JP2009004371A - Olivine type composite oxide for nonaqueous electrolyte secondary battery and its manufacturing method therefor, and secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium iron composite oxide high in the charging/discharging capacities, excelling in filling properties and in storage characteristics. <P>SOLUTION: An olivine type composite oxide for a nonaqueous electrolyte secondary battery has composition represented by Li<SB>x</SB>Fe<SB>1-y</SB>M<SB>y</SB>PO<SB>4</SB>(0.9<x<1.3; 0.001<y<0.3; M: Mg, Zr, Mn, Ti, Ce, Cr, Co, or Ni), contains a sulfate ion of 1,000 ppm or lower, a sodium ion of 1,000 ppm or lower, has an average primary particle size of 0.5 μm or smaller, and an average secondary particle size of 20-50 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  Provided is a lithium iron composite oxide having a large charge / discharge capacity and excellent filling properties and storage characteristics.

  In recent years, electronic devices such as AV devices and personal computers are rapidly becoming portable and cordless, and there is an increasing demand for secondary batteries having a small size, light weight, and high energy density as power sources for driving these devices. In recent years, in consideration of the global environment, electric vehicles and hybrid vehicles have been developed and put into practical use, and the demand for a lithium ion secondary battery having excellent storage characteristics as a large-scale application is increasing. Under such circumstances, a lithium ion secondary battery having advantages such as a large charge / discharge capacity and high safety has attracted attention.

Recently, as a positive electrode active material useful for a high energy type lithium ion secondary battery having a voltage of 3.5 V class, olivine type LiFePO ₄ has attracted attention as a battery having a high charge / discharge capacity. However, since this material has essentially high electrical resistance and poor filling properties as an electrode, improvement in characteristics is required.

That is, olivine-type LiFePO ₄ is composed of a strong phosphoric acid tetrahedral skeleton, an oxygen octahedron centered on iron ions contributing to redox, and lithium ions. Due to this crystal structure, the crystal structure is stable even when the charge / discharge reaction is repeated, and the cycle characteristics are not deteriorated. However, there are drawbacks in that the movement path of lithium ions is one-dimensional and there are few free electrons. In order to solve this problem, research has been conducted on materials in which Mn, Mg, Zr, Nb, etc. are added to a part of olivine-type LiFePO ₄ , but no material that has solved these problems has yet been obtained. However, there is a demand for a material having a smaller electric resistance.

In addition, LiFePO ₄ has a characteristic that the smaller the primary particle size constituting the powder, the better the charge / discharge characteristics at a high rate. Therefore, in order to obtain an olivine-type LiFePO ₄ composite oxide positive electrode with excellent characteristics, they are densely packed. It is necessary to control the aggregation state so as to form a network with aggregated secondary particles and a low electrical resistance material such as carbon. However, the positive electrode combined with carbon or the like is bulky and has a drawback that a substantial lithium ion density that can be filled per unit volume is lowered. Therefore, in order to secure the charge / discharge capacity per unit volume, olivine-type LiFePO ₄ having a small amount of impurities and a small electric resistance is obtained, and primary particles having a small crystallite size are passed through a conductive auxiliary agent having a small electric resistance. There is a need to form secondary assemblies with high density.

In addition, in the method for producing an olivine-type LiFePO ₄ composite oxide, in order to obtain a small primary crystallite having a high filling property and a small amount of an amorphous part, iron having a controlled solid content and fine particles having high solid phase reactivity. It is necessary to perform firing under low temperature and short time conditions using the system composite hydroxide particles.

That is, it is required to produce an olivine-type LiFePO ₄ composite oxide having a high filling property, a small impurity crystal phase, and a low electrical resistance as a positive electrode active material for a non-aqueous electrolyte secondary battery by an industrial method with a low environmental load. Has been.

Conventionally, various improvements have been made to improve various characteristics of the olivine-type LiFePO ₄ composite oxide. For example, a technique (Patent Document 1) for adding other kinds of metals to the Fe site of olivine-type LiFePO ₄ to reduce electrical resistance, and improving the tap density during the production of olivine-type LiFePO ₄ to form a composite with carbon Technology (Patent Document 2), Technology for obtaining an excellent positive electrode active material using an iron oxide raw material (Patent Document 3), Technology using a material obtained by aggregating a valence 3 iron compound (Patent Document 4), etc. It has been known.

JP 2005-514304 A JP 2006-032241 A Special table 2003-520405 gazette JP 2006-347805 A

As a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing a composite oxide powder of olivine-type LiFePO ₄ that satisfies the above-mentioned characteristics is currently most demanded, but has not been established yet.

In other words, the technique described in Patent Document 1 is a technique in which another metal is added in order to propose structural stabilization and electrical resistance of the olivine-type LiFePO ₄ composite oxide. There is no mention of state controls.

The technique described in Patent Document 2 is a technique for forming an aggregate with carbon in the production of an olivine-type LiFePO ₄ composite oxide. However, the size control of primary particles and the control of the aggregate state of the composite with carbon are not possible. There is a drawback that it is difficult. Moreover, since the manufacturing process is long, there is a risk of causing contamination such as metal powder.

  Furthermore, the technique described in Patent Document 3 is difficult to synthesize fine primary particles because the solid phase reactivity of iron oxide used as a raw material is not sufficient.

  The technique described in Patent Document 4 is a technique that can perform a synthesis reaction using a general-purpose and inexpensive trivalent iron compound as a raw material while maintaining the particle shape. However, contamination that cannot be ignored because a bead mill is used. In addition, the iron oxide particles used are large and the ion diffusion efficiency during the solid phase reaction is low.

Therefore, the present invention has a technical problem to establish an efficient industrial method with a small environmental load of olivine type LiFePO ₄ having a high filling property and a small impurity crystal phase.

  The technical problem can be achieved by the present invention as follows.

That is, the present invention is a composition of _{Li x Fe 1-y M y} PO 4 (0.9 <x <1.3,0.001 <y <0.3, M: Mg, Zr, Mn, Ti, Ce , Cr, Co, Ni), the sulfate ion content is 1000 ppm or less, the sodium ion content is 1000 ppm or less, the average primary particle size is 0.5 μm or less, and the average 2 An olivine-type composite oxide for a non-aqueous electrolyte secondary battery, wherein the secondary particle size is 2.0 to 50 μm (Invention 1).

  Further, the present invention is an olivine type composite oxide for a non-aqueous electrolyte secondary battery in which the average secondary particle size particle size distribution deviation σ / M is 0.3 or less in the olivine type composite oxide (the present invention). 2).

  The present invention is the olivine-type composite oxide for a non-aqueous electrolyte secondary battery, wherein the olivine-type composite oxide contains 0.2 to 10% of a carbon compound inside and / or on the surface of the secondary particles (this book). Invention 3).

The present invention also relates to Li _x Fe _{1- y My} PO ₄ (0.9 <x <1.3, 0.001 <y <0.3, M: Mg, Zr, Mn, (Ti, Ce, Cr, Co, Ni) A method for producing a composite oxide comprising an iron raw material, a phosphorus raw material, a lithium raw material, and a reducing carbon compound in an aqueous solution in a temperature range of 70 to 160 ° C. And then drying and heat-treating at 300 to 750 ° C. in a non-oxidizing atmosphere or a reducing atmosphere. The iron raw material has a BET specific surface area of 30 to 400 m ² / g, An olivine-type composite oxide production method using an iron compound having an amount of 50 ml / 100 g or more and an average secondary particle diameter of 2 to 50 μm (Invention 4).

  Further, the present invention provides the olivine-type composite oxide according to the present invention 4, wherein the iron compound contains one or more elements selected from Mg, Zr, Mn, Ti, Ce, Cr, Co and Ni. This is a method (Invention 5).

  Further, the present invention is the iron compound according to the present invention 4, wherein the iron compound contains lithium compound particles in the center and contains one or more elements selected from Mg, Zr, Mn, Ti, Ce, Cr, Co and Ni. It is a manufacturing method of olivine type complex oxide which is particles (invention 6).

  Further, the present invention is a non-aqueous electrolyte secondary battery using the olivine-type composite oxide described above as a positive electrode active material or a part thereof (Invention 7).

Since the composite oxide of olivine type LiFePO _{4 according} to the present invention has a residual sulfate ion content of 1000 ppm or less and a residual sodium ion content of 1000 ppm or less, the electrical resistance is low, and the structure of the olivine type LiFePO ₄ during electrode reaction Is stable.
In addition, the composite oxide of olivine-type LiFePO _{4 according} to the present invention improves the rate characteristics during charge / discharge because the primary particles have a crystallite size of 0.5 μm or less and a secondary agglomerated particle size of 2 μm to 50 μm. It can be made.
Furthermore, since the olivine-type LiFePO ₄ composite oxide according to the present invention has a density of 1.30 g / cc or more at a pressure of 1 t / cm ² , the filling property is improved and the battery capacity per volume is improved. be able to.
Therefore, the olivine-type LiFePO ₄ composite oxide according to the present invention is suitable as a positive electrode active material for a non-aqueous electrolyte secondary battery.

  The configuration of the present invention will be described in more detail as follows.

First, the olivine type (LiFePO ₄ ) composite oxide for a non-aqueous electrolyte secondary battery according to the present invention will be described.

The composition of the olivine-type composite oxide according to the present invention is Li _x Fe _{1- y My} PO ₄ (0.90 <x <1.30, 0.001 <y <0.3, M: Mg, Zr, Mn, Ti, Ce, Cr, Co, Ni).
When x is out of the above range, a LiFePO ₄ composite oxide having a high battery capacity cannot be obtained. More preferably, 0.98 ≦ x ≦ 1.10.
When y is outside the above range, the initial charge / discharge capacity is significantly reduced. The substitution element M is more preferably Mg, Zr, Mn, Ti, Ce, or Co. More preferably, 0.001 <x ≦ 0.25, and still more preferably 0.005 ≦ x ≦ 0.20.

  The olivine-type composite oxide according to the present invention has a residual sulfate ion amount of 1000 ppm or less, and good storage characteristics can be obtained in a non-aqueous electrolyte secondary battery. When the residual amount exceeds 1000 ppm, impurities such as lithium sulfate are mixed in the olivine-type composite oxide, and these impurities cause a decomposition reaction during charge and discharge, and the reaction with the electrolyte during high-temperature storage is promoted. Increase in resistance after storage becomes severe. Preferably it is 0-500 ppm.

  In addition, when the amount of residual sodium ions is 1000 ppm or less, good storage characteristics can be obtained in a nonaqueous electrolyte secondary battery. When the residual amount exceeds 1000 ppm, impurities such as sodium ferrate are mixed in the olivine-type complex oxide, and these impurities cause a decomposition reaction during charge and discharge, which accelerates the reaction with the electrolyte during high-temperature storage. The resistance rises after storage. Preferably it is 0-500 ppm.

  The average primary particle diameter (crystallite size) of the primary particles of the olivine-type composite oxide according to the present invention is 0.50 μm or less. When the average particle diameter of the primary particles exceeds 0.50 μm, the charge / discharge capacity at a high charge / discharge rate becomes small. Preferably it is 0.02-0.40 micrometer.

  The average particle diameter of the secondary particles of the olivine-type composite oxide according to the present invention is 2.0 to 50 μm. An average particle size of less than 2.0 μm is not preferable because the packing density is lowered and the reactivity with the electrolytic solution is increased. When it exceeds 50 μm, it is difficult to produce industrially. Preferably it is 3.0-20.0 micrometers.

  The particle size distribution deviation σ / M of the average secondary particle diameter of the olivine-type composite oxide according to the present invention is preferably 0.3 or less (σ is a standard deviation, and M is an average secondary particle diameter). When the particle size distribution deviation σ / M of the average secondary particle size of the positive electrode active material is larger than 0.3, the variation in the characteristics relating to conductivity increases.

  The particle shape of the secondary particles of the olivine-type composite oxide according to the present invention is preferably spherical or flat and has few acute angles.

  The olivine-type composite oxide according to the present invention has a carbon content of 0.2 to 10%, and is preferably present inside and / or on the surface of the secondary particles. When the carbon content is less than 0.2%, the electrical resistivity increases. Moreover, when it exceeds 10%, a filling rate will become small and the initial stage charge / discharge capacity per volume will become small. Preferably it is 0.5 to 8.0%.

The BET specific surface area of the olivine-type composite oxide according to the present invention is preferably ² to 25 m ² / g. When the BET specific surface area value is less than 2 m ² / g, the charge / discharge rate decreases. If it exceeds 25 m ² / g, the filling density is lowered and the reactivity with the electrolytic solution is increased. More preferably, it is 5-20 m < ² > / g.

The compression density when the olivine-type composite oxide according to the present invention is pressurized at 1 t / cm ² is preferably 2.30 g / cc or more. When the compression density is less than 2.30 g / cc, the battery capacity per volume decreases. More preferably, it is 2.40 g / cc or more, and the closer to the true density, the better. Since the olivine-type complex oxide according to the present invention has a structure in which primary particles are densely assembled, it is considered that the compression density is high.

  Next, a method for producing the olivine type complex oxide according to the present invention will be described.

  The olivine-type composite oxide according to the present invention impregnates a lithium phosphate compound solution in which a reducing carbon-based compound is dissolved inside an aggregate of iron-based composite hydroxide particles, and the resulting mixture is non-oxidized. Can be obtained by firing under neutral or reducing conditions.

In the present invention, iron-based composite hydroxide aggregated particles can be used as the iron raw material. The iron-based composite hydroxide aggregated particles are prepared by adding 0.1 to 1.8 mol / l ferrous sulfate, 0.1 to 18.5 mol / l aqueous alkali solution, and if necessary, dissimilar metal sulfate. It can be obtained by slowly supplying a solution mixed so as to have a molar ratio to a reaction tank which is always stirred at the same time, and carrying out an air oxidation reaction while maintaining the pH of the reaction tank at 9.3 or higher.
In the above air oxidation reaction, the reaction tank before the addition of the metal salt mixed solution and the alkali solution contains a substance that becomes the core of the aggregate of iron-based composite hydroxide aggregated particles such as lithium carbonate particles and lithium phosphate. The suspension may be preloaded.
In order to increase the specific surface area of the obtained iron-based composite aggregated particles, the air oxidation reaction temperature is preferably 50 ° C. or lower and the reaction pH is 13.0 or lower.

The iron-based composite hydroxide aggregated particles in the present invention preferably have an average particle size of 2 to 15 μm and a BET specific surface area of 10 to 150 m ² / g. Further, the pore volume of 0.1 μm or less of the iron-based composite hydroxide aggregated particles is preferably 0.5 cc / g or more.

  In order to remove by-products generated by the reaction, a filter press, a vacuum filter, a filter thickener, or the like can be used.

  The iron-based composite hydroxide aggregated particles that have been subjected to the washing treatment can remove excess water using a ventilating dryer, a freeze vacuum dryer, a spray dryer, or the like.

  The dried iron-based composite hydroxide agglomerated particle powder is obtained by using a Henschel mixer, a rakai machine, a high-speed mixer, a universal stirrer, a ball mill and other dry and wet mixers, and a phosphorus compound containing a reducing carbon compound. Mix with aqueous solution containing acid and lithium.

After mixing, the reaction is carried out in the liquid at a temperature range of 70 to 160 ° C. The reaction time is preferably 0.2 to 12 hours.
After completion of the reaction, excess water can be removed using a ventilating dryer, a freeze vacuum dryer, a spray dryer or the like. Moreover, since the iron-based composite hydroxide aggregated particles and the phosphate and lithium salt are easily separated at the time of removing water, it is preferable to remove the water while stirring.

The addition amount of phosphate and lithium salt is preferably in the range of 95 to 105 and 90 to 120 in terms of mole percent with respect to the sum of iron ions and different metal ions contained in the iron-based composite hydroxide aggregated particles, respectively. .
As the phosphate, orthophosphoric acid, phosphorus pentoxide and the like can be used. As the lithium salt, lithium carbonate, lithium hydroxide or the like can be used. Further, lithium dihydrogen phosphate, ammonium hydrogen phosphate and the like can be used.
Examples of the carbon-based compound having reducibility that can coexist in the phosphoric acid and lithium salt solution include sucrose, citric acid, ascorbic acid, starch, mannan, trehalose and the like.

  The average particle diameter of each of the mixed phosphate and lithium salt is preferably 2 μm or less. When the particle size exceeds 2 μm, the solid phase reaction during the heat treatment hardly occurs at a low temperature. Further, it is not preferable that the iron-based composite hydroxide aggregated particles and the phosphate and lithium salt mixture are separated from each other.

The average particle diameter of the iron-based composite hydroxide aggregated particles and the phosphate and lithium salt mixture is preferably ² to 50 μm and the BET specific surface area is preferably 0.2 to 15.0 m ² / g.

  The iron-based composite hydroxide aggregated particles and the phosphate and lithium salt mixture can be heat-treated in a gas flow box muffle furnace, a gas flow rotary furnace, a fluidized heat treatment furnace, or the like.

The baking temperature is preferably 400 ° C to 700 ° C. When the temperature is lower than 400 ° C., the solid phase reaction and the reduction reaction of iron ions do not proceed sufficiently, and other crystal phases of the olivine type (LiFePO ₄ ) composite oxide remain. Since the primary crystallite size is 0.5 μm or more, it is not preferable. The atmosphere during firing is preferably a non-oxidizing or reducing gas atmosphere. The firing time is preferably 2 to 20 hours.

Next, a positive electrode using a positive electrode active material made of an olivine type (LiFePO ₄ ) composite oxide according to the present invention will be described.

  When manufacturing a positive electrode using the olivine type complex oxide according to the present invention, a conductive agent and a binder are added and mixed according to a conventional method. As the conductive agent, acetylene black, carbon black, graphite and the like are preferable, and as the binder, polytetrafluoroethylene, polyvinylidene fluoride and the like are preferable.

  The secondary battery manufactured using the olivine-type complex oxide according to the present invention includes the positive electrode, the negative electrode, and the electrolyte.

  As the negative electrode active material, lithium metal, lithium / aluminum alloy, lithium / tin alloy, graphite, graphite, or the like can be used.

  In addition to the combination of ethylene carbonate and diethyl carbonate, an organic solvent containing at least one of carbonates such as propylene carbonate and dimethyl carbonate and ethers such as dimethoxyethane can be used as the solvent for the electrolytic solution.

  Further, as the electrolyte, in addition to lithium hexafluorophosphate, at least one lithium salt such as lithium perchlorate and lithium tetrafluoroborate can be dissolved in the above solvent and used.

  The secondary battery manufactured using the olivine-type composite oxide according to the present invention has a C / 20 charge / discharge rate, an initial discharge capacity of 140 to 160 mAh / g, a charge / discharge rate of 5C, and an initial discharge capacity of 70. It is about -110 mAh / g.

<Action>
The olivine type (LiFePO ₄ ) composite oxide according to the present invention has the above-mentioned properties because the residual sulfate ion content is 1000 ppm or less and the sodium ion is 1000 ppm or less, the average primary particle size is 0.5 μ or less, and the average secondary Since the primary particles of the fine olivine-type composite oxide that is electrochemically active due to the particle diameter of 2 to 50 μm and the spherical shape have become a dense aggregate with an average secondary particle diameter of 2 to 50 μm, high filling properties The present inventors have estimated that the battery has high charge / discharge characteristics and high rate characteristics.

A typical embodiment of the present invention is as follows.

The average secondary particle size (M) is the number average particle size of 1000 particles measured using Hitachi S-4800 scanning electron microscope. σ was calculated from the measurement data.
The average primary particle size was measured using a Hitachi S-4800 scanning electron microscope as described above.
The specific surface area is a specific surface area determined by the BET one-point continuous method using MONOSORB [manufactured by Yuasa Ionics Co., Ltd.] after drying and deaeration of the sample under nitrogen gas at 120 ° C. for 45 minutes.
The density at the time of pressurization is a density when a pressure of 1 t / cm ² is applied.
The amount of sulfate ion was determined by burning the sample with carbon and sulfur measuring device EMIA-820 [manufactured by Horiba Ltd.] in a combustion furnace in an oxygen stream and converting the measured sulfur content. Amount.
The carbon content was measured using a carbon and sulfur measuring device EMIA-820 [manufactured by Horiba Ltd.].
The amount of different metal elements and residual sodium ions were measured using an emission plasma analyzer ICAP-6500 [manufactured by Thermo Fisher Scientific Co.].
X-ray diffraction was performed with Cu-Kα, 50 kV, 200 mA using an X-ray diffractometer RINT-2500 [manufactured by Rigaku Corporation].

The initial charge / discharge characteristics and high-temperature storage characteristics of the coin cell were evaluated using olivine type complex oxide.
First, 90% by weight of olivine type composite oxide as a positive electrode active material, 3% by weight of acetylene black as a conductive material and 3% by weight of graphite KS-16, 4% by weight of polyvinylidene fluoride dissolved in N-methylpyrrolidone as a binder And then applied to an Al metal foil and dried at 150 ° C. This sheet was punched to 16 cmφ, and then pressure-bonded at 5 t / cm ² , and an electrode having a thickness of 50 μm was used for the positive electrode. A CR2032-type coin cell was prepared by using metallic lithium punched to 16 cmφ as a negative electrode and a solution obtained by mixing EC and DMC in which 1 mol / l LiPF ₆ was dissolved at a volume ratio of 1: 2 as an electrolytic solution.
The initial charge / discharge characteristics are as follows: at room temperature, the charge is performed at 0.2 mA / cm ² up to 4.5 V, and then the discharge is performed at 0.2 mA / cm ² up to 2.0 V. Capacity and initial efficiency were measured.

[Example 1]
8. An ion exchange water is charged into the reaction tank in advance so as to have a volume of 100 L, and then 1.6 mol / l ferrous sulfate and magnesium sulfate are mixed so that Fe: Mg = 99: 1. A 0 mol / l sodium hydroxide aqueous solution was slowly fed into the reaction vessel over 8 hours so that the pH was simultaneously 11 ± 0.5.
The reaction tank was always stirred and air oxidized with a blade-type stirrer, and the liquid temperature was kept at 40 ° C. When the metal salt concentration of the reaction solution reached 0.6 mol / l, the supply of the mixed solution of ferrous sulfate and magnesium sulfate and the aqueous sodium hydroxide solution was stopped. Next, an air oxidation reaction was performed for 4 hours until all the iron ions in the reaction solution became trivalent.

After the reaction, the removed slurry was washed with 5 times the amount of water using a filter press and then dried with a ventilated dryer for 14 hours.
As a result of measuring the composition of the obtained powder with a light emission plasma analyzer, it was found that Fe: Mg = 99.1: 0.9, sulfate ion (SO ₄ ) content 150 ppm, and sodium ion content 75 ppm. It was found that the BET specific surface area was 83 m ² / g and the oil absorption was 68 ml / 100 g. As a result of observation with a scanning microscope, it was found that the average diameter of the aggregated particles was 3.3 μm. As a result of X-ray diffraction measurement, it was found that the crystal structure of the aggregated powder was αFeOOH type.

  An SEM photograph of the obtained aggregated hydrous iron oxide particles is shown in FIG. It can be seen that it has an agglomerate aggregate structure.

  1000 g of iron-based composite hydroxide aggregated particles were put into a heating type mixing stirrer with an internal volume of 20 L, and heated to 95 ° C. while stirring. Thereafter, 3645 g of 3 wt% sucrose and 32 wt% lithium dihydrogen phosphate-containing solution were added over 30 minutes while stirring. After completion of the addition, the reaction was carried out for 360 minutes while maintaining the temperature in the mixing stirrer at 95 ° C. Thereafter, the temperature in the mixing stirrer was raised to 120 ° C. to obtain 1775 g of a dry reaction powder. As a result of observation with a scanning microscope, it was found that the average diameter of the mixed composite powder was 4.2 μm. As a result of X-ray diffraction measurement, it was found that the crystal structure of the aggregated powder was a Tavorite type.

  FIG. 2 shows an SEM photograph of the obtained composite aggregated powder containing phosphorus ions, phosphate ions, and iron ions.

This mixture was fired at 550 ° C. for 4 hours in a nitrogen gas atmosphere and crushed.
The obtained fired product has a chemical composition of Li _1.02 Fe _0.99 Mg _0.01 PO ₄ , a carbon content of 0.56 wt%, a sulfate ion (SO ₄ ) content of 180 ppm, a sodium content of 170 ppm, an average The primary particle diameter was 0.3 μm, the shape of the aggregate was spherical, the average secondary particle diameter was 4.0 μm, and the compression density was 2.35 g / cc. As a result of X-ray diffraction measurement, the crystal structure was found to be olivine type. An electron micrograph of the obtained olivine-type composite oxide is shown in FIG.

[Example 2]
Example 1 except that the solution composition of the metal salt was continuously supplied to an aqueous solution in which ferrous sulfate, magnesium sulfate, and ceric sulfate were mixed so that Fe: Mg: Ce = 98.5: 1: 0.5. In the same manner as above, iron-based composite hydroxide aggregated particles having a chemical composition of Fe _0.99 Mg _0.01 OOH, 0.05Ce (OH) ₄ were obtained. Thereafter, an olivine type (LiFePO ₄ ) composite oxide having a chemical composition of Li _1.02 Fe _0.985 Mg _0.01 Ce _0.005 PO ₄ was obtained in the same manner as in Example 1.

[Example 3]
After adding 1110 g of lithium carbonate-added ion exchange water in advance to a volume of 100 L to the reaction vessel, 1.5 mol / l of ferrous sulfate and manganese sulfate were mixed so that Fe: Mn = 95: 5. The aqueous solution and 9.0 mol / l sodium hydroxide aqueous solution were slowly fed into the reaction vessel over 12 hours so that the pH was 12 ± 0.2 at the same time.
The reaction tank was always stirred and air-oxidized with a blade-type stirrer, and the liquid temperature was kept at 30 ° C. When the metal salt concentration of the reaction solution reached 0.6 mol / l, the supply of the mixed solution of ferrous sulfate and manganese sulfate and the aqueous sodium hydroxide solution were stopped. Next, an air oxidation reaction was performed for 4 hours until all the iron ions in the reaction solution became trivalent.
After the reaction, the removed slurry was washed with 20 times the amount of water using a filter press, and then dried with a ventilated dryer for 14 hours.
As a result of measuring the composition of the obtained powder with a light emission plasma analyzer, Fe: Mn = 95.1: 4.9, sulfate ion (SO ₄ ) content 130 ppm, sodium ion content 85 ppm, lithium ion content 890 ppm I found out. It was found that the BET specific surface area was 103 m ² / g and the oil absorption was 64 ml / 100 g. As a result of observation with a scanning microscope, it was found that the average diameter of the aggregated particles was 10.2 μm. As a result of X-ray diffraction measurement, it was found that the crystal structure of the agglomerated powder was αFeOOH type.
1000 g of the obtained iron-based composite hydroxide aggregated particles and 3640 g of a solution containing 3 wt% ascorbic acid and 32 wt% lithium dihydrogen phosphate were placed in an autoclave with an internal volume of 20 L, and the temperature was raised to 120 ° C. while stirring. And held for 1 hour. Next, the temperature of the autoclave was cooled to 60 ° C., and the contents were taken out. Thereafter, the contents were transferred into a mixing stirrer, the temperature was raised to 120 ° C. while stirring, and stirring and drying was performed for 60 minutes to obtain 1760 g of a reaction mixed powder. As a result of observation with a scanning microscope, it was found that the average diameter of the reaction mixed composite powder was 10.9 μm. As a result of X-ray diffraction measurement, it was found that the crystal structure of the aggregated powder was a Tavorite type.
Next, this mixture was baked at 550 ° C. for 4 hours in a hydrogen gas atmosphere and crushed.
The resulting fired product has a chemical composition of Li _1.01 Fe _0.95 Mn _0.05 PO ₄ , a carbon content of 0.59 wt%, a sulfate ion (SO ₄ ) content of 250 ppm, and a sodium content of 205 ppm. The average primary particle size was 0.09 μm, the shape of the aggregate was spherical, the average secondary particle size was 11.3 μm, and the compression density was 2.50 g / cc. As a result of X-ray diffraction measurement, the crystal structure was found to be olivine type.

[Example 4]
An iron-based composite water was prepared in the same manner as in Example 1 except that the solution composition of the metal salt was continuously supplied to an aqueous solution in which ferrous sulfate and titanium tetrachloride were mixed so that Fe: Ti = 98.0: 2. Oxide aggregated particles were obtained. The obtained mixture containing iron-based composite hydroxide aggregated particles, phosphorus and lithium was calcined at 450 ° C. for 5 hours in a hydrogen gas atmosphere and crushed.
The obtained fired product has a chemical composition of Li _1.02 Fe _0.98 Ti _0.02 PO ₄ , a carbon content of 0.89 wt%, a sulfate ion (SO ₄ ) content of 240 ppm, a sodium content of 160 ppm, an average The primary particle size was 0.08 μm, the aggregate shape was spherical, the average secondary particle size was 5.9 μm, and the compression density was 2.45 g / cc. As a result of X-ray diffraction measurement, the crystal structure was found to be olivine type.

[Example 5]
An iron-based composite hydroxide was prepared in the same manner as in Example 1 except that the metal salt solution composition was continuously supplied to an aqueous solution in which ferrous sulfate and zirconium oxychloride were mixed so that Fe: Ti = 99.0: 1. Agglomerated particles were obtained. 1000 g of the obtained iron-based composite hydroxide aggregated particles and 2 L of ion-exchanged water were put into a stainless steel container having an internal volume of 10 L, and heated to 90 ° C. with stirring. Thereafter, 60 g of mannan powder and 60 g of sucrose were added over 10 minutes while stirring. Thereafter, 3645 g of a 32 wt% lithium dihydrogen phosphate-containing solution was added over 10 minutes. After completion of the addition, stirring was performed for 60 minutes to obtain a paste-like mixture. The obtained paste-like mixture was placed in a stainless steel vat and dried for 24 hours with a ventilating dryer.
As a result of observing the obtained dry powder with a scanning microscope, it was found that the average diameter of the mixed composite powder was 7.3 μm.
This mixture was calcined at 500 ° C. for 4 hours in a hydrogen gas atmosphere and crushed.
The obtained fired product has a chemical composition of Li _1.02 Fe _0.99 Zr _0.01 PO ₄ , a carbon content of 1.23 wt%, a sulfate ion (SO ₄ ) content of 260 ppm, and a sodium content of 120 ppm. The average primary particle size was 0.07 μm, the shape of the aggregate was spherical, the average secondary particle size was 7.2 μm, and the compression density was 2.60. As a result of X-ray diffraction measurement, the crystal structure was found to be olivine type.

[Comparative Example 1]
A 3.0 mol / l sodium hydroxide aqueous solution was charged in the reaction vessel in advance so as to have a volume of 50 L, and then 1.0 mol / l of ferrous sulfate and magnesium sulfate was adjusted to Fe: Mg = 99: 1. 20 l of the mixed aqueous solution was supplied to the reaction vessel in 5 minutes. The reaction tank was always stirred and air-oxidized with a blade-type stirrer, and the liquid temperature was maintained at 55 ° C. Next, an air oxidation reaction was performed for 12 hours until all the iron ions in the reaction solution became trivalent. After the reaction, the removed slurry was washed with 5 times the amount of water using a filter press and then dried with a ventilated dryer for 14 hours. As a result of measuring the composition of the obtained powder with a light emission plasma analyzer, it was found that Fe: Mg = 99.1: 0.9, the sulfate ion (SO ₄ ) content was 180 ppm, and the sodium ion content was 92 ppm. It was found that the BET specific surface area was 17 m ² / g and the oil absorption was 42 ml / 100 g. As a result of observation with a scanning microscope, it was found that the primary particles were needle-like having an average major axis diameter of 0.8 μm and an average minor axis diameter of 0.05 μm, and no agglomerated particles were formed. As a result of X-ray diffraction measurement, it was found that the crystal structure of the powder was αFeOOH type.
Thereafter, an olivine type composite oxide having a chemical composition of Li _1.02 Fe _0.99 Mg _0.01 PO ₄ was obtained in the same manner as in Example 1.

[Comparative Example 2]
A 1.36 mol / l sodium hydroxide aqueous solution was charged in the reaction vessel in advance so as to have a volume of 50 L, and 1.7 mol / l of ferrous sulfate and magnesium sulfate were adjusted to Fe: Mg = 99: 1. 20 l of the mixed aqueous solution was supplied to the reaction vessel in 5 minutes. The reaction tank was always stirred and air oxidized with a blade-type stirrer, and the liquid temperature was kept at 90 ° C. Next, an air oxidation reaction was performed for 6 hours until all the dissolved divalent iron ions in the reaction solution disappeared. After the reaction, the removed slurry was washed with 5 times the amount of water using a filter press and then dried with a ventilated dryer for 14 hours.
As a result of measuring the composition of the obtained powder with an emission plasma analyzer, it was found that Fe: Mg = 99.1: 0.9, the sulfate ion (SO ₄ ) content was 4580 ppm, and the sodium ion content was 392 ppm. It was found that the BET specific surface area was 4.3 m ² / g and the oil absorption was 28 ml / 100 g. As a result of observation with a scanning microscope, it was found that the average particle diameter of the primary particles was a polyhedron having a particle size of 0.3 μm and no aggregated particles were formed. Further, as a result of X-ray diffraction measurement, it was found that the crystal structure of the powder was Fe ₃ O ₄ type. Thereafter, an olivine type composite oxide having a chemical composition of Li _1.02 Fe _0.99 Mg _0.01 PO ₄ was obtained in the same manner as in Example 1.

  Table 1 shows the composition, crystal phase, average particle diameter, BET specific surface area, oil absorption, and aggregate particle size of the iron-based compounds obtained in Examples 1 to 5 and Comparative Examples 1 and 2.

Table 2 shows the reaction mixture average particle size, heat treatment conditions, composition, average particle diameter after heat treatment, and compression density obtained in Examples 1 to 5 and Comparative Examples 1 and 2.
In addition, the thing of a comparative example exists from the state of a primary particle to the coarse aggregated particle (secondary particle), and was a thing with wide distribution.

Next, Table 3 shows the results of initial charge / discharge characteristics evaluation using coin cells using the olivine type (LiFePO ₄ ) composite oxide obtained in Examples 1 to 5 and Comparative Examples 1 and 2.

From the above results, the olivine type (LiFePO ₄ ) composite oxide according to the present invention has a large charge / discharge capacity, excellent filling properties and rate characteristics during charge / discharge, and is effective as an active material for non-aqueous electrolyte batteries. Was confirmed.

  By using an olivine-type composite oxide positive electrode active material having a residual sulfate ion content of 1000 ppm or less and a residual sodium ion content of 1000 ppm or less according to the present invention, the charge / discharge capacity is large, and the chargeability and storage characteristics are excellent. A nonaqueous electrolyte battery can be obtained.

2 is a SEM photograph of iron-based composite hydroxide aggregated particles obtained in Example 1. 4 is a SEM photograph of lithium, phosphorus, and iron-based composite hydroxide aggregated particles obtained in Example 1. 3 is an olivine-type composite oxide obtained in Example 1.

Claims (7)

Composition of _{Li x Fe 1-y M y} PO 4 (0.9 <x <1.3,0.001 <y <0.3, M: Mg, Zr, Mn, Ti, Ce, Cr, Co, Ni ), The sulfate ion content is 1000 ppm or less, the sodium ion content is 1000 ppm or less, the average primary particle size is 0.5 μm or less, and the average secondary particle size is 2. An olivine-type composite oxide for a nonaqueous electrolyte secondary battery, characterized by having a thickness of 0 to 50 μm. 2. The olivine-type composite oxide according to claim 1, wherein the average secondary particle size particle size distribution deviation σ / M is 0.3 or less. The olivine-type composite oxide according to claim 1 or 2, wherein the olivine-type composite oxide for a non-aqueous electrolyte secondary battery contains 0.2 to 10% of a carbon compound inside and / or on the surface of the secondary particles. _{Li x Fe 1-y M y} PO 4 (0.9 <x <1.3,0.001 <y <0.3 having an olivine type structure, M: Mg, Zr, Mn , Ti, Ce, Cr, Co, Ni) is a method for producing a composite oxide, wherein an iron raw material, a phosphorus raw material, a lithium raw material, and a reducing carbon-based compound are reacted in an aqueous solution in a temperature range of 70 to 160 ° C. and then dried. In the production method characterized by heat treatment at 300 to 750 ° C. in a non-oxidizing atmosphere or a reducing atmosphere, the iron raw material has a BET specific surface area of 30 to 400 m ² / g and an oil absorption of 50 ml / 100 g or more. A method for producing an olivine-type composite oxide comprising using an iron compound having an average secondary particle diameter of 2 to 50 μm. 5. The method for producing an olivine-type composite oxide according to claim 4, wherein the iron compound contains one or more elements selected from Mg, Zr, Mn, Ti, Ce, Cr, Co, and Ni. 5. The olivine-type composite according to claim 4, wherein the iron compound is an iron compound particle containing at least one element selected from Mg, Zr, Mn, Ti, Ce, Cr, Co, and Ni, with lithium compound particles existing in the center. Production method of oxide. A non-aqueous electrolyte secondary battery using the olivine-type composite oxide according to claim 1 as a positive electrode active material or a part thereof.