron adjacent to the divalent iron during the heat treatment and prevent undesirable side reactions such as reoxidation. Further, when a raw material component having a pre-controlled particle size distribution is used as the raw material component in the slurry, the agglomerated particles obtained through the slurry preparation, the bead mill treatment, and the agglomeration treatment are heat-treated to produce LiFePO _4. Even after becoming, it acts to maintain many characteristics of the particle size distribution before the heat treatment, and functions to prevent excessive sintering of the primary particles and the secondary particles.

Thus, the olivine-type lithium iron composite oxide represented by LiFePO ₄ obtained by the production method of the present invention is composed of aggregated particles having a controlled particle size in which fine primary particles are gathered. A carbonaceous particle layer derived from a carbon-containing compound is provided on the surface. Reflecting such a form, the non-aqueous electrolyte secondary battery using the lithium iron composite oxide obtained in the present invention as a positive electrode active material exhibits excellent battery characteristics because the interfacial charge transfer reaction proceeds smoothly. To do. In other words, a large current can be passed to obtain power, and a highly reliable safety and a long life can be achieved.

  On the other hand, in the conventional method for producing lithium iron composite oxide, even if each constituent raw material component can be miniaturized, a component having poor affinity and a large difference in specific gravity, particularly between an iron compound and a carbon-containing compound. Thus, the micro-mixing cannot be sufficiently performed, resulting in leaving unreacted portions and reoxidized portions in the manufactured lithium iron composite oxide. In addition, primary particles and fine secondary particles that are independent during heat treatment serve as a binder, and large primary particles and agglomerated particles are frequently generated. It is presumed that such a defect causes deterioration of cycle characteristics and load characteristics when a conventional lithium iron composite oxide is used as an electrode active material for a non-aqueous electrolyte secondary battery.

The present invention can produce a lithium iron composite oxide represented by LiFePO ₄ using a trivalent iron compound as a raw material component, and the obtained lithium iron composite oxide can exhibit high performance battery characteristics. There is a feature. In the present invention, the iron compound that can be used as a raw material component can be selected from a wide range of iron compounds as long as it contains trivalent iron. Of these, iron oxide containing trivalent iron is preferably used because it is easy to obtain and handle and is inexpensive. As iron oxide, not only Fe ₂ O ₃ but also Fe ₃ O ₄ or FeOOH can be suitably used. Acicular iron oxide having strong anisotropy is also preferably used.

  Any lithium compound can be used as long as it contains lithium as the lithium compound used in the production of the lithium iron composite oxide of the present invention. However, from the viewpoint of easy handling, lithium oxides, hydroxides, salts, or a mixture of two or more of these compounds are preferred.

  The phosphorus compound used for production of the lithium iron composite oxide of the present invention is not limited at all. Among them, phosphoric acid, iron phosphate, lithium phosphate, ammonium phosphate, or phosphate esters such as triethyl phosphate and 2-ethylhexyldiphenyl phosphate can be exemplified because they are easily available and easy to handle. Any of these can be preferably used.

  The carbon-containing compound used in the present invention can also be selected from a wide range of compounds containing carbon. Among them, a compound having a carbon content of preferably 35% by weight or more and being in a liquid state or a solid state at normal temperature is preferable because the reduction reaction from trivalent iron to divalent iron efficiently proceeds. It is. 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 and polystyrene Examples thereof include resins and plastics such as polyacrylonitrile, cellulose, epoxy resin and phenol resin, and carbonaceous materials such as acetylene black, carbon black and graphite. Further, 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 of the lithium iron composite oxide is refined by a bead mill. The raw material component to be refined needs to contain at least an iron compound containing trivalent iron and a carbon-containing compound. However, in addition to this, it is preferable that a part, preferably all of the lithium compound and / or phosphorus compound, stoichiometrically necessary for the production of the lithium iron composite oxide represented by LiFePO ₄ is included. In this case, it is preferable because homogeneous mixing of the raw material components can be performed simultaneously with the refinement of the raw material components.

  The refinement treatment by the bead mill of the present invention is performed in the form of a slurry prepared by adding a dispersion medium to a raw material component containing at least a trivalent iron compound and a carbon-containing compound. In the bead mill, not only the raw material components are miniaturized, but also an iron compound and a carbon-containing compound that have a poor affinity for each other and are not easily adapted to each other are brought into strong contact with each other, and are placed in close proximity to each other and uniformly dispersed. In the present invention, each raw material component including a trivalent iron compound and a carbon-containing compound contained in a slurry to be used in a bead mill is preferably used by adjusting the average diameter of primary particles thereof to 10 μm or less. In particular, the trivalent iron compound preferably has an average primary particle diameter D50 of 10 μm or less, particularly 6 μm or less. If the average diameter of the primary particles is larger than 10 μm, the bead mill conditions suitable for the present invention are not preferable because it takes a long time for miniaturization or insufficient miniaturization.

  In addition, the primary particle of the raw material component in this invention is a primary particle confirmed by SEM observation, and does not point out the primary particle on crystallography.

  As beads used in the bead mill, various materials are used as long as they do not interfere with the production reaction of the lithium iron composite oxide, and zirconia is preferably used. The particle diameter of the beads is preferably 10 mm or less, particularly preferably 5 mm or less. As the dispersion medium of the slurry, any of water, a water-containing medium, hydrocarbon, or halogenated carbon can be used. Among these, water or a water-containing medium is preferable because it is easy to handle and inexpensive.

In the micronization process using the bead mill of the present invention, conditions such as the bead filling amount and the processing temperature are performed under the normal conditions of the bead mill. However, in the treatment with the bead mill of the present invention, when the average primary particle diameter of the trivalent iron compound is x (μm) and the particle diameter of the beads used in the bead mill is y (mm), in FIG. When the axis is the primary particle diameter (μm) of the iron compound and the y-axis is the particle diameter (mm) of the beads used in the bead mill, the following conditions (1), (2) and (3) are satisfied. It is necessary to carry out a miniaturization process. Here, the average primary particle diameter of the trivalent iron compound is obtained by SEM. When the iron compound particles are not spherical, for example, in the case of needle-like, cylindrical, disk-like particles, The major axis, that is, the larger average size.

(1) When x ≦ 0.6, y ≦ 10.0
(2) When 0.6 <x ≦ 2.0,
y ≦ −0.342x ³ + 1.768x ² -3.158x + 2.322
(3) When 2.0 <x ≦ 10.0, y ≦ 0.35

In the above range, when the refinement treatment is performed by a bead mill, strong interaction between these raw material components is performed together with the refinement of the trivalent iron compound particles and the carbon-containing compound particles. Thus, a lithium iron composite represented by LiFePO ₄ having a desired particle size and having a desired particle size that can express high-performance battery characteristics from a trivalent iron compound iron source such as iron oxide, which has been difficult in the past. Enables stable and efficient production of oxides.

The refinement treatment by the bead mill according to the present invention can be carried out more effectively when implemented under the conditions satisfying the following (1), (2) and (3) in FIG. An olivine type lithium iron composite oxide having excellent characteristics can be obtained.

(1) When x ≦ 0.6, y ≦ 5.0
(2) When 0.6 <x ≦ 2.0,
y ≦ −0.342x ³ + 1.768x ² -3.158x + 2.322
(3) When 2.0 <x ≦ 10.0, y ≦ 0.35

  Thus, in the present invention, the average particle diameter D50 of raw material components such as iron compound particles of trivalent iron and carbon-containing compound particles in the slurry after being refined by a bead mill is 1 μm or less. preferable. In addition, as a raw material component, it is also possible to use a raw material component in which D50 is smaller than 1 μm. In this case, raw material components other than the iron compound containing trivalent iron and the carbon-containing compound can be mixed with other raw material components without being subjected to bead mill treatment, and subjected to the next heat treatment step. However, the iron compound and the carbon-containing compound containing trivalent iron may be used in any case where the average particle diameter D50 is smaller than 1 μm, or in the case where each of them is preliminarily refined by a bead mill. It is preferable to mix them into a slurry and to subject the slurry to a bead mill treatment.

  In the treatment of the slurry containing the raw material component by the bead mill, the raw material compounds constituting the raw material component can be individually processed, divided into two or more groups, or collectively processed at once. When processing at once, it is possible to complete the homogenous mixing of the raw materials simultaneously with the miniaturization of the raw material compounds.

  In the present invention, the refined raw material component particles are then agglomerated. 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. For example, it is preferable to use a method in which the bead-milled slurry is placed under heating and / or reduced pressure, preferably while stirring and applying a shearing force, to agglomerate raw material components, remove the medium, 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.

  Further, a means for simultaneously aggregating and drying raw material component particles by supplying a slurry refined by a bead mill in a dry air stream is also preferably used. Furthermore, the raw material components can be coagulated and dried simultaneously by spray drying the slurry treated in the bead mill, which is suitable for the present invention. The agglomerated particles of the raw material component thus agglomerated preferably have an average particle diameter D50 of 20 μm or less.

The agglomerated particles of the raw material components thus obtained are then heat treated when the agglomerated particles contain stoichiometric amounts of lithium and phosphorus compounds necessary for the synthesis of LiFePO ₄ . On the other hand, when the agglomerated particles do not contain a stoichiometric amount of lithium compound and / or phosphorus compound necessary for the synthesis of LiFePO ₄ , lithium compound and / or phosphorus compound particles are added thereto. In this case, the amount of the lithium compound and / or phosphorus compound particles added is made to be the stoichiometric amount necessary for the synthesis of LiFePO ₄ by the heat treatment of the aggregated particles after the addition. The average particle size of the added lithium compound and / or phosphorus compound is preferably 10 μm or less, particularly 6 μm or less. These particles can be added by a dry method or a wet method.

In the present invention, the raw material component aggregated particles are then heat-treated at 300 to 1150 ° C, preferably 350 to 1100 ° C. Through the heat treatment, a lithium iron composite oxide represented by LiFePO ₄ is synthesized. If the heat treatment temperature is lower than 300 ° C., the synthesis reaction does not proceed easily. If the heat treatment temperature is higher than 1150 ° C., undesired reaction products are frequently generated, making it difficult to repair. The heat treatment time varies greatly depending on the degree of refinement of the raw material components to be subjected to the heat treatment, the uniformity of mixing, the treatment system, the temperature, and the like. In the present invention, the heat treatment is preferably performed in the range of several seconds to 48 hours. Although heat treatment outside the range of the treatment time is possible, even if the heat treatment is less than the second order and exceeds 48 hours, it is difficult to improve the characteristics.

Since the heat treatment in the present invention essentially reduces the trivalent iron compound to the divalent iron compound and proceeds the synthesis reaction of the olivine type structure LiFePO ₄ , the oxygen concentration in the treatment atmosphere is originally LiFePO ₄ . Affects the synthesis reaction. However, in the present invention, the carbon component compound and iron compound that function as a reducing agent are present in the vicinity of the raw material components by the above-described bead mill treatment and agglomeration treatment, so that the heat treatment can be completed even in the atmosphere. Is possible. Further, there is no problem even when a method for completing the reaction with a short heat treatment is used or when the ratio of the atmospheric gas in the heat treatment atmosphere is small with respect to the raw material.

  The heat treatment can also be performed in an inert atmosphere or 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 components, it is also effective to dilute the reducing gas with an inert gas such as nitrogen.

In the present invention, LiFePO ₄ can also be directly synthesized from a slurry of raw material components using a spray pyrolysis technique. In the present invention, the slurry subjected to the bead mill treatment is supplied while being sprayed into a furnace adjusted to an appropriate heat treatment temperature, whereby the agglomeration treatment, drying, and heat treatment are performed in one step, and LiFePO ₄ is allowed to flow. 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.

  For the purpose of improving powder characteristics and electrochemical characteristics, the olivine-type lithium iron composite oxide produced in the present invention is blended with substances other than the aforementioned iron compound, lithium compound, phosphate compound and carbon-containing compound. can do. 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, etc., powders of these simple substances or various compounds (for example, oxides, hydroxides, peroxides, salts, alkoxides, acylates, chelates, etc.) It can be suitably used in the form of a liquid, solution, dispersion, etc., alone or in combination of two or more. They are blended in and / or on the surface of the lithium iron composite oxide of the present invention.

  These materials may be used as a raw material component or a further raw material component in the above-described production process of the lithium iron composite oxide, or after the lithium iron composite oxide is synthesized, It can also be added.

  The lithium iron composite oxide having an olivine structure obtained by the production 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 nonaqueous electrolyte secondary battery using the electrode active material of the present invention has a large charge / discharge capacity and a 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 obtained by the production method of the present invention that can achieve both high energy density and high load characteristics that can be powered and highly reliable safety is used as a positive electrode for medium- and large-sized secondary batteries and in-vehicle secondary batteries. It can be effectively applied as an active material.

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 maintenance ratio (%) = 100th cycle discharge capacity / initial discharge capacity × 100

Example 1
An agglomerated needle-like crystal having a particle size of 1.0 μm in the major axis direction and a particle size of 0.3 μm in the minor axis direction and acicular iron oxide ( Fe 2 Fe) observed by SEM with an iron content of 69.2 wt% ₂ O ₃₎ of 322.8G, ammonium dihydrogen phosphate 460.1G, lithium carbonate 147.8 g, a 24.2g of carbon black (carbon content 95.7 wt%) was weighed into a stainless steel vat, further After 500 g of 2-propanol (IPA) was added and mixed, pure water was added to prepare 5 kg of slurry. This slurry was subjected to bead milling using zirconia beads having a diameter of 0.2 mm for 1 hour to obtain a slurry having a D50 of 0.18 μm. Next, this slurry was spray-dried to obtain a powder having a D50 of 7.36 μm.

This powder was heat-treated at 550 ° C. for 5 hours while flowing nitrogen gas containing 10 vol% of hydrogen gas at 0.8 liter / min to obtain 526 g of powder (A) having D50 of 8.03 μm. 2, 3 and 4 are X-ray diffraction patterns, particle size distributions, and SEM observation photographs of the powder (A). From the figure, it can be seen that the powder (A) is LiFePO ₄ with good crystallinity, in which fine primary particles are aggregated.

  20 parts by weight of N-methylpyrrolidone was added to 90 parts by weight of the powder (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 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
LiFePO ₄ powder (B) having a D50 of 4.87 μm was carried out in the same manner as in Example 1 except that 0.5 mm diameter zirconia beads were used instead of 0.2 mm diameter zirconia beads. 532 g was obtained.
A positive electrode plate was produced in the same manner as in Example 1 except that the powder (B) was used instead of the powder (A), and the charge / discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

Example 3 (comparative example)
LiFePO ₄ powder (C) having a D50 of 5.53 μm was carried out in the same manner as in Example 1 except that zirconia beads having a diameter of 1.0 mm were used instead of zirconia beads having a diameter of 0.2 mm. 535 g was obtained.
A positive electrode plate was produced in the same manner as in Example 1 except that the powder (c) was used instead of the powder (A), and the charge / discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

Example 4
From SEM, 323.8 g of pseudospherical iron oxide ( Fe ₂ O ₃ ) having an iron content of 69.0% by weight, which was observed to be aggregates of bulk crystals having an average particle size of 1.8 μm, was obtained by diphosphoric acid phosphate. 460.1 g of ammonium hydrogen, 147.8 g of lithium carbonate, and 24.2 g of carbon black were weighed into a stainless steel vat, and further 500 g of IPA was added and blended, and then pure water was added to prepare a 5 kg slurry. This slurry was subjected to bead milling for 3 hours using 0.3 mm zirconia beads to obtain a slurry having a D50 of 0.30 μm. Next, this slurry was spray-dried to obtain a powder having a D50 of 3.72 μm.
This powder was heat-treated in a nitrogen gas stream at 0.8 liter / min for 5 hours at 600 ° C. to obtain 541 g of LiFePO ₄ powder (D) having a D50 of 3.66 μm.
A positive electrode plate was produced in the same manner as in Example 1 except that the powder (D) was used instead of the powder (A), and the charge / discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

Example 5 (comparative example)
LiFePO ₄ powder (E) having a D50 of 4.48 μm was carried out in the same manner as in Example 4 except that 0.5 mm diameter zirconia beads were used instead of 0.2 mm diameter zirconia beads. 538 g was obtained.
A positive electrode plate was produced in the same manner as in Example 1 except that the powder (E) was used instead of the powder (A), and the charge / discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

Example 6
From SEM, it was observed that needle-like crystals having a particle diameter of 0.4 μm in the major axis direction and a particle diameter of 0.1 μm or less in the minor axis direction were aggregated. Acicular iron oxide having an iron content of 67.5 wt% ( Fe ₂ O ₃₎ of 330.9G, ammonium dihydrogen phosphate 460.1G, lithium carbonate 147.8 g, from the 24.2g of carbon black was weighed into a stainless steel vat, and further blend by adding IPA of 500g Pure water was added to prepare a 5 kg slurry. This slurry was subjected to bead mill treatment for 1 hour using 0.5 mm zirconia beads to obtain a slurry having a D50 of 0.23 μm. This slurry was spray-dried to obtain a powder having a D50 of 3.83 μm.
The obtained powder was heat-treated in a nitrogen gas stream at 0.8 liter / min for 5 hours at 600 ° C. to obtain 524 g of LiFePO ₄ powder (F) having a D50 of 4.11 μm.
A positive electrode plate was produced in the same manner as in Example 1 except that the powder (F) was used instead of the powder (A), and the charge / discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

Example 7
By carrying out in the same manner as in Example 6 except that zirconia beads having a diameter of 5.0 mm were used instead of zirconia beads having a diameter of 0.5 mm, 537 g of LiFePO ₄ powder (G) having a D50 of 4.62 μm. Got.
A positive electrode plate was produced in the same manner as in Example 1 except that the powder (G) was used instead of the powder (A), and the charge / discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

Example 8
322.8 g of the same acicular iron oxide used in Example 1 and 24.2 g of carbon black were weighed into a stainless steel bat, and 500 g of IPA was added and blended. Then, 2 kg of slurry was prepared by adding pure water. This slurry was bead milled with 0.2 mm zirconia beads for 1 hour, then 3 kg of aqueous slurry containing 460.1 g of ammonium dihydrogen phosphate and 147.8 g of lithium carbonate was added. The beads were milled with 0 mm zirconia beads for 30 minutes. Next, this slurry was spray-dried to obtain a powder having a D50 of 8.95 μm. This powder was heat-treated in the same manner as in Example 1 to obtain 517 g of LiFePO ₄ powder (H) having a D50 of 11.7 μm.
A positive electrode plate was produced in the same manner as in Example 1 except that the powder (H) was used instead of the powder (A), and the charge / discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

Example 9
322.8 g of the same acicular iron oxide used in Example 1, 460.1 g of ammonium dihydrogen phosphate, 147.8 g of lithium carbonate, 57.2 g of sucrose (carbon content 42.1% by weight) were stainless steel. A 5 kg slurry was prepared by weighing in a vat and adding pure water. Using this slurry, the subsequent steps were processed in the same manner as in Example 1 to obtain 530 g of LiFePO ₄ powder (J) having a D50 of 10.4 μm.
A positive electrode plate was produced in the same manner as in Example 1 except that the powder (J) was used instead of the powder (A), and the charge / discharge characteristics were examined in the same manner as in Example 1. The results are shown in Table 1.

In the figure showing the preferred bead mill treatment conditions of the present invention, the horizontal axis represents the average primary particle diameter of the starting iron compound, and the vertical axis represents the particle diameter of beads used in the bead mill. In the figure, the conditions of Examples and Comparative Examples of the present invention are plotted. 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 (8)

A method for producing a lithium iron composite oxide represented by LiFePO ₄ having an olivine structure, wherein at least the valence of an iron compound, a carbon-containing compound, a lithium compound, and a phosphorus compound containing iron having a valence of 3 number 3 of the raw material component containing iron compounds and carbon-containing compounds of iron, a slurry containing a dispersion medium, under SL (1), (2) and (3) satisfies the condition (here, x is an iron compound The average primary particle diameter (μm), y is the particle diameter of the beads used in the bead mill (mm).) If that does not contain a stoichiometric amount of the lithium compounds required for the synthesis of LiFePO ₄ and / or phosphorus compounds, lithium compounds with respect to the agglomerated particles and / or mixture containing the phosphorus compound 3 Method for producing a lithium-iron composite oxide, characterized in that the heat treatment at 0 to 1,150 ° C..
(1) When x ≦ 0.6, y ≦ 10.0
(2) When 0.6 <x ≦ 2.0,
y ≦ −0.342x ³ + 1.768x ² −3.158x + 2.322
(3) When 2.0 <x ≦ 10.0, y ≦ 0.35 The method for producing a lithium iron composite oxide according to claim 1, wherein the raw material component in the slurry contains a stoichiometric amount of a lithium compound and / or a phosphorus compound necessary for the synthesis of LiFePO ₄ .   The production method according to claim 1 or 2, wherein the dispersion medium is water or a medium containing water.   The production method according to any one of claims 1 to 3, wherein the carbon-containing compound has a carbon content of 35% by weight or more and is in a liquid state or a solid state at room temperature.   The production method according to any one of claims 1 to 4, wherein the agglomeration treatment is performed by separating and collecting the refined raw material components from the slurry after the refinement treatment in the bead mill.   The manufacturing method according to any one of claims 1 to 5, wherein the heat treatment is performed in the air, in an inert atmosphere, or in a reducing atmosphere.   The production method according to any one of claims 1 to 6, wherein the agglomeration treatment and the heat treatment are performed by spraying the slurry after the refinement treatment with a bead mill into a heating furnace.   The electrode active material for nonaqueous electrolyte secondary batteries containing the lithium iron complex oxide obtained by the manufacturing method of any one of Claims 1-7.

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