JP2004259471A - Manufacturing method of positive electrode active material for lithium ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a positive electrode active material for a lithium ion battery capable of providing a battery with an excellent charge-discharge characteristic when used as the positive electrode active material of the lithium ion battery, and formed of a lithium phosphate compound having an olivine structure being a single phase and controlled in particle diameter with a large specific surface area. <P>SOLUTION: This manufacturing method of a positive electrode active material for a lithium ion battery is used for manufacturing the positive electrode active material for the lithium ion battery formed of a lithium phosphate compound having an olivine structure. The manufacturing method is characterized by spraying and decomposing a solution or suspension containing lithium, a metal other than lithium and phosphorus to bake the obtained thermally decomposed product. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a positive electrode active material for a lithium ion battery which can realize excellent battery characteristics at low cost.
[0002]
[Prior art]
In recent years, secondary batteries for use in portable electronic devices and hybrid vehicles have been developed. As typical secondary batteries, lead storage batteries, alkaline storage batteries, lithium ion batteries, and the like are known. Among these secondary batteries, lithium ion batteries are characterized by having high output and high energy density.
A lithium ion battery includes a positive electrode having an active material capable of reversibly inserting and removing lithium ions, a negative electrode, and a non-aqueous electrolyte. As the positive electrode active material used for this positive electrode, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ A composite oxide of lithium and a transition metal is used.
[0003]
By the way, these composite oxides use rare and expensive metals such as Co and Ni with a small amount of resources, or use LiMn. ₂ O ₄ As described above, there is a drawback that the life is short because Mn elutes during use.
In order to compensate for such a disadvantage, LiFePO using iron, which is an inexpensive metal, is used. ₄ Such positive electrode active materials of lithium metal phosphate compounds have been proposed (see Patent Documents 1 and 2). This compound is characterized by having an olivine structure as a crystal structure.
[0004]
As a method for producing such a positive electrode active material for a lithium ion battery of a lithium metal phosphate compound having an olivine structure, a solid-phase reaction method is used in the same manner as a conventional method for producing a composite oxide positive electrode material.
For example, LiFePO ₄ In the case of the above, lithium salts such as lithium carbonate, lithium nitrate and lithium hydroxide, divalent iron salts such as iron oxalate (II), iron (II) sulfate and iron (II) acetate, and phosphoric acid After mixing phosphates such as ammonium dihydrogen at a predetermined molar ratio, calcining is performed at a temperature of about 200 to 400 ° C. to thermally decompose various salts, and then firing at 400 to 800 ° C. Synthesized by
[0005]
However, since the driving force in this synthesis reaction is caused by mass transfer due to thermal diffusion in the solid, the mass transfer speed is very slow.The reason for the synthesis is how homogeneous each material is. It depends. Therefore, it is necessary to pulverize and mix the calcined thermal decomposition product well. Further, even when the pulverization and mixing are completed to a certain degree, even if the pulverization and mixing are performed to some extent, the mass transfer rate at the time of baking is very slow, so that baking for a very long time, usually 24 hours or more, is required. Further, in order to obtain a single phase of the target substance, pulverization and firing may be repeated several times.
[0006]
By the way, with respect to the lithium metal phosphate compound having the olivine structure as described above, even if the homogeneity of each material is improved by repeating pulverization and firing, the lithium ion using this compound as a positive electrode active material In the case of batteries, a satisfactory capacity has not been obtained.
As the cause, it is mentioned that a lithium metal phosphate compound having an olivine structure has a slow insertion / desorption rate of lithium ions. Therefore, in order to solve this drawback, the specific surface area of the lithium metal phosphate compound having an olivine structure, which is a part involved in the insertion and desorption of lithium ions, is increased so that the insertion and desorption of lithium ions per unit weight can be achieved. Proposals have been made to increase the charge-discharge capacity of a lithium ion battery by increasing the amount of separation reaction, and for that purpose, a method of adjusting the temperature conditions and the like in a solid-state reaction has been proposed (see Patent Document 3). .
[0007]
[Patent Document 1]
Japanese Patent Application Laid-Open No. Hei 9-171827
[Patent Document 2]
JP-A-9-134725
[Patent Document 3]
JP 2002-15735 A
[0008]
[Problems to be solved by the invention]
By the way, in order to increase the specific surface area of the lithium metal phosphate compound having an olivine structure, it is most common to reduce the particle diameter, and for that purpose, the reaction temperature at the time of synthesis in the solid-phase reaction method is increased. It is necessary to lower it or shorten the reaction time. However, in order to obtain a lithium metal phosphate compound having an olivine structure in a single phase by the ordinary solid-state reaction method as described above, it is necessary to calcine a sufficiently pulverized thermal decomposition product for a long time. In particular, in the synthesis of a lithium metal phosphate compound having an olivine structure, since there are three kinds of chemical species of lithium, a metal other than lithium, and phosphoric acid, high-temperature baking is required to obtain a single phase. Required.
[0009]
Further, when a conventional solid-phase reaction is used, there is a problem that it is difficult to obtain a single phase of a lithium metal phosphate compound having an olivine structure at a low temperature.
Difficult reasons include the non-uniformity of the pyrolysis products from calcination. Usually, the thermal decomposition by calcination is carried out by mixing salts of three chemical species of lithium, metal and phosphoric acid, putting them in a heat-resistant container such as a crucible, and heating to several hundred degrees in an electric furnace or the like. Since the thermal decomposition temperatures of the salts of the chemical species are different from each other, the chemical species that has been pyrolyzed first becomes highly active in the temperature rise process, and the aggregation of the chemical species progresses. There is a possibility that it will end.
Furthermore, unlike conventional composite oxides, phosphoric acid, which is uniquely contained in a lithium metal phosphate compound having an olivine structure, is condensed by heating to form polyphosphoric acid. There is a problem of promoting non-uniformity of the film.
[0010]
On the other hand, LiCoO ₂ The positive electrode active material of a composite oxide such as that described above simply requires two kinds of metals, such as lithium and cobalt, to react with oxygen in the atmosphere. Easy to obtain phase. As described above, it is difficult to obtain a single layer of the lithium metal phosphate compound having an olivine structure by firing at a low temperature, and it is also difficult to obtain a large specific surface area by reducing the particle diameter.
[0011]
The present invention has been made in order to solve the above problems, and when used as a positive electrode active material of a lithium ion battery, a battery having excellent charge / discharge characteristics can be obtained, and furthermore, it is a single phase, It is an object of the present invention to provide a method for producing a positive electrode active material for a lithium ion battery comprising a lithium metal phosphate compound having a controlled specific particle diameter and a large specific surface area and having an olivine structure.
[0012]
[Means for Solving the Problems]
The present inventors have conducted intensive studies and found that a lithium metal phosphate compound having an olivine structure that satisfies various conditions such as a single phase, control of particle size, and a large specific surface area requires lithium and lithium. It has been found that a solution or suspension containing a metal other than lithium and phosphorus is subjected to spray pyrolysis, and the obtained pyrolysis product may be fired.
[0013]
That is, the method for producing a positive electrode active material for a lithium ion battery of the present invention is a method for producing a positive electrode active material for a lithium ion battery comprising a lithium metal phosphate compound having an olivine structure, wherein lithium and a metal other than lithium are used. The solution or suspension containing phosphorus is spray pyrolyzed, and the obtained pyrolysis product is calcined.
[0014]
It is preferable that the temperature during the firing is lower than the temperature during the spray pyrolysis.
The lithium metal phosphate compound having the olivine structure has a general formula: Li _x A _y PO ₄ (However, A is at least one selected from Cr, Mn, Fe, Co, Ni, and Cu, and is preferably represented by 0 <x <2, 0 <y ≦ 1).
It is preferable to add an electronic conductive substance and / or a precursor of the electronic conductive substance to the solution or suspension.
The electron conductive substance is preferably a simple carbon, and the precursor of the electron conductive substance is preferably an organic compound.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the method for producing a positive electrode active material for a lithium ion battery of the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the invention unless otherwise specified.
[0016]
The method for producing a positive electrode active material for a lithium ion battery according to the present embodiment is a method for producing a positive electrode active material for a lithium ion battery comprising a lithium metal phosphate compound having an olivine structure, comprising lithium, a metal other than lithium, and phosphorus. And a suspension containing these are spray-pyrolyzed and the resulting pyrolysis product is calcined.
[0017]
The source of lithium, the source of metal other than lithium, and the source of phosphorus when preparing the above solution or suspension are not particularly limited, but they do not cause a reaction or agglomeration before spraying, and a uniform liquid phase. And a stable spray state must be obtained.
Here, the lithium source is preferably a lithium salt, the metal source other than lithium is preferably a salt of a metal other than lithium, and the phosphorus source is preferably phosphoric acid or phosphate.
[0018]
As the lithium salt, for example, LiCl, LiNO ₃ , LiOH, Li ₂ CO ₃ , LiCH ₃ COO or the like can be used.
The metal other than lithium is not particularly limited, but is preferably one or more selected from Cr, Mn, Fe, Co, Ni, and Cu.
As a salt of a metal other than lithium, for example, MnCl ₂ , Mn (CH ₃ COO) ₂ , FeCl ₂ , FeBr ₂ , Fe (CH ₃ COO) ₂ , Co (NO ₃ ) ₂ , Co (CH ₃ COO) ₂ , NiCl ₂ Etc. can be used.
As the phosphoric acid or phosphate, H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ Etc. can be used.
[0019]
These raw materials are dissolved or dispersed in a solvent to form a uniform solution or suspension, and the solution or suspension is subjected to spray pyrolysis.
Spray pyrolysis is a process in which a solution or suspension atomized by ultrasonic waves is introduced into a reactor kept at a high temperature by a carrier gas to rapidly dehydrate the atomized particles and at the same time pyrolyze. How to
As the solvent, for example, water, alcohols, ketones, and the like can be used, but water is preferable in terms of ease of use and safety.
The concentration of the raw material components in this solution or suspension is not particularly limited as long as it can be sprayed, but is preferably 1 to 30% by weight in order to obtain a good spray state.
[0020]
The particle size of the droplets at the time of spraying is preferably 1 to 50 μm, and more preferably 4 to 10 μm.
As the carrier gas, nitrogen gas or argon gas, which is an inert gas, is preferable because it prevents oxidation of the raw material metal.
The atmosphere in the reaction furnace is preferably an inert gas such as nitrogen gas or argon gas in order to prevent oxidation of the raw material metal as described above.
[0021]
The temperature in the reaction furnace, which is the temperature at the time of thermal decomposition of the raw material, is preferably 400 to 900 ° C, more preferably 500 to 800 ° C.
The reason is that if the temperature in the reaction furnace is lower than 400 ° C., the thermal decomposition of the raw materials is insufficient and the water cannot be completely removed. This is because the stoichiometric composition of the obtained pyrolysis product cannot be maintained.
[0022]
Thus, the pyrolysis product obtained by the pyrolysis is sent out of the reactor by the carrier gas and collected.
The pyrolysis product thus collected is fired, for example, in an electric furnace or the like. Here, the reason why the pyrolysis product once generated is calcined is that, in order to form a complex crystal structure such as an olivine structure, the heating time during spray pyrolysis is extremely short, and depending on the reaction conditions, crystal defects or crystal defects may occur. This is because crystal disorder may be included.
If the thermal decomposition product contains crystal defects or crystal disorder, the battery characteristics may be adversely affected.
[0023]
The calcination temperature is preferably lower than the temperature during spray pyrolysis, and particularly preferably 100 to 300 ° C. lower than the temperature during spray pyrolysis.
Here, the reason why it is better to calcine at a temperature lower than the temperature at the time of spray pyrolysis is because the pyrolysis product obtained by spray pyrolysis is in a very active state, so that the When firing in a high temperature range as used, particles grow immediately, the specific surface area decreases, the reaction area as the positive electrode active material decreases, and the phosphate group is also in a highly active state. This is because they easily condense to form a polyphosphate and inhibit the synthesis of a lithium metal phosphate compound having an olivine structure.
[0024]
In consideration of the above points, the firing temperature of the pyrolysis product is preferably from 300 to 600 ° C, more preferably from 400 to 500 ° C.
If the firing temperature is lower than 300 ° C., sufficient mass transfer for removing crystal defects and crystal disorder does not occur. On the other hand, if the firing temperature is higher than 600 ° C., particle growth and phosphoric acid group condensation occur. Because.
The firing time is preferably 30 minutes to 12 hours.
[0025]
As described above, a solution containing lithium, a metal other than lithium, and phosphorus, or a suspension containing these are spray-pyrolyzed, and the obtained pyrolysis product is calcined to obtain a simple substance. A lithium metal phosphate compound having one phase, a controlled particle size, and an olivine structure having a large specific surface area can be obtained.
As the lithium metal phosphate compound having the olivine structure, a general formula: Li _x A _y PO ₄ (However, A is at least one selected from Cr, Mn, Fe, Co, Ni, and Cu, and is preferably represented by 0 <x <2, 0 <y ≦ 1). According to the production method, a lithium metal phosphate compound having an olivine structure having this composition can be obtained easily and at low cost.
[0026]
In the production method of the present embodiment, the time during which the raw material is heated during spray pyrolysis is much shorter than that of the conventional solid-phase reaction, so that aggregation or phosphoric acid due to the difference in pyrolysis temperature is reduced. The thermal decomposition can be completed before polyphosphoric acid is generated by the condensation of. Furthermore, since the raw material is thermally decomposed in a state of being suspended as droplets in a carrier gas composed of an inert gas such as nitrogen gas or argon gas, each species is uniformly mixed in the solution or suspension. The thermal decomposition product can be obtained while maintaining the state. Furthermore, since these pyrolysis products are heated only for a very short time during spray pyrolysis, active chemical species generated by pyrolysis do not form aggregates and remain active.
[0027]
By baking the pyrolysis product thus obtained at a temperature lower than the temperature at the time of spray pyrolysis, a lithium metal phosphate compound having a single-phase olivine structure can be synthesized. Therefore, the growth of particles is suppressed, and a lithium metal phosphate compound having an olivine structure having a small particle size and a large specific surface area can be obtained. The lithium metal phosphate compound having an olivine structure thus obtained has an average particle size of 0.1 to 0.8 μm, and depending on conditions, 0.1 to 0.5 μm. 0.0 to 10.0m ² / G, 8.0 to 10.0 m depending on conditions ² / G.
[0028]
When the thus obtained lithium metal phosphate compound having an olivine structure is used as a positive electrode active material of a lithium ion battery, the reaction area becomes large, so that a large discharge capacity can be obtained.
Therefore, it is possible to obtain a lithium ion battery having very excellent initial discharge capacity of 100 mAh / g or more.
Further, the lithium metal phosphate compound having an olivine structure obtained in this manner is compositionally uniform, does not form aggregates and the like, and is an excellent single phase. In addition, since the step of pulverizing the pyrolysis product, which is indispensable in the conventional solid-phase reaction method, is not required, the manufacturing process can be simplified.
[0029]
In the production method of the present embodiment, an electronic conductive substance or a precursor of the electronic conductive substance can be added to the solution or suspension in order to accelerate the insertion / desorption rate of lithium ions.
As the electron conductive substance, it is only necessary to have electronic conductivity. For example, various conductive substances such as carbon, gold, silver, and palladium can be used, and carbon is preferable. When carbon alone is used as the electron conductive substance, for example, carbon black, acetylene black, graphite and the like can be used, and any one of carbon black and acetylene black is particularly preferable.
[0030]
In addition, as a precursor of the electron conductive substance, a substance having electron conductivity after a thermal decomposition reaction may be used. For example, precursors of various conductive substances such as a carbon compound and an organometallic compound can be used. However, when a carbon compound is used as a precursor of the electron conductive substance, an organic compound can be used. The organic compound is not particularly limited as long as it does not volatilize upon heating, and is not particularly limited. For example, polyethylene glycol, polypropylene glycol, polyethylene imine, polyvinyl alcohol, polyacrylic acid (salt), polyvinyl butyral, polyvinyl pyrrolidone, or These copolymers are preferably used.
[0031]
Further, for example, sugars such as sugar alcohols, sugar esters, and cellulose, or polyglycerin, polyglycerin esters, sorbitan esters, polyoxyethylene sorbitan, and various water-soluble organic surfactants can be used. Further, if a phosphoric acid ester, a phosphoric acid ester salt, or the like is used, it can be used as a phosphorus component simultaneously with a carbon component.
[0032]
In this case, each raw material component is uniformly dispersed and mixed in a solvent, and if a good spray state can be obtained, each component does not have to be dissolved in the solvent. Is more preferably soluble in a solvent.
In addition, if the above-mentioned electronic conductive substance or the precursor of the electronic conductive substance is also soluble in the solvent, the components are uniformly mixed at the molecular level by dissolving in the solvent, so that the composition is shifted or varied. This is preferable because a particulate material free of odor is obtained.
[0033]
At the time of spray pyrolysis of the above solution or suspension, the above-mentioned electronic conductive substance or the precursor of the electronic conductive substance uniformly dispersed in the solution or suspension is also uniformly dispersed in the droplet. Exist in a distributed manner. Therefore, when a thermal decomposition product is generated, it is taken in a state where it is uniformly present in the thermal decomposition product, and a thermal decomposition product in which an electronic conductive substance is interposed between lithium metal phosphate compounds having an olivine structure. Things are obtained. In addition, lithium metal phosphate compounds having an olivine structure are joined to each other via an electronic conductive substance, and lithium metal phosphate compounds having individual olivine structures are coated with the electronic conductive substance, thereby generating thermal decomposition. The outside of the object is also covered with the electronic conductive material.
[0034]
In addition, the electronic conductive substance or the precursor of the electronic conductive substance taken into the thermal decomposition product attracts each other, and the precursor of the electronic conductive substance changes into the electronic conductive substance at the time of heating. The volatile substance is present in the pyrolysis product forming a network-like structure.
When a carbon component is used as the electron conductive material and an organic compound is used as a precursor thereof, when an organic compound that is soluble in a solvent is used, not only the other components but also the carbon component is dissolved in the solution. Dispersed and mixed uniformly at the level. Therefore, when a pyrolysis product is generated, carbon particles are more uniformly present in the pyrolysis product, and a better network-like structure is formed.
Thus, the organic compound is preferably a compound that is soluble in a solvent. In particular, when the solvent is water, a water-soluble organic compound is preferable.
[0035]
The lithium metal phosphate compound having an olivine structure obtained by the production method of the present embodiment is obtained by adding an electron conductive substance such as carbon to the lithium metal phosphate compound having an olivine structure. Since supply and release are facilitated, charge correction accompanying the insertion and desorption of lithium ions can be quickly performed. Thereby, high discharge capacity, stable charge / discharge cycle performance, high filling property, high output, and the like can be realized.
[0036]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
[0037]
A. Preparation of positive electrode active material for lithium ion battery
(Example 1)
LiCl, FeCl ₂ And H ₃ PO ₄ Were weighed so that their molar ratio was 1: 1: 1 and the concentration was 0.1 mol / kg, and they were dissolved in pure water to form an aqueous solution. Next, the aqueous solution is sprayed into nitrogen gas by an ultrasonic atomizer to form a mist, and the mist is introduced into a heat treatment furnace maintained at 600 ° C. using the nitrogen gas as a carrier gas to perform thermal decomposition. Was.
Thereafter, the thermally decomposed product was recovered and calcined at 400 ° C. for 12 hours in a nitrogen atmosphere to obtain a positive electrode active material powder.
[0038]
Next, an X-ray diffraction apparatus was used to obtain a powder X-ray diffraction pattern (chart) of the powder, and the powder was identified by a Hanawait method, and the phase of the powder was examined. The obtained powder was a single phase having an olivine structure.
The specific surface area measured by the BET method was 8.1 m. ² / G, average particle size was 0.3 μm.
[0039]
(Example 2)
LiNO ₃ , Co (NO ₃ ) ₂ And H ₃ PO ₄ Were weighed so that their molar ratio was 1: 1: 1 and the concentration was 0.1 mol / kg, and they were dissolved in pure water to form an aqueous solution. Next, the aqueous solution is sprayed into nitrogen gas by an ultrasonic atomizer to form a mist, and the mist is introduced into a heat treatment furnace maintained at 550 ° C. using the nitrogen gas as a carrier gas to perform thermal decomposition. Was.
Thereafter, the thermally decomposed product was recovered and calcined at 400 ° C. for 12 hours in a nitrogen atmosphere to obtain a positive electrode active material powder.
[0040]
Next, when the phase was examined in the same manner as in Example 1, it was a single phase having an olivine structure.
The specific surface area measured by the BET method was 8.7 m. ² / G, and the average particle size was 0.1 μm.
[0041]
(Example 3)
LiNO ₃ , Co (NO ₃ ) ₂ And H ₃ PO ₄ Were weighed such that their molar ratio was 1: 1: 1 and the concentration was 0.1 mol / kg, and these were dissolved in pure water to form an aqueous solution. Next, this aqueous solution is sprayed into nitrogen gas by an ultrasonic atomizer to form a mist, and the mist is introduced into a heat treatment furnace maintained at 600 ° C. using the nitrogen gas as a carrier gas to perform thermal decomposition. Was.
Thereafter, the thermally decomposed product was collected and calcined at 500 ° C. for 1 hour in a nitrogen atmosphere to obtain a positive electrode active material powder.
[0042]
Next, when the phase was examined in the same manner as in Example 1, it was a single phase having an olivine structure.
The specific surface area measured by the BET method was 8.0 m. ² / G, average particle size was 0.3 μm.
[0043]
(Example 4)
LiOH, FeCl ₂ And H ₃ PO ₄ Were weighed so that their molar ratio was 1: 1: 1 and the concentration was 0.1 mol / kg, and they were dissolved in pure water to form an aqueous solution. Next, 1.2 g of acetylene black was dispersed in 1 kg of this aqueous solution to form a suspension. Thereafter, the suspension is sprayed into nitrogen gas by an ultrasonic atomizer to form a mist, and the mist is introduced into a heat treatment furnace maintained at 800 ° C. using the nitrogen gas as a carrier gas to perform thermal decomposition. Was.
Thereafter, the thermally decomposed product was recovered and baked at 600 ° C. for 30 minutes in a nitrogen atmosphere to obtain a positive electrode active material powder.
[0044]
Next, when the phase was examined in the same manner as in Example 1, it was a single phase having an olivine structure.
The specific surface area measured by the BET method is 6.9 m ² / G, average particle size was 0.5 μm.
[0045]
(Example 5)
LiOH, FeCl ₂ And H ₃ PO ₄ Were weighed so that their molar ratio was 1: 1: 1 and the concentration was 0.1 mol / kg, and they were dissolved in pure water to form an aqueous solution. Next, 2.9 g of sucrose was dissolved in 1 kg of this aqueous solution. Thereafter, the solution is sprayed into nitrogen gas by an ultrasonic atomizer to form a mist, and the mist is introduced into a heat treatment furnace maintained at 800 ° C. using the nitrogen gas as a carrier gas to perform thermal decomposition. Was.
Thereafter, the thermally decomposed product was recovered and baked at 600 ° C. for 30 minutes in a nitrogen atmosphere to obtain a positive electrode active material powder.
[0046]
Next, when the phase was examined in the same manner as in Example 1, it was a single phase having an olivine structure.
The specific surface area measured by the BET method was 7.1 m. ² / G, average particle size was 0.4 μm.
[0047]
(Comparative Example 1)
Li ₂ CO ₃ , Fe (CH ₃ COO) ₂ And NH ₄ H ₂ PO ₄ Are weighed so that their molar ratios are 1: 1: 1, and these and acetone are charged into a nitrogen-filled ball mill, and the ball mill is operated at a predetermined rotation speed for 12 hours to obtain a wet type. Mixing was performed. The obtained mixture was filtered, dried and pulverized to obtain a powder having a predetermined particle size, and this powder was calcined at 300 ° C. for 3 hours in a nitrogen atmosphere.
After the obtained calcined powder was pulverized, it was again calcined in a nitrogen atmosphere at 400 ° C. for 24 hours to obtain a positive electrode active material powder.
[0048]
Next, when the phases were examined in the same manner as in Example 1, a single phase having an olivine structure was not obtained, and an unknown phase was included.
The specific surface area measured by the BET method was 8.5 m. ² / G, average particle size was 0.3 μm.
[0049]
(Comparative Example 2)
Li ₂ CO ₃ , Co (CH ₃ COO) ₂ And NH ₄ H ₂ PO ₄ Are weighed so that their molar ratios are 1: 1: 1, and these and acetone are charged into a nitrogen-filled ball mill, and the ball mill is operated at a predetermined rotation speed for 12 hours to obtain a wet type. Mixing was performed. The obtained mixture was filtered, dried and pulverized to obtain a powder having a predetermined particle size, and this powder was calcined at 300 ° C. for 3 hours in a nitrogen atmosphere.
After the obtained calcined powder was pulverized, it was calcined in a nitrogen atmosphere at 400 ° C. for 24 hours to obtain a positive electrode active material powder.
[0050]
Next, when the phases were examined in the same manner as in Example 1, a single phase having an olivine structure was not obtained, and an unknown phase was included.
The specific surface area measured by the BET method was 8.7 m. ² / G, average particle size was 0.2 μm.
[0051]
(Comparative Example 3)
Li ₂ CO ₃ , Co (CH ₃ COO) ₂ And NH ₄ H ₂ PO ₄ Are weighed so that their molar ratios are 1: 1: 1, and these and acetone are charged into a nitrogen-filled ball mill, and the ball mill is operated at a predetermined rotation speed for 12 hours to obtain a wet type. Mixing was performed. The obtained mixture was filtered, dried and pulverized to obtain a powder having a predetermined particle size, and this powder was calcined at 300 ° C. for 3 hours in a nitrogen atmosphere.
After the obtained calcined powder was pulverized, it was calcined in a nitrogen atmosphere at 800 ° C. for 24 hours to obtain a positive electrode active material powder.
[0052]
Next, when the phases were examined in the same manner as in Example 1, a single phase having an olivine structure was not obtained, and an unknown phase was included.
The specific surface area measured by the BET method is 1.8 m ² / G, average particle size was 4.0 μm.
[0053]
(Comparative Example 4)
LiCl, FeCl ₂ And H ₃ PO ₄ Are weighed so that their molar ratios are 1: 1: 1, and these and acetone are charged into a nitrogen-filled ball mill, and the ball mill is operated at a predetermined rotation speed for 12 hours to obtain a wet type. Mixing was performed. The obtained mixture was filtered, dried and pulverized to obtain a powder having a predetermined particle size, and this powder was calcined at 300 ° C. for 3 hours in a nitrogen atmosphere.
The obtained calcined powder was pulverized and then calcined in a nitrogen atmosphere at 800 ° C. for 24 hours to obtain a positive electrode active material powder.
[0054]
Next, when the phases were examined in the same manner as in Example 1, a single phase having an olivine structure was not obtained, and an unknown phase was included.
The specific surface area measured by the BET method is 1.8 m ² / G, average particle size was 4.0 μm.
[0055]
(Comparative Example 5)
LiCl, FeCl ₂ And H ₃ PO ₄ Were weighed so that their molar ratio was 1: 1: 1 and the concentration was 0.1 mol / kg, and they were dissolved in pure water to form an aqueous solution. Next, the aqueous solution is sprayed into nitrogen gas by an ultrasonic atomizer to form a mist, and the mist is introduced into a heat treatment furnace maintained at 600 ° C. using the nitrogen gas as a carrier gas to perform thermal decomposition. Was.
Thereafter, the thermal decomposition product was recovered to obtain a positive electrode active material powder.
[0056]
Next, an X-ray diffraction apparatus was used to obtain a powder X-ray diffraction pattern (chart) of the powder, and the powder was identified by a Hanawait method, and the phase of the powder was examined. In the obtained powder, some traces of an unknown phase were observed together with the olivine structure.
The specific surface area measured by the BET method was 8.1 m. ² / G, average particle size was 0.3 μm.
[0057]
B. Fabrication of lithium ion secondary battery
70 mg of each of the positive electrode active material powders obtained in Examples 1 to 5 and Comparative Examples 1 to 5, 18 mg of acetylene black as a conductive additive, and 12 mg of polytetrafluoroethylene (PTFE) as a binder were weighed, and mortars and the like. These were mixed, kneaded, and rolled to obtain electrode material-bonded films corresponding to the respective positive electrode active materials.
[0058]
After pressing these films on an aluminum mesh current collector, the area is 2 cm ² Were punched out to obtain positive electrodes of Examples 1 to 5 and Comparative Examples 1 to 5.
After the obtained positive electrode was vacuum-dried using a vacuum dryer, the batteries of Examples 1 to 5 and Comparative Examples 1 to 5 were dried under a dry Ar atmosphere using an HS standard cell (manufactured by Hosen Co., Ltd.). Produced.
Here, metal lithium is used for the negative electrode, a porous polypropylene film is used for the separator, and 1 mol of LiPF is used for the electrolyte solution. ₆ The solutions were each used. In addition, LiPF ₆ As a solvent used for the solution, a solvent having a ratio of ethylene carbonate: diethyl carbonate of 1: 1 was used.
[0059]
In Examples 1 to 5 described above, metallic lithium was used as the negative electrode active material in order to reflect the behavior of the positive electrode active material itself in data. ₄ Ti ₅ O ₁₂ And the like. Further, a solid electrolyte may be used instead of the electrolyte solution and the separator.
[0060]
C. Battery charge / discharge test
A battery charge / discharge test was performed on each of the batteries of Examples 1 to 5 and Comparative Examples 1 to 5. The test conditions for the battery charge / discharge test were as follows: Examples 1, 4, 5 and Comparative Examples 1, 4, and 5 had a cutoff voltage of 3 to 4 V, other cutoff voltages of 4 to 5 V, and a current density of 0. 5mA / cm ² And at room temperature (25 ° C.).
FIG. 1 shows the initial discharge characteristics of Examples 1 to 5 and Comparative Examples 1 to 5.
In this figure, Examples 1 to 5 are represented by E1 to E5, and Comparative Examples 1 to 5 are represented by R1 to R5.
[0061]
According to this figure, in Examples 1 to 5, discharge capacity was obtained by using a lithium metal phosphate compound having an olivine structure synthesized by firing a spray pyrolysis product of a raw material salt as a positive electrode active material. Was 100 mAh / g or more, and in some cases 140 mAh / g or more, indicating that a large discharge capacity was obtained. In addition, it was confirmed that all of these lithium metal phosphate compounds were of a single phase having an olivine structure, and the specific surface area was also confirmed to be larger than Comparative Examples 1 to 4. .
[0062]
On the other hand, in Comparative Examples 1 and 2, since the raw material salt was thermally decomposed by calcining in a normal electric furnace, it was unknown at the same firing temperature as in Examples 1 and 2. It was confirmed that a single phase having an olivine structure was not obtained. Also, the discharge capacity was 40 mAh / g or less, which was very small as compared with Examples 1 and 2, and the battery characteristics were inferior.
Comparative Examples 3 and 4 were obtained by calcining the raw material salts by thermal calcination in a normal electric furnace and calcining them at a high temperature. Thus, a single phase having an olivine structure was obtained. The specific surface area was very small, so the discharge capacity was as small as 80 mAh / g or less, and the battery characteristics were poor.
[0063]
In Comparative Example 5, the raw material salt was subjected to spray pyrolysis. However, since the firing step was omitted, a complete olivine structure could not be formed only by spray pyrolysis. Therefore, although the specific surface area is large, the crystal contains defects and mismatches inside the crystal, which hinders the movement of lithium ions in the crystal.
Therefore, the discharge capacity was as small as 80 mAh / g or less, and the battery characteristics were poor.
[0064]
【The invention's effect】
As described above, according to the method for producing a positive electrode active material for a lithium ion battery, a solution or suspension containing lithium, a metal other than lithium, and phosphorus is subjected to spray pyrolysis, and the resulting pyrolysis product is produced. Since the material is fired, a lithium metal phosphate compound having a single phase, a controlled particle size, and an olivine structure having a large specific surface area can be produced.
Therefore, if the lithium metal phosphate compound having the olivine structure is applied to the positive electrode active material of a lithium ion battery, the charge correction accompanying the insertion and desorption of lithium ions can be promptly performed, and as a result, a high discharge capacity can be obtained. A battery excellent in stable charge / discharge cycle performance, high filling property, high output, and the like can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing initial discharge characteristics of lithium ion secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 5 of the present invention.

Claims (6)

A method for producing a positive electrode active material for a lithium ion battery comprising a lithium metal phosphate compound having an olivine structure,
A method for producing a positive electrode active material for a lithium ion battery, comprising spray-pyrolyzing a solution or suspension containing lithium, a metal other than lithium, and phosphorus, and firing the obtained pyrolysis product. The method according to claim 1, wherein a temperature during the firing is lower than a temperature during the spray pyrolysis. The lithium metal phosphate compound having an olivine structure,
General formula: Li _x A _y PO ₄ (where A is at least one selected from Cr, Mn, Fe, Co, Ni, Cu, and is represented by 0 <x <2, 0 <y ≦ 1) The method for producing a positive electrode active material for a lithium ion battery according to claim 1 or 2, wherein: 4. The method for producing a positive electrode active material for a lithium ion battery according to claim 1, wherein an electronic conductive material and / or a precursor of the electronic conductive material are added to the solution or the suspension. The method for producing a positive electrode active material for a lithium ion battery according to claim 4, wherein the electron conductive material is carbon alone. 5. The method according to claim 4, wherein the precursor of the electronic conductive material is an organic compound.

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